Evaluation of Powder Materials

Q. We have been looking for a second source for our powder materials to avoid being too dependent on one company for supply. Our plan is to have them supply a smaller percentage of our powder, but be available to supply all of our colors if we need them. My question is: what issues should we consider in order to evaluate different suppliers and pick the best one? We know that the price per pound is one item, but how can we be sure it is good powder? E.M.

A. If you have a lot of volume it can be useful to have two sources of supply. You can often get the best technology and price by working with more than one manufacturer. In order to evaluate the best supplier you will have to do a lot of work. When you evaluate the cost be sure that you look at applied cost, not just the cost per pound. The applied cost is critical because it must be very close to the existing material. Applied cost factors in the film thickness, material utilization percent and specific gravity of the material. The formula is:

192.3 × material utilization/film thickness × specific gravity = square feet per pound

The number 192.3 is the coverage in square feet at 1 mil thick if the specific gravity is 1.0 and material utilization is 100 percent. The specific gravity is a measurement of density, and it reflects the percent of resin (the film forming component in the powder) and the percent of other ingredients added for color, filler or other properties. Generally speaking, a high-specific-gravity powder will provide less coverage.

Once you have established a theoretical coverage and applied cost, you should evaluate the material properties that affect application. Check fluidization to see if the product reacts well in the feed hopper and is easy to spray. Check application to see if it hides at a low film build and fills in the Faraday areas effectively. Check the overspray powder to see how much the particle size distribution shifts after the powder has been recovered. If the material applies well and reclaims well you can start looking at the final part of the evaluation. How stable is it in storage? Is it compatible with the powder from the other supplier? How well can the potential supplier service you?

Answer all of these questions and you should have a good idea of who to work with.