Use a hard object to mark or scratch the coating film on the surface of the paint film to measure the hardness of the coating film. The commonly used methods are the pencil hardness method and the scratch needle method. A commonly used scratch hardness is the pencil hardness, which is a rapid test method and is often used in the field of paint films on rigid substrates.
The pencil hardness method has two methods: manual operation and instrument test. It uses a pencil with known hardness to measure the hardness of the coating film. The pencil hardness (instrumental test) is used as the hardness of the coating film. Pencils should be standard high-grade drawing pencils manufactured by specified manufacturers. The pencil lead does not contain lead but graphite and china clay. It is not sharpened as it is for writing, but it is ground vertically with sandpaper to make it flat. When testing, it is at an angle of 45° to the sample and is forwarded with just enough force not to break the lead. push. The results are expressed as just hardness without scratching. Experienced people can reproduce the results of soil hardness level 1.
Different countries adopt different pencil hardness grading. my country's national standard GB6739-86 "Measurement Method of Coating Film Hardness with Pencil" stipulates that the pencils used are 13 grades from 6H to 6B, 6H is the hardest, and 6B is the softest. As the referee test, the instrument test method should be used, and the general instrument model is the QHQ pencil scratch Hardness Tester.
The scratch test method uses the needle tip of the instrument to scratch the coating film. The stress generated when the needle is pushed on the paint film exceeds the elongation strength of the paint film and breaks. The film hardness is represented by the scratch resistance of the coating film. Whether it is penetrated by the needle under the specified load, or the minimum load required to penetrate the coating by the needle. There are two kinds of instruments in use now: automatic type and manual type. The automatic type can directly display the results from the electrical instrument relying on the conductivity. my country's national standard GB9279 88 "Paint and Varnish Scratch Test" stipulates that the automatic type instrument should be used as the arbitration test. instrument. The dynamic instrument is used as the instrument of the referee test.
