Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Dust removal apparatus
The present invention relates to an apparatus for
removing dust released during treatment of a moving web
of fibre material, particularly cellulosic fibre
material, such as in machines for cutting and rewinding
paper webs, in printing machines and in the dry end of
paper machines, e.g. in the production of a soft creping
paper web which is creped off a Yankee cylinder by means
of a creping doctor and spread by means of one or more
spreading means comprising a first dust suction box
including an elongated housing having an inner suction
chamber in communication with a vacuum source, said
housing having a first inlet in the form of a suction gap
communicating with the suction chamber, and said housing
also including a main part and first and second parts
which define said suction gap between them.
Dust in the form of fibres and other particles are
released from the web when creping off a soft crepe paper
web, e.g. a tissue web, from a Yankee cylinder. To remove
this dust it has been proposed in US patent No. 4,019,953
(SE-381 899) to arrange a collection container below the
area where the dust is produced. A compressed air pipe
and a Suction pipe are connected to this in order to
remove dusty air drawn across the direction of transport
of the web by jets of compressed air. Compressed air must
be blown on since merely drawing off the dust by means of
ventilation has little effect in view of poor distance
action. Such a device is cumbersome, bulky and relatively
inefficient since it only takes care of some of the dust
falling down below the dust-producing area. The high
speeds of modern tissue machines, namely in the region of
near 25 m/s, contribute to the unsatisfactory result
since dusty air is entrained along on both sides of the
fast-moving tissue web which is delicate due to its low
grammage.
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The release of dust from the surface of a paper web is a
problem when cutting and rewinding the paper web, for
instance. US patent No. 3,775,806 (SE-319 969) proposes
an apparatus for dust-suction of the surface of a paper
web. To avoid the web being drawn in towards the suction
device and coming into contact with this, thus causing
damage to the web, air is blown on at the same time as
the suction. The proposed dust-suction device therefore
comprises a horizontal sheet-metal channel, open at the
top, which surrounds a rectangular blowing pipe and
extends transversely across the web. The side of the
blowing pipe facing the web has openings facing away from
each other in order to direct air jets substantially
parallel to the web both with and against the direction
of transport of the web, thus fixing the distance between
web and dust suction device. Intermediate openings of the
same type may be arranged to direct air jets towards the
surface of the web to achieve a better dust suction
effect by blowing dust off the surface. The air supplied
and the dust entrained are withdrawn perpendicularly to
the web, through the two gaps formed upstream and
downstream of the blowing pipe, between it and the
surrounding sheet-metal channel, to which a means for
drawing off air is connected. The wall parts of the
sheet-metal channel located nearest the web may be
vertically movable up and down enabling them to be set in
such a manner that the dust-carrying air blown on does
not flow past the suction gaps, neither does the web
scrape against said wall parts and become damaged. The
dust-suction effect achieved with the arrangement
according to US-3,775,806 does not, however, fulfil
modern requirements with regard to also taking care of
the dust that accompanies the air around a fast-moving
paper web. Furthermore, the arrangement is both bulky and
expensive to purchase and to operate due to the air flows
required by the blow-on technique.
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US-4,906,333 (SE-B 459 105) proposes an apparatus for
removing dust in the boundary layer of a creped web. This
apparatus comprises a web-wide hood and a flat cover
plate that closes the hood while defining a space in
which subatmospheric pressure prevails, and forming a
suction gap between the cover plate and an angled strip
at the front side edge of the hood. The cover plate is
located immediately next to the creped web so that,
during transport, it is held close to the cover plate and
said suction gap will be located in the dust-containing
boundary layer. A lower part of the angled strip faces
towards the space and lies parallel with the cover plate
in order to define the suction gap, thereby ensuring that
its width remains constant in the direction of flow of
the air. A suction gap formed in this way easily becomes
clogged with dust after a relatively short time in
operation and must therefore be cleaned at regular
intervals. Another problem is that the web may be damaged
by the front edge and flat cover plate, causing a break
in the web. The problem is aggravated since the web is
drawn by the air flow up towards the front edge of the
cover plate. Said space in the hood is irregular in
shape, with several corners and edges that detrimentally
affect that air flow so that local whirls of air
containing dust occur, the flow of the air towards the
outlet gradually deteriorates and dust collects along the
walls near said corners and edges, which in turn results
in poorer suction effect so that the suction gap becomes
more easily clogged by dust particles for this reason as
well.
However, the problem of suction inlets and channels
becoming clogged is general to all known apparatus for
removing dust released during treatment of a moving web
of fibre material. Installing nozzles inside the actual
suction channel has been suggested so that air can be
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blown in the opposite direction through the gap at
regular intervals, in order to remove collections of dust
when the suction source has been disconnected. Such
interruptions in operation are undesirable since dust is
produced continuously and will be blown out into the
surroundings, causing further deterioration of the
working environment.
US-5,466,298 discloses a dust suction system with
upstream and downstream curved surfaces in a suction
inlet opening which is directed vertically downwardly.
Pressurized air is directed to the web and flows along
the curved downstream wall of the suction inlet opening
by the Coanda effect.
The object of the invention is to provide an improved
apparatus for taking care of and removing the dust
released during treatment of a moving web of fibre
material, thereby achieving improved working environment
for the operating personnel.
The apparatus according to the invention is characterized
in that the main part is shaped as or substantially as
part of a cylinder to provide a corresponding curved
inner side in the suction chamber; that the suction gap
comprises an inwardly converging outer section that
defines a gradual throttling, and an inwardly diverging
inner section that defines a gradual enlargement, said
sections merging at a transition where the throttling is
maximal, said transition having a minimal extension seen
in the flow direction of the air through the suction gap;
that the first inlet forming part comprises a flat
surface that defines the whole or most of its side of
said enlargement; and that the second inlet forming part
comprises both a curved surface having predetermined
radius and such an arc length that it defines the whole
of its side of the throttling and an initial part of the
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enlargement section, and also an inner, flat surface
extending at a tangent from the curved surface and
forming an acute angle a. with a tangent to the curved
surface at said transition.
5
The invention will be described in more detail with
reference to the accompanying drawings.
Figure 1 is a schematic side view of a section between a
Yankee cylinder and a reel-up in a soft crepe paper
machine, said section being provided with a plurality of
dust removal apparatus according to the invention.
Figure 2 is a side view of an apparatus according to a
first preferred embodiment of the invention.
Figure 3 is a cross section along the line III-III in
Figure 2.
Figure 4 is a side view of an apparatus according to a
second preferred embodiment of the invention.
Figure 5 is a cross section along the line V-V in
Figure 4.
Figure 6 is a side view of an apparatus according to a
third preferred embodiment of the invention.
Figure 7 is a cross section along the line VII-VII in
Figure 6.
Figure 8 is a through-section of an apparatus according
to a fourth preferred embodiment of the invention.
At the dry end of a soft crepe paper machine shown
schematically in Figure 1, a paper web 1 adhering to the
envelope surface of a Yankee cylinder 2, rotating
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counter-clockwise, is led downwards to a creping doctor
3. There the paper web 1 is creped off the Yankee
cylinder 2 by a creping blade 4 mounted in a holder 5
that extends substantially vertically up from a doctor
beam 6. From the creping blade 4 the creped paper web 1
runs obliquely downwards and passes a first spreading
means 7 in the form of a bow-shaped curved beam, and a
second spreading means 8 which will be explained below in
more detail, a calender 9, a grammage scanner 10 and a
deflection roll 11 before arriving at a reel-up 12. In
the embodiment shown the reel-up 12 comprises a drum
reel-up with a supporting cylinder 13. An empty reeling
drum 14 has just been lowered to abutment with the
supporting cylinder l3, beside which a recently finished
reel 15 of soft crepe paper is shown.
Dust is liberated from the paper web 1 during creping,
and some of this dust will be entrained in a boundary
layer on each side of the creped paper web 1 which is
moving at high speed, while almost all the remaining dust
will fall down towards the doctor beam 6. Dusty air will
also flow out of the hood covering the Yankee cylinder
when the paper web 1 runs out of the hood, this dust then
falling down to the paper web. In order to take care of
and remove at least a considerable part of the dust
content in the boundary air layers and in the air in the
spaces on both sides of the paper web 1, a plurality of
dust removal apparatus are applied between the creping
doctor and the grammage scanner 10. For the sake of
clarity these dust removal apparatus are shown with the
front end piece removed. ,
Figure 2 shows from the side an apparatus according to a ;
first embodiment of the invention comprising a dust
suction box 18 and attachment elements 19 for mounting
the apparatus on the lower side of the doctor beam 6 of
the creping doctor 3 to remove dust released when the
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soft crepe paper web 1 is creped off the Yankee cylinder
2. The dust suction box 18 comprises an elongated housing
20 having an inner suction chamber 21, see Figure 3,
closed at one end by an inspection hatch 22 and at the
other end being in communication with a suction source
(not shown) via a coaxial pipe socket 23 and a hose (not
shown). The housing 20 has a web-wide inlet 24 in the
form of a suction gap communicating directly with the
suction chamber 21. The wall of the housing 20 includes a
main part 25 in the form of a part of a cylinder, and
first and second parts 26, 27, tangentially joining each
end of the main part 25 and defining said inlet 24 in
form of a suction gap between them. A curved or cylinder
arc formed surface 34 is defined within the area for the
main part 25 on its inner side, i.e. in the suction
chamber 21. An inspection hatch 28 is arranged on the
lower side of the housing in the vicinity of the outlet
end.
The suction gap 24 comprises an inwardly converging outer
section 29 that defines a gradual throttling, and an
inwardly diverging inner section 30 that defines a
gradual enlargement, said sections 29, 30 merging at a
transition 31 where the throttling is maximal and the
extension minimal seen in the flow direction of the air
through the suction gap 24.
The first inlet forming part 26 has an outer curved or
cylinder arc formed surface 32 with predetermined radius,
and an inner flat surface 33 merging tangentially into
both the inner curved surface 34 of the main part 25 and
the outer curved surface 32, the point of tangent in the
latter case being located in the vicinity of the
transition 31 to the enlargement 30.
The second inlet forming part 27 has an outer flat
surface 35 which is located in a plane that is a tangent
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to the outer curved surface 32 of the first inlet forming
part 26, and a curved or cylinder arc formed surface 36
with predetermined radius, the outer flat surface 35 is a
tangent to the curved surface 36. The curved surface 36
has such an arc length that it defines its side of the
throttling 29 and an initial part of the enlargement 30,
as well as the actual transition 31 therebetween. The
second inlet forming part 27 also has an inner, flat
surface 37 extending at a tangent from the curved surface
36 and forming an acute angle cc with a tangent 38 to the
curved surface 36 at said transition 31. Said angle cc is
20-50°, preferably 30-40°. In order to achieve the best
function it is important that the radius of the curved
surface 36 of the second inlet part 27 is as large as or
larger than the width of the suction gap 24 at said
transition 31 (maximum throttling).
In Figure 4 an apparatus according to a second embodiment
of the invention is shown from the side. This apparatus
comprises said second spreading means 8 and a dust
suction box 118 for removing dust present in the air
whirling in the spaces before and after the web spreading
means 8. The apparatus comprises journalling means (not
shown) by means of which it is pivotable and vertically
adjustable so that the spreading means 8 can be adjusted
in relation to the paper web. The dust suction box 118
comprises an elongated housing 120 having an inner
suction chamber 121 provided at one end with a pipe
socket 123 communicating with a suction source (not
shown) via a hose (not shown). The housing 120 is closed
at the ends by end pieces 140, 141. The housing 120 has a
first web-wide inlet 124, see Figure 5, in the form of a
suction gap communicating directly with the suction
chamber 121. The housing 120 includes a main part 125
having the form of a part of a cylinder, and first and
second parts 126, 127, tangentially joining each end of
the main part 125 and defining said suction gap formed
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inlet 124 between them. A curved or cylinder arc formed
surface 134 is formed within the area for the main part
125 on its inner side, i.e. in the suction chamber 121.
The suction gap 124 comprises an inwardly converging
outer section 129 that defines a gradual throttling, and
an inwardly diverging inner section 130 that defines a
gradual enlargement, said sections 129, 130 merging at a
transition 131 where the throttling is maximal, said
transition having a minimal extension seen in the flow
direction of the air through the suction gap 124.
The first inlet forming part 126 comprises a flat surface
133 that merges tangentially with the internal curved
surface 134 of the main part 125.
The second inlet forming part 127 has an outer flat
surface 135 and a curved or cylinder arc formed surface
136 having predetermined radius, the outer flat surface
135 being a tangent to the curved surface 136. The curved
surface 136 has such an arc length that it defines its
side of the throttling 129 and an initial part of the
enlargement 130 as well as the actual transition 131
therebetween. Furthermore, the second inlet forming part
127 has an inner flat surface 137 extending at a tangent
from the curved surface 136 and forming an acute angle a
with a tangent 138 to the curved surface 136 at said
transition 131. Said angle cx is 20-50°, preferably
30-40°. To achieve the best function it is important that
the radius of the curved surface 136 of the second inlet
part 127 is as large as or larger than the width of the
suction gap 124 at the transition 131 (maximum
throttling).
The housing 120 is also provided with a second inlet 224
divided into several parts separated by partitions 253 in
the wall of the housing. Each such part of the inlet has
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first and second inlet parts 226, 227 defining the inlet
224 between them in the form of a suction gap. The second
inlet part 227 is supported by a wall 240 in the shape of
a cylinder arc hinged to the main part 125 and situated
5 outside the circle arc described by the main part 125.
The suction gap 224 comprises an inwardly converging
outer section 229 that defines a gradual throttling, and
an inwardly diverging inner section 230 that defines a
10 gradual enlargement, said sections 229, 230 merging at a
transition 231 where the throttling is maximal, said
transition having a minimal extension seen in the flow
direction of the air through the suction gap 224. The
first inlet forming part 226 has a flat surface 233
directed radially in relation to the inner curved surface
134 of the main part 125.
The second inlet forming part 227 has an outer flat
surface 235 and a curved or cylinder arc formed surface
236 with predetermined radius, the outer flat surface 235
is a tangent to the curved surface 236. The curved
surface 236 has such an arc length that it defines its
side of the throttling 229 and also the whole of the
enlargement 230, as well as the actual transition 231
therebetween. To achieve the best function it is
important that the radius of the curved surface 236 of
the second inlet part 227 is as large as or larger than
the width of the suction gap 224 at the transition 231
(maximum throttling).
Following the enlargement 230 is an inlet channel 241 of
constant cross section, which opens in an opening 242 in
the main part 125, said opening being defined in axial
direction by said partitions 253. The inlet channel 241
is defined by inner surfaces 243, 244 of the inlet parts
226, 227.
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Said spreading means 8, termed as a shoe, comprises a
tube 245 situated upstream and a tube 246 situated
downstream. The tubes are curved in a bow-shape in the
same way as the conventional spreading bar 7 and face
away from each other so that the greatest distance
between them is at the middle and the shortest distance
at their ends. The tubes are also oriented in relation to
each other so that a flat plane 249 intersecting the
curved centre line of the one tube 245 also intersects
the curved centre line of the other tube 246. The two
tubes are supported by a common, flat, stable bottom
plate 247 that is a tangent to the main part 125 of the
dust suction box and welded thereto. The spreading shoe
8, which is symmetrical, also comprises an upper arched
support plate 248 welded to the tubes 245, 246, the
support plate 248 thus being in connection tangentially
with the tubes, seen in each cross section thereof. The
arched support plate comprises an inclined part 250
located upstream and an inclined part 251 located
downstream and a top transition 252 between them, which
is curved. Since the tubes 245, 246 are situated in one
and the same plane 249 with regard to their centre lines,
as described above, the parts 250, 251 sloping in the
direction of travel of the web will also slope from the
middle out towards the edges, i.e. transversely to the
direction of travel of the web, depending on the
curvature of the tubes 245, 246, the transverse slope
being greatest at the tubes 245, 246 and decreasing
gradually to zero in the direction of the top transition
252. The inclination is suitably such that the support
parts 250, 251 encompass an obtuse angle in the range of
150-170°. The upper side of the support plate forms a
sliding surface for the paper web 1 to run over. The
paper web is effectively spread since the spreading
occurs during a long distance in the direction of travel
of the web corresponding to the width of the spreading
shoe 8.
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As can be seen in Figure 5, part of the bottom plate 247
forms the first inlet part 126 of the housing 120, the
inlet part thus being extended to the tube 246, the
curved surface of which has a favourable effect on the
process of flow of air towards the suction gap 124. At
the second inlet gap 224, the first inlet part 226
extends from the bottom plate 247 at an angle of 45°.
Figure 6 is a view from the side of an apparatus
according to a third embodiment of the invention
comprising journalling means 340 and a dust suction box
318 for removing dust from the air whirling in the spaces
before and after the conventional spreading bar 7 above
which this apparatus is mounted, as can be seen in Figure
1. The dust suction box 318 comprises an elongated
housing 320 having an inner suction chamber 321, see
Figure 7, that communicates with a suction source (not
shown) via a coaxial pipe socket 323. The housing is
otherwise closed at the ends by end pieces 350, 351. The
housing 320 has a first web-wide inlet 324, in the form
of a suction gap communicating with the suction chamber
321. The housing 320 includes a main part 325
substantially in the form of a part of a cylinder, and
first and second parts 326, 327 defining said suction gap
inlet 324 between them. Curved or cylinder arc formed
surfaces 334a, 334b, are formed within the area for the
main part 325 on its inner side, i.e. in the suction
chamber 321.
The suction gap 324 comprises an inwardly converging
outer section 329 that defines a gradual throttling, and
an inwardly diverging inner section 330 that defines a
gradual enlargement, said sections 329, 330 merging at a
transition 331 where the throttling is maximal, said
transition having a minimal extension seen in the flow
direction of the air through the suction gap 334.
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The first inlet forming part 326 comprises a reinforcing
pipe 342 and a separate inner plate 343 having a free
inner edge 344. The inlet part 326 has an outer surface
332, curved or in the form of a cylinder arc with
predetermined radius, and an inner flat surface 333 that
merges tangentially with the coaxial pipe socket 323 and
the outer curved surface 332.
The second inlet forming part 327 has a part 341 hinged
to the main part 325 which enables the inlet part 327 to
also function as an inspection hatch, thereby allowing
access to the suction chamber 321 in open position. As
can be seen in Figure 7, the inlet part 327 has an outer
flat surface 335 and a curved or cylinder arc formed
surface 336 having predetermined radius, the outer flat
surface 335 being tangent to the curved surface 336. The
curved surface 336 has such an arc length that it defines
its side of the throttling 329 and an initial part of the
enlargement 330 as well as the actual transition 331
therebetween. Furthermore, the second inlet part 327 has
an inner flat surface 337 extending at a tangent from the
curved surface 336 and forming an acute angle c~ with a
tangent 338 to the curved surface 336 at said transition
331. Said angle n! is 20-50°, preferably 30-40°. To
achieve the best function it is important that the radius
of the curved surface 336 of the second inlet part 327 is
as large as or larger than the width of the suction gap
324 at the transition 331 (maximum throttling).
The housing 320 is also provided with a second inlet 424.
For this purpose the housing is provided with an
additional set of first and second parts 426, 427
defining the inlet 424 between them in the form of a
suction gap. The first inlet part 426 is formed by a
profile plate 440 secured to the above-mentioned inner
plate 343 at its inner edge 344 and to the
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above-mentioned reinforcing pipe 342. The second inlet
part 427 comprises a part 441 hinged to the main part 325
enabling the inlet part 427 to function also as an
inspection hatch providing access to the suction chamber
321 when in open position.
The suction gap 424 comprises an inwardly converging
outer section 429 that defines a gradual throttling, and
an inwardly-diverging inner section 430 that defines a
gradual enlargement, said sections 429, 430 merging at a
transition 431 where the throttling is maximal, said
transition having a minimal extension seen in the flow
direction of the air through the suction gap 424.
The first inlet forming part 426 has a surface 432,
curved or in the shape of a cylinder arc with
predetermined radius, and an inner flat surface 433
directed substantially radially in relation to the inner
curved surface 334 of the main part 325 and merging
tangentially into the outer curved surface 432, the point
of tangent being situated at the transition 431 to the
enlargement 430.
The second inlet forming part 427 has an outer flat
surface 435 and a curved or cylinder arc formed surface
436 with predetermined radius, the outer flat surface 435
being a tangent to the curved surface 436. The curved
surface 436 has such an arc length that it defines its
side of the throttling 429 and also a part of the
enlargement 430, as well as the actual transition 43I
between them. Furthermore, the second inlet part 427 has
an inner, flat surface 437 extending at a tangent from
the curved surface 436 and forming an acute angle a. with
a tangent 438 to the curved surface 436 at said
transition 431. Said angle ~x is 20-50°, preferably
30-40°. To achieve the best function it is important that
the radius of the curved surface 436 of the second inlet
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part 427 is as large as or larger than the width of the
suction gap 424 at the transition 431 (maximum
throttling).
5 Said journalling means comprise a shaft extension 345 and
said pipe socket 323, which also functions as a shaft
extension. The shaft extensions 345, 323 rest on stands
346 via holders 347. The apparatus is fixed in a desired
operating position with regard to the angle of the inlets
10 224 and 324 in relation to the spreading bar 7 by means
of first screw elements 348. The apparatus is set in a
desired operating position with regard to its level above
the spreading bar 7 by means of second screw elements
349.
Figure 8 shows a through-section of an apparatus
according to a fourth embodiment of the invention
comprising two suction boxes 18', 18" of substantially the
same design as that according to Figure 2 with the
exception of the design of the first inlet part 26', 26~~,
in that the outer curved surface 32 and the inner flat
surface 33 are replaced by a flat surface 60 and 61,
respectively, merging tangentially into the internal
curved surface 134', 134" of the main part 125', 125" and
defining its side of the throttling 29', 29" and
enlargement 30', 30". The apparatus also comprises an
unperforated web-wide cover plate 62 to which the dust
suction boxes are secured at a distance from each other
and mirrored so that the inlets 24', 24" face away from
each other. Inclined reinforcement plates 63, 64 are
secured to respective dust suction boxes and the cover
plate 62. The cover plate 62 is flat except at its end
parts 65, 66 situated downstream and upstream, these
being bent away from the paper web 1 and located outside
each inlet. The part of the cover plate 62 inside each
end part 65, 66 forms the first inlet part 26', 26~~ of the
housing 20', 20" which, on its inner side has said flat
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surfaces 60, 61. Each dust suction box has two pipe
sockets 67, 68 arranged on the main part of the housing
at a distance from the inlet and communicating with a
suction source (not shown). The pipe sockets 67, 68
replace the end outlet 23 according to Figure 2.
Arranging bent end parts 65, 66 situated downstream and
upstream prevents the paper web from coming into contact
with the edges of the cover plate 62. This is
particularly important if the paper web arrives at the
apparatus and leaves it in a run that in both cases forms
a small angle with the plane of the cover plate 62. 59
denotes an end plate which closes one of the ends of each
suction chamber 21~, 21".
The inlet parts are preferably arranged at any of the
described inlets, movable in relation to each other in
order to control the size of the maximum throttling at
said transition depending on each particular operation,
suitably within the interval 10-30 nun, preferably
0.5-1 inch (12.7-25.4 mm). The suction gap 324 situated
downstream in the embodiment according to Figure 7 may
also be arranged to be completely r_losed. In all cases it
is preferably the second inlet part 27, etc., that can be
displaced and locked in the desired position, while the
first inlet part 26, etc., is stationary.
Designing the dust suction box in accordance with the
present invention enables the dust to be efficiently
removed with increased operating reliability and improved
working environment. The proposed geometry of the
passages through which the dust-carrying air passes
results in considerably less risk of dust adhering to the
walls than with known constructions. The valuable
improvement of removing the dust from the areas
surrounding the paper web is achieved by several
cooperating, thoroughly thought-through features. One
feature resides in the design of the suction gap with an
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initial throttling to cause gradually increasing speed
that culminates in the short transition to the subsequent
expansion of the air with maximum throttling so that the
dust is entrained with the increasing speed of the air
flow, through the suction gap. The dust does not
therefore have sufficient time to become adhered to the
walls. Another feature is the curved surfaces of the
throttling. The air endeavours to follow these curved
surfaces while forming a thin layer of air resulting in a
higher speed than the air outside said layer of air, so
that the dust particles have even less time to become
adhered to the curved surfaces. A further feature is the
cylindrical inner surface of the suction chamber which
causes the air to be guided toward this and round in a
spiral or rotary process towards the outlet or outlets,
without disturbing local whirl formations which might
allow the dust particles time to become adhered to the
walls.
It is also a considerable advantage that the principle
according to the invention for designing the dust suction
box can be used for all dust suction boxes installed at
various points between Yankee cylinder and reel-up.
The invention is described in connection with the removal
of dust released during the manufacture of a soft crepe
paper web which is creped off a Yankee cylinder, but may
of course be used for other moving webs of fibre material
where dust is released during various types of treatment,
such as in machines for cutting and re-winding paper
webs, in printing machines and in the dry end of paper
machines of types other than those specifically described
above.
