Brightening Aluminum on vintage BMW Motorcycles
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Q. I am not sure if your web page is only for the finishing industry, but if someone has a solution (pun intended) to my problem, it could be financially rewarding.
For many years, I, along with other restorers have been looking for a way to brighten the alloy engine, gearbox and final drive castings on BMW motorcycles. A chemical cleaning method is desired, since media blasting and brushing tend to change the surface texture. No finishing process is applied to the castings and in time, they darken, stain etc. for the usual reasons. Repeated application of commercial aluminum brighteners will leave a black deposit on the surface. Products such as Indo 326 etc. would be suitable if the black deposit could be removed. I would appreciate it if you could direct me as appropriate to an information source, or the classification of chemical required so that I can contact one of your advertisers for a local distributor.
from many frustrated vintage BMW ownersAvery Frail
A. Users are the most important part of an industry, Avery; our site is restricted to metal finishing topics, but not to metal finishing people :-)
I would guess that the black deposit is copper & silicon, and the other alloying elements in the casting. As you dissolve away aluminum with repeated applications, the surface becomes ever richer in these other materials. It is possible to make pure aluminum mirror-bright by chemical bright dipping followed by anodizing; in fact, this is how most reflectors on outdoor lights and medical lights are made. Alloying elements make it more difficult to obtain mirror brightness, but not necessarily impossible--it depends.
Albright & Wilson is a major supplier of proprietary aluminum bright dipping solutions. You might also check the yellow pages under anodizing, plating, or metal finishing to see if any local shops do aluminum bright dipping, as well as reviewing the Shop Directory here.
Whether the alloy in question can be made permanently bright by immersion bright dipping and anodizing is a question I can't answer--experimentation would be necessary. But my feeling is that it will be impossible to get and keep a mirror finish unless the parts are disassembled, and properly bright-dipped and anodized in immersion tanks using chemicals you wouldn't want to mess with except in an industrial setting.
Everything you could want to know about aluminum bright dipping and finishing can be found in The Surface Treatment & Finishing of Aluminum and its Alloys.
Ted Mooney, P.E.
Pine Beach, New Jersey
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