Seamless pipe Mannesmann Plug Mill Process is somewhat similar to Mandrel Mill Process with major difference in rolling plug mill in place of mandrel mill.
In the rolling plug mill, a pair of conical shaped rolls – one arranged above the other – operates in the opposite direction to the material flow. The thick-walled hollow pipe shell, with a cylindrical mandrel inside it, is guided towards the plug mill rolls. As soon as it is gripped by the tapered portion of the work pass, a small material wave is sheared off the hollow pipe shell. This wave is forged to the desired wall thickness on the mandrel by the smoothing portion of the work pass, with the hollow pipe shell plus mandrel moving backwards in the same direction as the rolls are rotating – i.e. in the opposite direction to the rolling – until they reach the idler pass of the rolls and are released. As the hollow pipe shell is rotated it is once again pushed forward between the rolls, and a new rolling cycle begins.
