The application of PLC in the plastic extrusion machine control system

A, description of system:

This company is a machinery manufacturer do 16 area of single screw extruder, the control unit contains host heating system, host speed control system, traction control system, cutting control system, and some safety protection function. Its working process, screw tubes, mould heating and heat preservation time after reaches the set temperature, open the host material, open traction after discharge, set the cutting length on the screen, after reaching set length start cutting machine.

Second, the system requirements

(1) extrusion system

Extrusion system, including screw, barrel, hopper, the nose, and mold, plastic and plastic into homogeneous melt by extrusion system, and in this process is set up under pressure, be screw continuous extrusion through the mould forming products.

(2) drive system

The role of the transmission system is driven screw, providing needed in the process of the screw in the torque and rotational speed, usually composed of motor, reducer and bearing, etc. Currently use most drive is the inverter, the inverter output stability or not directly related to the stability of the extrusion.

(3) the heating cooling system

In the process of heating and cooling is plastic extruding and necessary conditions:

1, now squeeze molding machine with electric heating, usually divided into resistance heating and induction heating, heating tablets, neck, head, the local in the fuselage. The plastic inside the heating installation by external heating tube, heating, to reach the temperature of the process operation demand.

2, cooling installation is to ensure that the plastic in the temperature range of technical requirement. Its purpose is to remove the screw rotating the excess heat generated by the shear friction, in order to prevent the temperature is too high to make plastic synthesis, scorch or finalize the design difficult. Barrel cooling can be divided into water and air cooling two kinds, ordinary small and medium-sized squeeze molding machine adopts air cooling is good, while more of the large separation by water or two ways of cooling; Screw oil cooling cooling mainly adopts center, purpose is to increase the rate of material solid walks, stable feed rate, improve product quality at the same time; But the cooling in the hopper, one is in order to enhance the transport of solid materials, avoid make jam the material plastic grains sticky with heating, 2 it is to guarantee the normal work of the local transmission.

(4) control system

Automatic control system consists of touch screen, PLC, pressure sensors, temperature sensors and some execution devices, etc. Automatic control system is an interface of man and machine, the machine all the parameters are set here, monitoring and the start-stop of the machine. Response to a degree of automation and reliability of the machine is here.

Three, system configuration and function realization

System composition:

Siemens man-machine interface SMARTLINE700 matches the company designed for molding machine keyboard

CPUUniMATCPU224

16 tcunimatun231-7 pl22

4 aiunimatun231 hc22 0

8 bf22 diunimatun221-1

32 bl22 dounimatun222-1

Siemens inverter, 440

Control scheme

The characteristics of this control scheme is, host and traction speed of the communication control reduces the PLC analog output of 2, 4 analog input, 2 emergency alarm input, digital output to 2. Using 16 road temperature measurement module, high integration, collecting signal of high precision, fast speed, using the PID temperature control precision, static is less than 1 degree. Low prices, the most obvious advantage of this set of system temperature control cost 1 road in about 100 yuan, and normal temperature control table price is quite, but after using this system the mechanical control level a level, improve the competitiveness of products, also improve the product's profits.

System function realization

1, Siemens SMARTLINE700 color touch-screen, screen can switch in both Chinese and English, to go for the keyboard, the beauty is generous.

2, using UniMATUN200CPU, the temperature control of as many as 40 area, can realize double cooling/heating output control.

3, the system speed synchronization, as well as stand-alone fine-tuning.

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

5, all the operation of the main machine status and parameters display.

6, automatic alarm prompt.

7, a screw heat preservation function, to prevent low temperature start the screw.

Eight, can realize the host pressure closed loop, traction pressure closed loop, and other functions.

9, can achieve the function of the whole machine preheating.

10, can detect damage is the original heating and thermocouple wire break.

11, can prevent the screw running on an empty stomach, avoid glue (axis) phenomenon.

12, easily extend the functionality, such as gravity feed.

13, guarantee is 0 hz start screw, prevent damage of the high-speed start screw device.

At present domestic most of the extruder is controlled by temperature control table, although the scheme has the advantage of low price but of great limitations on the control function. After using this solution to the whole process of extrusion process parameters such as melt pressure and temperature, paragraphs body temperature, screw and traction speed, feed feed rate, ratio of various materials, such as current voltage of the motor parameters online detection, and its intrinsic to the closed-loop control. This to ensure stability in the process conditions, improve the accuracy of the product is very favorable. Man-machine interface, using human-machine interface reaction of alarm information, the staff is easy to troubleshoot. Improve the production efficiency.

The control scheme of applications including:

- plastic different profile extrusion production line

- single wall, wall and foam pipe extrusion line

- plastic sheet extrusion production line

- plastic sheet extrusion line

- machine co-extrusion production line, the single-layer/multi-layer plastic film production line

- granulating production line

Aluminous model multiple tube production line

Four, the conclusion

This control system in plastic extruding system achieve the expected purpose, according to important, plastic extrusion system in the practical choice one hundred million d automation UniMATCPU and UniMATI/O module, improve the system stability, and to a certain extent, save the cost system. In the operation state of the system is good, has been applied to the production lines, brought objective of benefit to the customer, has good application prospect.