Metal deforming – By use of roller or roller-like tool-element – Including tautening of work during deformation
Reexamination Certificate
2000-02-24
2001-07-03
Butler, Rodney A. (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
Including tautening of work during deformation
Reexamination Certificate
active
06253592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to rolling apparatuses for bars. In particular, the present invention relates to a high-speed rolling apparatus for bars, which can provide simple, easy, and highly accurate tension-control. The tension is applied to the bars between a finishing mill and a sizing mill provided downstream from the finishing mill. The bars can have various shapes and can include reinforcing wire rods.
2. Description of Related Art
In general, bars are produced by rolling processes including rough rolling, intermediate rolling, finish rolling by a finishing mill including a plurality of roll stands, and a sizing rolling by a sizing mill including a plurality of roll stands.
In these bar rolling processes, the tension that is applied to the bars between each mill must be controlled so that breakage and buckling do not occur during rolling. Accurate tension-control is particularly important in high-speed rolling.
Methods for controlling tension are known, such as a method for controlling motor current of mill stands and another method that uses a looper.
A method for controlling motor current of mill stands is disclosed, for example, in Japanese Unexamined Patent Application Publication Nos. Sho-57-72716 and Sho-61-226108. In this method, the motor current applied for roll stand control is regulated so that the motor current is set to provide a tensionless state when the bar is engaged by a roll stand of the subsequent process. The motor current to provide a tensionless state is obtained by storing a current value before the roll stand of the following process engages the bar. This method is called the “current memory method”.
However, it is very difficult to practice high-speed rolling by using the current memory method. For example, when the distance between each mill is 10 meters and the bar runs at a high speed of 100 m/s, the current for providing a tensionless state must be applied in less than 0.1 second, which is practically impossible to achieve.
Another known method is the “torque arm memory method.” In this method, the tension applied to the bars is obtained from a torque arm value of the roll axle, which is obtained from a rolling torque obtained by a current value varying according to rolling resistance, and a rolling reactive force (actual value) detected by a detector of the mill for detecting rolling load. In the torque arm memory method, a looper sets the torque arm value to a proper value for controlling the bar tension directly.
However, in methods that use a looper, the looper cannot follow the high-speed transfer of a material such as a bar for control purposes, which is at more than 100 meters per second.
Moreover, it is difficult to use a rolling load detector, which is used in the torque arm memory method, in a planetary cross rolling mill (which includes conical rolls that rotate and revolve) generally used for rolling bars. It is difficult to use such rolling load detectors due to higher costs because precise measuring and controlling technologies are required to use them.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a rolling apparatus that can achieve highly accurate tension control by only a very simple facility improvement.
It is also an object of the present invention to provide a rolling method that utilizes the rolling apparatus.
The present invention can be applied to a rolling apparatus for bars that includes a sizing mill downstream of a finishing mill.
The rolling apparatus can be a high-speed rolling apparatus that conveys the bars at a speed, for example, of at least about 100 m/s.
This invention is achieved by considering the relationship of motor power between a finishing mill and a sizing mill. Highly accurate tension control is enabled by changing the relationship of the motor power while avoiding problems caused thereby. The motor power is determined according to the capacity of electrical facilities, in which the most upstream sizing mill motor is provided having less power than the finishing mill motor, so that a small tension variation can be converted to a large variation in the electric current of motors. The highly accurate tension control can be performed, according to the invention, by using a method in which the current applied to a mill motor in a sizing mill is controlled to a desired value.
A rolling apparatus for bars according to an exemplary embodiment of the present invention comprises a finishing mill, a mill motor that drives the finishing mill, a most upstream sizing mill downstream of the finishing mill, and a mill motor that drives the sizing mill. In the rolling apparatus, the finishing mill motor power (Wf) and the most upstream sizing mill motor power (Ws) satisfy the following expression: Wf/Ws≧5.
A method for rolling bars according to another exemplary embodiment of the present invention utilizes a rolling apparatus including a finishing mill and an associated mill motor, and a sizing mill downstream of the finishing mill and having an associated mill motor. The finishing mill motor power (Wf) and the most upstream sizing mill motor power (Ws) satisfy the following expression: Wf/Ws≧5. The method for rolling bars comprises controlling a tensile force applied to the bars by controlling an electric current applied to the mill motor that drives the sizing mill.
REFERENCES:
patent: 4379395 (1983-04-01), Konishi et al.
patent: 4706479 (1987-11-01), Tominaga
patent: 57-72716 (1982-05-01), None
patent: 61-226108 (1986-10-01), None
Ogawa Takao
Sakurai Tomoyasu
Butler Rodney A.
Kawasaki Steel Corporation
Oliff & Berridg,e PLC
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