Straightening

in metalworking, the elimination or reduction of unnecessary curvatures in metal items by the application of external forces. Straightening is used in the production of sheets, tubes, rails, beams, and other milled items. It is also used, although less frequently, in metal consumption, for example, by forges and metal structures shops.

Distinctions are made between press straightening (batch straightening) on straightening presses, parallel-roll straightening (continuous straightening) on straightening machines, and rotary straightening by untwisting and stretching on rotary straightening machines.

In press straightening, the item to be straightened is placed on two supports and force applied to the uneven surface causes elastoplastic deflection. Major disadvantages are the low precision of the straightening operation and the significant residual stress.

In parallel-roll straightening, the item moves in an axial direction and undergoes repeated elastoplastic deflection. The ovality of cross sections of bodies of revolution is eliminated at the same time by the spiral motion.

Stretch straightening, a type of rotary straightening, is used for thin sheets and bands, which may be elongated during the straightening process by 1.5–2.5 percent. Twisted tubes with cross sections that are not rounded are straightened by elastoplastic revolving-arbor straightening, which is sometimes combined with stretch straightening.

(1) A process performed on rolled stock, wire, long forgings, stampings, castings, and machined parts to eliminate distortions and warpage that occur as a result of imperfections in manufacturing methods, operational overloads, or other factors. Straightening is usually done on cold stock by means of plastic deformation.

(2) In railroading, the aligning of track that has been displaced to either one or the other side by the action of rolling stock upon both rails of the track. The aligning is necessary to provide smooth travel for trains.