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Powder Room

Powder coating parts for your car and how it's done.

By Michael Knowling

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Powder coating is one of the most popular surface finishes used on modified and show cars - and with good reason. It can be successfully applied to any metal (so long as it is in good condition), it lifts the part's appearance and it lasts for years. Plus, it also forms a barrier to help protect the part from various types of corrosion. However, depending on the metal's composition and its intended application, it may need special preparation using thinners for example. Just about every colour is available in a choice of matt and glossy finish, and there are also some oddball-looking rough finishes to be found.

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We had a bare aluminium strut brace lying around that we'd fabricated, and thought it'd be an ideal subject to get powder coated. Because the underbonnet scenery of the lucky car included some silver and grey colours, we chose to have the bar coated in silver. For this reason, the colour difference between the un-coated aluminium and the finished product is hard to pick in our photos - but rest assured, there is a major improvement in surface finish.

Preparation

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The initial step was to submerge the bar in a series of four baths for around 5 minutes each. The first was an acid etching bath, which eats slightly into the aluminium and removes any oil and grease. Once our aluminium brace was lifted out, the cleaning effect was obvious as it had a much greater shine. It was then suspended in the air for a while to allow the acid to drip off, and it then went into a water bath. This simply rinses all the acid from the surface, making it ready for the next step.

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Our bar then got lowered into a chromate bath that treats the metal to enable the powder coat to bind to the part's surface better. It also allows the part to flex slightly without having the powder coat flake off. Once again, the object then gets lowered into another water bath for a final rinse and is then left to dry. Note that sometimes parts like this can fill up with these fluids through small pinprick-sized holes in weld lines, etc. It is important the part is then drained and heated until dry, prior to coating and baking.

Applying the Powder Coat

The application of the powder coat is conducted in a purpose-built booth in which the part is hung from hooks in front of the operator. Interestingly, the business that coated our strut bar told us that their elaborate air extraction system goes through separate air/powder separator and filters, which actually catch the wasted powder in a tray ready to be used again. However, because different colours are frequently being applied during the day they don't usually keep this excess for re-use.

The process of coating a part can be quite fast, but more time is often spent loading in the desired powder colour into the system and flushing the previous colour out of the lines. The hanging hooks that are used to suspend the object in the booth are also cleaned off and spayed with the new colour to ensure none of the last colour makes its way onto the object.

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Putting the powder onto the part is a special gun that puts an electrostatic charge into the powder particles as they passed through the nozzle. This static charge holds the powder to the object prior to baking - and it is capable of holding it there for at least days! The gun puts out a fine spray (almost a mist) of powder that has the ability to wrap around corners and edges slightly, enabling more intricate forms to be covered quite thoroughly. An even coat is applied all over, using the gun in a similar method to a conventional spray gun.

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Baking

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Still covered in the static-charged powder, the object is hung from a rack and locked inside a large oven. The oven used to cook our strut bar was set at 190 degrees Celsius and it went in along with some other components for around 20 minutes. Here the high temperature of the part triggers a catalyst inside the powder. This causes the coating to change from a powder into a liquid similar to paint. It then bakes onto the surface, and any slight imperfections disappear as the liquid flows very, very slightly.

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After twenty minutes the rack was taken out of the oven and allowed to cool. That's it - and here's how it turned out (remember, we chose a similar finish to the original aluminium!).

As with any painted surface, it is recommended that you regularly clean the object and give it a polish when it needs it. This will make certain you'll get the maximum service life and best appearance out of the coated part at all times.

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