Application of Mold Temperature Machine in Injection Mold

        1. The heat balance control of injection molding machines and the heat conduction of molds are the key to producing injection molded parts. Inside the mold, the heat brought by plastics (such as thermoplastic) is transferred through thermal radiation to the material and the steel of the mold, and through convection to the thermally conductive fluid. In addition, heat is transferred to the atmosphere and mold base through thermal radiation. The heat absorbed by the conductive fluid is taken away by the mold temperature machine. The thermal balance of the mold can be described as P=Pm Ps. In the formula, P is the heat carried away by the mold temperature machine; Pm is the heat introduced by the plastic; Ps represents the heat emitted by the mold into the atmosphere.

        2. The purpose of controlling mold temperature and the impact of mold temperature on injection molded parts. In the 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 successfully achieved, the cycle time can be optimized to ensure stable and high-quality injection molded parts. Mold temperature can affect surface quality, fluidity, shrinkage, injection cycle, and deformation. Excessive or insufficient mold temperature can have different effects on different materials. For thermoplastic plastics, a higher mold temperature usually improves surface quality and flowability, but prolongs cooling time and injection cycle. A lower mold temperature will reduce the shrinkage inside the mold, but it will increase the shrinkage rate of the injection molded part after demolding. For thermosetting plastics, a higher mold temperature usually reduces the cycle time, and the time is determined by the time required for the part to cool. In addition, in the processing of plastic, a higher mold temperature will also reduce the plasticizing time and the number of cycles.

        3. The temperature control system consists of three parts: the mold, the mold temperature machine, and the thermal conductive 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: firstly, within the mold, the surface area of the cooling channel must be large enough, and the diameter of the flow channel must match the pump's capacity (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 channels can reduce 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 maintain the temperature of the thermal conductive fluid within the range of 1 ℃ -3 ℃, depending on the quality requirements of the injection molded parts. The third is that thermal conductive fluids must have good thermal conductivity, and most importantly, they must be able to introduce or export a large amount of heat in a short period of time. From a thermodynamic perspective, water is clearly better than oil.

        4. The working principle of 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. Usually, the pump in the power transmission system causes the hot fluid to reach the mold from the water tank equipped with a 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 section; The controller regulates the temperature of the hot fluid, thereby indirectly adjusting 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 liquid, 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.www.jiashengsz.com

        5. The types of mold temperature machines are classified based on the heat transfer fluid (water or heat transfer oil) used. The maximum outlet temperature of a water transport mold heater is usually 95 ℃. Use an oil operated mold temperature machine for applications with a working temperature of ≥ 150 ℃. Usually, a mold temperature machine with an open water tank for heating is suitable for water or oil temperature machines, with a maximum outlet temperature of 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 has been developed, which can allow an outlet temperature of 160 ℃ or higher. Due to the much better thermal conductivity of water compared to oil at the same temperature when the temperature is above 90 ℃, this machine has outstanding high-temperature working ability. In addition, there is also a forced flow mold temperature machine. For safety reasons, this mold temperature machine is designed to operate at a temperature above 150 ℃ and uses thermal oil. In order to prevent the oil in the heater of the mold heater from overheating, the machine uses a forced flow pumping system, and the heater is composed of a certain number of stacked pipes, which have heating elements with fins for guiding water.

        6. The uneven temperature distribution within the mold is also related to the time points during the injection cycle. After injection, the temperature of the mold cavity reaches its maximum, when the hot melt touches the cold wall of the mold cavity. When the part is removed, the temperature drops to the lowest. The function of a mold temperature machine is to maintain a constant temperature at θ 2 minutes and θ Between 2max, which means preventing temperature difference △ θ W fluctuates up and down during the production process or gaps. The following control methods are applicable to controlling the temperature of the mold: controlling fluid temperature is the most commonly used method, and the control accuracy can meet the requirements of most situations. Using this control method, the temperature displayed on the controller is not consistent with the mold temperature; The temperature fluctuation of the mold is quite large because the thermal factors affecting the mold are not directly measured and compensated for, including changes in injection cycle, injection speed, melting temperature, and room temperature. Next is the direct control of mold temperature. This method involves installing a temperature sensor inside the mold, which is only used when the precision requirements for mold temperature control are 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 that affect the mold can be directly measured and compensated for. In general, the stability of mold temperature is better than by controlling fluid temperature. In addition, mold temperature control has good repeatability in the production process control. The third is joint control. Joint control is a combination of the above methods, which can simultaneously control the temperature of the fluid and the mold. In joint control, the position of the temperature sensor in the mold is extremely important. When placing the temperature sensor, it is necessary to consider the shape, structure, and position of the cooling channel. In addition, temperature sensors should be placed in a location that 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. It is best to use digital interfaces such as RS485 for operability, reliability, and anti-interference considerations. Information can be transmitted between the control unit and the injection molding machine through software. The mold temperature machine can also be automatically controlled.

        7. The configuration and use of the mold temperature machine should be comprehensively judged based on the processed material, mold weight, required preheating time, and production rate kg/h. When using heat transfer oil, the operator must comply with the following safety regulations: do not place the mold temperature machine near the heat source furnace; The joint should be made of tapered, leak proof, and temperature and pressure resistant hoses or hard pipes; Regularly check the temperature control circuit, mold temperature machine, joints, and molds for leaks, and ensure their functionality is normal; Regularly replace the heat transfer oil; Artificial synthetic oil should be selected, with good thermal stability and low tendency to coking. It is crucial to choose the appropriate thermal conductivity fluid in the use of the mold temperature machine. Using water as a thermal fluid is economical, clean, and easy to use. Once a temperature control circuit such as a hose coupling leaks, the water flowing out can be directly discharged into the sewer. But using water as a heat conducting fluid also has drawbacks: the boiling point of water is low; According to the composition of the water, it may corrode and scale, causing an increase in pressure loss and a decrease in heat exchange efficiency between the mold and the fluid. When using water as a heat conducting fluid, the following precautions should be considered: pre-treatment of the temperature control circuit with anti-corrosion agents; Use a filter before the water inlet; Regularly clean the water temperature machine and mold with rust remover. There is no disadvantage of water when using heat transfer oil. Oil has a high boiling point and can be used for temperatures above 300 ℃ or even higher, but the heat transfer coefficient of heat transfer oil is only 1/3 of that of water, so oil temperature machines are not as widely used in injection molding as water temperature machines.