Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DEVICE FOR PROCESSING A METAL SLAB, PLATE OR STRIP, AND
PRODUCT PRODUCED USING THIS DEVICE
The invention relates to a device for processing a metal slab, plate or strip,
comprising
a rolling mill stand with a roll nip between two driveable rolls, the rolling
mill stand
being designed to roll a metal slab, plate or strip between the rolls.
A device of this type is known and is in very widespread use in the metal
industry for
reducing the thickness of a cast slab, plate or strip and for improving the
mechanical
properties of a slab, plate or strip. The rolling which is carried out using
the device
takes place during the processing of thick slabs and plates, usually at
elevated
temperature. During the rolling of thin plates and strips, the plate or strip
is not raised
to an elevated temperature prior to the rolling.
Working with the known device has the drawback that the improvements to the
mechanical properties are produced primarily in the outermost layers of the
rolled
product and only to a lesser extent or not at all in the interior of the
product. This is true
in particular of thick slabs.
2 0 It is an object of the invention to provide a device for processing a
metal slab, plate or
strip with which the mechanical properties of the processed product can be
improved.
It is another object of the invention to provide a device of this type which
allows
mechanical properties of the interior of a slab, plate or strip to be
improved.
Yet another object of the invention is to provide a device of this type which
is able to
improve the mechanical properties in a simple way.
It is also an object of the invention to use the device according to the
invention to
3 0 provide improved metal slabs, plates and strips.
According to a first aspect of the invention, one or more of these objects are
achieved
by a device for processing a metal slab, plate or strip, comprising a rolling
mill stand
with a roll nip between two driveable rolls, the rolling mill stand being
designed to roll
3 5 a metal slab, plate or strip between the rolls, which device is provided
with feed means
which are designed to guide the slab, plate or strip between the rolls at an
angle of
between 5° and 45° with respect to the perpendicular to the
plane through the center
axes of the rolls.
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Surprisingly, it has been found that by feeding a metal slab, plate or strip
at an angle
between the rolls of a rolling mill stand, shearing occurs over the entire
thickness of the
slab, plate or strip. This shearing is also more or less constant over the
entire thickness.
Firstly, this allows grain refinement to occur over the entire thickness.
During standard
rolling, shearing and therefore grain refinement will only occur at the
surfaces.
Secondly, the shearing closes up pores in the metal which are usually formed
during the
casting of aluminum, for example. Therefore, using the device according to the
invention closes up pores over the entire thickness of the material. Both
effects are
important mainly for relatively thick material. The shearing also causes the
eutectic
particles which may be present in the material to be broken up, which results
in an
improved toughness. The feed means which are added to the device in accordance
with
the invention therefore results, in a simple manner, in an improvement to the
material
which it produces. Feeding a slab, plate or strip in at an angle also leads to
the rolls
having an improved grip on the front of the material which is introduced, with
the
result that the reduction in thickness of the material does not have to be as
great as in
standard rolling, in which the material is introduced between the rolls at an
angle of 0°.
The feeding in at an angle also prevents or reduces the "refusal" of a slab,
when the
rolling mill stand does not take hold of the slab on account of the reduction
being too
2 0 high.
In addition to rolling a slab, plate or strip made from a single metal or a
single metal
alloy, the device according to the invention can also be used to roll a slab,
strip or plate
comprising two or more layers of metal, in which case the metal layers may
consist of
2 5 the same metal alloy, of different metal alloys or of different metals or
metal alloys.
The feed means are preferably designed to introduce the slab, plate or strip
between the
rolls at an angle of between 10° and 25° with respect to the
perpendicular to the plane
through the center axes of the rolls, more preferably at an angle of between
15° and
3 0 25°, and even more preferably at an angle of substantially
20°. In the case of feeding at
between 10° and 25° and preferably between 15° and
25°, the shearing is relatively
great while the angle is not so great as to impede feed to the roll nip. In
many cases, it
has been found that the feeding can be carried out optimally at an angle of
substantially
20°.
According to an advantageous embodiment of the device, the feed means comprise
a
feed surface or a roller table. This easily allows the material to be fed at
an angle
between the rolls. Other designs of the feed means are also possible.
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The angle between the feed means and the rolling mill stand is preferably
adjustable.
This allows the angle to be adapted to the thickness of the slab, plate or
strip as desired,
for example if the thickness of the material means that a specific
introduction angle is
desirable. Then, if desired the further rolling using the device can be
continued at a
different angle.
To increase the degree of shearing, the rolling mill stand is preferably
designed in such
a manner that, during use, the rolls have different peripheral velocities, the
difference in
peripheral velocity amounting to at least 5% and at most 100%, and preferably
at least
5% and at most 50%, more preferably at least 5% and at most 20%. The
difference in
peripheral velocity is partly determined by the thickness of the material; in
addition, the
shearing increases as the difference in peripheral velocity between the rolls
becomes
greater. Greater shearing is advantageous since it leads to greater grain
refinement and
improved closing up of the pores. On the other hand, if there is a high
difference in
velocity, there is a high risk of slipping between the rolls and the material,
which would
result in irregular shearing.
According to an advantageous embodiment, the rolls have a different diameter
and/or
2 0 can be driven at different rotational speeds. This makes it possible to
obtain the
difference in peripheral velocity.
The device is preferably provided with one or more following rolling mill
stands with
driveable rolls which are positioned downstream of the rolling mill stand, as
seen in the
2 5 rolling direction. This allows a slab, plate or strip to be subjected to a
rolling operation
two or more times without interruption, so that a desired result can be
achieved more
quickly using this device. Obviously, it is also possible for the material to
be passed
through the same device twice, but this takes more time, particularly when
strip
material is being rolled.
3 0 According to an advantageous embodiment, the device is designed, during
use, to feed
the metal slab, plate or strip to at least one of the one or more following
rolling mill
stands at an angle of between 5° and 45°, preferably at an angle
of between 10° and 25°
and more preferably between 15° and 25°, the angle preferably
being adjustable. As a
result, at these rolling mill stands the material is passed between the rolls
at an angle,
3 5 and therefore is subjected to shearing over the entire thickness at these
rolling mill
stands. The result of this is that the material undergoes considerable
shearing in one
pass through the device. The same benefits apply as for the rolling mill stand
to which
the material is fed first.
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It is preferably also true of the following rolling mill stands that at least
one of the one
or more following rolling mill stands is designed in such a manner that,
during use, the
rolls have a different peripheral velocity, in which case the rolls preferably
have a
different diameter and/or can be driven at different rotational speeds. By
also providing
the rolls of the following rolling mill stands with a different peripheral
velocity, the
shearing which is imparted to the material as it passes through the device is
increased
further. The same statements apply here as those made in connection with the
difference in velocity between the rolls of the first rolling mill stand
through which the
.0 material is passed.
According to a preferred embodiment, at least one of the one or more following
rolling
mill stands has a roll nip which is situated outside the plane of symmetry of
the roll nip
of the rolling mill stand. As a result, it is easy for the material to be
passed at an angle
to said following rolling mill stand.
It is preferable for support rolls to be arranged upstream of the one or more
following
rolling mill stands, as seen in the direction of rolling, in order to support
and/or guide
the metal slab, plate or strip. These support rolls can feed the material to
the following
2 0 rolling mill stands, for example, at the desired angle.
According to a preferred embodiment of a device without following rolling mill
stands,
the device is provided on both sides with feed means which are designed to
pass the
slab, plate or strip between the rolls at an angle of between 5° and
45° with respect to
2 5 the perpendicular to the plane through the center axes of the rolls,
preferably at an
angle of between 10° and 25°, the angle between the feed means
being adjustable
between 0 and 45° and it being possible for the rolls to be driven in
both directions of
rotation. With the aid of this device, it is possible for material to be
passed back and
forth through the device, and each time the material can be supplied at an
angle of
3 0 between 5 and 45° and preferably between 10° and 25°
and can be guided out of the
device at an angle of 0°.
According to a second aspect of the invention, one or more of the
abovementioned
objects is achieved by a device for processing a metal strip, comprising a
rolling mill
3 5 stand with a roll nip between two driveable rolls, the rolling mill stand
being designed
to roll the metal strip between the rolls, which device is provided with one
or more
following rolling mill stands with driveable rolls, and in that the rolling
mill stand and
one or more following rolling mill stands are designed in such a manner that,
during
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use, their rolls have different peripheral velocities, the difference in
peripheral velocity
amounting to at least 5% and at most 100%.
In this device, therefore, the material is passed through two or more rolling
mill stands,
the rolls of each rolling mill stand in each case having a different
peripheral velocity
from one another. As a result, the material is passed without interruption
through two
or more rolling mill stands which each apply shearing to the material across
the entire
thickness of the material. Therefore, using this device leads to considerable
shearing of
the material, with the associated advantages as described above.
This device according to the second aspect of the invention can also be used,
in
addition to the rolling of a slab, plate or strip consisting of a single metal
or a single
metal alloy, to roll a slab, strip or plate comprising two or more layers of
metal, in
which case the layers of metal may consist of the same metal alloy, of
different metal
alloys or of different metals or metal alloys.
In this device, the difference in peripheral velocity is preferably at least
5% and at most
50%, and preferably at least 5% and at most 20%, for the same reasons as those
explained above.
In this case too, it is preferable for the rolls of the rolling mill stand and
the following
rolling mill stands to have different diameters and/or to be driveable at
different
rotational speeds, as explained in connection with the first aspect of the
invention.
2 5 According to an advantageous embodiment, in this case too, at least one of
the one or
more following rolling mill stands has a roll nip which is situated outside
the plane of
symmetry of the roll nip of the rolling mill stand, for similar reasons to
those given in
connection with the device according to the first aspect of the invention.
3 0 Also, in this case it is preferable for support rolls to be arranged
upstream of the one or
more following rolling mill stands, as seen in the direction of rolling, in
order to
support and/or guide the metal strip. This is for the same reasons as those
which have
been explained above.
3 5 It is preferable for feed means to be arranged upstream of the rolling
mill stand, as seen
in the direction of rolling, these feed means being designed to guide the
strip between
the rolls at an angle of between 5° and 45° with respect to the
perpendicular to the
plane through the center axes of the rolls, preferably at an angle of between
10° and 25°
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and more preferably between 15° and 25°, the feed means
preferably comprising a feed
surface or a roller table. This measure enables the rolls to gain a good grip
on the
material which is to be introduced.
The invention also relates to a slab, plate or strip produced using the above
devices, the
slab, plate or strip having a substantially uniform shearing over its
thickness.
The metal is preferably aluminum or steel or stainless steel or copper or
magnesium or
titanium or one of their alloys. These are metals which are in industrial use,
and it is
desirable for them to have good mechanical properties.
The invention will be explained below on the basis of an exemplary embodiment
and
with reference to the appended drawing, in which:
Figure 1 shows a highly diagrammatic illustration of an exemplary embodiment
of a
device according to the invention.
The figure shows an embodiment of the device 1 with a first rolling mill stand
11 and
two following rolling mill stands 12, 13, diagrammatically indicated by a
rectangle.
2 0 Each rolling mill stand has respective rolls l la,b, l2a,b and l3a,b.
Upstream of the first
rolling mill stand 11 there is a feed surface 10 over which a slab of metal 2,
for
example of aluminum, can be supplied. The means for supplying the slab 2 and
the
means for driving the rolling mill stands are not shown; means of this type
are known
to the person skilled in this field.
In this exemplary embodiment, the rolling mill stands are arranged in such a
manner
that rolling mill stand 11 and 13 have a common plane of symmetry P which runs
through the center of their respective roll nips. The plane Q through the
center axes of
the rolls l la, 11b of the rolling mill stand 11 is perpendicular thereto, as
is the plane T
3 0 through the center axes of the rolls 13a, 13b of the rolling mill stand
13.
The rolling mill stand 12 has a plane S passing through the center axes of its
rolls 12a,
12b, which is likewise perpendicular to the plane P. The plane of symmetry R
through
the center of the roll nip of the rolling mill stand 12, however, is offset
upward with
3 5 respect to the plane P. As a result, the slab 2 is passed at an angle to
rolling mill stand
12 and then at an angle to rolling mill stand 13.
The feed surface 10 is at an angle a with respect to the plane P, a usually
being
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approximately 20°. The angle oc is adjustable and can be matched to the
type and
thickness of the material.
Support and guide rolls l5a,b l6a,b, l7a,b and l8a,b are arranged between the
rolling
mill stands 11, 12 and 13 in order to guide the slab 2 to the rolling mill
stands 12 and
13 after it has been rolled in rolling mill stand 11 and to support it over
this path.
The rolls lla and llb have different diameters, so that, given an identical
angular
velocity, they have different peripheral velocities. The rolls 12a, 12b also
have different
diameters, but in this case the difference in size is reversed. This
arrangement means
that the shearing in the slab 2 as it passes through the rolling mill stands
11, 12 will
have an inverted profile. The material which is displaced during passage
through
rolling mill stand 11 is, as it were, displaced back during passage through
rolling mill
stand 12.
In this exemplary embodiment, the rolling mill stand 13 has rolls 13a, 13b
with an
identical diameter. This stand rolls the slab 2 in the customary way, but it
is also
possible for the rolls 13a, 13b to be provided with a different rotational
speed and
therefore a different peripheral velocity. If the latter situation applies,
the rolling mill
2 0 stand 13 will also contribute to the shearing in the slab 2.
It will be clear that the device according to the invention can be used to
roll slabs,
plates and strips of different types of metal, such as steel, aluminum,
stainless steel,
copper, magnesium or titanium, and it is also possible to roll two or more
slabs of metal
2 5 resting on top of one another. The slabs may consist of different metals
or different
alloys from one another. If necessary, adjustments which lie within the scope
of the
person skilled in the art may be made to the device.
The device which has been described above and is illustrated in Figure 1
results in a
3 0 slab, plate or strip being guided through and rolled by the device in the
form of a coil. It
will be clear that rolling mill stands may also be arranged in other ways with
respect to
one another, that it is possible to use more or fewer rolling mill stands and
that the
device can also be used only with rolling mill stand 11. The rolls may also
optionally
have different diameters andlor be driven at different angular velocities. The
supporting
3 5 and/or guiding of the slab, plate or strip can also be carried out using
other means.
It is also possible for the feed surface 10 to be replaced by other feed
means, such as a
roller table, or a single feed roll for strip material, which feed roll has to
be arranged in
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such a manner that the strip material is passed into the roll nip of the
rolling mill stand
11 at the angle a.
Another embodiment of the device according to the invention (not shown) is
that in
which the feed surface 10 is omitted and in which there are at least two
rolling mill
stands, for example rolling mill stand 11 and rolling mill stand 12, the rolls
of these
rolling nnill stands having different peripheral velocities and the difference
in peripheral
velocity amounting to at least 5% and most 100%. The arrangement and further
design
of the rolling mill stands may be identical to that shown in Figure 1 and can
be altered
in a similar way.
The invention will be explained with reference to an exemplary embodiment.
Experiments were carried out using slabs of aluminum AA7050 with a thickness
of
25 32.5 mm. These slabs were rolled once in a rolling device with two rolls,
of which the
top roll had a diameter of 165 mm and the bottom roll had a diameter of 135
nun. After
rolling, the slabs had a thickness of 30.5 mm.
The slabs were introduced at different angles varying between 5° and
45°. The
2 0 temperature of the slabs when they were introduced into the rolling device
was
approximately 450°C. The two rolls were driven at a speed of 5
revolutions per minute.
After rolling, the slabs had a certain curvature, which was highly dependent
on the
angle of introduction. The straightness of the slab after rolling can to a
large extent be
2 5 determined by the angle of introduction, in which context the optimum
angle of
introduction will be dependent on the degree of reduction in the size of the
slab, the
type of material and alloy, and the temperature. For the slabs of aluminum
which have
been rolled in the experiment described above, an optimum angle of
introduction is
approximately 20°.
A shear angle of 20° was measured in the slabs of aluminum which were
rolled in
accordance with the experiment described above. Using this measurement and the
reduction in the size of the slab, it is possible to calculate an equivalent
strain in
accordance with the following formula:
2
~e9 = ~ ' ~xx + ~YY
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This formula is used to make it possible to present the strain in one
dimension and is
known from the book "Fundamentals of metal forming" by R.H. Wagoner and J.L.
Chenot, John Wiley & Sons, 1997.
Therefore, in the slabs which have been rolled in accordance with the
experiment, the
equivalent strain is
eeq - 2 In 32.5 2 + 1 (tan 20° ) 2 ~ 0.25 .
30.5 2
In the case of rolling with an ordinary roll, shearing does not take place
across the
thickness of the plate and the equivalent strain is therefore only
2
- 2 In 32.5 ~ 0.07
30.5
(working on the basis of a uniform strain over the entire thickness of the
plate).
Therefore, the rolling using the method according to the invention results in
an
equivalent strain which is three to four times higher than with conventional
rolling
without any difference in peripheral velocity. A high equivalent strain means
less
2 0 porosity in the slab, greater recrystalization and therefore greater grain
refinement, and
more extensive breaking up of the second-phase particles (constituent
particles) in the
slab. These effects are generally known to the person skilled in this field of
engineering
if the equivalent strain increases. Therefore, the rolling according to the
invention
means that the resulting properties of the material are greatly improved as a
result of
2 5 the use of the method according to the invention.
