April 2003 Q&A

Thin-Line Masking

I’m working on a product that requires a clean shutoff between two painted surfaces. We are incorporating a design groove for the mask to rest in but are in the middle of a tug-of-war on just how wide and deep that groove must be. Our industrial design department would like no groove, while the painter wants a 1mm groove. I realize it is not possible to avoid a groove, but 1mm seems a bit much. Are there any industry guidelines on the minimum requirements? What about masking materials? The masks will be custom molded to fit the product securely. We’re using a basecoat clearcoat product that is UV-curable.

No, there are no such rules because appearance standards vary extensively from one product to another. Thin-line masking tape may solve your problem to the point where the clearcoat will bury any discernible ridge between the two colors. Ask masking suppliers about this product. The auto companies have done two-tone and three-tone paint jobs this way for many years. I agree with your design team; I don’t know why you would want to have an actual groove in the product just to enable paint masking.

Looking For Olive Drab Powder Coating

We are a contract electronic manufacturing company and are looking for a manufacturer of a powder coating the color of military olive drab green. Our local powder coating companies tell us that olive drab is a custom color and that we’d have to purchase 250 pounds of powder that is custom mixed. Our requirement is to have about 200 communication boxes coated and that would require 10 to 20 pounds. Do you know of a supplier that stocks military green as a standard color.

I don’t know of any. A number of companies coat their products with an olive drab powder coating, but it probably doesn’t meet mil spec (if that is essential). Search on the Internet for olive drab powder coatings and you’ll find what I’ve mentioned.

I’m assuming that your company does not powder coat—does it? Understand that since this material will be sprayed-to-waste it will probably require more than 10 to 20 pounds of powder coating for 200 boxes, unless the communication enclosures are miniscule.

Better Water Needed to Meet Salt Spray Requirements

I have a five-step pretreatment system (wash, rinse, phosphatize, rinse, sealer rinse) for a powder coating facility. I have well water with a 410 ppm level of total dissolved solids (TDS). I am wondering if this is preventing me from achieving a 1,000-hour salt spray life. I am informed our phosphate coating weight is adequate and I have observed no contamination on a clean white rag wiped across parts after stages 1 and 2.

A brief test using distilled water to rinse a specimen in place of our second pretreatment stage has yielded 1,000-plus hours on carbon steel, compared to 350 hours when the system is used normally.

I have no documented evidence this relatively new system has ever met 1000 hours of salt spray resistance. Do I need a deionized water supply? I am using more than 1,000 gallons per seven hours of running time, with overflow and evaporation makeup.

I would appreciate any advice you may be able to provide. My chemical suppliers are not as helpful as I had hoped. Also, could you please tell me what your consulting services cost?

Better-quality water can make a dramatic improvement in salt spray hours. You don’t have to change all your water usage to deionized or reverse osmosis water, but what is certainly needed is a final rinse using water with low TDS. You can use DI/RO water just for stage five; or better, you can install a few risers to rinse parts with DI/RO water immediately after stage five. With the latter option, it is possible to rent DI units to produce enough DI water at a reasonable cost. You haven’t mentioned how large or complex the parts are, but about one to three gallons per minute will probably be sufficient flow.

Thanks for asking about my consulting rates. I charge by the hour for all time spent, plus normal travel and living costs. Seldom are more than two to three days required for me to resolve coating problems for clients.