Welding Copper Pipe: A welding machine
Safety: Wear the correct protective gear and keep working conditions per OSHA standards: Safety glasses, auto darkening welding helmet, welding jacket and pants, leather boots with rubber soles, long leather gloves(no holes), respirator, grounded metal welding table, and a full fire extinguisher. Remove all flammables from your non-flammable working surface(right?). The welding helmet protects your eyes and skin from any sparks for both, and also shields ultraviolet rays that can damage your vision. Note: any exposed skin will get you a bad sunburn, so be careful, ouch. Be sure to fully ventilate the area. Keep everything dry to protect against electric shock. Use a foot pedal and only have the welder on ONLY when welding. Its tempting to just leave it on for a second while you move to get something but don’t do it! Keep cylinders away from the welding area and fasten in your cart.
Figure 1 Auto-darkening helmet for welding copper pipe. Don’t hesitate, use the auto-darkening type
Only weld shiny clean copper. Remove all contaminants including platings….The weld will turn out like crap if everything is not cleaned(wipe sweating copper pipes free of all condensation, dirt, ect with isopropyl alcohol, then wipe dry with a clean rag).
Use a wire grinder, sanding cloth, wire brush, ect. to remove all the copper oxide and make everything shiny. Clamp work in place and you are finally ready to weld copper pipe.
Picking materials: Try to use oxygen-free, or, P-deoxidized copper, it gives off less hazardous fumes. Don’t use copper alloys.
Picking your welding equipment: Most welders prefer an old school oxy/acetylene torch set up. Copper is extremely heat conductive which means the heat spreads quickly from one end to the other. The torch can lay in enough heat on the whole surface to easily preheat whereas a welding machine just injects heat onto a small surface area…leading to a tricky situation to not overheat your copper but still heat enough to weld copper(preheating in a furnace will resolve some of this issue but who has one of those ??). This welding machine pinpoint heat issue also can cause distortion of the metal and could lead to cracking. But despite this, lets talk about machine welding.
Welding with a machine. Use a MIG or TIG machine with a pedal. Look at your welders handbook for the proper amperage for the metal thickness you are working with. Because copper is so heat conductive you’ll need a lot of amps. Use argon or helium gas and adjust per the manual…use helium for thicker metals. Test out on scrap metal the same thickness before trying on your final product.
Figure 2 How to weld copper pipe
Start your puddle: hold the arc at 70 degrees to the surface for a couple seconds with a very small swirling motion to get your puddle started. Once started get moving and feed your LEAD FREE silver copper alloy rod onto the puddle, again with a small swirling motion…keep quickly advancing the welder and rod until you are done. The end result should look like a stack of dimes laid on a steep angle. The end result is that the filler metal all mixes with the two pieces you are welding together. Practice on flat horizontal metal before attempting vertical joints. Its easy for the puddle to just drip away on vertical joints and requires exacting finesse. Let the copper all cool naturally in air to avoid cracking.
Figure 3 Welding like a stack of dimes
Here’s some useful melting point info:
METAL Melting point(F)
How to weld copper with oxygen acetylene will be in another article. Sweating copper pipe is on the main page.