Pencil hardness test


A set of drawing pencil leads with known hardness are used to scratch the paint film, and the hardness of the paint film can be expressed by the pencil hardness level that can penetrate the paint film to reach the substrate.
(1) Material instruments
A group of Zhonghua brand advanced drawing pencils, hardness grades are 9H, 8H, 7H, 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B,6B, in which 9H is the hardest,6B is the softest. Drawing eraser,400# water sandpaper, pencil sharpener, pencil hardness tester.
(2) Operation method
Manual method or instrument test method can be used. The manual method may give different results to different operators, and the instrument test method should be used to pretend that the arbitration test is conducted.


Use a pencil sharpener to cut off the pencil rod, expose the pencil lead 3~6mm(do not loosen or cut the lead core), hold the pencil so that it is 9o° with the 400# sandpaper, and draw circles on the sandpaper to rub the lead core end face until the end face is flat and the edge of the pen is sharp (the edge must not be broken or notched). The pencil should be rotated 18o degrees after each use, or re-sharpened before use


① Manual operation of the test method as shown in Figure 21-20, fix the paint sample on the horizontal surface, hold the cut lead core, and make it at a 45° Angle with the paint film surface, and push forward at a speed of 1cm/s (the pencil is not broken) for about 1cm. If two or more of them scratch the paint film, use a harder pencil to scratch until you find a pencil that does not scratch the paint film. The hardness of the pencil represents the pencil hardness of the measured paint film


② Instrument test put the painted sample on the test bench of the tester, the paint surface is facing up, adjust the vertical line of the center of gravity of the weight through the tester to the intersection of the pencil end and the paint film, load the sharpened pencil into the paint film at a 45° Angle, adjust the load on the pencil with the balance weight to make the pencil just contact the sample, tighten the stop screw, so that the pencil end leaves the surface of the paint film, on the weight table Add a weight of (1 0.05)kg and loosen the stop screw so that the pencil end is in contact with the paint film. Move the moving arm of the test stand, make the sample and the pencil end move 3mm in reverse, the moving speed is about 0.5mm/s, then tighten the stop screw, turn the pencil 180°(to ensure that the pen end surface is not damaged) and change the position of the sample, in turn plow out five marks, with this method from the hardest pencil to test, and successively change the lower level of the pencil, until the five marks are found only For a pencil that has damaged the paint film at one time, its next level of pencil represents the pencil hardness of the measured paint film. If the paint film is not damaged by plowing, this grade of pencil represents the pencil hardness of the measured paint film.

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