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Lesson 3.2DeformChapter 3 · Bulk forming

Rolling

Pull metal through the gap between turning rolls

Rolling squeezes metal between two turning rolls to make it thinner and longer, much like a pasta machine flattens dough. Car body panels, drink-can sheet, steel beams and rails all come from rolling mills. Most steel and aluminum passes through rolls at some stage of its life.

Rolling: a real photo
Photo: European Coal and Steel Community, CC BY-SA 4.0, via Wikimedia Commons
Two turning rolls pull the metal through a gap smaller than its thicknessEach pass makes the metal thinner and longer; its width barely changes.Inside one roll stand(side view)hot slabthinner stripupper rolllower roll1hot slab enters2turning rolls gripthe slab and pull it in3comes out thinner, longer, fasterA hot strip mill(overview, not to scale)reheating furnaceroughing millfinishing standswater sprayscoil45Key:metal being shapedrolls and machine partsheatcooling water
Rolling: one roll stand up close, then a whole hot strip millTop: what happens inside one roll stand. Bottom: how a hot strip mill chains many stands. Circled numbers match the steps below.

How it works

  1. Feed the slab. A slab (a thick, flat block of metal, often about 20–25 cm thick for steel) arrives from a reheating furnace at about 1,100–1,250 °C. Cold rolling, used for thin and precise sheet, starts from already-rolled strip at room temperature.

  2. The rolls bite. Friction between the turning rolls and the slab grips it and drags it in. The roll gap (the opening between the rolls) is set smaller than the incoming thickness.

  3. Squeeze and stretch. In the gap the metal is pressed thinner. Its volume stays the same, so it comes out longer and faster than it went in, while its width barely changes.

  4. Repeat, stand after stand. Each pass removes only part of the thickness. A hot strip mill first passes the steel back and forth through a roughing mill. Then a row of finishing stands, each with a smaller gap, takes it to its final thickness.

  5. Cool and coil. Water sprays cool the strip, and a coiler winds it into a coil weighing many tonnes. Plates and bars are cut to length instead, and grooved rolls shape beams and rails (shape rolling).

Key facts

Materials
Steels, aluminum, copper and brass, titanium, nickel alloys, zinc
Typical parts
Sheet and plate, strip coils, foil, bars and rods, I-beams, rails
Part size
Strip up to about 2 m wide and often over a kilometer long per coil; from plates over 100 mm thick down to foil thinner than a hair
Precision
Hot-rolled: about ±0.1–0.2 mm on thickness. Cold-rolled: about ±0.01–0.05 mm
Surface finish
Hot-rolled: dark, flaky oxide skin (mill scale). Cold-rolled: smooth and bright, ready for paint or plating
Batch size it suits
Very high volume: a large hot strip mill rolls millions of tonnes a year
Tooling and machine cost
Rolls: thousands to hundreds of thousands of dollars each. A full hot strip mill: hundreds of millions of dollars or more
Speed
Strip can leave the last finishing stand at up to about 20 m/s (over 70 km/h)

Strengths and limits

Strengths

  • Very fast and cheap per tonne; mills run around the clock
  • Long products with a uniform thickness and cross-section
  • Hot rolling breaks up the coarse cast structure, making the metal tougher
  • Cold rolling gives smooth, precise and stronger sheet

Limits

  • Huge investment, so only large producers own mills
  • Only constant cross-sections (flat, bar, beam, rail); no complex 3D shapes
  • Hot-rolled surfaces carry scale and have looser tolerances
  • Cold-rolled metal hardens; it often needs annealing (softening by heating) between passes

Where it's used

  • AutomotiveBody panels, chassis rails, wheels made from rolled sheet
  • ConstructionI-beams and H-beams, rebar (reinforcing bar), roofing and cladding sheet
  • PackagingDrink-can sheet, aluminum foil, tinplate for food cans
  • TransportRailway rails, ship plate, aircraft aluminum sheet
  • Appliances and electronicsWasher and fridge cabinets, copper foil for circuit boards
  • EnergyPlate for pipelines, electrical steel for transformers and motors

How to recognize it

  • A long product with the same thickness or cross-section all along its length: sheet, plate, bar, beam or rail.
  • Hot-rolled steel has a dark blue-grey, slightly flaky skin; cold-rolled steel is smooth, flat and bright.
  • Faint streaks running along the length of bright sheet, showing the rolling direction.
  • Raised letters or numbers repeating along a rail or beam, pressed in by the last roll stand.

Compare with

Forging3.1forging shapes one piece at a time with blows; rolling squeezes continuously, ideal for long, uniform products.Extrusion3.3extrusion pushes metal through a shaped hole to make a complex profile in one pass; rolling builds simpler sections over many passes.Calendering2.7the same roll-squeezing idea, applied to plastic and rubber sheet.

Watch it

Shubham Kola · Animated basics of hot and cold rolling

AIST Association for Iron & Steel Technology · The whole route from slab to coil

ArcelorMittal Belgium · A real hot strip mill running at full speed

Factory Secrets: How It's Made (third-party channel) · How grooved rolls shape giant steel beams

See real photos

Remember

  • Rolling makes metal thinner and longer by pulling it through a gap between turning rolls.
  • Hot rolling shapes big slabs cheaply; cold rolling gives thin, smooth, precise sheet.
  • Sheet, plate, foil, beams and rails all come out of rolling mills.

More in Bulk forming

All 100 processes
3.1ShortForging (open-die and closed-die)Squeeze hot metal between flat or shaped diesOpen the lesson3.3Extrusion (aluminum profiles and plastic pipes)Push metal or plastic through a shaped dieOpen the lesson3.4Wire drawingPull a rod through ever-smaller diesOpen the lesson3.5Cold headingCut wire into blanks and punch a head, coldOpen the lesson3.6Thread rolling and tappingPress a thread onto a blank, or cut or press one in a holeOpen the lesson

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