There are two main types of electric resistancealloys. Nickel-chromium (e.g. 80 Ni, 20 Cr) wasdeveloped around the turn of the century andwas soon used as heating element material inindustrial furnaces as well as in electric house-hold appliances.

In the thirties Kanthal introduced a newresistance heating alloy based on iron-chro-mium-aluminium with a longer life and a highermaximum operating temperature than nickel-chromium.

The two main types of alloys have their ownspecific properties, with advantages and dis-advantages, and are supplied in many differentgrades and forms. Kanthal manufactures bothtypes of alloys under the names NIKROTHAL(nickel-chromium) and KANTHAL (iron-chro-mium-aluminium).

In general KANTHAL is superior to NIKROTHAL in respect of performance andlife and is therefore nowadays a standardmaterial choice when it comes to metallic heating elements for industrial furnaces. Themost important advantages are:

  • Higher maximum element temperature of1425°C 2600°Fcompared to 1250°C 2280°F
  • Longer life (2–4 times)
  • Higher surface load
  • Higher resistivity
  • Lower density
  • No spalling oxide, which may contaminatethe goods and the furnace and also causeshort circuit or failure of elements and gasburners.

For the furnace user, using KANTHAL resultsin less material at a lower price and also – a longer life. Table 1 shows an example ofweight saving – and lower cost – obtained byusing KANTHAL instead of nickel-chromiumalloys. This lower element weight will alsoresult in considerable cost savings in the support system, because fewer suspensionhooks are necessary.

The NIKROTHAL alloy may have specialadvantages if you need a heating elementhaving very good mechanical properties in thehot state. KANTHAL APM has, however, creepstrength at elevated temperatures in the samelevel as NiCr 80/20.

Table 1. A 120 kW furnace equipped with R.O.B. elements. 3 elements of 40 kW each, 380 V.

Element Data NiCr 80/20 KANTHAL AF
Furnace temperature, °C °F 1000       1850 1000       1830
Element temperature, °C °F 1068       1955 1106       2025
Hot resistance, Rw 3.61 3.61
Temperature factor, Ct 1.05 1.06
Cold resistance, R20 3.44 3.41
Wire diameter, mm in 5.5       0.217 5.5       0.217
Surface load, W/cm2W/in2 3.9       19.9 3.98       25.7
Wire length, m, ft3 elements 224.9       738 174.6       573
Wire weight, kg,lb3 elements 44.4       98 29.6       65

Weight saving:

44.4—29.6 44.4 = 33%

98—65 98 = 33%