What is powder coating?
Powder coating is a finish where dry paint powder is sprayed onto a part with an electrostatic charge, then baked in an oven until it melts and cures into a hard, even coat. It's one of the most common finishes for fabricated steel and aluminium parts, and it's priced by surface area.
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What does powder coating mean in fabrication?
Powder coating happens in three stages:
- Pre-treatment: the part is cleaned and degreased, and often blasted or given a conversion coating so the powder bonds to it.
- Application: a spray gun charges the powder, so it clings to the earthed part in an even layer.
- Curing: the part goes into an oven, where the powder flows out and hardens. The powder's datasheet sets the schedule; many polyester powders cure in 10 to 20 minutes at 180 to 200 °C (356 to 392 °F), measured at the metal.
Coats are commonly 60 to 80 microns (2.4 to 3.1 mils) thick. Colours are specified by RAL code, such as RAL 9005 for jet black, along with a gloss level and a texture.
How is powder coating used?
Many fabrication shops send powder coating to a specialist coater; others run their own line. Before parts go, the shop checks:
- edges: deburred, and on oxygen-cut steel, free of the oxide layer that makes powder flake
- threads and holes that must stay clear, which need masking or plugging
- hang points: a hole or tab the coater can hang the part from, if the design allows
- galvanised parts, which need specific preparation to stop trapped gas bubbling through the coat
Coaters charge by area, per square metre or square foot, and many have a minimum charge per batch.
Why does powder coating matter?
The coating is what the customer sees, so its problems reach the customer. Most coating failures start before the powder goes on: sharp edges where the coat goes thin, dross or oxide that lets it lift, or contamination the pre-treatment didn't remove. That's why coating and deburring are quoted together.
Coating also adds lead time. An outside coater's turnaround, plus freight both ways, belongs in the quoted delivery date.
Oxide edges on laser-cut steel
Mild steel cut with oxygen leaves a thin oxide layer on the cut edge, and powder applied over it can flake off along the edge. Shops deal with it in three ways:
- cutting with nitrogen or air, which leaves a clean, oxide-free edge
- grinding, blasting or edge-rounding the cut edges before coating
- telling the coater, so the pre-treatment removes it
Nitrogen cutting costs more in gas but saves a cleaning step on every part, so the choice depends on volume.
Powder coating and quoting
Powder coating is priced on surface area: the area of every part, both faces and the edges, multiplied by the coater's rate, plus handling and markup. Tempus Tools measures both faces and the edges of each part to get its full surface area, then multiplies it by your coating rate, so coating lands on the same quote as the cutting.
Further reading: Deburring meaning: what it is and why it matters in metal fabrication
Related terms
Price coating from each part's real area
Tempus Tools measures both faces and the edges of every part, applies your coating rate and adds powder coating to the quote alongside the cutting.
FAQs
How is powder coating priced?
By surface area, in square metres or square feet, counting both faces of the part and its edges. Some coaters also charge for masking and colour changes, and many have a minimum charge per batch, which matters on small orders.
How thick is powder coating?
Coats are commonly 60 to 80 microns (2.4 to 3.1 mils). The powder's datasheet gives the range for each product. A coat that's too thick can leave an uneven, orange-peel finish and can fill fine threads and small holes.
Can you powder coat galvanised steel?
Yes, with the right preparation. Galvanised coatings can release trapped gas in the oven, leaving pinholes or bubbles in the powder. Coaters prevent this with specific pre-treatment, pre-heating the parts or using a degassing powder, so tell them the parts are galvanised.
Why does powder coating flake off laser-cut edges?
The usual causes are the oxide layer that oxygen cutting leaves on mild steel edges, and sharp edges where the coat goes thin. Cutting with nitrogen or air, or cleaning and rounding the edges before coating, fixes both.
What is a RAL colour?
RAL is a European colour standard that gives each colour a code, such as RAL 9005 for jet black or RAL 9016 for traffic white. Customers use RAL codes to specify powder coat colours, along with the gloss level and texture they want.