1.What is the experimental principle of the drop weight impact test?
The drop hammer impact test is the mainstream method specified in international and domestic standards. By controlling the mass and drop height of the hammer, a specific energy impact is applied to the coating surface to observe whether the coating is damaged (such as cracks, peeling, bottom exposure, etc.).
2.What are the key parameters of drop weight impact test?
Punch specifications: Common spherical punches with a diameter of 12.7mm (0.5 inches) or 20mm (simulating the impact of objects of different sizes).
Weight: Usually 0.5kg, 1kg, 2kg, etc. (adjusted according to the expected impact energy).
Drop height: Control the impact energy by adjusting the height (energy = mass × gravitational acceleration × height, in J), and the common energy range is 0.5J-5J (such as 0.5J, 1J, 2J gradients are specified in GB/T 13448 standard).
Specimen requirements: The specimen size is usually 150mm×70mm, and the coating must be intact and the surface must not be pre-damaged.
3.What are the evaluation criteria for drop weight impact test?
If the coating has no cracks, no peeling, and no bottom exposure (substrate is not exposed), it is judged as "passed"; if the coating cracks, separates from the substrate (peeling), or the metal substrate is exposed, it is judged as "failed". Some standards also require the recording of the "minimum damage energy" (i.e. the impact energy value that just causes the coating to break).
4.What are other auxiliary detection methods?
Pendulum impact test
Applicable to evaluate the toughness of coating under low-speed, large deformation impact. The pendulum is used to impact the sample when it swings, and the energy absorbed by the coating or the degree of damage is measured. However, it is less used in color-coated coil inspection, and is more used for impact toughness testing of metal materials themselves.
Drop ball impact test
A steel ball with a fixed mass is dropped from a specific height to impact the coating surface to observe whether the coating has pits, cracks or peeling. This method is simple to operate, but the energy control accuracy is low, and it is usually used for rapid screening or non-strict inspection scenarios.
5.What are the precautions for testing?
Sample status: Ensure that the sample surface is free of pre-treatment damage such as oil stains and scratches, and the coating is completely cured.
Environmental conditions: The test must be carried out under standard temperature and humidity conditions to avoid the coating becoming brittle due to low temperature or softening due to high temperature, which will affect the accuracy of the results.
Repeated tests: At least 3-5 parallel samples of the same batch of samples must be tested, and the average value or qualified rate must be determined to reduce accidental errors.