Rolling mills are machines that shape metal by passing it through two rolls. They are used to flatten and reduce metal to a sheet or plate.
How Rolling Mills Work
Most rolling mills feature two or more rolls arranged in a symmetrical pattern, with half above the work and half below the work to be rolled. Typically, the rolls are mounted one above the other and rotate at the same speed in opposite directions. The metal is passed through the machine multiple times with the spaces between the cylinders decreasing each time so the metal becomes increasingly thinner.
Types of Rolling Mills
Rolling mills can be either hot or cold, depending on the temperature of the metalworking application.
- Hot rolling mills are used in applications where large piece of metal, often including slabs or billets, are heated above their recrystallization temperature. Once heated, the metal is deformed between the rollers to form thin cross-sections. Due to recrystallization, hot rolling mills reduce the typical grain size of a metal, while still maintaining an equiaxed microstructure.
- Cold rolling mills pass metals though the rollers at a temperature below its recrystallization temperature. This process is typically used to decrease the thickness of plate and sheet metal by increasing the metal’s yield strength and hardness through the introduction of defects to its crystal structure. The defects produced by cold rolling mills prevent slip and reduce the grain size of the metal, which results in Hall-Petch hardening.
Rolling mills may include a series of rolling stands, and are also classified by their purpose or design.
Specifications and Applications
When choosing rolling mills, roll diameter and the type of metal to roll are important specifications to consider. For each series, model, and type of machine, three diameters may be listed: work rolls, back-up rolls, and roll journal. Other parameters include maximum separation force at 1000 feet per minute (fpm), total column area, and estimated floor space.
Rolling mills include both small, manually-operated bench top systems and large, powered machines. They are used in the production of bars, rods, wire rods, bands, hoops, metal shapes, plates, and jewelry.