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The Significance of Particle Size in Powder Coating Transfer Efficiency

August 6, 2019

Looking deep, coating particles are clearly incredibly fine. They're discharged from an electrostatic gun, driven forward by compressed air, then there's a split-second of airborne drift. At this point, a workpiece with an opposing charge attracts the tiny pigment-loaded grains. On the charged surface, a thin film accumulates. It forms an even coating on the treated part. So far, so good, but what happens now if the particles change size?

What Decides Powder Coating Grain Size?

Picture a large mixer. It's filled with pigmentation agents and thermoplastic resins and special flow facilitating additives. Again, that's a satisfyingly standard foundation, which is used to create infinite variations of coating particles. The mix homogenizes and melts, and then it cools into a large tablet. Here's where the important stage takes place. With the mix cooled, a grinding machine breaks the solid sheets down into a mountain of tiny particles. Sieved and packaged, the powder coating intermixture receives its label.

Fine Powder Sizes Charge Faster

The organic polymers are dry and powdery, as they're obviously intended to be, and they're labelled with a standard powder size. In fact, now thinking in terms of multiple product packages, manufacturers can tailor the size of the particles so that some products behave in a predefined manner. For instance, fine grains absorb higher charges, perhaps because there are more of them and they can crowd closer together than coarse particles. At any rate, that feature is desirable when working on an improved wraparound effect. Flowing with the electrostatic fields and air currents, the finer grains swing easily around the external edges of a grounded workpiece.

Beating Back the Orange Peel Effect

Lighter particles lay down a thinner powder-coated finish. Logically, coarser or larger dry particles will produce a thicker finish. That's just common sense, right? Now, what if the discharged powder carries fine and coarse grains? Fluidizing and curing at different rates in the end sequence oven, the smoothness of the coating decreases until a rough, uneven texture is produced. This is the so-called orange peel effect. A change to the temperature ramping settings on a powder coating oven can quickly fix this issue. If it still causes texture problems, the entire batch of powder may need re-sieving. This action will optimize the powder size distribution of the particles.

Using Faraday Cage problems as a final example, it's not easy to get powdery fines to settle evenly within hidden part's cavities. In this case, coarser, more densely ground down grains anchor themselves faster within areas that create such field effects. Finally, going back to machine maintenance and powder reclamation concerns, fine powdery deposits will cause larger-than-life system hitches. The fine particulate matter causes nozzle clogs and other maintenance-hampering headaches.

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

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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