The medium frequency induction furnace is not only widely used in the production of steel and alloys, but also in the production of cast iron, especially in the casting workshop of the cycle operation. Compared with the power frequency induction furnace, it has the following advantages:

(1) The melting speed is fast and the production efficiency is high.

(2) Adaptability and flexible use.

(3) The electromagnetic stirring effect is better.

(4) Easy to start and operate. The complete set of medium frequency induction furnace includes: power supply, electrical control part, furnace part, transmission and water cooling system. The soft fault of the induction melting furnace, that is, the complex fault of the induction melting furnace can be roughly divided into several types such as poor circuit contact, poor circuit insulation, and poor component characteristics. Although the fault point of circuit insulation is theoretically detectable by megohmmeter or multimeter, due to the existence of water cooling system inside the device and other factors, it is difficult to judge the fault during the actual maintenance process.

1. Basic ideas and methods of fault checking

Induction melting furnace is mainly composed of load (including furnace switch, water-cooled cable, busbar and furnace induction coil, etc.), compensation capacitor, smoothing reactor and control cabinet (including main circuit and control circuit). After the equipment fails, the basic maintenance ideas are first considered from simple faults to prevent complicated faults. First, at the accident site, the operator should be asked in detail about the phenomenon and related situations, and obtain useful information related to the fault. In order to achieve twice the result with half the effort, and secondly in the case of conditions (without damaging the components), you can start the device to observe the fault phenomenon yourself, which helps to determine the fault range in time, thus eliminating many unnecessary cumbersome checks, if If the fault phenomenon and related conditions still cannot determine the fault range, it must be checked according to the complex fault check procedure. Commonly used fault detection methods are: alternative method, release test method, visual inspection method, contrast method, etc., and can be flexibly used according to actual conditions during specific operations.

2. Inspection method for complex faults

In the case of more complex faults, the inspection program should follow the thinking method from simple to complex, from load to control cabinet, and gradually eliminated. The check of the smoothing reactor is troublesome. If the reactance coil is used for a long time, it is better to use the replacement of the intact part to eliminate the fault. After the reactor failure may be eliminated, the fault range is gradually reduced, and combined with other inspection methods to eliminate the fault.

3. Maintenance case

Case 1: After the device is started, the power button has been turned to the end, but the indication value of each meter is still small, and the device cannot operate normally. According to the fault phenomenon, the fault range can be roughly determined in the rectification section.

Minute. Using the oscilloscope to detect the DC voltage waveform output from the rectifier bridge, it can be found that the conduction of a rectifier thyristor is not very good, but no abnormality is detected in the detection of the voltage waveform across each thyristor. The replacement method is used (the thyristor is used instead of the rectifier bridge). Zhongyuan thyristor)

After the elimination, the faulty component was found to be a phase A rectifier thyristor. Analysis: For some complex faults caused by poor electrical components, due to the limited instruments used in the inspection and other conditions, it is not easy to carry out accurate detection. The alternative method and the exclusion method are simple and effective, and are

A common method of removing such failures.

Case 2: The induction melting furnace starts normally, but when the relay switches the circuit after the startup, the overcurrent protection action is accompanied by the thyristor damage.

According to the fault phenomenon, the fault range is initially determined in the inverter control loop. The visual inspection found that the resistor on the inverter pulse forming circuit seems to have overheating. During the hand touch and shaking check, one foot is pulled out from the solder joint and re-welded firmly. After the troubleshooting. Analysis: circuit generation

Poor touch, it is difficult to measure directly with the meter, and the visual inspection method is most effective in dealing with such troubles.

Case 3: The intermediate frequency starts normally. When the voltage rises to 400V, the smoothing reactor has a slight impact sound. When it rises to full power, the overcurrent action stops.

During the inspection, a breakdown of the inverter tube was found to be damaged, and no abnormalities were found in the inspection by the maintenance personnel (the relief capacitor was not gradually removed by the release test method, but the insulation test was performed). However, in the test after the inspection, the device returned to normal. During the trial of melting a molten steel, it was found that one of the capacitors in the compensation capacitor leaked oil, and the capacitor was removed after the capacitor was replaced.

Case 4: The induction melting furnace is operating normally, but occasionally overcurrent occurs.

Protection action; the fault phenomenon gradually increases with the passage of time, the overcurrent protection action becomes frequent and irregular, and the phenomenon of breakdown of the inverter thyristor breakdown occurs from time to time. First, the circuit was found to have no abnormality. After the circuit was short-circuited by the detachment test method, the induction melting furnace returned to normal operation. Analysis: It may be because the cooling water pump has been used for a long time, and the output performance is deteriorated, causing serious fluctuations in the water pressure in the water-cooling system of the device, causing an irregular momentary disconnection of the electrical contact of the hydraulic relay, thereby causing the device to over-current protection malfunction. . Misleading by the fault phenomenon (the early overcurrent action occurs when the device is full power stage and the steel material is added), the maintenance personnel mistakenly think that the internal circuit of the device is faulty, and spend a lot of time on the comprehensive inspection. If the external factors of the device are excluded by the exclusion method, the fault handling will be easy and avoid many detours.

4. Conclusion

According to some fault cases in the induction melting furnace, this paper discusses the general maintenance procedures and maintenance methods of complex faults on the site, so as to avoid the misjudgment of faults caused by environmental factors, and save many The necessary cumbersome inspections provide a maintenance and repair ideas for quick troubleshooting and normal operation of the equipment.