US 3032404 A
Description (OCR text may contain errors)
United States Patent once 3,032,404 Patented May 1, 1962 3,032,404 METAL PHOSPHIDE FILLER FOR GRINDING WHEELS Thomas E. Douglass, Dayton, and Clarence B. Tilton, Springfield, Ohio, assignors to Simonds Worden White Company, Dayton, Ohio, a corporation of Ohio N Drawing. Filed Apr. 17, 1961, Ser. No. 103,247 7 Claims. (Cl. 51-298) This application is a continuation-in-part of an earlier application Serial No. 840,819, filed September 18, 1959, now abandoned in favor of the present application.
This invention relates to abrasive articles such as grinding wheels and more particularlyv to grinding wheels in which abrasive grains are united into an integral unit by bonding agents containing an'improved filler material.
One object of the present invention is to provide an improved grinding Wheel of the types intended for snagging, semi-finish grinding and finish grinding, yield-ing higher ratios of material removed from the ground article per unit of weight loss of the grinding wheel than have heretofore been considered possible. Another object of the invention is to provide a grinding wheel comprising abrasive grains, held together by a filler containing bond in Which the filler consists of one or more compounds of phosphorus in which the phosphorus is di-, trior penta-valent.
A more specific object of the invention is an improved grinding wheel in which heavy metal phosphides are employed as fillers.
Still a further and preferred object is an improved grind-ing wheel in which the filler includes a heavy metal phosphide and potassium aluminum fluoride.
More specifically, it is an object of invention to provide an abrasive grinding wheel wherein metal phosphides and especially heavy metal phosphides either alone or accompanied by potassium aluminum fluoride constitute the fillers, and wherein, together, with resinoid, vitrified or rubberoid bonding agents, the fillers and the grains of abrasive material are united into a unitary or integral body of the wheel of the resinoid, vitrified or rubber bonded type.
These and other objects will become apparent in the description which follows.
One manner in which the quality of a grinding wheel has been expressed is set forth in the ratio of total pounds of material removed from the surface being ground by the grinding wheel in one hour compared with the total pounds of the wheel which are lost or consumed per hour during such use. The determination of the actual efficiency of a grinding wheel is further complicated by the effects of pressure, temperature and possible chemical action at the high pressure and high temperature experienced by the Wheel in actual service.
One of the more generally accepted theories of grinding action at the point of contact between the grinding Wheel and the surface being ground is that when an abrasive grain removes a fragment of metal, this frag ment should be reacted chemically or altered in 'some way so that it will not weld back to the metal surface from which it has been cut or torn. Since the temperature at the point of grinding is often in the region of 2000' F. to 2200 F. it will be readily appreciated that most of 'the materials that have previously been used as fillers in grinding wheels will become chemically active and may even be decomposed in service.
The present invention pertains to improvements in grinding or abrasive wheels of the type described in Kistler United States Patent 2,308,981 and others of a similar nature, intended specifically for snagging, semi-finish grinding or finish grinding, whether of the resinoid, vitrified or rubber-bonded type. Such wheels are generally composed of abrasive grains such as aluminum oxide or silicon carbide or other abrasive particles which may constitute from about 60% to as much as by weight of the total wheel by weight. The abrasive particles are held together by the bonding agents used-whether resin, rubber or other bonding material. In addition, the bond often contains interpersed throughout the composition one or more materials designated as fillers.
Upon studying the performance of a large number of fillers previously known in the art including sulfides, cryolite, fluoborates, various salts including salts of lead, and other materials not hitherto known to be useful, and after comparison of the quality or performance ratings of grinding wheels formulated with such materials, it was found that wheels containing heavy metal phosphides gave outstanding service and that their performance was enhanced still further when a small but significant amount of potassium aluminum fluoride was incorporated in bond composition.
While we do not wish to be bound by any specific theory, it appears that heavy metal phosphides and particularly manganese phosphides are effective largely because of superior chemical properties at the high temperatures encountered in service. The potassium aluminum fluoride when present appears to melt at these temperatures and to act as a lubricant for the metal fragments detached from the surface being ground and thereby prevents them from welding onto the freshly ground surface.
The heavy metal phosphides and other materials employed as fillers are preferably dry, finely divided solids in order that they may be readily interspersed throughout the bond. As a general rule, the larger the amount of filler the higher is the quality of the wheel, up to a point; after that, greater amounts detract from the quality of the wheel. The improved filler of the present invention should constitute from 10% to 40% by volume of the total bond and preferably between 20% and 40% for certain types of grind-ing wheels.
One example of the manufacture of a grinding wheel according to this invention is as follows:
A suitable quantity of abrasive grains, e.g. alumina or silicon carbide, is Wet with furfural in a mixing chamber. In a separate mixing tub suitable quantities of A stage phenolformaldehyde resin, manganese phosphide, lime (CaO), potassium aluminum fluoride and hexamethylene tetramine are blended to a homogeneous dry powder mass. This dry mixture is added slowly to the furfural wetted abrasive grains with mixing, until a uniform granular mix is obtained. The mixture is put into a mold, pressed and cured at approximately 350 F. in the mold.
Quantities of the various ingredients vary widely for different structures and grades of wheels, as is known in the art.
One typical formulation used with excellent results is In this composition the phosphide comprises about 5.29/ 15.37 or 35% of the filler, by volume and the filler comprises about 36% of the bond, by volume.
In a comparative test involving grinding carbon steel (SAE 4145) two grinding wheels prepared as above described and containing identical grade structure and resinoid bond composition except that one filler contained 35.5% by volume of maganese phosphide and the other filler container 35.5% by volume of FeS. The ratio of M/ L, i.e. pounds of metal removed/ unit of wheel lost in grinding with the wheel bearing the phosphide was 61.867 where the same ratio for the sulfide bearing wheel was only 45.93; an improvement of 32.5% in performance.
The improvement in performance is further indicated by the factor known as cutting efliciency, or the ratio of the energy input in kwh. to the pounds of metal removed. In the same test these ratios were as follows: 0.160 for the phosphide bearing Wheel and 0.175 for the sulphide bearing wheel. Since grain grade and structure were the same, the wheel with the lower cutting efiiciency is the most economical. It can be readily seen that the formula for cutting efficiency,
E kwh. (energy input) M(lbs. metal removed) Phosphide Sulfide Percent bearing hearing improvewheel wheel ment Nil L 60. 48 45. 93 32 Another method of determining the performance of the grinding is by measuring the number of pounds of metal a grinding wheel can remove per hour. Tests were conducted under identical conditions with wheels prepared as above described and the following results were obtained:
Sulfide Phosphide Phosphide Metal removed/hour 46. 35 50. 18 49. 77
Instead of manganese phosphide, we have found that other heavy metal phosphides may be used with like results, including the phosphides of chromium, molybdenum, iron, copper, nickel, cobalt, tin, aluminum, vanadium and other heavy metals, in which the phosphorus exists in its divalent, trivalent or pentavalent form.
In terms of the total bond, it is preferred that the phosphide constitute between about and 50% by weight of the total bond weight and that, when present, the potassium aluminum fluoride should constitute from -25% of the total bond by weight. Optimum results on snagging wheels were obtained with wheels in which the phosphide constituted about 36.1% by weight of the total bond. With an abrasive wheel of this composition, a ratio of weight of material removed to weight of material 10st from the wheel as high as 61.8:1 have been obtained.
The invention may be embodied in a rubber bonded grinding wheel which may be formed by blending on suitable mills, either natural or synthetic rubbers, manganese sulfide, suitable rubber curing agents, e.g. sulfur, accelerator, ZnO and anti-oxidants together with the abrasive gram.
Any of the manganese phosphides may be utilized as an active filler in accordance with this invention either alone or in combination with other metallic or non-metallic phosphides or with such other agents as cryolite, potassium aluminum fluoride or other fillers that may be suitable for this purpose. That is to say that these phosphides may be used in combination with other known active agents to decrease the cost of grinding by the user. The composition and structure of the abrasive article may be varied widely and the manganese phosphide may be incorporated into a grinding wheel in any suitable or desirable manner.
The above disclosure is to be interpreted as illustrating the general principles of this invention and the preferred types and compositions of abrasive articles, and not as limitations on the invention, except as it may be limited by the appended claims.
What is claimed as new is as follows:
1. An abrasive article comprising abrasive grains, a bond material uniting the grains as an integral body and a filler consisting essentially of finely divided solid heavy metal phosphide interspersed throughout the bond.
2. An abrasive article comprisingabrasive grains and a resinoid bond which units the grains as an integral body, said bond having intimately associated therewith a filler consisting essentially of a heavy metal phosphide which constitutes from 10 to 40% by volume of the bond mass.
3. An abrasive article comprising abrasive grains, a vulcanized rubber bond uniting the grains integrally and a filler consisting essentially of from 10 to 40% by volume of heavy metal phosphide interspersed therethrough.
4. An abrasive article comprising abrasive grains, a bond uniting the grains as an integral body which has as its primary constituent a phenol-formaldehyde condensation product, and a solid granular filler incorporated in the bond consisting essentially of heavy metal phosphide in an amount which constitutes from 10 to 40% of the bond mass, by volume.
5. A grinding wheel comprising abrasive grains, a bond uniting the grains as an integral body which has as its primary constituents a phenol-formaldehyde condensation product, and manganese phosphide dispersed through the bond as a filler constituting from 10 to 40% of the volume of said bond.
6. An abrasive airticle comprising abrasive grains, an organic bond uniting the grains as an integral body and a filler interspersed throughout the bond consisting essentially of potassium aluminum fluoride and heavy metal phosphide which together constitute from 10 to 40% by volume of the bond mass.
7. An abrasive article comprising abrasive grains, an organic bond uniting the grains as an integral bodyand a filler interspersed throughout the bond consisting essentially of potassium aluminum fluoride and manganese phosphide which together constitute from 10 to 40% by volume of the bond mass.
References Cited in the file of this patent UNITED STATES PATENTS 2,216,135 Rainier Oct. 1, 1940 2,308,981 Kistler Jan. 19, 1943 2,308,982 Kistler Jan. 19, 1943 2,939,777 Gregor et al June 7, 1960 2,940,841 Gregor et a1 June 14, 1960 2,940,842 Phillips June 14, 1960