Brazing and soldering

Topic overview

In brazing and soldering, the base material does not melt . The joint is formed by melting the filler metal, wetting the surface and filling the clearance between components by capillary action. Strength is governed not only by filler-metal strength, but especially by surface cleanliness, capillary clearance, overlap, interfacial diffusion, heating method and flux residues. From an IWE perspective, this is a separate joining technology, not “weaker welding”.

The filler metal should melt from contact with the heated component, not solely from the flame. If the wire melts in the flame while the components remain cold or oxidised, the filler beads up and does not flow through the joint.

The filler metal has a liquidus below approximately 450 °C. Typical tin-based solders according to ISO 9453 include SnCu, SnAgCu, SnBi and SnSb; legacy SnPb alloys are subject to legal restrictions. Applications include electrical engineering, sheet-metal enclosures, precision mechanics and low-temperature sealing joints.

The filler metal has a liquidus above approximately 450 °C, while the base material does not melt. Filler metals according to ISO 17672 include silver-, CuP-, copper-, CuZn-, AlSi- and nickel-based alloys. Applications include piping, heat exchangers, tools, stainless steel, copper, brass and carbides.

What the module covers

• Brazing and soldering — soft, hard and high-temperature joining
• Technical principle
• What to remember
• Soldering
• Brazing
• High-temperature brazing
• Braze welding
• Capillary clearance and overlap