May 9, 2009

Spin Polishing

Spin Polishing like wheel polishing, usually induces scratches with directional characteristics, which must subsequently by smoothed by buffing. Any subsurface porosity only 25 to 50 µm below the surface, which is encountered with some castings, usually is exposed by wheel polishing or spin polishing. Depending on the size of these pores, relatively thick leveling copper is required to avoid defective electroplates when subsurface pores are exposed.

Vibrating tubs loaded with plastic media, such as polyurethane impregnated with an abrasive such as aluminum oxide, smooth the surfaces of die castings in 4 hr or less when frequencies are in the range of 1600 to 3000 cycles/min and amplitudes are adjusted to 0.8 to 6.4 mm. Vibratory machines produce a finish of 0.15 to 0.20 µm. Media and zinc parts are usually loaded in ratio of 5.1 to 6.1. Surface gouges might occur with smaller ratio.

Small parts adaptable to barrel cleaning and plating are frequently prone to blistering when they are heated after barrel plating if surface defects are not removed beforehand. Vibratory finishing appears to be the best method of erasing defects, densifying surface layers before plating, and minimizing process blistering. The use of dual shaft machines reduces the time required for removing surface defects.

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