Determination of film Hardness by Indentation

When measuring the hardness of plastic, rubber, metal, etc., various methods based on the resistance when the test object is pressed in from the outside by another object under the pressure of weight are commonly used.

To this end, various instruments that are generally not suitable for dry testing of thinner paint films (although from the principle of testing, they can be used for this purpose) can be used.

The indentation method is also suitable for studying the solidification process of polymers.

CH Zhurkov used this method when experimenting with the process of various polymers changing from a colloidal state to a solid state. Hardness is measured by measuring the depth of a steel ball (7 mm in diameter) into a cylindrical polymer sample (15 mm in diameter and 4–5 mm thick) under a fixed load.

The hardness of the paint film can be measured on the instrument shown in Figure 122 by the indentation method. (Related instrument: Hardness Tester)

Instrument 49 is formed by the brass rigidity of assembling counterweight 2. Its bottom is that the quartz cylinder 3 (bottom diameter is 6 millimeters) of circle leaves imprint on varnish film 4 when this 1 bar bears load. In order to leave the impression of the quartz cylinder on the paint film, the harder the paint film, the greater the load on the lever must be. The bottom edge of the cylinder is polished, its shape is a bull sphere, and the plane of its upper part forms an angle of 4° with the horizontal. When measuring the hardness of the varnish film, the glass plate 5 should be placed at a certain angle. This angle allows horizontal light reflected by the glass plate to strike the cylinder and be reflected by its bottom spherical surface. The optical grade reflected by the spherical surface is injected into the microscope 6 again, and the contact surface between the paint film and the paint film can be seen in the microscope, and its shape is a black circle 8. The diameter of small countries that appear to be in contact in the microscope can be measured using a microheliometer. Measurements were performed at 70X magnification.

In addition to measuring the diameter of the contact plane with a fixed weight on the shaft, it is also possible to change the load in order to obtain a certain diameter of the contact surface. If too large a weight has to be used in order to obtain a flat surface of the necessary size (in the case of a very hard paint film), a quartz jig with a diameter of 3 mm can be used.