Note: Descriptions are shown in the official language in which they were submitted.
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KPF13447 WO
Voith Patent GmbH
89522 Heidenheim
Apparatus for guiding a material web strip
The invention relates to an apparatus for guiding a
material web strip in a running direction having a
housing, in which a vacuum generating device is
arranged.
In the following text, the invention will be described
in conjunction with a paper web as an example of a
material web strip. However, said invention can also be
used in the case of other material webs and material
web strips which are cut from them.
In the course of its production and processing, a paper
web has to be guided through various processing
devices, among them a drying section, a pressing
section, a calender and optionally a coating apparatus
or a gluing apparatus. To this end, in many cases the
procedure is such that a material web strip having a
width of the order of magnitude of from 200 to 300 mm
is cut at the edge of the paper web and said strip is
first of all guided through the processing device. As
soon as said material web strip has traveled so far
that a tensile force can be exerted on it, the paper
web is cut to the correct width, with the result that
it can pass with its full width through the
corresponding processing device.
In addition to what are known as cable guiding
arrangements, apparatuses which operate with vacuum are
also used for guiding the material web strip. Here, an
air-permeable belt runs around a housing as a rule, on
which air-permeable belt the material web lies. The
belt is supported on a plate which is provided with
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holes or slots. A vacuum is generated on that side of
the plate which faces away from the belt, with the
result that the material web strip is attracted by
suction on the other side of the belt.
One example of an apparatus of this type is known from
EP 1 127 978 Bl. Here, a plurality of turbines are
arranged in the housing, which turbines suck air
through the belt, in order to hold the material web
strip firmly on the other side of the belt.
Another embodiment is known from EP 1 342 844 A2. Here,
a plurality of "doctor blades" are arranged in the
housing, which doctor blades end shortly below the
inner side of the belt and, as it were, peel off the
air layer which is situated there. As a result, a
vacuum is also generated on the outer side of the belt,
by way of which vacuum the web or at any rate its
material web strip can be attracted firmly by suction.
In the case of machines which operate faster and
faster, however, it is difficult in all cases to ensure
that the material web strip is guided so stably that it
can be transferred without problems to a following
transport device, for example a cable guiding
arrangement or another vacuum conveyor.
The invention is based on the object of guiding a
material web strip reliably.
In an apparatus of the type which is mentioned in the
introduction, this object is achieved by the fact that
a plurality of vacuum chambers are arranged in the
housing behind one another in the running direction, of
which each has at least one suction device.
The time which is required to load the material web
strip with the full vacuum is shortened by way of this
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embodiment. The material web strip is guided over the
housing and in the process increasingly covers a vacuum
chamber. However, as long as the vacuum chamber is not
yet completely covered, "surrounding air" can be sucked
through the remaining opening, with the result that the
vacuum in the vacuum chamber is still too weak in many
cases to firmly hold the material web strip reliably.
However, as soon as the material web strip has covered
the vacuum chamber completely, the vacuum which is made
available by the suction device acts to its full extent
on the material web strip. Since a plurality of vacuum
chambers are arranged behind one another in the running
direction, the length of each vacuum chamber is shorter
than that of the overall apparatus, with the result
that it is concluded earlier at the same speed. If the
material web strip is held firmly at the first vacuum
chamber in the running direction, it is already
stabilized to a certain extent. However, the holding
force which results from surface area times vacuum is
still too low in many cases to firmly hold the material
web strip reliably overall. However, this unstable
situation lasts only for a short time because the
material web strip continues to run and then covers the
next chamber or chambers in the running direction, with
the result that the vacuum which is situated there also
acts on the material web strip. The holding force which
acts on the material web strip is therefore built up in
steps.
A first vacuum chamber in the running direction of the
material web strip preferably has a greater number of
suction devices than a vacuum chamber which is arranged
behind it in the running direction of the material web
strip. It is therefore possible to generate a higher
vacuum in the first vacuum chamber, as long as the
material web strip has not yet covered said vacuum
chamber completely. More air is namely conveyed away on
account of the plurality of suction devices, with the
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result that the material web strip is then held firmly
on the fabric or another air-permeable belt with high
reliability, if the first vacuum chamber is not yet
completely closed. The highest vacuum occurs when the
first vacuum chamber is covered completely by the
material web strip. After the material web strip is
stabilized in this way over the first vacuum chamber, a
lower vacuum is sufficient to transport the material
web strip as far as the end of the apparatus. Since the
vacuum chambers are covered gradually and then act with
the full vacuum on the material web strip, the holding
force on the air-permeable belt at the end of the
apparatus is very great. Slipping of the material web
strip is reduced or even prevented.
The suction devices are preferably configured as
suction nozzles. Suction nozzles can be installed
simply. They are supplied with compressed air, with the
result that the energy supply which is necessary for
suction can also be provided in a simple way.
A boundary wall is preferably filled with suction
devices in the first vacuum chamber. Such a large
number of suction devices are therefore provided that
this wall, for example the base of the vacuum chamber,
is covered completely or at any rate virtually
completely with suction devices. Here, the suction
devices are not only the openings, through which the
suction air is sucked out of the vacuum chamber, but
also the elements which surround the suction openings.
The vacuum can be generated, as it were, over the full
surface area by the fact that a correspondingly large
number of suction devices are provided which are
distributed over the boundary wall.
The vacuum chambers preferably have a guiding side,
along which the material web strip runs, and a base
which lies opposite the guiding side, the suction
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devices acting through the base. This embodiment has
the advantage that the contaminants are sucked toward
the base and can then be removed through the suction
devices. In the long term, practically no dirt can
therefore accumulate in the vacuum chamber. This is
true independently of whether the apparatus is operated
in such a way that the material web strip is guided
above it or below it in the direction of gravity. It is
important in this context that the air flow can be
sucked in, as it were, in a straight line from the side
which causes dirt into the opposite side.
The guiding side and the base preferably extend
parallel to one another. The vacuum chambers therefore
have a constant height in the running direction. This
simplifies the manufacturing.
It is preferred here that the guiding side and the base
are at a spacing in the range from 5 to 35 mm, in
particular in the range from 10 to 20 mm. The volume of
the vacuum chamber is therefore firstly kept so low
that a sufficient vacuum can be generated relatively
quickly with acceptable expenditure. Secondly, there is
a sufficient spacing between the guiding side and the
base, with the result that the flow cross section is
large enough for the air which is to be extracted by
suction.
The suction devices are preferably arranged
symmetrically in relation to a center axis which
extends parallel to the running direction. The vacuum
can therefore also be generated symmetrically with
regard to the center axis, which likewise contributes
to a stabilization of the material web strip on the
air-permeable belt. If there is only one suction
device, for example one suction nozzle, in the vacuum
chamber, this suction nozzle is divided by the center
axis. If there are two suction nozzles in the vacuum
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chamber, they are arranged symmetrically on both sides
of the center axis.
At least two adjacent vacuum chambers are preferably
divided from one another by a dividing wall which
encloses at least in sections an angle with respect to
the running direction, which angle is greater than 950
or smaller than 85 . In other words, the dividing wall
extends at least in sections at an angle which does not
equal 90 with respect to the running direction. This
has the advantage that the material web strip covers
two vacuum chambers at least temporarily. Dead zones
are therefore avoided which could possibly lead to an
instability of the material web strip. If the material
web strip runs with its start over the dividing wall,
it is loaded at the same time by the vacuums in two
vacuum chambers, the first vacuum chamber in the
running direction acting more strongly on the material
web strip.
It is preferred here that the dividing wall has two
limbs which are inclined in opposite directions with
respect to the running direction. Said two limbs are
preferably inclined in the running direction. This
results in turn in symmetrical conditions, which has a
favorable effect on the stabilization of the material
web strip.
The limbs preferably abut one another in a V-shape. The
dividing wall therefore has two substantially straight
sections, with the result that it is easy to
manufacture. As soon as the material web strip passes
with its start over the tip of the "V", it is also
loaded with vacuum by the following vacuum chamber.
At least in the case of one vacuum chamber, the
dividing wall preferably extends on both sides of the
suction device in the running direction. The suction
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device is therefore positioned relatively closely
behind the dividing wall, with the result that the
vacuum can act relatively early on the material web
strip, that is to say practically immediately when the
material web strip has been guided over the dividing
wall. This already results after a short time in
conditions, by way of which the material web strip can
be guided stably. If the dividing wall is of V-shaped
configuration, the suction device is situated, as it
were, in the knuckle of the "V".
The housing preferably has an intermediate wall which
delimits the vacuum chamber. By way of this, it is
possible to keep the volume of the vacuum chambers
small. The smaller the volume, the quicker the air
which is situated in it can be extracted by suction and
the vacuum can be built up. The level of the vacuum is
therefore not influenced significantly. It is therefore
no longer necessary to suck the entire housing empty,
in order to generate the vacuum.
The intermediate wall is preferably configured in the
shape of a trough with inclined side walls. The
inclined side walls firstly contribute to a reduction
in the volume. Secondly, they also help to discharge
dirt particles or water which penetrate into the vacuum
chamber toward the suction devices.
It is preferred here that the side walls are inclined
toward the suction device in the direction of gravity.
This also facilitates the discharging of contaminants.
A compressed air supply line for the suction nozzles is
preferably arranged between the housing and the
intermediate wall. Said compressed air supply line is
therefore not visible in any case within the apparatus
and does not disturb further. The risk that it is
damaged is also reduced.
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A vacuum chamber preferably has a volume of at most 21,
in particular of at most 1 1. A volume which is this
small can be sucked empty relatively quickly, with the
result that even fast running material web strips which
are at a speed, for example, of the order of magnitude
of 1800 m/min can be held stably very quickly.
At least one vacuum chamber is preferably divided into
at least two compartments parallel to the running
direction. This is preferably the first vacuum chamber
in the running direction. If the material web strip is
cut out of the material web, it can occur that it does
not come to lie precisely centrally on the vacuum
chamber. In this case, there is the risk that it does
not cover the vacuum chamber completely, with the
result that surrounding air can still be sucked in
laterally, as a result of which the holding force is
reduced. If the vacuum chamber is then divided into at
least two compartments parallel to the running
direction, the chance is great that at least one of
said compartments is covered completely by the material
web strip. The material web strip is then held with the
full force at least in this compartment.
It is preferred here that each compartment is delimited
in the running direction by a V-shaped dividing wall.
This results in the advantages which have been
described generally above in conjunction with a vacuum
chamber. The V-shaped dividing wall does not produce a
dead zone when the material web strip moves over the
dividing wall. Rather, when it moves over the dividing
wall, said material web strip is then loaded by the
vacuum in two adjacent compartments in the running
direction.
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In accordance with another aspect, there is provided an
apparatus for guiding a material web strip in a running
direction having a housing, in which a vacuum generating
device is arranged, wherein a plurality of vacuum
chambers are arranged in the housing behind one another
in the running direction, of which each has at least one
suction device, wherein a first vacuum chamber in the
running direction of the material web strip has a greater
number of suction devices than a vacuum chamber which is
arranged behind it in the running direction of the
material web strip.
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In the following text, the invention will be described
using one preferred exemplary embodiment in conjunction
with the drawing, in which:
fig. 1 shows a perspective illustration of an
apparatus for guiding a material web strip in
the open state,
fig. 2 shows a plan view of the apparatus according
to fig. 1,
fig. 3 shows a section
according to fig. 2,
and
fig. 4 shows a sectional view through a suction
nozzle.
An apparatus 1 for guiding a material web strip (not
shown in greater detail) in a running direction 2 has a
housing 3 which is provided with a deflecting roller 4
at its front end and with a deflecting roller 5 at its
rear end. A drive journal 6, to which a drive motor
(not shown in greater detail) can be connected, is
provided for the deflecting roller 5 at the rear end.
An air-permeable belt which is not shown in the drawing
for reasons of clarity is guided over the two
deflecting rollers 4, 5. Said belt can be configured,
for example, as a fabric.
The housing 3 has a covering plate (likewise not shown
in greater detail) which is provided with openings, for
example in the form of slots. The covering plate has
been omitted, in order for it to be possible to
illustrate details from the interior of the apparatus
1. During operation, the air-permeable belt rests on
the covering plate. The material web strip then lies on
the belt, which material web strip is loaded with
vacuum through the covering plate and the air-permeable
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belt and is thus sucked firmly onto the outer side of
the air-permeable belt.
Six vacuum chambers 7-12 are provided in the housing 3.
The vacuum chambers are divided from one another by
dividing walls 13-17. In plan view, each dividing wall
13-17 has a V-shape, that is to say two limbs 18, 19
which extend at an angle of approximately 45 with
respect to the running direction 2.
Each vacuum chamber 7-12 is provided with at least one
suction device in the form of a suction nozzle 20a-20e,
21-25. Here, the first suction chamber 7 in the running
direction 2 has a greater number of suction nozzles
20a-20e than the suction chambers 8-12 which are
arranged further to the rear in the running direction
2. In the present exemplary embodiment, the first
vacuum chamber 7 has five suction nozzles 20a-20e.
However, it is also possible to provide the first
vacuum chamber 7 only with three or four suction
nozzles.
The suction nozzles 20-25 are arranged in a base 26 of
the vacuum chamber 7-12. The base 26 is a boundary wall
which lies opposite a guiding side 27, along which the
material web strip is guided. The air-permeable belt,
against which the material web strip bears (not shown),
is situated on the guiding side 27. The base 26 and the
guiding side 27 extend parallel to one another at a
spacing in the range from 5 to 35 mm, preferably at a
spacing in the range from 10 to 20 mm.
As is apparent from figs 1 and 2, the suction nozzles
20a-20e are arranged in the first vacuum chamber 7 in
the running direction 2 in such a way that they fill
the base 26. There would therefore be no space for a
further suction nozzle 20a-20e. As a result, it is
possible not only to build up a vacuum relatively
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quickly in the first vacuum chamber 7 when the material
web strip is guided over the vacuum chamber 7, but also
to allow the vacuum to already act to a sufficient
extent on the material web strip when the material web
strip has not yet closed the vacuum chamber 7
completely.
In contrast, the respective suction nozzle 21-25 is
arranged in the remaining vacuum chambers 8-12 in such
a way that it is relatively close to the dividing wall
13-17, with the result that it is still overhung by the
respective dividing wall 13-17 on both sides in the
running direction 2. The suction nozzle 21-25 is
situated, as it were, in the "knuckle" of the "V".
As is apparent, in particular, from fig. 3, the housing
3 has an intermediate wall 28 which delimits the vacuum
chambers 7-12. The intermediate wall 28 has two
inclined side walls 29, 30 which are inclined in the
direction of the suction nozzles 20-25. If the
apparatus 1 is arranged as shown in fig. 3, that is to
say the material web strip is guided above the housing
3 in the direction of gravity, dirt particles or water
droplets which enter the vacuum chambers 7-12 are
guided by the side walls 29, 30 in the direction of the
suction nozzle 20-25, with the result that they can be
removed easily. However, the same is also true in the
case of "upside down" operation because even then an
air flow is produced which conveys dirt particles away
via the side walls 29, 30 and the base 26.
Fig. 4 diagrammatically shows a suction nozzle 23 in
section. The suction nozzle 23 has a compressed air
inlet 31, through which compressed air can be blown in.
Furthermore, the suction nozzle 23 has a suction inlet
32. The compressed air which enters through the
compressed air inlet 31 passes through a gap between
the differently hatched parts of the suction nozzle 23
and then flows out through an outlet 33. Here, it
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drives suction air with it which has entered through
the suction inlet 32. The suction nozzle 23 operates
according to the venturi principle. The volume of the
vacuum chambers 7-12 is kept small by the intermediate
wall 28. The intermediate wall 28 can be designed in
such a way that each vacuum chamber 7-12 has a volume
of approximately 2 1 or less, for example 1 1.
A compressed air supply line 34 is arranged in the
housing 3, to be precise between the intermediate wall
28 and the actual housing wall, with the result that
the compressed air supply line 34 is visible to the
outside in a nondisruptive way. The compressed air
supply line 34 is connected to the respective suction
nozzles 20-25 in each case via a branch line 35.
A vacuum chamber 7-12 has a length in the running
direction 2 of approximately 300 mm. At a web speed of
1800 m/min, it takes approximately 1/100 of a second
until a vacuum chamber 7-12 is covered by the material
web strip. Depending on the setting, a suction nozzle
has a suction performance of, for example, 4500 1/min,
with the result that approximately 0.75 1 of air can be
sucked out of each vacuum chamber 7-12 in 1/100 of a
second. If the vacuum chamber 7-12 has a volume of from
1 to 2 1, the material web strip is reliably held
firmly, as soon as it has moved over a vacuum chamber
7-12. In order to build up the vacuum which is required
for this purpose, it is not necessary to remove all the
air from the vacuum chamber 7-12.
Since the dividing walls 13-17 have the shown V-shape
(other shapes are also possible, as long as they do not
extend at right angles to the running direction 2),
when being conveyed in the running direction 2, the
material web strip is loaded at the same time by the
vacuum in two adjacent vacuum chambers 7-12, as soon as
it begins to cross a dividing wall 13-17. Dead zones
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are therefore avoided. It is also helpful here that the
suction nozzles 21-25 are arranged relatively close
behind the dividing walls 13-17, with the result that
the vacuum which is generated as a result can also act
relatively quickly on the material web strip.
As is apparent from fig. 3, the suction nozzles 20-25
in practice open at the level of the base 26. In every
case, they are arranged in such a way that air is
sucked away through the base. This has a considerable
advantage for the self-cleaning effect of the
apparatus. If fibers, dust or water accumulate in the
vacuum chambers 7-12, these contaminants are sucked in
through the suction nozzles 20-25 and blown out on the
underside of the apparatus 1.
The length of the apparatus can then be used to
influence the force, by way of which the material web
strip is held firmly and guided. One zone, that is to
say one vacuum chamber 7-12, has a length of the order
of magnitude of from 250 to 400 mm. Depending on how
long one wishes to guide the material web strip, more
or fewer vacuum chambers 7-12 then have to be connected
behind one another. For example, a vacuum of 28 mbar
can be generated in the first vacuum chamber 7 in the
running direction 2. A vacuum of from 5 to 20 mbar is
then sufficient in the following vacuum chambers 8-12.
The suction nozzles 20-25 are arranged symmetrically in
relation to a center axis 36. If therefore a vacuum
chamber 8-12 has only one suction nozzle 21-25, said
suction nozzle 21-25 is divided by the center axis 36.
If, as in the first vacuum chamber 7, a plurality of
suction nozzles 20a-20e are provided, they are arranged
symmetrically with respect to the center axis 36. As a
result, pressure conditions which are likewise
symmetrical with respect to the center axis 36 can be
realized in the vacuum chambers 7-12. A displacement of
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the material web strip by different pressures can be
ruled out in practice.
However, it can occur that the material web strip is
already displaced to the side during cutting. In this
case, it can be favorable to divide the individual
vacuum chambers 7-12 into two or three compartments
parallel to the running direction 2. In the case of a
division into two compartments, an intermediate wall
would be arranged where the center axis 36 is situated.
In this case, each compartment is provided with a
dedicated suction nozzle 20-25, the first compartment
of each row in the running direction again having more
suction nozzles than the compartments which are
arranged behind it in the running direction.
When the division of the vacuum chambers 7-12 into
individual compartments is carried out, it will be
expedient also to design the dividing walls 13-17
between the individual compartments to be V-shaped in
the running direction, in order to achieve the
abovementioned advantages.
