Re: flame cutting on copper


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Posted by Stuart Powell on April 02, 1999 at 21:02:30:

In Reply to: Re: flame cutting on copper posted by Valerie on September 24, 1997 at 13:56:54:


: : I'm a newbie at metal working. I want to do brazing and flame cutting on copper, what kind of torch do I need for doing this?

: As far as cutting copper with a torch, it can't be done. You can melt a path and make it drip away but a cutting torch really doesn't "cut it"! A bandsaw or shear will produce a good cut.

: Copper is a great thermal conductor. This makes it hard to weld with low-energy input processes. Oxyfuel would take a long time to get the weld area hot enough because the metal is quickly pulling the heat away. It can be done, but it takes time to get it hot enough. Oxyfuel is not a preferred method for welding because it does not adequately protect the molten metal. Flux needs to be used. Oxyfuel welding is recommended only for small, non-critical applications (including repair) when arc welding equipment is not available.

: This isn't to say that your oxyfuel rig is useless! You can do brazing or soldering on copper or its alloys (bronze, brass, others). Instead of melting the base material, the metal is heated and flux is used to help clean the joint and to help the filler material flow. In the case of brazing, there are silver alloys or copper-phosphorus alloys available for copper brazing. A regular gas welding torch tip would be used. The size designation depends upon the thickness of the metal. You need oxy-acetylene, not acetylene-air torch. Acetylene and air torches are great for small parts where you want to keep the heat down. Copper needs more heat than this torch can provide unless your parts are very small.

: Soldering will not give you good color match as the brazing filler will. But it uses a lower temperature. The metal must be very clean to start.

: If you have access to a GTAW (Gas Tungsten Arc Welding or TIG) torch, this is best for the bronze alloys. The argon gas shield keeps the metal clean and prevents oxidization. The color match can be perfect, since you can use the same metal for the filler as you have for the base metal.

: Shielded Metal Arc welding (SMAW) can be used. The welding can be accomplished quickly since the temperature of the arc is hotter and more concentrated than in the gas torch. The disadvantage is that you don't always get good color match (depending on the alloy) and it is hard for some people to control.

: If you are doing production work on copper alloys, the GMAW (called Gas Metal Arc, wire-feed or MIG) process works well. You are limited to the types of wire available. You also need to experiment with the set up of the machine and the welds it produces. It is easy to make a good-looking weld that is really not melted into the base metal if you do not have the right set up. Weld a joint and bust it in a vise. Look at the weld joint and see if there was enough heat.

: Here is info from AWS Welding Handbook, Vol 4, Ed 7:

: "...welding rods of Type ERCu or ERCuSi can be used for copper, depending upon the desired joint properties. A commercial flux designed for welding copper alloys can be used. The welding rod and the joint surfaces should be coated with flux. The flame should be adjusted to neutral when flux is used and slightly oxidizing for welding without flux. The torch tip size should be one to two sizes larger than the one normally used for the same thickness of steel."

: Low brasses can be welded using RCuZn-A, RCuZn-B, RCuZn-C rods. Copper-tin (Phosphor Bronze) uses RCuSn-A or RCuZn-C.

: Silicon Bronze uses RCuSi.

: For the brazing alloys, the numbering system has a "B" in the front, following with the materials in the filler. Ag means silver, P is phosphorus, Zn is zinc, Cu is copper. For specific information, I would make sure that you know what type of copper alloy you have (or what type of copper) and then purchase the flux and filler together at your supplier.

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