How nichrome is made

The glowing wire in a toaster protects itself. Heat grows a skin of chromium oxide that keeps out the air.

stations: 8
things upstream: 29
raw sources: 15
steps from the ground: 6

The short version

Eighty percent nickel and twenty percent chromium give the classic grade of this heating alloy, patented back in 1906. It resists current about 66 times better than copper. One supplier melts it under vacuum, anneals the ingot, forges and rolls it hot, cold-draws it through many passes, anneals again, then pickles and polishes the wire.

Melt the alloy charge

Nickel and chromium go into a vacuum induction furnace, with traces of iron, silicon or manganese at the supplier FANMETAL. ASTM and DIN standards specify the percentages. The A grade is 80% nickel and 20% chromium by mass.

Goes in
Nickel Chromium
Soak the ingot

The solid ingot is annealed so that metals which separated as it cooled spread evenly through it again.
Forge and roll hot

Hot ingots are forged, then rolled. A solution treatment between these steps refines the grain and relieves internal stress. The alloy's good ductility allows this and the drawing to come.
Draw to thin wire

Rod is pulled cold through narrowing dies in many passes until it reaches a set electrical resistance per meter. Standards hold wire over 0.127 millimeters to within 5 percent of that value.
Anneal under vacuum

Cold drawing leaves the wire hard. A vacuum anneal gives back its plasticity.
Pickle and polish

Pickling strips off oxide scale, and electrolytic polishing leaves a smooth surface.
Coil or flatten

Round wire is wound tightly into coils or flattened into ribbon 0.3 to 4 millimeters wide, a form toasters wind around a mica card. Coils can relax to up to 10 times their wound length in use.
Test the batch

FANMETAL runs composition analysis, mechanical tests, non-destructive testing and visual inspection before shipping.

End of the lineNichrome Next it goes into electric kettle, toaster.

Worth repeating

Albert Marsh patented nichrome in 1906, making it the oldest documented resistance heating alloy.
Hot-wire foam cutters use nichrome wire.
Sculptors use nichrome wire inside clay to help soft pieces hold their shape in the kiln.