FIELD OF THE INVENTION
The invention relates to a method of manufacturing of Alumina based wear resistance materials from calcined bauxite as a source of raw material and the product thus produced has good abrasion resistance for use as lining material in the coal and ash handling equipments in the powder plants and other wear resistance applications.
BACKGROUND OF THE INVENTION
High Alumina based abrasion resistance material is known to be used for lining of the pipes, bends and other equipments of coal and ash handling in power plants and other industries where the erosion is very severe, to extend the life of these equipments or components. These products for example, high alumina based abrasion resistance material has very high wear resistance as measured by relative abrasion index or by known jet erosions methods, hence the products are generally prepared from ceramic materials containing about 80 to 90 % A1203 and balance being sintering aids or additives. The sintering aid is typically oxides and clays minerals which form the liquid phase during sintering at around 1500 to 1700 °C. These products are made from calcined alumina and with clay and Mn02, mixed in dry or wet form and spray dried if mixed in wet form and pressed into tiles and fired at 1500 to 1700 °C to get complete densification characterized by zero water absorption test.
Patent CA 2020486 discloses a wear-resistant alumina material formed by liquid phase sintering of a mixture of about 70 to 95 wt % of crystalline AI203 particles

and about 30 to 5 wt % of glass phase-forming components in a nitrogenizing atmosphere at about 1550 °C.
In JP 2180747, Magnesia and silica each having <=0.3 micron average particle size are added in 0.025-0.12% in total, to alpha-alumina powder having 0.05-0.3 micron average particle size, in 2-15 molar ratio of MgO to Si02, and are pulverized and mixed. The mixture is molded and sintered at 1,300-1,550 deg.C to obtain wear resistant alumina ceramics.
In JP 20090091196, alumina ceramic of excellent in wear resistance is prepared from 99 % AI203 and sintering aid comprising three components Si02, Cao and MgO, totaling to 0.2%.
CN 1673173 discloses a method in which nanometer crystal alpha-AI203 powder prepared through wet chemical process, is added into submicron level alpha-AI203 powder adopting MgO and Si02 as the sintering assistant, and sintering is temperature is maintained at 1420-1500 deg. C for 3 hr.
US 2003029094 teaches a method for the production of a sintered, microcrystalline alpha-AI203-based shaped body, wherein an alpha-AI203 powder having an average particle diameter of <2 microns is used as starting material, and processed with at least one binder and a solvent subsequently extruded and sintered at a temperature rage between 1300 DEG C. and 1750 DEGC.
Indian Patent 198068 discloses an improved additive composition useful for

preparation of alumina based abrasion resistant material having improved wear properties, and methods for their preparation. AI203 is in the range of 4-5n.m. The sintering temperature of liner materials can be reduced to relatively low temperature (1480 to 1500 °C). Similar method for improved process for the production of alumina based wear resistant ceramics is also disclosed in Indian Patent 182524.
All the above prior art methods use expensive because of use of Alumina as raw material. On the other hand, the use of less expensive base minerals sources like bauxite have not generally been used for producing high alumina based wear resistance products, but used mainly for refractory products.
Indian Patent No. 73343 relating to abrasive grain material of sintered bauxite, Indian Patent No. 89651 related to method of making Sintered bauxite tumbling media, Indian Patent No. 131439 related to Process for manufacturing of abrasion resistant aluminous refractories, and Indian Patent No. 210326A process for producing dense high alumina content grains from low-grade bauxite ores and fine grain bayer's alumina, are not however, for high alumina containing wear resistance ceramics.
US 2310953A teaches a process for making ceramic materials from bauxite and it particularly relates to processes of preparing hard, dense and amorphous refractories from, bauxite without fusion. The process used upto 10% flux for sintering at low temp, which doesn't disclose any wear resistance properties and is amorphous.

US 5645618A discloses method for making an abrasive article. US 3895150A relates to low cost, strong, highly wear resistant ceramic articles, the wear resistance being comparable to that of cemented carbides. The ceramic articles are fabricated from certain bauxite and bauxite like materials by a process of hot-pressing. This process is very energy intensive and special hot presses are required. US 3784388A and GB 1269144A also disclose the ceramic articles by hot-pressed bauxite compositions, 78-79 percent AI203, less than 9 percent Si02, 2-8 percent Fe203, 2-4 percent Ti02 and a total of less than 3 percent CaO, MgO, Na20. This also use hot pressing.
Thus, the above-mentioned prior art methods either use costly hot pressing method and use bauxite for refractory application. The present inventors accordingly recognized that replacing the calcined alumina by right kind of bauxite mineral and preparing high wear resistance ceramic products by conventional sintering process is a cost-effective process for producing such wear resistance products.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method of manufacturing Alumina ceramics with high abrasion resistance for wear resistance applications, which eliminates the disadvantages of prior art.
Another object of the present invention is to propose a method of manufacturing Alumina ceramics with high abrasion resistance for wear resistance applications, which produces Alumina ceramics having abrasion resistance at least 15 times

higher than Mild steel when used as lining materials in power plant and industrial equipments.
A further object of the invention is to propose a method of manufacturing Alumina ceramics with high abrasion resistance for wear resistance applications, in which an economic composition of bauxite mineral is used as a starting material for producing Alumina based wear resistance products.
SUMMARY OF THE INVENTION
Accordingly, there is provided an Alumina based wear resistance material produced from alumina containing mineral such as calcined bauxite which has AI203 as a predominant constituent along with other oxides such as Fe203, Ti203, Si02, MgO and CaO.
Moreover, according to the present invention, there is provided a method of manufacturing Alumina based wear resistance material wherein calcined bauxite mineral having AI203 above 83% is selected. This raw material is mixed with calcined alumina to increase AI203 content, if required, compacted into tiles, and fired at 1540 to 1580 C. The product thus produced has water absorption near to zero, bulk density of above 3.35 gm/cc and abrasion resistance as measured by relative abrasion resistance (RAI) is above 15.
In the present invention the product formed has improved physical, mechanical and wear properties suitable for lining coal and ash handling equipments in powder plants and other industrial applications.

DETAILED DESCRIPTION OF the INVENTION
In the present invention, there is provided a method of manufacturing Alumina based wear resistance ceramic products comprising of Alpha AI203 as major crystalline phase using low cost bauxite as raw material. The cost of this raw material is below half of that of calcined alumina used commonly for this type of products. The bauxite raw material a calcined one and have AI203 content 80 to 90 % preferably 83 to 86 % which are produced by beneficiation of bauxite mines. It is important to choose the bauxite so that balance chemical oxides present will form glassy phase and helps in sintering. AI203 content may be further increased in the ceramic product by adding small amount of calcined alumina content. It is also possible to use other ceramic grains such as fused mullite to increase thermal shock resistance in addition to wear resistance. The particle size of the bauxite should be below 100 mesh more preferably 170 mesh. The production method involves the mixing of calcined bauxite and any additional ceramic powder with organic binders. Organic binders are chosen depend on the process of fabrication of shapes. Process of pressing, extrusion, casting can be employed depending on the shapes and sizes of the product to be manufactured. For pressing tiles, PVA binder is commonly used. For extrusion methyl cellulose can be used. The dried products are fired in the kilns at 1540-1580°C , more preferably 1550 to 1570 °C . The products have water absorption below 1 %, Bulk density of above 3.35 g/cc and , abrasion resistance as measured by relative abrasion resistance (RAI) is above 15

Examples
Example 1. Calcined bauxite having 83.5 % AI203 is mixed with PVA binder making it suitable for fabrication of tiles by pressing. Pressed tiles are fired at 1560 C. Fired tiles have bulk density of 3.41 gm/cc and water absorption of <0.1 %. Relative abrasion resistance (RAI) is 17 indicating this is 17 times better wear resistance than mild steel
Example 2: The tiles are produced as per examplel. But the source of alumina used is Calcined bauxite having 85.5 % AI203. The products has bulk density of 3.44 gm/cc , water absorption of 0.17 % and Relative abrasion resistance (RAI) is 26
Example 3: The tiles are produced as per examplel. 9 kgs of Calcined bauxite having 83 % AI203 is mixed with 1 kg of calcined alumina before mixing with PVA solution. The fired product has Bulk density of 3.45 gm/cc, water absorption of 0.09 % and RAI of 28

WE CLAIM
1. A method of manufacturing Alumina ceramics with high abrasion
resistance for wear resistance applications, comprising the steps of:
- selecting source of Al203 as calcined bauxite mineral having Al203 content of more than 83%
- compacting the selected mineral to form tiles; and
- firing the tiles in an oven maintaining a temperature between 1540°C and 1580°C for a period such that the produced alumina ceramics exhibits substantially zero water absorption property.

2. The method as claimed in claim 1, wherein the bulk density of the alumina ceramics is more than 3.35 gms/cc.
3. The method as claimed in claim 1, wherein the abrasion resistance of the product measured in terms of relative abrasion resistance index (RAI) is above 15.
4. The method as claimed in claim 1, comprising optionally mixing of calcined alumina with the selected calcined bauxite mineral to increase AI2O3 content.