0Cr13Al4 0Cr21Al4 Fecral Alloy Wire / Ribbon / Flat Wire For Furnace Heating

0Cr13Al4 0Cr21Al4 Fecral Alloy Wire/ Ribbon/ Flat Wire for Furnace Heating

FeCrAl alloy retains its form when used in high-power electrical heating elements. The developer of this FeCrAl material, TANKII of hallstahammar, Sweden, introduced the metal in 1989. Since then its use in non-electrical applications has been increasing. TANKII's Roger Berglund describes the production of the alloy and the properties of this material that make it suitable for use at high temperatures.

The most common element type for pottery, as well as for glass annealing, fusing, slumping and decorating, is open coiled resistance wire. There are two primary types of resistance material that are used: nickel-chrome (NiCr) and iron-chrome-aluminum (FeCrAl). The grade of NiCr used in these applications is 80-20 (80% nickel, 20% chrome), as it has the highest temperature capability, 2190oF/1200oC. NiCr has the advantage of not deforming when it is heated, so that it requires only intermittent support. FeCrAl also comes in a variety of grades, with a highest temperature of 2550oF/1400oC (TANKII's A-1 alloy, for example). This is the standard wire for pottery kilns. As well as a higher temperature capability, FeCrAl requires less wire to achieve the same heat as NiCr, which translates into lower element costs (approximately 30% less for the material component). FeCrAl elements must be completely supported, however, as they will deform when hot. Usually grooves are built into the walls of a furnace to fully support the element coils. Alternatively, elements can be supported inside glass tubes or on ceramic tubes through the center of the coil, which gives improved heat radiation, but can add significantly to the furnace cost. FeCrAl also becomes brittle once fired and must subsequently be handled with care. FeCrAl is magnetic; NiCr is not, which is the easiest way to tell them apart. Coiled wire elements are relatively easy to fabricate, and some people wind their own, though commercially fabricated elements are readily available.

Resistance wire is only marginally suitable for glass melting. The maximum wire temperature of FeCrAl is 2550oF/1400oC, but the maximum furnace temperature this provides is approximately 2450oF/1350oC, and a maximum melt temperature of approximately 2280oF/1250oC. This means that for typical melt temperatures the elements will be working at their top limit, which will wear them out relatively quickly. Vapours from the melt can also be corrosive to the element material. To protect elements used under these conditions there is an element conditioning process that is desirable for FeCrAl elements, which requires heating the elements, in air, above 1830oF/1000oC, and holding for several hours. This develops an aluminum oxide coating on the outer element surface, which can dramatically improve element life.