US3402035A

US3402035A - Abrasive wheel having a metal coated graphite lubricant therein

Info

Publication number: US3402035A
Application number: US523237A
Authority: US
Inventors: Thomas J Martin
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-12-07
Filing date: 1965-12-07
Publication date: 1968-09-17
Anticipated expiration: 1985-09-17

Description

T J. MARTIN Sept. 17, 1968 ABRASIVE WHEEL HAVING A METAL COATED GRAPHITE LUBRICANT THEREIN Filed Dec. 7, 1965 Inventor Thomas J. Mar-k in.

United States Patent 3,402,035 ABRASIVE WHEEL HAVING A METAL COATED GRAPHITE LUBRICANT THEREIN Thomas J. Martin, 97 Dover St., La Grange, Ill. 60525 Filed Dec. 7, 1965, Ser. No. 523,237 Claims. (Cl. 51--298) ABSTRACT OF THE DISCLOSURE A diamond abrasive wheel wherein the diamond particles are dispersed in a bonding matrix and wherein a compound solid lubricant material for said wheel is defined by graphite particles having a metallic coating bonded thereto is dispersed within the wheel in the voids between the diamond abrasive particles whereby, in use, the graphite lubricant particles are dispensed to permit flow of graphite over the surface of the wheel.

The present invention relates to an improved abrasive wheel of the type having diamond abrasive particles and more particularly it relates to an improved diamond abrasive wheel having a solid lubricant material therein. The present invention further relates to a method for the preparation of the improved abrasive wheel.

One of the significant problems in the use of any grinding or abrasive Wheel resides in the provision of a suitable and constant lubrication in the interfacial area defined between the abrasive wheel and the workpiece. It can readily be seen that failure to provide lubrication at the interface may give rise to damage to the material being worked on or early deterioration of the abrasive wheel. Failure to suitably lubricate the interface will result in the generation of high temperatures at the interface due to the friction between the abrasive wheel and the workpiece. Water is a commonly used lubricating and cooling material. However, introduction of water at the interface obscures the surface of the material being worked on and, accordingly, progress of the work may not be observed carefully during grinding.

It is well known that graphite is a very good lubricating material. It should 'be observed, however, that graphite powder is very light and difficult to control. For this reason external introduction of graphite to the work interface between the abrasive wheel and the workpiece is impractical. Attempts have been made from time to time to introduce graphite into the diamond abrasive section of a diamond grinding wheel. A wheel structure of this type would be very desirable in that the abrasive wheel would carry its own lubricating material and external lubrication of the work interface during use of the wheel would not be required. However, the attempts to include graphite particles within the diamand abrasive section of the abrasive wheel were generally unsatisfactory in that the graphite particles would not suitably bond with any material used in preparation of the abrasive wheel and the resultant structure ws highly unstable. Bonded abrasive sections including graphite particles as a part of the section had a low characteristic inherent strength which resulted in an unstable abrasive section. Attempts to bond other good lubricating materials, such as molybdenum disulfide, into a resin or metal matrix abrasive section were equally unsuccessful.

The present invention is directed to the provision of an improved grinding or abrasive wheel having a graphite lubricant material secured within the diamond abrasive section of the grinding wheel. The Wheel of the present invention does not have the low inherent strength and instability characteristic of prior structures where attempts were made to include graphite as a lubricant within the body of the abrasive wheel. In the structure disclosed herein the graphite lubricant particles are substantially enveloped with a very thin coating of metal. The metal coating of the graphite core material is compatible with either a metal or resin matrix material used for containing and bonding the abrasive particles to the wheel base. In one form of the invention nickel is employed as the material to define the metal coating about the graphite particles. A satisfactory envelope thickness is about two microns.

The metal coated graphite material is uniformly dispersed throughout the abrasive section defined on the grinding wheel. The metal envelope of the graphite lubricating particles bonds securely to the matrix material in which the abrasive and lubricating particle-s are disposed to define a finished structure that is stable in use and that has high inherent strength. In use, of course, the graphite lubricating particles will be released and will flow over the abrasive particles and between said abrasive particles and the workpiece to lubricate the interface and to prevent the generation of excessive frictional grinding temperatures. It should be observed that if high temperatures are permitted to develop in the working area the abrasive section of the grinding wheel may rapidly deteriorate due to a breaking down of the bond between the abrasive particles, the matrix in which said particles are dispersed and the wheel base. Thus, the reduction of friction in the interfacial area by lubrication will effectively extend the useful life of the abrasive wheel.

It is, accordingly, a general object of the present invention to provide an improved abrasive wheel.

A further object of the present invention resides in the provision of an improved abrasive Wheel of the type having diamond abrasive particles.

Another object of the present invention resides in the provision of an improved diamond abrasive wheel having solid lubricant material disposed within the body of the Wheel to obviate the need for external application of a lubricant during use of the wheel.

An additional object of the present invention resides in the provision of an improved diamond abrasive wheel having diamond abrasive particles and solid lubricant particles dispersed within a matrix and with the matrix and particles bonded to a wheel base.

A further object of the present invention resides in the provision of an improved diamond abrasive wheel having solid lubricant particles bonded within a thermosetting resin matrix whereby during use the lubricant particles are released to flow over the diamond abrasive particles to lubricate the interface between the abrasive particles and the workpiece.

Still another object of the present invention resides in the provision of an abrasive wheel having graphite lubricant particles dispersed within the wheel structure which particles are disposed within a metal envelope material to define a structure that may be bonded to a thermosetting resin or other matrix.

An additional object of the present invention resides in the provision of a method for preparing an abrasive wheel having graphite lubricant particles therein and wherein the particles are bonded within a matrix material for release during use to flow over the abrasive particles.

Another object of the present invention resides in the provision of a method for the preparation of an abrasive Wheel wherein diamond abrasive particles and metal coated graphite particles are dispersed within and bonded to a thermosetting resin.

The novel features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a top plan view of a mold with a premachined wheel base element which assembly is adapted for use in preparation of the abrasive wheel described herein;

FIGURE 2 is .a side view, in section, of the mold and wheel base assembly of FIGURE 1 showing the matrix, abrasive particle and lubricant particle mixture disposed in a recess in the wheel base and illustrating compression of the mixture on to the wheel base;

FIGURE 3 is a side view, in section. of the abrasive wheel of the present invention in one stage of processing with the abrasive materials section compressed into the wheel base recess, said arbasive materials section being bonded to the wheel base at this stage of processing;

FIGURE 4 is a side view, in section, of the wheel of FIGURE 3 with the central portion of the wheel base removed and the wheel in condition for use;

FIGURE 5 is a schematic representation of the abrasive materials section of the grinding wheel showing the abrasive particles and metal coated graphite lubricating particles interspersed within the matrix; and

FIGURE 6 is an enlarged schematic representation, in section, of a graphite particle showing a portion of the metal envelope about said particle.

The method of making the abrasive wheel of the present invention will be discussed in connection with the preparation of a diamond abrasive wheel with the abrasive section thereof being secured to an aluminum base. While the ratio of ingredients included in the abrasive section may vary it should be noted that the compression forces, the temperatures, the bonding and curing cycles (or sintering cycle when using metal powders) will be adjusted to accommodate the requirements of the material.

The materials in the abrasive section of the diamond abrasive grinding wheel of the present invention will include diamond abrasive particles, a thermo-setting bonding resin and the composite powder lubricating material defined by a graphite particle core disposed within a metal envelope. It should be observed that supplementary abrasive particles also may be used such as, for example, an aluminum oxide. The use of the supplementary abrasive particles is a matter of choice for the manufacturer and forms no part of the present invention.

The diamond abrasive particles may be natural diamonds or synthesized diamonds having a grit size of 80 mesh to 20 micron. One resin that may be used as the matrix material is a thermosetting plastic material commercially available under the trade names Monsanto No. 755 and Monsanto No. 795 both of said resins identified by the trade name herein being generically known as phenol formaldehyde. In one embodiment of the invention a combination of the above resins was used in a mixture comprising 15 parts of the No. 755 resin to 10 parts of the No. 795 resin. The composite lubricating particles used in one form of the invention were defined by a graphite core material comprising approximately 25% by weight of the composite particle and 75% by weight nickel in the envelope surrounding the graphite lubricating particle. A particle of this composition is approximately 43% nickel and 57% graphite core material, by volume. The average particle size of the lubricating medium is about 280 mesh. It should be observed that grinding wheels have been made using lubricating particles of difiiering compositions. For example, in another mode of the invention metal coated graphite particles were employed comprising approximately 85% nickel and graphite by weight.

One method of making the abrasive wheel of the present invention will be described in connection with the use of the apparatus shown in FIGURES 1 and 2 of the drawings. It should be observed, however, that other means may be used to prepare the abrasive wheel which are different from the device schematically represented in FIGURES 1 and 2.

A generally circular mold 10 is provided which forms part of the means for forming the abrasive wheel disclosed herein. A generally circular opening 12 is defined in the mold 10. A wheel base member 14 is received within the opening 12 of said mold. The wheel base 14 defines a recess 16 and a core section 18.

The diamond abrasive particles, thermosetting bonding resin matrix and metal coated graphite lubricating particles are premixed in the desired ratio and a predetermined amount thereof then is placed in the annular opening 20 defined by the walls of the recess 16 of the wheel base 14 and the inner periphery of the opening 12 of mold 10. A sufficient amount of the mixture of materials is inserted in the annular opening 20 so that the upper surface is approximately flush with the upper surface of the core 18.

It should be observed that a metal powder may be used as the matrix material in which case the diamond abrasive particles and the coated graphite particles will be mixed with the metal powder. The mixture will be processed in much the same manner as that set forth herein for the resin matrix except that the metal powder must be sintered to bond it to the particles of the mixture and to the wheel base. This sintering temperature may vary depending upon the powder used as a matrix material. However, the temperatures in sintering or in use should not exceed about 2000 F. to avoid break-down of the coated graphite par tices which serve to lubricate the wheel-work interface.

A ram member then is brought down upon the upper surface of the mixture M to compress the materials within the opening defined by the recess 16 and the inner surface 12. A compressive force of approximately 3000 lbs. per. sq. inch is exerted upon the ram 22 and thereby upon the mixture M within the recess 16. The temperature of the assembly then is raised to approximately 215 degrees Fahrenheit while maintaining the pressure of about 3000 lb. per sq. inch upon the mixture M. When the temperature of about 215 degrees Fahrenheit has been reached for the assembly heating of the assembly is terminated and the pressure maintained while the assembly temperature drops to ambient temperature levels. The wheel base and mixture M (which is now bonded to the base) is removed from the mold 10 and is heated for approximately 20 hours at about 300 degrees Fahrenheit. This will cure the resin matrix and permanently secure the mixture M to the wheel base 14. After curing the wheel base is machined to remove the core and central portion as schematically illustrated at 25 in FIGURE 4. In this manner means will be provided for securing the finished abrasive wheel to a mandrel or other power source.

As shown in FIGURE 5 of the drawings, the metal coated graphite lubricating particles 32. are generally dispersed in the interstices between the diamond abrasive particles 30 in the mixture M. It should be observed, of course, that the

particles

30 and 32 are bonded to and secured with the resin matrix.

The form of the metal coated graphite lubricant particles 32 is schematically represented in FIGURE 6 shown in section. As seen in FIGURE 6 the graphite particle is disposed within the metal envelope 38. The composite powder used in the abrasive wheel of the present invention generally consists of a core material (in this specific intance, graphite) coated with a metallic substance which may be nickel or cobalt metal. In general, the coating process for the composite powders involves hydrogen reduction of a metal from a metal bearing solution onto a suspended core material, as disclosed in U.S. Patents 2,853,398 and 3,062,680. It should be observed that many different combinations of composite powders may be prepared. Core materials ranging in particle size from .5 micron to Az-inch in diameter may be coated and the coating thickness is readily variable. It has been suggested that minimum coating thicknesses of one to two microns is necessary to provide satisfactory coverage of the core material.

Many different mixture compositions may be used in the preparation of abrasive wheels in accord with the present invention. Some of the compositions are presented below as follows where all percentages are by volume unless otherwise stated.

EXAMPLE I An abrasive wheel may be prepared by bonding a mixture M to an aluminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 25 Resin #755,10% #795) 25 Aluminum oxide abrasive (180/220 grit) Composite lubricant particle (43% Ni, 57% graphite) 30 EXAMPLE II In another form of the invention as abrasive wheel may be prepared by bonding a mixture M to an aluminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) Resin (15% #755, 15% #795) Composite lubricant particle (43% Ni, 57% graphite) 45 EXAMPLE III An abrasive Wheel also may be prepared by bonding the mixture M to an aluminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 25 Resin (15%, #755, 10% #795) 25 Composite lubricant particle (43% Ni, 57% graphite) 50 EXAMPLE IV An abrasive wheel may be prepared by bonding a mixture M to an aluminum wheel base, said mixture having the following composition:

Percent by volume Diamond abrasive (180/220 grit) 12.5

Resin (15% #755, 10% #795) 25 Composite lubricant particle (43% Ni, 57% graphite) 60 EXAMPLE V While a specific embodiment of the present invention is shown and described it will, of course, be understood that other modifications and alternative constructions may be used without departing from the true spirit and scope of the invention. It is intended by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An improved abrasive wheel of the type having diamond abrasive particles comprising: a phenol formaldehyde thermosetting matrix material; diamond abrasive particles dispersed throughout the matrix in random manner and secured in the wheel form by said matrix; and a complete matrix entrapped solid lubricant material for said wheel defined by graphite particles having a metallic coating thereabout, said metallic coating defining means for bonding the graphite lubricant particles within the matrix and being dispersable in use to permit flow of the graphite particles over the surface of the diamond abrasive particles said metallic coating selected from the group consisting of nickel or cobalt.

2. The wheel of claim 1 wherein the percentages by volume of the materials in the wheel may be about:

Percent Diamond abrasive particles 12.5 to 25 Matrix 15 to 30 Metal coated graphite lubricant 30 to 62.5

3. The wheel of claim 1 wherein the diamond abrasive particles are of approximately /220 grit size.

4. The wheel of claim 1 wherein the graphite lubricant material includes a metallic coating approximately several microns in thickness.

5. The wheel of claim 1 wherein the metallic coating of the graphite lubricant material is nickel.

6. The wheel of claim 5 wherein the composite lubricant material is about 43% by volume nickel as the metallic coating and about 57% by volume graphite.

7. A method for preparing an improved abrasive wheel of the type having diamond abrasive particles secured in a phenol formaldehyde thermosetting resin matrix and having a nickel or cobalt coated graphite lubricant material dispersed in said matrix, said method including the steps of:

mixing together in the resin matrix the diamond abrasive particles and the metal coated lubricant particles;

placing the mixed materials onto a wheel base of the desired support characteristics and physical dimens1ons; compressing the mixture of materials onto the wheel base with approximately 3,000 p.s.i.g. pressure;

heating the mixture of materials and at least the adjacent wheel base area to about 215 F.; and

heating the wheel base and mixture of materials thereon to a given temperature for a time sutficient to cure the thermosetting resin matrix and secure the diamond abrasive particles and metal coated lubricant particles therein.

8. The method of claim 7 wherein the materials are permitted to cool after heating to about 215 F. while maintaining compression of the material.

9. The method of claim 7 wherein the wheel base and mixture of materials is maintained at about 300 F. for approximately 20 hours to cure the resin.

10. The method of claim 7 wherein the mixed materials are placed into a recess in the wheel base prior to bonding thereto.

References Cited UNITED STATES PATENTS 2,367,995 1/ 1945 Buckey 51295 3,062,633 11/1962 Coes 51295 3,168,387 2/1965 Adams 51295 3,316,073 4/1967 Kelso 51295 3,317,295 5/ 1967 K'uzrnick 51308 3,321,287 5/ 1967 Hunsberger et a1 51308 DONALD J. ARNOLD, Primary Examiner.