Abstract: This article describes the transformation of the daytime frequency converter to the plastic industry's quantitative pump injection molding machine, with obvious energy saving effect.
Keywords: Injection molding machine Inverter Production process
I. Overview:
Injection molding machine equipment is widely used in various processing industries. It uses the injection molding method.
Plastic injection molding is the use of plastic three states, with the help of injection molding machines and molds, molding the desired plastic products. Although the used injection molding machines are not the same, the process content and the basic process to be completed are still the same. The process of the horizontal screw injection molding machine will be described as an example.
1, clamping and locking
The injection molding process is a cyclical working process. Generally, the mold clamping is the starting point of the process. The moving speed of the moving platen during the mold clamping needs to meet the slow-fast-slow requirement, and there is a low-voltage protection stage. The role of low-voltage protection is to ensure that the mold clamps the mold smoothly, reduces the impact, shortens the mold closing time, thereby shortening the molding cycle. On the other hand, when the moving mold and the fixed mold are close to each other, foreign matter or mold inside the mold is avoided. Loose inserts damage the mold. Finally, it is a high-pressure and low-speed mode-locking stage. The role of this stage is to ensure that the mold has enough locking force so as to avoid overflowing during injection and pressure holding.
2, injection device forward
When the clamping mechanism is closed and locked, the injection block moves the oil cylinder as a whole to move the injection device forward, ensuring that the nozzle is in conformity with the sprue of the mold, and is ready for the injection stage.
3, injection and pressure
After the above two working processes are completed, the injection cylinder of the injection device works to push the screw of the injection machine forward so that the molten material in the front of the injection cylinder is injected into the mold cavity at a high pressure and high speed. At this point, the pressure acting on the molten material at the head of the screw is called injection pressure, also called primary pressure. After the molten material is injected into the mold cavity, due to the cold and heat conduction of the mold, volume shrinkage of the material in the mold cavity occurs. In order to ensure the compactness, dimensional accuracy, strength and rigidity of the plastic products, the mold of the injection system must be fed with a certain pressure until the plastic of the gating system (the key is the gate) is frozen. At this point, the pressure acting on the melt by the screw is called the pressure holding pressure, also called the secondary pressure.
4, product cooling and pre-plasticization
With the further development of the mold, the deep material in the mold casting system tends to freeze. Especially when the gate freezes, the pressure-retaining operation has lost its feeding effect. At this time, the pressure holding pressure can be removed to make the product in the mold. Cool enough to shape.
At the same time, the screw drive drives the screw drive, and the plastic in the hopper is forwarded by the screw. Under the external heating of the barrel heating system and the shearing and mixing of the screw, the plastic gradually melts and plasticizes and is transported by the screw. At the end of the cartridge, there is a certain pressure. This pressure is established according to the plastic adjustment of the back pressure valve of the hydraulic system of the injection molding machine and overcome the resistance of the back movement of the screw, collectively referred to as the pre-plastic back pressure, the purpose of which is to ensure the quality of plasticization. As the screw rotates continuously, the molten material is continuously fed to the end of the barrel. The pressure generated at the end of the screw forces the screw to continuously move backward. When the distance is shifted to a certain distance, the frit at the end of the barrel is sufficient for the next time. When the injection volume, due to product cooling and pre-molding at the same time the general requirements of the pre-plastic time does not exceed the cooling time of the product, so as not to affect the molding cycle.
5, injection device
Whether the injection device retreats depends on the process of processing the plastic. Some of them return backwards after being pre-plasticized, and some are returned before pre-plasticizing, and some are returned before pre-reforming, and some injection devices are not returned at all, such as hot runner molds. The purpose of the injection device needs to be returned is to avoid prolonged contact between the nozzle and the cold mold so that the material temperature in the nozzle is too low and affects the quality of the next injection molding and product. In order to facilitate the clearing, some often return the injection device.
6, open and eject products
After the product in the mold is cooled and set, the mold clamping mechanism opens the mold. Under the joint action of the ejector ejector system and the ejector mechanism of the mold, the product is automatically dropped to prepare for the next molding process.
According to the above actions, the time-series program can be drawn into the curve of the working process of the injection machine (see Figure 1).
Injection molding machine power frequency and frequency conversion power consumption curve (Figure 1)
Second, the feasibility of frequency conversion of injection molding machine:
A general injection molding machine equipment, in a complete injection molding process in the clamping, injection, filling, melt, cooling, open mold and other stages of the pressure requirements are different, open the stage only to ensure that the smaller pressure Can, but to melt, cooling, but it requires a lot of pressure to ensure product quality and productivity. According to the principle of injection molding machine, we know that the higher the speed of the motor, the greater the injection pressure. Therefore, it is entirely feasible to realize variable-speed and energy-saving by using the inverter to control the motor of the injection molding machine.
At present, most injection molding machine manufacturers do not use energy-saving converter technology, or the star-delta start-up, which is directly powered by the power frequency grid, has a large starting current, and wastes power; if the frequency conversion speed regulation is used The soft start of the injection molding machine motor can be realized, and the operating frequency can be automatically changed according to the pressure requirements of various process stages to achieve the purpose of energy saving and efficiency enhancement. These functions can be realized through the inverter's flow pressure analog feedback or multi-speed adjustment. With the characteristics of rapid investment recovery.
Third, the program description:
At present, some injection molding machines have adopted variable-frequency energy-saving technologies and have received remarkable results in energy saving, ultra-quiet, efficient, and reliable, and can greatly reduce the power consumption of injection molding machines. This has been very well evaluated among many injection molding machine users. And trust. Through the testing and improvement of some experts, the frequency conversion energy-saving technology of injection molding machines has become increasingly perfect.
The general frequency conversion energy-saving transformation of the injection molding machine is usually used to control the power signal of the proportional control valve, and after the conversion processing is used as a given signal of the output frequency of the frequency converter, or the clamping, injection, and fusion of the injection molding machine. After process signals such as glue, cooling, and mold opening are processed as multi-speed or program control signals of the inverter (also a given signal of the inverter output frequency), this adjustment method is used to satisfy various processes of the injection molding machine for fuel supply. Pressure and flow requirements, and achieve energy-saving purposes. (See Figure 2)
In order to achieve the best working condition of the injection molding machine in frequency conversion regulation, our company has specially researched and developed an automatic switching circuit for the pressure and flow dual signal control loops of the injection molding machine. It can vary the flow and pressure requirements of the various working links of the injection molding machine. The signal is automatically selected so that it is easier to use when processing some high-precision plastic products.
Fourth, the principle and feasibility of energy-saving machine
1. Theory
Output power of oil pump: pt=p×Qt=p×v×n (1)
Theoretical torque of oil pump: Tt=1/2π×p×V (2)
P is the pressure, Qt is the flow rate, V is the displacement of the oil pump, and n is the rotation speed of the oil pump. Substituting (2) into the formula (1) yields:
Pt=2π×Tt×n (3)
If the energy loss from the mechanical energy to the hydraulic energy conversion process is neglected, it can be approximated that the output power of the oil pump is equal to the product of the motor output torque and the motor rotation speed. Therefore, it can be seen that when the system requires low flow, the power required by the system is actually very low. However, the actual situation is that since the motor is always running at the power frequency of 50 Hz, it cannot reduce the speed according to the actual demand, thereby reducing the flow. Therefore, excess hydraulic oil can only flow back to the tank through the proportional flow valve, causing wasted energy.
2, pump frequency conversion speed saving operation
From the process of P=f(t) in the injection molding machine in Figure 1, it can be seen that its main oil pump pressure varies and fluctuates at different times. This has the possibility of energy saving and has a great potential. According to statistics, the energy saving rate of injection molding machines can generally reach 25%-60%. It is well known that when the injection molding machine is not using a frequency converter, the main pump motor always operates at a constant speed, which is an extremely uneconomical operation mode.
The energy-saving controller of the injection molding machine will control the current signal of the proportional flow valve (0-1A) according to the proportion of the flow rate set in each production stage to obtain a proportional 0-1 meter to open the proportional opening of the solenoid valve. To provide the pressure needed for the system. Excess flow overflows through the overflow valve. Connect the proportional flow signal to the power-saving controller of the injection molding machine as the drive command to control the rotation speed of the hydraulic drive motor. The oil pump only replenish the consumed part of the oil circuit. The oil pump motor runs the corresponding speed according to the proportional command and outputs the corresponding flow. To provide the pressure needed for the system. That is, how much you need to provide, at the source so that it does not produce waste. Therefore, the frequency conversion energy-saving system has obvious power-saving effect in the entire production process of the injection molding machine, so that it can save energy and save energy and bring considerable economic benefits to the user.
Fifth, application case
Project Case 1: Transformation of a Large Injection Molding Machine in Nanhai Xinfeng Plastic Factory, Guangdong
Shenzhen Riye Electric Co., Ltd. cooperated with an energy-saving equipment technology development company in Dongguan City to carry out frequency conversion transformation of the four main pump 55KW large injection molding machines (Donghua 800) of Guangdong Nanhai Xinfeng Plastics Factory. The maximum pressure of the machine can be achieved. 2000 tons, the maximum amount of up to 16,000 grams, about 1-2 minutes to produce six medium and large water pipe joints. This is a model for the successful application of frequency converter technology transformation. It has been put into production for half a year, works normally, and the average energy saving rate is more than 35%. It is welcomed by users. After six months of application comparison, the plant It has been determined that another six injection molding machines will also use frequency converters for technological transformation. Fully explain the application of frequency converter to large-scale injection molding machine energy-saving technological transformation program is correct and effective, it is worth recommending to everyone.
1. Selection of industrial frequency, frequency conversion main circuit and frequency converter
The main oil pump 55KW, selected Shenzhen ZHIYE Electric Co., Ltd. ZY3200-ZY055T4 inverter four, after six months of use to prove the performance of the inverter is good, reliable, high energy-saving rate, the main circuit uses frequency - frequency conversion two sets of power Power supply mode (ie double frequency control with frequency conversion and power frequency interlocking interchange) to ensure uninterrupted operation.
2. Matters needing attention in frequency conversion transformation application
1 It is necessary to use an injection molding machine with proportional flow control for frequency conversion energy-saving transformation.
2 variable pump does not need to carry out frequency conversion energy-saving transformation. Because the variable pump itself has a certain energy-saving effect, increasing the frequency converter can not show its advantages.
3 Some relay-controlled injection molding machine speeds use manual adjustment of the flow valve to control the speed, and the effect of frequency conversion energy-saving reform is not ideal. For special requirements for small injection molding machines and roller-to-inverter response speeds, frequency conversion energy-saving transformations must be performed with caution.
4 In general, the installation of energy-saving inverter will not affect the operation of the injection molding machine, in order to ensure the production efficiency, some process parameters need to be adjusted
(4) How to obtain the control signal correctly, and realize the optimal combination of frequency converter and injection molding machine is very important. We use the schematic block diagram of the solution (see Figure 3).
Figure 3 Frequency Control Flowchart
3. Economic Benefit Analysis
Injection Molding Machine and Production Status Table (1)
Injection molding machine model
main motor power
Product name
Product material
Power Saver Model
Donghua 800
55+55KW
pipe connector
PVC
SY3200-ZY55T4
Power frequency, frequency conversion operation energy meter (2)
Electric meter initial value
The final value of the meter
time
power consumption
Saving electricity
Saving rate
Power frequency operation
28
78.6
1 hour
50.6
Variable frequency operation
78.6
108.7
1 hour
30.1
20.5
40.52%
Return on investment analysis:
Savings per month: 20.5 degrees/hour x 22 hours/day x 28 days = 12628 degrees/month
Monthly electricity savings: 12628 degrees × 0.6 yuan / degree = 7576.8 yuan
Annual electricity savings: 7576.8 yuan/month*12 months=90921.6 yuan
Payback period of investment: 63,800 yuan ÷ 7576.8 yuan / month × 28 days / month = 235 days
Project case 2: An injection molding plant Renxing presses to carry out energy-saving renovation
On March 1, 2004, our company carried out a plastic energy-saving transformation on a toy factory. The energy-saving rate reached 35.86%. The analysis of the transformation process is as follows:
1. Object:
Injection Molding Machine and Production Status Table (3)
Injection molding machine model
main motor power
Product name
Product material
Power Saver Model
Renxing presses
45KW
Plastic bucket
ABS
SY3200-ZY045T4
2. Comparison of current and power meter readings before and after retrofit
(1) Comparison of operating currents before and after retrofit
Current Comparison Diagram Before and After Rebuilding (4)
Sequence of actions
Closing
Injection molding
Hold pressure
Back material
cool down
Mold
thimble
Current (before change)
63.2
90.7
67
80
55.4
63
75
Current (after change)
16.5
80
15.4
65
12
18
37
Saving rate
73.89%
11.8%
77.01%
18.75%
78.34%
71.42%
50.66%
According to the comparison result in Table (4), it can be known that the current after the inverter has been adjusted has obviously decreased
(2) Comparison of active power meter readings before and after transformation
Calculation results of power meter and power capacity under the frequency table (5) Date: 2004.3.9
The specific time
Yield
hour
Meter
energy used
Hourly electricity
Unit product electricity
09:30-13:30
670
4
0-162.7
162.7
40.675
0.2429
13:31-17:30
700
4
326.9
164.2
41.05
0.2326
Total count
1370
8
326.9
Average
171.25
40.8625
0.2387
From the above table, the power consumption per unit product can be calculated:
The average power consumption of a single product = 326.9/1370 = 0.2387
Frequency conversion active power meter and calculation result of capacity table (6) Date: 2004.3.10
The specific time
Yield
hour
Meter
energy used
Hourly electricity
Unit product electricity
09:30-13:30
663
4
326.9-430.5
103.6
25.9
0.1563
13:31-17:30
695
4
534.8
104.3
26.075
0.1501
Total count
1358
8
207.9
Average
169.75
25.98
0.1531
From the above table, the power consumption per unit product can be calculated:
The average power consumption of a single product=207.9/1358=0.1531
After using frequency conversion saver efficiency = 169.75/171.25 = 99.13%
Based on the above consumption, you can calculate the percentage of electricity saved after the renovation:
Energy-saving rate = (P frequency - P frequency) / P frequency = (0.2387-0.1531) / 0.2387 = 35.86%
3. Impact on production stability, product quality, and machine performance after transformation
Comparison of Production Quantity Before and After Rebuilding Table (7)
8 hours production
Hourly output
Affecting production
effectiveness
Transformation of the former
1370
171.25
-1.5
-0.88%
After transformation
1358
169.75
(1) Stability of production
After the frequency conversion and speed regulation operation, there was no obvious change in production per hour. Production was reduced by 1.5 per hour, and the production efficiency fell by only 0.88%. The specific data is shown in Table (7).
(2) Product quality: no quality problems were found after inspection by the factory FQC
(3) Machine performance: After the frequency conversion speed regulation is adopted, the surface temperature of the motor is increased. The temperature of the power frequency running motor is 53.6°C. The maximum temperature of the motor during frequency conversion operation is 57.5°C. It is still within the motor safety range. This is As the motor operates throughout the entire cycle, depending on the production process, the cooling fan of the motor is reduced. It is recommended to keep the cooling fan and motor clean.
6. Several technical problems in the field reconstruction
At present, there are various types of variable frequency energy savers for injection molding machines on the market, and the technical content and product quality are uneven. As a result, some specific problems have arisen in the field transformation, some of which are normal phenomena after adopting variable frequency speed control technology, while others are Belongs to the shortcomings that should be overcome in the product or application.
6.1 Motor High-frequency Noise Is Sharper Than Mains
Because the inverter output voltage is composed of many pulse trains, there are higher harmonics, which will cause the motor to have different loudness and slightly sharper sound when it is running at different speeds. This is a normal phenomenon and can be reduced by increasing the frequency of the variable carrier wave. Wailing sound.
6.2 The temperature of the motor is slightly higher than the temperature when the mains is running
Due to the existence of output harmonics, the copper loss and iron loss of the motor are increased. Therefore, the temperature of the motor during frequency conversion and power saving operation is slightly higher than the temperature during the commercial operation. At the same time, in the middle and low-speed operation stage, the motor cooling fan speed decreases, the heat dissipation capacity decreases, and the temperature rise may rise by about 3 to 5°C. Since the insulation level of the ordinary oil pump motor is above Class B or Class F, the temperature rise of the motor is still within the allowable range and will not affect the use and life of the motor.
6.3 interfere with the normal operation of the injection molding machine,
The harmonics generated by the inverter will have some interference with some control circuits of the injection molding machine, which will affect the normal operation of the injection molding machine. In particular, some inverters with rough manufacturing processes and high harmonic content are more obvious in the unstable injection molding machines. This requires us to take some measures at the scene to solve the interference problem. The interference sources mainly include the following two aspects: (1) RF interference generated by high-order harmonics through wires. This type of interference can be resolved by installing equipment that suppresses RF interference at the input or output side of the frequency conversion device, such as the magnetic ring. Or filters, etc.; (2) Input harmonics are generated by the power supply coupling to other electrical equipment. This type of interference can be installed at the input side of the inverter device, or the installation of the line-side AC reactor has a certain effect. In addition, other devices under the same power supply are preferably capable of isolated power supply.
6.4 Impact on the efficiency of injection molding production
The frequency conversion energy saver has a certain acceleration/deceleration time during the control of the speed of the oil pump motor. Compared with the original solenoid valve opening speed, there is a certain lag, resulting in a prolonged unit processing cycle and a certain impact on the production efficiency, due to the day industry SY3200 frequency conversion energy The device can use flow and pressure signal control, and modify some injection molding machine parameters according to the situation, it can better solve this problem.
References:
<1> Du Jincheng. Electric Frequency Conversion Speed ​​Control Design Technology [M]. Beijing: China Electric Power Press, 2001
<2> Zhang Yanbin. SPWM frequency conversion speed regulation application technology [M]. Beijing: Machinery Industry Press, 2002
<3> Daily SY3200 Inverter User Manual
Stud Triac is developed on the basis of common thyristors. It can not only replace two thyristors with reverse polarity in parallel, but also requires only one trigger circuit and is an ideal AC switch device. . Its English name TRIAC is the meaning of the triac.
China leading manufacturers and suppliers of Stud Triac,Ir Stud Triac, and we are specialize in Stud Type Triac,Sc108 Data Triac Stud, etc.
Stud Triac,Ir Stud Triac,Stud Type Triac,Sc108 Data Triac Stud
YANGZHOU POSITIONING TECH CO., LTD. , https://www.yzpst.com