Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1997-06-06
1999-11-02
Jones, Deborah
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428614, B32B 1501
Patent
active
059767120
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a multilayer material for sliding elements which having a backing and an overlay of lead bronze. The invention also relates to a process for producing sliding elements which an overlay of lead-tin-copper is applied to the prefabricated semi-finished product by electroplating, as well as to means for carrying out the process.
2. Description of Prior Developments
Sliding elements should be understood to mean all types of bearing liners as well, inter alia, as pistons and piston rings. Overlays of multilayer materials for sliding elements are generally produced by electroplating in appropriate electrolyte baths. There have hitherto generally been used for this purpose fluoroborate-containing baths, which exhibit a number of disadvantages, however.
When baths are used, organic constituents and tin oxidation inevitably cause impurities to arise, which detract from the quality of the electroplated layer. As a rule, owing to their greater weight these impurities settle on the bottom of the tank and do not affect electroplating unless the bath is moved. However, if circulation of the bath cannot be effected for these reasons, a concentration gradient of the metal ions provided for plating arises. Since the sliding elements to be plated, such as bearing liners for example, are stacked one above the other in receptacles, an increase in layer thickness from top to bottom will inevitably occur.
Such concentration gradients could be prevented by constant movement of the bath, though a prerequisite of this would be that no impurities are whirled up or that the bath is filterable. The tetravalent tin oxide, which is present in fluoroborate baths, is generally not filterable, however. Moreover, undesired tin oxidation would be encouraged by the increased oxygen supply from the air.
A further disadvantage of known baths consists in the fact that, despite the provision of a thief cathode in the electroplating bath, it is impossible to prevent currentless deposition of bearing metals on the bearing backing during the electroplating process. Owing to the high copper concentrations, for example in electrolytes for ternary layers, copper is deposited currentlessly and without check on the bearing backings of the bearing liners, which process is known as cementation. This copper layer exhibits only limited bonding to the steel backing and thus has a tendency, after tinning, towards bubble formation and flaking. On the one hand, this entails a material loss and on the other hand, the operability of the bearing may be impaired by flaking of the cementation layer.
The current densities used are limited to 2.2 A/dm.sup.2 in known electroplating baths. Although higher current densities shorten the electroplating process, the deposition rates of the metals diverge within the bearing liner surface and receiving stack, such that the deposited layer no longer has the desired composition. Stable deposition is not possible, therefore, at higher current densities.
Some overlays, especially ternary layers, produced with known baths exhibit considerable variations in thickness, which may possibly necessitate post-machining. Furthermore, the tin is not evenly distributed in the overlay, which may cause aggregation and coarse crystalline deposits, known as tin-agglomerations. This inhomogeneous structure of the overlay promotes tin diffusion, which occurs when the sliding element is exposed to relatively high heat levels during operation, such that such overlays may only be applied to an intermediate layer, such as a nickel barrier for example, which prevents tin diffusion into the lead-bronze layer thereunder, as described, for example, in E. Romer "Werkstoff und Schichtaufbau bei Gleitlagern" ("Material and Layer Structure in Plain Bearings"), an offprint from ZFW Zeitschrift fur Werkstofftechnik ("Journal of Materials Technology"), volume 4, issue 7, Verlag Chemie Weinheim/Bergstra.beta.e 1973. Only through this additional measure has it hitherto been possible to imp
REFERENCES:
patent: 5137792 (1992-08-01), Hodes et al.
patent: 5185216 (1993-02-01), Tanaka et al.
Heyer Joachim
Huhn Hans-Ulrich
Muller Klaus
Staschko Klaus
David Darlene
Federal-Mogul Wiesbaden GmbH
Jones Deborah
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