Why choose a vacuum brazing furnace?

Vacuum Brazing Furnace Principle

The main difference in vacuum brazing furnace  lies in the heating furnace used. Vacuum brazing involves drawing a vacuum into the effective space of the furnace. The workpiece, equipped with brazing filler metal, is heated in this vacuum environment, completely blocking oxygen and other impurities from the air. A series of beneficial physicochemical reactions under vacuum conditions achieve film removal and wetting. Generally, no flux is added during the brazing process. Under high temperature, the brazing filler metal melts and fills the gap, forming a high-quality brazed joint. In fact, in a vacuum environment, oxidation of the base material and brazing filler metal is significantly reduced. Simultaneously, the decrease in oxygen partial pressure causes the decomposition of the oxide film, achieving removal or destruction, promoting the wettability of the molten brazing filler metal, and enhancing its gap-filling ability.

Currently, vacuum brazing furnaces can be divided into hot-wall vacuum brazing furnaces and cold-wall vacuum brazing furnaces. The former consists of a vacuum container and a general-purpose resistance heating furnace (similar to the brazing equipment in an air furnace), allowing products to be fed into the resistance heating furnace at different temperatures as needed. The latter integrates the heating furnace and the vacuum brazing chamber, raising the temperature from room temperature to the brazing temperature. Cold-wall vacuum brazing furnaces are generally more commonly used.

Key features of vacuum brazing furnaces:

No oxidation or other issues: In a vacuum environment, air is removed, and the melting and filling process of the brazing filler metal isolates oxygen, carbon, nitrogen, and other elements from the air, thus preventing oxidation and carbon buildup.

High-quality brazed joints: Since no flux is used, internal quality issues such as flux residue and inclusions are eliminated. The vacuum environment improves the escape conditions of pores in the brazing filler metal, resulting in a significantly improved, bright, and oxidation-free brazed joint appearance.

Low stress:The high-temperature environment ensures uniform heating, significantly reducing stress caused by uneven heating of parts. **Wide applicability:** Ideal for joining dissimilar metals, similar metals, reactive metals, and even non-metallic materials.

Unsuitable for brazing high vapor pressure elements: Vacuum brazing is not recommended for metals containing high vapor pressures such as manganese, lithium, and magnesium; measures must be taken to suppress element volatilization.

High initial investment and maintenance costs:Involving electrical control systems, operation and maintenance are relatively complex, resulting in high equipment and maintenance costs.

Superior Welding Quality of Vacuum Brazing

In welding processes, the quality of the brazed seam directly determines the performance and service life of the weldment. Vacuum brazing furnaces, with their unique vacuum environment, fundamentally solve common quality problems in traditional welding processes. Firstly, the complete avoidance of oxidation and carbonization is a core highlight. The vacuum environment uses a specialized vacuum pump unit to remove air from the effective space within the furnace, reducing the concentration of elements that readily react with metals, such as oxygen, carbon, and nitrogen, to extremely low levels. When the weldment with the brazing filler metal is heated at high temperatures, the base metal and the filler metal will not react with oxygen in the air to form an oxide layer, nor will carbon intrusion cause carbonization and performance degradation in the base metal—this is crucial for ensuring stable mechanical properties after welding, especially for metals sensitive to oxidation and carbon content, such as stainless steel and titanium alloys.

Secondly, the elimination of flux residue and internal inclusions further enhances the purity of the brazed seam. In traditional brazing processes, flux is added to remove the oxide film on the metal surface and promote solder wetting. However, if the flux is not thoroughly cleaned, residual chemical components can form inclusions inside the brazed joint, reducing joint strength and potentially causing structural failure due to corrosion during subsequent use. Vacuum brazing furnaces utilize physicochemical reactions under vacuum conditions. The significant decrease in oxygen partial pressure causes the oxide film already formed on the base material surface to decompose, achieving “flux-free film removal.” This process not only avoids the quality risks associated with flux residue but also reduces harmful gases generated by flux volatilization, balancing quality and environmental protection.

Furthermore, the vacuum environment promotes the escape of pores, significantly improving the density of the brazed joint. During high-temperature brazing, the solder may dissolve some gases (such as hydrogen and nitrogen). If these gases cannot escape in time before cooling and solidification, pores will form inside the brazed joint, reducing connection strength and sealing. In a vacuum environment, the furnace pressure is much lower than atmospheric pressure, significantly reducing the solubility of gases in the brazing filler metal. Simultaneously, the vacuum environment provides a more unobstructed escape path for gas molecules, allowing dissolved gases to escape quickly during the melting of the filler metal, effectively reducing porosity. The resulting brazed seam not only has a uniform and dense internal structure but also exhibits a bright, oxidation-free appearance, eliminating the need for subsequent surface treatments such as grinding and pickling. This saves processing costs and avoids the negative impact of secondary processing on the quality of the brazed seam.