Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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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 bar- rel, 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 cir- culation. 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 plat- ing process. Some are trying to do this by reducing the amount of drag-out or car- ryover 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. Another approach to minimizing water usage is the application of spray rins- ing equipment rather than an immersion rinse. Water manifolds with spray noz- zles directed on the outside of the barrel wash the barrel and contained workload. Sometimes the barrel is rotated, tumbling the work, while being sprayed. It is expected that water usage is reduced. This method is not effective for all types of work, an example being cupped parts or convoluted workpieces. A variation on this is to actually spray or rinse down the entire plating assembly. This not only rins- es the workload but prolongs the service life of the equipment by rinsing away any solution that may attack the barrel assembly support superstructure and com- ponents. Another type of spray rinsing equipment incorporates an interior man- ifold in the barrel and water connection equipment on the outside of the barrel to spray directly onto the work inside the barrel for rinsing. Again, water conser- vation is the goal for which this equipment has been designed. RATE OF PRODUCTION Reasonable production may be maintained with total workload surface area ranging between 60 and 100 ft2 per single barrel. Amperage settings can vary sub- 335

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