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The standard metering screw has three zones: the feed zone, where the plastic first enters the screw and is conveyed along a constant root diameter; the transition zone, where the plastic is conveyed, compressed and melted along a root diameter that increases with a constant taper; and the meter zone, where the melting of the plastic is completed and the melt is conveyed forward along a constant root diameter reaching a temperature and viscosity to form parts.

The screw profile is described as the length, in diameters or flights, of each of the three sections of the screw. A 10-5-5 profile indicates 10 diameters in feed, 5 diameters in transition and 5 diameters in meter. General purpose screws typically use a 10-5-5 profile.

The length of each section has an impact on how a resin reaches a melt condition, as follows:

  • A longer feed section creates a greater potential throughput.
  • A longer transition means less shear heat and more time to compress and melt the resin, and the converse is also true.
  • A longer meter section develops more pumping pressure vital to extrusion.
  • A shorter meter means less time to assure an isothermal melt quality.

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Industry Applications - Resins

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