Laboratory “Large diameter tubes”, JSC “Russian Scientifi c and Research Institute of the Tube and Pipe Industries” (Chelyabinsk, Russia):

Ilyichev V. G., Cand. Eng., Sr. Researcher
Zalavin Ya. E., Eng., e-mail: zalavin@rosniti.ru

We consider the technological features of formation of the cross section geometry of the billet perimeter in manufacture of large diameter tubes for the conditions of forming the marginal are as in a two-roll mill. Providing the proper geometry of cross section of the marginal areas of tube billet as maximal close (ideally coinci ding) to the geometry of cross section of the main part of perimeter (roll-formed at the previous technological stage in a sheet bending machine) is the basic requirement to final bending operation. Additionally, billet thinning as a result of rolling of separate especially loaded sections, as well as burrs and marks should be excluded during final bending. It is shown that spontaneous billet rotation about the longitudinal axis arises in the case of the different distances between sheet edges and width of the guide ring in the process of bending. It causes geometrical deviation of actual bending area comparing with preset one. The experimental data, the results of numerical simulations and proposals about elimination of such defects via equipping of a bending stand bending with additional device for stabilization of the state of the deformed section in a roll pass. Taking into account these considerations, the roll pass design for bending operation has been developed; it provides bending with increased shift of the vertical equatorial plane of a roll pass relating to the vertical symmetrical plane of tube billet.

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