Heater Catalog - Watlow

Specialty HeatersCoil/Cable HeatersInternal Construction (Continued)Disk End of SheathNo Wire Junction in theResistance Wire—Madefrom One Continuous Length ofResistance WireEnd Disk WeldedPrior to SwagingJunction Cavity is Backfilledwith MgO after ResistanceWires are JunctionedEnd Disk Welded AfterResistance Wires are JunctionedSheathCoiled ResistanceWireResistance Wires Junctionedafter Sheath is Drawn to SizeSheathStraight ResistanceWireHigh DensityMgO from theSwaging ProcessCompacted MgO fromthe Drawing ProcessCoiled InternalResistance WireThe end of the heater sheath opposite from the leadexit end is called the disk end.With coil construction methods, the internal resistancewires form a 180° bend inside the sheath and do notrequire a junction. After the end cap has been weldedin place, the entire area at the end of the sheath isswaged to provide maximum density of the magnesiumoxide (MgO).Straight (Uncoiled)Resistance WireWith straight construction, the internal wires—whetherresistance or thermocouple—must be junctioned beforethe heater sheath can be finished. MgO is removed fromthe tip of the sheath to expose the wires which arejunctioned by welding. MgO powder is backfilled intothe cavity surrounding the junctioned wires and lightlycompacted. The end cap is inserted and weldedinto place.ThermocouplesInternal thermocouples are available in ASTM Type Jor K calibration with both the coil or straight constructionmethods.Coil:0.125 in. (3.2 mm) round0.128 x 0.128 in. (3.3 x 3.3 mm) square0.102 x 0.156 in. (2.6 x 4.0 mm) rectangularStraight:0.125 in. (3.2 mm) round0.157 in. (4.0 mm) round0.188 in. (4.8 mm) round0.128 x 0.128 in. (3.3 x 3.3 mm) square0.102 x 0.156 in. (2.6 x 4.0 mm) rectangularWATLOW ®471