What are the influencing factors of the coating thickness gauge?
a The 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 The standard sheet is used to calibrate the instrument; the test piece to be coated can also be used for calibration.
b Base metal electrical properties
The conductivity of the base metal affects the measurement, and the 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.
c 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. See attached table 1 for the critical thickness value of this instrument.
d edge effect
The instrument is sensitive to abrupt changes in the surface shape of the test piece. It is therefore unreliable to measure near the edge or inside corners of the test piece.
e curvature
The curvature of the test piece has an effect on the measurement. This effect always increases significantly with decreasing radius of curvature. Therefore, measurements on the surface of curved test pieces are not reliable.
f Deformation of the specimen
The probe deforms soft-covered specimens so reliable data can be obtained on these specimens.
g surface roughness
The surface roughness of the base metal and the coating has an effect on 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 also 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.
g magnetic field
The strong magnetic field generated by various electrical equipment around will seriously interfere with the magnetic thickness measurement work.
h Adhesive substance
The instrument is sensitive to the attached substances that hinder the close contact between the probe and the surface of the covering layer. Therefore, the attached substances must be removed to ensure that the probe of the instrument is in direct contact with the surface of the test piece.
i Probe pressure
The amount of pressure exerted by the probe on the test piece will affect the reading of the measurement, so the pressure should be kept constant.
j Orientation of probe
The way the probe is placed has an effect on the measurement. During the measurement, the probe should be kept perpendicular to the surface of the sample.
Terms of use
a Base metal properties
For the magnetic method, the magnetic properties and surface roughness of the base metal of the standard piece shall be similar to those of the test piece base metal. For the eddy current method, the electrical properties of the base metal of the standard sheet should be similar to those of the test piece base metal.
b base metal thickness
Check whether the base metal thickness exceeds the critical thickness, if not, use one of the methods in 3.3 to calibrate.
c edge effect
Measurements should not be made close to sudden changes in the test piece, such as edges, holes and inner corners.
d Curvature
Measurements shall not be made on curved surfaces of test pieces.
e Number of readings
Often several readings must be taken within each measurement area since each reading from the instrument is not identical. Local variations in cover thickness also require multiple measurements in any given area, especially when the surface is rough.
f surface cleanliness
Before measurement, any attached substances on the surface should be removed, such as dust, grease and corrosion products, etc., but do not remove any covering substances
