Setting Up 2
An air ventilation system should also be installed. In the electroplating process, there is much that goes into the air from the buffing process and from the vapors rising off the vats. An enclosed shop will also become very humid. Chromic acid and the acid used in the pickling process will get in the air and be detrimental to health. A good ventilation system is a must to maintain a safe working environment. Fumes in particular from the chronic acid vat must be controlled. Those fumes will destroy the inside of the nose. Exhaust systems are available that suck the fumes away and expel them to the outside via a scrubber. They have side ducts that run along the entire length of the sides of the vats. It is hoped that the aspiring plater would practice good safety and health procedures. There are too many small shops that damage the health of the employees in the interest of saving money by avoiding proper ventilation equipment. Technology has done much to help with fume control. There are solutions that can be added to bath solutions that float on top and control the fumes, yet do not interfere with the electroplating process if properly used.
There are also Styrofoam or plastic balls that are floated on vats, particularly pickling vats, to help control evaporation. They also save greatly on heating costs as they help maintain the temperature of the vats.
The electric current necessary for the electroplating process is supplied by a direct current generator(s). The generators have heavy metal bars, called bus bars that supply the current to each vat. In a typical arrangement, though not an ideal one as discussed previously, there will be a central cathode bar from which the jigs or workpiece racks are suspended, and on either side will be the anode bars from which are suspended anodes by means of hooks. This makes it easy to move the anodes around and deliver current to the proper places. The bus bars are usually made of copper. If using aluminum bus bars, the connection points should be silver plated. Bus bars can be a source of contamination if they are allowed to corrode into solution. The bath formulas show the recommended amount of current (amperes) per square foot of workpiece surface. If you see a recommended ASF Camps per square foot) of 10—20, then you would multiply the number of square feet of surface area of your workpiece times 10 thru 20 and adjust the current setting on your DC generator accordingly. To calculate square feet, multiply workpiece length times its width. How many generators you use depend on their capacity and on how many vats you will
have. A typical arrangement could have two generators; one for the soap tank (assuming an electric caustic is used) and chromic acid vat, and the other for the nickel vat. Each generator would be able to supply at least 3000 amperes. Rectifiers are today the major source of current supply. They transform the alternating current present in the power lines at the shop into direct current. They are generally used for smaller current requirements, while motor generators are used for very large current requirements. While the DC generators supply a steady source of direct current, the rectifiers have a pulsating current as they block the reverse flow of electricity. It is important if you are using a rectifier that it is appropriate for a particular bath, i.e., the chronic acid vat is sensitive to pulsating current and only rectifiers that smooth out the pulses (ripples) should be used.
A good generator/rectifier will last a long time. It should be protected from the abrasive airborne dust generated by the buffing process. Direct shorts should also be avoided. It would be desirable to have a switch that can reverse the current-useful when stripping old plates. Just as cathodic plating deposits metal on the workpiece, anodic etching reverses the polarities and causes the workpiece to lose its plates. Generators/rectifiers come in all sizes. FiBS Equipment Corp. (see suppliers list) can provide generators up to 10,000 amps. It may be possible to locate used ones locally from other plating shops in your area. The suppliers list in this manual also lists a Glacier Machinery Company that supplies quality used equipment.
The electrolyzing process is done in vats with the solutions usually above room temperature. The heating is accomplished with immersion heaters and controllers that maintain a constant temperature. In the past, vats were often heated by raising them from the floor and installing gas burners under the tank. Formerly, the heaters were of a lead coil design. Today’s materials include Teflon, glass and graphite. Teflon will not corrode, nor will it attract stray currents. AMETEK, Haveg Division, 900 Greenbank Road, Wilmington, DE 19808 is one source of this type of heater.
Racks are the holding fixtures used to suspend the workpiece from the cathode bar, into the solutions. These can be custom made to fit each individual situation.
The racks have hooks of copper or stainless steel that hook over the cathode bar. During the electroplating process, these can be clamped with large spring clamps to the bus bar to ensure good electrical contact. The parts of the racks that come into contact with the solution are coated to prevent chromium and nickel deposition and unwanted current draw. Pyramid Plastics, Tolber Division, 220 West 5th Hope, Ark., 71801 sells “Microtape” and various plastisol coatings that are effective for protecting the racks in the plating tank. The actual hooking point where the rack connects with the workpiece must be bare to permit transfer of electricity, and this part will plate. Anodic etching at periodic intervals will remove these deposits. Krome King, 113 Covert Street, P0 Box 516, Leslie, Michigan, 49251- 0516, is one supplier of racks. Racks may also be home-made. Small parts such as nuts and bolts are plated using a process called barrel plating. They are placed in large quantities inside a porous barrel which is revolved in the plating solution. Negative current is supplied to the barrel by means of danglers and the rotating small parts inside pass the current around amongst themselves and receive an even plate as they tumble.
If automobile and truck bumpers are to be plated, a hydraulic press will be needed to straighten them and push out dents. A 15 ton press should be adequate.
An arc welder or mig welder may be desired to repair parts with torn metal prior to plating. Otherwise, the workpiece will have to be sent out.
Anodes are the movable bars that hang suspended from the anode bus bar. They supply the positive current to the bath. They are strategically placed about the workpiece to provide it with sufficient current to plate. Anodes are usually constructed of a pure grade of the plating metal and are intended to corrode into solution at a rate equal to the metal that is removed from the solution and deposited onto the workpiece. If this occurs, the bath is said to be in balance. Chromium is an exception. Chromium anodes are not used; rather insoluble lead anodes are used. This requires that periodic additions of chromic acid be made to the bath to replenish it. Anodes also come in other shapes such as balls and “popcorn”. These small anodes are placed in a metal basket and bagged. Controlling the amount of anode surface is easy as balls can be added or removed as needed.
In electroplating texts, frequent mention is made of cathode efficiency and anode efficiency. When metal salts as used in electroplating are dissolved into the bath, they ionize. An ion is an atom that has either gained or lost electrons in its outer shell. In this state, it will seek to restore its normal electron complement. The cathode supplies negative current to the bath and can be thought of as a source of electrons. The metal ions will be attracted to the cathode (workpiece) so as to restore their normal electron balance. Upon reaching the workpiece, they receive the balance of their lost electrons and their orbit interlocks with the orbits of the workpiece atoms’ orbits and thus attach to the workpiece. An example is copper. If copper sulfate is dissolved into a bath, the copper disassociates from the sulfur and in the process, loses two electrons. It is attracted to the cathode (workpiece) in order to restore its normal electron state. Upon reaching the workpiece, it picks up two electrons and attaches to the workpiece. At the same time, an atom of copper from the copper anode which supplies the positive current to the bath, dissolves from the anode into the bath and leaves behind on the anode two electrons that travel up the anode to the power supply and complete the circuit. This atom of copper, actually an ion of copper, repeats the same process. The rate of deposition onto the cathode can be mathematically calculated. If the rate of deposition is less than it theoretically should be, the cathode is said to be less than 100% efficient. If the anode gives up atoms at a rate less than what it theoretically should, it is said to be less than 100 % efficient. You can see that if the anode is more efficient relative to the cathode, more metal ions will enter the solution than are taken from it. If the cathode efficiency exceeds that of the anode, more ions will be removed from the solution than are deposited into it.
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