Question

During injection modeling process, the screw plays a critical role for melting and mixing of material. Please describe the three sections of a typical screw and their functions 2. (10 points)

Answer 1

The main components of an injection moulding machine include: the injection unit, the mould and the clamp unit.

Injection unit: in this unit the polymer is gradually melted by simultaneous
application of external heating from the barrel and pressure.

Mould: the mould comprises a cavity and a cooling system. Here, the
molten polymer is injected under pressure into the cavity and solidifies by
controlled cooling, acquiring its final form.

Clamp unit: this unit is essential to maintain the pressure inside the mould
and keep the mould closed during the cycle of injection.

Injection Molding Machine Heater Mold Cavity Plastic Granules Mold Hopper Reciprocating Screw Bare!NoziClamping Injection Moveable Platen Nozzle

The screw plays an important role in the plastic injection moulding process as it is used both to plasticise the polymer and to inject it into the mould. The major functions of the screw are achieved at different sections along its length, which are: feed zone, compression and metering zone .

The feed zone brings the feedstock into the injection machine and moves the material along the screw. The polymer is then conveyed forward and compressed before reaching the compression zone, where it is gradually melted by simultaneous application of external heating from the barrel heaters and also from the internal viscous shear (75% of the supplied heat is in the form of viscous shearing by the motion of the screw). Finally, in the metering zone, which is confined to the last few turns on the screw, the uniformity of the melt is increased before injection.

Hopper Barrel Motor Screw Checking ring Heater bands Screw metering zone Screw compression zone Screw feed zone