• Three high: for reversing one length above the other simultaneously.
• Four high (tandem): backing rolls give more support to the rolls in contact with
product for initial reduction of ingots.
• Cluster mills: very low roll deflection obtained due to many supporting rolls above
the driven rolls that are in contact with product. For cold rolling thin sheets and foil to
close dimensional tolerances.
• Levelling rolls: used to improve flatness of strip product after main rolling
operations.
• Flat rolling: for long continuous lengths (long discontinuous lengths in reality) of flat
product. The height between the rolls is adjusted lower on each reversing cycle, or the
product is passed through a series of tandem rollers with decreasing roller gap and
increasing speed, to reduce the product to its final thickness. Tandem roll system has
higher production rates.
• Shape rolling: billet is passed through a series of shaped grooves on same roll or a
set of rolls in order to gradually form the final shape; typically used for structural
sections.
• Transverse or cross rolling: wedge-shaped forms in a pair of rolls create the final shape
on short-cropped bars in one revolution. For parts with axial symmetry such as
spanners.
• Ring rolling: an internal roller (idler) and external roller (driven) impart pressure on to the
thickness of a doughnut-shaped metal preform. As the thickness decreases, the diameter
increases. For creating seamless rings used for pressure vessels, jet engine parts and
bearing races. Rectangular cross-sections and contours are also possible. Can be readily
automated.
• Pack rolling: operation where two or more layers of metal are rolled together.
• Thread rolling: wire or rod is passed between two flat plates, one moving and the
other stationary, with a thread form engraved on surfaces. Used to produce threaded
fasteners with excellent strength and surface integrity at high production rates and no
waste.
• Roll forming: forming of long lengths of sheet metal into complex profiles using a series
of rolls (see PRIMA 4.9).
• Calandering: thermoplastic raw material is passed between a series of heated rollers in
order to produce sheet product.
Economic Considerations
• Production rates are high. Continuous process with speeds ranging from
20 to 500 m/min.
• Production rates for related processes: transverse rolling up to 100/h and thread rolling up
to 30,000/h.