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How can I weld naval brass?


Frequently Asked Questions

Naval brass is a copper alloy of approximate composition Cu 60%, Zn 39% and Sn 0.75%. The presence of zinc reduces the weldability of brasses with respect to copper, moreover, the low boiling point of zinc means that copious zinc fume is evolved during welding. Suitable ventilation precautions must be taken before welding to deal with both zinc fume and, less visible, copper fume. The addition of tin to brasses gives added corrosion resistance in marine environments. Tin has been linked to the phenomenon of hot-shortness in brasses, however, this is only true at concentrations above about 1%.

Naval brass is weldable using gas-shielded arc processes (e.g. MIG and TIG). Welding using the manual metal arc (MMA) process is not recommended for naval brass or any other zinc-bearing copper alloy. The gas used for shielding will vary according to whether welding is manual or automatic and the thickness of the section. When welding manually, argon is generally used if the section is less than 3mm thick, however, when welding thick sections automatically a mixture of 75% helium with 25% argon may be used.

TIG welding is most often used on square-edged components less than 1.6mm thick, with no filler metal being required. However, work in the thickness range 1.6mm - 9.5mm requires a suitable filler metal. Components thicker than 9.5mm are not normally TIG welded - unless MIG welding methods are unavailable/inappropriate. The preferred electrode for TIG welding brass is thoriated tungsten because of its greater resistance to contamination from zinc. Direct current, electrode negative (DCEN) conditions should be used.

MIG can be used for welding brasses over 3mm thick and is capable of deposition rates well in excess of those achievable with a comparable TIG set-up. Only direct current electrode positive (DCEP) conditions should be used when welding any form of copper alloys with this method. Generally, components are prepared as single V grooves for work 3 - 13mm thick, and as double V or double U groves for thicknesses in excess of this range.

MIG welding should be performed in the flat position with spray transfer conditions, however, some acceptable fillet welds may be produced in the horizontal position.

Filler metals for MIG or TIG welding brasses should not contain zinc. This is because the zinc tends to vaporise in the arc, leading to zinc loss and porosity in the weld. Welds should be made using either silicon bronze (Cu-Si-Mn) or aluminium bronze (Cu-Al(Fe,Ni)) consumables. Preheating is not usually necessary, although preheats of up to 250°C have been applied to thick-section material.

Details of available types of welding consumable for copper and its alloys are given in BS EN 14640:2005.

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