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Material World
Process · Changes the form, not the material

Rolling

Squeeze it between rollers until it is thinner and longer. Most metal a person ever sees has been through this, and nothing else is remotely as cheap.

Metal is passed between rotating rolls that reduce its thickness and extend its length. It is the highest-volume metal forming process there is by a wide margin: plate, sheet, strip, foil, rail, beam and bar are all rolled, and the great majority of all steel and aluminium produced passes through a rolling mill.

Hot rolling, above the recrystallisation temperature, achieves large reductions and leaves a soft product with an oxide scale. Cold rolling, below it, gives a better surface and closer tolerance and work-hardens the metal as it goes — which is a strengthening mechanism, and the reason cold-rolled sheet is stronger and less ductile than hot-rolled.

Rolling also imposes direction. Grains elongate along the rolling direction and the sheet becomes anisotropic, which matters to anyone pressing it into a shape and is the origin of the earing a deep-drawn cup shows at its rim.

Uses

Structural sections and rail; plate for ships and pressure vessels; sheet and strip for vehicle bodies, appliances and cans; foil down to a few micrometres; and the bar and rod that machining and wire drawing start from.

Beyond metals, the same principle calenders rubber and polymer sheet, and rolls paper.

History

Small mills for lead and precious metals from the sixteenth century; Henry Cort's grooved rolls in 1783 made rolling structural iron practical and, with puddling, effectively created the wrought-iron industry the early railways were built from.

The continuous wide strip mill, an American development of the 1920s, is what made cheap sheet steel available — and therefore the pressed-steel car body, the domestic appliance and the tin can in the volumes that followed.

Economic significance

It is the reason flat metal is cheap. A modern hot strip mill is a capital asset measured in billions and produces several million tonnes a year, and the cost per tonne of shaping falls to almost nothing at that scale.

That scale is also the industry's rigidity: a mill runs continuously or uneconomically, which is why steel overcapacity is such a persistent trade dispute and why mills close permanently rather than idling.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

takes as input

  • 5000 series aluminium alloy — alloy · to plate and sheet, and it work-hardens as it goes — which is where its strength comes from, there being no heat treatment available
  • 7000 series aluminium alloy — alloy · to the plate and sheet that aerospace structure is machined and formed from
  • Steel — alloy · into plate, section, sheet and rail — the great majority of all steel made passes through a rolling mill
  • Electrical steel — alloy · and the rolling is the metallurgy rather than the shaping: the Goss texture that makes transformer steel work is produced by the rolling and annealing sequence, not by the composition

is used in

  • Automotive manufacture — industry · the continuous wide strip mill is what made the pressed-steel car body possible

Sources

  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • Material World
    Our own writing

Where it comes from, and what it becomes

Follow Rolling back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Rolling → takes as input (into plate, section, sheet and rail — the great majority of all steel made passes through a rolling mill) → Steel → is composed of → Iron → is produced by (as pig iron, high in carbon and brittle until refined) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Rolling → takes as input (to plate and sheet, and it work-hardens as it goes — which is where its strength comes from, there being no heat treatment available) → 5000 series aluminium alloy → is produced by (magnesium into aluminium, and it must be melted under cover because magnesium burns) → Alloying and melting → takes as input (the base metal of both brass and bronze) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Rolling → takes as input (to the plate and sheet that aerospace structure is machined and formed from) → 7000 series aluminium alloy → is produced by (zinc and magnesium into aluminium, then solution treated and aged — the strength comes from the heat treatment, not from the melt) → Alloying and melting → takes as input (the base metal of both brass and bronze) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
  • Rolling → takes as input (and the rolling is the metallurgy rather than the shaping: the Goss texture that makes transformer steel work is produced by the rolling and annealing sequence, not by the composition) → Electrical steel → is composed of (the balance, and the magnetism — everything else in the alloy is there to manage iron's shortcomings as a core) → Iron → is produced by (as pig iron, high in carbon and brittle until refined) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
  • Rolling → takes as input (into plate, section, sheet and rail — the great majority of all steel made passes through a rolling mill) → Steel → is composed of → Iron → is extracted from (the most-used iron ore, though magnetite is richer) → Hematite
  • Rolling → takes as input (and the rolling is the metallurgy rather than the shaping: the Goss texture that makes transformer steel work is produced by the rolling and annealing sequence, not by the composition) → Electrical steel → is composed of (the balance, and the magnetism — everything else in the alloy is there to manage iron's shortcomings as a core) → Iron → is extracted from (the most-used iron ore, though magnetite is richer) → Hematite

These are the most distinct paths back. Rolling can be traced through others besides.

Downstream — what it becomes