Radiant tube closed heating, electric heating element surface temperature higher than the furnace temperature about 100 ℃ to 150 ℃.So when select material to analyze furnace temperature and atmosphere in furnace temperature, choosing the right heating material.This company produces the radiant tube used Cr20Ni80 (nickel chrome) Cr25A15, Cr21A16Nb, Cr27A17Mo2 (iron chromium aluminum) materials, such as the material chemical composition / % in the following table:Cr20Ni80 use between 500 ℃ to 800 ℃, because of its stability, a single, homogeneous solid solution of organization, so it has good room temperature and high temperature mechanical properties, uniform electric physical properties and good processing properties.Using low temperature and long service life, is not easy to damage, etc, the difference in iron chromium aluminum electric heating alloy material.Cr25A15, Cr21A16Nb, Cr27A17Mo2 use between 800 ℃ to 1200 ℃, three kinds of materials use temperature rise in turn.Low plasticity, high brittleness is iron chromium aluminum is the chief drawback of electrothermal alloy material, especially between 400 ℃ to 800 ℃, use for a long time can make the material in precipitation "CrFe" type metal compounds, lead alloy plastic fell sharply, appear serious embrittlement phenomenon, so iron chromium aluminum series electric heating alloy material to avoid forming in this temperature region and use.Surface load refers to the unit surface area on the electric heating element for electrical values.The surface of the material using load intensity is higher, shorter service life of the material, but also the consumption of materials of the smaller.So, reasonable choice of components heat load intensity, the electric heating element has high thermal efficiency, long service life, the comprehensive effect of saving material.