There are two important characteristics of hot pressing materials:
(1) Plastic memory
Plastic memory can make plastics become rubber-like after heating, and close to the mold, is an important characteristic of materials. Because of this characteristic, the poorly formed products can be heated outside the die to restore the original flat shape.
(2) Hot strength and hot elongation
Thermal strength and thermal elongation are two properties related to plastic memory. Thermal strength is the strength left over from plastics when heated. Some plastics lose all their strength and become soft and sticky when heated, but some plastics still have strength rebound when heated. Plastics with high thermal strength can be extended on dies, but plastics with low thermal strength can tear quickly when extended. Therefore, the material with strong thermal strength is the material with high thermal tear strength.
In addition, the forming temperature range of materials is also an important characteristic. Excellent hot-pressing materials can be changed into soft rubber shape in a wide range, such as acrylic plastics, which can be formed at 125-175 degrees C. Certain materials can be formed at a slightly higher softening point.
Special attention should be paid to plastic materials during hot pressing. Some plastic memory stresses may occur during forming and the ideal products can not be obtained. Therefore, the forming temperature and pressure are limited to a certain extent. Moreover, in hot pressing process, it will also produce a certain degree of extension. Therefore, when choosing materials, we must pay attention to the forming temperature. When hot-pressing, it is better to operate in a small range of time and temperature.
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