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Why Silver finish on wheels is a problem (archive)
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Posted by kwillmorth on June 24, 2000 at 09:40:06:

Paint is not a precise science. Not even powder coating. My company does powder coating on the order of thousands of parts a day. we do mostly silver, gray, white, dark bronze and black. The two dark finishes are no real problem and can be duplicated easily day by day. Gray isn't too bad at all, but can shift from neutral to warm in different batch runs. White and silver are problematic and give us the biggest headaches.

If it's a humid day the powder lays on the product a little thicker. dry days it tends to get a touch thinner. On silver over aluminum, this means one day the base metal might actually be ever so slightly visible through the finish, on another not at all. Next you put the parts through a baking oven at 450 degrees, for some 40 minutes or so. A touch longer or warmer, the parts color is warmer (yellower) and smoother or more glossy. A touch cooler, or shorter in curing and the part will be flatter and less warm in color.

Silver is a complete bitch because it includes suspended aluminum powder in the resin to give it its metalic look. Aluminum tends to settle out of the resin somewhat, so the first wheel in a batch might be less metalic that the last one out of the same box of material. Each box of powder is a little different than the other, compounding the situation.

Two part finishes like I believe the Roadstars are, with a base silver color and a clear powder overcoat, mean the parts get baked twice and have two layers of finish applied. This will compound the variables tremedously!

If you have a line set up to do parts with a certain color, all day, every day, then you can control most of the variables and make fairly consistant parts within batches and reasonable matches from batch to batch. This is done by drawing powder from a large hopper of many boxes of material, mixed up and continually agitated to make sure it stays all mixed up. Further you have a conveyer system built to control oven time, and are constantly monitoring each run to a standard, adjusting variables in the process to make each part a consistant color.

Unfortunately, if you are just painting one wheel at a time, you do none of this. You just grab a box of powder that is specified to match, blow it on the part and bake it.. done. What comes out the other end is the best that can be done... end of story. And it will never match the original part, as the chances that that one single part will have been finished within the same variables as the original are slimmer than winning the lottery... not a chance.

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