Graphic Analysis Nondestructive Testing Method for Non-magnetic Coated Film thickness on Magnetic Metal Substrate

This paper mainly discusses the non-destructive testing method of non-magnetic layer thickness on the magnetic metal substrate. As a very important branch of thickness measurement, the detection of the thickness of non-magnetic coatings on magnetic metal substrates is mainly used in the detection of coating thicknesses such as steel surface paint, electroplating and enamel, and is widely used in the detection of chemical, pharmaceutical and other industrial sectors. The following is an analysis and discussion of the measurement principles of the two coating thickness measuring instruments, the mechanical method and the magnetoresistance method, and the technical characteristics of several commonly used coating thickness measurements in the domestic market. The mechanical Thickness Gauge is an instrument that uses a purely mechanical method to non-destructively measure the thickness of a non-magnetic coating on a magnetic metal substrate. The measurement principle is shown in Figure 1. The lower part of the figure is the measured object, which is composed of a ferromagnetic substrate and a coating, and the rest is a mechanical magnetic thickness measuring device, or a probe. The core element of the probe is the permanent magnet in the middle, preferably made of NdFeB strong magnetic material, and the permanent magnet is supported by springs in the housing of the probe. When measuring, the lower end of the probe is in contact with the object to be measured. Due to the magnetic attraction of the magnetic substrate and the permanent magnet in the probe, the permanent magnet will overcome the elastic force of the spring and move downward. The displacement depends on the thickness of the coating. If the coating is thin, the magnetic attraction force is large, and the displacement of the long-term magnet is large; if the coating is thick, the magnetic attraction force is small, and the displacement of the permanent magnet is small.