Refurbishing Gas Cylinders

Q. We refurbish LPG cylinders and apply powder coating over the shot-blasted cylinders, but we have trouble getting coverage into the deep areas where the collar and foot-ring are welded onto the pressure vessel. We hand-spray the cylinders in those critical areas prior to conveying the part through the auto-spray, which uses reciprocators and electrostatic guns. We have tried all sorts of nozzles, but still the problem persists. Since the cylinders are being used outdoors, rust lines are developing at the gap areas. The electrostatic charging is fine, but the powder is not getting deep enough in those gaps. I am looking for a nozzle that can resolve this problem. —C.T.

A. The areas you describe are hard to cover because you have a tough angle to penetrate and you also have electrostatic resistance. A fan spray tip would be the best, with a gun or guns focused on the problem area in a fixed position. Rotation of the part is helpful so that the gap is exposed to the spray pattern from every angle. You also need the right flow rate to push the powder into the recess, but avoid excess velocity and keep the micro-amps low (<25). Be aware that if you use automatic guns only, you will have heavier film build on the rest of the part, but you should be able to get the gap coated with a fan spray nozzle and the right settings.