Application of plastic extruder
Application of ACI Frequency Inverter in Plastic Machinery
The plastic is heated by the extrusion system of the extruder to form a uniform melt. Under the pressure of the plastic extrusion, the screw rod is continuously fixed temperature, quantitative and constant pressure extrusion die. Most of the thermoplastic materials are used in this method. Extruder has a variety of different models and specifications, the most commonly used extruder is a screw extruder. By using AC inverter, the host machine can be used to fully meet the technological requirements of the extruder, and to achieve the necessary process control parameters. After many years of practical operation, the operation is stable, the adaptability of the product is strong, and the economic benefit is obvious.
一.The host is a plastic extruder extruding machine, which is composed of extrusion system, transmission system and heating cooling system.
1. The extrusion system comprises a screw, a machine barrel, a hopper, a die, and a mold are formed into a homogeneous melt by the extrusion system. Under the pressure of the process, the screw rod is continuously extruded out of the nose.
2. Drive system
The function of transmission system is driving screw, and the torque and rotational speed of the screw in the extrusion process are usually composed of motor, reducer, bearing and so on.
3. Heating and cooling device
Heating and cooling is a necessary condition for the plastic extrusion process.
二. Auxiliary equipment
Plastic extrusion unit auxiliary mainly includes a wire releasing device, straightening device, preheating device, cooling device, traction device, meter, spark testing machine and wire device. The use of extrusion unit is not the same as the auxiliary equipment. Such as cutting machine, dryer, printer, etc..
三. Control system
Control system of plastic extrusion machine includes heating system, cooling system and process parameter measuring system, which is mainly composed of electrical appliances, instruments and actuators (i.e. control panel and console). Its main function is: motor control and regulation of the main auxiliary output, which meets technological requirements of speed and power, let the main and auxiliary coordination work together, adjust the temperature, pressure, flow rate of plastic and achieve the control of the entire unit or automatic control.
The electrical control of the extrusion unit can be divided into two parts, transmission control and temperature control, which achieves the control of the extrusion process including temperature, pressure, screw speed, screw barrel cooling, cooling, cooling and diameter of the products. Screw speed control is the core of the whole set of equipment.
Screw speed regulation and stability is one of the important technological requirements of the host drive. The screw speed directly determines the amount of glue and the extrusion speed. Normal production always wants to achieve the highest possible speed to achieve high yield, which needs a large range of speed and speed stability. Because the fluctuation of the rotational speed will lead to the fluctuation of the extrusion quantity, which will affect the quality of the extrusion. In the case of no change in the speed of the traction line, the outer diameter of the cable will be changed. If the traction device line speed fluctuations will also cause changes in the outer diameter of the cable. The screw and the pulling line speed can be reflected by the corresponding instrument on the operating table, which should be closely observed to ensure high quality and high yield.
Disadvantages of traditional control systems:
（1） In the traditional control system of screw extruder, The screw is driven by DC motor. In the case of direct drive, the screw is driven directly by the gear box. In the case of indirect transmission, the screw is driven by a belt and a traction drive. There are some disadvantages in the traditional DC motor: For example, DC motor brush should be replaced once every month. In the multi dust or corrosive environment, the DC motor needs to be cleaned regularly, and sometimes it is even need to clean the cooling air from the outside of the workshop for the DC motor.
（2）The disadvantage of the indirect drive screw extruder is that it is in the belt slip, the belt will cause a certain energy loss, and more mechanical devices will increase the possibility of wear and failure. But the biggest drawbacks of DC motor noise is too large, brush sparking, rotor pollution, motor temperature is too high, the exhaust is not sufficient and the vibration of the motor. Therefore, the use of DC motor of the screw extruder maintenance costs are high, the initial cost of the DC motor is also higher.
四，Realization of frequency conversion transformation.
V11 ACI series inverter is used in extrusion equipment with a high quality of the operating characteristics. This is due to the vector control inverter itself can provide a good product performance decisions.
1）High performance CPU provides higher frequency response
V11 ACI series inverter built-in high speed CPU, with high control precision, fast response frequency performance.
The process requirements of the extruder are mainly controlled by the constant pressure of the outlet, which control the speed at the beginning of the work. The equipment needs to switch to pressure control when reach the pressure demand. Switching process should be no impact and need the control of high frequency inverters which receive the pressure signal.
2） Vector control to provide high torque output at low frequency
The main drive motor of the extruder is driven by the parallel shaft helical gear reducer, which drives the screw to rotate.
In the past, the extruder used V/F control inverter.Due to the starting torque of the load to be considered which needs to set the corresponding torque. If the torque is set too high, the excitation will be too large at low frequency and light load, and it is easy to cause serious heating of the motor, which will affect the stable operation of the equipment.
The no speed sensor vector inverter V11 ACI series, the use of motor identification function can be set up motor model, which Not only can save electric energy, but also eliminate the phenomenon of heating of the motor, and improve the stability of the system due to the increase of the excitation current in low frequency operation.
3）Torque limit and slip compensation are automatically set according to the structure of the motor, the speed control accuracy is as high as 0.1%.