Abstract: This paper introduces the principle of the equipment of inverter as well as principle, method and notice of the energe – saving of the injection moulding machine.

 

Keywords: inverter, injection moulding machine, energy – saving

 

I. Introduction

The plastics processing industry is one of the fastest developing light industries, and injection molding machines are widely applied in various processing industries. In the processing costs, electricity accounts for a significant proportion. Especially in recent years, the electricity prices have remained high, and the country has introduced various policies on electricity restriction, so the competition is becoming intense. It has become urgent to decrease the production costs and improve the competitiveness of the products.

 

  1. Analysis of the application environment (characteristics of the customer, the application environment, mechanism composition and its characteristics, specific requirements of the customer, etc.)

 

Injection molding machines, adopting the injection molding method, have been widely applied in various processing industries. Plastic injection molding, making use of the three states of plastics, by means of injection molding machines and molds, forms the required plastics. Although the injection molding machines used are different, the processing content and basic steps are the same. Take the processing of the horizontal screw injection molding machine below as an example for demonstration.

 

Horizontal screw injection molding machine

I5300_injection_molding_machine_20171016_1

I5300_injection_molding_machine_20171016_1

  1. Structure of the injection molding machine:

1 .Nozzle; 2. Nozzle flange; 3. Screw check valve; 4. Electric heating rings; 5. Melting barrel;  6. Screw; 7. Hopper; 8. Bearings; 9. Hydraulic motor; 10. Carriage cylinder;     11. Carriage mechanism; 12. Carriage cylinder plug; 13. Injection cylinder; 14. Carriage base; 15. Center adjustment screw; 16. Transmission unit; 17. Sliding guide-rod of the transmission unit; 18. Sliding guide-rod support

II. Working process of the injection molding machine

The working process of the injection molding machine is mainly composed of the following steps:

 

(1)Molding and locking

The process of injection molding is a cycle operation process, generally using molding as the starting point. In the molding process, the speed of the movable plate is required to meet the slow – fast – slow demand, and with a low-pressure protection stage. The role of low-pressure protection, on the one hand, is to ensure a smooth molding of the mold, reduce the impact and mold-closing time, thus shortening the molding cycle; on the other hand, it is to avoid foreign matter in the mold or the inserts of the mold being loosened or falling off and damaging the mold when a movable mold moves near a fixed mold. The last step is the high-pressure low-speed mode-locking stage, whose role is to ensure that the mold has enough locking force to avoid edge overflow or other phenomenon during injection and pressure maintaining.

 

(2)Injection device moving forward

When the mold mechanism is closed and locked, the injection base works as a whole to move the cylinder, to move the injection device forward and to ensure that the nozzle and the sprue runner are fit, thus preparing for the injection stage.

 

(3)Injection and maintaining pressure

After completing the above two working steps, the injection cylinder of the injection device works to push the injection screw forward, so that the melting material in the front of the barrel is injected into the mold chamber under high-pressure at high-speed. At this time the pressure of the screw head on the melting material is called the injection pressure, also known as the primary pressure. After the material is injected into the mold chamber, the cold and hot conduction of the mold leads to the contraction of the material volume. In order to ensure the density, dimensional accuracy, strength and rigidity of the plastic, the molds of the injection system must be added at a certain pressure for feeding until the plastic of the gating system (with the sprue as the key point) is solidified. At this time the pressure of the screw on the melting material is called maintaining pressure, also known as the secondary pressure.

 

(4)Cooling and pre-plastification of the products

With the further cooling of the mold, the deep material in the mold gating system tends to solidify gradually. Especially when the sprue is solid, the maintaining pressure has lost the effect of feeding at this time, the maintaining pressure can be removed, so that products in the mold can be adequately cooled and shaped.

 

Meanwhile, the screw gearing drives the screw to transmit, and the plastic in the hopper is transmitted forward by the screw. Under the external heating from the barrel heating system and the shearing and compounding effect of the screw, the plastic is gradually melted and plasticized, and transported to the end of the barrel, producing a certain pressure. This pressure is established according to the back pressure valve of the hydraulic system of the processed plastic adjusting injection machine and the resistance overcoming the screw to move back, known collectively as the pre-plastic back pressure, with the aim to ensure the quality of plasticization. As the screw keeps rotating, the melting material is also transported to the end of the barrel. The pressure generated from the screw end forces the screw to continuously move backward. After moving backward to a certain distance, the melting material at the barrel end is sufficient for the next injection, so the screw stops. Since the cooling and pre-plasticization of the products are performed at the same time, generally the pre-plasticization time is required not more than the cooling time of the products, so as not to affect the shaping cycle time.

 

(5)Drawing back of the injection device

Whether the injection device draws back is based on the technology to process the plastics. Some draw back after the pre-plasticization; some draw back before the pre-plasticization; and some injection devices do not draw back, such as the hot runner mold. The purpose of the injection device drawing back is to avoid prolonged contact between the nozzle and the cold mold, because that will lead to the temperature of the material within the nozzle becoming too low to affect the next injection molding and the quality of products. In some cases, to facilitate the clearing of material, the injection devices are often required to draw back.

 

(6)Mold unloading and product ejection

After the products in the mold are cooled and molded, the assembly mechanism unloads the mold. Under the combined effects of the ejection system of the injection machine and the mold, the products will be automatically ejected and ready for the next molding process.

According to the above actions, the program can chronologically draw the curve diagram of the work process of the injection machine.

I5300_injection_molding_machine

I5300_injection_molding_machine

Electricity consumption curve of the injection molding machine operation at grid frequency and variable frequency

 

III. Autoanalysis of the products and debugging process

  1. Energy-saving principle of the injection molding machine

Energy-saving principle of the injection molding machine

When changing the load flow and pressure, traditional quantitative pump injection molding machines usually adjust with a valve. At that time the input power changes a little, a lot of energy is lost on the valve in the form of pressure difference, resulting in leakage. The IACDRIVE energy saving cabinet can automatically adjust the pump speed and regulate the oil supply pump, according to the pressure and speed setting requirements in the current operating state of the injection molding machine, such as mold-locking, injecting, melting, mold unloading, ejecting and other stages. It keeps the actual fuel supply of the pump and the actual load flow of the injection molding machine consistent at any operating step, ensures that the energy consumption of the motor is the least required in the entire changing range of load, eliminates the leakage, and ensures that the motor operates smoothly and precisely. With an IACDRIVE energy saving cabinet, the injection molding machine can achieve soft starting of the oil pump, increase the motor power factor COS ∮ and dynamically adjust the motor power output of the injection molding machine, so as to achieve the aim of energy-saving.

 

  1. The IACDRIVE injection molding machine’s special frequency inverter —I5300

The I5300 series high-performance vector energy-saving cabinet is the latest product, gathering the experience of many years of research and development, production and on-site transformation of injection molding machine energy saving cabinets. Mainly aimed at energy-saving transformation of the injection molding machine, it has introduced the superior performance of vector control technology to the injection molding machine energy-saving field, solved the previous problem that V/F control mode affects the production cycle, and increased the energy-saving rate.

 

* Control mode: without PG vector control (SVC); with PG vector control (VC); V/F control;

* Frequency setting method: The signals comparison of pressure and flow channels;

* Signal conversion panel, using the Hoare module, changes the proportional valve of injection molding machine pressure and flow 0~1A signal into 0 ~ 10V signal to feedback the frequency inverter or directly connects to 0 ~ 10V signal;

* Big torque at low frequency: quick starting without affecting the production cycle;

* Good ability at overload: under the high pressure from plastic injecting and other conditions, it will not escape, so as to ensure the quality of the product;

* IP21 protection grade; fully enclosed design; dual-use of cabinet and wall hanging. Anti-Dust; anti-gas; anti-corrosion; environmental adaptability is good; the life of the equipment extends;

* 15KW~55KW full range of built-in DC reactor, effectively improves the power factor and improves the overall efficiency and stability, and effectively eliminates the impact from the high harmonics of the input side on the energy saving cabinet and reduces external interference;

* Main supply / energy-saving dual-circuit security safety design ensuring the system is trouble-free and does not affect production;

* With the functions of automatic reset and power-off reset, to ensure continuous production and production efficiency;

* With the function of autolocking fault protection;

* Good at anti-interference; input / output power cables are installed with filtering rings; the strong and weak electricity are separated, giving full consideration to safety requirements;

* With built-in PID controller, easily composing the closed-loop control system temperature, pressure, flow volume and other process parameters;

* Energy-saving is 5%~10% more than that of V/F control mode.

 

  1. Connection diagram of the application of I5300 in injection molding machine
I5300_injection_molding_machine

I5300_injection_molding_machine

Standard connection diagram of the application of I5300 in injection molding machine

  1. Technological advantages of IACDRIVE injection molding machine— I5300 energy saving cabinets in the injection molding machine industry

 

(1) IACDRIVE injection molding machine special frequency inverters — I5300 energy saving cabinets use Sensorless vector controls, so the starting torque is high,150% of rated torque (SVC) at 0.5 Hz; dynamic response is quick, with the step change torque response time < 200 ms; speed-stabilizing accuracy is 0.5%.  Quick dynamic response can effectively solve the problem of long processing cycles due to long acceleration and deceleration of the injection molding machine pump controlled by the frequency inverter.

 

(2) IACDRIVE injection molding machine special frequency inverters — I5300 energy saving cabinets can directly accept 0 ~ 1A current signals, and can selectively obtain the speed control signal of the injection molding machine from the two channels of input: proportional flow control valve signal and pressure valve signal. At the same time it can accept 0 ~ 10V voltage signals to compensate for the signal acquisition of some segments of the process of the injection molding machine to achieve a perfect control effect;

 

(3) The unique torque control performance of the IACDRIVE injection molding machine special frequency inverter — I5300 energy saving cabinet, effectively controls the load current without affecting the instantaneous torque. Specially designed for the injection molding machine industry, it effectively avoids the common problem of traditional frequency inverters being quick to engage unnecessary over-current protection, and avoids frequency inverter damage due to frequent protection or high currents, thus guaranteeing the reliable and trouble-free operation of the injection molding machine;

 

(4) Aimed at the current status of the domestic power grid and knowing that most frequency inverters causing waveform distortion,IACDRIVE injection molding machine special frequency inverters — I5300 energy saving cabinets have standard built in DC reactors to improve the operating conditions of the frequency inverter and increase the power factor of the energy-saving system by about 0.95. Thus preventing rectifier bridge or filter capacitor damage caused by poor quality of the power grid, and effectively reduces the fault rate and external interference of the frequency inverter;

 

(5) Good anti-interference; input / output power cables are installed with filtering rings; the strong and weak electricity are separated, giving full consideration to safety requirements;

 

(6) Grid power supply / energy-saving dual-circuit security safety design ensures the system is trouble-free and does not affect production;

 

(7) IP21 protection grade; fully enclosed design; dual-use of cabinet and wall hanging. Anti-dust; anti-gas; anti-corrosion; environmental adaptability is good; the life of the equipment is extended;

 

  1. Successful case of IACDRIVE injection molding machine— I5300 energy saving cabinets and the solutions

    I5300_injection_molding_machine

    I5300_injection_molding_machine

Application:

 

Type of the injection molding machine HAI TAI
Motor parameters
Rated power 45KW Rated voltage 380V
Rated current 90A Rated rotation speed 980rpm
Type of the equipped frequency inverter I5300-45G-4

 

Perform in strict accordance with the debugging steps provided by our company, specific debugging steps:

 

(1) Installation of the power cable

The connection of the power cable is as follows: correctly find the main AC contact starting the motor; disconnect the three-phase AC wire between the air switch of the injection molding machine and the main contact (Note: if the main AC contact is connected to other power cables, shift them to the air switch); then connect the <r, t=””>three-phase power cables of the energy saving cabinet to the air switch, and the <u, w=””>three-phase output cables to the main AC contact.</u,></r,>

 

(2) Connection of the signal cable 

Signal cable connection is as follows: correctly find the proportion flow signals and proportion pressure signals. When the signal is a current signal, on the signal acquisition card 1IA, 1IB are channel-one input terminals for current signal; the corresponding internal channel is AI3: its function code is P0.03 = 2, and the corresponding parameters are set to P5.25 – P5.29; 1IA is the positive input terminal of the differential current, whereas 1IB is the negative input terminal of the differential current. 2IA, 2IB are channel-two input terminals for the current signal; the corresponding internal channel is AI4: its function code is P0.04 = 1, and the corresponding parameters are set to P5.30 – P5.34; 2IA is the positive input terminal of the differential current, whereas 2IB is the negative input terminal of the differential current. In addition, the two signal channel combination pattern is set by the parameter P0.06. Pay attention to the current flow direction of the signal cable in connection, which can be determined by whether the indicating light is on when the machine is operating (the brightness changes with the strength of the current signal); when the current signal is more than 0.6A, it the indicates correct connection if the lights are all on.

 

(3) Parameter settings

① After all cables are connected, test the directions of the main supply and energy-saving, and measure the signals of two channels with the multimeter.

② Perform auto-tuning of the motor parameters.

③ Debugging of the trial run

 

Prior to debugging, first control the trial run with the keyboard to see whether it operates normally and whether the motor parameters are accurate.

 

Ⅰ: Set P0.00 = 0 (open-loop vector control), P0.11 = 0.1s (acceleration time), P0.10 = 50.00Hz. Repeatedly accelerate and decelerate for times, there is no OC fault.

Ⅱ: After the motor achieves (P2.01) the rated frequency of the motor, check the output voltage with the shift key on the keyboard. It is normal if the output voltage (P2.03) is around the rated frequency of the motor, and basic motor parameters are accurate.

Ⅲ: When the motor achieves 1/2 (P2.01) of the rated frequency of the motor, check the output voltage. It is normal if the voltage is around 1/2 (P2.03) of the rated frequency of the motor.

Ⅵ: Change the following basic parameters:

P0.00 0 P0.08 50 P7.04 0
P0.01 1 P0.09 0 P8.16 3
P0.02 2 P0.11 0.5 P8.18 1.0
P0.03 2 P0.12 1.0
P0.04 1 P1.14 0
P0.06 3 P4.12 1

 

Ⅶ:Parameters adjusting the signal amplification proportion are as follows:

P5.25 0.00 P5.30 0.00
P5.26 0.4 P5.31 0.4
P5.27 9.6 P5.32 9.7
P5.28 100 P5.32 100

 

In the production at the main supply, parameters of the flow and pressure can be independently adjusted. First change P0.06 to 0. Observe the flow parameters of channel-one, and then correct them by adjusting the parameters P5.25-P5.28, with the corresponding analog frequency of the energy saving cabinet. Then change P0.06 to 1. Observe the pressure parameters of channel-two, and then correct them by adjusting the parameters P5.30-P5.33, with the corresponding analog frequency of the energy saving cabinet. Finally, change P0.06 to 3, which is the standard comparison and input of the two channels.

Note: it is prohibited to switch to energy-saving mode in the operation under the main supply.

 

  1. Specific results and customers’ evaluation

 

  1. Total 46 nos I5300(power range: 30~75kW) have been installed, the energy saving ratio is about 30%
  2. User’s specific using results:
  3. The production costs are significantly reduced; the energy-saving effect is remarkable;
  4. The noise in the operating environment is reduced; the temperature of the oil system is lowered;
  5. The motor is started smoothly, so the impact on the power grid and the machine is reduced, and the equipment maintenance is reduced;
  6. The efficiency of the power grid is increased and the power grid capacity used is reduced, thus the cost of power grid expansion is saved;
  7. The impact of mold-locking open is reduced, which will extend the service life of machinery and molds;
  8. The service life of hydraulic system is extended, thus maintenance times will be fewer and a lot of maintenance costs will be saved;
  9. It has a variety of motor protections, such as over-voltage, over-current and absent phase;
  10. Energy-saving and power frequency can be easily switched, to ensure that the production is not affected when fault occurs in the energy-saving system.

 

  1. Conclusion

The experience of the application of I5300 series vector energy-saving cabinets with injection molding machines is rich, and the product is stable and reliable in operation. It can effectively solve the current problems faced by the frequency transformation of injection molding machines; it is an effective method for energy-saving. It is worth promoting in the plastics industry.

 

References

  1. Operation manual
  2. Introduction of the Structure and Principles of the Injection Molding Machine