GB2271780A

GB2271780A - Process for producing sliding bearing

Info

Publication number: GB2271780A
Application number: GB9322459A
Authority: GB
Inventors: Motomu Wada; Hideo Ishikawa; Yoshikazu Fujisawa; Makoto Tsuji; Tadashi Tanaka
Original assignee: Honda Motor Co Ltd; Daido Metal Co Ltd
Current assignee: Honda Motor Co Ltd; Daido Metal Co Ltd
Priority date: 1992-02-28
Filing date: 1993-03-01
Publication date: 1994-04-27
Anticipated expiration: 2013-03-01
Also published as: JPH05239690A; WO1993017154A1; GB2271780B; GB9322459D0; DE4390686T1; JPH07122158B2; DE4390686C2

Abstract

A process for producing a sliding bearing which is provided with a lead alloy overlay and excellent in fatigue resistance, said process comprising the steps of forming on a bearing metal layer a substrate layer formed of either lead or a lead alloy and containing a number of pyramidal crystal grains with the apexes facing toward the mating member, coating the surface of the substrate layer with a diffusing metal, and forming a lead alloy overlay having on the surface thereof a number of deformed pyramidal crystal grains having rounded apexes and edges by diffusing the diffusing metal into the pyramidal crystal grains through heat treatment.

Description

SPECIFICATION TITLE OF THE INVENTION PROCESS FOR PRODUCING SLIDE BEARING FIELD OF THE INVENTION The present invention relates to a process for producing a slide bearing, e.g., a slide bearing for an internal combustion engine used in an automobile, a ship, a building machine or the like.

PRIOR ART In general, a slide bearing for an internal combustion engine is produced by a process which includes the steps of: processing, into a semi-cylindrical shape, a laminated plate having a bearing alloy layer made of Cu alloy, Al alloy or the like, which is bonded on a backing made of steel, and forming a Pb-alloy overlay on the bearing alloy layer.

The main functions of the Pb-alloy overlay include an enhancing of a conforming property of the bearing with a shaft to be supported such as a crankshaft, a confining of foreign matters incorporated into a lubricating oil, an enhancing of the corrosion resistance to an organic acid produced as a result of deterioration of the lubricating oil. In order to improve these functions, a slide bearing has been conventionally produced and used which has a Pb-alloy overlay containing various amounts of Sn, Cu, In. etc., which are alloy elements, as disclosed in U.S. Patent No.2,605,149 and Japanese Patent Publication No.22498/64.

However, there is a tendency that the slide bearings are used under severe conditions of a high speed rotation and a high load, because of the pursuit of an increase in power in a recent automobile engine. Under such a circumstance, it is impossible to appropriately accommodate the increase in power by the process in which the constituents of the lead alloy overlay are adjusted. For this reason, it has been desired to develop a Pb-alloy overlay having excellent seizure and fatigue resistances.

Thereupon, to meet such a desire, a slide bearing has been developed which include a Pb-alloy overlay having a number of pyramidal crystal grains with an apex directed toward a slide surface. The Pb-alloy overlay has a good oil retention and hence, exhibits an excellent seizure resistance (see Japanese Patent Application Laid-open No.215696/91).

SUMMARY OF THE INVENTION The present invention has been developed under such a technical background, and it is an object of the present invention to provide a process for producing a slide bearing, wherein a slide bearing can be produced which includes a Pballoy overlay having crystal grains of the type described above, which have an improved fatigue resistance.

To achieve the above object, according to the present invention, there is provided a process for producing a slide bearing, comprising the steps of: forming, on a bearing alloy layer, a to-be-treated layer having a large number pyramidal crystal grains with their apexes directed toward a mating member and consisting of one of Pb and a Pb alloy; coating a surface of the to-be-treated layer with a diffusing metal; and diffusing the diffusing metal into the pyramidal crystal grains by a thermal treatment to form a Pb-alloy overlay which is provided on a surface thereof with a number of deformed pyramidal crystal grains with their apexes and ridge-lines rounded, the above steps being carried out successively.

With the above producing process, it is possible to easily obtain the Pb-alloy overlay which has the large number of deformed pyramidal crystal grains on the surface thereof.

Because the apex and each ridge-line of each of the deformed pyramidal crystal grains are rounded, each of the deformed pyramidal crystal grains exhibits a function of dispersing and reducing a concentrated load acting on the surface of the Pballoy overlay due to a variation in pressure of an oil membrane.

This improves the fatigue resistance of the Pb-alloy overlay.

In addition, the Pb-alloy overlay exhibits an excellent seizure resistance, because it has the good oil retention, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a plan view of a slide bearing; Fig.2 is a sectional view taken along a line II-II in Fig.1; Fig.3 is a schematic sectional view showing deformed pyramidal crystal grains on a Pb-alloy overlay; Fig.4 is a diagrammatic perspective view of the deformed pyramidal crystal grain; Fig.5 is a schematic sectional view showing pyramidal crystal grains on a layer to be treated; Fig.6 is a photomicrograph showing a crystal structure on a surface of the layer to be treated; Fig.7 is a diagrammatic perspective view of the pyramidal crystal grain; Fig.8 is a photomicrograph showing a crystal structure on a surface of the Pb-alloy overlay; Fig.9 is a photomicrograph showing a crystal structure on a surface of a layer to be treated for comparison; and Fig.10 is a graph showing results of a fatigue test.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig.1, a slide bearing 1 is used for a journal portion of a crankshaft in an engine, a large end of a connecting rod or the like. The slide bearing 1 is formed into a cylindrical shape from a combination of a pair of semicylindrical members 2 and 3. The journal portion of the crankshaft or the like is disposed in sliding contact with an inner peripheral surface of the slide bearing 1.

As shown in Fig.2, each of the semi-cylindrical members 2 and 3 is composed of a metal backing 4, a bearing alloy layer 5 and an overlay 6 made of Pb alloy (which will be referred to as Pb-alloy overlay hereinafter). The metal backing 4 is made of low carbon steel, high carbon steel, stainless steel or special steel. A thickness of the metal backing 4 is determined by a set thickness of the slide bearing. The bearing alloy layer 5 is made of Cu alloy or Al alloy used for the known bearing or the like. A thickness of the bearing alloy layer 5 is in a range of 0.05 to 0.5 mm, but is set in a range of 0.2 to 0.4 mm for the slide bearing used for a usual automobile engine.

As shown in Figs.3 and 4, the Pb-alloy overlay 6 has a number of a deformed pyramidal crystal grains c1. An apex a of each of the grains are directed toward a mating member. The apex a and each ridge-line b of the grain are rounded. Each of the ridge-line b is rounded in a direction along such ridgeline b and in a direction perpendicular to such direction.

The Pb-alloy overlay 6 contains at least one diffusing metal (an alloy element) selected from the group consisting of Sn, In, Sb, Bi, Ga, Tl and Ag in an amount from 3 % by weight (inclusive) to 30 % by weight (inclusive). If the diffusing metal content is less than 3 % by weight, the slide bearing has a lower mechanical strength, for example, a lower hardness and a lower tensile strength, and is lacking in corrosion resistance to an organic acid produced upon deterioration of a lubricating oil. On the other hand, if the diffusing metal content exceeds 30 % by weight, the slide bearing has a significantly reduced mechanical strength in a temperature range of 100 to 130 "C at which the slide bearing is used. A preferred diffusing metal content is from 5 % by weight (inclusive) to 20 % by weight (inclusive). In this case, a preferred diffusing metal is Sn, In, Sb and Bi. A thickness of the Pb-alloy overlay 6 is in a range of 5 to 50 cam, but is set in a range of 10 to 20 g m for the slide bearing used for a usual automobile engine.

A Cu-plated layer or an Ni-plated layer may be provided, if necessary, between the metal backing 4 and the bearing alloy layer 5. And a plated layer such as Ni, Ag, Cu, Co, Fe, etc., or a alloy-plated layer such as alloys of such metals may be provided, if necessary, between the bearing alloy layer 5 and the Pb-alloy overlay 6.

In producing the slide bearing 1, following steps are conducted in sequence: a step of forming a layer to be treated 7 on the bearing alloy layer 5 by a plating, which layer is made of one of Pb and a Pb alloy and has a number of pyramidal crystal grains C2 with their apexes a directed toward a mating member, as shown in Fig.5; the step of subjecting the- layer 7 to a plating treatment to coat the surface of the layer 7 with a diffusing metal; and a step of diffusing the diffusing metal into the pyramidal crystal grains c2 by a thermal treatment to form a Pb-alloy overlay 6 having, on a surface thereof, a number of deformed pyramidal crystal grains cl with their apexes a and ridge-lines b both rounded, as shown in Fig.3.

The Pb alloy forming the layer to be treated 7 includes Pb in an amount from 70 % by weight (inclusive) to 97 % by weight (inclusive) and one or more alloy elements such as Sn, Cu, etc.

in an amount from 3 % by weight (inclusive) to 30 % by weight (inclusive).

The size of the pyramidal crystal grain on the layer to be treated 7 is adjusted by a cathode current density or the like.

For example, if the cathode current density is increased, the size of the pyramidal crystal grain is increased.

The deformed pyramidal crystal grains c1 on the Pb-alloy overlay 6 has a structure in which the diffusing metal is diffused in the pyramidal crystal grain c2, and/or a structure in which the diffusing metal is diffused in the pyramidal crystal grain c2 and the surface thereof is coated with a thin layer of the diffusing metal.

[Example 1] A Cu alloy powder for a bearing was spread on a metal backing made of steel plate, and was sintered to provide a laminated plate having a bearing alloy layer which is a sinter, and the metal backing. This laminated plate was cut in a predetermined size to provide a number of cut pieces. Each of the cut pieces was subjected to a pressing to fabricate a semicylindrical member.

Each of the semi-cylindrical members was subjected successively to preliminary treatments, i.e., a usual solvent degreasing treatment, an electrolytically degreasing treatment and a pickling treatment. Then, each bearing alloy layer was subjected to a usual watt Ni-plating treatment under conditions of a bath temperature of sot and a cathode current density of 6 A/dm2 to form an Ni-plated layer having a thickness of 1.5cm.

A plurality of pairs of the Ni-plated layers were subjected to a plating treatment under conditions of a bath temperature of 10 to 35 DC and a cathode current density of 3 to 15 A/dm2 by use of a borofluoride-plating bath containing Pb2+, Sn2+ and Cu2+ adjusted in ranges of 40 to 180 g/l, 0 to 35 g/l and 0 to 5 g/l, respectively, thereby forming a to-betreated layer of Pb alloy.

Fig.6 is a photomicrograph (10,000 magnifications) showing a crystal structure on a surface of the to-be-treated layer. In Fig.6, a number of pyramidal crystal grains with their apexes directed toward a mating member are observed.

The surface of the to-be-treated layer was observed by a microscope to measure a length d of a base and a height h of the pyramidal crystal grain, as shown in Fig.7.

A plurality of pairs of the to-be-treated layers were subjected to an In-plating treatment under conditions of a bath temperature of 30"C and a cathode current density of 1 A/dm2 by use of a sulfamic acid bath containing 10 to 50 g/l of In3+ to form a diffusing metal layer of In.

Then, each of the diffusing metal layers and each of the to-be-treated layers were subjected to a thermal treatment under conditions of 150 to 200 "C and 60 to 20 minutes to diffuse In into the pyramidal crystal grains, thereby forming a Pb-alloy overlay having, on its surface, a number of deformed pyramidal crystal grains with their apexes and each ridge-line both rounded. In this manner, slide bearings of examples 1 to 3 were produced.

Fig.8 is a photomicrograph (10,000 magnifications) showing a crystal structure on a surface of the Pb-alloy overlay in Example 1. In Fig.8, a number of deformed pyramidal crystal grains are observed.

Example 2] A pair of the to-be-treated layer formed under the same conditions as in Example 1 were subjected to a plating treatment under conditions of a bath temperature of 25"C and a cathode current density of 2 A/dm2 by use of a fluoride bath containing 40 to 50 g/l of Sn2+ and 1 to 3 g/l of Sb to form a diffusing metal layer of an Sn-Sb alloy containing of 15 % by weight of tin (Sn). Then, the diffusing metal layer was subjected to, a thermal treatment under the same conditions as in Example 1 to form a Pb-alloy overlay likewise having a number of deformed pyramidal crystal grains, thus producing a slide bearing of example 4.

[Example 3] A pair of the to-be-treated layer formed under the same conditions as in Example 1 were subjected to a plating treatment under conditions of a bath temperature of 20t and a cathode current density of 1 to 5 A/dm2 by use of a perchloric acid bath containing 10 to 30 g/l of Bi2+ to form a diffusing metal layer of bismuth (Bi). Then, the diffusing metal layer was subjected to a thermal treatment under the same conditions as in Example 1 to form a Pb-alloy overlay likewise having a number of deformed pyramidal crystal grains, thus producing a slide bearing of example 5.

Table 1 shows the shape of the crystal grains on the surface of the to-be-treated surface, the material of the diffusing metal layer, the composition of the Pb-alloy overlay and the like for the slide bearings of example 1 to 4 produced according to the present invention and for slide bearings of comparative example 6 to 9.

In Table 1, the slide bearings of example 6 to 8 were produced without the formation and thermal treatment of a diffusing metal layer. Therefore, a to-be-treated layer corresponds to a Pb-alloy overlay. The slide bearing of example 9 was produced by a procedure which includes the steps of: forming a to-be-treated layer having a flat surface on an Niplated layer under a different plating condition, as shown in a photomicrograph (10,000 magnifications) in Fig.9, subjecting the to-be-treated layer to a plating treatment to form a diffusing metal layer of tin (Sn), and subjecting the latter to a thermal treatment under the same conditions as in Example 1.

Table 1

To-be-treated layer DML* Pb-alloy overlay Ex* Crystal grains Chemical constituents on surface T* MA* T* (% by weight) SC* S* L* H* Pb Sn Cu In Sb Bi 1 Pyramid 5 4 19 In 1 Balance10 1 3.5 - - DP* 2 Pyramid 8 6 18 In 2 Balance - 1 7 - - DP* 3 Pyramid 10 8 17 In 3 Balance 7 - 10 - - DP* 4 Pyramid 10 8 18 SnSb 2 Balance 10 1 - 0.3 - DP* 5 Pyramid 10 8 18 Bi 2 Balance 10 1 - - 10 DP* 6 Pyramid 5 4 20 - - Balance 10 1.5 - - - Pyramid 7 Pyramid 10 8 20 - - Balance 10 1.5 - - - Pyramid 8 Pyramid 5 4 20 - - Balance 2 0.5 - - - Pyramid 9 Flat - - 19 Sn 1 Balance 11 1.5 - - - Flat Ex* = Example S* = Shape L* = Length d ( m) H* = Height h (#m) T* = Thickness (#m) MA* = Material DP* = Deformed pyramid DML* = Diffusing metal layer SC* = Shape of crystal grain on surface Then, in order to examine the fatigue resistance of each of the slide bearings, a following fatigue test was carried out using a rotative load test machine.For the purpose of simulating the locus of a crankshaft during rotation of an automobile engine at a high speed, a running-in (breaking-in) operation was conducted for 30 minutes under a condition in which an unbalanced weight was attached to a rotary shaft and a load was applied to the entire periphery of the slide bearing.

Thereafter, the number of revolutions was stepwise increased.

After a lapse of 20 hours at each preset number of revolutions, the state of the Pb-alloy overlay was examined to determine a maximum surface pressure causing no fatigue of the lead alloy overlay. The test conditions are as follows: A material for the rotary shaft is a hardened carbon steel (JIS S55C); a diameter of the rotary shaft is of 53 mm; a bearing width of the rotary shaft is of 14.5 mm; the maximum number of revolutions is of 6,500 rpm; the maximum surface pressure is of 350 kg f/cm2; a lubricating oil used is SAE20 (a trade name); the pressure of oil supplied is of 3.0 kg f/cm2; and the temperature of the lubricating oil in an inlet is of 130"C.

Fig.10 illustrates test results for the examples 1 to 9.

As apparent from Fig.10, the slide bearings of the examples 1 to 5 produced according to the present invention have an excellent fatigue resistance, as compared with the slide bearings of the comparative examples 6 to 9.

Effect of the Invention According to the present invention, by using the specified process, as described above, a slide bearing having a Pb-alloy overlay which exhibits an excellent fatigue resistance can easily be produced under severe conditions of a high speed rotation and a high load.

Claims

WHAT IS CLAIMED IS

1. A process for producing a slide bearing, comprising the steps of forming, on a bearing alloy layer, a to-be-treated layer having a number of pyramidal crystal grains with their apexes directed toward a mating member and consisting of one of Pb and a Pb alloy; coating a surface of said to-be-treated layer with a diffusing metal; and diffusing said diffusing metal into said pyramidal crystal grains by a thermal treatment to form a Pb-alloy overlay which is provided on a surface thereof with a number of deformed pyramidal crystal grains with their apexes and ridge-lines rounded, said steps being carried out successively.

2. A process for producing a slide bearing according to claim 1, wherein said diffusing metal is at least one element selected from the group consisting of Sn, In, Sb, Bi, Ga, Tl and Ag, and the content of said diffusing metal is from 3 % by weight (inclusive) to 30 % by weight (inclusive).