Title of Invention	"IMPROVED REFRACTORY SLIDE GATE PLATE AND PROCESS FOR MAKING THE SAME".
Abstract	Improved refractory slide gate plate and a process of preparation of the same. The refractory slide gate plate has high oxidation resistance and excellent thermal spalling properties, The refractory slide gate plate comprises from 60 to 90 % by wt. of a first mix comprising a combination of fined / sintered / tabular alumina and/or magnesia grains and powders ; and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders of silicon metal, alumina and iron oxide. The process comprises providing a first mix comprising a combination of one or more of fused, sintered, tabular alumina and/or magnesia grains and powders ; providing a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide ; mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; compacting this mixture of the first and second mix by ceramic fabrication technique, drying the unfired compact; firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and cooling the fired product.

Title of Invention

"IMPROVED REFRACTORY SLIDE GATE PLATE AND PROCESS FOR MAKING THE SAME".

Abstract

Improved refractory slide gate plate and a process of preparation of the same. The refractory slide gate plate has high oxidation resistance and excellent thermal spalling properties, The refractory slide gate plate comprises from 60 to 90 % by wt. of a first mix comprising a combination of fined / sintered / tabular alumina and/or magnesia grains and powders ; and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders of silicon metal, alumina and iron oxide. The process comprises providing a first mix comprising a combination of one or more of fused, sintered, tabular alumina and/or magnesia grains and powders ; providing a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide ; mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; compacting this mixture of the first and second mix by ceramic fabrication technique, drying the unfired compact; firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and cooling the fired product.

Full Text	Field of Invention The present invention relates to improved refractory slide gate plates and a process of preparation of the same. More particularly the invention relates to improved refractory slide gate plates having high oxidation resistance, excellent thermal spalling, and improved mechanical properties like cold crushing strength, modulus of elasticity, cold modulus of rupture and hot modulus of rupture, as also corrosion resistance. Background and Prior Art It is well known that refractory slide gates are used in steel melting and casting shops to achieve controlled flow of molten metal and slag. These gates are made of refractory materials that are capable of withstanding high heat, thermal shock, erosion, abrasion, oxidation, and corrosion during their use. Currently, the slide gate plates are made of alumina-carbon or magnesia-carbon materials that perform reasonably satisfactorily under the operating conditions aforementioned. However, one of the main limitations of these conventional alumina-carbon and / or magnesia-carbon refractory slide gate plates is their poor oxidation resistance due to the presence of carbon that gets relatively easily oxidized thus reducing the useful life of the plates. The known process for making the conventional alumina-carbon or magnesia-carbon refractory slide gate plate plates, generally involves the following process steps: - mixing the raw materials like alumina, magnesia, phenolic resins, graphite and small amounts of other additives ; - compacting the mixture to the desired size & shape to obtain 'green / unfired' compact; - baking, coking and firing the 'green / unfired' compact at high temperatures of up to about 1300°C in the absence of oxygen/ air; and, - subjecting the heat-treated product obtained as above, that is alumina-carbon / magnesia-carbon refractory, to machining / finishing operations and 'canned' in 2 metal enclosures to obtain the final slide gate plate refractory product that is used in steel melting and casting shops / plants. In the slide gate plates made of alumina / magnesia - carbon, it is understood that: • the alumina or magnesia provides abrasion / erosion / corrosion resistance as well as refractoriness; • the graphite / carbon provides low wettability with respect to molten metal / slag; and, • the additives offer oxidation resistance. The applicants of the present invention have found that the oxidation resistance and other properties like thermal spalling and corrosion resistance of the refractory slide gate may be significantly improved by eliminating the use of carbonaceous raw materials and by combining a first mix (also referred to as GROG ) and second mix (also referred to as BOND), under appropriate conditions in which the first mixture is a combination of fused / sintered / tabular alumina and / or magnesia grains and the second mixture is an intimate mixture of fine powders of silicon metal, alumina and iron oxide. Objects of the Invention It is thus the principal object of the present invention to provide new, improved refractory slide gate plates that possess all the characteristics of the conventional alumina-carbon / magnesia-carbon products used in the current state of the art with the added advantages of high oxidation resistance and improved thermal spalling & corrosion resistance properties. It is a further object of the present invention to eliminate / minimize the operational and performance limitations related to the conventional refractory slide gates by making developments and improvements in the materials. Yet another object of the present invention is to provide a method for producing the improved refractory slide gate plates. 3 Summary of the Invention Thus according to the principal aspect of the present invention there is provided an improved refractory slide gate plate having high oxidative resistance, thermal spalling and corrosion resistance comprising from 50 to 90 % by wt. of a first mix comprising a combination of one or more of fused / sintered / tabular alumina or magnesia grains and powders, and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide. The said improved refractory slide gate plates have improved thermal spalling and oxidation resistance. The said refractory slide gate plates have bulk density in the region of 2.3 to 3.2 g/cc; apparent porosity in the region of 18 to 25%; cold crushing strength in the region of 60 to 180 MPa; modulus of elasticity in the region of 20 to 70 GPa; cold modulus of rupture in the region of 14 to 50 MPa; hot modulus of rupture in the region of 15 to 70 MPa. According to further aspect of the present invention there is provided a process for making said refractory slide gate plates comprising the steps of: i) providing a first mix (GROG) comprising a combination of one or more of fused / sintered / tabular alumina and/or magnesia grains and powders ii) providing a second mix (BOND) comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide ; iii) mixing from 50 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; with each other iv) compacting this mixture of the first and second mix by standard, well known ceramic fabrication techniques v) drying the unfired compacts; vi) firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and vii) cooling the fired product 4 Detailed Description of the Present Invention In the present invention, the known advantages of the anti-abrasion / erosion properties and high refractoriness of alumina / magnesia have been retained while eliminating the usage of carbonaceous raw materials like phenolic resins, graphite and carbon that limit the useful life of the corresponding products. The inventors have found that the second mix (BOND), when subjected to high temperature firing under defined conditions, forms a strong high-temperature ceramic bond in situ (due to reaction sintering) and surrounds the first mix (GROG) holding these aggregates with a strong force. The combination of the first and second mixes resulting in the refractory slide gate plates of the present invention has improved oxidation resistant and thermal spalling properties. The improved refractory slide gate plates have a preferred bulk density of 2.6 g/cc; preferred apparent porosity of 20 %; preferred cold crushing strength of 75 MPa; preferred modulus of elasticity of 25 GPa; preferred cold modulus of rupture of 15 MPa; hot modulus of rupture of 30 Mpa This high temperature ceramic bond formed between the first and the second mix comprises of complex inorganic phases in the alumina - silicon - nitrogen- oxygen system and exhibits: • high thermal spalling resistance; • excellent oxidation resistance; • low wettability and corrosion by molten metal/slag; and, • high refractoriness. About 50 to 90 % of the first mix ("GROG") is mixed with the 10 to 40 % of the second mix ("BOND"), compacted to the required size and shape by known ceramic fabrication techniques, and fired at high temperatures (up to 1550°C) in a controlled (nitrogenous) atmosphere to obtain improved refractory slide gate plates. By varying the composition of the second mix, the ratio of the first mix to second mix as also the firing conditions, it is possible to make refractory slide plate compositions having a range of high temperature physical and chemical properties that allow for customizing the compositions and, therefore, the concomitant properties for the desired application in the steel casting or melting shops. 5 The first mix can be selected from the fused, sintered, tabular, reactive varieties alumina / magnesia available in the market. The inventors have also observed that fused / sintered mullite (an alumino-silicate) or spinel (a magnesium-aluminate) grains and powders can be used advantageously in place of alumina / magnesia grains, although this latter material is the preferred material. The first mix, forming 50 to 90% of the final mixture, consists of alumina and/or magnesia grains and powders ranging in particle size from [standard] mesh 6 to -325 in desired proportions The second mix comprises of fine powders (-325 mesh) of silicon, alumina and iron oxide. In fact, the composition of the second mix itself can be varied by varying the silicon to alumina proportion, so that the corresponding fired refractory has different desired properties. The ceramic fabrication of an intimate mixture of the above raw materials (i.e., first and second mix) to obtain the green unfired compact, of desired size and shape, can be accomplished by compaction in hydraulic or friction screw presses, in vibratory compaction machines, using pneumatic ramming or tamping equipment, or by the well known slip casting technique. The firing or reaction sintering of the above green compacts is carried out in sealed, air / gas-tight ceramic muffles or boxes under a positive pressure of high purity nitrogen gas at temperatures up to 1550°C, but preferably around 1430°C. It is possible, however, that the nitrogenous atmosphere in the ceramic muffle / box is created by incorporating organic / inorganic compounds that produce nitrogen in situ inside the ceramic muffle / box during the firing cycle, Optionally small amounts up to 5% of temporary or green binders like dextrine starch, lingo-sulphonates, polyvinyl alcohol, etc can be used during mixing operation to improve the handling strength of the green unfired compacts. Thus improved refractory slide gate plates are made by mixing desired amounts of first and second mix, compacting them by conventional ceramic fabrication techniques and firing them under nitrogenous atmosphere at high temperatures (up to 1550°C). The refractory slide gate plates and the process of the present invention are described with respect to following non limiting exempla nary illustrations: 1) 60 to 90 %, preferably 70% of, the first mix comprising of alumina and/or magnesia grains and powders is weighed into a conventional counter current bowl type or a planetary mixer and mixed for about 10 minutes to obtain a dry, homogeneous mixture. 2) In a separate mixer, the ingredients, namely silicon metal, alumina, iron oxide in a ratio described above of the second mix are thoroughly mixed and stored as BOND 3) Into the mixer containing the first mix required amount of an aqueous suspension / solution of the green / temporary binders (like dextrine, glycerine, lingo-sulphonates, etc) are added. 4) 10 to 40 %, preferably 30 % of second mix is slowly added into the counter current mixer containing the wet first mix and mixed for about 10 to 40 minutes, preferably 30 minutes; lumps formed, if any, are broken by passing the mixture of first and second mix through an appropriate wire mesh screen on vibratory screening equipment. 5) Desired amount of the mix, screened as above, is poured into a moulding die and compacted to the pre-determined density in suitable moulding equipment like hydraulic or friction-screw press, vibro-compactor, slip caster, etc. 6) The green or un-fired compacts are loaded on to shelves of a drier rack and allowed to dry, to a final moisture level of 0 to 1%, preferably 0.5% by initial drying in air followed by hot air oven. 7) The dried compact is loaded into a refractory muffle / box made of silicon carbide refractory, and, fired as per desired temperature - time cycle in an oil-fired kiln. The final soak temperature is maintained at 1430° to 1550°C, preferably at 1430°C, for a soak 7 period of about 1 - 8 hours preferably for 6 hours The firing is done under controlled (nitrogenous) atmosphere at a pressure of 5 -15 mm water gauge. 8) After cooling, the fired product - new improved slide gate refractory - is characterized for different physical and chemical properties. The refractory slide gate plates according to the invention and prepared by the method of present invention along with their properties (Examples 1 to 6) are provided in Table 1. It may be noted that for Examples 1 to5 the compaction is achieved by hydraulic / friction screw pressing of the GROG + BOND mixtures. Example 6 relates to samples compacted by (vibro-) slip casting method. This thus uses another method of compaction of the present invention. TABLE 1 Example GROG BOND BD AP CCS MoE C- H- No. w/w % w/w % g/cc % MPa GPa MoR MoR MPa MPa 1 90 10 2.98- 2 85 15 2.97- 3 80 20 2.93- 4 75 25 2.92- 5 70 30 2.90- 6 70 30 2.58- 2.62 190 Note: B D - Bulk Density; A P - Apparent Porosity; CCS- Cold Crushing Strength; MoE - Modulus of Elasticity; C-MoR - Cold Modulus of Rupture; H-MoR - Hot Modulus of Rupture The examples thus demonstrate the refractory slide gate plates of present invention having improved properties. It would be seen that the best result is obtained from composition wherein the GROG and BOND are present at 70% and 30 % respectively, s Refractory slide gate plates of the present invention are tested for thermal spalling and oxidation resistance properties. They are compared with conventional refractory slide gate plates formed of alumina -carbon. The data is provided in Table II. For assessing thermal spalling properties the refractory slide gate plates are heated to a temperature of 1000°C and, immediately exposed to ambient temperature. The number of cycles at which crack appears is monitored. It is found that for the conventional A1203-C or MgO-C refractory slide gate plates the crack appears at 15-20 cycles while that for refractory slide gate plates of present invention such cracks appear only after 40-50 cycles. For assessing oxidation resistance properties, the refractory slide gate plates were heated to a temperature of 1000°C under oxidizing atmosphere. The weight loss / gain in each case is measured. It is found that the weight loss in case of the conventional refractory slide gate plates is 10-12% while in the case of that of the refractory slide gate plates of the present invention a small weight gain of 1 to 2% is observed. TABLE II Properties Conventional A12O3-C Refractory slide gate plates refractory slide gate plates of present invention 40-50 cycles Thermal Spalling 15-20 Cycles Oxidation resistance 10-12% 1-2% The results demonstrate the improved thermal spalling and oxidation resistance properties achieved by the refractory slide gate plates formed according to the present invention compared with the conventional carbon containing product. 9 WE CLAIM: 1. Improved refractory slide gate plate having high oxidative resistance, thermal spalling and corrosion resistance comprising: from 50 to 90 % by wt. of a first mix comprising a combination of one or more of fused / sintered / tabular alumina and/or magnesia grains and powders, and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide. 2. Improved refractory slide gate plates as claimed in claim 1 having bulk density in the region of 2.3 to 3.2 g/cc; apparent porosity of 18 to 25%; cold crushing strength of 60 to 180 MPa; modulus of elasticity of 20 to 70 GPa; cold modulus of rupture of 14 to 50 MPa; hot modulus of rupture in the region of 15 to 70 MPa. 3. Improved refractory slide gate plate as claimed in claims 1 to 2 wherein the particle size of alumina and/or magnesia grains and powder present in the first mix ranges from mesh 6 to -325 mesh in varying proportions 4. Improved refractory slide gate plate as claimed in claims 1 to 2 wherein the first mix comprises alumina and/or magnesia grains optionally substituted by an alumino-silicate (mullite) or magnesium-aluminate spinel (fused / sintered) grains and powders 5. Improved refractory slide gate plate as claimed in claim 1 to 4 wherein the second mix comprises silicon metal of finer than 200 mesh, preferably minus 325 mesh, and alumina of preferably the reactive variety. 6. Improved refractory slide gate plate as claimed in claim 1 to 5 wherein the second mix comprises of fine powders (-325 mesh) of silicon, alumina and iron oxide in varied proportion of silicon to alumina such that the corresponding fired refractory has different desired properties. 10 7. Improved refractory slide gate plate as claimed in claim 6 wherein the second mix comprises silicon metal powder comprising more than 95% silicon content, iron oxide comprising at least 85% Fe2O3 content. 8. Improved refractory slide gate plate as claimed in any preceding claim wherein the said refractory slide gate plate has preferred bulk density of 2.6 g/cc; preferred apparent porosity of 20 %; preferred cold crushing strength of 75 MPa; preferred modulus of elasticity of 25 GPa; preferred cold modulus of rupture of 15 MPa; hot modulus of rupture of 30 Mpa . 9. A process for making refractory slide gate plate as claimed in claims 1 to 8 comprising the steps of: a. providing a first mix comprising a combination of one or more of fused, sintered , tabular alumina and/or magnesia grains and powders; b. providing a second mix comprising an intimate mixture of fine powders of silicon, alumina and iron oxide c. mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; d. compacting the first and second mix by any one of the standard ceramic fabrication techniques; e. drying the unfired compact; f. firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and g. cooling the fired product 10. A process as claimed in claim 9 wherein the first mix is formed by mixing alumina and/or magnesia grains and powders in the particle size ranging from 6 to -325 mesh in a conventional mixer and mixed for 10 minutes to get a homogenised mixture. 11. A process as claimed in claims 9 and 10 wherein aqueous suspension or solution of green /temporary binders are further added to the first mix. 11 12. A process as claimed in claims 9 to 11 wherein the green or temporary binders are selected from dextrine, glycerine, lingo sulphonates, polyvinyl alcohol and the like. 13. A process as claimed in claim 9 wherein the second mix is prepared by mixing fine powders of -325 mesh of silicon, alumina and iron oxide in a separate mixing equipment 14. A process as claimed in claims 9 to 13 wherein the second mix is mixed with the wet first mix for 10 to 40 minutes, preferably 30 minutes and passed through vibrating wire mesh screening equipment. 15. A process as claimed in claims 9 to 14 wherein compaction of the first mix and second mix is achieved by conventional ceramic fabrication methods selected from hydraulic or friction-screw pressing, vibro-compaction, pneumatic tamping, vibro-slip casting and the like. 16. A process as claimed in claims 8 to 14 wherein drying of the unfired compact is carried on to a final moisture level of 0 to 1%, preferably 0.5% by initial drying in air followed by hot air oven. 17. A process as claimed in claims 9 to 16 wherein the firing of the dried green / un-fired compacts is carried out at temperatures of 1430°C to 1550°C, preferably at 1430°C, for a soak period of about 1-8 hours preferably for 6 hours 18. A process as claimed in claims 9 to 17 wherein the firing is carried out in refractory muffle / box made of silicon carbide refractory. 19. A process as claimed in Claim 8 to 18 wherein the gaseous atmosphere inside the refractory muffle / box is filled with pure Nitrogen gas at a pressure of 5 - 15 mm water gauge. 20. Improved refractory slide gate plate as claimed in claims 1 to 8 substantially as herein described with reference to the illustrative examples. 21. A process as claimed in claims 9 to 19 substantially as herein described with reference to the illustrative examples. Improved refractory slide gate plate and a process of preparation of the same. The refractory slide gate plate has high oxidation resistance and excellent thermal spalling properties, The refractory slide gate plate comprises from 60 to 90 % by wt. of a first mix comprising a combination of fined / sintered / tabular alumina and/or magnesia grains and powders ; and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders of silicon metal, alumina and iron oxide. The process comprises providing a first mix comprising a combination of one or more of fused, sintered, tabular alumina and/or magnesia grains and powders ; providing a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide ; mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; compacting this mixture of the first and second mix by ceramic fabrication technique, drying the unfired compact; firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and cooling the fired product.

Full Text

Field of Invention
The present invention relates to improved refractory slide gate plates and a process of preparation of the same. More particularly the invention relates to improved refractory slide gate plates having high oxidation resistance, excellent thermal spalling, and improved mechanical properties like cold crushing strength, modulus of elasticity, cold modulus of rupture and hot modulus of rupture, as also corrosion resistance.
Background and Prior Art
It is well known that refractory slide gates are used in steel melting and casting shops to achieve controlled flow of molten metal and slag. These gates are made of refractory materials that are capable of withstanding high heat, thermal shock, erosion, abrasion, oxidation, and corrosion during their use. Currently, the slide gate plates are made of alumina-carbon or magnesia-carbon materials that perform reasonably satisfactorily under the operating conditions aforementioned. However, one of the main limitations of these conventional alumina-carbon and / or magnesia-carbon refractory slide gate plates is their poor oxidation resistance due to the presence of carbon that gets relatively easily oxidized thus reducing the useful life of the plates.
The known process for making the conventional alumina-carbon or magnesia-carbon refractory slide gate plate plates, generally involves the following process steps:
- mixing the raw materials like alumina, magnesia, phenolic resins, graphite and small amounts of other additives ;
- compacting the mixture to the desired size & shape to obtain 'green / unfired' compact;
- baking, coking and firing the 'green / unfired' compact at high temperatures of up to about 1300°C in the absence of oxygen/ air; and,
- subjecting the heat-treated product obtained as above, that is alumina-carbon / magnesia-carbon refractory, to machining / finishing operations and 'canned' in

2
metal enclosures to obtain the final slide gate plate refractory product that is used in steel melting and casting shops / plants.
In the slide gate plates made of alumina / magnesia - carbon, it is understood that:
• the alumina or magnesia provides abrasion / erosion / corrosion resistance as well as refractoriness;
• the graphite / carbon provides low wettability with respect to molten metal / slag; and,
• the additives offer oxidation resistance.
The applicants of the present invention have found that the oxidation resistance and other properties like thermal spalling and corrosion resistance of the refractory slide gate may be significantly improved by eliminating the use of carbonaceous raw materials and by combining a first mix (also referred to as GROG ) and second mix (also referred to as BOND), under appropriate conditions in which the first mixture is a combination of fused / sintered / tabular alumina and / or magnesia grains and the second mixture is an intimate mixture of fine powders of silicon metal, alumina and iron oxide.
Objects of the Invention
It is thus the principal object of the present invention to provide new, improved refractory slide gate plates that possess all the characteristics of the conventional alumina-carbon / magnesia-carbon products used in the current state of the art with the added advantages of high oxidation resistance and improved thermal spalling & corrosion resistance properties.
It is a further object of the present invention to eliminate / minimize the operational and performance limitations related to the conventional refractory slide gates by making developments and improvements in the materials.
Yet another object of the present invention is to provide a method for producing the improved refractory slide gate plates.

3
Summary of the Invention
Thus according to the principal aspect of the present invention there is provided an improved refractory slide gate plate having high oxidative resistance, thermal spalling and corrosion resistance comprising
from 50 to 90 % by wt. of a first mix comprising a combination of one or more of fused / sintered / tabular alumina or magnesia grains and powders, and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide.
The said improved refractory slide gate plates have improved thermal spalling and oxidation resistance. The said refractory slide gate plates have bulk density in the region of 2.3 to 3.2 g/cc; apparent porosity in the region of 18 to 25%; cold crushing strength in the region of 60 to 180 MPa; modulus of elasticity in the region of 20 to 70 GPa; cold modulus of rupture in the region of 14 to 50 MPa; hot modulus of rupture in the region of 15 to 70 MPa.
According to further aspect of the present invention there is provided a process for making said refractory slide gate plates comprising the steps of:
i) providing a first mix (GROG) comprising a combination of one or more
of fused / sintered / tabular alumina and/or magnesia grains and
powders ii) providing a second mix (BOND) comprising an intimate mixture of fine
powders selected from silicon metal, alumina and iron oxide ; iii) mixing from 50 to 90 % by wt. of the first mix and from 10 to 40 % by
wt. of the second mix; with each other iv) compacting this mixture of the first and second mix by standard, well
known ceramic fabrication techniques v) drying the unfired compacts; vi) firing the dried compact in a controlled nitrogenous atmosphere at high
temperatures up to 1550°C ; and vii) cooling the fired product

4
Detailed Description of the Present Invention
In the present invention, the known advantages of the anti-abrasion / erosion properties and high refractoriness of alumina / magnesia have been retained while eliminating the usage of carbonaceous raw materials like phenolic resins, graphite and carbon that limit the useful life of the corresponding products. The inventors have found that the second mix (BOND), when subjected to high temperature firing under defined conditions, forms a strong high-temperature ceramic bond in situ (due to reaction sintering) and surrounds the first mix (GROG) holding these aggregates with a strong force. The combination of the first and second mixes resulting in the refractory slide gate plates of the present invention has improved oxidation resistant and thermal spalling properties.
The improved refractory slide gate plates have a preferred bulk density of 2.6 g/cc; preferred apparent porosity of 20 %; preferred cold crushing strength of 75 MPa; preferred modulus of elasticity of 25 GPa; preferred cold modulus of rupture of 15 MPa; hot modulus of rupture of 30 Mpa
This high temperature ceramic bond formed between the first and the second mix comprises of complex inorganic phases in the alumina - silicon - nitrogen- oxygen system and exhibits:
• high thermal spalling resistance;
• excellent oxidation resistance;
• low wettability and corrosion by molten metal/slag; and,
• high refractoriness.
About 50 to 90 % of the first mix ("GROG") is mixed with the 10 to 40 % of the second mix ("BOND"), compacted to the required size and shape by known ceramic fabrication techniques, and fired at high temperatures (up to 1550°C) in a controlled (nitrogenous) atmosphere to obtain improved refractory slide gate plates. By varying the composition of the second mix, the ratio of the first mix to second mix as also the firing conditions, it is possible to make refractory slide plate compositions having a range of high temperature physical and chemical properties that allow for customizing the compositions and, therefore, the concomitant properties for the desired application in the steel casting or melting shops.

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The first mix can be selected from the fused, sintered, tabular, reactive varieties alumina / magnesia available in the market. The inventors have also observed that fused / sintered mullite (an alumino-silicate) or spinel (a magnesium-aluminate) grains and powders can be used advantageously in place of alumina / magnesia grains, although this latter material is the preferred material.
The first mix, forming 50 to 90% of the final mixture, consists of alumina and/or magnesia grains and powders ranging in particle size from [standard] mesh 6 to -325 in desired proportions
The second mix comprises of fine powders (-325 mesh) of silicon, alumina and iron oxide. In fact, the composition of the second mix itself can be varied by varying the silicon to alumina proportion, so that the corresponding fired refractory has different desired properties.
The ceramic fabrication of an intimate mixture of the above raw materials (i.e., first and second mix) to obtain the green unfired compact, of desired size and shape, can be accomplished by compaction in hydraulic or friction screw presses, in vibratory compaction machines, using pneumatic ramming or tamping equipment, or by the well known slip casting technique.
The firing or reaction sintering of the above green compacts is carried out in sealed, air / gas-tight ceramic muffles or boxes under a positive pressure of high purity nitrogen gas at temperatures up to 1550°C, but preferably around 1430°C. It is possible, however, that the nitrogenous atmosphere in the ceramic muffle / box is created by incorporating organic / inorganic compounds that produce nitrogen in situ inside the ceramic muffle / box during the firing cycle,
Optionally small amounts up to 5% of temporary or green binders like dextrine starch, lingo-sulphonates, polyvinyl alcohol, etc can be used during mixing operation to improve the handling strength of the green unfired compacts.

Thus improved refractory slide gate plates are made by mixing desired amounts of first and second mix, compacting them by conventional ceramic fabrication techniques and firing them under nitrogenous atmosphere at high temperatures (up to 1550°C).
The refractory slide gate plates and the process of the present invention are described with respect to following non limiting exempla nary illustrations:
1) 60 to 90 %, preferably 70% of, the first mix comprising of alumina and/or magnesia grains and powders is weighed into a conventional counter current bowl type or a planetary mixer and mixed for about 10 minutes to obtain a dry, homogeneous mixture.
2) In a separate mixer, the ingredients, namely silicon metal, alumina, iron oxide in a ratio described above of the second mix are thoroughly mixed and stored as BOND
3) Into the mixer containing the first mix required amount of an aqueous suspension / solution of the green / temporary binders (like dextrine, glycerine, lingo-sulphonates, etc) are added.
4) 10 to 40 %, preferably 30 % of second mix is slowly added into the counter current mixer containing the wet first mix and mixed for about 10 to 40 minutes, preferably 30 minutes; lumps formed, if any, are broken by passing the mixture of first and second mix through an appropriate wire mesh screen on vibratory screening equipment.
5) Desired amount of the mix, screened as above, is poured into a moulding die and compacted to the pre-determined density in suitable moulding equipment like hydraulic or friction-screw press, vibro-compactor, slip caster, etc.
6) The green or un-fired compacts are loaded on to shelves of a drier rack and allowed to dry, to a final moisture level of 0 to 1%, preferably 0.5% by initial drying in air followed by hot air oven.
7) The dried compact is loaded into a refractory muffle / box made of silicon carbide refractory, and, fired as per desired temperature - time cycle in an oil-fired kiln. The final soak temperature is maintained at 1430° to 1550°C, preferably at 1430°C, for a soak

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period of about 1 - 8 hours preferably for 6 hours The firing is done under controlled (nitrogenous) atmosphere at a pressure of 5 -15 mm water gauge.
8) After cooling, the fired product - new improved slide gate refractory - is characterized for different physical and chemical properties.
The refractory slide gate plates according to the invention and prepared by the method of present invention along with their properties (Examples 1 to 6) are provided in Table 1. It may be noted that for Examples 1 to5 the compaction is achieved by hydraulic / friction screw pressing of the GROG + BOND mixtures.
Example 6 relates to samples compacted by (vibro-) slip casting method. This thus uses another method of compaction of the present invention.
TABLE 1
Example GROG BOND BD AP CCS MoE C- H-
No. w/w % w/w % g/cc % MPa GPa MoR MoR
MPa MPa
1 90 10 2.98- 2 85 15 2.97- 3 80 20 2.93- 4 75 25 2.92- 5 70 30 2.90- 6 70 30 2.58- 2.62 190
Note: B D - Bulk Density; A P - Apparent Porosity; CCS- Cold Crushing Strength; MoE - Modulus of Elasticity; C-MoR - Cold Modulus of Rupture; H-MoR - Hot Modulus of Rupture
The examples thus demonstrate the refractory slide gate plates of present invention having improved properties. It would be seen that the best result is obtained from composition wherein the GROG and BOND are present at 70% and 30 % respectively,

s
Refractory slide gate plates of the present invention are tested for thermal spalling and oxidation resistance properties. They are compared with conventional refractory slide gate plates formed of alumina -carbon. The data is provided in Table II.
For assessing thermal spalling properties the refractory slide gate plates are heated to a temperature of 1000°C and, immediately exposed to ambient temperature. The number of cycles at which crack appears is monitored. It is found that for the conventional A1203-C or MgO-C refractory slide gate plates the crack appears at 15-20 cycles while that for refractory slide gate plates of present invention such cracks appear only after 40-50 cycles.
For assessing oxidation resistance properties, the refractory slide gate plates were heated to a temperature of 1000°C under oxidizing atmosphere. The weight loss / gain in each case is measured. It is found that the weight loss in case of the conventional refractory slide gate plates is 10-12% while in the case of that of the refractory slide gate plates of the present invention a small weight gain of 1 to 2% is observed.
TABLE II
Properties Conventional A12O3-C Refractory slide gate plates
refractory slide gate plates of present invention
40-50 cycles
Thermal Spalling 15-20 Cycles
Oxidation resistance 10-12% 1-2%
The results demonstrate the improved thermal spalling and oxidation resistance properties achieved by the refractory slide gate plates formed according to the present invention compared with the conventional carbon containing product.

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WE CLAIM:
1. Improved refractory slide gate plate having high oxidative resistance, thermal spalling
and corrosion resistance comprising:
from 50 to 90 % by wt. of a first mix comprising a combination of one or more of fused / sintered / tabular alumina and/or magnesia grains and powders, and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide.
2. Improved refractory slide gate plates as claimed in claim 1 having bulk density in the region of 2.3 to 3.2 g/cc; apparent porosity of 18 to 25%; cold crushing strength of 60 to 180 MPa; modulus of elasticity of 20 to 70 GPa; cold modulus of rupture of 14 to 50 MPa; hot modulus of rupture in the region of 15 to 70 MPa.
3. Improved refractory slide gate plate as claimed in claims 1 to 2 wherein the particle size of alumina and/or magnesia grains and powder present in the first mix ranges from mesh 6 to -325 mesh in varying proportions
4. Improved refractory slide gate plate as claimed in claims 1 to 2 wherein the first mix comprises alumina and/or magnesia grains optionally substituted by an alumino-silicate (mullite) or magnesium-aluminate spinel (fused / sintered) grains and powders
5. Improved refractory slide gate plate as claimed in claim 1 to 4 wherein the second mix comprises silicon metal of finer than 200 mesh, preferably minus 325 mesh, and alumina of preferably the reactive variety.
6. Improved refractory slide gate plate as claimed in claim 1 to 5 wherein the second mix comprises of fine powders (-325 mesh) of silicon, alumina and iron oxide in varied proportion of silicon to alumina such that the corresponding fired refractory has different desired properties.

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7. Improved refractory slide gate plate as claimed in claim 6 wherein the second mix comprises silicon metal powder comprising more than 95% silicon content, iron oxide comprising at least 85% Fe2O3 content.
8. Improved refractory slide gate plate as claimed in any preceding claim wherein the said refractory slide gate plate has preferred bulk density of 2.6 g/cc; preferred apparent porosity of 20 %; preferred cold crushing strength of 75 MPa; preferred modulus of elasticity of 25 GPa; preferred cold modulus of rupture of 15 MPa; hot modulus of rupture of 30 Mpa .
9. A process for making refractory slide gate plate as claimed in claims 1 to 8 comprising the steps of:
a. providing a first mix comprising a combination of one or more of fused,
sintered , tabular alumina and/or magnesia grains and powders;
b. providing a second mix comprising an intimate mixture of fine powders of
silicon, alumina and iron oxide
c. mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt.
of the second mix;
d. compacting the first and second mix by any one of the standard ceramic
fabrication techniques;
e. drying the unfired compact;
f. firing the dried compact in a controlled nitrogenous atmosphere at high
temperatures up to 1550°C ; and
g. cooling the fired product
10. A process as claimed in claim 9 wherein the first mix is formed by mixing alumina and/or magnesia grains and powders in the particle size ranging from 6 to -325 mesh in a conventional mixer and mixed for 10 minutes to get a homogenised mixture.
11. A process as claimed in claims 9 and 10 wherein aqueous suspension or solution of green /temporary binders are further added to the first mix.

11
12. A process as claimed in claims 9 to 11 wherein the green or temporary binders are selected from dextrine, glycerine, lingo sulphonates, polyvinyl alcohol and the like.
13. A process as claimed in claim 9 wherein the second mix is prepared by mixing fine powders of -325 mesh of silicon, alumina and iron oxide in a separate mixing equipment
14. A process as claimed in claims 9 to 13 wherein the second mix is mixed with the wet first mix for 10 to 40 minutes, preferably 30 minutes and passed through vibrating wire mesh screening equipment.
15. A process as claimed in claims 9 to 14 wherein compaction of the first mix and second mix is achieved by conventional ceramic fabrication methods selected from hydraulic or friction-screw pressing, vibro-compaction, pneumatic tamping, vibro-slip casting and the like.
16. A process as claimed in claims 8 to 14 wherein drying of the unfired compact is carried on to a final moisture level of 0 to 1%, preferably 0.5% by initial drying in air followed by hot air oven.
17. A process as claimed in claims 9 to 16 wherein the firing of the dried green / un-fired compacts is carried out at temperatures of 1430°C to 1550°C, preferably at 1430°C, for a soak period of about 1-8 hours preferably for 6 hours
18. A process as claimed in claims 9 to 17 wherein the firing is carried out in refractory muffle / box made of silicon carbide refractory.
19. A process as claimed in Claim 8 to 18 wherein the gaseous atmosphere inside the refractory muffle / box is filled with pure Nitrogen gas at a pressure of 5 - 15 mm water gauge.

20. Improved refractory slide gate plate as claimed in claims 1 to 8 substantially as herein described with reference to the illustrative examples.
21. A process as claimed in claims 9 to 19 substantially as herein described with reference to the illustrative examples.
Improved refractory slide gate plate and a process of preparation of the same. The refractory slide gate plate has high oxidation resistance and excellent thermal spalling properties, The refractory slide gate plate comprises from 60 to 90 % by wt. of a first mix comprising a combination of fined / sintered / tabular alumina and/or magnesia grains and powders ; and from 10 to 40 % by wt. of a second mix comprising an intimate mixture of fine powders of silicon metal, alumina and iron oxide. The process comprises providing a first mix comprising a combination of one or more of fused, sintered, tabular alumina and/or magnesia grains and powders ; providing a second mix comprising an intimate mixture of fine powders selected from silicon metal, alumina and iron oxide ; mixing from 60 to 90 % by wt. of the first mix and from 10 to 40 % by wt. of the second mix; compacting this mixture of the first and second mix by ceramic fabrication technique, drying the unfired compact; firing the dried compact in a controlled nitrogenous atmosphere at high temperatures up to 1550°C ; and cooling the fired product.

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Patent Number

203255

Indian Patent Application Number

00098/KOL/2003

PG Journal Number

11/2007

Publication Date

16-Mar-2007

Grant Date

16-Mar-2007

Date of Filing

20-Feb-2003

Name of Patentee

IFGL REFRACTORIES LTD.,

Applicant Address

3, NETAJI SUBHAS ROAD, KOLKATA - 700 001

Inventors:

#	Inventor's Name	Inventor's Address
1	BAJORIA Pradeep	IFGL REFRACTORIES LTD., 3, NETAJI SUBHAS ROAD, KOLKATA - 700 001
2	BANERJEE Gautam	IFGL REFRACTORIES LTD., 3, NETAJI SUBHAS ROAD, KOLKATA - 700 001
3	SHASHI MOHON A.L.	C/O.VIPRA 164/A, 24th CROSS, 6th BLOCK, JAYANAGAR, BAGALORE 560 082

PCT International Classification Number

C04B 35/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA