Metal Finishing Guide Book


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Barrels are used to plate chrome where ample current and continuous-contact are available (when gentle abrasion of the part surface is not a problem). One can infer from the previous example that a barrel���s value and versatility depend on its capability to (1) plate a particular finish and (2) function propFig. 5. Barrel assembly equipped for use erly in system solutions and temperain a rack plating line. tures. This capability is determined by the materials, construction, and detail features incorporated into the barrel unit. Some barrel equipment lines have the capability to produce more than one plated metal or finish type; however, most plating lines are dedicated to one finish type. Elimination of ���drag-out��� in a plating line that produces more than one finish type is a primary concern. Drag-out, or cross-contamination, of the different plated metals in stations used for: rinsing, sealing, chromating and cleaning can be minimized by incorporating an ���up-rotation��� sequence in the barrel operation. Up-rotation is discussed in the section ���Hoist Systems, Tanks, and Ancillary Equipment.��� WORKLOAD The barrel plater needs to evaluate each of the following items to decide if the desired finish on a particular part can be barrel plated: finish function (relative to use of the part), part configuration, part size, part weight, calculated part surface area, and total workload volume and square foot surface area. The workload capacity is usually 40 to 60% of the total interior barrel volume. The maximum workload volume is usually determined based on total square foot surface area of the load and the capacity of the bath chemistry and electrical equipment to plate. Other factors are the weight of the individual workpieces and their propensity to damage the finish or serviceability of other parts in the load. Damage of this type is usually the result of the weight, configuration, or edge characteristics of the parts as they tumble against each other in the barrel. As designated in the section about the uses of barrel plating, plated-finish functions are of three basic types: corrosion protection to increase the useful service life beyond performance of the un-plated base material; decoration for appearance, which also enhances the value of the base material; and engineering applications to attain (add material) or maintain a dimensional requirement and/or as a bearing surface. There are requirements for plated finishes that need to perform more than one of the previously mentioned three basic functions. Barrel plating is most commonly used to finish parts for corrosion protection. Decorative finishes are successfully barrel plated when surface effects from part contact are controlled to an acceptable level. Engineering finishes are not usually applied by barrel plating. Fig. 6. Special-length barrel assembly for Configuration of the workpieces plating elongated parts or for use in a affects the ability of work to be sucrack plating line. 423

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