How to choose the correct location of the gate?

The gate is a short groove with a small cross-sectional area, which is used to connect the runner and the mold cavity. The cross-sectional area should be small in order to achieve the following effects:
-The gate will be cold soon after the mold cavity is filled
-It is easy to remove the gate
-Only a few remains are left after the gate removed
-Make it easier to control the filling of multiple mold cavities
-Avoid excessive filling

1.Set the gate at the thickest part of the product, which can provide better filling and holding pressure effects. If the holding pressure is insufficient, the thinner area will solidify faster than the thicker area. Therefore, it needs to avoid placing the gate at the place where the thickness changes suddenly and avoid hysteresis or short shots.
2.It had better to place the gate at the center of the product because it can provide equal flow length and the size of the flow length will affect the required injection pressure.Inject the plastic material from the center makes the holding pressure uniform in all directions, which can avoid uneven volume shrinkage.
3.When the plastic flows into the runner, the plastic first cools down and solidifies when it approaches the mold surface. When the plastic flows forward, it only flows through the solidified plastic layer. Due to plastic is a low heat transfer material, solid plastic can form an insulating layer and keep it flow.

Therefore, in an ideal situation, the gate should be set at the cross-runner layer to achieve the best plastic flow effect. This is most common in circular and hexagonal cross-runners. However, trapezoidal cross-runners cannot achieve this effect because the gate cannot be set in the middle of the runners.

When confirming the gate position, the following principles should be adhered to:
A.The plastic material injected into each part of the mold cavity should be as even as possible.
B.At all stages of the injection process, the plastic material injected into the mold should maintain a uniform and stable flow state.
C.It should be considered the situation such as cold welding line, bubbles, sink marks, voids, short shot and spraying.
D.The gate removed operation should be as easy as possible, preferably automatic operation.
E.The gate position should be coordinated with all parts.

There is no hard and fast rule for gate design, which is mostly based on experience. However, there are two basic elements that must be considered:
A.To reduce the pressure loss when the plastic passes through, it had better to choose the larger gate cross-sectional area and the shorter runner length.
B.The gate must be narrow to facilitate cold freezing and prevent excessive plastic back flow. In addition, the gate should be set in the center of the runner, and its cross-section should be as circular as possible. Besides, the gate open and closed is usually determined by the mold opening and closing.

The size of the gate can be determined by the cross-sectional area and the gate length. The following factors can determine the optimal gate size:
-Material flow property
-Part thickness
-Amount of material injected into the mold cavity
-Melting temperature

-Mold temperature