Injection molding machine transformation case

Injection molding machine inverter conversion energy-saving applications Abstract: This article describes the inverter industry in the plastic industry, the quantitative pump injection molding machine transformation, energy-saving effect is obvious.
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 injection molding machines used are not the same, the content of the process to be completed and

The basic process is still the same. The process of horizontal screw injection molding machine will be described as an example.

Closing and locking

The injection molding process is a cyclic process. Generally, the mold clamping is used as the starting point of the process. The movement speed of the movable platen during the mold clamping process must meet the requirements of slow-fast-slow and low-voltage protection.

stage. The role of low-voltage protection on the one hand is to ensure a smooth mold clamping, reduce the impact, shorten the mold closing time, thereby shortening the molding cycle; the other is when the moving mold and the fixed mold are close to

Avoid foreign matter in the mold or mold insert loose to 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 sufficient locking force to avoid injection and packing pressure.

There is a phenomenon such as overflow.
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.

Injection and holding 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 screw head acts on the melt

The pressure on the material is called injection pressure, also known as a 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 of plastic products

Sex, dimensional accuracy, strength, and stiffness must be such that the mold of the injection system applies a certain amount of pressure until the plastic in the gating system (the gate is the gate) freezes. Screw at this time

The pressure on the frit is called hold pressure, also called secondary pressure.

Product cooling and pre-plastication

With the further squeezing of the mold, the deep material in the mold pouring system tends to freeze, especially when the gate freezes, the pressure keeping has lost the feeding effect. At this time, the pressure holding pressure can be unloaded to make the product

In the mold fully cool and shape.
At the same time, the screw drive drives the screw drive and the plastic in the hopper is conveyed by the screw forward. Under the external heating of the barrel heating system and the shearing and mixing of the screw, the plastic gradually melts.

It melts and is transported by the screw to the end of the barrel, producing a certain pressure. This pressure is based on the back pressure valve that regulates the hydraulic system of the injection molding machine and the resistance to the movement of the back of the screw.

, collectively referred to as pre-plastic back pressure, its purpose is to ensure the quality of plasticization. As the screw rotates constantly, 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 backwards.

Moving, when moved to a distance, the frit at the end of the barrel is sufficient to meet the next injection volume, because the product cooling and pre-molding at the same time the general requirements of the pre-plastic time does not exceed the product cooling time, so as to avoid

Affect the molding cycle.
5, injection device
Whether the injection device retreats depends on the process of processing the plastic. Some of them returned back after pre-plasticization, some returned before pre-plasticization, some returned before pre-reforming, and some injection devices did not return 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. Some to facilitate the clearing, also

The injection device is often returned.
6, open and eject products
After the product in the mold is cooled and set, the mold clamping mechanism opens the mold. In the joint action of the ejection mechanism of the injection machine and the ejector mechanism of the mold, the product is automatically topped off and made 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).

Second, the feasibility of frequency conversion of injection molding machine:
A general-purpose injection molding machine equipment, in a complete injection molding process, the pressure requirements for the stages of clamping, injection, filling, melting, cooling, and mold opening are different.

Smaller pressure can be used, but it requires a lot of pressure when melting and cooling to ensure product quality and productivity. According to the principle of injection molding machine, we know that the higher the motor speed, the injection pressure also

The bigger the inverter is, the better the variable-speed and energy-saving of the motor of the injection molding machine is achieved.
At present, most injection molding machine manufacturers do not use energy-saving converter technology, or star-delta start-up, which is directly powered by the power frequency grid, and has large starting currents and wastes power.

If the method of variable frequency speed regulation is adopted, the soft start of the motor of the injection molding machine 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 improvement.

. 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 used in many injection molding machines.

Users get very good evaluation 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 frequency conversion energy-saving transformation of the general injection molding machine is usually: the power signal that will be used to control the adjustment of the proportional control valve, after the conversion processing is used as a given signal of the output frequency of the frequency converter, or will be

After the process control signals of the molding machine, injection molding, glue injection, cooling, and mold opening of the molding machine are processed, the multi-speed or program control signal of the inverter (also the given signal of the output frequency of the inverter) is processed.

) This adjustment method is used to meet the pressure and flow requirements of the injection molding machine for various processes, and achieve the purpose of energy conservation. (See Figure 2)
In order to realize the optimum working conditions of the injection molding machine during the frequency conversion adjustment, our company has specially researched and developed an automatic switching circuit for the pressure and flow control of the injection molding machine with dual signal control loops, which can be based on each injection molding machine.

The flow of different working links and the different pressure requirements automatically select signals, which makes it easier to use when processing some high-precision plastic products.
Energy-saving principle and feasibility analysis of presses

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. So you can see

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 50Hz power frequency, it cannot be based on actual needs.

Try to reduce its speed, 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 the P=f(t) process of the injection molding machine in Fig. 1, it can be seen that its main oil pump pressure varies and fluctuates at different time intervals. This has the potential for 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 power saving controller of the injection molding machine controls the current signal of the proportional flow valve (0-1A) according to the ratio of the flow rate set in each production stage to obtain a proportional 0-1 A/M meter to open.

The proportional opening of the solenoid valve provides the pressure required by 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 a drive command to control the oil

Pressing the rotational speed of the drive motor, the oil pump only replenishes the part consumed in the oil circuit. The oil pump motor runs the corresponding rotational speed according to the proportional command and outputs the corresponding flow to provide the pressure required by the system. Ie need

How much is provided, it does not waste at the source. Therefore, the frequency conversion power saving system has obvious power saving effect in the entire production process of the injection molding machine, so that energy saving can be achieved in a large scale.

Electricity brings considerable economic benefits to users.
V. Application Cases Project Case 1: Transformation of a large-scale injection molding machine in Nanhai Xinfeng Plastic Factory, Guangdong
Shenzhen Riye Electric Co., Ltd. cooperated with an energy-saving equipment technology development co., LTD. of Dongguan City, and developed a new 55KW large injection molding machine (by Donghua 800) for Guangdong Nanhai Xinfeng Plastic Factory.

The frequency conversion transformation was carried out. The maximum pressure of this machine can reach 2,000 tons, and the maximum feeding capacity can reach 16,000 grams. Six medium and large-sized water pipe joints can be produced in about 1-2 minutes. This is a successful technical transformation of the inverter

The model 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 factory has confirmed another six injection molding machines.

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.

Selection of industrial frequency, frequency conversion main circuit and frequency converter

The main oil pump 55KW is selected from Shenzhen ZHIYA Electric Co., Ltd. ZY3200-ZY055T4 frequency converter four, after six months of use, proves that the frequency converter has good performance, reliable operation, high energy-saving rate, the main power

The road adopts the power frequency-frequency conversion two sets of power supply methods (ie, dual-loop control of frequency conversion and power frequency interlocking interchange) to ensure uninterrupted work.
Matters needing attention in frequency conversion transformation application
1. It is necessary to use an injection molding machine with proportional flow control to carry out frequency conversion energy saving transformation.
2. The 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 relays control the speed of the injection molding machine is to use the hand to adjust the flow valve control speed, the effect of frequency conversion energy-saving reform is not ideal. For small injection molding machines also roll-to-inverter response speed

Special requirements require careful conversion of frequency conversion energy.
4. Under normal circumstances, the installation of energy-saving inverter will not affect the operation of the injection molding machine, in order to ensure production efficiency, some process parameters need to be adjusted
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%
(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 FQC inspection by the factory. (3) Machine performance: After frequency conversion was adopted, the surface temperature of the motor was increased. The frequency of the motor was 53.6°C. The maximum temperature is 57.5°C, still in

Within the scope of motor safety, this is due to the fact that during the entire cycle of the motor, depending on the production process, the motor's cooling fans have reduced wind power. 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. Therefore, there are some specific problems in the on-site reconstruction, and some are used.

The normal phenomenon after the frequency conversion velocity modulation technology, and some are the shortcomings that should overcome in the product or the application.
6.1 Motor High-frequency Noise Is Sharper Than Mains
Since the output voltage of the inverter is composed of many pulse trains, there are higher harmonics, and when the motor rotates at different speeds, different loudness and slightly sharp sound will be emitted. This is a normal phenomenon.

, And can reduce the squeak by reducing the frequency of the variable frequency carrier.
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

During the transfer phase, the cooling fan speed of the motor is reduced, the heat dissipation capacity is reduced, and the temperature rise may increase by about 3 to 5°C. Because the general oil pump motor insulation class is in class B or F above, so the motor temperature rise is still in

The allowable range 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 frequency conversion device will interfere with some control circuits of the injection molding machine and affect the normal operation of the injection molding machine, especially some inverters with rough manufacturing process and large harmonic content.

The performance of the injection molding machine with unstable process is more obvious, which requires us to take some measures to solve the interference problem at the scene. The interference sources mainly have the following two aspects: (1) Higher harmonics pass the wire

The radio frequency interference generated can be solved by installing equipment that suppresses radio frequency interference on the input or output side of the frequency conversion device, such as a magnetic ring or a filter; (2) Input harmonics pass through

The power source is coupled to other electrical equipment to form interference, and such interference can be installed on the input side of the frequency conversion device, or the installation of the line-side AC reactor has a certain effect; in addition, the same

It is best that other devices under a power supply can perform isolated power supply.
6.4 Influence on the efficiency of injection molding production Frequency conversion energy saver has a certain acceleration/deceleration time during the control of the speed of the oil pump motor, which has a certain lag compared to the original solenoid valve opening speed, resulting in a unit processing cycle.

The period is prolonged, and the production efficiency is affected. As the SY3200 inverter energy-saving device of the day can adopt two-way signal control of flow rate and pressure, and at the same time modify some injection molding machine parameters according to the situation, it can

Better solve this problem.