A welding hammer, also called a slag hammer or chipping hammer for welding, is the welder’s hand tool for knocking the slag layer off a completed weld bead. The head carries a point on one side and a narrow, vertically set chisel edge on the other, so slag can be prised loose both in a fillet and along a straight run.
In processes using a coated stick electrode or flux-cored wire, a layer of solidified slag forms over the weld pool. It protects the hot metal from the air while it cools, but it has to come off afterwards. If slag is left in place the bead cannot be inspected and — more seriously — a following pass traps inclusions, which weakens the joint.
Shape and construction
- Point and chisel set at right angles, so you can work both the toe of the bead and the root of the joint without turning the hammer over.
- Light in weight — the action is tapping, not striking. A heavy hammer damages the weld metal.
- Spring handle or coiled steel spring on many models: this absorbs the shock and stops the hammer jumping out of your hand when the slag suddenly releases.
Using it in practice
- Let the weld cool a little first. Warm slag releases more easily than cold, but never strike a still-glowing bead: you will leave dents in the soft metal.
- Work away from yourself, tapping along the edge of the bead rather than on top of it.
- Follow with a wire brush until the bead is bright and can be judged. On multi-pass welds, do this between every pass.
- Inspect the bead straight after de-slagging for porosity, undercut and lack of fusion — these only show on a clean weld.
Points to watch
- Always wear safety glasses. Slag flies off sharp and hot; this is the most common cause of eye injuries in welding work.
- Keep a separate brush and hammer for stainless steel. Tools used on mild steel carry over iron particles that later show as rust staining on stainless.
- Do not confuse it with a mason’s chipping hammer. That tool has two pointed heads and is meant for knocking mortar and render off masonry.
- In MIG/MAG and TIG welding little or no slag is produced; there a brush is usually all you need.
Related terms
- Welding on
- Welding
- Chipping hammer
- Hammer
- Reinforcing steel
- Milling
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