EP1860206A1

EP1860206A1 - A method and device for stabilising the lateral position of an elongated metallic element

Info

Publication number: EP1860206A1
Application number: EP06114319A
Authority: EP
Inventors: Jan-Erik Eriksson; Stefan Israelsson-Tampe; Conny Svahn; Bengt Rydholm; Carl-Fredrik Lindberg
Original assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Current assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Priority date: 2006-05-22
Filing date: 2006-05-22
Publication date: 2007-11-28

Abstract

A device for stabilising the lateral position of an elongated metallic element (4) continuously moving from a first roll (1) to a second roll (2), said device comprising a member (6, 10) for an application of a magnetic field onto the element (4). Said member (6, 7) generates a magnetic field resulting in said lateral force onto said element (4), causing a generally permanent lateral off-set of the element (4) from a predetermined extension line that it would present without the action of said magnetic field.

Description

TECHNICAL FIELD

The present invention relates to a method of stabilising the lateral position of an elongated metallic element continuously moving from a first roll to a second roll, said method comprising an application of a magnetic field onto the elongated element.
The present invention also relates to a device for stabilising the lateral position of an elongated metallic element continuously moving from a first roll to a second roll, said device comprising a member for an application of a magnetic field onto the elongated element.

BACKGROUND OF THE INVENTION

During galvanisation of a metallic strip or sheet, for example a steel strip, said strip passes continuously through a bath containing a molten metal, such as zinc. Normally, a first roll guiding the strip is submersed in the bath. From said first roll the strip extends to and moves towards a second roll located vertically above the bath. The second roll may be arranged at a considerable distance, such as up to 70 meters, from the first roll. The travelling speed of the strip may be as high as 200 m/min or even more. Normally, there are also provided further rolls, for stabilising and/or guiding purposes.
Within a distance from the bath surface within which the layer of molten metal is still in a liquid state, there may be provided an arrangement for the purpose of affecting any property of the molten metal. Typically such an arrangement comprises a so called electromagnetic wiper by means of which a walking magnetic field is generated for the purpose of wiping excessive molten metal off from said layer and back into the bath. Thereby a desired thin and even layer of molten metal is to be generated on the strip. Alternatively or in addition to said wiper arrangement there may also be provided an arrangement that generates an electromagnetic field rather for dampening purposes than for wiping purposes. Dampening is referred to as a dampening of the inherent motion of the molten metal in order to prevent any splashing thereof.
As the strip travels from the first roll to the second roll at high speed it is desirable from many aspects that it has a relatively stable position in its lateral direction. Lateral instability, i.e. lateral oscillations or vibrations, will, for example, result in less precise wiping and dampening results. The wiping or dampening arrangements will, typically, comprise a first and a second magnetic core provided with electric phase windings and arranged on opposite sides of the strip, thereby generating large, generally equal attraction forces on the strip in opposite lateral directions.
A lateral oscillation of the strip, even a very small one, will inevitably result in the strip coming closer to one of the magnetic cores of a pair of magnetic cores of the arrangement or arrangements mentioned above. Thereby, since the level of the attraction force generated by said magnetic core is dependent on the distance between the strip and the magnetic core, the attraction force acting on the strip towards the closest magnetic core will be increased, resulting in the strip being bent towards said core. In other words, the magnitude of the attraction force between a magnetic pole and the strip will vary between 0 and a maximum force, Fmax, depending on the distance between pole and strip. For a specific strip it has been found that the attraction force may vary between 0 and 3000 N/m due to changing current magnitude and lateral displacement. The electromagnetic poles located on opposite sides of the strip are in a common phase, and, accordingly, the opposite attraction forces follow that same common phase. However, the strip has natural lateral oscillations. At a certain distance from a central position between opposite poles, the attraction force towards the most adjacent pole reaches a maximum. Further closer to the pole, the increase of said force is very small. The force will oscillate, and, due to this, the natural oscillation of the strip might be amplified and the strip might start jumping or flipping from side to side, in relation to the central position.
Prior art suggests the use of a device for stabilising the lateral position of the strip. Such a device may, typically, comprise a first and a second magnetic core, arranged on opposite sides of the strip, preferably adjacent to or in the region of the wiping or dampening arrangement. Each core may be provided with a winding supplied with a DC-current in order to generate a static magnetic field that will result in an attraction force between the magnetic core and the strip. The opposite attraction forces will, to a certain degree, prevent the strip from oscillating in the lateral direction. However, in the region of any wiping or dampening arrangement like the ones described above, the same phenomena as has been described will continue to exist, even though somewhat restrained.

THE OBJECT OF THE INVENTION

It is the object of the invention to present a method and a device by means of which a reliable and effective stabilising effect can be obtained in a lateral direction on a travelling elongated element like the metallic strip described above.
In particular the invention should result in not only suppressing but even preventing the lateral oscillation of an elongated element as described above between the opposite magnetic cores of a wiping, dampening or otherwise condition-affecting electromagnetic arrangement.

SUMMARY OF THE INVENTION

The object of the invention is achieved by means of the initially defined method, characterised in that, by means of said magnetic field, a lateral force is applied to said element, causing a generally permanent lateral off-set of the element from a predetermined extension line that it would present without the action of said magnetic field. The off-set is permanent in the sense that it continually keeps the elongated element on one and the same side with regard to said extension line, which corresponds to a straight line between the peripheries of said first and second rolls defined by the elongated element when extending straight from the periphery of the first roll to the periphery of the second roll. The magnitude of the off-set at a given point of the length of the elongated element may vary over time, but is, preferably, as constant as possible.
The object of the invention is also achieved by means of the initially defined device, characterised in that said member generates a magnetic field resulting in said lateral force onto said element, causing a generally permanent lateral off-set of the element from a predetermined extension line that it would present without the action of said magnetic field.
According to a preferred embodiment the elongated element is bent by means of said force. By bending the strip and holding the strip in the bent position, a more stable lateral position may be obtained than by trying to hold the strip in a straight position. The magnitude of the radius of curvature of the bent strip may change somewhat during operation, but, according to the invention, it is permanently positive with regard to the line or plane defined by the straight strip. In other words, the strip is permanently bent only in one out of two opposite directions.
Preferably the elongated element is continuously transported through a bath of molten metal, and the condition of the molten metal attached to the surface of the elongated element is affected by means of an electromagnetic field applied onto said elongated element, said lateral force being located such that the lateral off set of the position of the elongated element is in the region of the electromagnetic field for affecting the condition of the condition of the molten metal. Typically, the electromagnetic fields for affecting any condition, such as the thickness or the motion of the layer of molten metal, generate pulling forces in opposite lateral directions, contributing to a lateral oscillation by reasons initially mentioned. The off-set of the strip in the region of the electromagnetic field will suppress the strip's tendency to flip from side to side, by promoting lateral displacement in one of the two opposite lateral directions.
According to one embodiment of the method the electromagnetic field is generated by means of a first and a second magnetic core provided on opposite sides of the elongated element, and, by means of said lateral force, the elongated element is off-set such that, in the region of said cores, it is closer to a first one of said cores. Thereby, an attraction force generated by the core closest to the elongated element will, due to the permanent displacement of the strip towards said core, permanently be large enough to prevent the opposite attraction force from pulling the strip over to become closer to the opposite core.
Preferably a magnetic field generating a field of force with a static component is applied for the purpose of generating said force.
According to one embodiment, said force is generated by means of at least a part of the electromagnetic field by means of which the condition of the molten metal attached to the surface of the elongated element is effected. It may happen that said electromagnetic field generates a static and a moving force component respectively. If two opposite electromagnetic fields are applied for conditioning the strip, or a coating on top of it, one of said fields may present a static component large enough for generating a sufficient lateral force in order to generate the permanent lateral off-set of the strip.
According to one embodiment of the method the lateral force is generated by setting up the first and second cores at different distances from the elongated element.
It is preferred that the magnetic force is generated by means of a magnetic core provided with a winding, said winding being supplied with a current in order to generate a field of force with a static component for generating said lateral force onto the elongated element.
Preferably said current is a DC-current.
According to a preferred embodiment of the device said member is provided to generate a lateral force large enough to bend the elongated element.
Preferably, the device according to the invention comprises a bath of molten metal through which the elongated element is continuously transported, and an arrangement for generating an electromagnetic field by means of which the condition of the molten metal attached to the surface of the elongated element is affected, said lateral force-generating member being located such that the lateral off-set of the position of the elongated element is in the region of the electromagnetic field for affecting the condition of the condition of the molten metal. Typically said arrangement comprises a so called electromagnetic wiper or an electromagnetic dampening device.
According to a preferred embodiment said arrangement comprises a first and a second magnetic core provided on opposite sides of the elongated element, wherein the lateral force-generating member is adapted to off-set the elongated element such that, in the region of said cores, it is closer to a first one of said cores. The lateral attraction force generated on the strip by each core will depend on the strength of the electromagnetic field generated thereby and distance between the core and the strip. The closer the gap, the larger the force. If, the strip is kept closer, or close enough, to one of said cores, and the magnetic fields of the cores are equally strong, the attraction force of that core may be large enough for preventing the strip from being occasionally pulled over to the other core due to the variations in electromagnetic field strength that will occasionally appear during operation.
Preferably, said lateral force-generating member generates a magnetic field that generates a field of force with a static component for the purpose of generating said force. Thereby, a continuous off-set of the elongate element will be permitted.
According to one embodiment of the inventive device said force is generated by means of said arrangement, for example by using one of the already existing magnetic cores thereof. Thereby, the requested off-set of the strip can be concentrated to, or be at a maximum, in the region of the magnetic cores of said arrangement, and, hence, a less strong magnetic field must be applied in order to achieve a pre-determined off-set in the region of said cores. Alternatively, there may be a separate device, or magnetic core, for the purpose of generating the requested lateral force.
Preferably, the first and second cores are set up at different distances from the elongated element. The cores and their corresponding windings and the currents with which they are supplied may, preferably be equal. When the arrangement operates, the core closest to the elongated element will generate a larger attraction force on the elongated element than does the other core due to the shorter gap, and hence there will be an off-set of the elongated element towards the first core, preferably large enough to prevent the elongated element from flipping over towards the second core.
According to the invention, it is preferred that the device comprises a magnetic core provided with a winding, said winding being supplied with a current in order to generate a field of force with a static component for generating said lateral force onto the elongated element. If the core is one of the cores of an arrangement such as the one disclosed above, e.g. of an electromagnetic wiper, the winding may be a winding separate from the winding used for generating the main electromagnetic field of said arrangement, for example a walking electromagnetic field.
According to one embodiment, said magnetic core is identical with said first magnetic core. I.e. one of the cores of said arrangement is used as the core for generating said lateral force.
According to an alternative embodiment, said magnetic core is separate from any one of said first and second magnetic cores. For example, it may be located downstream the cores of said arrangement, as seen in the travelling direction of the elongated element.
Preferably, said current is a DC-current.
Further features and advantages of the present invention will be presented in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now, by way of example, be presented more in detail with reference to the annexed drawing, on which:

Fig. 1 is a schematic side view of a device according to a first embodiment of the invention,
Fig. 2, is a schematic view of a device according to a second embodiment of the invention,
Fig. 3 is an enlarged view of a part of the device shown in fig. 2.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a first embodiment of the device according to the invention. The device comprises a first guiding roll 1, a second guiding roll 2, a bath 3 filled with a molten metal, preferably zinc, and an elongated element formed by a metal strip 4 running around and from the first roll 1 through the bath 3 to the second roll 2. Moreover, downstream the bath 3 as seen in the travelling direction of the strip 4, the device comprises an arrangement 5 for affecting a layer or coating of molten metal attached to the metal strip 4 as the latter leaves the bath 3. Said arrangement 5 comprises a first magnetic core 6 and a second magnetic core 7, said cores 6, 7 being located on opposite sides of the strip 4. Each magnetic core 6, 7 is provided with a first winding 8 and a second winding 9, supplied with a current of a first phase and a second phase respectively, in order to define a so called electromagnetic wiper for the purpose wiping excessive molten metal off the elongated element 4.
The phase windings 8, 9 of each core 6, 7 are supplied with an AC-current and generate an alternating magnetic field, also called a walking magnetic field, on the strip 4. the magnetic field generates a current in the coating of molten metal, said current resulting in a force on the coating acting in a direction opposite to the travelling direction of the strip 4. Accordingly, excessive molten metal is wiped off from the strip 4 in a direction towards the bath 3.
The device according to fig. 1 also comprises a member 10 for the application of a static magnetic field onto the elongated element or strip 4. Said member 10 generates a magnetic field resulting in said lateral attraction force onto said element 4, causing a generally permanent lateral off-set of the element 4 from a predetermined extension line that it would present without the action of said magnetic field. In fig. 1 the off-set, that will appear only during operation of said member 10, is indicated with a broken line. In the region of the opposite magnetic cores 6, 7 of said arrangement 5, there will be an off-set large enough for preventing the strip 4 from flipping or oscillating between a position closest to a first magnetic core 6 and a second magnetic core 6 due to fluctuations of the magnetic fields thereof and to the inherent lateral oscillations of the strip 4. Instead the attraction force generated by the first magnetic core 6 on the strip 4 will be constantly sufficient for holding the strip 4 in a position in which it is bent towards that magnetic core in relation to a straight line which it would follow if not affected by said arrangement 5 and said member 10.
Fig. 2 shows an alternative embodiment in which the member 10 is incorporated in a first one 6 of the opposite magnetic cores 6, 7 of the arrangement 5. Thereby, the first magnetic core 6 is equipped with a further winding 11 in addition to the windings 8, 9 previously mentioned. The further winding 11 is, during operation, supplied with a DC-current in order to generate a static magnetic field strong enough to result in a permanent off-set of the strip 4 towards the first magnetic core 6 in relation to the initial, unaffected position of the strip 4. This embodiment has the advantage of requiring less space in the vertical direction than does the embodiment of fig. 1, and it also has the advantage of focusing the maximum off-set of the strip 4 to the region of the electromagnetic field of the respective opposite magnetic cores 6, 7. Thereby it is preferred that the region of maximum lateral force generated by the further member 10 coincides with the region of maximum lateral force generated by said magnetic cores 6, 7 of said arrangement 5.
Fig. 3 shows a further embodiment, in which the cores 6, 7 of the arrangement 5 have been positioned or set up laterally asymmetrically in relation to the strip 4. The original, unaffected position of the non-bent or non off-set strip is indicated with a full line in fig. 3, while the off-set position during operation is indicated with a dotted line. The lateral distance a between the first magnetic core 6 and the original position of the strip 4 is less than the lateral distance b between the second magnetic core 7 and the original position of the strip 4. At least the first magnetic core 6 generates a magnetic field with a permanent static component, either as a part of the magnetic field generated by the main windings 8, 9 of the arrangement 5 or as a separate field generated by means of a supplementary winding like the winding 11 presented in connection to fig. 2. Herein, permanent is referred to as a permanently existing field during operation of the device.
The magnetic field or field component will generate an permanent attraction force on the strip 4 such that the latter will be permanently pulled towards the first magnetic core 6. The distance a between core 6 and strip 7 in its original position as well as the strength of the static field of force should be adapted such that any lateral oscillation that would normally occur and by which the strip 4 alternates between a position closest to the first core 6 and a position closest to the second core 7 is suppressed.
In any of the embodiments of the inventive device it might be advantageous from a stabilisation point of view to have an off-set that is larger than the gap between the opposite poles or cores 6, 7 of the arrangement 5. The desired off-set is dependent on the longitudinal force applied to the elongated element 4 and the distance between the first and second rolls 1, 2 (which typically might be some 40 meters), as well as inherent mechanical properties of the elongated element. The distance between first roll 1 and the level of the cores 6, 7 of said arrangement may be in the order of 1 meter. It might be preferred that the off-set of the elongated element 5 is 1/200 or more of said distance, e.g. 5 mm for a 1 meter distance between first roll and said arrangement. Preferably, the off-set may be more than 1 cm, preferably in the range of 1-10 cm. The gap between the cores 6, 7 may be as little as 20 mm. Thus in order to obtain a satisfying off-set it might be necessary to have the cores 6, 7 displaced in the off-set direction. It might also be necessary to displace any separate member 10 for generation of the lateral force on the elongated element 4 in order to obtain the most preferred lateral off-set of the elongated element 4. Accordingly, In fig. 3, once an initial lateral off-set, as indicated with the dotted line, has been established, the whole package including the opposite cores or poles 6, 7 should be move to the left in relation to the first roll 1 in order to obtain a further stabilising lateral off-set of the elongated element 4. Thus the inventive method may include the steps of generating an initial lateral off set by means of a member 6, 10 adapted thereto, and then amplifying said off-set by a lateral displacement of said member 6, 10 in the off-set direction, and, possibly a corresponding lateral displacement of the opposing cores 6, 7 of said arrangement 5. For this purpose the device according to the invention should be provided with means for a sufficient lateral displacement of said member 6, 10 and/or the cores 6, 7 of said arrangement 5, or the whole arrangement 5.

Claims

A method of stabilising the lateral position of an elongated metallic element (4) continuously moving from a first roll (1) to a second roll (2), said method comprising an application of a magnetic field onto the element (4), characterised in that, by means of said magnetic field a lateral force is applied to said element (4), causing a generally permanent lateral off set of the element (4) from a predetermined extension line that it would present without the action of said magnetic field.
A method according to claim 1, characterised in that the elongated element (4) is bent by means of said force.
A method according to claim 1 or 2, characterised in that the elongated element (4) is continuously transported through a bath (3) of molten metal, and that the condition of the molten metal attached to the surface of the elongated element (4) is affected by means of an electromagnetic field applied onto said elongated element (4), said lateral force being located such that the lateral off-set of the position of the elongated element (4) is in the region of the electromagnetic field for affecting the condition of the condition of the molten metal.
A method according to claim 3, characterised in that the electromagnetic field is generated by means of a first and a second magnetic core (6, 7) provided on opposite sides of the elongated element (4), and that, by means of said lateral force, the elongated element (4) is off-set such that, in the region of said cores (6, 7), it is closer to a first one (6) of said cores (6, 7).
A method according to any one of claims 1-4, characterised in that a magnetic field generating a field of force with a static component is applied for the purpose of generating said force.
A method according to any one of claims 3-5, characterised in that said force is generated by means of at least a part of the electromagnetic field by means of which the condition of the molten metal attached to the surface of the elongated element (4) is effected.
A method according to claim 6, characterised in that the force is generated by setting up the first and second cores (6, 7) at different distances from the elongated element (4).
A method according to any one of claims 3-7, characterised in that the magnetic force is generated by means of a magnetic core (6, 10) provided with a winding (11), said winding being supplied with a current in order to generate a magnetic field with a static component generating said lateral force onto the elongated element (4).
A method according to any one of claims 8, characterised in that said current has a DC-component.
A device for stabilising the lateral position of an elongated metallic element (4) continuously moving from a first roll (1) to a second roll (2), said device comprising a member (6, 10) for an application of a magnetic field onto the element (4), characterised in that said member (6, 10) generates a magnetic field resulting in a lateral force onto said element (4), causing a generally permanent lateral off-set of the element (4) from a predetermined extension line that it would present without the action of said magnetic field.
A device according to claim 10, characterised in that said member (6, 10) is provided to generate a lateral force large enough to bend the elongated element (4).
A device according to claim 10 or 11, characterised in that it comprises a bath (3) of molten metal through which the elongated element (4) is continuously transported, and an arrangement (5) for generating an electromagnetic field by means of which the condition of the molten metal attached to the surface of the elongated element (4) is affected, said lateral force-generating member (6, 10) being located such that the lateral off-set of the position of the elongated element (4) is in the region of the electromagnetic field for affecting the condition of the condition of the molten metal.
A device according to claim 12, characterised in that said arrangement comprises a first and a second magnetic core (6, 7) provided on opposite sides of the elongated element (4), and that the lateral force-generating member (6, 10) is adapted to off-set the elongated element (4) such that, in the region of said cores (6, 7), it is closer to a first one of said cores.
A device according to any one of claims 10-13, characterised in that said lateral force-generating member (6, 10) generates a field of force with a static component for the purpose of generating said force.
A device according to any one of claims 12-14, characterised in that said force is generated by means of said arrangement (5).
A device according to claim 15, characterised in that the first and second cores (6, 7) are set up at different distances from the elongated element (4).
A device according to any one of claims 10-16, characterised in that it comprises a magnetic core (6, 10) provided with a winding (11), said winding (11) being supplied with a current in order to generate a magnetic field that generates a field of force with a static component for generating said lateral force onto the elongated element (4).
A device according to claim 13 and 17, characterised in that said magnetic core (6) for generating said field of force is identical with said first magnetic core (6).
A device according to claim 13 and 17, characterised in that said magnetic core (10) for generating said field force is separate from any one of said first and second magnetic cores (6, 7).
A device according to any one of claims 17-19, characterised in that said current has a DC-component.