Heater Catalog - Watlow

High-Temperature HeatersCeramic Fiber HeatersApplication HintsApplications• High temperature furnaces• Metal melting, holding and transfer• Semiconductor processing• Glass, ceramicand wireprocessing• Analyticalinstrumentation• Fluidized beds• Laboratory andR&D• Other highEmbedded Coil Elementstemperatureprocess applications• Optimum performance for high temperature, enclosedfurnace chambers• Coiled elements readily conform to complex curvedsurfaces, especially small custom chamber shapes• Coiled element design works best in higher voltage,lower current situations• Use where lower watt density requirements and lowduty cycle operations are expected• Available in stock and standard units of medium wattdensity, rated up to 2000°F (1093°C). When ordering,refer to charts on pages 449 to 451.• Never use ceramic fiber heaters forconduction heating applications. Theseheaters are designed for radiant heattransfer only.• Use appropriate mounting methods including pins,washers, clamping straps, overlapping edge clamps,interlocking edges, etc. Generally, these methodswork better than cementing ceramic fiber heaters, ascementing will not accommodate the expansion andcontraction caused by thermal cycling of surroundingmetal structures.• Keep furnace loads free of oils, lubricants and othercontaminants that can vaporize at high temperatures.Ceramic fiber heaters have a porosity exceeding90 percent and cannot be sealed against contaminationinfiltration and possible damage to the heatingelement wire.• Use low mass thermocouples that are responsive torapidly changing radiant energy transfer conditions.Without proper temperature control, ceramic fiberheaters can generate sufficient heat for self destruction.• Mount a thermocouple junction directly above anelement and within 1 /16 in. (1.6 mm) of the heatedsurface. Embedded ceramic mounting tubes areavailable as an option to position 0.125 in. (3.2 mm)diameter thermocouples inside the fiber, directly behindand between the elements. Heater wire operatingtemperatures are critical and wires should be monitoredat the hottest point within the application.• Electrical connections made in heated portions of theapplication must be rated for the appropriate currentsand anticipate ambient temperatures. To ensuregood electrical connections, use compression-typeconnection devices located as far away from thehottest area of the application. This minimizes thepossibility of electrical connection degradation causedby thermal expansion, contraction and high temperatureoxidation.• Ceramic fiber products shrink at high temperatures.During the first 24 hours of operation at temperaturesbetween 1600 and 2200°F (870 to 1204°C), shrinkageof up to 4 percent can occur. Fill all gaps between unitscreated by shrinkage with loose ceramic fiber insulation.Watlow offers a “pre-firing” process that pre-shrinksand dimensionally stabilizes units before shipping.Contact your Watlow representative for further details.• Use additional back-up insulation for maximum energyefficiency and appropriate safety considerations. Useonly insulation with inorganic fibers and binders to avoidcorrosive fumes that could damage heater elements.• Handle all units and leads with care. Ceramic fiberheaters are very resistant to thermal cycling and thermalshock, but are easily subject to mechanical damagefrom careless handling.• Repair of minor mechanical damage, made withunapproved or unknown cements, could damage thewire elements at high temperatures. If unsure, contactyour Watlow representative before making repairs.Several accessory items are available from the factoryfor repair purposes.WATLOW ®435