Example 8 Uniform Cadmium Plating of Coupling Leaving External Teeth Unplated

A coupling that, except for the external teeth, was cadmium plated all over to a specified depth of 8 to 13 ^m (320 to 520 ^in.) is also shown in Fig. 8. Spline and internal bore dimensions were critical and had to be held to a tolerance of ±5 ^m

(±200 ^in.) after plating. Again, uniformity of plate thickness was achieved by centering a 6.4 mm (4 in.) diameter anode in the bore during plating.

Simple cylindrical, cuboid, and channel shapes, such as those shown in Fig. 9, usually require conforming anodes in order to achieve complete coverage of plate and reasonable plating uniformity. Dimensional limits that definitely require the use of an internal anode are indicated for each geometric shape.

Fig. 9 Typical workpiece configurations with accompanying dimensions that require the use of conforming anodes to ensure uniform plate thickness oi mojjf

Fig. 9 Typical workpiece configurations with accompanying dimensions that require the use of conforming anodes to ensure uniform plate thickness

Normal Variations. Even under preferred production conditions, some variation in plate thickness must be anticipated. Usually, this normal scatter is acceptable and falls within the specified range of allowable variation.

In general, barrel plating produces greater variations in thickness than still plating. In barrel plating, factors such as the weight, size, and shape of the part usually exert a greater influence on uniformity of plate thickness than they do in still or automatic plating.

Screws, nuts, and other small parts of fairly regular shape will usually coat uniformly in barrel plating. Parts that are likely to nest because they have large flat areas or cup-shape recesses exhibit wide variations in coating thickness. Variations decrease somewhat as the thickness of plate increases.

Variations in plate thickness obtained on production parts are detailed in the example that follows:

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