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.
Edge gate: generally make in parting surface of mold, feeding from the edge of the plastic part, the gate cross-section is generally rectangular, as shown in picture 1. The depth of the side gate determines the condensing elbow of the gate, the gate thickness depth is generally 0.5-0.75 times then the wall thickness, and some have the same thickness as the wall thickness, which is generally determined according to the injection volume of the plastic part.
The side gate is the most widely used gate, suitable for various shapes of products, but not suitable for thin and long cylindrical products.
Advantages of side gate:
1. The gate is easy to separate from the part, it is generally in the non-critical surface of part, because the gate thickness is thinner than the wall thickness of the product, so it is more convenient to remove, when the part take out from the mold nand not cooled enought, it can be removed by hand or pliers;
2. It can prevent the plastic from flowing backward, the size and thickness of the side gate are relatively small, after the pressure is maintained during injection molding, the gate position is faster to solidify, so the plastic in the thicker glue position in the product is not easy to flow back through the gate;
3. Frictional heat is generated at the gate, which can raise the temperature of the plastic again and promote filling;
4. The tab gate (as shown in picture 2) can effectively prevent product flow marks;
5. Fan gate (as shown in picture 3) can be filled evenly to prevent product deformation, the plastic melt flows smoothly into the cavity without flow marks and weld marks, and the molding quality is good;
Disadvantages of side gate:
1. Pressure loss too much, the plastic pass from the main runner, the runner, and the sub- runner before reaching to the gate area, the injection pressure loss too much, due to the side gate is normally make in side of part;
2. Plastic with insufficient fluidity is easy to cause insufficient filling or shutting down;
3. The gate needs to be removed manually, which cannot realize fully automated production;
4. There will be a mark on the edge of the part after moving the gate, which is not suitable for products with high appearance requirements.