Mill scale to showroom: how a raw blank becomes a finished part
Powder coat only lasts if what’s under it is right. Follow a raw steel blank through blast, pretreatment, booth and oven — and see why the invisible step matters most.
COVER · SHOP FLOORWhat’s wrong with a raw blank
Fresh off the laser, a steel part wears two things powder hates: mill scale — the blue-grey oxide skin from the rolling mill — and a film of oil. Spray colour straight onto either and it looks fine for a month, then flakes off in sheets. Everything good about a finish happens before the colour goes on.
Blast and clean
Steel gets shot-blasted — abrasive fired at the surface — which strips the mill scale and rust and leaves a fine "key", a micro-roughness the coating grips. Aluminium and stainless are chemically cleaned and etched instead. Either way the part comes out bare, bright and hungry for the next step.
Pretreatment — the invisible step
Now the part runs through a multi-stage chemical wash — degrease, rinse, a conversion coat (phosphate or zirconium), rinse again. You can’t see the result, but this microscopic layer is what bonds the powder to the metal and blocks corrosion from creeping under it. Skip it to save an hour and the finish fails in a season.
Nobody ever admired the pretreatment. It’s also the only reason the coat is still there in five years.
Coat and cure
Dry and masked, the part is hung and sprayed: powder carries an electrostatic charge and wraps to the earthed metal, even around edges. Then it bakes — around 180–200 °C — and the powder melts, flows and chemically cross-links into a single tough film. That heat cure, not drying, is what makes powder harder than any wet paint.
Inspect, and out the door
Cooled, the finish is checked for colour, gloss, coverage and film thickness, masking is pulled from threads and earth points, and the part is packed to arrive unmarked. What started as a scaly grey blank leaves as the finished part you pictured — ready to install.
- 01 Colour and gloss to spec Checked against the RAL and gloss on the order, not by eye alone.
- 02 Film thickness in range Gauged — too thin under-protects, too thick chips at edges.
- 03 Masking removed Threads, mating faces and earth points bare and clean.
- 04 Packed to travel Edges and faces protected so it arrives the way it left.
Want a finish that’s still on in ten years? It’s made under the colour, not in it. Send us the job and we’ll blast, pre-treat, coat and cure it right the first time.