The hardness of the solidified film is the key index to evaluate the film quality, and it is also an important index to study whether the coil coating can be processed. The hardness test methods of solidified coating include pendulum hardness, pencil hardness and shore hardness. Pencil hardness is easy to operate and widely used in color steel plate industry.
The coating hardness of color steel plate is usually related to the coating composition and curing conditions. In addition, the thickness of the coating has a significant effect on the hardness of the cured film. When the coating is thin, the temperature absorption is more uniform, the curing is even and thorough, and the overall hardness of the coating is high; the heat absorption effect of the thick coating has gradient effect, the curing is uneven, and the overall hardness is low.
Generally, pencil indentation hardness tester is used to test the coating hardness of color coated steel plate, that is, 14 grades of pencil lead with known hardness within 6h-6b are used to destroy the coating, of which 6h is the hardest and 6b is the softest. There are two methods: hand pencil method and instrument pencil method.
Sharpen the pencil with a pencil sharpener to expose the 4-6mm cylindrical core. Hold the pencil so that it is perpendicular to the surface of 400 sandpaper. Polish the sandpaper until the end face is flat and the edge is sharp. Then, keep the pencil at an angle of 45 ° with the coating, and apply enough uniform pressure downward and forward to break the pencil edge or plow the coating. The stroke of a pencil is 6.5mm. The test should start with the hardest marked pencil and test each marked pencil in turn. Each grade of pencil shall be scratched 5 times until at least 4 of the 5 times can not break the coated pencil. The pencil hardness is the pencil hardness of the tested coating.
B instrument pencil method
After being processed by hand pencil method, the color steel plate pencil is fixed on the instrument trolley, so that the pencil tip can contact the sample surface freely. Push the trolley so that it moves 6.5 meters over the sample. As with the manual method, test each marker in turn. Each grade of pencil shall be scratched 5 times until at least 4 of the 5 times can not break the coated pencil. The pencil hardness is the pencil hardness of the tested coating.
So far, there are many specifications of pencil hardness tester, such as QHQ (desktop) and qhq-a (portable), etc. pencil scratch hardness tester produced by many manufacturers should be sold on the market, and can be used as a supporting instrument for this test.