Metal Finishing Guide Book


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pulleys on the output shaft of the drive motor and the input shaft of the speed reducer. Moving the belt onto other steps in the pulley yields a different speed for each step. Many present-day systems use directly coupled C-flange motors bolted directly to the reducer. The speed-change adjustment capability for these is achieved electrically through the control panel by using adjustable drive controls. For a long time, it was thought that process tanks with more than three to five stations should be avoided. This is because smaller duplicate tanks, doing the same process, will allow the plating line to continue in operation if a bath needs to be replaced or one of the tanks requires maintenance. Separate tanks for the same process can be plumbed to each other for uniformity of the baths. Each tank can be isolated with valves, when necessary, for maintenance. Experience has shown, however, that many platers prefer to use single-unit, multi-station tanks because the bath is more homogeneous and the temperature more uniform. They schedule maintenance at downtimes and have been able to make emergency repairs in a short time, when necessary, in order not to interrupt production. NEW DEVELOPMENTS There have been some notable developments in barrel plating systems in recent years. As the industry moves toward increasing efficiencies and decreasing waste, rinsing and drying are receiving attention as operations that can be modified, or automated, to provide savings. "In-the-barrel" drying eliminates labor needed for transfer of the work from the barrel to the dryer basket, and the loading and unloading of the dryer. When equipment is provided to dry the work in the barrel, workflow is more efficient. The plater must, however, consider the type of workpieces because some do not lend themselves well to in-the-barrel drying. Adequate airflow through the load may not be possible for some types of work. This is particularly true for workpieces that tend to nest together, reducing air circulation. Also, some parts and finish types can be negatively affected when they are tumbled in the dry condition. Benefits from minimizing water usage and wastewater-treatment costs have caused equipment suppliers to develop equipment to use less water during the plating process. Some are trying to do this by reducing the amount of drag-out or carryover contamination between solution tanks in a plating line. Barrel manufacturers have approached this problem with a number of different solutions; however, most focus on the same basic property of barrel design, the perforations. Different hole geometries, mesh screen, thin-wall construction, and greater percentage of open area are all available today on just about any size plating barrel. While some of these designs may demonstrate a noticeable reduction of drag-out, it can come at the expense of reduced workload capacity and equipment service life. Another development is to connect separate rinse tanks from different parts of the line together, in sequence of descending water quality, to optimize the use of the water before it is sent through the filtration and treatment process. In other words, the water is taken advantage of for more turns and less water is added to the rinse tanks, in total. Of course, not all rinse tanks can be handled together this way because cross-contamination could negatively affect some steps in the finishing process. For where it is practicable, the water savings can be significant. For example, acid rinse baths can be further utilized for the cleaning rinses, as the next step after the cleaning stations is normally the acid dipping or pickling. Also, the acid rinses can have a neutralizing effect on the cleaning rinses. 377

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