Application of UniMAT PLC in Control System of Plastic Recycling Granulator

1. System overview:

The research institute develops and produces 16-zone single-screw plastic recycling granulator for customers. Its control unit includes host heating system, host speed regulation system, traction control system, cutting control system and some safety protection functions. In the working process, the screw barrel and the mold are heated, and after reaching the set temperature, they are kept warm for a certain period of time, the main machine is turned on to extrude the material, and the traction is turned on after the material is discharged, the cutting length is set on the screen, and the cutting machine is started after reaching the set length.

2. System requirements

• 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 the extrusion system, and is continuously extruded by the screw through the mold under the pressure established in this process to form products.

• Transmission system

The function of the transmission system is to drive the screw to provide the torque and speed required by the screw during the extrusion process, usually consisting of a motor, a reducer and a bearing. At present, the most used drive is the inverter, and the stability of the output of the inverter is directly related to the stability of extrusion.

• Heating and cooling system

Heating and cooling are necessary conditions in the plastic extrusion process:

①Nowadays, plastic recycling and granulating machines usually use electric heating, which is divided into resistance heating and induction heating. The heating sheet is installed in the fuselage, machine neck, and machine head. The heating device heats up the plastic in the barrel externally to reach the temperature required for the process operation.

②The cooling device is set up 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, so as to prevent the plastic from being synthesized, scorched or difficult to shape due to excessive temperature. There are two types of barrel cooling: water cooling and air cooling. Air cooling is more suitable for ordinary small and medium-sized extruders, and water cooling or two separate cooling methods are often used for large-scale extruders. The screw cooling mainly uses central oil cooling to increase material solid delivery. rate, stabilize the output, and improve product quality; but the cooling at the hopper is to enhance the conveying effect on solid materials and avoid sticky plastic particles due to temperature rise to block the feed port, and the second is to ensure the normal operation of the transmission part.

• Automatic control system

The automatic control system includes touch screen, PLC, pressure sensor, temperature sensor and some executive devices. The automatic control system is an interface between man and machine, where all parameters of the machine must be set, monitored and started and stopped. It reflects the degree of automation and reliability of a machine here.

3. System function realization

①Using UniMAT500, the screen can be switched between Chinese and English, with a special keyboard outside, beautiful and generous.

②Using UniMATUN200CPU, temperature control up to 40 zones, can realize dual output control of heating and cooling.

③System speed synchronization, and stand-alone fine-tuning.

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

⑤Running display of main machine status and parameters of the whole line.

⑥Automatic alarm prompt.

⑦There is a screw insulation function to prevent the screw from starting when the material temperature is low.

⑧It can realize the main engine pressure closed loop, traction pressure closed loop and other functions.

⑨It can realize the preheating function of the whole machine.

⑩It can detect whether the heating element is damaged or the thermocouple is broken.

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

⑫Very convenient extended functions, such as weightless feeding.

⑬Guaranteed to be 0Hz starting screw, which prevents damage to the equipment by the high-speed starting screw.

At present, most plastic recycling granulators in China adopt the scheme of temperature control meter control. Although this scheme has the advantage of low price, it has great limitations in control function. After adopting this scheme, the technological parameters of the entire extrusion process, such as melt pressure and temperature, temperature of each section of the fuselage, screw and traction speed, feeding amount, ratio of various raw materials, and current and voltage of the motor, can be adjusted. On-line detection, and with its own inherent closed-loop control. This is extremely beneficial to ensure the stability of process conditions and improve the precision of products. Using the man-machine interface, using the alarm information reflected by the man-machine interface, the staff can easily troubleshoot. Increased production efficiency.