The temperature of the gas filled tube furnace cannot rise

The temperature of the tube furnace with gas supply cannot rise, which may be caused by various factors such as heating system, gas environment, control system, furnace structure or operation mode. The following is a detailed analysis of the reasons and corresponding solutions:

1. Heating system malfunction
a. Heating element damaged
Reason: Heating elements such as heating wires, silicon carbon rods, or silicon molybdenum rods are aging, broken, or have poor contact, resulting in insufficient heating power.
Phenomenon: The furnace temperature rises slowly, or the local temperature is too low.
Solution:
Use a multimeter to check the resistance value of the heating element, compare it with the rated value, and determine whether there is an open circuit or short circuit.
Replace damaged heating elements to ensure secure installation and good contact.
b. Power supply issues
Reason: Unstable power supply voltage, aging circuit or contactor failure, resulting in insufficient input power.
Phenomenon: The furnace temperature cannot reach the set value, or the voltage fluctuates during the heating process.
Solution:
Check the power circuit to ensure there is no damage, looseness, or short circuit.
Use a voltmeter to monitor the input voltage and ensure it is within the rated range.
Replace the faulty contactor or circuit breaker.
c. Transformer or thyristor failure
Reason: Transformer turn to turn short circuit, thyristor breakdown or trigger circuit failure, resulting in a decrease in output power.
Phenomenon: Slow rise in furnace temperature or power fluctuations during heating process.
Solution:
Check the resistance of the transformer winding to determine if there is a short circuit.
Use an oscilloscope to detect the trigger signal of the thyristor and confirm that the trigger is normal.
Replace the faulty transformer or thyristor.

2. Gas environmental impact
a. Cooling effect of introducing gas
Reason: The excessive flow of gas (such as cold air and nitrogen) introduced carries away a large amount of heat, resulting in a decrease in furnace temperature.
Phenomenon: Slow rise in furnace temperature or temperature fluctuations during heating process.
Solution:
Adjust the gas flow meter to reduce the incoming gas flow rate, or use preheated gas (such as heating through a preheater before introducing).
Install baffles or flow guides at the entrance of the furnace tube to reduce the direct impact of gas on the heating zone.
b. Poor thermal conductivity of gas
Reason: The low thermal conductivity of the introduced gases (such as argon and hydrogen) leads to a decrease in heat transfer efficiency.
Phenomenon: The furnace temperature rises slowly or the heating uniformity is poor.
Solution:
Choose a gas with better thermal conductivity (such as a mixture of nitrogen and hydrogen).
Optimize the airflow distribution inside the furnace by using porous plates or uniform flow devices to improve the heat exchange efficiency between gas and samples.
c. Gas oxidation or reduction reactions
Reason: The introduced gas (such as oxygen, hydrogen) reacts with the sample or furnace tube material, consuming heat or producing by-products.
Phenomenon: The furnace temperature rises slowly, or the surface of the sample changes color or cracks.
Solution:
Strictly control gas purity to avoid impurities from participating in the reaction.
Before introducing gas, first evacuate and then introduce high-purity gas to eliminate residual oxygen.

3. Control system issues
a. Temperature sensor malfunction
Reason: Sensors such as thermocouples, thermistors, or infrared thermometers are damaged, offset, or have poor contact, resulting in inaccurate temperature measurements.
Phenomenon: The actual furnace temperature does not match the displayed temperature, or the heating system malfunctions.
Solution:
Use a standard temperature source to calibrate the sensor and confirm the measurement accuracy.
Replace the faulty sensor to ensure correct installation position and avoid thermal radiation interference.
b. Temperature controller parameter setting error
Reason: Improper setting of PID parameters (proportional, integral, derivative) leads to slow response or oscillation of the heating system.
Phenomenon: The furnace temperature rises slowly, or there are significant temperature fluctuations during the heating process.
Solution:
Adjust the PID parameters again, using self-tuning function or manual debugging to make the system respond quickly and stably.
Set a reasonable heating rate (such as 5-10 ℃/min) to avoid sudden temperature changes.
c. Program control logic error
Reason: Error in programming the heating program, such as setting the stage temperature too low, insufficient holding time, or incorrect jump conditions.
Phenomenon: The furnace temperature cannot reach the set value, or the program is interrupted during the heating process.
Solution:
Check the heating program to confirm that the temperature, time, and jump conditions for each stage are correct.
Simulate running the program and observe whether the heating system response meets expectations.

4. Furnace structure issues
a. Poor sealing of furnace tubes
Reason: Air leakage at the connection between the furnace tube, flange, and seal, resulting in heat loss or gas mixing.
Phenomenon: Slow rise in furnace temperature, or gas leakage alarm during heating process.
Solution:
Check if the seals (such as O-rings, graphite gaskets) are aging or damaged, and replace them with new seals.
Tighten the flange bolts evenly to ensure a smooth and scratch free sealing surface.
b. The insulation layer of the furnace body is damaged
Reason: Thermal insulation materials such as insulation cotton and ceramic fiberboard are aging, falling off, or getting damp, causing heat loss.
Phenomenon: The furnace temperature rises slowly, or the temperature of the furnace shell is too high.
Solution:
Check the insulation layer, repair or replace damaged parts.
Cover the outer surface of the insulation layer with aluminum foil or reflective film to reduce radiation heat dissipation.
c. Mismatch in furnace tube size
Reason: The inner diameter of the furnace tube is too large or the sample is placed improperly, resulting in a decrease in heat transfer efficiency.
Phenomenon: Slow rise in furnace temperature, or uneven heating of the sample.
Solution:
Select furnace tubes with appropriate inner diameters to ensure that the sample is in close contact with the heating zone.
Optimize the sample placement method, such as using brackets or washers to fix the sample and reduce thermal resistance.

5. Improper operation method
a. The heating rate is too fast
Reason: The heating rate exceeds the capacity of the furnace tube or sample, resulting in thermal stress cracking or temperature control failure.
Phenomenon: The furnace temperature rises slowly, or there are significant temperature fluctuations during the heating process.
Solution:
Set a reasonable heating rate (such as 5-10 ℃/min) to avoid sudden temperature changes.
Set insulation stages at key temperature points (such as material phase transition temperature) to ensure temperature uniformity.
b. Excessive sample load
Reason: The sample quality or volume is too large, resulting in a decrease in heat transfer efficiency.
Phenomenon: Slow rise in furnace temperature, or uneven heating of the sample.
Solution:
Reduce the sample size for a single experiment or adopt a batch processing method.
Optimize sample shape (such as flakes, particles) to reduce thermal resistance.
c. Untreated gas
Reason: The incoming cold gas directly impacts the heating zone, causing a local temperature drop.
Phenomenon: Slow rise in furnace temperature or temperature fluctuations during heating process.
Solution:
Before introducing gas, first evacuate and then introduce preheated gas (such as heating to near furnace temperature through a preheater).
Install baffles or flow guides at the entrance of the furnace tube to reduce the direct impact of gas on the heating zone.