Factors Affecting Coating Thickness Gauge Values
There are various factors that affect thickness gauge values. For the coating thickness gauge alone, there are mainly the following reasons that cause inaccurate measurement.
1) Magnetic properties of the base metal
The magnetic thickness measurement is affected by the magnetic change of the base metal (in practical applications, the magnetic change of low carbon steel can be considered slight), in order to avoid the influence of heat treatment and cold working factors, it should be used Standard sheet to calibrate the instrument;
Calibration can also be performed with a test piece to be coated.
2) Edge effects
The coating thickness gauge is sensitive to the abrupt change of the surface shape of the test piece. It is therefore unreliable to measure near the edge or inside corners of the test piece.
3) Base metal thickness
Every instrument has a critical thickness of the base metal. Above this thickness, the measurement is not affected by the thickness of the base metal.
4) Attached substances
The coating thickness gauge is sensitive to the attached substances that prevent the close contact between the measuring head and the surface of the coating layer. Therefore, the attached substances must be removed to ensure that the measuring head of the instrument is in direct contact with the surface of the test piece.
5) Probe pressure
The pressure exerted by the probe on the test piece will affect the measurement reading, so keep the pressure constant.
6) Electrical properties of the base metal
The electrical conductivity of the base metal affects the measurement, and the electrical conductivity of the base metal is related to its material composition and heat treatment method. The instrument is calibrated using a standard sheet having the same properties as the base metal of the test piece.
7) Curvature
The curvature of the test piece affects the measurement. This effect always increases significantly with decreasing radius of curvature. Therefore, measurements on the surface of curved test pieces are not reliable.
8) Deformation of the test piece
The stylus deforms soft-covered specimens, so reliable data can be obtained on these specimens.
9) Surface roughness
The surface roughness of the base metal and the coating affects the measurement. The greater the roughness, the greater the impact. Rough surface will cause systematic error and accidental error, and the number of measurements should be increased at different positions for each measurement to overcome this accidental error. If the base metal is rough, it is necessary to take several positions on the uncoated base metal test piece with similar roughness to calibrate the zero point of the instrument; or use a solution that does not corrode the base metal to dissolve and remove the covering layer, and then calibrate the instrument. zero.
10) Magnetic field
The strong magnetic field generated by various electrical equipment around will seriously interfere with the magnetic thickness measurement work.
11) Orientation of probe
The way the probe is placed affects the measurement. During the measurement, the probe should be kept perpendicular to the surface of the sample.
