When PET Preform Injection, should pay attention to what?

Hits:Updated:2016-07-11 15:07:53【Print】

  1, plastic processing
  Since PET macromolecules containing aliphatic group having a certain hydrophilic, the pellets at high temperatures sensitive to water, when the moisture content exceeds the limit, in the processing of PET molecular weight decreases, products colored and brittle. Difficulties of this, before processing the material must be dried, the drying temperature is 150 ℃, more than 4 hours, usually 170 ℃, 3-4 hours. Available methods of air-launched test material is completely dry.
  The proportion of recycled material is generally not more than 25% recycled material and should be thoroughly dried.
  2, injection molding machine selection
  Since the melting point of PET stable after a short time, and high melting point, and therefore the need to use more temperature control section, less heat from the friction of plastics injection systems and products (including materials outlet) can not be less than the actual weight of the machine injection the amount of 2/3. Based on these requirements, the Ramada in recent years has developed a series of small PET special plasticizing systems. Clamping force by more than 6300t / m2 selection.
  3, mold and gate design
  PET Preform general use of hot runner molding, injection molds and machine template between the best insulation panels have a thickness of about 12mm, and insulation boards must be able to withstand high pressures. Exhaust gas must be sufficient to avoid local overheating or broken, but the vent depth is generally not more than 0.03mm, or prone to flash.
  4, melt temperature
  Available air-launched law measure. 270-295 ℃ range, enhanced levels GF-PET can be set to 290-315 ℃ and the like.
  5, injection speed
  Usually faster injection, injection to prevent premature solidification. But excessive shear rate the material brittle. Plunger is usually complete within 4 seconds.
  6, back pressure
  Low as possible, so as not to wear. Generally does not exceed 100bar. Usually no need to use.
  7, retention time
  Do not use too long residence time to prevent the molecular weight decreases. Avoid temperatures above 300 ℃. If the shutdown is less than 15 minutes. Only for air emission treatment; if more than 15 minutes, then use a clean viscosity PE, and the barrel temperature was lowered to PE temperature until then boot up.
  8 Notes
  ⑴ recycled material can not be too large, otherwise easy to produce at lower feed "bridging" and affect plastics.
  ⑵ If the mold temperature control poor or improper material temperature control, easy to produce "white mist" and opaque. Low and uniform mold temperature, cooling speed, ranging from crystalline product transparency.
  
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