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PET plastic processing method, how much you know
The rheological properties of PET in the molten state, stress on the influence of the viscosity is bigger than the temperature, therefore, mainly from the pressure to change the melt flow rate. 1, plastic processing because of PET macromolecular contains aliphatic, has certain hydrophilicity, aggregate at high temperature is more sensitive to water, when the moisture content is more than the limit, in the processing of PET molecular weight drops, products with color, crisp. Trapped here, in front of the processing must be carried out on the material drying, the drying temperature is 150 ℃, more than 4 hours, generally is 170 ℃, 3 - 4 hours. Air-launched available to test whether the material completely dry. 2, selection of injection molding machine PET since the stable time is short, after melting point and melting point is high, so need more temperature control section and plasticizing injection system, the friction heat generating less when products and actual weight not less than two-thirds of injection machine. Based on these requirements, ramada in recent years, the development of small and medium-sized series of PET special plasticizing system. Clamping force by more than 6300 t/m2. 3, mould and PET bottle embryo gate design general use molding mould of hot flow path, between the mold and injection molding machine template have the insulation board, its thickness is about 12 mm, and heat insulation board must be able to bear high pressure. Exhaust must be sufficient to avoid local overheating or fracture, but its vent depth generally not more than 0. 3 mm, otherwise prone to flash. 4, melt temperature available air-launched measure method. 270 - GF - 295 ℃, enhance the level PET can be set to 290 - 315 ℃, etc. 5, generally faster injection, injection speed can prevent premature solidification injection. But too fast, high shear rate makes material brittle. Shot is usually done in 4 seconds. 6, the lower the back pressure, the better to avoid wear and tear. Is generally not more than 100 bar. Usually do not need to use. 7, residence time, do not use the long residence time, in order to prevent the molecular weight decreased. As far as possible avoid temperature above 300 ℃. If the downtime is less than 15 minutes. Just make air-launched processing; If more than 15 minutes, then use PE clean, viscosity and the barrel temperature drop to PE, until it is. 8, note if the mold temperature control is not good, or improper material temperature control, easy to produce 'white mist and opaque. Die temperature low and uniform, cooling speed, transparent crystal is less products.