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POWER PACKS: Power packs, also known as rec- tifiers, change alternating cur- rent into the direct current that is used for the plating opera- tion. Power packs are durable and portable. These attributes are necessary because the power packs are routinely transport- ed to the work site. This may be from plant to plant or to vari- ous locations within the same plant. Power packs specifically designed for selective plating have several features that set them apart from rectifiers used in tank finishing operations. Typical Features on a Selective Plating Power Pack • Voltmeter • Ammeter • Ampere-Hour Meter • Pole Changer • Audible Reverse Current Alarm • Overload Protection • Twistlock Connections for Output Leads • Constant Current and Constant Voltage Operation Power packs have forward-reverse cur- rent switches. These switches allow the direction of direct current flow (polar- ity) to be changed quickly. This is necessary because the combination of prepara- tory steps and a final finishing step usually requires several rapid changes in the direction of current flow. These power packs incorporate several safety devices such as fast acting circuit breakers which minimize damage, in case the anode, handle or lead accidental- ly come in contact with the work surface, causing a short circuit and arcing. A voltmeter displays the voltage setting for each step in a finishing procedure. An ammeter displays the amperage for each step as it is being carried out. This allows the operator to make adjustments to the current density during the prepara- tory or plating operation. A precision ampere-hour meter provides data to accu- rately control the thickness of an electroplated deposit or anodized coating. SOLUTIONS: Selective Plating solutions can be divided into three groups according to their use. Refer to Table I which lists commonly used solutions. The first group contains solutions that are used to prepare various types of base materials for finishing. As the name suggests, preparatory solutions are used to prepare the surface so that the final step, whether it is brush plating, anodizing or electropolishing will produce a quality end product. A quality end product will 340