Note: Descriptions are shown in the official language in which they were submitted.
s ~ 5~i6
Il ~DE~ATERING P~CS
Il Background of the I~vention
¦ The field of the lnvention relates to mechanisms
Il ~or extracting water from a web of materlal, and more particu- ~
11 larly from a fibrous web formed in a papermaking machine. I
¦~ During the ~apermaking process, a web i5 formed by
depositing a ~ibrou.s slurry on a forminq wire. A large amount
of water is drained from the slurry during this process, after
which the ne~ly-formed web proceeds to a press section. The
press section ~ncludes a series o press nips. The web finally
proceeds to a drying section including heated dryer drums where
the water content is reduced to a desirable level.
In vi`ew of the high cost of energv, it is desirable
Il to remove as much water as possible from the web prior to its
l.S I entering the drying section. The dryer drums in this section
l are often heated by steam and costs can be substantial if a
i large amount of water needs to be removedO
The use of exte~ded press nips has been Eound to be
l advantageous over the use of nips formed by pairs of adjacent
rollers. By extending the time the web is subjected to pressure
~ in the nip, a greater amount of water can be removed. This fact
I has been recogni~ed by those skilled in the art, and several
patents have been granted in the area. These patents include
Il Re. 30,268, 4,201,624, 4,229,253 and 4~229~254O
1l In using extended press nips to dewater a fibrous web,
the web has typically been sandwiched between two moisture-
Il absorbing ~elts and a ~elt. The felts are trained around a
I I cylindrical press roll with the web between them while the belt
.i~ arranged for applying pressure to the felts and roll. A
pressure shoe exerts pressure on the belt in the press area.
. ' ~
_.~, , . .. ,, , . .......................... ,, I
,. . . '; ~' , . '
6 l
A problem has been encountered during the dewatering
of webs in extended nips. It has been found that a bulge deve-
lopes in the belt ahead of the nip. This problem is recognized
in U~S. Patent Nos. 4,229,253 and 4,229,254, and certain belt
S constructions are suggested for overcoming the problem.
.
Summary of_the Invention
The invention is directed to an apparatus for dewater-
ing a fibrous web including an extended press nip provided by a
roll and a specifically designed bel~ which is forced toward
the .roll by a pressure shoe for applying pressure to the
fibrous web and one or more web transporting papermakers felts
in the nip. The belt comprises a base fabric which is
impregnated with a thermoplastic or thermosetting polymeric
material. The base fabric which can be single layer or
multilayer, is sufficiently open to allow total impregnation
of the material to eliminate any voids in the final fabric. A
significant advantage of this belt construction is that it can
be made in any length since it does not require a mandrel during
the manufacture thereof. A base fabric is provided endless
u~ing conventional fabric technology and then coated and
impregnated with the polymeric material.
The resulting structure is both light in weight and
sufficiently stable to operate under paper machine conditions`.
It has sufficient abrasion resi5tance to resist any wear that
might take place in the extended nip apparatus. Unlike materials
which are built up in the manner of a rubber tire and can flow
and/or delaminate, ~e invention provides a belt which will
maintain its integrity. It also solves the problem of bulging
near the press nips. The belt has a uniform smooth polymeric
30 surface Which is engaged by a pressure shoe applying pressure
' ', '.: ,' . - ,
r-r-
l~ in the direction of the roll.
11
¦ Brief Description of the Drawi_gs
Figure 1 is a side elevational view o~ an extended
¦ press nip according to the invention;
5 ¦ Figure 2 is a partially sectional front view of
I the press nip shown in Figure l; and
Figure 3 is a sectional side elevational view of the
belt employed in the invention.
Detailed Description cf the Invention
.. . . . _ _ . ___ _
An extended press nip is provided by the invention
for dewatering a tra~elling web of material. The nip 10 is
defined by a cylindrical press roll 12, a pressure shoe 14
having an arcuate surface facing the press roll, and a belt 16
arranged such that it bears against the surface of the press
lS roll. The arcuate surface of the pressure shoe has about the
same radius o curvature as the press roll. The distance between
the press roll and the pressure shoe may be adjusted by means
of conventional hydraulic or mechanical apparatus (not shown~
connected to a rod 18 pivotally secured to the shoe 14~ The
rod may also be actuated to apply the desired pressure to the
shoe. It will be appreciated that the pressure shoe and press
roll described above and shown in Figures 1-2 are conventional
and that Qther arrangements may be utilized in accordance with
the invention.
The belt 16 employed in accordance with the invention
is shown in detail in Figure 3~ It has proven to be superior
to belts currently known to the art both from an operational
standpoint and for manufacturing considerations. The belt 16
comprises a base fabric 20 which is impregnated with a polymeric
materiai. 22. Thermosetting resins such as polyurethanes have been
_ 3 _
. . ~ , A'
/ ' ' ~'' ~ ' .
~ . y''~
35~6
found to be suitable impregnating materials. Thermoplastic
polymers such as polypropylene are also acceptable.
The base fabric 20 is sufficiently open to allow total
impregnation. This eliminates the possibility of any voids form-
I ing in the final fabric which would allow the lubrication usedbetween the belt and shoe to pass through the belt and contami-
nate the felt and fibrous web. It is endless in final construc-
tion and uniform in thickness~ The fabric must also be made to
have sufficient stability under paper machine conditions. In
other words, it must have length stability, width stability,
and guideability.
The thermoplastic resin or thermosetting resin used,
should be a substantially one hundred percent solid composition
to avoid the formation of bubbles during the curing process of
the resin in the belt structure.
The belt has at least one smooth side 16' which
contacts the pressure shoe 14.
Belts manufactured in accordance with the invention
have heen found to have many desirable characteristics. They
move easily over the pressure shoe and are capable of trans-
mitting pressure from the shoe to the web and press roll.
Sufficient flexibi.lity is obtained, and the belts have proven to
be unaffected by lubricant applied prior to entering the press nip.
In comparison with belts currently known to the art,
the invention provides a belt which is relatively thin and light
in weight~ Thick belts have the disadvantage of tending to flow
while within the nip. For example a 24'6" X170" belt impregnated
with a thermosettiny resin in accordance with the invention weighs
about two hundred pounds. A similar size belt naving bulge-
resistant characteristics and having a structure defined in theabove mentioned patents weighs about twelve hundred pounds.
Unlike the heavier belts, the invention does not require a
, - ;
.
reinforcing structure.
The manufacture of the belt according to the invention
I may be accomplished economically and without the need for
I mandrels or autoclaves which limit the size of other belts.
5 1l A belt of any length can accordingly be produced. The base
¦ structure is first woven~ A web may be needled into the woven
,I base if desired. If the base structure has not been wo~en endlesls
it is then joined endless using conventional joining techni~ues
I applicable to formi`ng fabrics in t~e paper industry. A pol~y-
¦¦ mer1c material is then appl;ed to the base fabric and forms amechanical interlock therewith. The resin is allowed to cure
for a sufficient period of time. After curing, the resin
surface may be sanded or ground to provide a belt of uniform
l caliper having at least one smooth surface.
~ A belt made in accordance with this invention may be
utilized with the apparatus shown in ~igure 1. The belt 16 is
positioned between the pressure shoe and the pressure roller.
I The smooth coated side 16~ of the belt is engaged by the shoe.
l A fibrous web 24 carried between first and second felts 26
1 and 27 respectively i`s introduced into the press nip 10. The
side of the belt 16 engaging the shoe 14 is lubricated by
lubricatlng means 28 positioned ahead of the nip.
The helt 16 is easil~ re~aired should a hole or
~ other surface irregularity de~elop therein. The damaged
1 portion is cleaned with a solvent and a suitable amount of
coating is applied with a blade. A heat gun is employed to
cure the surface which can then he sanded.
S
.. .. .... -
-
s~i
Because of the excellent flexibility characteristics
of the base structure and the fact that the coating can be
kept to a minimum, the suxface of the belt will have less
tendency to fail due to bending fatigue. This is due to the
fact that, because of the low caliper, the surface plane of the
coated surface is at a minimum distance :From the neutral axis
of bending . This reduces the percentage of elongation and
compression at the surface plane during bending
Example 1
A two-layered monofilament base fabric was flat woven,
heat s~abilized, and joined endless using normal joining tech-
niques. The fabric was then coated with a 100~ solid polyure-
thane resin Dupont Adiprene L 100 and cured. The coating step
may be accomplished through the use of a doctor blade or the
like to obtain a smooth surface. If the outside surface of the
base fabric is coated, it may be turned inside out for use in
the application.
e 2
A monofilament fabric is woven into a two layer weave
having 5uficient openness. It is heatset and joined endless.
The endless fabric is placed on a finishing machine including
a pair of rollers. One of the rollers is an oil heated cylinder.
A polyurethane sheet of proper uniform caliper is placed on the
inside surface of the fabric and allowed to pass between the
heated cylinder and the fabric structure. The temperature
of the oil cylinder is maintained at a substantially constant
level to obtain uniform melting and fusing of the plastic film.
The sheet is trimmed so that there is no overlap in the material
to be pressed into the fabric structure. As the fabric and sheet
pass around the heated cylinder, sufficient heat is maintained
.. ., ...... ,., - . : .,
;
to cause the polyurethane to flow into -the fabric. A pressure
roll may be used against the outside of the fabric to insure
complete impregnation. The polyurethane is plasticised and
forced into the voids of the fabric. A smooth surface is obtainec
which does not require any further flnishing steps. The use of a
100% polymeric sheet also eliminates any problems which could
develop in the finished fabric resulting from the use of an
impregnation compound containing solvents or water. After the
fabxic has undergone the pressing operation, the edges are
trimmed and sealed for operation in a papermaking machine.
Example 3
A monofilament polyester base fabric having sufficient
openness for impregnation is provided. The fabric is a two
layer weave having both width and length stability. A polypropy-
lene film having a thickness of about 0.020 inches or more isfused to the base fabric in the manner described in Example 2.
The temperature of the oil cylinder is maintained at a sub-
stantially constant level to obtain uniform melting and fusing
of the plastic film. The base fabric has a higher melting
temperature than the polypropylene film and is not disturbed
by the heating process. After the fabric has underyone the
pressing operation, the edges are trimmed and sealed for
operation in a paper-making machine.
It will be appreciated that the belt utilized in
the invention may include a base fabric made from various
polymeric materials having the necessary properties for
application in paperma]cing machines. Materials other than
polyurethane and polypropylene may also be employed as the
coating material.
