Terry_Cowan (16K)

Using Silicon Bronze Filler Rod on Steel

© Ron Covell 2007

There are many metalworkers who have not yet learned the benefits of using Silicon Bronze filler rod when TIG welding steel. Perhaps the greatest advantage is that bronze rod 'pulls' the metal less, so you'll get a lot less distortion (warping) when welding, and this is particularly noticeable when welding on large sheet metal panels.

First, let's note that although brass and bronze have a similar appearance, their properties are distinctly different. While both are copper-based, brass is an alloy of copper and zinc, and bronze is an alloy of copper and tin.

Most metalworkers are familiar with the process of brazing steel panels together. This is usually done with an oxy-acetylene torch, using either bare brass rod dipped in brazing flux, or by using flux-coated brazing rod, which is readily available at welding stores. Brazing certainly has its place, but it is not really feasible to TIG weld with brass rod, since the zinc gives off fumes when heated, and the violent fuming pollutes the argon gas shield around the weld. An additional concern is that the zinc fumes are poisonous, so you must be very careful to protect yourself from the dangerous fumes, either by using proper ventilation, or an appropriate respirator.

One of the biggest drawbacks to brazing sheet metal autobody panels is that neither paint nor plastic auto body filler stick to brass very well, and over the years I have seen countless brazed repairs that have failed because of cracks in paint or plastic applied over them.

When welding steel panels with bronze rod, this problem is eliminated, since both paint and plastic filler bond to bronze very well. Bronze has only about half the tensile strength of steel, so I wouldn't recommend using it as an all-purpose replacement for steel filler rod, but for non-structural repairs it can offer some real benefits. On older cars, especially those made in the pre-unibody days, virtually all of the panels are non-structural. On newer cars, some panels are structural, so be sure you know how the panel is utilized before you decide to use bronze rod for a repair. Bronze filler rod sticks very well to steel, but on sheet metal panels, I would prefer an overlapped joint over a butt joint, due to the lower tensile strength of the bronze. For any inside or outside corner joint, the bronze rod should achieve the same strength as the base metal, since the bead size will be several times the base metal thickness, and this is a situation where you will get MUCH less distortion than you would if using steel filler rod.

In cases where you need to add a lot of rod to a steel part (filling divots on parts to be chrome plated, for example) the smaller amount of distortion offered by the bronze rod is a HUGE advantage. In industry, there are several varieties of bronze (phosphor bronze, naval bronze, etc.) but for welding on mild steel, I'd stick with Silicon Bronze filler rod. The trade name that I am most familiar with is 'Everdur', and most welding stores stock this rod.

It is also possible to MIG weld with bronze wire, but since bronze is softer than steel, it's much more difficult to feed it a long distance to the gun, so using a spoolgun is preferred, if that's an option. It is possible to feed it through a standard MIG cable, but you must be very careful to keep the cable as straight as possible, and .030" diameter wire will feed much better than .023". It may help to use a contact tip that is just slightly oversize, too, to keep the wire from binding, and creating a 'birds nest' inside the machine.

For MIG welding with bronze wire, you should use pure argon shielding gas, not CO2 or an Argon CO2 mix. I traveled in Australia recently, and visited a brand-new state-or-the-art facility where they taught collision repair. They use bronze wire extensively when making non-structural repairs on new cars, which came as a surprise to me. Pulsed MIG machines are preferred for MIG welding with bronze wire, but even a 'standard' non-pulsed machine can do an adequate job.

If you've not yet experienced the joy of using bronze rod or wire on steel, I think you will enjoy its benefits, and we can all use a little help from time to time for some of our difficult metal projects!





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