I had a customer contact me about the performance of his EXAIR Super Air Knives. They were painting panels using an electrophoretic process. This process uses an electrical voltage to put a charge on the steel panel for coating. As the parts get dipped, the oppositely charged coating is attracted to the surface. The parts then get rinsed before going into an oven to cross link and set the paint. They purchased two 48 inch (122 cm) long Super Air Knife Kits, model 110248, and he mounted one on each side of the steel panels to blow water off after the rinse cycle. The 46 inch (117 cm) long panels were attached to a rack hanging on an overhead conveying system. As the panels left the rinsing system, the Super Air Knives would blow the water off both sides. The customer saw some visual defects caused by water droplets and had concerns about the effectiveness of the Super Air Knife.
In these cases, we have to do some forensics to solve the problem. Usually poor performance is caused by undersized fittings, tubing, quick disconnects, improperly sized pneumatic accessories, and/or too small of an air compressor. As we went through the checklist, he did have the correct sized pipe, fittings, and compressed air requirements to operate the Super Air Knife properly.
I then went back to the basics in the setup of the Super Air Knife. I found out that he positioned the Super Air Knife to be perpendicular to the panels. With the air flow hitting the surface at a 90 degree angle, it was allowing the water to be splashed back onto the cleaned areas. I had a few suggestions to help improve the drying process.
- Angle – EXAIR machined a chamfer on the cap of the Super Air Knife, and it can be used as a starting position for a mounting angle. The chamfer should be parallel with the target. This will create an air flow angle at about 45 degrees. This angle will increase the contact area and contact time which is very beneficial for removing water, debris and/or heat. See the below picture in showing the chamfer.
- Distance – For optimum performance, the Air Knife should be between 3 inches and 12 inches (76mm to 305mm) from the target. If you are too close, the amplification ratio is sacrificed, and the force is reduced. If you are too far, the air pattern will start to morph, and the velocity and force will begin to decrease. It can still work, but the efficiency is reduced.
- Counter-Flow – The air flow should be blowing against the target, in a counter-flow direction. Example; if the parts are moving from left to right, you would want the Super Air Knife to blow from right to left. This will allow the contamination to be blown back away from the cleaned surfaces, and it will increase the impact force to remove contamination i.e. a head-on collision vs. a rear-end collision.
Many customers like to start with their Super Air Knives aiming directly at the target, as described in the above application. This can decrease the efficiency for blowing off contamination or removing heat. The diagram below shows how the angle can really help to improve the performance.