A box-type electric heating furnace in a heat treatment workshop experienced furnace temperature fluctuations exceeding ±8°C, resulting in uneven workpiece hardness. The following investigation covers three areas: thermocouples, PID parameters, and furnace chamber sealing, along with maintenance solutions.
The thermocouple should be inserted into the furnace chamber to a depth of no less than 8 times its protective tube diameter, and the terminal connections need to be tightened regularly. A standard thermocouple should be used for comparison once every quarter, and replacement is required when the deviation exceeds 2.5°C. Compensation wires must not be laid in the same conduit as power lines to avoid introducing interference.
Most temperature controllers have an auto-tuning function that can automatically calculate the proportional, integral, and derivative parameters. If the overshoot still exceeds 5% after auto-tuning, the proportional band can be appropriately reduced and the integral time increased. During manual fine-tuning, change only one parameter at a time and observe for two complete cycles before adjusting the next one.
Aging door seals can cause heat leakage, resulting in lower temperatures near the furnace opening. It is recommended to check the compression of the seal every six months, and replace it if it is less than 60% of its original thickness. When through-cracks appear in the refractory bricks of the furnace lining, they should be filled with refractory mortar of the same material to avoid thermal short circuits.
The resistance value of heating wires increases after long-term high-temperature operation. When the three-phase current imbalance exceeds 10%, check whether individual elements are broken or severely oxidized. When replacing, ensure uniform spacing between the elements and the furnace wall to prevent localized overheating. The KJX-30-10 industrial electric heating furnace has a rated power of 30 kW and a maximum operating temperature of 1000°C. The furnace chamber dimensions can be customized according to process requirements, making it suitable for metal heat treatment, ceramic sintering, glass annealing, and other applications.
