of 2 /2
JPCL / April 2005 / PCE 27 www.paintsquare.com andheld coating thickness gages are common inspection tools used by applicators and inspectors. With a little care and mainte- nance, mechanical and electronic gages can be relied upon to give many years of dependable service. This article focuses on maintaining electronic gages. Don’t Wait To Calibrate Prior to first use, and occasionally thereafter, it is always a good idea to review the instruction manual to famil- iarize yourself with an instrument’s features and capabilities. Record the make, model, serial number, and date of purchase inside the manual, and high- light maintenance and calibration tips. Now is the best time to establish a calibration interval. Calibration is the act of measuring known coating thickness standards (called “calibration” standards) and verifying that the results are within tolerance. How often the gage should have its calibration checked depends upon many factors, including frequency of use; the application in question; and the level of care taken during use, handling, and storage. If you use your coating thickness gage frequently, measure coatings on abrasive surfaces, or use the gage roughly, your gage may require a rel- atively shorter calibra- tion interval. Make your calibration inter- val longer if your gage spends most of its time on the shelf. If you are uncertain about how often to calibrate the gage, start with a one- year calibration inter- val from the date of calibration, date of purchase, or date of receipt. What do you do at these intervals? That depends upon the quality system you have in place. Some owners simply measure a sample part when the gage is new and record the result. This sample is then saved and used to regularly check the operation and accuracy of the gage. The best and most universally accepted method, however, is to measure calibration standards according to a docu- mented procedure. Calibration standards are available as either certified coated metal plates or plastic shims. Coated metal plates are usually more accurate. The process of mea- suring them is described in a document called a “Calibration Procedure,” which some manufacturers give upon request at no charge. Alternatively, you can return the instrument to the manufacturer or to a qualified lab to have this work per- formed for a nominal fee. Use ItDon’t Abuse It Now that you have taken care of the paperwork, take prac- tice measurements with the test panels or shims that came with your coating thickness gage. You can even use office furniture or other handy coated parts to ensure the gage works properly and that you are using it correctly. Gages come in all different shapes and sizes. So get to know the proper way to hold and operate your particular model. The majority of hand held instruments take one measurement at a time. Lift the probe away from the surface between measure- ments. Dragging the probe reduces probe life. Once the gage has been put into service, it should always be inspected prior to use. Look for obvious damage, particularly to the probe or probe cable. Constant-pressure probes should move up and down freely. While the gage body can work even when scratched, nicked, or covered with paint overspray, the probe cannot. So examine the probe carefully. Pay particular Looking After Your Coating Thickness Gage E quipment Maintenance H By David Beamish, DeFelsko Corporation Continued An electronic, handheld coating thickness gage Calibration standards are available as either coated metal plates (top) or plastic shims (bottom) Photos courtesy of the author Wrong Way Correct Way For best results and longest life, grip the sliding probe sleeve with your fingers low to the surface.