Barrel Heaters - Hasmak.com.tr

W A T L O W<strong>Heaters</strong>Mica StripApplications andTechnical DataContinuedCalculating Watt DensityWatt density is the amount ofwattage per square inch of heatedarea. To determine watt density,divide the total wattage by theheated area.Watt Density =Total WattsHeated AreaTo apply this equation we mustdefine the term “heated area.”Heated area is the total contactsurface of the heater less areas ofno heat that are found aroundterminals, mounting holes, etc.Heated Area =Total Contact Area - No-Heat AreaTo calculate the heated area:Heated Area =(Length - No-Heat) x WidthMaximum Allowable Watt DensityThe following derating factorsare applicable to the MaximumAllowable Watt Density graph.Please review these factors and thegraph to determine the maximumwatt density for the application.Derating Factors:• For heaters mounted less than25 mm (1 in.) apart on a metal part,derate by 5 percent.• For heaters mounted within76 mm (3 in.) of a reflectivesurface, derate by 10 percent.• For heaters mounted 51-150 mm(2-6 in.) apart and radiating towardeach other, derate by 10 percent.• For heaters mounted within25 mm (1 in.) of a reflectivesurface, derate by 20 percent.• For heaters mounted less than51 mm (2 in.) apart and radiatingtoward each other, derate by20 percent.• For termination Types 2 and 5,as well as lead Types C, E and H(see illustrations on page 318that are less than 51 mm (2 in.)wide, derate as follows: zinccoatedunits by 10 percent andstainless steel units by 20 percent.Application HintsTo maximize the performance of amica strip heater, ensure:• Small heaters with 32.3 cm 2 (5 in 2 )or less of heated area are120VÅ(ac). These heaters can bewired in series for a 240VÅ(ac)power supply.• The surface to be heated is cleanand smooth, so that heat is transferredefficiently. Even small airgaps can cause hot spotting.• Terminal post nuts are not overlytightened. Although the posts aresecurely riveted to the elements,excessive torque could break theconnection.Part Temperature—°F12001000800600400200Maximum Allowable Watt DensityWatt Density—W/cm 21 2 3 4 56 7 8Std.Std.Suspended in airMounted to part using holesMounted to part using clamps5 10 15 20 25 30 35 40 45 50 55Std.500400300200100Part Temperature—°CThermoforming<strong>Heaters</strong>Watt Density—W/in 2319