Why choose vacuum brazing for stainless steel heat ex-changer

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Stainless steel has the characteristics of high corrosion resistance, high strength, good heat resistance and good hygiene, so stainless steel heat ex-changers are widely used in chemical, food, pharmaceutical, petroleum, marine and other industrial fields. The traditional brazing process requires the use of flux and the participation of air or protective gas, which is easy to produce residues and the joint quality is not high. Vacuum brazing is carried out in a vacuum environment, without the use of flux, high work-piece quality and environmental protection. Therefore, vacuum brazing is particularly important and is increasingly used.

Principle mechanism of stainless steel vacuum brazing

Stainless steel vacuum brazing is a joining process in which the filler metal or alloy is heated to the melting temperature (above 450°C; 842°F) and distributed between two or more closely fitting parts by capillary action. During the brazing process, the molten filler metal diffuses into the base metal part. This forms a very strong sealed joint. Brazing is better than welding because it can evenly heat the entire part, thereby reducing deformation. In summary, vacuum brazing of stainless steel is a process based on the melting, wetting and diffusion of the brazing material in a vacuum environment to achieve welding.

Advantages of vacuum brazing compared to conventional brazing

Item	Traditional brazing process	Vacuum brazing process
Brazing environment	Air or protective gas, flux required	Vacuum environment, no flux required
Joint quality	Oxidation and residue, slightly poor corrosion resistance and strength	Clean joint without oxidation, high strength, good corrosion resistance
Heating method	Flame, induction heating, uneven temperature distribution	Vacuum furnace uniform heating, uniform temperature distribution
Braze material	Flux-containing brazing material	High-purity brazing material, no flux residue
Production efficiency and cost	Simple equipment, suitable for small batches, high cleaning cost	High equipment cost, suitable for large-scale production, low long-term cleaning cost
Environmental protection and cleanliness	Produce residues, waste treatment is not environmentally friendly	No residue, no pollution, more environmentally friendly
Applicable scenarios	Low requirements, suitable for general applications	Applicable to special occasions with high reliability and high cleanliness

Analysis of vacuum brazing process practice of stainless steel heat ex-changer

Selection of brazing material

The selection of brazing material is crucial for the brazing of stainless steel heat ex-changers. Nickel-based brazing material is suitable for high temperature and high pressure working environment and has good corrosion resistance. Silver-based materials have good wettability and low brazing temperature, which is suitable for heat ex-changers with complex structures. Copper-based brazing material has relatively low cost, but its corrosion resistance is relatively weak.

Process flow

Before processing, the surface of the stainless steel heat ex-changer should be degrease and decontaminated to ensure the cleanliness of the brazing area, so as to achieve good wetting effect. The joint gap should be reasonably designed during assembly, usually between 0.03-0.1 mm. The next step is vacuum preheating, gradually raising the temperature (about 900-1200℃) to melt the test brazing material and penetrate the joint gap. Then slowly cool to room temperature to avoid thermal stress and cracks in stainless steel.

Factors affecting the quality of brazed joints

There are many factors that affect the quality of brazed joints. Such as brazing temperature, brazing gap, insulation time, cooling rate, etc. Since nickel-based brazing alloy BNi2 has a relatively low liquidus temperature and high high temperature resistance, it can also make the brazing alloy have good wettability and fluidity. BNi2 contains elements such as boron and silicon, which will generate brittle intermetallic compounds such as borides and silicides during the brazing process, which will reduce the strength of the joint. The formation of such brittle compounds is closely related to factors such as brazing thickness, brazing temperature, and insulation time, which directly affect the interaction process between the brazing alloy and the parent material.

Vacuum brazing is a brazing process with good application prospects in the current production process of stainless steel heat ex-changers. In practice, in order to meet the production needs of stainless steel heat ex-changers, raw materials, vacuum brazing temperature, surface treatment process, brazing environment, vacuum degree, insulation time, etc. should be strictly controlled to reduce the loss of brazing alloy, discontinuous welds, corrosion and other defects, and ensure the welding quality of stainless steel heat exchanges. At the same time, while clearly recognizing the scientific application value of heat treatment technology, it can explore the most suitable heat treatment scheme according to the specific conditions and production requirements of stainless steel heat ex-changers to meet the design requirements and subsequent process requirements of aluminum alloy radiators and improve the quality of heat ex-changers.

Equipment selection: The RVB series vacuum brazing furnace produced by SIMUWU is a high-quality product for vacuum heat treatment of molds. Good temperature control accuracy and uniformity ensure the effective implementation of the vacuum brazing process. SIMUWU focuses on the manufacture of vacuum furnaces and has more than ten years of relevant experience. It has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum gas quenching furnaces, vacuum oil quenching furnaces, vacuum brazing furnaces, etc., which are widely sold in developed and developing countries. For detailed technical information, please click on the official website below:

Keywords: Vacuum furnace, Vacuum brazing furnace, Stainless steel vacuum brazing, Stainless steel heat ex-changer vacuum brazing