There are several methods of processing available to the electroplater. They include rack, basket, barrel, basket, and brush plating. Either automated or manual methods can be used depending upon the volume of work to be processed at one time.
A. Rack Processing
A plating rack is a device that holds the part in a fixed position during the plating cycle. It connects the part electrically via the bus bar to the dc power supply. The plating rack is usually fabricated of copper with phosphor-bronze contact tips to hold the workpiece. The rack is then coated with a plastisol to prevent the various solutions from corroding copper spines; the tips are left bare so as to make electrical contact with the part.
Racks should be designed so that the parts are held in a proper position with respect to the processing limitations that were previously discussed. The weight, volume, current requirement of parts to be processed at one time must also be considered when designing racks. The top of the rack is normally fabricated to form a hook. It is this hook and contact point that rest on the copper bus bar for electrical contact. The hook must be designed so as to assure a constant current flow. Plating racks are normally used for large parts that cannot be processed by other means. Due to the necessity for manually loading and unloading, the rack method is usually the most expensive.
B. Barrel Processing
Barrel processing is used for plating small parts in bulk. As a rule bulk processing is much less expensive than manually racking the parts. Items such as nuts, bolts, screws, washers, and other small parts can be effectively processed in barrels. These parts can be loaded in quantities of up to 250 lb in appropriately sized plating barrels.
Most plating barrels are of the horizontal type and are six sided. A removable door on one side allows for the loading and unloading of the parts. These barrels are now usually fabricated of polypropylene, thus providing strength to withstand the various loads, as well as, chemical resistance to the various solutions at the operating temperature. Plating barrels are perforated with small holes on the sides to allow for circulation of the electrolyte and electrical contact with the work inside. Electrical contact is made by flexible danglers through the side that touch the load inside. Plating barrels are either of the fully or partially submerged variety and are rotated slowly so that the load of parts is constantly in motion and all surfaces are coated with electrolyte and make contact electrically.
Due to the restriction of electrical flow, plating speed is slower with barrel processing than it is for rack processing. The larger volume of work with less labor usually makes barrel processing more economical for overall plating of small parts.
C. Basket Processing
Basket processing is similar to barrel in that the parts are processed in bulk. A conductive metallic basket is generally used. The basket is suspended by a hook from the cathodic bus bar. Basket processing is a manual operation due to the necessity of periodic shaking or mixing the load of parts so that all surfaces make contact and receive a uniform deposit. Due to higher labor requirements basket processing is not widely used in practice today. It has been almost entirely replaced by the more efficient barrel processing method.
D. Brush Processing
Brush plating is used for localized or selective plating. A normal plating tank is not used since the parts are either overly large or disassembly and removal of the part would be cost prohibitive, such as where a repair of plating is required.
A brush plating setup consists of a small dc rectifier, an ammeter, and a portable hand-held anodic brush wrapped with a material, such as cotton, nylon, or dynel, that absorbs the plating solution. The plating solution can be applied to the brush either by dipping or by pumping it through a hollow core. The part is made the cathode by a suitable electrical connection.
The brush containing the plating solution is manually moved over the entire surface to be plated until the desired thickness is achieved. Brush plating requires the same cleaning and activation steps that are used in more conventional methods. This cleaning and activation are, however, done manually.
Brush plating can be done on such substrates as steel, copper, or the stainless steels. It is not recommended for the more active substrates, such as aluminum, magnesium, or titanium, because they cannot be activated properly manually and poor adhesion be expected. Brush plating is not economical for any considerable number of parts. It is only used on a one of a kind job, usually of large size, and one that may be plated in place without total disassembly.