Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF I~ENTION
(a) Field of Invention
The present invention relates to papermaking
and more particularly to pressing a sheet, such as paper,
using at least four press rollers disposed in contact
with one another along a circuit as a closed train to
define a sealed chamber therebetween for the passage of
air thereto and through the sheet via a pervious roller
wall.
I0 (b) Description of Prior Art
In papermaking, a wet slurry of pulp is formed
into a continuous sheet by drainage at travelling-mesh
means, then the formed sheet is pressed between rollers
for more drainage, after which the sheet is dried by heat.
As is well known in the art, removal of moisture by
pressing is less costly than removal by heat. This is
mainly because moisture removal by pressing utilizes
little space, equipment and energy compared to moisture
re val by heat. Heating is costly in the main because
fuel is costly, a chain of equipment from fuel tank to
paper-machine dryers comprises a great part of a paper
mill, while a chain of energy exchanges from fuel tank
to vapor exhaust at paper-machine dryers lose energy at
every stage of energy exchange.
The present invention is directed toward
removing moisture by the less costly means, namely
pressing. As is also well known, pressing a sheet helps
to interlock fibers for paper strength, and the present
invention therefore is directed toward providing as many
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nips as posslble in a small space. Multi-nip rollers
are known for pressing a sheet to remove moisture thereof
as is disclosed in U.S. patent ~o. 4,173,249 issued on
November 6, 1979 to Holkko. The present invention is
an improved multi-nip suction press which overcomes some
of the disadvantages of the prior art such as taught by
the above referred to patent~ The disadvantage of using
a liquid press medium as in this reference is that it ~
causes the sheet to re-pulp after it passes through the
- 10 nips, as some of the water being squeezed out is trapped
between the impervious sheets and opposed rollers form-
ing the liquid medium chamber and redistributed into the
pulp. Also, there is no means to extract the water from
the nips and in the case of the upper nips, water will
build up in that region as it cannot be released by
gravity.
SUMMARY OF I~VE~TION
It is a feature of the present invention to
provide a multi-nip suction press which substantially
overcomes the above-mentioned disadvantages.
Another feature of the present invention is
to provide a multi-nip suction press wherein air is
utilized as a draining medium and passes through the pulp
and into a sealed chamber formed between the nips of the
press rollers to extract water from the pulp.
Another feature of the present invention is
to provide a multi-nip suction press which is econo~ic
to operate compared to prior art devices and which results
in energy conservation.
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Another feature of the present invention is to
guide a sheet of pulp through a closed train of rollers
; and registered with one another independent of diameter
and speed.
Another feature of the present inyention is to
provide a multi-nip suction press ~herein nip pressure
may increase progressively as the sheet advances from
nip to nip,
Another feature of the present invention is to
prouide a multi-nip suction press having the several nips
disposed in succession along a closed train and wherein
oscillations commonly caused in pressing and due to normal
variations in felt weave are substantially cancelled,
Another ~eature of the present invention is to
provide a multi-nip suction press having a central sealed
chamber and pump means to displace air in that chamber to
cause air to pass through the sheet to remove water
therefrom,
In accordance with one aspect of the present
invention there is provided a four nip press for use in
drying a web comprising in combination four press rollers,
each of which are mounted for rotation about a substantially
horizontal axis in a press operating mode, said rollers being
arranged such that each roller is in rolling contact with two
other rollers to thereby provide a closed train of rollers having
~ a nip at the respective contact lines between the rollers
; adapted to pass said web therethrough, said arranged rollers
defining an enclosed central zone into which said web is
received and discharged from circumferentially of ones of said
rollers and at least one of said rollers being powered for
; rotation.
According to the ahove features, from a broad
aspect, the present invention provides a drying apparatus
for use in a papermaking machine and comprising at least
four press rollers in nip contact with one another in
succession in a closed train to define a substantially
sealed chamber between the press rollers and chamher end
walls. At least one of the press rollers is a hollow
roller having a pervious outer wall to support at least
one endless ~elt disposed for a uni-directional advance
over an outer support surface of at least some of the
rollers and passing through all of the nip contacts.
The endless felt is a pervious carrier for a paper sheet.
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to be dried. Resilient support means is provided for
at least one press roller. Drive means is also provided
for at least one press roller. Conduit means permits
air movement through the hollow roller and the chamber.
Air displacement means is connected to the conduit
means. The air movement passes through the sheet car-
ried on the felt whereby to extract moisture from the
sheet and for convection of the moisture by the conduit
means.
The present invention yields new results
not present in prior art. Surface register is
automatic, independent of roller diameters, because
surface contact is obtained throughout the closed train.
For example, surface travel in register continues, even
though a roller be ground slightly smaller in
diameter, and even though that roller rotates slightly
faster than before. The reason of course is that surface
contact around the closed circuit results in all press
rollers having one surface speed in common. Also, a
roll ground smaller than before is assured of nip contact,
and air-tightness, with mating rollers by having resilient
support means~
- A chamber is formed by the press rollers, useful
as an air box with positive or negative pressure, for
air through drying of a sheet when the chamber ends are
sealed and connected to air-pump means. The press rollers
themselves form the sides, top and bottom of the chamber
and with end sealing walls, the press rollers com~ined
thereby perform a new and useful function. In this new
combination, air pressure in a pervious roller affects
the pressure of that roller against its matlng rollers
whereby strength of that air pressure becomes a medium
for controlling nip pressure.
In the present invention, a sheet is supported
and carried from nip to nip without any open draw,
important in avoiding sheet stress and breakage. This
support eliminates need for a costly array of equipment
for bringing nip speeds into register. Surface contact
around the closed circuit maintains that register among
nips.
In the present invention, any press roller
disposed for air-through drying has a working arc that
is substantial compared to conventional press rollers,
thereby intensifying the drying process. When communica-
; 15 tion with air-pump means is through a roller periphery,
air flow reverses through the periphery at each revolu-
tion thus back washing roll pores. In the present
invention, roll pores retain their air pressure throughout
a revolution, without exposure to the atmosphere, whereby
sheet drying is intensified over known art. As a large
portion of air-pumping energy is expanded in changing
the pressure of the roll pores, this new combination saves
expending that energy at each revolution, and noise is
correspondingly reduced. Through-drying is achieved in
the present invention by any of several methods such as:
(a) Utilizing the above-mentioned air chamber
as a conduit means having end sealing walls communicating
with air-pump means;
(b) Utilizing peripheral seal means at a per-
vious roller arc juxtaposed from a sheet and-felt
wrapped arc and having hollow shafting for the pervious
roller communicate with air-pump means. The peripheral
seal means are preferably external to the pervious
roller for maintaining air pressure in roll pores
throughout a roll revolution;
(c) Utilizing external air~box means at a
pervious roller arc juxtaposed from a sheet-and-felt
wrapped arc and having conduit means between the air
box and an air-pump means.
In the present invention, types of rollers
may be chosen to suit best a roll location in that
combination, because location in the roller circuit
helps to determine whether a roller should be pervious
or impervious, hard or soft, or be slightly bigger or
smaller than mating rollers~ These distinctive qual`ities
of a press roller are somewhat analogous to rings of
organic chemical c~mpounds having distinctive locations
in relationship with one another in that compound.
Also, press rollers may be added to whatever limits are
practical, in forming a closed train. Comparing that
closed train or circuit to a ring of an organic compound,
complete rings may be added as an open series, integrally
connected to adjoining rings without any open draw of
sheet from ring to ring.
It is well known that two hard-surfaced rollers
at a press nip quickly wear out a felt, while soft
surfacing at least one of those rollers will prolong
felt life. As is also well known, a damp sheet sticks
to the smoother of two surfaces in a nip, and granite is
used commonly for pressing directly against a damp sheet
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because its texture releases a sheet~ Accordingly, a
granite roller would be preferred in the present
invention where a sheet touches a nip roll directly,
but other surfaces would be acceptable in roller
combinations for double felting because the sheet would
no longer touch a press roll directlyO Choice of
suitable roller surface in this new combination would
be apparent to those skilled in the art.
Return runs of felts are so well known as to
stretch roll, guide roll, cleaning systems and variable
configuration that they are not detailed herein. Like-
wise, felt rollers are not counted herein as press
rollers, althollgh they are necessary to the invention
for guiding felts, Further, press framing is so well
known as to support means and resilient mounting that
framing is not detailed herein. Drive means is so well
known for paper machine rollers including such as
universal-joint drives, intermediate-roll drives and
helper drives that drive means are not detailed herein~
In addition, press rollers mentioned herein as being in
rolling or nip contact are understood to have that
contact through felting, and during operation through
a sheet as well.
DESCRIPTION OF PREFERRED EMBODIME~TS
A preferred embodiment of the present invention
will now be descrihed with reference to the accompanying
drawings, in which:
FIGURE 1 is a schematic illustration of an
example of the multi-nip s~ction press of the present
invention;
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FIGURE 2 is a schematic illustration of a
still further example of the multi-nip suction press of
the present invention, and
FIGURE 3 is a schematic illustration of a
still further example of the multi-nip suction press as
utilized in a double felted press.
Referring now to the drawings and more particu-
larly to Figure 1, there is shown the multi-nip suction
press or drying apparatus of the present invention, as
generally illustrated at 10. This apparatus is for
; utilization in a papermaking machine for pressing and
drying a sheet of pulp stock 11. Ilhe press comprises at
least four press rollers, herein stationary solid rollers
12 and 12', plus rollers 13 and 15. Roller 12 may be
resiliently biased by biasing means schematically illus-
j trated at 14. In this embodiment roller 12 touches the
sheet directly and would preferably be of granite for
sheet release. Rollers 13 and 15 could be soft surfaced
while roller 12' could be hard surfaced. At least one
of the rollers, herein roller 15 is a hollow roller hav-
ing a pervious outer wall 16 in registry with endless
belt 17 which is a pervious carrier of the paper stock
of sheet 11 to be dried.
The four press rollers 12, 12', 13 and 15 are
in close contact with one another in a succession as a
closed train whereby to define nips at the area of contact
therebetween and these are indicated by reference numeral
18. Thus, the four rollers will define four nips which
will apply pressure on the endless felt and paper stock
passing therebetween.
The endless felt 17 advances in a uni-direction
as indicated by arrow 19 and is a pervious carrier for the
paper sheet whereby air may pass therethrough to convect
water out of the pulp stock. One of the rollers has a
drive connected thereto, by means well known in the art,
for imparting rotation to all of the four rollers.
A substantially sealed chamber 20 is defined in
the area between the rollers 12, 12', 13 and 15 and
between chamber end walls 21, (herein shown in phantom
line). In order to achieve air movement between the-per-
vious hollow roller 15 and the chamber 20, there is pro-
vided suitable conduit means which may be constructed in
several ways. As shown in Figure 1, an air box 22 is
mounted in an e~ternal sealed relationship with another
surface of the roll 15, and a conduit 23 is connected to
the box 22 for the convection of air with moisture therein,
Similarly, the roll 13 may be a pervious roller and may
i have a conduit 24 connected thereto for the convection of
¦ air and moisture. A further conduit 25 is connected to
one of the end walls 21 for the ingress of air under pres-
sure. Thus, the chamber 20 will force air through the
pulp stock and felt 17 passing throu~h the pervious outer
wall of rolls 13 and 15 thereby forcing moisture out of
the pulp stock, through to the endless felt 17 and into
the hollow rolls 13 and 15 for convection of air and
moisture by conduits 23 and 2~. It is pointed out that
the roller 13 is suitably sealed in its opened area by
means such as a solid shoe 26. By shoe 26 being external
to roller 13, the rim of 13 remains continuously shielded
from atmospheric pressure and the shoe is more accessible
than an internal seal would be.
In its operation, as the pulp stock enters
the multi-nip press, water is squeeæed out at a first
nip. The pulp stock is then subjected to a suction by
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the hollow roller 15 in its travel area within the chamber
20. Thereafter the pulp stock is again squeezed at a
second and third nip and enters into the chamber 20 for
a second travel while subjected to a suction along a
surface area of the second press roller 13. 'rhus, the
paper stock exits the multi-nip press in a drier condition
than possible with known prior art mu:Lti-nip press devices.
Referring now to Figure 2 there is shown
another example of the conduit means. As herein shown,
a single hollow roller is provided with a pervious
surface and resiliently biased against three other
rollers. For e~ample, roller 28 may be a granite solid
roller and rollers 29 and 30 may be rubber rollers.
Air is exhuasted from the chamber 20 via the eY~haust
conduit 25 and this causes an ingress of air, as shown
by arrows 30 through the felt 17 and the paper stoc~ which
is located between the felt and a large outer surface ~ortion
of the pervious roller 27 causing moisture to be drawn within
the roller 27 and exhausted through conduit 25 via the central
chamber 20, The invention should not be limited to the
cor~binations of the air convection means disclosed herein,
as other arrangernents of air convection are possible.
Referring now to Fi~ure 3, there is shown the
invention as utilized in a double felted press. As herein
shown, a second endless felt 31 is driven in an endless
manner about the rollers 12, 12', 13 and 15 and in
registry with the other endless felt 17. The pulp stock
11 is trapped between the felts. Both endless felts are
of a porous construction. The operation of the double
felted press, for the removal of moisture of the pulp
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stock, is the same as that disclosed for Figure 1.
It is within the ambit of the present inven-
tion to cover any obvious modifications of the examples
of the preferred ~mbodiment described herein. For
example, the multi-nip suction press may comprise six
rollers defining a chamber therebetween with air being
injected into the chamber and out of four pervious rollers.
In a still further foreseeable arrangement there may be
provided seven rollers, three axially aligned with two
pairs of granite rollers in nip contact between these
whereby to define ~wo sealed chambers with the exhaust
being made through three pervious rollers and air fed
to both of the chambers~
In another example of seven rollers in accor-
dance with the invention there may be one roller fixed
centrally, three plain rollers at substantially 120 degree
locations in external nip contact therewith, two pervious
rollers each in nip contact with two of the three plain
rollers and one sealing roller in nip contact ~ith two of
the three plain rollers whereby to define chamber means
at substàntially 120 degree directions outside the roller
fixed centrally.
.
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