Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
1999-10-26
2002-06-11
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
C072S010400, C072S014500, C072S241400, C072S241800, C072S248000, C072S247000
Reexamination Certificate
active
06401506
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for rolling a strip made of a metal such as steel, and also relates to a rolling mill therefor.
DESCRIPTION OF THE PRIOR ART
In the case of rolling a metal strip, it is important that the ratio of the elongation, of a workpiece to be rolled, on the work side and on the drive side are made to be equal to each other. When the ratio of elongation on the work side and that on the drive side are different from each other, a defect, such as a camber, and a failure in the dimensional accuracy, such as wedge-shaped strip thickness occur. Further, problems may be caused when a strip is rolled. For example, (lateral) traveling or trail crash of a workpiece to be rolled may be caused in the process of threading.
In order to make the ratio of elongation of the workpiece to be rolled on the work side to be the same as that on the drive side, a difference between a position of reduction of a rolling mill on the work side and that on the drive side is adjusted, that is, leveling is adjusted. Leveling is usually adjusted by an operator in such a manner that he observes and adjusts leveling carefully when roll positioning devices are set before the start of rolling and also when roll positioning devices are set in the process of rolling. However, it is impossible to completely solve the above problems of defective quality such as camber and wedge-shaped strip thickness, and also it is impossible to completely solve the above problems of threading, such as (lateral) traveling and pinching, of a trailing end of a workpiece to be rolled.
Japanese Examined Patent Publicatior. No. 58-51771 discloses a technique in which leveling is adjusted according to a ratio of a difference between a load cell load of a rolling mill on the work side and that on the drive side, to the sum of the load cell load of the rolling mill on the work side and that on the drive side. However, the difference between the load cell load of the rolling mill on the work side and that on the drive side includes various disturbances in addition to an influence caused by (lateral) traveling of the workpiece to be rolled. Accordingly, when control is conducted according to the ratio of the difference between the work side load and the drive side load, there is a possibility that (lateral) traveling is facilitated by the control.
Further, Japanese Unexamined Patent Publication 59-191510 discloses a technique in which leveling is adjusted when a slippage of a piece of a work to be rolled is directly detected on the entry side of a rolling mill, that is, when a quantity of (lateral) traveling is directly detected on the entry side of a rolling mill. However, in the case of rolling a long workpiece or in the case of tandem-rolling, even if leveling is not adjusted appropriately, (lateral) traveling is not caused in many cases because of the weight of the workpiece to be rolled on the upstream side of the rolling mill and also because of a condition of restriction of the workpiece by the rolling mill on the upstream side. Therefore, according to the above methods disclosed in the Patent Publications, in the case of rolling a long workpiece or in the case of tandem-rolling, it is impossible to detect a quantity of (lateral) traveling although leveling is not adjusted appropriately. For the above reasons, it is impossible to use any of the above methods as the most appropriate method of controlling the leveling.
Further, for example, according to the method in which a quantity of (lateral) traveling is detected on the delivery side of a rolling mill, the detected value includes: a difference between the delivery speed of a workpiece on the work side and that on the drive side; and a displacement of the workpiece to be rolled in the width direction which already exists in the workpiece to be rolled on the delivery side of the rolling mill because of camber of the workpiece. For the above reasons, it is impossible to use the quantity of (lateral) traveling, which is measured, for optimizing control of leveling so that a ratio of elongation of the workpiece, which is in the roll bite of the rolling mill when the quality of traveling is measured, on the work side, and a ratio of elongation of the workpiece on the drive side, can be made to be equal to each other.
When a quantity of (lateral) traveling is directly measured by the above methods, it is impossible to optimize leveling only by these methods. Further, according to the above methods, a phenomenon occurring in the roll bite is not directly measured. Therefore, the methods tend to be affected by disturbance, and furthermore a delay is caused in the control of leveling, which is an essential defect of the methods.
On the other hand, a difference between a rolling load on the work side and that on the drive side transmits information of asymmetry with respect to the work and the drive side without delay. Therefore, this difference between the rolling load on the work side and that on the drive side can be the most important information for optimized control of leveling. However as described above, the difference between the rolling load on the work side and that on the drive side detected by the load cell includes not only a quantity of (lateral) traveling of the workpiece to be rolled but also various disturbance. Therefore, it is necessary to specify the disturbance and accurately estimate the difference between the rolling on the work side and that on the drive side.
As a result of a close investigation and analysis, the present inventors found the following. The difference between the rolling load measured by the load cell of the rolling mill on the work side and that on the drive side includes not only asymmetry of the rolling load distribution between the work rolls with respect to the mill center, but also thrust acting in the axial direction of the roll axis between the work roll and the backup roll in the case of a four rolling mill, and also between the work roll and the intermediate roll and also between the intermediate roll and the backup roll in the case of a six-high rolling mill. This thrust is the most important factor included in the difference between the rolling load on the work side and that on the drive side.
Thrust forces acting between these rolls give the rolls a redundant moment, and a difference between the rolling load on the work side and that on the drive side is changed so that the balance can be kept with respect to this moment. For the above reasons, this thrust force becomes a serious disturbance with respect to the object of determing, by the difference between the load measured by the load cells of the rolling mill on the work side and that on the drive side, asymmetry of the rolling load distribution on the work and the drive side. Further, concerning this thrust force generated between the rolls, not only the intensity of the thrust force is changed, but also the direction of the thrust force is inverted in the process of rolling. Therefore, it is very difficult to estimate the thrust force.
When the zero point adjustment of reduction of the rolling mill is conducted, rolls are tightened to a predetermined load of zero adjustment by the method of kiss-roll tightening. In this case, not only the above thrust force between the rolls but also the thrust force between the top and the bottom work roll becomes disturbed.
In the zero point adjustment of reduction, the reduction point is reset and the zero point of leveling is reset at the same time so that a load measured by the load cell on the work side and a load measured by the load cell on the drive side can be equal to a predetermined value. When the thrust force acts between the rolls at this time as described above and disturbance is included in the difference between the load measured by the load cell on the work side and the load measured by the load cell on the drive side, it becomes impossible to conduct an accurate zero point adjustment of leveling, and this error of zero point adjustment is caused at all times when leveling is
Ishii Atsushi
Koumoto Katsuhiko
Ogawa Shigeru
Ohta Satoru
Yamada Kenji
Kenyon & Kenyon
Nippon Steel Corporation
Tolan Ed
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