These three requirements: seamless surface, short injection molding cycle and high molding accuracy require special precision injection mold cooling technology, one of which is variable temperature temperature control technology, which has been widely used in recent years.
Variable temperature temperature control technology
Variable temperature control: The mold temperature is not constant, but is controlled according to the specified temperature profile during the injection molding process. The temperature of the mold during injection is 10-30 ° C higher than the glass transition temperature of the injection molding material. After the injection is completed, the mold temperature is rapidly lowered to the mold release temperature. With this technology, plastic parts with no flow marks, no deformation, and a very smooth surface can be produced. There are several techniques available for variable temperature control:
Quick mold heating method
Induction heating
Infrared heating
Electric heating
Hot water heating
All of these techniques use refrigerant to quickly cool the mold to the mold release temperature.
For the shortened loop time, the heating method based on CPH technology [1] using high-performance ceramic heating elements or steam heating has proven to be the most effective method.
Achieving this dynamic process requires that the temperature control channel be close to the contour of the model to ensure rapid heating and cooling. It must also be considered that due to the different wall thicknesses, the different areas of the workpiece have different heat conduction. The more cooling channels that flow through the mold, the closer to the chamber, the higher the precision with which the cooling process can be controlled and adjusted. As a prerequisite, each cooling channel requires its own temperature control.
For injection molds with temperature control of hot and cold water, there is a new modular valve block consisting of 6 valves (see photo), which integrates a hot water and a cold water temperature control unit for easy access. The thermal cycle system for the variable temperature control of the injection mold, a pneumatic pilot control module controls six pneumatic valves to perform hot and cold switching according to the injection cycle. The advantage of this solution is that it is very compact and as an option to integrate the temperature control module.
Modular 8611eCONTROL universal controller and Buerkert instrumentation
Near chamber temperature control
The requirements for variable temperature control and short loop time are somewhat contradictory, and this contradiction can be solved by new mold techniques such as "Segmented Temperature Control" [2] or Lasercusing [3]. With these techniques, the cooling passages can be placed very close to the mold cavity, which allows a three-dimensional structure to be channeled within the mold for an ideal cooling channel configuration.
In the injection molding process, precise temperature control is necessary, and the control object is the uniform temperature of the inner wall of the mold cavity. Temperature control can be performed in a mold close to the chamber or by measuring the temperature of the refrigerant in the return line. The mold wall temperature can be repeated to the most important metric coolant flow rate at the correct temperature control point, using a very compact impeller sensor integrated into the custom system for flow measurement and transmitting the instantaneous flow measurement value to the controller The controller controls the flow of refrigerant in each channel and quickly corrects for deviations through innovative proportional control valve technology. This temperature control as needed greatly improves surface quality and greatly reduces cycle time.
Innovative valve technology
The newly developed proportional solenoid valve enables a multi-circuit flow control loop that works in parallel. This new proportional solenoid valve has the advantage of using a special-shaped spring to make the electromagnet core run without friction and prevent stick-slip effects. Performance: high response sensitivity (0.1% of the final value), minimal reverse error and excellent control performance. The new proportional solenoid valve has a turn-up ratio of 1:100, so even small flow deviations can be controlled with extremely precise valve corrections.
Turbine flow sensor, base plate mounted or separately mounted, maximum operating temperature 160 ° C
Process control valve with micro positioner 4mm – 15mm
The decisive parameters used to measure the cooling process of the workpiece are the return water temperature and water flow, which helps to control the cooling of the workpiece and mold in a reliable and accurate manner. Dr. Egon Hüfner, engineer at Bürkert, said: “The return flow of each cooling channel must be measured. Each channel must have a valve and a sensor.†In order to measure the heat absorbed by the cooling process, the temperature of the inlet and outlet is also Need to measure. The response time of the most advanced flow sensor to detect flow changes is 100–300 milliseconds, and the regulator can complete flow regulation in 0.3–0.5 seconds. The turbine flow sensor is especially suitable for small size and extremely fast response times. Electromagnetic flowmeters are also available for pipes with a diameter greater than 6 mm.
Actuator design
The valve should be selected based on the flow rate and the degree of contamination of the coolant. Dr. Hüfner said: “For large flow and dirty liquids, direct acting valves are recommended. For liquids with a maximum temperature of 200 ° C, pneumatic on-off valves or regulating valves can be selected.†If the valve is opened according to the absorbed heat At the time, the switching temperature control mode can be adopted in the cooling phase during the injection molding process.
For small flow and very clean coolant, for example, there is a central water treatment unit with a water temperature below 120 °C, servo-assisted solenoid valves are ideal. Although the valve has a small pilot hole, the valve has a nominal diameter of up to 20 mm. The new generation of Bürkert switching valves has eliminated the pilot holes in the diaphragm and is therefore not sensitive to contaminated coolant.
Depending on the workpiece, multi-channel temperature control includes more or less cooling circuits. Direct-acting or servo-assisted proportional solenoid valves have obvious advantages, and their opening can be quickly adjusted to any range of 0-100%. position. This dynamic regulator technology allows flow control to be based on pre-programmed flow curves tailored to the workpiece.
It is an ideal choice for pneumatic valves with high temperature, high pressure and high flow rate. The minimum diameter is 4mm.
In order to control the valve opening, an auxiliary electronic control unit is necessary. The opening degree of the proportional solenoid valve is controlled by a pulse width modulation (PWM) signal. The opening degree of the general program control valve is controlled by the positioner. The valve position control system is integrated in the positioner, and the valve position of the process valve can be used. Control to a specific opening.
Decentralized temperature control
Typical flow control systems include flow sensors (turbine or ultrasonic), proportional valves, and flow controllers with cascade temperature control and a variety of valves. The flow controller plays a decisive role in the system and must be able to handle various sensor signals such as temperature, pressure or flow, and must also be able to handle pneumatic and electronic control systems. Bürkert's new universal controller eCONTROL has all these features, the most important of which are:
-Temperature adjustment
-Pressure control
-flow control
-Controllable switch solenoid valve, proportional solenoid valve, program control valve and electric control valve
- Input as standard sensor signal (4-20ma standard signal, frequency, PT100)
- Communicate with the central control unit with a 4-20ma signal to provide setpoint and process value feedback
- Easy to set up according to the selected application (flow, temperature or pressure control)
- Stores parameters for most Bürkert valves and sensors
The eCONTROL is also available in a panel type with a mounting opening size of 1/16 DIN that can be installed in an existing control cabinet.
Multi-channel cooling module: including flow sensor, temperature sensor and proportional solenoid valve
Proportional solenoid valve: diameter 0.05mm–20mm
The valve block can operate in 3 states: idle (V2 and V5 open), heating (V1, V3 and V5 open) or cooling (V2, V4 and V6 open)
Variable temperature control module with 6 valves
Decentralized control has the following advantages in particular:
Perfect combination of sensor, valve and adjustment controller
The whole machine control system can focus on its mission
Facilitate the renovation of equipment. Simply taking simple optimizations can greatly shorten the cooling cycle and greatly optimize the quality of the workpiece.
Hyundai Parts,Machinery Spare Parts,Hyundai Aftermarket Parts,Dump Truck Spare Parts
JINING SHANTE SONGZHENG CONSTRUCTION MACHINERY CO.LTD , https://www.huaxinbrush.com