1、Introduction
The principle of a plastic extruder is that solid plastic melts and plasticizes under the conditions of heating and the rotation pressure of the extruder screw, and continuous plastic products with the same cross-sectional shape as the die are produced through a die of a specific shape. The drive of the extruder used to be mostly DC drive or electromagnetic speed control. The former has complicated maintenance and huge costs, which affect the efficiency of equipment use, while the latter has low speed control accuracy and low product grade, which greatly affect the development of the extruder.
Due to the rapid development of AC variable frequency technology in our country in recent years, and frequency conversion speed regulation is incomparable in terms of frequency range, dynamic response, speed control accuracy, low frequency torque, speed difference compensation, communication function, intelligent control, power factor, work efficiency and convenience of use, it is highly favored by extruder manufacturers. In new extruder machinery, especially plastic machinery, high-performance inverters have been adopted, and existing old extruder equipment will also enter a new round of transformation.
2、Control scheme and principle
（1）Control process
The structure of the screw extruder is shown in the figure below. After the plastic granules are fed from the hopper, they are heated and plasticized, and then pushed to the outlet of the extruder by the rotation of the screw. The final product shape is determined by the basic die head. The typical screw speed of a common single screw extruder is about 100r/min, while that of a twin-screw extruder for mixing is 200r/min~500r/min. The speed of a low-speed twin-screw extruder used for profile extrusion is usually 10r/min~40r/min.
Figure 2.1 Structure of Screw Extruder
（2）FR500A Control Principle Diagram
The FRECON FR500A series inverter 55KW is used for drive on site. The main control part adopts analog input for speed regulation, and the external control button for startup. The FRECON FR500A series inverter has the following unique advantages: open-loop vector control, achieving high precision and high torque, with multiple protection measures. The torque response time is extremely short, and it has an automatic torque boost function at low speed; software and hardware filtering processing effectively improves system reliability. It significantly reduces noise interference and prevents electromagnetic interference with other equipment from causing misoperation.
Figure 2.2
（3）Control Requirements
ØThe inverter cannot operate if the temperature of the heating device has not reached the set temperature
ØAn interlock circuit must be formed through an external circuit
ØThe inverter cannot start before the hydraulic pump starts
ØWhen equipment malfunctions, the inverter must stop operating
（4）Parameter debugging table
Figure 2.3
3、FR500A Series Inverter Application Site
（1）FR500A Control System
（2）FRECON Technology Engineer Working Site
（3）Extrusion Machine Equipment
（4）Power Unit
