Note: Descriptions are shown in the official language in which they were submitted.
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PRESS SECTION FOR A PAPER MACHINE
This invention relates generally to paper making
machines and, more particularly, to press sections for
paper machines.
The present invention is specifically directed to
a paper machine press section which comprises at least
four successive nips between which the web from which
water is drained runs as a closed draw, i.e., without
any open draws, supported on a fabric or roll face, the
nips being constructed and arranged so that detouring
of the web takes place substantially symmetrically and
to a substantially equal extent through both faces of
the web. The press section includes a first fabric
which functions as a pick-up felt onto the lower face
of which the web is transferred from the forming wire
to be carried into a first detouring press nip formed
between a first pair of press rolls in which a second
fabric comprises a lower felt. The web is carried from
the first nip by the second fabric into the second nip
formed between a second pair of rolls, the web being
detached from the second fabric after the second nip to
follow along with the upper roll of the second nip into
the third nip formed between the upper roll of the
second nip and a smooth-faced roll. The fourth nip of
the press section, which is a detouring nip and is
provided with a press felt of its own, is formed
between the smooth-faced roll and another press roll.
The nips are arranged in a manner such that detouring
of the web takes place in the first nip through both
faces of the web, and in the second nip substantially
through only one face of the web, namely that face
contacting the second fabric, and in the fourth nip in
the opposite direction relative to the detouring
direction in the second nip. The third nip is a
substantially non-dewatering smoothing and transfer
nip.
In paper machines which run at high speeds or
which are used for the manufacture of low-strength
paper qualities, i.e., fine-paper machines, so-called
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closed draw systems are necessary so that the web is
always supported by means of a felt as it passes from
the wire section to the press section. These systems
operate in a manner such that the transfer felt of the
press section is passed into contact with the web on
the wire. The transfer felt may be pressed against the
web on the wire by means of a rotary roll so that the
web adheres to the felt and is detached from the wire
whereupon the web carrying felt carries the web into
the first press nip of the press section.
us is well known, the pick-up arrangement and
press section of a paper machine utilizes several press
felts which function both as means for supporting the
web and, additionally, as means which contribute to the
detouring of the web in the various press nips.
Ordinarily, a single felt is provided at each web
treatment point although in certain cases a single felt
may contribute to the treatment of the web at two or
even more points.
The invention constitutes an improvement in the
"Simpers" press section available from the company
Valet Ox of Finland, the applicant herein, and has
resulted from several years of experience in the use of
the "Simpers" press section.
Reference is made to our published Finnish Patent
Application No. 50,651, which corresponds to US.
Patent 4,285,766, in connection with the details of the
construction of the "Simpers" press section. The
"Simpers" press section is a compact, fully closed
press section in which the paper web coming from the
wire is passed through a first nip formed between two
hollow-faced and/or suction rolls and between two felts
such that the detouring of the paper web takes place
through both of the web faces. The press section
further includes a smooth-faced roll provided with at
least one doctor and which forms the second nip with
one of the rolls of the first nip. Detouring of the
web takes place in the second nip through the face of
the web that is in contact with the second roll in the
Do MURK
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first nip. In this prior art press section there is at
least one additional nip after the second nip which is
formed between the smooth-faced roll, which constitutes
a central roll whose diameter is larger than the
diameters of the other press rolls in the press
section, and a hollow-faced roll. A felt runs through
this additional nip which is situated at a point on the
central roll which is substantially diametrically
opposite from the point of the central roll at which
the second nip is formed.
lo The conventional press section described above has
a possible drawback in that it does not provide a fully
symmetric detrain of the web in so far as the
distribution of fines and filler agents under all
circumstances and, in particular, in the case of fine
paper grades.
A drawback of conventional press sections is that
it is not possible in all cases to obtain a
sufficiently smooth face on both sides of the web. The
provision of smooth faces on both sides of the web
becomes quite important in the case of fine paper
grades.
With respect to the prior art which to applicant's
knowledge is most closely related to the present
invention, reference is made to published European
Patent Application No. 81 630083.4 (Publication No.
0055206) of Bullet Corporation. A press section is
disclosed therein similar to the press section to which
the present invention is directed In this press
section the upper roll of the second nip is a press
roll having a porous elastomers coating. This press
roll, which forms two nips in conjunction with other
rolls, is subjected to large loads and a siyniflcant
drawback of the press section is that it has been found
difficult to obtain a sufficiently durable elastic
coating for this press roll. For this reason it has
been necessary to replace this press roll on a frequent
basis. Such roll replacement is a cumbersome operation
which results in relatively long down times for the
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paper machine. At the same time the acquisition and
storage of several reserve rolls is expensive and
requires significant storage space. Moreover,
difficulties have also been encountered in achieving a
balance between the porosity of the roll on the one
hand and a sufficient smoothness of the roll face on
the other hand, particularly for the manufacture of
fine paper grades.
In accordance with the present invention there is
provided an improvement in a press section for a paper
machine including at least four successive nips between
which the web from which water is drained runs as a
closed draw supported on at least one of a fabric and
roll face, without open draw, and in which press
section the web is detoured substantially
symmetrically through both faces of the web, the press
section including a first fabric which functions as a
pick-up felt and onto a lower face of which the web
adheres, a first detouring press nip formed between a
first pair of press rolls into which the web is carried
by the first fabric which comprises an upper fabric in
the first detouring press nip, a second fabric
comprising a lower felt in the first detouring press
nip, a second nip formed between a second pair of upper
and lower rolls and into which the web is carried by
the second fabric, a third substantially non-dewatering
smoothing and transfer nip formed between the upper
roll of the second nip and a smooth-faced roll, the web
being detached from the second fabric after passing
throuyh the second nip to follow along with the upper
roll of the second nip into the third nip, a fourth
detouring nip formed between the smooth-faced roll and
a detouring press roll, a press felt passing through
the fourth detouring nip, and wherein the first,
second, third and fourth nips are arranged such that in
the first nip detouring takes place through both races
of the web, in the second nip detouring takes place in
a first direction through only the one face of the web
which contacts the second fabric which carries the web
into the second nip, and in the fourth nip detouring
wakes place in a second direction opposite from the
first direction.
The improvement of the invention comprises a belt
felt running over a sector ox the face of the upper
roll of the second nip between and through the second
and third nips, the belt felt being substantially water
non-receiving and having a smooth-faced outer surface
having surface properties such that the web is detached
from the second fabric after passing through the second
nip and adheres to the belt felt and is supported
thereon, the belt felt transferring the web into the
third substantially non-dewatering smoothing and
transfer nip, whereupon the web becomes detached from
the belt felt at least in part due to the surface
properties thereof and adheres to the smooth-faced
press roll of the third nip on the face of which the
Deb is carried into the fourth press nip.
By constructing a paper making machine in this
way, there is achieved full symmetric detouring of
the paper web with respect to the distribution of fines
and filler agents under all circumstances, and, in
particular, in the manufacture of fine paper grades.
When a smooth-faced belt felt is run over a sector
of the upper roll of the second nip in accordance with
the invention, that roll also constituting a lower roll
in the third nip, the smoothness of the outer face of
the belt felt can be optimally selected in view of the
desired smoothness of the face of the web to be
manufactured since the belt felt need not be a
water-receiving element. Moreover, replacement of the
belt felt can be carried out considerably more rapidly
than, for example, the replacement of the roll provided
with an elastic and porous coating and which operates
in a corresponding position in accordance with the
teachings of the aforementioned European Patent
Application Publication No. 0055206. It is also more
economical to maintain a reserve stock of belt felts as
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compared to the costs required for maintaining a stock
of corresponding elastomers covered rolls. Further,
transfer of the web onto the smooth-faced roll forming
the third press nip together with the upper roll of the
second press nip becomes more reliable when the web is
conducted by means of the belt felt in accordance with
the present invention.
A more complete appreciation of the present
invention and many of the attendant advantages thereof
will be readily understood by reference to the
following detailed description when considered in
connection with the accompanying drawing in which the
sole figure is a schematic side elevation view of a
press section constructed in accordance with the
present invention, illustrating a portion of the frame
lo construction as well as portion of the wire and drying
sections of the paper machine.
Referring now to the drawing; a web, such as a
fine paper web, which has been drained on a forming
wire 10 is transferred onto a first felt 20 of the
press section in the region of a suction zone aye of a
pick-up roll 24 at the detachment point P on the run of
the forming wire 10 between rolls 11 and 12. The web W
adheres to the bottom face of the first felt 20 on the
suction zone aye of the pick-up roll 24 and is
transferred on the bottom face of the felt 20 to the
press section.
The first detouring press nip No in the press
section is formed between a first pair of press rolls
including a lower suction roll 32 having a suction zone
aye and an upper press roll 22 provided with a hollow
face 23. The first felt 20, guided by guide rolls 21,
comprises an upper press fabric in the first nip No. A
lower felt 30 guided by guide rolls 31 acts as the
lower fabric in the first press nip No. The first nip
No thus constitutes a double felled press nip and the
web is detoured therein in a highly efficient manner
substantially symmetrically through both faces of the
web W, i.e., both upwardly and downwardly. The first
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felt 20 is reconditioned by conventional felt
reconditioning means 25. The pick-up roll 24 is
fastened to a projecting portion 26 of the frame 100 of
the press section by means of pivotal side supports 27.
The second detouring press nip No in the press
section is formed between a second pair of upper and
lower rolls, namely a lower roll 33 having a hollow
face 34 and an upper roll 42. The second felt 30
carries the web into the second nip No and acts as a
lower fabric therein. As seen in the figure, the first
and second nips No and No are substantially horizontal
nips and the second fabric 30 and the web supported
thereby has a substantially horizontal run between the
first and second nips. After passing through the
second nip No, the web W adheres to the outer surface
of the belt felt 40 and changes its direction to follow
the belt felt over a sector of the face of the upper
roll 42 of the second nip No. The magnitude of the
central angle defined by the sector of the upper roll
42 over which the belt felt and web carried thereby
change direction is in the range of between about 90
to 180, and preferably is in the range of between
about 120 to 150.
In accordance with the present invention, the belt
felt 40 which is arranged to run around the upper roll
42 of the second nip No guided by guide rolls 41 has a
smooth-faced outer surface. Moreover, it is an
essential characteristic of the belt felt 40 that it is
substantially water non-receiving and that its surface
is sufficiently smooth that the web W after passing
through the second nip No adheres to and follows along
with the belt felt 40, i.e., is detached from the
second, water-receiving felt 30 which has a coarser
surface than the belt felt. In addition to these
functions, the belt felt 40 also functions to smooth
one side of the web, which may advantageously
constitute a fine-paper web W. The opposite side of
the web W is smoothed against the smooth-face 44 of the
roll 43 which may advantageously comprise a rock roll.
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The rock roll 43 together with the upper roll 42 of the
second press nip No forms the third nip No in the press
section, the third nip being mainly a transfer and
smoothing nip for the web.
Importantly, the use of a belt felt I having the
properties and characteristics described above in
accordance with the invention eliminates the
criticality of the surface properties of the press roll
I Thus, -the various disadvantages inherent in, for
example, the press section disclosed in the European
Patent Application Publication No. 0055206 discussed
above are overcome.
A fourth detouring press nip No is formed between
the smooth-faced rock roll 43 and a press roll 52
having a hollow face 53. A conventional press felt 50
runs through the fourth press nip No guided by guide
rolls 51. The felt 50 is reconditioned by conventional
felt reconditioning means OWE
It is apparent from the foregoing that in the
first nip No, detouring of the web occurs
substantially symmetrically through both faces of the
web. In-the second nip No, detouring takes place
substantially entirely in a first direction towards the
second felt 30 through only that face of the web which
contacts the second felt since the belt felt 40 is
substantially water non receiving. As noted above, the
third nip No functions as a smoothing and transfer nip
since there are no water-receiving fabrics which pass
there through. In the fourth nip No, detouring takes
place in a second direction towards the press felt 50,
i.e., in a direction opposite from the first direction
of detouring in the second nip No. In this manner, an
efficient and substantially symmetrical detouring is
ensured in addition to a symmetrical distribution of
fines and filler agents within the web. This is
important especially in the case of fine paper grades
for the production of which the press section of the
present invention is mainly intended
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The belt felt 40 may, for example, be constructed
of mesh-like reinforcement fabric which provides good
resistance to tension. The fabric is preferably
impregnated with plastic, rubber or a similar material.
By appropriate selection of the properties of the face
of the belt felt 40 that contacts the web W, it is
possible to affect the properties of one face of the
web and in particular its smoothness in a predictable
manner as will be understood by those skilled in the
art. Although the belt felt 40 may be to at least some
lo extent water-receiving and even slightly air permeable,
the permeability of the belt felt I has no essential
significance. It will be understood that it is the
properties of the surface of the belt felt 40 which
contacts the web W and, in particular, the smoothness
of this surface and the adhesion properties of the
surface relative to the web which are important. These
properties must be such as to reliably ensure that the
web will follow the belt felt 40 after the second nip
No, i.e., will become detached from the press felt 30.
After the last nip No, the web is detached from
the smooth face 44 of the rock roll 43 by means of a
guide roll 560 The face 44 of rock roll 43 is kept
clean by means of a doctor 45.
After the press section, the web W is passed to a
conventional drying section which includes a lead-in
cylinder 62, a drying cylinder 63 of an upper line of
cylinders, and a drying cylinder 64 of a lower line of
drying cylinders. The web W is transferred onto a
support fabric 60 as it travels over cylinder 62, the
fabric 60 being guided by guide roll 61.
Obviously, numerous modifications and variations
of the present invention are possible in the light of
the above teachings It is therefore to be understood
that within the scope of the claims appended hereto the
invention may be practiced otherwise than as
specifically disclosed herein.
