Metal Finishing Guide Book


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for very small parts or workpieces that cumulatively pry and wedge into crevices. Other modern innovations to automate operation of plating barrel doors are sometimes utilized to eliminate manual labor for opening, loading, and closing. In equipment systems of this type the barrel door usually remains an Fig. 10. Dangler-style interior barrel cathode integral functional component of the contacts. barrel assembly rather than a separate item to be manually manipulated. In addition to the inherent labor savings, the safety of the overall finishing operation is increased because significant labor interaction with the equipment is eliminated. Automatic barrel operation translates into system automation, which can greatly enhance efficiency and eliminate costs. Other additional automated aspects of barrels, hoist systems, and related material handling equipment can be configured in which the equipment automatically sizes and weighs workloads, loads the barrels, closes the barrels for processing, opens the barrels, and unloads the finished work to conveying equipment for further processing or drying (see Fig. 4). This is the ultimate evolution of a barrel-finishing system. Detail Components There are important equipment features that substantially affect plating system performance and serviceability. It is very important to consider these items and their benefits when selecting barrel-plating equipment. Horizontal barrel assemblies equipped with an idler gear will result in fully submerged operation of the barrel, ensuring maximum current and solution access to the work. Fully submerged barrel plating also minimizes any potential for problems with accumulated or trapped hydrogen. Barrel rotation causes a cascading action of the workload inside the barrel. Because of this, the center of gravity of the workload is shifted to one side of the barrel assembly. Tank-driven, horizontal barrel assemblies equipped with an idler gear offset the center of gravity of the cascading workload to the proper side to best resist the tendency of the rotating tank drive gear to lift the barrel contacts from the tank contact points; therefore, use of an idler gear on the barrel assembly helps maintain, and optimizes, good electrical contact between the barrel assembly contacts and the cathode contact saddles of the tank. Conversely, a barrel assembly without an idler gear promotes poor electrical contact because the center of gravity of the workload is shifted to the opposite side and works against maintaining good, positive, constant contact. Another positive feature is hanger arms made of non-conducting materials such as plastic. Non-conducting hanger arms eliminate "treeing", stray currents, and possible loss of plating-current efficiency. (Treeing is the accumulation of deposited metal on the plating barrel or any components of the barrel assembly because of stray currents.) Design simplicity and efficiency of barrel equipment are important for ease of maintenance, particularly for components operating below the solution level. The use of alloy fasteners that are nonreactive to the chemical system in use is especially important for acid-based plating systems such as chloride zinc. 375

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