http://ylscps.com The mold temperature machine is indeed very broad in scope of application, and this chapter mainly introduces the application of the mold temperature machine in injection molds in detail, which includes controlling the uneven temperature of the points in the mold. It is related to the time point in the injection cycle; the configuration of the mold temperature machine and the configuration of the mold temperature machine should be comprehensively determined according to the material being processed, the weight of the mold, the required warm-up time and the productivity kg / h; the purpose of controlling the temperature of the mold Effects of mold temperature and mold temperature on injection molded parts In the injection molding process, the main purpose of controlling the mold temperature is to heat the mold to the working temperature, and the second is to keep the mold temperature constant at the working temperature. In the injection molding process, the main purpose of controlling the mold temperature is to heat the mold to the working temperature, and the second is to keep the mold temperature constant at the working temperature; the working principle of the mold temperature machine consists of a water tank, heating and cooling system, power transmission system, liquid level control system and Temperature sensor, injection port and other components; the type of mold temperature machine is based on the use of thermal fluid (water or thermal oil) to Points. The maximum outlet temperature of the water transport type mold temperature machine is usually 95 ° C; the heat balance control of the injection mold is the key to the production of injection parts, and the seven major aspects are summarized as follows:
First, control the temperature unevenness in the mold, and it is also related to the time point in the injection cycle. After injection, the temperature of the mold cavity rises to the highest level. At this time, the hot melt hits the cold wall of the mold cavity. When the parts are removed, the temperature is minimized. The function of the mold temperature machine is to keep the temperature constant between θ2min and θ2max, that is, to prevent the temperature difference Δθw from fluctuating up and down during the production process or the gap. The following control methods are suitable for controlling the temperature of the mold: controlling the temperature of the fluid is the most commonly used method, and the control accuracy can meet the requirements of most situations. Using this control method, it is shown that the temperature of the controller and the mold temperature are not consistent; the temperature fluctuation of the mold is quite large, because the thermal factors affecting the mold are not directly measured and compensated for these factors, including changes in the injection cycle, injection speed, 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 will be used only when the mold temperature control accuracy is relatively high. The main features of mold temperature control include: the temperature set by the controller is consistent with the mold temperature; the thermal factors affecting the mold can be directly measured and compensated. In general, mold temperature stability is better than by controlling fluid temperature. In addition, mold temperature control has better repeatability in production process control. The third is joint control. Joint control is a combination of the above methods, which can control the temperature of the fluid and the mold at the same time. In joint control, the position of the temperature sensor in the mold is extremely important. When placing the temperature sensor, the shape, structure, and location of the cooling channel must be considered. In addition, the temperature sensor should be placed where the quality of the injection molded part is decisive. There are many ways to connect one or more mold temperature machines to the injection molding machine controller. It is best to use a digital interface such as RS485 for operability, reliability and anti-interference considerations. Information can be transferred between the control unit and the injection molding machine via software. The mold temperature machine can also be controlled automatically.
Second, the configuration of the mold temperature machine and the configuration of the use of the mold temperature machine should be based on the processing materials, the weight of the mold, the required warm-up time and productivity kg / h to comprehensively determine. When using thermal oil, the operator must observe the safety regulations: Do not place the mold temperature machine near the heat source stove; use a tapered leak-proof and temperature or pressure resistant hose or hard pipe; regular inspection Temperature control loop mold temperature machine, joints and molds are leak-free and function properly; regular replacement of heat transfer oil; artificial synthetic oil should be used, good thermal stability, and low coking tendency. In the use of the mold temperature machine, it is extremely important to choose the appropriate thermal fluid. The use of water as a heat-conducting fluid is economical, clean, and easy to use. Once the temperature control circuit such as a hose coupling leaks, the water flowing out can be directly discharged to the sewer. However, using water as a heat-conducting fluid also has disadvantages: the boiling point of water is low; depending on the composition of the water, it may corrode and scale, causing an increase in pressure loss and a decrease in the efficiency of heat exchange between the mold and the fluid. When using water as the heat transfer fluid, the following precautions should be considered: pre-treat the temperature control circuit with an anti-corrosive agent; use a filter before the water inlet; and regularly clean the water temperature machine and mold with a rust-removing agent. There is no disadvantage of water when using thermal oil. Oils have high boiling points, and they can be used in situations where the temperature is higher than 300 ° C or even higher, but the heat transfer coefficient of heat transfer oil is only 1/3 of water, so oil temperature machines are not as widely used as water temperature machines in injection molding.
Third, the purpose of controlling the mold temperature and the impact of the mold temperature on the injection molded parts In the injection molding process, the main purpose of controlling the mold temperature is to heat the mold to the working temperature, and the second is to keep the mold temperature 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 the injection molded parts. Mold temperature will affect surface quality, fluidity, shrinkage, injection cycle and deformation. Excessive or insufficient mold temperature will have different effects on different materials. For thermoplastics, higher mold temperatures usually improve surface quality and fluidity, but extend cooling times and injection cycles. A lower mold temperature will reduce the shrinkage in the mold, but will increase the shrinkage of the injection molded part after demolding. For thermosetting plastics, a higher mold temperature usually reduces cycle time, and the time is determined by the time required for the part to cool. In addition, in the processing of plastics, a higher mold temperature will reduce the plasticization time and reduce the number of cycles.
Preparatory conditions for effective control of the mold temperature The temperature control system consists of a mold, a mold temperature machine, and a heat-conducting 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 flow channel must match the capacity of the pump (pump pressure). The temperature distribution in the cavity has a great influence on part deformation and internal pressure. The proper setting of the cooling channel can reduce the internal pressure, thereby improving the quality of the injection molded part. It can also reduce cycle times and reduce product costs. Secondly, the mold temperature machine must be able to make the temperature of the heat-conducting fluid constant within the range of 1 ° C-3 ° C, which is determined according to the quality requirements of the injection molded part. The third is that the heat-conducting fluid must have good heat-conducting ability. Most importantly, it must be able to introduce or extract a large amount of heat in a short time. From a thermodynamic point of view, water is significantly better than oil.
V. 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 with built-in heater and cooler, and then returns from the mold to the water tank. The temperature sensor measures the temperature of the hot fluid and transmits the data to the Controller; the controller regulates the temperature of the hot fluid, thereby indirectly regulating the temperature of the mold. If the mold temperature machine is in production and 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.
Six, the type of mold temperature machine is divided according to the thermal fluid (water or thermal oil) used. The maximum outlet temperature is usually 95 ° C with a water transport mold temperature machine. Use the oil transport type mold temperature machine for the working temperature ≥150 ℃. Under normal circumstances, the mold temperature machine with an open water tank is suitable for water temperature or oil temperature machine, the maximum outlet temperature is 90 ℃ to 150 ℃, the main characteristics of this type of mold temperature machine is simple design, economical price. On the basis of this machine, a high-temperature water temperature machine has been derived. The allowable outlet temperature is 160 ° C or higher. When the temperature is higher than 90 ° C, the thermal conductivity of water is higher than that of oil at the same temperature. Much better, so this machine has outstanding high temperature working ability. In addition to this, there is a forced-flow mold temperature machine. For safety reasons, this mold temperature machine is designed to work at a temperature of 150 ° C or higher, using thermal oil. In order to prevent the oil in the heater of the mold temperature machine from overheating, the machine uses a forced-flow pumping system, and the heater consists of a certain number of tubes stacked with finned heating elements in the tubes for diversion.
7. Thermal balance control of injection mold The heat conduction of injection molding machine and mold is the key to the production of 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-conducting 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 equilibrium 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 from the mold to the atmosphere.
Familiar with and master the above seven aspects of the application of the mold temperature machine in the injection mold, will certainly be more proficient in the actual operation process, the same is also a systematic understanding of the application of chiller equipment in the actual production line Can help!
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