Application of the hottest mold warming machine in

2022-08-17
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The application of mold temperature machine in injection mold

1. The heat balance control of injection mold the heat conduction of injection machine and mold is the key to the production of injection molded parts. Inside the mold, the heat brought by plastic (such as thermoplastic) is transferred to the material and the steel of the mold through thermal radiation, and to the heat-conducting fluid through convection. In addition, heat is transferred to the atmosphere and mold base through thermal radiation. The heat absorbed by the heat conducting fluid is taken away by the mold temperature machine. The heat balance of the die 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 plastic; PS is the heat emitted by the mold to the atmosphere

2. The purpose of controlling mold temperature and the influence of mold temperature on injection molded parts in injection molding process, the main purpose of controlling mold temperature is to heat the mold to the working temperature, and 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 and high quality of injection molded parts. Mold temperature will affect surface quality, fluidity, shrinkage, injection cycle and deformation. Too high or insufficient mold temperature will have different effects on different materials. For thermoplastics, a higher mold temperature usually improves the surface quality and fluidity, but prolongs the cooling time and injection cycle. A lower mold temperature will reduce the shrinkage in the mold, but will increase the shrinkage of injection molded parts after demoulding. For thermosetting plastics, a higher mold temperature usually reduces the cycle time, and the time is determined by the time it takes for the parts to cool down, which has formed a good industrial advantage. In addition, in the processing of plastics, a higher mold temperature will also reduce the plasticizing time and reduce the number of cycles

3. Preparation conditions for effective control of mold temperature. The temperature control system is composed of mold, mold temperature machine and heat conducting 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 conditions: first, in the mold, the surface area of the cooling channel must be large enough, and the diameter of the channel 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 parts. The reasonable setting of cooling channel can reduce the internal pressure and improve the quality of injection molded parts. It can also shorten the cycle time and reduce the product cost. Secondly, the mold temperature machine must be able to keep the temperature of the heat-conducting fluid constant in the range of 1 ℃ - 3 ℃, which is determined according to the quality requirements of the injection molded parts. The third is that the heat conducting fluid must have good heat conduction ability. The most important thing is that it can import or export a large amount of heat in a short time. From the perspective of thermodynamics, water is obviously better than oil

4. 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 devices. Usually, 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 return to the water tank from the mold; 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, and the unit of F shear area is square millimeter (mm2), so as to indirectly adjust the temperature of the mold. If the mold temperature machine is in production and the mold temperature exceeds the set value of the controller, the controller will open the solenoid valve and connect the water inlet pipe until the temperature of the hot fluid, that is, the mold temperature returns to the set value. If the mold temperature is lower than the set value, the controller will turn on the heater

5. The type of mold temperature machine is divided according to the heat-conducting fluid (water or heat-conducting oil) used. Usually, the maximum outlet temperature of water transporting mold temperature machine is 95 ℃. The oil transporting mold temperature machine is used for occasions with working temperature ≥ 150 ℃. Generally, the mold temperature machine with open water tank heating is suitable for water temperature machine or oil temperature machine. The maximum outlet temperature is 90 ℃ to 150 ℃. The main characteristics of this mold temperature machine are simple design and economical price. On the basis of this machine, a high-temperature water temperature machine is derived. Its allowable outlet temperature is 160 ℃ or higher. When the temperature is higher than 90 ℃, the thermal conductivity of water is much better than that of oil at the same temperature. Therefore, this machine has outstanding high-temperature working ability. In addition to times, there is also a forced flow mold temperature machine. For safety reasons, this mold temperature machine is designed to work at a temperature of more than 150 ℃ and uses heat transfer 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 is composed of a certain number of stacked tubes, in which there are finned heating elements for diversion

6. Control the uneven temperature 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 the highest, when the hot melt touches the cold wall of the mold cavity, and the temperature drops to the lowest after the parts are removed. The function of mold temperature machine is to keep the temperature constant at θ 2min and θ 2max, that is to say, to prevent the temperature difference △ θ W fluctuates up and down in the production process or gap. The following control methods are suitable for controlling the temperature of the mold: controlling the fluid temperature is the most commonly used method, and the control accuracy can meet the requirements of most cases. Using this control method, it shows that the temperature of the controller is different from that of the mold before the use of the electronic tensile testing machine; The temperature fluctuation of the mold is quite large, because the thermal factors affecting the mold are not directly measured and compensated. These factors include the change of injection cycle, injection speed, melting temperature and room temperature. The second is the direct control of mold temperature. This method is to install a temperature sensor inside the mold, which can be used only when the mold temperature control accuracy is relatively high. The main characteristics 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. Generally, the stability of mold temperature is better than that by controlling fluid temperature. In addition, the mold temperature control has good repeatability in the production process control. The third is joint control. Joint control is the synthesis of the above methods, which can control the temperature of fluid and mold at the same time. In the joint control, the position of the temperature sensor in the mold is extremely important. When placing the temperature sensor, we must consider the shape, structure and the position of the cooling channel. In addition, the temperature sensor should be placed where it plays a decisive role in the quality of injection molded parts. There are many ways to connect one or more mold temperature machines to the injection molding machine controller. Considering operability, reliability and anti-interference, it is best to use digital interfaces, such as RS485. Information can be transferred between the control unit and the injection molding machine through software. The mold temperature machine can also be controlled automatically

7. The configuration of mold warming machine and the configuration of using mold warming machine should be comprehensively determined according to the processed materials, the weight of the mold, the required preheating time and the productivity kg/h. When using heat transfer oil, the operator must abide by such safety regulations: do not put the mold temperature machine near the heat source stove; The joints shall be made of taper leakproof hoses or rigid pipes with temperature and pressure resistance; Regularly check whether the mold temperature machine, joint and mold of the temperature control circuit have leakage and whether the function is normal; Replace the heat transfer oil regularly; Synthetic oil should be selected with good thermal stability and small coking tendency. In the use of mold temperature machine, it is very critical to select the appropriate heat-conducting fluid. Using water as heat conducting fluid is economical, clean and easy to use. Once the temperature control circuit such as hose coupling leaks, the water flowing out can be directly discharged to the sewer. However, using water as heat transfer fluid also has disadvantages: the boiling point of water is low; Depending on the composition of the water, corrosion and scaling may occur, resulting in increased pressure loss and decreased heat exchange efficiency between the mold and the fluid, etc. When using water as heat-conducting fluid, the following precautions should be considered: pre treat the temperature control circuit with corrosion inhibitor; Use filter before water inlet; Regularly clean the water temperature machine and mold with rust remover. There is no disadvantage of water when using heat transfer oil. The boiling point of oil is high. They can be used when the temperature is higher than 300 ℃ or even higher, but the heat transfer coefficient of heat transfer oil is only 1/3 of that of water. Therefore, oil temperature machines are not widely used in injection molding as water temperature machines. (end)

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