WO1997030845A1

WO1997030845A1 - Bearing materials

Info

Publication number: WO1997030845A1
Application number: PCT/GB1997/000272
Authority: WO
Inventors: William Peter Brown
Original assignee: Glacier Vandervell Limited
Priority date: 1996-02-21
Filing date: 1997-01-31
Publication date: 1997-08-28
Also published as: GB9603617D0

Abstract

Aluminium bearing alloy is roll bonded to a steel backing using an intermediate layer of aluminium containing a minor proportion of preferably 0.1 to 8 % by weight of copper.

Description

BEARING MATERIALS

This invention relates to aluminium alloy bearing materials and to bearings made therefrom. In particular it is concerned with aluminium alloy bearings bonded to a steel backing which serves to support and strengthen the aluminium alloy component.

Aluminium bearing alloys are well-known, for example from GB-A-1069143. Manufacture generally features the steps of forming the aluminium component by casting a billet which is rolled down to a relatively thin strip which is in turn roll bonded onto a steel backing strip. Developing appropriate bearing properties in the resultant bimetal strip often requires one or more heat treatments, including annealing and treatments aimed at developing or improving the metallurgical structure of the aluminium alloy component. These are followed by shaping and machining operations to produce a finished bearing.

Where as is usual, the aluminium alloy includes a relatively low melting component such as a minor proportion of tin, there is a risk that heat treatment will seriously damage the interface bond between the steel backing and the aluminium alloy. Tin wets steel fairly readily and can therefore wick along the interface, resulting in reduced bond strength or even separation. For this reason, it is common practice to adopt one of two expedients to counter this. Thus the steel may be plated with a metal such as nickel which has a much higher resistance to wetting, or a substantially pure aluminium interlayer may be provided at the roll bonding stage. This interlayer serves to isolate the tin component of the bearing alloy from the steel.

For example, GB-A-2,239,059 discloses the use of aluminium alloy foils with a hardness of from 40 to 70% of that of the bearing alloy.

According to the present invention, a method of making an aluminium alloy bearing material comprising an aluminium bearing alloy bonded to a steel backing layer, wherein an intermediate layer of aluminium containing a minor proportion of copper is interposed between the alloy layer and the steel layer prior to bonding them together comprises the steps of producing a desired alloy composition in suitable form, bonding the alloy to a steel backing, raising the temperature of the bonded material to a temperature of at least 400°C but less than 525°C and wherein the aggregate time to heat temperature and the dwell time at temperature lies within the range from 240 minutes to 60 seconds and subsequently cooling said bonded material at a cooling rate of at least 50°C/minute for at least part of the temperature drop to ambient temperature.

This has the effect of causing the copper to form a supersaturated solution at room temperature in the aluminium intermediate layer, thereby indirectly strengthening the interlayer.

It has been found that by including at least enough copper, and optionally also silicon, to be capable of forming a supersaturated solution in the aluminium at room temperature, subsequent heat treatments aimed at developing good bearing properties in the bearing alloy itself can also be used to develop strength in the otherwise relatively weak aluminium interlayer. It is also observed that with a foil containing copper and possibly also silicon, that during heat treatments these elements are not lost from the bearing alloy to the foil by diffusion. Such a loss would lead to a reduction in the effectiveness of the solution treatment on the strength of the bearing alloy. Significant improvements in the overall strength of the composite bearing material may be achieved, without any other modification of the alloy or of the normal manufacturing process.

In order that the invention be better understood a preferred embodiment of it will now be described by way of example.

Firstly, a comparative sample was made by the route set out in EP-A-0205893. An alloy having the composition Al-Snl2 - Si4-Cul was continuously cast into billet form of 25mm thickness. The billets were homogenised by annealing at 490°C, for 16 hours. This was followed by machining them to a thickness of 19mm and subsequent rolling in several passes to 7.6mm thickness. A final annealing treatment was applied to relieve stresses due to the rolling operations. The strip was then roll bonded under pressure to a 0.8mm thick strip of aluminium foil, which was applied to only one side of the alloy strip. The clad composite strip was further rolled down, to a thickness of 0.89mm; the foil clad face was cleaned, roughened by abrasion and then roll bonded under pressure to a steel strip 2.5mm thick. The roll bonded bimetal product had a steel backing l.5mm thick with an alloy/foil lining layer of total thickness θ./5mm.

At that point, the bearing alloy component exhibited a hardness of about 76Hv. It was then heat treated in an air circulating oven for 3 hours, at a temperature of 350°C. At that stage, the bearing alloy hardness was about 37Hv. The heat treated strip was subjected to a further heat treatment comprising rapidly heating in a fluidised bed, to 475°C for a total time of 160 seconds. The strip took about 40 seconds to attain 420°C and the remaining 120 seconds was constituted by heating from 420°C to 475^βC, with a brief dwell time at 475°C. The heated strip was then cooled at a rate of about 150°C/minute. The surface hardness of the alloy was approximately 47Hv (Example 1) . Exactly the same procedures were then followed using as an interlayer, an aluminium foil containing 1% by weight of copper and one containing 4% by weight of silicon and 1% by weight of copper. The surface hardness of the alloy after the fluidised bed/cooling treatment was approximately 47Hv (Example 2) .

Samples of the materials were made into bearings and fatigue tested using a standard test rig under the following conditions.

1. Shaft speed 2800 rev/minute,

2. Initial load 90 MPa,

3. Load increased after 20 hours at each load level, by 7MPa, until failure point reached,

4. Oil temperature 80^βC. XA£LE_l

Microhardness measurements were made on samples of finished bearings at distances separated by 25μm from the surface of the bearing through the bonding foil to the steel. The results are shown in Table 2.

SEE SEPARATE TABLE: REF SPEC-JAC\CHART.594 It can be seen from the foregoing that the aluminium alloy bearing material of the present invention was stronger and more uniform in properties than a corresponding bearing material using pure aluminium as an interlayer between the alloy and the steel backing.

Claims

1. A method of making an aluminium alloy bearing material comprising an aluminium bearing alloy bonded to a steel backing layer, wherein an intermediate later of aluminium containing a minor proportion of copper is interposed between the alloy layer and the steel layer prior to bonding them together, comprising the steps of producing a desired alloy composition in suitable form, bonding the alloy to a steel backing, raising the temperature of the bonded material to a temperature of at least 400°C but less than 525° and wherein the aggregate time to heat temperature and the dwell time at temperature lies within the range from

240 minutes to 60 seconds and subsequently cooling said bonded material at a cooling rate of at least 50°C/minute for at least part of the temperature drop to ambient temperature

2. A method according to claim 1 in which the aluminium alloy contains copper and silicon in minor proportions, the balance being aluminium.

3. A method according to claim 1 or claim 2 wherein the intermediate layer contains at least enough copper to form a supersaturated solution at room temperature.

4. A method according to claim 1 or claim 2 wherein the intermediate layer contains from 0.1 to 8% by weight of copper.

5. A method according to any preceding claim wherein the intermediate layer contains from 0.5 to 5% by weight of copper.

6. A method according to any of claims 2-5 wherein the intermediate layer contains from 0.1 to 10% by weight of silicon.

7. A method according to any of claims 2-5 wherein the intermediate layer contains from 1.5 to 5% by weight of silicon.

8. A method according to claim 6 wherein said intermediate layer is bonded to the aluminium alloy strip prior to bonding the latter to the steel backing.

9. A method of making an aluminium alloy method bonded to a steel backing substantially as described with reference to Examples 2 and 3.