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A process called “powder coating” is often mentioned in the numerous television documentaries on vehicle repair and restoration. How does it differ from conventional spray painting? PB
Powder Coating is a kind of “paint” that is more resistant to chipping, scratching or flaking. Because it comes as a dry powder and not a liquid, it does not have a solvent that evaporates, it doesn’t run or sag during application, it can be applied more evenly to multi-faceted surfaces, and it can be built-up into thicker layers.
And because it is cured using UV light at lower temperatures than the high bake for liquid paints, it can be applied to a wide range of materials without distorting them.
It is extensively used to paint the bodywork domestic appliances which suffer a lot of bumps and abrasive touches, and in cars is most commonly used for painting wheel rims which suffer a lot more dirt and wear and tear than the rest of the bodywork.
The invisible “magic” of the process is how you get a dry powder (like talc) to stick to a smooth, clean, dry and often vertical surface. The answer is electromagnetic force – what you and I would call “static”.
The workpiece and the powder are suitably “charged” so when they meet, they act like magnets to each other, not just hanging on but physically bonding together.
When the layer of powder is cured, it goes through a “soft” phase and additionally acts like a “glue” before hardening at a slightly higher temperature that turns it into a hard and shiny skin.
Electromagnetism is also used by car manufacturers when dipping or spraying body parts in liquid paint.
There’s a lot more static around that you might realise, thanks to what is known as the “triboelectric effect” caused by friction between different materials…such as seawater and the hull of a boat, or your hairbrush and you head!
There’s even a party trick to demonstrate it. Take an empty and dry beer bottle and rub it vigorously up and down over several centimetres in the corner of two smooth walls in a room.
If conditions are right and static has been generated, you can let go of the bottle and it will remain stuck to the walls. And a force than can hold the weight of a bottle can certainly hold a grain of talc weighing a millionth of a gram!
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