Tips For Selecting The Location Of Injection Mold Gates

1. Gate location requirements

(1) Appearance requirements (gate marks, weld lines);

(2) Product function requirements;

(3) mold processing requirements;

(4) warpage deformation of the product;

(5) The gate capacity is not easy to remove.

2. Impact on production and function

(1) FlowLength determines the injection pressure, the clamping force, and the shortened full flow length of the product to reduce the injection pressure and clamping force.

(2) The position of the gate will affect the holding pressure, the pressure holding pressure, whether the holding pressure is balanced, and keep the gate away from the future force position of the product (such as the bearing) to avoid residual stress. The gate position must consider the exhaust. To avoid accumulation of wind, do not place the gate in a weaker place or in the embedding to avoid misalignment (CoreShaft).

3. Tips for choosing a gate location

(1) Place the gate at the thickest part of the product, and the pouring from the thickest part can provide better filling and pressure holding effect. If the holding pressure is insufficient, the thinner area will solidify faster than the thicker area, avoiding the gate being placed at a sudden change in thickness 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 the same length of flow, the length of the flow will affect the required injection pressure, and the central pouring will make the pressure in all directions uniform. Can avoid uneven volume shrinkage.

(3) Gate: The gate is a short groove with a small cross-sectional area for connecting the flow channel and the cavity. The cross-sectional area is small, so as to obtain the following effects:

1) soon after the mold hole is injected, the gate is cold-knotted;

2) The water removal port is simple;

3) Only a few traces are left after the water removal is completed;

4) making the filling of multiple cavity points easier to control;

5) Reduce the excessive amount of filler.

There are no hard and fast rules for designing gates. Most of them are based on experience, but there are two basic elements that need to 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 shall be narrow so as to be easy to cold and prevent excessive plastic from flowing backwards. Therefore, the gate is in the center of the flow channel, and its cross section should be as circular as possible. However, the gate switch is usually made of a module. The switch to decide.

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

1) rubber flow characteristics;

2) the thickness of the module;

3) the amount of rubber injected into the cavity;

4) melting temperature;

5) Tool temperature.

When determining the location of the gate, the following principles should be followed:

(1) The rubber injected into each part of the cavity should be as even as possible.

(2) The rubber compound injected into the mold shall maintain a uniform and stable flow front at all stages of the injection process.

(3) It should be considered that there may be weld marks, bubbles, pockets, imaginary position, insufficient shot glue and glue spray.

(4) It should be as easy as possible to make the water removal operation easy, it is best to operate automatically.

(5) The position of the gate should be compatible with all aspects.

4. Balance of the gate

If a balanced runner system is not available, the following gate balancing method can be used to achieve the goal of uniform injection molding. This method is suitable for molds with a large number of cavities.

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 another case, when the cavity has different projected areas, the gate needs to be balanced. In this case, to determine the size of the gate, first determine the size of one of the gates and find the corresponding one. Comparing the ratio of the cavity volume, and applying this ratio to the comparison of the gate and the corresponding cavity, the size of each gate can be successively obtained. After the actual test, the gate can be balanced. operating.

5. The position of the gate in the runner

When the plastic flows into the flow channel, the plastic first heats down (cools) and solidifies near the die face. When the plastic flows forward, it only flows through the solidified plastic layer. And because the plastic is a low heat transfer material, the solid plastic is formed. The green layer and the retaining layer are still flowable. Therefore, in the ideal case, the gate should be placed in the cross-flow layer position to make the best plastic flow effect. This is most common in circular and hexagonal cross-flow channels. However, the trapezoidal cross flow can not achieve this effect, because the gate can not be placed in the middle of the flow channel.

 

6. DirectGate or SprueGate

The sprue supplies plastic directly to the finished product. The sprue is attached to the finished product. The molds on the two plates are usually one out, but in the design of the three-plate mold or the hot runner mold, one can More than a beer.

Disadvantages: The formation of a stencil on the surface of the finished product will affect the appearance of the finished product. The size of the stencil is the fine diameter hole of the sputum.

7. The draft angle of the nozzle, the length of the nozzle

Therefore, the large water-jet printing can be reduced, as long as the delay of the above-mentioned nozzle is reduced. However, the diameter of the nozzle is affected by the diameter of the nozzle, and the nozzle is easy to be out of the mold, and the draft angle cannot be less than 3 degrees. Only the length of the nozzle can be shortened, and the furnace can be extended.

Gate selection: The gate is the connecting part of the flow channel and the cavity. It is also the last part of the injection molding system. Its basic functions are:

(1) The molten plastic from the flow path enters the filled cavity at the fastest speed.

(2) After the cavity is filled, the gate can be quickly cooled and closed to prevent the plastic cavity from flowing back without cooling.

8. Summary

The design of the gate is related to the size and shape of the plastic part, the mold structure, the injection process conditions and the performance of the plastic part. However, according to the above two basic functions, the gate section is small and the length is short, because only this can satisfy the increase. Large flow rate, rapid cooling and sealing, easy to separate plastic parts and minimum gate residue.

The main points of the gate design can be summarized as follows:

(1) The gate is opened in a thick section of the plastic part, so that the molten material flows into the thin section from the thick material section to ensure complete filling;

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

(3) The choice of gate location should be beneficial to exclude air in the cavity;

(4) The gate should not be allowed to flush the melt directly into the cavity, otherwise a swirling flow will occur, leaving a spiral mark on the plastic part, especially the narrow gate is more prone to such defects;

(5) The choice of gate location should prevent the formation of stitching lines on the plastic surface. Especially in the ring or cylindrical plastic parts, the cold material should be added at the melt casting of the surface of the gate. well;

(6) The gate position of the injection mold with the elongated core should be far from the forming core, and the forming core should not be deformed by the flow;

(7) When forming large or flat plastic parts, a double gate can be used to prevent warpage, deformation and lack of material;

(8) The gate should be opened as far as possible without affecting the appearance of the plastic part, 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 flow channels to consider the balance of the gates, and try to make the molten materials uniformly charge at the same time.

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