Title of Invention

AN YTTRIA STABILIZED ZIRCONIA COATED THERMAL-RESISTANT COPPER TUYERS FOR USE IN IRON BLAST FURNACE

Abstract

There is disclosed an improved high thermal resistant copper tuyere for use in a blast fumace, said tuycre having a combination ceramic outer top coating made of yttria and zirconia. There is further disclosed a method for preparing highly thermal resistant copper tuyeres for use in blast furnace comprising the following steps: a. Machining the surface of the tuyere to be coated to expose fresh metal surface, b. Grit blasting and cleaning the surface for increasing the adhesion characteristics of the surface, c. Degreasing and pre-heating the surface to accept a metal alloy bond coat made of Ni-Cr-Al-Y, d. Applying by plasma spray said metal alloy coating preferably in several runs to obtain desired thickness of the bond coat, e. Cooling the bond layer coated surface, followed by, f. Applying a top coat of combination ceramic made of yttria stabilized zirconia by plasma technique till desired thickness is obtained and, g. Finally, cooling the coated tuyere to room temperature.

Full Text

Introduction to the Field of the Invention: In one aspect, this invention relates to a method for improving the thermal resistance of objects and/or working surfaces exposed to high temperatures in iron steel manufacturing. In another aspect, this invention relates to objects and/or working surfaces exposed to high temperatures in steel manufacturing having improved thermal resistance. Prior Art and Drawbacks: In the manufacture of steel, the production of iron from the ores is the first major step. This is universally carried out in a majority of installations with the help of a blast furnace where iron ore, reducing agent like coke and fluxing agent like limestone are used. It is well known that a blast furnace is a counter current heterogeneous reactive heat transfer system involving dynamic interaction between gaseous, liquid and solid phases. Pre-heated air. one of the inputs for iron making, is introduced through cast high purity copper tuyeres. The tuyeres are important components of blast furnaces. The tuyeres, 18-20 in number, are double-walled, high purity (around 99.5%) cast copper structures, through which pre-heated air (1100°C) is introduced into the blast furnace. These tuyeres are located at the intersection of bosh and the hearth of the furnace along the entire periphery. As the tuyeres are exposed to the hottest region in the blast furnace, where the raceway adiabatic flame temperature, RAFT, may frequently exceed 2000° C, the tuyeres are cooled internally by circulating water. The tuyere failure may take place due to accidental contact with burning coke particles/lumps, slag or hot metal drops leading to highly localized thermal load on relatively small area causing burn out. The sudden tuyere failure adversely affects the stable operation of blast furnace and consequently, its productivity. It is known to apply thermal barrier coatings to the tuyere to withstand this failure. Thus for example, US Patent 5989488 suggests a blast tuyere of a blast furnace, comprising: A tuyere trunk having a tuyere body and a tuyere nose said tuyere body and tuyere nose each having a cooling chamber, at least the upper half of the outer surface of a portion of said tuyere trunk projecting into said blast furnace being coated with a shell layer made of a material having a higher melting point then the melting point of Cu and higher than the temperature of a hot metal in said blast furnace, and a metal jacket fitted onto the outside of said shell layer. Japanese Patent 11217611 suggest almost the same modified tuyere. Japanese Patent 09302405 suggest a procedure to improve the service iives of furnaces and to reduce the cost of lining refractories, at the time of melting a stainless steel in blast furnaces, by alternately executing smelting reduction blowing and de-carburization blowing in the same blast furnace. In Japanese Patent No. 09268305, it is proposed to make it possible to smoothly execute the work to withdraw a blast furnace tuyere sonde of a water cooled structure by forming a dry film of molybdenum disuifide on the outside surface of the main body of this blast furnace tuyere sonde. These prior art and other practices in industry fail short of increasing the life cycle of tuyeres to make the system and practice economical. Objects of the invention: It is therefore an object of this invention to propose an improved method for increasing the iife of tuyeres by applying highly thermal resistant ceramic coatings on to the desired surface. It is another object of this invention to propose such a method by which the performance characteristics of the tuyeres can be improved. It is a further object of this invention to propose such a method, which will need only indigenously avaiiabie material for coating the desired areas of the tuyeres. It is a still further object of the invention to propose such a method whose technique is simple and does not require high skilled labour or expert supervision. Yet another object of this invention is to propose an improved tuyere having higher thermal resistance than hitherto possible and having extended life and improved performance characteristics. A still more object of this invention is to propose such an improved tuyere which can be fully indigenously made. The overall blast furnace operation becomes very economical and efficient. These and other objects of the invention will be more clear from the following paragraphs. Brief Statement of the Invention: According to the basic aspect of the invention, there is provided an yttria stabilized Zirconia coated thermal-resistant copper tuyere for use in iron blast furnace characterized in that the copper outer surface of the tuyere having a highly thermal resistant coating comprising an (i) intermediate bond coating on said copper outer surface of a metal alloy bond coating comprising (a) Cr-15 to 19 % (b) Al- 3 to 5 % (c ) Y- 3 to 5 % and (d) Ni- balance amount and (ii) an outer top ceramic coating applied on said metal alloy bond coating and having a combination ceramic outer top coating made of Yttria and Zirconia. The top coat is provided on an intermediate bond coat of metal alloy based on Nickel, on the copper outer surface of the tuyere and the metal alloy bond coating is made of nickel based chromium containing alloy. The alloy bond coating is made predominantly of Ni, followed by Cr, Al and Y and is made of atleast about 70% by weight of nickel, the balance being made of Cr, Al and Y; The amount of Cr in the bond coating is about 4-5 times the amount of Al or Y; The metal alloy bond coating is preferably made of the following by weight %, a. C:15%-19% b. AI:3-5% c. Y:3-5% and d. Ni- Balance. According to a further aspect of the present invention, there is provided a method of preparing highly thermal resistant copper tuyeres for use in blast furnace comprising the following steps: a. Machining the surface of the tuyere to be coated to expose fresh metal surface; b. Grit blasting and cleaning the surface for increasing the adhesion characteristics of the surface; c. Degreasing and pre-heating the surface to accept a metal alloy bond coat made of Ni-Cr-AI-Y, d. Applying by plasma spray said metal alloy coating preferably in several runs to obtain desired thickness of the bond coat, e. Cooling the bond layer coated surface, followed by, f. Applying a top coat of combination ceramic made of yttria stabilized zirconia by plasma technique till desired thickness is obtained and, g. Finally, cooling the coated tuyere to room temperature. In this method, the following conditions are maintained: - a. The zirconia is stabilized by 8% by weight of yttria, b. The top coat is provided on an intermediate bond coat of metal alloy on the copper outer surface of the tuyere, c. The metal alloy bond coating is made of nickel based chromium containing alloy, d. The alloy bond coating is made predominantly of Ni, followed by Cr, Al and Y, e. The metal alloy bond coating is made of atleast about 70% by weight of nickel, the balance being made of Cr, Al and Y, f. The amount of Cr in the bond coating is about 4-5 times the amount of Al or Y, g. The metal alloy bond coating is made of the following in weight %:- a. Cr-15 to 19% b. Al - 3 to 5% c. Y - 3 to 5% d. Ni - Balance. h. The bond coat and top coat are essentially powders with granulometric particle sizes of -100+325 mesh and -230 mesh respectively, i. The top coat is made of 8% yttria stabilized zirconia and, j. Plasma coating parameters are preferably the following: - Current - 700-800 Amperes Voltage - 40-60 volts DC. Stand-off distance of plasma spray gun from job surface - 4 to 6 inches. Brief Description of the Drawings: Figure 1 shows a cross-section of the portion of the tuyere, which in normal operations, hangs inside the blast furnace Detailed Description of the Drawings: It will be seen from the drawings that the tuyere (1), is double walled (1a, 1b) with an annular chamber (1C) at its nose end for circulating cooling water. Under use conditions, the nose portion (2) remains inside the blast furnace at the intersection of the bosh and the hearth of the furnace. Since, the tuyeres are mounted in the usual manner around this region circumferentially, these mounting details are neither shown in the drawings nor do these form any novel feature of the invention. Usually 18-20 such tuyeres are mounted as per practice in industry. In the nose portion, marked by numeral (2), there is provided a high thermal resistant coating as per the features of this invention. As against the prior art coatings, known to us and discussed earlier, we have departed from the same and have successfully provided a combination ceramic coating of materials of high thermal resistance. Our investigations have shown that yttria stabilized zirconia coating would be well suited for our purposes. In order to promote the adhesion of the top coat to extend the life of the coating, we have found that an initial bond coating would be ideal. We have been able to successfully provide a long lasting combination ceramic coating on the exposed portion of the tuyere by employing an intermediate metal alloy bond coating on the bare outer surface of the copper tuyeres. The metal alloy has been carefully selected after several trials. Simulated experiments have been conducted to arrive at an idea! combination of the metal alloy bond coat and the combination ceramic top coat. The top coat is shown by the numeral 3 which covers the nose portion as well as the conical portion of the tuyere. Additional Details of the Invention: Thermal barrier coatings applied to the exposed/working surfaces of the tuyere lead to considerable reduction in the incidence of tuyere failure on account of burn-out. The ceramic coatings provide a thermal barrier to the heat flux between the hot 7one of the furnace and the tuyere members. The coatings are applied to the flat nose surface of tuyeres, which is exposed to the high temperature in the furnace and conico-cylindrical surface of the tuyere, which hangs inside the furnace; this is roughly 5-7 inches from the nose (Figure 1). The main properties, which are taken into account for selection of thermal barrier coatings are high melting point of the ceramic material, its low thermal conductivity, its phase stability at the tuyere body temperature, its bonding characteristics with the copper substrate and commercial availability of the bond powders/materials. The invention will now be more clearly described with reference to the example. Fresh copper tuyeres were coated by argon plasma spray deposition technique after careful surface preparation. Ni-Cr-Ai-Y alloy bond coat was followed by the ceramic 8% ytiria (Y2O3) stabilized zirconia (ZrO2) top coat. The coated tuyeres were then installed in predetermined and vulnerable positions in a blast furnace to avaluate their performance under plant working conditions. In order to promote adhesion of ceramic 8% yttria (Y2O3) stabilized zirconia (ZrO2) with the tuyere substrate, a bond coat of Ni-Cr-AI-Y alloy (15-19% Cr, 3-5% Al, 3-5% Y, balance Ni) was initially applied on copper tuyere surface. The coating materials tor Ni-Cr-AI-Y bond coat and 8% yttria (Y2O3) stabilized ZrO2 top coat are essentially powders with granulometric particle sizes of -100+325 mesh and -230 mesh respectively. The surface to be coated (Figure 1) was machined down by 1-2 mm on diameter followed by grit blasting for better mechanical anchorage of the coatings. The surface was then degreased with acetone and preheated to 120-150° C with an argon plasma torch. Initially, the bond coat of Ni-Cr-AI-Y alloy was deposited on the tuyere surface. Following argon plasma spray parameters were employed. Current - 700-800 Amperes Voltage - 40-60 volts DC. Stand-off distance of plasma spray gun from job surface - 4 to 6 inches. Around 0.4 mm thickness of bond coat was built up in four runs. The job surface was then allowed to coo! to around 50-100° C. Following this, the top coat was deposited. The overall thickness of the coating (bond coat and top coat included) was around 1.0 to 2.0 mm. The coating powders employed were commercially available plasma grade powders. The tuyeres were mounted onto a horizontal turn table and rotated at 3-4 r.p.m. during the coating process. Following the application of the coating, the surface was allowed to cool to the ambient temperature and the surface was inspected for cracks and other defects. The plasma coating results in dense, adherent and mechanically stable zirconia coating, which acts as a thermal barrier to the heat flux, thus ieading to significant improvement in the service life of the tuyeres. The coated tuyeres exhibited a service life of more than 500 days as compared with the average service life of 72 days for an un-coated tuyere. This translates into an augmentation in service life by nearly 7 times. Advantages of the Invention: The advantages are many. 1. This is a technical advancement in the field having International application and importance. 2. The longevity of tuyere being increased, there are less interruptions in blast furnace operation and hence more production time is utilized. 3. Since replacement or repair of tuyere is reduced considerably, the process of producing pig iron in a blast furnace is economical. 4. Inventories and stores are reduced. 5. Capital investment is controlled. 6. Indirectly, there is positive contribution to pollution control. We Claim: 1. An Yttria stabilized Zirconia coated thermal-resistant copper tuyere for use in iron blast furnace characterized in that the copper outer surface of the tuyere having a highly thermal resistant coating comprising an (i) intermediate bond coating on said copper outer surface of a metal alloy bond coating comprising (a) Cr- 15 to 19 % (b) Al- 3 to 5 % (c ) Y- 3 to 5 % and (d) Ni- balance amount and (ii) an outer top ceramic coating applied on said metal alloy bond coating and having a combination ceramic outer top coating made of Yttria and Zirconia. 2. A tuyere as claimed in claim 1, wherein, the top coat is made of yttria (Y2 O3) stabilized zirconia (ZrO2). 3. A tuyere as claimed in claim 1, wherein, the zirconia is stabilized by 8% by weight of yttria. 4. A tuyere as claimed in claims 1 to 3, wherein, the top coat is provided on an intermediate bond coat of metal alloy based on Nickel, on the copper outer surface of the tuyere. 5. A tuyere as claimed in claim 4, wherein, the metal alloy coating is made of nickel based chromium containing alloy. 6. A tuyere as claimed in claim 5, wherein, the alloy bond coating is made predominantly of Ni, followed by Cr, Al and Y. 7. A tuyere as claimed in claim 6, wherein, the metal alloy bond coating is made of atleast about 70% by weight of nickel, the balance being made of Cr, Al and Y. 8. A tuyere as claimed in claim 7, wherein, the amount of Cr in bond coating is about 4-5 times the amount of Al or Y. 9. A method for preparing highly stable thermal resistant copper tuyeres for use in blast furnace comprising the following steps: a. Machining the surface of the tuyeres to be coated to expose fresh metal surface, b. Grit blasting and cleaning the surface for increasing the adhesion characteristics of the surface, c. Degreasing and pre-heating the surface to about 120-150°C accept a metal alloy bond coat made of Ni-Cr-AI-Y, comprising a. C:15%-19% b. AI:3-5% c. Y:3-5% and d. Ni- Balance. d. Applying by plasma spray gun said metal alloy bond coating preferably in several runs to obtain desired thickness of the bond coat, e. Cooling the bond layer coated surface, followed by, f. Applying a top coat of combination ceramic made of yttria stabilized zirconia by plasma technique till desired thickness is obtained and, g. Finally, cooling the coated tuyere to room temperature. 10. A method as claimed in claim 9, wherein, the zirconia is stabilized by 8% by weight of yttria. 11. A method as claimed in claims 9 and 10, wherein the top coat is provided on an intermediate bond coat of metal alloy on the copper outer surface of the tuyeres. 12. A method as claimed in claims 9 to 11, wherein the metal alloy bond coating is made nickel based chromium containing alloy. 13. A method as claimed in claims 9 to 12, wherein the alloy bond coating is made predominantly of Ni, followed by Cr, Al and Y. 14. A method as claimed in claims 9 to 13, wherein the metal alloy bond coating is made of atleast about 70% by weight of nickel, the balance being made of Cr, Al and Y. 15. A method as claimed in claims 9 to 14, wherein the amount of Cr in bond coating is about 4-5 times the amount of Al or Y. 16. A method as claimed in claims 9 to 15, wherein the bond coat and top coat are essentially powders with granulometric particle sizes of -100 +325 mesh and -230 mesh respectively. 17. A method as claimed in any one of claims 9 to 16, wherein the top coat is made of 8% yttria stabilized zirconia. 18. A method as claimed in any one of claims 4 to 13, wherein plasma coating parameters are preferably the following: Current :700-800 Amperes Voltage :40-60 Volts DC Stand-off distance of plasma spray gun from job surface :4 to 6 inches 19. A highly stable thermal resistant/barrier coated tuyere for use in blast furnaces substantially as hereindescribed with reference to the accompanied drawing. 20. A method for preparing highly stable thermal resistant/barrier coated tuyere for use in blast furnaces substantially as hereindescribed. There is disclosed an improved high thermal resistant copper tuyere for use in a blast fumace, said tuycre having a combination ceramic outer top coating made of yttria and zirconia. There is further disclosed a method for preparing highly thermal resistant copper tuyeres for use in blast furnace comprising the following steps: a. Machining the surface of the tuyere to be coated to expose fresh metal surface, b. Grit blasting and cleaning the surface for increasing the adhesion characteristics of the surface, c. Degreasing and pre-heating the surface to accept a metal alloy bond coat made of Ni-Cr-Al-Y, d. Applying by plasma spray said metal alloy coating preferably in several runs to obtain desired thickness of the bond coat, e. Cooling the bond layer coated surface, followed by, f. Applying a top coat of combination ceramic made of yttria stabilized zirconia by plasma technique till desired thickness is obtained and, g. Finally, cooling the coated tuyere to room temperature.

Documents:

570-CAL-2001-CORRESPONDENCE.pdf

570-CAL-2001-FORM 27.pdf

570-cal-2001-granted-abstract.pdf

570-cal-2001-granted-claims.pdf

570-cal-2001-granted-correspondence.pdf

570-cal-2001-granted-description (complete).pdf

570-cal-2001-granted-drawings.pdf

570-cal-2001-granted-examination report.pdf

570-cal-2001-granted-form 1.pdf

570-cal-2001-granted-form 13.pdf

570-cal-2001-granted-form 18.pdf

570-cal-2001-granted-form 2.pdf

570-cal-2001-granted-form 3.pdf

570-cal-2001-granted-pa.pdf

570-cal-2001-granted-reply to examination report.pdf

570-cal-2001-granted-specification.pdf