Brazing is a metal joining process where two or more base metal components are joined by melting a filler material between their closely positioned surfaces. The key rule for brazing involves several critical steps:
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Cleaning and Preparation: Before brazing, the materials must be thoroughly cleaned to remove all oxides, contaminants, and oils. Mechanical cleaning methods like grinding, wire brushing, or blasting are often used to ensure the surfaces are free from impurities and to roughen the surfaces for better braze alloy flow.
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Application of Braze Alloy: The braze alloy, which has a lower melting point than the base materials, is applied carefully to avoid excessive amounts, especially in thin sections. The alloy should be positioned over the joint to utilize gravitational forces, and when using pastes, the joints should not be completely sealed to allow for venting during the furnace cycle.
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Furnace Cycle and Atmosphere Control: The furnace cycle must be controlled to prevent distortion and ensure even temperature distribution. Brazing is typically performed at temperatures 40-65°C above the melting point of the braze alloy. The atmosphere must be devoid of oxidants, with conditions such as neutral gas (pure nitrogen), low oxygen content (< 100 ppm), and low humidity (< -40°C) to prevent oxide reformation.
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Joint Design and Technique: Proper joint design and technique are crucial to prevent common problems like splatter, quench cracking, and distortion. This includes using stop-off paints to control the flow of braze alloy and ensuring the heat input is balanced across the joint.
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Post-Brazing Considerations: After brazing, the assembly should cool under controlled conditions to avoid rapid quenching, which can lead to distortion or cracking.
These rules ensure that the brazing process results in a strong, reliable joint by managing the application of the braze alloy, controlling the furnace environment, and carefully preparing and designing the joint.
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