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Application in control system of plastic extrude

Abstract: Aiming at the problems of high cost, low speed and low precision in the control system of plastic extruder, the application of UniMAT PLC in the control system of plastic extruder was put forward. The results show that UniMAT PLC reduces the cost and achieves the effect of fast speed and high accuracy.

Keywords: 16TC (UN 231-7PL22), UniMAT CPU224,485 communication

1. System overview,

The company's 16-zone single screw extruder for machinery manufacturers, its control unit contains the host heating system, host speed control system, traction control system, cutting control system and some safety protection functions. Its working process, screw barrel, mold heating, after reaching the set temperature holding a certain time, open the main machine extrusion, after discharging open traction, set the cutting length on the screen, reach the set length to start the cutting machine.

2.system requirements

(1) extrusion system

The extrusion system consists of a screw, barrel, hopper, head and die. Plastic is plasticized into a uniform melt through the extrusion system and is continuously extruded by the screw to form a product through the die under the pressure set in the process.

(2) transmission system

The function of the drive system is to drive the screw, which provides the torque and rotational speed required by the screw in the extrusion process, usually composed of motor, reducer and bearing. At present, the most commonly used driver is the frequency converter, the stability of the output of the frequency converter is directly related to the stability of the extrusion.

(3) heating and cooling system

Heating and cooling are the necessary conditions for plastic extrusion.

1. Now the extruder usually uses electric heating, divided into resistance heating and induction heating, heating sheet installed in the fuselage, neck, nose parts. The heating installation is made of the plastic inside the external heating cylinder, which is heated to reach the required temperature for the process operation.

2, cooling installation is to ensure that the plastic is in the temperature range of the process requirements. Its role is to sweep the screw rotation shear friction generated by excessive heat, to prevent the temperature is too high to make plastic synthesis, scorching or setting difficult. Barrel cooling can be divided into water cooling and air cooling. Air cooling is more suitable for ordinary small and medium-sized extruders, while water cooling or two separate cooling methods are used for large-scale extruders. One is to enhance the conveying effect of solid materials, to avoid the plastic particles sticking and blocking the inlet due to heating, and the other is to ensure the normal operation of the transmission part.

(4) automatic control systemThe automatic control system includes touch screen, PLC, pressure sensor, temperature sensor and some executive devices. Automatic control system is an interface between human and machine. All the parameters of the machine should be set, monitored and started or stopped here. The automation and reliability of a machine are reflected here.

Report errors

3.system configuration and function realization

System composition:

SIEMENS human-machine interface SMARTLINE 700 is equipped with the keyboard designed for plastic machine.

CPU UniMAT CPU224

16TC UniMAT UN231-7PL22

4AI UniMAT UN231-0HC22

8DI UniMAT UN221-1BF22

32DO UniMAT UN222-1BL22

SIEMENS inverter 440

Control scheme.


The main engine and traction governor adopt communication control to reduce the analog output of PLC by 2 analog input by 4, alarm input by 2 and digital output by 2. Adopting 16-channel temperature measuring module, it has high integration, high precision and speed of collecting signal, high precision of temperature control by PID, and less than 1 degree static state. The most obvious advantage of this system is low price, the cost of one way temperature control is about 100 yuan, and the price of ordinary thermometer is equivalent, but the use of this system to improve the level of mechanical control of a grade, improve the competitiveness of the product, but also improve the profit of the product.


System function realization

1. Using Siemens SMARTLINE 700 color touch screen, the screen can be switched between Chinese and English, with a special keyboard, beautiful and generous.

2. Adopting UniMAT UN200 CPU and temperature control of up to 40 zones, heating and cooling dual output control can be realized.

3.system speed synchronization, and single machine fine tuning.

4. speed real-time display, torque, current and pressure detection.

5., the operation and display of main machine status and parameters across the whole line.

6.Automatic alarm prompt.

7, screw insulation function, to prevent the start of the screw when the material temperature is low.

8.can achieve the main engine pressure closed-loop, traction pressure closed-loop function.

9. It can realize the pre heating function of the whole machine.

10. It is possible to detect whether the heating is damaged or not.

11. It can prevent the screw from running on an empty stomach and avoid sticking.

12. very convenient expansion function, such as weightless feed.

13. guarantee is 0Hz start screw, prevent high-speed start screw damage equipment.


At present, most extruders in China adopt the temperature control meter control scheme. Although the scheme has the advantage of low price, it has great limitations in the control function. With this scheme, the parameters of the whole extrusion process, such as melt pressure and temperature, body temperature of each section, rotational speed of screw and traction, feed rate, ratio of various raw materials, current and voltage of motor, can be measured on-line and controlled by its inherent closed loop. This is very advantageous for ensuring the stability of technological conditions and improving the accuracy of products. Using the man-machine interface and the alarm information reflected from the man-machine interface, the staff can easily remove the fault. The production efficiency is improved.


The application areas of these control schemes include:

Plastic profile extrusion line

Single wall, multi wall and foaming pipe extrusion line

- plastic sheet extrusion line

- plastic sheet extrusion line

Multi Machine Co extrusion production line, single layer / multilayer plastic film production line.

- granulation production line

- aluminum plastic composite pipe production line

4.concluding

According to the importance of the plastic extrusion system in practice, the control system chooses the UniMAT CPU and UniMAT I/O modules of billion-dimension automation, which improves the stability of the system and saves the cost of the system to a certain extent. The system is in good condition after being put into operation, and has been applied to many production lines, bringing objective benefits to customers, and has a good application prospect.


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