Mold temperature machine is utilized to heat or cool the mold and maintain its working temperature, ensure the quality of injection molded parts and optimize processing time. In the injection molding industry, the temperature of the mold plays a key role in the quality of the injection molded parts and the injection time.
Heat balance control of injection mold thermal conduction of injection moulding machines and molds is essential for the production of injection molded parts. Inside the mold, heat from plastic (such as thermoplastics) is passed through heat radiation to the material and the steel of the mold, passing through the connection to the conduction fluid. In addition, heat is passed through thermal radiation to the atmosphere and the mold holder. The heat absorbed by the conduction heat is taken away from the mold temperature machine. The heat balance of the mold can be characterized as: P=pm-ps. In the formula, p is the heat taken away from the mold temperature; PM is the heat that is introduced into the plastic; PS is the heat that the mold emits into the atmosphere.
The purpose of controlling the mold temperature and the influence of the mold temperature on 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. The above two points to do successful, you can rationalize the cycle time, and thus ensure the stability of injection molded parts of high quality. Mold temperature can affect the surface quality, fluidity, shrinkage, injection cycle and deformation. The mold temperature is too high or insufficient for different materials will bring diverse effects. For thermoplastics, a superior mold temperature usually improves surface quality and fluidity, but prolongs the cooling time and injection cycle. A lower die temperature will reduce shrinkage in the mold, but will increase the shrinkage of injection molded parts after demoulding. For Thermosetting plastic, a higher mold temperature usually reduces the cycle time and is determined by the time required for the cooling of the parts. In addition, in the plastic processing, a higher mold temperature will reduce the plasticizing time, reduce cycle time.
The preparation conditions for effective control of mold temperature The temperature control system consists of three parts of decease, mold temperature and heat conduction. In order to ensure that the heat can be added to the mold or removed, the system parts must meet the following conditions: First, in the mold, the surface area of the cooling channel must be large enough, the flow path diameter to match the pump capacity (pump pressure). The temperature distribution in the cavity has a pronounced influence on the deformation and internal pressure of the parts. The proper setting of the cooling channel can reduce the internal pressure and improve the quality of the injection molded parts. It can also shorten the cycle time and reduce product costs. The second is the mold temperature machine must be able to make the temperature of the heat conduction constant in the range of 1℃-3℃, specifically according to the quality requirements of injection molded parts. Third, the thermal conductivity must have excellent heat conduction ability, it is important to be able to import or export a lot of heat in a short time. From the thermodynamic point of view, water is obviously better than oil.
Working principle mold temperature machine by the water tank, heating cooling system, power transmission system, liquid level control system and temperature sensor, injection port and other components. In general, the pump in the power transmission system enables the thermal fluid to reach the mold from the tank fitted with the built-in heater and cooler, and then back to the water tank from the mold, the temperature sensor measures the temperature of the heat flow and transmits the data to the control part of the controller, and the controller regulates the temperature of the heat flow, If the die temperature in production, the mold temperature exceeds the set value of the controller, the controller will open the solenoid valve into the water pipe until the temperature of the hot liquid, that is, the mold temperature back to the set value. If the mold temperature is below the set value, the controller will open the heater.
Type of mold temperature machine is based on the use of the conductive fluid (water or heat conduction oil) to be divided. With the cloud-water mold temperature machine usually outlet temperature 95 ℃. Use of oil-transporting mold temperature machine for operating temperature 150℃ occasions. Under normal circumstances, with open water tank heating mold temperature machine suitable for water temperature machine or oil temperature machine, outlet temperature of 90 ℃ to 150 ℃, the main feature of this mold temperature is simple design, price economy. On the basis of this machine, a kind of high-temperature water temperature machine is derived. It's permissible outlet temperature is 160 ℃ or higher, because the temperature is higher than 90 ℃, the heat conductivity of water than the same temperature of the oil much better, so the machine has a prominent high-temperature working ability. In addition to the time, there is a forced flow of the mold temperature machine, for safety reasons, this model temperature design work temperature of more than 150 ℃, the use of thermal oil. To prevent overheating of the oil in the heater, the machine uses a forced flow pumping system, and the heater is composed of a number of pipe stacks, with a heating element fitted with fins for diversion.
Controlling the temperature in the mold is uneven, and also related to the time point in the injection cycle. After injection the cavity temperature rises to the high point, when the hot melt touches the cold wall of the mold cavity, when the part is removed, the temperature drops too low. The function of the mold temperature machine is to keep the temperature constant between θ2min and Θ2max, which means to prevent the temperature difference θw fluctuation in the production process or gap. The following control methods are suitable for controlling the temperature of the mold: the control of the fluid temperature is a shared method, and the control accuracy can meet most of the requirements. Using this control method, the temperature and die temperature of the controller are not consistent; the temperature fluctuation of the mould is quite large, because the heat factor affecting the mold is not directly measured and compensated for these factors including the change of injection cycle, injection speed, melting temperature and room temperature. The second is the absolute control of mold temperature. The method is tantamount to install the temperature sensor inside the mold, which is adopted when the die temperature control precision is high. The main characteristics of the mold temperature control include: the temperature of the controller is consistent with the mold temperature, and thermal factors affecting the mold can be directly measured and compensated. Generally, mold temperature stability is better than through the control of the fluid temperature. In addition, the mold temperature controls in the production process control of a better repeatability. The third is joint control. Joint control is the synthesis of the above method, which can simultaneously control the temperature of fluids and molds. In the dual control, the temperature sensor in the mold position is extremely important, when placing the temperature sensor, must consider the shape, the structure and the cooling channel position. In addition, the temperature sensor should be positioned in the place where the quality of the injection molded part is decisive. There are many ways to connect one or more mold temperature machine to the controller of the injection molding machine. Use digital interfaces, such as RS 485, from operation, reliability, and anti-jamming considerations. Information can be passed between the control unit and the injection molding machine through the software. Mold temperature can also be automatically controlled.
Mold temperature machine configuration and the use of mold temperature machine configuration should be based on the processing of materials, mold weight, the required preheating time and productivity kg/h to comprehensively determine. When using heat-conducting oil, the operator must comply with such safety requirements: do not place the mold temperature machine near the heat source stove; The joint uses a taper-proof and temperature-resistant hose or hard tube, and periodically inspects the temperature control loop mold temperature machine, the joint and the mold have no leakage, function is normal; regular replacement of thermal oil The artificial synthetic oil should be selected, with good thermal stability and small coking tendency. In the use of mold temperature machine, it is extremely important to select the proper heat conduction fluid. Water for the thermal conductivity of the economy, clean, easy to use, once the temperature control circuit such as hose connector leakage, the flow of water can be directly released to the sewer. However, water as a guide to heat flow also has disadvantages: the boiling point of water is low, according to the composition of water, may be corrosion and scaling, resulting in increased pressure loss and mold and fluid heat exchange efficiency drop and so on. When using water as a heat conduction fluid, the following precautions should be considered: pre-treatment of the temperature control circuit with anticorrosive agent, filter used in inlet, and regular use of rust remover to clean the water cooler and mould. There is not of water when using heat-conducting oil. The boiling point of oil is high, they can be used for temperatures above 300 ℃ or even higher, but the heat transfer coefficient of thermal conductivity is only 1/3 of the water, so the oil temperature in injection molding is not widely used in the water cooler.