Filler materials and shielding gases: choice of consumables

Two welders with same machine and method can deliver very different results if they choose different consumables. Electrode type wire type and shielding gas are not random choices — they fit specific materials tasks and requirements for appearance and strength and wrong choice can give welding defects even when technique is otherwise fine

With MMA welding the electrode is both current conductor and filler material and the coating around the metal core is crucial for the result. The most common types are rutile basic and cellulose-coated electrodes as well as special electrodes for stainless steel and other materials.

• 01Rutile electrodes: easy to ignite and control, give a neat and smooth weld — suitable for ordinary construction work and thinner plates
• 02Basic electrodes: produce stronger, more ductile welds with better resistance to crack formation — often used for heavier structures and pressure vessels
• 03Cellulose-coated electrodes: provide deep fusion and work well for root runs among other things in pipe welding
• 04Special electrodes: adapted to stainless steel, cast iron, or other materials requiring a specific filler material

Hydrogen in the weld metal is measured in ml per 100 g of weld metal. According to ISO/TR 17844, rutile and cellulosic electrodes belong to the highest hydrogen class (A, more than 15 ml), while basic electrodes can reach classes B to D. Example: ESAB's basic OK 48.00 is marked H5, and the data sheet states less than 4.0 ml of hydrogen per 100 g of weld metal. How hot and for how long the electrodes must be dried is stated in the manufacturer's data sheet — follow it.

With wire welding (MIG/MAG) and TIG the wire is chosen according to the base material's composition so the filler material's strength and chemistry match what is being welded. For unalloyed and low-alloyed steel a wire with a composition close to the base material is typically used while stainless steel and aluminium require their own specialized wire types — often with the addition of stabilizing elements as already mentioned for stainless.

The shielding gas's job is to shield the weld pool from air's oxygen and nitrogen which would otherwise contaminate the weld and create pores. Argon is an inert (noble) gas that doesn't react with the weld pool and is typically used in TIG welding and in MIG welding of aluminum and stainless steel. CO2 is an active gas that reacts chemically with the weld pool, gives good penetration and is cheaper to run but can produce more splatter and a rougher seam.

In practice, with MAG welding, a gas mixture of argon and CO2 is often used instead of pure CO2, because the mixture provides a smoother arc, less spatter and a neater weld, while still having a sufficiently active component to provide good wetting and fusion.

The choice of electrode, wire and gas is always linked to material, material thickness, welding position and requirements for the finished joint. On certified and documented work, the choice is also not free — it is set out in the approved welding procedure (WPS), and the welder's task is to use exactly the consumable that the procedure prescribes, not what happens to be closest.