Methods and apparatus for heating metal parts with magnetically driven

Abstract

Methods and apparatus for the welding and heat treating of metal parts in which an electric arc extends between a pair of adjacent metal parts or between an electrode and one or more metal parts with the arc traversing the metal part or parts a plurality of times during the heating cycle. For finite length metal parts, i.e. when the surface or surfaces to be heated do not provide closed paths to be followed by the arc, the arc is initiated, caused to follow the surface, extinguished and then reinitiated, or is caused to traverse the surfaces in alternately opposite directions after initiation. With finite length metal parts, run-off tabs are provided at the ends of the surfaces to prevent overheating at such ends. A magnetic field causes the arc to traverse the surfaces and may be modified in strength or distribution to vary traverse rate. Also, by varying the magnetic field path, by superimposing another magnetic field or by gas pressure, the arc may be caused to follow paths which traverse entire surfaces even though arc cross-section is less than the width of surfaces. The arc may be direct or alternating current and the magnetic field may be constant or variable in both magnitude and polarity. Sensors responsive to arc position may be used to control reversal of direction of arc movement, arc speed, magnetic field, etc.