The arc is only required to iginite the rod. Rapid oxidation occurs at the point of contact between the arc and alloy wires within the cutting rod. This chemical reaction heats the wires to their respective kindling points. The temperatures attained by the burning exothermic rod are far in excess of the melting point of the target work material. The rod will continue to burn for as long as oxygen is supplied, or until it is consumed.
Ultrathermic systems differ from their traditional counterparts in a number of ways.
Both are processes utilizing oxygen as fuel, but oxyacetylene burns at approximately 5800 degrees F using acetylene as a secondary fuel. Setup is lengthy, involving two regulators, two sets of hoses and a variable torch. Preheating is required before cutting can take place. Ultrathermic systems use only oxygen and the consumable alloy fuel rods. There are no hazardous secondary fuels.