Copper Backing Bar

The copper backing is a cooled piece of copper that you place behind the root. It absorbs the heat of the weld pool and prevents the molten bath from running through or burning through. This gives you a clean, pore-free root. The copper must be clean and smooth, otherwise the molten metal will stick or the weld will be messy. If you position the backing correctly, you avoid burn-through and achieve a uniform weld shape.