What are the factors that affect the accuracy of coating thickness gauge measurements?
1. Magnetic properties of the base metal: Thickness measurement by magnetic method is affected by changes in the magnetic properties of the base metal (in practical applications, the changes in the magnetic properties of low carbon steel can be considered slight). In order to avoid the influence of heat treatment and cold working factors, the test method should be used. The instrument can be calibrated using a standard piece whose base metal has the same properties; the test piece to be coated can also be used for calibration.
2. Base metal thickness: Each instrument has a critical thickness of the base metal. Above this thickness, the measurement is not affected by the thickness of the base metal. The critical thickness value of this instrument is shown in Appendix Table 1.
3. Electrical properties of the base metal: The conductivity of the base metal has an impact on the measurement, and the conductivity of the base metal is related to its material composition and heat treatment method. Use a standard piece with the same properties as the base metal of the specimen to calibrate the instrument.
4. Edge effect: the coating thickness gauge is sensitive to sudden changes in the surface shape of the specimen. Measurements near the edges or inside corners of the specimen are therefore unreliable.
5. Curvature: The curvature of the specimen has an impact on the measurement. This effect always increases significantly with decreasing radius of curvature. Therefore, measurements on the surface of bent specimens are unreliable.
6. Deformation of the test piece: The probe will deform the soft covering test piece, so reliable data can be measured on these test pieces.
7. Surface roughness: The surface roughness of the base metal and covering layer has an impact on the measurement. As the roughness increases, the impact increases. Rough surfaces will cause systematic errors and accidental errors. For each measurement, the number of measurements should be increased at different positions to overcome such accidental errors. If the base metal is rough, you must also calibrate the zero point of the instrument by taking several positions on an uncoated base metal specimen with similar roughness; or use a solution that is not corrosive to the base metal to dissolve and remove the covering layer, and then calibrate the instrument. zero point.
8. Attached substances: This instrument is sensitive to attached substances that prevent the probe from close contact with the surface of the covering layer. Therefore, the attached substances must be removed to ensure direct contact between the instrument probe and the surface of the test piece.
9. Orientation of the coating thickness gauge probe: The placement of the probe has an impact on the measurement. During measurement, the probe should be kept perpendicular to the surface of the sample.
10. Probe pressure: The amount of pressure exerted by the probe on the test piece will affect the measured reading. Therefore, the pressure must be kept constant.
11. Magnetic field: The strong magnetic field generated by various surrounding electrical equipment will seriously interfere with the magnetic thickness measurement work.
