Gate Design Considerations:
1.Injection molding gate is a small opening between the runners and the mold cavity. their location, quantity, shape and size, etc. have a great influence on product appearance, dimensional , physical characteristics and production efficiency.
2.The gate size is dependent on product weight, material and gate types. The length, depth and width of a gate should be minimized as long as that product physicall performance and production efficiency can be guaranteed.
3.If the gate is too small, injection molding defects like uncompleted filling, sink mark and flow marks will occur, and molding shrinkage rate will increase.
4.If the gate is too big, excessive residual stress may happen around the gate, cause deformation or cracks on production, and also it will be difficult to remove the gate after molding.
Gate Types
1.Direct Gate: Melt material enters the mold cavity directly through the sprue, suitable for shell-/box-shaped molds that feature a deep single cavity. With a short runner, the advantages of direct gate is :little pressure loss and convenient venting,the disadvantage of direct gate is: the gate is difficult to remove after molding, with visible gate marks left.
2.Fan Gate: The gate gets larger to become a fan shape from the runner to the mold cavity direction. This type of gate is suitable for slender or flat and thin products, because it is able to reduce flow marks and directional stress. The angle of the fan is dependent on product shapes. The cross sectional area of the gate must be smaller than that of the runner.
3.Pin Point Gate: The type of gate that has a sectional area as small as that of a pin. It is usually used for plastic materials that boast excellent fluidity. Normally, the length of the gate is no larger than its diameter, sIt is widely used for the production of covers, housings and large-area products, The advantage is that the gate is removed from molding part automatically and with very small gate mark.The disadvantage is that the small size gate may lead to loss of pressure and cause some injection molding defects during production (flow marks, burnt marks and black spots, etc.). The shapes of pin point gate include diamond, single-point, double-point and multi-point, etc. It uses the three-plate mold, with a pore size of about 0.25 – 1.5mm.
4.Side Gate: Usually located on one side of the product. the side gate is referred to as the standard gate. The side gate is generally designed on the parting surface. The plastic melt fills the mold cavity from the inside or the outside, the cross-section is mostly rectangular , and the shear rate of the melt and the freezing time of the gate can be adjusted by changing the width and thickness of the gate.
5.Sub Gate: This type of gate is usually inclined and lurks on one side of the parting surface.this is why people call them submarine gate.The material is injected in from outer side or the inside. The pin sized gate will be cut off automatically during mold release, thus suitable for automatic production. The sub gates have several variations.
- Sub gate in cavity side
- Submarine gate in core side
- Banana gate
The banana gate is a kind of circular-shaped submarine gate structure(look like banana). Usually used for two-plate molds, the gate allows the melt material to flow in directly from the parting surface.
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