RESISTANCE WIRES AND STRIPS

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 newr esistance heating alloy based on iron-chro-miumaluminium with a longer life and a highermaximum operating temperature than nickelchromium. 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.

The most important advantages are :

• Higher maximum element temperature of 1425°C (2600°F) compared to 1250°C (2280°F)
• Longer life (2–4 times)
• Higher resistivity
• Lower density
• No spalling oxide, which may contaminate the goods and the furnace and also cause short circuit or failure of elements and gas burners.

For the furnace user, using KANTHAL results in less material at a lower price and also – a longer life. Table 1 shows an example of weight saving – and lower cost – obtained by using KANTHAL instead of nickel-chromium alloys.

This lower element weight will also result in considerable cost savings in the support system, because fewer suspension hooks are necessary.

The NIKROTHAL alloy may have special advantages if you need a heating element having very good mechanical properties in the hot state. KANTHAL APM has, however, creep strength at elevated temperatures in the same level as NiCr 80/20.

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

each, 380 V