Title of Invention	A METHOD OF FORMING A CERAMIC LINING ON THE INSIDE SURFACE OF A HOLLOW TRUNCATED RIGHT CIRCULAR CONE
Abstract	The present invention discloses a method of forming a ceramic lining of uniform thickness on the inward surface of a hollow ax symmetric cone, such as on the inside surface of a hollow truncated right circular cone. The method of the present invention provides a ceramic lining on the inside surface of a hollow truncated right circular cone by simultaneous biaxial rotation of the hollow truncated right circular cone and carrying out a hermit reaction inside such a cone while it is rotating. This is accomplished by carrying out a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as an exothermic hermit reaction, inside a hollow ax symmetric cone, such as on the inside surface of a hollow truncated right circular cone subjected to biaxial rotation.

Title of Invention

A METHOD OF FORMING A CERAMIC LINING ON THE INSIDE SURFACE OF A HOLLOW TRUNCATED RIGHT CIRCULAR CONE

Abstract

The present invention discloses a method of forming a ceramic lining of uniform thickness on the inward surface of a hollow ax symmetric cone, such as on the inside surface of a hollow truncated right circular cone. The method of the present invention provides a ceramic lining on the inside surface of a hollow truncated right circular cone by simultaneous biaxial rotation of the hollow truncated right circular cone and carrying out a hermit reaction inside such a cone while it is rotating. This is accomplished by carrying out a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as an exothermic hermit reaction, inside a hollow ax symmetric cone, such as on the inside surface of a hollow truncated right circular cone subjected to biaxial rotation.

Full Text	The present invention relates to a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone. The method of the present invention is particularly useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as a truncated right circular cone. The present invention more particularly provides a method for producing ceramic lining on the inward surface of hollow truncated right circular cone to be used in high temperature applications as thermal barrier coatings. The novel method of the present invention is applicable to any hollow cone and is most applicable to a truncated hollow right circular cone. Any highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, is useful in the present method. Many thermit reactions, which readily meet these requirements, are more preferred owing to the easy availability of the starting materials at lower cost and easiness in controlling the reaction. Axisymmetric convergent - divergent nozzles and tubular parts are important components in the chemical and engineering industry, particularly in propulsion units in aerospace and high-end automotive industries. These components are generally made of a metal, such as iron, nickel and aluminum, and are exposed to high temperatures during operations. These metal components are protected from high temperatures by thermal barrier coatings. Ceramics having high melting points, low thermal conductivities, low densities and good wear, corrosion and oxidation resistances are promising materials for such thermal barrier applications. Many spray and vapor deposition methods are commercially available for providing such components with thermal barrier coatings made of ceramics. However, these methods are time, energy and cost consuming and limited to coating thickness of up to about 2mm. Reference may be made to US Patent No. 4,363,832; titled: Method for providing ceramic lining to a hollow body by thermit reaction. According to the invention, a thermit mixture, for example, composed of aluminum powder and an iron oxide is placed in the hollow space of the hollow body, which is rotated at a high speed so as that the thermit mixture is pressed against the wall of the hollow body by the centrifugal force and the thermit mixture is ignited, for example, by contacting with an acetylene flame. The thermit reaction of the thermit mixture propagates under the influence of the centrifugal force so that the molten metal formed from the reducible metal oxide and the ceramic oxide formed from the strongly reductive element are separated into stratified layers by virtue of their density difference with the ceramic oxide forming the innermost layer and the metal forming the intermediate layer between the ceramic oxide layer and the wall of the hollow body with strong bonding of the ceramic oxide layer upon solidification by cooling. The method uses a highly exothermic thermit reaction, capable of self-propagation, to synthesize the desired ceramic in molten condition. The reaction is carried out inside a metal tube, while the tube is rotated about its axis, to form a ceramic lining of uniform thickness. O. Odawara and J. Ikeuchi used this method (Journal of American Ceramic society, 69 (4), PP: 80-81, 1986) to provide ceramic-ceramic composite lining to a metal pipe. Also, 0. Odawara used this method to produce long ceramic lined pipes (Journal of American Ceramic society, 73 (4) PP: 629-33, 1990). However, this method is not useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone. Because, the products of the thermit reaction slide over the inner surface of the cone under the effect of centrifugal force and collect near its largest diameter with the formation of a circular hole in the center of the thermit products. This way the formation of uniform thickness of ceramic lining on the inside surface of the cone is prevented in this method. Reference may also be made to the gravitational thermit process disclosed in Japanese Patent No. 8889676, for fabricating a ceramic lined metal pipe. Here, a pipe is held vertically and loosely filled with a thermit mixture. The mixture at the top of the pipe is ignited to initiate the thermit reaction. The reaction then propagates from the top to the bottom of the pipe. The molten ceramic product of the thermit reaction is deposited on the inside surface of the pipe as a layer and forms a solidified ceramic lining. Reference may be drawn to the Japanese Patent No. JP3229881, titled: Method for applying ceramics lining on inside surface of pipe, wherein the ceramics lining on the inside surface of a large-diameter pipe is formed by inserting an inside pipe which is capped with a thin-film material, and has many holes into the pipe, packing a thermit reaction agent into the spacing between the two pipes and firing the agent at the time of lining the inside surface of the pipe with ceramics by utilizing a thermit method. Reference may also be drawn to the Japanese Patent No. JP 61076681, titled: Ceramic lining method of metallic tubular body; wherein is disclosed how to form easily a ceramic layer on the inside wall surface of a metallic tubular body by pressurizing and packing a powder mixture composed of a strong reducing element and metallic oxide at specific density into the hollow part of the tubular body, heating the packing material in the upper part and progressing reaction toward the lower part. These prior art methods of forming ceramic linings inside pipes are neither intended nor useful to form a thick ceramic lining of uniform thickness on the inward surface of a hollow truncated right circular cone. From the details and drawbacks of hitherto known prior art methods of forming ceramic linings inside hollow metal pipes, it is clear that there is a definite need and scope for the development of a method to provide ceramic lining to a hollow truncated right circular cone. The main objective of the present invention is to provide a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, which obviates the drawbacks of the herein above referred prior art. Another objective of the present invention is to provide a simple, convenient and inexpensive method of forming a ceramic lining on the inward surface of a hollow truncated right circular cone. The above objectives are achieved by providing a novel method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as of a hollow truncated right circular cone, wherein a thermit reaction is carried out inside such a cone while it is subjected to biaxial rotation. The present invention discloses a method of forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone. The method of the present invention provides a ceramic lining on the inside surface of a hollow truncated right circular cone by simultaneous biaxial rotation of the hollow truncated right circular cone and carrying out a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as a thermit reaction inside such a cone while it is rotating. This is accomplished by carrying out preferably a highly exothermic thermit reaction, capable of self-propagation and resulting in molten products, inside a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone subjected to biaxial rotation. Thermit reactions, which readily meet these requirements, are more preferred owing to the easy availability of the starting materials at lower cost and easiness in controlling the reaction. Accordingly, the present invention provides a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, which comprises effecting a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as an exothermic thermit reaction of a thermit mixture containing a strongly reductive element and a reducible metal oxide, capable of self-propagation and resulting in molten products, inside a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone, characterized in that the said exothermic thermit reaction is effected inside the cone while the said cone is being subjected to biaxial rotation about its axis and about an external axis. In an embodiment of the present invention, the thermit mixture contains at least one strongly reductive element selected from aluminum, magnesium, zirconium or silicon. In another embodiment of the present invention, the thermit mixture contains at least one strongly reducible metal oxide selected from oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc or manganese. In a still another embodiment of the present invention, the thermit mixture contains aluminum and ferric oxide as strongly reductive element and strongly reducible metal oxide, respectively. In a yet another embodiment of the present invention, the aluminum and ferric oxide in the thermit mixture are in stoichiometric amounts. In a still yet another embodiment of the present invention, the powders of aluminum and ferric oxide are of particle size of at least -170 mesh. In a further embodiment of the present invention, the thermit mixture is packed in the hollow cone to about 20 to 60% of the theoretical density of the thermit mixture. In a yet further embodiment of the present invention, the biaxial rotation is effected at speeds of rotation of the hollow cone about its axis, N1, and about an external axis, N2, being selected such that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end and the big end of the hollow right circular cone faces the external axis, N2, of rotation and the following condition is satisfied: N2/N1 = ((r/R)tan0)05 wherein, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 6 is the semi apex angle of the cone. In a still further embodiment of the present invention, the method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, comprises: (a) inserting a hollow truncated right circular cone in a supporting block having a hole matching with the external geometry of the said hollow truncated right circular cone, the said matching hole in the supporting block being provided with a circular cavity formed inside the cylindrical hole extending below the small end of the hollow truncated right circular cone; (b) fixing a refractory core to the said supporting block such that the core is introduced at the center of the small end of the said hollow truncated right circular cone and the core seals the bottom of the said supporting block; (c) packing the said hollow truncated right circular cone with a powdery thermit mixture comprising of powders of a strongly reducible metal oxide and a reductant metal; (d) fixing firmly by means such as flanges and fasteners in a biaxial rotary fixture, the said supporting block along with the said thermit mixture packed hollow truncated right circular cone in such a manner that the axes of the supporting block, refractory core and the truncated hollow right circular cone coincide. (e) subjecting the assembly to biaxial rotation about the axis of the cone and simultaneously rotating it about an external axis normal to and coplanar with the axis of the cone, such that the resultant centrifugal force at the small end of the hollow truncated right circular cone is normal to the inside surface of the said cone; (f) igniting the said thermit mixture packed in the said truncated hollow right circular cone being subjected to biaxial rotation; (g) continuing the biaxial rotation for a time period in the range of 5 to 30 minutes; (h) stopping the biaxial rotation and separating the refractory core and a solidified metal ring formed in the supporting block cavity to obtain a ceramic lined hollow truncated right circular cone. In another embodiment of the present invention, the hollow space of the cone is of axisymmetric truncated geometry of conic sections, such as circular, parabolic, elliptical. In yet another embodiment of the present invention, the supporting block and core is thermally conducting and capable of withstanding thermal and physical stress and is inert and non-wetting with respect to the products of the thermit reaction and made of material preferably graphite. In still another embodiment of the present invention, the cavity in the supporting block is a circular groove made coaxial with the axis of the supporting block and can be of any cross-section with the side of the cavity, facing the axis of the supporting block/hollow cone, open. In still yet another embodiment of the present invention, the size of the cavity is such that its volume is at least equal to the volume of the metal product produced by the thermit reaction of the thermit mixture packed in the hollow cone. In a further embodiment of the present invention, the means for igniting the thermit mixture packed in the hollow truncated right circular cone is such as a rotary igniter, an oxy-acetylene flame. In a yet further embodiment of the present invention, the size of the refractory core is such that the radial gap between the refractory core and the inner diameter of the truncated hollow cone at the small end is at least the thickness of the ceramic lining being formed and sufficiently large to facilitate easy passage of the molten metal product of the thermit reaction into the said cavity. In a still further embodiment of the present invention, the free surface of the thermit mixture is made concave by scraping the packed thermit mixture by rotating a parabolic or an elliptical metal template about the axis of the hollow cone and taking reference of the big end of the hollow cone. In another embodiment of the present invention, the hollow truncated right circular cone is made of a metal such as iron, nickel, aluminum and their alloys. In yet another embodiment of the present invention, the hollow truncated right circular cone and its contents are subjected to biaxial rotation using prime movers, preferably variable speed electric motors. In still another embodiment of the present invention, the hollow truncated right circular cone, along with its contents, is subjected to biaxial rotation such that the resultant centrifugal force at any point on the inside surface of the cone is sufficient to cause complete separation of the metal and ceramic products of the thermit reaction. In still yet another embodiment of the present invention, the thermit mixture is diluted with the ceramic product of the thermit reaction to lower the adiabatic temperature of the thermit reaction. In the present invention there is provided a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, which comprises the steps of: (1) Inserting a hollow truncated right circular cone in a supporting block having a hole matching with the external geometry of the said hollow truncated right circular cone. The said matching hole made in a supporting block is provided with a circular cavity formed inside the cylindrical hole in the supporting block, the said cylindrical hole extending below the small end of the hollow truncated right circular cone. (2) Fixing a refractory core to the said supporting block such that the core is introduced at the center of the small end of the said hollow truncated right circular cone and the core seals the bottom of the said supporting block. (3) Packing the said hollow truncated right circular cone with a powdery thermit mixture comprising of powders of a strongly reducible metal oxide and a reductant metal. (4) Fixing firmly the said supporting block, along with the said hollow truncated right circular cone packed with the thermit mixture to a rotary fixture made of steel flanges by steel fasteners. The hollow truncated right circular cone and the refractory core are fitted to the supporting block firmly in a rotary fixture in such a way that the axes of the supporting block, refractory core and the truncated hollow right circular cone coincide. (5) Rotating the whole assembly about the axis of the cone and simultaneously rotating it about an external axis (biaxial rotation), normal to and coplanar with the axis of the cone, such that the resultant centrifugal force at the small end of the hollow truncated right circular cone is normal to the inside surface of the cone. (6) Heating the powdery thermit mixture in the truncated hollow right circular cone locally at least at one point on its free surface to a sufficiently high temperature, depending on the type of thermit reaction, using an igniter so as to cause ignition of the thermit mixture and initiate the thermit reaction which propagates through the remaining thermit mixture in the cone converting all the reactants to molten products, namely, a stable oxide of the metal reductant and the metal of the reducible metal oxide with the lighter molten metal oxide depositing over the inner surface of the hollow truncated right circular cone as a ceramic lining and the denser molten metal filling the cavity. (7) Continuing the biaxial rotation for time between 5 to 30 minutes to allow the reaction products to solidify and cool. (8) stopping the biaxial rotation and separating the ceramic lined hollow right circular cone from the supporting block, the solidified metal ring in the cavity and the refractory core to get a ceramic lined hollow truncated right circular cone. In a feature of the present invention, hollow truncated right circular cone is made of a material capable of withstanding thermal shock due to the instantaneous heat released by the exothermic reaction and stresses induced by centrifugal forces. In another feature of the present invention, the hollow truncated right circular cone is made of a metal such as iron, nickel, aluminum and their alloys. In yet another feature of the present invention, the supporting block is of sufficient strength to withstand the stresses induced in it by the biaxial rotation of the supporting block and the components it supports. In still another feature of the present invention, the supporting block is made of a material capable of withstanding thermal shock due to the instantaneous heat released by the exothermic reaction and stresses induced by centrifugal forces. In still yet another feature of the present invention, the supporting block is made of a material having good thermal conductivity to act as a heat sink to prevent destruction of the cone being ceramic lined. In a further feature of the present invention, the supporting block is made of a material having low density and high temperature capability, such as graphite. In a still further feature of the present invention, the cavity in the supporting block can be of any cross section with the side of the cavity, facing the axis of the supporting block/hollow cone, open. In a yet further feature of the present invention, the core is capable of withstanding thermal shock due to exothermic reaction heat and stresses induced by the centrifugal forces and the core material is inert and non-wetting with respect to the products of the thermit reaction being carried out and is made of a material such as graphite. In another feature of the present invention, the thermit reaction is initiated by striking an arc between two mild steel electrodes of a rotary igniter and bringing the arc in contact with the thermit mixture packed in the hollow cone. The novelty of the present invention lies in providing a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone. The novelty of the present invention has been achieved by the non-obvious inventive steps of biaxial rotation of the hollow truncated right circular cone and carrying out a thermit reaction inside such a cone while it is rotating. The reaction should be sufficiently exothermic to produce the products in molten condition. The biaxial rotation of the cone is carried out in such a way that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end. This is possible when the big end of the hollow right circular cone faces the external axis of rotation. The supporting block housing the cone is provided with a cavity for the deposition of denser metal product while the lower density ceramic material spreads over the inner surface of the cone to form the lining. The method of the present invention which is particularly useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as a truncated right circular cone is illustrated in figurel of the drawing accompanying this specification in which the numerals indicated refers to: 1. Hollow truncated right circular cone 2. Cavity 3. Refractory core 4. Thermit mixture 5. Igniter 6. Supporting block 7. Rotary fixture N1. The speed of rotation of the cone about its axis N2. The speed of rotation of the cone about an external axis. A thermit mixture is a mixture of powders of a strongly reductive element and a reducible metal oxide. When a thermit reaction is carried out using such a thermit mixture, the oxide of the strongly reductive element and the metal of the reducible metal oxide are produced as products. The strongly reductive element can be aluminum, zirconium, magnesium or silicon to get the respective oxide as the ceramic product. The strongly reducible metal oxide can be chosen from the oxides of iron, nickel, copper, molybdenum, vanadium, titanium, manganese etc. to form the respective metal product. In addition, the thermit mixture may contain other components, either an element such as carbon, boron or silicon or a compound such as boric oxide, to form carbide, boride or silicide in place of pure metal product produced in a conventional thermit reaction. Thus, thermit based reactions can also be used in the present method to provide a hollow truncated right circular cone with ceramic-ceramic composite linings. A few thermit and thermit based reactions useful for the present method and their estimated heats of reaction (AH) and adiabatic temperatures (Ta Reaction Fe2O3+2AI _ 2Fe2O3+3Zr - MnO2+Si _ Fe2O3+3Mg - MoO3+2AI+2Si - 2MoO3+4AI+C _ MoO3+2AI+B _ 3Cr2O3+6AI+4C - 3WO3+14AI+6SiO2 - 2WO3+6AI+B2O3 - A powdery mixture of a thermit or thermit based reaction containing non-stoichiometric amounts of the reactants can also be used in the present invention, if the reaction self propagates after ignition and the products produced are in molten state. Additionally, one of the products of a thermit or thermit based reaction can be added as an inert diluents to lower the adiabatic temperature of the reaction while maintaining the self propagating nature of the reaction. When the ceramic product of such a reaction is used as inert diluents, the yield of that product can be increased using the same amount of the stoichiometric mixture of the thermit or thermit based reaction. When a thermit or thermit based reaction is not self propagating, prior heating of the thermit mixture to a suitable temperature is the primary requisite. If the thermit reaction is difficult to ignite, ignition under an inert gas cover may help to initiate the ignition of the thermit mixture. If the adiabatic temperature of a reaction is higher than the boiling or sublimation temperature of any of the reactants, the present method may be carried out under inert gas pressure. A homogeneous powdery mixture is prepared by uniformly blending the powders of the reactants, in stoichiometric amounts, of a thermit or thermit based reaction in a mechanical mixer or blender, preferably sealed, for 12 to 24 hours. The powders used are preferably of -200mesh size and baked at about 120° C for 12 to 24 hours before mixing. In the next step, the given hollow truncated right circular cone is placed in the matching hole of a supporting block that is provided with a circular cavity below the small end of the hollow cone. The cavity in the supporting block is formed such that the volume of the cavity is at least equal to the volume of the metal product produced in the thermit reaction. A cylindrical refractory core of diameter equal to or less than the inner diameter of the ceramic lined cone at its small end is located in the supporting block such that the core is projecting inside the small end of the cone by at least the thickness of the ceramic lining. The refractory core may be hollow with the top, in contact with the thermit mixture, closed. The supporting block and the core can be made of a material capable of resisting high temperatures with good thermal shock resistance. Also, it is preferable that the material used for supporting block and core is inert and non-wetting with respect to the products of the reaction being carried out. Although many metals and ceramics are useful for making supporting block and core, graphite is adequate in most cases owing to its easy availability at low cost and good properties, such as high temperature capability, tolerable inertness to many materials at high temperatures, easy machinability, good thermal shock resistance and strength at elevated temperatures. In the next step, the speeds of rotation of the hollow cone about its axis, N1, and about the external axis, N2, are selected such that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end. This is possible when the big end of the hollow right circular cone faces the external axis of rotation and the following condition is satisfied: Where, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 9 is the semi apex angle of the cone. These speeds are chosen such that the resultant centrifugal force at the small end of the hollow cone is sufficient to cause complete separation of the thermit products. Otherwise, the hollow cone will be lined with a mixture of ceramic+metal or ceramic+ceramic materials, depending upon the composition of the starting mixture. In the next step, the hollow cone is packed with the prepared thermit or thermit based reaction mixture. The thermit mixture in the hollow space of the cone can be packed with uniform thickness of thermit over the inside surface of the cone or simply packed to some depth of the cone. However, the best results are obtained when the free surface of the thermit mixture is made concave with a parabolic or an elliptical geometry. This can be done by scraping the packed thermit mixture by rotating a parabolic or an elliptical metal template about the axis of the hollow cone and taking reference of the big end of the hollow cone. Although the bottom of the concave geometry of the filled thermit mixture (or the bottom of the free surface of the filled thermit mixture) can touch the flat end of the ceramic core or the geometry can be cut by the core exposing the flat end of the core, it is preferable to select a suitable concave geometry such that the bottom of the free surface of the filled thermit mixture is about 3mm above the flat end of the core. Also, it is preferable to select a suitable concave geometry so as to form about 3mm thick thermit powder along the circumference of the big end of the cone. The packed thermit mixture should have a green density of less than a critical value (about 60% theoretical density for the thermit mixture comprising of iron oxide and aluminum) so that the reaction can self propagate without extinguishing. The concave geometry of the free surface is so selected that the quantity of the thermit mixture packed in the hollow right circular cone is sufficient to form the require thickness of the ceramic lining on the inside surface of the hollow cone. The supporting block, hollow right circular cone packed with the thermit mixture and the core are fitted together firmly to a rotary fixture made of steel flanges. The rotary fixture is then mounted in a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers are preferably variable speed motors. The rotary fixture is mounted in the machine so that the big end of the hollow cone faces the external axis of rotation, the axis of the hollow cone is normal to the external axis of rotation and the external axis is coplanar with the axis of the cone. In the next step, the rotary fixture along with its contents is rotated about the axis of the cone and about the external axis at the predetermined speeds of N1 and N2, respectively. In the next step, the thermit or thermit based reaction is initiated on the free surface of the powdery thermit mixture, packed in the hollow cone, by heating it locally on its free surface to or above its ignition temperature. This may be carried out, for example, by bringing an electric arc, struck between two electrodes, in contact with the free surface of the powdery mixture packed in the hollow cone. The thermit reaction, thus initiated, rapidly propagates through the remaining powdery mixture in the hollow cone to convert all the reactants into products, namely a ceramic and a metal. The high exothermic heat released by the thermit reaction results in the ceramic and metal products in molten condition. Under the effect of the biaxial rotation, the denser molten metal product collects in the cavity and the lighter molten ceramic product is deposited on the inner surface of the cone as a uniform layer. It is desirable to keep the products of the thermit reaction in molten condition for a longer duration while in rotation so that the molten ceramic product spread uniformly over the inward surface of the hollow cone and the gases, contained in the powdery mixture and those produced by the reaction, escape to the ambient. The present method can be carried out inside an enclosure and the enclosure can be evacuated to remove the gases trapped in the powdery mixture. Back filling the enclosure with an inert gas, such as argon, can improve the quality of the solidified ceramic lining. This approach also helps in overcoming the problem of ignition of some thermit or thermit based reactions in air when such reactions are employed in the present method. The rotation of the assembly is continued for 5 to 30 minutes to allow the molten products to solidify and cool by losing heat to the surroundings. After solidification and cooling, a ceramic lining of uniform thickness is formed on the inner surface of the cone. The rotation of the assembly is stopped and the ceramic lined hollow truncated right circular cone is separated from the rotary fixture, metal product collected in the cavity and the ceramic core. The following examples are given by way of illustration of the present invention in actual practice and should not be construed to limit the scope of the present invention in any way. Example -1 Ferric oxide and aluminium powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 100g of ferric oxide and 33.8g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone, fabricated from mild steel sheet of 2mm thickness, was used for ceramic lining using aluminium oxide. The hollow cone had internal diameters of 85mm and 35mm at big and small ends, respectively, and a height of about 42mm. The hollow cone had a semi apex angle of about 30.75°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a circular recess of 45mm diameter with rectangular crossection, 4mmx5mm, to form the cavity inside the cylindrical hole of 35mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 32mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 4mm above that end. The hollow metal cone was packed with about 75g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=58.6y) was formed in the packed thermit mixture. The parabolic concave surface had 75mm diameter at the big end of the hollow cone and a depth of 24mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 50g after scraping. The green density of the thermit mixture packed in the hollow cone was about 19.5% of the estimated theoretical density (4.2409 g.cm"3) of the thermit mixture. The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1702 rpm about the axis of the cone and 402 rpm about the external axis that was at a distance of about 186mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of mild steel of 2mm thickness with a semi apex angle of about 30.75°, was lined with about 1mm thick aluminum oxide ceramic. Example -2 Ferric oxide and aluminium powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 100g of ferric oxide and 33.8g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone of 2mm wall thickness, machined from stainless steel, was used for ceramic lining using aluminum oxide. The hollow cone had internal diameters of 91mm and 51mm at big and small ends, respectively, and a height of about 36mm. The hollow cone had a semi apex angle of about 29°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a circular cavity of nearly a right angle triangle crossection with 5.9mm of sides. This cavity was formed by assembling graphite components inside the cylindrical hole of 70mm formed at the end of the conical hole in the block. The cavity was open to the hollow space of the cone by approximately 1 mm wide circular gap facing the core. The volume of the cavity was sufficient to accommodate the quantity of iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 47mm and length 5mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 4mm above that end. The hollow metal cone was packed with about 80g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=64y) is formed in the packed thermit mixture. The parabolic concave surface had 80mm diameter at the big end of the hollow cone and a depth of 25mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 66g. The green density of the thermit mixture packed in the hollow cone was about 20% of the estimated theoretical density (4.2409 g.cm" 3) of the thermit mixture. The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1400 rpm about the axis of the cone and 386 rpm about the external axis that was at a distance of about 186mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 20 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of mild steel of 2mm thickness with a semi apex angle of about 29°, was lined with about 1mm thick aluminum oxide ceramic. Example - 3 Ferric oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 150g of ferric oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 111.8mm and 85.5mm at big and small ends, respectively, and a height of about 49mm. The hollow cone had a semi apex angle of about 15° The cone was mounted in a cylindrical supporting block, 120mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 102mm diameter circular recess of rectangular crossection, 4mm x 9mm, to form the cavity inside the cylindrical hole of 84mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 81mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 130g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminium sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=66y) was formed in the packed thermit mixture. The parabolic concave surface had 108mm diameter at the big end of the hollow cone and a depth of 44mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 110g after scraping. The green density of the thermit mixture packed in the hollow cone was about 20% of the estimated theoretical density (4.2409 g/cc) of the thermit mixture. The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1166rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic. Example - 4 Ferric oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 150g of ferric oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 111.8mm and 85.5mm at big and small ends, respectively, and a height of about 49mm. The hollow cone had a semi apex angle of about 15°. The cone was mounted in a cylindrical supporting block, 120mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 102mm diameter circular recess of rectangular crossection, 4mm x 9mm, to form the cavity inside the cylindrical hole of 84mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 81mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 130g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating an elliptical metal template, made of 1mm thick aluminium sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a concave free surface with a segment of an elliptical geometry ((X/64.9)2+(Y/319.2)2=1) was formed in the packed thermit mixture. The segment of the elliptical concave surface had 85mm diameter at the big end of the hollow cone and about 60mm diameter at the small end. The amount of the thermit mixture packed in the hollow metal cone was found to be about 115g after scraping. The green density of the thermit mixture packed in the hollow cone was about 20% of the theoretical density (4.2409 g.cm"3) of the thermit mixture. The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1166rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic. Example - 5 Ferric oxide, Aluminum oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. An aluminum oxide diluted thermit mixture was prepared by intimately mixing 150g of ferric oxide, 13.04g of Aluminum oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The dilution was just enough to avoid vaporization of iron product of the thermit reaction. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 85.3mm and 36mm at big and small ends, respectively, and a height of about 92mm. The hollow cone had a semi apex angle of about 15°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 110mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 60 mm diameter circular recess of rectangular crossection, 4mm x 12mm, to form the cavity inside the cylindrical hole of 36mm diameter formed at the small end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 33mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 140g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a combined parabolic + elliptical metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. The parabolic geometry (x2=24.728y) was about 50mm deep from the big end of the hollow cone. The elliptical geometry ((x/28.985)2+(y/180)2) = 1) was 32mm deep from the end of the parabolic geometry. This way a concave free surface of parabolic + elliptic combined geometry was formed in the packed thermit mixture. The parabolic concave surface had 78mm diameter at the big end of the hollow cone. The amount of the thermit mixture packed in the hollow metal cone was found to be about 109g after scraping. The green density of the thermit mixture packed in the hollow cone was about 19.1% of the estimated theoretical density (4.2230 g/cc) of the thermit mixture. The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1714rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of this diluted thermit reaction is about 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic. The above ceramic lined hollow truncated right circular cones obtained in the examples 1 to 5 were tested by blowing hot gases through it. The test parameters were as follows: Gas pressure : 11.5Kgf/cm2 Gas temperature: 1930°K Duration : SOsecs The test results obtained were as follows: .(Table Removed) The above test results confirm the low thermal conductivity and stability of the ceramic lining. The present inventive method of forming a ceramic lining on the inside surface of a hollow truncated right circular cone has been demonstrated in actual practice as detailed in the examples herein above. The desired ceramic was produced by a thermit reaction. As the estimated adiabatic temperature of the thermit reaction was higher than the melting point of the ceramic product, the desired ceramic was produced in molten state. The resultant centrifugal force due to biaxial rotation of the hollow cone was made normal to the inside surface of the hollow cone at its small end. The free surface of the thermit powder packed in the cone was made concave with parabolic, elliptical or their combinations to get best ceramic linings by this method. The present method is useful for forming ceramic linings from other ceramics, not covered in these examples, using suitable strong exothermic reactions. The present method is useful for ceramic lining of hollow truncated right circular cones with other semi apex angles between 0°and 90°, not covered in these examples. The present method is also useful for ceramic lining of other axisymmetric components having parabolic or elliptic inside hollow surface. In general, the method is most useful for ceramic lining of a hollow truncated axisymmetric body with the inside surface having conical, parabolic or elliptical geometry. The main advantages of the present invention are: 1. The method requires no furnace to produce the required ceramic material in molten state for forming the ceramic lining. 2. The power consumption is minimal. 3. The method is simple, easy and inexpensive. 4. No sophisticated and costly equipments are involved. 5. The method is useful for ceramic lining of a hollow truncated right circular cone. 6. The method is useful for ceramic lining of a hollow axisymmetric body, such as a hollow surface having conical, parabolic or elliptical geometry. 7. The time required to form the ceramic lining is short. 8. The time for ceramic lining does not greatly depend on the size of the hollow component. We claim: 1. A method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, which comprises effecting a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as an exothermic thermit reaction of a thermit mixture containing a strongly reductive element and a reducible metal oxide, capable of self-propagation and resulting in molten products, inside a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone, characterized in that the said exothermic thermit reaction is effected inside the cone while the said cone is being subjected to biaxial rotation about its axis and about an external axis. 2. A method as claimed in claim 1, wherein the thermit mixture contains at least one strongly reductive element selected from aluminum, magnesium, zirconium or silicon. 3. A method as claimed in claim 1-2, wherein the thermit mixture contains at least one strongly reducible metal oxide selected from oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc or manganese. 4. A method as claimed in claim 1-3, wherein the thermit mixture contains aluminum and ferric oxide as strongly reductive element and strongly reducible metal oxide, respectively. 5. A method as claimed in claim 1-4, wherein the the aluminum and ferric oxide in the thermit mixture are in stoichiometric amounts. 6. A method as claimed in claim 1-5, wherein the powders of aluminum and ferric oxide are of particle size of at least -170 mesh. 7. A method as claimed in claim 1-6, wherein the thermit mixture is packed in the hollow cone to about 20 to 60% of the theoretical density of the thermit mixture. 8. A method as claimed in claim 1-7, wherein the the biaxial rotation is effected at speeds of rotation of the hollow cone about its axis, N1, and about an external axis, N2, being selected such that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end and the big end of the hollow right circular cone faces the external axis, N2, of rotation and the following condition is satisfied: N2/N1 = ((r/R)tan9)05 wherein, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 9 is the semi apex angle of the cone. 9. A method as claimed in claim 1-8, wherein the method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, comprises: (a) inserting a hollow truncated right circular cone in a supporting block having a hole matching with the external geometry of the said hollow truncated right circular cone, the said matching hole in the supporting block being provided with a circular cavity formed inside the cylindrical hole extending below the small end of the hollow truncated right circular cone; (b) fixing a refractory core to the said supporting block such that the core is introduced at the center of the small end of the said hollow truncated right circular cone and the core seals the bottom of the said supporting block; (c) packing the said hollow truncated right circular cone with a powdery thermit mixture comprising of powders of a strongly reducible metal oxide and a reductant metal; (d) fixing firmly by means such as flanges and fasteners in a biaxial rotary fixture, the said supporting block along with the said thermit mixture packed hollow truncated right circular cone in such a manner that the axes of the supporting block, refractory core and the truncated hollow right circular cone coincide. (e) subjecting the assembly to biaxial rotation about the axis of the cone and simultaneously rotating it about an external axis normal to and coplanar with the axis of the cone, such that the resultant centrifugal force at the small end of the hollow truncated right circular cone is normal to the inside surface of the said cone; (f) igniting the said thermit mixture packed in the said truncated hollow right circular cone being subjected to biaxial rotation; (g) continuing the biaxial rotation for a time period in the range of 5 to 30 minutes; (h) stopping the biaxial rotation and separating the refractory core and a solidified metal ring formed in the supporting block cavity to obtain a ceramic lined hollow truncated right circular cone. 10. A method as claimed in claim 9, wherein the hollow space of the cone is of axisymmetric truncated geometry of conic sections, such as circular, parabolic, elliptical. 11. A method as claimed in claim 9-10, wherein the supporting block and core is thermally conducting and capable of withstanding thermal and physical stress and is inert and non- wetting with respect to the products of the thermit reaction and made of material preferably graphite. 12. A method as claimed in claim 9-11, wherein the cavity in the supporting block is a circular groove made coaxial with the axis of the supporting block and can be of any cross- section with the side of the cavity, facing the axis of the supporting block/hollow cone, open. 13. A method as claimed in claim 9-12, wherein the size of the cavity is such that its volume is at least equal to the volume of the metal product produced by the thermit reaction of the thermit mixture packed in the hollow cone. 14. A method as claimed in claim 9-13, wherein the means for igniting the thermit mixture packed in the hollow truncated right circular cone is such as a rotary igniter, an oxy- acetylene flame. 15. A method as claimed in claim 9-14, wherein the size of the refractory core is such that the radial gap between the refractory core and the inner diameter of the truncated hollow cone at the small end is at least the thickness of the ceramic lining being formed and sufficiently large to facilitate easy passage of the molten metal product of the thermit reaction into the said cavity. 16. A method as claimed in claim 9-15, wherein the the free surface of the thermit mixture is made concave by scraping the packed thermit mixture by rotating a parabolic or an elliptical metal template about the axis of the hollow cone and taking reference of the big end of the hollow cone. 17. A method as claimed in claim 9-16, wherein the hollow truncated right circular cone is made of a metal such as iron, nickel, aluminum and their alloys. 18. A method as claimed in claim 9-17, wherein the hollow truncated right circular cone and its contents are subjected to biaxial rotation using prime movers, preferably variable speed electric motors. 19. A method as claimed in claim 9-18, wherein the hollow truncated right circular cone, along with its contents, is subjected to biaxial rotation such that the resultant centrifugal force at any point on the inside surface of the cone is sufficient to cause complete separation of the metal and ceramic products of the thermit reaction. 20. A method as claimed in claim 9-19, wherein the thermit mixture is diluted with the ceramic product of the thermit reaction to lower the adiabatic temperature of the thermit reaction. 21. A method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, substantially as herein described with reference to the examples and drawing accompanying this specification.

Full Text

The present invention relates to a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone. The method of the present invention is particularly useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as a truncated right circular cone. The present invention more particularly provides a method for producing ceramic lining on the inward surface of hollow truncated right circular cone to be used in high temperature applications as thermal barrier coatings.
The novel method of the present invention is applicable to any hollow cone and is most applicable to a truncated hollow right circular cone. Any highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, is useful in the present method. Many thermit reactions, which readily meet these requirements, are more preferred owing to the easy availability of the starting materials at lower cost and easiness in controlling the reaction.
Axisymmetric convergent - divergent nozzles and tubular parts are important components in the chemical and engineering industry, particularly in propulsion units in aerospace and high-end automotive industries. These components are generally made of a metal, such as iron, nickel and aluminum, and are exposed to high temperatures during operations. These metal components are protected from high temperatures by thermal barrier coatings. Ceramics having high melting points, low thermal conductivities, low densities and good wear, corrosion and oxidation resistances are promising materials for such thermal barrier applications. Many spray and vapor deposition methods are commercially available for providing such components with thermal barrier coatings made of ceramics. However, these methods are time, energy and cost consuming and limited to coating thickness of up to about 2mm.
Reference may be made to US Patent No. 4,363,832; titled: Method for providing ceramic lining to a hollow body by thermit reaction. According to the invention, a thermit mixture, for example, composed of aluminum powder and an iron oxide is placed in the hollow space of the hollow body, which is rotated at a high speed so as that the thermit mixture is pressed against the wall of the hollow body by the centrifugal force and the thermit mixture is ignited, for example, by contacting with an acetylene flame. The thermit reaction of the thermit mixture propagates under the influence of the centrifugal force so that the molten metal formed from the reducible metal oxide and the ceramic oxide formed from the strongly
reductive element are separated into stratified layers by virtue of their density difference with the ceramic oxide forming the innermost layer and the metal forming the intermediate layer between the ceramic oxide layer and the wall of the hollow body with strong bonding of the ceramic oxide layer upon solidification by cooling. The method uses a highly exothermic thermit reaction, capable of self-propagation, to synthesize the desired ceramic in molten condition. The reaction is carried out inside a metal tube, while the tube is rotated about its axis, to form a ceramic lining of uniform thickness. O. Odawara and J. Ikeuchi used this method (Journal of American Ceramic society, 69 (4), PP: 80-81, 1986) to provide ceramic-ceramic composite lining to a metal pipe. Also, 0. Odawara used this method to produce long ceramic lined pipes (Journal of American Ceramic society, 73 (4) PP: 629-33, 1990). However, this method is not useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone. Because, the products of the thermit reaction slide over the inner surface of the cone under the effect of centrifugal force and collect near its largest diameter with the formation of a circular hole in the center of the thermit products. This way the formation of uniform thickness of ceramic lining on the inside surface of the cone is prevented in this method.
Reference may also be made to the gravitational thermit process disclosed in Japanese Patent No. 8889676, for fabricating a ceramic lined metal pipe. Here, a pipe is held vertically and loosely filled with a thermit mixture. The mixture at the top of the pipe is ignited to initiate the thermit reaction. The reaction then propagates from the top to the bottom of the pipe. The molten ceramic product of the thermit reaction is deposited on the inside surface of the pipe as a layer and forms a solidified ceramic lining.
Reference may be drawn to the Japanese Patent No. JP3229881, titled: Method for applying ceramics lining on inside surface of pipe, wherein the ceramics lining on the inside surface of a large-diameter pipe is formed by inserting an inside pipe which is capped with a thin-film material, and has many holes into the pipe, packing a thermit reaction agent into the spacing between the two pipes and firing the agent at the time of lining the inside surface of the pipe with ceramics by utilizing a thermit method.
Reference may also be drawn to the Japanese Patent No. JP 61076681, titled: Ceramic lining method of metallic tubular body; wherein is disclosed how to form easily a ceramic layer on the inside wall surface of a metallic tubular body by pressurizing and packing a
powder mixture composed of a strong reducing element and metallic oxide at specific density into the hollow part of the tubular body, heating the packing material in the upper part and progressing reaction toward the lower part.
These prior art methods of forming ceramic linings inside pipes are neither intended nor useful to form a thick ceramic lining of uniform thickness on the inward surface of a hollow truncated right circular cone.
From the details and drawbacks of hitherto known prior art methods of forming ceramic linings inside hollow metal pipes, it is clear that there is a definite need and scope for the development of a method to provide ceramic lining to a hollow truncated right circular cone.
The main objective of the present invention is to provide a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, which obviates the drawbacks of the herein above referred prior art.
Another objective of the present invention is to provide a simple, convenient and inexpensive method of forming a ceramic lining on the inward surface of a hollow truncated right circular cone.
The above objectives are achieved by providing a novel method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as of a hollow truncated right circular cone, wherein a thermit reaction is carried out inside such a cone while it is subjected to biaxial rotation.
The present invention discloses a method of forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone. The method of the present invention provides a ceramic lining on the inside surface of a hollow truncated right circular cone by simultaneous biaxial rotation of the hollow truncated right circular cone and carrying out a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as a thermit reaction inside such a cone while it is rotating. This is accomplished by carrying out preferably a highly exothermic thermit reaction, capable of self-propagation and resulting in molten products, inside a hollow axisymmetric cone,
such as on the inside surface of a hollow truncated right circular cone subjected to biaxial rotation. Thermit reactions, which readily meet these requirements, are more preferred owing to the easy availability of the starting materials at lower cost and easiness in controlling the reaction.
Accordingly, the present invention provides a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, which comprises effecting a highly exothermic reaction, capable of self-propagation after ignition and releasing sufficient heat to result in molten product or products, such as an exothermic thermit reaction of a thermit mixture containing a strongly reductive element and a reducible metal oxide, capable of self-propagation and resulting in molten products, inside a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone, characterized in that the said exothermic thermit reaction is effected inside the cone while the said cone is being subjected to biaxial rotation about its axis and about an external axis.
In an embodiment of the present invention, the thermit mixture contains at least one strongly reductive element selected from aluminum, magnesium, zirconium or silicon.
In another embodiment of the present invention, the thermit mixture contains at least one strongly reducible metal oxide selected from oxides of iron, nickel, copper, tungsten, titanium, molybdenum, vanadium, chromium, niobium, zinc or manganese.
In a still another embodiment of the present invention, the thermit mixture contains aluminum and ferric oxide as strongly reductive element and strongly reducible metal oxide, respectively.
In a yet another embodiment of the present invention, the aluminum and ferric oxide in the thermit mixture are in stoichiometric amounts.
In a still yet another embodiment of the present invention, the powders of aluminum and ferric oxide are of particle size of at least -170 mesh.
In a further embodiment of the present invention, the thermit mixture is packed in the hollow cone to about 20 to 60% of the theoretical density of the thermit mixture.
In a yet further embodiment of the present invention, the biaxial rotation is effected at speeds of rotation of the hollow cone about its axis, N1, and about an external axis, N2, being selected such that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end and the big end of the hollow right circular cone faces the external axis, N2, of rotation and the following condition is satisfied:
N2/N1 = ((r/R)tan0)05
wherein, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 6 is the semi apex angle of the cone.
In a still further embodiment of the present invention, the method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, comprises:
(a) inserting a hollow truncated right circular cone in a supporting block having a hole
matching with the external geometry of the said hollow truncated right circular cone, the said
matching hole in the supporting block being provided with a circular cavity formed inside the
cylindrical hole extending below the small end of the hollow truncated right circular cone;
(b) fixing a refractory core to the said supporting block such that the core is introduced at the
center of the small end of the said hollow truncated right circular cone and the core seals the
bottom of the said supporting block;
(c) packing the said hollow truncated right circular cone with a powdery thermit mixture
comprising of powders of a strongly reducible metal oxide and a reductant metal;
(d) fixing firmly by means such as flanges and fasteners in a biaxial rotary fixture, the said
supporting block along with the said thermit mixture packed hollow truncated right circular
cone in such a manner that the axes of the supporting block, refractory core and the
truncated hollow right circular cone coincide.
(e) subjecting the assembly to biaxial rotation about the axis of the cone and simultaneously
rotating it about an external axis normal to and coplanar with the axis of the cone, such that
the resultant centrifugal force at the small end of the hollow truncated right circular cone is
normal to the inside surface of the said cone;
(f) igniting the said thermit mixture packed in the said truncated hollow right circular cone
being subjected to biaxial rotation;
(g) continuing the biaxial rotation for a time period in the range of 5 to 30 minutes;
(h) stopping the biaxial rotation and separating the refractory core and a solidified metal ring formed in the supporting block cavity to obtain a ceramic lined hollow truncated right circular cone.
In another embodiment of the present invention, the hollow space of the cone is of axisymmetric truncated geometry of conic sections, such as circular, parabolic, elliptical.
In yet another embodiment of the present invention, the supporting block and core is thermally conducting and capable of withstanding thermal and physical stress and is inert and non-wetting with respect to the products of the thermit reaction and made of material preferably graphite.
In still another embodiment of the present invention, the cavity in the supporting block is a circular groove made coaxial with the axis of the supporting block and can be of any cross-section with the side of the cavity, facing the axis of the supporting block/hollow cone, open.
In still yet another embodiment of the present invention, the size of the cavity is such that its volume is at least equal to the volume of the metal product produced by the thermit reaction of the thermit mixture packed in the hollow cone.
In a further embodiment of the present invention, the means for igniting the thermit mixture packed in the hollow truncated right circular cone is such as a rotary igniter, an oxy-acetylene flame.
In a yet further embodiment of the present invention, the size of the refractory core is such that the radial gap between the refractory core and the inner diameter of the truncated hollow cone at the small end is at least the thickness of the ceramic lining being formed and sufficiently large to facilitate easy passage of the molten metal product of the thermit reaction into the said cavity.
In a still further embodiment of the present invention, the free surface of the thermit mixture is made concave by scraping the packed thermit mixture by rotating a parabolic or an elliptical metal template about the axis of the hollow cone and taking reference of the big end of the hollow cone.
In another embodiment of the present invention, the hollow truncated right circular cone is made of a metal such as iron, nickel, aluminum and their alloys.
In yet another embodiment of the present invention, the hollow truncated right circular cone and its contents are subjected to biaxial rotation using prime movers, preferably variable speed electric motors.
In still another embodiment of the present invention, the hollow truncated right circular cone, along with its contents, is subjected to biaxial rotation such that the resultant centrifugal force at any point on the inside surface of the cone is sufficient to cause complete separation of the metal and ceramic products of the thermit reaction.
In still yet another embodiment of the present invention, the thermit mixture is diluted with the ceramic product of the thermit reaction to lower the adiabatic temperature of the thermit reaction.
In the present invention there is provided a method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, which comprises the steps of:
(1) Inserting a hollow truncated right circular cone in a supporting block having a hole
matching with the external geometry of the said hollow truncated right circular cone. The
said matching hole made in a supporting block is provided with a circular cavity formed
inside the cylindrical hole in the supporting block, the said cylindrical hole extending below
the small end of the hollow truncated right circular cone.
(2) Fixing a refractory core to the said supporting block such that the core is introduced at
the center of the small end of the said hollow truncated right circular cone and the core seals
the bottom of the said supporting block.
(3) Packing the said hollow truncated right circular cone with a powdery thermit mixture
comprising of powders of a strongly reducible metal oxide and a reductant metal.
(4) Fixing firmly the said supporting block, along with the said hollow truncated right circular
cone packed with the thermit mixture to a rotary fixture made of steel flanges by steel
fasteners. The hollow truncated right circular cone and the refractory core are fitted to the
supporting block firmly in a rotary fixture in such a way that the axes of the supporting block,
refractory core and the truncated hollow right circular cone coincide.
(5) Rotating the whole assembly about the axis of the cone and simultaneously rotating it
about an external axis (biaxial rotation), normal to and coplanar with the axis of the cone,
such that the resultant centrifugal force at the small end of the hollow truncated right circular
cone is normal to the inside surface of the cone.
(6) Heating the powdery thermit mixture in the truncated hollow right circular cone locally at
least at one point on its free surface to a sufficiently high temperature, depending on the type
of thermit reaction, using an igniter so as to cause ignition of the thermit mixture and initiate
the thermit reaction which propagates through the remaining thermit mixture in the cone
converting all the reactants to molten products, namely, a stable oxide of the metal reductant
and the metal of the reducible metal oxide with the lighter molten metal oxide depositing over
the inner surface of the hollow truncated right circular cone as a ceramic lining and the
denser molten metal filling the cavity.
(7) Continuing the biaxial rotation for time between 5 to 30 minutes to allow the reaction
products to solidify and cool.
(8) stopping the biaxial rotation and separating the ceramic lined hollow right circular cone
from the supporting block, the solidified metal ring in the cavity and the refractory core to get
a ceramic lined hollow truncated right circular cone.
In a feature of the present invention, hollow truncated right circular cone is made of a material capable of withstanding thermal shock due to the instantaneous heat released by the exothermic reaction and stresses induced by centrifugal forces.
In another feature of the present invention, the hollow truncated right circular cone is made of a metal such as iron, nickel, aluminum and their alloys.
In yet another feature of the present invention, the supporting block is of sufficient strength to withstand the stresses induced in it by the biaxial rotation of the supporting block and the components it supports.
In still another feature of the present invention, the supporting block is made of a material capable of withstanding thermal shock due to the instantaneous heat released by the exothermic reaction and stresses induced by centrifugal forces.

In still yet another feature of the present invention, the supporting block is made of a material having good thermal conductivity to act as a heat sink to prevent destruction of the cone being ceramic lined.
In a further feature of the present invention, the supporting block is made of a material having low density and high temperature capability, such as graphite.
In a still further feature of the present invention, the cavity in the supporting block can be of any cross section with the side of the cavity, facing the axis of the supporting block/hollow cone, open.
In a yet further feature of the present invention, the core is capable of withstanding thermal shock due to exothermic reaction heat and stresses induced by the centrifugal forces and the core material is inert and non-wetting with respect to the products of the thermit reaction being carried out and is made of a material such as graphite.
In another feature of the present invention, the thermit reaction is initiated by striking an arc between two mild steel electrodes of a rotary igniter and bringing the arc in contact with the thermit mixture packed in the hollow cone.
The novelty of the present invention lies in providing a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular cone.
The novelty of the present invention has been achieved by the non-obvious inventive steps of biaxial rotation of the hollow truncated right circular cone and carrying out a thermit reaction inside such a cone while it is rotating. The reaction should be sufficiently exothermic to produce the products in molten condition. The biaxial rotation of the cone is carried out in such a way that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end. This is possible when the big end of the hollow right circular cone faces the external axis of rotation. The supporting block housing the cone is provided with a cavity for the deposition of denser metal product while the lower density ceramic material spreads over the inner surface of the cone to form the lining.
The method of the present invention which is particularly useful for forming a ceramic lining of uniform thickness on the inward surface of a hollow axisymmetric cone, such as a truncated right circular cone is illustrated in figurel of the drawing accompanying this specification in which the numerals indicated refers to:
1. Hollow truncated right circular cone
2. Cavity
3. Refractory core
4. Thermit mixture
5. Igniter
6. Supporting block
7. Rotary fixture
N1. The speed of rotation of the cone about its axis
N2. The speed of rotation of the cone about an external axis.
A thermit mixture is a mixture of powders of a strongly reductive element and a reducible metal oxide. When a thermit reaction is carried out using such a thermit mixture, the oxide of the strongly reductive element and the metal of the reducible metal oxide are produced as products. The strongly reductive element can be aluminum, zirconium, magnesium or silicon to get the respective oxide as the ceramic product. The strongly reducible metal oxide can be chosen from the oxides of iron, nickel, copper, molybdenum, vanadium, titanium, manganese etc. to form the respective metal product. In addition, the thermit mixture may contain other components, either an element such as carbon, boron or silicon or a compound such as boric oxide, to form carbide, boride or silicide in place of pure metal product produced in a conventional thermit reaction. Thus, thermit based reactions can also be used in the present method to provide a hollow truncated right circular cone with ceramic-ceramic composite linings. A few thermit and thermit based reactions useful for the present method and their estimated heats of reaction (AH) and adiabatic temperatures (Ta Reaction
Fe2O3+2AI _
2Fe2O3+3Zr -
MnO2+Si _
Fe2O3+3Mg -
MoO3+2AI+2Si -
2MoO3+4AI+C _
MoO3+2AI+B _
3Cr2O3+6AI+4C -
3WO3+14AI+6SiO2 -
2WO3+6AI+B2O3 -
A powdery mixture of a thermit or thermit based reaction containing non-stoichiometric amounts of the reactants can also be used in the present invention, if the reaction self propagates after ignition and the products produced are in molten state. Additionally, one of the products of a thermit or thermit based reaction can be added as an inert diluents to lower the adiabatic temperature of the reaction while maintaining the self propagating nature of the reaction. When the ceramic product of such a reaction is used as inert diluents, the yield of that product can be increased using the same amount of the stoichiometric mixture of the thermit or thermit based reaction. When a thermit or thermit based reaction is not self propagating, prior heating of the thermit mixture to a suitable temperature is the primary requisite. If the thermit reaction is difficult to ignite, ignition under an inert gas cover may help to initiate the ignition of the thermit mixture. If the adiabatic temperature of a reaction is higher than the boiling or sublimation temperature of any of the reactants, the present method may be carried out under inert gas pressure.
A homogeneous powdery mixture is prepared by uniformly blending the powders of the reactants, in stoichiometric amounts, of a thermit or thermit based reaction in a mechanical mixer or blender, preferably sealed, for 12 to 24 hours. The powders used are preferably of -200mesh size and baked at about 120° C for 12 to 24 hours before mixing.
In the next step, the given hollow truncated right circular cone is placed in the matching hole of a supporting block that is provided with a circular cavity below the small end of the hollow cone. The cavity in the supporting block is formed such that the volume of the cavity is at least equal to the volume of the metal product produced in the thermit reaction. A cylindrical refractory core of diameter equal to or less than the inner diameter of the ceramic lined cone at its small end is located in the supporting block such that the core is projecting inside the small end of the cone by at least the thickness of the ceramic lining. The refractory core may be hollow with the top, in contact with the thermit mixture, closed. The supporting block and the core can be made of a material capable of resisting high temperatures with good thermal shock resistance. Also, it is preferable that the material used for supporting block and core is inert and non-wetting with respect to the products of the reaction being carried out. Although many metals and ceramics are useful for making supporting block and core, graphite is adequate in most cases owing to its easy availability at low cost and good properties, such as high temperature capability, tolerable inertness to many materials at high temperatures, easy machinability, good thermal shock resistance and strength at elevated temperatures.
In the next step, the speeds of rotation of the hollow cone about its axis, N1, and about the external axis, N2, are selected such that the resultant centrifugal force is normal to the inside surface of the hollow cone at its small end. This is possible when the big end of the hollow right circular cone faces the external axis of rotation and the following condition is satisfied:
Where, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 9 is the semi apex angle of the cone. These speeds are chosen such that the resultant centrifugal force at the small end of the hollow cone is sufficient to cause complete separation of the thermit products. Otherwise, the hollow cone will be lined with a mixture of ceramic+metal or ceramic+ceramic materials, depending upon the composition of the starting mixture.
In the next step, the hollow cone is packed with the prepared thermit or thermit based reaction mixture. The thermit mixture in the hollow space of the cone can be packed with uniform thickness of thermit over the inside surface of the cone or simply packed to some depth of the cone. However, the best results are obtained when the free surface of the thermit mixture is made concave with a parabolic or an elliptical geometry. This can be done by scraping the packed thermit mixture by rotating a parabolic or an elliptical metal template
about the axis of the hollow cone and taking reference of the big end of the hollow cone. Although the bottom of the concave geometry of the filled thermit mixture (or the bottom of the free surface of the filled thermit mixture) can touch the flat end of the ceramic core or the geometry can be cut by the core exposing the flat end of the core, it is preferable to select a suitable concave geometry such that the bottom of the free surface of the filled thermit mixture is about 3mm above the flat end of the core. Also, it is preferable to select a suitable concave geometry so as to form about 3mm thick thermit powder along the circumference of the big end of the cone. The packed thermit mixture should have a green density of less than a critical value (about 60% theoretical density for the thermit mixture comprising of iron oxide and aluminum) so that the reaction can self propagate without extinguishing. The concave geometry of the free surface is so selected that the quantity of the thermit mixture packed in the hollow right circular cone is sufficient to form the require thickness of the ceramic lining on the inside surface of the hollow cone.
The supporting block, hollow right circular cone packed with the thermit mixture and the core are fitted together firmly to a rotary fixture made of steel flanges. The rotary fixture is then mounted in a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers are preferably variable speed motors. The rotary fixture is mounted in the machine so that the big end of the hollow cone faces the external axis of rotation, the axis of the hollow cone is normal to the external axis of rotation and the external axis is coplanar with the axis of the cone.
In the next step, the rotary fixture along with its contents is rotated about the axis of the cone and about the external axis at the predetermined speeds of N1 and N2, respectively.
In the next step, the thermit or thermit based reaction is initiated on the free surface of the powdery thermit mixture, packed in the hollow cone, by heating it locally on its free surface to or above its ignition temperature. This may be carried out, for example, by bringing an electric arc, struck between two electrodes, in contact with the free surface of the powdery mixture packed in the hollow cone. The thermit reaction, thus initiated, rapidly propagates through the remaining powdery mixture in the hollow cone to convert all the reactants into products, namely a ceramic and a metal. The high exothermic heat released by the thermit reaction results in the ceramic and metal products in molten condition. Under the effect of the biaxial rotation, the denser molten metal product collects in the cavity and the lighter
molten ceramic product is deposited on the inner surface of the cone as a uniform layer. It is desirable to keep the products of the thermit reaction in molten condition for a longer duration while in rotation so that the molten ceramic product spread uniformly over the inward surface of the hollow cone and the gases, contained in the powdery mixture and those produced by the reaction, escape to the ambient. The present method can be carried out inside an enclosure and the enclosure can be evacuated to remove the gases trapped in the powdery mixture. Back filling the enclosure with an inert gas, such as argon, can improve the quality of the solidified ceramic lining. This approach also helps in overcoming the problem of ignition of some thermit or thermit based reactions in air when such reactions are employed in the present method.
The rotation of the assembly is continued for 5 to 30 minutes to allow the molten products to solidify and cool by losing heat to the surroundings. After solidification and cooling, a ceramic lining of uniform thickness is formed on the inner surface of the cone.
The rotation of the assembly is stopped and the ceramic lined hollow truncated right circular cone is separated from the rotary fixture, metal product collected in the cavity and the ceramic core.
The following examples are given by way of illustration of the present invention in actual practice and should not be construed to limit the scope of the present invention in any way.
Example -1
Ferric oxide and aluminium powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 100g of ferric oxide and 33.8g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use.
A hollow truncated right circular cone, fabricated from mild steel sheet of 2mm thickness, was used for ceramic lining using aluminium oxide. The hollow cone had internal diameters of 85mm and 35mm at big and small ends, respectively, and a height of about 42mm. The hollow cone had a semi apex angle of about 30.75°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis.
The supporting block was provided with a circular recess of 45mm diameter with rectangular crossection, 4mmx5mm, to form the cavity inside the cylindrical hole of 35mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 32mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 4mm above that end. The hollow metal cone was packed with about 75g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=58.6y) was formed in the packed thermit mixture. The parabolic concave surface had 75mm diameter at the big end of the hollow cone and a depth of 24mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 50g after scraping. The green density of the thermit mixture packed in the hollow cone was about 19.5% of the estimated theoretical density (4.2409 g.cm"3) of the thermit mixture.
The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1702 rpm about the axis of the cone and 402 rpm about the external axis that was at a distance of about 186mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the
inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of mild steel of 2mm thickness with a semi apex angle of about 30.75°, was lined with about 1mm thick aluminum oxide ceramic.
Example -2
Ferric oxide and aluminium powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 100g of ferric oxide and 33.8g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use.
A hollow truncated right circular cone of 2mm wall thickness, machined from stainless steel, was used for ceramic lining using aluminum oxide. The hollow cone had internal diameters of 91mm and 51mm at big and small ends, respectively, and a height of about 36mm. The hollow cone had a semi apex angle of about 29°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a circular cavity of nearly a right angle triangle crossection with 5.9mm of sides. This cavity was formed by assembling graphite components inside the cylindrical hole of 70mm formed at the end of the conical hole in the block. The cavity was open to the hollow space of the cone by approximately 1 mm wide circular gap facing the core. The volume of the cavity was sufficient to accommodate the quantity of iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 47mm and length 5mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 4mm above that end. The hollow metal cone was packed with about 80g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=64y) is formed in the packed thermit mixture. The parabolic concave surface had 80mm diameter at the big end of the hollow
cone and a depth of 25mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 66g. The green density of the thermit mixture packed in the hollow cone was about 20% of the estimated theoretical density (4.2409 g.cm" 3) of the thermit mixture.
The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1400 rpm about the axis of the cone and 386 rpm about the external axis that was at a distance of about 186mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 20 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of mild steel of 2mm thickness with a semi apex angle of about 29°, was lined with about 1mm thick aluminum oxide ceramic.
Example - 3
Ferric oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 150g of ferric oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours.
The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use.
A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 111.8mm and 85.5mm at big and small ends, respectively, and a height of about 49mm. The hollow cone had a semi apex angle of about 15° The cone was mounted in a cylindrical supporting block, 120mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 102mm diameter circular recess of rectangular crossection, 4mm x 9mm, to form the cavity inside the cylindrical hole of 84mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 81mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 130g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a parabolic metal template, made of 1mm thick aluminium sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a free surface of concave parabolic geometry (x2=66y) was formed in the packed thermit mixture. The parabolic concave surface had 108mm diameter at the big end of the hollow cone and a depth of 44mm at the center. The amount of the thermit mixture packed in the hollow metal cone was found to be about 110g after scraping. The green density of the thermit mixture packed in the hollow cone was about 20% of the estimated theoretical density (4.2409 g/cc) of the thermit mixture.
The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1166rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone.
While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the parabolic free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic.
Example - 4
Ferric oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared by intimately mixing 150g of ferric oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The mixture was stored in a desiccator prior to use.
A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 111.8mm and 85.5mm at big and small ends, respectively, and a height of about 49mm. The hollow cone had a semi apex angle of about 15°. The cone was mounted in a cylindrical supporting block, 120mm diameter and 60mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 102mm diameter circular recess of rectangular crossection, 4mm x 9mm, to form the cavity inside the cylindrical hole of 84mm formed at the end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of
diameter 81mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 130g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating an elliptical metal template, made of 1mm thick aluminium sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. This way a concave free surface with a segment of an elliptical geometry ((X/64.9)2+(Y/319.2)2=1) was formed in the packed thermit mixture. The segment of the elliptical concave surface had 85mm diameter at the big end of the hollow cone and about 60mm diameter at the small end. The amount of the thermit mixture packed in the hollow metal cone was found to be about 115g after scraping. The green density of the thermit mixture packed in the hollow cone was about 20% of the theoretical density (4.2409 g.cm"3) of the thermit mixture.
The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1166rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of the thermit reaction is 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone,
made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic.
Example - 5
Ferric oxide, Aluminum oxide and aluminum powders, having particles of size -325 mesh, were dried in an electric oven at 120°C for 12 hours. An aluminum oxide diluted thermit mixture was prepared by intimately mixing 150g of ferric oxide, 13.04g of Aluminum oxide and 50.7g of aluminum in a sealed double cone blender for 12 hours. The mixing ratio was nearly stoichiometric. The dilution was just enough to avoid vaporization of iron product of the thermit reaction. The mixture was stored in a desiccator prior to use. A hollow truncated right circular cone, made of stainless steel of 2mm wall thickness, was used for ceramic lining using aluminum oxide. The cone was prepared by machining. The hollow cone had internal diameters of 85.3mm and 36mm at big and small ends, respectively, and a height of about 92mm. The hollow cone had a semi apex angle of about 15°. The cone was mounted in a cylindrical supporting block, 95mm diameter and 110mm length, machined from graphite with a conical hole, similar to the outside geometry of the metal hollow cone, at its center along the axis. The supporting block was provided with a 60 mm diameter circular recess of rectangular crossection, 4mm x 12mm, to form the cavity inside the cylindrical hole of 36mm diameter formed at the small end of the conical hole in the block. The size of the cavity was sufficient to accommodate the quantity of molten iron produced after the reaction of all the thermit mixture taken in the metal hollow cone. A graphite core of diameter 33mm and length 10mm was prepared by machining and fitted to the supporting block such that the core is at the center of the small end of the metal hollow cone and it projects about 3mm above that end. The hollow metal cone was packed with about 140g of the prepared thermit mixture by hand. The packed thermit mixture was scraped by rotating a combined parabolic + elliptical metal template, made of 1mm thick aluminum sheet, about the axis of the hollow cone and taking reference of the big end of the hollow cone. The parabolic geometry (x2=24.728y) was about 50mm deep from the big end of the hollow cone. The elliptical geometry ((x/28.985)2+(y/180)2) = 1) was 32mm deep from the end of the parabolic geometry. This way a concave free surface of parabolic + elliptic combined geometry was formed in the packed thermit mixture. The parabolic concave surface had 78mm diameter at the big end of the hollow cone. The amount of the thermit mixture packed in the hollow metal cone was found to be about 109g after scraping. The
green density of the thermit mixture packed in the hollow cone was about 19.1% of the estimated theoretical density (4.2230 g/cc) of the thermit mixture.
The supporting block along with the hollow cone packed with the thermit mixture was fitted firmly to a rotary fixture, made of steel flanges, by steel fasteners. The rotary fixture was mounted on the shaft of a machine capable of causing the required biaxial rotation of the hollow right circular cone using prime movers. The prime movers used were variable speed motors. The rotary fixture was so mounted in the machine that the big end of the hollow cone faced the external axis of rotation, the axis of the hollow cone was normal to the external axis of rotation and the external axis was coplanar with the axis of the cone. The rotary fixture was rotated at about 1714rpm about the axis of the cone and 230rpm about the external axis that was at a distance of about 280mm from the small end of the hollow cone. While the hollow cone with the thermit mixture was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes of a rotary igniter, in contact with the bottom of the free surface of the packed thermit mixture in the hollow steel cone. The reaction then propagated rapidly through the remaining thermit mixture in the hollow cone and was completed quickly. As the estimated adiabatic temperature of this diluted thermit reaction is about 3133K which is higher than the melting points of the products, the products were produced in molten state. The molten products got separated due to their differing densities. The denser molten metal is pushed into the cavity and collected there, while the lighter molten metal oxide deposited as a uniform layer over the inside surface of the hollow cone by the effect of biaxial rotation. The biaxial rotation of the whole assembly was continued for about 15 more minutes to allow the molten thermit products to solidify and cool. The ceramic lined hollow cone was then separated from the supporting block, the solidified iron casting in the cavity and the ceramic core by mechanical means. Thus a hollow truncated right circular cone, made of stainless steel of 2mm thickness with a semi apex angle of about 15°, was lined with about 1.5mm thick aluminum oxide ceramic.
The above ceramic lined hollow truncated right circular cones obtained in the examples 1 to
5 were tested by blowing hot gases through it. The test parameters were as follows:
Gas pressure : 11.5Kgf/cm2
Gas temperature: 1930°K
Duration : SOsecs
The test results obtained were as follows:

.(Table Removed)
The above test results confirm the low thermal conductivity and stability of the ceramic lining.
The present inventive method of forming a ceramic lining on the inside surface of a hollow truncated right circular cone has been demonstrated in actual practice as detailed in the examples herein above. The desired ceramic was produced by a thermit reaction. As the estimated adiabatic temperature of the thermit reaction was higher than the melting point of the ceramic product, the desired ceramic was produced in molten state. The resultant centrifugal force due to biaxial rotation of the hollow cone was made normal to the inside surface of the hollow cone at its small end. The free surface of the thermit powder packed in the cone was made concave with parabolic, elliptical or their combinations to get best ceramic linings by this method. The present method is useful for forming ceramic linings from other ceramics, not covered in these examples, using suitable strong exothermic reactions. The present method is useful for ceramic lining of hollow truncated right circular cones with other semi apex angles between 0°and 90°, not covered in these examples. The present method is also useful for ceramic lining of other axisymmetric components having parabolic or elliptic inside hollow surface. In general, the method is most useful for ceramic lining of a hollow truncated axisymmetric body with the inside surface having conical, parabolic or elliptical geometry.
The main advantages of the present invention are:
1. The method requires no furnace to produce the required ceramic material in molten state
for forming the ceramic lining.
2. The power consumption is minimal.
3. The method is simple, easy and inexpensive.
4. No sophisticated and costly equipments are involved.
5. The method is useful for ceramic lining of a hollow truncated right circular cone.
6. The method is useful for ceramic lining of a hollow axisymmetric body, such as a hollow
surface having conical, parabolic or elliptical geometry.
7. The time required to form the ceramic lining is short.
8. The time for ceramic lining does not greatly depend on the size of the hollow component.

We claim:
1. A method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone,
which comprises effecting a highly exothermic reaction, capable of self-propagation after
ignition and releasing sufficient heat to result in molten product or products, such as an
exothermic thermit reaction of a thermit mixture containing a strongly reductive element and
a reducible metal oxide, capable of self-propagation and resulting in molten products, inside
a hollow axisymmetric cone, such as on the inside surface of a hollow truncated right circular
cone, characterized in that the said exothermic thermit reaction is effected inside the cone
while the said cone is being subjected to biaxial rotation about its axis and about an external
axis.
2. A method as claimed in claim 1, wherein the thermit mixture contains at least one strongly
reductive element selected from aluminum, magnesium, zirconium or silicon.
3. A method as claimed in claim 1-2, wherein the thermit mixture contains at least one
strongly reducible metal oxide selected from oxides of iron, nickel, copper, tungsten,
titanium, molybdenum, vanadium, chromium, niobium, zinc or manganese.
4. A method as claimed in claim 1-3, wherein the thermit mixture contains aluminum and
ferric oxide as strongly reductive element and strongly reducible metal oxide, respectively.
5. A method as claimed in claim 1-4, wherein the the aluminum and ferric oxide in the thermit
mixture are in stoichiometric amounts.
6. A method as claimed in claim 1-5, wherein the powders of aluminum and ferric oxide are
of particle size of at least -170 mesh.
7. A method as claimed in claim 1-6, wherein the thermit mixture is packed in the hollow
cone to about 20 to 60% of the theoretical density of the thermit mixture.
8. A method as claimed in claim 1-7, wherein the the biaxial rotation is effected at speeds of
rotation of the hollow cone about its axis, N1, and about an external axis, N2, being selected
such that the resultant centrifugal force is normal to the inside surface of the hollow cone at
its small end and the big end of the hollow right circular cone faces the external axis, N2, of rotation and the following condition is satisfied:
N2/N1 = ((r/R)tan9)05
wherein, r is the radius of the cone at the small end, R is the radius of the cone at the big end and 9 is the semi apex angle of the cone.
9. A method as claimed in claim 1-8, wherein the method of forming a ceramic lining on the inside surface of a hollow axisymmetric cone, such as a hollow truncated right circular cone, comprises:
(a) inserting a hollow truncated right circular cone in a supporting block having a hole
matching with the external geometry of the said hollow truncated right circular cone, the said
matching hole in the supporting block being provided with a circular cavity formed inside the
cylindrical hole extending below the small end of the hollow truncated right circular cone;
(b) fixing a refractory core to the said supporting block such that the core is introduced at the
center of the small end of the said hollow truncated right circular cone and the core seals the
bottom of the said supporting block;
(c) packing the said hollow truncated right circular cone with a powdery thermit mixture
comprising of powders of a strongly reducible metal oxide and a reductant metal;
(d) fixing firmly by means such as flanges and fasteners in a biaxial rotary fixture, the said
supporting block along with the said thermit mixture packed hollow truncated right circular
cone in such a manner that the axes of the supporting block, refractory core and the
truncated hollow right circular cone coincide.
(e) subjecting the assembly to biaxial rotation about the axis of the cone and simultaneously
rotating it about an external axis normal to and coplanar with the axis of the cone, such that
the resultant centrifugal force at the small end of the hollow truncated right circular cone is
normal to the inside surface of the said cone;
(f) igniting the said thermit mixture packed in the said truncated hollow right circular cone
being subjected to biaxial rotation;
(g) continuing the biaxial rotation for a time period in the range of 5 to 30 minutes;
(h) stopping the biaxial rotation and separating the refractory core and a solidified metal ring formed in the supporting block cavity to obtain a ceramic lined hollow truncated right circular cone.
10. A method as claimed in claim 9, wherein the hollow space of the cone is of axisymmetric
truncated geometry of conic sections, such as circular, parabolic, elliptical.
11. A method as claimed in claim 9-10, wherein the supporting block and core is thermally
conducting and capable of withstanding thermal and physical stress and is inert and non-
wetting with respect to the products of the thermit reaction and made of material preferably
graphite.
12. A method as claimed in claim 9-11, wherein the cavity in the supporting block is a
circular groove made coaxial with the axis of the supporting block and can be of any cross-
section with the side of the cavity, facing the axis of the supporting block/hollow cone, open.
13. A method as claimed in claim 9-12, wherein the size of the cavity is such that its volume
is at least equal to the volume of the metal product produced by the thermit reaction of the
thermit mixture packed in the hollow cone.
14. A method as claimed in claim 9-13, wherein the means for igniting the thermit mixture
packed in the hollow truncated right circular cone is such as a rotary igniter, an oxy-
acetylene flame.
15. A method as claimed in claim 9-14, wherein the size of the refractory core is such that
the radial gap between the refractory core and the inner diameter of the truncated hollow
cone at the small end is at least the thickness of the ceramic lining being formed and
sufficiently large to facilitate easy passage of the molten metal product of the thermit reaction
into the said cavity.
16. A method as claimed in claim 9-15, wherein the the free surface of the thermit mixture is
made concave by scraping the packed thermit mixture by rotating a parabolic or an elliptical
metal template about the axis of the hollow cone and taking reference of the big end of the
hollow cone.
17. A method as claimed in claim 9-16, wherein the hollow truncated right circular cone is
made of a metal such as iron, nickel, aluminum and their alloys.
18. A method as claimed in claim 9-17, wherein the hollow truncated right circular cone and
its contents are subjected to biaxial rotation using prime movers, preferably variable speed
electric motors.
19. A method as claimed in claim 9-18, wherein the hollow truncated right circular cone,
along with its contents, is subjected to biaxial rotation such that the resultant centrifugal force
at any point on the inside surface of the cone is sufficient to cause complete separation of
the metal and ceramic products of the thermit reaction.
20. A method as claimed in claim 9-19, wherein the thermit mixture is diluted with the
ceramic product of the thermit reaction to lower the adiabatic temperature of the thermit
reaction.
21. A method of forming a ceramic lining on the inside surface of a hollow axisymmetric
cone, substantially as herein described with reference to the examples and drawing
accompanying this specification.

Documents:

993-del-2007-abstract.pdf

993-del-2007-Claims-(16-09-2014).pdf

993-del-2007-claims.pdf

993-del-2007-Correspondence Others-(16-09-2014).pdf

993-del-2007-correspondence-others.pdf

993-del-2007-description (complete).pdf

993-del-2007-drawings.pdf

993-del-2007-form-1.pdf

993-del-2007-Form-2-(16-09-2014).pdf

993-del-2007-form-2.pdf

993-del-2007-form-3.pdf

993-del-2007-form-5.pdf

« Previous Patent

Next Patent »

Patent Number

263489

Indian Patent Application Number

993/DEL/2007

PG Journal Number

44/2014

Publication Date

31-Oct-2014

Grant Date

30-Oct-2014

Date of Filing

08-May-2007

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110 001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	RAJAIYENGAR SESHADRI	NATIONAL AEROSPACE, LABORATORIES, P.B.NO.1779, KODIHALLI,AIRPORT ROAD, BANGALORE-560017
2	ARUMUGAM ARUL PALIGAN	NATIONAL AEROSPACE, LABORATORIES, P.B.NO.1779, KODIHALLI,AIRPORT ROAD, BANGALORE-560017

PCT International Classification Number

C04B28/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA