High temperature graphite vacuum furnace cannot be evacuated

High temperature graphite vacuum furnace cannot vacuum up, which may be caused by vacuum pump failure, aging or damage of seals, leakage, aging of vacuum gauges or pump oil, valve failure, contamination of furnace body or workpiece, and other reasons. The following is a specific analysis and solution:

vacuum pump failure
Possible reasons: pump oil contamination, insufficient or too thin, poor or damaged vacuum pump operation, pump overheating, mechanical expansion leading to small gaps, improper cleaning causing debris to enter the oil.
Solution: Clean the vacuum pump, replace with new vacuum pump oil, replace with a new pump, strengthen the cooling of the pump, check if the power supply is normal, repair or replace damaged vacuum pump parts.

Seal aging or damage
Possible reasons: long-term aging, corrosion, or damage of seals, loosening of pipeline connections, air leakage of solenoid valves, pipe joints, vacuum pump suction valves, and sealing gaskets around the working chamber.
Solution: Check and replace aging or broken seals to ensure good sealing, inspect pipeline connections, solenoid valves, pipe joints, etc., and repair or replace them.

leak
Possible reason: Leakage points with large external leaks can be detected using flame detection. Based on the principle that airflow can cause the flame to deviate, a vacuum is first drawn and a candle or lighter is used to gradually search near the suspicious point. If the flame deviates towards the leakage point, the leakage point can be found. Internal leakage needs to be investigated from different vacuum working areas of the vacuum furnace. After the vacuum system reaches a certain pressure value, the winding and evaporation systems should be started separately, and the reading of the vacuum gauge should be observed for a brief decrease before climbing, which can preliminarily determine the direction of the internal leakage point. Internal leakage often occurs on equipment with water cooling points. No suspicious points were found during the inspection of external leakage, but the pumping speed of the mechanical pump is significantly low, the vacuum gauge reading is low, the mechanical pump oil quickly emulsifies, and the iron-based components in the vacuum chamber are obviously corroded. With the above conditions, it can be basically inferred that there is internal leakage.
Solution: After finding the leakage point, repair it according to its location and size, such as tightening loose parts, replacing damaged parts, resealing, etc. For internal leaks, more complex troubleshooting and repair processes may be required, such as inspecting and repairing the leakage points of the water cooling system.

Vacuum gauge or pump oil aging
Possible reasons: aging of high vacuum gauge, aging of diffusion pump oil, etc.
Solution: Replace the vacuum gauge tube and replace the diffusion pump oil.

valve failure
Possible reasons: malfunction of solenoid valve, aging or damage of valve.
Solution: Repair or replace the valve.

Furnace or workpiece contamination
Possible reasons: moisture absorption on the inner wall of the furnace shell, air release from insulation materials, air release from heat exchangers, air release from fixtures used by brazing workers in the furnace, and air release from materials of products to be brazed.
Solution: Perform oven drying treatment to remove moisture and gas from the furnace body and workpiece. For components such as heat exchangers, the baking effect may not be satisfactory, and it is necessary to fill gas after baking and start the fan for hot air circulation to solve the problem.