Note: Descriptions are shown in the official language in which they were submitted.
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The field of the invention relates to a method
of manufacturing an endless belt particularly for use in
an extended press nip.
During the papermaking process, a web is formed
by depositing a fibrous slurry on a forming wire. A large
amount of water is drained from the slurry during this process,
after which the newly-formed web proceeds to a press section.
~he press section includes a series of 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 view of the high cost of energy, it is desirable
to remove as much water as possible from the web prior to
its entering the drying section. m e dryer drums in this
section are often heated by steam and costs can be substantial
if a large amount of water needs to be removed.
The use of extended press nips has been found to
be 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. Ihis fact has been recognized by those skilled in
the art, and several patents have been granted in the area.
~hese patents include Re. 30,268, 4,201,624, 4,229,253 and
4,229,254.
In using extended press nips to dewater a fibrous
web, the web has typically been sandwiched between two
moisture-absorbing felts and a belt. The felts are trained
around a cylindrical press roll with the web between them
while the belt is arranged for applying pressure to the felts
and roll. A pressure shoe exerts pressure on the belt in
the press area.
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A problem has been encountered during the
dewatering of webs in extended nips. It has been found
that a bulge developps 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 constructions are suggested for
overcoming the problem.
m e belt comprises a base fabric which is
impregnated with a thermoplastic or thermosetting polymeric
material. me base fabric which can be single layer or
multilayer, is sufficiently open to allow total irnpregnation
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. ~ base fabric is
provided endless using conventional fabric technology and
then coated and impregnated with the polymeric material.
A method for manufacturing the endless belt
comprises-coating and impregnating of polymeric resin by
doctoring into the fabric and curing said resin to form a
smooth surface.
m e resulting structure is both light in weight
and sufficiently stable to operate under paper machine
conditions. It has sufficient abrasion resistance 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, the invention provides
a belt which will maintain its integrity. It also solves
the problem of bulging near the press nips. ~le belt has a
uniform smooth polymeric surface which is engaged by a
pressure shoe applying pressure in the direction of -the roll.
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Having thus generally described the nature of the
invention, reference will now be made to the accompanyin~
drawings, showing by way of illustration, a preferred
embodiment thereof, and in which:
Figure 1 is a side elevational view of an
extended press nip according to the
invention'
Figure 2 is a partially sectional front view of
the press nip shown in Figure 1, and
Figure 3 is a sectional side elevational view
of the belt employed in the invention.
An extended press nip is provided by the invention
for dewatering a travelling web of material. m e nip 10
i9 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 roll. The arcuate surface of the
pressure shoe has about the same radius of curvature as
the press roll. m e distance between the press roll and
the pressure shoe may ~e 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 other arrangements may be utilized in accordance
with the invention.
m e 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
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which is impregnated with a polymeric material 22. Thermo-
setting resins such as polyurethanes have been 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 forming in the final fabric which would allow the
lubrication used between the belt and shoe to pass through
the belt and contaminate the felt and fibrous web. It is
endless in final construction and uniform in thickness.
m e 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. --
me 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.
Ihe belt has at least one smooth side 16' which
contacts the pressure shoe 14.
Belts manufactured in accordance with the invention
have been found to have many desirable characteristics. They
move easily over the pressure shoe and are capable of trans-
mitting pressure ~rom the shoe to the web and press roll.
Sufficient flexibility 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" x 170" belt impre-
gnated with a thermosetting resin in accordance with the
invention weighs about two hundred pounds. A similar size
belt having bulge-resistant characteristics and having a
structure defined in the above mentioned patents weighs about
twelve hundred pounds. Unlike the heavier belts, the in-
vention does not require a reinforcing structure.
m e manufacture of the belt according to the
invention may be accomplished economically and without the
need for mandrels or autoclaves which limit the size of
other belts. A ~elt of any length can accordingly be
produced. m e base structure is first woven. A web may
be needled into the woven base if desired. If the base
structure has not been woven endless it is then joined
endless using conventional joining techniques applicable
to forming fabrics in the paper industry. A polymeric
material is then applied to the base fabric and forms a
mechanical 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 caliper having at least one smooth surface~
A belt made in accordance with this invention may
be utilized with the apparatus shown in Figure 1. me
belt 16 is positioned between the pressure shoe and the
pressure roller. The smooth coated side 16' of the belt
is engaged by the shoe. A fibrous web 24 carried between
first and second felts 26 and 27 respectively is introduced
into the press nip 10~ The side of the belt 16 engaging
the shoe 14 is lubricated by lubricating means 28 positioned
ahead of the nip.
The belt 16 is easily repaired should a hole or
other surface irregularity develop therein. me damaged
portion is cleaned with a solvent and a suitable amount o~
coating is applied with a blade. ~ heat gun is employed to
cure the surface which can then be sanded.
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Because of the excellent flexibility characteristics
of the base structure and the fact that the coating can be
kept to a minimu~, the surface of the belt will have less
tendency to fail due to bending fatigue. mis 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. mis 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 stabilized, and joined endless using normal
joining techniques~ me fabric was then coated with a 100%
solid polyurethane 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.
Example 2
A monofilament fabric is woven into a two layer
2G weave having sufficient 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. m e 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
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the polyurethane to flow into the fabric~ A pressure
roll may be used against the outside of the fabric to
insure complete impreqnation. The polyurethane is
plasticised and forced into the voids of the fabric.
A smooth surface is obtained which does not require any
further finishing 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 fabric has undergone the pressing operation, the
edges are trimmed and sealed for operation in a paper-
making machine.
Example 3
A monofilament polyester base fabric having
sufficient openness for impregnation is provided. m e
fabric is a two layer weave having both width and length
stability. A polypropylene film having a thickness of
about 0.020 inches or more is fused to the base fabric
in the manner described in Example 2. m e temperature
of the oil cylinder is maintained at a substantially
constant level to obtain uniform melting and fusing of
the plastic film. l~e base fabric has a higher melting
temperature than the polypropylene film and is not dis-
turbed by the heating process. After th~ fabric has
undergone 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 paper-making machines. Materials other than
polyurethane and polypropylene may also be employed as the
coating material.
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This application is a division of application
Serial No. 411,393, filed September 14, 1982.
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