Posted by bruce paul fink on November 11, 1997 at 20:57:50:

In Reply to: Re: Welding yellow brass posted by Valerie on October 06, 1997 at 18:51:13:

: : work is done in yellow brass. TIG works great and MIG OK for the bronze and aluminum, but oxidizes the zinc in yellow brass giving a rough surface. I'm using an air cooled TIG with rod that I cast from the same metal. I would deeply appreciate suggestions.

: As you figured, it is the zinc that is giving you the problem. The zinc turns to a metal fume at low temperatures and interferes with your shielding gas and also the cleanliness of your tungsten with the GTAW process. Some yellow brass compositions also have lead in them which also fumes at a low temperature.

: Casting your own rods is a great way to achieve color match. With the lost wax process, a drinking straw can be used to make the shape of the rod. I found it best to bottom cast rods so that the pressure forced the molten metal the whole length of the tube.

: As far as getting a good weld on the yellow brass - try not to get a large molten puddle too hot for too long. My AWS (American Welding Society) Handbook says that due to the high zinc content, it is very difficult to use this with the GTAW process. They suggest using one of these rods: RBCuZn-A (Naval Brass), RCuZn-B (low-fuming brass) or RCuZn-C (another low fuming brass). These are used with oxyfuel - done as braze welding. It would seem that the rod with the "C" on the end would be the best color match becuae there is no nickel in that particular rod.

: Of course, you can try doing the braze welding with your own rods. I would check out the different powdered fluxes available at your welding supplier. Heat the end of rod a little and then dip it in a hole in top of the container. When the rod is hot, it will pick up just enough flux to make it work. The disadvantage with having your uncoated rods is that you can only go so far before stopping to dip the rod again.

: Another tidbit from AWS: "Copper-zinc filler metals cannot be used as electrodes for arc welding because of the low melting temperature and high vapor pressure of zinc. The zinc vapor would boil from the molten weld pool, and the weld metal would be porous."

: Anyway, try the braze weld with the oxyfuel. It will take a bit of time to get the metal to molten temp, but you will not have as much problem with the fuming.

From an old-timer sculptor doing it for over thirty-five years

bpfink@ neca.com

Good notes. Here's another quick tip for those doing their own castings: Instead of casting your own welding rods for the best color match with soda straws (which also works but are short) use regular thin (1/16 to 1/8 inch dia.) welding rods or wire lengths but dip them in wax first to build up the desired varying thicknesses and substitute them for the air vents on your castings. These can then be any varying thickness you want to later weld with.

If using plaster or ceramic shell based investments the steel rod can be removed once it is either set up or after the burnout.

I prefer to remove them before burnout by catching the warmed investment at the right time and gently pulling them out with a vice grip. This also makes an air and wax release channel for the other wax body to escape during the burnout (helping to eliminate any flashing). On castings where a straight channel won't work for the air vents...use wax dipped 'other stuff'....

Most of my casts are limited to about 300# bronze pours per investment as that is my handy sized one man foundry studio limit (I'm an old man that always works alone) so I tend to rest well at night and don't work to prove a point. This 'other stuff' has in the past been anything from flexible steel cable dipped in wax first (and therefore able to bend around the form) to nylon string dipped in wax so it is left in and burns out with all the rest.

This system will make welding rods that are nearer the height of the investment (for me about 2 to 5 feet) and at any diameter needed for the welds of the finish.

If the wax you use is too hard or resistant to pull the core rod at whatever temperature you are getting when the investment sets and you still want to pull it out...first mix it with paint thinner by heating the wax to a minimally liquid but cool state and then pouring the warmed wax INTO THE THINNER... (eliminating chances of any flash points) This softens the wax to more of a heavy grease consistency (depending on proportions used) that will allow the rods or cables to pull out (now we are getting into a more technical area and if this 'sounds' dangerous to you don't do it. Safety first).

bruce paul fink

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