This method is applicable to the determination of the indentation test on single-layer coating films or multi-layer coating films of paints and varnishes. The hardness of the paint film is measured from the length of the indentation when the indenter presses the film under specified conditions using a Buckholtz indenter. The results of the indentation resistance test are expressed as a function of the reciprocal of the indentation length.
(1) Buckholz indentation Tester, also known as Brinell indentation Hardness Tester, consists of an indentation device and a measuring device, as shown in the figure.
① The indentation device is shown in Figure 1-4-13, which consists of a rectangular metal block, an indenter and two pointed feet. The whole device weighs (1000±5) g. The position of the indenter and two pointed feet on the main body makes the instrument more stable when placed on a flat surface. The payload on the indenter weighs (500 ± 5) g. The indenter is a metal wheel with a sharp blade made of hard tool steel. The section of the indenter's rotating shaft and the diameter of the indenter are shown in the figure, and the figure shows the shape of the indentation produced.
②The measuring device consists of a microscope with a magnification of 20 times and an eyepiece equipped with a 0.1mm scale. The illumination of the indented surface is provided by the instrument itself with a light source with an incident angle of more than 60°. The microscope should be mounted vertically above the illuminated indentation surface as shown. Adjust the focus so that the image formed by the indentation and the image formed by the scale are produced simultaneously, as shown in the figure.
(2) Stopwatch.
(3) Test plate Glass plate or other agreed substrates.
3. Measurement method
(1) Gently place the indenter on the painted surface of the test panel. When placing it, first make the feet of the device contact the test panel, and then carefully put down the indenter.
(2) Use a stopwatch to count the time, and after placing it for (30±1) s, lift the device away from the test plate. It should be the indenter first, and then the feet of the device.
(3) Within (35 ± 5) seconds after removing the indenter , use a microscope to place it at the measurement position, measure the length , and take it as the indentation length, expressed in millimeters (mm), accurate to 0.1 mm.
4. Result presentation
The resistance of the coating to the pressure of the indenter is expressed by the length of the formed indentation, and the result is expressed by the indentation resistance:
H=100/L
In the formula, H—indentation resistance;
L—indentation length, mm.
Carry out five tests on different parts of the same test plate, and calculate the arithmetic mean value.
Table 1 shows the relationship between indentation length and indentation resistance. Indentation depth and coating thickness are also listed.
Table 1 Relationship between indentation length and indentation resistance, indentation depth and coating thickness
5. Reference standard
National standard GB/T 9275 "Paints and varnishes - Buckholz indentation test".
