GB2079867A

GB2079867A - Plain bearing

Info

Publication number: GB2079867A
Application number: GB8023069A
Authority: GB
Original assignee: Glacier Metal Co Ltd
Current assignee: Federal Mogul Engineering Ltd
Priority date: 1980-07-15
Filing date: 1980-07-15
Publication date: 1982-01-27
Also published as: GB2079867B

Abstract

A plain bearing comprises a metal backing and a lining of polyetheretherketone, a thermoplastics containing the repeating unit: <IMAGE> The backing may be of aluminium or steel with an aluminium foil interlayer. The lining may be applied as a powder, a sheet or as a solution and is heated to between 160 DEG C and 180 DEG C and allowed to cool slowly, without curing, to achieve 40% crystallinity. The lining can comprise a bearing layer or an overlay.

Description

SPECIFICATION Plain bearings and methods of making the same The present invention relates to plain bearings having a metal backing and a plastics lining, particularly those which are to be used with a liquid lubricant. Such bearings include bushes, half bearings, pads for tilting pad thrust bearings, tilting pad journal bearings, machine tool slides and marine stern tubes. The invention is also applicable generally to two relatively sliding surfaces such as pistons operating in cylinders and poppet valves in an internal combustion engine.

Such bearings are known per se but many suffer from a relatively poor fatigue strength which renders their use in certain applications impractical. It is therefore an object of the invention to provide a bearing having a high fatigue strength.

Furthermore, certain known methods of applying a plastics lining to a metal backing involve a curing step after the lining has been placed on the backing. The high temperatures and long curing times involved can result in an annealing of the backing alloy thereby changing the desired characteristics and can also lead to chemical reactions taking place at the plastics/metal interface which can severely impair the bond. It is therefore a further object of the invention to provide a process for applying the lining to the backing which does not involve so extreme a treatment that a change in the characteristics of the backing alloy may result nor which may result in reactions taking place at the interface which might impair the bond.

It is also known to provide plain bearings with an overlay coating. Overlays are intended for the running in of engines so that the surfaces can bed down early in the life of the engine and to provide corrosion protection to vulnerable bearing alloys, such as CuPb, and also to protect against siezure to which many strong harder bearing alloys, such as AlSi, are prone. The low thickness of the overlay enables it to withstand higher fatigue loadings than thick linings of the same alloy. Overlays may be applied to a metallic bearing layer and are themselves usually metallic comprising alloys of lead tin copper, lead cadmium or indium, have a thickness of between 10 and 30 microns and are applied to the bearing surface generally by electro-plating.However, electro-plating is a difficult process to control to produce the necessary quality in mass production, and with the desired consistency of quality.

It is an object of the invention to provide a plain bearing in which a plastics lining may be applied in a sufficiently thin layer to constitute an overlay and in which the resulting overlay has a high fatigue strength.

According to the present invention, a plain bearing comprises a metal backing having a lining of polyetheretherketone. Polyetheretherketone is a tough crystalline thermoplastic aromatic polyetherketone containing the repeating unit:-

and having an inherent viscosity of at least 0.7. The polymer may conveniently be made by the polycondensation of hydroquinone and a 4-4'-dihalobenzophenone (a proportion of which is 4-4'difluorobenzophenone) and an alkali metal carbonate or bicarbonate, as described in European Patent Application Publication No. 0001879 in the name of I.C.I.

The metal backing may be aluminium or aluminium alloy, steel with a bonding layer of aluminium or aluminium alloy foil or steel with an adherent layer of porous sintered powdered metal or any alternative surface which provides a mechanical key, for example a wire mesh which may subsequently be attached to a further backing e.g. by soldering.

The lining may be a thick coating (e.g. 0.25 to 5 mm) which may be deposited in a single coating operating or may be an overlay (e.g. 10 to 30y). In the latter case the overlay is preferably applied to a metal bearing lining e.g. Al/Si, Cu/Pb, Al/Si etc.

Preferably, the polymer lining has a high crystallinity, preferably greater than 40%.

According to another aspect of the invention, a method of forming a plain bearing comprises applying polyetheretherketone to a metallic backing and allowing the coated backing to cool slowly from a temperature of between 370 and 1 6O0C to ambient. The cooling rate is preferably sufficiently slow to result in the polymer having at least 40% crystallinity. Preferably, no curing of the polymer takes place.

The polymer may be applied in sheet form, as a powder or in solution but is preferably pre-dried by heating to 200 C for 1 hour prior to use as a powder, prior to forming into a sheet or prior to solution.

When applied as a sheet the polymer may be extruded and bonded to the backing simultaneously or may be extruded as a sheet and subsequently pressure bonded or roll-bonded to the heated backing.

The coated backing may be allowed to cool slowly, but where further forming is required, it may be preferable to shock cool the coated backing in order to render the polymer amorphous. In this state the polymer is more ductile and so the coated backing can be formed into the desired shape. The formed bearings then preferably re-heated e.g. to temperature of about 1 60 to 1 800C and allowed to cool slowly to achieve the desired crystallinity. By putting the polymer into the amorphous state prior to the slow cooling/crystallisation step, it is possible to reduce internal stresses in the bearing layer. It may not be necessary to melt the polymer and preferably no curing takes place, thus the iikelihood of any chemical action at the interface is minimised.

When applied as powder, the polymer may be spread on to the backing preferably using a vibrating feed hopper. The backing is preferably heated to a temperature to melt the powder. The powder may then be roll bonded to the backing.

An alternative method of applying the polymer, as a sheet or as a powder may be to use a pressure bonding method. In this case the backing may be formed into the desired shape and placed in a mould.

The polymer may then be placed on top of the backing, either as a sheet of the correct shape or as a powder in the desired quantity, and subsequently pressure bonded. This method may be particularly applicable to the formation of flat bearings such as thrust pads or washers.

The polymer may also be applied to the backing in solution e.g. by dipping, spraying, roller coating, or spreading, though any other known method of applying a solution to a substrate may be used. The solvent is preferably evaporated. The solvent is preferably benzyl benzoate though any suitable solvent may be used for example diphenyl sulphone or a mixture thereof with benzyl benzoate. This method may be particularly suitable for applying overlays.

Fatigue tests have been carried out to compare the strength of a polyetheretherketone bearing layer with known bearing layers, namely, white metal, polyphenylene sulphide and aluminium/tin. The tests comprised cyclically transmitting a load through an oil film to a coated half bearing. This approximates to a big-end crankshaft in an internal combustion engine. The load was applied for 20 hours (3.6 million cycles) and then repeated at a higher load until the bearing failed. The results are summarized in Table I which shows results for a coating of about 5COy (i.e. a thick coating) and a coating of about 20p (i.e. an overlay). The figures given are the loads in megapascalls at which failure was observed.

TABLE I

500p 20u White Metal 41 79 Polyphenylene Sulphide 69 0 Aluminium/tin 20X 97 180 Polyetheretherketone 118 230 As can be seen, the results suggest that the fatigue strength of polyetheretherketone is superior in all cases. No results were obtained for a polyphenylene sulphide overlay due to the difficulty in depositing such a thin layer of this material.

The invention may be carried into practice in various ways as will be illustrated in the following Examples:-- Examples 1-14 describe methods of applying thick coatings and Examples 1 5-21 are examples of overlay coatings.

EXAMPLE 1 Pre-dried polyetherether ketone polymer powder was extruded into a tape 1 5 cm in wide 500 microns thick and 100 m long and coiled. The backing used was a 1 mm steel sheet having a 5 micron copper plated overlayer and a porous layer of 11% tin/bronze (BS 60-100 mesh sieve) 2 mm thick sintered to the copper. This backing was heated to 35O-3700C by an induction heater and the polyetherethe;ketone was roll-bonded to the backing. The coated backing was then rapidly cooled to below the glass transition temperature (1400C) in less than 5 seconds by immersing the coated backing in cold water. This rendered the polymer amorphous. The coated backing was then cut into blanks and formed into bushes which were reheated to between 1 60 and 1 800C, held at that temperature for 1 5 minutes and then allowed to cool naturally thereby rendering the polymer crystalline.

EXAMPLE 2 Example 1 was repeated up to and including the roll-bonding stage. Thereafter the coated backing was allowed to cool slowly by passing the coated backing into an insulated tunnel at a temperature between 140 and 1 70 C for a dwell time of 1 minute. This provided a coating with a high crystallinity (greater than 40%). The coated backing was then allowed to cool naturally and cut into blanks and finally formed into thrust washers.

EXAMPLE 3 The polymer sheet described in Example 1 was extruded and simultaneously pressure bonded to the backing described in Example 1. The coated backing was then cooled rapidly to a temperature below the glass transition temperature (1 400C) in less than 5 seconds by immersing the coated backing in cold water. This rendered the polymer amorphous. The coated backing was then cut into blanks and formed into bushes which were heated to a temperature between 1 60 and 1 800C. The coated backing was held at this temperature for 1 5 minutes and allowed to cool naturally thereby rendering the coating more than 40% crystalline.

EXAMPLE 4 Example 3 was repeated but an extruded coated backing was simply allowed to cool slowly by passing it into an insulated tunnel held at a temperature between 140 and 1 7O0C for a dwell time of 1 minute. This rendered the coating more than 40% crystalline. The coated backing was then cut into blanks to form thrust washers.

In each of Examples 1 to 4 a pale cream coloured opaque layer of polyetheretherketone having a crystallinity of greater than 40% was found to be strongly adhered to the backing.

EXAMPLE 5 Pre-dried polyetheretherketone in the form of a powder was spread from a vibrating feed hopper to a depth of 1 2 mum of powder onto the substrate described in Example 1. This was heated to a temperature of between 360 and 3700C by induction heating. This was hot rolled to coalesce the powder into a continuous homogenous lining. This was then rapidly cooled to a temperature below the glass transition temperature and was subjected to the same process as that described in Example 1.

EXAMPLE 6 Example 5 was repeated but after hot roll bonding the powder to form a lining the coated backing was allowed to cool in the same way as described in Example 2.

The coatings obtained in Examples 5 and 6 were similar to those obtained in Examples 1 to 4.

EXAMPLE 7 Pre-dried polyetheretherketone was extruded into a sheet having a thickness of 1 mm a width of 300 mm and a length of 1 500 mm. In this case the substrate was a steel sheet of the same dimensions but having a thickness of 13 mm and having a copper overlayer and bronze sintered layer as described in Example 1. This steel blank was heated in an oven in a non-oxydising atmosphere (nitrogen blanket) up to a temperature of 3600C. The sheet of polyetheretherketone was laid on the hot blank and cold rolled in a rolling mill giving a total reduction in thickness of 250 microns. The coated blank was then heated in an oven to 350 C and quenched in a water bath thus rendering the lining amorphous.The coated backing was then formed into a half shell and re-heated to a temperature of between 1 60 and 1 8O0C for 1 5 minutes, the formed blank was then allowed to cool naturally and machined finally to the required dimensions.

EXAMPLE 8 Pre-dried poiyetheretherketone in powder form was spread to a thickness of 1 T mm by means of a vibrating feed hopper onto a substrate as described in Example 7. This was then heated by induction heating to a temperature of between 360 and 3700 C. The covered blank was rolled to consolidate the powder into a continuous coherent lining. The coated blank was then rapidly cooled, formed, re-heated and finished as described in Example 7.

EXAMPLE 9 Tilting pad thrust washer segments comprising investment cast steel pads 1 cm thick having a 5 micron copper plate and a 2 mm 11% tin/bronze layer sintered to the copper were pre-heated in an oven to a temperature of 370 C under a nitrogen blanket. Shapes corresponding to that of the pads were stamped from a polyetheretherketone tape 2 mm thick and were placed in position on top of the steel pads in a press. The press was activated using a pressure of some 200 psi thereby forcing the polymer into the sinter intestices. The coated pads were cooled slowly in the mould thereby giving the coating a crystallinity of 40%.

EXAMPLE 10 Example 9 was repeated but a measured quantity of pre-dried polyetheretherketone powder was placed in the press on top of each of the steel pads. The coated pads produced required some subsequent machining to achieve the desired finish.

EXAMPLES 11-14 Examples 11-14 correspond to Examples 1-4 but in each case the substrate comprised a mesh formed from woven bronze wire having a thickness of 50 microns and being spaced apart by 1 50 microns. The pressure if which in Examples 1 1 caused the polymer to enter the intestices of the sinter causes, in Examples 11-14, the polymer to partially fill the voids between the mesh strands thereby keying the polymer to the mesh while leaving the back of the mesh exposed. In each of these Examples a satisfactory adherent coating was obtained which could be attached to a stronger metal backing by any suitable means for example soldering.

EXAMPLE 15 Eight percent pre-dried polyetheretherketone was mixed with 92% benzyl benzoate. The mixture was heated to a temperature between 250 and 290 C by which time the polymer had dissolved in the benzyl benzoate. A cold bearing blank formed from an aluminium alloy including 6% tin or 11% silicon was immersed for 0.5 seconds and withdrawn. A coating of the solution had adhered to the blank. The coated blank was transferred to an air circulatory oven and maintained at a temperature between 300 and 3100C for 5 minutes. When the solvent had evaporated the coated blank was allowed to cool naturally. A layer of polyetheretherketone 0.01 mm in thickness having a crystallinity of greater than 40% was found to be strongly adherent to the backing.

EXAMPLE 16 Thirty percent polyetheretherketone was dissolved in diphenyl sulphone and held at a temperature of between 250 and 2900C. A bearing blank similar to that used in Example 15 was immersed in the solution for 2 minutes thus allowing the blank and the solution to reach a thermal equilibrium. The blank, with an adherent coating of solution, was withdrawn and transferred to an oven at a temperature of 3400C where it was left until the solvent had evaporated. The coated blank was then allowed to cool naturally. A coating similar to that obtained in Example 1 5 was obtained.

EXAMPLE 17 A suspension of pre-dried polyetheretherketone was prepared by mixing 30% polyetheretherketone with 10% diphenyl sulphone and 60% benzyl benzoate, heating the mixture to a temperature between 250 and 2900C in order to dissolve the polymer and subsequently cooling the solution to room temperature while maintaining a vigorous agitation. A fine cloudy suspension was thus formed. The suspension was sprayed on to two blanks of an aluminium alloy containing 6% tin or 11% silicon, one of which was at room temperature and the other of which was heated to about 2500C. The sprayed blanks were transferred to an oven where they were held at a temperature of between 340 and 360 C for 5 minutes. The coated blanks were allowed to cool naturally. An adherent coating of polyetheretherketone having a thickness of 0.01 mm and a crystallinity of 40% was produced on each blank.

EXAMPLES 18-21 Examples 1 8-21 were carried out in the same way as Example 1 5-17 but with a substrate comprising an alloy of 10% tin and 10% lead, the balance being copper. This was chemically etched to clean and activate the surface and to increase the surface area prior to coating. Coatings were obtained similar to those obtained in Examples 1 5 to 1 7.

Claims

1. A plain bearing comprising a metal backing having a lining of polyetheretherketone.

2. A bearing as claimed in claim 1 in which the backing is aluminium or aluminium alloy or steel with a bonding layer of aluminium or aluminium alloy.

3. A bearing as claimed in cfaim 1 or claim 2 in which the lining is a thick coating, from 0.25 to 5 mm.

4. A bearing as claimed in claim 1 or claim 2 in which the lining is an overlay, from 10 to 30 microns.

5. A bearing as claimed in claim 4 in which the overlay is applied to a metallic bearing lining.

6. A bearing as claimed in any preceding claim in which the polymer lining has a crystallinity greater than 40%.

7. A method of forming a plain bearing comprising applying polyetheretherketone to a metallic backing and allowing the coated backing to cool slowly from a temperature of between 3700C and 1 6000 to ambient.

8. A method as claimed in claim 7 in which the cooling rate is sufficiently slow to result in the polymer having a crystallinity of at least 40%.

9. A method as claimed in claim 7 or claim 8 in which substantially no curing of the polymer takes place.

10. A method as claimed in any of claims 7 to 9 in which the polymer is applied in sheet form.

11. A method as claimed in any of claims 7 to 9 in which the polymer is applied as a powder.

12. A method as claimed in claim 11 in which the backing is heated to a temperature sufficient to melt the powder.

13. A method as claimed in any of claims 7 to 9 in which the polymer is applied in solution.

14. A method as claimed in claim 13 in which the solvent is benzyl benzoate.

1 5. A method as claimed in any of claims 7 to 14 in which the polymer is pre-dried by heating to 200 C for 1 hour prior to use.

1 6. A method as claimed in any of claims 7 to 1 5 in which the coated backing is shock cooled and is subsequently reheated to a temperature of between 1 600C and 1 8O0C and allowed to cool slowly.

1 7. A method as claimed in any of claims 7 to 11 in which the polymer is attached to the backing by a pressure bonding method.

18. A method of forming a plain bearing substantially as herein specifically described with reference to any one of the accompanying examples.

1 9. A plain bearing having a lining of polyetheretherketone when made by a method as claimed in any of claims 7 to 1 8.