Experiment on plywood
The tests were carried out on five pieces of birch plywood with dimensions 110x110x4 mm. The paint to be tested is applied to the board from all sides; the board is first kept at 40°C for 4 hours, and then dried to constant weight under heavy speed. The weight of paint removed should be about the same on each board (relevant instrument: dry time meter). Weigh on an industrial balance with an accuracy of 0.01 g. The prepared test plate is placed in a parallel position on a tripod with a height of 200 mm and a ring diameter of about 150 mm (Figure 228). Light the gas lamp (the diameter of the ignition hole is 9 mm), and adjust the flame to a height of 40 mm. Then, place the gas lamp under the test panel so that the distance from the edge of the test panel to the lamp is 30 mm. After a full two cents, remove the gas lamp, record the open flame (open flame) and self-burning time of the sample, and then weigh the sample and calculate its weight loss according to the formula:
If, after the gas lamp is removed, the sample extinguishes rapidly and smokes without igniting, and its weight loss does not exceed 20%, the coating is considered to withstand the test.
The test conditions will be more stringent if the specimen is placed on the tripod not in a horizontal position but at an angle of 45°.
Combustion tests in small "fire tubes"
The fire tube test is a well-established method for determining the fire performance of paints. During the test, five pine slats with a size of 10x10x150 mm were selected and planed accurately with a planer along the wood grain according to a curved ruler. The wooden strips should not have surface cracks and side cracks; the moisture content of the wood is 7% to 9%. On the surface of the wooden strip 10 mm away from one end of the wooden strip, a hole with a diameter of 1 mm is drilled, and then the wooden strip is coated with the paint to be tested and dried to constant weight.
Place the prepared sample in a small fire tube made of iron skin (165 mm long, 50 mm in diameter, see Figure 229) for testing. In order to carry out this test, the sample must be hung on the iron hook connected to the balance beam in the tube, and the pointer of the balance should be fixed to the extreme left with weights.
A gas lamp (1000~1100°C) with a flame height of 40 mm is placed under the 5 mm sample drawn from the fire tube.
The test continued for 1 point of gold. After every 10 seconds, record the lost weight according to the indication of the balance pointer, and record the time when the sample starts to burn and its tendency to ignite (smoke). After the test, the sample is weighed again.
It can be considered that the coating film can withstand the test. When carrying out the test, it is necessary to use moisture-fixed wood. The curved seam that represents combustion process and wood humidity relation is as shown in accompanying drawing 230.
