FIELD OF THE INVENTION
This invention concerns a system to control the surface profile of
the back-up rolls in four-high rolling stands and the back-up roll used in the
said system as set forth in the respective main claims.
The invention is employed in four-high rolling stands for flat products,
to set and maintain the determined configuration of the surface profile of the
rolling rolls in order to obtain a substantially uniform thickness of the rolled
flat product over its entire width.
BACKGROUND OF THE INVENTION
In rolling stands for strip or sheet it is known that a desired deformation
has to be made on the working rolls in order to contrast the elastic deflection
caused thereon by the rolled stock passing through.
For it is well-known that the behaviour of the working rolls during
the rolling process can be likened to a beam constrained at the ends, in such a
way that the rolling pressures generate on the rolls a deflection which is greatest
in correspondence with the centre and which is a function of the width of the rolled
If this deflection is not compensated, it causes a disuniformity
in the thickness and problems with the planarity of the product, both lengthwise
and especially widthwise; this situation is more and more unacceptable, given
the high standards of quality required by the market.
In order to limit the elastic deflection of the rolls, and still
allow working rolls of a small diameter to be used in order to exploit their intrinsic
advantages, four-high rolling stands have been proposed wherein each of the two
working rolls is associated with a back-up roll.
The back-up rolls transmit the rolling pressure to the relative working
rolls and cause a structural strengthening thereof which limits the deformation.
In this type of stand, the deformation which contrasts the deflection
of the working rolls is performed on the back-up rolls which, through contact,
transmit the deformation to the working rolls themselves.
The different pressures imparted to the working rolls, depending
for example on the different width or the type of product which is to be rolled,
cause different deformations of the working rolls and therefore it is impossible
to mechanically set a curve to the back-up rolls which is optimum for a range
of products and for the whole duration of a rolling cycle.
To solve these problems, a plurality of devices of various types
have been proposed - mechanical, hydraulic, pneumatic or other - which are able
to vary in line, and possibly in a differentiated manner along the width, the surface
profile of the back-up rolls according to the requirements of processing.
However, these solutions only give a limited accuracy and are shown
to be inadequate in the case of rolled products which are particularly thin and/or
with particularly strict parameters of quality.
Moreover, when it is necessary to correct the configuration of the
profile of the back-up rolls during the rolling cycle, it takes a long time to
carry out this correction, and therefore it causes a long section of rolled stock
to be produced which is unacceptable in quality.
SU-A-1039598 describes a rolling roll comprising means to adjust
the profile consisting of electric windings and magnetostrictive converters, that
is to say, made of material suitable to be deformed if it is subjected to the
action of a variable magnetic field.
The roll comprises a rotation shaft on which the electric windings
are attached and a sleeve within the body of which the magnetostrictive converters
are located, arranged in concentric rings around the rotation shaft.
This reciprocal configuration of the electric windings and the magnetostrictive
rings has the disadvantage that the density of the magnetic field generated is
not uniform over all the sections of the magnetostrictive ring and moreover the
lines of force are arranged on the ring in an incorrect way.
Moreover, because of the dispersion of the lines of force there is
a deterioration, apart from a lack of uniformity, in the effect of mechanical deformation
of the magnetostrictive rings.
These disadvantages are even more serious if we consider that it
is necessary to control the profile of the rolls with absolute precision, given
that an imprecise control has serious consequences on the planarity and uniformity
of the surface of the rolled stock.
The present applicant has designed, tested and embodied this invention
to overcome the shortcomings of the state of the art and to achieve further advantages.
SUMMARY OF THE INVENTION
The invention is set forth and characterised in the respective main
claims, while the dependent claims describe variants of the idea of the main embodiment.
The purpose of the invention is to provide a system which will give
an accurate regulation and a constant control of the configuration of the profile
of the back-up rolls, and therefore of the mating working rolls, in four-high rolling
stands, in order to obtain a rolled flat product of optimum quality.
A further purpose of the invention is to obtain a system which will
allow rapid variations to be made in line, substantially in real time, to the configuration
of the profile of the back-up rolls, the variations being correlated to the geometric
and dimensional characteristics of the product leaving the rolling stand.
The system according to the invention includes the use of back-up
rolls made at least partly of magnetostrictive material, which is able to modify
its molecular structure, and therefore to increase/decrease its volume, if subjected
to the action of a magnetic field.
According to a first embodiment of the invention, the back-up rolls
comprise a core inside which the rotation shaft is arranged, an outer covering
and an intermediate layer defining an annular space wherein are housed, in contact
with the outer covering, a plurality of deforming elements consisting of magnetostrictive
bars arranged radially and associated with relative coils which generate the magnetic
The magnetostrictive bars may be of any shape whatsoever which is
compatible with the spaces available and with the structure of the roll.
According to a first embodiment, on each magnetostrictive bar a relative
coil is wound, the ends of which are connected to electric supply means, each coil
being able to be fed independently and autonomously from the other.
According to a variant, a coil is wound around a defined number of
In another variant, the deforming elements, consisting of the radial
bars arranged between the inner core and the outer lining, are gathered in a ring
around the whole circumference of the section of the inner core, there being a
plurality of these ring-shaped collections distanced and distributed along the
length of the roll.
Between one radial bar and the adjacent one there is a space.
According to another embodiment, the deforming elements consist of
rings made of magnetostrictive material, distributed along the length of the roll;
a relative coil is wound onto the rings.
According to a variant of this embodiment, each ring is divided into
sectors, onto each of which a respective coil is wound, fed independently from
the other coils.
According to the invention, the influence of a magnetic field causes
a variation in size of the magnetostrictive rings or bars, particularly in a lengthwise
or in a radial direction.
This variation in size causes radial thrusts which deform the outer
covering of the back-up rolls and therefore vary their surface profile.
By modulating the current fed to each coil, or to each group of coils,
it is possible to cause differentiated and controlled variations in size, both
in terms of time and in terms of space over the length of the roll, according to
the requirements of the rolling cycle.
Since the coils are wound directly onto the magnetostrictive deforming
elements and rotate together the same, the density of the magnetic field generated
on the sections of the elements is extremely uniform.
Moreover, the lines of force of the magnetic field are opportunely
arranged uniformly, in a radial direction with respect to the axis of the roll,
which makes the deformation of the magnetostrictive element more efficient.
Moreover, there is a reduced dispersion of the lines of force of
the field, which close almost completely on the magnetostrictive element.
According to the invention, the correct setting of the configuration
of the back-up rolls is determined by a control and regulation unit which, according
to signals received by sensors located at the outlet of the rolling stand, causes
the deformation of the back-up rolls to be distributed in a desired manner.
To be more exact, the sensors monitor the thickness of the rolled
stock over its whole width and condition the differentiated activation of the specific
coils in such a way as to obtain the desired configuration of the back-up roll.
These variations to the configuration of the back-up rolls are extremely
accurate and immediate, and thus it is possible to make corrections to the profile
of the rolls substantially in real time, with response times in the order of 50
milliseconds, even during the rolling cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
The attached Figures are given as a non-restrictive example, and
show in diagram form some preferential embodiments of the invention, as follows:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
- Fig. 1
- shows in diagram form a four-high rolling stand using the system according
to the invention;
- Fig. 2
- shows a component of the back-up rolls according to the invention;
- Fig. 3
- shows a lengthwise cross section of a back-up roll according to the invention;
- Fig. 4a
- shows the section from "A" to "A" of Fig. 3;
- Fig. 4b
- shows a variant of Fig. 4a.
- Fig. 5a
- shows another variant of Fig. 4a;
- Fig. 5b
- shows a variant of Fig. 5a.
With reference to the attached figures, the number 10 denotes the
overall system according to the invention to control the surface profile of the
back-up rolls 13 in four-high rolling stands 11.
To be more exact, the system 10 makes it possible to deform the surface
of the back-up rolls 13 at specific localised points, with a consequent transmission
of this deformation to the working rolls 12, in order to contrast the deformations
which derive from the thrusts of the rolled stock 14 as it passes through and to
obtain a better control of the planarity and thickness of the said rolled stock
The back-up rolls 13 and the working rolls 12 have their respective
axes of rotation lying on a single plane perpendicular to the rolling plane defined
by the working rolls 12.
The system 10, which is shown diagrammatically in Fig. 1, provides
back-up rolls 13 comprising elements made of magnetostrictive material.
In this case, the back-up rolls 13 comprise an inner core 15, made
of rigid and non-deformable material and containing the rotation shaft, an outer
covering 16, made of conventional material which can be at least partly deformed,
and a space 17 between the inner core 15 and the outer covering 16.
Inside the space 17 there is a plurality of deforming elements 18
arranged radially around the inner core 15.
Each of the deforming elements 18, in the embodiments shown in Figs.
3, 4a, 4b, consists of at least a magnetostrictive bar 19, on the lateral surface
of which a coil 20 is wound.
In Fig. 4a, on each magnetostrictive bar 19 a relative coil 20 is
In the variant shown in Fig. 4b, on a determined number of magnetostrictive
bars 19 arranged adjacent, a single coil 20 is wound.
The magnetostrictive bars 19 are arranged in contact with the inner
core 15 and the outer covering 16 in correspondence respectively with the heads
19a and 19b.
In this case, the deforming elements 18 are arranged in annular groups
21 substantially parallel to each other and separated lengthwise so as to cover
a substantial part of the length of the back-up rolls 13 (Fig. 3).
In the variant shown in Fig. 5a, the deforming elements 18 consist
of rings 119 made of magnetostrictive material which occupy the entire space 17
between the inner core 15 and the outer covering 16.
Onto each ring 119 a respective coil 120 is wound, the ends 27 of
which are connected to supply means.
A plurality of rings 119 are arranged along the length of the roll
13 so as to cover a substantial part thereof; on each of the rings 119 a respective
coil 120 is wound, the coils 120 can be fed independently from each other.
In the further variant shown in Fig. 5b, the rings are divided into
sectors 119a, on each of which a respective coil 120 is wound, which can be fed
independently of the other coils 120 of the same ring or of different rings.
Due to the characteristics of the magnetostrictive material, the
bars 19 or the rings 119 undergo a variation in size if immersed in a magnetic
This variation of size is more accentuated along the length "L" of
the magnetostrictive bars 19 (Fig. 2), or in a radial direction to the ring 119,
while it is substantially negligible in the transverse direction.
The variation in size gives rise to an axial thrust of the magnetostrictive
bars 19 or of the sections of the ring 119 which acts on the outer covering 16
and causes a localised deformation thereof, also due to the contrast caused by
the inner core 15.
The invention provides the controlled and possibly differentiated
supply of power to the individual coils 20 of each deforming element 18, or to
the coils 20, 120 associated with each individual annular group 21 or with each
ring, so as to cause a localised deformation of the outer covering 16, in the direction
of the length of the back-up roll 13, according to the specific necessities dictated
by the rolling cycle.
Power is supplied to the coils 20, 120 by means of revolving or sliding
contacts 22, connected to the relative supply circuits 23.
The revolving or sliding contacts 22, in this case, act on circuits
made on the inner core 15 and associated with the coils 20, 120.
In this case, the supply of power to the coils 20, 120 is regulated
by a control and regulation assembly 24 (Fig. 1).
To be more exact, the control and regulation assembly 24 acts in
feedback according to information supplied by sensors 25 placed at the outlet of
the four-high rolling stand 11 and suitable to monitor the planarity and the thickness
of the rolled stock 14 leaving the four-high rolling stand 11.
This information is sent by means of inlet circuits 26 to the control
and regulation assembly 24 which regulates in a differentiated manner the intensity
of the current circulating in each coil 20, 120 so as to define the most suitable
configuration for the back-up rolls 13.
In this way it is possible to determine a concave or convex curve
of the back-up rolls 13 by feeding the coils 20, 120 of the central annular groups
21 or rings 119 respectively with an electric current of greater or lesser intensity
with respect to the coils 20, 120 of the outer annular groups 21 or rings 119.
In the same way, it is possible to set other, different configurations
of the back-up rolls 13 by feeding in a differentiated manner the individual annular
groups 21 or rings 119 or the individual coils 20, 120 thereof.
Therefore the invention makes it possible to correct, substantially
continuously and in real time, the configuration of the back-up rolls 13, in such
a way as to allow rolled stock 14 to be obtained which is characterised by high
standards of quality in terms of planarity and uniformity of thickness.
The direct winding of the coils 20, 120 and the rotation of the coils
20, 120 as a single body with the relative magnetostrictive deforming elements
guarantees a uniform density of the magnetic field, minimum dispersion and an
optimum arrangement of the lines of force of the field.