Metal Finishing Guide Book


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Figure 3. When combined with color-on-demand technology, dense phase application equipment can provide color changes in 20 seconds or less. uniformly without bounce-back due to the low velocity of powder and without defects caused by too high of a current. When a powder gun is at its optimum distance from the part–the effective charging voltage of the powder is optimized and current draw is low. When the gun-to-part distance decreases, effective voltage also decreases and the current increases. This causes a defect on the powder coated surface of the part commonly known as back ionization. In the case of cavities, this can result in what is known as the Faraday Cage Effect, resulting in poor powder coverage of the surface of the cavity. Dense phase with its low powder velocity and the resulting reduced bounce back—coupled with AFC current control—makes it the perfect match for use with robots for all powder coating applications. This is especially true for those that require frequent color changes. Because dense phase pump is purge-able in both directions, the powder delivery line can be cleaned quickly and effectively. When coupled with "color-on-demand" technology, dense phase technology provides automatic color changes in less than 20 seconds. When combined with automatic gun presets that control application parameters—such as powder flow and electrostatics (KV and AFC) for each and every part as well as each and every powder—powder coaters now have the ultimate tool for productivity and flexibility in their powder coating operations. Office furniture manufacturers in Japan have been using dense phase technology, robotics and color-on-demand technology for several years now to powder coat effectively and change colors quickly using multiple dense phase guns on a single robot—and sometimes using multiple robots on the same booth. Additionally, dense phase technology is not limited to organic powders. It can also be used to pump and spray PE (porcelain enamel) powders. An appliance manufacturer in North America is currently using dense phase guns on robots to apply porcelain enamel powder to oven cavities. In the end, these manu163

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