How to Measure the Pencil Hardness of Film?

The pencil hardness of the coating film can be measured according to the method in the national standard "Pencil Test Method for Coating Film Hardness" (GB/T 6739-1996). This standard stipulates the method of measuring the hardness of the coating film by scratching the coating film with a pencil of known hardness number.

This standard stipulates 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) A method - 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.

c 400# 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.

h Preparation of the test pencil Use a pencil sharpener to cut off the wooden part, so that the lead core is cylindrical and exposes about 3mm. Then place 400# water sandpaper on a hard surface, 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 On the test sample placement platform of the testing machine. 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, then tighten the fixing screws so that the pencil leaves the coating surface and fix the connecting rod. Add a weight of 1.00kg±0.05kg to the place where the weight is placed, and loosen the fixing screw so that the tip of the pencil lead touches the coating surface, and the load of the weight is added 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 two or more times is selected, and write down the hardness mark o that is one grade lower than the hardness mark of this pencil.

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. Scratches on the coating film: For two pencils whose hardness marks are adjacent to each other, find out the scratches on the coating film. Phenomena are not subject to examination. If there is a scratch on the film element at the test site, you can wipe off the powder with a straight line, and perform a daily visual inspection by facing the vertical f scratch direction at an angle of 4° to the surface of the test sample. Bruises are considered abrasions.

After scratching more than two coats (including two coats) and scratching more than two coats of pencil, use the pencil hardness label of less than two coats of scratches as the pencil hardness of the coating film.

(2) B method - manual method

①Material

The test is carried out with a pencil connected to the testing machine (pencil Hardness Tester).

b. Great Wall brand advanced drawing eraser.

c400# water sandpaper.

d. Pencil sharpener.

②Test steps

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 template on a horizontal joint surface, and fix the coating film to l:, as shown . Hold the pencil at an angle of about 45°, take the lead of the pencil as a small break, and push it on the film-removing surface, push the pressure to the front of the Tester at a uniform (about 1cm/s) speed, with a distance of about 1cm, and press it on the film-coated surface Swipe.

d. Every time you scrape one line, re-grind the tip of the lead-pen core, and use a pencil with the same hardness mark to scratch five times repeatedly.

e Scratching of the coating film: In the two scratching tests, if there are two or more than two scratches and it is considered that the bottom plate of the sample plate has not been scratched to form the bottom coating film, then use the previous hardness scale (the hardness is higher by one Grade) pencils carry out the same test until the pin pen whose coating film has been scratched two or more times is found, and the following hardness number is the last one (that is, the hardness is one level lower) of the pencil hardness number.

f. Scratching of the coating film: In the five scratch tests, if there are two or more than two scratches on the coating film, use the pencil with the previous hardness mark (a little harder than it) Pencil) Carry out the same test until the pencil whose coating film has been scratched two or more times is found, and write down the hardness number of the last digit of the hardness number of this pencil.