ELECTROMAGNETIC DEVICE FOR STABILIZING AND REDUCING THE DEFORMATION OF A STRIP
MADE OF FERROMAGNETIC MATERIAL, AND RELATED PROCESS
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FIELD OF THE INVENTION
The present invention falls within the scope of processes and systems for coating flat
bodies made of ferromagnetic material such as a steel strip. In particular, the
invention relates to a device for stabilizing a metal strip made of ferromagnetic
material within the scope of a process for coating the same metal strip with molten
metal (e.g. a galvanizing process). The present invention also relates to a system for
coating a metal strip with molten metal comprising said electromagnetic device.
Lastly, the present invention relates to a process for stabilizing and/or correcting the
deformation of a strip made of ferromagnetic material, such as e.g. a metal strip.
STATE OF THE ART
As known, strips made of ferromagnetic material, such as e.g. metal strips, are
coated on the outside by means of a suitable coating process. With reference to
figure 1, a first conventional coating process provides passing the metal strip 4 in a
molten metal bath 7 contained in a pot 1 . The metal strip 4 enters bath 7 from the
top of pot 1 1 at a certain inclination and is guided out of the pot in vertical direction
by means of the rolls 2, 3 which are submerged in the pot. In particular, to obtain the
trajectory of the metal strip 4, a roll 2 called "sink roll" is arranged, while further
corrective rolls 3 are provided to partly correct the deformation of the metal strip 4,
also called "crossbow", and for the partial stabilization thereof.
Installed downstream of pot 11 , i.e. at the output of the molten metal bath 7, there is
a unit for removing the excess coating consisting of air knives (air or inert gases) or
magnetic knives 5 which wipe the surface of the metal strip 4 in order to send back
the excess molten metal towards bath 7. Then, the metal strip 4 undergoes cooling by
means of jet-coolers 5' arranged vertically along the transportation direction of the
strip itself. Then, the metal strip 4 reaches an upper roll 6 in conditions such not to
compromise the quality of the coated surface after contact with the upper roll itself.
Therefore, this coating process requires that the metal strip 4 is supported vertically
so as to remain tensioned only between two points, whose distance is normally
between 30 and 50 metres.
With reference to figure 2, instead of using large molten metal pots (up to 400 tons),
coating processes have recently been developed providing relatively small magnetic
containment pots 111'. Such pots 111' do not contain mechanical moving parts but
instead comprise an electromagnetic device 8 by means of which the molten metal
bath is kept suspended while the metal strip 4 passes through the bath in vertical
direction. More accurately, the metal strip 4 enters the magnetic containment pot 111'
from an inlet opening 9 located on the bottom of the pot itself, then it comes out from
an outlet opening opposite to the inlet opening.
In the two coating processes described and schematized in figures 1 and 2, the metal
strip 4 is subject to vibrations mainly caused by the presence of the jet-coolers 5' and
of the knives 5. In the case of the process in figure 1, the clearances of the
mechanical guide members employed, in particular the rolls 2, 3, are sources of
vibrations, while in the case of the process in figure 2, the electromagnetic device 8
for the levitation of the molten metal 7 is another source of vibration. As already
indicated above, in the process in figure 1 the metal strip is also affected by a static
deformation (crossbow) due to local plasticization of the metal strip which occurs
close to the submerged rolls 2, 3. This phenomenon also strongly disturbs the feeding
stability of the metal strip 4. Furthermore, in the case of the process in figure 2, the
lower free surface of the metal bath 7 may also be disturbed by the vibration of the
metal strip 4 with subsequent emission of splashes of molten metal from the surface
itself.
These drawbacks determine the variation of the coating thickness along the metal
strip 4, with the need of providing a thicker coating with respect to the one required for
the classification of the product. As indeed known, the reference standards impose a
minimum threshold of the coating thickness which is not to be exceeded. The
oscillations and the static deformation of the metal strip 4 indeed induce a nonuniform
distribution of the coating and a reduced effectiveness of the action of the gas
and/or electromagnetic knives which therefore must operate at greater distances to
prevent accidental contact with the metal strip. In this regard, it is noted that usually
an over-coating is provided which is at least such as to ensure the minimum threshold
required on 95% of the metal strip 4 . In other cases, the feeding speed of the strip is
reduced with a subsequent and disadvantageous reduction in productivity.
It is also noted that in the case of the process in figure 2, the emission of liquid metal
splashes through the inlet opening 9 of pot 111' also negatively influences the quality
of the coating. In fact, such splashes stick on the activated surface of the metal strip 4
with which they instantly react before entering the metal bath 7. Such a phenomenon
generates points with different alloy composition on the surface of the metal strip 4
and therefore a poor quality of the metal strip 4.
Therefore the above considerations reveal the need to reduce the oscillations and
deformations on the metal strip 4 as much as possible during the related coating
process and in particular, during the feeding thereof upstream and/or downstream of
the pot containing the molten metal. Electromagnetic device have already been
developed for improving the stability of the metal strip, which are installed in the area
in which the vibration is to be minimized (for example, near the area in which the gas
knives are located).
Figure 3 is a view relating to an electromagnetic device currently employed for locally
stabilizing a metal strip 4 during the feeding thereof within the scope of a coating
process of the strip. The device in figure 3 consists of a plurality of pairs of
electromagnetic actuators 0, 10', 10", 10"', each of which being formed by two
electromagnets which face each other reciprocally. All pairs of electromagnetic
actuators are aligned with at least one other pair of electromagnetic actuators
according to a direction 100' orthogonal to the direction of the transportation direction
100 of the metal strip 4. Each pair of electromagnetic actuators is fed with current
supplied by means of power amplifiers which may be controlled both with an open
loop and with a closed loop. The control signal which determines the level of current
which feeds the electromagnets in one pair of electromagnets is generated according
to operating information such as the actual position of the metal strip 4 with respect to
a theoretical pass-line, the thickness and uniformity of the coating, the thickness
and/or width of the metal strip 4 or also the speed line. In particular, in the example
illustrated in figure 3, the signal comes from position sensors 11, 11', 11", 11"
adapted to detect the position of the metal strip 4 with respect to a theoretical passline.
More accurately, each sensor signal is used to activate the electromagnets
facing each other of a corresponding pair of electromagnets. In essence, each signal
provided by the position sensors 11, 1 ' , 11", 11" has the purpose of controlling a
corresponding pair of electromagnets 10, 10', 10", 10"'. For this reason, the number
of sensors 11, 11', 1 " , 11" must necessarily correspond to the number of pairs of
electromagnets 10, 10', 10", 10"'.
Figure 4 is a top view of the device of figure 3 and shows the action of the
electromagnets on the metal strip 4. In particular, the electromagnets in each pair of
electromagnets 10, 10', 10", 10"' exert forces on the metal strip 4 the resultants 14,
14', 14" of which act on the metal strip 4 in very accurate points which however do
not correspond to the theoretical points 15, 15', 15" in which the resultants
themselves should be applied to make the metal strip 4 truly stable (i.e. coinciding
with the theoretical plane 50), i.e. to block the oscillations thereof and compensate the
static deformation thereof.
It is clear from that above that a limited number of electromagnets does not allow all
the possible configurations which may be taken on by the metal strip 4, to be
corrected. Likewise, it is also noted that a limited number of electromagnets
determines further problems relating to the effect of the force exerted on the edges 4'
of the metal strip 4. The resultant force exerted by each electromagnet indeed
depends on the extension of the part of the metal strip 4 facing the electromagnets
and hence varies as the transversal dimension (width 4") of the strip varies (see
figure 7).
In this regard, figures 5 and 7 each show a metal strip 4 and the force applied by four
electromagnets 13. The two figures differ from each other in the reciprocal distance
between the electromagnets 3 and in the different width 4" of the metal strip 4. It is
noted that the forces generated by the four electromagnets 13 are applied locally so
they are not effective at the edges 4' of the metal strip 4. This condition causes a
necessary increase of the supply current on the electromagnets 3 to reach the level
required by the compensation of the deformation. However, this determines a fast
saturation of the electromagnets 13 and possible overload problems.
With reference to figure 6, an obvious improvement to the solution in figure 5 could be
obtained by increasing the number of electromagnets 13 arranged along the
transversal direction 100' and thus by bringing the electromagnets as close together
as possible. However, this solution could lead to a substantially "notched" distribution
of the forces acting on the metal strip 4 and in a significant increase of the number of
power supply and cables required to drive the various electromagnets 13, with
subsequent increased complexity of the device also in terms of control and the
related costs thereof.
Another example of an electromagnetic device employed for stabilizing a metal strip 4
is shown in patent application WO2006/101446 in which, to solve the problem of the
adaptation of the system to the variation of width of the strip, a minimum number of
three electromagnets is provided which are suitable for eliminating the three main
vibration mode shapes of the strip. In patent application EP 784520, side magnets
are arranged to locally stabilize a metal strip, which are made movable so as to adapt
their position according to the width of the metal strip, i.e. so as to concentrate the
force if required at least at the edges of the strip. It is apparent that the two last
solutions indicated certainly cannot be considered satisfactory because they are only
relatively effective in the presence of certain vibration mode shapes, i.e. under certain
and well-defined conditions of instability.
SUMMARY OF THE INVENTION
Hence, it is the primary task of the present invention to provide an electromagnetic
device for stabilizing and reducing the deformation of a strip made of ferromagnetic
material, e.g. a metal strip, during a process for coating the strip. Within the scope of
this task, one object of the present invention is to provide an electromagnetic device
capable of effectively reducing the vibrations of the ferromagnetic strip and capable of
compensating for any static deformation (crossbow) generated in the strip. Another
object of the present invention is to provide a device which, within the scope of a
process based on the electromagnetic levitation of the liquid metal, is capable of
eliminating the liquid metal leakage, induced by the magnetic field required for the
levitation of the molten metal. Not last object of the present invention is to provide a
device which is reliable and easy to make at competitive costs.
Therefore, the present invention relates to an electromagnetic device comprising first
electromagnets aligned along a direction parallel to a first theoretical pass-line of said
metal strip and orthogonal to a transportation direction of the strip, in turn parallel to
said theoretical plane. The electromagnetic device also comprises second
electromagnets positioned in a position mirroring said first electromagnets with
respect to said theoretical pass-line of the metal strip. Each of the electromagnets
includes a core comprising at least one pole and one feeding coil wound about said
pole.
The electromagnetic device according to the invention also comprises a first
connection element made of ferromagnetic material which connects said at least one
pole of the first electromagnets, and a second connection element made of
ferromagnetic material which connects said at least one pole of the second
electromagnets. Such a second connection element is positioned in a position
substantially mirroring the position of said first connection element with respect to
said theoretical pass-line of said metal strip.
Furthermore, one other aspect of the present invention relates to a system for coating
a strip made of ferromagnetic material comprising an electromagnetic device
according to the present invention.
According to a further aspect of the invention, the above problem are solved by
means of a process for stabilizing and/or correcting the deformation of a strip made of
ferromagnetic material during the feeding thereof, implemented by means of the
above device, said process comprising the steps of:
- generating first independent magnetic fields and second independent magnetic
fields in a position mirroring said first independent magnetic fields with respect to a
theoretical pass-line of said strip;
- conveying and distributing said first magnetic fields, through first means for
conveying and distributing magnetic fields, so as to generate a first continuous
magnetic field distributed along a transversal direction parallel to said strip;
- conveying and distributing said second magnetic fields, by means of second means
for conveying and distributing magnetic fields, so as to generate a second continuous
magnetic field distributed along said transversal direction in a position mirroring said
first continuous magnetic field generated by said first means for conveying and
distributing magnetic fields.
BRIEF DESCRIPTION OF THE FIGURES
Further features and advantages of the invention will become more apparent in light
of the detailed description of preferred, but not exclusive, embodiments of an
electromagnetic device according to the present invention, disclosed by way of a nonlimiting
example, with the aid of accompanying drawings in which:
- figures 1 and 2 are schematic views relating to a first system and to a second
system, respectively, for coating a metal strip;
- figures 3 and 4 are a perspective view and a top view, respectively, of an
electromagnetic device known from the state of the art;
- figures 5, 6 and 7 are further views relating to electromagnetic devices known from
the state of the art;
- figure 8 is a top view relating to a first embodiment of an electromagnetic device
according to the present invention;
- figures 9 and 10 are views relating to possible applications of the electromagnetic
device in figure 8;
- figure 1 is a perspective view of the electromagnetic device according to claim 8;
- figures 12, 13, 14 and 15 are views relating to possible operating modes of the
electromagnetic device in figures 8 and 9;
- figures 16 and 17 are a top view and a perspective view, respectively, relating to a
second embodiment of an electromagnetic device according to the present invention;
- figures 18 and 19 are side views relating to possible embodiments of an
electromagnet of the electromagnetic device in the figures from 8 to 11;
- figures 20 and 2 1 are side views relating to possible embodiments of an
electromagnet of the electromagnetic device in the figures from 6 to 17;
- figure 22 is a perspective view relating to a third embodiment of a device according
to the present invention.
The same numbers and the same reference letters in the figures identify the same
elements or components.
DETAILED DESCRIPTION OF THE INVENTION
The electromagnetic device 1 according to the present invention may be used for
stabilizing a ferromagnetic strip (hereinafter more simply indicated as "strip 4") and
minimizing the deformation thereof (e.g. cross-bow) preferably during a liquid metal
coating process. In particular, the electromagnetic device 1 is particularly suited to be
used for stabilizing a strip 4 within the scope of a system which performs a coating
process such as for example, the one schematically shown in figure 1 or in figure 2 . It
will become apparent from the following description how the electromagnetic device
according to the invention may also not only be used to correct any deformation on a
strip made of ferromagnetic material, but possibly also to intentionally cause a
deformation on the strip.
Figures 8 to 22 refer to possible embodiments of an electromagnetic device 1
according to the present invention. The electromagnetic device 1 according to the
invention comprises first electromagnets 15, 15', 15", 15"' and second
electromagnets 16, 16', 16", 16"'. The first electromagnets 15, 15', 15", 15"' are
aligned along a transversal direction 100' substantially parallel to a theoretical passline
50 of strip 4 and orthogonal to a transportation direction 100 parallel to said
theoretical plane. Similarly, the second electromagnets 16, 16', 16", 16"' are aligned
along a direction which is also parallel to the theoretical pass-line 50 of strip 4 and
orthogonal to said transportation direction 100. More accurately, with respect to said
theoretical plane 50, the first electromagnets 15, 15', 15", 15"' are positioned in a
position mirroring the position taken on by the second electromagnets 16, 16', 16",
16"'. For the objects of the invention, the expression theoretical pass-line 50 intends
indicating a plane along which strip 4 should theoretically be supplied under an ideal
condition of no vibrations and disturbances.
According to the present invention, each of the first and of the second electromagnets
15, 15', 15", 15"', 16, 16', 16", 16"' has a core comprising at least one pole and at
least one coil wound about said pole and fed with a current whose intensity is
preferably adjustable.
According to a preferred embodiment shown in the figures, the core has a
substantially "E"-shaped structure, i.e. comprising three poles 18, 18', 18" and a yoke
19 which connects said poles 18, 18', 18" to each other. Said poles 18, 18', 18" and
said yoke 19 may be made of ferromagnetic material, which is laminated or not
laminated. More accurately, the core comprises a first pole 18, a second pole 18' in
raised position with respect to said first pole 18 and a middle pole 18" in intermediate
position between said first pole 18 and said second pole 18'. Each of said
electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' also comprises at least one
feeding coil wound about one of said poles 18, 18', 18". In an alternative embodiment
not shown in the figures, the core of the electromagnets 15, 15', 15", 15"', 16, 16',
16", 16"' could only comprise two poles, about at least one of which a coil is wound.
Hence, the core of the electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' could have
a substantially "C"-shaped rather than an "E"-shaped structure like the one described
above.
The first electromagnets serve the purpose of generating, by means of feeding the
respective coil or coils, first magnetic fields on a first side of said strip 4. Therefore,
such first magnetic fields are independently generated and adjusted. In other words,
each of them may have, with respect to the others, a different intensity resulting from
a different supply current of the coil or of the coils. Similarly, the second
electromagnets 16, 16', 16", 16"' serve the purpose of generating second magnetic
fields, which are also independent, in a position mirroring the one of the first magnetic
fields.
According to the present invention, the electromagnetic device 1 also comprises a
first connection element 26 made of ferromagnetic material and a second connection
element 26' made of ferromagnetic material. The first connection element 26
connects the cores of the first electromagnets 15, 15', 15", 15"'to each other, while
the second connection element 26' connects the cores of the second electromagnets
16, 16', 16", 16"'. The first connection element 26 and the second connection
element 26' have a mirroring position with respect to the theoretical feeding plane 50.
In particular, in the embodiments shown in the figures, the first connection element 26
connects the middle poles 18" of the first electromagnets 15, 15', 15", 15"' to each
other, while the second connection element 26' connects the middle poles 18" of the
second electromagnets 16, 16', 16", 16"'.
Figure 8 is a schematic view relating to a first embodiment of device 1 according to
the present invention. The first connection element 26 and the second connection
element 26' are preferably made in the shape of a bar with a rectangular section,
made of ferromagnetic material, which is laminated or not laminated. As indicated
above, the two connection elements 26, 26' have a mirroring position with respect to
the theoretical plane 50 and are arranged so that the longitudinal axis 103 thereof is
parallel to the transversal alignment direction 100' of the electromagnets 5, 15', 15",
15"', 16, 16', 16", 16"', i.e. orthogonal to the transportation direction 100 of strip 4. In
particular, according to a preferred embodiment, the two connection elements 26, 26'
have an extension measured along said transversal direction 100', which is greater
than or equal to the extension of strip 4 measured along said transversal direction.
The first connection element 26 serves the purpose of conveying and distributing the
first magnetic fields generated by the first electromagnets 15, 15', 15", 15"' by
generating a first continuous magnetic field distributed along the transversal direction
100'. In essence, the first continuous magnetic field generated by the first connection
element 26 consists of a "first magnetic field source" distributed in space, whose lines
of force act on all the points of the cross section of strip 4. Similarly, the second
connection element serves the purpose of conveying and distributing the second
magnetic fields generated by the second electromagnets 16, 16', 16", 16"' by
generating a second continuous magnetic field distributed along the transversal
direction 00' in position mirroring the first continuous magnetic field generated by the
first connection element 26. The second connection element 26' in essence consists
of a "second magnetic field source" distributed in space in a position mirroring the first
source defined by the first connection element 26.
By feeding the coils of various electromagnets with various currents and thanks to the
two connection elements 26, 26', practically continuous distribution in space of the
forces is obtained along the entire cross section of strip 4, regardless of the width
thereof. To this end, it is pointed out that during processing, the width of strip 4 may
also vary several times during the same campaign. The device according to the
invention advantageously implements an intentional distribution of force regardless of
the width of the strip. It is also noted how by uniformly generating a continuous and
variable force along the entire length of strip 4, device 1 according to the invention -
unlike the devices of the known art - does not require the use of moving parts for
moving the source of force so as to also be able to exert forces on the edges of the
strip.
The case shown in figure 8 with broken line indicates a possible deformation of the
metal strip 4 (hereinafter also indicated as "deformation of the metal strip 4"), while
the solid line indicates the position achieved by the metal strip 4 thanks to the device
1 according to the present invention. Hence by varying the feed of the coils of the
electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' of device 1, in addition to
obtaining a wanted orientation of the forces, it is also possible to obtain a continuous
distribution thereof along the entire section of the metal strip 4 (i.e. substantially
between the two edges 4'). This means that unlike that achieved by traditional
devices, applied to each point of the cross section of the metal strip 4 is a determinate
force which intensity and which orientation contribute to minimizing the deviation of
the strip from the ideal condition (theoretical plane 50).
For example, in the case in figure 8, the forces 45 along a first half of the width of the
metal strip 4 are oriented in a first direction to minimize a first deviation 46 from the
correct theoretical position, i.e. from the theoretical pass-line 50. Instead, the other
half of the metal strip 4 is subject to forces 45' oriented in a second direction opposite
to the first because the direction of the deviation thereof from the theoretical plane 50
is also opposite.
Instead, figures 9 and 0 show other possible deformations of the metal strip 4 which
may be corrected by means of an electromagnetic device 1 according to the present
invention. In particular, it is noted that the deformation shown in figure 10 is
comparable to the one shown in figure 4, which, as indicated above, may not be
corrected effectively by means of traditional electromagnetic devices which provide a
system of forces applied only to the portions of sections of the metal strip facing the
electromagnets. Instead, the two connection elements 26, 26' provided in the
electromagnetic device 1 according to the invention determine a distribution of forces
which involves the entire section of the metal strip 4.
The possibility is apparent from the examples shown in figures 8, 9 and 10, offered by
the electromagnetic device 1 for correcting any deformation of the metal strip 4, i.e.
the possibility of substantially keeping the metal strip 4 along the theoretical plane 50.
The result is that the electromagnetic device 1 according to the invention is highly
versatile from a functional point of view therefore it may be used, within the scope of a
coating process, both to correct the vibrations generated by the removal units (gas or
magnetic knives) and to correct the deformations generated by the rolls within the
scope of coating based on an electromagnetic levitation of the liquid bath.
Figures 12 to 15 show further possible distributions of forces which can be obtained
by conveniently varying the levels of current (indicated with references 23, 23', 23",
23"') which feed the coils of the electromagnets 15, 15', 15", 15"', 16, 16', 16", 16'".
The metal strip 4 and the first electromagnets 15, 15', 15", 15"' are only shown in
such figures solely to simplify the depictions. Figure 13 shows the distribution of the
forces and in particular, the position of the related resultant force 22 obtained by
feeding one of the present electromagnets (indicated with reference 15') with a first
level of current 23. Instead, the distribution of forces shown in the schematization in
figure 14 is determined by the simultaneous activation of two electromagnets 15' and
15" fed with two different levels of current 23" and 23"'. Lastly, the distribution of
force shown in figure 5 is the result of the simultaneous activation of two adjacent
electromagnets 15', 15" whose feeding coils are fed with the same level of current
23'. It is noted from the comparison between figures 13, 14 and 15 that the point of
application of the resultant 22 of the forces varies according to the number and the
position of the activated electromagnets, and also to the level of current which feeds
the feeding coils of the electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"'
themselves.
Figures 18 and 19 laterally show an electromagnet (indicated with reference 15)
which can be employed for the device already shown in figures 8 to 11. In particular,
figure 18 shows a preferred embodiment in which the electromagnet comprises a
single feeding coil 17 wound about the middle pole 18" of the core. This solution
advantageously allows the volumes of the coil to be contained in height.
Instead, figure 19 shows an alternative solution in which three feeding coils are
provided: a middle coil 17 wound about the middle pole 18", a first auxiliary coil 17'
wound about the first pole 18 and a second auxiliary coil 17" wound about the second
pole 18'. In order to reduce the weights, the indicated feeding coils (the middle coil 17
and the auxiliary coils 17', 17") may also be water-cooled. Preferably the poles 18,
18', 18" have a prismatic shape with a rectangular section.
Yoke 19 of the core also has a prismatic shape with a rectangular section and
connects the end sections 38 of the three poles 18, 18', 18" which are resting on a
plane 5 1 which is substantially parallel to said theoretical plane 50. The middle pole
18" is connected to the related connection element 26 at a further end section 38'
opposite to section 38 connected to yoke 19.
With reference to figure 11, the minimum section required for each of said connection
elements 26, 26' is at least one fifth of the square of length 32 of a middle pole 18"
connected by the connection element 26 itself. In particular, such a length 32 is
measured along a direction substantially parallel to said theoretical moving plane 50.
It has been seen that an optimal uniformity is obtained of the forces acting on the
metal strip 4 by means of sections which are greater than or equal to such a minimum
section, while at the same time preventing the saturation of the core.
Again, with reference to figures 18 and 19, according to a preferred embodiment, the
first pole 18 and the second pole 18' do not frontally extend beyond the related
connection element 26, 26 connected to the middle pole 18", for each of said
electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' of device 1. This in essence
means that for each of said electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"',
distance 35 of the corresponding connection element 26, 26' from the theoretical
plane 50 is less than, or equal to distance 35' of the first 18 and of the second 18'
pole from the theoretical plane 50 itself (in particular, see figure 18). To this end, it is
noted that such a distance 35' from the theoretical plane 50 is the same for said first
18 and for said second pole 18'.
Figures 16 and 17 relate to a second embodiment of a device according to the
present invention. In this case, device 1 comprises a first connection body 27 which
connects the yokes 19 of the first electromagnets 15, 15', 15", 15"' to each other.
Device 1 also comprises a second connection body 27' which connects the yokes 9
of the second electromagnets 16, 16', 16", 16"' to each other. In particular, the first
connection body 27 connects the rear sections of the yokes 19 of the first
electromagnets 15, 15', 15", 15"' to each other. The expression "rear section" in
essence means the section of the yoke farthest from the theoretical pass-line 50. As
shown in top view in figure 6, the second connection body 27' connects the rear
sections of the yokes 19 of the second electromagnets 16, 16', 16", 16"' in an entirely
similar way.
Figures 20 and 2 1 are side views which show the configuration of an electromagnet
relating to the electromagnetic device shown in figures 16 and 17. In particular, figure
20 shows the presence of one single coil 17 wound about the middle pole 18",
similarly to what indicated for the solution in figure 18. Instead, figure 2 1 shows a
solution which provides three coils 17, 17', 17" similarly to what provided for the
solution in the above-described figure 17. With regards to what described above for
the solutions in figures 18 and 19, the solutions in figures 20 and 2 1 are also to be
considered valid.
According to an embodiment accurately shown in figures 20 and 2 1, the first
connection body 27 and the second connection body 27' are obtained in the shape of
a plate made of ferromagnetic material, which is laminated or not laminated. In
particular, such a plate has a section which height 37, measured according to a
direction parallel to the theoretical pass-line 50, is greater than, or equal to each
height of the yokes 19 connected by the same connection body. Furthermore, each of
said connection bodies 27, 27' in the shape of a bar has a thickness of at least 1 mm
measured according to a direction orthogonal to said theoretical pass-line 50.
It has been noted that an even greater distribution and uniformity of the forces
exerted by the electromagnets on strip 4 is obtained by employing the two connection
bodies 27, 27'. To this end, considering figure 16 again, a different distribution of the
forces 45, 45' is noted with respect to the distribution which is obtainable by the
device in figure 8, the deformation of strip 4 being equal. In particular, it is noted that
in the solution in figure 16, a more progressive distribution of the forces is obtainable
with respect to the one in figure 8 and hence an even more effective correction of the
position of strip 4. It has also been noted that the presence of the two connection
bodies 27, 27' also advantageously reduces the saturation of the core of the
electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' with related advantages that this
involves in terms of operability of device 1.
To this end, figure 22 shows a further possible embodiment of the electromagnetic
device 1 according to the invention in which the yokes 19 of the cores of the first
electromagnets 15, 15', 15", 15"' are made in a single piece, i.e. in a single body 28.
Similarly, the yokes 19 of the cores of the second electromagnets 16, 16', 16", 16"'
are also made in a single body (not shown in the figures).
The solution in figure 22 significantly increases the magnetic efficiency of the
electromagnetic device 1 thus further limiting the problems relating to saturation. It is
also noted that for this further solution, the use of a "single body" 28 provides
increased rigidity to the structure of the electromagnetic device 1 by likewise being
able to advantageously be shaped to form the metal support structure of the device.
In particular, such a single body 28 can also be equipped with fixing members for
allowing the positioning thereof, for example, within a system for coating strip 4 as
those schematized in figures 1 and 2.
For any of the above-described embodiments, the electromagnetic device 1
according to the invention comprises a plurality of position sensors adapted to detect
the position of predetermined points on strip 4 with respect to the theoretical pass-line
50. According to the type of position sensors, they may be positioned more or less
close to the region of space delimited by a first side by said first connection element
26 and by a second side, opposite to the first, by said above-described second
connection element 26'.
For any of the above-described embodiments, the activation of the electromagnets
15, 15', 15", 15"', 16, 16', 16", 16"' of device 1 (i.e. the feeding of the coils of the
electromagnets) is controlled according to the information deriving from the above
sensors. To this end, the employment of eddy-current sensors has been shown to be
particularly advantageous. However, it is understood that other types of sensors could
be employed, for example of capacitive type or laser sensors.
According to a preferred embodiment, the eddy-current sensors are preferably fewer
in number than the number of electromagnets of device 1. Each of these sensors is
positioned so as to detect, in a predetermined point, the position of strip 4, i.e. the
deviation thereof from a reference plane which may be, for example, the theoretical
plane 50. The signals deriving from such sensors are sent to a processing unit which
processes them to reconstruct the true shape of the strip (deformation). In particular,
the processing unit implements an interpolating function which starting from known
points, reconstructs the true shape of strip 4. According to the true shape of strip 4,
the processing unit determines the distribution of the forces to be applied to the strip
in order to minimize the deviation thereof from the theoretical pass-line 50. According
to such a distribution, a unit for controlling the electromagnets (possibly
corresponding to the processing unit) controls the supply of the feeding coils 17, 17',
17" of the electromagnets 15, 15', 15", 15"', 16, 16', 16", 16"' by assigning sufficient
levels of current to generate the forces required.
It is noted that, unlike traditional electromechanical devices, the sensor signals are
advantageously used to .simultaneously control the feeding of all the electromagnets
of the electromagnetic device. Obviously, this allows a more accurate and uniform
correction. Moreover, the employment of an interpolating function for calculating the
deformation of the strip advantageously allows to reduce the number of sensors to be
applied - and therefore the overall costs - to be contained.
According to a preferred device, the eddy-current sensors are positioned on both
sides of strip 4 so as to be, two by two, in a symmetrical position with respect to the
theoretical pass-line 50. It has been noted that this particular arrangement allows to
automatically calibrate the measuring system by starting from the knowledge of the
distance between the two sensors reciprocally facing each other because such a
distance is known. This particular arrangement of the sensors also allows the noise to
be reduced which may be generated on the signal of one of the sensors due to the
proximity of the magnetic fields generated by the electromagnets 15, 15', 15", 15"',
16, 16', 16", 16"'.
The electromagnetic device according to the invention allows to accomplish the
preset tasks and objects. In particular, the device allows the oscillations and
deformations of the strip to be minimized. This involves an advantageous reduction of
the over-coating required to ensure the minimum coating threshold required. The
increased stability of the strip also allows to increase the production line speed
thereof and this is obviously translated into reduced production costs i.e. increased
productivity. At the same time, the superficial quality of the coating is highly improved.
The device according to the invention also proves to be highly versatile from an
operational point of view because it is capable of effectively adapting to the various
widths of metal strips.
The present invention also relates to a system for coating a metal strip 4 which
comprises at least one device 1 according to that described above, for stabilizing the
position of the metal strip 4 during the feeding thereof. In a first embodiment, the
system may be of the type schematized in figure 1 or alternatively of the type
schematized in figure 2. In both cases, the system according to the invention
comprises a unit for removing the excess coating. Such a unit comprises gas knives
and/or magnetic knives.
According to a first installation mode, device 1 according to the invention may be
positioned on the support structure which also carries said unit for removing the
excess coating. By means of the sensors belonging to the electromagnetic device 1,
this operating position allows the actual position of the metal strip 4 to be known with
respect to the gas knives 5 and /or the magnetic knives of the removal unit. This
allows the knives to be neared/distanced according to the true position of the strip
and this translates into a subsequent saving of gas or of electric energy in the case of
electromagnetic knives.
In the case of a system of the type in figure 2, the electromagnetic device 1 according
to the invention may also be positioned below magnetic levitation pot 111'. This
position allows the reduction of the vibration of the metal strip 4 induced by the action
of the intense magnetic fields required for the levitation of the molten metal 7.
The process for stabilizing and/or correcting the deformation of a strip 4 made of
ferromagnetic material (e.g. a metal strip) of the present invention provides
generating first independent magnetic fields and second independent magnetic fields
in position mirroring the first magnetic fields with respect to a theoretical pass-line 50
of strip 4. The process provides conveying and distributing said first magnetic fields,
by means of first means for conveying and distributing magnetic fields, so as to
generate a first continuous magnetic field distributed along a transversal direction
100' parallel to said strip 4. The process according to the invention also provides
conveying and distributing said second magnetic fields, by means of second means
for conveying and distributing magnetic fields, by generating a second continuous
magnetic field and distributed in position mirroring the one of said magnetic field
distributed with respect to said theoretical pass-line 50 of strip 4.
The first magnetic fields and the second magnetic fields are generated by means of
electromagnets comprising at least one core and one feeding coil. The supply of
electric current in the feeding coil generates a magnetic field which is concentrated in
the core of the respective electromagnet. Essentially, the single feeding coils consist
of sources of independent magnetic fields which act in a concentrated area of space.
By means of the first means and the second means for conveying and distributing
magnetic fields, the first and the second magnetic fields are essentially redistributed
in the space so as to generate a first source distributed in the space (i.e. the first
continuous magnetic field) and a second source distributed in the space (i.e. the
second continuous magnetic field).
During feeding, strip 4 is arranged between the two continuous magnetic fields thus
generated so that any point of the cross section thereof is magnetized, i.e. it is
subjected to the effects of forces generated by the continuous magnetic fields.
Essentially, the magnetization of strip 4 occurs as reflected action of the presence of
the first and of the second magnetic field generated by the first and second conveying
and distributing means, respectively. Generated on each point of the cross section of
strip 4 are forces whose distribution, in terms of intensity and direction, corresponds
to the one of the continuous magnetic fields generated by conveying and distributing
the first and the second magnetic fields generated by the electromagnets.
It is apparent that the electromagnetic device 1 in the embodiments shown in the
above-described figures accurately allows the process according to the invention to
be carried out. In particular, it is noted that in the case of the electromagnetic device
, the first magnetic fields are generated by the first electromagnets 15, 15', 5", 15"',
while the second magnetic fields are generated by the second electromagnets 16,
16', 16", 16"'. The first means for conveying and distributing magnetic fields consist of
the first connection element 26. Similarly, the second means for conveying and
distributing magnetic fields consists of the second connection element 26' mirroring
the first.
It is noted that the process according to the invention may be used to stabilize and
minimizing the deformation of a metal strip during the feeding thereof within the scope
of a production process, but could also be employed to induce, although not to
necessarily reduce and eliminate, a deformation on a strip made of ferromagnetic
material.
CLAIMS
1. An electromagnetic device (1) for stabilizing and reducing the deformation of a
strip (4) made of ferromagnetic material during its feeding, said device (1) comprising:
first electromagnets ( 15, 15', 15", 15"') aligned along a transversal direction
(100') parallel to a theoretical pass-line (50) of said strip (4) and orthogonal to a
transportation direction (100) of said strip (4);
second electromagnets ( 16, 16', 16", 16"') arranged in a position mirroring the
first electromagnets (15, 15', 15", 15"') with respect to said theoretical pass-line (50)
of said strip (4),
wherein each of said first and second electromagnets (15, 15', 15", 15"', 16, 16', 16",
16"') comprises a core provided with at least one pole (18, 18', 18") and at least one
feeding coil (17, 17', 17") wound about said at least one pole (18, 18', 18") and
wherein said device ( 1) further comprises:
- a first connection element (26) made of ferromagnetic material which connects the
cores of said first electromagnets ( 15, 15', 15", 15"');
- a second connection element (26') made of ferromagnetic material which connects
the cores of said second electromagnets (16, 16', 16", 16"'), said second connection
element (26') being placed in a position substantially mirroring the position of said first
connection element (26) with respect to said theoretical pass-line (50) of said strip
made of ferromagnetic material (4).
2. An electromagnetic device ( 1) according to claim 1, wherein each of said first and
second electromagnets (15, 15', 15", 15"', 16, 16', 16", 16"') comprises:
- a first pole (18);
- a second pole (18') in a position above said first pole ( 18);
- a middle pole (18") interposed between said first pole (18) and said second pole
(18');
- a yoke (19) which connects said first pole (18), said second pole (18') and said third
pole (18");
and wherein said first connection element (26) made of ferromagnetic material
connects the middle poles (18") of said first electromagnets (15, 15', 15", 15"') and
wherein said second connection element (26') made of ferromagnetic material
connects the middle poles (18") of said second electromagnets (16, 16', 16", 16"').
3. An electromagnetic device (1) according to claim 1 or 2, wherein said device ( 1)
comprises a plurality of position sensors adapted to measure the position of said strip
(4) with respect to said theoretical moving plane (50), each feeding coil (18, 18', 18")
of each of said electromagnets ( 15, 15', 15", 15"', 16, 16', 16", 16"') being fed
according to said position of said strip (4) with respect to said theoretical moving
plane (50).
4. An electromagnetic device (1) according to claim 3, wherein said sensors are
placed on opposite sides with respect to said theoretical moving plane (50) of said
strip (4) so as to be, two by two, in a mirroring position with respect to said theoretical
plane (50).
5. An electromagnetic device ( 1) according to any one of the claims from 1 to 4,
wherein said at least one feeding coil (17) is wound about said middle pole (18").
6. An electromagnetic device (1) according to any one of the claims from 1 to 5,
wherein each of said electromagnets (15, 15', 15", 15"', 16, 16', 16", 16"') comprises:
- a middle feeding coil ( 17) wound about said middle pole (18");
- a first auxiliary feeding coil (17') wound about said first pole (18);
- a second auxiliary feeding coil (17") wound about said second pole (18').
7. An electromagnetic device ( 1 ) according to any one of the claims from 1 to 6,
wherein said first and second connection elements (26, 26') have an extension,
measured according to said transversal direction (100'), which is greater than or
equal to the extension of said strip (4), also measured along said transversal direction
(100').
8. An electromagnetic device (1) according to any one of the claims from 1 to 7,
wherein said first and second connection elements (26, 26') consist of a bar made of
ferromagnetic material which is laminated or not laminated and with a rectangular
section, said bar having a section which is greater than or equal to one fifth of the
square of the length (32) of each middle pole (18") connected by the bar itself.
9. An electromagnetic device (1) according to any one of the claims from 1 to 8,
wherein the distance (35) of one of said first and second connection elements (26,
26') from said theoretical pass-line (50) is less than or equal to the distance (35') of
said first pole (18) and of said second pole (18') from the same theoretical plane (50),
said distances (35, 35') being measured according to a direction substantially
orthogonal to said theoretical pass-line (50).
10. A device ( 1) according to any one of the claims from 1 to 9, comprising:
- a first connecting body (27) made of ferromagnetic material which connects the
individual yokes ( 19) of the first electromagnets ( 15, 15', 15", 15"') to one another;
- a second connecting body (27') made of ferromagnetic material which connects the
individual yokes (19) of the second electromagnets ( 16, 16', 16", 16"') to one another.
1 . A device (1) according to claim 10, wherein each of said connecting bodies (27,
27') comprises a plate made of ferromagnetic material having a rectangular section
and wherein, for each of said connecting bodies (27, 27'), the height (37) of said
section measured according to a direction parallel to said theoretical pass-line (50), is
greater than or equal to the height of the connected yokes (19).
12. A device (1) according to claim 2, wherein the yokes (19) of the first
electromagnets (15, 15', 15", 15"') and/or the yokes (19) of said second
electromagnets (16, 16', 16", 16"') are made in a single body (28).
13. A system of coating the strip (4) made of metal, with a molten metal, comprising
the device ( 1) according to any one of the claims from 1 to 12.
14. A system according to claim 13, comprising:
- a pot ( 111) containing a molten metal bath (7);
- a unit (5) for removing the excess coating placed downstream of said pot ( 1 11) ;
- a support structure for supporting said pot ( 1 11) ;
wherein said device ( 1) is placed on said support structure.
15. A system according to claim 13, wherein a pot ( 111') is provided for containing a
molten metal bath and an electromagnetic apparatus (8) is provided for keeping said
molten metal bath suspended within said pot ( 1 11'), said pot ( 111') comprising an
inlet opening (9) for introducing said metal strip (4) and an outlet opening for said
metal strip, opposite to said inlet opening (9), said device ( 1) being operatively placed
at said inlet opening (9).
16. A process for stabilizing and/or correcting the deformation of a strip (4) made of
ferromagnetic material during its feeding, by means of the device according to claim
1, said process comprising the steps of:
- generating first independent magnetic fields and second independent magnetic
fields in a position mirroring said first independent magnetic fields with respect to a
theoretical pass-line (50) of said strip (4);
- conveying and distributing said first magnetic fields, by means of first means for
conveying and distributing magnetic fields, so as to generate a first continuous
magnetic field distributed along a transversal direction (100') parallel to said strip;
- conveying and distributing said second magnetic fields, by means of second means
for conveying and distributing magnetic fields, so as to generate a second continuous
magnetic field distributed along said transversal direction (100') in a position mirroring
said first continuous magnetic field generated by said first means for conveying and
distributing magnetic fields.