The Application Of WIN-PSS-IV In Variable Pump Injection Machine


The Application of WIN-PSS-IV in Variable Pump Injection Machine

Abstract:

This essay mainly introduces the successful application of WINNER-branded vector control inverter in the variable pump injection machine. Then, this essay also explains control system and features of the variable pump injection machine, and the differences from constant pump injection machine.

Key word:

WIN-PSS-IV invertervariable pump injection machine, energy saving reform

I Foreword

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 producers’ agenda.

The injection 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. Shenzhen Winner S&T Co., Ltd, after several years’ research on the variable pump injection machine, successfully launched the new model- WIN-PSS-IV -which can help the variable pump injection machine save 10%-20% energy. Shenzhen Winner accordingly positions itself as one of the pioneers in the variable pump injection machine energy saving field in China.

II Introduction of constant pump and variable pump injection 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
  • pPressure difference between the two sides of the proportional speed valve
  • QyFlow of overflow valve     PbPressure of oil pump
  • QbFlow of oil pump          VbDisplacement of oil pump
  • nMotor speed

As shown above, the system adopts the constant pump for oil supply, and the motor speed n and the displacement of the oil pump Vb are constant.

  • 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)

Production process of the injection machine commonly contains several sections, and the flow and pressure in different sections are different. Previously, the plastic producers used the flow valve and pressure valve to produce the needed flow and pressure, which, however, not only caused a mass of energy wasted but also increased wear risk of the equipment. In contrast, if the inverter is installed, it can produce appropriate flow to meet the production requirements through adjusting the motor speed of the injection machine, and dramatically reduce the overflow, so as to saving a lot of energy.

2)Variable pump injection machine

The variable pump injection machine commonly adopts the proportional variable pump as its drive component. Please refer to the 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
pPressure difference between the two sides of the proportional speed valve
Pb
Pressure of oil pump     QbFlow of oil pump    nMotor speed

(1) When the system is in the mode of flow control, Pb is more than P1 but less than the rated pressure of the injection machine. The proportional overflow valve will close. When the load changes, p will change, so that Q1 will change. Those changes will be transmitted to the adjusting piston through the flow and pressure feedback valve, and the adjusting piston will accordingly drive the sloping plate of the variable pump to change the displacement of the oil pump, and eventually determine Qb.

(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.

III 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.

IV Winner’s WIN-PSS-IV power saving system

After several years’ research, Shenzhen Winner launches the WIN-PSS-IV model, 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:

Please refer to the Fig below:

Working principle: When Qb approaches or hit the flow setting of the oil pump, the system enters the flow control mode. The inverter’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:

Please refer to the Fig below:

The control system of the inverter is equipped with an intelligent converting card. The inverter 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 inverter to the pressure control mode. Meanwhile, The PID control function is enabled which can maintain the system pressure constant. At this time, the inverter’s output frequency is proportional to the pressure difference. Because the pressure difference is quite small, the inverter’s output frequency and the motor speed will both decrease rapidly. The electrical system is shown as follows:

Features of WIN-PSS-IV:

  • With the open-loop operation mode, WIN-PSS-IV 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.

V Field operation analysis

A plastic plant in Dongguan has reconstructed some of its variable pump injection machines with WIN-PSS-IV. Field operation shows the inverter 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

VI Conclusion

Based upon several years’ research, Shenzhen Winner has accumulated a lot of valuable experience. With the successful application of its WIN-PSS-IV power saving system in the injection machine, we are so confident that Winner is doom to stand out in this domain.