Friction coefficient and temperature of the hottes

Friction coefficient and temperature of materials

Abstract: This paper introduces the influence of temperature change on the friction coefficient of materials, and analyzes the actual testing requirements for the friction coefficient of thin films in practical applications

key words: friction coefficient temperature stick slip

1 friction coefficient

friction coefficient is a measure of the friction between two surfaces, which represents the friction behavior of materials. The friction coefficient of the film surface depends on the adhesion of the film surface (surface tension and crystallinity), additives (slippery agents, pigments, etc.), and surface polishing. During the following operation procedures, it is necessary to strictly control the friction coefficient of materials, such as when the film crosses the free roll, bag forming, product winding film, and stacking of packaging bags and other containers. In addition to the internal variable factors of materials that can affect the friction coefficient of materials, environmental factors (such as the speed of machine operation, temperature, electrostatic accumulation, and humidity) It can also affect the test results of friction coefficient

2 Effect of temperature on friction coefficient

the change of molecular motion state of polymer materials is called relaxation from the viewpoint of dynamics. When the temperature rises, on the one hand, different angles may appear, which can improve the thermal motion ability of each motion unit. On the other hand, due to thermal expansion, the distance between molecules increases, that is, the free volume inside the polymer increases, which increases the activity space of each motion unit, which is conducive to molecular motion, shortening the relaxation time and accelerating the relaxation process. With the relaxation of polymers, their thermodynamic properties, viscoelastic properties and other physical properties will change dramatically. As the order of items in the most commonly used list, the friction coefficient of materials is a very important mechanical index, which is also affected by the rise of temperature. Generally speaking, with the increase of ambient temperature, the friction coefficient of the material surface will change to a certain extent, but the magnitude of the change varies with the material

3 temperature rise test

in order to verify the influence of temperature change on the friction coefficient value, the nine production lines in charge of Section Chief Zeng have been running at full load for nearly one time. The author specially selected several groups of representative materials to measure their friction coefficient at different temperatures. The following is the detailed test information and results of two groups of tests:

sample: PC film, aluminum foil composite film

test equipment: Labthink fpt-f1 friction coefficient/peel tester (which can realize the automatic temperature between room temperature and 99.9 ℃)

test temperature: room temperature ~ 90.0 ℃

test data:

it can be seen from Figure 1 that the increase of test temperature significantly affects the friction coefficient of materials, but for different samples, The effect of temperature is different; Moreover, for the same sample, with the increase of temperature, the variation trend of dynamic friction coefficient is likely to be different from that of static friction coefficient. For example, for PC film, the growth trend of static friction coefficient with the increase of temperature is relatively stable, but the variation trend of dynamic friction coefficient fluctuates greatly, but the overall trend of dynamic friction coefficient also increases. For aluminum foil composite film, the growth trend of friction coefficient is not as good as that of PC film, and its dynamic friction coefficient basically remains stable with the increase of temperature. It should be noted that during the friction test above 74 ℃, obvious stick slip phenomenon occurred during the test, that is, the sliding phenomenon is unstable and intermittent

4 actual requirements

the friction in the actual packaging process is often both a drag force and a resistance, so the size of the friction coefficient must be effectively controlled to make it within an appropriate range. For coiled materials for automatic packaging, it is generally required that the inner friction coefficient is relatively small, while the outer friction coefficient is moderate. The friction coefficient of the inner layer should not be too small, otherwise it may cause instability of stacking during bag making and forming, resulting in misalignment. The outer friction coefficient is too large, which will cause too much resistance in the packaging process to roughly stretch and deform the material, and too small may cause the drag mechanism to slip, resulting in inaccurate electric eye tracking and cutting positioning. The friction coefficient of the composite film is affected by the content of opening agent and smoothing agent of the inner material, as well as the stiffness and smoothness of the film

when studying the friction coefficient of materials, special attention should be paid to the influence of temperature on the friction coefficient. As mentioned earlier, different temperatures will lead to significant changes in the friction coefficient, and it is necessary to obtain the measured data through actual detection. The friction coefficient of a material may increase or decrease significantly with the change of temperature, and may also maintain a certain data stability. Considering that the actual operating temperature of the production line is often not well controlled near room temperature, it is necessary to measure not only the friction coefficient of packaging materials at room temperature, but also the friction coefficient at the actual ambient temperature. To complete this test, you can change the ambient temperature of the laboratory (it is advisable when the required temperature is not much different from the room temperature), or with the help of the automatic temperature control function of the detection equipment, such as Labthink fpt-f1, you can control the test temperature between room temperature and 99.9 ℃, which is convenient for the test operation

Author: Zhao Jiang

from: Jinan Languang Electromechanical Technology Company