The grid method is a standard for testing the adhesion of coatings coated with sub-metallic hot rods. The test standard is GB/T9793-1997, which is formulated with reference to ISO2063, and the standard has been updated to the third edition (2003).
There are two types of knives used in the IS0 2409 cross-hatch test, multi-edged and single-edged. Since multi-edged knives are not easy to cut the paint film smoothly for >120µrn dry film thickness or harder coatings, it is recommended to use single-edged knives . In order to avoid human errors, an electric cross-cut adhesion Tester has been developed, which can automatically cross-cut and the tool pressure can be adjusted in advance. Some instrument companies, such as the 430 type produced by the German Jirichzen Instrument Company, can perform tests of various specifications such as single-row, multi-row, star and mold. With single-edged cutters, instruments with different pitches are also required. Transparent pressure-sensitive tape and a 2x or 3x magnifying glass are also indispensable test materials. (Related instrument: adhesion test method)
Different paint films determine different grid spacing, and the hardness of the substrate also affects it, as shown in Table 7-12.
The test procedure is as follows:
①Measure the paint film to determine the proper cutting spacing;
② Cut the paint film at a constant speed with a stable pressure and an appropriate spacing, and penetrate the surface of the substrate;
③Repeat the above operations, and cut the paint film in parallel and equal numbers again at an angle of 9o° to form a grid;
④Sweep the surface with a soft brush, roll off the tape in a steady state, and cut off a length of 75mm;
⑤ Put it on the grid parallel to the marked line from the middle of the tape, leaving at least 20mm of length outside the grid for grasping by hand, smoothing the tape with your fingers;
⑥Grab one end of the tape, within 0.5~1.0s, open the tape at an angle close to 60°, keep the tape as a reference, and check the state of the cut part (Table 7-13).
The adhesion test of the metal coating is carried out according to the grid test in Appendix A1 of GB/T9793-1997 (as shown in Figure 7-8). If there is no peeling of the coating from the substrate or separation between layers of the metal coating, it is considered as the bonding strength test qualified.
Use the cutting tool in Appendix A1 to cut out the grid specified in Table 7-l4. The size and depth of the cutting marks are required to cut the coating to the base metal.
