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ADT inverter in plastic injection
SOLUTION SOLUTION

ADT inverter in plastic injection

ADT VFD used in plastic film blowing machine

 

i Introduction


The film blowing machine is a machinery that heats and melts plastic particles and then blows them into a film.


1. Production process and production principle

The dried polyethylene particles are added into the material hopper, and the particles itself fall into the screw barrel. When the pellets are in contact with screw thread, the plastic particles are moved forward by the rotating screw. In this process, the friction between the particles and the screw and barrel along with the external heating on the barrel part, the plastic particles are heated and melted. The melted plastic is extruded from the die head. After cooling and blowing process through V plate, the plastic film is wound into rolls by traction roller.

2. The film blowing machine is mainly composed of extruder, machine head, die head, cooling device, foam stabilizer, V plate, traction roller and coiling device.


II Advantages of ADT frequency inverter retrofit scheme on plastic film blowing machine


1) Smooth speed regulation within a specific range. Adjust the speed of main motor and traction roller motor accordingly for different products production task.

2) Stable start and stop due to the constant torque control by the AD300 series AC drives. Mechanical impact is greatly reduced and the NG products at the starting period is also reduced.

3) Motor only rotates in one direction

4) Working performance is very stable.


iii VFDs selection, Parameters setup and wiring


Inverter selection:


AD300-T4045G/055P for extruding main motor

AD300-T42R2GB/4R0PB for film take-up roller


The extruding motor is started by external terminal, which is controlled by the machine control system. The frequency is given by 485 Modbus communication, which is also controlled by the machine control system.


The take-up roller inverter is set to use torque control mode. There are 2 potentiometers on machine. They are controlling the inverter’s torque and speed limit via AI1 and AI2. In film take-up inverter, proper torque value is set to keep the constant torque during rolling process. The faster the film is feeding, the faster the roller rolling up. Auto torque boost value can be set to adjust the torque when the film roll diameter becomes larger. Or use the potentiometer to adjust the torque value when the diameter gets larger. Or tension sensor pendulum can be used to realized the PID control for constant tension control.


Take-up roller inverter parameters setting:

 

F0.01=1 Control mode choose vector control 2

F0.02=1 Run mode choose terminal control

F3.10=2 Torque control choose AI1 torque setting

F3.12=2 Torque control speed limit by AI2

F3.27=12Hz Torque boost frequency in torque control mode

F3.28=15% Torque boost value in torque control mode


Film roll-up roller inverter wiring

 

Cable connected to inverter
Inverter terminals
Remark
Power supply cable
R.S.T
 
 
Motor cable
U.V.W
 
 
External start signal cable
X1
 
 
Potentiometer cable control the torque
AI1/10V/GND
AI1 selection V
Speed limit potentiometer cable 
AI2/10V/GND
AI2 Selection V
Error Alarm signal cable 
TA/TC
 
 

 

ADT VFD for injection machine energy saving retrofit


Overview


ADT frequency inverter for plastic injection machine accepts the processed pressure and flow signal from the injection machine control panel. The control panel outputs 0~10V signal to VFD for frequency regulating at different production processes of injection. The processes include mold closing, injection, pressure keeping, and mold opening. This can save the extra energy. The energy saving efficiency is proved to be up to 20%~70%.


i the introduction of injection energy-saving controller:


1. AD300 variable frequency drive is a universal AC drive that can be used to plastic injection machine for energy saving.  It is suitable for various injection molding machines that control the injection pressure and flow by proportional valve.


2. The AD300 system is powered by AC 380V. The machine controller sends the pressure and flow signals to AD300 inputs. In different processes of mold clamping, injection, pressure holding, and mold opening, the 0~10V signal is output to control the running frequency of the inverter.


ii the principle of energy saving:


The injection machine’s electricity consumption mainly comes from heating part and the oil pump.


1. The current heating method has very low efficiency. There is 50% of the heat power can not be utilized and just wasted. 

2. The oil pump motor runs at full speed. When oil pressure is not required, it is in an idling state and consumes electric energy.


The energy-saving control system of the AD300 is applied to control the oil pump running, synchronously tracking the pressure and flow at different stages to realize the different speeds at different stages, thus achieving the purpose of power saving. That is to say, the AD300 VFD changes the oil pump speed and output power according to the load changing, which saves the extra power consumed during the process when the injected product is cooling. At the same time, the power factor is also improved. The actual testing shows that the energy saving efficiency can be 20%~68% in AD300 controlled injection machine. The energy saving efficiency varies to the injection machine conditions, machine capacity, injection circulation time, injected product features and materials, etc.


iii AD300 AC drives Features and functions in injection machine:


1) Power saving effect 20%~70%.

2) Motor soft starting, reduce the mechanical impact

3) Dynamic regulates the oil pump output power

4) Eliminate the throttling loss at high pressure

5) Protections for under-voltage, over-voltage, over-load, SC, phase lost, etc.

6) System forms closed-loop control. The power, pressure, and flow is controlled synchronously, which greatly reduce the vibration at mold clamping and mold opening. It makes the production stable, rise the product quality, reduce the faulty time, and extend the machine service life.

7) The energy-saving solution and the original system is kept at the same time. When VFD is in maintenance, the original system without VFD can be used.


iv Application case:


AD300 frequency inverter is widely used on injection machines in areas such as Foshan, Shandong, Jiangsu, Zhejiang, etc. The system is favored by the customers mostly. Take one case for example as follows.


1. Case location: One plastic products factory in Foshan city. The injection machine make is Haitian. Motor 37kW, injection 500g

2. Performance comparing

(1) Before the transformation, the machine uses 22KWh per hour; after retrofit the consumed electricity per hour is 12Kwh.

(2) The equipment runs smoothly without impact, and operates well.

 

AD300 series VSD injection molding machine case study


I. Industry Overview:


Plastic materials have become one of the main materials for industrial, agricultural and civil use. The injection molding machine is a special plastic molding machine. It utilizes the thermo plasticity of plastics, the heated and melted plastic is quickly poured into the cavity. After high pressure maintaining and cooling for a certain period of time, the plastic material is formed various structural sections and plastic products. Applying frequency inverters to injection molding machines can save energy, improve productivity and product quality, reduce oil pollution and noise pollution, and extend the life of the machine.


ii the working process of the injection molding machine


1) mold clamping: the mold quickly approaches the specific position for clamping, and when it is confirmed that no foreign matter exists, the system turns to high pressure and locks the mold.

2) the injection table moves forward: the injecting nozzle close to the mold.

3)Injection: The injection screw injects the melted plastic into the cavity at a certain pressure and speed.

4) Pressure maintaining and cooling: through this process, the plastic products in the cavity is cooled and formed.

5) injection preparing: The hydraulic motor drives the screw to retreat, and the plastic particles added in the hopper are pushed forward for injection preparing. The screw retreats to the predetermined position, stops rotating, and prepares for the next injection.

6)The injection table retreats, mold opening

7)Eject the product.


These actions are performed by a hydraulic system on a conventional injection molding machine. The pressure and flow generated by the coordination of the oil pump and the different valves provide the thrust and movement speed required by the cylinder and hydraulic motor.


iii The theory of energy saving by frequency inverter


For the plastic products industry, electricity consumption is the main part of its production cost, and injection molding machine is one of the main energy-consuming equipment of plastic products factory. Therefore, reducing the energy consumption of injection molding machine has become the effective ways of cost reduction of the injection molding industry and the competitiveness of products.


1) Overflow loss:

The traditional injection molding machine uses a fixed pump to supply oil. The various injection molding process have different requirements on speed and pressure. It uses the proportional valve to adjust the overflow and bypass the excess oil back to the fuel tank. In the whole process, the rotation speed of the motor is constant, so the oil supply quantity is also fixed. As the execution action is intermittent, it is not possible to be full load. So a fix quantity of oil supply is very wasteful. According to the actual measurement, the waste is about 50%. Frequency conversion energy saving is to detect the proportional pressure and proportional flow signal from the numerical control system of the injection molding machine in real time to adjust the motor speed (ie, flow regulation) required for each working process in time, so that the flow and pressure of the pump work can just meet the system's need. And in the non-operating state (mainly in the cooling process), let the motor stop running, so that the energy saving space is further increased. The frequency conversion energy-saving retrofit of the injection molding machine can bring huge energy saving effect.


2) Throttle loss:

When the hydraulic oil flows through the orifice of the valve, there is a certain pressure drop, which is the throttling loss. Since the throttle valve has a large throttle area, most of the throttling loss occur on the proportional valve. At the same time, due to the long-term full-speed circulation of hydraulic oil and the mechanical friction of the hydraulic parts, the oil temperature is too high, the noise is too large, and the mechanical life is shortened.


3) Design margin loss:

Usually in the design, the pump motor sharing is generally considered. And the design is based on the demanded maximum capacity. Therefore, the design capacity of the oil pump motor is much higher than the actual demand, and there is a phenomenon of “large horse drawing small carriage”, resulting in a large waste of electric energy.


iv the advantages of the inverter in the energy-saving transformation of the injection molding machine:


1) Speed ​​regulation and energy saving:

The frequency inverter performs real-time sampling by the proportional valve signal, so that the output frequency changes linearly with the analog signal of the proportional valve, so that the motor speed is reduced during the process requiring less pressure and flow, thereby reducing the output power of the motor. In cooling and semi-finished product placing periods, the motor stops running and minimize the energy loss of the motor over the entire load range.


2) Improve the power factor:

Reactive power not only increases the line loss and the heat of the equipment, but more importantly the power factor reducing results in a decrease in the active power of the grid. From the formula S2 = P² + Q², Q = S * SIN φ, P = S * COS φ, where

S-apparent power,  Q-Reactive power, P-active power, COSφ-power factor. It can be seen that the larger the COSφ, the larger the active power P. The COSφ value of the ordinary quantitative pump injection molding machine is between 0.6 and 0.8. After using the variable speed drive, the compensation effect of the filter capacitor in the inverter makes COSφ≈1, thereby reducing the reactive power loss and increasing the power grid’s active power.


3. Soft start:

The original motor is directly started or using Y/△ start, the starting current is 3-7 times of rated current, which will cause serious impact to the electromechanical equipment and the power supply grid, and also increase the grid capacity. The large current and vibration generated during startup will shorten the equipment service life. The soft start function of the inverter will limit the starting current to the current limit level set in the inverter, which will reduce the impact on the power grid and the capacity of the power grid, and prolong the use of the machine and molds.


V AD300 variable speed drives control features in injection machine retrofit


1. The injection molding extension card and AD300 series AC drives will form a dedicated VFD specially for plastic injection molding machine.

2. The inverter has strong overload capability (180% rated current for 20 seconds), effectively avoiding the occurrence of overcurrent faults and improving the stability of the system operation

3. The vector control mode is adopted. The Acc/Dec time is shorten, response speed increased, and production efficiency improved.

4. The parameter setting is simple and the debugging is convenient.


vi the wiring diagram of AD300 on the injection molding machine:

 

 


VII Normally used parameters setting

 

Parameter  Description Setting value
F0.02 Run  control mode 1
F0.03 Frequency reference 1 1
F0.04 Frequency reference 2 2
F0.05 Frequency reference selection 2
F0.19 Acc. Time Set as actual need
F0.20 Dec. time Set as actual need
F6.03 X3 terminal defining 8
F6.14 Max analog quantity physical value 1 Set as actual need
F6.19 Max analog quantity physical value 2 Set as actual need

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