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.