Grinding tool

#This invention relates to an improved rotary tool adapted for grinding under a flowing liquid film wherein the particles of abrasive are metal-bonded to a rigid supporting surface.

#In the wet grinding of hard materials such as amethyst and sapphire with metal-bonded abrasive, e. g., diamond particles, it is known that a limiting factor governing the cutting rate is the accumulation and packing of detritus at the roots of the particles of abrasive, filling the intergranular spaces and ultimately burying the abrasive grains. For all practical purposes the cutting action ceases when the abrasive grains are buried in the detritus.

#To improve the removal or scavenging of the detritus from the intergranular interstices it was taught, e.g., by G. F. Keeleric in U.S. Pat. No. 2,820,746 issued Jan. 21, 1958, to cluster the abrasive into tiny dots less than 1/4 inch in diameter leaving a major portion of the area unoccupied by abrasive. The density of population of abrasive particles per total working area of the tool was thereby reduced significantly. With this configuration the initial cutting rate was substantially increased. However, under hard grinding conditions, e.g., with a sapphire workpiece, the cutting rate dropped to about half of the initial rate within a relatively short service period.

#In the drawings:

#FIG. 1 is a perspective view of a grinding disk of the preferred embodiment with an annular grooved working area.

#FIG. 2 is a section through 2--2 of FIG. 1 enlarged to show details of the grooves and of the bonding of the abrasive particles in the surface of the working elements.

#Referring now to FIG. 1 the circular disk 1 is shown with a central opening 3 adapted for mounting on a vertical rotatable arbor, not shown. A network of grooves 4 traverses an annular portion of the top face of the disk, herein designated as the working area, subdividing the working area into working element surfaces 5 and grooves 4, leaving a central area 6 free of grooves and uncoated with abrasive particles and adapted to engage the washer and nut, not shown, of the arbor on which it is to be mounted.

#FIG. 2 is an enlarged sectional view taken along 2--2 of FIG. 1 of disk 1 showing the rectangular cross-section of the groove 4 having a uniform depth D and a uniform width W. The working element surface 5 is studded with particles of abrasive 7 rigidly bonded to the supporting face 8 of the main body 9 of the disk by means of a coating of metal 10 deposited thereover to a thickness t which is greater than one half of the nominal diameter d of the abrasive particles 7 but less than the full diameter, i.e., d/2<t<d. A coating of such adequate thickness is seen in FIG. 2 to engage each particle of abrasive at its root at a re-entrant angle, firmly anchoring it in the coating and locking it into position. Each particle is thus rigidly bonded to the supporting surface 8. The strength of this bond depends on several factors, but primarily on the strength of the metal comprising the coating and secondarily on the strength of the material of construction of the body 9 of the disk 1.

#The particles of abrasive may be selected from any of the materials commonly used for this purpose, e.g., diamond fragments, silicon carbide, and aluminum oxide products such as emery and corundum and, indeed, softer materials, all of these being well known in the art, but because of the high cost of producing the tool of the present disclosure I prefer to use industrial diamond fragments because this is the hardest abrasive material and outlasts all others, hence becomes cheaper in the long run. The abrasive particle size may range from 50,000 M (0.5 microns) to 20 M (840 microns).