Multi-roll metal strip leveler

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.