The vacuum degree of the graphite furnace in the laboratory cannot be increased

10-23-2025       Author: KJ technology

The inability to increase the vacuum degree of the laboratory graphite vacuum furnace may be caused by leakage, decreased pump pumping speed, contamination of the furnace body or workpiece, etc. The following are some possible reasons and corresponding solutions:

1. Leakage issue

Aging, corrosion or damage of seals: Check and replace aging or broken seals to ensure good sealing.

Loose pipeline connections: Check the pipeline connections to ensure they are tight and leak free.

Electromagnetic valve, pipe joint, vacuum pump suction valve, and sealing gasket around the working chamber are leaking: Check and repair or replace these components.

Internal leakage: Internal leakage often occurs on equipment with water cooling points. If no suspicious points are found during the inspection of the 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 significantly corroded, it can be basically inferred that there is an internal leakage if the above conditions are met. At this point, the cavity should be cleaned first, and then cooling water should be supplied. Carefully check if there are any wet spots in the water supply pipeline, which are the leakage points.

2. Pump pumping speed decreases

Pump oil contamination, insufficient or too thin: Clean the vacuum pump and replace it with new vacuum pump oil.

Poor or damaged operation of vacuum pump: Replace with a new pump or repair damaged vacuum pump parts.

Overheating of the pump and expansion of mechanical components leading to insufficient clearance: Strengthen the cooling of the pump to ensure that it operates at normal temperature.

Oxidation of diffusion pump oil and diffusion nozzles at all levels: Remove the nozzles at all levels and wipe them one by one with metallographic sandpaper until the natural color of the aluminum is removed. And inject a certain amount of diffusion pump oil into the diffusion pump chamber, and then install the nozzles at each stage step by step.

The oil in the front stage pump is too dirty or contains water: Drain the oil from the mechanical pump oil tank, clean the tank, inject clean vacuum pump oil, and observe the oil level.

3. Furnace or workpiece contamination

Moisture absorption on the inner wall of the furnace shell: When the weather is relatively humid in the south, the inner wall of the furnace shell is prone to moisture absorption, causing a false impression of air leakage. At this point, baking treatment can be carried out.

Thermal insulation material venting: Thermal insulation materials used in vacuum furnaces generally include metals, carbon materials, and ceramic fibers. Ceramic fibers have good insulation effect at low temperatures, but they have a large suction capacity. At this point, oven treatment can also be considered, but the heat exchanger effect of the oven is not significant, and gas needs to be filled after the oven to start the fan for hot air circulation.

Heat exchanger venting: The fin area of the heat exchanger is particularly large, and it is easy to release the adsorbed gas. Similarly, it can be considered to fill the oven with gas and start the fan for hot air circulation.

Gas release of fixtures and materials for products to be brazed, especially for Ni based brazing materials for automotive EGR systems. After assembly, the products are not dried before entering the vacuum brazing furnace. At this point, it should be ensured that the product is dried before vacuum treatment.

4. Other possible reasons

Suction valve O-ring detachment: Remove the vacuum tube from the pump nozzle, remove the suction nozzle, take out the compression spring and suction valve, gently stretch the O-ring several times, re insert it into the groove, and then install it.

Oil return valve blockage: Remove the oil return valve and clean it.

Blockage of cooling water pipeline: Check whether the cooling water pipeline is unobstructed, ensure sufficient cooling water supply, and clean the blockage.