GB2238089A

GB2238089A - Method of producing a plain bearing

Info

Publication number: GB2238089A
Application number: GB9019028A
Authority: GB
Inventors: Tadashi Tanaka; Masaaki Sakamoto; Hideyuki Kidokoro
Original assignee: Daido Metal Co Ltd
Current assignee: Daido Metal Co Ltd
Priority date: 1989-09-28
Filing date: 1990-08-31
Publication date: 1991-05-22
Anticipated expiration: 2010-08-31
Also published as: KR910006513A; DE4027362A1; GB9019028D0; JPH03115560A; GB2238089B

Abstract

A method of producing a plain bearing having an alloy surface layer comprises placing a bearing component (1) in a vacuum chamber (7) filled with low pressure argon, bombarding it with argon ions to remove any oxide or other unwanted surface material, then heating the component and depositing an alloy layer on it by sputtering. The bearing component may be of Cu/Pb/Sn alloy or Al/Si/Zn alloy, and the surface layer may be of Pb/Sn/In alloy or Pb/Sn alloy respectively. <IMAGE>

Description

W is :2 a c) a ':3 1 COMPOSITE BEARINGS The invention relates to a method

of producing a composite bearing, for example a split bearing for use in an internal combustion engine, having an alloy surface layer or layer of alloy plating. In particular, the invention relates to an improved method for depositing an alloy surface layer or layer of alloy plating onto a plain bearing component having a surface of a different alloy.

Plain or sliding bearings frequently comprise a base material with a layer of bearing alloy on top. The bearing alloy is then coated or plated with a surface layer of another alloy. The surface layer may be deposited on the surface of the bearing alloy layer by electroplating or directly, by sputtering.

The conventional method of producing the surface layer by electroplating involves a huge amount of expenditure on water drainage and also requires strict liquid control. The process also involves complicated process steps. Furthermore, a problem arises in the case where a surface layer made of an alloy containing idium is to be provided by electroplating, since direct electroplating of such an alloy is impossible. In such cases it has been common practice to electroplate the bearing alloy surface with lead alloy first, and then further electroplate the lead alloy layer with indium alloy or indium. Thermal treatment would then be used to diffuse the indium into the other components and ensure even distribution of the components.

1 X 2 is Another possible method is to use sputtering, however the following problem arises with this method. over a period of time, the surface of the bearing alloy layer deteriorates to form a layer having modified properties, and furthermore an oxide layer also forms. Conventionally, the alloy surface layer has been provided directly by sputtering without removing the unwanted material which has built-up over the passage of time on the bearing alloy layer. Therefore, the bonding strength between the bearing alloy layer and the surface layer has been low, resulting in a tendency for the surface layer to exfoliate or detach. In addition, the sputtering method is not suitable for mass-production.

An object of the invention is thus to provide a method of producing a plain or sliding bearing, having a surface layer, which alleviates the above and other problems associated with the conventional techniques.

According to the present invention there is provided a method of producing a composite bearing comprising bombarding the surface of a bearing material with ions, heating the bearing material, and forming a surface layer on the said surface by vapour deposition. The invention also extends to a bearing when prepared by the method of the invention.

The ion bombardment is normally carried out in a vacuum chamber in at least a partial vacuum until all or substantially all of any oxide or deteriorated surface layer on the bearing component surface has been removed from the surface under the action of the ion bombardment. The surface of the bearing component is thereby cleaned and prepared to receive the layer of second alloy, resulting in the second alloy layer being i i i i 3 bonded to the surface much more effectively.

Preferably, the heating of the bearing component is carried out until the bearing component or at least the surface of the bearing component becomes activated. Thereby a bond of even greater strength is achieved between the surface layer and the surface of the component.

Preferably a diffusion-preventing layer of copper or nickel or copper or nickel alloy is deposited between the bearing component surface and the surface layer of first alloy.

It will be appreciated that the bearing component surface is normally provided by a layer of bearing alloy material on a base of some other material.

A problem with the conventional sputtering, or PVD method, is that the adhesion between the surface layer and the bearing component is poor. The bearing alloy layer of the bearing component is covered by an oxide film and/or a surface layer having modified properties.

Since aluminium alloy in particular is normally covered by a chemically inert and tough oxide film, the bonding or adhesion of the surface layer deposited by the PVD method onto the aluminium bearing alloy layer is impaired. In order to eliminate the oxide film and deteriorated surface layer, therefore, in the method of the invention a voltage may be applied to the bearing component, with the component used as a cathode, in an atmosphere preferably of argon, thereby causing cations to bombard the surface of the bearing alloy. This bombarding energy eliminates the oxide film and the deteriorated, or modified surface layer. Thereafter, a thin alloy film or surface layer is provided on the bearing alloy surface by the PVD (physical vapour 4 deposition) method. Thereby, a method of achieving a high bonding strength. In addition, heating the plain, or sliding bearing material in an evacuated chamber increases the energy available for reaction between the sliding bearing alloy and the alloy surface layer, to accelerate the alloying between the two. This makes it possible to obtain higher bonding or adhesion therebetween and in addition enhances the bonding between the grains of the surface layer alloy to obtain a layer of greater strength and durability.

The thickness of the surface layer is normally at least 3 microns in order to prevent seizure occurring when partial collision occurs between a shaft and the bearing. The maximum thickness is normally 60 microns for the sake of mechanical strength and economy.

Provision of a 0.1 to 5 micron diffusionpreventing layer of Nickel or Copper or alloys thereof between the bearing alloy layer and the surface layer by the PVD method or by electroplating, is often desirable. This serves not only to prevent indium or tin, when such elements are used, from diffusing from the surface layer onto the bearing alloy layer, but also to improve the corrosion resistance and thereby enhance the performance of the sliding bearing.

Figure 1 shows an exemplary apparatus for carrying out the method of the present invention.

The following procedure was carried out using plain bearings with bearing alloy layers consisting of the alloys shown in Table 1 and bearing surface layer components, or surface plating components as shown in Table 1. A magnetron sputtering device was used.

Referring to the Figure, a half bearing member 1, i.e. one half of a plain or sliding split bearing, 1 comprising a base material and a layer of bearing alloy, was mounted on a rotary member 6 and put into a vacuum chamber 7 which was then evacuated to 1.3 X 10-3 Pa (10-5 Torr). Then, argon gas was introduced and the vacuum in the chamber was maintained at 1.3 Pa to 0.13 Pa (10-2 to 10-3 Torr). Next, using the half bearing member 1 as a cathode, a potential of 500 V was applied between the half bearing and an anode 3 to cause a glow discharge. The half bearing 1 was thereby bombarded with positively charged argon ions, and this was continued until the surface oxide film and modified or deteriorated surface of the bearing alloy layer was removed. Thereafter, the chamber was again evacuated in order to clean the interior.

Argon gas was re-introduced into the vacuum chamber and the chamber maintained at 1.3 to 0.13 Pa (10-2 to 10-3 Torr). A target 2 was then prepared, by bonding to it a cast plate containing components to be deposited as a surface layer on the bearing alloy layer of the half bearing.

A potential of 800 V was applied between this target as a cathode and the anode 3 to cause a glow discharge. The target 2 was thereby bombarded with positively charged argon ions, to free particles from the surface of the target. The half bearing was arranged in line with the target to receive any particles being emitted from it, which were then deposited onto the inner surface of the half bearing. The target was subjected to a magnetic field provided by a magnet 4 to encourage efficient vacuum evaporation of the bearing surface layer components from the target. Furthermore, the half bearing member 1 was rotated on the rotary member 6 while being heated to k 6 2000C by a heater 5. The evaporation was effected after the member 1 had been heated so as to increase the energy of reaction between the bearing alloy and the surface layer components thereby to accelerate alloying between them. Consequently, a higher level of adhesion was obtained between the bearing alloy layer and the surface layer and in addition the bonding between the particles of the surface layer alloy was improved, whereby a strong, durable surface layer was produced.

As shown in Table 1, experiments were performed with and without argon bombarding and heating prior to sputtering, in order to compare the properties of bearings produced by different production methods. Furthermore, the properties of bearings produced by the present method were compared with those of bearings produced by the electroplating method.

Tests were then conducted on half bearings produced by the above methods, to determine the strength of the bond between the bearing alloy layer and surface layer. The results of these bonding tests are shown in Table 2. The bonding tests were conducted as follows. After a half bearing to be tested had been forcibly made flat, the tip of a circular cross-section bar (10 mm in diameter) was bonded to the surface layers of opposed faces of the test piece, using epoxy resin. Then, the bars were pulled apart axially on a tensile testing machine and the breaking load was measured.

The measured value was divided by the crosssectional area of the bar to determine a figure for the bonding strength or adhesion strength. As apparent from Table 2, the adhesion strength is improved over I.

0 7 that achieved with conventional PVD. In the case of an aluminium bearing alloy where a strong aluminium oxide f ilm is removed in the method of the invention, the adhesion strength is greatly improved over the conventional sputtering method. Also, by heating the half bearings, the adhesion strength is further increased. Particularly in the case of a copper alloy, copper/tin compounds form from reaction between the bearing alloy and the tin component of the surface layer at the interface between layers, thereby greatly increasing the adhesion strength.

The usual sputtering method is indeed inferior to the electroplating method in terms of adhesion strength. By using the method according to the invention, however, it is possible to achieve adhesion strength equivalent to that achievable with the electroplating method.

Next, tests were performed using a seizure machine and the results of these are shown in Table 3.

The test conditions were to apply a cumulative load in increments of 50 kgf/cm2 to a test piece rotating at a circumferential velocity of 10 m per second, to determine the surface pressure at which seizure occurred. Each successive load was applied for 10 minutes.

As shown in Table 3, bearings made using the usual sputtering method exhibited results inferior to those exhibited by bearings made using the electroplating method. Application of a large load to the surface layer whilst it is rotating at high speed produces high temperatures and a large shearing load at the surface layer. The poor adhesion strength exhibited by bearings produced by the conventional sputtering method I.- 8 resulted in early exfoliation, or detachment of the surface layer, resulting in seizure.

On the other hand, the bearings produced according to the method of the invention had improved adhesion strength and could tolerate a much greater load before seizure occurred. Furthermore, these bearings exhibited adhesion strength which compared favourably with that of bearings produced by the electroplating method.

The above tests were carried out on half bearings. However, this is only illustrative and the invention equally applies to the production of other types of bearing member such as, for example, thrust washers and so forth.

k 1 n Table 1

Production Surface Layer Bearing Alloy Heating of No. Method Components (Wtg.) Bombarding Bearing (Wto.) 1 Method of Pb-7Sn-5In Cu-23Pb-3Sn performed performed Invention Conventional 2 Sputtering Pb-7Sn-SIn Cu-23Pb-3Sn not performed not performed Method 3 Electroplating Pb-7Sn-5In Cu-23Pb-3Sn Method 4 Method of Pb-10Sn A1-5Si-4Zn performed performed Invention Conventional Sputtering Pb-10Sn Al5Si-4Zn not performed not performed Method 6 Electroplating Pb-10Sn A1-5Si-4Zn Method ill k ---Q k k, /D - Table 2

No. Bonding Strength No. Bonding Strength (kgf/iT'm 2 (kgf/mm 2 1 2 or more 4 2 or more 2 0.6 5 0.4 3 2 or more 6 2 or more The mark () indicates that breakage occurred at the portion of bonding.

Table 3

Seizure Load 11,11 (!-"jf ",C-,n 2) i i200 1 1250 2 900 1200 1 i 5; 0 Lo d Seizure a 1 (kaflem 1 7 1000 i As has been described above, the PVD or sputter. method is used to produce a sur4i-ace layer on plain, or sliding bearings. The PVD method does not reauire a drainage facility as in the case of the electroplating method and has the further advantacre that it is possible automatically to control the steps of the PVD method, so that it may be possible to arrange for the I production of bearings without an operator. Further, the bearing surface layer components can be deposited onto the inner surf ace of the bearing by PVD and no further treatment is then required. The components of the surface layer are prepared in the form of a target plate by casting, or if casting is difficult, by sintering or composite-bonding the components together. Thus the thermal treatment step, necessary with the electroplating method in order to diffuse the components of the two layers, is eliminated.

In addition, the described method not only uses argon bombardment to remove deteriorated alloy oxide film and dirt at the bonding interface, but also accelerates alloying at the bonding interface by heating, thereby improving adhesion. The problem of mass production using the PVD method is therefore solved, and bearings produced by the method of the invention have excellent anti-seizure properties.

5.

Claims

CLAIMS.

2.

A method of producing a composite bearing comprising bombarding the surface of a bearing material with ions, heating the bearing material, and forming a surface layer on the said surface by vapour deposition.

A method as claimed in claim 1 in which the bombarding, heating and forming are all carried out in at least a partial vacuum.

3. A method as claimed in claim 1 or claim 2 in which the ions are argon ions.

4.

A method as claimed in any one of the preceding claims in which the ion bombardment removes at least part of both an oxide f ilm and a modif ied surface layer of the bearing material.

A method as claimed in any one of the preceding claims in which the bearing material is heated to 2000C.

6. A method as claimed in any one of the preceding claims including depositing an intermediate layer of nickel or copper-based alloy between the bearing material and the surface layer.

A method as claimed in any one of the preceding claims in which the surface layer is deposited to a thickness of between 3 and 60 micrometres.

c 1 1 8. A method of producing a composite bearing substantially as specifically herein described with reference to figure I and/or with reference to items 1 and 4 of table 1.

9. A composite bearing when produced as claimed any one of the preceding claims.

Published 1991 at The Patent Office. State House. 66/71 High Holbom. London WC1 R 41T- Further copies may be obtained from Sales Branch, Unit 6. Nine Mile Point Cwnifelinfach, Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd, St Majy Cray. Kent.