Improved electrode null for high current density die plasma arc

摘要

The diameter of a hafnium insert (44) press fit into the bottom end of a copper electrode (42) varies as a function of the level of a current carried by the electrode. The diameter is the minimum necessary to support emission at that current level while also protecting the copper body against attack by the arc. The insert (44) is generally circular and preferably extends completely through the bottom wall (42g) to a circulating flow of cooling water at a hollow interior (48) of the electrode. The bottom wall includes an annular recess (42d) in a portion of the copper wall surrounding the insert. A coolant tube (56) extends into the recess in a spaced relationship to provide a high flow velocity of the coolant over the interior rear surface of the electrode.