The thermal performance temperature of plastics has a great influence on the properties of polymer materials, especially for the performance of linear polymers. Thermosetting plastics have a cross-linked structure. Generally, the mechanical strength does not change much under 200 ° C, but the high temperature will decompose and will not melt and cannot be processed. Among thermoplastics, crystalline polymers differ somewhat from amorphous polymers. Plastics are generally rigid at the glass transition temperature and are easily deformed above the glass transition temperature. The heat distortion temperature is usually used to characterize the limit temperature of the plastic deformation resistance of the plastic, generally in the range of 37-200 ° C, but when the plastic and glass fiber and other reinforcing materials are combined, the heat distortion temperature of the material can be greatly improved. Since plastics are pyrolyzed at high temperatures to produce various gases, and most of the decomposition gases are harmful to the human body, attention should be paid to environmental pollution and safety to humans. Tables 1-14 and 1-17 list the heat distortion temperature, service temperature and embrittlement temperature of various plastics, respectively. Figure 1-16 shows the comparison of the continuous heat-resistant temperatures of various plastics, the comparison of the glass transition temperature and melting point of various plastics of 1-17 series, and Figure 1-18 shows the comparison of the thermal conductivity of various plastics.
The effect of temperature on the mechanical properties of the polymer. In general, the modulus of elasticity, compressive strength, flexural strength, and hardness of plastics decrease with increasing temperature. In most cases, impact strength and elongation increase with increasing temperature. In addition, elevated temperatures accelerate chemical attack and chemistry. Promotes aging and even pyrolysis. Therefore, if the designed plastic part is not used at room temperature, the calculation of the mechanical properties data at normal temperature cannot be used.
The thermal deformation of the polymer generally follows the law of thermal expansion and contraction. When the temperature changes, the length and volume of the plastic product change, and this characteristic is usually characterized by the coefficient of linear expansion. When the designed plastic parts need to be matched with the metal parts, the matching of the expansion coefficients of the two groups should be considered, otherwise serious deformation will occur. Once the matching size is improperly designed, the shaft and the sleeve of the moving fit will be stuck.