| 摘要 |
PURPOSE:To maintain the powder density of insulator uniformly throughout the inside and outside of a coiled heating element in order to improve the durability of the heating element by a method wherein gaps do not be produced at the inside of the coiled heating element and at the bottom of a metal tubing even at the axially extended state after the swaging. CONSTITUTION:Electrical insulating material consisting of magnesia powder and the like are filled among the metal tubing 1, the coiled heating element 2 and an electrode shaft 13 as the insulator 5 for the prevention of the shorts between the element 2 and the tubing 1 or the electrode shaft 13. The metal tubing 1 housed said element 2 said shaft 13 and said insulator 5 therewithin is subjected to the swaging so as to be formed by radially compressing. Where, a bar insulator 12 housed inside the coiled heating element 2 is the sintered magnesia powder which is composed by sintering the previously moulded electrically molten magnesia powder set with binder at the predetermined temperature and hardening with the evaporation of the binder and rendered to have the compressive strength of the order of 2-8Kg/mm.<2> by adjusting the temperature and time for sintering. |
