Powder Coating Q&A: Hanging Parts

Q. We are having a lot of trouble with rejects. We can do a good job some days and get out a lot of good parts but we are not as consistent as we need to be. One of my concerns is the way we rack our parts and take care of our hooks and racks. Some of our racks have a lot of powder build- up on the contacts and rack maintenance is spotty. We have some racks that are banged up and we use some hooks that do not hold as many parts as we could fit on the line if we had a better racking scheme. Is there any way to qualify the impact of racking on the powder coating process?

A. This is an interesting question. If I were to single out the biggest and most obvious loss of revenue in a coating shop I would say it is poor racking. It is very common to see large line gaps, bent and broken racks, twisted hooks, too much powder build up on racks, racks that are only partially full, different hooks or racks being used for the same part or just bad rack designs. The cost of poor racking is ridiculously high.

Yes, the costs can be evaluated to determine the difference between a good racking arrangement and a poor racking arrangement. First, you need to understand the principles of good racking. Good density is a key. Parts should be grouped close enough together to reduce the space around them so the ratio of metal to air is high. There is a limit to density; there must be enough space around a part to make it easy to cover. But within reason, more is better. Second, the parts should be positioned so that they can be easily accessed and easy to see. They should be held in a stable and consistent position. There should not be large gaps between racks as long as there is sufficient time to coat the parts based on the line speed and number of guns. Contacts must always be clean so that there is no way a part can be insulated from earth ground by coating build-up. Good racking is an important key to profitable coating.

To determine the cost associated with the racking, you need to evaluate what your throughput could be if you had proper racks and compare it to how you run it now. You can build samples to test theories and compare the defect rates to any other rack method. If you can quantify the current rack capacity and quality you can compare them to any other rack option. It is simple math to evaluate the number of parts per foot and the number of good parts versus bad. Many companies waste a lot of dollars by using sub-optimum racks because they do not want to invest in tooling, they do not want too many different rack designs around or they just do not even evaluate it at all. Evaluate the options and there is a good chance you can improve the throughput and reduce costs by using the right racking scheme. Consider a rack that holds one part like a simple hook. You know you can hold two parts if you build a special tool. The tool cost will be $600 for a full set of two piece racks. If you divide your fixed cost by your production throughput you can determine the savings. Then you can see how long it will take to recover the $600 investment. If you run the part a lot your return on investment will be fast. If you run it infrequently the ROI may be too slow. If you improve your first pass yield the ROI could be very fast. Always evaluate options and chose the smartest racking method, even when it means investing in a new tool.

Originally published in the January 2016 issue.