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What equipment is used to measure chemfilm ohmage? [California] 

August 2, 2007

I am developing an aluminum sheet metal part that will be chem filmed and must meet Mil-DTL-5541 [link is to spec at TechStreet]F, CLASS 3. Where can I buy the equipment to measure a resistance not greater than 5,000 microhms per square inch with a nominal electrode pressure of 200 psi?

Mark Stauder
Mechanical Design Engineer - Irvine, CA

Build it or buy it! We tried for years to locate such a piece of test equipment and finally we purchased a load cell to measure force, machined a copper electrode 1" x 1", and put the unit into a hydraulic controled anvil press. Using a simple amp/volt meter between the copper electrode and the test piece we were able to measure the surface resistance. The alternative is to have an outside electrical testing house measure it for you which is often easier and cheaper when you factor in the cost of calibration. Lastly, once you've settled in on a chromate product and defined the process needed to stay below the maximum resistance, you'll find the result doesn't vary. The spec you reference doesn't require that you measure the resistance (whereas AMS 2473 might), MIL-C-5541 Class 3 requires the use of a QPL-approved product which has demonstrated its ability to meet the resistance requirement when operated per the manufacturer's data sheet.

Milt Stevenson, Jr. Anoplate Corp Syracuse, NY, USA

Not sure whether these are commercially available.
The design is relatively simple. See MIL-DTL-81706 [link is to spec at TechStreet]B CHEMICAL CONVERSION MATERIALS FOR COATING ALUMINUM.

Ken Vlach - Goleta, California