Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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11-120P
APPAP~ATUS AND PROC~SS FOR A ~ECURLING SYSTEM
BACKGROUND OF THE INVENTION
This invention relates to a decurling operation and
more specifically to a steam shower decurling system which
is markedly more efficient and effective in achieving
improved decurling capacity than traditional steam shower
operations.
As iS commonly known, when a web material is supplied
in the form of a roll there is an initial curl in the web
depending on such factors as the length of time the roll
has been stored in stock and variation in the roll dia-
meter, such as the curvature of the different convolutions
making up the roll. In order to compensate for these
influences on the straightness of a web, it has been found
necessary to provide certain prescribed treatments to
straighten the web material such as described in U.S.
Patents 3,1aS,6:16 and 3,649,447, ~o that when it is ulti~
mately cut lnto sheets, the handling of the sheets may be
facilitated and the undesirable curling effect eliminated.
While these existing devices for straightening webs have
been found useful, they have not been altogether satis-
factory in ~he sense that they are expensive and/or re-
quire complicated mechanisms.
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In the case of paper, it is known that increasing the
moisture con~ent of the paper will lead to less trouble
from curling than paper having a lower moisture content.
~ith respect to a coated sheet, for example, it is known
that the latter will tend to curl towards the last side
coated, and thus moisture is applied to the side opposite
to which the sheet otherwise would tend to curl. Thus, as
regards the paper industry, the controlled and uniform
application of moisture to raw stock and/or coated webs is
a goal of distinct importance.
Several methods have been proposed for applying mois-
ture to a moving sheet or web. Examples of these include
roll applicators such as the Dahlgren-type systems, elec-
trostatic systems such as disclosed in U.S. Patent 3,467,541
and steam shower devices. Other examples for adding
moisture to a web include a method and apparatus for
applying steam to and condensing moisture on a web that is
backed by a heat conducting body, as disclosed in U.S.
Patent 2,370,811 and ~ device that directs a humid atmos-
phere towards the web, as disclosed in U.S. Patent 3,238,635.
While these and other techniques have been Eound useful
in applying moisture to a paper work piece so as to minimize
the undesirable curling properties of the paper, there
have been found inherent disadvantages in their use. In
one instance for example, condensation of steam vapor on
the web is produced because the web is backed by a heat
sink or me-~al roll through which a cooling fluid is passed.
In the case where humid atmosphere is directed toward the
web the SySteln has been proven to be inefficient. Furthermore,
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in the case where steam showers are employed directly,
decurling has been strictly governed by the steam pressure
employed at the shower head. Lack of eEfective decurling
leads to the utilization or reliance upon excessive steam
pressures and/or reduced machine speeds. A change in
pressure has been demonstrated to have an effect on other
important variables such as the web ternperature, web-to-
shower distance and steam billowing. In addition, decurling
regulated by steam pressure alone is uneconomical and
inefficient. With a free floating web, a high level of
exhaust is required to counter the rise in web~to-shower
distance and to control the billowing effect resulting
from the additional steam usage, the increased amount of
steam required, which is essential to decurling, being
drawn away by the exhaust. The resulting lack of decurling
capacity leads to costly limitations on both quantity and
quality.
SUMMARY OF THE TNVENTION
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It is, therefore, an object of the present invention
to provide a steam decurling system ~or a web material,
such as a coated paper stock, which will overcome the
above noted disadvantages.
It is a further object of the present invention to
provide a steam decurling configuration which stabilizes
¦ the web material in the vicinity of the site of steam
I emission.
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It is another object of the present invention to provide
a steam decurling apparatus and process which effectively
regulates the distance of the web material to the steam
shower under variable operating conditions.
Sti~, a further object of the present invention is to
provide a system whereby the web to shower distance is
maintained relatively constant without contact with the
web material.
Another object of the present invention is to provide
a steam decurling system which eliminates fluttering of
the treated web material to produce a more uniform steam
application and penetration.
It is still another object of the present invention to
effectively cool the web so as to realixe more eficient
steam condensation.
Yet, still a further object oE the pre.sent invention
is to provide a decurling configuration wherein the area
about tha steam shower is confined so as to closely
control the billowing effect produced by the steam with
minimal exhaust.
Yet, another object of the present invention is to
provide an effective decurling operation while substan-
tially reducing the amount of normal steam pressure
required during the process.
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The foregoing objects and others are accomplished in
accordance with the present invention generally speaking,
by providing a steam decurling system wherein a paper web9
or the like, is driven through a steam shower environment
for purposes of increasing the moisture content of the web
material. The steam showers are emitted from a source7
such as a steam pipe, from beneath the surface of the web
material. Positioned above the web and spaced therefrom
is at least one air source assembly so designed to
effectively control and regulate the distance of the web-
to-steam shower source under variable operating conditions
without contacting the web material. By carefully con-
trolling the distance between the web material and the
source of the steam7 the deposit of the steam on the web
surface is more uniform and the resulting decurling effect
more dynamic. It is preferred that the air foils be
positioned just prior to the outlet for the steam from the
respective steam source. The above described method and
configuration provide for a close regulation of those
factors which have the most influential effect upon a
decurling operation.
It has been determined in the course of the present
invention that the factors found to most significant in
controlling the curling effect related to paper technology
and more specifically to the fabrication of coated paper
webs, are the web-to-moisture source distance, web
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temperature, steam pressure, and exhaust leve~. By
implementing the system of the present invention, the
regulation of these factors has been effectively achieved.
The configuration of the present invention provides for
reliable control of the distance between the web material
and the source of the steam shower without contacting the
web material which effectively elirninates the fluttering
effect resulting from excessive steam pressures applied,
producing a more uniform steam application and penetra-
tion. The utili~ation of the air foil system has an
additional cooling effect upon the web surface, thus
causing more efficient steam condensation on the web. By
confining the area about the steam shower, the billowing
efEect produced by the steam, under pressure, is minimized
thus eliminating the necessity of extreme exhaust COD-
ditions.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is Eurther illustrated by way of the
accompanying drawings wherein E'ig. 1 represents a con-
ventional steam shower decurling con~iguration and Fig. 2
represents the steam shower decurling system of the
present invention.
DETAILED DESCRIPTION
¦ Referring now to Fig. 1 there is seen a stearn shower
¦ decurling structure generally designated 1 consisting oE a
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steam shower housing ~ and the source~ oE steam repre~ented
herein as two,steam pipes 3 and 4 with related orifices 5
and 6. A web material 7 from feedroll 8 passes above the
steam pipes 3 and 4 and is taken up on idle roll 9. Ex-
haust cha~bers 10 are provided for re~loval of excess steam.
In the instant illustration decurl ing i5 regulated by
steam pressure alone with a free-floating web. Under
these conditions, the steam pressure applied adversely
effects the resulting web-to-steam shower distance and
leads to excessive steam billowing. In order to counter
this effect? high level exhausting is implemented which
leads to excessive removal of sLeam by the exhaust system
therefore requiring a step up in steam usage.
In Fig. 2 is seen the steam decurling unit of the
present invention generally designated 20 comprising the
steam showe~ housing 21 containing the steam sources,
herein represented as steam pipes 22 and 23. The steam
showers are emitted from the steam pipe orifices 24 and
25, respectively. The web sheet 26 Erom feed roll 27 is
introduced above the steam pipes 22 and 23 to take up roll
28. Position~d above the web ~aterial are two air ~oil
assealbly units generally designated 31 and 32. Each air
foil asse~bly comprises air foil housing~ 33 and 34 and
infeed ducts 35 and 36 attached to some remote air blower
(not shown). Exhaust units 29 are provided for the
contro'lled venting of the steam during the steam shower
process. When the moisture is uniformly applied to a
coated web or paper sheet, the web is ~ed in a manner such
that the moisture is applied to the side opposite to which
the coating was last applied.
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Each foil is positioned or offset just prior to the
steam pipe orifices 24 and 25 such that the leading edges
of the air foil units 33 and 34 are located approximately
1/2" to 3/4" prior to the orifice or center line of the
representative steam pipe 22 and 23. The foil pressure is
maintained such that the web material 26 floats uniformly
between the foil units 33 and 34 and the sources of the
steam showers 22 and 23 so that the distance between the
steam pipe orifices and the web material is maintained
substantially constant. For optimum results, it is pre-
ferred that this distance between the web and steam shower
orifice be about 1/2 the distance (d) between the air foil
and the steam shower source. The offset of the air foils
from the steam pipe orifices avoids potential damage to
the web surface due to high steam pressures while providing
a cushioning effect on the web in the area immediately
above the steam pipe orifices. The utilization of the air
foil maintains the web-to-steam source distance constant
without contacting the surface of the web material. This
is especially significant when the upper surface oE the
web material has a coating thereon. Elimination of
unnecessary contact reduces the possibility of imparting
surEace impairment to the web.
-The utilization of the air foils of the present
invention to maintain a fixed steam pipe-to-web distance
insures that the deposition of steam on the web surface is
more uniform thus resulting in a more satisfactory
decurling process. Furthermore, the presence of the air
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foil stabilizes the web in the vicinity immmediaLely above
the steam pipe orifices while preventing web contact with
either the foil surface or the steam pipes, with the air
film promoting temperature reduction enabling adequate and
sufficient steam condensation at the web surface. rhe
preferred air foils pressure~range is from about 7 to 9
inches of water. Steam pressure is generally regulated at
about 5 lbs. with it being preferred that the steam
pressure not exceed 30 lbs. Furthermore, with the
increase oE the speed of the web material it has generally
been found necessary to increase the steam pressure in
order to penetrate the air ~ilm barrier along the web
surface. In the case of the present invention, the
increase in the web speed does not necessarily require an
increase in steam pressure in order to achieve the desired
surface exposure to the moisture.
Although in the present illustration the con~iguration
nas been represented as containing two stearn sources
adjacent the two air foil units, this is ~or purposes of
describin~ the system oE the present invention and is not
intended to be a limiting ~actor thereo~.
The invention being thus described, it will be obvious
that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and
scope o~ the invention, and all such modi~ications as
would be obvious to one skilled in the art are intended to
be included within the scope of the following claims.
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