Bearings

Abstract: Bearings and a method of manufacture thereof are described, the method comprising the steps of forming a half bearing of a desired size from a leaded bronze alloy (14) having a strong backing material (12), indenting (26) the bore surface (24) of the leaded bronze alloy, depositing a layer (28) of a lead-based overlay material onto the indented bore surface, depositing a layer of indium (30) onto the lead-based overlay material surface and heat treating to diffuse the indium at least into the lead-based overlay material.

Description: The present invention relates to bearings having a strong backing material such as steel, a layer of a lead containing copper-based bearing alloy bonded to the backing and a layer of a soft, indium containing lead based overlay alloy on the bearing alloy. US-A-4,400,099 describes a bearing having a surface provided with a continuous helical groove which is filled with a soft overlay material. The resulting composite surface consists of bands of a harder bearing material alternating with bands of a softer overlay material which provides a capacity for dirt embeddability. The described bearing, however, also has a hard interlayer of, for example, a nickel-based material interposed between the bearing material and the overlay. There is some evidence to suggest that this interlayer increases the possibility of seizure on being exposed due to overlay wear. In the bearing described the edges of the interlayer are continuously exposed because of the geometrical constitution of the bearing. In US-A-4,718,155 a randomly indented surface is described, the surface being overlay plated and machined to provide a uniform running surface. This bearing again has a harder interlayer of, for example, nickel but owing to the randomly indented surface, exposure, as a result of overlay wear, produces a discontinuous, randomly shaped area of interlayer which has been found to be superior to other known bearings. It is, however, considered by the present applicants that complete omission of the interlayer is a desirable objective, especially in highly loaded bearings. According to a first aspect of the present invention a method of making a sliding bearing comprises the steps of forming a half bearing of a desired size from a leaded bronze alloy having a strong backing material, indenting the bore surface of the leaded bronze alloy, depositing a layer of a lead-based overlay material onto the indented bore surface, depositing a layer of indium onto the lead-based overlay material surface and heat treating to diffuse the indium at least into the lead-based overlay material. The leaded-bronze bearing substrate alloy may be chosen from the class of copper based alloys generally comprising from 0.5 to 10wt% of tin and from 10 to 35 wt% of lead. The leaded-bronze substrate alloy may be either sintered or cast. The strong backing material may be steel, for example. The surface of the leaded bronze substrate alloy may be indented by any known methods, such methods including, for example, shot peening, indenting by knurling , machining of pits or grooves. The depth of the indentations may lie in the range 0.010 - 0.25 mm. The overlay alloy is formed preferably by first electro-depositing a layer of a lead-based material, such as substantially pure lead onto the indented surface, machining, which may include any suitable method such as turning or broaching, to a desired bore size, electro-depositing a thin layer of indium onto the lead-based material and then heat treating to diffuse the indium into at least the lead based overlay material. Where the bore is machined or broached prior to deposition of the indium layer the final depth of the indentations may be substantially less than originally applied. It is possible to deposit the indium layer prior to machining of the lead layer, the bearing is then heat treated to diffuse the indium into the overlay which is finally machined back to the desired bore size. It is felt, however, that whilst this is perfectly feasible and a practical technical option it is nevertheless economically undesirable in that it is wasteful of the expensive element, indium. An advantage of the bearing of the present invention is where the indium is not only diffused into the overlay material to enhance corrosion resistance but also into the leaded bronze including the lead phase lying adjacent the surface. Therefore, even when the overlay is worn through, exposing the underlying leaded bronze, corrosion of the lead phase is controlled by the presence of indium in the lead pools adjacent the surface. A tribologically beneficial copper indium intermetallic is also formed in the bronze matrix adjacent the surface. According to a second aspect of the present invention there is provided a sliding bearing when made by the first aspect. In order that the present invention may be more fully understood, examples will now be described by way of illustration only with reference to the accompanying drawings, of which: Figure 1 shows a schematic section through a bearing having a lining with an overlay produced by the method of the present invention; Figures 2(a) to 2(f) show the detail 'A' of the lining of Figure 1 and the steps to produce the overlay; Figures 3(a) and 3(b) show an alternative overlay embodiment to Figures 2(a) to 2(f); and Figure 4 which shows a schematic diagram of a bearing having indentations applied to the bore. Referring now to Figure 1, and Figures 2(a) to 2(f) and where the same features have common reference numerals. A section of a bearing is shown generally at 10. The bearing comprises a steel backing 12 and a lining 14 of a leaded bronze bearing alloy having an overlay 16. A portion of the lining 14 and overlay 16 is shown in the detail box 'A'. The steps to produce the overlay 16 are depicted in Figures 2(a) to 2(f) and which show the portion in the box 'A' in various stages of processing. The leaded bronze alloy comprises a bronze matrix 20 having lead pools 22 therein. The first stage of processing is to produce a smooth bore surface 24 wherein some of the lead pools 22 intersect the surface 24 (Figure 2(a)). The surface 24 is then provided with indentations 26, in this instance, by knurling (Figure 2 (b)). The knurled surface is then electro-plated with a lead overlay coating 28 (Figure 2(c)) which is then broached back to a desired bore dimension to leave a surface comprising the original lead pools 22 intersecting the surface, indentations 26 filled with lead overlay 28 and bronze matrix alloy 20 (Figure 2(d)). A thin surface layer 30 of indium is then applied by electro deposition (Figure 2(e)), the indium coated bearing then being heat treated for 1 hour at 140°C to diffuse the indium into the surface to form a lead indium overlay alloy 32 and also form an intermetallic 34 with the indium (Figure 2(f)). Figures 3(a) and 3(b) show an alternative overlay where after deposition of the lead overlay coating 28 the bearing is broached back to leave a continuous lead layer 36 over the entire surface. After deposition of an indium layer (not shown) and subsequent diffusion heat treatment there is formed a lead-indium alloy 38 over the entire surface (Figure 3(b)). Figure 4 shows schematically a pair of bearings 40 about to have a knurled finish applied to the bore 42. The bearings 40 are held in a clamping arrangement 44 mounted on a lathe faceplate 46 for rotation. A knurling tool 48 is mounted on a radially and axially moveable arm 50. A knurled surface is formed on the bore 42 which is then provided with an overlay as described with regard to the preceding figures. In some circumstances it may be desirable to lightly machine the knurled surface prior to overlay deposition.

Claims: A method of making a sliding bearing, the method being characterised by comprising the steps of forming a half bearing of a desired size from a leaded bronze alloy (14) having a strong backing material (12), indenting (26) the bore surface (24) of the leaded bronze alloy, depositing a layer (28) of a lead-based overlay material onto the indented bore surface, depositing a layer (30) of indium onto the lead-based overlay material surface and heat treating to diffuse the indium at least into the lead-based overlay material. A method according to claim 1 characterised in that the leaded bronze alloy contains from 0.5 to 10 wt% of tin and from 10 to 35 wt% of lead. A method according to either claim 1 or claim 2 characterised in that the indentation depth lies in the range from 0.01 to 0.25 mm. A method according to any one preceding claim characterised in that the surface of the lead-based overlay material is machined prior to deposition of the indium layer. A method according to any one preceding claim from 1 to 3 characterised in that the overlay is machined after heat treatment to diffuse the indium into the lead based material. A method according to any one preceding claim characterised in that the final bearing surface comprises a mixture of areas of lead based overlay (32) and leaded bronze (34) having indium diffused thereinto. A method according to any one preceding claim from 1 to 5 characterised in that the final bearing surface comprises a continuous lead based overlay phase (38) having indium diffused thereinto. A bearing characterised by being made by the method of any one of preceding claims 1 to 7.

Inventors: GREEN DONALD, GREEN, DONALD
Applicants: VANDERVELL LTD, VANDERVELL LIMITED
Application year: 1990
Main classification: F16C33
IPC codes: C23C26, F16C33, B23K9, C22C9