Metal deforming – By use of roller or roller-like tool-element – Plural roller-couples
Reexamination Certificate
2000-10-17
2002-03-19
Tolan, Ed (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
Plural roller-couples
C072S008600, C072S011400, C072S205000, C072S227000, C072S365200
Reexamination Certificate
active
06357273
ABSTRACT:
FIELD OF THE INVENTION
Our present invention relates to a method of reducing waste, i.e. the length of scrap to be removed from strip in the rolling of metal strip from segments connected by means of weld seams, especially in the cold rolling of austenitic and ferritic stainless steel strip. The invention also relates to an apparatus for this purpose, namely, a tandem strip-rolling line for continuous rolling of metal strip having weld seams connecting successive lengths thereof. In this connection the invention relates as well to a method of operating a tandem strip-rolling line to reduce the scrap length which must be cut from the strip at a weld seam.
BACKGROUND OF THE INVENTION
Tandem-rolling lines can have two or more rolling stands, successively traversed by the steel strip and, of course, the weld seam connecting successive lengths of steel strip.
In such tandem strip-rolling lines, the strip is fed in a substantially direct straight line between the rolling stands or is engaged in a looping device between the stands so that the loop which is formed between the stands can compensate for the difference in length of the strip resulting from the rolling process. Such tandem lines can also be provided in line in strip-processing lines which can be of the controlling-line type, a pickling line or a cold-rolling line for stainless steel strip or the like.
The rolling lines are operated continuously, i.e. metal strip is unwound from coils and the leading end of each length unwound from a coil is welded by a transverse weld seam to the trailing end of the strip previously unwound from a coil and already formed as part of the continuous strip.
To allow weld seams to pass through the rolling stands, the latter are generally opened for such passage. This is especially the case for austenitic and ferritic metal strip. Because of the simultaneous opening of the rolling stands for passage of the weld seam, the portions of the strip immediately upstream and immediately downstream of the respective weld are usually not rolled at all or are only partly rolled and must be cut at a downstream end of the tandem rolling line from the strip. The cut out portion represents scrap. The resulting scrap length has depended in the past on the spacing between the successive stands of the tandem line and can be about 20 m per coil of the strip. This corresponds approximately to twice the spacing between the two rolling stands of the tandem line.
With conventional tandem lines, each weld seam is stopped as it approaches the first or the upstream rolling stand, the rolling stands are opened, the weld seam is moved to a location downstream of the second or downstream rolling stand and the rolling stands are then closed. The opportunity to change the mill rolls is frequently taken while the stands are open. As a consequence, the minimum scrap length is about twice the distance between the rolling stands because over this distance the strip is only engaged by the rolls of one of the two rolling stands and is only partly rolled. The roll replacement is effected depending upon the product made, even one to ten coils.
In cold rolling of stainless steel, certain tension conditions must be maintained in terms of the inlet and outlet tensions at a rolling stand to avoid slip in the stands and instability associated therewith and which can give rise to tearing of the strip. A tearing of the strip can result in severe production losses because of down time and increased percentages of scrap being produced. For measuring of the strip tension, strip-tension measuring rollers are frequently used and the metal strip is usually slipped around strip-tensioning rollers only through an angle or arc of some 5° to some 15°. Force-measuring sensors, e.g. strain gauges, measure the horizontal and/or vertical force components which are applied by the metal strip to the strip tension-measuring rollers. The strip tension measurement thus depends on the ability of the strip to form such loops by bending easily.
With metal strip of greater strip thickness, the ability to readily bend to form such loops cannot be ensured and the metal strip of higher thickness may act more or less like a bending beam. In that case, even with zero strip tension, a force will be applied to strip-tension measuring rollers and can negatively affect the strip measurement. In addition the weight of the strip itself can be superimposed upon other forces applied to the strip-measuring rollers and thus can be another factor introducing measurement errors as a function of strip thickness into tension measurement.
Since these effects and their variations cannot usually be taken into consideration in advance, errors in the strip-tension measurements can also give rise to strip tearing.
A further problem which arises in the cold rolling of stainless steel strip and especially with hot-rolled stainless steel strip is that the lengths of strip tend to vary significantly in terms of strip thickness, strip cross sectional shape (strip profile) and strip strength from coil to coil. To accommodate this, it is necessary that the rolling stand be preadjusted sufficiently well prior to the start of rolling of the particular length. With improper adjusting, the strip can be overrolled and this can lead to strip tearing.
OBJECTS OF THE INVENTION
The principal object of the present invention is to provide an improved method of operating a tandem-rolling line for strip as described at the outset whereby the scrap loss upon passage of the weld seam through the rolling stands can be significantly reduced.
It is the object of this invention to provide an improved tandem-rolling line by which the method can be practiced.
Another object of the invention is to provide a method and apparatus for the rolling of strip with reduced scrap lengths whereby precise strip-tension measurements can be maintained between the rolling stands and which enables exact preadjustment of the rolling stands in a simple and reliable manner.
SUMMARY OF THE INVENTION
These objects are attained, in accordance with the invention in a method which results in a reduction of the scrap length in the rolling of metal strip formed by weld seams between lengths of the strip and especially in the cold rolling of austenitic and ferritic stainless steel strip in a continuous tandem rolling line with at least two rolling stands. According to the invention, as the respective weld seam approaches the first rolling stand and while the weld seam is upstream thereof, the strip is stopped or displaced at a creep while the second rolling stand further rolls the metal strip ahead of that weld seam and the metal strip to be thus further rolled is delivered by a strip store between the two rolling stands. The first rolling stand is opened and the weld seam passed through it, whereupon the first rolling stand is closed. The weld seam is brought to a standstill ahead of the second rolling stand or is advanced in a creeping or crawling mode while the first rolling stand rolls the metal strip upstream of the weld seam and this rolled metal strip is taken up in the strip store. The second rolling stand is then opened and the weld seam passed through it, whereupon the second rolling stand is closed. The weld seam is cut out of the metal strip at the outlet side of the line.
More particularly, the method of operating the tandem strip rolling line can comprise the steps of:
(a) reducing a speed of the strip upstream of the first rolling stand upon an approach of one of the weld seams thereto while continuing to roll the strip at the second rolling stand at a normal rolling speed;
(b) delivering the strip at the normal rolling speed to the second rolling stand during step (a) from a store of strip in strip storage located between the first and second rolling stands;
(c) thereafter opening the first rolling stand, passing the one of the weld seams therethrough and closing the first rolling stand on the strip;
(d) rolling the strip downstream of the one of the weld seams at the normal rolling speed;
(e) while the strip downstream of
Noe Andreas
N{acute over (oe)} Rolf
BWG Bergwerk- und Walzwerk -Maschinenbau GmbH
Herbert Dubno
Tolan Ed
LandOfFree
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