What is vacuum brazing and its advantages

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For many chemical equipment manufacturers, brazing is rarely used and welding engineers do not know much about it. However, in air separation units (ASUs), vacuum brazing is often used to weld aluminum plate-fin heat exchangers. So today it is necessary to introduce to you what vacuum brazing is.

Definition of brazing

Brazing belongs to solid-phase connection. It is different from other methods. The base material does not melt during brazing. A brazing material with a lower melting point than the base material is used. The heating temperature is lower than the solidus line of the base material and higher than the liquidus line of the brazing material. When the connected parts and the brazing material are heated to the melting point of the brazing material, the liquid brazing material is used to wet the surface of the base material, spread and dissolve and diffuse with the base material, and wet in the gap of the base material, capillary flow, fill the gap and dissolve and diffuse with the base material to achieve the connection between the parts.

Advantages and disadvantages of brazing

Compared with the fusion welding method, brazing has the following advantages:

The heating temperature of brazing is low, and the effect on the structure and performance of the base material is small.

The brazing joint is flat and smooth, with beautiful appearance and small deformation of the weldment. Especially when using uniform heating (such as furnace brazing), the deformation of the weldment can be reduced to a minimum, and the dimensional accuracy of the weldment can be easily guaranteed. Some brazing methods can weld dozens or hundreds of welds at a time, with high production efficiency.

However, brazing also has its own disadvantages. The strength of the brazing joint is relatively low, the heat resistance is relatively poor, and the electrochemical corrosion caused by the large difference in the composition of the base material and the brazing filler metal leads to poor corrosion resistance and high assembly requirements. According to the different brazing fillers used, brazing is generally divided into:

1.Soft brazing-the liquidus temperature of the brazing filler metal is lower than 450℃

2.Hard brazing filler metal-the liquidus temperature of the brazing filler metal is higher than 450℃

Principle of furnace brazing

Here we mainly introduce furnace brazing: furnace brazing can be widely used for workpieces where the brazing filler metal can be placed near or inside the joint in advance. This method is particularly suitable for high-productivity brazing. The pre-placed brazing fillers include wire, foil, chips, rods, powder, paste and strips, etc.

Furnace brazing can be divided into air furnace brazing, protective atmosphere furnace brazing and vacuum furnace brazing. The characteristics of furnace brazing are that the workpiece is heated as a whole, the heating is uniform, the workpiece deformation is small, but the heating is slow. One furnace can braze multiple pieces at the same time to make up for the lack of slow heating.

Principle of vacuum brazing

Vacuum brazing: Brazing in a furnace or welding room with air evacuated is an economical method to connect many joints of the same or different metals. No flux is used in the process.

Vacuum brazing is particularly suitable for joints with large and continuous brazing areas. Such joints:

a) It is difficult to completely remove the solid or liquid flux at the brazing interface during brazing

b) The protective gas is not completely effective because the atmosphere cannot completely exhaust the gas hidden in the close brazing interface.

Advantages and disadvantages of vacuum brazing

Vacuuming fundamentally removes all gases in the brazing area, so there is no need to purify the supplied atmosphere. The pressure used for vacuum brazing in industry is generally 0.065MPa or higher.

Some oxides of the parent material will decompose at the vacuum brazing temperature. The difficult problem of the brazing interface sometimes being contaminated by outgassing of the base metal can be considered non-existent. At high temperatures, there is a low pressure around the base metal and the brazing material, which allows volatile impurities and gases in the metal to be expelled. This characteristic is also a disadvantage, because due to the low surrounding pressure, the brazing material, the base metal and the elements in them will evaporate at the brazing temperature.

Since some elements are volatile in a vacuum, vacuum furnace brazing is not suitable for brazing materials containing high contents of elements such as zinc, cadmium, manganese, phosphorus, etc., nor for base metals containing large amounts of these elements.

If you have a need for a vacuum brazing furnace, please contact us.

Model	Working Zone Size(W*H*L)	Max. Temperature	Ultimate Pressure	Temperature Uniformity	LoadingCapacity
RHVB-446H	400*400*600mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	200Kg
RHVB-557H	500*500*700mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	300Kg
RHVB-669H	600*600*900mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	500Kg
RHVB-7710H	700*700*1000mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	700Kg
RHVB-8812H	800*800*1200mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	1000Kg
RHVB-9915H	900*900*1500mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	1200Kg
RHVB-101013H	1000*1000*1300mm	1300℃	6.7*10-1Pa ~10-3Pa	±5℃	1500Kg
Remark: The working zone of equipment could be customized base on customer’s production.

Learn More:

Purpose of vacuum brazing furnace

Vacuum Sintering Furnaces for Ceramics

What Is The Benefits Of Vacuum Hardening?