Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Patent
1995-07-06
1998-03-03
Larson, Lowell A.
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
72 86, 72 123, 723652, B21B 3700
Patent
active
057222797
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an operation control method for ensuring stable positioning of rolled work during the rolling process in a tandem rolling operation for metal strips, and also relates to a tandem rolling mill in which the method is used.
BACKGROUND ART
Tandem rolling of metal strips is a process capable of mass-producing high-precision light-gauge metal strips. Since tension can be applied to rolled work between roll stands constituting a tandem rolling mill, the tandem rolling process provides a very stable rolling operation. When tension is applied to rolled work, if the difference in screwdown settings between the working and driving sides (hereinafter referred to as the screwdown leveling) deviates somewhat from an optimum value, for example, such deviation usually does not directly lead to strip side-tracking since the difference does not directly result in a difference in elongation but the difference in elongation between the working side and the driving side is suppressed because of a redistribution of the tension.
At the leading and trailing ends of the rolled work, however, since backward or forward tension cannot be applied, the stabilizing effect mentioned above is reduced by half, increasing the possibility of strip side-tracking. In particular, backward tension has such a significant effect that strip side-tracking known as tail crash is likely to occur when the trailing end passes a roller at which the backward tension is released. To prevent this, screwdown swiveling control, called strip travel control, has been practiced in the prior art. In the description hereinafter given, a shortened term "left and right" will often be used to refer to the working side and driving side. Further, in this specification, sideways excursions of rolled work from the mill center will be referred to as "strip travel".
It is believed that the primary cause for tail crashes is the strip travel caused by the difference in elongation, between left and right, near the trailing end of the rolled work. In the prior art method of strip travel control, control of the difference in screwdown settings between left and right of the roll stand concerned (leveling control) is started from the moment that the phenomenon of tail crash is to begin to show, that is, the moment that the trailing end of the rolled work has exited the preceding roll stand. This control is performed by detecting the difference in rolling loads between left and right of the roll stand concerned or by using a detection signal or the like representing the work's off-center amount detected by a strip travel sensor.
In the above strip travel control of the prior art, since control is, in effect, started when the trailing end of the rolled work has exited the preceding roll stand, the operating time for control is short and the control may not be in time to prevent a tail crash. Furthermore, if there is a deviation from an optimum value in the screwdown leveling of the roll stand concerned, strip travel occurs at the moment that the trailing end of the work exits the preceding roll stand, since the backward tension that has been acting on the rolled work is released and the compensating effect provided by the difference in tension between left and right is lost. If the screwdown leveling control is performed after such a symptom has appeared, it is often too late to correct the situation.
DISCLOSURE OF THE INVENTION
Accordingly, the invention discloses a method of maintaining the screwdown leveling of each roll stand in a tandem rolling mill in an optimum condition by starting control while in a steady-state rolling condition before the trailing end of rolled work exits the preceding roll stand, not after that, and also discloses a tandem rolling mill for implementing the method.
The greatest change that occurs when the trailing end of rolled work exits the preceding roll stand is, needless to say, the loss of backward tension. Accordingly, if abrupt strip travel begins at this instant in time, a reasonable guess
REFERENCES:
patent: 4269051 (1981-05-01), Clarke et al.
patent: 4674309 (1987-06-01), Fabian et al.
patent: 5018377 (1991-05-01), Lawson
patent: 5103662 (1992-04-01), Fapiano
patent: 5172579 (1992-12-01), Nojima
patent: 5404738 (1995-04-01), Sekiguchi
patent: 5509285 (1996-04-01), Anbe
Ishii Atsushi
Nakamoto Takehiro
Ogawa Shigeru
Omi Hiroshi
Yamada Kenji
Larson Lowell A.
Nippon Steel Corporation
Tolan Ed
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