Discussion on frequency conversion operation of in

2022-08-24
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Introduction plastic machinery is an important pillar of the development of the plastic industry. It provides advanced technical equipment for the plastic industry. Its development is the basis of the development of the plastic industry and is also affected by the development of the plastic industry. Worldwide, the three major types of plastic machinery are injection molding machines and extruders: extrusion production lines and blow molding machines, which account for more than 80% of the total output value of plastic machinery, of which injection molding machines account for more than half of the total of these three types of machinery. The author makes a brief introduction to the frequency conversion operation of the injection molding machine from his personal experience, from its characteristics and field application

2. Introduction to the work of injection molding machine system

to do a good job in the frequency converter of injection molding machine, we must first start with injection molding. The injection molding process is generally divided into the following steps: mold locking → injection and pressure maintaining → melt feeding → cooling and shaping → mold opening ejector pin. The completion of each action has a delicate coordination of several parameters such as time, pressure, speed and position, that is to say, the displacement at a certain position has corresponding pressure and speed, and its pressure and speed are variable in different positions and times. At the same time, after each action is completed, a termination signal is sent to the program controller, and the program controller sends the instruction to execute the next action after receiving the signal. In addition, there are also some weaknesses in the injection molding machine system itself: first, there is a very violent mutation process within the action of the injection molding machine: for example, the mode locking over transfer switch should be turned to the loading range, and the new polyurethane baycusan? C 1010 can help easily realize these two requirements that seem difficult to coordinate, and the mutation is very intense; For another example, in the injection process, the working condition of the injection process of slow injection → fast → slow → fast → slow is also very intense, which has a great impact on the machine and affects the life of the whole injection system. Second, the acting oil circuit braking cannot reach the design accuracy. The opening and closing of the oil circuit braking depends on the solenoid valve, and the action of the solenoid valve depends on the voltage and current provided by the process controller. Because most injection molding machines do not have dead cycle control, the opening and closing accuracy of the valve will be greatly reduced, especially when the opening and closing degree of the valve is less than 10% and more than 90%, the repetition accuracy and stability of the action are extremely poor, When an action is executed in this state, it is difficult to ensure its stability and repetition accuracy. Third, the oil seal of the oil cylinder performing the action is damaged, and there is internal leakage, so the reliability and stability of the action is not high. This is because the actual oil consumption of the load is less than the oil supply of the oil pump most of the time, causing the hydraulic oil under high pressure to overflow through the overflow valve, proportional valve and other hydraulic components. The overflow part not only does no useful work, but also generates heat, causing the hydraulic oil to heat, which is both energy consuming and harmful. Using the frequency conversion operation of the injection molding machine can solve these problems well, which not only improves the accuracy and stability of the whole injection molding system, reduces the huge mechanical impact, prolongs the service life of the system, but also saves a lot of electric energy

3. Variable frequency operation of injection molding machine:

3.1. Basic principle of variable frequency operation and energy saving

the traditional injection molding machine uses a quantitative pump to supply oil, and each action in the injection molding process has different requirements for speed and pressure. It bypasses the excess oil back to the oil tank by overflow regulation through the proportional valve of the injection molding machine. In the whole process, the speed of the motor is constant, so the oil supply is also fixed, Since the execution action is intermittent and cannot be full load, there is a lot of waste space for quantitative oil supply, which is at least about 50% according to the actual measurement. Frequency conversion energy saving is aimed at this waste of space. According to the action signals sent by the injection molding machine, adjust the motor speed (i.e. flow regulation) required by each action in a timely and appropriate manner, so that the amount of oil pumped can just meet the needs of the action, and stop the motor in the non action state, so that the energy-saving space is further increased, Therefore, the energy-saving transformation of the injection molding machine and the rigid polyurethane insulation board are derived products that can bring great energy-saving effects

3.2. On site operation of dzb series injection molding machine special frequency converter

3.2.1. The principle block diagram of dzb series injection molding machine special frequency converter is shown in Figure 1

3.2.2. The main circuit diagram of dzb series injection molding machine special frequency conversion cabinet is shown in Figure 2

3.2.3. Installation of frequency converter:

dzb series injection molding machine special frequency converter adopts cabinet structure. Therefore, the installation is very simple. In addition to the usual three wire input and three wire output, the grounding of the frequency converter is also very important and must be safe and reliable. The flow signal and pressure signal of the injection molding machine need to be connected to the (0 ~ 1a) special signal interface inside the frequency converter

3.2.4. Debugging of frequency converter:

(1) setting of acceleration and deceleration time: in order to meet the purpose of energy saving, the frequency converter controls the motor to adjust the speed of the motor in time with the change of feedback. Because its acceleration and deceleration must have a certain time, if the acceleration time is set too long, it will affect the response speed of the action, resulting in some actions being slow or even impossible to complete; If the acceleration time is too short, it will lead to overcurrent when the system accelerates, and the frequency converter may frequently carry out overload protection. Therefore, the setting of this time should be appropriate to ensure the normal use of the frequency converter without affecting production. The setting of deceleration time is the same, too long will affect the action response and energy saving effect; If it is too short, DC bus overvoltage and overcurrent will occur, and the frequency converter will also be protected. The acceleration and deceleration time setting range of Fuling frequency converter is wide, which can be set arbitrarily from 0.1 to 999.9 seconds. The commissioning personnel can set it according to the specific working conditions. If there are special working conditions, energy consumption braking can be used

(2) overload protection is a basic function of frequency converter. Now let's understand the level of overload capacity, which directly affects the continuity of injection molding production. Generally speaking, overload protection is an important indicator to measure the reliability of frequency converter. The strength of overload capacity is related to the allowable overload time and the percentage of allowable overload, which is characterized by inverse time limit. The overload protection of general frequency converter is set to 150% for 1 minute. The special inverter of Fuling injection molding machine has strong overload capacity, and its overcurrent protection is widened to 180% of the rated current for 1 minute; The short-circuit protection current is also designed to be 300% of the rated current

(3) the function selection and overvoltage protection of overvoltage stall are also a protection function of the frequency converter. If the selection and setting are incorrect, normal production will be affected. This is mainly because the actual speed of the motor will be higher than the output synchronous speed of the frequency converter due to the effect of load inertia during the deceleration operation of the frequency converter. At this time, the motor will feed back electric energy to the frequency converter, causing the voltage of the DC bus of the frequency converter to rise. Because the Fuling frequency converter uses a self-excited switching power supply internally, the working voltage range is wide, which is ± 20% of the rated voltage. Of course, because the motor is in the generator phase

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