Method of making electrical heating elements

1,114,550. Resistance heating elements. GENERAL ELECTRIC CO. 2 Dec., 1966 [3 Jan., 1966], No. 54110/66. Heading H5H. The magnesium oxide filling 12 of a metal sheathed heating element 11 is in the form of fused spherical particles (Fig. 3, not shown) and is made by introducing finely divided magnesium oxide into a plasma formed in a stream of gas in a radio-frequency induction torch, allowing the particles to fall through the plasma and then quenching them in a water bath. The gas must contain oxygen to a partial pressure of at least 0À1 atmosphere to prevent reduction of the oxide and is preferably two parts argon to one part oxygen. After recovery from the water bath, the particles of magnesium oxide are compacted around the heating coil by a swaging or rolling operation and then the metal sheath is fitted. This may be of lead for lowtemperature heaters or for high temperatures of " Inconel " (Registered Trade Mark).