Grinding tool for machining brittle materials and a method of making a grinding tool

Abstract

The invention relates to a grinding tool for machining brittle materials. The grinding tool has a core and an abrasive rim. The abrasive rim has abrasive particles embedded in a matrix. The matrix has a metallic bonding agent and possibly also a polymeric bonding agent. The metallic bonding agent contains silicon nitride in an amount that constitutes 0.02%-5.0% by volume of the metallic bonding agent. The invention also relates to a method of manufacturing the grinding tool. In the method, abrasive particles are mixed with metal powder and silicon nitride and the mixture is sintered. Polymeric powder may also be added before sintering.

1 . A grinding tool for machining hard and/or brittle materials which grinding tool comprises a core and an abrasive rim, the abrasive rim comprising abrasive particles embedded in a matrix, the matrix comprising a metallic bonding agent which is a sintered bronze alloy, the metallic bonding agent constituting 50%-100% by volume of the matrix, the metallic bonding agent containing silicon nitride in an amount that constitutes 0.02%-5.0% by volume of the metallic bonding agent characterized in that the silicon nitride is present in the shape of grains having an average grain size which is less than 10 μm and above 0.1 μm. 
     
     
         2 . The grinding tool according to  claim 1 , wherein the matrix further comprises a polymeric bonding agent that has been sintered together with the metallic bonding agent such that the polymeric bonding agent and the metallic bonding agent form a connected network. 
     
     
         3 . The grinding tool according to  claim 1 , wherein the silicon nitride comprises 0.3%-5.0% by volume of the metallic bonding agent. 
     
     
         4 . The grinding tool according to  claim 2 , wherein the polymeric bonding agent comprises polyimide. 
     
     
         5 . The grinding tool according to  claim 1 , wherein the matrix additionally comprises graphite. 
     
     
         6 . The grinding tool according to  claim 1 , wherein the metallic bonding agent is a bronze alloy that comprises copper, tin and silver. 
     
     
         7 . The grinding tool according to  claim 1 , wherein the abrasive particles comprise diamond particles. 
     
     
         8 . The grinding tool according to  claim 7 , wherein the abrasive particles have a mean particle size in the range of 4 μm-181 μm. 
     
     
         9 . The grinding tool according to  claim 8 , wherein the abrasive particles comprise a coating of copper. 
     
     
         10 . A method of making a grinding tool which method comprises sintering abrasive particles together with metallic powder that comprises copper and tin such that the sintering results in a matrix in which the abrasive particles are embedded, the matrix comprising a metallic bonding agent which is a sintered bronze alloy, characterized in that silicon nitride in the form of a powder is added to the metallic powder before sintering and to such an extent that the silicon nitride will constitute 0.02%-5.0% by volume of the metallic bonding agent and wherein the silicon nitride which is added is in the shape of grains having an average grain size which is less than 10 μm and above 0.1 μm. 
     
     
         11 . The method according to  claim 10 , wherein the metallic powder additionally comprises silver. 
     
     
         12 . The method according to  claim 10 , wherein a polymer is added to the metallic powder before sintering, preferably in the form of
 polyimide powder, such that also a polymeric bonding agent is formed which is a part of the matrix.   
     
     
         13 . The method according to  claim 10 , wherein the method comprises: mixing the powder material for the bonding agents of the matrix with the abrasive particles; compacting the mixture in a cold press; curing the compacted mixture in a kiln at a temperature in the range of 380° C.-520° C., preferably 400° C.-500° C., for a period of 120-150 minutes; thereafter placing the compacted and cured mixture in a press and subjecting it to a pressure of 1500-2000 kg/cm 2 ; and holding the pressure until the mixture has reached a temperature below 300° C. 
     
     
         14 . The method according to  claim 10 , wherein filler material is added to the mixture of metallic powder and abrasive particles before the sintering operation and wherein the filler material comprises graphite. 
     
     
         15 . The grinding tool according to  claim 3 , wherein the silicon nitride comprises 0.5%-3% by volume of the metallic bonding agent. 
     
     
         16 . The grinding tool according to  claim 15 , wherein the silicon nitride comprises 0.5%-2% by volume of the metallic bonding agent. 
     
     
         17 . The grinding tool according to  claim 1 , wherein the abrasive particles comprise cubic boron nitride particles. 
     
     
         18 . The grinding tool according to  claim 8 , wherein the abrasive particles have a mean particle size in the range of 46 μm-91 μm. 
     
     
         19 . The grinding tool according to  claim 8 , wherein the abrasive particles have a coating of nickel.