Braze On
By Alliages Industries
Comprehensive guide to Brazing with silver and CuP alloy
for HVAC and plumbing
​Brazing is a precise and reliable process when done correctly. This guide outlines the best practices for brazing with silver and copper-phosphorus (CuP) alloys to ensure high-quality, durable joints.
Before brazing
Surface preparation
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Clean the surfaces: Mechanically remove all oxides, grease, and contaminants to ensure optimal bonding.
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Inspect thoroughly: Eliminate all foreign particles; even minute debris can compromise the joint.
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Ensure proper fit: Maintain a clearance of 0.05 to 0.1 mm between the surfaces to leverage capillary action effectively.
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Joint geometry
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Use regular, precise shapes for the parts to be joined. Ensure tubes and fittings are aligned properly.
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Use a tube cutter for precise cuts and deburr edges while creating a slight chamfer.
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Check for dimensional accuracy; avoid ovality in tube diameters.
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Flux application
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For copper-to-copper joints using CuP alloys, flux is unnecessary as the alloy is self-fluxing.
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When brazing brass or other metals, apply an appropriate flux sparingly, avoiding excess flux entering the tube.
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Safety and Regulations
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Avoid cadmium-based alloys, especially for water supply systems, as they are prohibited under EU regulations (Directive 91/338/EEC).
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Use silver-rich alloys (e.g., 34% silver) for sensitive connections and CuP alloys with silver (e.g., 5–15%) for basic applications. Avoid low-silver CuP alloys for applications under significant mechanical stress or vibrations.
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During brazing
Heating process
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Use a neutral flame and heat the densest part of the joint. Allow the joint's temperature to melt the alloy, not the direct flame.
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Avoid prolonged heating, which can lead to oxidation or alloy drips.
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Critical Guidelines
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Do not move the parts during brazing. Stability ensures uniform flow and bonding.
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Avoid brazing oxidized, stressed, or liquid-containing parts.
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Never re-braze previously brazed components; this can weaken the joint.
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Refrigeration Industry Requirements
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When brazing refrigeration systems, use an inert gas (dry nitrogen) during the process to prevent oxidation inside the system. Maintain a flow rate of 30–90 l/min.
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After brazing
Cleaning and Inspection
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Wash away flux residues with hot water. Ensure all residue is removed, as leftover flux can lead to corrosion.
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Avoid thermal shock by cooling parts gradually. Sudden cooling may induce stress or cracking, particularly in cadmium-free silver alloys.
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Purge the System
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For refrigeration and HVAC systems, flush conduits with an inert gas. Never use oxygen to purge, as it can create hazards.
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Advantages of Following Best Practices
By adhering to these guidelines, you ensure:
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Superior mechanical resistance: Joints withstand pressure, vibration, and torque.
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Enhanced chemical durability: Compatible with modern refrigerants and aggressive fluids.
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Exceptional sealing: Joints remain leak-proof and free from porosity.
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Tips for optimal results
Heating recommendations
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Heat the base metal, not the filler alloy, for consistent melting and flow.
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Maintain uniform joint temperature, just slightly above the liquidus point of the alloy.
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Examples of joint design
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Recommended: Joints with smooth, aligned surfaces and consistent gaps.
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To Avoid: Misaligned or uneven joints that hinder capillary action and alloy flow.
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