Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to an extended nip press section
apparatus for pressing water from a formed web. More particularly, the
present invention relates to an extended nip press section apparatus for
inhibiting two-sidedness of the resultant pressed web.
In recent years, press sections for papermaking machines have
become relatively complex. For example, some press sections include four
or five press nips in order to maximize the dryness of the out-going pressed
web and to minimize two-sidedness of the resultant sheet.
Two-sidedness is a problem which basically comes about as a result
of water flowing more in one direction than another away from the web
during passage of the web through a press nip. At least in theory, if the
web is supported between two identical press felts and is guided between
a pair of identical counter-rotating press rolls, the resultant web will have
minimal two-sidedness. That is, both sides of the resultant web will have
substantially the same surface characteristics thereon.
However, in practice, a pair of identical counter-rotating press rolls
does not achieve maximum water removal, and it is very important to
provide a press which removes as much water as possible in order to
minimize the amount of steam required in a subsequent web drying section.
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Consequently, the aforementioned very large multiple nip presses
have been built that require considerable maintenance due to the size
thereof and the number of felts that require periodic changing.
In press sections of the aforementioned type, release rolls associated
with such presses are often fabricated from granite.
Moreover, with the ever-increasing demand for higher production
rates, such massive granite rolls must of necessity be rotated at a higher
rotational speed. Accordingly, several fatalities have resulted from such
granite rolls breaking apart under the aforementioned conditions.
Additionally, by pressing the web against the smooth surface of a
granite or substitute granite release roll, the sheet attains a smooth surface
on the roll side and a relatively rough surface on the felt side.
Such two-sidedness has typically necessitated the provision of an
additional nip with the release roll on the oppasite side of the sheet in an
attempt to correct the two-sidedness problem.
The aforementioned presses also typically include suction rolls which
are expensive to maintain and which limit the potential loading capabilities
of the nip and can cause shadow marking in the sheet.
Therefore, there is a need in the papermaking art for a simple, single
nip press section which overcomes the aforementioned problems
associated with prior art arrangements.
Therefore, it is a primary objective of the present invention to provide
an extended nip press section apparatus that overcomes the
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aforementioned inadequacies of the prior art arrangements and which
makes a considerable contribution to the art of pressing a web of paper to
remove water therefrom.
Another object of the present invention is the provision of an
extended nip press section apparatus which includes a press felt having a
water permeability which is less than the water permeability of the pick-up
felt so that the web predictably follows the press felt rather than the pick-
up felt and which inhibits two-sidedness in the resultant pressed web.
Another object of the present invention is the provision of an
extended nip press section apparatus which is extremely compact and
which avoids the problem of rewetting the web.
Other objects and advantages of the present invention will be readily
apparent to those skilled in the art by a consideration of the detailed
description contained hereinafter, taken in conjunction with the annexed
drawings.
Summary Of The Invention
The present invention relates to an extended nip press section
apparatus for pressing water from a formed web. The apparatus includes
an elongate press shoe and a vented backing roll which cooperates with the
shoe for defining therebetween an extended nip for the passage
therethrough of the web.
A bearing blanket slidingly cooperates with the shoe and extends
through the extended nip with the blanket being disposed between the web
and the shoe.
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A pick-up felt extends through the extended nip for conveying the
web to and through the extended nip.
A press felt extends through the extended nip such that the web is
disposed between the press felt and the pick-up felt during movement
thereof through the extended nip. The press felt has a water permeability
which is less than that of the pick-up felt such that the web predictably
follows the press felt rather than the pick-up felt when the pick-up felt
diverges relative to the press felt downstream relative to the extended nip.
The arrangement is such that two-sidedness of the resultant pressed web
is inhibited.
In one embodiment of the present invention, the elongate press shoe
is hydrodynamic shoe, and in another embodiment of the present invention,
the press shoe is a hydrostatic shoe.
In both embodiments of the present invention, the press shoe is
disposed beneath the vented backing roll.
The vented backing roll has a cylindrical circumferential surface
which defines a plurality of blind drilled holes according to one embodiment
of the present invention.
In another embodiment of the present invention, the cylindrical
circumferential surface of the backing roll defines a plurality of
circumferential grooves.
The press section apparatus also includes a saveall which cooperates
with the vented backing roll for collecting water removed from the web
during movement of the web through the extended nip.
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Additionally, the bearing blanket defines a plurality of grooves on a
surface thereof which faces towards the press felt for assisting drainage
from the extended nip.
The press section apparatus includes a steam box which is disposed
on one side of the pick-up felt for applying steam to the web supported
beneath the pick-up felt upstream relative to the press felt.
Additionally, a vacuum box is disposed on an opposite side of the
web and pick-up felt relative to the steam box. The vacuum box is
connected to a source of partial vacuum such that the steam from the
steam box is drawn into the web. The arrangement is such that the
viscosity of the water within the web is decreased by the application
thereto of the steam so that the subsequent removal of the water from the
web during passage thereof through the extended nip is facilitated.
The press felt in a specific embodiment of the present invention
includes a base fabric and a permeability control layer which is disposed
contiguously on one side of the base fabric.
Additionally, a layer of batt fibers is disposed contiguously relative to
the permeability control layer such that the permeability control layer is
disposed between the layer of batt fibers and the base fabric for inhibiting
rewetting of the web downstream relative to the extended nip and for
predictably assisting the web to follow the press felt rather than the pick-
up felt downstream relative to the extended nip.
In a preferred embodiment of the present invention as shown in Fig.
12, the press section is inverted such that the pick-up felt is disposed
between the shoe and the web.
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Furthermore, the press felt extends through the extended nip with
the press felt being disposed between the backing roll and the web so that
the web is disposed between the pick-up felt and the press felt.
The backing roll can be either a plane roll or a vented roll and the
bearing blanket can be a plane blanket or a grooved blanket or alternatively
a blanket with blind drilled drainage holes defined therein.
Many modifications and variations of the present invention will be
readily apparent to those skilled in the art by a consideration of the
detailed
description contained hereinafter, taken in conjunction with the annexed
drawings. However, such modifications and variations fall within the spirit
and scope of the present invention as defined by the appended claims.
Figure 1 is a side-elevational view of an extended nip press section
apparatus according to the present invention for pressing water from a
formed web;
Figure 2 is an enlarged view of the extended nip showing the press
shoe as a hydrodynamic shoe;
Figure 3 is a similar view to that shown in Figure 2, but shows an
alternative embodiment of the present invention in which the press shoe is
a hydrostatic shoe;
Figure 4 is a perspective view of the vented backing roll showing the
surface thereof defining a plurality of blind drilled holes;
Figure 5 is a similar view to that shown in Figure 4, but shows an
alternative embodiment of the present invention in which the surface of the
backing roll defines a plurality of circumferential grooves;
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Figure 6 is a top plan view of a portion of the bearing blanket shown
in Figure 1 showing a plain surface thereon;
Figure 7 is a similar view to that shown in Figure 6, but shows the
surface of the bearing blanket towards the press felt defining a plurality of
grooves for assisting drainage of water from the extended nip;
Figure 8 is an enlarged sectional view of the press felt showing the
base fabric, control layer and the layer of batt fibers;
Figure 9 is a graph showing a pressure profile obtained using the
apparatus according to the present invention;
Figure 10 is a graph showing another pressure profile achieved using
the apparatus according to the present invention;
Figure 11 is a graph showing yet ~ another pressure profile obtained
using the apparatus according to the present invention.
Figure 12 is a side elevational view of a preferred embodiment of the
present invention; and
Figure 13 is a side elevational view of an alternative embodiment of
the arrangement shown in Figure 12.
Similar reference characters refer to similar parts throughout the
various embodiments of the present invention.
Figure 1 is a side-elevational view of an extended nip press section
apparatus, generally designated 10 according to the present invention, for
pressing water, as indicated by the arrow 12, from a formed web W. The
press section apparatus 10 includes an elongate press shoe 14 and a
vented backing roll 16 which cooperates with the shoe 14 for defining
therebetween an extended nip 18 for the passage therethrough of the web
W.
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A bearing blanket 20 slidably cooperates with the shoe 14 and
extends through the extended nip 18. The blanket 20 is disposed between
the web W and the shoe 14.
A pick-up felt 22 extends through the extended nip 18 for conveying
the web W to and through the extended nip 18. The pick-up felt 22 is
disposed between the backing roll 16 and the web W such that the web W
is conveyed between the pick-up felt 22 and the blanket 20 during
movement thereof through the extended nip 18.
A press felt 24 extends through the extended nip 18 and is disposed
between the blanket 20 and the web W such that the web W is disposed
between the press felt 24 and the pick-up felt 22 during movement of the
web W through the extended nip 18. The press felt 24 has a water
permeability which is less than the water permeability of the pick-up felt
22. The arrangement is such that the web W predictably follows the press
felt 24 rather than the pick-up felt 22 when the pick-up felt 22 diverges
relative to the press felt 24 downstream relative to the extended nip 18.
The arrangement is such that two-sidedness of the resultant pressed web
W is inhibited.
Figure 2 is an enlarged side-elevational view of the elongate press
shoe 14 showing the press shoe 14 as a hydrodynamic shoe.
Figure 3 is a similar view to that shown in Figure 2, but shows the
press shoe 14A as a hydrostatic shoe.
As shown in Figure 1, the press shoe 14 is disposed beneath the
vented backing roll 16.
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Figure 4 is a perspective view of the vented backing roll 16 shown in
Figure 1. As shown in Figure 4, the backing roll 18 has a cylindrical
circumferential surface 26 which defines a plurality of blind drilled holes
28, 29 and 30.
Figure 5 is a similar view to that shown in Figure 4, but shows the
vented backing roll 16B as having a cylindrical circumferential surface 26B
which defines a plurality of circumferential grooves 28B, 29B and 30B.
In the preferred embodiment of the present invention as shown in
Figure 7 , the apparatus 10 includes a saveall 32 which cooperates with the
vented backing roll 16 for collecting water 12 removed from the web W
during movement of the web W through the extended nip 18.
Figure 6 is an enlarged top plan view of the bearing blanket 20
showing the surface thereof as being a plain surface.
Figure 7 is a similar view to that shown in Figure 6, but shows an
alternative embodiment of the present invention in which the bearing
blanket 20C defines a plurality of grooves 34,35 and 36 on a surface
thereof facing towards the press felt 24 for assisting drainage from the
extended nip 18.
As shown in Figure 1, the apparatus 10 also includes a steam box
38 which is disposed on one side 40 of the pick-up felt 22 for applying
steam to the web W supported beneath the pick-up felt 22 upstream
relative to the press felt 24.
A vacuum box 42 is disposed on an opposite side 44 of the web W
and pick-up felt 22 relative to the steam box 38. The vacuum box 42 is
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connected to a source of partial vacuum 46 such that steam from the
steam box 38 is drawn into the web W. The arrangement is such that the
viscosity of water within the web W is decreased by the application thereto
of the steam so that the subsequent removal of the water from the web W
during passage thereof through the extended nip 18 is facilitated.
Figure 8 is an enlarged sectional view of the press felt 24 which
includes a base fabric 48 and a permeability control layer 50 disposed
contiguously on one side 52 of the base fabric 48.
A layer of batt fibers 54 are disposed contiguously relative to the
permeability control layer 50 such that the permeability control layer 50 is
disposed between the layer of batt fibers 54 and the base fabric 48 for
inhibiting rewetting of the web W downstream relative to the extended nip
18 and for predictably assisting the web W to follow the press felt 24
rather than the pick-up felt 22 downstream relative to the extended nip 18.
Figures 9, 10 and 11 are graphs showing various pressure profiles
56,58 and 60, respectively, obtained using the equipment according to the
present invention.
In operation of the apparatus 10 shown in Figure 1, the web is
transferred to the pick-up felt 22 such that the web is disposed beneath the
pick-up felt 22.
Steam is applied through the web and is drawn into the web by the
vacuum box 42.
The web sandwiched between the pick-up felt 22 and the press felt
24 is guided towards the extended nip 18 where water is removed
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therefrom into the saveall 32, which cooperates with the vented backing
roll 16 for collecting water 12 removed from the web.
Because of the permeability control layer 50 within the press felt 24,
the web predictably follows the press felt 24 rather than the pick-up felt
22. Thereafter, the web is transferred from the press felt 24 into the
downstream dryer section, generally designated 62.
In a preferred embodiment of the present invention as shown in Fig.
12, the press section is inverted such that the pick-up felt 22d is disposed
between the shoe 14d and the web Wd.
Furthermore, the press felt 24d extends through the extended nip
18d with the press felt 24d being disposed between the backing roll 16d
and the web Wd so that the web is disposed between the pick-up felt 22d
and the press felt 24d.
The backing roll 16d can be either a plane roll as shown in Fig. 12 or
a vented roll 16e as shown in Fig. 13. Also, the bearing blanket 20d can
be a plane blanket or a grooved blanket or alternatively a blanket with blind
drilled drainage holes defined therein.
The present invention provides a double felted extended nip press,
which is particularly capable of pressing a news or fine paper sheet as dry
as any of the traditional multi-nip press sections.
