Zhejiang Ceeto Mold Co.,Ltd. have skilled plastic injection molds designers, let us show you how to design the gate or runners.
The gate, also known as the feed gate, is a short short runner connecting the diverter and the cavity (except for the direct gate), which is a key part of the pouring system. Its main functions are:
After the cavity is filled, the melt first condenses at the gate to prevent its backflow.
② Easy to remove the condensate of the pouring system at the gate. The cross-sectional area of the gate is about 0.03 ~ 0.09 of the cross-sectional area of the diverter. Gate length is about 0.5mm ~ 2mm, the specific size of the gate is generally determined according to experience, take its lower limit value, and then gradually correct when testing the mold.
When the plastic melt passes through the gate, the shear rate increases, and the internal friction of the melt intensifies, which increases the temperature of the material flow, reduces the viscosity, improves the flow performance, and is conducive to filling. However, the size of the gate is too small, which will increase the pressure loss, accelerate the solidification, make the feeding difficult, and even form the spray phenomenon, which affects the quality of the plastic parts.
There are several forms of gate:
(1) Straight gate
The direct gate is also called the center gate, which has small flow resistance and fast feeding speed, and is often used to form large and deep plastic parts in single-cavity molds. It is suitable for all kinds of plastics, especially those with high viscosity and poor fluidity, such as PC, PSF, etc.
With the straight gate forming shallow and flat plastic parts will produce bending and warping phenomenon, while removing the gate inconvenience, there are obvious gate traces, sometimes because of the gate location heat concentration, cavity sealing late, internal stress and become the source of cracks, so the design, the gate should be as small as possible. When forming thin-walled plastic parts, the diameter of the gate root is at most 2 times the wall thickness of the plastic parts.
(2) Side gate
The side gate is also called the edge gate, its section is rectangular, generally open on the parting surface, feed from the side of the plastic part, the gate position can be selected reasonably according to the need, especially suitable for a mold with multiple cavities. As shown in Figure 10-12, generally B=1.5 mm to 5 mm, h=0.5 mm to 2 mm(or 1/3 to 2/3 of the wall thickness of the plastic part), and L=0.7 mm to 2 mm.
(3) Point the gate
A point gate, also called a pin point gate, is a small gate, as shown in Figure 10-14. Plastic melt through it has a high shear rate. It is widely used in various shell plastic parts. When opening the mold, the gate can be pulled off by itself.
The joint between the gate and the plastic part can be designed to have a small boss in order to prevent damage to the plastic part when the point gate is pulled off
The point gate has a small cross-sectional area, fast condensation, is not conducive to feeding, and is not suitable for plastic parts with thick walls.
(4) latent gate
Also known as shear gate, it is evolved from the point gate, the point gate is used for three plate mold, and the latent gate is used for two plate mold, thus simplifying the mold structure. The latent gate is arranged in the hidden part of the inside or outside of the plastic part, which does not affect the beautiful appearance of the plastic part. The gate is cut off when the plastic part is pushed out, but a strong thrust is required, and it is not suitable for strong plastics.
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