| Title of Invention | A FRIT AND A METHOD OF MANUFACTURING THE SAME |
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| Abstract | The present invention relates to a Frit comprising of the following composition: Weight % (i) Silica 35 - 75 (ii) Boron Oxide 8 - 25 (iii) Alumina 8-15 (iv) Sodium Oxide 3 - 20 (v) Potassium oxide 1 - 7 (vi) Calcium oxide 1 - 9 and the method of manufacturing the same and a coating for carbon-containing refractory article comprising of the said Frit. |
| Full Text | FORM 2 THE PATENTS ACT,1970 (39 OF 1970) & THE PATENT RULES, 2003 COMPLETE SPECIFICATION [SECTION 10; RULE 13] "FRIT, METHOD OF MANUFACTURING FRIT AND COATING FOR REFRACTORY ARTICLE COMPRISING SAID FRIT" APPLICANT: PRISM CEMENT LIMITED NATIONALITY: COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956 ADDRESS: WINDSOR 7™ FLOOR, KALINA, CST ROAD, SANTACRUZ-E MUMBAI - 400 098, MAHARASHTRA, INDIA THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED FIELD OF INVENTION The present invention relates to a Frit and a method for manufacturing the same. More particularly, it relates to a Frit for use in Refractory coating. The invention also relates to a coating for carbon-containing refractory article comprising of the said frit. BACKGROUND OF THE INVENTION Traditionally, refractory articles which are used in iron and steel industry for continuous casting of molten steel in steel plants are made of alumina, magnesia, alumino-silicate, silicon carbide, chrome, zirconia, silica etc. Carbon is often incorporated along with these refractory articles especially in its components like submerged entry nozzle (SEN), slide gate plates, submerged entry shroud to protect the refractory articles from attack and erosion by molten metal and slag. Carbon is used in the form of graphite, carbon black, pitch coke and the like. Alumina-carbon refractories are quite popular for continuous casting of molten steel in steel plants. However the carbon is susceptible to oxidation by air at temperature above 600 degree centigrade, which can deteriorate the properties of refractory during preheat and casting operation. Hence carbon must be protected so that properties of refractory do not get deteriorated during preheating at the temperature of 1400 to 1450 degree centigrade and/or casting at about 1550 to 1600 degree centigrade during the casting time which varies between 5-7 hours. PRIOR ART Frit is generally used for coating non-refractory articles. Such frit has high softening point generally above 850 degree centigrade and therefore cannot be used for coating refractory articles. Coatings for refractory articles are not known to contain frit. Coating for refractory articles known in the prior art contain refractory filler, fluxing/fusing material and metalloid. EP - A - 0252621 discloses a coating mass comprising of refractory filler - 35 to 70 % w/w, fluxing/fusible material (Boron compound or Boron Glass) - 20 to 40% w/w, metalloid (aluminum and silicon) - 10 to 25% w/w. However, the use of fusible material in higher dosage i.e. 20 - 40 % w/w as stated above may increase the fluidity of the coating mass and same may cause the flow down of the coating mass. Boron based compound normally softens at low temperature (292 degree centigrade) whereas the refractory article has the ability to withstand the temperature of 1650 to 1700 degree centigrade. More use of low temperature fluxing material after reaction with the refractory article brings down the refractoriness of the refractory article and because of this refractory article will soften at lower temperature during use and same will cause reduction in the service life. U.S. Patent No. 5,856,015 describes a coating mass to be used with liquid carrier comprising of Silica- 40 to 80% w/w, fluxing material (Boron Oxide) - 5 to 20% w/w, oxide of alumina/calcia/magnesia - 5 to 20% w/w, Metal oxide of arsenic/antimony/bismuth/lead/ vanadium /tin (wetting aid) - 0.5 to 10% w/w, Metalloids - 30% w/w wherein particle size is 1 to 250 microns and preferably 10 to 50 microns. In the above coating mass, a high temperature wetting aid is used. These wetting aids have the following limitations:- a) Most of the metal oxides mentioned are toxic in nature. Use of the same is banned in most of the countries. These types of oxides in raw form are more dangerous to handle. b) Softening/melting temperature of these oxides (wetting aids) are relatively high. Melting point of these compounds is Lead oxide - 888 degree centigrade, Vanadium oxide - 690 degree centigrade, Bismuth oxide - 820 to 860 degree centigrade, Tin oxide - 1127 degree centigrade ( decomposition temp), Antimony oxide - 656 degree centigrade, Arsenic oxide - 193 degree centigrade (it sublimes). As the carbon oxidation starts at about 600 degree centigrade, coating mass needs to melt at temperature near to 600 degree centigrade. Boron based compounds of these coating masses though melt at low temperature, use of those toxic compounds does not satisfy the softening temperature requirement fully. c) The particle size distribution is in broader range i.e. 1 - 250 microns (preferably 10-50 microns). This wide variation (more coarse) in particle sizes reduces the surface area which does not favor good sintering and increases the chance of segregation i.e. unsatisfactory dispersion and texture. d) Use of raw boron salts cause the removal of chemically combined water. During the removal, pinholes may develop on the coating. In case of both the above coating mass, the fusible/fluxing mass is used in raw form i.e. unfritted form. In case of application with liquid carrier, the alkali component of the fluxing material gets leached out to some extent and reacts with the carrier to cause precipitation. As a result, proper painting/brushing/spraying cannot be done. Further, in both dry and liquid type, due to presence of higher percentages of fluxing material in raw form, coating mass after application may get spalled due to brittleness of glassy material and the coating comes out by cracking. Use of Borosilicate glass instead of raw boron compound has also been reported. It has also got following limitations, a) It melts at about 820 degree centigrade which is relatively higher for application in coating mass. Percentages of low boron compound possibly raises the melting point. b) Absence of alumina raises the temperature of melting possibly due to devitrification. c) It has higher coefficient of expansion (8 x 10-6 per degree centigrade at 350 degree centigrade) which can deteriorate the spalling resistance. SUMMARY OF THE INVENTION This invention therefore proposes a frit for refractory coating having low softening point at around 680 degree centigrade and a method of manufacturing the same. It also proposes, a coating comprising of the said frit. The said coating may be either in dry form or dry powder with liquid carrier. According to this invention a Frit comprises the following composition: Weight % (i) Silica 35 - 75 (ii) Boron Oxide 8-25 (iii) Alumina 8-15 (iv) Sodium Oxide 3-20 (v) Potassium Oxide 1 - 7 (vi) Calcium Oxide I - 9 And a method of manufacturing the above Frit comprises of the following steps: (i) The following components are thoroughly mixed; Weight % Borax 35-45 Potash Feldspar 30-35 Quartz 10 -16 Calcined Alumina 1.5 - 2.5 Soda ash 5-9 Calcite 1 - 3 (ii) the above mixture is melted; (iii) the molten mass is quenched; and (iv) the quenched mass is ground to make fine powder. The invention also proposes a coating for carbon-containing refractory article comprising of the following :- (i) Frit having composition disclosed above. (i) Refractory filler, for example, any one or more of Silicon Carbide, Alumina, Silica, Chrome, Zirconia, Magnesia, (ii) Metalloid for example any one or more of Silicon, Aluminium, Magnesium. (iii) Binding material, for example Salts of Aluminum, Salts of Magnesium, Salts of Calcium and/or Salts of Zirconium. METHOD OF MANUFACTURING 1] The following raw material Weight % Borax 35-45 Potash Feldspar 30-35 Quartz 10 - 16 Calcined Alumina 1.5- 2.5 Soda ash 5-9 Calcite 1 - 3 after proportioning is mixed in ribbon mixer for 1-2 hours, and fed in batch type smelter for firing at 1000 to 1500 degree centigrade for 10 - 15 minutes. The temperature of firing is optimized to obtain highest density and minimum coefficient of expansion. This produces a Frit having the following properties:- Frit smelting temperature (degree centigrade) 1300 1400 1450 1500 Density, g/cc 2.25 2.28 2.31 2.33 Coefficient of thermal expansion/ degree centigrade, measured at 350 degree centigrade 4.5x10-6 5.0x10-6 5.1 x10-6 6.2X10-6 However, in a more preferable embodiment of this invention, the mixture of raw material is heated between 1450 to 1500 degree centigrade to achieve proper melting. It is then discharged and quenched with cold water. In a preferable embodiment the frit is dried. The frit is then charged in ball mill for grinding for 10 to 12 hours. Frit, grinding media ratio is kept at 60 - 75 Kg: 135 kg to 150 kg to attend the required particle size distribution (PSD), Dry grinding is reported to reduce the leaching of alkali from the frit. After checking the particle size distribution (PSD), the material is used as one of the ingredient to make the coating mass according to the present invention. The PSD was checked in case of dry grinding by grinding with variation in time. Higher D50 causes segregation whereas very fine grinding causes coagulation, PSD 8hrs 10hrs 12hrs 14hrs D50 in micron 17 14 11 10 The above method produces the frit containing the following composition. Weight % (i) Silica 35 - 75 (ii) Boron Oxide 8 - 25 (iii) Alumina 8-15 (iv) Sodium Oxide 3 - 20 (v) Potassium oxide 1-7 (vi) Calcium oxide 1-9 11] The frit produced by the above method along with the following components having preferable specifications stated therebelow are thoroughly mixed according to the batch composition stated hereinbelow to produce the coating mass according to this invention. Batch Composition of Coating Mass (Wt%) Frit Powder 45 - 60 Refractory Filler 17-24 Metalloid 18-25 Binding Material 3 - 6 Preferable Specification of Raw Materials A. Frit as obtained by the method as mentioned above. B. Metalloid Specific Gravity 2.3 Melting Point 1440° C Solubility in water Insoluble Chemical Analysis (Wt%) Silicon 98 (min) Iron 1 (max) Particle size > 75 Micron 1% max, > 45 Micron 5% max C. Refractory Fillers Specific Gravity 3.2 Melting Point 2700 degree C Solubility in water Insoluble Chemical Analysis (Wt %) Silicon 68 Carbon 29 Free Carbon 0.60 Si02 0.70 A1203 0.15 Fe203 0.50 D. BINDING MATERIAL Grain size Less than 240 mesh Specific Gravity 2.56 A1203 55 - 57 (Wt %) Solubility in water Insoluble In a still preferable embodiment the above coating mass is mixed with dispersant, binder and water in the following percentage to obtain properties stated therebelow. w/w Coating Mass 100.0 Dispersant 0.2 - 0.4 Binder 0.2 - 0.5 Water 35-40 Both the dispersant and the binder are acrylic based. PROPERTIES OF coating mass in liquid mass: Density: 1.62 -1.64 gm/cc Viscosity (B4): 118 -120 Seconds EXAMPLES The following Examples would further explain/describe the present invention. However, the said examples in no way limit the scope of the invention. Batch Composition (Wt%) Composition 1 Composition 2 Composition 3 Borax Penta hydrate 38.0 44.8 41.0 Potash Feldspar 35.8 30.2 32.8 Quartz/Siliceous Material 15.2 14.0 14.4 Calcined Alumina 2.2 1.5 1.9 Soda Ash 6.0 8.0 7.9 Calcite 2.8 2.5 2.0 The above raw materials for frit are mixed as per above method of manufacturing in the above given proportion. The properties of the Frit obtained using the above-mentioned composition, are indicated below PROPERITES:- Parameters Composition 1 Composition 2 Composition 3 Softening Temperature degree centigrade 698 665 680 Maturing Temperature degree centigrade 880 830 850 Coefficient of thermal expansion measured at 350 degree centigrade, / degree centigrade 5.2x10-6 5.3x10-6 5,lxl0-6 Properties of Ground Frit Residue on 300 Mesh Median (D50), Micron 10-15 10-15 10-15 ADVANTAGES 1.0 The frit has been developed by encapsulating the various oxides/ non-oxide materials through melting so that the pinhole/other defects which are commonly encountered in case of unfritted boron compound due to removal of chemically combined water, can be avoided. This developed mass is in fritted form and superior to raw boron based compounds. 2.0 The frit has been made without use of any toxic materials which are having higher softening point as compared to boron oxide of alkali metals. Non use of these toxic materials make the mass user friendly. 3.0 The frit is made with the use of alumina to ensure proper vitrification so that proper glassy material can be made at lower temperature. This helps softening of the coating at lower temperature i.e. about 680 degree centigrade as against more than 800 degree centigrade in case of borosilicate glass. 4.0 The thermal expansion coefficient of frit is kept at lower side i.e. between 5.1 X 10 -6 to 6.2 X 10 -6 / degree centigrade thereby it avoids spalling and cracking during heating and cooling of the article. It helps to generate less stress and thus eliminate the breakage of coating during use and ensure better adhesion. 5.0 Frit composition has a flexibility to make it suitable for refractories which are subjected to higher temperature. 6.0 Particle size D50(median)( range 10-30 micron) is kept at narrow range of 10-15 micron for better dispersion, more surface area which helps in better sintering and uniform texture. It helps in better coating of the refractory and also penetration in the micro pores present in the refractory body to arrest infiltration of air which reduces the oxidation of the carbon in the refractory article. 7.0. The frit in the refractory glaze is major component of the coating mass which stops/inhibit oxidation of carbon present in the alumina - carbon and other carbon incorporated refractory articles. 8.0. Frit due to water quenching develops lot of cracks and hence it is easy to grind to very fine size (10 -30 micron). This being a component of coating mass contributes in better wetting of the refractory articles. 9.0. The coating according to the present invention contains less percentage of Boron compound in the form of frit, which improves the life of refractory article coated with the said coating. WE CLAIM: 1. A Frit comprising of the following composition: Weight % (i) Silica 35 - 75 (ii) Boron Oxide 8 - 25 (iii) Alumina 8-15 (iv) Sodium Oxide 3-20 (v) Potassium oxide 1 - 7 (vi) Calcium oxide 1 - 9 2. A method of manufacturing Frit as claimed in Claim 1 comprising of the following steps: (i) The following components are thoroughly mixed; Weight % Borax 35-45 Potash Feldspar 30 - 35 Quartz 10-16 Calcined Alumina 1.5 - 2.5 Soda ash 5-9 Calcite 1 - 3 (ii) the above mixture is melted; (iii) the molten mass is quenched; and (iv) the quenched mass is ground to make fine powder. 3. A method as claimed in Claim 2 wherein in step (i), the components are mixed for at least one hour. 4. A method as claimed in Claim 2 wherein in step (ii), the mixture in step (i) is heated between 1000 degree centigrade and 1500 degree centigrade for a period of 5 to 15 minutes, to melt the mixture. 5. A method as claimed in Claim 2 wherein in step (iv), the quenched mass is dried before grinding it. 6. A method as claimed in Claim 2 wherein in step (iv), the quenched mass is ground in a ball mill. 7. A coating for carbon - containing refractory article comprising of the following: (i) Frit as claimed in Claim 1 above; (ii) Refractory filler, like any one or more of Silicon Carbide, Alumina, Silica, Chrome, Zirconia, Magnesia, (iii) Metalloid, like any one or more of Silicon, Aluminium, Magnesium. (iv) Binding material, like Salts of Aluminum, Salts of Magnesium, Salts of Calcium and/or Salts of Zirconium. 8. A coating as claimed in Claim 7 wherein composition of its constituents are in the following percentage: Weight % (i) Frit claimed in Claim 1 45- 60 (ii) Refractory Filler 17-24 (iii) Metalloid 18-25 (iv) Binding material 3 - 6 9. A coating as claimed in Claim 7 further comprising of acrylic based dispersion, acrylic based binder and water. |
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| Patent Number | 268566 | |||||||||
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| Indian Patent Application Number | 175/MUM/2010 | |||||||||
| PG Journal Number | 36/2015 | |||||||||
| Publication Date | 04-Sep-2015 | |||||||||
| Grant Date | 03-Sep-2015 | |||||||||
| Date of Filing | 22-Jan-2010 | |||||||||
| Name of Patentee | PRISM CEMENT LIMITED | |||||||||
| Applicant Address | WINDSOR, 7TH FLOOR, KALINA, C.S.T.ROAD, SANTACRUZ(E), MUMBAI 400098, MHARASHTRA, INDIA | |||||||||
Inventors:
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| PCT International Classification Number | C03C3/16 | |||||||||
| PCT International Application Number | N/A | |||||||||
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