The gate in the injection mold, also known as the feed gate, is a short and short flow path connecting the diverter and the cavity (except for the direct gate). This is a key part of the gate control system. Its main functions are:   ① After the cavity is full, the melt condenses at the gate to prevent it from flowing back. ② It is easy to cut off the condensate of the pouring system at the gate. The cross-sectional area of ​​the gate is about 0.03 to 0.09 of the cross-sectional area of ​​the runner. The length of the gate is about 0.5mm to 2mm. The specific size of the gate is usually determined by experience. Take the lower limit value and then gradually correct it during the test.   When the plastic melt passes through the gate, the shear rate increases and the internal friction of the melt intensifies, thereby increasing the temperature of the material flow, reducing the viscosity, improving the flow performance and facilitating filling. However, if the gate size is too small, the pressure loss will increase, the condensation water will accelerate, the shrinkage will be difficult, and even the spraying phenomenon will form, affecting the quality of the plastic parts.   There are several types of gates in injection molds:   (1) Straight gate   The straight gate is also called the center gate. This gate has low resistance and fast feeding speed. It is usually used in single-cavity molds to form large and deep plastic parts. It is suitable for various plastics, especially plastics with high viscosity and poor fluidity, such as PC and PSF. When forming shallow and flat plastic parts with straight gates, bending and warping will occur. At the same time, the inconvenience of removing the gate will have obvious gate marks. Sometimes due to the concentration of heat at the gate, the cavity sealing w