DESC:FIELD OF THE INVENTION
The present invention relates to abrasion and impact resistance parts used on grinding rolls. The present invention in particular relates to abrasion and impact resistance parts comprising of functionally gradient composite block of sintered carbide and ceramic embedded with Hi-chrome. The present invention further provides grinding rolls bearing abrasion and impact resistance parts in a segmented form and methods of manufacturing the same.

BACKGROUND OF INVENTION
Rolls especially grinding rolls are used in various industries for crushing of coal, clinker and limestone and continuous emphasis is placed on the materials used for plating those rolls and the performance of the materials. Several types of materials are used as a grinding parts such as welded hardfacing, Ni-Hard, high chrome cast iron and ceramic embedded cast iron. Most of the cement, power and mining industries operating under continuous grinding have to replace or weld of crushing part every few weeks to sustain adequate performance.

High Cr cast irons are used in various applications where stability in an abrasive environment such as, cement, power plant, mineral industries and steel making plant is a principal requirement. It has been observed that the primary coarse carbides causes a drastic drop of toughness, and the use of hypereutectic alloys is very limited.

US20080102300 relates to a metal matrix ceramic composite (MMCC) wear-parts comprising a wearing portion formed by a ceramic cake and is impregnated by metal and carbides.

JP2008038171 (A) provides a metal matrix-ceramic composite material wearing part containing wear portion formed of a ceramic cake impregnated with the metal.

WO2013084080 relates to a metal matrix ceramic composite (MMCC) comprising of ceramic form, wherein the ceramic form comprising a mixture of ceramic grains comprising alumina, at least one binder and carbon particles, wherein the said ceramic form is embedded in molten metal.

US2004147207 relates to a method for improving wear and tear on support bodies for plates or grinding belts in large-scale grinders. The support body has a base body, onto which an abrasion-resistant primary layer of at least 0.3 mm thickness is applied using a thermal spraying process. This is configured as an inhomogeneous layer with an oxide entrapment of a specific porosity.

CN104174832 (A) discloses a casting method for a wear-resistant grinding roll wherein the wear-resistant grinding roll comprises an inner layer made of a ductile cast iron material and an outer layer made of a chromium-contained cast iron material.

JPS5758970 discloses double rolls without the occurrence of roll cracking by centrifugally casting an inside ring material made of cast steel, and casting cast iron of high hardness on the surface of the inside ring material in the state of limiting its outside surface temp. Though such rolls are likely to be high abrasion resistant, they are likely to be deformed/dented during the crushing process in coal mines and even if a minor part of the roll is distorted then the complete roll needs to be replaced which is highly cost and time consuming procedure.

Prior art technology suffers from the following disadvantages such as high risk of breakage due to low impact resistance. Further if micro crack is generated in a particular point it propagates through the whole roller resulting in breakage of the roller. Also ceramic particles will pull out due to fast wear of the matrix phase.

US6086003 relates to a roll press for processing very abrasive materials, comprising at least two press rolls of which each includes a wear layer arranged on a basic body. The wear layer comprises substantially plane zones of a highly wear-resistant material while the spaces between the highly wear-resistant zones are filled with a material of different wear resistance. In this case the highly wear resistant material with spaces in between is plated on the roll as a single undisturbed layer and those spaces are filled with wear-resistant material. Further these rolls have low wear resistance compare to metal matrix ceramic composites (MMCC) as also low impact resistance compare to sintered carbide alloy powder technology (SAPT). Further due to the complex manufacturing process the cost of roll press is higher than the SAPT and MMCC wear composite.

Further the usual techniques employed are casting method whereas the present inventors have found that usage of powder metallurgy process helps in providing better abrasion resistance and corrosion resistance. Powder matrix processes help in sustaining excellent properties when compared to metals, in terms of corrosion and wear resistance and thermal stability. Powder matrix have been used as an engineering materials for excellent thermal, chemical and mechanical properties but its applications are limited due to low fracture toughness.

The present inventors have surprisingly found that providing multiple different layers of Sintered carbide alloy, Ceramic embedded Hi-chrome alloy and back up plate over the base iron layer through powder metallurgical process helps in providing highly effective abrasion and corrosion resistance to the grinding rolls. Further providing the said layers in segmented/ patterned manner helps in easy removal and replacement of the wear composites.

OBJECT OF THE INVENTION
It is an object of the present invention to provide a High abrasion and impact resistance functionally gradient composite block comprising of Sintered carbide alloy layer; Ceramic embedded Hi-Chrome alloy layer and backup plate layer.

It is another object of the present invention to provide Grinding rolls with Functionally Gradient Composite Block having better wear properties.

It is another object of the present invention to provide grinding rolls with Functionally Gradient Composite Block having which enhances shelf life of rolls.

It is yet another object of the present invention to give enhanced life to grinding rolls by giving better wear properties which decreases downtime and also increases productivity.

It is yet another object of the present invention to provide Grinding rolls with Functionally Gradient Composite Block comprising of outer layer of Sintered carbide alloy blocks consisting of grooves comprising carbides of different metals.

It is yet another object of the present invention to provide Grinding rolls with Functionally Gradient Composite Block comprising of middle layer of Ceramic embedded Hi-Chrome alloy wherein the Hi-chrome alloy layer consists of metal Nb.

It is yet another object of the present invention to provide Grinding rolls with Functionally Gradient Composite Block comprising of a third layer of backup plate and which is metallurgically bonded to the base surface of the grinding rolls.

It is yet another object of the present invention to provide Grinding rolls with Functionally Gradient Composite Block in a segmented pattern.
It is yet another object of the present invention to provide a method for efficient metallurgical bonding of the Sintered carbide alloy layer, ceramic embedded Hi-Chrome alloy layer and backup plate layer so as to provide a single block which is efficiently plated over the base surface of the roller.

It is yet another object of the present invention to provide a novel process for efficient anti-wear layer over the roll surface.

SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a High abrasion and impact resistance functionally gradient composite block comprising of Sintered carbide alloy layer; Ceramic embedded Hi-Chrome alloy layer and backup plate layer.

According to another aspect of the present invention there is provided Sintered carbide alloy block having grooves which comprises of carbide alloys with strong wear resistance.

According to another aspect of the present invention, there is provided sintered carbide alloy block having grooves comprising of carbide alloys of different metals wherein the carbide alloys are sintered into the grooves through powder metallurgical hot isostatically pressed technology.

According to another aspect of the present invention there is provided ceramic embedded Hi-chrome alloy block, wherein the Hi-chrome alloy block consists of carbon, silicon, manganese, sulphur, phosphorus, chromium, molybdenum, and Niobium.

According to another aspect of the present invention, there is provided a process for preparation of functionally gradient composite block with high abrasion and impact resistance comprising the steps of:
a. Forming of carbide alloy powder block ‘1’;
b. Sintering the carbide alloy powder block at around 1250 to 1450°C for at least 60 minutes to obtain composite block ‘1a’;
c. Powder metallurgical Hot isostatic pressing of carbide into composite block ‘1a’ at around 1100-1300 °C to obtain composite block ‘1b’;
d. Metallurgical fusing of composite block ‘1a’ with composite block ‘1b’;
e. Preparing Ceramic embedded Hi-chrome block ‘2’ by Unique sand casting process at a temperature of 1400-1600°C;
f. Placing block ‘1’ on the block ‘2’ and both the layers are placed on backup plate ‘3’ using a binder material followed by metallurgical bonding at around 800-1200°C to form a functionally gradient composite block.

According to another aspect of the present invention, there is provided a process for efficient anti-wear layer over the roll surface of grinding rolls comprising the steps of:
? Placing a segment of functionally gradient composite block layer over the lower ring/side of grinding roll;
? Bolting the segmented functionally gradient composite block layer from the lower side of roll;
? Fixing the upper and lower rings in place through the bolts to obtain grinding rolls with functionally gradient composite block.

According to another aspect of the present invention, there is provided Grinding rolls with high abrasion and impact resistance functionally gradient composite block in a segmented manner.

DESCRIPTION OF THE INVENTION
The present invention provides a High abrasion and impact resistance functionally gradient composite block comprising of Sintered carbide alloy layer; Ceramic embedded Hi-Chrome alloy layer and backup plate layer.

The present invention provides an efficient abrasive and corrosive resistance functionally gradient composite block fused onto a grinding roll through the usage of specific material and manufacturing process for grinding roll.

According to one embodiment the present invention provides a High abrasion and impact resistance Grinding rolls layered with wear composites comprising of Sintered carbide alloy layer; Ceramic embedded Hi-Chrome Alloy layer and backup plate.

The present invention provides Sintered carbide alloy powder technology indigenously developed by IMCO Alloys and claimed in patent application no: 230/MUM/2007 which is metallurgically bonded over the Ceramic embedded Hi-chrome alloy layer.

According to yet another embodiment there is provided sintered alloy block having grooves comprising of carbide alloys of different metals wherein the carbide alloys are sintered into the grooves through powder metallurgical hot isostatically pressed technology.

According to another embodiment, the present invention provides Sintered alloy block having grooves which comprises of carbide alloys with strong wear resistance.

Sintered carbide alloy composite (block 1) is prepared by the process disclosed and claimed in patent application no: 230/MUM/2007 followed by hot isostatic pressing of metal carbide into the grooves present on the Sintered carbide alloy composite. The process parameters for Hot isostatic Pressing depend on particle size and shape of the carbides to be incorporated into the block ‘1’ and is carried out at around 1100-1300°C.

Hi-chrome alloy comprises of Carbon, Silicon, Manganese, chromium, Molybdenum in the form of carbides. Also small amount of Niobium is added to achieve requisite bonding and high hardness in the matrix of Hi-chrome alloy embedded with ceramic. The Hi-chrome alloy is embedded with ceramic in the range of 6.5-10.5%.

The back up plate layer is steel preferably mild steel.

The different composite layers provided on the base surface are as depicted in Figure 1 which are as follows:
No. 1 layer refers to Sintered Carbide alloy layer along with hot isostatically pressed plate which provides extremely strong abrasion & corrosion resistance and helps in preventing all type of wear & corrosion for longer duration,
No.2 layer refers to ceramic embedded Hi-chrome alloy layer which provides excellent abrasion resistance and wear resistance;
No. 3 layer is a back up plate which acts as a buffer and helps in handling the load transmission.

According to yet another embodiment, the present invention provides a process for preparation of functionally gradient composite block with high abrasion and impact resistance comprising the steps of:
? Forming of carbide alloy powder block ‘1’;
? Sintering the carbide alloy powder block at around 1250 to 1450°C for at least 60 minutes to obtain composite block ‘1a’;
? Powder metallurgical Hot isostatic pressing of carbide into composite block ‘1a’ at around 1100-1300 °C to obtain composite block ‘1b’;
? Metallurgical fusing of composite block ‘1a’ with composite block ‘1b’;
? Preparing Ceramic embedded Hi-chrome block ‘2’ by Unique sand casting process at a temperature of 1400-1600°C;
? Placing block ‘1’ on the block ‘2’ and both the layers are placed on backup plate ‘3’ using a binder material followed by metallurgical bonding at around 800-1200°C to form a functionally gradient composite block.

The metallurgical bonding in step (f) is conducted preferably at 1000°C-1200°C followed by holding for at least 30 min and subsequent purging of nitrogen gas, which helps to form a functionally gradient composite block and achieve the required eutectic carbides with desired structure.

The binder used in Step (f) is Copper-silver alloy. The Chemical composition of the Copper-Silver alloy is as follows:
Silver: 52-70%;
Copper: 15-45%;
Mn: 2-10%;
Ni: 1-5%;
Other elements: 0.15% max

The thickness of each layer in the functional gradient block is as follows:
Backup plate –5- 15mm
Ceramic embedded Hi chrome alloy layer-15- 80 mm,
Sintered carbide alloy layer – 5-30 mm

In this process the composite layers made by Sintered alloy powder technology of chrome and its alloy along with carbides, oxides, borides. The alloying elements of sintered carbide alloy powders are tungsten, cobalt, chromium, molybdenum, vanadium, titanium, boron, nickel and niobium. These are mixed to the powder comprising of carbon, silicon, sulphur, phosphorus and iron powder by blending process to prepare composite block ‘1A’ with groves. The particles sizes of the alloying elements are in the range of 15-150 um.

Higher densification and fine microstructure are achieved in Sintered Alloy powder block ‘1A’ by using hot isostatic pressing at 1100-1300oC under pressure to fuse carbides of different metals/elements into the grooves. The matrix of the sintered carbide alloy powder (SAP) along with the grooves consist of fine and uniformly dispersed fine carbide of one or more of the carbide forming elements such as iron, tungsten, molybdenum, chromium, vanadium, titanium, niobium and silicon etc. Particle size of the austenite is fine and uniformly dispersed. Therefore, the transformed martensite will also be fine and uniformly dispersed. Martensite confers an outstanding combination of strength and Toughness to the sintered carbide alloy and contributes to increase in hardness without sacrificing too much of ductility.

Thus the present invention provides a method for producing wear resistant functionally gradient composite block of Sintered carbide alloy powder with grooves comprising highly wear resistant carbides of different elements/metals.

A special process is used to fabricate high chrome cast iron matrix surface composites reinforced with ceramic particles. The combination of metal and ceramic in a granularised form creates a metal matrix composite. Within the MMC layer the granularised ceramic is encapsulated by the high chrome metal. The result is that it provides the extreme hardness of ceramic with the durable reliability and ductility of a high chrome alloy. The metal matrix composite is between 2 -2.5 times better than Hi-chrome alloys. Ceramic embedded Hi-chrome layer as used in the present application has been depicted in Figure 3.

The Sintered carbide alloy powder block/Plate is further exposed to metallurgical bonding with Ceramic embedded HiCr. Both the plates are then metallurgically fused to structural steel back plate and a binder layer acts as an intermediate layer to form anti wear composites which is than fused over grinding rolls in segmented/patterned manner to be used in cement, power plant, mineral industries and steel making plant.

Sintered carbide alloy block, Ceramic embedded Hi-chrome block are placed on the backup plate using a special binder at temperature from 800oC to-1200oC, followed by a controlled gas quench to achieve a unique diffusion -aided metallurgical bond.

The alloy powder block '1' (fig. 1.) is manufactured by compacting the alloy powders in a die, forming briquetters and then sintering in a controlled atmosphere to achieve the required shape as shown in fig. 1. The composite block '1' is placed on the ceramic embedded HiCr alloy block '2' and both are placed on the backup plate (3) at temperature from 800-1200°C for duly metallurgical bonding, holding for at least 30 min to achieve a unique diffusion- aided metallurgical bond and high hardness.

According to yet another embodiment there is provided ceramic embedded Hi-chrome alloy wherein the Hi-chrome alloy block consists of carbon, silicon, manganese, sulphur, phosphorus, chromium, molybdenum, and Niobium.

According to yet another embodiment, highly wear resistant functionally gradient composite block comprising distinct composite layer, and reinforcing carbide and ceramic layers are provided over the base surface in segmented pattern.

The sintered carbide alloy powder layer along with the ceramic embedded Hi-chrome layer takes care of the wear while load transmission is handled by the backup plate effectively resulting in extremely strong abrasion resistance and excellent impact resistance. The superior performance of carbide alloys powder segments can be attributed to the fine microstructure and micro segregation observed in sintered alloy powder technology.

The matrix of the sintered carbide composites consist of fine and uniformly dispersed fine carbide of one or more of the carbide forming elements such as iron, tungsten, molybdenum, chromium, vanadium, titanium, niobium and silicon etc. On the other hand white cast iron structure consist of uneven grains of different size such as columner grains, equiaxial grain, chilled crystals and hence is very brittle. Example of the microstructures of functional gradient sintered carbide and 19-3 Cr-Mo white iron are given in Figure 2. Fig 2(a) shows that the matrix of the sintered carbide composites consist of fine and uniformly dispersed fine carbide resulting excellent impact and wear resistance and Fig 2(b) shows the matrix for white cast iron.

Particle size of the austenite is fine and uniformly dispersed. Therefore, the transformed martensite will also be fine and uniformly dispersed. This contributes to increase in hardness without sacrificing too much of ductility. But in white cast iron casting austenite to martensite transformation is dependent on the section thickness typically, for a large section martensite formation is limited to a few surface layers.
In the present method the carbide formation and segregation is limited by the particle dimension. Hence the segregation will be at the micro level contributing to excellent hardness, wear resistant with adequate ductility. While in white cast iron casting, during solidification the carbides as well as high melting inter metallics are pushed to the liquid solid front. This causes macro and inter dendrite coarse segregation which is extremely brittle.

The fine grain structure will exhibit a large grain boundary area. During brazing, grain boundaries being active site contributes to enhance diffusion of brazing alloys resulting in excellent bond strength. On the other hand in white cast iron casting coarse carbides as well as grains in casting lead decreased grain boundaries or interfacial area which reduces the diffusion and hence ability to braze or weld.

The superior performance of carbide alloys powder alloys can be attributed to the fine microstructure and micro segregation observed in atomized functionally gradient sintered carbide alloys.

According to yet another embodiment, the present invention provides Grinding rolls with high abrasion and impact resistance functionally gradient composite block in a segmented manner.

Industrial rollers discussed in prior art are essentially made of Hi-chrome alloy casted in a continuous pattern like a single layer or sheet which gets eroded easily during the crushing process. The present inventors have found that providing segmented composite alloys essentially comprising of: backup plate, Ceramic embedded Hi-chrome alloy and Sintered Carbide alloy helps in prolonging the shelf life of the roller as also helps in easy replacement and removal of worn out segments. Further these segments are bolted from the lower side of roller which acts as a latching mechanism to hold the segment in place and helps in easy removal and replacement. The additional advantage of this feature is that worn out parts can be efficiently and economically replaced easily without any requirement of removing and replacing the complete layer.

According to yet another embodiment, the present invention provides a process for efficient anti-wear layer over the roll surface of grinding rolls comprising the steps of:
? Placing a segment of functionally gradient composite block layer (1) over the lower ring/side (2) of grinding roll;
? Bolting the segmented functionally gradient composite block layer (1) from the lower side of roll;
? Fixing the upper and lower rings in place through the bolts (3) to obtain grinding rolls with functionally gradient composite block.

Figure 1.2 shows an exploded view of the Grinding Roll along with functionally gradient composite block.
(1) is the segment as shown in Figure 1
(2) is the lower ring which is bolted from the lower side of roller. It acts as a latching mechanism which holds the segment in place
(3) are the bolts that are used to fix the upper and lower rings in place
(4) is the inner housing of the roller

Figure 1.3 above shows an assembled roller with all above specified elements

Series of tests were carried out to evaluate the wear resistance properties of the functionally gradient sintered carbide alloys.
a. Abrasion wear Test as per ASTM G 65 of C 45
The test procedure involves first step to clean specimen followed by weigh the specimen nearest to 0.001 to 0.0001 gm. Next step is to seat the specimen securely in the holder and add the weight to lever arm and set the stop watch for 30 min. Maintain uniform curtain of sand by flowing sand at prescribed rate and then start the wheel rotation and lower the lever arm carefully to allow the specimen to contact along the horizontal diametral line of the wheel. After completion of test, lift the specimen away from the wheel and stop the sand flow and wheel rotation. Remove the specimen and reweigh to know the mass loss of specimen. The mass loss is then measured, using weighing machine, by subtracting the mass of specimen after test from the mass of specimen before test.
Test Parameters:
Speed of the rubber wheel – 200 RPM, Test Load – 135 N
Rate of Sand flow- 300-400 g/min, Each Test Duration – 30 min
As established in ASTM G 65 Standard the final report of this test is shown in terms of mass loss:
Description High Cr Cast Iron Ceramic embedded
High Chromium Functionally gradient sintered Carbide
Initial wt. (g) 144.2188 198.6063 184.6973
Final wt.(g) 144.1173 198.5641 184.6591
Mass Loss (g) 0.1015 0.0422 0.0382
Density (g/cc) 7.54 7.05 13.95
Volume loss (mm3) 13.4615385 5.9858156028 2.7383512545

Wear out surface of (a) Functionally gradient sintered carbide (b) Ceramic embedded High Cr cast iron and (c) High Cr cast iron has been depicted in Fig. 4.
Graphical representation of the said results is depicted in Fig. 5.

Thus from the above test, it is concluded that:
? Incorporation of ceramic as a second phase increased the abrasion wear resistance (by~55%) of Hi-Chrome cast iron matrix with respect to Hi-Cr cast iron.
? The SAPT containing carbide forming elements possesses the optimum abrasion wear resistant, viz, volume loss reduced by 54 and 80% as compared to Hi-Cr cast iron and Hi-Cr-Ceramic respectively.
? Incorporation of different gradient increased the abrasion wear resistance of MMCC with respect to High cr cast iron.

b. Drop test
Description MMCC
Table Height (m) 1
Ball weight (kg) 7.5

? No effect was observed on the plate surface from the impact test with no prior scratching or stress concentrators.
? No crack was observed after impact test.
? The drop test results are depicted in Fig. 6.

c. Bond Strength:
The bond strength is calculated using tensile testing method and the minimum bond strength required is 300MPa. The samples used for tensile test (Bond strength) is depicted in Figure 7.
The test details are given below:
Sample size (SAPT) – 100x50x20 mm thick
Cross sectional area- 50x20 mm2
Bonding area – 2x50x10 mm2 (for 2 side)
Maximum load – 305.7 KN
Bond Strength- 305.7 MPa.

d. Observations & Conclusion:
? The sample is to be considered as a diffused bond between Hi-Cr Ceramic & SAPT (Sintered Alloy Powder Technology) fused on a back up plate as a final greater result.
? Combination of SAPT & Hi-Cr Ceramic is 2 to 2.5 times greater than Hi-Cr Ceramic alone.

Brief Description of Figures:
Fig 1. Different layers present in the functional gradient block.
Fig 1.2. Exploded view of the Grinding Roll along with functionally gradient composite block.
Figure 1.3 Assembled view of roller.
Fig 2. Microstructures of (a) functionally gradient sintered carbide alloys and (b) white cast iron
Fig 3. Ceramic embedded Hi-chrome layer
Fig 4. Wear out surface of (a) Functionally gradient sintered carbide
(b) Ceramic embedded High Cr cast iron and (c) High Cr cast iron
Fig 5. Graphical representation of the Wear test results
Fig 6. Drop test sample (a) Before Impact & (b) After Impact
Fig 7. Sample for tensile test (Bond strength)

Features of the Grinding roller with functionally gradient composite blocks as provided in the present application are as follows:
1) Sintered Alloyed Powder block which is isostatically hot pressed is first duly fused to Ceramic embedded Hi-Chrome block and further metallurgically bonded to a Backup plate.
2) The distinguishing and most effective feature of the present invention is that the sintered carbide alloy layer takes care of the primary wear; the ceramic embedded metal matrix composite takes care of the secondary wear while the load transmission is handled by the backup plate as a buffer resulting in extremely strong abrasion resistance and excellent impact resistance.
3) In the present application, the SAPT layer consisting of a combination of Primary and Secondary Carbides wears out first, making way for Ceramic embedded Hi-Chrome alloy to wear out consequently and entire load is buffer cushioned by the backup plate. This gives added life factor compared to prior art.
4) The matrix of the sintered carbide composites consist of fine and uniformly dispersed fine carbide of one or more of the carbide forming elements such as iron, tungsten, molybdenum, chromium, vanadium, titanium, niobium and silicon etc. It is revealed that Sintered carbide has better wearability and corrosion resistance than casting materials.
5) Segmentation of wear parts means low risk of cracking. Therefore, wear-resistant but relatively brittle segments in Sintered carbide can be used. Furthermore, the HiCr segments are suitable for repetitive hardfacing, resulting in double life of the hard faced layer. In case of very abrasive materials, HiCr segments with embedded ceramic inserts ensure considerably increased life. The segments must be replaced when worn out.
6) Sintered carbide segments with embedded ceramic inserts ensure considerably increased life.
7) Sintered carbide composites consist of fine and uniformly dispersed fine carbide of one or more of the carbide forming elements.
8) Easy to replace worn out segments.
9) Reduced downtime for replacement.
,CLAIMS:1. High abrasion and impact resistance functionally gradient composite blocks fused over grinding rolls wherein the composite blocks comprises of Sintered carbide alloy layer; Ceramic embedded Hi-Chrome Alloy layer and backup plate/layer of steel.
2. The High abrasion and impact resistance functionally gradient composite block as claimed in claim 1 wherein the Sintered carbide alloy blocks comprises of composites consisting of fine and uniformly dispersed fine carbide forming elements selected from iron, tungsten, molybdenum, chromium, vanadium, titanium, niobium and silicon.
3. The High abrasion and impact resistance functionally gradient composite block as claimed in claim 2 wherein the carbide alloy is sintered into the grooves through powder metallurgical hot isostatically pressed technology.
4. The High abrasion and impact resistance functionally gradient composite block as claimed in claim 1 wherein the ceramic embedded Hi-chrome alloy block consists of elements selected from carbon, silicon, manganese, sulphur, phosphorus, chromium, molybdenum, and Niobium.
5. A process for preparation of functionally gradient composite block with high abrasion and impact resistance comprising the steps of:
a. Forming of carbide alloy powder block ‘1’;
b. Sintering the carbide alloy powder block at around 1250 to 1450°C for at least 60 minutes to obtain composite block ‘1a’;
c. Powder metallurgical Hot isostatic pressing of carbide into composite block ‘1a’ at around 1100-1300 °C to obtain composite block ‘1b’;
d. Metallurgical fusing of composite block ‘1a’ with composite block ‘1b’;
e. Preparing Ceramic embedded Hi-chrome block ‘2’ by Unique sand casting process at a temperature of 1400-1600°C;
f. Placing block ‘1’ on the block ‘2’ and both the layers are placed on backup plate ‘3’ using a binder material followed by metallurgical bonding at around 800-1200°C to form a functionally gradient composite block.
6. The process for preparation of functionally gradient composite block as claimed in claim 5 wherein the binder material in step (f) is Copper-silver alloy.
7. The process for the preparation of functionally gradient composite block as claimed in claim 5 wherein the metallurgical bonding is preferably carried out at 1000-1200°C.
8. A process for efficient anti-wear layer over the roll surface of grinding rolls comprising the steps of:
a. Placing a segment of functionally gradient composite block layer over the lower ring/side of grinding roll;
b. Bolting the segmented functionally gradient composite block layer from the lower side of roll;
c. Fixing the upper and lower rings in place through the bolts to obtain grinding rolls with functionally gradient composite block.
9. The High abrasion and impact resistance functionally gradient composite block as claimed in any one of the preceding claims wherein the functionally gradient composite block/layers are provided in a segmented manner over the grinding rolls.
10. Grinding rolls with high abrasion and impact resistance functionally gradient composite block in a segmented manner.
Dated this the 20th day of April 2018