GB2084609A

GB2084609A - Pb-based bearing alloy

Info

Publication number: GB2084609A
Application number: GB8128750A
Authority: GB
Original assignee: Miba Gleitlager Austria GmbH
Current assignee: Miba Gleitlager Austria GmbH
Priority date: 1980-10-02
Filing date: 1981-09-23
Publication date: 1982-04-15
Also published as: ATA490880A; AT366418B; DE3136817A1; GB2084609B; DE3136817C2

Abstract

A multilayer sliding surface bearing has an electrodeposited bearing alloy layer which consists of 15 to 20% by weight tin, 1.5 to 2.5% by weight copper, balance lead. This alloy has a high fatigue strength and a high resistance to corrosion. <IMAGE>

Description

SPECIFICATiON Multilayer sliding surface bearing having an electrodeposited bearing alloy layer This invention relates to a multilayer sliding surface bearing having an electrodeposited bearing alloy layer.

Investigations regarding the influence of the copper content of the fatigue strength of an electrodeposited bearing alloy layer which consists of lead with additions of tin and copper have shown that if the alloy has a conventional lead content of 10% by weight the bearing alloy layer has a maximum mean life if its copper content is about 3% by weight and that said mean life decreases strongly with higher and lower copper contents. In view of these investigation results, a copper content below 6% by weight preferably about 3% by weight, has been desired.

In order to increase the wear resistance and the fatigue limit, a copper content above 6% by weight and a higher tin content, preferably of 14% by weight, have been used. Owing to its higher copper content, the bearing alloy layer had a higher resistance to mechanical wear than the conventional bearing alloy layers and the expected decrease of the fatigue strength was avoided because the tin content was increased too in dependence on the increase of the copper content.

On the other hand, such alloys have the disadvantage that they have a relatively high brittleness owing to their higher copper content, and that they have only a low resistance to corrosion. For this reason said alloy is only of restricted usefulness in bearing layers of multilayer sliding surface bearings, e.g., for supercharged diesel engines. As lubricants are e,'pected to meet increasingly higher requirements more additives are included in the oil so that the bearing layer is subjected to chemical attack and to increase wear due to erosion and corrosion.

Owing to its high copper content, the alloy is highly susceptible to such erosive and corrosive wear.

It is an object of the invention to avoid these disadvantages and to provide a multilayer sliding surface bearing having a bearing alloy layer which has a high fatigue limit and a high resistance to corrosion.

This object is accomplished according to the invention in that the alloy consists of 15 to 20% by weight of tin, 1.5 to 2.5% by weight of copper, balance lead. As the resistance to corrosion increases with a decrease of the copper content and an increase in the tin content, the use of the alloy according to the invention will ensure a much higher resistance to corrosion. It is surprising, however, that in spite of the relatively low copper content in conjunction with a high tin content a high fatigue limit will be obtained even at relatively high temperatures in spite of the relatively low copper content if the tin content is high.For this reason the use of the novel alloy permits the manufacture of multilayer sliding surface bearings which meet all requirements and specifically have a high resistance to wear by corrosion and erosion under the action of lubricants used in high-duty engines.

Particularly reliable results will be obtained if the bearing alloy layer consists of 17% by weight tin, 2% by weight copper, balance lead.

Whereas cast bearing alloys are known which consist mainly of lead and have a tin content of an order of 1 5% by weight and a copper content of an order of 1% by weight, said cast alloys contain also about 14% by weight antimony so that a major portion of the tin is combined in the primary crystals SbSn and Cu 6Sn5 and cannot contribute to the corrosion resistance of the matrix. Another known alloy (U.S. Patent Specification 2,262,304), contains no antimony and consists of 20% by weight tin, up to 1% by weight of each of silver, copper and bismuth, balance lead. In such alloys the formation of primary crystals will be decreased but cannot be suppressed.This is not significant when said known alloy is used for corrosion-resisting coatings rather than for bearing alloy layers for multilayer sliding surface bearings, where the fatigue limit is also highly significant. Said alloys are cast rather than electrodeposited and owing to their heterogeneous structure and the large thickness of the layer have inherently only a low fatigue limit and for this reason cannot teach how an electrodepositable bearing alloy must be composed which has a high fatigue limit in conjunction with a sufficiently high corrosion resistance. In that connection it must be borne in mind that It is inconsistent with the experience known in the art that an alloy having a decreased copper content will have a high wear resistance and a high fatigue limit.

The accompanying drawing shows graphs in which the fatigue limit of the bearing alloy layer according to the invention and its resistance to erosion and corrosion are compared with the corresponding properties of the conventional bearing alloy layer.

Figure 1 is a graph representing the mean life of the bearing layer until fracture occurs for a known alloy and an alloy according to the invention, based on the number of load reversals performed, and Figure 2 is a graph representing for the known bearing alloy layer and the bearing alloy layer according to the invention the mean weight losses which have been obtained under identical testing conditions and indicate the wear due to erosion and corrosion.

As is directly apparent from Figure 1, an alloy according to the invention consisting of 17% by weight tin, 2% by weight copper, balance lead, has been subjected to 22 x 106 load reversals. The bearing alloy layer had a thickness of 1 5 micrometers. The mean bearing loadpamounted to a pulsating stress of 70 N/mm2. The oil inlet temperature amounted to 1 4OCC. The height of the rectangle 1 in Figure 1 corresponds to the number of load reversals performed and in comparison to the height of the rectangle 2, corresponding to 14 x 106 load reversals, shows the superiority of the bearing alloy layer according to the invention as far as the fatigue strength is concerned.The number of load reversals represented by the rectangle 2 was obtained under the same testing conditions with a bearing alloy layer consisting of 10% by weight tin, 3% by weight copper, balance lead. If the copper content of such known alloy were decreased to 2% by weight or copper were omitted entirely, the results of the known investigations on the influence of the copper content of the fatigue strength suggest that the decrease of the copper content would result in a lower fatigue strength, as is represented by the dotted-line rectangles 3 and 4 corresponding to 10.5 x 106 load reversals for 2% by weight copper and 2.5 x 106 for 0% by weight copper. Contrary to said expectation, the teaching of the invention to decrease the copper content and to increase the tin content in accordance therewith permits the provision of an alloy having a much higher fatigue strength.

The use of the alloy according to the invention results not only in a higher fatigue strength but also in a high resistance to erosion and corrosion.

This can be read from the graph shown in Figure 2, where the height of the rectangle 5 corresponds to the mean weight loss of the bearing alloy layer according to the invention with which the results represented in Figure 1 were obtained too. In a multilayer bearing having a nominal diameter of 61.3 mm, a width of 12 mm and a bearing alloy layer according to the invention having a thickness of 15 micrometers, a mean weight loss of 22 mg was measursd after an operating time of 40 hours.

The lubricant consisted of used oil having an inlet temperature of 1 400 C. During said tests the bearing speed amounted to 1000 r.p.m. The mean bearing load p consisted of a pulsating stress of 45 N/mm2.

Under the same test conditions, a mean weight loss of 37 mg was measured for a conventional bearing alloy layer consisting of 10% by weight tin, 3% by weight copper, balance lead, and a mean weight loss of 40 mg for a copper-free bearing alloy layer consisting of 10% by weight tin, balance lead, as is represented by rectangles 6 and 7. This comparison shows directly that the alloy according to the invention has a much higher resistance to erosion and corrosion. The weight losses indicated in dotted lines in the rectangles 5 and 6 were obtained if new oil was used and show for both alloys losses of the same order of 5 mg.

This was to be expected because when new oil is used the wear due to erosion and corrosion is less significant and only the resistance to mechanical wear is important. For the copper-free alloy, corresponding values have not been found because the fatigue fracture occured before. Only the used oils, which are more aggressive, subject the bearing alloy layer to erosion and corrosion so that the resistance of the layer to erosion and corrosion can be determined by a measurement of the mean weight loss.

Claims

1. A multilayer sliding surface bearing having an electrodeposited bearing alloy layer consisting mainly of lead and containing additions of tin and copper, characterized in that the alloy consists of 1 5 to 20% by weight tin, 1.5 to 2.5% by weight copper, balance lead.

2. A multilayer sliding surface bearing according to claim 1, characterizea' in that the alloy consists of 17% by weight tin, 2% by weight copper, balance lead.

3. A multilayer sliding surface bearing substantially as herein described with reference to the accompanying drawings.