How to use magnetic method to measure thickness of dry film?

Dry film thickness

In actual work, a large number of dry film thickness measurements are encountered, because the measurement of certain physical properties of coatings and the testing of special properties such as weather resistance require the coating to be made into test panels and tested under a certain film thickness. There are many methods for measuring dry film thickness. According to the working principle, they are basically divided into two types: magnetic method and mechanical method. In addition, there are microscope methods. This article describes the measurement of dry film thickness by magnetic method.

1. Scope and description

This method is a non-destructive instrument test method. According to the different substrates to be tested, it can be divided into magnetic Thickness Gauge and non-magnetic Thickness Gauge, which are suitable for the determination of dry film thickness of paint film on magnetic metal substrate and non-magnetic metal substrate respectively. It is the current dry film thickness Measurement Instrument. main method.

The magnetic Thickness Gauge mainly uses the principle of electromagnetic field reluctance to measure the thickness of the paint film through the magnitude of the magnetic flux flowing into the steel substrate, that is, the change of the magnetic flux caused by the change of the gap between the magnet and the magnetic substrate. There is also the principle of magnetic attraction method, that is, to measure the paint film thickness by the force required to overcome the magnetic attraction between the permanent magnet and the magnetic substrate. The non-magnetic Thickness Gauge uses the principle of eddy current thickness measurement to measure, that is, the size of the induced eddy current changes with the thickness of the instrument probe coil and the paint film thickness of the metal substrate. The thickness of the coating on the magnetic backplane.

2. Instruments and Materials

Thickness gauge: the accuracy is 2μm, there are desktop and portable, and the specifications include dial type and digital display type, as shown in the figure below.

Take the arithmetic mean of the thickness of each point as the average thickness of the paint film.

3. Measurement method

(1) Dial Thickness Gauge

① Manually place the measuring head on the paint film to be tested, slowly push the instrument dial forward with your fingers, stop pushing when you hear a "click", and the reading pointed by the pointer is the paint film thickness of the sample.

②Automatically push the dial forward to the maximum range, press the button, and the instrument will automatically measure.

(2) The digital display magnetic Thickness Gauge is carefully adjusted to the zero position on a reference surface similar in nature to the test substrate, and then calibrated with the standard sheet attached to the instrument. When measuring, put the probe on the sample plate, take measurements at the upper, middle and lower positions not less than 1cm from the edge, and read the paint film thickness value.

5.Reference standard

National standard GB/T 13452. 2 "Determination of paint film thickness of colored paint and clear paint".