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Injection Mold Gate Location Selection Techniques
Jun 30, 2018

The core tips: The design of the gate is related to the size of the plastic parts, the shape of the mold structure, the injection process conditions and the performance of the plastic parts. But according to the above two basic functions, the gate section is small and the length is short because only In order to meet the requirements of increasing the speed of flow material, rapid cooling and closing, and facilitating the separation of plastic parts and the minimum of gate marks.

 First, the gate location requirements

1. Appearance requirements (gate trace, weld line)

2. Product function requirements

3 mold processing requirements

4. Warpage of the product

5. It is not easy to remove the sprue


Second, the impact on production and function

1. Flow Length determines the injection pressure, clamping force, and shortening of the full length of the product filling to reduce the injection pressure and clamping force.

2. The position of the gate will affect the holding pressure, the size of the holding pressure, and whether the holding pressure is balanced. Keep the gate away from the future force position of the product (such as the bearing) to avoid residual stress. The position of the gate must be considered for exhausting. Avoid accumulation of wind Do not place the sprue on the weaker part of the product or in the place where it is embedded to avoid the Core Shaft.


Third, choose the gate location skills


1. Place the gate at the thickest part of the product. Pouring from the thickest part provides better filling and holding pressure. If the pressure is insufficient, the thinner area will solidify faster than the thicker area, avoid placing the gate at sudden thickness changes to avoid hysteresis or short shots.


2. If possible, pouring from the center of the product, placing the gate in the center of the product can provide equal length of stream, the length of the stream will affect the required injection pressure, the central pouring will make the pressure maintaining pressure in all directions uniform, Non-uniform volume shrinkage can be avoided.


3. Gate: The gate is a short slot with a small cross-sectional area to connect the flow channel with the mold cavity. The area of the cross-sectional area is therefore small. The purpose is to obtain the following effects:

1) soon after the injection molding, the gate is cold

2) Easy dewatering

3) leaving only a trace of the water outlet

4) It is easier to control the filling of multiple cavity

5) Reduce excess filler


The method of designing gates does not impose any hard rules. Most of them are based on experience. However, there are two basic elements that must be compromised:

1. The larger the cross-sectional area of the gate, the better, and the shorter the length of the channel, the better, to reduce the pressure loss when the plastic passes.

2. The gate must be narrow so that it can be easily cold-junction and prevent excessive plastic backflow. Therefore, the gate is in the center of the runner, and its cross-section should be as round as possible. However, the gate switch is usually made of a module. Switch to decide.

3. Gate size: The size of the gate can be determined by the cross-sectional area and gate length. The following factors can determine the optimal gate size:

1) Rubber flow characteristics

2) The thickness of the module

3) The amount of glue injected into the cavity

4) Melting temperature

5) mold temperature


When determining the location of the gate, adhere to the following principles:

1. The glue injected into each part of the cavity should be averaged as much as possible.

2. Injecting the rubber material of the mold, in the various stages of the filling process, should maintain a uniform and stable flow front.

3. Consideration should be given to possible occurrences of weld marks, air bubbles, cavities, voids, insufficient glue and glue.

4. The operation of the water removal port should be as easy as possible, and it is best to operate automatically.

5. The position of the gate should cooperate with all aspects.


Fourth, the balance of the gate

If a balanced runner system cannot be obtained, the following gate balance method may be used to achieve the goal of uniform injection molding. This method is applicable to the mold with a large number of cavity points.

There are two ways to balance the gate: changing the length of the gate channel and changing the cross-sectional area of the gate. In the other case, that is, when the cavity has a different projected area, the gate needs to balance. At this time, to determine the size of the gate, we must first determine the size of one of the gates, find it and its corresponding The ratio of the cavity volume is compared with the ratio, and this ratio is applied to the comparison of the gate and the corresponding mold cavity, then the size of each gate can be calculated successively. After the actual injection, the balance of the gate can be completed. operating.


Fifth, the location of the gate in the runner

When the plastic flows into the flow path, the plastic approaches the mold surface first to cool (cool) and solidify. The plastic flows through the solidified plastic layer only when it flows forward again. Because the plastic is a low heat transfer material, solid plastic forms. The emerald layer and the retention layer are still flowable. Therefore, in the ideal case, the gate should be placed in the cross-flow layer position, so that the best plastic flow effect. This situation is most common in round and hexagonal cross-flow channel However, the trapezoidal cross flow can not achieve this effect, because the gate can not be set in the middle of the flow channel.


6. Direct Gate or Sprue Gate

The sprue supplies the plastic directly to the finished product. The runner adheres to the finished product. In the mold of the two plates, the large nozzle is usually one, but in the design of the three plate mold or the hot runner mold, one can More beer.

Disadvantages: The formation of water jets on the surface of the finished product will affect the appearance of the finished product. The size of the water jet prints lies in the fine diameter holes in the nozzle.


Seven, Tsui Tsui's release angle, the length of the nozzle

Therefore, the large water orifice can be reduced in size, as long as the above-mentioned nozzle is changed to a smaller size. However, the diameter of the nozzle is affected by the diameter of the nozzle, and the nozzle must be easy to eject. The ejection angle cannot be less than 3 degrees. Only the nozzle length can be shortened.

Gate selection: The gate is the connecting part of the runner and the cavity. It is also the last part of the injection mold feeding system. Its basic role is:

1) Bring molten plastic from the runner into the full cavity at the fastest speed.

2) After the cavity is filled, the gate can be quickly cooled and sealed to prevent the cavity from returning to the uncooled plastic.


Eight, summary


The design of the gate is related to the size of the plastic parts, the shape of the mold structure, the injection process conditions and the properties of the plastic parts. However, according to the above two basic functions, the gate section is small and the length is short, because only in this way can the increase be satisfied Large flow material speed, fast cooling and closing, easy to separate plastic parts, and minimum requirements for gate marks.


Gate design points can be summarized as follows:

1. The gate is set at the thicker part of the plastic part, so that the molten material flows from the thick material section into the thin section to ensure that the mold is completely filled;

2. The choice of gate location should minimize the plastic filling process to reduce pressure loss;

3. The choice of gate location should be conducive to the exclusion of air in the cavity;

4. The gate should not make the molten material rush straight into the cavity, otherwise it will produce turbulence, leaving traces on the plastic parts, especially the narrow gate is more prone to this defect;

5. The position of the gate should be chosen so as to prevent seam lines from being produced on the surface of the plastic. In particular, in a circular or cylindrical plastic part, a cold material well should be added to the molten material at the gate surface. ;

6. The position of the gate of the injection mold with a slender core should be far away from the forming core, and the forming core should not be deformed by the material flow;

7. When forming large or flat plastic parts, multiple gates may be used to prevent warping, deformation, and lack of material;

8. Gates should be set as far as possible without affecting the appearance of plastic parts, such as the bottom of the edge;

9. The size of the gate depends on the size, shape and plastic properties of the plastic part;

10. When designing multiple cavity injection molds, consider the balance of the runners in consideration of the balance of the runners, and try to achieve even charging of the molten material at the same time.