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What aspects should be focused on during the daily inspection of the induction coil of a medium-frequency electric furnace?
The daily inspection of the induction coil of the medium-frequency electric furnace is the key to preventing faults and extending its service life. It is necessary to focus on four core aspects: visible damage, cooling efficiency, insulation condition, and structural stability. Specifically, the following aspects should be given particular attention:
I. Appearance and visible Damage Examination
Surface burns and damages
Focus on checking the surface of the coil (especially the inner side close to the charge) for any slag points, scorch marks or breakdown holes formed by the splashing of molten steel/iron (high-temperature splashes can directly damage the insulation layer).
Check whether there are mechanical scratches or cracks at the corners and inter-turn gaps of the coil (physical damage caused by hoisting or impact of furnace charges can easily lead to subsequent insulation failure).
Foreign substances between turns and cleanliness
Metal debris, slag and dust stuck between the turns of the coil (metal foreign objects can cause inter-turn short circuits, and dust accumulation will affect heat dissipation).
Ii. Inspection of the Cooling Water Circuit Status (Core!)"
The induction coil relies on water cooling for heat dissipation. A fault in the waterway will directly lead to overheating and burnout, which requires special attention
Leakage and Sealing
Check whether there is any dripping or seepage at the water inlet and outlet interfaces, valves, and hose connections. (Aging of the sealing ring or loose joints are common causes. The sealing ring needs to be replaced or the interface tightened in time.)
Observe whether the hose has bulges, hardens or cracks. (In a long-term high-temperature environment, the hose is prone to aging and needs to be replaced immediately to avoid bursting.)
Water flow smoothness
Touch the pipes at different parts of the coil with your hand to feel if the temperature is uniform. If a local area is obviously hot (more than 5℃ higher than other areas), it indicates that there may be scale or blockage inside. Mark it and conduct a subsequent in-depth inspection.
Observe the return water pipeline (or flowmeter) : If the return water flow significantly decreases or the water flow is intermittent, it may be that the filter is clogged or there are foreign objects in the pipeline. It is necessary to clean them in time.
Return water temperature and pressure
Record the return water temperature (normally it should be ≤40℃). If the temperature suddenly rises by more than 5℃ during a single operation or remains consistently above 45℃, the machine needs to be shut down for inspection (it may be due to insufficient flow or local blockage).
Check whether the inlet water pressure is stable (in line with the equipment's rated value, usually 0.2-0.4MPa). A sudden drop in pressure may indicate pipeline rupture or pump failure.
Iii. Preliminary Judgment of Insulation Condition
Although daily inspections do not conduct precise insulation tests, insulation risks can be quickly determined through "appearance + abnormal phenomena"
Discharge and precursors of insulation breakdown
Observe whether there are white powder-like discharge marks or black carbonization spots on the surface of the coil and near the terminal blocks (a typical feature of local breakdown of the insulation layer, mostly caused by moisture or impurities).
If you hear a "sizzling" discharge sound or see a weak spark during operation, stop the machine immediately (it may be that the insulation between turns or to ground has been broken down).
Moisture and contamination
Check whether there is condensation or moisture on the surface of the coil (which is prone to occur when the environmental humidity is high or the cooling water temperature is too low, and moisture will cause the insulation resistance to decrease). If so, ventilation and drying are required.
Iv. Structural Fixation and Deformation Inspection
Coils are prone to loosening or deformation under high-frequency magnetic fields and vibrations, which affects the magnetic field distribution and heat dissipation.
Loosening and displacement of fasteners
Check whether the coil binding straps (glass ribbons/metal ribbons) are broken or loose, and whether the support bolts are loose (vibration can cause the fixation to fail and the coil to shift easily).
Confirm whether the distance between the coil and the furnace shell is uniform (if it is partially close to the shell, it may cause discharge to the ground).
Deformation and bulging
Observe whether there are local bulges, depressions or abnormal inter-turn spacings in the coil (sudden increase or decrease in the spacings of certain turns) (mostly caused by uneven thermal expansion and contraction at high temperatures or support failure, which can lead to disordered magnetic field distribution and local overheating).
V. Correlation Investigation of Abnormal Phenomena during Operation
If the following situations occur during operation, the coil should be immediately checked:
The pointer of the ammeter/voltmeter fluctuates violently (possibly due to inter-turn short circuit or poor contact);
A burnt smell can be detected near the furnace body (a sign of overheating and burning of the insulation layer).
A "spark" bright light appears in the coil area (directly indicating insulation breakdown).
Summary
Daily inspections require "observing with the eyes, touching with the hands, and listening with the ears"
Visual inspection: Check for damage, leakage, and discharge marks;
Touch by hand: Feel the water temperature, the hardness of the pipeline, and the tightness of the fasteners.
Ear listening: Identify abnormal sounds during operation (discharge sounds, vibration noises).
After each inspection, abnormal points should be recorded. Minor issues (such as small area burns, slight water leakage) should be dealt with promptly, while serious problems (such as insulation breakdown, obvious deformation) should be stopped immediately to prevent the fault from expanding.