Method, computer program and rolling mill train for rolling a metal strip
The invention relates to a method, a computer program and a rolling mill train for cold rolling a metal strip ( 200 ). In order to achieve a shortening of undesired off-gauge lengths, the method according to the invention provides that the head ( 210 ) of the metal strip ( 200 ) already undergoes a thickness reduction at the first active rolling stand (n) in the rolling mill train, and then is transported on to the next rolling stand, in order to undergo a further thickness reduction there. The method according to the invention also provides for further reducing the initial pass thickness at the n-th rolling stand in accordance with the tensile stress that has built up in the meantime between the n+1-th and the n-th rolling stand.
1. Method of cold rolling a metal strip ( 200 ) in a tandem rolling mill train with 1≦n≦N wherein N corresponds to the total number of active rolling stands arranged one after the other in a rolling direction with N being two or more as desired, comprising the following steps:
a) setting a roll gap of an n-th active rolling stand ( 300 ) to a predetermined first initial pass thickness D k,n where k=1 so that the first initial pass thickness D of the roll gap is smaller than a thickness of a metal strip head ( 210 ) defining a beginning end of the metal strip; thereafter
b) transporting the metal strip in the rolling direction toward the n-th active rolling stand with the strip head ( 210 ) facing the n-th rolling stand ( 300 ); thereafter
c) continuously passing the metal strip including the metal strip head through the roll gap of the n-th active rolling stand to reduce the thickness of the metal strip and the metal strip head to the first initial pass thickness D k=1,n of the roll gap of the n-th active rolling stand;
d) setting a roll gap of the n+1-th active rolling stand ( 300 ) to a predetermined initial pass thickness D k=1,n+1 , which is smaller than the first initial pass thickness D k=1,n of the n-th active rolling stand;
e) transporting the metal strip in the rolling direction to the n+1-th active rolling stand with the strip head facing the n+1-th rolling stand; thereafter
f) continuously passing the metal strip including the metal strip head through the roll gap of the n+1-th active rolling stand to reduce the thickness of the metal strip and the metal strip head to the initial pass thickness D k=1,n+1 of the roll gap of the n+1-th active rolling stand;
g) building up a tensile stress in the metal strip between the n-th and the n+1-th active rolling stands after the strip head reaches the n+1-th rolling stand and before the strip head reaches a winder located downstream in the rolling direction of the N-th rolling stand;
characterized by:
h) reducing the initial pass thickness of the roll gap of the n-th active rolling stand in accordance with the built-up tensile stress between the n-th and the n+1-th active rolling stands, to a second predetermined initial pass thickness D 2,n which is smaller than the first initial pass thickness D k=1,n of the n-th active rolling stand.
2. Method according to claim 1 ,
characterized by
repeating in each case the steps d) to h) for n=n+1 to n=N−1.
3. Method according to claim 2 ,
characterized by:
further transporting the metal strip after passing the N-th rolling stand with the first initial pass thickness D k=1,N to a winding device;
winding the beginning of the strip of the metal strip on the winding device ( 400 ); and
building up a tensile stress in the metal strip between the winding device and the N-th rolling stand; and
reducing the initial pass thickness of the N-th rolling stand in accordance with the tensile stress between the N-th rolling stand and the winding device ( 400 ) to a second predetermined initial pass thickness D 2,N , which is smaller than the first initial pass thickness D k=1,N of the N-th rolling stand and smaller than the current initial pass thickness D k,N−1 of the N−1-th rolling stand.
4. Method according to claim 1 ,
characterized in that,
after the build-up of the tensile stress between the n-th and the n+1-th rolling stands, the roll gap of at least one of the additional upstream rolling stands x, where 1≦x≦n−1, is also further reduced to a respective predetermined initial pass thickness.
5. Method according to claim 4 ,
characterized in that the initial pass thicknesses and distribution of the initial pass thicknesses of all active rolling stands ( 300 ) of the rolling mill train for rolling the metal strip are calculated beforehand so that the k-th predetermined initial pass thickness D k,N of the N-th rolling stand is a desired target thickness for the metal strip.
6. Method according to claim 1 ,
characterized in that the set initial pass thicknesses or roll gap heights for individual rolling stands ( 300 ) are calculated beforehand so that, taking into consideration expected tensile stresses and material properties of the metal strip, they allow in each case a maximum possible thickness reduction for the metal strip.
7. Method according to claim 1 ,
characterized in that
the reduction of the initial pass thicknesses of the roll gaps of the rolling stands occur continuously in a form of a ramp over the course of time.
8. Method according to claim 7 ,
characterized in that
the reduction of the initial pass thickness at the n+1-th rolling stand starts only when the thickness-reduced area of the metal strip, which is produced by a previous rolling stand, reaches the n+1-th rolling stand.