By allowing the peeled paint film to grow at low temperatures, good comparative characteristics of the cold resistance of various paint materials can also be obtained. In principle, this test can be carried out in any instrument for measuring the tension and tensile strength of the paint film (the instrument additionally uses a special accessory to gradually cool the paint film to the required temperature). However, these methods have not been applied in actual tests of paint films. The most interesting is the HNNWN type instrument for testing the cold resistance of rubber. The principle of this instrument can also be used in the test of paint film. The structure of HNNWN type instrument is as shown in accompanying drawing 237.
A metal cylinder 2 is installed on the wooden base 1, and the cylinder is composed of two sleeves, and a heat-insulating lining is arranged between the two sleeves. The sleeve 3 of the inside can be filled with alcohol and solid carbon dioxide in the instrument in the past.
The test piece 6 is fixed in the cores 4 and 5 in the Bakelite cylinder 7, and two wide incisions are cut on the side of the cylinder 7, that is, almost on its entire surface. The upper clip 4 is fixed on the thin copper system 8 with the help of Xiaojun, while the lower central part is supported in the end of the Bakelite cylinder fixed on the support 9 with its own shoulder (circle). This brace is welded to steel tubes 10 that are movable along columns 11 . In order to facilitate the lifting of the container containing the cooling mixture, a counterweight 12 that can slide along the guide post 13 can be used.
The test piece can be deformed by means of a load placed on the base 14 (the base 14 is drawn on the copper wire 8 on the other side of the pulley 15). Only one set of weights is attached to the device; there are three weights of 1000 grams, two weights of 500 grams and two weights of 200 grams, a total of 4400 grams. The extensibility of the sample can be read on the continuous scale.
Temperature can be measured with thermocouples. The adjustment of temperature can be carried out by adding ethanol or carbonic acid gas. The test is to measure the relative elongation of the sample at room temperature first, and then measure the relative elongation of the same test piece at low temperature. (Related Instruments: Tensile Tester)
