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Powder Coat Adhesion Testing Process

July 4, 2019

Just to clarify matters, there are ways of testing powder coat adhesion strength. That fact may come as something of a surprise, especially when you remember just how hard it is to part a baked-in coating from its surface, but there are test procedures that are designed to get around such challenges. Fused to a workpiece or not, the testing process measures adhesion integrity most effectively.

Fully Cured Adhesion Testing

Upon leaving the curing oven, a powder coated part has gained a new skin. It's coloured and shiny, or dull and textured. Whatever the finish is, it's entirely weatherproof and impact-resilient too. Is that really the case, though? Can the quality-control department just accept that statement and give the workpiece a tick of quality-assured completion? That's something of an unwarranted assertion, no? To really make the QC department happy, let's test the coating and measure its adhesion strength.

Introducing the Test Techniques

Let's start with a crosshatch test. A utility knife cuts a pattern into the coating to check for overbake or underbake issues. The cuts go all the way down to the substrate. At this point, a special type of contact tape is applied to the cut area. If any of the powder coating finish comes away with the pressure-sensitive tape, then the current run of cured parts has an adhesion defect. If the results of this test are inconclusive, the next test is tried out. This time around, the Mandrel Bend Test puts stress on the treated part. If the coating cracks or peels away, the finish isn't properly fused to the workpiece surface.

Running an Adhesion Test Station

Of course, as evidenced by all this talk about cutting and bending, these are destructive tests. In theory, the crosshatch test uses a recoverable test procedure, but the part will need to be stripped and recoated all over again. Bend tests can't be recovered, obviously, so use a waste workpiece if this technique is going to be utilized. As a variation on a theme, impact analysis involves the dropping of a heavy ball onto a powder coated part. If the depression made by that ball introduces a crack, then the coating isn't adhering.

Things only get tougher for powder coat adhesion test candidates. They're tortured by knives and crushed by mandrel bending machines. There's even a salt test technique, which sprays a surface with abrasive crystals. To confirm finish integrity, these destructive tests really are an essential measure, so a current batch run should always include one or two waste pieces, which will be sent for testing.

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

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20 Burgess Road,
Bayswater North VIC 3153

Phone: (03) 9761 7676

Fax: (03) 9761 7671

Email: gpfactory@bigpond.com

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