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The application and energy saving of frequency converter in plastic knitting industry

this paper introduces the application and energy saving principle of frequency converter in plastic knitting industry, and explains that the frequency conversion speed regulation technology has the promotion and application value in plastic knitting equipment

Keywords: frequency converter, plastic knitting, speed regulation, energy saving, economic benefits


the plastic knitting industry has a history of nearly three decades in China. The plastic knitting industry has grown from scratch, from small to large, has become an indispensable part of the national economy, and plays a decisive role in product packaging

transmission technology is widely used in industrial equipment, and plastic knitting equipment is no exception. With the development of manufacturing level in China and transmission technology at home and abroad, plastic knitting equipment has changed from the early 5 The tested sample should be fixed in the middle of the sample rack as far as possible, and cannot be placed on one side casually, otherwise it will cause the basket of the cold and hot impact test box to tilt, and the single motor mechanical coupling drive will develop to the independent speed regulation of multiple motors, from the earliest slip motor to DC motor. With the rapid development of frequency conversion technology, frequency conversion speed regulation has become a trend, a trend, and three-phase asynchronous motor can be applied to all power links of plastic knitting equipment, The full frequency conversion control mode of the production line is realized

variable frequency speed regulation has the advantages of small volume, light weight, high precision, strong versatility, advanced technology, rich functions, complete protection, high reliability, simple operation and so on. It is superior to any previous speed regulation mode, and it is also simpler and more convenient in maintenance than other control modes. Although China's industry has developed rapidly in recent years, the development of power resources is still lagging behind the industrial development, which directly affects the development of China's industry. Power consumption is also an important part of energy consumption in enterprise production, which directly affects the economic benefits of enterprises

about 80% of the electric energy of plastic knitting enterprises is consumed by various motor drives. AC motors can not only drive various process transmission rollers, but also drive fan loads, which has considerable power-saving potential, which also provides a broader application world for the application of frequency conversion technology in plastic knitting equipment

1 principle of variable frequency speed regulation

variable frequency speed regulation is a speed regulation form adopted according to the working principle of three-phase asynchronous motor. The motor speed regulation formula is n=60f (1-s)/p, where: n is the speed of the motor; P is the magnetic field of motor stator winding. Jinan bububujingzhi experimental machine factory Jinan new era Gold Testing Instrument Co., Ltd. has been producing and manufacturing for more than 10 years; F frequency of power supply for motor; S is the slip rate. The motor used in plastic knitting industry is generally 4 poles, and the number of magnetic poles is 2. The power frequency of our country is 50Hz. According to the formula calculation, the synchronous speed of this motor is 1500r/min. Therefore, when the number of poles of the motor is constant, the speed regulation can only be carried out by changing the power supply frequency f of the motor according to the formula. The speed of the asynchronous motor corresponds to the speed of the synchronous motor. Changing the power supply frequency of the motor changes the speed of the motor. When the power frequency increases, the synchronous speed n increases, and the actual speed also increases; The power frequency decreases, the synchronous speed of the motor decreases, and the actual speed of the motor also decreases. This kind of speed regulation by changing the voltage and frequency of the motor is called variable frequency speed regulation. In the whole process of variable frequency speed regulation, under a fixed torque T, the slip rate s is basically unchanged. With the decrease of motor speed n, the motor magnetic field angular velocity bristle also decreases, and the motor input power pm=t bristle and output power p=pm (1-s) also decrease. The loss has not increased, so it can be seen that variable frequency speed regulation is a more efficient speed regulation method in motor control. Variable frequency speed regulation of motor can realize stepless speed regulation function, and according to different load types, the relationship between V and F can be flexibly adjusted to meet the application of various occasions

2 application of variable frequency speed regulation

2.1 application of variable frequency speed regulation in plastic knitting equipment extruders have many kinds and uses, but their principles are basically the same, that is, melt and extrude plastic

its working principle is that the screw rotates in the barrel, and after three links of solid conveying, melt conveying and melt conveying, the melt enters the die head from the barrel. If it is a round die head, the melt is pulled, cut and divided into flat wires after extrusion, and can also be blown. In the case of flat die head, the melt is pulled after extrusion and cut into wires, which can also produce flat wires. It can also be used to produce composite cloth after extrusion flat die and coating die with woven cloth, paper, etc. The transmission system of the extruder is composed of speed regulating motor, reducer, coupling, base, bearing, etc. Its zigzag percentage changes from 8% to 43% to provide a stable speed and torque for the screw, which provides power and transmits torque for the extruder. Due to the needs of the process, there are two requirements for the screw speed of the extruder, one is stepless speed regulation, and the other is a certain adjustment range, so as to control the extrusion volume to meet different raw materials and processing requirements. Since the head pressure of the extruder is high when starting, it needs an acceleration process from static to rotation, and the screw speed will gradually accelerate from slow, so the governor is required to control the motor to run smoothly at low speed when starting. In the process of use, the pressure of the screw and the speed of the extruder motor are not constant, and there are fluctuations in a working cycle, which is also not allowed in the process. This is because on the one hand, it causes a waste of power, on the other hand, it increases the friction between the barrel and the screw, and generates a lot of heat, which requires the installation of cooling fans, thus further wasting energy. At the same time, when the motor works on a low-speed load, the power factor is low and the electric reactive power consumption is also large. To sum up, there is energy waste in the traditional control mode. The best working mode is to adopt the frequency conversion speed regulation scheme, which has the characteristics of fast response to load changes, strong short-term overload capacity, and can accurately control the pressure of the screw. Taking Schneider inverter atv71 as an example, using the built-in PID regulating circuit, the melt pressure in the barrel is controlled in real time. Under the condition of ensuring the pressure required for work, the working energy consumption is greatly reduced, the electric quality is effectively improved, and the reactive power is saved

2.2 application of variable frequency speed regulation on drafting roller

drafting roller is an important part of plastic knitting equipment. The control of drafting ratio determines the control of two important indicators: relative breaking force and elongation at break of flat wire. At the same time, it also determines whether to split wires and whether the linear density is uniform. The draft ratio adjustment control diagram is shown in Figure 1

taking Figure 1 as an example, to realize the drafting ratio is to form a speed difference between the traction roll and the drafting roll, so that the flat wire can be stretched between the two rolls, meeting the requirements of the process. In order to ensure the quality of products, the drafting roll and traction roll motors need to have high control accuracy, and have a good synchronization effect when the speed is increased and decreased synchronously. The variable frequency speed regulation system is a high-efficiency and high-performance speed regulation system, which fully meets the process requirements

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