1) The plastic material is compressed by heat, and the coefficient of linear expansion is much larger than that of metal;

2) The rigidity of general plastic materials is an order of magnitude lower than that of metals;

3) The mechanical properties of plastic raw materials will decrease significantly under long-term heating;

4) The general plastic material is temporarily stressed under normal temperature and under the stress of its yield strength, and permanent deformation will occur;

5) Wholesale of plastic raw materials is very sensitive to gap damage;

6) The mechanical properties of plastic raw materials are usually much lower than that of metals, but some composite materials have higher specific strength and specific modulus than metal. If the product design is reasonable, it will be more advantageous;

7) Generally, the mechanical properties of plastic raw materials are anisotropic;

8) Some plastic materials will absorb moisture and cause dimensional and performance changes;

9) Some plastics are flammable. Classification of plastic materials.