In order to measure the elasticity of the paint film, Lazarief and Golichenstein (HNNJIK) proposed an instrument called an elasticity Tester. Elasticity can be measured according to the ability of the stretched paint film to recover its original length after the tensile stress applied for the same time is removed. Strain occurs by stretching a lay-flat paint film to a certain length. Elasticity can be measured by the following formula:
Over time, the residual strain can be measured to give an idea of the elasticity of the paint film.
This method can be used to determine the elasticity of all paint materials (including drying oils, cooked oils, oil-based paints, oil-based varnishes, natural resins and synthetic paints) whose peeled paint film can be expanded up to 5% without tearing. Resin can be made into enamel, most nitro lacquers and nitro paints, etc.). The sketch and overview of the HNNJIK elastic gauge are shown in Figure 133. Clips 1 and 2 are used to fix the paint film. Clip 1 is fixed, and clip 2 can move in the guide rail.
The gripper can be moved using a helix 3 rotating in a web 4 . Screw then utilizes handle 5 to start. The distance between the two clips can be measured using a micrometer 6 and a thin plate 7 with marks, which is connected to the clip 2 . A few hundredths of millimeters are measured on the side of the cylinder 8 that is divided into 100 equal parts together with the wire 3. The pitch of the screw is equal to 1 mm; so the graduation of the cylinder corresponds to 0,01 mm. At the back of the center, 0.5 mm below the edge of the paint film, tension the metal wire (spring) in the instrument horizontally. (Related instrument: bending Tester)
When conducting the test, the stripped paint film must be placed between two millimeter coordinate papers, and a piece of paint film in the shape of a 60 mm long and 5 cm wide paint film should be cut with a blade. Cut out two rectangles of the same size from the paper. Turn the handle to move the elastic gauge: the stator moves to a distance of 35 mm from the fixed clip; then, fix the paint sample between the western pieces of paper in the clip so that each side enters the clip 5 mm, leaving The 50mm empty space is not clamped.
After the paint film is fixed, cut the strip of paper and remove it, and then accurately measure the length of the paint film. Therefore, the handle must be carefully turned to remove the clip and pull the paint film until its most slack part is on the same level as the tensioned wire (spring). In this position, the paint film can be considered to be relatively taut. It is inappropriate to stretch the paint film more tightly, because the stretched paint film will relax slightly after a short period of time under its own weight. When measuring the surface of a relatively tight paint film, the quasi-stone angle should reach 0.01 mm. After the length of the paint film has been measured, turn the handle to extend the paint film to the predetermined length. Oil-based paint, lacquer, enamel, etc. have an extension of 10% of the original length, while nitro lacquer is 3-5% of the original length.
Keep the paint film under tension for 30 minutes, and then quickly turn the handle to restore the movable part to its original position when the paint film is relatively stretched. At this time, the relaxation well of the paint film is gradually shortened. After one hour, the movable clamps are carefully removed so that the paint film regains the same relative tension as when the length was originally measured, and then the length of the paint film is measured again with the same accuracy.
The elasticity of the paint film depends on its "life" (Bo3pacT), its degree of stretching, and the time it remains in an elongated state. Therefore, when several paint materials are tested for comparison, the test conditions need to be the same. The paint film thickness should also be the same when testing different samples.
