Metal Finishing Guide Book


Issue link:

Contents of this Issue


Page 383 of 843

HOIST SYSTEMS, TANKS, AND ANCILLARY EQUIPMENT It is important to the performance capabilities of a barrel hoist and tank system to review the following items and include the advantageous features where possible. Most barrel-plating tanks are designed to maintain the solution level approximately 5 in. below the top rim of each tank. At this level, the plating barrels should run fully submerged, eliminating the potential for excess hydrogen accumulation. Operating with a solution level higher than 5 in. below the top rim of a tank can cause the solution to be splashed out during barrel entry or exit, resulting in wasted solution, treatment issues, and, possibly, environmental problems. Solution loss and adjacent tank drag-out contamination can also be minimized by equipping the barrel hoist system with "up-barrel rotation". A drive mechanism on the hoist rotates the barrel and load in the overhead, above-tank position, facilitating better drainage before moving to the next process station. This is especially helpful when finishing cupped, or complex-shaped, parts. Locating the plating-tank anodes (including anode baskets or holders) in the closest proximity to the barrel exteriors, without allowing mechanical interference, ensures greatest current densities for the workload. Anodes that are contour curved to just clear the outside rotational diameter of the barrels can result in 10 to 20% increase in current density. For horizontal barrels, vertical adjustment capability of tank-mounted barrel drives should optimize engagement of the gears. Drives that are adjusted too high will carry the weight of the loaded barrel assembly on the drive gear, resulting in excessive stress on the gear, drive shaft, and bearings. This causes premature wear and failure of these components. Reducer oil leakage is also a potential resulting problem. In addition, when the weight of the barrel unit is concentrated on the drive gear and drive shaft rather than on the plating or electro-clean tank saddles, proper contact is not possible. If the drive gear carries the barrel assembly, the contacts are most often lifted out of position. When a tank drive unit is adjusted too low, poor drive-gear engagement results. Sometimes the driven barrel gear hops across the tank drive gear and the unit does not turn. This situation not only results in premature gear wear because of abrasion but also in poor plating because of poor electrical contact. It is best to alternate tank drive rotation in a barrel plating line in each subsequent/following process station. The advantage of having approximately an equal number of drives rotating the barrels in the opposite direction is to ensure even wear on all drive components (bearings, gears, etc.) and greatly extending service life. Alternate rotation of drives certainly minimizes replacement requirements and downtime. The teeth of the steel gears on barrel assemblies and tank drives should be greased to enhance service life and fully engaged performance. Displaced grease will not negatively affect the tank baths because the gears are normally located beyond and below the tank end wall. Barrel drives, whether tank or barrel mounted, can have provision to change barrel rotation speed. This is to allow for change of workload type or plating finish. For example, a lower rotation speed is often better for very delicate or heavy parts to minimize abrasion. A faster rotation speed may be used to produce a more uniform plated finish or more readily break up loads of nesting or sticking parts. Allowing for change of barrel rotation speed maximizes the capability to produce the greatest variety of finishes on a larger variety of parts. Certain tank drives provide for speed change by using multiple-sheave belt 376

Articles in this issue

view archives of Metal Finishing Guide Book - 2013