How to ensure stable pressure inside a high vacuum brazing furnace when brazing above 1200°C?

Rational Configuration and Maintenance of Vacuum Pump Systems

Selecting the Appropriate Vacuum Pump: When the operating temperature of a high-vacuum brazing furnace reaches above 1200°C, it is necessary to choose a vacuum pump with a high pumping speed and good ultimate vacuum. For example, a combination of diffusion pump and mechanical pump is a common configuration. The mechanical pump acts as the forepump, first extracting a large amount of gas from the furnace to reach a certain vacuum level, after which the diffusion pump further improves the vacuum. The diffusion pump can operate effectively in high-temperature environments, and its pumping speed can be selected based on the furnace volume and required pumping time to ensure timely extraction of gases inside the furnace and maintain stable pressure.

Maintenance of Vacuum Pumps: Regular inspection and maintenance of vacuum pumps are key to ensuring pressure stability. For mechanical pumps, lubricating oil should be replaced regularly to prevent performance degradation caused by oil carbonization at high temperatures. Diffusion pumps require regular checks of the pump oil quality and level, as the oil deteriorates gradually under high temperature and high vacuum conditions. Additionally, the sealing performance of the vacuum pump, such as seals and gaskets, should be inspected; even minor leaks can cause pressure fluctuations inside the furnace.

Sealing Design and Inspection of the Furnace Body

Selection of Sealing Materials: In high-temperature environments above 1200°C, the sealing materials of the furnace body need to have good high-temperature resistance. For example, metal sealing materials such as nickel-based alloys or stainless steel gaskets can be used. These metal seals maintain good elasticity and sealing performance at high temperatures and do not age or deform like ordinary rubber seals. Additionally, metal sealing materials have a low outgassing rate, which helps maintain the high vacuum inside the furnace.

Design and Inspection of Sealing Structures: The furnace sealing structure should be designed to withstand high temperatures and pressure differences between inside and outside. For example, a double-layer sealing structure or a sealing structure with cooling channels can be used. The double-layer seal provides redundant sealing protection; if one layer fails, the other can maintain the seal. Sealing structures with cooling channels can reduce the temperature of the sealing area by circulating cooling water, thereby extending the service life of the sealing materials. Regular inspections of the furnace sealing structure should be conducted, such as using a helium mass spectrometer leak detector to identify leaks promptly and repair sealing issues.

Gas Control During the Brazing Process

Pre-treatment of Raw Materials: Before placing workpieces into the high-vacuum brazing furnace, the brazing materials and the workpieces to be brazed must be thoroughly cleaned and pre-treated. Remove oils, oxides, and other impurities from the material surfaces, as these impurities generate large amounts of gas at high temperatures. For example, use organic solvents to clean oil from the workpiece surfaces and remove oxides by acid pickling or mechanical polishing. This reduces the amount of gas generated during brazing and helps maintain pressure stability.

Control of Protective Gas Injection: In some cases, a small amount of protective gas, such as high-purity argon, may need to be introduced into the furnace. When injecting protective gas, precise gas flow controllers should be used to regulate the amount of gas introduced. Moreover, based on feedback from the furnace pressure sensors, the gas injection and extraction should be adjusted in real time to keep the furnace pressure within a stable range. For example, set an allowable pressure fluctuation range; when the pressure falls below the lower limit, inject protective gas appropriately; when the pressure exceeds the upper limit, increase the pumping speed of the vacuum pump.

By implementing the above measures, the stability of the furnace pressure during brazing at temperatures above 1200°C in a high-vacuum brazing furnace can be effectively ensured, thereby guaranteeing brazing quality.