a machine used in rolling mills to level the surface of sheet steel. Straightening machines are divided into roll-type machines, which are the most common type, and stretching machines.
Roll-type straightening machines are designed for straightening thin and thick sheets in either the cold or hot states; stretching machines are designed mainly for cold straightening of thin sheets (steel and nonferrous metals) of which stringent quality requirements are made. The straightening process is based on elastoplastic flexing of the sheet upon passing between powered rolls arranged in a roll stand in two staggered rows. The precision of straightening depends on the spacing of the rolls (the greater the spacing, the lower the precision) and on the dimensions and number of rolls (the greater the number of rolls, the higher the precision). There are usually seven to 23 straightening rolls. Most modern straightening machines have supporting rolls in addition to the straightening rolls. The rate of straightening is 0.1-6.0 m/sec, depending on the thickness of the sheet.
The process of straightening in machines of the stretching type is based on the generation in the sheet of stresses approaching the yield point by the application of a stretching force. A straightening machine of the stretching type consists of a stand, two clamping heads, mechanism for moving the working head, and a drive. Stretching machines with hydraulically driven working heads are being used widely.
A combined stretching/bending method for continuous straightening of metal sheets is also being used. The bending is performed on a straightening machine, and the stretching is accomplished in devices with large-diameter rolls mounted on both sides of the straightening machine.