Injection Molding Machine Nozzle and Cylinder

In this post, we will talk about the working principle and characteristics of the injection molding machine nozzle and cylinder.

1. Injection Nozzle

(1) Straight nozzle

Straight nozzles are the most commonly used nozzles.

Its characteristics are:

  • The spherical surface of the nozzle is directly in contact with the spherical surface of mold gate. And the arc radius and flow path of the nozzle are smaller than that of the mold.
  • When injecting, the high-pressure melt is directly filled into the mold cavity through the runner system of the mold, with fast speed, small pressure loss.
  • The manufacturing and installationis very convenient.

(2) Locking nozzle

It mainly solves the salivation problem of straight nozzles, and is suitable for the processing of low-viscosity polymers (such as PA).


During plasticizing, the nozzle can be closed to prevent melt salivation out. And when it is injected, it can be opened under the action of injection pressure, so that the melt can be injected into the mold cavity.

injection nozzle-1
injection nozzle-2

2. Injection cylinder

Working principle:

The hydraulic oil is fed into the injection cylinder, and drive the screw forward or backward.

The injection cylinder push the screw for injection and hydraulic motor drive the screw to rotate for backward realizing plasticization.

3. Carriage cylinder

When hydraulic oil is fed into the carriage cylinder, the forward or backward action of the injection seat is realized.

And ensure that the injection nozzle is in close contact with the arc surface of the mold gate to generate injection seat pressure that can seal the melt against the injection pressure.

4. Accuracy requirements for injection unit

(1) After the nozzle is assembled, it is necessary to ensure that the nozzle is tightly engaged with mold gate.

(2) It is required to make the centerline of the injection unit concentric with the centerline of the plastic product.

In order to ensure the matching accuracy between the injection screw and the inner hole of the barrel, the parallelism between the two injection cylinder holes and the positioning center hole of the barrel and the symmetry of the center line must be guaranteed.

(3) For horizontal injection molding machines, the parallelism of the two guide holes of the carriage cylinder and the symmetry to the center must also be guaranteed.

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