OBRABOTKAMETALLOV technology Vol. 25 No. 2 2023 30 seconds to eliminate the influence of vibrations. After the mass value stopped fluctuating, its value was recorded in the table. Then the density values of each brand of a coolant were calculated according to the following formula: r = , m V (1) where m is the coolant mass, kg; V is the coolant volume, m3 (which was equal to 120·10–6 m3). Investigation of the wetting properties of a coolant The wetting properties of the coolant are evaluated by the value of the wetting edge angle Θ. The values of the wetting edge angle were measured using an electronic digital microscope. For these studies, a workpiece made of the same alloy as the roller, used in the studies of the lubricating properties of a coolant, was used. During the tests, the axis of the electron microscope lens was installed in the same plane with the surface of the workpiece since in this position it is possible to set the true value of the wetting edge angle. The digital microscope is shown in figure 2. Fig. 2. Digital microscope During the tests, the investigated coolant was applied to the dry surface of the workpiece using a pipette. After the coolant drop assumed a static position, an image of this drop was recorded using a microscope. According to this technique, images of drops of all coolants were obtained. An example of such an image is shown in figure 3. The assessment of the wetting edge angle of every coolant on the surface of the steel workpiece was carried out using a computer drawing software COMPASS v18. In this case, a straight line was drawn, which is a projection of the surface of the workpiece, as well as a line that is a projection of the interface between the coolant drop and the surrounding air. At the intersection point of the constructed lines, a tangent line was drawn to the surface line of the coolant drop. The wetting edge angle was the angle between the tangent Fig. 3. A drop of a coolant on the surface of a steel workpiece: 1 – a coolant drop; 2 – a steel workpiece
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