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Common Maintenance Methods for Medium-Frequency Induction Furnaces
Aug 30,2020
Medium-Frequency Induction Furnace Maintenance Methods
One, Medium-frequency furnace The repair methods are also similar to those used in traditional Chinese medicine—looking, listening, asking, and feeling the pulse.
Specifically as follows:
1. Visual Inspection: Check visually for loose wiring, loose screws, dust or moisture, and any signs of arcing or sparking. If you identify any issues, address them promptly.
2. Listening: Turn on the equipment and listen carefully for any unusual sounds, such as abnormal noises from the reactor or sparking sounds from the furnace body. Address any issues promptly upon detection.
3. Question: When performing maintenance, maintenance personnel should ask the operator and furnace operator about any abnormalities during equipment operation, and proceed with inspection only after gaining a clear understanding of the situation.
4. Testing refers to using instruments for inspection and measurement, such as multimeters and oscilloscopes, to check whether any components have been punctured or damaged.
II. Specific Steps for Medium-Frequency Furnace Maintenance:
First, divide the equipment into three parts.
1. Rectification For part of the inspection, use a multimeter to check whether the rectifier thyristor has broken down.
① To measure a rectifier thyristor, use a multimeter (a pointer-type multimeter is preferred) and set it to the R×1 kΩ range. The resistance measured across the anode and cathode of the thyristor in-circuit should be between 30 and 40 kΩ. If the resistance falls below 30 kΩ, the device may operate unreliably and trigger protective actions repeatedly; consider replacing it. If the resistance drops below 20 kΩ, replace it immediately to avoid more serious potential hazards.
② When using the R×1 Ω range on a multimeter to measure the resistance between the gate and cathode of a thyristor, the reading should be around 15 Ω. If the resistance is greater than 25 Ω or less than 8 Ω, the device’s performance is poor, which may lead to unstable operation. If the resistance is above 30 Ω or below 6 Ω, there’s no need to worry further—simply replace the thyristor immediately to avoid creating even greater risks.
③ Check whether the rectifier trigger pulses are missing by observing whether the light-emitting diode is lit. If the LED doesn’t light up, it can be assumed that there’s a problem with the trigger board. Perform a visual inspection to check for loose wiring, desoldering, or blackened marks on the trigger board. If any abnormalities are found, replace the trigger board.
2. The inverter section. Checking the inverter section is slightly more complex than checking the rectifier section, but as long as you proceed carefully and meticulously, all issues can be resolved.
① Using a multimeter (a pointer-type multimeter is preferred), set the meter to the R×1 KΩ range and measure the resistance between the anode and cathode of the thyristor in-circuit. The resistance should be above 7 kΩ. If the resistance is less than 7 kΩ, the device may operate unreliably and trigger protective actions repeatedly; in such cases, consider replacing the thyristor.
② When using the R×1 Ω range on a multimeter to measure the resistance between the gate and cathode of a thyristor, the reading should be around 1.5 Ω. If the resistance is greater than 25 Ω or less than 8 Ω, the thyristor’s performance is poor, which may lead to unstable operation. If the resistance is above 30 Ω or below 6 Ω, there’s no need to further consider it—simply replace the thyristor immediately to avoid creating even greater potential hazards.
③ Check whether the inverter trigger pulses are missing by observing whether the light-emitting diode is lit. If the LED doesn’t light up, it can be assumed that there’s a problem with the trigger board. Perform a visual inspection to check for loose wiring, desoldering, or any signs of burning and discoloration on the trigger board.
Replace it if an abnormality is detected.
④ Use a multimeter to check whether the resistor and capacitor in the protection circuit are open-circuited or whether the protective capacitor has failed and broken down. Replace any components found to be defective immediately.
3. Capacitor and furnace body section,
① If the equipment is malfunctioning and fails to start, first check whether the capacitor has broken down or whether the water cable is disconnected. Replace or address any issues found promptly.
② Check whether the induction coil has inter-turn arcing or water leakage.
③ Is the furnace body damp or contaminated with metallic dust, etc.?
④ Is the furnace lining too thin and leaking molten steel? If any issues are detected, address them promptly—do not continue operating with the problem.
Work while sick to avoid creating greater potential for failure.
Section 2: Common Fault Inspection and Maintenance of Intermediate-Frequency Furnaces
1. The medium-frequency furnace cannot be started.
1. First, use a multimeter to check whether the thyristor is punctured or exhibits any other abnormalities. If any abnormalities are found, replace it.
2. Perform a visual inspection to check for broken wires, desoldering or cold solder joints, and loose screws. If any issues are found, replace or address them promptly.
3. Measure whether the capacitor is shorted and whether the water cable is broken. If any issues are found, replace or address them promptly.
4. Send the control power supply and check whether all indicator lights on the circuit board are lighting up normally, and whether the pulse board’s indicator light is illuminated. If any abnormalities are detected, replace the circuit board or the pulse board with new ones.
5. If the above steps still fail to start the system, proceed with measuring and replacing the intermediate-frequency transformer. Check whether the current transformer has been deformed due to overheating or whether its winding has broken; if so, replace it with a new one.
6. Measure whether the incoming line voltage is abnormal or if any phase is missing, and address any issues promptly upon detection.
7. Check whether the water system’s temperature and pressure are abnormal, and take appropriate action if necessary.
8. Check whether there is any furnace-to-furnace leakage, short circuits between the induction coil and the furnace body, or even try running an empty furnace to see if it can start up.
In summary, the issues mentioned above can usually be resolved through the steps outlined above. The key is to be meticulous and patient, leaving no tiny detail overlooked. Sometimes, after several days of troubleshooting without success, you’ll finally discover that a screw has come loose—details like these are precisely the ones that people tend to overlook most easily. I hope that when you encounter problems, you won’t panic but instead remain calm, careful, and confident. With this mindset, you’ll surely be able to pinpoint and eliminate the fault.
2. Frequently burning thyristors—continuous burning of thyristors,
1. The thyristor frequently trips unexpectedly. This fault can be attributed to the following reasons:
① The water temperature is high—above 50 degrees—and the water pressure is low—less than 0.1 megapascal—indicating that there’s a blockage in the water line.
② There is a problem with the RC snubber circuit: the resistor is open-circuited, and the capacitor has failed.
③ Degradation of the pulse trigger board performance and cold solder joints in the trigger wires.
④ The reactor has inter-turn short circuits causing abnormal noises and leakage current.
⑤ The intermediate-frequency transformer’s current transformer is abnormal.
⑥ The induction coil of the furnace body exhibits electrical leakage and arcing.
2. Continuously burn the thyristor at a fixed position.
This type of fault has a relatively small scope and is more targeted and easier to address.
The inspection will focus on the following points:
① Replace the trigger board. There’s a possibility that the pulse transformer has inter-turn leakage, a phenomenon that cannot be measured or diagnosed on-site—only replacement will suffice.
② Check whether the resistor in the RC protection circuit is open-circuited and whether the capacitor has lost its capacitance. Use a multimeter to perform the measurement.
③ During work, use a temperature gun to check whether the thyristor’s temperature is high. Typically, if the temperature exceeds 50 degrees, it could lead to silicon burnout. This situation might be caused by an obstruction in the water circuit, scale buildup in the radiator, or blockage from impurities. Heat dissipation...
The tool clamp screw is loose.
If, after following the above steps and finding no abnormalities, you replace the silicon with a new one and continue firing, it’s possible that the water jacket has aged over time, causing the silicon surface to become depressed and uneven. In this case, be sure to replace the water jacket immediately to prevent future problems!
Remember to regularly tighten the radiator screws with a wrench—ideally, a torque wrench would be best. For SCRs rated at 2000A or higher, the tightening torque for the screws should exceed 70 kN. Never take chances or rely on luck.
In summary, when troubleshooting, you must be meticulous and thorough, leaving no detail overlooked in order to effectively resolve the issue. Never rely on luck or take things lightly. Additionally, always prioritize safety and never be careless, lest you inadvertently cause unnecessary problems.
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Kangda Electric Furnace specializes in the manufacture of the following equipment: KGCL series medium-frequency power supplies, KGPS series medium-frequency power supplies, GTR series medium-frequency induction heating furnaces...
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