Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
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IMPROVEMENTS IN OR RELATING TO APPARATUS FOR
DE-WATERING FIBROUS SUSPENSIONS
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The present invention relates to apparatus for
- 5 de-watering fibrous suspension, and more particularly
but not exclusively to de-watering apparatus on a
paper machine of the Inverform type in which water is
removed predominantly upwardly by suction boxes located
above the traveling top forming wire of a continuously
moving sandwich formed by the top and bottom wires and
à layer or web of fibrous suspension between them.
Still more particularly, the invention relates to an
improved cover for a suction box.
; In paper forming machines water is removed from
- 15 the fibrous suspension by suction boxes or foil boxes
or augmented vacuum foil boxes. These boxes may be
disposed either above or below the layer or web of
fibrous suspension formed between top and bottom
traveling wires. All boxes of the aforementioned
types have a cover, and these covers may comprise a
plurality of elongate foils which extend transversely
relative to the direction of movement of the web of
fibrous suspension. In known designs the covers,
formed by the foils or suction box covers, are attached
to the suction boxes in such a manner that the suction
box has to be removed to replace the foils or the
cover when a different design style of cover is
required. This requires the paper machine to be
stopped for lengthy periods in order to rework the
main construction
In the case of inverted suction boxes, i.e.
where the water is removed upwardly, there is a greater
tendency for the plugging up of the foils to occur,
compared to conventional underwear suction boxes.
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In British Patent Jo. 1582342 the active surface of a
suction box de-watering apparatus is defined by a plurality
of foils. Each foil is secured directly to the suction box
by a respective mounting block. Mach individual foil
mounting must be machined at a different angle and since
this is a large size component the machining of the suction
box is complex and expensive.
It is an aim of the present invention to provide improved
de-watering apparatus in which the covers for suction boxes
and the like can be changed more easily than known designs
and with minimum paper machine down time.
It is a further aim of the present invention to provide
de-watering apparatus for an inverted suction box which has
a reduced tendency to plug.
In accordance with the present invention then, there is
provided apparatus for de-watering a fibrous suspension
through a traveling, forming wire with which it is in
contact, comprising a suction housing; a cover for the
suction housing; at least two plank members comprising part
of the cover and extending in a direction generally trays-
verse to the direction of travel of the forming wire, each
plank member being releasable secured to the suction housing
and being spaced from said suction housing so as to form a
space between each plank member and the suction housing;
each plank member having a plurality of spaced-apart pins,
each pin having two ends, each pin having one end thereof
attached to and projecting from the plank member, said
plurality of pins also being disposed in a plurality of
spaced-apart rows extending in a direction generally trays-
verse to the direction of travel of the forming wire; each plank member having a plurality of foil strips, each foil strip
being secured to the plank member at the other end of each
of a plurality of spaced-apart pins in a row to define, with
the other foil strips, a space between the foil strips and
the plank member, and an active surface over the foil strips.
By employing planks, the number of mounting blocks
carried by the suction box are reduced and accordingly
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less machining is required. Furthermore, the number of
different angles which have to be machined are reduced to
the number of planks employed by virtue of the fact that
each plank carries several foils. The plank-pin design is
also much easier to manufacture and needs only a small amount
of machining. The pins are welded to the planks and the
machined surfaces are few and are parallel to each other.
The pins are disposed in parallel spaced apart rows and
the foil strips, which are elongate members, are secured
either directly but preferably indirectly to one or more rows
of pins by the free end of each of the pins in the row or
rows so that the foils are spaced from the plank member. An
elongate mounting bar having a T-shaped cross-section is
preferably interposed between the ends of the pins in one row
and the foil. In other words, each foil strip is preferably
supported by a, or a respective, mounting bar which is, or
are, carried by and secured to the free end of the pins
forming the rows. Preferably the adjacent rows of pins are
staggered relative to one another in order to minimize any
tendency to plug.
In order to obtain a low deflection and high stiffness
in the mounting of the foils, a requirement which is
especially important for ceramic foils, it is usual to
thicken the foil mounting plates. In known arrangements
this increases the depth of the channel between adjacent
foils and increases the tendency to plug. By securing the
foils to planks using pins the foil mounting plate thickness
may be reduced without sacrificing the desired low deflection
and high stiffness and thereby the tendency to plug is
reduced.
The foil strips define an active surface which in use is
in contact with the top forming wire in the case of an
inverted suction box or the bottom wire in the case of a con-
ventionally orientated suction box. The active surface
defined by the rows of foil strips may be straight or curved.
The foil strips extend in a direction which is transverse
with respect to the direction of movement of the fibrous
suspension through the apparatus. Where the active surface is
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curved, this may be conveniently achieved by arranging
for the plank members to be inclined relative to one
another. The pins preferably project perpendicularly
from the plank member. Slots are formed between
adjacent foil strips and the width of the slots may
be varied easily using different width of foil strips.
- By virtue of the aforementioned construction, a
complete plank member can be easily withdrawn and
replaced by another when a different cover design is
required, i.e. a cover having, for example, foil
strips of different shape or spacing or when changing
foil material from plastic or ceramic. The flexibility
afforded by this arrangement renders the water removal
to be tuned more easily to the requirements of a
particular grade of paper. Furthermore, the change-
over is less time consuming because the invention
renders it unnecessary to remove the suction box to
change the cover design.
A channel is defined between the plank members
and the foil strips, through which channel the water
passes after removal from the fibrous suspension.
The small pins only cause minimal obstruction to the
fly of water there through, and it is easy to keep
clean. The shallow depth of the channel ensures high
water velocities without being too small to be cleaned
properly. The arrangement avoids problems with
plugging of the open slots in known designs.
In order to increase water speeds in the area
above the foil mounting, compressed air may be intro-
duped at low pressure, above the planks and distributed
uniformly to the space between the planks and foil
mountings by way of drilling in the planks. The
introduction of compressed air in conjunction with a
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whir which is adjustable controls the flow of a thin layer
of water above the foil mounting. This water flows at high
speed over the foil mounting and thereby contributes to a
reduction in plugging by preventing the fires from
S depositing over the box intervals.
The present invention will now be described further by
way of example only, with reference to the accompanying
drawings, in which:-
Figure 1 is a sectional view of one embodiment of
apparatus according to the invention,
Figure 2 is a sectional view of a second embodiment of
apparatus according to the invention,
Figure 3 is a fragmentary detailed sectional view of
one possible mounting arrangement, and
Figure 4 is a sectional plan view taken along line
IV-IV of Figure 1 showing spacing of the mounting pins
securing the foils to a plank member.
referring to Figure 1, there is shown a section through
part of a de-watering apparatus in accordance with the
present invention. The drawing illustrates part of a
housing 1 of an inverted suction box 5 and the cover 3
therefore The suction box 5 is, in use, mounted above the
traveling top forming wire of a paper forming machine (not
indicated in the drawing). The suction box serves to remove
water from a layer or web of fibrous suspension disposed
between top and bottom forming wires. A plurality of foil
strips 7 define an active surface which, in use, is in
contact with the top forming wire.
The housing 1 of the suction box 5 has a base 9 to which
mounting blocks 11 are secured. These mounting blocks serve
to support plank members 13 which are releasable secured
thereto by bolts 15. In the illustrated embodiment four
plank members aye, 13b, 13c and 13d are provided. Each
plank member 13 carries a number of the foil strips 7 which
are secured to the plank member 13 by way of a plurality of
spaced apart pins 17. The foil strips 7 are elongate
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members which extend in a direction transverse to the
direction of movement of the fibrous web through the
machine. The pins 17 are disposed in parallel rows and
project perpendicularly from the plane of the plank member
to which they are connected. The pins in adjacent rows are
preferably staggered in order to facilitate water flow. The
left hand plank member 13 of Figure 1 carries four such rows
of pins and each row carries a respective foil strip 7.
Similarly the plank member second from left in Figure 1
carries four rows of pins and a foil strip 7 secured to
each row. Each foil strip 7 is secured to a row of pins by
way of an elongated mounting bar 19 which supports the
foils strip. The elongate mounting bar is fastened to the
free end of each of the pins in the row. The elongate bar
may be extruded T-section stainless steel.
Preferably the pins are welded to the plank member.
The construction using planks with a number of foils secured
to each reduces the amount of machining. The mounting
blocks 11 are machined at the appropriate angle required
for each plank. Thus, the number of angles to be machined
is reduced by four in the case where the plank carries four
foils. The guides for receiving the foils are machined
parallel to the plank mounting machine, thus further
reducing the machining time. The foils may be machined
flat, i.e. parallel to the plank mounting faces or, to
obtain higher accuracy of application, half the foil may be
machined at a small angle.
Figure 3 shows a detail of a preferred mounting arrange-
mint, from which it will be seen that the mounting block 11
is welded to the base of the suction box 9. The transverse
edges of the plank members aye, 13b are machined to
compliment the machining on the mounting block 11 to arrive
at the desired angle for the plank members aye, 13b and
hence the foils 7 carried thereby. Washers 14 and bolts 15
are employed to secure the plank members to the mounting
blocks. As illustrated the pins 17 carry at their free
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ends an elongate strip member 18 to which the mounting bar
19 is secured by set screws 20.
Referring to Figure 4, this illustrates the spacing of
the mounting pins 17 which secure the foil strips 7 to the
plank members 13. Only part of the foil strip length is
illustrated commencing from one end and extending in the
cross machine direction transverse to the direction of move-
mint of the fibrous web through the machine, but the view
illustrates how the pins 17 are spaced along the length of
the toil 7 and are staggered transversely relative to
adjacent foils. For the majority of the length of the foil,
the pin spacing is regular as shown by the spacing between
pins aye, 17b; 17c, 17d; 17g, eye, 17f; 17h, 17i; of
adjacent foils.
The plank member 13 disposed on the right of Figure 1
carries four rows of pins 17 but only two foil strips 7.
These foil strips are wider than the strips shown on the
left of the drawing and each of these wider strips is
secured to the plank member by two rows of pins 17. As in
the case of the plank members shown on the left, each row
of pins carries an elongate mounting bar 19.
The plank member second from the right carries two foil
strips. One of these is supported on two rows of pins 17,
in the same manner as illustrated for the right hand plank
member, whilst the second of these strips 21 is secured to
the plank member by way of a bracket 23.
A leading foil strip 25 is carried by a bracket 27,
which is releasable secured to the suction box housing and
a trailing foil strip is similarly carried by a bracket 29
which is releasable secured to the suction box housing.
When designing items 25, 21 and 28, care is taken to avoid
any areas that could create any dead flow areas in order to
avoid fire deposits and plugging. A channel 31 is defined
between the plank members aye, 13b and the foils strips 7,
and a channel 33 is defined between the plank members 13c,
13d and the foil strips 7.
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The foil strips 7 are spaced apart to define
transversely directed slots 35.therebetween. Water
passes through these slots and the channels 31,33 and
is removed by way of respective passages 37 and 39.
A whir 41 may be introduced between the channel
31 and the passage 37 and between the channel 33 and
passage 39. Where a whir is incorporated, air pressure
can be introduced through the cavity 45 formed between
the bottom wall of the suction box housing and the
plank members 13.
The introduction of air serves to increase the
water speed. Compressed air is fed at low pressure
into the cavity 45 and distributed to the channel 31
by lines of drilling I By way of example these
are only illustrated on plank 13b but the other planks
may also be provided with corresponding drilling.
The drilling are arranged so that uniform air disk -
tribution is achieved. The whir 41 is preferably
made adjustable and is positioned in such a way that
only a thin layer of water flows above the foil
mounting while air s filling the space above it. This
prevents air from escaping. The thin high speed layer
of water rushing over the foil mounting contributes to
--a reduction in plugging by preventing the fires from
depositing over the box intervals.
The width of the slots may be varied by changing
the shape of the foil strips. Where the active surface
is required to be substantially horizontal the plank
members are preferably mounted in a horizontal position.
It is envisaged that the adjacent rows Go pins
may be of different lengths in order to achieve the
desired curvature of the active surface. Preferably
the pins would be of the same length in order to
standardize planks for interchangeability.
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The embodiment of Figure 2 is essentially the
same as that described with reference to Figure 1, and
corresponding reference reimburse have been used to
denote like parts.
$ In the embodiment, each of the foil strips 7
is supported by a respective row of pins 17. The shape
of the foils 7 is different in this embodiment. Four
plank members 13 are shown to the left of the passage
37 and two to the left of the passage 39.
The foils 7 may be either plastics or ceramic.
Preferably the parts of Figure 1 are a plastics
material such as HOP and the parts of Figure 2 are
a ceramic material.
The embodiments described above have the
advantages that there are no bridging pieces along
the length of the slots 35 and the material on the
sides of each slot can be kept to a minimum. In the
case of ceramic covers the need for holding bolts in
the slots is avoided. The T-bar mounting and pins
can be easily electropolished individually and, when
using ceramics, the foil surface can be glazed to
promote cleanliness. Plastic foil strips can be
machined on planers to a high surface finish on the
side of the slots, whereas the present machining
process by milling of slots in plastic covers does not
lend itself to good surface finish.
The provision of the planks carrying the foils
enables plastics foils to be replaced with ceramic
foils and vice-versa without changing the suction box
design. Naturally, the open area of the active
surface can be changed easily by employing foils of
different widths. Furthermore, part of the cover
mounting can be changed without having to change the
complete cover.
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The invention reduces the number of spaces
required since only four strips and their mounting-or
only individual strips need to be kept on hand, instead
of a complete cover. The invention enables the suction
box to be designed and manufactured without comprom-
icing any future need for a different cover configure
anion. The amount of machining of the suction box is
minimized. The use of individual foil strips consider-
ably reduces the cost of ceramic and plastic covers.
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