The Best Method for Coating Aluminum Extrusions

Q. My company has a vertical, liquid painting operation using electrostatic discs and painting aluminum extrusions with high solids polyesters to a meet AAMA (American Aluminum Manufacturers Association) 2603 specifications. We used to have a horizontal powder coat line, but we discontinued use due to low demand for the shorter lengths of aluminum extrusion that we could run on that line. I have two questions:

1. We are seeing powder coated products being offered at cheaper prices than liquid painted products. How do powder coaters paint for less than liquid paint? Is it labor, better transfer efficiency? What?

2. Which is better, at high volume production, a vertical line, or a horizontal line? We are trying to decide what to plan for our future.—T.B.

A. You asked why powder is less expensive than liquid on aluminum extrusions. When one coating method is less costly than another, it often is related to a number of cost items. It may be related to the cost of the coating material, labor, environmental factors and simple efficiency of the system. In the case of powder versus liquid, it starts with environmental issues. Powder does need to exhaust plant air from the booths, because it does not have any vapor in the exhaust stream. That removes the cost of air supply necessary for liquid coating booths. Powder does not generate solvent-laden hazardous waste and avoids the expense associated with frequent filter replacement. Material utilization can be very high if the system is designed to reuse overspray. Powder also comes ready to spray and it does not need to be mixed or adjusted to achieve the right viscosity for spray. So in this way, powder provides several cost advantages over liquid while providing a high quality finish.

You also want to know which is best for aluminum extrusion coating, vertical hanging or horizontal hanging. There are a number of advantages to the vertical system. They can run much longer parts that are very popular in the extrusion market. The parts can hang very close together with a lower line speed, leading to very high transfer efficiency. Obviously, the system is much taller, but it is also much shorter in lineal travel than a horizontal system. Keep in mind that vertical hanging does require some unique loading and unloading capability due to the conveyor elevation. But in general, vertical lines have been very successful and offer several advantages.