As the core equipment for material heat treatment, the stability of vacuum atmosphere furnace directly affects the accuracy of experimental data and sample quality. The following summarizes the detailed manifestations, causes, and solutions of common faults from six key modules:

1、 Abnormal heating system

Fault phenomenon: Delayed heating rate, actual temperature below the set value, or localized overheating.

Core reason:

-Aging of electric heating elements: Silicon carbon rods/molybdenum wires experience grain coarsening and increased resistance under long-term high temperature, leading to a decrease in power;

-Poor contact: The electrode terminals are oxidized and loose, resulting in increased current transmission losses;

-Thermocouple failure: Compensation wire insulation layer damage causing signal drift, or hot end contacts being covered by volatile substances.

Solution:

Regularly measure the resistance of the electric heating element (new silicon carbide rod is about a few hundred ohms), and replace it if it exceeds the standard;

Polish the electrode contacts with sandpaper and apply conductive paste, and fix the wiring nuts with a torque wrench;

When calibrating thermocouples, the hot end should be placed in the center of the furnace, avoiding areas where the airflow is blowing directly.

2、 Insufficient vacuum degree

Typical performance: The ultimate vacuum is more than 30% lower than the theoretical value, and the pressure quickly rises during the holding period.

Hazard tracing:

-Sealing ring failure: O-ring cracks due to high temperature aging or deformation caused by flange compression during installation;

-Performance degradation of vacuum pump: blockage of oil mist filter leads to a decrease in pumping speed and excessive wear and clearance of rotary blades;

-Concealed leakage points: minor leaks such as cracked sealant on the observation window and dynamic sealing failure of the valve stem.

Diagnostic skills:

Segmented leak detection method: Close the high valve and only open the low valve to test the front-end pipeline, gradually narrowing the leakage range;

The helium mass spectrometer leak detector can accurately locate small leakage rates at the level of 0.1 Pa · m ³/s.

3、 Inaccurate atmosphere control

Abnormal features: The flow meter displays large fluctuations and the outlet gas composition deviates from the set ratio.

Key link investigation:

-Mass flow controller (MFC) calibration offset: Long term exposure to corrosive gases causes sensor zero drift;

-Poor uniformity of gas mixture: Insufficient buffer volume for multiple gas convergence, resulting in pulsating flow;

-Back pressure regulating valve stuck: Particle accumulation in the valve body hinders piston movement.

Maintenance points:

Flush the gas circuit with nitrogen every quarter and replace the MFC pre filter; For reactive gases such as NH3, a corrosion-resistant Hastelloy gas path is used.

4、 Temperature control program disorder

Symptom examples: PID parameter self-tuning failure, abnormal jump in inter segment cooling rate.

Software and hardware incentives:

-Electromagnetic interference from temperature control meter: Harmonics generated by the frequency converter are coupled into the control board through transmission cables;

-Relay contact sintering: frequent switching of high current loads leads to contact adhesion;

-Aging of Solid State Relays (SSRs): Increased conduction voltage drop leads to insufficient output power.

Protective measures:

Install an independent grounding wire to eliminate electromagnetic interference; Choose automotive grade gold-plated contact relays; SSR conducts replacement experiments every year.

5、 Sealing failure of furnace body

High risk: Air backflow can cause oxidation reactions, or condensation and corrosion of the inner wall in the cooling section.

Key inspection areas:

-Wear of furnace door gear rack: frequent opening and closing leads to excessive transmission clearance and insufficient sealing pressure;

-Loosening of flange bolts: The difference in expansion coefficients of different materials at high temperatures leads to stress release;

-Observation window quartz glass cracking: Microscopic cracks are generated by rapid cooling and thermal shock.

Repair plan:

Replace the metal wrapped gasket filled with polytetrafluoroethylene; Adopting a stepped heating program to reduce thermal stress.

6、 Circulating water system malfunction

Chain reaction: When the water temperature is too high, it triggers overload protection shutdown, causing scale to clog the heat exchanger and reduce cooling efficiency.

Prevention and control strategies:

-Install a plate heat exchanger to pre treat the cooling water and maintain the inlet water temperature below 25 ℃;

-Clean the water tank filter monthly and use descaling agents to clean the condenser pipes quarterly;

-Configure dual water source automatic switching device to prevent interruption of the main water supply.