Hollow body grinding materials

Abstract

A grinding material comprising a multiplicity of hollow bodies whose walls are formed of abrasive grains and a bonding means and are arranged to be stable in resistance to grinding forces.

What we claim is: 
     
       1. A grinding material comprising a multiplicity of hollow bodies whose walls contain .Iadd.substantially therein .Iaddend.abrasive grains in an amount of more than 50% of the wall surface and a bonding means selected from the group consisting of a synthetic resin, a ceramic binder and a metallic binder .[.and are.]. .Iadd.for bonding said abrasive grains to each other at said wall surface, said walls being .Iaddend. arranged to be stable in resistance to grinding forces, the mean diameter of said hollow bodies .[.are.]. measured parallel to a grinding surface .[.lies.]. .Iadd.lying .Iaddend.between 0.1 and 8 mm and .[.is.]. .Iadd.being .Iaddend.not more than 50 times the mean grain diameter, .[.and the abrasive grains are contained substantially within the walls of the hollow bodies.]. .Iadd.whereby during grinding a multiplicity of fresh abrasive grains become continuously available at the grinding surface wherein the grinding action of the grinding surface depends exclusively on the size of the abrasive grains.Iaddend.  . 
     
     
       2. A grinding material as claimed in claim 1 wherein the thickness of the walls of the hollow bodies is on average less than 10 times the mean abrasive grain diameter. 
     
     
       3. A grinding material of claim 2 wherein the abrasive grains are disposed in the walls of the hollow bodies substantially in one layer. 
     
     
       4. A grinding material as claim in claim 1 wherein the abrasive grains are contained in the walls of the hollow bodies in a tightly-packed arrangement. 
     
     
       5. The grinding material of claim 4 wherein the bonding means content of the walls by weight is not greater than twice their grain content. 
     
     
       6. A grinding material as claim in claim 1 wherein the hollow body walls each surround a carrier particle, whose mechanical strength of resistance to the stresses occurring during grinding is substantially less than that of the hollow body walls. 
     
     
       7. A grinding material as claimed in claim 1 wherein all the constituents of the hollow bodies not participating in the formation of the walls are more easily removable under grinding conditions than the walls. 
     
     
       8. A grinding material as claimed in claim 7 wherein the frictional stress produced at a surface to be ground by the constituents of the hollow bodies not participating in the formation of the walls is less than a fifth of the frictional stress caused by the walls. 
     
     
       9. A grinding material as claimed in claim 6 wherein the carrier particle is thin-walled. 
     
     
       10. A grinding material as claimed in claim 7 wherein at least some of the hollow bodies contain a substance which is fluid under grinding conditions. 
     
     
       11. A grinding material as claimed in claim 7 wherein at least some of the hollow bodies contain a substance which is in powder form under grinding conditions. 
     
     
       12. A grinding material as claimed in claim 1 wherein the mean overall diameter of the hollow bodies measured parallel to a grinding surface is about three to 50 times as large as the mean grain diameter. 
     
     
       13. A grinding tool made from the grinding material as claim in claim 1 wherein the hollow bodies are bonded together. 
     
     
       14. A grinding tool as claimed in claim 13 wherein the hollow bodies are bonded to a base material to form a grinding or abrasive belt. 
     
     
       15. A grinding tool as claimed in claim 13 wherein the hollow bodies are bonded together to form a grinding body. 
     
     
       16. The grinding material of claim 1 wherein said hollow bodies are of a copolymer having abrasive grains of corundum. 
     
     
       17. A process for the production of a grinding material comprising expanding polymeric material to form a multiplicity of hollow bodies having a diameter of 0.1-8.0 mm, coating said hollow bodies with abrasive grains so that said abrasive grains are substantially in one layer, and depositing said coated material onto a substrate having a layer of bonding material. 
     
     
       18. A process according to claim 17 wherein said substrate is a belt. 
     
     
       19. A process according to claim 17 wherein said hollow bodies contain a grinding adjuvant. 
     
     
       20. A process as claimed in claim 17 wherein the abrasive grains are bonded by means of an age-hardening bonding material to the surfaces of hollow thermoplastic beads and the hollow bodies thereby formed are next heated to a temperature at which the hollow bead melts but the bonding material remains sufficiently firm.  .Iadd.21. A grinding material as claimed in claim 1, wherein the hollow bodies are individual hollow spheres. .Iaddend. .Iadd.22. A grinding material as claimed in claim 1, wherein each hollow body consists of a thin walled bubble type carrier particle and said abrasive grains bonded to the walls of said carrier particle by said bonding means. .Iaddend..Iadd. 23. A grinding material as claimed in claim 1, wherein the bonding means is a synthetic resin and the abrasive grains are selected from the group consisting of molten aluminum oxide, molten zirconium oxide, mixtures of these oxides, silicon carbide, diamond, flint, graphite and emery.