Brief introduction of the molding technology of th

Brief introduction of pet preform molding technology

in the molding process of preform, the best condition is to quickly, evenly and completely melt at the lowest possible temperature and in the shortest possible time, so as to minimize the decrease of IV, the production of AA and the transparency as much as possible. Related process conditions are:

temperature

molding temperature refers to the temperature of the barrel and hot runner. Only 30% of the heat in the forming process comes from external heating and 70% from internal friction heat. Therefore, in addition to proper heating, shear heat should also be used

injection and pressure maintaining

injection is to overcome the resistance in the runner and fill the molten material into the mold. For bottle blanks, it is best to have three stages of speed and pressure, which decrease in turn

the injection speed is too slow, the shear is not enough, and the universal tensile testing machine is cooled before it is full, resulting in the product is not full or under injected; Too fast, insufficient exhaust in the mold cavity, resulting in insufficient filling, shrinkage and high AA

pressure maintaining has two important functions: preventing melt backflow and ensuring cooling under pressure (improving cooling effect). Too high will cause excessive filling and mold expansion, and the internal stress will be high, which may also crystallize. Too low will cause shrinkage, deformation of bottle blank (insufficient cooling), gate problems such as pinholes, bubbles, etc., because the cooling rate at the gate decreases. The pressure holding time should also be appropriate. If it is too short, it will also cause the needle. Then its degree of non environmental protection is much higher than that of plastic bag holes, wire drawing, etc

pressure relief

pressure relief is to reduce the pressure in the hot runner, prevent gate blockage, inflexible needle valve action, etc. But too much will cause shrinkage, wiredrawing, pinholes, etc

back pressure

back pressure is the kneading force applied by the hydraulic system to the molten material through the screw during the rotation of the screw driven by the oil motor. Function: strengthen the plasticization of pet and eliminate bubbles. It can be adjusted to 0 at the beginning of startup, and then slowly add it up after the bottle blank is finished. The back pressure when there is no bubble or scar in the bottle blank is the appropriate back pressure. If the shear force is too high, problems such as poor molding, gate plugging and pyrolysis will occur

buffer zone

buffer zone is the margin in front of the screw head after each injection. Too little will cause poor molding, and too much will cause pet decomposition. Generally, it is appropriate to adjust slowly from less to more until the bottle blank does not fog or crystallize

cooling

pet modern aviation industry develops transparency in innovation, and the reason why bottle blanks are transparent depends on cooling. Poor cooling will reduce the cooling rate of the bottle blank, which will lead to shrinkage, deformation of the bottle blank and affect the circulation time. To avoid this situation, it is necessary to do a good job: water quality treatment, regular cleaning of water channels, inspection of water flow and pressure, disassembly and cleaning of cores and cavities, etc

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