Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming multiple superposed electrolytic coatings
Patent
1998-08-21
2000-07-11
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming multiple superposed electrolytic coatings
205238, 205253, 252 622, 106 123, C25D 500, C25D 356, C25D 360, E04B 174, C23C 1600
Patent
active
060867426
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for producing multilayer material for plain bearings comprising a steel backing and a bronze layer, on which a lead- or tin-based binary layer and a molybdenum-based running-layer are deposited in succession by electroplating. The invention also relates to an electroplating bath for carrying out this process.
2. Description of the Related Art
The development of ever more powerful engines also increases the demands made of the bearings installed in these engines with regard to sustained load carrying capacity, wear resistance and corrosion protection.
Since a particularly significant aspect as far as these bearings are concerned is the improvement of conformation layers, which have to withstand an extremely high surface pressure, plain bearings have been developed which comprise a molybdenum-based running-in layer.
A sliding element is known from DE 29 26 708 A1, on the overlay of which there is provided a molybdenum oxide layer, which has a uniform, micro-flawed structure and is from 0.0005 to 0.003 mm thick. This molybdenum oxide layer is applied to a ternary overlay of PbSn10Cu2, for example. These known plain bearings are distinguished by low wear and enhanced corrosion resistance. However, these materials are not satisfactory if relatively high running speed stability and improved running-in behaviour are required.
Tests with binary overlays, such as PbCu3 for example, which fulfil these requirements somewhat better, have shown, however, that adhesion of the molybdenum oxide layer is unsatisfactory. It became evident that using conventional electrolytes resulted in streaked deposition of the PbCu layer after only a few production batches or a short service life. Light and dark areas were noted, the adhesion of the molybdenum oxide layer being extremely poor in the light areas. In contrast, adhesion in the dark areas of the binary layer was excellent. Furthermore, fluctuations in layer thickness of 12 .mu.m or more were evident, which is unacceptable in the case of highly loadable bearings.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a process and an electroplating bath with which the adhesion of molybdenum oxide layers to binary overlays is improved.
This object is achieved using a process in which, for deposition of the binary layer, an electroplating bath is used which comprises a non-ionic wetting agent and a benzene derivative and in which, after deposition of the binary layer and prior to deposition of the running-in layer, anodic activation of at least one surface layer of the binary layer is effected.
PbCu layers with copper contents of from 1 to 10%, PbSn layers with tin contents of from 10 to 30% and tin-antimony layers with antimony contents of from 1 to 10% a are particularly suitable for use as binary layers.
First of all, it was attempted, with the aid of a PbCu electrolyte, to improve the stability of the electroplating bath by adding organic components. If the PbCu electrolyte is operated without organic components, the deposits obtained are thoroughly non-uniform and uncontrolled. In the low current density range copper is preferentially deposited. At higher current densities separate deposition of PbCu and Pb phases occurs. The addition of benzene derivatives, especially resorcinol, in an amount of up to 10 g/l, succeeded in modifying this deposition behaviour only insignificantly. Non-ionic wetting agents were then tried, these being added in amounts of up to 10 mg/l. It was noted that, although these non-ionic wetting agents increasingly inhibit copper deposition, the deposition behaviour from the point of view of dispersion and layer thickness profile remained unsatisfactory. Thus, for example, it was noted that the layer reduced considerably at oil-holes.
It has surprisingly emerged that it is by combining non-ionic wetting agents and benzene derivatives that a clear improvement may be obtained. However, the synergistic action of the two organic components a
REFERENCES:
patent: 3226308 (1965-12-01), Pochapsky et al.
patent: 4363854 (1982-12-01), Hodes et al.
Loshkarev et al., "Production of Antifriction Lead-Tin Coatings From a Fluoroborate Electrolyte With Additives", Vopr. Khim. Khim. Tekhnol., vol. 56, pp. 58-63. (abstract only), 1979 no month available.
Huhn Hans-Ulrich
Muller Klaus
Wiebach Dietmar
Glyco-Metall-Werke Glyco B.V. & Co. KG
Gorgos Kathryn
Wong Edna
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