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Variable temperature control allows injection molding technology to be solved

2018-05-29
Variable temperature control allows injection molding technology to be solved


The automotive and consumer goods industries have increasingly stringent requirements on the quality of injection products, and therefore put forward new requirements for the injection molding process. Seamless surfaces, shorter injection cycles, and high forming accuracy – these three challenges require injection molding. The development of a special cooling technology, variable temperature control is a highly efficient solution.
    Variable temperature control tool
    Variable mold temperature control means that the mold temperature is not maintained, but is controlled in accordance with a defined temperature profile during an injection cycle. At the time of injection, the temperature is almost as high as the temperature of the injected material; after injection, the mold needs to cool down quickly to cure the material quickly. Therefore, with this technology, it is possible to produce plastic parts without any streamlined, deformed high-gloss surface.
    There are a number of techniques that can be used to achieve variable mold temperature control, such as the use of two cooling circuits (steam/water or oil/oil), liquid cooling combined with induction heating, infrared heating combined with liquid cooling, or electric heating with heating elements and liquids The combination of cooling, as well as CPH high-performance ceramic dynamic die temperature precision control technology or two cycles of temperature control.
    The realization of dynamic temperature control of injection molding requires the opening of a temperature slot close to the contour of the mold for rapid heating and cooling. Taking into account the different wall thicknesses everywhere, heat is conducted in different ways in different areas of the workpiece. The more the cooling channel runs through the die or the closer to the die cavity, the more accurate the adjustment of the cooling process. The premise is that each cooling channel has its own temperature control. For smaller tools, the channel is located less than 1.5 mm of the cavity. Large molds are built in two halves and require long, temperature-controlled passages along the contour of the tool.
    Closed cavity temperature control
    Varying temperature control and short cycle time requirements are somewhat contradictory, but such conflicts can be resolved by new technologies such as “segment tool temperature control”. Using these techniques, the cooling channel will be very close to the mold cavity, and a three-dimensional channel structure can be implemented in the mold to obtain the ideal cooling channel configuration.
    Temperature control can be achieved by measuring the in-mold temperature close to the mold cavity or measuring the temperature of the re-circulated cooling fluid. Thermocouples or resistance thermometers are commonly used, such as using the PT100 as a sensor, measuring the current temperature, and passing this information to a controller, and then adjusting the flow of coolant in each channel. The control method is to inject steam or hot water heating, water cooling. This type of temperature control greatly improves the surface quality and significantly reduces the cycle time.
    Valve technology innovation
    New developments in proportional solenoid valves have led to the implementation of multi-circuit parallel operating temperature regulation circuits. The advantage of these valves is that they use magnetic cores without friction bearings and avoid stick-slip effects through special forms of springs. This can be reflected by excellent records, including the most important reaction sensitivity (0.1% of the final value), minimal reverse error, and excellent tuning performance. The new solenoid valve has a measuring range of 1:100, which allows it to adapt to even very subtle temperature changes, such as very fine changes caused by the valve corrective action.
    The decisive test values used to measure the cooling process of the workpiece are the return temperature and the outlet flow, which helps to adjust the coolant volume in an absolutely reliable and accurate manner. The state-of-the-art sensor detects changes between 100 and 300 milliseconds and the control valve adjusts the flow in 0.3 to 1 second. Impeller sensors are particularly suitable because of their small frame size and excellent response time.
    Actuator Engineering
    The choice of valve depends on the flow and the degree of contamination of the coolant. For high flow rates and contaminated fluids, direct acting valves are recommended. For temperatures up to 180°C, pneumatically operated On/Off or regulating valves are appropriate. Depending on the amount of heat lost, if the valve opening time is to be controlled, on/off temperature control or pulse cooling is used during the injection molding cycle cooling phase.
    For low flow rates and clean cooling liquids, servo-assisted solenoid valves are very good if there is a central water treatment device and the water temperature is below 90 degrees Celsius.
    For more or less cooling depending on the nature of the workpiece, the use of multi-channel temperature control, the use of pneumatic valves, direct-acting or servo-assisted solenoid valves all provide a clear advantage. Their crack opening can be quickly adjusted between 0-100%. Such a dynamic regulating valve technology makes it possible to preset the temperature profile according to the workpiece. Rapid temperature control protection and enhanced valve durability. With pneumatic control valves, the nominal diameter is not limited by the fluid pressure. It usually ranges from 4 to 20 mm or even higher. To adjust the opening of a particular crack requires a supplemental electronic control. This proportional control valve is implemented by pulse regulation (PWM). Compared to a normal process control valve, this is a positioner control valve that is assisted by a combined valve positioning control. It adjusts the process valve piston to a specific crack opening.
     Distributed mold temperature control
     Typically, the integrated process system includes a flow sensor, proportional valve, and flow controller. The controller plays a decisive role in the system because it must be able to handle different sensor signals, such as temperature, pressure or flow, and it must be able to communicate with pneumatic and electrical control systems.
     The most important features are: temperature regulation; pressure control; flow control; on/off solenoid valve control, proportional valve, process control valve and electric control valve; input normal sensor signal (standard signal 4 to 20mA, frequency, PT100) Setpoints communicate with the central control unit with a 4-20mA, process value feedback; easily set by selected application (flow, temperature, or pressure control); remember most valve and sensor data. eCONTROL can also be made as a panel in perforated 1/16 DIN standard and can be integrated into existing control cabinets. The decentralized mold temperature system simplifies the control of the machine so that they can focus on their correct tasks.
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