Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
k ~ 2G2~8
7-37
/JFG:vn
A SPECIAL BELT FOR USE IN
EXTENDED NIP PRESSES ON PAPER MACHINES
Backqround of the Invention
Field of the Invention
The present invention relates to mechanisms for
extracting water from a web of material, and more particularly
from a fibrous web being processed into a paper product on a
papermaking machine. Specifically, the present invention is
an impermeable belt designed for use in conjunction with an
extended nip press on a papermaking machine.
Description of the Prior Art
During the papermaking process, a fibrous web is
formed on a forming wire by depositing a fibrous slurry
thereon. A large amount of water is drained from the slurry
during this process, after which the newly formed web proceeds
to a press section. The press section includes a series of
press nips, in which the fibrous web is subjected to
compressive forces designed to remove water therefrom. The
web finally proceeds to a drying section which includes heated
dryer drums around which the web is directed. The heated
dryer drums reduce the water content of the web to a desirable
level through evaporation.
Rislng energy costs have made it increasingly
desirable to remove as much water as possible from the web
prior to its entering the dryer section. The dryer drums are
often heated from within by steam and related costs can be
- substantial, especially when a large amount of water needs to
be removed from the web.
-I -
.
::--::-:: - -.-
2 ~ 8 .
Traditionally, press sections have included a series
of nips formed by pairs of adjacènt cylindrical press rollers.
Recently, the use of extended press nips has been found to be
advantageous over the use of nips formed by pairs of adjacent
rollers. The longer the web can be subjected to pressure in
the nip, the more water can be removed there, and,
consequently, the less will remain to be removed through
evaporation in the dryer section.
The present invention relates to extended nip presses
of the shoe type. In this variet~ of extended nip press, the
nip is formed between a cylindrical press roller and an
arcuate pressure shoe. The latter has a cylindrically concave
surface having a radius of curvature close to that of the
cylindrical press roller. When roller and shoe are bought
into close physical proximity, a nip is formed which can be
five to ten times longer in the machine direction than one
formed between two press rollers. This increases the so-
called dwell time of the fibrous web in the extended nip while
maintaining the same level of pressure per square inch
pressing force used in a two-roller press. The result of his
new ext~nded nip technology has been a dramatic increase in
dewatering of the fibrous web in the extended nip when
compared to conventional nips on paper machines.
An extended nip press of the shoe type requires a
special belt, such as that shown in Canadian Patent No.
1,188,556. This belt is designed to protect the press fabric
supporting, carrying, and dewatering the fibrous web from the
accelerated wear that would result from direct, sliding
contact over the stationary pressure shoe. Such a belt must
be made with a smooth impervious surface that rides, or slides,
over the stationary shoe on a lubricating film of oil. The
belt moves through the nip at roughly the same speed as the
;
~'
t- .
20~4g~8
press fabric thereby subjecting the press fabric to minimal
amounts of rubbing against stationary components.
The normal configuration for an extended nip press
involves the use of two press fabrics. The components in the
nip can be listed in the following sequence: a grooved
cylindrical press roller, a first press fabric, the fibrous web
or nascent paper, sheet, a second press fabric, the special
belt, the lubricating film, and the arcuate pressure shoe.
All of the extended nip presses currently in commercial
operation are of the above confi~uration. However, this so-
called double-felted extended nip press is limited to certain
types of paper grades. To expand the application of the
extended nip press to finer paper grades and newsprint, it will
be necessary to develop a single-felted extended nip press.
In a single-felted extended nip press, the components
in the nip would be listed in the following sequence: a smooth
cylindrical press roller, the fibrous web or nascent paper
sheet, the press fabric, the special belt, the lubricating
film, and the arcuate pressure shoe.
In the double-felted extended nip press, the water
pressed~from the fibrous web can pass into either of the two
press fabrics, as well as into the grooves provided in the
cylindrical press roller. In the single-felted extended nip
press, two of these sinks for water storage have been
eliminated. There is only one felt and, because the fibrous
web contacts the cylindrical press roller directly, this roller
must have a smooth surface. Clearly, this loss of temporary
water storage space must be replaced if a single-felted
extended nip press is ever to achieve widespread use. It is
absolutely mandatory that voids be provided in the nip of the
press, so that water pressed from the paper sheet in a single-
felted extended nip press will have a place to be stored.
: :,,,::~,: - :-
2a24~5~
~_. !
Two approaches have been taken to achieve a
satisfactory solution of this problem. Canadian Patent No.
1,190,779 shows an extended nip press belt having voids on the
felt side. These voids arise from the weave pattern of the
base fabric and the absence of impregnation on the felt side
of the belt, and provide a place into which liquid can be
transferred during passage of the fibrous web, press fabric,
and special belt through the nip.
The other approach is represented by U.S. Patents No.
4,5S9,258 and 4,643,916. These s~ow an extended nip press belt
having grooves on the felt side to store water pressed from the
fibrous web.
While these two approaches were directed primarily
toward achieving a solution-to the water-removal problem in a
single-felted extended nip press, it has been found that use
of either belt in a double-felted extended nip press leads to
enhanced dewatering.
In practice, however, it has also been found that
satisfactory grooved ENP belts cannot be produced for
commercial use. All attempts to make this structure to date
have re~sulted in a product which fails due to delamination of
grooves, and/or collapse of the grooves. The present invention
is a special belt for an extended nip press which would not be
susceptible to delamination.
~' .
Summary of the Invention
But for the problems noted above, the special extended
nip press belts having grooves cut into a polyurethane-coated
surface demonstrate good dewatering capabilities when used on
extended nip presses. The present invention is an extended nip
press belt which is not susceptible to these problems by reason
: I :
'~
- ~-"~ ,' :: ~
f~ ` 2024 85~
of its physical structure, and can be viewed as an improvement
of the belt shown in Canadian Patent No. l,190,779.
Accordingly, the present invention is a belt for use
on an extended nip press on a papermachine for dewatering a
fibrous web being processed into some form of paper product.
The belt includes a base fabric having the form of an endless
loop, and therefore having an inner surface and outer surface.
The inner surface is coated with a polymeric resin, which
partially impregnates the base fabric; that is, the coating
does not completely pass throug~h the structure of the base
fabric. This coating renders the base fabric impervious to
liquids, is smooth and of uniform thickness. The coated side
of the belt is in contact with the arcuate pressure shoe during
use on an extended nip press. More exactly, it slides over the
surface of the arcuate pressure shoe on a film of lubricating
oil supplied thereto.
The outer surface, or felt side, of the belt is
different from that shown in Canadian Patent No. 1,190,779.
It is characterized by a plurality of flat monofilament yarns
suitably attached to the base fabric. The flat monofilament
yarns aefine channels therebetween for accommodating water
pressed from the fibrous web. The channels formed in this
manner are not crushed by pressures delivered in the nip, as
are those in prior-art belts. Neither is delamination of the
grooves a problem, as the flat monofilament yarns are woven
into the structure of the base fabric.
The present invention will be particularly described
below, with frequent reference made to the accompanying
figures.
, ,
~024858 ~
Brief Description of the Drawinqs
Figure 1 is a side elevational view of an extended
press nip for which the belt of the present invention is
designed.
Figure 2 is a partially sectioned front view of the
press n-ip shown ln Figure 1.
Figure 3 is a plan view of the belt of the present
invention.
Figure 4 is a sectional view of the belt of the present
invention taken along lines 4-4 in Figure 3.
Figure 5 is a sectional view of the belt of the present
invention taken along line 5-5 in Figure 3.
Detailed Description of the Preferred Embodiment -~
A single-felted extended nip press for dewatering a
fibrous web being processed into a paper product on a paper
machine is shown in Figures 1 and 2. The press nip 10 is
defined by a smooth cylindrical press roller 12, an arcuate
pressure shoe 14, and a belt 16 of the present invention
arranged such that it bears against the surface of the
cylindrical press roller 12. The arcuate pressure shoe 14 has
about the same radius of curvature as the cylindrical press
roller 12. The distance between the cylindrical press roller
12 and the arcuate pressure shoe 14 may be adjusted by means
of conventional hydraulic or mechanical apparatus, which is not
shown, connected to rod 18 pivotally secured to arcuate
pressure shoe 14. The rod 18 may also be actuated to apply the
desired pressure to the arcuate pressure shoe 14. It will be
appreciated that the cylindrical press roller 12 and arcuate
pressure shoe 14 described above and shown in Figures l and 2
are conventional in the art.
.
~-- 20~4858
Also shown in Figures 1 and 2 are a papermaker's wet
press fabric 15 and a fibrous web 17 being processed into a
paper sheet. The motions of the belt 16, press fabric 15,
fibrous web 17 and cylindrical press roller 12 are as indicated
by the arrows in Figure 1.
A plan view of the belt 16 of the present invention is
provided in Figure 3. It has an outer surface 19 and an inner
surface 20. The belt 16 includes a base fabric which takes the
form of an endless loop. The base fabric can be produced, or
woven, in endless form, or can be produced in flat form, such
as by flat weaving, and joined into endless form by a seam.
Seaming into endless form should preferably be done before the
inner surface of the belt 16 is coated with polymeric resin.
One embodiment of the belt 16 is shown in greater
detail in Figure 4, which is a sectional view taken along line
4-4 in Figure 3. As such, it is a section taken in the machine
direction, that is, around the loop of belt 16. The outer
surface 19 and the inner surface 20 are as generally indicated.
The belt 16 comprises a multi-layer woven base fabric 22 of
machine-direction yarns 24 and cross-machine direction yarns
26 which has been impregnated from its inner surface 20 with
a polymeric resin, such as, for example, polyurethane, to
render it impervious to liquids, including lubricating oil.
The inner surface 20 is on the so-called shoe side of the belt
16.
The base fabric 22 is sufficiently open to allow
impregnation to eliminate the possibility of undesirable voids
forming in the belt 16 on the shoe side, the inner surface 20
facing the arcuate pressure shoe 14. Voids are particularly
undesirable because they would allow the lubricating oil used
between the belt 16 and the arcuate pressure shoe 14 to pass
B -`
through the belt 16 and contaminate the press felt and fibrous
web. ~ ~ 2 0 2 ~ ~ ~ 8
Once coated and impregnated with polymeric resin, the
inner side 20 of the belt 16 can be ground smooth and the belt
given a uniform thickness for lubricated sliding contact with
the arcuate pressure shoe 14 in the press nip 10.
The outer~side 19 of the belt 16 is characterized by
flat monofilament yarns 28 running in the machine direction.
These are attached to base fabric 22 by occasional cross-
machine direction yarns 30. It should be understood that the
view presented in Figure 4, and that presented in Figure 5, are
in a somewhat exaggerated scale in order to represent the parts
of the present invention more clearly.
The purpose of flat monofilament yarns 28 can be more
clearly explained with reference to Figure 5, which is a
sectional view taken along line 5-5 in Figure 3. As such, it
is a section taken in the cross-machine direction, that is,
across the loop of belt 16. Components have been given the
same identifying numerals as in Figure 4. The flat
monofilament yarns 28 are seen in cross-section and are
attached to the base fabric 22 by the occasional interweaving
with cross-machine direction yarns 30. Channels 32 are formed
between flat monofilament yarns 28 for the removal of water
pressed from the fibrous web in the nip 10. Preferably, the
flat monofilament yarns 28 would be arranged to provide eight
to ten channels 32 per inch. Channels 32 having the dimensions
.025" wide by .lOO" deep have been found to give good results.
While Figures 4 and 5 show the flat monofilament yarns
28 lying in the machine direction, which is the preferred
alternative, they could instead be oriented in the cross-
machine direction with good result.
.
.
.
As illustrated in Figures 4 and 5, the flat
monofilament yarns 28 would preferably be arranged in such a
way that they would have long floats, through occasional C ~ 2~248~8
interweaving with cross-machine direction yarns 30, which would
provide channels or voids between the flat monofilament yarns
28 into which water could flow. The same would apply and be
preferred~for thq case where the flat monofilament yarns 28
have a cross-machine direction orientation.
In general, the belt 16 of the present invention can
be dewatered outside the nip 10 f~r more easily that the belt
shown in Canadian Patent No. l,190,779. The mesh on the felt
side of the latter tends to trap water; this is not the case
with the channels 32 of the present belt 16.
It should be easily understood that modifications to
the above would be obvious to anyone skilled in the art without
departing from the scope of the appended claims.
