Method for operating a roll stand for stepped rolling

1. A method for operating a roll stand ( 100 ) during stepped rolling of a metal strip ( 200 ), wherein an outfeed-side strip accumulator ( 110 ) with at least one roller unit ( 114 ) and an upcoiler ( 120 ) are arranged downstream of the roll stand, the method comprising:

feeding the metal strip ( 200 ) into the roll stand ( 100 ) on an infeed side;

stepped rolling of the metal strip in the roll stand ( 100 ) such that a leading and a trailing section ( 220 , 210 ) of the metal strip have different thicknesses with a difference in thickness (Ahi);

passing the metal strip ( 200 ) through the outfeed-side strip accumulator ( 110 ); and

coiling of the metal strip having the different thicknesses downstream of the strip accumulator ( 110 ) into a coil by the upcoiler ( 120 );

controlling a position of the roller unit ( 114 ) of the outfeed-side strip accumulator ( 110 ) to individually predetermined target positions (Psoll v, Psoll n) respectively for the leading and the trailing section of the metal strip ( 200 ); and

controlling an outfeed-side strip tension of the metal strip ( 200 ) with the upcoiler ( 120 ) as an actuator to a predetermined outfeed-side target strip tension.

2. The method according to claim 1 ,

wherein the target position (Psoll n with n=i+1) predetermined for the trailing section ( 210 ) of the metal strip ( 200 ) is calculated from the target position (Psoll v with v=i) predetermined for the leading section ( 220 ) of the metal strip as

Psoll n =Psoll v+Δp,

wherein a change in target position (Δp) is determined by

calculating a change in the outfeed speed (ΔVexi) of the metal strip from the roll stand in accordance with the difference in thickness (Ahi); and

integrating the difference in speed (Vex i−Vhi) of the metal strip over time into a resulting change in length (Δsi) of the metal strip ( 200 ) on the outfeed side of the roll stand ( 100 ); and

calculating the change in the target position (Δp) of the roller unit ( 114 ) in the strip accumulator to compensate for the change in length (Δsi) of the metal strip during a transition from the leading to the trailing section ( 220 , 210 ).

3. The method according to claim 2 ,

wherein the necessary change in the target position (Δp) of the roller unit ( 114 ) resulting from the difference in thickness (Δhi) is calculated in advance in terms of time in a process model for the stepped rolling, before or while the difference in thickness (Δhi) is realized by a change in a roll gap between work rolls ( 105 ) of the roll stand, and

wherein the roller unit ( 114 ) is adjusted to its new changed target position (Psoll n with n=i+1) and in this respect is pre-controlled before a size of the roll gap is changed by the difference in thickness (Δhi).

4. The method according to claim 1 ,

wherein a drag reel ( 80 ) for providing the metal strip is arranged on the infeed side of the roll stand ( 100 ), and

wherein at least one infeed-side strip accumulator ( 90 ) for the metal strip is arranged between the drag reel and the roll stand,

wherein the method further comprises the following steps:

controlling a rotational speed of the drag reel ( 80 ) to a predetermined winding target speed; and

controlling an infeed-side strip tension of the metal strip ( 200 ) to a predetermined infeed-side target strip tension with the infeed-side strip accumulator ( 90 ) as an actuator.

5. The method according to claim 1 ,

wherein the metal strip ( 200 ) fed into the roll stand ( 100 ) on the infeed side has a constant initial thickness (h 0 ).

6. The method according to claim 1 ,

wherein the metal strip is cold-rolled during the stepped rolling.