DESCRIPTION: AT A BEGINER'S LEVEL , DISCUSSES METAL
PREPARATION, EQUIPMENT, BATH FORMULAS FOR PLATING
CHROME, NICKEL, SILVER, GOLD, COPPER, ZINC, AMONG
AUTHOR: RANDELL NYBORG
Pickling is necessary to properly "activate" the workpiece so it will accept a plate. Non-pickled metal has a hardened and distorted surface which will not bond properly. This surface must be removed in order to expose the true crystalline structure into which the electrodeposited metal crystals can crow. See figure 6.
Mechanical methods can be used as well such as sandblasting or sanding, but acidic pickling does not damage the surface as much. A sulfuric acid pickle is probably the best for the hobbyist plater as it is cheap and relatively non-fuming. Muriatic acid is also used. Add 5-10 ounces of sulfuric acid to one gallon of water. Never add water to acid. Smaller quantities can be made up by proportionate reduction of water and acid. Steel is pickled in solutions at 130 degrees Fahrenheit for 1 to 2 minutes. The part must not be allowed to pickle for too long in order to avoid excessive etching and potential hydrogen embrittlement. Anodic etching is often used to speed up the pickling process. The workpiece is made anodic (positive) and the current turned on for up to 20 seconds. Voltage used should be 4 to 6 volts. The larger the part, the more current capacity will be required, although voltage requirements will not increase. The part will gas freely and the surface should activate. In some applications, the chromic acid vat is used for both pickling and plating. The workpiece is allowed to warm up in the chromic acid vat. Anodic current is applied for a few seconds, the current is then reversed and electroplating ensues. Repeated use of this technique however, will cause the chromic acid solution to contaminate with iron through dissolution of the steel workpiece. Also, excessive anodic etching will promote hydrogen embrittlement. Sometimes in the pickling process, particularly with electropickling, a light or dark smut will form on the workpiece. This should be removed by mechanical means such as rubbing with steel wool prior to immersion in the plating vat. Allowing the smut to remain will interfere with the plating process. Smut is more frequently associated with higher carbon steels.
To achieve maximum brightness or to salvage dull plates, the plating may be buffed with cloth wheels into which an abrasive has been introduced. Use a stitched cloth wheel with Tripoli compound, then follow up with a loose cloth wheel and white rouge compound at speeds of about 2000 Rpm. Eastwood Company has a good supply of polishing equipment for hobbyists.
TABLE OF CONTENTS:1.THEORY