Metal Alloy and Ceramic Heating Elements for Electrical Furnaces
Electrical resistance heating is the leading thermal processing method for industrial heat treatment applications due to its unparalleled levels of efficiency. Gas furnaces use combustion methods to increase the temperature values of process chambers, relying on thermal distribution via ceramic insulation or convection to uniformly treat materials or components. This method can be unsuitable for chemically-sensitive processes and can result in higher degrees of energy loss compared to electrical heating.
Comparing the Maximum Watt Loading of Heating Elements
Metallic alloy and ceramic heating elements in electrical furnaces convert 100% of supplied electricity into heat. These components are typically categorized by their ability or inability to perform in the presence of oxygen. Protective environments may be required to isolate heating rods fabricated from metallic alloys such as tungsten (W), molybdenum (Mo), tantalum (Ta), and graphite (C). Ceramic heating elements such as silicon carbide (SiC) are not sensitive to oxidation and are suitable for operation at elevated temperatures in atmospheric conditions.
Temperature and atmosphere requirements are the two most critical metrics for selecting materials for a furnace’s heating elements. The temperature value refers directly to the operating temperature of the element and not the value of the heat treatment chamber. This is determined by the relationship of the watt loading, the furnace temperature, and the radiating capacity of the heating element itself. For example, an energized silicon carbide ceramic heating element requires a maximum watt loading of roughly 10 – 14 W/cm2 to generate a furnace temperature in the region of 800°C (1472°F). This loading value is gradually reduced as temperature values climb towards temperatures of 1700°C (3092°F).
The relationship between watt loading and temperature for iron-chrome-aluminium alloy heaters represents a much steeper drop-off than that of silicon carbide ceramic heating elements, with a maximum watt loading cut-off at temperatures of 1400°C (2552°F). However, there are numerous additional factors to consider beyond watt-loading efficiency when choosing a material for furnace heating elements.
Iron-chrome-aluminum heaters are comparatively cheap for initial installation but represent reduced longevity and functionalities compared to ceramic heating elements with increased thermal properties. These materials support thermal processing at furnace temperatures of up to 1300°C (2372°F) with improved chemical resistances and lower densities than alternative metallic alloy heating elements.
Silicon carbide heating elements are preferable for use in higher temperature applications where furnace temperatures continuously and intermittently exceed 1600°C (2912°F). These heating elements are extremely rigid and can be manufactured as straight rods, multi-leg, and spiral-cut elements. This ceramic material far exceeds the thermal capabilities of metallic alloy heating elements but is more susceptible to damage via thermal shock.
Choosing a Heating Element Material with Thermcraft
Thermcraft is a leading manufacturer of thermal processing equipment for industrial, academic, and commercial applications. Our metal alloy and ceramic heating elements have been installed into an array of innovative furnace designs for an array of heat treatment procedures, including annealing, curing, and sintering.