vacuum brazing furnace welding effect

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The brazing method in vacuum furnace is a new one without flux under vacuum condition. Because the brazing is in the vacuum environment, it can effectively eliminate the harmful effect of air on the workpiece, so it can be successfully brazed without applying flux.
It is mainly used to braze metals and alloys that are difficult to braze, such as aluminum alloy, titanium alloy, high temperature alloy, refractory alloy and ceramics. The brazed joint is bright and compact, with good mechanical properties and corrosion resistance.
Vacuum brazing equipment is generally not used for needle welding of carbon steel and low alloy steel.

The brazing equipment in vacuum furnace is mainly composed of vacuum brazing furnace and vacuum system.
There are two types of vacuum brazing furnace: hot furnace and cold furnace. The two types of furnaces can be heated by natural gas or electric heating. They can be designed as side loading furnace, bottom loading furnace or top loading furnace (Kang type). The vacuum system can be used in general.

Vacuum system mainly includes vacuum unit, vacuum pipeline, vacuum valve, etc. Vacuum unit is usually composed of rotary vane mechanical pump and oil diffusion pump. The vacuum degree of less than 1.35 × 10-1pa can only be obtained by mechanical pump alone. In order to obtain high vacuum, oil diffusion pump must be used at the same time, at this time, the vacuum degree of 1.35 × 10-4Pa can be achieved. The gas pressure in the system is measured with a vacuum gauge.

Brazing in vacuum furnace is used in the furnace or brazing chamber with air drawn out, especially for the joints with large and continuous brazing area, and also for the connection of some special metals, including titanium, zirconium, niobium, molybdenum and tantalum, with a wide range of applications. However, vacuum brazing also has the following disadvantages:
① Under vacuum conditions, metals are easy to volatilize, so it is not suitable to use vacuum brazing for the base metal and filler metal of welding volatile elements. If it is necessary to use, the corresponding complex process measures should be adopted.
② The influence of vacuum brazing on the surface roughness, assembly quality and fit tolerance of brazed parts is more sensitive, which requires higher theoretical level of working environment and operators.
③ Vacuum equipment is complex, one-time investment is large and maintenance cost is high.

So, how to implement brazing process in vacuum furnace?
During the brazing operation in the vacuum furnace, put the welded parts into the furnace (or into the brazing container), close the furnace door (or close the brazing container cover), and pre vacuum before heating. Start the mechanical pump first, turn the steering valve after the vacuum degree reaches 1.35pa, turn off the direct path between the mechanical pump and the brazing furnace, make the pipeline connect with the brazing furnace through the diffusion pump, work by the mechanical pump and the diffusion pump for a limited time, pump the brazing furnace to the required vacuum degree, and then start the electric heating.

During the whole process of heating up, the vacuum unit shall work continuously to maintain the vacuum degree in the furnace, offset the air leakage at various interfaces of the vacuum system and brazing furnace, release the adsorbed gas and water vapor on the furnace wall, fixture and weldment, and volatilize the metal and oxide to reduce the true air drop.
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 (such as nickel base superalloy) whose oxide is difficult to decompose,
Part of the vacuum brazing is used for base metal or solder volatilization at brazing temperature and high vacuum.

When special precautions must be taken to ensure high purity, vacuum cleaning method shall be used before dry hydrogen brazing. In the same way, dry hydrogen or inert gas purification before vacuuming will help to obtain better results in high vacuum brazing.

Learn More : Vacuum Brazing Furnace / SIMUWU© Vacuum Furnace