Title of Invention	A METAL MATRIX CERAMIC COMPOSITE (MMCC) WEAR PART AND METHOD OF PREPARING THE SAME
Abstract	A metal matrix ceramic composite wear part comprises a wearing portion formed by a ceramic cake impregnated by metal. The ceramic cake comprises ceramic grains comprising alumina, and gains of a carbide. The inclusion of carbide grains reduces wear. Preferably the alumina comprising grains comprise alumina, zirconia and titanium oxide, wherein alumina is preferably present in an amount of 30 to 65%, zirconia in an amount of 30 to 65% and titanium oxide in an amount of 1 to 7%, all percentage being expressed in weight of the grains. Preferably the ceramic cake further comprises fine ceramic powder, preferably in the range of 1 to 4% by weight of the grains.

Title of Invention

A METAL MATRIX CERAMIC COMPOSITE (MMCC) WEAR PART AND METHOD OF PREPARING THE SAME

Abstract

A metal matrix ceramic composite wear part comprises a wearing portion formed by a ceramic cake impregnated by metal. The ceramic cake comprises ceramic grains comprising alumina, and gains of a carbide. The inclusion of carbide grains reduces wear. Preferably the alumina comprising grains comprise alumina, zirconia and titanium oxide, wherein alumina is preferably present in an amount of 30 to 65%, zirconia in an amount of 30 to 65% and titanium oxide in an amount of 1 to 7%, all percentage being expressed in weight of the grains. Preferably the ceramic cake further comprises fine ceramic powder, preferably in the range of 1 to 4% by weight of the grains.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (Se section 10, rule 13) "IMPROVED WEAR RESISTANT METAL MAXTRIX CERAMIC COMPOSITE PART, CERAMIC CAKE FOR A METAL MATRIX CERAMIC COMPOSITE PART, METHOD OF MANUFACTURE THEREOF, GRINDING ROLL AND TABLE LINER COMPRISING A METAL MATRIX CERAMIC COMPOSITE PART" We, AIA Engineering Ltd., of 115, G.V.M.M. Estate, Odhav Road, Ahmedabad - 382 410, India; The following specification particularly describes and ascertains the invention and the manner in which it is to be performed. 1 FIELD OF INVENTION The invention relates to a metal matrix ceramic composite wear part and a ceramic cake for use in a metal ceramic wear part. The invention also relates to a method for manufacturing a ceramic cake for use in a metal matrix ceramic composite wear part. The invention further relates to a grinding roll comprising a metal matrix ceramic composite wear part and to a table liner for a vertical mill comprising a metal matrix ceramic composite wear part. Many industrial applications involve components which are subjected to wear during the life time of the component. The applications of parts requiring wear resistance are quite common in cement, mining and thermal power generation industries. Historically, 12% Mn steel and Nihards were used for wear resistant applications during first half of twentieth century. During last 50 years, high chromium irons have been successfully used for wear resistance applications and have largely replaced Nihard and 12% Mn. Steel materials. The search for further improved wear resistance has continued and during last 15 years metal matrix ceramic composites are being used with varying degree of success for wear resistant applications. The present invention is in the same area and substantially improves the economics and wear properties as compared to presently used composites. Metal matrix ceramic composites comprise ceramic parts embedded in a metal matrix. Back ground and prior art references With reference to metal matrix ceramic composites, the first decision is naturally the choice of ceramic material, usually in the form of grains. Alumina is known to be a good abrasive material. 2 In this connection, US patent (No. 3,181,939 dated 04.05.1965) by Douglas W. Marshal (assignee Norton Company, Mass, USA) is relevant. The patent describes manufacture of fused alumina zirconia abrasives which combine good wear resistance characteristics of alumina and toughness of zirconia. Thus, alumina/zirconia grains appear to be a most suitable candidate for metal matrix ceramic composites. Ullmann's Encyclopedia of Industrial Chemistry, Fifth Complete revision, part Al, Volume Al, paragraph 2.2 describes useful alumina/zirconia grains. The art of casting with embedded hard material was taught in a German patent (by Dr. Wahl) No. 7326661 dated 20.07.73. A Japanese patent by Mr. Tamura of KHI (patent No. 62286661 dated 12.12.87) described a method of impregnating ceramic particles with molten metal to produce composite casting with good wear resistance. A European patent (No. EP 0575858B1 dated 23.06.92) filed by Staub Fritz (assignee Zuzel Inotech AG) describes production of metal matrix ceramic composite casting with porous ceramic members at the wearing face. The ceramic particles used are described as corundum, zirconium oxide or magnesium oxide. In US patent 6399176B1 dated 04.06.2002 production of composite wear component by casting is described. Ceramic cakes were introduced on the wear surface consisting of homogeneous solid solution of 20-80% alumina and 80-20% zirconia. Although there are therefore many examples of composite wear components there remains a need for further improvement of the wear resistance. Such further improvement will increase the effectiveness of the wear component. Object of invention It is an object of the invention to provide a metal matrix ceramic composite wear part and a ceramic cake for use in a metal ceramic wear part with improved wear resistance. The 3 known devices need improvement. When a composite wear part is worn down, the part must be replaced. Consequently any device using the wear part cannot be used during replacement of the worn out part. Replacement of the worn out part leads to a loss in operative time of the device. An improvement in the wear resistance leads to a decrease in percentage of time lost to replacing worn parts of such devices as grinding rolls and table liner using metal matrix ceramic composite wear parts. Summary of invention The invention provides for a metal matrix ceramic composite wear part, said wear part comprising a wearing portion formed by a ceramic cake impregnated by metal, wherein the ceramic cake comprises ceramic grains comprising at least alumina, and wherein the ceramic cake further comprises grains comprising a material chosen from the group consisting of boron carbide, silicon carbide or tungsten carbide. The present invention provides for ceramic cakes that show improved wear resistance. Preferably the amount of carbide grains lies between 1 and 25% in weight of the ceramic cake for boron carbide, preferably 2 and 10% in weight. A very small amount of carbide grains will have only a moderate effect, whereas a large addition of carbide grains does not to provide an added advantage. In preferred embodiment the carbide grains are mainly comprised of boron carbide. Boron carbide is the hardest of the mentioned carbide materials and the lightest. Thus, the present invention succeeds in improving wear characteristics of metal matrix ceramic composite parts, achieved by using an addition of carbide grains to the grains comprising alumina. In a preferred embodiment the ceramic grains comprise alumina, zirconia and titanium oxide, wherein alumina is present in a grain on average for an amount of 30 4 to 65 %; zirconia is present for an amount of 30 to 65% and titanium oxide for an amount of 1 to 7%, all percentages being expressed in weight of the grains. The inclusion of zirconia in the alumina comprising grains has, a positive effect on the wear resistance of the grains. Inclusion of titanium oxide into the grains has a further positive effect oh the wear resistance.. Titanium oxide is in itself considerably softer than alumina and zirconia, which makes the positive effect all the more remarkable. Preferably the amount of titanium oxide lies between 2 of 6 percent, most preferably between 3 and 5.5% in weight. The positive effect on the wear resistance is most pronounced in these weight percentages. The percentages of alumina and zirconia are preferably between 40 and 55% alumina and 40 to 50% zirconia. It is remarked that the alumina/zirconia/titanium oxide composition may vary from grain to grain within the metal matrix ceramic composite wear part. All percentages mentioned above relate to average percentages over the grains. Moreover, for even more preferred embodiments, the inventors have realized that, when producing a ceramic cake from grains, the binding properties of the grains are important because the grains are relatively coarse. Therefore, there is a need for addition of other constituents to the ceramic grains to improve bonding between the grains and mouldability of the material from which the ceramic cake is produced. One such constituent is sodium silicate which helps bind the grains and improves mouldability. The inventors have realized that addition of very fine ceramic powder, preferably mainly comprised of aluminum oxide powder, not only improves mouldability but also the hardness of the cake thus increasing the wear resistance of the final product "Very fine powder" means powder of a size considerably smaller (at least one, preferably two orders of magnitude) than the size of the alumina/zirconia/titania ceramic grains. Such small ceramic powder is preferably mixed in a percentage in -5 weight in relation to the weight of the ceramic grains (alumina/zirconia and carbide) of between 1 and 4%. Preferably the grain size of the fine ceramic powder is in the range of FEPA 1000-1400 grit sizes. Preferably the grain size of the alumina comprising grains and the carbide grains is in the range of FEPA 6-12 grit sizes. The mixture of previously described ceramic grains, a fine ceramic (alumina) powder and Sodium Silicate is preferably filled in flexible, preferably rubber core boxes of suitable shapes. The cakes still in core boxes are gassed and baked to develop good strength. The prepared ceramic cakes are located at desired surfaces of moulds and liquid metal is poured into the cavity to produce metal matrix ceramic composite castings. Brief description of the figures These and further aspects of the invention will be explained in greater detail by way of example and with reference to the accompanying drawings, in which Fig. 1 illustrates a ceramic cake as per prior art Fig. 2 illustrates a ceramic cake with infiltrated metal as per prior art Fig. 3 illustrates a ceramic cake for a metal matrix ceramic composite wear part in accordance with the invention. Fig. 4 illustrates illustrate rubber core box Fig. 5 illustrates a grinding rolls comprising a metal matrix ceramic composite wear part, Fig. 6 illustrates a table liner comprising a metal matrix ceramic composite wear part Figures 7 and 8 illustrate ceramic cake arrangements. 6 The figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the figures. Detailed description and embodiments of the present invention Figure 1 illustrates a ceramic cake as per prior art. The ceramic cake 1 comprises ceramic grains 2 and often a binder 3. The binder is in figure 1 schematically indicated as a thin layer around some of the grains. Figure 2 illustrates a ceramic cake 1 of figure 1 impregnated by metal 4 to form a metal matrix ceramic composite wear part (MMCC). To impregnate the ceramic cake molten metal is introduced. The molten metal fills the spaces between the grains 2 to produce a metal matrix ceramic composite part. The metal forms the matrix for the ceramic grains. For this reason such parts are called "metal matrix ceramic composite parts". The applications of parts requiring wear resistance are quite common in cement, mining and thermal power generation industries. The present invention has succeeded in improving wear characteristics of metal matrix ceramic composite parts, achieved by introducing ceramic grains at the wearing surface. The invention combines in the ceramic cake the use of alumina/zirconia grains and grains of boron, silicon or tungsten carbide. Figure 3 schematically illustrates a ceramic cake for a metal matrix ceramic composite wear part in accordance with the invention. The difference between figure 1 as per prior art and figure 3 is the addition of boron, silicon or tungsten carbide grains 5 as well as fine alumina powder 6. In two experimental runs 5 and 20% by weight of boron carbide grains were included in the ceramic cake. In the two cakes 87%, respectively 72% of the ceramic cake was comprised of alumina/zirconia/titania grains comprising alumina in the range of 30-65%, zirconia in the range of 65-30%) and titanium oxide in the range of 1-7%, where on average the alumina and zirconia contents in the alumina/zirconia/titanium oxide grains were -7 approximately 50% and the titanium oxide content approximately 5%, 3% of the weight of the ceramic cake was fine alumina powder and approximately 5% of the weight of the ceramic cake was a inorganic binder. In the examples each alumina and zirconia comprising grain was, on a microscopic level, composed of a phase mixture of different solid phases. The grains were not formed as a homogeneous solid solution. Alumina/zirconia grains used in the preferred examples have as components alumina and zirconia. Inside such grains, the composition is not homogeneous but a phase mixture is present, i.e. different parts of the grain have a different composition, some parts forming a solid phase comprising a first percentage of alumina and a second percentage zirconia, other parts forming a different solid phase or solid phases having different percentages alumina and zirconia or being mainly composed of alumina or zirconia. These solid phases may comprise titania. The grain as a whole is in the form of a phase mixture. 5% in weight of boron carbide corresponds, due to the difference in specific gravity of the carbide grains with the specific gravity of alumina-zirconia comprising grains, to approximately 7.5% in volume. 20% in weight correspond to approximately 27,5% in volume. Given the difference in specific gravity between boron carbide (approximately 2.5 gr/cc) and alumina/zirconia (approximately 3.8 gr/cc) this means that a percentage in weight between 1% and 25% corresponds to a percentage in volume of the carbide grains in the ceramic material between 1.5% and 34%. When the same size particles, i.e. the volume of each the alumina/zirconia and the boron carbide grain would be the same, is used this would mean that one in 60 to 1 in 3 of the total of alumina-zirconia comprising grains and carbide grains is a carbide grain. The same volume percentage range leads for silicon carbide grains which have a higher specific gravity of 3.2 gr/cc to a range in weight between 1.2% and 30%) and for tungsten carbide grains which have an even higher specific gravity of 15 gr/cc to a range in weight between 5.6%) and 66%). The boron carbide grains and the alumina/zirconia/titinia grains in the examples had the same grit size, in the examples the grits size was FEPA 10. 8 The wear of ceramic metal composites having such ceramic cakes including boron carbide grains was compared to the wear of ceramic metal composites with the same constitution but lacking the boron carbide grains. Addition of 5% boron carbide grains by weight proved to decrease the wear rate by approximately 15%; with addition of 20% boron carbide grains by weight no further decrease in wear rate was noticed. As explained above, these results are contrary to the prior art. Surprisingly addition of even a relatively small amount of carbide grains has a positive effect. The increase of wear resistance is not proportional to the amount of boron carbide grains added, which is an indication of the presence of a cooperative effect wherein inclusion of even a relatively minor amount of carbide (between 2 and 10%) has a protective effect increasing the wear resistance. The advantageous effect proved to be substantially higher in a region around 5% than for 20%o. A preferred range is weight for boron carbide is between 2 and 10% weight. A preferred range in weight for boron carbide grains between 2 and 10% in weight corresponds for silicon carbide to a range in weight between 2.5% and 12.5% in weight and for tungsten carbide to a range in weight between 3.6% and 40%. The grain sizes of ceramic grains are normally designated in terms of grit sizes. The grit sizes recommended to be used for producing metal matrix ceramic composite ranges from 6-12 grit sizes as per FEPA standard. Preferably the alumina/zirconia and carbide grains are of comparable grit size, i.e. not differing by more than 4 grit sizes, preferably not more than two grit sizes. In order to be able to introduce such grains at desired locations, it is necessary to form cakes of required shape. Moreover, such cakes have to possess adequate strength to withstand eventual engulfing by liquid metal. Addition of very fine ceramic powder, preferably comprising aluminum oxide powder, along with Sodium Silicate, has shown to provide improved mouldability and achieve an increase in strength. Addition of 1000-1400, preferably 1200 grit fine Aluminium Oxide powder imparts thixotropic properties. Preferably fine alumina powder is used, but within the 9 framework of this preferred embodiment of the invention other fine ceramic powders, for instance zirconia or alumina/zirconia powders could be used. Figure 4 shows schematically the inclusion of fine alumina powder 6. The mixture of previously described mineral particles and ceramic, preferably alumina powder is preferably mixed with suitable binder such as Sodium Silicate. However, the inventor has realized that such mix sometimes does not have adequate green strength (i.e. the strength in the green, not yet baked state) and the shapes of ceramic cakes are, as the inventor has realized, preferably supported in flexible, preferably rubber, for instance silicone rubber core boxes. Use of rubber core boxes for manufacturing of ceramic cakes is a feature of a preferred embodiment of the method of the invention. Figure 4 schematically shows the use of a rubber core box 7 around ceramic cakes 1. The mixture described above is filled in the rubber core boxes of desired shapes and treated with Carbon Dioxide to develop adequate strength for handling. Further ceramic shapes in the rubber core boxes are heated to temperature between 80 -220°c for one to four hours so that adequate strength is developed. The cakes are located at desired surfaces of refractory moulds. After closing the mould assemblies, liquid metal is poured into the cavity. The liquid metal composition is selected depending up on the application. High impact applications may require steel and low impact applications may tolerate irons. The chromium steels may contain between 0.2-1.2% C and 2-8% Cr, with addition of other alloying elements such as Mn, Mo, Ni & Cu. The Mn. Steel may contain between 0.8-1.2% C and 8-14%) Mn with other elements such as Si, Cr, S & P present additions and impurities. The irons may contain between 1 - 3.5% C, 11-28% Cr with addition of other alloying elements Mo, Ni and Cu. 10 Generally for wear resistance applications, the above types of steels and irons are commonly used. However, the process is equally applicable for any non-ferrous alloys also. The moulds are disturbed after adequate cooling time and the wear parts thus produced are subjected to special heat treatment so that metallic portion develops better wear resistance Examples A wear part described as grinding roll used by thermal power stations was produced using the above process. This part was produced using centrifugal casting process. The manufacturing sequence involved production of cakes of mineral grains, introduction of the cakes and production of composite castings called inserts, location of inserts into centrifugal die, pouring of SG iron in to the spinning die to develop composite casting. The casting thus produced was heat treated and tried in wear application. It was observed to improve the life of wear components substantially. Figure 5 illustrates a vertical spindle mill having cast metal matrix ceramic composite parts MMCC on grinding table 8 and grinding rolls 9. Another wear part described as table liner for a vertical mill was produced. Cakes of mineral grains were introduced at the wear surface of the part of the casting. The casting was produced using conventional foundry casting process. Figure 6 very schematically shows a table liner 10 with metal matrix ceramic composite parts MMCC as inserts. The casting was heat treated and machined and tried for wear characteristics. Significant improvement of up to 15% in wear resistance, see examples above, was noticed by the addition of carbide grains for table liners for vertical mills. The figure 3 illustrates a simple design for the ceramic cake. Within the framework of the invention the ceramic cake may be formed in various shapes and forms and 11 ceramic cakes may be arranged in various patterns. Figures 7 and 8 illustrate such shapes and forms and patterns. Figure 7 shows an arrangement of strip like ceramic cakes. Figure 8 shows a ceramic cake which is provided with large holes 11 and small holes 12. These holes are provided on a rectangular grid. The figures 7 and 8 are given as examples. It is remarked that within the concept of the invention the use of a mix of the mentioned carbide grains is enclosed. Advantages of present invention Present invention allows the use of metal ceramic wear parts with better wear resistant properties than metal ceramic wear parts known from the prior arts. In a preferred embodiment the present invention improves the wear resistance even further and improves mouldability of mixes by addition of fine ceramic powder, preferably of alumina. The use of flexible, preferably silicone rubber core, boxes which is a part of an embodiment of the present invention also facilitates manufacturing of cakes of complex shape. 12 WE CLAIM: 1. A metal matrix ceramic composite wear part (MMCC), said wear part comprising a wearing portion formed by a ceramic cake (1) impregnated by metal (4), wherein the ceramic cake comprises ceramic grains (2) comprising alumina, wherein the ceramic cake (1) further comprises grains (5) comprising a material chosen from the group consisting of boron carbide, silicon carbide or tungsten carbide. 2. A metal matrix ceramic composite wear part as claim in claim 1, wherein the carbide is boron carbide. 3. A metal matrix ceramic composite wear part as claimed in claim 2, wherein the boron carbide content in the ceramic cake lies between 1% and 25% in weight. 4. A metal matrix ceramic composite wear part as claimed in claim 3, wherein the boron carbide content in the ceramic cake is lies between 2% and 10% in weight. 5. A metal matrix ceramic composite wear part as claimed in claim 1, wherein the carbide is silicon carbide. 6. A metal matrix ceramic composite wear part as claimed in claim 5, wherein the silicon carbide content in the ceramic cake lies between 1.2% and 30% in weight. 7. A metal matrix ceramic composite wear part as claimed in claim 5, wherein the silicon carbide content in the ceramic cake lies between 2.5% and 12.5% in weight. 8. A metal matrix ceramic composite wear part as claimed in claim 1 wherein the carbide is tungsten carbide. 13. 9. A metal matrix ceramic composite wear part as claimed in claim 8, wherein the tungsten carbide content in the ceramic cake lies between 5.6% and 66% in weight. 10. A metal matrix ceramic composite wear part as claimed in claim 8, wherein the tungsten carbide content in the ceramic cake lies between 3.6% and 40% in weight. 11. A metal matrix ceramic composite wear part as claimed in any of the preceding claims, wherein the alumina comprising grains comprise alumina, zirconia and an amount of titanium oxide. 12. A metal matrix ceramic composite wear part as claimed in claim wherein the titanium oxide content in the alumina comprising grains lies between 2 and 6% by weight. 13. A metal matrix ceramic composite as claimed in claim 12, wherein the amount of titanium oxide in the alumina/zirconia comprising grains lies between 3 and 5.5 % in weight. 14. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the amount of alumina lies between 40 and 55% in weight. 15. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the amount of zirconia lies between 40 and 50% in weight. 16. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic grains are in the range of FEPA 6-12 grit sizes 17. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic cake further comprises fine ceramic powder (6). 14 18. A metal matrix ceramic composite wear part as claimed in claim 17, wherein the ceramic cake comprises 1 to 4% of fine ceramic powder, expressed in weight of the ceramic grains. 19. A metal matrix ceramic composite wear part as claimed in claims 17 or 18, wherein the fine ceramic powder (6) has a grit size at least two orders of magnitude smaller that the grit size of the ceramic grains (2, 5). 20. A metal matrix ceramic composite wear part as claimed in any of the claims 17 to 19, wherein the fine ceramic powder comprises alumina powder. 21. A metal matrix ceramic composite wear part as claimed in any of the claims 17 to 20 wherein the fine ceramic powder is in the range of FEPA 1000-1400 grit sizes. 22. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic cake comprises sodium silicate as a binder (3). 23. A metal matrix ceramic composite wear part as claimed in claim 12 comprising sodium silicate binder in the range of 4-6%. 24. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the metal matrix ceramic composite wear part comprises either chrome steel containing between 0.2-1.2% C and 2-8% Cr, with addition of other alloying elements such as Mn, Mo, Ni & Cu or comprises Mn Steel containing between 0.8-1.2%) C and 8-14% Mn with other elements such as Si, Cr, S & P present additions and impurities or the irons containing between 1 - 3.5%) C, 11-28% Cr with addition of other alloying elements Mo, Ni and Cu. 25. A ceramic cake (1) for a metal matrix ceramic composite wear part (MMCC) as claimed in any of the preceding claims. 15 26. A method of manufacturing a ceramic cake (1) as claimed in claim 25 wherein a mixture of ceramic grains (2, 5), fine ceramic powder (6) and a binder (3) is poured in a flexible holder (7) and hardened. 27. A method of manufacturing a ceramic cake as claimed in claim 26, wherein the flexible holder is a silicone rubber core box. 28. A method of manufacturing a ceramic cake as claimed in any of the claims 26 and 27, wherein the cake is hardened by gassing with CO2 gas and baked in an oven in the temperature rate of 80-200°C for one to four hours. 29. Grinding roll (9) comprising a metal matrix ceramic composite wear part (MMCC) as claimed in any of the claims 1 to 24. 30. Grinding roll mill comprising a grinding roll as claimed in claim 29. 31. Table liner (10) for a vertical mill comprising a metal matrix ceramic composite wear part (MMCC) as claimed in any of the claims 1 to 24. 32. Vertical mill comprising a table liner as claimed in claim 31. Dated this 31st Day of October, 2006 RAJESHWARI H. OF K & S PARTNERS ATTORNEY FOR THE APPLICANTS. -16- Abstract: A metal matrix ceramic composite wear part comprises a wearing portion formed by a ceramic cake impregnated by metal. The ceramic cake comprises ceramic grains comprising alumina, and grains of a carbide. The inclusion of carbide grains reduces wear. Preferably the alumina comprising grains comprise alumina, zirconia and titanium oxide, wherein alumina is preferably present in an amount of 30 to 65 %, zirconia in an amount of 30 to 65% and titanium oxide in an amount of 1 to 7%, all percentages being expressed in weight of the grains. Preferably the ceramic cake further comprises fine ceramic powder, preferably in the range of 1 to 4% by weight of the grains. -17

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Se section 10, rule 13)
"IMPROVED WEAR RESISTANT METAL MAXTRIX CERAMIC COMPOSITE PART,
CERAMIC CAKE FOR A METAL MATRIX CERAMIC COMPOSITE PART, METHOD OF
MANUFACTURE THEREOF, GRINDING ROLL AND TABLE LINER COMPRISING A METAL
MATRIX CERAMIC COMPOSITE PART"
We, AIA Engineering Ltd., of 115, G.V.M.M. Estate, Odhav Road, Ahmedabad - 382 410, India;
The following specification particularly describes and ascertains the invention and the manner in which it is to be performed.
1

FIELD OF INVENTION
The invention relates to a metal matrix ceramic composite wear part and a ceramic cake for use in a metal ceramic wear part. The invention also relates to a method for manufacturing a ceramic cake for use in a metal matrix ceramic composite wear part. The invention further relates to a grinding roll comprising a metal matrix ceramic composite wear part and to a table liner for a vertical mill comprising a metal matrix ceramic composite wear part.
Many industrial applications involve components which are subjected to wear during the life time of the component. The applications of parts requiring wear resistance are quite common in cement, mining and thermal power generation industries. Historically, 12% Mn steel and Nihards were used for wear resistant applications during first half of twentieth century. During last 50 years, high chromium irons have been successfully used for wear resistance applications and have largely replaced Nihard and 12% Mn. Steel materials.
The search for further improved wear resistance has continued and during last 15 years metal matrix ceramic composites are being used with varying degree of success for wear resistant applications. The present invention is in the same area and substantially improves the economics and wear properties as compared to presently used composites. Metal matrix ceramic composites comprise ceramic parts embedded in a metal matrix.
Back ground and prior art references
With reference to metal matrix ceramic composites, the first decision is naturally the choice of ceramic material, usually in the form of grains. Alumina is known to be a good abrasive material.
2

In this connection, US patent (No. 3,181,939 dated 04.05.1965) by Douglas W. Marshal (assignee Norton Company, Mass, USA) is relevant. The patent describes manufacture of fused alumina zirconia abrasives which combine good wear resistance characteristics of alumina and toughness of zirconia. Thus, alumina/zirconia grains appear to be a most suitable candidate for metal matrix ceramic composites. Ullmann's Encyclopedia of Industrial Chemistry, Fifth Complete revision, part Al, Volume Al, paragraph 2.2 describes useful alumina/zirconia grains.
The art of casting with embedded hard material was taught in a German patent (by Dr. Wahl) No. 7326661 dated 20.07.73.
A Japanese patent by Mr. Tamura of KHI (patent No. 62286661 dated 12.12.87) described a method of impregnating ceramic particles with molten metal to produce composite casting with good wear resistance.
A European patent (No. EP 0575858B1 dated 23.06.92) filed by Staub Fritz (assignee Zuzel Inotech AG) describes production of metal matrix ceramic composite casting with porous ceramic members at the wearing face. The ceramic particles used are described as corundum, zirconium oxide or magnesium oxide.
In US patent 6399176B1 dated 04.06.2002 production of composite wear component by casting is described. Ceramic cakes were introduced on the wear surface consisting of homogeneous solid solution of 20-80% alumina and 80-20% zirconia.
Although there are therefore many examples of composite wear components there remains a need for further improvement of the wear resistance. Such further improvement will increase the effectiveness of the wear component.
Object of invention
It is an object of the invention to provide a metal matrix ceramic composite wear part and
a ceramic cake for use in a metal ceramic wear part with improved wear resistance. The
3

known devices need improvement. When a composite wear part is worn down, the part must be replaced. Consequently any device using the wear part cannot be used during replacement of the worn out part. Replacement of the worn out part leads to a loss in operative time of the device. An improvement in the wear resistance leads to a decrease in percentage of time lost to replacing worn parts of such devices as grinding rolls and table liner using metal matrix ceramic composite wear parts.
Summary of invention
The invention provides for a metal matrix ceramic composite wear part, said wear part comprising a wearing portion formed by a ceramic cake impregnated by metal, wherein the ceramic cake comprises ceramic grains comprising at least alumina, and wherein the ceramic cake further comprises grains comprising a material chosen from the group consisting of boron carbide, silicon carbide or tungsten carbide.
The present invention provides for ceramic cakes that show improved wear resistance.
Preferably the amount of carbide grains lies between 1 and 25% in weight of the ceramic cake for boron carbide, preferably 2 and 10% in weight. A very small amount of carbide grains will have only a moderate effect, whereas a large addition of carbide grains does not to provide an added advantage.
In preferred embodiment the carbide grains are mainly comprised of boron carbide. Boron carbide is the hardest of the mentioned carbide materials and the lightest.
Thus, the present invention succeeds in improving wear characteristics of metal matrix ceramic composite parts, achieved by using an addition of carbide grains to the grains comprising alumina.
In a preferred embodiment the ceramic grains comprise alumina, zirconia and titanium oxide, wherein alumina is present in a grain on average for an amount of 30
4

to 65 %; zirconia is present for an amount of 30 to 65% and titanium oxide for an amount of 1 to 7%, all percentages being expressed in weight of the grains.
The inclusion of zirconia in the alumina comprising grains has, a positive effect on the wear resistance of the grains. Inclusion of titanium oxide into the grains has a further positive effect oh the wear resistance.. Titanium oxide is in itself considerably softer than alumina and zirconia, which makes the positive effect all the more remarkable. Preferably the amount of titanium oxide lies between 2 of 6 percent, most preferably between 3 and 5.5% in weight. The positive effect on the wear resistance is most pronounced in these weight percentages.
The percentages of alumina and zirconia are preferably between 40 and 55% alumina and 40 to 50% zirconia.
It is remarked that the alumina/zirconia/titanium oxide composition may vary from grain to grain within the metal matrix ceramic composite wear part. All percentages mentioned above relate to average percentages over the grains.
Moreover, for even more preferred embodiments, the inventors have realized that, when producing a ceramic cake from grains, the binding properties of the grains are important because the grains are relatively coarse. Therefore, there is a need for addition of other constituents to the ceramic grains to improve bonding between the grains and mouldability of the material from which the ceramic cake is produced. One such constituent is sodium silicate which helps bind the grains and improves mouldability.
The inventors have realized that addition of very fine ceramic powder, preferably mainly comprised of aluminum oxide powder, not only improves mouldability but also the hardness of the cake thus increasing the wear resistance of the final product "Very fine powder" means powder of a size considerably smaller (at least one, preferably two orders of magnitude) than the size of the alumina/zirconia/titania ceramic grains. Such small ceramic powder is preferably mixed in a percentage in
-5

weight in relation to the weight of the ceramic grains (alumina/zirconia and carbide) of between 1 and 4%. Preferably the grain size of the fine ceramic powder is in the range of FEPA 1000-1400 grit sizes. Preferably the grain size of the alumina comprising grains and the carbide grains is in the range of FEPA 6-12 grit sizes.
The mixture of previously described ceramic grains, a fine ceramic (alumina) powder and Sodium Silicate is preferably filled in flexible, preferably rubber core boxes of suitable shapes. The cakes still in core boxes are gassed and baked to develop good strength.
The prepared ceramic cakes are located at desired surfaces of moulds and liquid metal is poured into the cavity to produce metal matrix ceramic composite castings.
Brief description of the figures
These and further aspects of the invention will be explained in greater detail by way of example and with reference to the accompanying drawings, in which
Fig. 1 illustrates a ceramic cake as per prior art
Fig. 2 illustrates a ceramic cake with infiltrated metal as per prior art
Fig. 3 illustrates a ceramic cake for a metal matrix ceramic composite
wear part in accordance with the invention.
Fig. 4 illustrates illustrate rubber core box
Fig. 5 illustrates a grinding rolls comprising a metal matrix ceramic
composite wear part,
Fig. 6 illustrates a table liner comprising a metal matrix ceramic composite
wear part
Figures 7 and 8 illustrate ceramic cake arrangements.
6

The figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the figures.
Detailed description and embodiments of the present invention
Figure 1 illustrates a ceramic cake as per prior art. The ceramic cake 1 comprises
ceramic grains 2 and often a binder 3. The binder is in figure 1 schematically
indicated as a thin layer around some of the grains.
Figure 2 illustrates a ceramic cake 1 of figure 1 impregnated by metal 4 to form a
metal matrix ceramic composite wear part (MMCC). To impregnate the ceramic cake
molten metal is introduced. The molten metal fills the spaces between the grains 2 to
produce a metal matrix ceramic composite part. The metal forms the matrix for the
ceramic grains. For this reason such parts are called "metal matrix ceramic composite
parts".
The applications of parts requiring wear resistance are quite common in cement,
mining and thermal power generation industries.
The present invention has succeeded in improving wear characteristics of metal
matrix ceramic composite parts, achieved by introducing ceramic grains at the
wearing surface. The invention combines in the ceramic cake the use of
alumina/zirconia grains and grains of boron, silicon or tungsten carbide.
Figure 3 schematically illustrates a ceramic cake for a metal matrix ceramic
composite wear part in accordance with the invention. The difference between figure
1 as per prior art and figure 3 is the addition of boron, silicon or tungsten carbide
grains 5 as well as fine alumina powder 6.
In two experimental runs 5 and 20% by weight of boron carbide grains were included in the ceramic cake.
In the two cakes 87%, respectively 72% of the ceramic cake was comprised of alumina/zirconia/titania grains comprising alumina in the range of 30-65%, zirconia in the range of 65-30%) and titanium oxide in the range of 1-7%, where on average the alumina and zirconia contents in the alumina/zirconia/titanium oxide grains were
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approximately 50% and the titanium oxide content approximately 5%, 3% of the weight of the ceramic cake was fine alumina powder and approximately 5% of the weight of the ceramic cake was a inorganic binder. In the examples each alumina and zirconia comprising grain was, on a microscopic level, composed of a phase mixture of different solid phases. The grains were not formed as a homogeneous solid solution. Alumina/zirconia grains used in the preferred examples have as components alumina and zirconia. Inside such grains, the composition is not homogeneous but a phase mixture is present, i.e. different parts of the grain have a different composition, some parts forming a solid phase comprising a first percentage of alumina and a second percentage zirconia, other parts forming a different solid phase or solid phases having different percentages alumina and zirconia or being mainly composed of alumina or zirconia. These solid phases may comprise titania. The grain as a whole is in the form of a phase mixture.
5% in weight of boron carbide corresponds, due to the difference in specific gravity of the carbide grains with the specific gravity of alumina-zirconia comprising grains, to approximately 7.5% in volume. 20% in weight correspond to approximately 27,5% in volume. Given the difference in specific gravity between boron carbide (approximately 2.5 gr/cc) and alumina/zirconia (approximately 3.8 gr/cc) this means that a percentage in weight between 1% and 25% corresponds to a percentage in volume of the carbide grains in the ceramic material between 1.5% and 34%. When the same size particles, i.e. the volume of each the alumina/zirconia and the boron carbide grain would be the same, is used this would mean that one in 60 to 1 in 3 of the total of alumina-zirconia comprising grains and carbide grains is a carbide grain. The same volume percentage range leads for silicon carbide grains which have a higher specific gravity of 3.2 gr/cc to a range in weight between 1.2% and 30%) and for tungsten carbide grains which have an even higher specific gravity of 15 gr/cc to a range in weight between 5.6%) and 66%).
The boron carbide grains and the alumina/zirconia/titinia grains in the examples had the same grit size, in the examples the grits size was FEPA 10.
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The wear of ceramic metal composites having such ceramic cakes including boron carbide grains was compared to the wear of ceramic metal composites with the same constitution but lacking the boron carbide grains.
Addition of 5% boron carbide grains by weight proved to decrease the wear rate by approximately 15%; with addition of 20% boron carbide grains by weight no further decrease in wear rate was noticed.
As explained above, these results are contrary to the prior art. Surprisingly addition of even a relatively small amount of carbide grains has a positive effect. The increase of wear resistance is not proportional to the amount of boron carbide grains added, which is an indication of the presence of a cooperative effect wherein inclusion of even a relatively minor amount of carbide (between 2 and 10%) has a protective effect increasing the wear resistance.
The advantageous effect proved to be substantially higher in a region around 5% than for 20%o. A preferred range is weight for boron carbide is between 2 and 10% weight. A preferred range in weight for boron carbide grains between 2 and 10% in weight corresponds for silicon carbide to a range in weight between 2.5% and 12.5% in weight and for tungsten carbide to a range in weight between 3.6% and 40%.
The grain sizes of ceramic grains are normally designated in terms of grit sizes. The grit sizes recommended to be used for producing metal matrix ceramic composite ranges from 6-12 grit sizes as per FEPA standard. Preferably the alumina/zirconia and carbide grains are of comparable grit size, i.e. not differing by more than 4 grit sizes, preferably not more than two grit sizes.
In order to be able to introduce such grains at desired locations, it is necessary to form cakes of required shape. Moreover, such cakes have to possess adequate strength to withstand eventual engulfing by liquid metal. Addition of very fine ceramic powder, preferably comprising aluminum oxide powder, along with Sodium Silicate, has shown to provide improved mouldability and achieve an increase in strength. Addition of 1000-1400, preferably 1200 grit fine Aluminium Oxide powder imparts thixotropic properties. Preferably fine alumina powder is used, but within the
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framework of this preferred embodiment of the invention other fine ceramic powders, for instance zirconia or alumina/zirconia powders could be used. Figure 4 shows schematically the inclusion of fine alumina powder 6.
The mixture of previously described mineral particles and ceramic, preferably alumina powder is preferably mixed with suitable binder such as Sodium Silicate. However, the inventor has realized that such mix sometimes does not have adequate green strength (i.e. the strength in the green, not yet baked state) and the shapes of ceramic cakes are, as the inventor has realized, preferably supported in flexible, preferably rubber, for instance silicone rubber core boxes. Use of rubber core boxes for manufacturing of ceramic cakes is a feature of a preferred embodiment of the method of the invention.
Figure 4 schematically shows the use of a rubber core box 7 around ceramic cakes 1.
The mixture described above is filled in the rubber core boxes of desired shapes and treated with Carbon Dioxide to develop adequate strength for handling. Further ceramic shapes in the rubber core boxes are heated to temperature between 80 -220°c for one to four hours so that adequate strength is developed.
The cakes are located at desired surfaces of refractory moulds. After closing the mould assemblies, liquid metal is poured into the cavity. The liquid metal composition is selected depending up on the application. High impact applications may require steel and low impact applications may tolerate irons. The chromium steels may contain between 0.2-1.2% C and 2-8% Cr, with addition of other alloying elements such as Mn, Mo, Ni & Cu. The Mn. Steel may contain between 0.8-1.2% C and 8-14%) Mn with other elements such as Si, Cr, S & P present additions and impurities. The irons may contain between 1 - 3.5% C, 11-28% Cr with addition of other alloying elements Mo, Ni and Cu.
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Generally for wear resistance applications, the above types of steels and irons are commonly used. However, the process is equally applicable for any non-ferrous alloys also.
The moulds are disturbed after adequate cooling time and the wear parts thus produced are subjected to special heat treatment so that metallic portion develops better wear resistance
Examples
A wear part described as grinding roll used by thermal power stations was produced using the above process. This part was produced using centrifugal casting process. The manufacturing sequence involved production of cakes of mineral grains, introduction of the cakes and production of composite castings called inserts, location of inserts into centrifugal die, pouring of SG iron in to the spinning die to develop composite casting. The casting thus produced was heat treated and tried in wear application. It was observed to improve the life of wear components substantially. Figure 5 illustrates a vertical spindle mill having cast metal matrix ceramic composite parts MMCC on grinding table 8 and grinding rolls 9.
Another wear part described as table liner for a vertical mill was produced. Cakes of mineral grains were introduced at the wear surface of the part of the casting. The casting was produced using conventional foundry casting process. Figure 6 very schematically shows a table liner 10 with metal matrix ceramic composite parts MMCC as inserts. The casting was heat treated and machined and tried for wear characteristics. Significant improvement of up to 15% in wear resistance, see examples above, was noticed by the addition of carbide grains for table liners for vertical mills.
The figure 3 illustrates a simple design for the ceramic cake. Within the framework of the invention the ceramic cake may be formed in various shapes and forms and
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ceramic cakes may be arranged in various patterns. Figures 7 and 8 illustrate such shapes and forms and patterns. Figure 7 shows an arrangement of strip like ceramic cakes. Figure 8 shows a ceramic cake which is provided with large holes 11 and small holes 12. These holes are provided on a rectangular grid. The figures 7 and 8 are given as examples.
It is remarked that within the concept of the invention the use of a mix of the mentioned carbide grains is enclosed.
Advantages of present invention
Present invention allows the use of metal ceramic wear parts with better wear resistant properties than metal ceramic wear parts known from the prior arts.
In a preferred embodiment the present invention improves the wear resistance even further and improves mouldability of mixes by addition of fine ceramic powder, preferably of alumina.
The use of flexible, preferably silicone rubber core, boxes which is a part of an embodiment of the present invention also facilitates manufacturing of cakes of complex shape.
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WE CLAIM:
1. A metal matrix ceramic composite wear part (MMCC), said wear part comprising a wearing portion formed by a ceramic cake (1) impregnated by metal (4), wherein the ceramic cake comprises ceramic grains (2) comprising alumina, wherein the ceramic cake (1) further comprises grains (5) comprising a material chosen from the group consisting of boron carbide, silicon carbide or tungsten carbide.
2. A metal matrix ceramic composite wear part as claim in claim 1, wherein the carbide is boron carbide.
3. A metal matrix ceramic composite wear part as claimed in claim 2, wherein the boron carbide content in the ceramic cake lies between 1% and 25% in weight.
4. A metal matrix ceramic composite wear part as claimed in claim 3, wherein the boron carbide content in the ceramic cake is lies between 2% and 10% in weight.
5. A metal matrix ceramic composite wear part as claimed in claim 1, wherein the carbide is silicon carbide.
6. A metal matrix ceramic composite wear part as claimed in claim 5, wherein the silicon carbide content in the ceramic cake lies between 1.2% and 30% in weight.
7. A metal matrix ceramic composite wear part as claimed in claim 5, wherein the silicon carbide content in the ceramic cake lies between 2.5% and 12.5% in weight.
8. A metal matrix ceramic composite wear part as claimed in claim 1 wherein the carbide is tungsten carbide.
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9. A metal matrix ceramic composite wear part as claimed in claim 8, wherein the tungsten carbide content in the ceramic cake lies between 5.6% and 66% in weight.
10. A metal matrix ceramic composite wear part as claimed in claim 8, wherein the tungsten carbide content in the ceramic cake lies between 3.6% and 40% in weight.
11. A metal matrix ceramic composite wear part as claimed in any of the preceding claims, wherein the alumina comprising grains comprise alumina, zirconia and an amount of titanium oxide.
12. A metal matrix ceramic composite wear part as claimed in claim wherein the titanium oxide content in the alumina comprising grains lies between 2 and 6% by weight.
13. A metal matrix ceramic composite as claimed in claim 12, wherein the amount of titanium oxide in the alumina/zirconia comprising grains lies between 3 and 5.5 % in weight.
14. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the amount of alumina lies between 40 and 55% in weight.
15. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the amount of zirconia lies between 40 and 50% in weight.
16. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic grains are in the range of FEPA 6-12 grit sizes
17. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic cake further comprises fine ceramic powder (6).
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18. A metal matrix ceramic composite wear part as claimed in claim 17, wherein the ceramic cake comprises 1 to 4% of fine ceramic powder, expressed in weight of the ceramic grains.
19. A metal matrix ceramic composite wear part as claimed in claims 17 or 18, wherein the fine ceramic powder (6) has a grit size at least two orders of magnitude smaller that the grit size of the ceramic grains (2, 5).
20. A metal matrix ceramic composite wear part as claimed in any of the claims 17 to 19, wherein the fine ceramic powder comprises alumina powder.
21. A metal matrix ceramic composite wear part as claimed in any of the claims 17 to 20 wherein the fine ceramic powder is in the range of FEPA 1000-1400 grit sizes.
22. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the ceramic cake comprises sodium silicate as a binder (3).
23. A metal matrix ceramic composite wear part as claimed in claim 12 comprising sodium silicate binder in the range of 4-6%.
24. A metal matrix ceramic composite wear part as claimed in any of the preceding claims wherein the metal matrix ceramic composite wear part comprises either chrome steel containing between 0.2-1.2% C and 2-8% Cr, with addition of other alloying elements such as Mn, Mo, Ni & Cu or comprises Mn Steel containing between 0.8-1.2%) C and 8-14% Mn with other elements such as Si, Cr, S & P present additions and impurities or the irons containing between 1 - 3.5%) C, 11-28% Cr with addition of other alloying elements Mo, Ni and Cu.
25. A ceramic cake (1) for a metal matrix ceramic composite wear part (MMCC) as claimed in any of the preceding claims.
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26. A method of manufacturing a ceramic cake (1) as claimed in claim 25 wherein a mixture of ceramic grains (2, 5), fine ceramic powder (6) and a binder (3) is poured in a flexible holder (7) and hardened.
27. A method of manufacturing a ceramic cake as claimed in claim 26, wherein the flexible holder is a silicone rubber core box.
28. A method of manufacturing a ceramic cake as claimed in any of the claims 26 and 27, wherein the cake is hardened by gassing with CO2 gas and baked in an oven in the temperature rate of 80-200°C for one to four hours.
29. Grinding roll (9) comprising a metal matrix ceramic composite wear part (MMCC) as claimed in any of the claims 1 to 24.
30. Grinding roll mill comprising a grinding roll as claimed in claim 29.
31. Table liner (10) for a vertical mill comprising a metal matrix ceramic composite wear part (MMCC) as claimed in any of the claims 1 to 24.
32. Vertical mill comprising a table liner as claimed in claim 31.
Dated this 31st Day of October, 2006

RAJESHWARI H. OF K & S PARTNERS ATTORNEY FOR THE APPLICANTS.
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Abstract:
A metal matrix ceramic composite wear part comprises a wearing portion formed by a ceramic cake impregnated by metal. The ceramic cake comprises ceramic grains comprising alumina, and grains of a carbide. The inclusion of carbide grains reduces wear. Preferably the alumina comprising grains comprise alumina, zirconia and titanium oxide, wherein alumina is preferably present in an amount of 30 to 65 %, zirconia in an amount of 30 to 65% and titanium oxide in an amount of 1 to 7%, all percentages being expressed in weight of the grains. Preferably the ceramic cake further comprises fine ceramic powder, preferably in the range of 1 to 4% by weight of the grains.
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A METAL MATRIX CERAMIC COMPOSITE (MMCC) WEAR PART AND METHOD OF PREPARING THE SAME

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