| 摘要 |
An elongated heater unit including an elongated resistor helix, terminals connected to the ends of the helix, at least a first surrounding metallic sheath, powder insulation material disposed within the first sheath and spacing the resistor helix from the sheath. The sheath is provided with at least one indentation and/or groove extending along at least a portion of the length of the first sheath. The method for constructing the heater unit includes forming the indentation by means of a roll with a protrusion, by utilizing a mandrel, by utilizing a temperature sensitive member or by utilizing a reducing sheath.
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