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I seek cook cok ke eh el sl Se, , The screw has three zones with a ring-plunger assembly. 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, Metering 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., , L/D RATIO, , ¥ The L/D ratio is the ratio of the flighted length (Effective Length) of the, screw to its outside diameter., , Y Most injection screws use a 20:1 L/D ratio. But it may range from 18:1 to, 24:1, , Y Inthe case of Thermoset it may range from 12:1 to 16:1., High L/D Ratio results the following ...., , ¥ More shear heat can be uniformly generated in the plastic without, degradation;, ¥ Greater the opportunity for mixing, resulting in a better homogeneity, of the melt., Y Greater the residence time of the plastic in the barrel possibly, permitting faster cycles of larger shots., COMPRESSION RATIO (CR), ¥ The ratio of the first flight depth of feed zone to the last flight depth of, meter zone ,, v Or,, , First Channel Volume of feed zone to last channel volume of metering, zone,, , Y Typically ranges from 1.5:1 to 4.5:1 for most thermoplastic materials., , Y Most injection screws classified as general purpose have a compression, ratio of 2.5:1 to 3.0:1., , Y Thermo set screws have a I:1 ratio.