5.considering if it's easy to remove the gate.
1. Flow length determines the injection pressure, clamping force, and if there is short shot issues. Shorten the flow length can reduce the injection pressure and clamping force.
2. The gate location will affect the holding pressure, the balance of the holding pressure. To avoid residual stress. it's better to keep the gate away from the future force position of the product (such as the bearing). The gate position must consider the vent to so as to avoid accumulation of winds. Do not place the gates in weak or embedded areas to avoid misalignment (CoreShaft)
Techniques of choosing the gate location.
1. Place the gate at the thickest part of the product so as to provide better filling and holding effect. If the 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, set the gate atthe 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 gate centered will make the pressure uniform in all directions so as to prevent the 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 injected, the gate is cold and frozen.
2) gate remove is easy
3) only tiny gate vestige left after the removal of gate.
4) Make the filling of multiple cavity easier to control
5) Reduce the excessive amount of filling
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. To reduce the pressure loss during resin flowing through, the larger the cross-sectional area of the gate, the better; and the shorter the length of the channel, the bette.
2. To prevent excessive plastic from flowing backwards, the gate must be narrow so that it can be easily cold and frozen . Therefore, the gate should be in the center of the flow channel, and its cross-section should be as circular as possible.
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 determine the optimal size of the gate:
1) characteristics of resin flowing
2) Thickness of the part
3) The Resin volum injected into the cavity
4) Melting temperature
5) mold temperature
When setting the gate location, the following principles should be followed:
1. The resin injected into each part of the cavity should be as even as possible.
2.Maintain a uniform and stable flow front at all stages of the injection process.
3. Consideration should be given to possible weld marks, bubbles, short shot..etc
4. It should be as easy as possible to make the gate removal operation easy, it is best to operate automatically.
5. The location of the gate should be compatible with all aspects.
The 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.
the location of the gate in the runner
When the resin flows into the runner, the plastic first heats down (cools) and solidifies near the mold plate. When the resin 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 conditons, the gate should be placed in the cross-flow layer position to make the best resin 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.
Direct Gate or Sprue Gate
The runner directly supplies the plastic to the finished product. The runner is adhered to the finished product. The mold in the two plates is usually one cavity, but in the design of the three-plate mold or the hot runner mold, it can be multi-cavities.
Disadvantages: The gate mark on the surface of the finished product will affect the appearance. The size of the gate mark lies in the fine diameter hole of the sprue bushing.
The key design points of gate can be summarized as follows:
1. The gate is set in a thick section of the plastic part, so that the molten material flows from the thick material section into the thin 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 eliminate air in the cavity;
4. The gate should not be allowed to flush the melt straight into the cavity, otherwise it will lead the flow line easily.
5. The choice of gate location should prevent the formation of weld lines on the plastic surface, especially in the ring or cylindrical plastic parts, the cold well should be added at the melting material pouring joint of the gate face
6. The gate position of the injection mold with the elongated core should be far from the core, so that the core is not deformed by the flow;
7. When forming large or flat plastic parts, double gates can be used to prevent warpage, deformation and short shot;
8. The gate should be set as far as possible to the PLS which willl not 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;
