[0001] This invention relates to a method of controlling roll deflection in a rolling mill.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] With reference to the drawing there is shown one embodiment of apparatus suitable
for use in the practice of the method of the invention.
[0012] 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.
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.