Relations between injection molds (1)

Contact relationship

1. The heat balance of the injection mold controls the heat conduction between the injection molding machine and the mold is the key to producing injection molded parts. Inside the mold, the heat brought by the plastic (such as thermoplastic) is transferred to the material and the steel of the mold through thermal radiation, and is transferred to the heat transfer fluid through convection. In addition, heat is transferred to the atmosphere and the mold base through thermal radiation. The heat absorbed by the heat transfer fluid is taken away by the mold temperature machine. The thermal balance of the mold can be described as: P=Pm-Ps. Where P is the heat taken away by the mold temperature machine; Pm is the heat introduced by the plastic; Ps is the heat emitted by the mold to the atmosphere.

2. Preliminary conditions for effective control of mold temperature The temperature control system consists of three parts: mold, mold temperature controller, and heat transfer fluid. In order to ensure that heat can be added to or removed from the mold, each part of the system must meet the following conditions: First, inside the mold, the surface area of ​​the cooling channel must be large enough, and the diameter of the runner must match the pump's capacity (pump pressure). The temperature distribution in the cavity has a great influence on part deformation and internal pressure. Reasonable setting of cooling channels can reduce the internal pressure, thereby improving the quality of injection molded parts. It can also shorten cycle time and reduce product costs. Secondly, the mold temperature machine must be able to keep the temperature of the heat transfer fluid within the range of 1°C to 3°C, depending on the quality requirements of the injection molded parts. The third is that the heat transfer fluid must have good thermal conductivity, and most importantly, it must be able to import or export a large amount of heat in a short time. From a thermodynamic point of view, water is clearly better than oil.

3. Working principle The mold temperature machine is composed of water tank, heating and cooling system, power transmission system, liquid level control system, temperature sensor, injection port and other components. Normally, the pump in the power transmission system makes the hot fluid reach the mold from the water tank equipped with built-in heater and cooler, and then from the mold back to the water tank; the temperature sensor measures the temperature of the hot fluid and transmits the data to the control part. Controller; The controller adjusts the temperature of the hot fluid, thereby indirectly adjusting the temperature of the mold. If the mold temperature machine is in production, the temperature of the mold exceeds the set value of the controller, the controller will open the solenoid valve to connect the water inlet pipe until the temperature of the hot fluid, that is, the temperature of the mold returns to the set value. If the mold temperature is lower than the set value, the controller will turn on the heater.