US3177564A - Fabricating self-lubricating articles - Google Patents

Description

April 13, 1965 J. A. REYNOLDS ETAL 3,177,564

FABRICATING SELF-LUBRICA'IING ARTICLES Filed March 25, 1963 Inventor Attorneys United States Patent Ofilice 3,177,564 Patented Apr. 13, 1965 3 177 564 FAaarcArrNe sarr rohmoArrNe ARTICLES Jefiirey Alan Reynolds and David Hall, Lcarnington Spa, England, assignors, by mesne assignments, to Gert Deventer, Munich, Germany Filed Mar. 25, 1963, Ser. No. 267,500 Claims priority, application Great Britain, Mar. 28, 1962, 11,86W62 9 Claims. (Cl. 29-1825) The present invention relates toa method of and apparatus for fabricating self-lubricating articles or components which comprise a layer-lattice solid lubricant incorporated in a powder metal matrix, and to articles or components made by the method.

Such articles are at present fabricated as a graphitecontaining metal powder moulding comprising a consolidated mass of a metal powder or powders comprising mixed grain sizes up to about 60 microns and colloidal graphite, the mixture having been sintered and compressed whereby the metal structure is stabilised with the colloidal graphite trapped under pressure in the interstices of the metal matrix, the moulding being machined to the shape and dimensions of the required article or component. The production of such mouldings is described in United States specification No. 2,974,039 and British specification Nos. 892,846 and 892,847. The principal metal powder comprises iron, copper, aluminum and/ or nickel, separately or in combination, to which may be added secondary metal powders such as zinc, tin, lead and cadmium, alone or in combination.

The present invention has for an object to reduce the cost of such articles and components by using the special self-lubricating material to provide only the hearing or wearing surface of the article or component, the self-lubricating material being bonded as a layer on a support comprising a metal backing sheet or strip which provides the required mechanical support for the self-lubricating layer.

From one aspect, the invention consists in a method for the manufacture of self-lubricating articles or components comprising intimately mixing one or more metal powders, comprising mixed grain sizes of up to about 60 microns, with a powdered solid lubricant comprising colloidal graphite and/ or molybdenum disulphide and/ or boron nitride (the lubricant occupying 3% to 50% of the total volume), loosely spreading the powder mixture in a layer on the surface of a metal backing strip, heating the backing strip, with the powder layer thereon, in an atmosphere which avoids undesirable oxidation or r action with the powder, to a sintering temperature below the melting point of the principal metal powder constiutent, rolling the strip with the powder layer thereon between rolls to compact the layer, and further heating the rolled composite strip, whereby to produce an annealed dense and coherent layer, comprising the metal powder matrix with the solid lubricant incorporated in the interstices of the matrix, which is bonded to the surface of the metal backing strip. The composite strip can be submitted to fabricating operations, such as blanking, forming and machining, to produce bearing shells, thrust washers, or other components.

In one embodiment of the method according to the invention, a strong metal backing strip, for example, of mild steel, is cleaned and, if necessary, copper plated prior to loosely spreading the powder mixture on the surface of the metal backing strip to the desired thickness. The powder mixture may comprise 79 /2 copper,

19 /2% tin and 8% graphite, the percentages being given by Weight. The backing strip, with the powder thereon, is heated in an atmosphere which avoids undesirable oxidation or reaction with the powder, to a sintering temperature below the equilibrium solidus of the alloy formed from the metal powder mixture concerned, for example between 600 and 750 C., and, after withdrawal from the furnace and being cooled, is then rolled to compact the powder layer. The composite strip is'then submitted to a further heat treatment to develop the bond between the metal powder grains, and between the metal powder grains and the backing strip, and to relieve the stresses in the metal powder matrix. The composite strip can then be submitted to conventional fabricating operations, such as blanking, forming and machining, in order to produce bearing shells, thrust washers or other components.

From another aspect the invention consists in an article or component having a self-lubricating surface and comprising a sheet metal backing on to at least one surface of which is roll-bonded a substantially dense and coherent layer, comprising a sintered metal matrix in the interstices of which is incorporated a layer-lattice solid lubricant, the lubricant occupying 3% to of the total volume of the layer.

The invention further consists in an apparatus for carrying out the process.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawing, in which:

FIGURE 1 is a diagrammatic side view of an apparatus for carrying out the process of this invention.

FIGURE 2 is a section along the line AA in FIG- URE 1.

FIGURE 3 is a plan view of the spreading arrangement, with the hopper removed.

FIGURE 4 is a perspective view of a shell bearing according to this invention.

Referring to the drawing, a mild steel backing strip 1 is fed from the coil 1a by driven straightening rollers 2, and, after being fed past the spreading device generally indicated by 3 where thepowder mixture 7 is loosely spread on the surface of the strip, passes through asintering furnace 4. After leaving the sintering furnace, the strip with thepowder layer 7 thereon is rolled between rollers 5 to consolidate the powder into a compact layer on the surface of the metal backing strip. After leaving the rollers 5 the composite strip passes through an annealingfurnace 6. The composite strip is drawn from the annealing furnace by pull-out rollers 8 and may then be cut into desired lengths, wound on to a roll or directly fed to machines for fabricating the components to be made.

In the spreadingdevice 3 thepowder mixture 7 is fed to the upper surface of the strip 1 from ahopper 9. The strip 1 moves in the spreading device on anendless belt 10 which is wider than the srip 1 and is supported by the rigid table 11. The strip is located laterally with respect to the hopper by means of inverted L-shaped guides 12 supported above thebelt 10. Thehopper 9 which is carried by theguides 12, has an outlet 9a which is of a depth to provide a layer ofpowder 7 on the strip exceeding the thickness of the required loosely spread layer. The side walls of theguides 12 keep thepower 7 on the strip, leaving side zones thereof uncovered by the powder. The powder layer is spread to cover these sides zones and to produce the powder layer of the required thickness by a generally V-shaped spreading blade orplough 3 13, excess powder being deflected over the sides of the metal backing strip 1 and on to the surface of thebelt 10. The powder which falls on to the belt is discharged into acollecting device 14 for feeding back to the is weak, and the compacted layer can be easily scratched and scraped oif the backing strip.

The rolled strip is then passed through an annealingfurnace 6 which may be similar to thesintering furnace 4, in which the powder is again heated to abouthopper 9.

The furnace 4-, havingrefractory walls 15, may be the same temperature as in thesintering furnace 4. heated in any suitable manner by heating means generally This annealing treatment develops the bond between the indicated at 16. The metal strip with the powder metal power grains, and between the grains and the thereon pa ses through a muffle 17 in the furnace havbacking strip, and relieves the stresses within the coming walls of a heat-resisting alloy, such as Inconcl, 1Q pacted layer. Upon leaving the annealing furnace the the nuflie containing an atmosphere which avoids unmetal grains have been firmly welded to each other and desirable oxidation or reaction with the powder, for ex- [0 th backing strip, producing a substantially dense ample an atmosphere of r ked o i whi h may and coherent layer, comprising the metal powder matrix be fed into th fii i thinlet 18, Excess gas with the solid lubricant incorporated in the interstices is burnt at the ends of the muffie. The outlet end of the of the matrix, Which is bonded to the Surface f h mufiie is provided with a water-cooledchill plate 19 maifli backing P- The layer is resistant to Scratch beyond th nd f the furnace h b Th i l t nd ing and the composite strip will withstand fabricating opof the muffle may also have a water-cooling passage 21) Bunions, to Produce, for p Shell hearings Such as therearound. shown in FIGURE 4.

The furnace should be arranged so that the tempera- If the si tered powder layer on the backing strip is ture of the powder will not be raised too quickly to the foiled instead of Cold, the Separate annealing sintering temperature. The time required to reach the nace may be dispensed with provided the rolling is sintering temperature should be at least 1 minute, prefereiiected ill a reducing P The T0115 y ably not less than 1 /2 minutes, in order to avoid crackp he located in the Sihtfifihg iumflce- It is ing of the powder layer. To achieve thi h fu 25 portant however, that the stresses in the compacted layer chamber can conveniently be about 9 feet long when Should be relievedthe metal strip is fed at a speed of 3 feet per minute. In 0116 Particllhir example, the Powder mixture The heating means 16 may be divided into sections prises 791/2% PP 121/270 tin and 8% coiioidai p which may be separately controlled to regulate the rate he, the Percentages hfiihg given y Weight The metal of rise of temperature. Any powder which may f ll powders have mixed grain sizes of from 5 to 60 microns off the strip in the muffle is collected in abox 21 in the and are Preferably of irregular P The metal P floor of the muffle, the bottom of which can be opened and graphite are intimately mixed before being fed to periodically to empty the collected powder. The box the pp The mild Steel Strip 1 y be about 21 should be located at a position where the temperathick and has its Surface, 011 Which the Powder ture is not sufficiently high to melt the powder. The is to Spread, PP P The 10056 P0Wder layer strip after being maintained at the sintering temperay have athickness of ",w h aft r si t rt fo a short i h passes i the cooling Zone ing and rolling is reduced to a thickness of about 0.040.". and over then plate 19 and is cooled Substantially The strip and powder are heated in the sintering furnace before leaving the mufih to about 725 C. in about 2 /2 minutes, and are held The Strip 1 with the Sinteredpowder 7 thereon is 40 at th1s temperature for about /2 minute before being then rolled cold by the rollers 5 so as to reduce the quickly cooled by Passmg over the.chln plate. The thickness of the powder layer and to improve the metal temlgeramre to Winch the pfwder 1s heated m the to-metal contact between the metal powder grains and funiace 13 also 725 Similar Slillfifill" and annealin tem eratures are suitbetween the metal powder grains and the backing strip, r g P b f f Th rd 1 b t m th bt t.) able for a powder mixture of 77 /2% copper, 12 /2% Y 19mlJ 0 6 so 1 In ere e Ween tin and 10% graphite, percentages being given by weight. whereby P siibstantlaliy fully compacted layer- Other compositions of powder mixtures are possible. The reductlon the thlckmss of the Powder layer may Various compositions which may be used are shown in be about 80%. the following table. The figures in brackets refer to At this Stage the bond hfitweel'l the metal Powder weight percentages, except where otherwise stated, and are grains, and between the grains and the backing strip, maxi a,

Group Principal Metal Powder Secondary Additions Lubricants bination with- Cu, Fe, Al, separately or combined, or further combined with Cu, in combination with Fe, in combination with Al, in combination with- Ni, separately or in com- Graphite, BN, M08: or any combination of these pro vided the total lies between 350% by volume of the finished compact.

Zn, Sn, Pb, Cd, Sb, Be, Mn,

separately or in any combination provided that the total does not exceed 15% with 0ptionally up to 5% Indium in Fe(2). Pb and/or In(15) separately or in any combination but not in total exceeding of the metallic content.

The backing strip should be made or plated with a metal which bonds with the metal grains of the powder mixture. For a mixture of which aluminium is the principal metal powder, the backing strip is preferably of aluminium.

If high percentages of lubricants (for example 12% or more) are to be incorporated, the colloidal lubricant grains (of about 1 micron) are first agglomerated by cold pressing, the agglomerate being comminuted to produce granules of about 200 to 500 microns which are then mixed with the metal powder or powders.

The backing strip can be provided with a compacted layer on both surfaces by submitting a composite strip having a compacted layer on one surface to a second treatment to provide a compacted layer on the other surface of the backing strip.

We claim:

1. The method for the manufacture of self-lubricating articles, comprising intimately mixing at least one metal powder, comprising mixed grain sizes of up to about 60 microns, with a powdered solid lubricant selected from the group consisting of colloidal graphite colloidal, molybdenum disulphide and colloidal boron nitride, thelubricant occuping 3% to 50% of the total volume of the mixture, loosely spreading the powder mixture in a layer on the surface of a metal backing strip, heating the backing strip, with the powder layer thereon, in an atmosphere which avoids undesirable oxidation and reaction with the powder, to a sintering temperature below the melting point of the principal metal powder constituent, rolling and further heating the strip with the powder layer thereon until an annealed dense and coherent layer is produced, comprising a metal powder matrix with discrete particles of the solid lubricant incorporated in the interstices of the matrix, which is bonded to the surface of the metal backing strip.

2. The method as claim in claim 1, wherein after heating to the sintering temperature, the strip and powder layer are cooled before rolling, and the rolled composite strip is submitted to a further heat treatment to develop the bond between the metal powder grains, and between the metal powder grains and the backing strip, and to relieve the stresses in the metal powder matrix.

3. The method as claimed in claim 1, which consists in heating the powder layer at a rate such that the time required to reach the sintering temperature in at least 1 minute.

4. The method as claimed in claim 1, wherein the rolling produces a reduction in the thickness of the loose powder layer of about 80%.

5. Method for the manufacture of self-lubricating articles which consists in intimately mixing at least one metal powder comprising mixed grain sizes of up to about 60 microns, with a powdered solid lubricant selected from the group consisting of colloidal graphite, colloidal molybdenum disulphide and colloidal boron nitride, the lubricant occupying 3% to 50% of the total volume of the mixture, loosely spreading the powder mixture in a layer on the surface of a metal backing strip, heating said backing strip with the powder layer thereon in a reducing atmosphere to a sintering temperature below the melting point of the principal metal powder constituent and at a rate such that the time required to reach the sintering temperature is at least one minute, cooling the strip with the sintered powder layer thereon, rolling the strip with the sintered powder layer thereon, to compact the layer and eliminate substantially all voids, submitting the rolled composite strip to further heat treatment to develop the bond between the metal powder grains and between the metal powder grains and the backing strip, and to relieve the stresses in the metal powder matrix, whereby to produce an annealed dense and coherent layer, comprising the metal powder matrix with discrete particles of the 6 solid lubricant incorporated in the interstices of the matrix, which is bonded to the surface of the metal backing strip.

6. An article having a self-lubricating surface and consisting of a sheet metal backing on to at least one sur face of which is bonded a substantially dense and coherent layer consisting of a sintered powder metal matrix of non-interconimunicating cells containing discrete particles of a layer-lattice solid lubricant, the lubricant occupying 3% to 50% of the total volume of the layer.

7. Apparatus for the manufacture of self-lubricating articles according toclaim 6, comprising a powder spreading device including an endless conveyor belt, of which the upper run is adapted to support the metal backing strip, two L-shaped guides extending above and longitudinally of the conveyor belt to define a guideway for the metal backing strip, a powder hopper above said guides and arranged to feed powder between said guides to a predetermined thickness, and a plough arranged downstream of said hopper and adapted to spread the powder on the metal strip to a thickness less than said predetermined thickness and to deflect the excess powder on to said conveyor belt; a sintering furnace including a tubular mutfie, heating means comprising separate sections for regulating the heat along said mufile, a chill plate at the end of said mufile for chilling the metal strip and the powder layer thereon; compacting rolls for compacting the powder layer on said strip; an annealing furnace including a tubular muffle; and mean for feeding the metal backing strip successively through said spreading device, said sintering furnace, said compacting rolls, and said annealing furnace.

8. In apparatus for making articles according toclaim 6, a powder spreading device comprising an endless conveyor belt, of which the upper run supports the metal backing strip, two L-shaped guides extending above and longitudinally of the conveyor belt to define a guideway for the metal backing strip, a powder hopper above said guides and arranged to feed powder between said guides to a predetermined thickness, and a generally V-shaped plough arranged downstream of said hopper and adapted to spread the powder on the metal strip to a thickness less than said predetermined thickness and to deflect the excess powder on to said conveyor belt.

9. Method for the manufacture of self-lubricating articles which consists in intimately mixing about to by weight of powdered copper and about 10% to 15% by weight of powdered tin, said metal powders comprising mixed grain sizes of up to about 60 microns, with about 8% to 12% by weight of colloidal graphite, loosely spreading the powder mixture in a layer on the copperplated surface of a mild steel backing strip, heating said backing strip with the powder layer thereon in a reducing atmosphere to a temperature of about 725 C. in a time of from 1 to 3 minutes cooling the strip with the powder layer thereon, rolling the strip with the powder layer thereon between rollers to reduce the thickness of the layer to about 20% of its original thickness, heating the rolled composite strip to about 725 C. to develop the bond between the metal powder grains and between the metal powder grains and the backing strip, and to relieve the stresses in the metal powder matrix, whereby to produce an annealed dense and coherent layer, comprising the copper-tin metal powder matrix with the colloidal graphite incorporated in the interstices of the matrix, which is bonded to the copper-plated surface of the backing strip.

References Cited in the file of this patent UNITED STATES PATENTS 2,198,253 Koehring Apr. 23, 1940 2,198,254 Koehring Apr. 23, 1940 2,299,877 Calkins Oct. 27, 1942 2,815,567 Gould et al Dec. 10, 1957 2,086,464 Lewis et al. May 30, 1961

Claims (1)

1. THE METHOD FOR THE MANUFACTURE OF SELF-LUBRICATING ATRICLES, COMPRISING INTIMATELY MIXING AT LEAST ONE METAL POWDER, COMPRISING MIXED GRAIN SIZES OF UP TO ABOUT 60 MICRONS, WITH A POEDERED SOLID LUBRICANT SELECTED FROM THE GROUP CONSISTING OF COLLODIAL GRAPHITE COLLOIDAL, MOLYBDENUM DISULPHIDE AND COLLOIDAL BORON NITRIDE, THE LUBRICANT OCCUPING 3% TO 50% OF THE TOLAT VOLUME OF THE MIXTURE, LOOSELY SPREADING THE POWDER MIXTURE IN A LAYER ON THE SURFACE OF A METAL BACKING STRIP, HEATING THE BACKING STRIP, WITH THE POWDER LAYER THEREON, IN AN ATMOSPHERE WHICH AVOIDS UNDERSIRABLE OXIDATION AND REACTION WITH THE POWDER, TO A SINTERING TEMPERATURE BELOW THE MELTING POINT OF THE PRINCIPAL METAL POWDER CONSTITUENT, ROLLING AND FURTHER HEATING THE STRIP WITH THE

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