Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
1. Field of Invention
The field of the invention relates to impermeable
belts with smooth inner surfaces and more particularly to a
belt used in an extended press nip for dewatering a fibrous
web formed in a papermaking machine.
2. Description of the Prior Art
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 pro-
cess, after which the newly-formed web proceeds to a press
section. The 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. The 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. This fact has been recognized by those skilled in
the art, and several patents have been granted in the area.
These U.S. patents include Re. 30,268 (May 6, 1980, Edgar J.
Justus), 4,201,624 tMay 6, 1980, William C. Mohr et al),
4,229,253 (October 21, 1980, Dennis C. Cronin) and 4,229,254
(October 21, 1980, Michael L. Gill).
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1 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
S belt is arranged for applying pressure to the felts and
roll. A pressure shoe exerts pressure on the belt in the
press area.
The belt is provided with a very smooth surface for
contacting the shoe so that it can transfer pressure to the
felts and the fibrous webs without overheating or wearing
away. Furthermore the belt must be impermeable to oil used
to lubricate its passage over the shoe which could conta-
minate the felts and the web. Heretofore the belt was made
by applying a polymer coating to the outer surface of an
endless fabric. Since the belt is arranged so that its
inner surface is the shoe-contacting surface, the endless
coated fabric i5 then reversed (i.e. turned inside out).
While this procedure was satisfactory for belts having a
length of 24 feet or more, it has been found that it is
difficult to reverse belts having a length of less than 24
feet. Furthermore it was found that it was difficult to,
apply the coating to the outer surface of shorter belts.
OBJECTIVES AND SUMMARY OF T~E INVENTION
An objective of the present invention is to provide a
relatively short belt with a smooth inner surface, adapted
to be used in an extended press nip.
Another objective is to provide a belt which is
impermeable to oil.
A further objective is to provide a method of producing
the above-mentioned belt.
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Other objectives and advantages shall become apparent
from the following description of the invention. According
to this invention a belt is constructed of an endless base
fabric embedded in a polymeric substance formed with a
smooth, frictionless inner surface. The belt is made by
providing a mandrel with a smooth outer surface, placing the
endless base fabric on said mandrel covering with an outer
shell, and then impregnating the base fabric with a polymer.
As the polymer solidifies the outer surface of the mandrel
forms a smooth inner polymer surface.
Therefore, a construction in accordance with the present
invention comprises an endless papermaking belt for use in a
papermaking extended nip press which includes an endless base
fabric of open construction, an impregnating material
penetrating the base fabric to form a smooth inner surface
thereon. The base fabric is completely contained within the
impregnating material.
Also, in accordance with the present invention, there is
provided a method of coating an endless base fabric, to
produce an endless belt with a smooth inner surface, for use
in an extended nip press. The method comprises the steps of
providing an endless base fabric of open construction,
providing a cylindrical mold with a smooth mandrel and a
concentric uniformly spaced outer shell, and disposing the
endless base fabric within the mold on the mandrel. The
method also comprises the steps of maintaining the
cylindrical mold in a stationary condition, providing a feed
means extending into the space between the mandrel and the
outer shell, and injecting a polymer into the space between
the mandrel and shell, using the feed means, to totally
impregnate the fabric of open construction and causing the
polymer to be cross-linked.
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Also, in accordance with the present invention, there is
provided a method of coating an endless base fabric, to
produce an endless belt with a smooth inner surface, for use
in an extended nip press. The method comprises the steps of
providing an endless base fabric of open construction,
providing a cylindrical mold with a smooth mandrel and a
concentric uniformly spaced outer shell, providing a feed
pipe having an exit and located in the uniformly spaced area
between the smooth mandrel and the outer shell. The method
also comprises the steps of disposing the endless base fabric
within the mold on the mandrel, and injecting a polymer via
the feed pipe directly into the space between the mandrel and
shell so as to totally impregnate the fabric of open
construction and causing the polymer to be cross-linked.
Also in accordance with the present invention, there is
provided a further method of coating an endless base fabric,
to produce an endless belt with a smooth inner surface, for
use in an extended nip press. The method comprises the steps
of providing an endless base fabric of open construction,
providing a cylindrical mold with a smooth mandrel, disposing
the endless base fabric within the mold on the mandrel. The
method also comprises the steps of hermetically sealing the
mold by covering it with a uniformly spaced outer shell,
injecting a polymer directly into the space between the
mandrel and the shell, and applying heat to the mold to
cross-link the polymer.
Brief Description of the Drawings
Figure 1 is a side elevational view of an extended press
nip employing the belt constructed according to the
invention;
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Figure 2 is a partially sectional front view of the
press nip shown in Fig. l;
Figure 3 is a sectional side elevational view of the
belt employed in the invention; and
Figure 4 is a partial sectional side view of the
apparatus used to produce the belt constructed in accordance
with the invention.
Detailed Description of the Invention
An extended press nip is provided by the invention for
dewatering a travelling 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 roll. The arcuate surface of the pressure shoe has
about the same radius of curvature as the press roll. The
distance between the press roll and the pressure shoe may be
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1 adjusted by means of conventional hvdraulic or mechanical
apparatus (not shown) connected to a r,od 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 as shown in Figures 1-2 are conventional and that
other arrangements are also well known in the art.
Paper web 24 is carried to and away from the nip by a
first felt 26. A second felt 28 is used to absorb the water
expressed from web 24 in the nip.
A lubricating means 30 is used to apply a lubricant
such as oil to the inner surface 16' of belt 16 to further
reduce friction between said inner surface and shoe 14. The
belt is entrained by rollers 32 used to drive the belt in a
predetermined path as shown.
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.
20 The belt 16 comprises a base fabric 34 which is impregnated
with a polymeric material 36. Thermosetting resins such as
polyurethanes have been found to be suitable impregnating
materials. Preferably a 100% polyurethane resin should be
used to avoid formation of bubbles during the curing of the
25 belt structure. Thermoplastic polymers such as
polypropylene are also acceptable.
The base fabric 34 is sufficiently open to allow total
impregnation. This eliminates the possibility of any voids
forming in the final fabric which would allow the
30 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. The
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l fabric must also be made to have sufficient stability under
paper machine conditions. In other words, it must have
- length stàbility, width stability, and guideability.
The base fabric may comprise a single or multi-layered
flat woven fabric which has been heat stabilized and joined
using normal joining techniques. The base fabric may be
made of polyester or other polymeric materials having the
necessary properties in accordance with the invention. The
base may be made endless by endless weaving also.
At least one of the sides or surfaces of thé belt, such
as side 16', is smooth for contacting 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
transmitting pressure from 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.
The belt is manufactured in a cylindrical mold 38
(Figure 4) with an outer shell 39 and a concentric mandrel
42. The mandrel is provided with a smooth outer surface 40.
The spacing between the outer shell 39 of the mold and the
inner mandrel determines the thickness or caliper of the
belt. The base fabric 32 is first placed on the smooth
mandrel surface 40 and then the mold 38 is hermetically
sealed with cover 44. Next, the pressure within the mold is
reduced by substantially removing the air contained therein
via a pipe 46 connected to a vacuum source (not shown).
After the pressure within the mold has been reduced, an
appropriate polymer is injected into the mold through pipe
48. Because of the low pressure inside the mold, the
polymer quic~ly fills the mold including the interstices of
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1 the fabric. Advantageously, a smooth inrer polymer surface
is formed along the mandrel surface 40. The polymer is
cross-linked by applving heat to the mold. After the
polymer has cured the finished belt may be removed from the
mold.
Alternatively a polymer catalyst mixture may be used
which is self cross linking if left undisturbed several
hours.
The resulting belt is shown in Figure 3, with the
fabric 34 being fully impregnated with and impermeable to
oil and other substances. The belt has a uniform caliper as
a result of the molding operation.
Numerous modifications can be made to the invention
without departing from its scope as defined in the appended
claims.
