Roll stand and method for rolling a rolled strip

1. A rolling stand ( 100 ) for rolling strip, especially metal strip, which comprises:

at least one roll housing on the drive side and at least one roll housing on the operating side of the rolling stand;

bending devices ( 11 ), which are rigidly connected with the respective roll housings for displacing and bending an upper and/or lower work roll ( 7 , 8 ) of the rolling stand ( 100 ) relative to the roll housings; and

a control unit ( 20 ) for controlling the bending devices ( 11 );

wherein at least one bending force strain gauge ( 30 ) is positioned in a neck of the work roll coaxially with a center line of the work roll, for direct measurement of the actual bending force exerted on the work roll ( 7 , 8 ) by the bending devices ( 11 ).

2. A rolling stand ( 100 ) in accordance with claim 1 , wherein at least one of the bending devices ( 11 ) is designed as a piston-cylinder unit, which at one of its ends is directly or indirectly connected with an upright ( 2 ) of the roll housing and at its other end has a lug ( 12 ) with an eye as a suitable place for receiving a pin for direct or indirect articulated connection with the work roll, where the pin is designed in the form of the bending force strain gauge ( 30 ).

3. A rolling stand ( 100 ) in accordance with claim 1 , wherein

in addition, the rolling stand has an upper back-up roll ( 4 ) assigned to the upper work roll ( 7 ); and

a lifting device ( 19 ) is provided for lifting the upper back-up roll ( 4 ) from the upper work roll ( 7 ) for a temper rolling operation of the rolling stand ( 100 ).

4. A rolling stand ( 100 ) in accordance with claim 1 , wherein the control unit ( 20 ) is designed as a closed-loop control unit ( 20 ′) for automatically controlling the bending of the work roll ( 7 , 8 ) to a preassigned set bending force in response to the measured actual bending force.

5. A rolling stand ( 100 ) in accordance with claim 4 , wherein the closed-loop control unit ( 20 ′) has separate closed-loop control systems for the drive side (AS) and the operating side (BS) of the rolling stand for actuating the bending devices on the respective sides.

6. A rolling stand ( 100 ) in accordance with claim 4 , wherein the closed-loop control unit ( 20 ′) has a common closed-loop control system for the drive side (AS) and the operating side (BS) of the rolling stand for the uniform actuation of the bending devices ( 11 ) for the drive side and operating side.

7. A rolling stand ( 100 ) in accordance with claim 4 , wherein the closed-loop control unit ( 20 ′) for each upright ( 2 ) of the roll housing has its own closed-loop control system for adjusting the bending force in bending devices ( 11 ) assigned to the upright ( 2 ) according to the bending force measured by the bending force strain gauge ( 30 ) assigned to the roll housing ( 2 ).

8. A rolling stand ( 100 ) in accordance with claim 4 , wherein

a position sensor ( 14 ) is assigned to at least one of the bending devices ( 11 ) for detecting its present actual displacement position; and

the closed-loop control system assigned to this bending device ( 11 ) is designed as a cascade control system for actuating the bending device with superior automatic bending force control and subordinate automatic position control or with superior automatic position control and subordinate automatic bending control.

9. A rolling stand ( 100 ) in accordance with claim 1 , comprising

a roughness detector (Ra) for detecting the local roughness on the surface of the rolled strip ( 200 ); and

a conversion device for converting the determined local roughness or a differential roughness between a desired roughness and the detected roughness to a set bending force as an input variable for the closed-loop control unit so as to realize the desired roughness.

10. A rolling stand ( 100 ) in accordance with claim 1 , wherein the control unit ( 20 ) is designed as an open-loop control unit ( 20 ″) for actuating the bending devices ( 11 ) with a predetermined control signal.

11. A rolling stand ( 100 ) in accordance with claim 10 , wherein

the control signal is designed to preassign a set bending force for the work roll ( 7 , 8 ); and

an evaluation unit ( 40 ) is provided for comparing the preassigned set bending force with the actual bending force measured by the bending force strain gauge.

12. A rolling stand ( 100 ) in accordance with claim 10 , wherein

the control signal is designed to actuate at least one of the bending devices ( 11 ) with a predetermined bending force/displacement-position set hysteresis loop;

a position sensor ( 14 ) is provided for detecting the current actual displacement position of the bending device ( 11 ); and

an evaluation unit ( 40 ) is provided to determine an actual hysteresis loop on the basis of the bending force measured by the bending force strain gauge ( 30 ) and the displacement position measured by the position sensor ( 14 ) and to compare the actual hysteresis loop of the bending device ( 11 ) with the set hysteresis loop.

13. A method for operating a rolling stand ( 100 ) for rolling a strip ( 200 ), where the rolling stand has at least one roll housing on the drive side (AS) and one roll housing on the operating side (BS) of the rolling stand and bending devices ( 11 ) for displacing and bending an upper and/or a lower work roll ( 7 , 8 ), which is supported between the roll housings, relative to the roll housings;

wherein

during the operation of the rolling stand ( 100 ), the actual bending force acting directly on the work roll ( 7 , 8 ), which represents the bending of the work roll ( 7 , 8 ), is measured at a neck of the work roll with a strain gauge coaxial with a center line of the work roll, and evaluated.

14. A method in accordance with claim 13 , wherein the directly measured actual bending force is used for automatically controlling the bending of the work roll ( 7 , 8 ).

15. A method in accordance with claim 14 , wherein

the actual bending forces are separately measured on the drive side (AS) and on the operating side (BS) and are then averaged to obtain an average actual bending force signal; and

the symmetrical bending devices ( 11 ) on the drive side and the operating side are actuated to automatically control the bending force to a uniform set bending force with an equal control signal according to the average actual bending force signal.

16. A method in accordance with claim 14 , wherein

the actual bending forces on the drive side (AS) and on the operating side (BS) are measured separately; and

the bending devices ( 11 ) on the drive side and the operating side are actuated with separate control signals according to the separately measured actual bending forces for the purpose of adjusting to the respective desired, possibly different, set bending forces.

17. A method in accordance with claim 14 , comprising individual automatic control of the at least one bending device assigned to one of the roll housings ( 2 ) to the desired set bending force in response to an actual bending force of the work roll that is individually measured in the vicinity of the same roll housing.

18. A method in accordance with claim 14 , wherein

in at least one of the bending devices ( 11 ), besides the actual bending force, the current actual displacement position is also determined in each case; and

this bending device ( 11 ) is automatically controlled with a cascade control system, in which either automatic bending force control is superior and automatic position control is subordinate or vice versa.

19. A method in accordance with claim 13 , wherein

the bending device ( 11 ) is actuated with a preassigned set bending force of a bending force/position set hysteresis loop;

the measured actual bending force or bending force/position actual hysteresis loop that then develops in the work roll ( 7 , 8 ) is compared with the preassigned set bending force or bending force/position set hysteresis loop; and

the result of this comparison is evaluated with respect to a possible malfunction.

20. A method in accordance with claim 13 , wherein the local surface roughness of the rolled strip ( 200 ) is detected and converted to a set bending force for the automatic bending force control system that is necessary to realize the desired roughness.