Commonly used calculation formulas for injection molding work (1)
1) Requirements for heat balance of hot runner system
The hot runner system must meet the requirements of heat balance, and its heat loss should be compensated by heating. Ideally, the hot runner system should be in an isothermal state. The requirement for the control of the hot runner system is to keep the deviation of the desired temperature to a minimum. For this, the following conditions should be met:
• Accurate design of heating element power;
• Heating elements are installed correctly in the system structure;
• Reasonably determine the heating position and temperature measurement point;
• Adequate thermal insulation measures and effects.
From the user's point of view, the conditions that should be met are:
• Good durability;
•Easy to replace;
• Good damage resistance, corrosion resistance, not easy to leak;
•The line connection is safe and reliable.
2) Type of heater
Commonly used heaters for hot runner molds are:
• Commonly used coil and strip coil heaters for nozzle heating;
•Rubber and tube heaters are commonly used for runner plate heating.
3) Temperature control of the hot runner system
•Accurate temperature control is the key factor to realize the automatic operation of the hot runner system. A common method is to use a temperature control meter to control the contactor.
• Its control principle is to control the opening and closing of the heating element by judging the temperature of the mold. When the mold temperature is lower than the set value, the contactor is closed, all the voltage is applied to the heating element, and its temperature rises rapidly; when the temperature reaches the set value, the contactor is disconnected.
• Thermocouples are installed near the flow path. The hysteresis of thermocouple temperature measurement makes the temperature control accuracy lower. The output control device of the pulse width modulation hot runner temperature control system adopts high-power bidirectional thyristor output, which has stable operation, reliable performance, and long service life of the heating element.
(5) Application examples of non-runner aggregate molds
