Bilateral heater unit

Abstract

A heater unit of bilateral construction is formed by forming a resistor assembly of a resistor helix extending between cylindrical terminals and overlapping the same, inserting the assembly in a sheath tube, filling the tube with MgO powder, placing laminated mica end plugs over the terminals and extending into the ends of the tube, bending the tube into a U-shape, pressing the legs of the U together and feeding the pressed unit through swaging dies to deform the tube over the entire length thereof to provide a heater unit of substantially circular cross section and having two legs of substantially semicircular cross section. The resistor helix in the area of the leg portions has a cross-sectional shape corresponding to the cross-sectional shape of the sheath and the terminals and mica plugs within the sheath are flattened to provide a similar cross-sectional shape thereby locking the terminals within the sheath.

I claim: 
     
       1. A heater unit comprising an elongated outer metallic sheath which is semicircular in cross-section along at least a portion of the length thereof including the end portions, metal terminal means at respective end portions of the sheath extending within and in the longitudinal direction of the sheath, said metal terminal means having a portion lying within the sheath and having a portion extending outwardly beyond the end of the sheath, said portion of said metal terminal means lying within the sheath having a cross-sectional shape corresponding substantially to the cross-sectional shape of the sheath, an insulating end plug surrounding said metal terminal means and extending at least partially within said sheath, a resistor .[.helix.]. .Iadd.means .Iaddend.disposed within the sheath and secured to portions of said metal terminal means and extending therebetween, said resistor .[.helix.]. .Iadd.means .Iaddend.having a cross-sectional shape corresponding to the cross-sectional shape of the surrounding sheath, and compacted powder insulation completely filling the sheath and spacing the resistor .[.helix.]. .Iadd.means .Iaddend.and a portion of the metal terminal means from the sheath. 
     
     
       2. A heater unit according to claim 1, wherein said resistor .[.helix.]. .Iadd.means .Iaddend.is in overlapping relation with said metal terminal means at the end portions thereof and is disposed within depressions formed in the end portions of said terminal means by compaction of said powder insulation. 
     
     
       3. A heater unit according to claim 2, wherein said metal terminal means is a solid member having a substantially cylindrical portion extending outwardly beyond the end of said end plug and a portion having a substantially semicircular cross-section in the area surrounded by said plug and within the area of said sheath. 
     
     
       4. A heater unit according to claim 2, wherein said metal terminal means includes an elongated member having an axially extending hollow portion filled with a flexible lead wire, said flexible lead wire having a portion extending outwardly beyond the end of said elongated member and beyond the end of said tubular sheath, said portion having an insulating coating thereon, and said elongated member having a cross-sectional shape corresponding to the cross-sectional shape of said sheath. 
     
     
       5. A heater unit according to claim 2, wherein said heater unit has a substantially circular cross-section formed by substantially parallel adjacent leg portions of semicircular cross-section and an interconnecting portion formed of said elongated sheath bent back upon itself and formed integrally with the adjacent parallel extending leg portions, each of said leg portions having said terminal means extending outwardly from adjacent end portions thereof. 
     
     
       6. A heater unit according to claim 5, wherein said interconnecting portion is provided with a substantially zero internal bend radius at the junction of adjacent leg portions and a substantially 180° return bend at the outer surface of said interconnecting portion. 
     
     
       7. A heater unit according to claim 5, wherein said resistor .[.helix.]. .Iadd.means .Iaddend.has a cross-sectional shape corresponding to the cross-sectional shape of the sheath such that said resistor .[.helix.]. .Iadd.means .Iaddend.has a semicircular cross-section in the area of said leg portions and a substantially circular cross-section at the middle area of said interconnecting portion between said leg portions. 
     
     
       8. A heater unit according to claim 7, wherein said end plugs are laminated mica plugs and said powder insulation is MgO powder. 
     
     
       9. A bilateral heater unit comprising an elongated sheath in the form of two substantially parallel adjacent leg portions interconnected by a return bend portion formed of said elongated sheath bent back upon itself and being integral with the adjacent parallel extending leg portions, each of said leg portions having terminal means extending outwardly from the adjacent end portion thereof and spaced from said sheath, a resistor .[.helix.]. .Iadd.means .Iaddend.secured to said terminal means of each of said leg portions and extending along the sheath between said terminal means, said sheath between said terminal means being completely filled with compacted powder insulation spacing said resistor .[.helix.]. .Iadd.means .Iaddend.from said sheath, each of said leg portions having a semicircular cross-section formed of a flat portion and an arcuate portion, said flat portion of said legs being adjacent one another such that heater unit is provided with a substantially circular cross-section, said interconnecting portion forming a substantially 180° return bend along the outer surface portion of said sheath and a substantially zero radius return bend along the inner surface portion of said sheath at the junction of the flat portions of said leg portions. 
     
     
       10. A bilateral heater unit comprising an elongated sheath in the form of two substantially parallel adjacent leg portions interconnected by a return bend portion formed of said elongated sheath bent back upon itself and being integral with the adjacent parallel extending leg portions, each of said leg portions having terminal means extending outwardly from the adjacent end portion thereof and spaced from said sheath, a resistor .[.helix.]. .Iadd.means .Iaddend.secured to said terminal means of each of said leg portions and extending along the sheath between said terminal means, said sheath between said terminal means being completely filled with compacted powder insulation spacing said resistor .[.helix.]. .Iadd.means .Iaddend.from said sheath, each of said leg portions having a semicircular cross-section formed of a flat portion and an arcuate portion, said flat portion of said legs being adjacent one another such that heater unit is provided with a substantially circular cross-section, said interconnecting portion forming a substantially 180° return bend along the outer surface portion of said sheath and a substantially zero radius return bend along the inner surface portion of said sheath at the junction of the flat portions of said leg portions, said resistor .[.helix.]. .Iadd.means .Iaddend.having a cross-sectional shape corresponding to the cross-sectional shape of said sheath such that said resistor .[.helix.]. .Iadd.means .Iaddend.has a semicircular cross-sectional shape in the area of said leg portions and a substantially circular cross-section in the middle area of the interconnecting portion. .Iadd. 11. A heater unit according to claim 1, wherein said resistor means is a resistor helix. .Iaddend..Iadd. 12. A heater unit according to claim 2, wherein said resistor means is a resistor helix. .Iaddend..Iadd. 13. A heater unit according to claim 7, wherein said resistor means is a resistor helix. .Iaddend..Iadd. 14. A heater unit according to claim 9, wherein said resistor means is a resistor helix. .Iaddend..Iadd. 15. A heater unit according to claim 10, wherein said resistor means is a resistor helix. .Iaddend.