Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2004

Powder coating Vs. Liquid Polyurethane on Aluminum Wheels

Q. We are an aluminum wheel repair facility using urethane paints on our reconditioned wheels. All machined wheels are pre-treated with PPG product DX-501 before spraying with clear. Will it hold up as well as powder and be durable? What are th pros and cons with powder coating?

Clear liquid polyurethane coatings are used quite extensively in the automotive industry. They're primarily used as the clear coat, top coat found on most cars and are formulated to be very durable. Clear powder coatings have not yet gained recognition in this area primarily due to aesthetic reasons. Clear powder coatings are used quit extensively by automotive wheel manufacturers, are durable and can be very cost-effective.

You don't tell me what your processes are, I will assume that the wheels are liquid coated then removed from the spray area, and allowed to air dry. The equipment expense involved for this type of application is minimal in comparison to the equipment needed for powder coating applications.

Powder coating application requires special electrostatic spray guns, and an oven to melt and cure the powder. Powder coatings have many advantages over liquid coating systems. Some of the primary ones are: Low VOC emissions (essentially none) Low toxicity and flammability, No solvent needed in application, Wide variety of colors, glosses, and textures.

Powder coatings also have limitations. Some are these are: High baking temperatures 325-400 degrees F, oven-curing restricts it to shop use, color change is labor intensive (costly), atomized powder in air may be explosive, initial equipment expense.

As with the liquid polyurethane coating system, the aluminum surface must be very clean, and free of any dirt, oil, or grease. The use of an aluminum pre-treatment or conversion coating is always recommended to promote good adhesion and provide good corrosion resistance. I recommend that you contact a local powder coating representative and discuss the possibilities of converting to a powder coating system.

Regards,

Jim Burke