Metal Finishing Guide Book


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Fig. 4. Multirectifier computer-controlled system. consisting of salts of various metals such as tin, nickel, and cobalt, and AC power is applied. The AC current causes the deposition of metallic particles in the pores of the anodic coating. By varying the relative amplitudes and times of the positive and negative half cycles of the AC output, numerous colors and finish characteristics can be obtained. The electrolytic coloring processes have become popular as they require less energy than competing methods. An ideal power supply for the two-step process will provide the opportunity to adjust the voltage and on-and-off times of the positive and negative portions of the output independently. This provides the maximum amount of flexibility to generate the broad range of colors available through electrolytic coloring. COMPUTERIZATION In the 1970s many metal finishers investigated modifications that would be required to upgrade their rectifiers to computer control. At that time, however, the price and risk of automation was too high for most companies, forcing them to continue using manual control. Today, the importance of incorporating some degree of automation into the metal-finishing processes is becoming more evident. For example, smaller firms find themselves at a disadvantage when competing against larger, more automated companies, especially for jobs where the finished parts require precise coating thickness and consistent finish qualities. Additionally, certain plating applications require multiple layer applications to achieve the desired coating thickness and surface quality. These multilayer processes demand extremely accurate and repeatable coatings. The major advantage of computer over manual control of a rectifier is the 743

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