Coating Thickness Measurement: The Fundamentals

Coating thickness measurement is a concern for both finishers and for companies receiving finished components. Defective coatings lead to rust. As a result, product liability requires quality control of coatings, and in many cases documentation of measurements in an electronic format. Conflicts can occur if a manufacturer and a customer of a finished good use different methods or types of instruments to determine coating thickness. This article will discuss the test methods available for determining coating thickness, common applications, and innovations in coating thickness instrumentation. The magnetic induction method measures non-magnetic coatings over ferrous substrates and magnetic coatings over non-magnetic substrates. The process is direct, in that a probe is placed on the part to be measured. When the probe is positioned, the linear distance between the probe tip that contacts the surface and the base substrate is measured. Inside the measurement probe is a coil that generates a changing magnetic field. When the probe is placed on the substrate, the magnetic flux density of this field is altered.