Abnormal temperature of tempering furnace under vacuum

Abnormal temperature of tempering electric furnace under vacuum may be caused by various factors. Common problems and solutions are as follows:

1. Types and causes of temperature anomalies
Low furnace temperature
Phenomenon: During the heating process, the furnace temperature cannot reach the set value, and the workpiece is not fully austenitized or the insulation time is prolonged.
Reason:
Heating element aging (such as resistance wire breakage, molybdenum strip oxidation).
Power supply system malfunction (unstable voltage, poor line contact).
The insulation performance of the furnace wall decreases (due to damage to insulation materials and inadequate sealing of the furnace body).
The furnace temperature is too high
Phenomenon: The actual temperature exceeds the set value, resulting in coarse grains, brittle structure, and decreased workpiece performance.
Reason:
Temperature control system malfunction (temperature controller failure, incorrect parameter settings).
Thermocouples are damaged or have large errors (poor contact, mismatched models).
Uneven distribution of furnace temperature
Phenomenon: There are differences in hardness and deformation degree of workpieces at different positions in the same furnace.
Reason:
Dense placement of workpieces (hindering thermal cycling).
Fan malfunction (poor airflow).
Abnormal fluctuations during the heating process
Phenomenon: The heating curve shakes, and the temperature fluctuates between high and low.
Reason:
Control circuit malfunction (temperature control module damaged).
Vacuum system leakage (aging of sealing strip, leakage of thermocouple inlet).
Loose electrical connections in the heating area (oxidation of wiring terminals).
Temperature drop during insulation stage
Phenomenon: Slow cooling occurs during the constant temperature stage, resulting in insufficient tissue transformation.
Reason:
Vacuum pump leakage (pump body seal damage, pipeline rupture).
Insufficient heating compensation (power regulation failure).
System setting error (deviation of insulation time parameter).

2. Solution method
Low furnace temperature treatment
Check and replace aging heating elements (such as molybdenum strips, resistance wires).
Confirm that the power supply voltage is stable, repair or replace the power supply line.
Repair or replace furnace lining materials (such as ceramic fibers, molybdenum screens).
High furnace temperature treatment
Calibrate or replace the thermocouple (ensuring model matching and good contact).
Check if the thermostat is malfunctioning (refer to normal equipment parameters for adjustment).
Avoid overheating operation (set temperature upper limit alarm).
Uneven distribution of furnace temperature treatment
Optimize the loading method of workpieces (maintain sufficient spacing and avoid dense stacking).
Regularly conduct furnace temperature uniformity tests (calibrated using infrared thermometers).
Adjust the heating system (such as adding an auxiliary heating zone).
Heating fluctuation treatment
Check if the vacuum degree is normal (vacuum gauge reading ≥ -95KPa).
Confirm that the heating circuit is in good contact (tighten the wiring terminals).
Repair the temperature control module (replace damaged relays or sensors).
Thermal insulation and cooling treatment
Check the sealing condition of the vacuum system (apply soapy water to check for leaks).
Add temperature control compensation function during the insulation stage (adjust PID parameters).
Recheck the process parameters to ensure accurate insulation time and temperature settings.

3. Preventive measures
regular maintenance
Check the performance of heating elements, thermocouples, and temperature controllers every quarter.
Replace the lining insulation material (such as ceramic fiber board) every year.
Operating Specifications
Avoid frequent starting and stopping of equipment (to reduce thermal shock).
Strictly set the temperature curve according to the process parameters (no arbitrary adjustment is allowed).
Spare Parts Management
Reserve commonly used spare parts (such as thermocouples, solid-state relays, sealing strips).
Establish a rapid response mechanism with equipment suppliers to ensure timely repairs in case of malfunctions.