System to control the surface profile of the back-up rolls in four high rolling stands and relative back-up roll

System to control the surface profile of the back-up rolls in four-high rolling stands (11) to produce flat products (14), the four-high rolling stand (11) comprising working rolls (12) and back-up rolls, wherein each back-up roll (13) comprises deforming elements (18) consisting of means made of magnetostrictive material (19, 119) on which coils (20, 120) are directly wound and connected with autonomous means of electric supply to generate a magnetic field, the system comprising a control and regulation unit (24), connected with at least means (25) to control the planarity and/or thickness of the rolled product (14) leaving the rolling stand (11), for the controlled activation and feed of each of the coils generating the magnetic field (20, 120). Back-up roll for four-high rolling stands comprising means made of magnetostrictive material to achieve the control system as described above.

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 stock. 
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 field. 
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 
magnetostrictive bars. 
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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
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 14. 
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 wound. 
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 field. 
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.