Detailed Safety Precautions for the Operation of Medium-Frequency Melting Furnaces
2021-12-10
1. The medium-frequency melting furnace should be used regularly and not left idle for extended periods. If the furnace has been stored unused for a long time, it’s essential to first run a fan for 1 hour to remove any moisture and dust buildup inside before powering it up at low wattage for a test run. Only after confirming that everything is functioning properly should you proceed with normal operation.
2. Always monitor water temperature and pressure; ensure all water lines remain unobstructed, with no leaks or blockages.
3. Closely monitor the readings displayed on the medium-frequency melting furnace instruments. The readings should remain stable without any stirring. If an instrument is damaged, it should be replaced promptly. The control cabinet is equipped with a fan that effectively cools the unit and helps remove excess moisture. Please keep an eye on the fan’s operation at all times, and replace it immediately if it fails.
4. Always monitor the suction force of the main AC contactor and air switch, as well as the temperature and color of the main contacts. If the contacts show signs of erosion or loosening, address the issue promptly by repairing or replacing them.
5. During the yellow mold season and rainy season, it is essential to ensure that condensation on thyristors and the main control board is promptly eliminated.
6. When observing the main circuit waveform, the oscilloscope's cathode must be disconnected from the power supply's ground wire to prevent electrical components from being damaged due to a series connection at the grounding point. Please pay special attention to safety, as the oscilloscope housing may be energized.
7. Before energizing, three 20–30A fuses should be connected to the incoming side of the three-phase power grid, along with proper arc protection. This setup effectively prevents short circuits in the medium-frequency power supply from causing damage—such as burning out thyristors and other critical components—as well as safeguarding the main circuitry and devices. This step is crucial for preventing short-circuit currents from spreading beyond the medium-frequency generator, potentially damaging unrelated components like distribution cabinets or power transformers. All maintenance personnel must thoroughly master this procedure.
8. Disconnect the inverter’s main circuit (remove the connecting cable from the smoothing reactor to the common anode of the inverter bridge). Then, connect six 200W/220V light bulbs (or three 2kW heating elements) in a configuration of 3 strings connected in parallel at the output end of the rectifier bridge, ensuring the rectification section operates under low-current conditions. This distribution check allows you to directly determine whether the fault lies in the rectifier or inverter section, preventing unnecessary and potentially costly repairs and minimizing the risk of introducing new human errors during troubleshooting.
9. Check the main waveform of the rectified output (referred to as the "rectification wave"). The rectification wave must be stable, accurate, smooth, and consistent across the entire phase-shift range with good linearity. If the waveform appears abnormal, it must be repaired and adjusted until it functions properly. If the waveform is normal, set the DC voltage to 300 volts and then allow the system to idle for 10 minutes. Next, inspect the resistors R1–R6 in each rectifier's SCR RC snubber circuit. All resistors should exhibit consistent temperatures; if not, it indicates a potential fault in the RC circuit, requiring a thorough investigation. Once the RC circuits are confirmed to be functioning correctly, proceed with full-voltage operation for another 10-minute period. If no issues arise during this final test, it can be concluded that the rectification section is essentially operating within specifications.
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2025-09-17