1. The properties and uses of PE (polyethylene)
PE, there are many kinds of high-density polyethylene (low-pressure polymerization), low-density polyethylene (high-pressure polymerization), linear low-density polyethylene, ultra-high molecular weight polyethylene, etc. The melting point is around 120-140°C, and the decomposition temperature is above 270°C.
Thermoplastic PE has excellent corrosion resistance and electrical insulation (especially high-frequency insulation), and can be enhanced by modification such as chlorination, irradiation, and glass fiber.
High-density polyethylene has high melting point, rigidity, hardness and strength, low water absorption, good electrical properties and radiation resistance; low-density polyethylene has good flexibility, elongation, impact strength and permeability; super High molecular weight polyethylene has high impact strength, fatigue resistance and wear resistance.
Low-pressure polyethylene is suitable for making corrosion-resistant parts and insulating parts, high-pressure polyethylene is suitable for making films, etc., and ultra-high molecular weight polyethylene is suitable for making shock absorption, wear-resistant and transmission parts.
2. Precautions for molding of PE (polyethylene)
The hygroscopicity of PE is very small, so you don't need to dry it before molding. If it is not stored properly, it can be dried at about 70°C for 2 hours.
The fluidity of PE is very good, and the melt viscosity is sensitive to pressure. It is not suitable to use a direct gate to prevent uneven shrinkage and increase internal stress. At the same time, attention should be paid to the selection of the gate position to prevent shrinkage and deformation.
Thermoplastic PE has a large shrinkage range and shrinkage value and obvious directionality, and is easy to deform and warp. Suitable for slow cooling. When soft PE plastic parts have shallow side grooves, forced demoulding can be used.
1. Performance and usage
PS is a commonly used transparent plastic, with a light transmittance of over 90%, second only to plexiglass, and a density of 1.05g/㎤, which is the density closest to water among plastics.
It is often used to indicate the injection volume and output of the injection molding machine. Excellent electrical insulation (especially high-frequency insulation), good coloring and water resistance, good chemical stability, average strength, but brittle, prone to stress embrittlement, not resistant to benzene, gasoline and other organic solvents. It is suitable for making insulating transparent parts, decorative parts, chemical instruments, optical instruments and other parts.
2. Precautions for molding
Thermoplastic PS is an amorphous plastic with low moisture absorption and good storage. It is not necessary to dry it before molding. It is recommended to dry it at 80°C for about 2 hours before molding. The molding temperature can be selected between 170-270°C, but the best molding temperature It is 185-215°C. Molding shrinkage rate, wide range of molding temperature, not easy to decompose, but large thermal expansion coefficient, easy to generate internal stress. Good fluidity, high mold temperature and low injection pressure are suitable. Prolonging the injection time is beneficial to reduce internal stress, prevent shrinkage cavity and deformation.
Various forms of gates can be used in the mold, and the gate is connected with the arc of the plastic part to avoid damage to the plastic part when the gate is removed. The demoulding slope is large, the ejection is uniform, and the wall thickness of the plastic part is uniform. It is best not to have inserts. If there are inserts, they should be preheated.