Note: Descriptions are shown in the official language in which they were submitted.
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FABRIC SUPPORT ELEMENT FOR A PAPERMAKING MACHINE
Fi~7L~ ~~ tl~~ Iaaveaat~~a~
This invention concerns a fabric support element for
use in a papermaking machine, a segrn.ent for use in th.e
element, a method of making the element and a papermal~ing
machine, or a forming section thereof, in which it is used.
8~,~~v~~~~a~a~, ~~ t~~ g~a~~aa,t~,~a~a
In the initial portion of the forming section of a
papermaking machine, an unsupported jet of highly aqueous
stock is ejected from the head box slice onto the surface
of a moving forming fabric. The unsupported jet will
typically traverse a distance of from about 6 cm to about
40 cm before impinging the surface of the forming fabric
at the point of impingement. The angle of impingement, a,
formed between the stock jet and the plane of the forming
fabric at the point of impingement has typically been from
about 4° to about 10° . It is well known that improved paper
formation can be obtained by minimizing both the angle of
and the length of the unsupported free jet. As the angle
a increases, the magnitude of the pressure exerted by the
jet on the surface of the forming fabric also increases.
Impingement angles greater than about 5° have
generally been found to create peak impingement pressures
that may cause sheet marking, low retention of papermaking
fines and fillers, and plugging of the forming fabric.
Therefore, the angle oc should be made as small as possible
so that, ideally, the unsupported stock jet impinges on the
fabric substantially tangentially.
As the unsupported length of the free stock jet
increases, its outside surface begins to break up into
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ridges and furrows, which will eventually cause sheet basis
weight variations. Further, finely dispersed fibers in the
stock start to reflocculate rapidly in the unsupported jet
prior to the point of impingement. Therefore, the
unsupported stocJ~ jet should be made as short ~.s possible
to minimize these effects.
Due to the competing space requirements of both the
head box slice lip structure and the adjacent upstream
rolls such as a breast roll or forming roll, it is
difficult to shorten the unsupported stock jet length
wi thout increas ing the angl a a . Even i f the head box s 1 ice
lips can be located so that the angle a is very small, and
the free jet is nearly tangential to the forming fabric,
air that is trapped in the small wedge shaped space between
the surface of the forming fabric and the surface of the
unsupported stock jet becomes entrained into the stock,
forming bubbles which are detrimental to sheet formation.
Several proposals have been made to overcome these
difficulties . Nelson et al, US 3, 440, 136 discloses a method
of avoiding air entrainment by evacuating the air from the
forming zone, and flooding this area with water. However
this proposal has been found to be difficult to realize in
practice. Irwin et al., US 4,734,164, disclose a forming
board for a single fabric machine in which the first blade
is slightly curved to permit the breast roll to be lowered
slightly. The difficulty with this proposal is that air is
trapped in the shallow wedge space between the jet and the
forming fabric as it passes over the unvented, solid
surface of the curved first blade. This air is forced into
the stock as bubbles which cause formation' defects.
l~alashenko, US 4, X02, 954, discloses a lead-in blade located
ahead of the curved blade element proposed by Irwin et al . ,
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which is said to reduce the amount of fluid pumped by the
forming fabric into the wedge shaped space between the jet
and the fabric. However, a small wedge shaped air space
remains. The pressure in this space is controlled by a
S vacuum pump t~ reduce the jet disturbance. Fwald in US
5,08~.,138 addresses the problem of excessive free jet
length by using curved turning bars to replace large
diameter breast rolls and a solid curved blade, but does
not avoid air entrapment at the wedge between the jet and
the fabric.
Fujiwara in US 4,425,188 uses longitudinal spaced
grooves in a twin wire forming shoe to generate cross-
directional flows to realign the fibers in the incipient
web so as to reduce machine direction fiber alignment.
Wildfong et al., in US 6,372,091, addresses the improved
removal of water by the use of grooves in the face of a
forming shoe.
However, although it is known that grooving the
forming shoe, also known as an impingement shoe, may
provide quality improvements in the resulting paper, it has
been found that there are problems associated with the use
of such grooves. Firstly, the grooves have been found to
fill quickly with stock and thus substantially lose their
advantageous effect, because there is no positive means to
remove quickly the drained fluid from the fabric contact
surface. Secondly, it has been found that the grooves may
create a foiling effect between the machine side of the
fabric and the groove interior, creating a level of suction
sufficient to cause a deterioration in paper quality.
Thirdly, it is difficult, time consuming and thus costly
to create precisely dimensioned grooves in the typical
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ceramic surfaces of these blades, and the integrity of the
ceramic can be compromised by the machining process.
The following terms have the meanings indicated below.
~ther terms used herein have the me~.nings normally
associated with them in the papermaking industry.
Cross-machine direction (CD) is a direction essentially
within the plane of the paper sheet and substantially
perpendicular to the machine direction (MD).
Downstream is a direction in the papermaking machine
essentially facing towards the reel where the finished
paper product exits the machine.
Fabric support element is any stationary element in a
papermaking machine over which at least one of the
papermaking machine fabrics passes in sliding contact,
including, but not limited to, shoes, blades, foils and
agitators in the forming section, and Uhle box covers in
the press section.
Laminar segments are relatively thin components, having a
thickness ranging from about 1mm (0.04 inch) or less to
about 254 mm (1 inch) or more which may be assembled in a
side-by-side relation in order to build up a fabric support
element of a desired width. Laminar segments are typically
formed of ceramic or other abrasion resistant materials.
Machine direction (MD) is a direction in the papermaking
machine substantially parallel to the ovel:all direction of
travel of a paper sheet.
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Machine side (MS) surface is the side of a fabric or fabric
support element which is opposite to the paper side surface
and is not in contact with the paper sheet.
5 Paper side (PS) surface is the side of a fabric or fabric
support element which is either in contact with, or facing,
the paper sheet being made on and conveyed through the
papermaking machine.
Upstream is a direction in the papermaking machine which
is essentially facing towards the headbox.
Vented describes the presence of open passageways~which
pass from the paper side surface through to the machine
side surface of a support element, i . e. from the fabric
contacting side through to the opposite side, the
passageways being referred to herein as flow-through vents.
It has now been found. that some of these
aforementioned difficulties can be completely or
substantially eliminated by the use of vents, which pass
completely through the impingement shoe and thus enable the
effective removal of sufficient fluid so as to prevent
filling of the grooves. These flow-though vents are open
from the paper side surface through to the machine side
surface of the impingement shoe, and enable the removal of
a greater amount of fluid, together with air which would
otherwise be entrapped between the forming fabric and the
stock jet, from the zone of initial impingement on the
impingement shoe than has previously been possible with
grooved surfaces such as defined by Wildfong et al. in US
6,37,091.
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It has further been found that these flow-through
vents allow for significant variations to both the angle
of impingement of the stock jet and the resultant position
of the point ~f impingement, without any appreciable
adverse effect on the resultant paper quality. This result
is very surprising since, previously, variations in the
angle of impingement of the stock jet lay as little as one-
half of one degree from an optimum value could produce
significant deleterious effects on sheet quality with
respect to sheet marling, retention and formation. The
present invention thus allows a broader range in the angle
of impingement of the stock jet than has previously been
practicable.
It has also been found that these flow-through vents
can be provided most advantageously by constructing the
impingement shoe from a plurality of relatively thin
laminar segments which are mounted together on a suitable
retaining means in the papermaking machine so as to be
essentially parallel to and in contact with one another and
oriented at a substantially constant angle to the machine
direction (NID). These laminar segments are preferably
shaped from a suitable material, such as a ceramic, so as
to have a machine side surface which is adapted to be
mounted on a retaining means, a paper side surface which
in use faces the forming fabric, an upstream surface (or
leading edge) and a downstream surface (or trailing
edge)and substantially parallel lateral mating surfaces
facing the cross-machine direction (CD) in use. The PS
surfaces of at least a first set of the segments together
define a fabric contact surface of the impingement shoe
which is intended to support the forming fabric. The
surface may have any desired profile which would be
suitable for the prevailing paper makl.ng requirements. t~
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second set of segments, whose PS surface profile may be
different from that of the first set, may be located at
suitable intervals in the CD between pairs of first
segments . Preferably, the second set of segments are shaped
so as to form ol2enings in the fabric contact surface of the
element and enable the definition of vents which will be
open from the Ps surface through the IBS surface.
Alternatively, spacing means can be integrally constructed
on one or both of the lateral CD surfaces of the first set
of segments only, in which case the impingement shoe will
generally be comprised of only such first segments. It has
been found that the spacing means, either integrally
constructed with the first set of segments, or comprising
second segments, can have a suitable configuration to
optimize the removal of fluid and entrapped air from the
stock jet.
It has also been determined that it is possible to
assemble a segmented fabric support element intended for
use in any section of a papermaking machine using a
plurality of at least first and second laminar segments
that are shaped so as to be mounted on a suitable retaining
means and located as required in any of the forming
section, press or dryer sections of a papermaking machine.
These first and second laminar segments are mounted on
known retaining means so as to be essentially parallel to
and in contact with one another and are oriented
substantially in the MD or at a constant angle thereto. The
construction and configuration of the segments are
substantially as described above in relation to an
impingement shoe, with the PS surfaces of at least the
first segments together defining a fabric contact surface
which is intended. to support a papermaking fabric. The PS
surfaces of at least the first and secolld segments are
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shaped so as to provide the PS surface of the element with
any desired profile when assembled which would be suitable
for the prevailing paper making conditions . The second set
of segments can be located as either spacing or profiling
meaxl5 at suitable intervals in the CD kaetween selected
pairs of first segments to enable the definition of
openings, which may, but do not necessarily, include vents
which will be open from the PS surface though the MS
surface of the element. The PS surface of the second and
first segments can be shaped so as to provide the assembled
element with either or both a desired MD and CD profile.
Third or fourth segments, or more, can also be used in a
like manner in combination with the first and second
segments.
The present invention seeks to provide a vented
impingement shoe for use in a papermaking machine, having
a plurality of flow-through vents extending from a profiled
upper surface and through the lower surface of the
impingement shoe.
The present invention seeks to provide a segmented
fabric support element for use in the impingement zone of
the forming section of a high speed paper making machine,
which element is comprised of a plurality of laminar
segments. The PS surfaces of the segments are shaped so as
to contribute to the overall desired profile of the fabric
contacting surface or PS of the element, and vents through
the element, if desired, are defined by openings between
selected laminar segments.
Thus, an impingement shoe constructed according to the
invention performs four principal functions. Firstly, it
serves to support the formixzg fabric as it enters the
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impingement zone, and secondly it serves to vent at least
a substantial proportion of any air which becomes trapped
in the wedge shaped space between the surface of the
forming fabric and the surface of the stock jet. Thirdly,
it permits drained water to be removed efficientl~r- and
speedily, and fourthly it provides a previously
unattainable tolerance in the location of the point of
impingement and the angle of impingement.
Further, the present invention seeks to provide a
stationary fabric support element for a papermaking
machine, which element is comprised of a plurality of at
least first and second relatively thin laminar segments.
Further, the present invention seeks to provide
segments for use in an impingement shoe or other stationary
fabric support element, such that the PS surfaces of at
least some of the segments contribute to a profiled fabric
contact surface of the element, and vents through the
2o element can be defined by openings between at least some
of the segments . The segments are shaped so that the fabric
support element can be mounted in a releasably secure
manner in a suitable retaining means.
Still further, the invention seeks to provide a
forming section for a papermaking machine, which forming
section includes a segmented fabric support element
including flow-through vents as an impingement shoe.
3o Still further, the invention seeks to provide a method
of making such an element assembled from a plurality of
segmelltS .
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Summary of the Invention
Thus in a first broad embodiment the present invention
seeks to provide a vented segmented fabric support element
for use as an impingement shoe in the initial impingement
5 gone of the formixZg section of a papermaking machine.
The impingement shoe is comprised of a plurality of
laminar segments which are constructed and arranged on a
common support means so as to be releasak~ly secured in
10 substantially parallel, contacting relation to one another,
and so that the forming fabric mopes in sliding contact
over a common PS fabric contacting surface of the segments .
In one alternative construction of the impingement
shoe, the laminar segments are identical in shape and can
include spacing means, which may be, but are not
necessarily, constructed integrally therewith.
In a second alternative construction, the impingement
shoe is comprised of at least first and second laminar
segments wherein the first segments contribute to the PS
fabric contacting surface and the second segments do not,
but instead are located between any two segments or between
groups of two or more segments. The second segments are
shaped so as to form vents between two adjacent segments
and, if desired, additional openings on the PS surface of
the element; these vents are open from the PS surface
through to the MS surface of the impingement shoe and allow
for the passage of fluid and entrained air from the stock
jet through the forming fabric. Optionally, this renting
can be augmented by vacuum means connected to the underside
of the impingement shoe. t~d~antageously, the second
segments can be hydrodynamically shaped so as to assist
with the iemo~al of large volumes of fluid moving at
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relatively high speeds. The second segments generally
separate a portion of the first segments so as to form
openings on the fabric contacting surface of the
impingement shoe. These openings can be oriented at any
desired angle to the N~, by suitably shaping the laminar
segments. Preferably, these openings will be slot-shaped
and oriented at an angle of from about 2 to about 20
degrees to the MD. Both the vents and openings will be
oriented at the same angle to the MD by virtue of the
construction of the impingement shoe.
In a third alternative construction, third segments
are provided and located as required between selected first
and second segments, the PS surface of the third segments
having a suitable profile for the intended application.
The releasably secure mounting of the segments can be
effected by various known means, such as a T-slot or
dovetail mount. Alternatively or additionally, the segments
can be provided with openings through which a rod or cable
can be threaded, for example as disclosed in Lee et al.,
in US 3 , X71, 953 , for a plurality of identical segments . The
rod or cable can thus be secured by known means to suitable
end blocks located at the sides of the forming section.
Thus the invention seeks to provide a vented
impingement shoe, for use in a paperniaking machine, located
adjacent to a point of impingement of a stock jet ejected
from a head box slice onto a moving forming fabric, the
impingement shoe having
(i) a leading edge located upstream of the point of
1mp111gement ;
(ii) a trailing edge;
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(iii)a machine side surface adapted to be releasably
secured by a securing means to the papermaking machine; and
(iv) a paper side surface, having predetermined cross
machine direction and machine direction profiles adapted
to support the forming fabric in sliding contact;
wherein the paper side surface includes a plurality of
vents which begin substantially adjacent t~ the leading
edge and end substantially adjacent to the trailing edge,
and extend from the paper side surface and through the
l0 machine side surface of the impingement shoe.
Preferably, the profiled PS surface of the impingement
shoe, between the leading and trailing edges, is
essentially generally convex, but can be of any suitable
configuration for the particular circumstances. This can
include an essentially circular convexly curved surface,
with a constant radius, or a surface having a radius of
curvature which increases towards the trailing edge, so
that the shaped trailing edge portion may be essentially
flat. Ti~hen intended for use in other areas of the
papermaking machine, i.e. other than as an impingement
shoe, the PS surface can be flat, grooved or otherwise
profiled. Such choice will be dependent on the papermaking
conditions at the intended area of use.
In a second broad embodiment, the present invention
seeks to provide a forming section of a papermaking machine
having a machine direction and a cross-machine direction,
which includes:
at least one forming fabric which moves in the machine
direction;
a head box including a head box slice which provides a j et
of paper making stock which impinges at an angle of
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impingement onto a first forming fabric at a point of
impingement;
a roll, about which the first forming fabric passes, and
which is located upstream of the head box slice;
a forming section, located downstream of the point of
impingement, including static support elements which. define
a fabric path through which each forming fabric passes;
wherein at least one forming fabric is provided with a
vented impingement shoe, located adj scent to the respective
points at which. the stock contacts each forming fabric,
each impingement shoe having
(1) a. leading edge;
(ii) a trailing edge;
(iii)a machine side surface adapted to be releasably
secured by a securing means to the papermaking machine; and
(iv)a paper side surface, having predetermined cross
machine direction and machine direction profiles including
fabric contacting surfaces adapted to support the forming
fabric in sliding contact;
wherein the paper side surface includes a plurality of
vents which begin substantially adjacent to the leading
edge and end substantially adjacent to the trailing edge,
and extend from the paper side surface and through the
machine side surface of the impingement shoe.
In a papermaking machine having two forming fabrics,
it will generally be preferable for the two impingement
shoes to be the same, their profiled fabric-supporting
surfaces having the same shape. However, for particular
situations, the two impingement shoes, and their profiled
fabric-supporting surfaces, can be of different shapes.
In addition to use as an impingement shoe, the
segmented fabric support element can be adapted for use in
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various locations in a papermaking machine, including as
a dewatering blade or a Uhle box cover.
In a third broad embodiment, the present invention
seeks to provide a fabric support element, for use in a
papermaking machine, having
(i) a leading edge;
(ii) a trailing edge;
(iii)a machine side surface adapted to Iae releasably
secured by a securing means to the papermaking machine; and
(iv) a paper side surface having predetermined cross
machine direction and machine direction profiles including
fabric contacting surfaces adapted to support a
papermaker's fabric in sliding contact;
wherein
(a) the element comprises a plurality of at least first and
second laminar segments;
(b) the fabric contacting paper side surface profile of the
first laminar segments differs from the paper side surface
profile of the second laminar segments; and
(c) at least some of the first and second laminar segments
contribute to the predetermined profile of the fabric
contacting paper side surface of the element.
In a fourth broad embodiment, the present invention
seeks to provide a papermaking machine, having a machine
direction and a cross-machine direction, which includes:
a papermaking fabric moving in the machine direction;
a fabric support element having
(i) a leading edge;
(ii) a trailing edge;
(iii) a machine side surface adapted to be releasably
secured by a securing means to the papermaking machine; and
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(iv) a paper side surface, having predetermined cross-
machine direction and machine direction profiles including
fabric contacting surfaces adapted to support the
papermaking fabric in sliding contact;
5 wherein
(a ) the element comprises a plurality of at least first and
second laminar segments;
(b) the paper side surface profile of the first laminar
segments differs from the paper side surface profile of the
10 second laminar segments; and
(c) at least some of the first laminar segments contribute
to the predetermined profile of the fabric contacting paper
side surface of the element.
15 In a fifth broad embodiment, the present invention
seeks to provide a segment, a plurality of which can be
releasably secured to comprise a stationary fabric support
element for supporting a moving papermaker's fabric, such
that the PS surfaces of at least some of the segments
contribute in the I~ to a profiled PS surface of the
element, and flow-through vents through the element can
be defined by spaces between at least some of the segments
and can be further defined by spacing means, so as to
contribute to the CD and MD profile of the element.
When the fabric support element is used as an
impingement shoe, it has been found advantageous for the
leading edge of the flow-through vents to have a
substantially convexly curved shape, and for the trailing
edge of the vents to have a. corresponding substantially
concavely curved shape. These shapes have been found to
assist in the management of the large volumes of fluid
which are drained through the fabric in the impingement
~ollG .
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Further, it has been found that the construction of
an impingement shoe or other stationary fabric support
element from a plurality of segments enables the use of
hard and abrasion resistant materials, such as ceramics,
for complex shapes, without the problems associated with
grinding intricate shapes or large scale casting associated
with creating such shapes for a larger component.
In a sixth broad embodiment this invention seeks to
provide a method of making a stationary fabric support
element for supporting a moving papermalcer~s fabric in a
papermaking machine comprising the steps of
(i) assembling a plurality of laminar segments in a spaced
apart and substantially parallel configuration, thereby
defining openings between at least some adjacent pairs of
the segments, the paper side surfaces of at least some of
the segments defining a composite paper side surface with
which the moving fabric can make sliding contact;
(ii) releasably securing the segments so that they are
oriented substantially parallel, or at a small angle, to
the machine direction, by a securing means to a retaining
means on the papermaking machine.
The invention will now be described with reference to
the attached drawings in which:
Figure 1 shows part of an open surface papermaking
machine including a vented impingement shoe;
Figures 2 and 3 show parts of two different twin
fabric papermaking machines;
Figures ~., 5 and 6 respectively show a segment of
each of three different embodiments of the invention;
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Figure 7 show alternative arrangements for the use of
optional profiles for the laminar segments of the
invention;
Figure 8 is an isometric view of a vented stationary
support element i11 an embodiment of the invention;
Figure 9 is a plan view of an arrangement for the
segments in an embodiment of the invention.
In Figures 1 to 3, only the parts of the papermaking
machine required for an understanding of this invention
axe shown.
Figure 1 shows the initial impingement gone of a paper
making machine which includes a vented impingement shoe
according to the teachings of this invention. The slice
lips 1A and 1B of the head box 10 deliver a jet of stock
onto the PS surface 13 of the forming fabric 3 at the
impingement point I. The forming fabric 3 passes around
the roll 6, wraps the vented impingement shoe 5, and then
passes over the first static support element 4 in the
forming section. The impingement shoe 5 is provided with
flow-through vents 20 which form slot-like openings 22 in
its PS surface. The impingement shoe 5 can be assembled
from a plurality of relatively thin laminar segments and
releasably secured to a suitable mounting means (not shown)
on a drainage box (not shown). Alternatively, the
impingement shoe 5 can comprise a single unitary
construction including flow-through vents 20.
As the moving forming fabric 3 and the stock jet 2
converge and meet at an angle of impingement ex, air 8 in
the wedge shaped space between the lower surface 9 of the
stoclc jet 2, the lower surface 11 of the head box lip 1B,
and the PS surface 13 of the forming fabric 3 becomes
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trapped and enters the forming fabric 3. This air,
together with some of the liquid in the forming fabric at
this point, passes through the MS surface 23 of the forming
fabric 3 into the flow-through vents 20, through the PS
surface 16 of the impingement shoe 5, and the fluid,
including the entrapped air 8, is drained out through the
MS surface 18 of the vented impingement shoe 5. The various
configurations and functions of the flow-through vents 20
are described in greater detail below with reference to
l0 Figures 4, 5 and 6. The vents 20 form openings 22, which
can be slot-like as shown in Figure 1, on the PS surface
16 of the impingement shoe 5 beginning proximate the
leading edge 12 and ending proximate the trailing edge 14.
In this arrangement, as the roll 6 can be located away
from the path of the forming fabric 3, and as the vented
impingement shoe 5 occupies far less space than the roll
6, it is possible to maintain the angle of impingement a
close to zero, and to reduce the unsupported length of the
stock jet 2 significantly. Further, all or a substantial
proportion of any entrained air 8 passes speedily along
with the liquid which drains through the MS surface 18 of
the vented impingement shoe 5 by means of the flow-through
vents 20, and is thus prevented from interfering in the
formation process within the stock in the forming section.
As is discussed in more detail below with reference
to Figure 6, the depth of the openings 22 can also be
increased in the profiled PS surface 16 towards the
trailing edge 14 of the vented impingement shoe 5, to allow
for the removal of additional liquid and entrapped air.
Figures 2 and 3 show the initial impingement zone of
a paper malting machine which has two forming fabrics, and
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which incorporates two vented impingement shoes 51 and 52,
according to the teachings of this invention. In
describing these two Figures the terms "upper" and "lower"
refer only to the orientation shown, although in practice
in a twin fabric machine the forming section is often
oriented vertically, or at some angle thereto. The vented
impingement shoes 51 and 52 include flow-through vents 120
which form slot-like openings 122 in the PS surfaces.
Figure 2 shows the impingement gone of a twin fabric
machine in which the point of impingement I of the stock
j et 2 on the lower forming fabric 31 precedes the point of
contact J between the upper forming fabric 32 and the
incipient web being carried on the PS surface of the lower
forming fabric 31. The point of impingement I is situated
at a location where the lower surface 123 of the lower
forming fabric 31 is supported by vented impingement shoe
51. Similarly, the point of contact J is situated at a
location where the PS surface 124 of the upper forming
fabric 32 is supported by vented impingement shoe 52. As
the moving forming fabric 31 and the stock jet 2 converge,
air 81 in the wedge shaped space between the lower surface
91 of the stock jet 2, the lower surface 101 of the head
box lip 1B, and the PS surface 113 of the forming fabric
31 becomes trapped and enters the forming fabric 31. This
air 81, together with some of the liquid carried by the
forming fabric 31 at this point, passes through the MS
surface 123 of the forming fabric 31 into the vents 120 in
the lower vented impingement shoe 51, and out through the
MS surface 118. The construction as regards the lower
forming fabric 31 is thus essentially the same as Figure
1. Downstream of the impingement point I the upper forming
fabric 32 converges at a point of contact J with the upper
side 92 of the stock jet 2, now supported by the lower
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forming fabric 31. Further air is trapped in the space 82
between the PS surface 112 of the upper forming fabric 32
and the surface 92 of the stock 2. This additional air,
and some of the liquid in the forming fabric 32, passes
5 through the MS surface 12~- of the forming fabric 32 into
the flow-through vents 120 and is vented from the
impingement shoe 52 at the MS surface 119.
Figure 3 shows an alternative arrangement to that of
10 Figure 2. The arrangement of the lower forming fabric 31
is the same. The upper forming fabric 32 converges with
the stock jet 2 at the same point as the lower forming
fabric 31, substantially at the point of impingement I.
In relation to the upper forming fabric 32, air 82 is now
15 trapped in the space bounded by the upper surface 92 of the
stock jet, the PS surface 112 of the upper forming fabric
32, and the upper surface 102 of the head box lip 1A.
Substantially all of the trapped air 82, together with some
of the liquid in the two forming fabrics, is vented through
20 the flow-through vents 120 through the MS surface 118 of
the lower vented impingement shoe 51 and through the MS
surface 119 of the vented impingement shoe 52.
In both of these twin fabric machines, the two vented
impingement shoes will often be the same, and have the same
convexly curved shape. However in some circumstances it
may be desirable to use two different vented impingement
shoes, which may have different convexly curved shapes.
Alternatively, in other circumstances, a twin fabric
machine can be provided with a single impingement shoe.
The vented impingement shoes shown in each of Figures
1, 2 and 3 can comprise a single unitary construction, or
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21
a plurality of laminar segments mounted in substantially
parallel relationship, as described in more detail below.
Referring now to Figures 4, 5, and 6, three different
configurations of laminar segment 55, 65 and 75
respectively a1"e Sh~w11. These are suitable foe use in a
vented impingement shoe 5, or for other stationary fabric
support elements 80 (shown in Figures 8 and 9), as
previously described. Referring first to Figure 4, laminar
segment 55 has a leading edge 212, a trailing edge 214, a
profiled PS surface 216, and a MS surface 218. ~penings 220
are provided at suitable locations in the laminar segment
55, through which a fastening means such as a rod or cable
(not shown) can be passed to facilitate releasable securing
of a plurality of laminar segments 55 to form an
impingement shoe 5. Further mounting means for the laminar
segment 55 can be provided at its lower surface 218, such
as indentations 221.
The PS surfaces 216 of the laminar segments 55 support
the fabric and together provide the fabric supporting PS
surface 16 of the vented impingement shoe 5, as shown in
Figure 1. Similarly, the MS surfaces 218 of the laminar
segments 55 together contribute to the MS surface 18 of the
vented impingement shoe 5.
Between adjacent pairs of laminar segments 55,
secondary segments 56, 57 and 58 are provided. These serve
two purposes, firstly to provide spacing by urging apart
adjacent laminar segments 55, and secondly to define the
configuration of vents 20 from the PS surface 16 of the
vented impingement shoe 5 through to the MS surface 18.
The secondary segments 56, 57 and 58 can comprise separate
segments o1: alternatively all or some can be constructed
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22
integrally with the laminar segments 55. As shown in Figure
4, a vent leading edge 258 is defined by each of secondary
segments 56 and 57, and a vent trailing edge 259 is defined
by each of secondary segments 57 and 58. The vent leading
edges 258 can be of ~.ny suitable configuration, but
preferably are sloped, either regularly or irregularly in
the direction towards the IBS surface 218 to define an
obtuse angle ~ or e5 with the downstream portion of the MS
surface 218.
Referring to Figure 5, laminar segment 65 has
substantially the same configuration as laminar segment 55
shown in Figure 4. However, the secondary segments 265, 266
and 267 together define substantially curved vents 20, the
trailing edge 269 of the first vent 20, which is defined
by second segment 266 being substantially concavely curved,
and the leading edge 268 and the trailing edge 269 of the
second vent 20 being respectively substantially convexly
and concavely curved.
The PS surfaces 260 of the secondary segments 255, 256
and 257, or 265, 266 and 267 can have any suitable
configuration. They can contribute to the fabric supporting
PS surface 16 of the vented impingement shoe 5, for example
as shown in relation to secondary segments 255 and 257, and
265 and 267. Alternatively, as shown in Figure 6, the PS
surface 260 of secondary segments 276 and 277 do not extend
to the fabric supporting PS surface 16 of the vented
impingement shoe 5, and together define an opening 22,
which provides for additional drainage of liquid and
entrapped air 8 at the trailing edges 214 of each laminar
segment 75 which define the trailing edge 14 of the vented
impingement shoe 5.
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23
Additionally, as best understood with reference to
Figures 7A to 7D, third laminar segments can be provided,
their paper side surfaces contributing in part to the paper
side surface 16 of a stationary fabric support element, and
having a suitable configuration, such as a shallow 'V° so
as to impart all agltatlon effect into the stock 2 carried
on the forming fabric 3.
Referring to Figure 7A, stationary fabric support
element 180 comprises first and second laminar segments 85A
and 858. The first laminar segments 85A are each mounted
substantially parallel to one another at a preselected
small angle ~ to the Nm, and abut in an angled manner the
similarly parallel second laminar segments 85B at a
notional intersection line 181 in the CD. Between the first
and second laminar segments 85A and 85B, third and fourth
laminar segments 86A and 86B, each having a different PS
surface profile from first and second laminar segments 85A
and 85B, are mounted in like manner, being releasably
secured by mounting means (not shown) to a subassembly of
the element 180. End. blocks 182 and 183 are provided at the
lateral edges 241 and 251 of the element 180.
Referring to Figure 7B, three examples of alternative
constructions for the laminar segments of this embodiment
are shown, illustrating differences in the PS surface.
Thus, the PS surface profile of first laminar segment 185A
comprises a shallow "V", the PS surface of second laminar
segment 285A comprises a deeper "V", and the PS surface of
third laminar segment 385A is substantially flat.
Figure 7C shows a schematic plan view of the grouping
of laminar segments for element 180 sho~nm in Figure 7B. In
this version, laminar segments 385A are interspaced
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24
alternately with laminar segments 185A and 285A. However,
third laminar segments having any of the PS surface
profiles of laminar segments 185A, 285A, 385A or the like,
can be used in combination with. laminar segments of any of
the general configurations shovm in Figures 4, 5 or 6,
depending on the intended use of the element 180.
Figure 7D shows a stationary fabric support element
280, having an alternative construction in which. the
leading laminar segments 85A, 86A are mounted at an angle
~1 to the CD, whereas the trailing laminar segments 858,
868, which abut the leading segments at notional
intersection line 281 in the CD, are mounted at an angle
2~~ to the CD. End blocks 282 and 283 are provided at the
lateral edges 242 and 243 respectively. Although Figure 7D
shows the use of two sets of laminar segments, it will be
appreciated that laminar segments 86A and 86B can be
replaced by segments having a combination of different
configurations, depending on the intended use of the
element 280, for example in the manner shown in the
schematic view in Figure 7C.
Referring to Figure 8, a vented stationary fabric
support element 80, for use in any of various locations in
a papermaking machine, is shown in an isometric view. The
element 80 comprises a plurality of laminar segments 85,
which can be of any one of the configurations of laminar
segments 55, 65 and 75 shown in Figures 4, 5 and 6
respectively, or any other suitable configuration. Selected
laminar segments 85 are urged into a spaced apart
relationship by second, third and fourth secondary laminar
segments collectively identified as laminar segments 86,
which can comprise separate segments of the configurations
of secondary segments 56, 57 and 58 (Figure 4), or 265, 266
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and 267 (Figure 5) or 275, 276, 277 (Figure 6), or any
other suitable configuration. Alternatively, as shown, the
secondary segments 86 can be of any suitable configuration
and be constructed integrally with the laminar segments 85.
5 The laminar segments 85 and 86 are releasably secured by
a suitable mounting means such as rods 88 and T-slot 8~ to
a subassembly 87 (not shown in detail), which in turn is
secured to the preselected location on the paperma)cing
machine. The rods 88 pass through the openings 220 in the
l0 laminar segments 85, to be releasably secured adjacent to
the lateral edges 24, 25 of the element 80. A suitably
shaped end block, such as end blocks 182, 183 shown in
Figure 7A, or end blocks 282, 283 shown in Figure 7D, can
be located at each of the lateral edges 24, 25 of the
15 element 80 to facilitate secure placement of the laminar
segments 85 in the construction of the element 80.
As can best be seen in Figure 9, the laminar segments
85 are releasably secured in a substantially parallel
20 relationship to each other, substantially in the Nm, but
at an angle a thereto. This angle E is preferably in the
range of about 2 degrees to about 20 degrees.
In operation, a preselected number of laminar segments
25 of the desired configuration, such as laminar segments 85,
can be aligned to form a segmented fabric support element
80, and mounted as shown in Figures 8 and 9, to a
subassembly 87, which in turn is mounted by suitable means
(not shown) at the desired location on the papermaking
machine, to support the papermaker's fabric at that
location. The first laminar segments 85 can be separated
as required by second, third and fourth. laminar segments
such as 56, 57 and 58(Figure 4), or 265, 266 and 267
(Figure 5, or 275, 276 axed 277 (Figure 6), or by groups of
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26
other suitably shaped laminar segments. The number, shape
and placement of the second or additional laminar segments
will be dictated by the prevailing papermaking conditions.
The P~ surface profile of element 80 can thus be
shaped so as t~ create desired beneficial effects in the
stock or nascent web carried on the fabric. For example,
the PS surface can be slotted in the manner previously
described, or it can have a MD profile such as a shallow
l0 °°~", or it can be substantially flat. The PS shape of this
surface is dictated by suitable choice of the laminar
segments used to assemble the fabric support element 80.
Flow-through vents 120 can be, but are not necessarily,
provided.
The laminar segments 55, 65, 75 or 85 of the invention
are preferably made of abrasion resistant materials such
as ceramics, or high density polyethylene. If the second,
third and fourth laminar segments (56, 57 and 58 and the
equ.ivalent), which are not in contact with the papermaking
fabric, are not formed integrally with the laminar
segments, they can readily be made of different materials
from the laminar segments.
