VFD in Injection Machine
This application is about VFD in variable pump injection machine, and also explains control system and features of the variable pump injection molding machine, and the differences from constant pump injection machine.
The plastic processing industry has gone through rapid and stable development in recent years. As the plastic enterprises increase more and more, competition goes scorching and how to reduce production cost and enhance product competitiveness tops all the plastic manufacturers' agenda.
The injection molding machine, the main production device in the plastic processing factory, always consumes as much as 70%-80% power of the factory's total. Thus, to reduce the power consumption can help the plastic producers secure a lot of money. However, for the energy saving reconstruction of the variable pump injection machine, even lots of professional energy saving companies find it no way. After several years' research on the variable pump injection machine, Gozuk successfully launched the new VFDs which can help the variable pump injection machine save 10%-20% energy. We position ourselves as one of the pioneers in the variable pump injection machine energy saving field in China.
Introduction of constant pump and variable pump
1) Constant pump injection machine
Currently, most reconstructed injection machines are fluid drive injection machines, whose fluid drive system is powered by the oil pump driven by the motor. The hydraulic oil pump is of vane pump, which indicates its fuel delivery is proportional to its speed. When the motor of the pump runs at a constant speed (50HZ), the fuel delivery will maintain the same. Please refer to the following Fig.:
2) Variable pump injection machine
The variable pump injection molding machine commonly adopts the proportional variable pump as its drive component. Please refer to following Fig. below: the system consists of proportional variable displacement piston pump of load sensing type, proportional overflow valve, proportional speed valve, pressure feedback valve and flow feedback valve.
(2) When the system is in the mode of pressure control, the obliquity of the variable pump's sloping plate is quite small, thus only a small quantity of hydraulic fluid goes through the proportional overflow valve, so as to ensure appropriate pressure. It can get corresponding output pressure by changing the input signal of the proportional overflow valve.
Energy saving principle of the variable pump injection machine
From the introduction above, we can draw a conclusion that compared with the constant pump injection machine, the variable pump injection machine can reduce a large quantity of overflow waste, making the motor maintain in the light load status. However, there is still massive energy being wasted as the motor always works at full speed and the speed cannot be adjusted, and. In addition, the machine's start mode is star-delta slowly start, which results in very low power factor.
Gozuk EDS2800 power saving system
After several years' research, Gozuk launches EDS2800 variable frequency drive, which can achieve exact control to the injection machine through speed control and PID closed-loop control.
When the oil pump works in the flow control mode:
Working principle: When Qb approaches or hit the flow setting of the oil pump, the system enters the flow control mode. The VFD's output frequency is proportional to the flow setting of the oil pump. During the process, Qb (Qb=Vb*n) fluctuates in accordance with the production requirement, thus radically eliminating the overflow energy loss.
When the machine works in the pressure control mode:
The control system of the variable frequency drive is equipped with an intelligent converting card. The VFD can firstly realize real-time monitoring to pressure fluctuation through the pressure sensor, and then compare the monitored value with the pressure setting. When the difference is small, the intelligent converting card will switch in time the VFD to the pressure control mode. Meanwhile, The PID control function is enabled which can maintain the system pressure constant. At this time, the VFDs output frequency is proportional to the pressure difference. Because the pressure difference is quite small, the VFD's output frequency and the motor speed will both decrease rapidly. The electrical system is shown as follows:
Features of EDS2800 VFD:
Field operation analysis
A plastic plant in Shenzhen has reconstructed some of its variable pump injection molding machines with Gozuk EDS2800 drives. Field operation shows the VFD owns high performance and high reliability, helping the plastic producer saving up to 20%.
Please refer to the table below for more detailed comparison.
The plastic processing industry has gone through rapid and stable development in recent years. As the plastic enterprises increase more and more, competition goes scorching and how to reduce production cost and enhance product competitiveness tops all the plastic manufacturers' agenda.
The injection molding machine, the main production device in the plastic processing factory, always consumes as much as 70%-80% power of the factory's total. Thus, to reduce the power consumption can help the plastic producers secure a lot of money. However, for the energy saving reconstruction of the variable pump injection machine, even lots of professional energy saving companies find it no way. After several years' research on the variable pump injection machine, Gozuk successfully launched the new VFDs which can help the variable pump injection machine save 10%-20% energy. We position ourselves as one of the pioneers in the variable pump injection machine energy saving field in China.
Introduction of constant pump and variable pump
1) Constant pump injection machine
Currently, most reconstructed injection machines are fluid drive injection machines, whose fluid drive system is powered by the oil pump driven by the motor. The hydraulic oil pump is of vane pump, which indicates its fuel delivery is proportional to its speed. When the motor of the pump runs at a constant speed (50HZ), the fuel delivery will maintain the same. Please refer to the following Fig.:
- A1: piston area of non-rod chamber in the oil cylinder
- F: Working load Q1: Working flow P1: Working pressure
- △p：Pressure difference between the two sides of the proportional speed valve
- Qy：Flow of overflow valve Pb：Pressure of oil pump
- Qb：Flow of oil pump Vb：Displacement of oil pump
- n：Motor speed
- Qb=Vb*n (Qb is a constant)
- Pb is set by the overflow valve
- Q1 is set by the constant speed valve
- P1=F/A1 (P1 is determined by F)
2) Variable pump injection machine
The variable pump injection molding machine commonly adopts the proportional variable pump as its drive component. Please refer to following Fig. below: the system consists of proportional variable displacement piston pump of load sensing type, proportional overflow valve, proportional speed valve, pressure feedback valve and flow feedback valve.
- A1: piston area of non-rod chamber in the oil cylinder
- F: Working load Q1: Working flow P1: Working pressure
- △p：Pressure difference between the two sides of the proportional speed valve
- Pb：Pressure of oil pump Qb：Flow of oil pump n：Motor speed
(2) When the system is in the mode of pressure control, the obliquity of the variable pump's sloping plate is quite small, thus only a small quantity of hydraulic fluid goes through the proportional overflow valve, so as to ensure appropriate pressure. It can get corresponding output pressure by changing the input signal of the proportional overflow valve.
Energy saving principle of the variable pump injection machine
From the introduction above, we can draw a conclusion that compared with the constant pump injection machine, the variable pump injection machine can reduce a large quantity of overflow waste, making the motor maintain in the light load status. However, there is still massive energy being wasted as the motor always works at full speed and the speed cannot be adjusted, and. In addition, the machine's start mode is star-delta slowly start, which results in very low power factor.
Gozuk EDS2800 power saving system
After several years' research, Gozuk launches EDS2800 variable frequency drive, which can achieve exact control to the injection machine through speed control and PID closed-loop control.
When the oil pump works in the flow control mode:
Working principle: When Qb approaches or hit the flow setting of the oil pump, the system enters the flow control mode. The VFD's output frequency is proportional to the flow setting of the oil pump. During the process, Qb (Qb=Vb*n) fluctuates in accordance with the production requirement, thus radically eliminating the overflow energy loss.
When the machine works in the pressure control mode:
The control system of the variable frequency drive is equipped with an intelligent converting card. The VFD can firstly realize real-time monitoring to pressure fluctuation through the pressure sensor, and then compare the monitored value with the pressure setting. When the difference is small, the intelligent converting card will switch in time the VFD to the pressure control mode. Meanwhile, The PID control function is enabled which can maintain the system pressure constant. At this time, the VFDs output frequency is proportional to the pressure difference. Because the pressure difference is quite small, the VFD's output frequency and the motor speed will both decrease rapidly. The electrical system is shown as follows:
Features of EDS2800 VFD:
- With the open-loop operation mode, this variable frequency drive can realize huge starting torque (It can hit 150% of the rating at 0.5HZ);
- Quick response: the response time is less than 200ms.
- Realize motor soft start; less inrush current; bate noise and ameliorate working environment
- Higher power factor, reduce reactive power loss of the grid
- High reliability: relieve vibration, ease mechanical wear, depress the temperature of oil, and prolong the using life of the equipments.
Field operation analysis
A plastic plant in Shenzhen has reconstructed some of its variable pump injection molding machines with Gozuk EDS2800 drives. Field operation shows the VFD owns high performance and high reliability, helping the plastic producer saving up to 20%.
Please refer to the table below for more detailed comparison.
| Item | Constant Pump Injection Machine | Variable Pump Injection Machine | Frequency Conversion Injection Machine |
| Start mode | Y/Δ start, heavy start current, lower power factor, large impact to the grid | Y/Δ start, heavy start current, lower power factor, large impact to the grid | Soft start, small start current, higher power factor, and less impact to the grid |
| Maintenance | Lower failure rate, lower repair cost | Medium failure rate, but high repair cost | Medium failure rate and medium repair cost |
| Mechanical wear | The motor and oil pump always run at full speed, with high wear risk | The motor and oil pump always run at full speed, with high wear risk | The speed of motor and oil pump is adjustable, dramatically reducing the wear risk |
| Oil temp & cooling water | High oil temp, and waste massive cooling water | Medium oil temp, and waste some cooling water | Lower oil temp, and just need a little cooling water |
| noise | medium | high | low |
| Hydraulic fluid cost | low | high | low |
| Power saving efficient | no | Low efficiency | High efficiency |
