This part of GB/T 20624 specifies the test method for the ability of dry coatings of Paints, varnish or related products to resist cracking or flaking from the substrate when subjected to a drop hammer (spherical punch with a diameter of 20mm) to deform under standard conditions. The test determines whether the coating meets the specific specification requirements by gradually increasing the drop height or weight of the weight, and evaluates its impact performance. This part is suitable for coating quality control and product grading. It provides accurate test procedures and standardized evaluation methods to ensure the repeatability and accuracy of the test.