Metal Finishing Guide Book


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Another approach to minimizing water usage is the application of spray rinsing equipment rather than an immersion rinse. Water manifolds with spray nozzles 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 rinses the workload but prolongs the service life of the equipment by rinsing away any solution that may attack the barrel assembly support superstructure and components. Another type of spray rinsing equipment incorporates an interior manifold 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 conservation 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 substantially with the type of plating. Most production barrel platers operate in the 15 to 40 Amps/ft2 range. Nickel plating can vary to 50 Amps/ft2. Take note that actual current density is higher because only the exposed surface of the workload in the direct path of the current at any time is plating. The exposed surface is much less than the total calculated surface of the entire load. All surfaces eventually receive the same relative exposure due to the tumbling action in barrel plating. Barrel tanks generally draw higher currents than still (rack) tanks of the same capacity; therefore, it is important to equip barrel tanks with greater anode area, usually in a 2 to 1 ratio to the total surface area of the workload. Barrel anodes corrode faster than rack-type plating anodes; however, the production is much greater than for a rack-type line. There are references located elsewhere in the Metal Finishing Guidebook that permit estimating the time required to deposit a given thickness for many types of plating. There is also information for selecting proper current densities and total cycle times. RECORDS Proper operation of a barrel-plating line requires the maintenance of records for each part and plating specification done in the shop. The data is generally entered in a computer database or on file cards and used to construct graphs and/or tables for thickness, time, area, and current relationships. Using the graphs or tables, a plater can make reasonably accurate initial judgments for processing new or unfamiliar work. Suggested items to record for each job include material, part surface areas, part weight, finish type, thickness required, current, and voltage used, as well as load size and plating time. SUMMARY Barrel plating has distinct advantages: the ability to finish a larger variety of work and producing a greater volume of work for a specified time period over what is generally possible from a rack-type finishing line. By incorporating as many aspects of the previously mentioned information as possible, the capacity and capability of a barrel finishing production line can be optimized. 378

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