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Process of Metal Pretreatment in Powder Coating

July 26, 2017

Like an eraser stripping away the smallest pencil mark from a premium sheet of paper, the powder coating metal pretreatment process cleans project workpieces until they're spotless. Bared metal is all that remains, which is as it should be because this denuded surface guarantees a uniform coating, courtesy of the electrostatic application cubicle. Just how deep does this pretreatment stage penetrate?

Optimally Prepared: Mechanical Abrasion

Before the electrostatic station is accessed, a metal workpiece makes a beeline for the metal pretreatment room. It's in here that corrosion, grime, and old paint are scrubbed away. A wire brush is part of a fundamental abrasion cleaning process, but for that extra-clean, extra-virginal look, sand blasting equipment purges every adhering particle. Better yet, a properly conducted sand blasting process refines the surface by smoothing out old scrapes and scratches until there's not a single irregular edge left.

Solution Prepped Objects: Chemically Clean

At the lower end of the spectrum, hot water and steam wash oil and dirt from the metal part. Beyond the power of pressure and steam, there are chemical compounds that do the job more efficiently. Mid-level degreasers and cleaning agents work well, but for an absolutely deoxidized metal frame, it's time to call in the acids and alkalines, the fluids that eat away stubborn oxidisation stains. These are the sprays and dipping baths that the parts pass through before they reach the conversion coating stage.

What is a Conversion Coating?

This is a targeted, alloy-dependent work phase. Remember, the metal part is completely naked now, so it'll oxidise if it doesn't immediately undergo the particle coating stage. In order to extend that period and really give the powder a surface to grip, the conversion spray, or bath, coats the workpiece in a temporary protection film, one that prevents corrosion and promotes the adherence properties of the metal. Phosphate coatings are common here, but there's a newer chemical coming, a solution known collectively as transition metal coatings.

The pretreatment process in the powder coating industry exists to denude the parts so that they will absolutely accept the dry powder. The conversion section of the process then improves underlying corrosion resistance and initial powder adherence. However, there are caveats to keep in mind. Aluminium, for instance, requires an alkaline bath, for it's a metal that oxidises readily. As for mild steel, this mainstay metal should be cleaned, possibly sand blasted, then coated in either iron phosphate or zinc phosphate before it's exposed to the powder coating cubicle.

GP Industries Pty Ltd

Head Office

1 Regal Court,
Vermont South VIC 3133

Phone: (03) 9802 1355

Fax: (03) 9802 6027

Email: gp_ind@bigpond.com


Factory G,
20 Burgess Road,
Bayswater North VIC 3153

Phone: (03) 9761 7676

Fax: (03) 9761 7671

Email: gpfactory@bigpond.com

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