US2815567A - Process for making bearings - Google Patents

Description

C. GQUUD ETAL 2,815,567

PROCESS FOR MAKING BEARINGS Filed April 15, 1S53 llnited tates Fine rnocnss non MAKING BEARINGS James C. Gould, Ann Arbor, and Norman W. Faustyn, Inkster, Mich, assignors to Federal-Mogul Qorporatron, Detroit, Mich., a corporation of Michigan Application April 15, 1953, Serial No. 348,917 6 Claims. (Cl. 29-420) This invention relates broadly to bearings. More specifically, the invention is concerned with a composite metal stock having a hard metal backing layer and a sintered surface layer formed from powdered metal, the composite being primarily adapted and preeminently suited for use in the manufacture of bearings. Also, the invention is concerned particularly with a method of forming the composite metal stock.

The metals and metal alloys which have the best hearing properties usually are too soft to hold their form when subject to the loads imposed thereon in use, and it therefore has become the practice in this art to superimpose a thin surface layer of the bearing metal on a hard backing member of steel or the like. The backing memeor is adequately tough and strong to retain its form under all conditions of use and it affords ample support for the essentially thin surface layer. At the same time, the desirable bearing properties of the surface layer metal are utilized.

A variety of metals and metallic alloys are used in the surface layer in bearings of the type referred to above. Aluminum is recognized as a superior bearing metal and is frequently used in this capacity. Also, other metals such as lead, tin, and cadmium sometimes are alloyed either individually or collectively with aluminum to produce a superior bearing metal. The usual procedure is to alloy the additive metals with the aluminum and then bond the alloy metal on the steel backing member by one of the various well-known methods. However, this procedure is subject to the disadvantage that only certain amounts of the desired additive metals are miscible with molten aluminum. For example, lead cannot be alloyed with molten aluminum in amounts greater than about 0.2%, and cadmium cannot be alloyed with molten aluminum in amounts greater than about 4.6% without undue segregation. While tin is miscible with molten aluminum in any proportion, upon freezing or solidifying the tin will segregate undesirably when present in amounts greater than approximately 7.0%. As a result, the practical art has been limited to the amounts specified above in alloying lead, tin, and cadmium with aluminum in the manufacture of bearings.

A primary object of the present invention is to provide a novel way of incorporating additive metals in aluminum in substantially greater proportions than are possible when using cast alloy procedures.

Another object of the invention is to provide a novel method of applying the bearing surface layer on a hard metal backing member in the manufacture of bearings.

Still another object of the invention is to provide a bearing of the above-mentioned character having a novel and superior bearing surface layer.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the drawing forming a part of this specification and wherein like numerals are employed to designate like parts throughout the same,

Fig. 1 is a diagrammatic view illustrating apparatus for applying a bearing surface layer on a hard metal backing member according to the present invention, and

Fig. 2 is a fragmentary perspective view of the composite metal stock produced by the apparatus illustrated in Fig. l.

The method of this invention for making a composite sheet-metal stock suitable for use in the manufacture of sleeve bearings and the like is illustrated diagrammatically in Fig. 1 of the drawing. A strip 10 of a suitable hard metal backing is unwound from a spool 12 and extended horizontally. Powdered metal 14 of predetermined composition in a hopper 16 suspended above and spaced slightly from the horizontally extended sheet metal 1! is deposited on the strip as it passes under the open mouth 18 of the hopper. The strip 10 bearing the powdered metal 18 moves horizontally away from the hopper 16 and passes under a gate or spreader 20 which smooths the powdered metal and distributes it evenly in a layer 21 of uniform thickness on the strip 10. From the gate 20 the backing strip 10 with the superposed layer 21 of powdered metal 14 is passed through an elongated boxlike enclosure 22 defining a chamber 24 in which it is subjected to temperature and pressure conditions sufiicient to accomplish the objects of this invention. A

nonoxidizing atmosphere preferably is maintained in the chamber 24 to prevent oxidation of the backing strip 10 and of the particles of powdered metal 14 at the elevated temperatures maintained in the chamber. Any suitable or conventional means (not shown) can be employed for creating the desired temperature in the chamber 24, and the backing strip 10 with the superposed layer 21 thereon preferably is heated in the chamber 24 to the desired temperature before being subjected to pressure. After the backing strip 10 and the layer 21 have been heated to the desired temperature, they are passed, while still hot, between rotatably driven upper and lower rolls 26 and 28 which exert sufiicient pressure thereon to form the layer 21 into a homogeneous sintered mass bonded to the back 10. It is desirable to exert sufiicient pressure to reduce the thickness of the backing strip 10 and to rupture the surfaces of the powdered metal particles so as to expose new, fresh sur faces thereon at the instant pressure is applied thereto. When adequate conditions of temperature and pressure are employed, an exceedingly strong bond is obtained between the individual metal particles in the powdered layer 21 and between the top layer formed by the metal particles and the backing strip 10. The composite strip thus formed leaves the rolls 26 and 28 and passes from the chamber 24 through a vertical partition 30 into a cooling chamber 32 where the temperature of the composite preferably is reduced relatively quickly in a nonoxidizing atmosphere. An opening 34 is provided in the distal end of the enclosure 32 through which the composite strip leaves the cooling chamber 32, and as the strip emerges from the chamber it conveniently can be rolled onto a spool 36.

Attention is now directed to Fig. 2 which shows an enlarged fragmentary view of the composite strip formed by the procedure described above. This strip comprises a hard metal backing member 38 and a superposed layer 40 of sintered powdered metal particles. The sintered surface layer 44 is bonded securely to the hacking me ber 38 and the bond is adequate to permit the composite to be formed by conventional stamping and forming operations into a hearing or the like. As suggested, the backing member 38 in the composite strip is flattened and reduced in thickness as is the surface layer 40 and it can be discerned by inspection of the strip through a microscope that the individual metal particles in the surface layer are flattened and elongated and bonded together. In this manner, it is possible to distinguish a composite strip formed according to the present inven tion from a similar composite in which the surface layer has been deposited in some other manner asby casting on the backing member.

It is contemplated that a suitable hard metal be used in the backing strip and preferably employed for this purpose in the bearing art. Thepurpose of the backing strip is to provide a back layer which imparts toughness and strength to the composite ultimately produced, and steel satisfactorily imparts this characteristic to the final product.

The surface layer 40 is formed of a mixture or blend of powdered aluminum and other powdered metalssuch as lead, tin, and cadmium. The word aluminum as used above means not only pure aluminum but aluminum alloyed or blended with other metals. Conventional aluminum alloys containing silicon, copper, nickel, magnesium, and the'like, are typical examples. In some applications pure aluminum is not sufficiently rigid for extreme heavy-duty work, and when this metal is used as a bearing surface it frequently is necessary or desirable to use the .aluminum alloys containing silicon, copper, nickel, magnesium, and the like, in order to impart the desired strength and toughness to the aluminum. *If aluminum alloys of .the type referred to are employed for this invention, they preferably are obtained as a pre- -alloyed powder rather than in the form of mechanical mixtures which have to be mixed and blended on the job. This is primarily a matter of expedience, however, and either procedure is operative in the practice of the invention.

As pointed out herea-bove, this invention has particular utility in the production of a composite having a surface layer which is exceedingly rich in certain additive metals. Aluminum has been conventional-1y employed as the surface layer and additive metals have frequently been 1211- loyed with the aluminum to enhance its bearing characteristics. However, as pointed out above, the prior art has been limited in the amounts of additive metals that could be employed by the ability of the additive metal to alloy with the aluminum. Although it is generally recognized that the bearing property of aluminum might be enhanced still further by incorporating greater amounts of the additive metals therein, this could not be done because the two metals are either not miscible when mixed in such amounts or would not alloy properly. The instant invention presents a novel and effective way of incorporating much larger amounts of the additive metals in the aluminum matrix and thus of producing an end product which is superior as a bearing metal to metals or metal alloys obtained by prior casting or equivalent procedures. When the metal powders are blended together according to the present invention, lead can be incorporated in the aluminum in amounts up to about tin can be incorporated in the aluminum in :the amount up to about 15%, and cadmium can be incorporated in the aluminum in amounts up to about 10%. Actually, the only factors which limit the amounts of the additive metals that can be incorporated in the aluminum are the physical properties of the end product ultimately produced. If the maximum proportions of the additive metals are increased substantially above the amounts given there is a significant loss by exudation of the low melting metal during roll reduction, a decrease in the internal cohesion of the particles within the aluminum compact, and a decrease in the quality of the bond between the surface layer 21 and the backing strip 10. Of these factors the first is .perhaps the most important in the manufacture of mechanical bearings. For this purpose, exudation of the low melting constituent or constituents during hot roll reduction appears to set the maximum allowable amount of the lower melting metal that can be incorporated in the surface alloy composition. Roll reduction bond test have been made using a blend of lead and aluminum powders containing lead in amounts up to 15%, and in every instance a satisfactory bond was obtained between the surface layer and the backing strip. In every instance the surface alloy was dense and ductile and the lead was finely distributed throughout the aluminum matrix. Similar tests have been made using blends of tin and aluminum powders containing tin in amounts up to 15% with equally satisfactory results. These blends containing tin up to the maximum amounts recommended produce strong, ductile alloys and result in an adequate bond between the surface layer and the backing strip. Equivalent results .are obtained using a blend of aluminum and cadmium powders containing cadmium in amounts up to 10%, and in every instance the surface layer can be successfully bonded to steel by roll reduction. The metal powders to be used for the surface layer 40 are thoroughly mixed together in any suitable manner as by tumbling in a conventional rotating drum, and the thoroughly mixed blend is then placed in the hopper 16 for depositing on the hard metal backing strip 10 in the manner hereinabove described.

The individual particles of metal powder can vary considerably in size but they preferably are within the range35 mesh through 325 mesh. It is desirable particularly in the case of the aluminum powders to have the particles distributed substantially entirely throughout this range in order to obtain maximum bond strength. Also, aside from the quality of bond, the ultimate physical properties of many metal powder compacts are highest with an evenly distributed range of particle sizes. It is desirable to maintain the particle sizes of the several powders incorporated in the blend about the same, but if some variation exists it is preferred that the additive powder be smaller in size than the matrix powder.-

The length of time the strip 10 and the superposed layer '21 is heated before rolling can vary within wide limits. In practice, the length of heating depends upon the speed at which the strip is passed through the heating chamber 24 and the length of the chamber in advance of the reducing rolls 26 and 28. The important thing is to raise the temperature of the metal a desired amount before subjecting the same to reduction rolling, and the length of time used to accomplish this object is relatively unimportant. Other things being equal, however, it is best not to leave the metal at an elevated temperature for an excessive length of time.

Also, the temperature and pressure employed in any particular instance may vary somewhat. Each in a sense is a function of the other. Lower temperatures can be used if there is a corresponding increase in the pressure employed. Conversely, the pressure may be reduced if the temperature is correspondingly increased. Temperatures in the neighborhood of 800-l000 F. are preferred, and at this temperature sufiicient pressure should be employed to reduce the thickness of the steel backing strip 10 by from 15 to 30%. About 1100 F. is probably the maximum temperature that should be employed in processes using powder aluminum on a steel backing member, because undesirable iron-aluminum compounds are formed above this temperature. If temperatures lower than the minimum temperature suggested are used, ex cessive pressures have to be employed in order to secure proper sintering of the powders and an adequate bond between the sintered surface layer and the hard metal backing layer. At temperatures between 900 F.1000 F. the optimum reduction of the steel backing member is between 20-25%.

As the backing strip 10 and the superposed powder layer 21 pass between the rolls 26 and 28, the powder is in an essentially fiufiy state. The first function of the roll 26 is to compress the powder so as to remove voids and then as the strip moves directly under the roll 26 the latter exerts sufficient pressure to deform and elongate the individual particles of metal powder. At the same time a scufling action occurs which ruptures or breaks the surfaces of the metal particles so as to expose fresh new metal to adjacent particles and to the backing member 10. This action occurring simultaneously with application of heat and pressure sinters the particles into a. continuous homogeneous mass which is bonded securely over its entire surface to the backing strip 10. The scrubbing action of the roll 26 on the particles of metal powder is an important function of the rolling operation. In the case of aluminum, for example, the roll breaks the aluminum oxide film from the particles and presents a clean aluminum surface which bonds or welds to the steel backing strip 10. Also, the deformation of the aluminum particles by the roll 26 apparently improves the bond between the aluminum and the steel as the elongation of the particles also produces fresh aluminum surface which is free of oxide for bonding to the steel. Here again it will be readily appreciated that the pressure must be suflicient to break the oxide coating on the aluminum particles so that there can be fresh metal-tometal contact between the particles and the steel if a properly bonded composite suitable for use in the manufacture of bearings is to be obtained.

In the cooling chamber 32, the temperature of the strip is reduced relatively quickly and preferably to about room temperature. In general, it is desirable to reduce the temperature of the composite relatively quickly after rolling in order to prevent formation of brittle compounds between the steel backing member and the surface bearing layer. Any temperature necessary to reduce the composite strip the desired amount can be maintained in the cooling chamber 32. Manifestly, this temperature may vary depending upon the related factors such as the size and length of the chamber 32 and linear speed of the composite strip.

As an alternative procedure it sometimes is desirable to roughen or serrate the top surface of the backing strip 10 as by shot blasting or sand blasting before the powder 14- is deposited thereon. Roughing the surface of the steel back in this manner facilitates the establishment of an adequate bond between the backing member and the surface layer with less rolling pressure. Also, this result can be obtained under certain circumstances by slip rolling. This requires the use of rolls of different diameter which travel at different surface or peripheral speeds. The effect of slip rolling is to enhance the scrubbing action of the rolls and thus produce an adequate bond with less pressure.

Having thus described the invention, we claim:

1. The method of making a composite sheet metal suitable for use in the manufacture of bearings and the like comprising superposing a surface layer of discrete metallic particles primarily of aluminum and another metal selected from the group consisting of lead, tin and cadmium on a hard metal backing member, heating the layer of metallic particles and said backing member while simultaneously pressing the heated metal particles and said backing member with sufficient force to reduce appreciably the thickness of both the backing member and the superposed layer, suflicient temperature being employed to effect at the pressure used a sintered bond between the individual metallic particles and between the metallic particles and said backing member, and then cooling the composite metal sheet thus produced, and wherein the metallic particles in said surface layer and said backing member are heated simultaneously to a temperature between about 800 and 1000 F. in a nonoxidizing atmosphere and wherein pressure is applied to the heated mass while still in the nonoxidizing atmosphere by passing the backing member with the metal particles thereon between rolls which are spaced so as to compress the metal powder sufficiently to remove voids between the individual particles and to produce a. sintered and compacted surface layer on the backing member, sufficient pressure being applied on each side of the metal composite to deform the individual particles in the surface layer'and the backing member and to effect a bond not only between the individual metallic particles in the surface layer but also between these particles and the backing member.

2. The method as set forth in claim 1 wherein the pressure applied to the metal composite is suflicient to reduce the metal back from 15 to 30% in thickness.

3. The method of making a composite metallic sheet suitable for use in the manufacture of bearings and the like comprising superposing on a hard metal backing member a surface layer consisting essentially of a mixture of a powdered metal selected from the group consisting of at least about 0.2% lead, at least about 7% tin, and at least about 4% cadmium, and the remainder powdered aluminum, all of the metallic particles in said mixture being uniformly intermingled, sintering the metal particles by the simultaneous application of heat and rolling pressure to the surface layer and backing member in a nonoxidizing atmosphere, sufficient pressure being employed to reduce the thickness of said backing member and sufiicient heat being employed to sinter the metallic particles together and to the backing member at the pressure employed, and then cooling the composite thus formed.

4. The method of making a composite metallic sheet suitable for use in the manufacture of bearings and the like comprising superposing on a ferrous metal backing member a surface layer consisting essentially of a mixture of a powdered metal selected from the group consisting of about 0.2% to 15% lead, about 7% to 15% tin and about 4% to 10% cadmium; and the remainder powdered aluminum, all of the metallic particles in said mixture being uniformly intermingled, sintering the metal particles by application of heat and rolling pressure to the surface layer and backing member in a nonoxidizing atmosphere, sufficient pressure being employed to reduce the thickness of the backing member from 15 to 30% and sufiicient heat being employed to sinter the metallic particles together and to the backing member at the pressure employed, and then cooling the composite thus formed.

5. The method of making a composite sheet metal suitable for use in the manufacture of bearings and the like comprising superposing a surface layer consisting essentially of discrete metallic particles primarily of aluminum and of a metal selected from the group consisting of about 0.2% to 15% lead, 7% to 15% tin and about 4% to 10% cadmium; on a hard metal backing member, heating the surface layer of metallic particles and said backing member and simultaneously subjecting said particles to a scrubbing pressure sufficient to deform the particles so as to disrupt any oxide film on the surfaces of the particles and to rupture said surfaces so as to expose metal from the interior of the particles at the surfaces thereof, said pressure being a rolling pressure applied to the surface layer and to the backing member so as to press the particles together and against the backing member and to reduce the thickness of the backing member whereby to unite the particles in the surface layer into an essentially homogeneous sintered and compacted mass and to bond the surface layer securely over its entire undersurface to said backing member.

6. The method of making an aluminum-faced bearing comprising superimposing on a steel backing member a layer consisting essentially of particles of aluminum in major amount and another metal in minor amount selected from the group consisting of lead, tin and cadmium, the proportion of said other metal and aluminum in said layer being greater than the proportion in which said other metal can be cast alloyed with aluminum, all of the metallic particles in said layer of powdered metal being uniformly intermingled, subjecting the backing member and the superposed layer of powdered metal to a scrubbing pressure sufficient to deform the particles so as to disrupt any oxide film on the surfaces of the particles and to rupture said surfaces so as to expose metal from the interior of the particles at the surfaces thereof and sufiicient also d to reduce the thickness of the steel backing member from 15% to 30% while heating said backing member and powdered metal layer in a nonoxidizin g atmosphere to a temperature sufllcient to sinter the metal particles to gether and to the backing member at the pressure em- 5 ployed.

References Cited in the file of this patent UNITED STATES PATENTS 1,703,177 Short Feb. 23, 1929 10 8 Koehring J Apr. 23, 1940' Koehring Apr. 23-, 1940 Sa-ndler Dec. 24, 1940 Marvin -4 May 6, 1941 Queneau May 13, 1941 Van Der Horst Dec. 17, 1946. Hensel Apr. 15, 1947 Hensel Nov. 28, 1950 Schultz Feb. 19, 1952.

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