When the material of the vacuum coating equipment is heated or cooled, it will deform, and the deformation is uniformly deformed in three directions. If the part has a certain thickness, when the surface is cooled, the surface is contracted first, but it is limited by the shrinkage after internal cooling. Therefore, during temperature change, the surface will be under tensile stress and the inside will be under compressive stress.
When the parts are heated, the surface is heated, and the interior is relatively cold, the surface expands first, but is limited by the internal expansion, so the surface will be under compressive stress and the inside will be under tensile stress. This is the deformation and additional thermal stress of vacuum coating machine parts caused by temperature changes.
The change of temperature makes the mechanical properties of materials change. For steel materials commonly used for mechanical parts, in addition to the slight increase in mechanical strength due to embrittlement in the temperature range of 200-300°C, the general trend is that the material strength limit and the yield limit increase with temperature, and gradually decreases. Low temperatures are relative to room temperature. The fatigue strength of materials at low temperatures increases with decreasing temperature. This is true for almost all metallic materials.
The stress values are constant, and the metal material has a slow plastic deformation at high temperature. This phenomenon is called creep, and the plastic deformation caused by creep is also an unrecoverable deformation.
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