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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.