The seven roll straightening machine is equipped with three upper rolls and four lower rolls, among which are oppositely and angularly arranged in three pairs. The layout is 2+2+2+1.
During the process of straightening, three pairs of rolls are driven via motor to rotate, which moves forward and squeezes the pipe to go through them and finally makes the pipe obtain high straightening accuracy.
The straightening process is realized through two different effects. One is the bending effect which is realized by adjusting the second pair of rolls to a slightly higher level than the first pair to allow a straightening effect to occur at a small fraction in the middle of the pipe subject to elastic-plastic deformation due to bending; the other effect is the straightening effect formed due to the local flattening deformation and the plastic deformation of the area in the cross section of the pipe. The satisfactory straightening of steel pipes can be obtained through the combination of the b