Test for Coverage in Faraday Areas

Q. What tests would you recommend if you want to measure Faraday Cage effect on the actual part to see how good the coating has covered and protected the part? Is there a special machine that can be used for this? Assume we have done everything we can do to get good paint coverage. Thanks. N.G.

 

A. Faraday areas are inside creases or cups that can be hard to coat when using electrostatic equipment. The inside area creates electrical resistance that limits coverage, and the force of compressed air can compound the problem by creating aerodynamic challenges as well. This combination of electrical resistance and swirling air current can make it hard to get adequate coverage in the inside area of a bind or seam.

Start your evaluation with a visual inspection after cure to see if any metal is bare or showing through a thin coating. If the appearance is good and you want to see how it compares with the rest of the surface, you can test it for voids using a low-voltage pin-hole tester. If you find thin spots or voids, you have thin coating in the Faraday area. You can also do salt spray or humidity testing to see if the Faraday area shows premature corrosion before the flatter surfaces.

You should also inspect the area before curing and compare it with the appearance after cure. The attraction in the Faraday area is weak and coating may cover it, but it is not adhered as well as other areas that do not have electrical resistance. If you see coverage before cure and then it looks worse after cure, you should check the airflow in the oven. Turbulence from an air curtain or discharge duct can blow powder out of the Faraday areas. Correct the airflow if you find this problem. You will need some professional advice to come up with the right corrections to reduce the velocity of air on the part.