Box-type electric furnace What are the proper maintenance methods? Maintenance, repair, and upkeep of box-type electric furnaces.
What are the proper maintenance methods for a box-type electric furnace?
In China, muffle furnaces are commonly referred to as resistance furnaces, electric furnaces, or simply muffle furnaces. A muffle furnace is a versatile heating device. Based on their physical configuration, they can be classified into box-type furnaces, tube-type furnaces, and crucible furnaces.
1. To ensure measurement accuracy, the temperature display of the XMT-type temperature controller shall be calibrated annually using a DC potentiometer to prevent significant measurement errors.
2. The instrument shall be placed in a dry, well-ventilated area free of corrosive gases, with an operating ambient temperature of 1050°C and a relative humidity not exceeding 85%.
3. Regularly inspect all hotline connections for looseness and verify that the contacts of AC contactors are in good condition; any faults detected should be repaired promptly.

4. If, in accordance with the aforementioned operating procedures, the product fails to function properly during normal use due to manufacturing defects, it shall be repaired or have its defective parts replaced free of charge within one year, up to and including replacement of the entire product. However, unless the manufacturer has first determined the root cause of the quality issue, the user shall not disassemble or reassemble the product on their own; otherwise, the user shall be responsible for all maintenance and repair costs.
5. For silicon-carbide-rod furnaces, when a silicon-carbide rod is found to be damaged, it should be replaced with a new rod of the same specification and with a resistance value that is closely matched. During replacement, first remove the protective end caps and the rod clamps, then carefully extract the damaged rod. Because silicon-carbide rods are brittle and prone to breakage, exercise caution during installation; the exposed portions at both ends must be of equal length, and the clamps must be securely tightened to ensure good contact with the rod. If the clamps show severe oxidation, they should be replaced. Any gaps around the mounting holes at the ends of the silicon-carbide rods should be sealed with asbestos rope. The muffle furnace temperature must not exceed the maximum operating temperature of 1350°C. Silicon-carbide rods may operate continuously at this temperature for up to 4 hours. After prolonged use of the muffle furnace, if turning the heating-power adjustment knob clockwise to its maximum position still fails to increase the heating current to the rated value—resulting in a significant deviation from the rated current and an inability to achieve the required heating power—it indicates that the silicon-carbide rods have aged. In such cases, the series-connected rods can be reconfigured to a parallel connection, allowing continued operation. When changing the wiring configuration, there is no need to dismantle the rods; simply modify the wiring. However, after making the change, care must be taken to adjust the heating-power knob gradually during operation, ensuring that the heating current does not exceed the rated value.

Operation of the Box-Type Electric Furnace

Box-type electric furnaces share the general characteristics of electric furnaces; however, when it comes to actual furnace maintenance, operational precautions, pre-commissioning preparations, and the commissioning and production process, they still have their own distinct features:
I. Operational Precautions
(1) When the temperature of the box-type electric furnace exceeds 400°C, abrupt cooling by fully opening the furnace door is prohibited.
(2) The maximum operating temperature shall not exceed the rated temperature.
(3) The charging load shall not be excessive, and the resulting temperature drop shall not exceed 50°C.
(4) Do not apply excessive force when loading the furnace to avoid damaging the furnace bottom.
II. Preparations Before Starting the Furnace
(1) Inspect the electrical control cabinet for tools or other conductive materials, and promptly remove any workpieces left inside the furnace.
(2) After closing the switch, check whether the electrical switch contacts are making proper contact.
(3) Verify that the temperature control instrument is functioning properly, and turn on its power switch to put it into operation.
III. Furnace Startup and Production
(1) Set the temperature on the automatic temperature control instrument according to process requirements.
(2) Set the “handle” control to the automatic mode to heat up.
(3) Heat the furnace from cold; once the desired temperature is reached, hold at that temperature for 2 hours before loading the workpieces. Continuous production is permitted, and consecutive furnace loads are allowed.
(4) Parts shall be placed evenly and securely within the furnace; as with vertical furnaces, contact between the parts and the heating elements is strictly prohibited.
(5) Operate strictly in accordance with the process specifications.

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