Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A BELT AS A REPLACEMENT FOR A
CONVENTIONAL PRESS ROLL COVER
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the removal of water from the
papersheet, wet felt combination in the nip of the press
rolls in a papermaking machine. More specifically, it
presents an elastic, compressible belt, whose total length is
greater than the circumference of a press roll, for use as a
replacement for a conventional press roll cover.
I
Description of the Related Art
An important step in the production of paper occurs in
the press section of the papermaking machine. There, a sheet
of fibrous material, either carried on top of a belt of
water-absorbing felt or held between two such belts, passes
through a series of openings between rolls. In each passage
through such an opening, referred to as the nip of the rolls,
water is squeezed from the fibrous material and absorbed by
the felt. The aim of this procedure is to remove as much
water as possible from the sheet before it emerges from the
press section of the machine and enters the dryer section.
In this way, less water will remain to be removed by heat in
the dryer section, and costs related to heat production will
be reduced.
In the dewatering presses, however, it is desirable to
apply pressure to the paper sheet, wet felt combination over
various time elements, depending on the type of paper being
manufactured. This so-called dwell time is related not only
to the speed of the sheet-felt combination, but also to the
compressibility of the roll surfaces. For short time
elements requiring high specific pressure, the press rolls
are equipped with very inelastic surfaces. Where it is
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desirable to extend this time element and to reduce the spe-
cific pressure, the press rolls are equipped with covers that
are compressible and elastic. The exact compressibility char-
acteristics of the press roll cover used depend on the par-
ticular conditions desired in the nip of the press.
Eventually, due to cyclical compressive fatigue,
press roll covers will fail in operation. It will then become
necessary to remove the press roll from the paper ~ch;ne for
either regrinding or recovering. Such a procedure can remove
the paper ~ch;ne from operation for a considerable length of
time.
This invention provides an alternate method of sup-
plying an elastic, compressible media in the nip of the press
instead of using the conventional press-roll cover. It is now
possible to produce a belt which has an elastic, compressible
surface similar to that of a conventional, press-roll cover.
Using the method envisioned here, such a belt, wrapped around
the shell of the press roll, would replace the press-roll
cover. In this way, the papermaker can be provided with the
elastic media needed in the press nip without actually cover-
ing the press roll.
SUMMARY OF THE INVENTION
The construction in accordance with the present in-
vention pertains to the press section of a papermachine
wherein water is removed from a wet sheet of fibrous material
during the manufacture of paper and the like, the press sec-
tion including at least one press roll extending across the
width of the papermachine. The press roll is cylindrical and
has a circumference, and has a press nip through which a com-
bination of the wet sheet of fibrous material and at least onewet-press felt fabric pass to dewater the wet sheet of fibrous
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material. The improvement comprises an elastic, compressible
belt, the belt providing an elastic, compressible medium in
endless form having a total length greater than the circum-
ference of the press roll and a width substantially equal to
that of the papermachine. The belt is supported by the press
roll and travels in the endless form about the press roll
under tension controlled by a movable stretch roll. The belt
further is directed about the press roll by a plurality of
guide rolls, so that the wet sheet of fibrous material may be
dewatered in the press nip against the elastic, compressible
medium in the form of the elastic, compressible belt. The belt
is used to replace a conventional press roll cover.
Accordingly, this invention, which includes an elas-
tic, compressible belt, whose total length is greater than the
circumference of a press roll, is to be used as a replacement
for the conventional press roll cover now used in the paper-
making industry. Supported by the shell of the press roll, the
belt would run independently through the nip in conjunction
with the sheet of fibrous material and wet felt combination.
Guide and stretch rolls would be required to direct and
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control the motion of the belt around the press roll and to
maintain its tension at a suitable level. The outer surface
of such a belt can be smooth, grooved, or have holes so that
it can replace roll covers having those surface
characteristics.
The user will benefit from the numerous, novel
advantages to be obtained through the application of this
invention. When compressive fatigue failure eventually
occurs in the elastic media of t~e belt, it would not be
necessary to remove the press roll completely from the paper
machine for recovering. Instead, one would simply shut down
the papermaking machine for the comparatively short span of
time required to remove the used belt from the machine and
install a new one in its place.
Assuming that compressive fatigue failure occurs after
some large number of compressive cycles, through the use of a
belt of the kind shown by this invention, a longer machine
running time will elapse before a given portion of the length
of the belt will have experienced the same number of
compressive cycles of passage through the nip as a given
portion of the press roll cover. This is because the belt
will be longer than the circumference of the press roll. The
belt will then by comparison have a much longer running life
than the press roll cover.
Since it will be easier to change a cover belt than
change a press roll cover, and since a cover belt represents
a smaller capital investment, in applying this invention the
papermaker will have an increased flexibility to change his
nip conditions as called for by the given application, and
will be required to carry fewer press rolls in his
maint~n~nce inventory. Machine "down" time during changes
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will be shorter than would be the case if an entire roll or
roll cover were being replaced.
Because of the ease of changing belts, the papermaker
will also be able to change from a smooth belt to a grooved
or perforated belt at his discretion.
BRIEF DESCRIPTION OF THE DRAWING
In Figure 1 is shown a set of press rolls in a
papermaking machine to which this invention has been
applied.
; Figures 2a-2d show portions of the surfaces of belts of
this invention having different surface characteristics.
Figures 3a-3d show side sectional views of the belts
depicted in Figures 2a-2d respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The main purpose of this invention is to provide the
papermaker with an elastic, compressible belt for use in the
press section of the papermaking machine. It is intended
that such a belt form the basis of an alternate method of
supplying an elastic media to the press nip and make it
unnecesc~ry in the future to actually cover the press rolls
with an elastic, compressible material. A mode in which this
invention can be put into use is illustrated in Figure 1.
The wet sheet of fibrous material 1, from which water is
being removed, is held between the top 2 and bottom 3 water-
absorbing felts as it passes between the upper 4 and lower 5
press rolls. The actual removal of water from the sheet 1
; occurs in the press nip 6, the region between the upper 4 and
lower 5 press rolls, where the combination of wet sheet 1 and
water-absorbing felts 2,3 is squeezed together. An elastic,
compressible belt 7 having a total length greater than the
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circumference of the lower press roll 5 and approximately the
same width as that roll 5 in the cross-machine direction, is
supported by the lower press roll 5 and moves through the
nip 6 with and below the combination of sheet 1 and water
absorbing felts 2, 3. Guide rolls 8 maintain a requisite
level of tension on the belt 7 and control and direct its
motion through the nip 6. A movable stretch roll 9 is used
to adjust the level of tension desired in the belt 7. The
mobility of the stretch roll 9 is indicated by the vertical
arrows above and below the circle representing it. All other
arrows indicate the motions of components of this system
during its regular operation.
Figures 2a-2d show four variants for that surface of the
belt 7 which makes contact with the press felt 3. Figure 2a
represents a smooth belt 7; Figure 2b shows a belt 7 whose
surface has grooves 10. Figure 2c shows a perforated belt 7
with holes 11 passing completely through its structure.
Figure 2d shows a belt 7 whose surface has depressions 12 not
passing completely through its structure.
Figures 3a-3d show side sectional views of the belts 7
in Figures 2a-2d respectively to present the grooves 10,
holes 11, and depressions 12 in greater detail.
Modifications would be obvious to one skilled in the art
without departing from the scope of the invention as defined
in the appended claims.
