The basics of injection mould design Flow channels and gates

Fri May 05 14:29:18 CST 2023

The plastic melt enters the mould cavity from the nozzle of the injection moulding machine via the main flow channel, runners and gates. The mouth of the mould cavity is called the gate. To prevent cured cold material from entering the cavity at the end of the nozzle, a cold well should be designed at the end of the runner.

First: Runner

The runner is the important passage from the main flow path to the gate and is the flow path for the molten plastic ejected from the injection moulding machine nozzle. The runners should be designed to have low resistance and to prevent cooling. Usually the runners are designed in a trapezoidal or circular shape.

Second: Gating

The design of the gate system, such as position, number, geometry and size is very important for productivity and dimensional accuracy. The role of the gate is summarised as follows:

1. to control the volume and direction of the plastic melt flowing into the mould cavityplastic moulds

2. to seal the melt in the mould cavity before curing and to prevent the melt from flowing back into the runner

3. generated by heat due to viscous dissipation

4. Easy to cut off the runner, simplifying post-processing of the product

Third: Gating balance

For multi-cavity moulds, where each cavity is evenly filled with plastic melt, it is important to achieve gate balance. As the plastic melt flows from the population to the end of the cavity, the polymer pressure drops accordingly. Therefore, gate balancing should optimise the length, width and depth of the gates.

A proper gate balancing and runner balancing design will avoid moulding defects such as flow marks, shrinkage, underfilling, dimensional fluctuations and weight variations during the actual moulding process of a multi-cavity mould.


The basic factors to be considered in gate positioning are: part design, flow and product end-use requirements.

The following points should be borne in mind:

1. Large parts requiring multiple gates should have gates positioned tightly enough to reduce pressure loss. This will minimise cooling at the point where the leading edges of the resin flow meet, thus providing better fusion line strength. A suitable gate size should be selected to allow for a reasonable pressure and rate of resin filling.

2. The length of the gate transition section should be kept as short as possible.

3. an impingement gate will help to ensure that the incoming fluid is directed against the cavity wall or core, thus avoiding swirling.

4. To avoid air entrapment, from the resin flow at the gate, air should be directed to the air vent.

5. The gate should be positioned so that the resin flows from thick-walled parts to thin-walled parts; so that the fusion line is minimised; and so that it is away from impact and stress zones.

6. To minimise swirls, radial spots and gate whitening, the gate should be at a suitable angle to the runner.

7. Pouring directly onto decorative surfaces can cause surface defects. If you need mould design information and software installation packages you can