The pressure of upper roller when prebending the plate is normal several times of the thickness of  the plate .At pressent ,the commom approaches is to increase the upper roll diameter to reduce the roll deflection or use the drum-roll to eliminate the deformation when rolling.
But it for the product diamter is less than the upper roll diameter, can only reduce roll diamter to meet manufacturing requirements,so it will increase increase the upper roller stiffness ,eliminate roll of deflection .upgrading the lifting pressure rollers, so marking th whole round.