In brazing, various gases are used to create an atmosphere that prevents oxidation and ensures the quality of the braze joint. The primary gases used include inert gases such as nitrogen, helium, and argon, as well as hydrogen in specific applications. Each gas serves different purposes depending on the specific requirements of the brazing process.
Inert Gases:
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Nitrogen (N2): This is the most commonly used inert gas in brazing due to its cost-effectiveness and ability to displace oxygen in the furnace atmosphere. Nitrogen is particularly effective for brazing copper and other non-ferrous materials. It must have a dew point of less than 51°C to ensure a dry environment that prevents the formation of oxides.
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Helium (He): Helium is another inert gas used in brazing, primarily due to its high thermal conductivity which aids in the heating process. It is less commonly used compared to nitrogen due to its higher cost.
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Argon (Ar): Argon is used in brazing, especially in processes that require a very stable and inert atmosphere. It is often used in conjunction with other gases or in vacuum brazing applications where high purity is required.
Hydrogen (H2): Hydrogen is used as an active agent in brazing atmospheres, particularly for the reduction of metal oxides. It is effective in creating a reducing environment that helps in the removal of surface oxides, facilitating better wetting and flow of the filler metal. However, the use of hydrogen is carefully controlled due to its flammability and potential for causing explosions if not handled properly.
Other Considerations:
- Oxygen and Water Vapor: Both are generally undesirable in brazing atmospheres as they promote oxidation. Oxygen content should be minimized, often specified as less than 100 ppm, and humidity is controlled by specifying a low dew point, typically below -40°C.
- Combination of Gases: In some advanced brazing processes, a blend of hydrogen and inert gases is used to optimize the brazing environment for specific materials and applications.
Each gas or gas mixture is selected based on the specific materials being brazed, the desired properties of the braze joint, and the safety considerations of the process. The choice of atmosphere is crucial in ensuring the integrity and reliability of the brazed components, especially in critical applications such as aerospace, automotive, and medical devices.
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