For some electric insulation paint materials, such as paint materials used for insulation of machine and equipment parts, a requirement called arc resistance or spark resistance is proposed.
In order to carry out the test, the following equipment is necessary: 1) a step-up transformer with a power of not less than 0.5 kW; 2) an AC mA ammeter with a measuring range from 0 to 30 mA; Messenger of brass electrodes (Fig. 220); 4) stopwatch.
For testing varnishes or enamels, two streams of the paint material must be applied to a bakelite disc with a thickness of 3-4 mm (relevant instrument: Thickness Gauge). Before applying the paint material, the thickness of the disc needs to be measured in two or three places. Mark the measured thickness on the back of the plate with a pin pen, and then measure the thickness at the marked mark on the plate coated with the paint film after the enamel paint is finished and dried at 18~20°C for 16 hours. Measure the paint film thickness according to the difference. The film thickness after drying should be equal to 60~80µ. Then clean the end wells of the electrodes and adjust the distance to 8 mm. (Related instrument: drying time Tester)
Thereafter, the apparatus (Fig. 220) was assembled, that is, one of the brass electrodes was connected in series to the high voltage terminal, while the other was grounded, and the milliampmeter was connected in the circuit.
Cover the window of the small chamber quickly, and connect the high voltage equipment well (see Figure 219). Then move the float (sliding small piece) of the rheostat until a spark discharge occurs between the electrodes and the current reaches 10 mA.
After this, the device is cut off, the window well of the chamber is opened to grind the two ends and the electrodes are placed on the surface to be tested so that the two electrodes are in contact with the surface.
Cover the window of the chamber, switch on the equipment and start the stopwatch at the same time. The occurrence of instantaneous discharge phenomenon can be recorded by a stopwatch. The arithmetic mean value of the ten measurements is taken as the actual action time of the electric arc (discharge) on the test surface.
