A heating element with higher service temperature limits may be applied to high-lcmpciaturc furnaces and offers good design flexibility However, the characteristics are restricted by the following.    

In general when a metal or alloy is healed in the atmosphere over a certain temperature, oxidation develops, and the oxidation resistance is quickly lost. This tcmpcratuic is called the oxidation resistance limit tcmpcraluic of each kind of metal or alloy. When the metal or alloy is healed over this limit temperature, significant oxide penetrates through the oxide film on the surfaoc and diffuses into the material. Some types of film begin to melt, and the oxidation resistance of the material deteriorates remarkably. Therefore, the metallic heating element also has its own oxidation resistance limit tcmpcratuie, which restricts the maximum scrvioc tcmpcratuie. In the case of the healing element, the maximum service tcmpcratuie has a direct relationship on the quality of the protective film formed on the surface. Pyromax contains A1 is very fine and has good adhesion as mentioned above, and a pure Al₂O₃ protective film is formed on it. With these features, the maximum sen-ice temperature is high. For example, the PX-C and PX-DS feature a maximum service temperature of I400°C which is the highest value among maximum service temperatures of alloy healing elements.     

Of course, the maximum service temperature of a heating element depends greatly on the materials composition. It also varies with the heating element dimensions and use conditions. Table 1 shows the relationship between the maximum service temperatures of Pyromax heating materials in the atmosphere and wire diameters. As shown in Table 1, the maximum service temperature depends on the steel types and wire diameter of Pyromax elements and drops when the wire diameter becomes thinner.   

The lifetime of the healing element depends on the service temperature, as clearly shown. In general, the lifetime of the heating element is shown in measurements in accordance with JIS C 2524 that specifies the method of measuring the lifetime of heating wires. The lifetime of an actually used heating element for industrial furnaces is determined by not only the composition of the healing material itself and the sen ice temperature but also the design and dimensions of the heating element, furnace structure, use ambience, use conditions, and other factors.