FORMING DEVICE FOR AS-ROLLED TYPE ULTRA HIGH STRENGTH RESISTANCE WELDED TUBE

PURPOSE:To manufacture the medium and small diameter resistance welded tube, etc., by an ultra high strength steel sheet as a proper product with high efficiency by specifying a curved radius of a side edge at an upper roll of a first stage stand in a breakdown roll group. CONSTITUTION:The ultra high strength steel sheet 1 is bent and formed by the breakdown roll group 3, sent to a work coil 6 and welding roll parts 7 via a cluster 4 and fin-pass stands 5 and subjected to resistance welding. At that time, a rolling phenomenon of the bent steel sheet 1 is prevented and suppressed pertinently by disposing side rolls 34 on which edge detention parts 34b are formed in the breakdown roll group 3. In addition, the three side edge curved radius RET at the upper roll 32 of the first stage stand in the breakdown roll group 3 is made equal to a value after subtracting the steel sheet thickness(t) subjected to working and alpha from the side edge curved radius REB of a lower roll. Consequently, effective curved forming is made possible regardless of the large spring back quantity of the ultra high strength steel sheet.