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I have had a stock set of wheels chrome plated on a Valkyrie and also purchased an aftermarket set of custom wheels from RC Components, and
in both cases the wheel bearings would not fit back in the hub due to the ever so small thickness of the plating, so have the dremel tool ready to remove the plating where the bearings are to be installed....
What fool would chrome plate anything without "masking off" the bearing/internals area!!!!
Stop-off lacquers
The most widely used stop-off materials are lacquers. There are a number of formulations commercially available, but the quick drying vinyl lacquers are the most commonly used stop offs for hard chromium plating. These feature application ease, adequate adhesion and ease of removal. Since they do not normally go through cleaning cycles, they are not strong in their resistance to alkaline cycles and cleaners. Depending on the complexity of a part and the drying time of the lacquer, it may take 30 to 40 minutes to apply three to five coats of lacquer, which is the minimum considered adequate for elimination of porosity. After plating, the lacquer is peeled, or chemically removed with a solvent. It is usually best to remove the lacquer at the conclusion of the plating cycle. If allowed to remain for days, the lacquer will become especially hard to remove.
Lacquers especially designed for hot alkaline cycles and acids are also available. These stress adhesion and maximum chemical resistance and consequently, are not easy to remove after plating. Tenacity through the baths and removability after the cycle are polarities which always represent a formulating compromise. Some lacquers feature ease of stripping but these may not exhibit the best adhesion.
Virtually all stop-off lacquers may be air dried. However, the required time will vary with such factors as coating thickness, temperature and humidity. Since they all contain volatiles which must be evaporated before immersion in hot solutions, force drying is recommended when possible, to eliminate some of the variables. This may be accomplished by forced air,
hot plates, or even ovens. Failure to completely dry the film may result in blisters, pin-holing and plate-through. Force drying will also usually enhance adhesion for tough cycles.
Waxes
Two commonly used types of waxes are high temperature chlorinated synthetic waxes and petroleum based microcrystalline, low-temperature waxes. The latter are much more widely used because they are less expensive, and because they present a lower level of toxicity.
A part must lend itself to dipping in order to use a wax. When practical, a wax is the most economical, most efficient method of masking because the wax may be salvaged and re used.
The low temperature waxes melt at about 180
°F, and will begin to soften and sag in the neighborhood of 145 to 150
°F. For this reason, they should not be used in solutions operating higher than 150
°F.
High temperature waxes are liquid at about 300
°F. These waxes can take anything in a plating cycle. Some may be made from chlorinated formulations, posing an odor and toxicity problem.
In order to obtain optimum adhesion with wax, the first coat should be only virgin wax and should be applied to a hot part. This can be achieved by preheating the part, in an oven or vapor degreaser, or leaving it in the wax pot until it has achieved temperature. The resultant first coat is very thin, but will be adherent.
One advantageous technique is to maintain two wax pots, one at a higher temperature, to apply the first thin coat and to facilitate removal after plating. Subsequent coats are applied as the part cools, and heavier deposits obtained.
After wax coating, the wax is manually removed from areas to be plated using cutting and scraping. Many operators prefer to trim the wax while it is still warm and easily carved and shaped. The waste trim should be tapered down to the area that is to be plated. This leaves only a thin residue on the areas to be plated, and reduces the tendency of the chromium deposit to build up at the wax border. After the part fully cools, the thin waxy residue, on any areas to be plated, is removed with live steam, solvents, pumice or water-slurry abrasive blasting.
After plating, the wax is removed by immersion in the hot used wax tank or in hot water or in a vapor degreaser. At least one plater has had great success by immersing the waxed part in the used wax tank to remove the bulk of the wax, followed by a hot (260°F) oil immersion followed by an alkaline electrocleaner. This eliminates vapor degreasing.
Wax pots are typically heated with electric heaters or oil jacketed tanks. The heat source should never directly touch the container holding the wax, as excessive temperature can decompose the wax, leading to poor adhesion.
Poor adhesion can also result from using a wax that has been contaminated with too much chromic acid (from re-use of masked wax).