Metal Finishing Guide Book


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are open on top and have no doors or clamps. The technique is to limit barrel motion to a back-and-forth (usually less than 180° of arc) rocking action about the horizontal axis, rather than 360° full rotation. The motion is more gentle for very delicate parts and can be a plus when treating parts that tend to nest, tangle, or "bridge" badly inside the barrel. Because agitation and tumbling are not as vigorous as full rotation, the operator/plater must take care to avoid possible non-uniform plating Fig. 3. Ministyle barrel assembly with selfcontained drive and integral-mesh, molded (particularly for parts that tend to baskets. nest). Processing is generally limited to smaller loads with these type barrels to avoid spillage and part loss because of the continuously open door. Oscillating barrels are not utilized as much as they were in the past. This is because operators/platers can use variable-speed drives to produce slower rotational speeds on full-rotation barrels to obtain equivalent results. Many older oscillating barrel installations have been converted to full-rotation operation. The second major barrel equipment style is the oblique barrel. It can be pictured as an open-top basket that rotates around an axis tilted to a maximum 45° from the vertical. Work capacity diminishes beyond a 45°-axis tilt. The major feature of oblique barrels is the elimination of doors or other closure devices. Because the top is open, unloading consists of raising the barrel about a pivot at the top of its rotational axis shaft to a position that dumps the workload. Similar to 180° horizontal oscillating barrels, this results in relatively small workloads and reduced tumbling action. Today, operators/platers can take advantage of fully automatic doors on full-rotation horizontal barrels to achieve the same advantage with greater ease and higher production. FINISH TYPES All common types of plating are done in barrels, including zinc (alkaline and acid in various chemical systems), cadmium, tin, copper, "precious-metals" (such as silver and gold), and nickel (both electrolytic and electroless). 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 368 Fig. 4. Fully automatic load/unload system with integral door barrel assembly for handsoff operation.

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