Hardness (scratching resistance method)

The test method allows to determine, under specific conditions, resistance to penetration by scratching, of a single coating or a multi-layer coating system, or a related product, through a half-spherical indentor needle. If using powder products, it is not necessary to use a special procedure, you have to identify any unusual features and register them as abnormal color, the presence of large or rough lumps, the presence of unrelated bodies, etc. Generally, the sample to be tested is obtained by mixing the powder with a liquid solution, and then it is placed on a substrate complies with the standard ISO 1514, as well as to obtain a sample with dimension of 50 mm x 180 mm. Once the samples are prepared, these are to be air-conditioned at temperature of (23 ± 2)°C and a relative humidity of (50 ± 5)% for a minimum period of 16 h. The preliminary stage is to examine the needle of the instrument, making sure that the hard tip is smooth, half-spherical and free from any contamination. Attach the needle to the spindle so that, when it is in position on the test panel, it will be perpendicular to the support. Balance the arm of the needle holder with adjustable counterweight. Make sure that the indicator device (voltmeter) is operational, by connecting the needle with the panel support. Lock the test panel onto the support with the coating test on top, with the longest side of the panel parallel to the direction in which the scratch will be made. Start the test, a load slightly lower than that expected to cause penetration of the coating, and thereafter, increase the mass on the instrument, with suitable increments so that it has a complete penetration in the coating. Observe the indicator device during the test, to determine whether there is the electric contact between the needle and the underlying panel. Then save the minimum load at which the needle penetrates the coating as specified. Repeat for the other two panels. The test results are obtained indicating the minimum load (g) which slightly penetrates the sample and the load that is completely penetrated the sample.

Instruments used to perform the test: Automatic scratch tester