Metal Finishing Guide Book


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A plating barrel may expand and contract as much as 3/8 in. in total length due to the different bath temperatures in a plating line. Changes in temperature cause stresses that can ���work��� a barrel to pieces. This is particularly critical for barrels constructed of materials with different coefficients of expansion. The effects of the temperature changes can be minimized with good design and quality construction. When barrels are Fig. 7. Barrel interior showing disk- and fabricated of a single type of plastic and strip-type contacts. joined by a plastic weld or fusion process, stress points are eliminated. Barrels made this way can expand and contract at a uniform rate, which greatly extends their useful service life. The use of metal fasteners for barrel assembly is a less desirable method because it results in stress points and the possibility of loosening. Minimizing the effects of temperature changes promotes barrel integrity and long service life. The capability of a barrel to be used in higher temperature baths can, as an added benefit, aid faster plating. Good equipment design will reduce maintenance and replacement part costs. Costs are reduced significantly when it is possible to replace individual wear parts and components. Wear parts that are manufactured as an integral piece of a larger component to reduce manufacturing costs should be avoided. Examples are: (1) trunnion hub-bearing surfaces molded integrally as a component of hanger-arm supports and (2) cylinder ���ring���, or ���bull���, gears that are also the barrel head. These perform the same as other equivalent parts when new, but when the wear part needs to be replaced, the larger piece, of which the wear part is a component, must be replaced. This can sometimes require the replacement of the entire plating barrel and can be very costly for the user. Detail Features For the majority of plating, flat-sided barrels are best. Flat-sided barrels produce ���pumping-action��� as a benefit of rotation. Pumping action is the inherent agitation of the bath caused by rotation of the flat-sided barrel. Round barrels do not produce pumping action as efficiently. Pumping action helps constantly replace metaldepleted solution from inside the barrel with fresh solution from the rest of 425

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