In the injection process, the main purpose of controlling the temperature of the mould is to heat the mould to the working temperature, and the second is to keep the temperature of the mould constant at the working temperature. If the above two points are successful, the cycle time can be optimized to ensure the stable high quality of injection parts.
Mold temperature will affect surface quality, fluidity, shrinkage, injection cycle and deformation. Excessive or insufficient die temperature will have different effects on different materials. For thermoplastics, higher die temperature usually improves surface quality and fluidity, but prolongs cooling time and injection cycle. A lower die temperature will reduce the shrinkage in the die, but it will increase the shrinkage of the injection parts after demoulding.
For thermosetting plastics, higher die temperature usually reduces cycle time, which is determined by the cooling time of parts. In addition, in plastic processing, higher die temperature will also reduce plasticizing time and cycle times.
Thermal balance control of injection moulds and heat conduction of injection moulds is the key to the production of injection moulds. Inside the die, heat from plastics (such as thermoplastics) is transferred to the material and the steel of the die by thermal radiation, and to the heat conducting fluid by convection.
In addition, heat is transferred to the atmosphere and the die base through thermal radiation. The heat absorbed by the heated fluid is taken away by the thermostat. The thermal balance of the die can be described as P=Pm-Ps. In the model, P is the heat carried away by the mould temperature machine; Pm is the heat introduced by the plastic; Ps is the heat emitted from the mould to the atmosphere.
Preparatory Conditions Temperature Control System for Effective Temperature Control of Die is composed of three parts: Die, Temperature Machine and Heat Conducting Fluid. In order to ensure that heat can be added to or removed from the die, the system must meet the following conditions: first, in the die, the surface area of the cooling passage must be large enough, and the diameter of the passage must match the capacity of the pump (pump pressure).
The temperature distribution in the cavity has a great influence on the deformation and internal pressure of the part. Reasonable setting of cooling passage can reduce the internal pressure and improve the quality of injection parts. It can also shorten cycle time and reduce product cost. Secondly, the mold temperature machine must be able to keep the temperature of the heat conducting fluid in the range of 1-3 C, which is determined according to the quality requirements of the injection parts. Thirdly, the heat conducting fluid must have good heat conductivity, and most importantly, it should be able to import or export a large amount of heat in a short time. From the thermodynamic point of view, water is obviously better than oil.
The working principle of the model temperature machine is composed of water tank, heating and cooling system, power transmission system, liquid level control system, temperature sensor, injection port and other devices. Usually, the pump in the power transmission system makes the hot fluid from the water tank with built-in heater and cooler to the mould, and then from the mould to the water tank; the temperature sensor measures the temperature of the hot fluid and transmits the data to the controller of the control part; the controller adjusts the temperature of the hot fluid, thus indirectly adjusting the temperature of the mould.
If the temperature of the mould exceeds the set value of the controller in production, the controller will open the solenoid valve and connect to the intake pipe until the temperature of the hot fluid, that is, the temperature of the mould returns to the set value.