Application of mold temperature machine in injection mold

There are basically two kinds of mould temperature control machine in the market, one is water as the medium, the other is heat transfer oil as the medium The difference between the two models is that water as the medium (water temperature machine or water model temperature machine for short) has the advantages of (1) no pollution (2) The operation cost is low, almost no money to buy media (3) The reaction rate is fast The advantages of using heat transfer oil as medium (oil temperature machine or oil mould temperature machine for short) are: (1) it is safe to operate under low pressure at high temperature (2) It can reach a larger temperature control range than the water type mold temperature machine The function of mold temperature machine is to heat and raise the mold temperature or cool and reduce the mold temperature to reach a reasonable temperature and control the injection working temperature, so as to ensure the stable quality of injection parts and optimize the processing time In the injection molding industry, the temperature of the mold plays a decisive role in the quality and time of the injection parts This paper will explain the application of mold temperature machine in injection mold from the following seven aspects: the heat balance of injection mold; the purpose of controlling mold temperature and the influence of mold temperature on injection parts; the preparation conditions of effectively controlling mold temperature; mold temperature machine; heat conducting fluid; the advantages and economy of mold temperature machine 1 The heat balance control of the injection mold and the heat conduction of the injection molding machine and the mold is the key to the production of injection molding parts Inside the mold, the heat brought by the plastic (such as thermoplastic) is transferred to the material and steel of the mold through thermal radiation, and transferred 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 In the formula, 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 In the injection molding process, the main purpose of controlling the 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 Zui can be optimized to ensure the stable and high quality of injection parts Mold temperature can affect surface quality, fluidity, shrinkage, injection cycle and deformation Too high or insufficient mold temperature will have different effects on different materials For plastic, higher mold temperature usually improves surface quality and fluidity, but prolongs cooling time and injection cycle A lower mold temperature will reduce the shrinkage in the mold, but it will increase the shrinkage of the injection molded parts after demoulding For thermosetting plastics, a higher mold temperature usually reduces cycle time, which is determined by the time required to cool the part In addition, in the plastic processing, higher mold temperature will reduce the plasticizing time and reduce the number of cycles 3 The temperature control system consists of mould, mould temperature machine and heat conducting fluid In order to ensure that the heat can be added to the mold or removed, 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 Reasonable setting of cooling channel can reduce the internal pressure and improve the quality of injection parts It can also shorten cycle time and reduce product cost Secondly, the mold temperature machine must be able to keep the temperature of the heat-conducting fluid in the range of 1 ℃ - 3 ℃, which is determined according to the quality requirements of the injection parts The third is that heat conducting fluid must have good heat conduction ability Zui is important that it can import or export a large amount of heat in a short time From the point of view of thermodynamics, water is obviously better than oil 4 The working principle of the model 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 In general, the pump in the power transmission system enables the hot fluid to arrive at the mold from the water tank equipped with the 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 body, so as to indirectly adjust the temperature of the mold If the temperature of the mould exceeds the set value of the controller during the production of the mould temperature machine, 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 mould 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 mould temperature machine is divided according to the heat conducting fluid (water or heat conducting oil) used Usually, the temperature at the big outlet of Zui is 95 ℃ The oil transfer mould temperature machine is used for the occasion of working temperature ≥ 150 ℃ Generally, the mould temperature machine with open water tank is suitable for water temperature machine or oil temperature machine The temperature of Zui big outlet is 90 ℃ - 150 ℃, the main characteristics of this kind of mould temperature machine are simple design and economic price On the basis of this kind of machine, a kind of high temperature water temperature machine is derived Its allowable outlet temperature is 160 ℃ or higher Because the thermal conductivity of water is much better than that of oil at the same temperature when the temperature is higher than 90 ℃, this machine has outstanding high temperature working energy In addition to the second, there is a forced flow mold temperature machine For safety reasons, the mold temperature machine is designed to work at a temperature above 150 ℃, using heat transfer oil In order to prevent the oil in the mould temperature machine from overheating, the machine uses a forced flow pumping system Heater 6 The temperature in the control mold is uneven, which is also related to the time point in the injection cycle After injection, the temperature of the mold cavity rises to Zui high, when the hot melt touches the cold wall of the mold cavity, when the parts are removed, the temperature drops to Zui low The function of the mould temperature machine is to keep the temperature constant between θ 2min and θ 2max, that is to prevent the temperature difference △ θ W from fluctuating up and down in the production process or gap The following control methods are applicable to the temperature control of the mold: the control of fluid temperature is a common method of Zui, and the control accuracy can meet the requirements of most cases Using this control method, it is shown that the temperature of the controller is not consistent with that of the mold; the temperature of the mold fluctuates greatly, because the thermal factors affecting the mold are not directly measured and compensated, including the change of injection cycle, injection speed, melting temperature and room temperature Next is the direct control of mold temperature The method is to install a temperature sensor in the mold, which can be used only when the mold temperature control accuracy is 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, the stability of mold temperature is better than by controlling the fluid temperature In addition, the mold temperature control has good repeatability in the production process control The third is joint control Combined control is the synthesis of the above methods, which can control the temperature of the fluid and the mold at the same time In the joint control, the position of the temperature sensor in the mold is very important When placing the temperature sensor, the shape, structure and the position of the cooling channel must be considered In addition, the temperature sensor should be placed in the place that plays a decisive role in the quality of the injection molding part There are many ways to connect one or more mold temperature machines to the injection molding machine controller Considering the operability, reliability and anti-interference, Zui can use digital interface well, such as RS 485 Information can be transferred between the control unit and the injection molding machine through software The mould temperature machine can also be controlled automatically 7 The configuration of die temperature machine and the configuration of using die temperature machine shall be determined comprehensively according to the processed materials, die weight, required preheating time and productivity kg / h When using heat transfer oil, the operator must abide by the following safety regulations: do not put the mould temperature machine near the heat source furnace; use the taper leakproof and temperature resistant and pressure resistant hose or hard tube for the joint; regularly check whether the mould temperature machine of temperature control circuit, the joint and the mould have leakage and normal function; regularly replace the heat transfer oil; select the synthetic oil to keep the heat stable Good quality, little coking tendency In the use of mould temperature machine, it is very important to choose proper heat conducting fluid Water is economical, clean and easy to use as heat-conducting fluid Once the temperature control circuit such as hose coupling leaks, the water flowing out can be directly discharged to the sewer But there are some disadvantages of using water as heat conducting fluid: the boiling point of water is low; according to the composition of water, corrosion and scaling may occur, resulting in the increase of pressure loss and the decrease of heat exchange efficiency between mold and fluid, etc When using water as heat conducting fluid, the following precautions should be considered: pretreatment of temperature control circuit with anti-corrosion agent; use of filter before water inlet; regular cleaning of water temperature machine and mould 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 in the case of temperature higher than 300 ℃ or even higher, but the heat transfer coefficient of heat transfer oil is only 1 / 3 of that of water, so the oil temperature machine is not widely used in injection molding.