The ceramic ferrule performs important tasks in stud welding:

It forms a chamber around the weld, thereby holding the plasma created by the arc on the weld and reducing the influence of the surrounding atmosphere.It concentrates the arc on the weld, enabling a correct welding bead to form. In addition the influence of arc blow is reduced.It reduces the cooling speed of the fused material and thereby prevents inadmissible hardening.Without the ceramic ferrule the arc would burn freely, leading to greater oxidation, spilling and pore formation in the weld. Only dry ceramic rings may be used because water dissociates in the arc creating hydrogen. The fused material can then absorb hydrogen which leads to greater pore and crack formation during cooling.