US3221392A

US3221392A - Method of making bearings

Info

Publication number: US3221392A
Application number: US392982A
Authority: US
Inventors: James C Gould; Gallatin Victor
Original assignee: Federal Mogul Bower Bearings Inc
Current assignee: Federal Mogul Bower Bearings Inc
Priority date: 1960-09-28
Filing date: 1964-07-30
Publication date: 1965-12-07
Anticipated expiration: 1982-12-07

Description

Dec. 7, 1965 J. c. GoULD ETAL 3,221,392

METHOD OF MAKING BEARINGS Original Filed Sept. 28, 1960 YNE/s( United States Patent O 3,221,392 METHGD F MAKING BEARINGS .lames C. Gould and Victor Gallatin, Ann Arbor, Mich.,

assignors to Federal-Mogul-Bower Bearings, Inc., Detroit, Mich., a corporation of Michigan @riginal application Sept. 28, 1960, Ser. No. 59,086. Di-

vided and this application July 30, 1964, Ser. No. 392,982

6 Claims. (Cl. 29--149.5)

This application is a division of co-pending application, Serial No. 59,086, filed September 28, 1960, by James C. Gould and Victor Gallatin for Method of Making Bearings, now abandoned.

The present invention broadly pertains to bearings, and more particularly to an improved composite bearing and method of making same comprising an aluminum-lead alloy bearing surface tenaciously bonded to a hard metal backing strip.

Composite bearings of the general type to which the present invention is applicable utilize a strong, hard metal backing strip to one surface of which a thin bearing surface layer is tenaciously bonded. Bearing layers have alternatively been applied to the hard metal backing strip by applying and bonding a thin sheet of the bearing metal to the surface of the hard metal backing member or by employing powder metallurgical techniques wherein a powder blend of bearing metals is applied to and sintered on the surface of the hard metal backing member becoming firmly bonded thereto. It is the function of the hard metal backing strip to support the bearing surface layer thereon and prevent excessive deformation thereof when subjected to high bearing loads during use.

A variety of metals such as copper and aluminum for example, have heretofore been employed in combination with one or more of the so-called lubricity metals such as for example, lead, tin, cadmium, and the like, to form a bearing surface layer which is tenaciously bonded to the hard metal backing strip. Of the foregoing metals, aluminum-lead alloys have been found particularly satisfactory for providing bearing surface layers which will withstand high loads, minimize the wear of unhardened shafts, and which have satisfactory fatigue characteristics. The extensive use of aluminum-lead alloys in composite bearings of the general type herein described has heretofore been limited due to the inability of alloying lead with aluminum in appreciable quantities. For example, the low miscibility of lead in molten aluminum restricts the quantity of lead therein to a level of only about 0.2%. The problem of providing aluminum-lead alloys containing greater quantities of lead therein was partly surmounted by resorting to powder metallurgical techniques for applying an aluminum-lead bearing surface layer to a hard metal backing strip. A method for achieving an aluminum-lead alloy containing a quantity of lead in an amount above the 0.2% limitation is disclosed in United States Patent No. 2,815,567 issued December 10, 1957 and assigned to the same assignee as the present invention. In accordance with the teachings of the aforementioned patent, aluminum-lead alloy surface layers containing up to about lead can be manufactured by preheating in a non-oxidizing atmosphere a powder blend comprising aluminum, or aluminum alloy powder and lead powder on the surface of a hard metal backing strip and thereafter compacting the bearing surface layer ICC and tenaciously bonding the compacted layer to the backing strip. However, the quantity of lead which could be alloyed with the aluminum by the method disclosed in the patent was limited to a level of about 15% because of the excessive exudation of molten lead from the bearing surface layer during the hot compacting thereof.

Accordingly, it is a primary object of the present invention to provide a unique aluminum-lead alloy and method of making same which contains a concentration of lead substantially in excess of that heretofore obtainable.

Another object of the present invention is to provide an improved method for applying and tenaciously bonding an aluminum-lead alloy layer to the surface of a hard metal backing member and which aluminum-lead alloy contains a concentration of lead ranging upwards to a level of about Still another object of the present invention is to provide an improved aluminum-lead alloy composite bearing and method of making same and which bearing is characterized by its high strength, excellent durability over a wide range of operating conditions, and which is of economical manufacture.

Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic view illustrating an apparatus for applying the aluminum-lead alloy bearing layer to the surface of a hard metal backing strip in accordance with the preferred practice of the present invention, and

FIGURE 2 is a fragmentary magnified View of the hot rolling compacting step of the composite bearing strip shown in FIGURE 1.

The novel aluminum-lead alloy and composite bearing produced therefrom are obtained through the surprising and unexpected discovery that by blending aluminum and lead monoxide powders in the appropriate proportions and thereafter preheating the blended powder at an elevated temperature in a reducing atmosphere the resultant preheated powder layer can be densied by hot rolling without incurring an appreciable loss of lead by exudation. The foregoing discovery has enabled the successful production of aluminum lead alloys containing up to about 70% lead and which alloy can be readily bonded in the form of a thin layer to the surface of a hard metal backing strip. It will be understood that the method herein described is also applicable to the manufacture of aluminum-lead alloys and composite bearing strips having lower lead contents with the range heretofore obtainable by the method disclosed in the aforementioned patent. The resultant aluminum-lead alloy produced is characterized as a densely compacted mass wherein the lead is finely distributed throughout the aluminum matrix and which includes a minor portion of unreduced lead monoxide ranging up to about 5% of the metallic lead constituent.

It will be understood that the compositions of the aluminum-lead bearing alloys as described in this specification and in the subjoined claims is expressed, unless otherwise noted, in terms of percentages by weight.

The composition of the aluminum-lead alloy produced is established by the relative proportions of powdered aluminum and lead monoxide (PbO) powder used in preparing the powder blend prior to processing. The aluminum powders which can satisfactorily be used in the practice of the present invention, include not only pure aluminum but conventional prealloyed aluminum powders containing other metals and/or elements such as, for example, silicon, copper, nickel, magnesium and the like. The use of prealloyed aluminum powders in lieu of a pure aluminum powder is generally desirable in order to impart the desired strength and toughness to the aluminum matrix to enable it to withstand high loading such as may be encountered in heavy duty operation. Two prealloyed aluminum powders which have been found to be eminently satisfactory include an alloy consisting essenstially of 96% aluminum and 4% silicon and an aluminum alloy consisting essentially of 98% aluminum, 1% nickel and 1% copper.

The particle size of the aluminum powder, regardless of whether it consists of a pure aluminum or prealloyed aluminum powder should be sufficiently small to facilitate obtaining a relatively uniform powder blend with the lead monoxide and moreover, to provide for a resultant alloy having a relatively line grain structure. Particles sizes ranging from about less than 100 mesh to about less than 325 mesh, and preferably less than 100 mesh with from about 40% to 50% thereof less than 325 mesh can be satisfactorily employed.

The lead content of the aluminum-lead alloy is introduced in the form of finely particulated lead monoxide (PbO) or litharge, which is preliminairly blended with the aluminum powder prior to processing. The lead monoxide or lithrage can range in particle size within the range of particle sizes specified above for the aluminum powders, and preferably is of a finer particle size facilitating uniform distribution during the blending operation and a tine distribution of lead in the resultant alloy. Of the variety of lead monoxide powders available, the conventional so-called Mill-Run litharge has provided excellent results when combined with varying proportions of aluminum powders. The nominal chemical analysis and particle size of a Mill-Run litharge utilized in the preparation of the aluminum lead alloys and composite bearings comprising the present invention is tabulated below:

M ill-Run ltharge analysis Nominal chemical analysis:

PbO more than 99.5% by wt. Total HcZHaOz insol 0.25% maximum. True Pb304 0.10% maximum. Free Pb 0.05 maximum. Particle size:

Average particle size 5 microns. Retained on 325 mesh screen Less than 1.0%.

Appropriate proportions of the aluminum and lead monoxide powders are preliminarily blended in a suitable vessel provided with agitation such as, for example, a ball or pebble mill, until a substantially homogeneous mixture is obtained. Since the lead monoxide powder is substantially completely reduced during the preheating step in a reducing atmosphere, the loss in weight thereof due to the liberation of oxygen must be allowed for to achieve a resultant alloy having the desired lead content. For example, to allow for the approximate 7% reduction in the weight of the lead monoxide, about 72% lead monoxide must be blended with about 28% aluminum powder to yield a resultant alloy containing about 70% lead. The blended powdered mass is thereafter applied to one surface of a suitable hard metal backing strip in accordance with the apparatus diagrammatically illustrated in FIG- URE 1. As lshown in the drawing a backing strip 4 of a suitable hard metal is unwound from a feed spool 6 and extended substantially horizontally therefrom. Any one of a variety of suitable hard metals can be satisfactorily employed for the backing strip 4 to impart the desired strength and toughness to the composite strip ultimately produced. Backing strips made of steel possess satisfactory strength and toughness and enable the resultant composite strip to be subjected to further mechanical working such as stamping or punching for example, to provide a composite bearing of the desired configuration and size.

The horizontally extended backing strip 4 passes beneath a metering aperture 8 at the base of a hopper 10 containing a substantially homogeneous blend of the aluminum and lead monoxide powders. As the backing strip 4 passes beneath the metering aperture 8 a predetermined layer of the powder blend 12 of the desired proportions is deposited on the upper surface of the backing strip. The backing strip 4 with the powder blend thereon thereafter passes under a gate or spreader 14 which smoothens and distributes the powder blend into a layer 16 of substantially uniform thickness. After passing the spreader 14 the backing strip 4 having the layer 16 of the powder blend 12 superposed thereon enters a preheating chamber 18 which is maintained at an elevated temperature and is provided with a reducing atmosphere. The reducing atmosphere in the preheating chamber 18 may consist of any one of a number of well known reducing gases, such as for example, a cracked gas atmosphere, which preferably contains a substantial percentage of hydrogen and/or carbon monoxide which on contacting the lead monoxide particles in the powder blend 12 causes a reduction thereof to elemental lead. The reducing atmosphere also serves to prevent oxidation of the surface of the hard metal backing strip 4 assuring a tenacious and uniform bond of the layer 16 to the backing strip.

The preheating chamber 18 is maintained at a temperature ranging from about 800 F. to about 1100 F. which causes a rapid reduction of the lead monoxide to elemental molten lead which diffuses between and wets the surfaces of the aluminum powder particles. Preheat temperatures in excess of about 1100 F. are undesirable inasmuch as -at these higher temperatures the aluminum particles react with the ferrous backing strip forming undesirable compounds. At temperatures below about 800 F. excessive pressures must be utilized in the hot rolling and compacting step hereinafter to be described to achieve an adequate bond between the preheated surface layer and the hard metal backing strip. Accordingly, it is preferred that the temperatures in the preheating chamber 18 be maintained within a range of about 800 to about 1000 F. Under the preheating con ditions employed, the lead monoxide powder is substantially completely reduced to metallic lead, that is, to a level of at least about Since lead monoxide itself possesses good bearing characteristics and has been successfully employed as a `solid lubricant in a variety of situations, the remaining unreduced percentage of lead monoxide in the alloy contributes to the total bearing properties of the alloy.

The backing strip 4 with the layer of the powder blend 12 thereon containing lead monoxide which has been substantially completely reduced in the preheating chamber 18, is passed between rotatably driven upper and lower compacting rolls 20 and 22, respectively, which exert sufficient pressure to form a relatively dense compacted layer 24 of the aluminum lead bearing alloy which is tenaciously bonded to the surface of the backing strip 4. During the hot compacting operation, only slight, if any, exudation of the molten lead occurs. This factor is surprising in view of the fact that excessive exudation occurred in the method disclosed in the aforementioned patent limiting the amount of lead in the alloy to a level of about 15%. The reason why exudation of lead is minimized even in alloys containing up to about 70% lead by using litharge in lieu of metallic lead is not completely understood. However, it is believed that coalescence of the minute molten lead particles is inhibited by the unreduced lead monoxide `therein which prevents agglomeration and resultant exudation on hot compacting.

The peripheral speed of the lower roll 22 is substantially equal to the linear feed rate of the backing strip 4. The peripheral speed of the upper roll 20, however, in contact with the layer 16 of the powder blend 12 is maintained at a speed le-ss than the linear feed rate of the backing strip. This results in a scuing action on the hot powder blend and comprises an important feature of the method for preparing the composite strip. Peripheral speeds of the upper roll 20 ranging from about one-tenth to about one-fifth the linear speed of the backing strip having the layer of powder blend thereon provide densely compacted bearing surface layers which are tenaciously bonded to the backing strip 4 over `substantially the entire area therebetween. The lower peripheral speed of the upper roll 20 causes the concurrent densification of the layer 16 through a combined compacting and extrusion effect and simultaneously deforms and elongates the individual aluminum powder particles causing an exposure of fresh new metal promoting the wetting of the surfaces thereof and their tenacious bonding to the backing strip 4. The compacting and extrusion effect provided by the reduced rotation of the upper roll is best illustrated by FIGURE 2 which shows the formation of a buildup or wave 26 of the powder blend layer adjacent to the inlet side of the upper roll 20 which is subsequently compacted and extruded into the dense compacted layer 24 as it passes between the rolls. The reduced rolling rate of the upper roll 20 can be achieved by any one of a number of well known methods such als, for example, an independent reduction drive mechanism or a slip clutch mechanism connected to the upper roll. Depending upon the specific composition and properties of the backing strip 4 employed, the hot rolling operation concurrently produces a reduction in the thickness of the backing strip 4 ranging up to about 5% of the original thickness. In addition to densifying, extruding, and bonding the backing strip and dense compacted layer 24 together, the hot rolling operation also serves to accurately size the thickness of the composite strip as it leaves the rolls,

The composite strip 2S emerging from the exit side of the hot rolling operation thereafter passes through a port in an intermediate partition 30 into a cooling chamber 32 which is provided with a non-oxidizing atmosphere and chamber 32 must be maintained to achieve the rapid o cooling will, of course, vary depending upon related factors such as the size and heat capacity of the composite strip, the length of the cooling chamber 32 and the linear speed of the composite strip therethrough.

Finally, the composite `strip 28 which has been cooled to about room temperature emerges through a port in an end partition 34 from the cooling chamber 32 and can be conveniently rolled on a take-up spool 36. In this form the resultant composite bearing strip can be fed through conventional stamping and forming operations to produce bearings of the desired configuration and size such as, for example, -sleeve type bearings and thrust washer bearings.

Analyses of the grain structure of the aluminum lead alloy based on photomicrographs taken of hydrofluoric acid etched surfaces of the alloys produced at a magniiication of 500, revealed a relatively fine distribution of lead throughout the aluminum or aluminum alloy matrix. The phases of lead were somewhat oriented in the direction of rolling.

The tensile strength of the aluminum lead alloy and the bond strength between the alloy surface layer and a steel backing strip are provided in the following table for four typical aluminum lead alloy compositions made in Sample Sample Sample Sample A B C D Properties:

Tensile Strength, psi-.. Bond. Strength (Shear),

In addition to the foregoing tensile and bond shear test data the -composite strip represented by samples A and B in the above table were formed into conventional sleeve or shell type bearings of the type employed in automobile engines and were tested under actual operating conditions. These tests substantiated the satisfactory operating characteristics of the composite bearings under full load. In addition, the composite strip represented by sample B above was shaped in the form of thrust washers suitable for use in automotive transmissions and have provided excellent performance over a wide range of test conditions exhibiting minimal wear, heat generation, and weight loss.

While it will be apparent that the preferred embodiments herein illustrated are well `calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. The method of making an aluminum lead alloy containing up to about 70% lead of which up to about 5% thereof is in the form of lead monoxide comprising the steps of providing a powder blend of aluminum and lead monoxide powders, preheating the said powder blend at a temperature ranging from about 800 F. to about 1100 F. in a reducing atmosphere until substantially all of the lead monoxide is reduced to metallic lea-d, compacting the preheated said powder blend into a relatively dense mass, and thereafter cooling the said dense mass.

2. The method of making an aluminum lead alloy containing up to about 70% lead of which up to about 5% thereof is in the form of lead monoxide comprising the steps of blending an aluminum alloy powder consisting primarily of aluminum with a lead monoxide powder in the proportions ranging up to about 72% lead monoxide powder and the balance aluminum powder providing therewith a substantially homogeneous powder blend, preheating the said powder blend at a temperature ranging from about 800 F. to about 1100 F. in a reducing atmosphere until at least about of the lead monoxide has been reduced to metallic lead, densifying the preheated said powder blend under pressure into a relatively dense mass, and thereafter cooling the said dense mass in a non-oxidizing atmosphere.

3. The method of making an aluminum lead alloy containing up to about 70% lead of which up to about 5% thereof is in the form of lead monoxide comprising the steps of blending an aluminum alloy powder consisting primarily of aluminum having a particle size less than mesh with a Mill Run litharge powder in the proportions ranging up to about 72% litharge and the balance aluminum alloy powder providing therewith a substantially homogeneous powder blend, preheating the said powder blend at a temperature ranging from about 800 F. to about 1000" F. in a reducing atmosphere until at least about 95% of the litharge has been reduced to metallic lead, densifying the preheated said powder blend under pressure into a relatively dense mass, and thereafter cooling the said dense mass in a non-oxidizing atmosphere.

4. The method of making a composite strip suitable for the manufacture of bearings and the like comprising the steps of providing a hard met-al backing strip and a substantially homogeneous powder blend of aluminum powder and lead monoxide powder in the proportions of up to about 72% lead monoxide powder and the balance aluminum powder, superposing a relatively uniform layer of said powder blend on said backing strip, preheating said layer of said powder blend in a reducing atmosphere at a temperature ranging from about 800 F. to about ll F. for a period of time sucient to substantially completely reduce said lead monoxide to metallic lead, densifying the preheated said layer on said backing strip by passing said strip and said layer thereon through a pair of rolls, one of said pairs of rolls in contact with said layer relating at a peripheral speed less than the linear speed of said layer causing concurrent compacting and extrusion of said layer and tenaciously bonding said layer to said backing strip, and thereafter rapidly cooling said composite strip in -a non-oxidizing atmosphere.

5. The method of making a composite strip suitable for the manufacture of bearings and the like comprising the steps of providing a hard metal backing strip and a substantially homogeneous powder blend comprising an aluminum alloy powder consisting primarily of aluminum and a lead monoxide powder in the proportion of up to about 72% lead monoxide powder and the balance aluminum powder, superposing a relatively uniform layer of said powder blend on said backing strip, preheating said layer of said powder blend in a reducing atmosphere at a temperature ranging from about 800 F. to about ll00 F. for a period of time suflcient to reduce at least about 95% of said lead monoxide to metallic lead, densifying the preheated said layer on said backing strip by passing said strip and said layer thereon through a pair of rollers, the one of said pair of rolls in contact with said layer rotating at a peripheral speed less than the linear speed of said layer causing concurrent compacting and o extrusion of said layer and a reduction of up to about 5% in the thickness of said backing strip whereby said layer is tenaciously bonded to said backing strip over substantially the entire surface therebetween, and thereafter rapidly cooling said composite strip in a non-oxidizing atmosphere.

6. The method of making a composite strip suitable for the manufacture of bearings and the like comprising the steps of providing a steel backing strip and a substantially homogeneous powder blend comprising an aluminum powder consisting primarily of aluminum and an alloying agent selected from the group consisting of silicon, copper, nickel, magnesium and mixtures thereof and a Mill Run litharge powder in the proportions of up to about 72% litharge and the balance aluminum alloy powder, superposing a relatively uniform layer of said powder blend on said backing strip, preheating said layer of said powder blend in a reducing atmosphere at a temperature ranging from about 800 F, to about 1000 F. for a period of time sufficient to reduce at least about of said litharge to metallic lead, densifying the preheated said layer on said backing strip by passing said strip and said layer thereon through a pair of rolls, the one of said pair of rolls in conta-ct with said layer rotating at a peripheral speed ranging from about one-tenth to about one-fifth the linear speed of said layer causing concurrent compacting and extrusion of said layer and up to about a 5% reduction in the thickness of said backing strip whereby said layer and said backing strip are tenaciously bonded together over substantially the entire surface therebetween, and thereafter rapidly cooling said composite strip in a non-oxidizing atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 2,198,253 4/1940 Koehring 29-149.5 2,749,604 6/1956 Latin 29-420.5 2,815,567 12/1957 Gould et al. 29-l9l.2 X 3,104,135 9/1963 Morrison et al. 29-149.5 X

WHITMORE A. WILTZ, Primary Examiner.

THOMAS H. EAGER, Examiner.

Claims

1. THE METHOD OF MAKING AN ALUMINUM LEAD ALLOY CONTAINING UP TO ABOUT 70% LEAD OF WHICH UP TO ABOUT 5% THEREOF IS IN THE FORM OF LEAD MONOXIDE COMPRISING THE STEPS OF PROVIDING A POWDER BLEND OF ALUMINUM AND LEAD MONOXIDE POWDERS, PREHEATING THE SAID POWDER BLEND AT A TEMPERATURE RANGING FROM ABOUT 800*F. TO ABOUT 1100*F. IN A REDUCING ATMOSPHERE UNTIL SUBSTANTIALLY ALL OF THE LEAD MONOXIDE IS REDUCED TO METALLIC LEAD, COMPACTING THE PREHEATED SAID POWDER BLEND INTO A RELATIVELY DENSE MASS, AND THEREAFTER COOLING THE SAID DENSE MASS.

4. THE METHOD OF MAKING A COMPOSITE STRIP SUITABLE FOR THE MANUFACTURE OF BEARINGS AND THE LIKE COMPRISING THE STEPS OF PROVIDING A HARD METAL BACKING STRIP AND A SUBSTANTIALLY HOMOGENEOUS POWDER BLEND OF ALUMINUM POWDER AND LEAD MONOXIDE POWDER IN THE PROPORTIONS OF UP TO ABOUT 72% LEAD MONOXIDE POWDER AND THE BALANCE ALUMINUM POWDER, SUPERPOSING A RELATIVELY UNIFORM LAYER OF SAID POWDER BLEND ON SAID BACKING STRIP, PREHEATING SAID LAYER OF SAID POWDER BLEND IN A REDUCING ATMOSPHERE AT A TEMPERATURE RANGING FROM ABOUT 800*F. TO ABOUT 1100*F. FOR A PERIOD OF TIME SUFFICINT TO SUBSTANTIALLY COMPLETELY REDUCE SAID LEAD MONOXIDE TO METALLIC LEAD, DENSIFYING THE PREHEATED SAID LAYER ON SAID BACKING STRIP BY PASSING SAID STRIP AND SAID LAYER THEREON THEREOF A PAIR OF ROLLS, ONE OF SAID PAIRS OF ROLLS IN CONTACT WITH SAID LAYER RELATING AT A PERIPHERAL SPEED LESS THAN THE LINEAR SPEED OF SAID LAYER CAUSING CONCURRENT COMPACTING AND EXTRUSION OF SAID LAYER AND TENACIOUSLY BONDING SAID LAYER TO SAID BACKING STRIP, AND THEREAFTER RAPIDLY COOLING SAID COMPOSITE STRIP IN A NON-OXIDIZING ATMOSPHERE.