Mon, 17 Sep 2018 06:34:34 +0000
Brazing in vacuum furnace
What are the brazing equipment in vacuum furnace?
The brazing equipment in vacuum furnace is mainly composed of two parts: vacuum brazing furnace and vacuum system. There are basically two types of vacuum brazing furnace: Hot fireplace and cold fireplace. The two types of furnaces can be heated or electrically heated by natural gas and can be designed as side-loaded, bottom-loaded or top-loaded (Kang-type) furnaces. The vacuum system can be used.
Vacuum system mainly includes vacuum unit, vacuum valve and so on. The vacuum unit is usually composed of a rotary chip mechanical pump and an oil diffusion pump. Only mechanical pumps can only get vacuum below 1.35×10^ (-1) Pa. To obtain vacuum, the oil diffusion pump must be used at the same time, and the vacuum degree of 1.35×10^ (-4) Pa can be achieved at this time. The gas pressure in the system is measured by a vacuum gauge.
How to implement brazing technology in vacuum furnace
When brazing in a vacuum furnace, the brazed parts are loaded into the furnace (or the brazing container), the furnace door (or the brazing container cover) is closed, and the vacuum is pre-pumped before heating. First start the mechanical pump, turn the steering valve until the vacuum reaches 1.35 Pa, turn off the direct circuit between the mechanical pump and the brazing furnace, make the pipeline communicate with the brazing furnace through the diffusion pump, rely on the mechanical pump and the diffusion pump to work in a limited time, pump the brazing furnace to the required vacuum, and then start heating. During the whole heating process, the vacuum unit should continue to work to maintain the vacuum degree in the furnace, counteract air leakage at various interfaces of the vacuum system and the brazing furnace, release adsorbed gas and water vapor from the furnace wall, clamps and weldments, and evaporate metal and oxide to reduce the vacuum. There are two kinds of vacuum brazing: high vacuum brazing and partial vacuum (medium vacuum) brazing. High vacuum brazing is very suitable for brazing the base metal whose oxide is difficult to decompose (such as nickel-based superalloy), and some vacuum brazing is used for the base metal or brazing materials in brazing temperature and high vacuum evaporation occasions.
When special precautions are required to ensure high purity, vacuum cleaning is used before dry hydrogen is brazed. Similarly, the use of dry hydrogen or inert gas purification before vacuum pumping will help to obtain better resources in high vacuum brazing.