1. Thermal cycle of injection molding mold Controlling the heat conduction of the plastic machine and mold is important for producing injection molded products. In the internal structure of the mold, the heat energy generated by the plastic (such as thermosetting plastic) is transmitted to the raw material and the stainless steel plate of the mold through radiant heat, and is transferred to the heat transfer fluid through the heat exchanger. In addition, the heat is transferred to the air and the mold base through radiant heat. The heat absorbed by the heat transfer fluid is taken away by the mold temperature controller. The thermodynamic cycle of the mold can be expressed as: P=Pm-Ps. In the formula, P is the heat brought by the mold temperature controller; Pm is the heat introduced by the plastic; Ps is the heat released by the mold to the air.
2. Preparation for effectively controlling mold temperature. The standard temperature automatic 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, all parts of the system must meet the following requirements: first of all, the internal structure of the mold, the area of the refrigeration channel must be large enough, and the flow channel aperture must match the capacity of the pump (the pump's work pressure). The temperature distribution in the die has a greater impact on part deformation and internal pressure. Effectively setting up refrigeration channels can reduce essential working pressure, thereby improving the quality of injection molded products. It can reduce cycle time and reduce production costs. Secondly, the mold temperature controller must be able to stabilize the temperature of the heat transfer fluid within the range of 1℃-3℃, which is actually determined according to the quality standards of injection molded products. The third is that the heat transfer fluid must have excellent thermal conductivity. The most important thing is that it must be able to import or export a large amount of heat in a short period of time. From a thermal perspective, water is clearly better than oil.
3. Principle The mold temperature controller is composed of a water storage tank, a heating and cooling system, a driving force transmission system, a liquid level control system, a temperature sensor, an inlet and other components. Generally speaking, the pump in the driving force transmission system causes the hot fluid to reach the mold from a water storage tank equipped with an embedded electric heater and cooling tower, and then returns from the mold to the water storage tank; the temperature sensor accurately measures the temperature of the hot fluid and The data is sent to a control panel that controls the part; the control panel adjusts the temperature of the hot fluid, thereby indirectly adjusting the temperature of the mold. If the mold temperature machine is in production and the temperature of the mold exceeds the preset value of the control panel, the control panel will turn on the relay to connect to the water inlet until the temperature of the hot gas liquid returns to the preset value. If the mold temperature is lower than the preset value, the control panel will turn on the electric heater.
4. The types of mold temperature controllers are distinguished according to the heat transfer fluid (water or heat transfer oil) used. Water-cooled mold temperature machines generally have a maximum inlet and outlet temperature of 95°C. The oil-operated mold temperature controller is used in places where the working temperature is ≥150℃. Generally speaking, mold temperature controllers with mouth-opening tank heating are suitable for use with mold temperature controllers or oil heaters. The maximum inlet and outlet temperatures are 90°C to 150°C. The main features of this type of mold temperature controller are that it is easy to set up and the price is economical. Based on this type of equipment, a continuous high-temperature mold temperature machine has been developed. Its allowable inlet and outlet temperature is 160°C or higher, because when the temperature is higher than 90°C, the thermal conductivity of water is higher than that at the same temperature. The oil is much better, so this type of equipment has outstanding high-temperature working capabilities. In addition, there is also a forced fluidity mold temperature controller. For safety reasons, this type of mold temperature controller is designed to work at a temperature above 150°C and uses thermal oil. In order to prevent the oil in the mold temperature heater from overheating, the equipment uses a forced fluid underwater concrete system, and the heater is composed of a certain number of laminated pipes, and the pipes are equipped with plate-fin heating Components are used for drainage.
5. Control the uneven temperature at various points in the mold, which is also related to the time point in the injection cycle. After injection, the temperature of the mold cavity rises to a maximum. At this time, the hot solution encounters the cold wall of the mold cavity. When the part is removed, the temperature drops to a minimum. The function of the mold temperature controller is to keep the temperature stable between θ2min and θ2max, in other words, to prevent the temperature difference Δθw from fluctuating during the processing or gap. The following types of control measures are suitable for controlling the temperature of the mold: Controlling the fluid temperature is the most commonly used method, and the accuracy can meet the requirements of most situations. The use of this control method shows that the temperature of the intelligent controller is not consistent with the mold temperature; the temperature of the mold fluctuates greatly, and the thermal factors that affect the mold are not directly measured and compensated. These factors include changes in injection cycle time, injection rate , melting temperature and room temperature. The second is the direct control of the mold temperature. This method is to install a temperature sensor inside the mold, which can only be used when the temperature accuracy of the mold is relatively high. The main features of mold temperature control include: the temperature set by the control panel is consistent with the mold temperature; thermal factors that damage the mold can be directly measured and compensated. Generally speaking, mold temperature is more reliable than controlling fluid temperature. In addition, the mold temperature control has good repeatability in the machining process control. The third is collaborative manipulation. Co-regulation is a combination of the above methods that simultaneously manipulates fluid and mold temperatures. In collaborative operation, the location of the temperature sensor in the mold is very important. When placing the temperature sensor, the shape, structure and location of the heat dissipation pipe must be taken into consideration. In addition, temperature sensors should be placed in areas that play a decisive role in the quality of injection molded products. There are many ways to connect one or several mold temperature controllers to the plastic machine control panel. From the perspective of operability, stability and anti-interference, it is best to use a data socket, such as RS485. Information can be transferred between the control unit and the plastic machine through mobile software. The mold temperature controller can also automatically control the system.
6. Configuration and application of mold temperature controller The configuration of mold temperature controller should be judged based on the raw materials processed, the net weight of the mold, the specified heating time period and the production efficiency kg/h. When using thermal oil, operators must follow these safety regulations: Do not place the mold temperature controller close to the heat source furnace; use smooth stop-leak and high-temperature and pressure-resistant plastic hoses or hoses for the connectors ; Regularly maintain the temperature control circuit mold temperature machine, check whether the connectors and molds are leaking, and whether the function is normal; regularly replace the heat transfer oil; artificial oil should be used, with good heat resistance and low slagging tendency. In the application of mold temperature controller, it is extremely important to select the appropriate heat transfer fluid. Tap water is economical, clean and simple to use as a heat transfer fluid. Once the temperature control circuit such as a plastic hose connector leaks, the outflowing water can be immediately discharged to the sewer pipe. However, water as a heat transfer fluid also has disadvantages: low air density; depending on the composition of the water, corrosion and scaling may occur, resulting in increased pressure loss and reduced heat exchange efficiency between the mold and the fluid. When using water as the heat transfer fluid, the following precautions should be taken into consideration: pre-treat the temperature control circuit with anti-corrosion agent; use a filter device in front of the water inlet pipe; regularly clean the mold temperature controller and mold with anti-rust treatment chemicals. There are no disadvantages of water when using thermal oil. Oil has a high boiling point, and they can be used at temperatures above 300°C or even higher. However, the heat transfer index of thermal oil is only 1/3 of water, so oil heaters are not used as mold temperature controllers in injection molding. common.