Metal deforming – With cleaning – descaling – or lubrication of work or product
Reexamination Certificate
2001-07-10
2003-04-15
Tolan, Ed (Department: 3725)
Metal deforming
With cleaning, descaling, or lubrication of work or product
C072S200000, C072S201000, C072S365200, C148S608000, C148S610000
Reexamination Certificate
active
06546771
ABSTRACT:
This application is a 35 USC 371 of PCT/SE99/02293 filed Dec. 8, 1999.
TECHNICAL FIELD
The invention relates to a method for manufacturing of strips of stainless steel, comprising rolling in cold condition of strips which in a foregoing process have been manufactured through strip casting and/or have been hot rolled. The invention also relates to a rolling mill line to be used at the carrying out of the method.
BACKGROUND OF THE INVENTION
Cold rolling of stainless steel strips is performed for one or several purposes. The basic purpose is generally to reduce the thickness of the starting strips, which normally have been hot rolled in a foregoing hot rolling line to a thickness of the hot rolled strips, which is not less than 1.5 mm and normally is in the order of 2-4 mm, but can be up to 6 mm. Conventionally, initial annealing, cooling, and descaling shot-blasting as well as pickling in one or more steps precede the cold rolling, for the achievement of a starting material for the cold rolling without oxides and scale residues from the foregoing hot rolling. As an alternative the hot rolling can completely or partly be replaced by manufacturing of strips through casting, which strips may have a thickness down to what is normal for hot rolled strips or be a few millimetres thicker, but also in this case the cold rolling normally is preceded by initial annealing, cooling, descaling shot-blasting, and pickling, to the extent the technique has been implemented at all. At the cold rolling, which conventionally is carried out in a plurality of consecutive cold rolling operations, possibly alternating with annealing, cooling, descaling, and pickling operations, the thickness can be reduced down to 1 mm and in some cases to even thinner gauges. At the same time it is possible to produce, in these conventional cold rolling mills, strips with a very fine surface, a so called 2B-surface, if the rolling is finished by heat treatment, pickling, and skin-pass-rolling, or even finer if bright annealing is employed. A cold rolling also may have as a main purpose or as an additional purpose to increase the strength of the strip material. For this purpose is has also been suggested, as a complement to cold rolling—EP 0 738 781—to cold stretch the strip subsequent to annealing, so that the strip is plasticised and is elongated permanently, at the same time as its thickness is reduced. Further is it known—U.S. Pat. No. 5,197,179 and—EP 0 837 147—to perform at least a first cold rolling operation on the cooled hot rolled strip or on the cooled cast strip prior to heat treatment, pickling, and possible further cold rolling operations in order to bring the strip to desired final gauge. It is, however, characteristic for methods and rolling mill lines known so far that they are expensive and/or difficult to adapt to widely disparate requirements as far as strip thickness, surface conditions, and strength of the final product are concerned. This particularly applies when hot rolling and subsequent cold rolling, as well as operations in connection with the hot rolling and the cold rolling are considered as an integrated process of production.
DISCLOSURE OF THE INVENTION
It is a purpose of the invention to attack and solve the above complex of problems. This, according a first aspect of the invention, can be achieved therein that the cold rolling is performed in a rolling mill line, which comprises, in the initial part of the line, at least two initial cold rolling mills in series, after said initial cold rolling mills at least one annealing surface and at least one pickling section, and in a terminating part of the line, at least one more cold rolling mill, that the cast and/or hot rolled strip, which is dark coloured by oxides on the surfaces of the strip, with the dark coloured oxides remaining on the surfaces of the strip, first is cold rolled in at least one of said initial cold rolling mills so that the thickness of the strip is reduced totally by 10-75%, that the strip then is annealed and pickled in said annealing and pickling sections and is cold rolled in said at least some more cold rolling mill so that its thickness is reduced by 2-20%, that the strip then is fed once more in the same direction through the same rolling mill line, wherein the strip is rolled again in at least one of said initial cold rolling mills so that the strip consecutively is cold rolled in at least one of said more cold rolling mills and in at least one of said initial cold rolling mills, comprising cold rolling in at least three cold rolling mills without intermediate annealing, reducing the thickness by totally 30-75% before the strip again is annealed and pickled. When the strip passes for the second time through the rolling mill line, the strip is preferably rolled again in one of said more cold rolling mills in the terminating part of the rolling mill line, but is this time only skin-pass-rolled, reducing the strip thickness by 0.2-1.5%.
As an alternative, any rolling in the terminating part of the line is excluded as the strip is being passed through the line for the first time, and this is particularly the case if only a skin-pass-rolling mill is provided there, in which case the strip is subjected to rolling in at least three consecutive cold rolling mills in the initial part of the line, as the strip a second time is caused to pass through the line, the strip being reduced by totally 30-75% before the strip again is annealed and pickled and possibly skin-pass-rolled.
The method which has been described above makes manufacturing of strips with very fine surface possible. In order to achieve such a surface it is, however, important that the strip is subjected to descaling prior to pickling, and that such descaling is performed in such a mode that the surfaces are not impaired. Conventionally, descaling is carried out though powerful shot-blasting in one or more steps, a treatment which however results in the undesired damages of the strip surfaces. According to an aspect of the invention, the descaling instead is carried out by bending the strip several times in different directions about rolls, at the same time as the strip is cold-stretched so that it is permanently elongated 2-10% prior to pickling according to a technique which is known per se through said EP 0 738 781. Through this treatment an efficient descaling is achieved without impairing the strip surfaces. This descaling can be completed with a mild shot-blasting, which can be performed before or after the descaling, preferably before aiming at removing only loose oxides in order, through accumulation of oxides, not do disturb subsequent descaling. If the shot-blasting is carried out subsequent to the descaling it is correspondingly achieved that loose oxides are removed, the shot-blasting in each case being carried out in such a mild way that the metallic surfaces of the strip are not impaired.
According to the above described first aspect of the invention, the strip passes twice through the cold rolling mill line. According to another aspect of the invention, this possibility is not utilised in the manufacturing of strips, when the aimed results in the first place are to provide a final product having a high yield strength and surfaces which are fine, even though they do not satisfy the requirements of 2B-quality. According to this aspect of the invention, the invention is characterised in that the cold rolling is performed in a rolling mill line, which comprises, in the initial part of the line, at least two initial cold rolling mills in series, after said initial cold rolling mills at least one annealing section and at least one pickling section, and in a terminating part of the line, at least one more cold rolling mill, that the cast and/or hot rolled strip, which is dark coloured by oxides on the surfaces of the strip, with the dark coloured oxides remaining on the surfaces of the strip, first is cold rolled in at least one of said initial cold rolling mills so that the thickness of the strip is reduced by totally 10-75%, that it then is anneal
Avestapolarit AB
Nixon & Vanderhye
Tolan Ed
LandOfFree
Method for manufacturing of strips and rolling mill line does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for manufacturing of strips and rolling mill line, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for manufacturing of strips and rolling mill line will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3088349