EP0159796A1

EP0159796A1 - Method for controlling roll deflection

Info

Publication number: EP0159796A1
Application number: EP85301812A
Authority: EP
Inventors: Paul Theodore Lovejoy
Original assignee: Allegheny Ludlum Steel Corp
Current assignee: Allegheny Ludlum Steel Corp
Priority date: 1984-04-02
Filing date: 1985-03-15
Publication date: 1985-10-30
Also published as: BR8501196A; JPS60213303A; KR850007731A

Abstract

® A method for controlling the roll deflection of the workrolls (4) in a rolling mill used for rolling metals and alloys in strip form; the method comprises applying force near the end of each workroll to move the workroll selectively toward and away from the direction of travel of the material (5) being rolled, said workroll movement resulting in the production of forces that counteract workroll bending moment produced during rolling.

Description

This invention relates to a method of controlling roll deflection in a rolling mill.
As is well known in the rolling of metal and alloy in the form of strip by the use of a rolling mill employing workrolls which are backed up and driven by back-up rolls, the forces required to produce the desired elongation and reduction in thickness of the metal are great and act primarily in a direction tending to separate the workrolls. These forces, are, therefore, typically referred to as roll separating forces. These roll separating forces may be diminished by the use of workrolls of relatively small diameter and this is typically the practice used in modern-day rolling mills. With workrolls of relatively small diameter, however, the workrolls are easily deflected by the great roll separating forces and torque forces produced during typical rolling operations.
The torque forces are the forces applied to rotate the workrolls during the rolling operation and the torque forces typically act in a generally horizontal direction opposite the direction of strip travel during rolling. The roll separating forces typically act in a direction generally vertical and normal to the plane of the strip during rolling.
It is known, therefore, that with rolling mills for strip wherein the upper and lower workrolls of the rolling mill are bent and deflected by the roll separating forces, the result is that the strip being rolled tends to develop defects in shape, such as wavy edges, and crown in which the longitudinal middle portion of the strip is increased in thickness during rolling. Specifically, the upper and lower workrolls during the rolling operation are deformed by the roll separating forces of the strip being rolled so that the middle portions of the workrolls are bent away from each other.
Various practices have been adopted to prevent or counteract strip variation during rolling caused by the action of the roll separating forces on the workrolls. Specifically, attempts have been made to control strip shape by grinding the workrolls with a variable cross section so that under load the rolls assume the desired shape. This practice suffers from the obvious disadvantage that it is effective only at one rolling load. Another practice has been to vary the cooling across the workrolls so that the resulting thermal expansion that occurs as the temperature of the roll increases during rolling can be used as a means of strip shape control. A rolling mill using two extra backup rolls, termed a six-high rolling mill, has been used to provide partial support across the work roll surface and to produce variation in the separating force distribution across the workroll to control strip shape by counteracting the action of the roll separating forces. An additional practice is to use a backup roll having a sleeve wherein hydraulic pressure can be introduced beneath the sleeve to cause the backup roll to expand where required to counteract the roll separating forces. Also, various techniques have been used to vary the tension distribution across the strip to in turn vary the degree of reduction across the roll bite.
It is an object of the present invention to provide a method wherein the workrolls are moved in a manner to compensate for roll bending or sag caused by the roll separating forces acting on the workrolls.
The present invention provides a method for use with a rolling mill having a pair of generally mutually opposed upper and lower workrolls defining a roll pass for material to be rolled therebetween and upper and lower backup rolls respectively for backing said upper and lower workrolls, said method being effective for continuously controlling and varying the deflection of said workrolls during a rolling operation to control the shape of the material being rolled by and passing between said workrolls, said method comprising selectively applying force near the ends of said workrolls to move said workrolls selectively toward and away from the direction of travel of said material passing between said workrolls.
A more complete understanding of the present invention will be obtained from the following description and accompanying drawing, the single Figure of which is a schematic showing of a rolling mill demonstrating the method of the invention.
Broadly, the invention is a practice for workroll deflection which practice or method is used with a rolling mill having a pair of generally mutually opposed upper and lower workrolls defining a roll pass for the material, preferably in strip or plate form to be rolled by passage therethrough. Upper and lower driven backup rolls are provided for driving and backing said upper and lower workrolls in the well known and conventional manner. During rolling the method of the invention is effective for continuously controlling and varying the deflection of the workrolls during the rolling operation to control the shape of the material being rolled by counteracting the bending moment produced during rolling.
In accordance with the method of the invention means are provided for applying force to selectively move the workrolls generally horizontally in a direction toward or away from the direction of strip travel. This may preferably be achieved by pushing the roll bearings forward or backward by the use of hydraulic piston-cylinder means. Consequently, in a conventional strip rolling operation the strip passes between the workrolls in a generally horizontal plane and the forces to move the workrolls are applied at the ends or bearings of the workrolls generally linearly to said horizontal plane and generally parallel to the direction of the strip passing between the workrolls during rolling. Specifically, as described above when the workrolls are moved in the direction of strip travel the torque force and the horizontal component of the roll separating force are opposed, which counteracts the bending moment that typically causes the workrolls to become generally concave. This in turn improves the cross-section uniformity of the strip being rolled.
With reference to the drawing there is shown one embodiment of apparatus suitable for use in the practice of the method of the invention.
As may be seen from the drawing the upper backup roll 2 is driven as by a conventional mill motor drive (not shown) to rotate this roll in the direction of the arrow. The backup roll is in turn in driving engagement with the workroll 4 rolling strip 5 which is moving in the direction of the arrow. The backup roll drives the workroll 4 to rotate it in the direction of the arrow. As indicated on the drawing, the forces affecting roll bending or deflection are the roll-separating force, the pressure of the deforming metal strip and the torque force. These forces act in the directions as indicated by the arrows in the drawing. The roll-separating force and the metal deformation forces have horizontal components and vertical components; the magnitude of the horizontal component increases as the workroll is moved in the direction of strip travel. With this positioning of the workroll as shown in the drawing the torque force opposes the horizontal component of the roll-separating force which in turn allows the applied bearing force to counteract the bending moment produced during rolling that deforms the workroll. This permits the control of strip shape defects by the application of bearing forces to the workroll in the generally horizontal direction, as indicated by the arrow in the drawing. In the schematic showing of the rolling mill in the Figure, for simplification of description only the upper workroll and upper backup roll of the rolling mill have been shown. It is understood that an opposed structure and function is duplicated beneath the strip. The horizontal strip tensions may also be involved in the summation of forces on the workrolls. These, however, are acting in opposite directions and often are of similar magnitudes so they can be reasonably ignored for purposes hereof.

Claims

1. A method for use with a rolling mill having a pair of generally mutually opposed upper (4) and lower workrolls defining a roll pass for material (5) to be rolled therebetween and upper (2) and lower backup rolls respectively for backing said upper and lower workrolls, said method being effective for continuously controlling and varying the deflection of said workrolls during a rolling operation to control the shape of the material being rolled by and passing between said workrolls, characterised in said method comprising selectively applying force near the ends of said workrolls to move said workrolls selectively toward and away from the direction of travel of said material passing between said workrolls.

2. A method according to claim 1, wherein said backup rolls drive said workrolls during rolling.

3. A method according to claim 1 or 2, wherein said workroll movement results in the production of forces that counteract roll bending moment produced during rolling.

4. A method according to claim 1, 2 or 3, wherein said material passes between said workrolls in a generally horizontal plane and said force is applied to said workrolls generally linearly to said horizontal plane and generally parallel to the direction of travel of said material passing between said workrolls during rolling.

5. A method for use with a rolling mill having a pair of generally mutually opposed upper (4) and lower workrolls defining a roll pass for material (5) in strip form to be rolled therebetween during passage in a generally horizontal plane and upper (2) and lower backup rolls respectively for driving and backing said upper and lower workrolls, said method being effective for continuously controlling and varying the deflection of said workrolls during a rolling operation to control the shape of the material being rolled by and passing between said workrolls, characterised in said method comprising selectively applying force near the ends of said workrolls to move said workrolls selectively toward and away from the direction of travel of said material passing between said workrolls, said force being applied to said workrolls generally linearly to said horizontal plane of said material and generally parallel to the direction of travel of said material passing between said workrolls during rolling, said workroll movement resulting in the production of forces that counteract workroll bending moment produced during rolling.