7 Most Common Injection Gates Used In Mold Design

Injection gates, also known as inlets, are a passageway from the manifold to the mold cavity and are the smallest and shortest part of the pouring system. In plastic product molding, it refers to the entrance and passageway where the plastic material enters the mold during pouring. Often refers to the casting system in general. The role is to use the tightening of the flow surface so that the feed material to achieve the effect of acceleration, A high shear rate can make the feed material good fluidity, viscous heating effect also has to raise the material temperature to reduce the role of viscosity.

After molding, the gate is the first to be cured and sealed, which has the function of preventing reflux of the feed material and avoiding the cavity pressure from dropping too fast, resulting in shrinkage and depression of the molded product. After molding, it is easy to cut out to separate the runner system and plastic parts. The following are the common injection gates methods in mold design

Injection Gates: Straight Gate

Main runner gates, which are non-restrictive gates

Advantages of Straight Gates: The plastic melt enters the cavity directly from the big end of the main flow channel, so it is characterized by low flow resistance, short process, and long replenishment time. Such a gate has a good melt flow state, the melt flows from the center part of the cavity bottom surface to the parting surface, which is conducive to the exhaust; this injection gates form makes the injection molded products and the casting system in the parting surface of the projection area is the smallest, the mold structure is compact, and the injection molding machine is subjected to uniform force.

Disadvantages Straight Gates: There is a large residual stress at the feed, which is easy to cause warping and deformation of the injection molded products, and at the same time, the injection gates are large, it is more difficult to remove the traces of the injection gates and the traces are large, which affects the aesthetics, so this type of gate is mostly used for injection molding of large and medium-sized long flow, deep cavity, cylinder or shell-shaped injection molded products, which is especially suitable for high viscosity plastics, such as polycarbonate, polysulfone and so on. In addition, this form of gate is only suitable for single cavity molds.

When designing these types of injection gates, to reduce the gate area in contact with the injection molded products and to prevent defects such as shrinkage and deformation from occurring there, on the one hand, the main flow channel cone angle with a small taper (2-4°) should be used as much as possible, and on the other hand, the thickness of the fixed mold plate and the fixed mold base should be reduced as much as possible.

Injection Gates: Side Gate

The side gate is generally opened on the parting surface, the plastic melt is filled with mold cavity from the inside or outside, and its cross-section shape is mostly rectangular (flat groove), Changing the width and thickness of the injection gates can adjust the shear rate of the melt and the freezing time of the gate. This kind of gate can choose its position according to the shape characteristics of the injection molded products, and it is easy to process and trim, so it is more widely used.

Advantages of Side Gate: The small cross-section of the gate can reduce the consumption of melt in the pouring system, and it is easy to remove the gate without obvious traces. It is suitable for various shapes of injection molded products, but it is not suitable for slender barrel-shaped injection molded products.

Disadvantages of Side Gate: the injection molded products and the gate can not be separated by themselves, there are fusion marks, injection pressure loss is larger, and the exhaust of deep cavity injection molded products is unfavorable.

Injection Gates: Tab Gate

It is processed directly on the parting surface and can be regarded as a variant of a rectangular gate. Part of the gate is overlapped on the product, so it will not leave traces of the gate on the side of the product, and it can effectively prevent spraying for flat-shaped products. However, it is easy to produce shrink marks at the sprue, and it is difficult to remove the sprue, and the sprue marks are more obvious.

Injection Gates: Submarine Gate

Advantages of Submarine Gate: Submarine gates are more flexible in their position and can feed the melt on the inner and outer surfaces of the plastic product. The runner is opened on the parting surface, the gate is submerged under the parting surface, and the melt enters the cavity obliquely. As the plastic products and runners are respectively set up to push out the mechanism, the gate is automatically cut off when the mold is opened, and the runner gel is automatically dislodged. At the same time, its mold structure is simpler than the three-plate mold structure, greatly improving production efficiency and reducing cost.

Disadvantage of Submarine Gate: It is not suitable for plastics which are too tough (such as PA type) or too brittle (such as PS type), the former is not easy to cut off and the latter is easy to break off and block the gate easily.

Injection Gates: Point Gate

Point gating is especially suitable for drum, shell and box shaped plastic products. For larger flat plastic products, more than one sprue can be set to reduce warping deformation; for thin-walled plastic products, the shear rate near the gate is too high, the residual stress is large, and it is easy to crack, so the wall thickness at the gate can be increased locally.

Advantages of Point Gate: small restrictions on the location of the point gate, a small trace of the gate, and the gate can be automatically pulled off when the mold is opened, which is conducive to automated operation.

Disadvantages of Point Gate: injection pressure is larger, in most cases must use a three-plate mold structure, its mold is relatively more complex, molding cycle is longer.

Injection Gates: Horn Submarine Gate

A Horn Submarine gate is a kind of arc-shaped latent gate structure form, generally used in two-plate molds, adopting the direct feeding method on the parting surface, made of two pieces of inserts put together, and its manifold and gate are designed on the inserts.

Advantages of Horn Submarine Gate: can be in the bottom surface of the product into the glue, with the characteristics of the point gate, the gate trace is small, the ejector can be automatically pulled off, easy to realize automation. If the head of the ejector pin is made into a cone, and the push-out mechanism is set in the runner, it is favorable for ejection.

Disadvantages of Horn Submarine Gate:: more complicated shape, need to use electrode processing gate.

Injection Gates: Fan-shaped Gate

The fan-shaped gate is generally opened on the parting surface, feeding from the outside of the cavity, the gate is gradually widened along the feeding direction, and the thickness is gradually thinned. The wave front of the plastic melt entering the cavity from the gate is relatively straight, which can reduce warping and deformation, and is suitable for molding plate-like plastic products with a larger width.