PE material: PE is also called polyethylene, which is one of the commonly used polymer materials in daily life. It is widely used in the manufacture of plastic bags, plastic films, and milk barrels.
PP material: polypropylene, polypropylene has high crystallinity and regular structure, so it has excellent mechanical properties. The value of the mechanical properties of polypropylene is higher than that of polyethylene, but it is still a low variety in plastic materials, and its tensile strength can only reach 30MPa or a slightly higher level. Polypropylene with a larger isotactic index has higher tensile strength, but as the isotactic index increases, the impact strength of the material decreases, but it does not change after falling to a certain value.
The above materials are commonly used in injection molding.
1. If the plasticizing capacity of the machine is too small, the plasticization of the plastic in the barrel is insufficient; if the plasticizing capacity of the machine is too large, the time for the plastic to be heated and sheared in the barrel is too long, the plastic is easy to age, and the product becomes brittle.
2. If the runner of the mold is too small or improperly configured, it should be arranged in a balanced and reasonable way or the size of the runner should be increased.
3. If the mold temperature is too high, demoulding is difficult; if the mold temperature is too low, the plastic will cool prematurely, the weld seam will be poorly fused, and it will be easy to crack, especially for high melting point plastics such as polycarbonate.
4. The raw materials are mixed with other impurities or mixed with inappropriate or excessive solvents or other additives.
5. The quality of the plastic itself is not good, for example, the molecular weight distribution is large, and the proportion of components containing uneven structures such as rigid molecular chains is too large; or it is polluted by other plastics, bad additives, dust and impurities, etc., which can cause brittleness reason.
6. The product has sharp corners, gaps or parts with great differences in thickness that are prone to stress cracking.
