In order to maintain an extruder nozzle or the like hot, a sleeve heater is used that basically comprises a tubular body in which is incorporated an electrical heating wire. Such a sleeve heater is typically slipped over the nozzle to be heated so it fits snugly therewith. When the wire is energized, the is nozzle or the like is appropriately heated. Thermostatic sensors can be built into the sleeve heater. In many situations the body being heated is not of perfectly uniform shape so the sleeve heater must be provided with cutouts or irregular formations that allow it to accommodate the contours of the body being heated. Furthermore in some situations specific regions of the body must be heated more or less than other regions, so the spacing of the turns or loops of the heating wire must be appropriately increased or decreased in the parts of the sleeve that will contact these regions.
Such a sleeve heater is typically made by winding the heating wire about a first tube and then fitting a second tube around the outside of this assembly and filling the space between them with heat-conducting potting. Fitting the heating wire to the inner tube is a tricky operation, in particular when nonuniform spacing of the turns is necessary or the wire must be guided around cutouts in the tubes. In general adapting such a system for a particular application is an extremely expensive and time-consuming chore.