The pencil hardness of the coating film can be measured according to the method in the national standard "Pencil Method for Film Hardness" (GB/T6739-1996). This standard stipulates the method of measuring the hardness of the coating film by scratching the coating film with a wrong pen with a known hardness mark, and expressing the hardness mark of the pencil.
This standard specifies two methods, A method and B method, A method uses the testing machine method, B method uses the manual method.
This standard applies to the determination of coating film hardness.
(1) Method A-testing machine method
①Materials and instruments
a. A set of Zhonghua brand advanced drawing pencils: 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B, of which 9H is the hardest, 6B the softest.
b. Great Wall brand advanced drawing rubber.
c4oo is water sandpaper.
d. Pencil sharpener.
e. The pencil Hardness Tester is shown in Figure 6-21.
②Test steps
a. Test conditions: Unless otherwise specified, the test conditions are in accordance with the provisions of GB9278.
Preparation of h test pencil: use a sharpener to cut off the wooden part, so that the lead core is in the shape of a national note and exposes about 3mm. Then place 400# water sandpaper on a hard plane, put the lead core vertically against the sandpaper to draw a circle, and grind slowly until the tip of the pencil is ground into a plane and the edge is sharp.
c Place the test plate on the testing machine's test sample platform. Put the coating film of the sample plate up, place it horizontally and fix it.
d. The weight of the testing machine passes the vertical line of the center of gravity so that the intersection point of the coating film surface touches the tip of the pencil lead, and the pencil is fixed on the pencil holder.
e Adjust the balance weight so that the load of the pencil loaded on the test sample is in the state of neither positive nor negative, and then tighten the fixing screws so that the pencil leaves the coating surface and fix the connecting rod. Put a weight of 1.00kg ± 0.05kg on the top of the heavy object, loosen the fixing screw, make the tip of the pencil lead touch the coating surface, and add the load of the heavy object to the tip.
f. Turn the hand wheel at a constant speed to move the test sample horizontally toward the opposite direction of the pencil lead for about 3mm, so that the lead scratches the surface of the coating film, and the moving speed is 0.5mrn/s. Move the test sample in a direction perpendicular to the moving direction to change the position and scratch five times. After each scratch, the tip of the pencil must be resharpened before use.
g. Scratching of the coating film: In the five scratching tests, if there are two or more scratches that do not scratch the substrate or the underlying coating film of the sample, use a pencil with a higher level of hardness Carry out the same test until the pencil that can scratch the coating film for two or more times is selected, and write down the hardness label that is one grade lower than the pencil hardness label.
③Assessment of the model: The evaluation of the model can be carried out in the following two ways.
a. The coating film is scratched: after two pencils with hardness marks adjacent to each other, find out the pencil whose coating film has been scratched for more than two lines (including two lines) or less than two lines, and put the pencil with less than two lines The hardness label is the pencil hardness of the coating film.
B. Coating scratches: For two pencils whose hardness marks are adjacent to each other, find out the pencils with more than two scratches (including two scratches) and two full scratches on the paint film, and then scrape less than two scratches. The pencil hardness label is used as the pencil hardness of the coating film.
(2) Method B-manual method
①Material
The wrong pen is used for the test: the method of connecting to the testing machine.
b. Great Wall brand advanced drawing eraser.
c. 4oo# water sandpaper.
d. Pencil sharpener.
②Test step ring
a. Test conditions: according to the testing machine method.
b. The preparation of the pencil for the test: the method of connecting to the testing machine.
c Place the sample on a horizontal joint surface, and fix the coating film upwards, as shown in Figure 6-22
Show. Hold the pin pen at an angle of about 45°, with the small break of the boat pen core as the degree, push on the film removal surface, push the pressure to the front of the Tester at a uniform (about 1cm/s) speed, and the distance is about 1cm, on the coating film Brush the face.
③Assessment of the model: connected to the testing machine method.
