Determination of cold resistance of films by bottom stamping method

This method is dedicated to the determination of the strength (durability) of paint films under dynamic strain at low temperatures.

In order to carry out this test, Chebotarevsky, Frolov and Smirnova have proposed a special adiabatic chamber (Fig. 235), which is equipped with a press base with an extended shaft and a segment damage detection The segment loss Detector is used to measure the damage of the whole piece of the coating film (that is, the situation of connecting into pieces) for a long time in the removal of the film. The damage Detector consists of the following parts: (1) electrolyte chamber with funnel, (2) pressure glass bottle with lens barrel at the bottom, (3) 5~6 volt battery, (4) 5~6 volt battery DC current voltmeter and (5) contact terminals for testing.

The small chamber (Fig. 236) of holding electrolyte is made of electric insulation green material (plexiglass, delta one wood wide or central cloth bakelite).

The small outdoor shell 1 is a cut-off cone inside, the cone is covered from one side by a cover 2, and a rubber tube is inserted in the hole of the cover, and this tube has an electrode 3 passing through it. The other side of the chamber was open; this side was covered with a painted panel during the test. The electrolyte enters through the lower tube 4, and when the small chamber is full, the excess electrolyte rises along the tube 5. A pressure wave glass bottle (volume 250 ml) is doubled by a rubber tube and connected to the small chamber.

The hydride on the surface of the electrode must be removed, check the circuit diagram on the segment damage Detector and check the voltage on the battery (5~6 volts) terminal, and put kilograms of dry ice in the heat-insulated chamber. Continually replenish ice as it is consumed while the equipment is in operation.

Pour the saturated alcohol solution of table salt (electrolyte) into the pressure glass bottle, and this solution is also cooled to the necessary temperature with small pieces of dry water before entering the small chamber. The temperature of the electrolyte was measured with an alcohol thermometer. The time required to cool down the press from the moment it is filled with 1 water is about 2 hours. The test specimens were prepared by coating a metal plate with a film.

The painting method, drying time, number of layers, paint film thickness, storage time of the sample before the test, etc., should be selected according to the specified technical conditions. (Related instruments: drying time Tester, Thickness Gauge)

In order to carry out the test on one corner of the test panel, the paint film shall be carefully removed and the contact terminals leading to the battery connection shall be wedged in the cleaned place.

Insert the test panel into the press through the cutout (hole) of the heat-insulating chamber with its painted side outward, and rotate the paper wheel to press it tightly against the supporting ring of the electrolyte chamber. After that, with the help of raising the pressure glass bottle, the electrolyte is introduced into the small chamber from below, and attention should be paid to make the pressure glass bottle higher than the small chamber so that a part of the electrolyte appears in the funnel. Adjust the ring scale to zero, then move the clutch to engage the inner screw. The control wheel rotates at a constant speed so that the test plate can be pressed to a depth of 1 mm within 10 to 12 seconds (the control wheel rotates 1 revolution per minute).

The temperature on the surface of the test plate can be measured by a surface (sheet-shaped) thermocouple. When the entire film is damaged and the current detected by the voltmeter of the damage Detector appears in the circuit, stop the rotation of the paper wheel and read the extrusion depth on the scale.

Cold resistance (at a known temperature) is expressed by the pressure depth of the metal bottom surface when the coating film on the metal bottom surface is damaged. The results of the measurements are expressed in millimeters. The difference between two parallel determinations should not exceed 0.1 mm.

After the test is over, pour the electrolytic solution into the pressure glass bottle so that the glass bottle is lower than the small chamber, and take out the test plate from the base of the press.

The cell of the electrolyte should be washed 3 times with hot water to remove the electrolysis residue; dry the metal part with a clean coarse white cloth, and apply petrolatum oil (Vaseline) to the well.

Using the above-mentioned equipment, the elasticity of the coating film in the range of +50°C to -50°C can be measured.