GlossaryKind of term: Manufacturing termPowder coating
What is powder coating?
Powder coating sprays dry powder electrostatically onto a part, after which it melts and cures in an oven into a closed paint film.
The powder is charged and the part earthed, so the powder clings until it has melted and cured in the oven. The colour usually appears on the drawing as a RAL number, often with gloss level and texture. The layer is usually thicker than an anodic or nickel layer, typically tens of micrometres, and provides colour and corrosion protection on steel and aluminium. Materials that cannot take the oven temperature, such as most plastics, are generally not candidates.
What decides the quality of a powder coat?
Adhesion and corrosion protection depend mainly on pretreatment: degreasing, blasting or a conversion coating for steel, a conversion coating for aluminium. The curing schedule follows from the powder, often an object temperature between about 160 and 200 °C for a set time. Electrostatic spraying gives thinner coats in internal corners and deep recesses, where the field is shielded, and the paint pulls back from sharp edges. The film insulates: earth points and electrical contact faces must stay bare.
How does powder coating work in practice?
Fits, threads, mounting faces and earth points are masked with tape, plugs or caps, or cleared afterwards. That masking is handwork per hole and per face, and on a part with many threaded holes it can take longer than the coating itself. The part has to hang somewhere, on a point that stays bare after coating. Coaters often charge per piece, per rack or per square metre, with a minimum per colour; a special colour on a small batch carries the whole colour change. Pretreatment and transport come on top.
What is powder coating often confused with?
Powder coating is not wet painting: wet paint is liquid, dries in air or in a lower-temperature oven and usually gives a thinner film per coat. Anodising converts the surface of the aluminium itself into an oxide layer; powder coating adds a layer of another material.
How do you see powder coating in Blake?
In Blake powder coating is a proposal from the drawing, shown with the part for you to confirm or correct. The coating gets its own estimate line from your subcontract library; if that line has no price yet, it stays open. More on estimating.
Frequently asked questions
Do I need to mask threads for powder coating?
Usually yes, or re-tap them after coating. The film is too thick for the clearance in a standard thread, and cured paint is hard to remove. Plugs or caps are the usual answer, which takes time per hole.
Why is a small batch of powder coating expensive?
Because coaters often charge a minimum per colour and have to change the line over. A standard colour in a regular run is cheaper; with a special colour for a handful of parts, those few pieces bear the full cost of the colour change.
How thick is a powder coat?
That depends on powder, method and specification; tens of micrometres per coat is common, with thinner spots in internal corners and on edges. If the drawing gives no thickness, ask when fits or mounting faces are involved.