Factors of influence on the accuracy of coating thickness gauge measurements
Magnetic properties of matrix metal
The magnetic method for thickness measurement is affected by the magnetic changes in the base metal (in practical applications, the magnetic changes in low-carbon steel can be considered minor). In order to avoid the influence of heat treatment and cold working factors, the instrument should be calibrated using a standard piece with the same properties as the base metal of the specimen; Calibration can also be performed using specimens to be coated.
Electrical properties of base metal B
Conductivity has an impact on 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.
C Base metal thickness
Each instrument has a critical thickness of the base metal. If the thickness is greater than this, the measurement is not affected by the thickness of the base metal. The critical thickness value of this instrument is shown in Appendix 1. The edge effect of this instrument is sensitive to sharp changes in the surface shape of the specimen. Therefore, measuring near the edge or inner corner of the specimen is unreliable.
Curvature of e
The curvature of the specimen has an impact on the measurement. This influence always increases significantly with the decrease of curvature radius. Therefore, measuring on the surface of bent specimens is unreliable.
Deformation of f specimen
The probe will cause deformation of the soft cover layer specimen, so reliable data can be measured on these specimens.
Surface roughness of g
The surface roughness of the base metal and covering layer has an impact on the measurement. The roughness increases and the impact increases. Rough surfaces can cause systematic and accidental errors. During each measurement, the number of measurements should be increased at different positions to overcome these accidental errors. If the substrate metal is rough, it is necessary to take several positions on the uncoated substrate metal specimen with similar roughness to calibrate the zero point of the instrument; Or dissolve the covering layer in a solution that does not corrode the base metal, and then calibrate the zero point of the instrument.
