Overview of electroplating process of sliding bearing anti-friction layer
If an anti-friction coating is directly electroplated on the lining metal, the tin in the coating will easily diffuse to the lining, causing the tin content in the coating to drop to less than 6% (mass) after the bearing has been working for a period of time. And whether it is a copper-based alloy lining or an aluminum-based alloy lining, it contains a certain amount of copper. The tin diffused into the lining can form a brittle intermetallic compound (Cu3Sn) with the copper. This not only reduces the mechanical properties of the coating, but also destroys the structure of the lining, resulting in a reduction in the overall mechanical properties of the bearing bush. The way to solve this problem is to electroplat a layer of nickel or nickel-based alloy barrier layer (also called gate layer or barrier layer) between the lining material and the anti-friction bottom layer to inhibit the diffusion of tin into the lining [1~2].
1. In addition to having a certain anti-corrosion effect, the tin or lead-tin alloy protective layer can also supplement the tin content in the anti-friction layer by diffusion during the operation of the bearing bush, so that the content of each component is in a relatively stable state. In addition, since this protective layer does not contain copper and is relatively soft, the bearing bush can meet good running-in requirements in the early stages of work.
This article mainly examines the electroplating process of the bearing friction reducing layer.
2 Development process
Research on anti-friction coatings started early abroad. In 1920, J. Grooff proposed the first patent for electroplating lead-tin alloy, and it was used for electroplating the inner surface of naval torpedo gas cylinders. In the 1940s, it began to be used for electroplating bearings. In 1952, Schults proposed a patent for electroplating lead-tin-copper ternary alloy on aluminum and aluminum-silicon (AlSi) alloy substrates. In 1953, Schoefe published a review of lead-tin-copper alloys used in bearing bushes. In 1976, Jong-Sang Kim, Su-ι Pyun and Hyo-Geun Lee published a paper on "Crystal plane orientation and micromorphology of lead-tin-copper electroplating layer" [7]. In 1980, Beebe proposed a ternary alloy electroplating production process containing 2~3% copper (mass), 9~12% tin (mass), and the rest is copper. The plating thickness is 15 μm. In 1982, Waterman and others proposed a solution to the replacement problem of copper ions (Cu2+) in the ternary alloy plating solution.
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