During on-site operation, a sudden deterioration in the furnace temperature uniformity of an industrial electric heating furnace is often related to the heating elements, furnace lining, or temperature measurement system. The following sections explain this from a maintenance perspective.
Resistance heating elements operate at high temperatures for long periods, and surface oxidation and local fusing are common problems. The resistance of the elements should be measured monthly after power-off, and replacement is recommended when the deviation exceeds 10% of the initial value. During replacement, ensure that the spacing between the elements and the inner wall of the furnace chamber is consistent to avoid local overheating caused by installation position deviation. For a 950°C working condition, high-temperature-resistant alloy resistance wire is recommended, and check whether the wiring terminals are loose or oxidized.
Cracks or spalling in the refractory material of the furnace lining will directly lead to increased heat loss and furnace temperature fluctuations. The inner wall of the furnace chamber should be inspected quarterly. Small-area cracks can be repaired with refractory mortar, while large-area spalling requires rebuilding. Moisture in the insulation layer will reduce its thermal insulation effect, so after shutdown the furnace door should be kept slightly open for ventilation. If the surface temperature of the furnace shell is found to rise abnormally, check whether the insulation layer has failed.
Thermocouples may drift after long-term use, so it is recommended to compare them with a standard thermocouple once every six months. Temperature control instruments need regular calibration, and adjustment or replacement should be made when the deviation exceeds ±5°C. Pay attention to the connection polarity of the compensating导线; reversing it will cause abnormal temperature display.
Before starting the furnace, confirm that the furnace door limit switch is normal and the over-temperature alarm device is effective. Avoid frequently opening the furnace door during operation to prevent thermal shock from damaging the furnace lining. Clean oxide scale and debris from the furnace chamber monthly, and check that the grounding resistance is less than 4Ω. For long-term shutdown, cut off the power supply and take moisture-proof measures.
