As a manufacturer of custom made car and motorcycle parts I often get asked about finishing metal items that I manufacture.
There are numerous finishing techniques and coating processes available and many different reasons why we may chose any particular one!
Paint, powder coat, clear coat, ceramic coating, chrome plating and nickel plating, anodising and hard chrome plating are all methods typically used in the custom car and motorcycle industry.
Chrome plating is a typical one that I come across regularly when repairing or re-manufacturing or modifying particularly motorcycle, but also some historic car parts. Hard chrome plating is also used in the refurbishment of fork stanchions on motorcycles.
Chrome plating is a process where by the metal is cleaned and polished, coated in copper, cleaned and often re-polished. Coated in Nickel and then a coating of chrome plate over.
1. Inspection. If I have old parts sent to me for modification or repair I first have to establish the condition of the existing part or parts. This is important as it is no good repairing or modifying the item if the original metal is in very poor condition. Old metal parts can corrode to the point that there is very little thickness left once the process of removing the old plating has been completed.
2. Stripping. Parts need to be stripped to bare metal; this process can involve removal of all paint, dirt, oil and grease, rust, old plating and any other foreign material. Typically then a process of sand blasting will be used to strip any old coating applied. It is at this point I sometimes realise that the material of the existing part is too thin to do anything with due to corrosion. Hence it is important to try and assess the part before any work (and cost) is completed.
3. Polishing. Polishing is the removal of surface material using a abrasive wheels and belts of decreasing grits to remove any marks or blemishes and “smooth” the surface. I start by using coarse-cutting sanding discs and belts, working down to soft cloth buffs. The result is a highly polished metal part with all pitting, scratches and impurities removed.
4. Cleaning. Parts must be exceptionally clean before plating — the smallest spec of dirt, grease, oil, buffing compound, rust, or any other foreign matter will cause imperfections in the finished item. For this purpose its common to use series of soap, acid and water solutions to guarantee a clean, spotless surface.
5. Copper Plating and Buffing. Parts are copper plated and then buffed to a brilliant shine. This is an important step in the process, copper offers an added layer of corrosion protection and helps to fill-in polishing lines and any marks. The actual copper coating may be very thin but this can be built up in layers to help fill in marks and blemishes (like a painter may use a filler material).
6. Nickel Plating. It is the nickel which provides the deep shine of a chromed part, in addition to providing another layer of protection for long-lasting chrome.
7. Chrome Plating. Chrome, the final plating step, is actually a protective coating over the shiny nickel which prevents the nickel from tarnishing.
Any number of layers of copper and nickel can be added to an item to build up the finish and what you will find is that in some less reputable companies these will be skimped on leaving you with an inferior quality of chrome plating that will not last as long and certainly not offer the corrosion protection expected.
If you want to know about chrome plating before you submit your parts to your chroming company ask them about their process. They should always use a “triple chrome plating” process – copper, nickel, chrome (3 steps). Some less reputable companies will use a nickel, nickel, chrome process or even just a nickel, chrome (2 step process). This obviously gives a far less desirable finish.
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