(1) Method points
It is when the pendulum that touches the surface of the paint film swings at a certain period. If the surface is softer, the swing of the pendulum decays faster. On the contrary, the decay is slower. Usually, the ratio of the damping time of swing decay in the swing angle range to the damping time of swing decay in the same swing angle range on the glass plate is used to express the paint film hardness.
When two pendulum-type damping Testers of König and Persoz pendulums are used to test the coating hardness, due to the different structures, weights, sizes, swing periods and swing amplitudes of the two pendulums, in addition , the interaction between the pendulum and the coating also depends on the complex elasticity and viscoelasticity of the coating, so a general conversion relationship cannot be established between the measurement results of the two pendulums. Therefore, when measuring the damping time of a certain paint film in the product standard, only one pendulum instrument is specified.
(2) Factors to be considered in choosing a pendulum damping Tester
① Usually the damping time of the Koenig pendulum is close to half of that of Persaz;
②The Persaz pendulum may slip on surfaces with a low coefficient of friction, which will invalidate the results, but for general paints and varnishes, this situation is difficult to occur;
③Because the environmental conditions have a great influence on the damping time of the paint film, the test should be carried out under the conditions of controlled temperature and humidity, and without vibration and airflow. In addition, the thickness of the paint film and the material of the substrate also affect the damping time.
The structures of Koenig's pendulum and Perthalz's pendulum are shown in the figure below. Although their shapes are different, the main structure is connected with an open frame by a cross bar. Two steel balls used as fulcrums are embedded under the cross bar, and the lower end of the frame forms a pointer-like tip.
Koenig Swing Rod Platinum Saaz Swing Rod
The hardness of the paint film is tested by the pendulum method. The paint should be painted on (90~100)mm×(100~120)mmX (1.2~5)mm (according to JG 40--62) float flat glass or polished On flat glass, and should be dried according to the conditions and time specified in the product standard. Unless otherwise specified, the dry test panel should be conditioned for at least 16 hours under the environmental conditions of temperature (23±2)°C and relative humidity (50±5)%. The entire test process should also be carried out under this condition.
