How do rolling mills turn thick metal into a thin sheet?

A rolling mill squeezes metal between turning rollers. The gap is smaller than the incoming piece's thickness, so the metal becomes thinner as it passes through. Much of the displaced material moves along the direction of travel, making the sheet longer.

The rollers turn in opposite directions so their contacting surfaces move the metal forward through the gap. Friction helps draw it in, while strong supports resist the force trying to push the rollers apart. The metal remains solid. A wide slab can pass through several sets of rollers, becoming thinner in stages rather than in one enormous squeeze.

The amount of metal does not simply disappear as the sheet thins. Apart from losses such as surface scale or trimmed edges, the same material occupies a new shape. If width stays approximately constant, halving thickness roughly doubles length. Actual rolling may also change width somewhat, so machines guide the material and control the process.

Some rolling happens while the metal is hot and easier to deform. Other rolling happens cooler to achieve a chosen surface, size or material condition. Deforming metal can change its internal structure, so later heating may be needed for the required properties. Gauges measure thickness and help control the roller gap during production.

The finished sheet can be wound into a large coil and later cut or formed into other products. A smooth, thin surface may therefore begin as a much thicker piece. Rolling achieves the transformation through repeated controlled squeezing and a careful account of where the material goes.