Hardness is an important property of the mechanical strength of the coating film, and its physical meaning can be understood as the resistance of the film to another object with a higher hardness acting on it. The test methods include the pendulum damping hardness elimination test method, the Si Walter hardness, Kleeman hardness, pencil hardness and Buckholtz hardness. From the perspective of its test method, a certain load is applied on a small joint area to measure the ability of the coating film to resist deformation. Therefore, the hardness of the coating film directly affects the scratch resistance and property of the coating film. Ability to resist abrasion loss.
1. Determination of pendulum hardness
The principle of pendulum hardness measurement is that when the pendulum in contact with the coating swings at a certain period, the softer the coating is, the faster the swing of the pendulum attenuates. In method A of GB/T1730-93, there are two types of pendulums: Konig pendulum and Persoz pendulum. Before the Konig pendulum is tested, it should be placed on a standard glass The damping time from 6° to 3° is corrected to (250±10)s; the Persaz pendulum should be placed on the standard glass plate first, and the damping time from 12° to 4° of the post should be adjusted to at least 420s. GB/T1730- Method B of 93 uses a double pendulum, and the swing time from 5° to 2° should be corrected to (440±6)s before the test, and the result is expressed by the ratio of the damping time of the coating surface to the damping time of the glass surface. (Related instrument: pendulum Hardness Tester)
2. Determination of pencil hardness (GB/T6739-86)
Use a set of known hardness of the sharp edge of the end face of the pen core of the boat pen, and scratch the coating film at an angle of 45° to the coating film. It is expressed by the hardness of the hardest pencil that cannot scratch the coating film. When operating by hand, due to the difference in force , The deviation is large, it can be tested with a special pencil Tester.
When the boat strokes the film, there are both pressure and shear force, which are different from the damping effect of the swing rod, and there is no conversion relationship between them. (Related Instrument: Pencil Hardness Tester)
3. Other hardness testing methods
The Swat hardness is measured by the number of times the metal ring swings back and forth on the paint film. The sensitivity is poor, but the test is faster than the rod damping method. It is generally used for rough determination of the paint film. ), to see whether the film is scratched under a certain load, or expressed by the minimum load at which the coating film is scratched, the test is only manual and automatic, and the arbitration test needs to use automatic testing (GB/T9279-88).
The Kholz hardness is an indentation test, which is only effective for hard coatings.
Pendulum method and pencil hardness method are usually used for hardness determination. Pencil hardness is widely used because of its quick and convenient testing.
