Sliding element and process for producing the same

Details Sliding element and process for producing the same Sliding element and process for producing the same

1995-07-27

1998-01-27

Zimmerman, John

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

428650, 428935, 205213, 384912, B32B 1520, C25D 530, C25D 544, F16C 3312

Patent

active

057120498

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/DE93/01131,filed Nov. 24, 1993.


BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a plain bearing having an electroplated tin layer bonded to an aluminum containing layer by a halogen free deposition containing zinc, copper, nickel and iron.
2. Description of Prior Developments
Compound plain bearings comprise a supporting steel shell with a layer of anti-friction metal which is mostly of an aluminum-tin alloy. In the majority of cases, the running surface of the bearing must be additionally provided with a usually electroplated coating of an alloy whose hardness is much lesser than that of the aluminum-tin alloy. The aluminum-tin anti-friction metal is itself capable of very limited conformation to the steel shaft during the running-in phase. The conformation process consists essentially of plastic deformation and also partial abrasion of the anti-friction coating. Aluminum-tin layers minimally plastically conform to the shaft and are not abraded with simultaneous smoothing of the running surface in the regions of the sliding surface which are in a state of mixed friction due to the geometrical imperfection of the bearing shell and shaft. Instead, in adverse conditions, roughening even scratching takes place in the hard regions. The formation of the lubricant film of uniform thickness is impaired by these variations in the running surface and local mixed friction which should be limited to the brake-in phase remains so that even after a relatively short operating time the bearing may be significantly damaged.
In order to improve the conformability of the bearing by deposition of a soft layer, the problem of electrochemical deposition onto aluminum alloys had to be solved.
From DE-AS 10 48 757 it is known to provide between the aluminum alloy and the overlay a silver layer to achieve better adhesion between the aluminum and the running surface. However, the silver bonding layer known from DE-AS 10 48 757 has the disadvantage that it must be at least 2.5 um thick to obtain sufficient bond to the thin zinc layer situated below it and to the backing layer of aluminum material. Moreover, deposition of the conventional silver bonding layer by electroplating is associated with critical working conditions so that the silver bonding known from DE-AS 10 48 757 was not successful in actual practice.
From DE-OS 15 33 214 it is known, for instance, to provide an intermediate layer of nickel between an outer layer of copper and inner layer of lead and tin. Nickel as a bonding base has been known to be successful in bearings for a long time in conjunction with surface-hardened shaft journals, which is the case with smaller engines. In such cases, it is relatively safe when after long operating times the soft outer layer is locally worn down to the nickel layer and the shaft gets into contact with nickel. The conditions are, however, different in the case of large diesel engines with soft journals.
Nickel deposited by electroplating on a bearing has a hardness which is higher than the surface hardness of shafts which are not surface-hardened. If, after wearing of the electroplated layer, the journal of the shaft reaches the nickel bonded base, two nearly equally hard materials, which are also very similar metallurgically, slide in contact with each other. This desirable pairing of elements in sliding contact causes wear of the journal which initially manifests itself as roughening and, in an advanced stage, ultimately as scratching.
In addition to its undesirable high hardness, the nickel layer also behaves adversely in another respect. At operational temperatures existing in a bearing, intermetallic phases may be formed within some thousands of operational hours between the nickel and tin, the hardness of the intermetallic phases being much greater than that of a layer of pure nickel. If the wear of the overlay proceeds slowly, the shaft comes into contact with the intermetallic layer which meanwhile has acquired a thickness of several um, and which then c

REFERENCES:
patent: 2676916 (1954-04-01), Zelley
patent: 2734024 (1956-02-01), Schultz
patent: 2745799 (1956-05-01), Patrie
patent: 2766195 (1956-10-01), Combs et al.
patent: 3616291 (1971-10-01), Wilson
patent: 3969199 (1976-07-01), Berdan et al.
patent: 4100038 (1978-07-01), Jongkind
patent: 4225397 (1980-09-01), Napier

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