Application case of frequency converter in plastic industry
With the widespread application of plastic products and the rapid increase in output, plastic machinery has become an important technical equipment in the building materials, packaging, electronic and electrical, automotive, petrochemical, machinery and other industries, and the demand has surged. The plastic machinery industry has become my country’s economy in the 21st century. The developing sunrise industry. With the development of my country's plastics industry, the growth rate of the plastics machinery industry in recent years has been around 30%, making it one of the fastest growing industries.
Today, when the world's energy is increasingly depleted, energy conservation has long been placed in a prominent position. Compared with some energy-rich countries in the world, China is an energy-short country. However, our utilization rate of energy, especially the most important form of utilization of energy, is very low, and there is an alarming waste phenomenon. In the development of new products, the development of new equipment and the transformation of original equipment, energy consumption must be taken as an important indicator. The plastic industry is a sunrise industry in the 21st century. However, its products are mainly produced through physical methods such as heating and pressurizing, which determines the high energy consumption characteristics of its production methods. For high energy consumption plastic products and equipment, how to save electricity has become an important means to enhance product competitiveness.
Plastic machinery is an important pillar of the development of the plastics industry. It provides advanced technology and equipment for the plastics industry. Its development is the basis for the development of the plastics industry and is also affected by the development of the plastics industry. From a global perspective, the three major categories of plastic machinery are injection molding machines, extruders: extrusion lines and blow molding machines, which account for more than 80% of the total output value of plastic machinery, and injection molding machines account for the total of these three types of machinery. More than half. We talk about the application of frequency converters in plastic machinery from personal experience, and make an introduction from their respective characteristics and field applications.
1. Brief introduction of special energy-saving system for injection molding machine
To make a good energy-saving system for injection molding machines, first start with injection molding. The injection molding process is generally divided into the following steps: mold clamping→injection holding pressure→melting glue feeding→cooling and shaping→mould opening→thimble. The completion of each action has a subtle coordination of several parameters such as time, pressure, speed, position, etc. That is to say, the displacement at a certain position has corresponding pressure and speed, and the pressure and the pressure at different positions and times The speed is variable. At the same time, after each action is completed, a termination signal is sent to the program controller, and the program controller sends an instruction to execute the next action after receiving the signal. In addition, the injection molding machine system itself has some weaknesses: First, there is a very violent sudden change in the movement of the injection molding machine: for example, during the clamping process, rapid mold clamping→slow low pressure mold protection→high pressure and high speed mold clamping is very sudden. In the injection process, the working conditions of slow injection→fast→slow→fast→slow injection are also very severe, and the impact on the machine is very large, affecting the life of the entire injection molding system. Second, the operating oil circuit brake cannot reach the designed accuracy. The opening and closing of the oil circuit brake depends on the solenoid valve, and the action of the solenoid valve depends on the voltage and current provided by the process controller, because most injection molding machines have Without infinite loop control, the valve opening and closing accuracy will be greatly reduced, especially when the valve opening and closing degree is below 10% and above 90%, the repeatability and stability of the action are extremely poor, and a certain action is here. It is difficult to guarantee its stability and repeatability when executed in the state. Third, the oil cylinder that executes the action has its own oil seal damage and internal leakage, and the reliability and stability of the action is not high. This is because most of the time, the actual fuel consumption of the load is less than the fuel supply of the oil pump, causing the hydraulic oil under high pressure to overflow through the overflow valve, proportional valve and other hydraulic components. The overflow part not only does not do any useful work, but also generates heat, causing the hydraulic oil to heat up, which is energy-consuming and harmful. After adopting the energy-saving system of the injection molding machine, these problems can be solved well, which not only improves the accuracy and stability of the entire injection molding system, reduces the huge mechanical shock, extends the service life of the system, and saves a lot of electric energy.
2. Brief introduction of frequency conversion application of extruder:
For example, the production line of plastic pipe making machine is mainly composed of plastic extruder, cooling tank and tractor. Before the transformation, the extruder and tractor were driven by AC slip motors, which had high power consumption, low transmission efficiency, poor speed accuracy, and insufficient speed, which affected the quality of the product and required technical transformation. After on-site investigation by our company's engineers, we believe that the use of frequency conversion speed regulation can solve the above-mentioned drawbacks.
After our company's frequency conversion transformation, the speed range, starting characteristics, dynamic response, adjustment accuracy, output characteristics, economic indicators and convenience of operation and monitoring are all superior to electromagnetic speed control. In addition, frequency conversion speed regulation also has the advantages of complete protection functions, strong versatility, small maintenance workload, safe and reliable operation, low power consumption, and long equipment life. It can start from zero to increase the speed steadily, and can choose the speed-up and speed-down curve, which saves significant energy and is highly praised by operators and maintenance personnel. It is worthy of being promoted on similar plastic processing machines, such as granulator, pipe making machine, mixing machine, etc.
3. Brief introduction of frequency conversion of hydraulic plastic hollow molding machine:
Based on many years of production site experience, the author has made in-depth investigations and studies on the performance of various types of plastic hollow molding machines in practice, and thus targeted various grades of hollow molding machines for partial or complete machines. The transformation of the company puts forward the concept of a frequency conversion hydraulic plastic hollow molding machine.
3.1 Working principle and characteristics of plastic hollow molding machine
According to the different driving methods, plastic hollow molding machines can be divided into two types: pneumatic and hydraulic. No matter which method is adopted, the mold is sent to the glue-bonding position, and after receiving the rubber blank, it returns to the blowing position. The compressed air of 5-6Mpa is introduced into the mold cavity through a blowing needle to blow the rubber blank into shape. The PLC-controlled pneumatic single/double-station plastic hollow molding machine adopts a fully pneumatic drive, which has fast response and high efficiency, but it is precisely because of the pneumatic method that according to the formula F=P·S. Where F is the clamping force, P is the working air pressure of the system, and S is the effective area of the piston. It can be seen that when the working pressure of the system is a certain value, the clamping force is proportional to the effective area of the piston. Once the cylinder diameter is determined, the clamping force is also determined. Taking the cylinder diameter of 150mm as an example, at a working pressure of 6MPa, only 10.38KN of force can be produced. So this type of model is only suitable for bottles under 500ml. At the same time, it should be pointed out that due to the use of full pneumatics, the air consumption is indirectly increased. If the power consumption of the air pump and its maintenance costs are converted into it, the unit consumption of the product is quite high.
It can be seen from the above that if a container with a capacity of 500ml or more is to be produced, only the clamping system using hydraulic cylinders is used. The hydraulic system can generate enough pressure to ensure the production and quality of various large-volume products. But today's most advanced hydraulic servo system is still expensive. For example, the Japanese Yuken Company uses the EFRG-03-125-C-50 proportional pressure flow control valve and the price is about 7,000 yuan, and a servo cylinder with a stroke of only 14mm and a bore of 120mm is priced at more than 10,000 yuan. Although the proportional pressure and flow control system is expensive, and the power consumption of the hydraulic system is about 30% of the power consumption of the whole machine, its excellent dynamic characteristics are enough to ensure the stable quality of the product, so it is still widely used [ 1, 2].
According to calculations, in addition to the externally provided air supply system, the energy consumption of the whole machine, taking the hydraulic double-station machine with the extruder screw diameter of 70mm as an example, when using PE (polyvinyl chloride) as raw material to produce 4500ml containers, electric heating Heating accounts for 22.6% of the power consumption of the whole machine, the motor of the extruder conveying system is 11kW, accounting for about 53%, and the hydraulic system is a 7.5kW motor, accounting for about 24.4%. In the hydraulic single station machine, when producing 280ml volume of PE material products, the power consumption of the hydraulic system accounts for 41.35% of the power consumption of the whole machine, electric heating accounts for 42.33%, and the extruder conveying system (frequency drive has been changed) consumes Electricity accounts for 16.32%. At present, the practice of most hollow molding machine manufacturers is to change the speed control of the slip motor to the frequency conversion speed control only in the extruder conveying system.
3.2 Working principle of variable frequency hollow molding machine
In summary, how to reduce the power consumption of the hydraulic system has become a key issue for the new generation of high-efficiency and energy-saving hydraulic systems. Traditional control theory pays attention to the method of system stability, which is to first ensure the existence of a stable system, and then use PID and other methods to adjust when the system stability changes. Constant pressure hydraulic system is its typical representative. The price is high energy consumption. The proportional hydraulic system has made great progress compared with the former. However, it can be seen from the structure of the proportional pressure proportional flow valve that it is still an extension of the above idea, but the valve opening is increased as much as possible by means of internal overflow. However, modern control theory pays more attention to dynamic stability and dynamic adjustment. As we all know, variable frequency speed regulation is a high-efficiency and high-performance speed regulation method, especially suitable for cage asynchronous motors. The development and application of pulse width modulation (PWM) technology, vector control technology, and speed sensorless technology have made AC motor variable frequency speed regulation have largely replaced DC speed regulation systems in many occasions. Judging from the current development status of the industrial control field, it also represents the level and direction of electric drive. With the continuous advent of various high-power intelligent power electronic devices and the rapid development of computer technology, frequency conversion speed regulation technology has become more mature. Its dynamic response speed and overload capacity have been able to meet the requirements of general hydraulic system dynamic stability, and its price has dropped to a level generally acceptable to users [3]. As a result, we incorporate variable frequency speed regulation technology into the hydraulic control system, transform the traditional quantitative pump into a "variable pump", and change the return flow adjustment into a volumetric adjustment. According to the production process, "distribute on demand" to achieve The purpose of efficient power saving.
The energy consumption of the whole machine consists of four parts, which are the heating system of the hollow molding machine, the extrusion mechanism, the proportional hydraulic system and the compressed air source. Except for the compressed air source provided by the external system, the rest are all provided by the power and electricity of the machine. The difference between this machine and the current common hollow molding machine is that it adds two links, one is the insulation system, and the other is the frequency conversion hydraulic system with D/A converter and synchronous controller. Regarding the thermal insulation system, a composite silicate thermal insulation material is only added to the heating tube, about 30mm thick, because the material is non-corrosive, has excellent thermal insulation performance and light bulk density. In one fell swoop, the heating system saves 30% of electricity. Because the insulation system is very simple, it is not the focus of this article.
Today, when the world's energy is increasingly depleted, energy conservation has long been placed in a prominent position. Compared with some energy-rich countries in the world, China is an energy-short country. However, our utilization rate of energy, especially the most important form of utilization of energy, is very low, and there is an alarming waste phenomenon. In the development of new products, the development of new equipment and the transformation of original equipment, energy consumption must be taken as an important indicator. The plastic industry is a sunrise industry in the 21st century. However, its products are mainly produced through physical methods such as heating and pressurizing, which determines the high energy consumption characteristics of its production methods. For high energy consumption plastic products and equipment, how to save electricity has become an important means to enhance product competitiveness.
Plastic machinery is an important pillar of the development of the plastics industry. It provides advanced technology and equipment for the plastics industry. Its development is the basis for the development of the plastics industry and is also affected by the development of the plastics industry. From a global perspective, the three major categories of plastic machinery are injection molding machines, extruders: extrusion lines and blow molding machines, which account for more than 80% of the total output value of plastic machinery, and injection molding machines account for the total of these three types of machinery. More than half. We talk about the application of frequency converters in plastic machinery from personal experience, and make an introduction from their respective characteristics and field applications.
1. Brief introduction of special energy-saving system for injection molding machine
To make a good energy-saving system for injection molding machines, first start with injection molding. The injection molding process is generally divided into the following steps: mold clamping→injection holding pressure→melting glue feeding→cooling and shaping→mould opening→thimble. The completion of each action has a subtle coordination of several parameters such as time, pressure, speed, position, etc. That is to say, the displacement at a certain position has corresponding pressure and speed, and the pressure and the pressure at different positions and times The speed is variable. At the same time, after each action is completed, a termination signal is sent to the program controller, and the program controller sends an instruction to execute the next action after receiving the signal. In addition, the injection molding machine system itself has some weaknesses: First, there is a very violent sudden change in the movement of the injection molding machine: for example, during the clamping process, rapid mold clamping→slow low pressure mold protection→high pressure and high speed mold clamping is very sudden. In the injection process, the working conditions of slow injection→fast→slow→fast→slow injection are also very severe, and the impact on the machine is very large, affecting the life of the entire injection molding system. Second, the operating oil circuit brake cannot reach the designed accuracy. The opening and closing of the oil circuit brake depends on the solenoid valve, and the action of the solenoid valve depends on the voltage and current provided by the process controller, because most injection molding machines have Without infinite loop control, the valve opening and closing accuracy will be greatly reduced, especially when the valve opening and closing degree is below 10% and above 90%, the repeatability and stability of the action are extremely poor, and a certain action is here. It is difficult to guarantee its stability and repeatability when executed in the state. Third, the oil cylinder that executes the action has its own oil seal damage and internal leakage, and the reliability and stability of the action is not high. This is because most of the time, the actual fuel consumption of the load is less than the fuel supply of the oil pump, causing the hydraulic oil under high pressure to overflow through the overflow valve, proportional valve and other hydraulic components. The overflow part not only does not do any useful work, but also generates heat, causing the hydraulic oil to heat up, which is energy-consuming and harmful. After adopting the energy-saving system of the injection molding machine, these problems can be solved well, which not only improves the accuracy and stability of the entire injection molding system, reduces the huge mechanical shock, extends the service life of the system, and saves a lot of electric energy.
2. Brief introduction of frequency conversion application of extruder:
For example, the production line of plastic pipe making machine is mainly composed of plastic extruder, cooling tank and tractor. Before the transformation, the extruder and tractor were driven by AC slip motors, which had high power consumption, low transmission efficiency, poor speed accuracy, and insufficient speed, which affected the quality of the product and required technical transformation. After on-site investigation by our company's engineers, we believe that the use of frequency conversion speed regulation can solve the above-mentioned drawbacks.
After our company's frequency conversion transformation, the speed range, starting characteristics, dynamic response, adjustment accuracy, output characteristics, economic indicators and convenience of operation and monitoring are all superior to electromagnetic speed control. In addition, frequency conversion speed regulation also has the advantages of complete protection functions, strong versatility, small maintenance workload, safe and reliable operation, low power consumption, and long equipment life. It can start from zero to increase the speed steadily, and can choose the speed-up and speed-down curve, which saves significant energy and is highly praised by operators and maintenance personnel. It is worthy of being promoted on similar plastic processing machines, such as granulator, pipe making machine, mixing machine, etc.
3. Brief introduction of frequency conversion of hydraulic plastic hollow molding machine:
Based on many years of production site experience, the author has made in-depth investigations and studies on the performance of various types of plastic hollow molding machines in practice, and thus targeted various grades of hollow molding machines for partial or complete machines. The transformation of the company puts forward the concept of a frequency conversion hydraulic plastic hollow molding machine.
3.1 Working principle and characteristics of plastic hollow molding machine
According to the different driving methods, plastic hollow molding machines can be divided into two types: pneumatic and hydraulic. No matter which method is adopted, the mold is sent to the glue-bonding position, and after receiving the rubber blank, it returns to the blowing position. The compressed air of 5-6Mpa is introduced into the mold cavity through a blowing needle to blow the rubber blank into shape. The PLC-controlled pneumatic single/double-station plastic hollow molding machine adopts a fully pneumatic drive, which has fast response and high efficiency, but it is precisely because of the pneumatic method that according to the formula F=P·S. Where F is the clamping force, P is the working air pressure of the system, and S is the effective area of the piston. It can be seen that when the working pressure of the system is a certain value, the clamping force is proportional to the effective area of the piston. Once the cylinder diameter is determined, the clamping force is also determined. Taking the cylinder diameter of 150mm as an example, at a working pressure of 6MPa, only 10.38KN of force can be produced. So this type of model is only suitable for bottles under 500ml. At the same time, it should be pointed out that due to the use of full pneumatics, the air consumption is indirectly increased. If the power consumption of the air pump and its maintenance costs are converted into it, the unit consumption of the product is quite high.
It can be seen from the above that if a container with a capacity of 500ml or more is to be produced, only the clamping system using hydraulic cylinders is used. The hydraulic system can generate enough pressure to ensure the production and quality of various large-volume products. But today's most advanced hydraulic servo system is still expensive. For example, the Japanese Yuken Company uses the EFRG-03-125-C-50 proportional pressure flow control valve and the price is about 7,000 yuan, and a servo cylinder with a stroke of only 14mm and a bore of 120mm is priced at more than 10,000 yuan. Although the proportional pressure and flow control system is expensive, and the power consumption of the hydraulic system is about 30% of the power consumption of the whole machine, its excellent dynamic characteristics are enough to ensure the stable quality of the product, so it is still widely used [ 1, 2].
According to calculations, in addition to the externally provided air supply system, the energy consumption of the whole machine, taking the hydraulic double-station machine with the extruder screw diameter of 70mm as an example, when using PE (polyvinyl chloride) as raw material to produce 4500ml containers, electric heating Heating accounts for 22.6% of the power consumption of the whole machine, the motor of the extruder conveying system is 11kW, accounting for about 53%, and the hydraulic system is a 7.5kW motor, accounting for about 24.4%. In the hydraulic single station machine, when producing 280ml volume of PE material products, the power consumption of the hydraulic system accounts for 41.35% of the power consumption of the whole machine, electric heating accounts for 42.33%, and the extruder conveying system (frequency drive has been changed) consumes Electricity accounts for 16.32%. At present, the practice of most hollow molding machine manufacturers is to change the speed control of the slip motor to the frequency conversion speed control only in the extruder conveying system.
3.2 Working principle of variable frequency hollow molding machine
In summary, how to reduce the power consumption of the hydraulic system has become a key issue for the new generation of high-efficiency and energy-saving hydraulic systems. Traditional control theory pays attention to the method of system stability, which is to first ensure the existence of a stable system, and then use PID and other methods to adjust when the system stability changes. Constant pressure hydraulic system is its typical representative. The price is high energy consumption. The proportional hydraulic system has made great progress compared with the former. However, it can be seen from the structure of the proportional pressure proportional flow valve that it is still an extension of the above idea, but the valve opening is increased as much as possible by means of internal overflow. However, modern control theory pays more attention to dynamic stability and dynamic adjustment. As we all know, variable frequency speed regulation is a high-efficiency and high-performance speed regulation method, especially suitable for cage asynchronous motors. The development and application of pulse width modulation (PWM) technology, vector control technology, and speed sensorless technology have made AC motor variable frequency speed regulation have largely replaced DC speed regulation systems in many occasions. Judging from the current development status of the industrial control field, it also represents the level and direction of electric drive. With the continuous advent of various high-power intelligent power electronic devices and the rapid development of computer technology, frequency conversion speed regulation technology has become more mature. Its dynamic response speed and overload capacity have been able to meet the requirements of general hydraulic system dynamic stability, and its price has dropped to a level generally acceptable to users [3]. As a result, we incorporate variable frequency speed regulation technology into the hydraulic control system, transform the traditional quantitative pump into a "variable pump", and change the return flow adjustment into a volumetric adjustment. According to the production process, "distribute on demand" to achieve The purpose of efficient power saving.
The energy consumption of the whole machine consists of four parts, which are the heating system of the hollow molding machine, the extrusion mechanism, the proportional hydraulic system and the compressed air source. Except for the compressed air source provided by the external system, the rest are all provided by the power and electricity of the machine. The difference between this machine and the current common hollow molding machine is that it adds two links, one is the insulation system, and the other is the frequency conversion hydraulic system with D/A converter and synchronous controller. Regarding the thermal insulation system, a composite silicate thermal insulation material is only added to the heating tube, about 30mm thick, because the material is non-corrosive, has excellent thermal insulation performance and light bulk density. In one fell swoop, the heating system saves 30% of electricity. Because the insulation system is very simple, it is not the focus of this article.
