Pet Bottle Preform injection molding process is one of the most important techniques for processing plastics. PET plastic bottles, most plastic packaging plants will use blow molding production process, but the injection molding process has a unique unique processing advantage. For PET for injection molding, the technician needs to consider many factors.
Introduction to polyester plastic
The PET chemical name is a polybutyl terephthalate, also known as a polyester. At present, the most commonly used customer is GF-PET, which is mainly used for preforms.
The rheological properties of PET in the molten state are better, and the effect of pressure on viscosity is greater than the effect of temperature. Therefore, the flow characteristics of the molten material are mainly changed by the pressure.
PET characteristics and characteristics:
PET has a glass transition temperature of about 165 ° C and a material temperature range of 120 to 220 ° C. PET has a strong hygroscopicity at high temperatures. For glass fiber reinforced PET materials, bending deformation easily occurs at high temperatures.
The crystallinity of the material can be increased by adding a crystal strengthening agent. Transparent products made of PET have gloss and heat distortion temperatures. Special additives such as mica can be added to the PET to minimize bending deformation. If a lower mold temperature is used, a transparent product can be obtained by using an unfilled PET material.
Injection molding process:
The injection molding method is mainly used to enhance the molding of PET. A screw type injection molding machine is usually used. Screws usually need to be hardened to avoid wear after long-term use. The length of the nozzle hole of the injection molding machine should be as short as possible, and the diameter of the injection molding machine should be controlled to about 3 mm.
Reinforced PET has a melting point of up to 260 °C. To prevent nozzle clogging, a higher power heater should be installed. Further, the tip end of the nozzle hole is preferably machined into an inverted cone as shown in Fig. 1, so that the molten material in the flow path and the nozzle can be easily cut.
Injection molding machine:
Injection molding is mainly used to enhance the molding of PET. PET can usually only be formed by a screw injection molding machine.
It is best to choose a mutant screw with a reverse ring on the top. This screw has a large surface hardness and wear resistance, and the ratio of length to diameter is not L / D = ( 15 ~ 20 ) : 1 compression ratio For 3: 1.
Materials with too large L/D stay in the barrel for too long, and excessive heat can cause degradation and affect product performance. The compression ratio is too small, the heat generated is small, the plasticization is easy, and the performance is poor. On the other hand, the glass fibers will break more and the mechanical properties of the fibers will decrease. When the glass fiber reinforced PET is reinforced, the inner wall of the cylinder is seriously worn, and the cylinder is made of a wear resistant material or lined with a wear resistant material.
Since the nozzle is short, the inner wall needs to be polished and the hole is as large as possible. Hydraulic brake valve nozzles perform well. The nozzle should have insulation and temperature control measures to ensure that the nozzle does not freeze and clog. However, the nozzle temperature should not be too high, otherwise it will cause salivation. Before starting molding, you must use low pressure PP material and clean the bucket.
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