GB2156011A - Bearing material - Google Patents

Abstract

Bearing material including an antimony wear indication layer 18 detectable in bearing lubricant as indication of wear and sandwiched between layers of lead 16, 20 and cobalt 14, 22 on each side with further bearing layers 12, 24 on the outside of the sandwich. The first layer of bearing material is preferably of lead-bronze and the overlay is preferably of lead-indium alloy. A further overlay of lead-tin- copper may also be provided. The backing layer is preferably of steel. <IMAGE>

Description

SPECIFICATION Bearing materials This invention relates to a multi-layer bearing liner.

It is current practice for certain engines to be bench tested using specially constructed plain crankshaft bearings. These bearings comprise a steel backing layer, a layer of a bearing metal or alloy, and a "sandwich" comprising a layer of nickel, a layer of silver, and another layer of nickel. An overlay comprising an alloy of lead, tin and copper is finally applied to the outermost nickel layer.

During the test period the lubricating oil is filtered, the filter being examined analytically for traces of silver. Engine stripping to check the bearings for damage is undertaken if the amount of silver exceeds a pre-determined level.

The layer of bearing metal or alloy applied to the steel backing is commonly a lead bronze.

The first layer of nickel is applied by electrodeposition and provides a bonding medium for the intermediate electrodeposited silver layer. The outermost nickel layer, again electrodeposited is considered to be necessary to prevent too early penetration of the silver layer by any dirt particles present in the lubricating oil.

This known use of silver as an indicator of bearing damage due to penetration of the overlay by dirt particles has a number of disadvantages. Firstly as is known to those skilled in the art, silver plating solutions, in the majority of cases contain potassium cyanide, a highly poisonous substance requiring specialised equipment for effluent treatment. Secondly and more importantly, due to the nature of silver plating solutions, it is extremely difficult to prevent silver depositing on the exposed steel surfaces of the backing layer. Any such silver must be removed from the backing, since the fit of the bearing in its housing is impaired. Thirdly, the high cost of silver makes construction of this type of bearing expensive.

Further, it is known that the first layer of nickel can form intermetallics by virtue of diffusion into the underlying lead-bronze. Thus nickel-tin and copper-nickel compounds may form particularly at temperatures experienced during normal engine running; such hard compounds are not good bearing materials. Should complete loss of overlying and underlying thin layers occur then crankshaft damage could result.

Again it is known that loss of tin takes place from the lead-tin-copper overlay because of diffusion into the outermost nickel layer forming a nickel-tin intermetallic. Again, should loss of the overlay occur crankshaft damage could result due to the poor tribological property of this compound.

The invention seeks to obviate or mitigate the aforementioned disadvantages by providing an alternative to silver as an indicator of bearing damage and to provide an alternative to nickel for use in the inner and outer layers of the "sandwich".

In selection of a suitable indicator metal, the choice is limited to those not already present in the engine, for obvious reasons, and to those that may be electrodeposited readily but with poor throwing power. Throwing power is a term well know to those versed in the art and relates the thickness of electrodeposits on the back and front of articles, when facing an anode, to the primary current distribution on these surfaces.

A metal solution with poor covering power is also desirable such that the tendency to plate on the reverse side of articles is much reduced.

The invention provides therefore a multi-layer bearing material including at least two layers of cobalt and at least one layer of antimony therebetween.

Preferably the bearing comprises a backing or support layer, a first layer of a bearing metal or bearing alloy, a sandwich of metal layers comprising a layer of cobalt, a layer of antimony, a further layer of cobalt and an overlay of bearing metal or alloy.

It was found however than when electrodepositing antimony on to the first layer of cobalt, poor adhesion resulted and again when electrodepositing the final cobalt layer on to the antimony to form a "sandwich", poor adhesion between these two layers again resulted. By the use of suitable etchants adhesion was improved but an indeterminate amount of metal was removed during the etching process rendering the provision of accurately defined layer thickness difficult to achieve. It was established that by electrodepositing a thin layer of lead on to the first cobalt layer, good adhesion of antimony to the thin lead layer is achieved. Similarly, by electrodepositing another thin layer of lead on to the antimony, good adhesion of the final cobalt layer to this second lead layer is obtained.

A lead-indium overlay may be applied by electrodepositing a relativeiy thick layer of lead followed by a layer of indium, but it is desirable to heat the finished bearing to around 1 40 C by a suitable means in order to bring about diffusion of the indium into the lead. During this process the underlying cobalt acts as an effective diffusion barrier preventing loss of indium from the overlay into the thin layer of lead beneath the cobalt. It has also been found that during the diffusion process some diffusion occurs between the antimony and the thin lead layers adjacent but only until the solid solubility of lead in antimony is reached, further diffusion being prevented by the cobalt layers on either side of the lead. The net result is that there is always an intact layer of antimony present to act as an indicator of bearing damage.

Desirably the sandwich comprises a layer of cobalt, a layer of lead, a layer of antimony, a further layer of lead and a further layer of cobalt. The backing layer is preferably of steel, the first layer of bearing material is preferably of lead-bronze and the overlay is preferably of leadindium alloy. An overlay of lead-tin-copper is also effective.

The invention also provides methods of making the bearing material set out in the preceding paragraphs.

Preferably the bearing material is made by providing a lead-bronze layer on a steel backing layer for example by coating or sintering and then electrodepositing the remaining layers in sequence.

Antimony may be readily electrodeposited from a number of solutions and this metal is not ordinarily present in engines. Furthermore it may be plated from a solution with low throwing and covering power so that it may easily be prevented by conventional means from depositing on the steel backs of bearing liners.

An embodiment of invention will now be described by way of example and with reference to the accompanying drawings; in which: Figure 1 is a cross-sectional view through a bearing material according to the invention, and Figure 2 is a graph showing certain tribological properties of cobalt and nickel.

The bearing liner shown in Fig. 1 comprises a steel backing layer 10 with a lead-bronze layer 1 2 cast thereon, the surface of the latter being machined prior to electrodepositing the following layers: Layer 14 0.000005" electrodeposited cobalt Layer 1 6 0.000025" electrodeposited lead Layer 18 0.0001" electrodeposited antimony Layer 20 0.000025" electrodeposited lead Layer 22 0.00005" electrodeposited cobalt Layer 24 0.00075"/ 0.00085" electrodeposited lead-indium The finished bearing was diffused for 1 > hours at 140"C. (Fig. 1 is not shown to scale).

By research it has been found that cobalt has superior tribological properties to nickel, as shown in Fig. 2, which shows the relationship between coefficient of friction and sliding speed for cobalt and nickel respectively. The experimental data was obtained in a Denison pin and disc machine for 3/16" diameter copper pins plated with cobalt and nickel respectively, the disc being steel. The lubricant was SAE 10W DEF-2101-D at 100-110"C with a load of 20 kg.

Cobalt also has the distinct advantage that it does not form compounds with constituents of lead-bronze or with those of the outer-bearing layer such as lead-tin-copper. It has also been found that cobalt does not form compounds with indium so that if a lead-indium bearing overlay is finally applied, no loss of indium occurs from the lead-indium overlay by diffusion into an underlying cobalt layer. Furthermore we have found that the wear properties of cobalt are superior to those of nickel, as shown in Table 1 the test conditions being as follows: "FIAT" WEAR TEST RIG Lubricating Oil Shell 20W/50 Disc Finish 5 microinch (max) Test Duration 1 5+ Hours Light Arm Test consists of a loaded arm applying a load to a rotating disc rubbing on the specimen.

The specimen weight loss for cobalt and disc weight loss are both considerably less than for nickel.

TABLE 1 Cobalt Max Specimen Wear Disc Test Wt. Loss inches metres Wt. Loss No. kgX10-7 X 10-4 10-7 kgX10-7 298A 4 8 203 11 300A 2 1 25 +8 302A 6 2 51 +2 304A +2 1 25 +7 310A +4 3 76 +4 313A +2 2 51 0 AV 0.7 2.8 71 +1.7 Nickel Max Specimen Wear Disc Test Wt. Loss inches metres Wt. Loss No. kgX 10-7 X 10-4 kgX10-7 299A 19 3 76 23 301A 5 2 51 0 303A +16 5 127 +13 307A 16 2 51 12 311A 13 2 51 16 314A 4 3 76 28 6.8 2.8 71 11.0

Claims (16)

1. A bearing material including at least two layers of cobalt and at least one layer of antimony therebetween.

2. A bearing material as claimed in claim 1 comprising a layer of lead between at least one of the cobalt layers and the antimony layer.

3. A bearing material as claimed in claim 1 or claim 2 comprising a layer of bearing metal or alloy on at least one of the cobalt layers.

4. A bearing material as claimed in claim 3 in which at least one layer of bearing metal or alloy is of lead-indium alloy.

5. A bearing material as claimed in claim 3 or claim 4 in which at least one layer of bearing metal or alloy is of lead-tin-copper alloy.

6. A bearing material as claimed in any one of claims 3 to 5 in which at least one layer of bearing metal or alloy is of lead-bronze alloy.

7. A bearing material as claimed in claim 1 in which the following layers are present in the following sequence: (a) Backing support (b) Bearing metal or alloy (c) Cobalt layer (d) Lead layer (e) Antimony layer (f) Lead layer (g) Cobalt layer (h) Bearing metal or alloy

8. A method of making the bearing material claimed in claim 1 comprising the steps of depositing on a layer of bearing metal or metal alloy backed by a support, the following layers; cobalt, antimony, cobalt, and further bearing metal or alloy.

9. A method of making the bearing material claimed in claim 7 comprising the steps of depositing on a layer of bearing metal or alloy backed by a support, the following layers; cobalt, lead, antimony, lead, cobalt and further bearing metal or alloy.

1 0. A method as claimed in claim 8 or claim 9 in which the further bearing metal or alloy is a lead-indium alloy.

11. A method as claimed in claim 8 or claim 9 in which the further bearing metal or alloy is provided by electrodepositing a layer of lead followed by a layer of indium, the material then being heated in order to bring about diffusion of the indium into the lead.

1 2. A method as claimed in claim 8 or claim 9 in which the further bearing metal or alloy is a lead-tin-copper alloy.

1 3. A method as claimed in any of claims 8 to 1 2 in which the layer of bearing material is lead-bronze.

14. A method as claimed in any of claims 8 to 1 3 in which at least one layer is electrodeposited on the preceding layer.

1 5. A method of making a bearing material substantially as hereinbefore described with reference to the accompanying drawings.

16. A bearing material substantially as hereinbefore described with reference to the accompanying drawings.