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Hot rolling

Updated Tuesday, 21st November 2017

Plates, flat sheets or billets of metal, heated to above their material recrystallisation temperature, are passed between two rollers. The result is a thinner cross section of material with a finer grain structure.

Flat sheet rolling

Long continuous lengths. Rolls may be reversed. Three-high mills also used. Roll gap altered on each pass.

Diagrams to demonstrate 'Hot rolling' - see article Copyrighted  image Icon Copyright: The Open University

Shaped rolling (L-section)

Flat slab passed through a series of rolls with shaped grooves in them (1–7).

Diagrams to demonstrate 'Hot rolling' - see article Copyrighted  image Icon Copyright: The Open University

Transverse rolling – two types:

Cross rolling

Circular wedge tools used. Heated bar cropped to length fed in transversely between rolls. One revolution of rolls only.

Diagrams to demonstrate 'Hot rolling' - see article Copyrighted  image Icon Copyright: The Open University

Flat die

Wedge tools are flat and dies are moved in one plane over each other.

Diagrams to demonstrate 'Hot rolling' - see article Copyrighted  image Icon Copyright: The Open University

Manufacture:

  1. The hot rolling of flat sheet is performed either on two-high or three-high reversing mills with roll diameters of 0.8–1.25 m. The thickness or gauge of the sheet can be varied by altering the gap between the rolls. Steel billets are rolled at temperatures of 1300 °C.
  2. Shaped rolling is used to produce shaped cross sections by passing the hot metal stock through a series of rotating sets of rolls with appropriately shaped grooves in the rolls.
  3. Transverse rolling differs from flat and shaped rolling in that the objective is to produce a component with a varied cross section. Other variations are called cross rolling (or wedge rolling), whereby a round billet is inserted transversely between rolls on to which are attached wedge-shaped tools. One revolution of the rolls deforms the billet into a shape such as “dog-bone” shape, for automotive transmission shafts of varying section and preforming bicycle pedal cranks.

Materials:

  1. Most metals and alloys can be hot rolled to a variety of shapes.
  2. The range of materials include the following:
    carbon and alloy steels
    stainless steels
    aluminium alloys
    copper alloys
    titanium alloys
    nickel-based alloys
  3. With hot rolling it is easier to deform difficult-to-work metals than with cold rolling.
  4. Cast ingot structures, at heavy deformations and at temperatures where recrystallisation occurs, promote recrystallisation. Control of the sheet temperature can produce fine-grained structures.

Design:

  1. Shaped rolling can be used to produce a wide variety of useful-shaped sections in continuous lengths: this includes T, L and U sections, aerofoil sections for blades, and bars of round, hexagonal or oval section.
  2. Transverse rolling is mainly used to alter the section of the bar to produce preforms for finishing using closed die forging operations. Process can produce axially symmetrical parts such as stepped shafts with or without taper, and cluster gear blanks.

See Also: Hot forging, Hot extrusion and Conform process.

This article is a part of Manupedia, a collection of information about some of the processes used to convert materials into useful objects.

 

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