Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Device for Coating Metal Strip and Method Therefor
The invention relates to a device for coating a metal strip
with a coating material. The device includes a coating
container filled with a liquid coating material, wherein the
coated strip is conducted vertically upwardly through or out
of the coating container, wherein a stripping nozzle for
stripping off any coating material from the strip surface
which is still liquid, wherein above the stripping nozzle is
arranged an electromagnetic device for stabilizing the
position of the strip in a center position, wherein the
device includes at least two magnets arranged on both sides
of the metal strip on the same level. The invention further
relates to a method for coating a metal strip with a coating
material.
Document DE 10 2007 045202 Al discloses a device for the
strip edge stabilization of a strip which includes at least
one sensor for recognizing the position of the at least one
strip edge, and at least one device for adjusting the strip
edge position in which, in dependence on the strip edge
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position, a means for strip edge stabilization can be
positioned transversely of the strip.
Devices for stabilizing the travel of a metal strip are also
known from publications DE 10 2006 052000 Al and DE 10 2005
060058 Al. A strip stabilization device is provided for
adjusting and stabilizing the distance of the strip in the
transverse direction between the blow nozzles.
A device of this type and a corresponding method are known.
DE 10 2008 039 244 Al shows a device for hot dip coating in
which the metal strip is conducted through the coating bath
and is vertically upwardly conducted out of the bath. Above
the coating container a stripping nozzle is arranged by
means of which the excess coating material is blown from the
strip surface. Above the stripping nozzle a strip
stabilization unit is arranged at a defined distance, by
means of which the strip is supposed to be held centrally in
the middle plane of the plant.
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A similar solution is known from WO 02/14574 Al. In
addition, details concerning the hot dip coating method are
shown in WO 01/11101 Al, EP 0 659 897 Bl, EP 0 854 940 31
and JP 1100 6046.
In hot dip coating plants, particularly in hot galvanizing
plants, different requirements are made with respect to
strip position and strip travel. Particularly in the area
of the stripping nozzles the strip vibrations are to be
reduced and the strip shape is to be influenced by systems
which operate without contact, the so-called electromagnetic
strip stabilization systems.
In plants with a downstream inductive heating system
(galvannealer) additional guide rollers are arranged above
the stripping nozzle in front of the heating device, to
ensure a quiet strip travel between the heating coils and to
avoid defects to the plant and on the strip by contact of
the strip therewith.
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Also, a stable concentric strip travel in plants with and
without subsequently arranged heating inductors is of great
importance for the strip cooling devices downstream of the
stripping nozzle in order to achieve a uniform cooling
effect. It is also here desired to avoid damage to the
plant and the strip surface.
Various systems have become known which exert tensile forces
on the steel strip without contact, namely
electromagnetically, in order to minimize strip movements in
the form of vibrations. Moreover, with these systems the
strip shape can be influenced transversely of the transport
direction.
The strip position perpendicular to the strip surface is
measured in the strip stabilization system by means of
distance sensors, and is regulated in a closed control loop.
At the same time, additional measuring devices can be used
within the subsequent devices as additional signals for the
strip position regulation.
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The following has been found to be disadvantageous: The
position of the strip stabilizing unit is defined by the
type of construction and focuses, in the previously known
solutions for the most part, on a spatial vicinity to the
stripping nozzle. Consequently, depending on the conception
there is a distance of the strip stabilization magnets from
the nozzle lip of the stripping nozzle (air discharge from
the nozzle).
As a result, the distance to the subsequently arranged
devices, such as for example, the heating inductors or to
the subsequently arranged strip cooling unit, is very large.
This means that the strip stabilizing magnets have no effect
or only a minimal effect on the strip movement at that
location and consequently, no possibility of influencing the
strip stability in the area spaced apart from the stripping
nozzle.
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However, if the strip stabilizing magnets are mounted
directly in front of the heating inductor or the strip
cooling unit, a respectively significantly reduced effect on
the centering of the strip in the area of the stripping
nozzle takes place.
Therefore, in the previously known plants always only one
selected position occurs which usually is adapted to the
effect in the area of the stripping nozzle, i.e. the strip
stabilizing magnets are usually arranged in the area of the
stripping nozzle.
However, the requirements made of a modern strip galvanizing
plant cannot be met or can only be met to a limited extent
by the known plants.
In view of these disadvantages, the invention is based on
the object to further develop a device for coating a metal
strip with a coating material as well as to further develop
a corresponding method in such a way that it is possible to
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react to the different requirements of the strip guidance
unit in a better and less complicated manner. Consequently,
the quality of the hot dip coating, particularly the hot
galvanizing, can be increased.
In accordance with the invention, this object is met with
respect to the device by means for adjusting the vertical
distance of the magnets from the stripping nozzle.
These means for adjusting the vertical distance may include
at least one lifting element which is connected directly or
indirectly to the stripping nozzle. In this case, the
stripping nozzle may have, or may be connected to, a frame
structure on which the at least one lifting element is
arranged.
A heating element for heating the strip may be arranged
above the stripping nozzle in order to be able to carry out
a so-called galvannealing process. In this regard, the
heating element is preferably constructed as an inductive
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,
,
,
element. In this case, the means for adjusting the vertical
position are preferably constructed for adjusting the
vertical distance of the magnets in the entire area of the
vertical extension between the stripping nozzle and the
heating element.
In addition, a cooling section can be arranged above the
heating element. A holding furnace can be arranged between
the heating element and the cooling section.
The means for adjusting the vertical distance may include at
least one hydraulic or pneumatic actuator; they can also
include at least one mechanical actuator, particularly a
spindle/nut system.
The method for coating a metal strip with a coating material
in which the strip is guided through liquid coating material
which is present in a coating container and is then
vertically upwardly conducted out of the coating container,
wherein above the coating container any coating material
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,
,
which is still liquid is stripped from the strip surface by
a stripping nozzle, and wherein above the stripping nozzle
the strip is stabilized by means of an electromagnetic
device for stabilizing the position of the strip in a
concentric position, wherein the device includes two magnets
arranged on both sides of the strip on the same level, is
characterized according to the invention in that the
vertical distance of the magnets from the stripping nozzle
is adjusted to a predetermined value, wherein, for adjusting
the distance, means for adjusting the vertical distance from
the stripping nozzle are actuated by a control.
The magnets are preferably always held concentrically in the
middle position when the vertical distance is adjusted.
Accordingly, at the core of the invention is the fact that
the position of the strip stabilizing magnets is not
stationary, but can be adapted to the respective
requirements by means of a suitable lifting device. In this
regard, the aligned (centered) and optimized position of the
strip stabilizing magnets relative to the traveling steel
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strip - in a direction perpendicular to the strip - is
always maintained by a mechanical coupling of the strip
stabilizing magnets with the stripping nozzle.
Based on physical considerations, it can be concluded that
the strip stabilizing system must be positioned as closely
as possible to the respective device or operating location
to achieve an optimum function and, thus, to reduce the
strip movements (Principle of St. Vernant). For example,
for an optimization of the coating with liquid metal this is
a position as close as possible to the stripping nozzles,
wherein, for a concentric and quiet strip travel within the
reheating device, the position of the contactless strip
stabilization should be selected as closely as possible near
this device. Consequently, it is useful to be able to reach
both positions (once near the stripping nozzle and once near
the heating device) by means of a suitable auxiliary device
without the loss of the stabilizing functions. Moreover,
additional positions can be reached which facilitate
influencing both plant portions (stripping nozzle and
heating device) with the strip stabilization.
,......
,
,
In accordance with the invention, the vertical position of
the strip stabilizing magnets, which are a component of a
strip stabilizing unit, can be adjusted flexibly to a
desired value by a lifting device. This takes place in
dependence on the state of operation or the desired
contactless influence on the strip position. Positioning
takes place preferably between the stripping nozzle and the
heating inductors, arranged downstream in the conveying
direction of the strip, for the galvannealing operation or a
subsequently arranged strip cooling operation.
The actuating means for the vertical adjustment of the
magnets remain always centered relative to the stripping
nozzle because they are mechanically coupled therewith.
Accordingly, the invention makes possible a changeable
position in a targeted manner of the strip stabilizing
magnets above the stripping nozzle in a hot annealing plant.
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Thus, the vertical adjustment possibility of the strip
stabilizing magnets relative to the stripping nozzle permits
any position for obtaining an optimized manner of operation
between the extreme locations directly at the stripping nozzle
and directly in front of the subsequently arranged heating
elements, or prior to strip cooling.
In combined applications in which the strip position
influences in the stripping nozzle as well as in the
subsequently arranged devices are important, the effects on
the respective devices are determined by means of a
mathematical model taking into consideration the tension
distribution in the strip; in the same manner, a vertical
position of the strip stabilizing magnets, which is optimal
for the case of application, is adjusted.
Accordingly, in one aspect the present invention resides in a
method for coating a metal strip with a coating material,
wherein the strip is guided through liquid coating material
contained in the coating container and is then vertically
upwardly conducted out of the coating container, wherein
above the coating container any coating material which is
still liquid is stripped of the strip surface by a stripping
nozzle, and wherein above the stripping nozzle the strip is
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stabilized by means of an electromagnetic device for
stabilizing the position of the strip in a center position,
wherein the device includes at least two magnets arranged on
both sides of the strip on the same level,
and wherein the vertical distance (H) of the magnets from the
stripping nozzle is adjusted by adjustment means in
accordance with a predetermined value, and wherein the
adjustment means are actuated by a control.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing, embodiments of the invention are illustrated.
In the drawing:
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Fig. 1 schematically shows a hot dip coating plant according
to a first embodiment of the invention,
Fig. 2 shows an alternative embodiment of the invention
similar to Fig. 1,
Fig. 3 is a perspective illustration of a holding frame for
the stripping nozzle on which magnets for strip
stabilization are arranged so as to be vertically
adjustable, and
Fig. 4 is a perspective illustration of the magnets for
strip stabilization, arranged in a vertical adjusting
device.
Fig. 1 is a sketch of a hot dip coating plant which serves
for coating a strip 1 with a coating metal. In the
embodiment, the strip 1 is introduced in the conventional
manner into a coating container 2 which contains liquid
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coating material. In this embodiment, a deflection of the
strip 1 into the vertical direction V is achieved by means
of a deflection roller 14. Of course, the CVGL method can
also be used in the same manner in which the strip 1 enters
the coating container 2 vertically from below and the bottom
opening is sealed by means of an electromagnetic closure.
After the coated strip 1 has left the coating container 2
vertically upwardly, any excess coating metal is blown away
by a stripping nozzle 3. A device 4 for stabilizing the
strip 1 is provided above the stripping nozzle 3. This
device 4 has as its core two electromagnets 6 arranged on
both sides of the strip 1. This makes it possible to
subject the strip to magnetic forces in a targeted manner
such that it is held in a symmetrical center position 5 of
the device.
It is essential that means 7 are provided by means of which
the vertical distance H of the magnets 6 from the stripping
nozzle 3 can be adjusted in a targeted manner. This is
illustrated in Fig. 1 by the double arrows next to the
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magnets 6 and by the fact that the magnets 6 are sketched
once (in a middle position) with solid lines and two further
alternative positions with broken lines, namely in a lower
position adjacent the stripping nozzle 3 and, in an upper
position at the upper end of the travel movement which can
be carried out with the means 7.
The distance of the magnets 6 from the upper end of the
stripping nozzle 3 is denoted by H and indicates to what
extent the magnets 6 have been raised by the means 7.
A cooling section 11 for the strip 1 is provided above the
stabilizing device 4 in Fig. 1. Above the cooling section
11, the strip 1 is deflected into the horizontal by a
deflection roller 13.
In Fig. 2, an alternative solution is sketched, wherein in
this case, compared to Fig. 1, an additional inductive
heating device 10 is provided above the strip stabilization
4 by means of which a galvannealing process can be carried
,......
out in the manner which is known per se. In this case, a
holding furnace 12 is provided between the heating device 10
and the cooling section 11.
Fig. 3 provides an idea of the construction of the proposed
device. It can be seen that the stripping nozzle 3 is
arranged at a frame structure 9 on which four elements 8 are
fastened by means of which the magnets 6 can be raised or
lowered relative to the stripping nozzle 3.
Further details of the structural configuration can be found
in Fig. 4. As can be seen in this case, four lifting
elements 8 - in the present embodiment constructed as
mechanical actuators in the form of spindle/nut systems -
are used for moving and adjusting the magnets 6 in the
vertical direction V. The stripping nozzles 3 are not
illustrated here; they can be found in the lower portion of
the illustration according to Fig. 4.
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When strip length changes occur, which lead to a
readjustment of the stripping nozzle, the position of the
strip stabilization is also changed due to the mechanical
coupling of the strip stabilizing magnets.
The infinitely variable vertical adjustment of the magnets 6
of the strip stabilization facilitates the following
procedure:
For the optimum galvannealing operation (GA operation), the
strip stabilizing unit 4, and especially the magnets 6, are
positioned by the means 7 (lifting device) directly
underneath the inductive heating elements 10. Since the
coating thickness for GA products is very thin (maximum
90g/m2) and, therefore, only small improvements in the
coating structure can be achieved through the effect of
strip stabilization, the main focus of the stabilizing
effect concerns the strip travel in the heating element 10
(GA inductor) and, thus, the quality of the GA coating.
Because of the mechanical coupling with the stripping nozzle
3, the stripping nozzle 3 and the magnets 6 of the strip
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stabilizing unit are always centered relative to the strip
1.
The effect of the strip stabilization into the area of the
stripping nozzle 3 is reduced in this case, but is not lost
because of the optimal position computation through a
mathematical model as it is used in this case. The magnets
6 are positioned more closely adjacent the heating elements
(GA inductors) than at the stripping nozzle 3, but with
the consideration of the physical effect in both directions.
In other coating products, the focus of the stabilization
effect is to minimize the strip movement within the
stripping nozzle 3. For this purpose, the position of the
magnets 6 of the strip stabilization is selected to be in
the area of the stripping nozzle 3.
The guide rollers in front of the heating element, which are
used in the previously known plants for stabilizing the
strip, are no longer required because it is now possible to
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. -
influence the stabilizing effect in a targeted manner over
the entire vertical range between the stripping nozzle and
the heating element.
The means 7 (lifting device) also facilitate in an
advantageous manner a manual cleaning of the stripping
nozzle 3 during operation. The strip stabilizing unit or
the magnets 6 are moved into a raised position without
losing the stabilizing effect. In previously known systems,
this is not possible. This gives the maintenance personnel
free access to the stripping nozzle 3 and, thus, can
manually clean the nozzle lips. This requirement is
available in any hot galvanizing plant.
Positioning of the magnets 6 of the strip stabilization
takes place, as explained above, with a device which may
include two guides, supports and appropriate clamping
devices which cause tensioning of the system and, thus, the
parallel alignment of the strip stabilization (of the
magnets 6) relative to the strip or to the stripping nozzle
carrier system. This device for changing the strip
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. -
stabilization position is fixedly mounted on the stripping
nozzle 3, which contains a frame structure with adjusting
elements for alignment.
Consequently, the invention in principle is a frame
construction which, in turn, is fixedly connected to the
basic frame construction of the stripping nozzle 3. This
means that with the alignment of the stripping nozzle 3
relative to the strip 1, a synchronous alignment of the
magnets 6 of the strip stabilization unit relative to the
strip 1 always takes place.
List of Reference Numerals
1 Strip
2 Coating container
3 Stripping nozzle
4 Device for stabilizing
Center position
6 Magnet
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7 Means for adjusting the vertical position
8 Lifting element
9 Frame structure
Heating element
11 Cooling section
12 Holding furnace
13 Deflection roller
14 Deflection roller
V Vertical direction
Distance
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