Note: Descriptions are shown in the official language in which they were submitted.
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~3~
The inventlon relate~ to ~n improved method and mechan-
ism ~or pressing wa~e~ rom ~ ~ravelin~ paper web, and more
particularly to ~ pre~ arrangement know~ a~ an extended press
nip wherein the web i6 sub3ect:ed to presslng pressures for a
longer period of ~i~R than the usual arr~ngement wherein it
pa~ses between two opposed pres~ roll&.
More par~icularly, the invention relates to a method and
structure having a press nip wherein the residence time of
the web in the nips iæ increased over tha~ of a roll couple
and wherein an impro~ed structure is used to extract watPr
from a web. Other structures have been provided heretofore
which have attempted to increase the time over which a web is
subjected to a pressure, and yet permit the web to continuP
movement at a speed necessary in a high ~peed papermaking
machine. Such struc~ures have met with degrees of success and
are exempli~ied by the disclosure~ of U.S. Pat. Nos. 3,748,225,
Busker et al; 3,783,097, (Re. 30,268), Ju~tus; 3,797,384, Hoff,
3, 798, 121, Busker et al; 3, 804, 707, Mohr; 3, 808, 092, Busker;
3,808,096, Busker e~ al, 3,840,42~, Busker et al; 3,853,698,
Mohr; and 4,201,624, Mohr. The devices and method discussed
by ~hese previous patents have taken advantage of the knowledge
that ~he static applica~ion of mechanical pressure to a wet
paper mat can reduce the moisture content in the mat to below
40%. Under the dynamic ~hort-term mechanical pressing which
occurs i~ thle usual paper machine where the web i5 run between
a ser:Le~ of nips formed between pregs roll ~ouples, it ~s often
difficult ~o maintain moisture levels below 60%. Attemp~s to
obtain increased dryness in the conventio~al roll-couples are
usually made by increasing the press nip pressure, but a
~ 7i~
plateau i5 ~oon reached w~ere m~or increaRe~ ~n roll loading
result in rela~ively ~mall decrease~ in mol~ture.
~ known, lt ~s far more efficient to remove water
i:n the press 6ec~iGn of ~ paper machin2 than ln the thermal
dryer ~ec~ion snd significant reduction i~ energy costs and
~gnifican~ reduction in the ~;pace needed or the dryer drum
sectlon of the machine are achieved for every fraction of a
percent o$ moisture thst can ~e additionally removed in the
press section. The difficulty of removing moisture in ~he
prees ~ection is increased with increase in machine speed be-
cause limiting factors are reached in press nip pressures in
that compacting and crushin~ of the web result~ with higher
nip pressures and resultant hi~her hydraulic pressures within
the paper mat. The most feasible way th~t has been discovered
to :increase water removal at high ~peeds has been to increase
the residence or pressure time to allow more time for flow to
occur within the paper mat and for the hydraulic pressure to
dissipate and for water to be pressed out of the web into the
felt.
THF, INVENTION
It is an object of the pre~ent invention to utilize the
principles of extended nip pressing increasing the time that a
web is subjected to pressing presstlre and to provide an improved
mechanism utilizing opposed shoes i~ a 6tructure which accommo-
dates relatively hlgh speed travel of a paper web and the appli-
cation o ~ pressing ~orce which i8 controlled to optimum nip
pressure for the type of paper being ~anufactured.
A further ob~ect of the invention ie to provide an im-
proved extended nip press of a relatively ~nccmplicated struc~
ture wh~ch i8 capable o continued operation over a long period
of time without requiring servicing or adjustment or signifi-
cant attention that would require stopping the machine.
A further obJect of th,e invention 16 to provide an im-
pro~ed ex~ended n~p press ~hilch has features of being able to
obtain uniform presslng pressure across the width of the travel-
ing web for more uniform water removal.
A still further object of the invention is to provide an
improved method and structure for an extended nip press which
improves the quali~y of the sheet, improves moisture removal,
performs a better pressing opera~ion and reduces rewetting.
A further object of the invention is to provide an im-
proved press nip which employs an extended nip principle and
has an improved structure for driving impervious belts which
sandwich the web and felts in the nlp.
A eature of the invention provides opposed shoes which
define a press nip between them with impervious belts sandwich-
ing the web and felts passing through the nip~ and the shoes
having hydraulic films of lubricant and being supported with
at least one of the shoes being pivotally mounted so th~t they
assume a hydraulically balanced position accommodating the
hydraulic pressure nf the film of lubricant which is carried be-
tween the shoe and the belt. Pressing forc~ is applied to the
nip by a piston and cylinder arrangement supplied with a hy~
draulic fluid so that the hydraulic fluid acts not only to
supply the pressing force, but also insures that this pressing
force will be absolutely uniform across the entire width of the
press nip. The opposed shoes are ~u~ficiently flexible so that
they csn bend along their length without introducing forces due
to t~eir bending that increase or decrease nip pressure along the
shoe length and with the application oE nip pressure solely
78;~
~hrough hydraulic flui~ completQly uniform pressure along ~he
full length of the nip can be ~ttained.
~ ther ob~ects, adv~ntages and features, aæ well as
equivalent ~tructures and methods which are intended to be
covered herein, will become more apparent with the teachin~ of
the principles of the invention in connection with the dis-
closure of the preferred embodiments thereof in the specifica-
tion, c~aims and drawings, in which:
~RAWINGS
The single Figure of the drawings, label~ed FIGURE 1 is
~ somewhat schematic slde elevational view of a press section
of a papermaking machine embodying the structure and principles
of the present invention.
DESCRIPTION
A nip N for pressing and dew~tering a web is formed be-
tween first and second shoes 10 and 11. The shoes ha~e a
relieved leading edge shown at 12 and 13 leading to a pressing
face 14 and 15. The pressing faces each face the extended nip
and are smooth and essentially straight so that they apply a
20 pressing pressure to the web W dur~ng the ~ime it is passing
through the nip. As will be recognized by those versed in the
art, the shoes extend laterally across the web for slightly
lonEJer than the web width, ~nd can be referred to as being elon-
gate ln the direction transverse of ~he web travel as indicated
by the directional arrow on the web.
The web i~ ~andwiched between felts 18 and 19 which pro-
vide means for receiving water pressed from the web, and the
felts and web are carried through the nip sandwiched between
looped endless lmpervious belts 16 and 17. The web is guided
lnto the nip and guided away from the nip by suitable guide
71~
m~mbers, not ~own, and the felt~ are similarly guided into and
out of the nip by T0~8 ~uch as 18a ~nd ~b for the upper felt
18, and rolls l9a and 19b ~or the lower felt lg.
The looped belts 16 and 17 a~e ~ade of extremely strong
reinforced rubber or similar material, and are driven at the
speed of tr~vel of the web so that they cArry th~ web and f~lts
through the nip, a~d ~he belt~ are tensioned on guide rolls
~hown for the bel~ 16 at 16a, 16b 9 16c and 16d. Roll 16c may
be a tension roll movable in the direction of the arrowed lines
10 by suitable tensioning mechanism, The lower belt 17 is guided
by similar tensioning rolls 17a, 17b, 1 7c and 17d, and suitable
mechanism is provided for the tension roll 17c ~o move it in the
direction of the arrowed linesfor maintaining the desired ten-
sion in the belt 17.
An important feature for proper treatment of the web is
the means of driving the belts, each of which is wrapped over
a grooved traction and guide rolls 20 and 22 for the belts 16
and 17 respectively. The belt is wrapped over these rolls for
an arc preferably in excess of 90, and it has been found that
an improved tracking and driving relation~hip is attained by
providing uniform circumerential grooves in the 6urface of the
roll with the grooves shown schematically by the broken lines
21 and 23 for the rolls 20 and 22 respectively. These grooves
are annular recesses cut a~ uniform intervals along the surface
oE the roll leaving flat land areas therebetween. These grooves
apparently permit the ~cape of any moisture which may be en-
trapped between the belt and rol1, and permit the belt to de-
pre~s slightly into th~ grooves,due to its being tensioned to
thereby increase the traction between the belt and rolls and
~1BO increase the uniformity oE drive and guiding ~elationship.
`
Uniform treatment af the belt~ i8 necessary 8~ that the web and
felts can be dragged uniformly hrough the ~lp.
The grooved traotion rolls 20 and 22 e~gage the outer
~urf2~e of the belt, which Ls the surface ~ha~ i~ ad;acent the
felts in the nip. Thus, no driving or traction forces are
applied to the inner ~urace of the belts which surfaces slide
over the shoes 10 and 11. Any abrasion caused by the drive is
not directed at the ~liding surface of the belt. Further, lt
i~ to ~e noted that it is the outer surface of the belt which
]- will be wet from i~s con~act with the fel~ so that this wetness
on the belt surface has be~n found to be accommodated by the
unique grooved traction rolls 20 and 22.
A film of lubricating fluid i5 co~tinuously developed
between the flat surfaces 14 and 15 of the shoes and the belts
due to the fact that their leading edges 12 and 13 are relieved
and a continuous supply of lubricant is delivered at the loca-
tion of these relieved edges by jets 24 and 25. The lubricant
may be of various substances, such as oil, and is applied in a
manner so that each of the shoes acts as a slipper bearing and
actually while the shoes press toward each other, the film of
lubricating liquid is continuous so that there is a hydraulic
transmission o the force of the shoe to the bel~ through the
lubricant. This, of course, reduces the friction between the
belt and the shoe, but also provides for a more improved press-
ing action in that pressure uniformity is enhanced due to ~he
fact that there is a body of l~quid between the face of ~he
shoe and lthe belt, and the liquid must adopt uniform pressure
along the elongate length of the shoe.
Because of the hydraulic reac~ivn against the shoe due
to the lubricsnt layer between the shoe and bel~, the shoes
8~
will tend to tlle to a neutral position. That i6, the 6hoes
~re e2ch ~hown as mounted on a central pivot 27 and 29. These
pivot6 are ~ocate~ approxi~ate~y midway between the front and
back edges of the 6hoe, ~nd the ~hoes will operate at a balanced
position wherein the hydraulic $orces o the lubricant ahead of
the pivot are the same as the hydraulic forces behind the pivot.
Edge seal~ m~y be p~o~ided at the edges of the belt to
prevent lubricant from migrating around the edge of the belt,
but experience has shown that the amount of lubricant passing
around the edge of the belt is minimal so that edge seals are
not absolutely essential. The trailing edge of the ~hoes are
rounded slightly at lOa and lla ~o reduce the concantration of
pressure against the belt as the bel~s emerge from the ~railing
edges of the shoes. While each shoe is pivotally mounted by
a pivot pin which extends laterally across ~he entire wldth
of the machine so that the shoe i6 pivotally supported about its
lateral axis, in some instances, it may be desired to pivotally
mount only one of the shoes. Thi~ will still achieve ehe hy-
draulic balance in the nip inasmuch s the one pivo~ed shoe will
pivot to a neutral position with hydraulic orces ahead of and
behind the pivot being uniform.
The shoes are supporeed on opposed heavy beams 26 and 28
above and below the shoes 10 ~nd 11. As referred to above, ehe
pivot pin 27 may be omitted in some instances, and the shoe 10
mounted rigiclly on the beam 26, and only the pivot pin 29 pro-
vided. This iB an alternate struceure~ but the pivotal support
for each of t:he shoes i9 preferred. The pivoe pins can be so
located relat:ive to the leading and trailing edge of the ~hoe
so that uniform pressure occurs throughout the lengeh of the
extended nip or may be set ~lightly downstream in the direction
of the web movement 50 that a slightly lower ~nit nip pressure
oceurs ahPad of the pin than ~Ifter the pivot pin. The shoes
will ass~me a position of bal~mce wherein the tot~l hydraulic
~orces of the lubricant in the nlp ahead of ehe pivot pin equal
those behind the pivot pin.
For applying the presslure to the shoes to attain the press-
ing force in the nip, the lower shoe is mounted on a piston 30
seated in a cylinder 31. Hydraulic liquid is deliv~red to the
pi ton beneath the cylinder by suitable means indicated by the
llne 32. The cylinder or channel 31 beneath the piston is
preferably continuous, or if separated, the same pressure is
applied to each of the chambers 80 that the upward force on the
shc,e is uniform throughout its length across the machine. If
the cylinder or chamber 31 ~s continuous, since the hydraulic
fluid will be at the same pressure throughout the continuous
cyl.inder 31, a uniform upward force will be appliPd to the shoe
throughout its length insuring $hat ~he pressing force in the
nip will be uniform across ~he machine. Wi~h high nip pressures,
the upper beam 26 may bow upwardly slightly in its middle, but
the ~hoes 10 and 11 are sufficiently limber B0 that they will
bow wlth tha beam without introducing any significant forces due
to their rasi~tance to bending, and thus the uniform pressure
ln ~he nip will not be altered. Similarly, the piston will bow
slightly to conform to the bending of the upper beam 2$, but the
amount of ~urvature due to ~his bowing will be ~nsigniicant and
will not affect the uniforml~y of pressure in the nip across
the machlne. If the lower beam 2~ bows downwardly, this shape
will not be transmitted to the shoes because the sole upward
force on t:he piston is derived rom ~he ~orce of the hydraulic
-8
liquid in the cylinder 31 beneath t:he piston.
In some instances, lt may be dei~irable to support the
upper shoe on a piston and cyli.nder arrangement similar to the
piston and cylinder 30 and 31 so that a force is applied bo~h
to the upper shoe and to the lower shoe. Or, of course; it
will be under~tood that the lower shoe may be supported directly
on a beam Oll a pivot pin without a piston and cylinder, and
the piston and cylinder be provided for the upper beam and upper
shoe. If a single piston and cylinder is u9ed, it is preferred
that it be used on the lower beam 28, because the weight of
the upper beam ~6 tends to counteract the upward reaction orce
from the shoe 10 applying pressure to the nip.
In operation the two belts 16 and 17 are driven at the
speed of travel of the web due to their frictional tracking en-
gagement with their driving rolls 20 and 22. The felts 18 and
19 are carried through the nip with the web between them, and
as water is pressed from the web from the time it enters the
nip N at the leading edge of the shoes 10 and 11 to where it
leaves the shoes, it is received by the felts which are dried
in ~he usual manner. Control of the pressure in the nip i8
obtained by the pressure of the hydraulic fluid delivered
through ~he line 32 to the cylinder chamber 31. 'rhe shoe3 can
be held in loose en~agement witn the belts at start-up and
pressure increased as the machine reaches operating speed, and
the pressure adj-lsted in accordance with the dei~ired operat~on
and the amoun~ of wa~er to be pressed from the web in the ex-
tended nip.
'rhe drlving rolls drive the belts at uniform speed n~tin-
taining constant and uniform traction despite any water which
remains on the surface of the belts. It i8 to be understood
t,hat the advantages o~ the l~lique driving rolls may be employed
in other orms o:E extended nip presses, ~uch a~, for example,
structures such as ~hown in Re 30, 268 by forcin~ a grooved
driving roll ~nto driving contact wlth ~he ou'cer iQurface of the
bel~ .
Other forms ~f ~tructures and modifications of the method
alling within the spirit and acope of the invention are in-
tended to be covered herein, and applicant is not limited by
the specific preferred embodiment of ~tructure illustrated.
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