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.
In mechanical measurement, a lever micrometer or a dial gauge is commonly used to measure the paint film thickness. When used, it is not limited by the nature of the substrate and the influence of conductive or magnetic pigments in the paint film . The measurement accuracy is high, up to 2µm, but it can only be measured on a small area of the sample, and the paint film needs to be hard enough. , in order to withstand close contact with the micrometer chuck or dial gauge stylus without indentation, and the paint film needs to be partially damaged during measurement. The micrometer method is suitable for the flat surface , and can also be used for the measurement of coatings on round rods. The test principle is to determine the distance between the two measuring surfaces of the lever micrometer to obtain the corresponding paint film thickness. The dial gauge method, also known as the indicator method, is suitable for measuring flat painted test panels. The test principle is to use the stylus of the instrument to measure the height difference between the paint film and the substrate to obtain the paint film thickness.
There are two methods A and B in the microscope method, which are used to measure the dry film thickness on different substrates respectively, and can be used as an arbitration test method. Method A is to measure the dry film thickness on the section cut from the test board or painted object general method. Especially useful when measuring changes in film thickness caused by uneven substrates . The principle of the test is to place the test block under the microscope after processing , and use the scale on the eyepiece to directly measure the thickness of the paint film. Method B does not involve the cutting of the test block, and it is measured . The test principle is to cut a V-shaped notch from the coating to the substrate, and use a microscope with a scale to measure the width of a' and b'. The graduation has been converted into the corresponding micron by the correction factor, so the actual thickness a and h of the paint film can be read directly from the microscope. In addition to measuring the total paint film thickness, this method can also measure the thickness of each layer of a multi-layer paint system.
