Multi-roll metal strip leveler
A metal strip leveler (B): the strip has a thickness (e) subject to a stress distribution. The leveler includes a row of upper rolls ( 1, 3, 5, 7, 9 . . . ) and a row of lower rolls ( 2, 4, 6, 8, 10 . . . ) having parallel axes, are longitudinally offset in a direction of line of passage (lp) and are offset in height, to define, by vertical imbrication (overlapping) of the rolls, an undulating path of the strip between the rolls. The imbrication occurs because the rows of rolls are interleaved partially to create an undulating path for the strip. At least two upper rolls ([ 1, 3]; [5, 7] ) and two lower rolls ([ 2, 4]; [6, 8] ) are arranged respectively above and below the line of passage, such that they form three vertical imbrication gaps. Those gaps have a profile of non-linear imbrication values (Imbr) that are either convex or concave with respect to a profile of linear imbrication values (Imbr_lin) in the direction of the line of passage.
1. A metal strip leveler configured to balance positive and negative stresses in a metal strip having an asymmetrical stress profile that is asymmetrical along its thickness with a neutral axis offset from the metal strip's center, and unbalanced negative and positive stresses above and below the neutral axis, the leveler comprising:
at least one leveling assembly that includes,
a row of upper rolls and a row of lower rolls that are arranged successively to define an undulating path for the passage of the metal strip in a pass-line direction along a pass line;
each of the upper and the lower rolls has a longitudinal axis that is parallel, offset along the pass-line direction, and offset in height relative to each longitudinal axis of each of the other rolls, the upper and lower rolls are imbricated to define the undulating path by vertical penetration of the rolls into the pass-line;
a programmable computer; and
a vertical adjustment actuator associated with each roll of the successively arranged rolls;
wherein the longitudinal axes of at least two of the upper rolls and the longitudinal axes of two of the lower rolls are respectively above and below the pass-line, and wherein there are at least four successive vertical penetration gaps into the pass-line each associated with a respective imbrication value to obtain, in order, a first imbrication value, a second imbrication value, a third imbrication value, and a fourth imbrication value, each of the four successive imbrication values is different from the other three of the four successive imbrication values, the first imbrication value and the second imbrication value are different by a first difference value, the second imbrication value and the third imbrication value are different by a second difference value different than the first difference value, and the third imbrication value and the fourth imbrication value are different by a third difference value different than the first difference value and the second difference value, whereby the four successive imbrication values vary non-linearly to define a non-linear penetration profile representing vertical penetration of the rolls into the pass-line, the non-linear penetration profile being curved relative to a profile of linear imbrication values, and the non-linear penetration profile varying non-linearly along the pass-line direction from the first roll to the last roll in the successively arranged rolls of the at least one leveling assembly, and
wherein the programmable computer has a data medium containing different stress profile models as a function of the mechanical properties of different materials of the strip to be leveled, and the programmable computer is configured to send control signals to the vertical adjustment actuators based on the leveling models to set the first imbrication value, the second imbrication value, the third imbrication value, and the fourth imbrication value to define the non-linear penetration profile in order to correct the asymmetrical stress profile by moving the neutral axis toward the metal strip's center, and balance the negative and positive stresses above and below the neutral axis.
2. The leveler as claimed in claim 1 , wherein each of the two upper rolls and the two lower rolls is adjustable in the thickness directions of the strip.
3. The leveler as claimed in claim 2 , further comprising a second leveling assembly that includes 2.2 times as many rolls as the at least one leveling assembly.
4. The leveler as claimed in claim 2 , further comprising a second leveling assembly that includes between 2.5 and 6 times as many rolls as the first leveling assembly.
5. The leveler as claimed in claim 1 , further comprising a first leveling assembly, and at least one second leveling assembly, wherein the two upper rolls and the two lower rolls of the at least one leveling assembly are arranged in the at least one second leveling assembly, the at least one second leveling assembly comprises an upper cassette and a lower cassette of a multi-roll leveler, in which the upper rolls are in the upper cassette and the lower rolls are in the lower cassette;
at least one of the upper and lower cassettes incorporates, for each of the rolls thereof, an individual vertical adjustment element for adjusting each roll in relation to the respective cassettes, in which the adjustment element includes a mechanical actuator or servomotor.
6. The leveler as claimed in claim 1 , further comprising a second leveling assembly that comprises upper rolls, and lower rolls, the upper rolls and the lower rolls of the at least one leveling assembly and the second leveling assembly being split between the at least one leveling assembly and the second leveling assembly.
7. The leveler as claimed in claim 6 , further comprising the first rolls of the second leveling assembly are arranged using non-linear penetration values in a concave or a convex manner, the non-linear penetration values being greater than the linear penetration values.
8. The leveler as claimed in claim 7 , further comprising the second leveling assembly has several pairs of upper and lower cassettes arranged in succession along the pass line direction.
9. The leveler as claimed in claim 1 , further comprising the profile of linear penetration values in the pass-line direction decreases from an entry toward an exit of at least one strip leveling portion along the pass line.
10. The leveler as claimed in claim 1 , further comprising at least two tensioners are arranged upstream and downstream respectively of at least one group of upper and lower rolls, for subjecting the strip to a tensile stress.
11. The leveler as claimed in claim 1 , wherein the programmable computer is a PLC control unit.
12. The leveler as claimed in claim 1 , wherein the at least three vertical gaps between the first pairs of successive upper and lower rolls have a first profile of non-linear penetration values on an operator side and at least three vertical gaps between the second pairs of successive upper and lower rolls have a second profile of non-linear penetration values different from the first profile on the motor side, in which the first and second pairs of rolls made up of different rolls.
13. The leveler as claimed in claim 1 , wherein the curved line is convex or concave.
14. A method of leveling a metal strip with a metal strip leveler configured to balance positive and negative stresses in the metal strip having an asymmetrical stress profile that is asymmetrical along its thickness with a neutral axis offset from the metal strip's center, and unbalanced negative and positive stresses above and below the neutral axis, the metal strip leveler comprising:
at least one leveling assembly that includes a row of upper rolls and a row of lower rolls that are arranged successively along a pass line, each of the upper and the lower rolls having a longitudinal axis that is parallel, offset along a pass-line direction, and offset in height relative to each longitudinal axis of each of the other rolls, the method comprising:
imbricating the upper and lower rolls to define an undulating path for the passage of the metal strip in the pass-line direction along the pass line by vertical penetration of the rolls into the pass-line, wherein the longitudinal axes of at least two of the upper rolls and the longitudinal axes of two of the lower rolls are respectively above and below the pass-line, and wherein there are at least four successive vertical penetration gaps into the pass-line;
correcting the asymmetrical stress profile by moving the neutral axis toward the metal strip's center, and balancing the negative and positive stresses above and below the neutral axis by setting each of the four successive vertical penetration gaps to obtain, in order, a first imbrication value, a second imbrication value, a third imbrication value, and a fourth imbrication value, each of the four imbrication values being different from the other three of the four successive vertical penetration values, the first imbrication value and the second imbrication value being different by a first difference value, the second imbrication value and the third imbrication value being different by a second difference value different than the first difference value, and the third imbrication value and the fourth imbrication value being different by a third difference value different than the first difference value and the second difference value to define a profile of non-linear imbrication values that vary non-linearly to define a non-linear penetration profile representing vertical penetration of the rolls into the pass-line, the non-linear penetration profile being curved relative to a profile of linear imbrication values, and the non-linear penetration profile varying non-linearly along the pass-line direction from the first roll to the last roll in the successively arranged rolls of the at least one leveling assembly; and
leveling the metal strip with the metal strip leveler.