Q. Are color changes for powder that are under one minute really possible? I spray all manual in one booth, but I have automatic guns in the other one, and we do reclaim some of our colors, but not all of them. M.G.

A. A single powder gun can be color changed by one person in less than one minute. It requires the right equipment to be able to quickly purge the gun interior and switch over to the new color, but it is possible. You can use a box feed system and clean the gun up, change the box and then start the new color. Or, you can use a manifold with a switch system and a series of dedicated feed hoppers for even-faster color change times.

Keep in mind that the actual color change time is partly dependent on how close the parts are racked. You may be able to physically change the gun over, but you cannot discharge a color too close to a part that is not supposed to be that color. If you are cleaning the gun and next part is only a couple of feet away, you will get some of the powder on that fresh part. Or if a coated part is still leaving the booth, you could get some of the new color on the trailing edge. Realistically, you can change the gun in around 20 or 30 sec, but the spacing is most likely going to be greater due to the risk of cross contamination.

Now, if you have the clean the booth walls, or if you have automatic guns, or if you intend to recover the colors for reuse, the game changes. Automatic guns can be purged automatically using a manifold system and a color-feed center. Booth walls can be cleaned more quickly if the booth construction is designed for fast color change. In a best-case scenario, you can go from reclaim color to reclaim color in 10 to 15 minutes with automatic guns. You can go much faster if you do not reclaim. These booths use cyclone recovery systems to avoid the time involved in moving collectors for reclaim colors. The cyclone itself does not necessarily speed up color change time unless it is fitted with the right features.

It all depends on what you need in terms of reclaim and what equipment you buy. You can get some very fast times if you invest in the right equipment.

Q. We have been coating aluminum alloys for some time with inconsistent results as far as field performance of the coating. We had some corrosion and adhesion failure when our product was used in a harsh environment. Following your advice in an earlier inquiry, we are now having a tri-chrome pretreatment process being done at a local vendor on all of our aluminum castings. We considered bringing this process into our own shop, but it ended up not being feasible for us to do in-house. So far our performance is excellent.

My question is about one casting we have in particular on a new product. The current alloy is A413. This is a structural part, and we have seen failures in testing. Our casting vendor tells us A380 would be much more suitable as its strength properties are better. I also know that the copper content is much higher in the alloy. Do you see any issues in powder coating this alloy now that we are doing the tri-chrome pretreatment process? T.S.

A. Copper content in an aluminum alloy does influence performance, but it does not tell the whole story. With a single powder layer and standard cleaning method (clean, iron phosphate with fluoride) the 380 will not have as good corrosion resistance as the 413. With chrome it will be very close to the same. If you want more confidence you could prime the surface and then topcoat. That will perform very well.