Heater
In a heater in which an electrically insulating material ( 4 ) including an oxide is filled between a heating element ( 2 ) made of metal including chromium and aluminum and a cover ( 3, 5, 6 ) for sealing the heating element ( 2 ), and in which a lead wire ( 7, 8 ) of the heating element ( 2 ) extends through a portion ( 5, 6 ) of an electrical insulator of the cover ( 3, 5, 6 ) in order to enable the heater to be used at temperatures higher than the prior art, an oxide film including aluminum oxide is formed on the surface of the heating element ( 2 ). The portion of the cover ( 3, 5, 6 ) excluding the portion ( 5, 6 ) serving as an electrical insulator is a metal pipe ( 3 ) that serves as a sheath and includes nickel and chromium, and an oxide film is formed on the surface of the metal pipe ( 3 ). Therefore, the heater can be used in dies for plastic forming or the like.
1. A heater in which an electrically insulating material comprising an oxide is tilled between a heating element comprising a metal including chromium and aluminum and a cover for sealing the heating element, and in which a lead wire of said heating element extends through a first portion of said cover, said first portion serving as an electrical insulator of said cover and together with said cover establishing a sealed environment for said heating element through an operating range of said heater, wherein an oxide film comprising aluminum oxide is formed on the surface of said heating element and wherein a portion of said cover excluding said first portion is a metal portion including nickel and chromium and an oxide film comprising chromium oxide is formed on the surface of the metal portion.
2. A heater according to claim 1 , characterized in that said heating element is in the form a spirally wound wire.
3. A heater in which an electrically insulating material comprising an oxide is filled between a heating element comprising a metal including chromium and aluminum and a cover for sealing the heating element, and in which a lead wire of said heating element extends through a first portion of said cover, said first portion serving as an electrical insulator of said cover, said heater made by the steps:
a) providing a metal pipe comprising nickel, cobalt, chromium, and iron;
b) heating said pipe so as to form an oxide film on the surface of said pipe;
c) providing a heating element comprising an iron-chromium-aluminum alloy;
d) winding said heating element into a coil;
e) heating said coil so as to form an aluminum oxide film on the surface of said heating element;
f) inserting said coil into said pipe;
g) rolling said pipe containing said coil so as to reduce the diameter of said pipe to less than 6.5 mmφ, thereby obtaining an incomplete sheathed heater; and
h) sealing both ends of said pipe with first and second lead glasses, with first and second lead wires penetrating at least one of said first and second lead glasses,
wherein said pipe and said first and second lead glasses form a cover that seals said heating element and wherein an oxide film comprising chromium oxide is formed on a surface of the metal portion of said cover.
4. The heater according to claim 3 wherein the steps for forming the heater further include:
heating the incomplete sheathed heater of step g) so as to reduce moisture therein prior to step h).
5. The heater according to claim 3 wherein magnesia powder is emplaced in the gap between said pipe and said coil.