First, the system overview:
The company's 16-zone single-screw extruder for machinery manufacturers, its control unit includes host heating system, host speed control system, traction control system, cutting control system and some safety protection functions. The working process, the screw barrel, the mold heating, after reaching the set temperature, keep warm for a certain period of time, open the host to squeeze the material, open the traction after discharging, set the cutting length on the screen, and start the cutting machine after reaching the set length.
Second, the system requirements
(1) Extrusion system
The extrusion system includes a screw, a barrel, a hopper, a machine head, and a mold. The plastic is plasticized into a uniform melt through an extrusion system, and is continuously extruded by a screw through a mold under the pressure established in the process. Products.
(2) Transmission system
The function of the drive system is to drive the screw, providing the torque and speed required by the screw during the extrusion process, usually consisting of a motor, a reducer and a bearing. The most used drive currently is the inverter, and the stability of the inverter output is directly related to the stability of the extrusion.
(3) Heating and cooling system
Heating and cooling are essential for plastic extrusion:
1. Today's extruders usually use electric heating, which is divided into resistance heating and induction heating. The heating sheets are installed in the fuselage, the neck and the parts of the machine head. The plastic in the external heating cylinder is heated and installed to raise the temperature to reach the temperature required for the process operation.
2. Cooling installation is to ensure that the plastic is in the temperature range required by the process. Its function is to remove the excess heat generated by the shear friction of the screw rotation to prevent the temperature from being too high to make the plastic synthesis, scorch or stereotype difficult. The barrel cooling is divided into two types: water cooling and air cooling. The ordinary medium and small extruders are more suitable for air cooling. The large ones are mostly water cooled or separated by two methods. The screw cooling is mainly center oil cooling. The purpose is to increase the material solids. Rate, stable discharge, and improve product quality; but in the hopper cooling, first, in order to enhance the transport of solid materials, to avoid the plastic particles sticky to block the material due to temperature rise, the second is to ensure the local operation of the transmission.
(4) Automatic control system
The automatic control system includes a touch screen, a plc, a pressure sensor, a temperature sensor, and some actuators. The automatic control system is an interface between the human and the machine. All the parameters of the machine must be set here, monitoring and starting and stopping of the machine. The degree of automation and reliability of a machine is reflected here.
Third, system configuration and function realization
System composition:
Siemens man-machine interface SMARTLINE700 with the keyboard designed by our company for plastic machine
CPUUniMATCPU224
16TCUniMATUN231-7PL22
4AIUniMATUN231-0HC22
8DIUniMATUN221-1BF22
32DOUniMATUN222-1BL22
Siemens inverter 440
Control plan
The characteristic of this control scheme is that the main engine and the traction governor adopt communication control to reduce the analog output of plc 2, the analog input 4, the alarm point input 2, the digital output start and stop 2. Adopting 16-channel temperature measurement module, the integration degree is high, the acquisition signal has high precision and high speed, and the precision of temperature control by PID is high, and the static is less than 1 degree. The most obvious advantage This system has a low price. The cost of one-way temperature control is about 100 yuan, which is equivalent to the price of an ordinary temperature control meter. However, after using this system, the mechanical control level is improved by one grade, which improves the competitiveness of the product and improves the product. The profit of the product.
System function implementation
1, using Siemens SMARTLINE700 color touch screen, the screen can be switched between Chinese and English, with a dedicated keyboard, beautiful and generous.
2, using UniMATUN200CPU, up to 40 zone temperature control, can achieve heating and cooling dual output control.
3, system speed synchronization, and single machine fine-tuning.
4, speed real-time display, torque, current and pressure detection.
5. The running display of the main machine status and parameters of the whole line.
6, automatic alarm prompts.
7. There is screw insulation function to prevent the screw from starting when the material temperature is low.
8, can achieve the main pressure closed loop, traction pressure closed loop and other functions.
9, can achieve the pre-heating function of the whole machine.
10. It can detect whether the heating element is damaged or the thermocouple is broken.
11. It can prevent the screw from running on an empty stomach and avoid the phenomenon of sticking bars (holding shaft).
12, very convenient expansion features, such as weight loss feeding.
13. It is guaranteed that the 0Hz starting screw prevents the high-speed starting screw from damaging the equipment.
At present, most domestic extruders adopt the scheme of temperature control table control. Although this scheme has the advantage of low price, it has great limitations in control functions. After adopting this scheme, the parameters of the whole extrusion process such as melt pressure and temperature, the temperature of each section of the fuselage, the speed of the screw and the traction, the feeding amount, the ratio of various raw materials, the current and voltage of the motor, etc. can be used. Online detection, and use its own inherent closed-loop control. This is extremely advantageous for ensuring the stability of the process conditions and improving the accuracy of the product. Using the human-machine interface and using the alarm information reflected by the human-machine interface, the staff can easily eliminate the fault. Increased production efficiency.
The application areas of the above control schemes include:
-Plastic profile extrusion line
-Single wall, multi-wall and foam pipe extrusion line
-Plastic sheet extrusion line
-Plastic sheet extrusion line
-Multi-machine co-extrusion production line, single-layer/multi-layer plastic film production line
- Granulation production line
-Aluminum-plastic composite pipe production line
Fourth, the conclusion
The control system achieves the intended purpose in the plastic extrusion system. According to the importance of the plastic extrusion system in practical use, the UniMATCPU and UniMATI/O modules of Yiwei Automation are selected to improve the stability of the system and save to a certain extent. The system cost. The system is in good condition after being put into operation, and has been applied to multiple production lines, which brings objective benefits to customers and has a good application prospect.
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