Brass and brazing go hand in hand

A Copper Development Association product story

Edited by the Engineeringtalk editorial team Nov 23, 2004

Brazing is synonymous with brass: not only is brazing an ideal method of joining brass but brass itself is often used as a filler when brazing steel.

Brazing is synonymous with brass: not only is brazing an ideal method of joining brass but brass itself is often used as a filler when brazing steel.

Brass is a versatile material, which lends itself to being joined by a plethora of hot and cold processes.

Locked seam and clinched joints, nuts and bolts, rivets (of all kinds) and adhesives are among the cold processes that may be used to successfully join brass.

The hot processes include soldering, brazing and welding.

Although brasses can be welded, a high degree of control and skill is required to ensure that the volatile zinc in the molten weld is not boiled off leaving a copper rich weld joint.

"In air silver brazing" takes place at above 600C but below the melting point of brass, and is an ideal method of producing strong, leak tight, electrically conductive, smooth joints in brass.

Silver brazing is also a perfect method of joining brass to other common engineering metals, eg steel, copper etc.

Brazing and soldering are defined as "thermal joining processes" (soldering takes place at below 450C and brazing above this temperature), where the molten filler is drawn into the gap between the two metals being joined by a capillary action.

Most air brazing operations require the use of a chemical flux to protect the metals from oxide formation and promote flow and wetting of the molten brazing alloy.

Anyone who has ever had the experience of brazing, will know the feeling of the ?magic moment? when the brazing medium flows.

If the choice of material and flux are correct, and the joint designed properly, it is almost instantaneous once the critical temperature is reached.

Specialist advice on brazing rod and flux selection, along with joint design, is available from Johnson Matthey (see www.jm-metaljoining.com).

The expression "silver brazing" comes about because the brazing filler rod contains a significant amount of silver, and the amount of silver present controls the melting point of the brazing rod.

As a rule of thumb, the higher the silver content, the lower the melting point, but this is also influenced by the other alloying elements present (typically copper, zinc and sometimes a small amount of tin) in the filler rod.

Brass brazing is a high temperature brazing process taking place at 900C, which uses a 60/40 brass with a only a nominal amount of silver present, and is typically used for joining of automotive, hydraulic components and tubular mild steel structures.

Brazing is believed to be many centuries old.

Johnson Matthey has been around for 200 of those years and continues to develop and pioneer new brazing alloys and fluxes that ensure brazing remains a highly competitive and cost-effective method of producing high integrity sound joints, not only in brass but a whole range of engineering materials.