Among the indirect measurement methods of paint film adhesion, this book only introduces two methods: the method of measuring on a press and the method of measuring with grid grooves. Both methods have certain practical value.
The test sample is applied to a metal plate measuring 7x7 mm. After drying in the air, after a certain period of time, use a sharp knife (should be perpendicular to the coating) on the paint film to make four cross cuts in a straight line (the cuts should reach the bottom surface), as shown in the figure 111 shown.
The test panel shall be centered in the compression apparatus (see page 252) so that the center of the notch coincides with the center of the instrument punch. . Then rotate the steering wheel at a speed of about 8-9 mm for 30 seconds, and observe the changes in the paint film.
When the paint film starts to fall off from the soil on the bottom surface (test panel), the depth of the brick penetration can be regarded as the standard of adhesion. When the adhesion is poor and the cohesion is strong, the paint film will fall off the surface in the form of separate petals; when both the adhesion and cohesion are good, the paint film will not change even though the metal is broken; When it is strong, but brittle (adhesion is greater than cohesion), the phenomenon of paint film falling (small cracks) will occur.
Figure 1l2 shows typical damage to some enamel coatings with different adhesion to metal.
When testing coatings on iron (black iron skin), iron plates with a thickness of 0.5 to 1 mm shall be used. The iron plate should be stretchable by more than 8-9 mm on the pressure adhesion Tester without breaking.
The results of tests carried out on a pressure adhesIon Meter can only provide a relative idea of adhesion; this type of adhesIon Meter is mainly suitable for testing coatings with poor adhesion to metals.
When testing various coating films with good adhesion, the difference between each coating film cannot be detected by using this adhesIon Meter.
As in testing the elasticity of the paint film, the speed of rotation of the energy wheel has a great influence on the results of the test. When the punch is pressed in quickly, the paint film can resist a large stress, so the test result appears to be too low. When the rudder turns very slowly, a relaxation process may occur and the test results may appear to be too high.
Complying with certain conditions—the same thickness of the paint film and the bottom surface, drying time, indentation speed, temperature and atmospheric humidity during the test—can ensure the reliability of the test results.
