In order to get the best injection quality, the gate type must be selected carefully, the coommon gate tyeps are: direct gate, side gate, pin-point gate, sub gate,valve gate of hot runner etc. Among them, the side gate is divided into tab gate, ear protection gate, fan gate, thin gate and so on, the sub gate is divided into sub gate, banana gate, downturning gate and so on.
According to the production automation, it is divided into manual removal and automatic removal, the side gate and direct gate are need to be manually removed after production,but the sub gate and pin-point gate and valve gate of hot runner are automatic removed.
Sub gate: The sub gate is evolved from pin-point gate and has a similar characteristic as pin-point gate, the difference is that the sub gate in one side of parting surface and enters the cavity in an oblique direction. Opening the mold elbow can automatically pull off the gate, and the gate position can be set on the side, end and back of the plastic part, so that there is no gate mark on the outer surface of the plastic part (as shown in picture 1ab), the structure of the same elbow mold can be simplified to a single parting surface structure.
1. The gate can be cut off automatically, eliminating the need for subsequent processing and realizing automatic production;
2. The gate position selection is big, it can be set freely on the outside or inside of the part;
3. The gate is small, which has little effect on the appearance of the product, and some sub gates are hard to see with the eyes;
4. The mold structure can be simplified, for some products with high appearance requirements, we must make a three-plate mold to realize it if we use the pin-point gate, but it only two-plate mold is needed if changing to sub gate, which reduces the mold structure complexity greatly, it also reduces the mold thickness and save the mold cost.
1. Pressure loss too much, it ususall in the range of Ø0.8~2.0mm due to the sub gate is relatively small, a large part of the pressure will be lost when the plastic pass through the small gate;
2. The processing is more complicated, this kind of small gate generally needs to place the mold core into a vertical angle to follow the gate, and then use EDM to make process(as shown in picture 2);