US2404598A - Method of making abrasive articles - Google Patents

Description

Patented July 23, 1946 STAT-ES METHOD OF MAKING ABRASIVE ARTICLES Julius F. Sachse, Summit, N. J., assignor to Metals Disintegrating Company, Inc., Elizabet N. J a Corporation of New Jersey I No Drawing. Application August 23, 1944,

V I Serial No.550,862

' 1Claim. (Cl.51 293) This invention relates to powder metallurgy and to the manufacture of metal bodies in which minute grains of nonmetallic abrasive materials are uniformly distributed. Such metallic bodies have many fields of use, including cutting or lapping wheels or stones, friction surfaces used as treads, brake linings, clutch facingsand the like, and wear-resisting surfaces of all kinds. In such uses the metallic portion of the body may perform as a structural member or contribute functions closely allied to the use to which the body is placed, but in every case the metal serves as a matric in which the abrasive is imbedded and held. Often it is only necessary to form a thin surfacing of such a metal-abrasive body, Sometimes, and particularly where the surface may wear away with us, it is desirable that the metal-abrasive body be of substantial depth. However, regardless of the use, it is always desirable that the grains of nonmetallic abrasive be uniformly distributed throughout the metal matrix and securely bonded thereto and that these grains be, within practical limits, of uniform size and quality so that the metal-abrasivebody may always present a surface of uniform characteristics.

It is lack of uniformity of the friction, cutting or wearing surface presented by these metalabrasive bodies and the readiness with which the abrasive grain is removed from the matrix which has been the greatest obstacle to their widespread use and low cost production, and it is the object of this invention to provide a method by which the components of such bodies may be manufactured.

Previously the art has used two general methods of making metal bodies which embody therein distributed grains of nonmetallic abrasives. One of these methods is based upon casting the molten metal around or on the abrasive grains or, alternatively, mixing the abrasive grains with the molten metal prior to casting. The other, and more flexible, method consists in forming the mixture of abrasive grains and particles of metal powder and compressing and molding this mixture into a body of the desired shape, in ac cordance with the well known practices used for the molding of metal powders. All such methods possess, in greater or lesser degree, the common fault of non-uniformity of product and insecure bonding of abrasive and matrix. This lack of uniformity is caused in part, and perhaps in greater part, by the diil'erences in density between the nonmetallic abrasives and the metal and, in part, by the difficulties encountered in physically handling and mixing relatively fine sized granular materials and by the insecurity of bonding that is inherent in this method. The present invention relates to those methods of forming metal-abrasive bodies in which the body is constructed by molding and compacting metal powder, and is predicated on a method of making a product to be used for this purpose, which product consists of metal powder the particles of which have nonmetallic abrasive grains'attached to their. surfaces, the sizeof thesegrains being of the order of about 1 to 25 microns. This product may be molded by the known powder metal lurgy methods into bodies of proper size and shape and, when so molded, forms a body having a wear-resisting friction or abrasive surface that is not only uniform from the standpoint of distribution of abrasive therein but is also uniform in the sense that the abrasive particles are of even size or are so minute in size that variation thereof is unimportant to many uses to which these metal-abrasive bodies may be put.- It is further characterized by the integrity of, bond. between the abrasive grains and the metallic matrix. V v

The nonmetallic abrasives to which reference is herein made are the metallicoxides which have, for-the purpose of the particular use contemplated, abrasive, cutting, lapping, polishing, wear-resisting or friction producing properties. As is well known, the common characteristic of such oxides is a hardness greater than that of the metals. Common examples are aluminum oxide, silicon oxide and magnesium oxide. Other less used oxide abrasives are zirconium dioxide, boron sesqui oxide and titanium dioxide. This listing is not inclusive but represents the more practical substances.

In the practice of this invention, I first select the desired abrasive and the desired base metal in which the abrasive is to be imbedded, because,

as will hereinafter appear, the base metal must be one, the oxide of which is reducible by reducing gases, such as hydrogen, at a lower temperature than is the oxide which composes the abrasive. A further requirement is that the matrix metal and the abrasive forming metal must be soluble in each other in the molten state in the proportions necessitated by the contemplated analysis of finished product. Thus, for instance, if aluminum oxide is the abrasive contemplated, a matrix may be selected from the metals set forth in List A. If silicon oxide is the abrasive selected, the matrix metal may be selected from 3 List B. As a further example, if magnesium Oxide is the abrasive desired, the matrix metal may be selected from List C.

List A List B List Zinc Iron Zinc Tin Nickel Nickel Iron Cobalt Copper Nickel Copper Cobalt Copper In each case the metals listed are metals the oxide of which is more easily reduced by reducing gas than is the oxide which forms the abrasive to which the list refers. elusive of metals not named and contain only the commoner and more usable matrix metals. Available standard data, or simple trial, may be used to determine whether a non-listed metal forms an oxide more easily reducible than the oxide from which the contemplated abrasive is made. In the practice of my invention, assuming the proper selection of abrasive and matrix metal has been made, the metal whose oxide forms the abrasive and the metal which is to form the matrix are alloyed together in such proportions that the conversion of the abrasive forming metal to the abrasive oxide will furnish in the final mixture the amount of abrasive required. The thus proportioned alloy is then reduced to the form of a powder by any well known disintegrating process, such as atomizing, pulverizing or the like. The disintegrated alloy is then heated to an elevated temperature, but below a temperature which would fuse the alloy sufliciently to destroy its powder form, and is subjected to the action of an oxidizing gas, such as, for example, air or oxygen, thus causing oxidation of the abrasive forming metal to the desired abrasive oxide, as well as causing oxidation of at least some of the base metal. As soon as this oxidation reaction is complete, to the ex-- tent that the desired quantity of abrasive oxide is formed, the treatment with the oxidizing gas is terminated and the product of this treatment is. reacted with the gaseous reducing agent, such as hydrogen or the like, to cause reduction of such oxide of the matrix metal as has been formed These lists are not exmatrix oxide. In the practice of my invention the product of the oxidizing step is usually in the form of a cake, and it is sometimes necessary or desirable that the oxidized product be cooled and pulverized before being submitted to the reducing treatment. The product produced by the final reduction step is cooled under conditions which do not admit of further oxidation, pulverized and screened, and the result is a metal powder, to the particles of which are attached grains of abrasive oxide, said grains being usually of very small size, in the order of about 1 to 25 microns.

As a specific example of my method of producing such product may be cited the preparation of a nickel powder bearing on its surface aluminum oxide grains. In this particular example a product containing 25 per cent. A1203 and per cent. nickel was desired. Therefore, 84.9 parts of nickel and 15.1 parts of aluminum were alloyed, atomized and screened to the desired size. The powdered alloy was then heated to a temperature of about 1200" C. in a stream of air for about 4 hours. Thereafter the product was cooled, pulverized and reheated to a temperature of about 800 C. and treated in a stream of hydrogen for about 2 hours. Thereafter the product was cooled under hydrogen, pulverized and screened. The resulting powdered product contained in mass about 25 per cent. A1203, the balance beingnickel with only traces of nickel oxide. The product consisted of minute particles of metal powder to which were attached very small particles of aluminum oxide. This product, when molded into proper shape and compressed under pressures of about 40,000 pounds per square inch formed a metal-abrasive body in which the abrasive grains were uniformly distributed.

Having thus described my invention, I claim:

In a method of making a metal powder product having grains of metal oxide abrasive attached to particles of said powder, comprising selecting metal from which abrasive oxide is to be formed, selecting a reducing gas, selecting as a powder metal a metal the oxide of which is reduced by said gas at a lower temperature than is said metal oxide abrasive, forming an alloy of said selected metal, placing said alloy in powder form, subjecting said alloy to an oxidizing gas and then treating the oxidized alloy powder in said reducing gas at a temperature at Which the oxide of said powder metal is reduced but below the temperature at which the said abrasive metal oxide is reduced.

JULIUS F. SACHSE.