Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1221~69
BAC K~; ~OUND O_I'fIE INVENTI ON
The present invention relates to a method for surface
sizing of a paper web to be employed in connection with the running
of a paper machine, as an "on-machine method", and, particularly,
for conducting the web which has been surface-sized on both of its
sides and thereby has been wetted, through the surface sizing steps
to a subsequent drying section of the paper machine.
The present inventi~n also relates to a paper machine
drying section adapted to be used in connection with carrying out
the method ~f the invention and which includes a prior drying
section constituted by a group of drying cylinders and which is
followed by a size press which in turn is followed by a subsequent
drying section of the paper machine comprising a plurality of drying
cylindexs.
Moreover, the present invention also relates to paper
manufactured by the method and apparatus of the invention, and in
particular, printing paper, e.g. newsprint.
In the following the terms "surface sizing" and "coating"
are used and both relate to a paper web treatment procedure where
the web is conducted in connection with a material solution or
suspension so that a part of this material adheres onto the web
surface and/or penetrates in the web. The materials used for said
purpose can be different mineral pigments for coating, e.g., starch
or glue solutions for sizing.
Surface sizing is a relatively simple and inexpensive
technique for improving the quality of paper products. The majority
~ XZ~69
~f fine and printing paper products produced are in fact surface
sized or coated.
Surface sizing is usually carried out in an on~machine
size press which forms a part of the paper machine. The surface
sizing of fine and printing paper products which contain mechanical
pulp is being carried out to an increasing extent, particularly
with a view towards offset use. Other types of paper products
which are surface sized or pre-coated in a size press include kraft
liner, different boards and various base papers.
In fact, there are many applications for size presses
which are currently known, these applications being divisible into
four categories, namely
(1) surface sizing of writing and printing papers;
(2) surface sizing and pre-coating of base papers;
(3) pigmenting and coating of paper; and
(4) manufacturing special grades of paper.
The surface sizing technique generally comprises running
the paper web through one or more size press nips of a size press.
The sizing agent is supplied in the press in contiguity with the
paper by creating a pool of size material before the size press nip
and through which the web passes whereupon it is wetted through ab-
sorption of the sizing material. The sizing is urged into the paper
web between the rolls of the size press by the action of hydro-
dynamic pressure. At the same time, due to the action of the hydro-
dynamic pressure, a film of sizing solution or suspension is formed
between the paper and the size press roll, this film becoming split
--2--
~ 2Z15~g
~t the exit side of the throat of the roll, lcaving ~chind ~ layer
of sizing on the surface of the paper. The amount of the sizing agent
that remains on the paper depends on the viscosity of the sizing agent,
the machine speed, the diameter of the size press roll, the surface
characteristics of the roll, the lineal pressure in the press nip and
factors resulting from the deformation o the roll.
The oldest among conventional size presses is the so-called
vertical press whexein the size press rolls are positioned one above
the other and the paper web runs horizontally between the rolls. In
the so-called horizontal size press, the rolls are situated in a
horizontal plane and the paper web run-~ vertically between them.
The third type of known size press is the so-called oblique press
wherein the size press rolls are disposed one above the other at an
angle of about 45. This latter size press is considered most suit-
able where the web is running through the paper machine at high speeds.
The diameters of the size press rolls are important when
the runability of thç machine is considered. In conventional size
presses, the rolls forming the nip have diameters on the order of
800 to 1~00 mm at running speeds of between 10 and 17 m/sec. It is
common practice to increase the roll diameter when the running
speed is increased in order to attempt the avoidance of splashing
in the throat of the size pool, such splashing interfering with uni-
form wetting of the paper web.
Rubber is usually used as the cover material of the size
press rolls. In some conventional size presses, the nip is defined
by a hard roll made of metal and a soft roll formed of rub~er. Thus,
12Z~69
both harder and soft~r pressing zones or nips are used in conven-
tional size presses. As noted above, at higher speeds of web
conduction, larger diameter rolls are utîlizedO
Another factor which contributes to a good surface
sizing of the paper web is that not only should the wetting time of
the web be at least of a certain duration but, additionally, the
pressure exerted on the paper web in the nip should be relatively
high, such as between 20 and 50 kN/m.
Regarding the state of the art with respect to s~ze
presses, reference is made as an example to Finnish Patent ~o.
28686 to Combined Locks Paper Co., of the united States, published
March 15, 1957. A paper coating machine is disclosed in this patent
which comprises a hard central roll having two nips defined in con-
junction therewith through which the paper web desired to be
treated is passed. The sizing, or other coating substance, is
initially introduced from a trough over a plurality of applicator
rolls onto the hard-surfaced roll from which it is pressed into the
web in the first nip. The other side of the web is coated by
introducing the coating substance onto the subsequent nip roll from
a trough by way of a plurality of applicator rolls. The coating
substance is thus pressed onto the surface of the web in the second
nip defined in conjunCtiQn with the hard central roll. According
to the teachings of this Finnish patent, the nips defined by the
nip rolls in the hard central roll are disposed relative to the
central roll substantially symmetrically with respect to the verti-
cal plane passing through the axis of thc central roll under a
i2;21~69
central angle of about 45 with respect to the vertical plane.
Moreover, according to the method disclosed in the
Finnish patent, the coating substance is introduced utilizing
small diameter applicator rolls. However, the present invention
relates to size presses in which the sizing or other coating sub-
stance is introduced by means of nozzles to form a pool located
between the paper web and the roll surface.
Reference is also made to ~.S. Patent No. 4,108,110,
U.S. Patent No. 4,391,217 assigned to the assignee of the instant
application, which relate to size presses. Reference is further
made to U.S. Patent No. 4,407,227 assigned to the assignee of the
instant application, which relates to a size press having a sub-
sequent web heating apparatus.
Moreover, reference is made to size presses of the type
with which the present invention is associated, which comprises
three coating rolls which are associated with each other to
define two press nips through which passes the paper web to be
treated in a manner such that both sides of the web receive
treatment in the nip.
In a size press of the type described above, the coat-
ing roll which constitutes the middle roll with respect to itsvertical position is situated so as to be a central roll of the
size press and in conjunction with which both coating nips are
formed such that the first coating nip is situated at an appro-
priate angular dlstance
~ - 5 -
~221569
above the horizon~al plane Whicll passes through the axis of the
central roll and such that the second coating nip is defined by the
third coating roll which is situated at an appropriate angular dis-
tance below the horizontal plane. Sizing supply means precede the
first nip in the direction of the run of the web on the central
roll which means supplies a first pool or layer of sizing into the
cleft or throat between the central roll and the web. Second sizing
supply means are situated to precede the second nip in the throat
defined by the central roll and the third coating roll. The second
size supplying means provide a second pool or layer o sizing on the
opposite side of the web with respect to the first sizing pool or
layer. The size press is arranged so that as the web runs in a
down~ard direction it is supported by the roll surface while the
sizing operation proceeds.
Since the size press arrangement of the present invention
is an "on-machine" arrangement which is adapted to be connected to
and ~unction with the drying section of a paper machine which pre-
cedes it as well as with the guide and drying means subsequent thereto,
it must be capable of runninq at a speed which is as high as that at
which the paper machine is being run. However, in many instances,
the size press as well as the equipment immediately subsequent thèreto
have constituted a limiting ~actor or bottle-neck which restricts the
speed of the paper machine.
It is the primary object of the present invention to elim-
inate this drawback.
i22~5691
It should be understood that although the ~bove dis-
cussion is directed to "size presses", the term "size" is used
herein in its broadest sense to designate known substances and
materials used in connection with the treatment of paper or board
webs and which are suited for use in apparatus of the type des-
cribed below.
The size press is an important aid in the paper making
industry and has enabled the quality of paper to be improved, new
types of paper to be developed, as well as new combinations o raw
materials to he adopted. However, as noted above, one of the dif-
ficult problems which arise in connection with surface sizing of
paper, as discussed above, is that surface sizing could not here-
tofore be utilized in connection with high speed paper machines.
Moreover, surface sizing has heretofore not been applicable to the
treatment of thin or weak paper types, such as those contained in
groundwood and fillers, and/or paper types manufactured of short
fibre pulp stoc];.
The size press is normally situated in the drying sec-
tion of a paper machine at a location where the water content of the
paper web prior to the size press is about 3% to ~/0. In some cases
water content may be as high as about 15%. The size press is pre-
ferably located in a drying section in a manner such that the
widest possible range of paper types can be run at maximum produc-
tion speeds in a manner which insures that the drying operation will
not become a bottleneck either before or after the size press.
lX21~;69
Another problem which frequently arises in connec~ion with
the surface sizing of paper results from the fact that the water
content of the paper web subsequent to running through the size
press varies over wide limits, such as within 15% to 55%.
More particularly, after the last nip of the size press,
the web normally remains adhered to the surface o.f the hard size
press roll and follows along therewith. It is advantageous to
detach the web from the hard roll as soon as possible. After
leaving the press, the web will increase in width as a result of
swelling of wetted fibers and since such expansion requires a given
minimum time to occur, the distance from the last sizing nip to the
next drying cylinder is conventionally arranged to be relatively
long. However, a long free draw between the last sizing nip and the
next drying cylinder creates problems for the reason that a high
amplitude, uncontrolled fluttering of the web will occur on this
free draw. Such fluttering frequently causes web breakage s~e, as n~ted
above, the web has a relatively high water content, i.e., up to
about 55%, on the free draw. TherefOre, in fact, it has not been
practical to use a size press in connection with thin webs and/or webs
formed of raw materials which do not provide sufficient strength for
the web in view of the surface sizing operation and the subsequent web
treatment steps. These problems become even more acute as the speed
of the paper machine is increased.
It is also known in the art to interpose a paper spreading
roll between the last size press nip and the subse~uent drying section
of the paper machine with a view toward preventing the formation of
wrinkles in the paper web.
-8-
~L22:1~i69
~ s ~ur~l~c~- ~no~ n ~ C art, ~lL~L lc(~villg thc iizc ~rcss,
the paper web may be dried in a standard multiple cylinder drier in
which the first drying cylinder after the size press operates without
a felt. In this connection, it has been necessary to maintain the
surface temperatures of the two drying cylinders next following the
~ize press at a relatively low level, e.g., about 70 to 80 C, since
higher drying temperatures would tend to damage the surface of the
paper. Moreover, the sizing or coating material and the associated
fibres would tend to adhere to the drying cylinder whereupon the
paper may give off dust and the like in spite of the surface sizing
operation. Attempts have been made in the art to avoid this draw-
back in connection with the manufacturing of pigment-coated paper by
drying the coated web surface with warm air immediately after it
leaves the size press.
The three-roll, two-nip size presses described above are
suitable for running at relatively high speeds in connection with
the two-sided surface sizing of the web and, therefore, such size
presses are applicable for use on modern high speed paper machines.
In such cases, however, it is apparent from the foregoing discussion
that the web treatment steps following the surface sizing becomes
the bottlenec~ in the paper making operation. In addition to the
drawbacXs mentioned abo~e, these subsequent treatment steps are
further encumbered in that a felt cannot be used in connection with
the initial drying cylinders aftex the size press which in itself
results in a reduced dryins capacity and in a tendency for web breaks
to occur at the free draws between said drying cylinders. It has
122~i6~
also been nccessary in conventional arrangcments to use at least as
the first drying cylinder after the size press a chromium-surfaced
or other relatively expensive cylinder in order to prevent adhesion
of the surface sized or coated web thereto.
Regarding the state of the art most closely related to
the present invention, reference is made by way of example to a
publication in TAPPI, Vol. 57, No. 6, 1974 by Donald W. Lawton
entitled "Airflo~ Floater Drying After A Size Press", Page 105-107.
Reference is made in this article to a conventional floater dryer
mounted in an oblique position subsequent to a single-nip size
press in the direction of web run. This arrangement differs from
that of the present invention in that, among other aspects, a return
roll is provided in the conventional arrangement after the size
press nip and before the floater dryer. The disadvantages of the
return roll are acknowledged in the article although the author
fails to recognize any means by which the drawback can be eliminated.
Thus, the use of such a return roll has been considered
necessary in view of practical considerations regarding the run-
ability of the machine. However, the return roll frequently de-
stroys the s~rface sized surface of the web. It is a further
disadvantage that when conventional floater dryers whose ai~. it is
to achieve a high drying efficiency are used, the opposed nozzles
of the floating dryer are spaced too closely and, accordingly, an
--10--
12Zl~;69
uncontrolled wave actîon is obtained which does not have an
amplitude and a wave length suitable to achieve stabili-
zation of the web. An additional risk which results f~ the overly
close spacing of the nozzles is that the web may come into contact
with the nozzle surfaces while in the conventional floating dryers
thereby causing web breakage. Yet another disadvantage of con-
ventional floating dryers is that it is not possible to substanti-
ally vary the angle at which the web enters the dryer without
risking web contact and breakage and that such floating dryers do
not spread the web in the cross-machine direction.
It is another object of the invention to avoid these draw-
backs inherent in the use of conventional floater dryers of the
type described above.
SUMMARY OF THE INVENTION
Accordingly, it is the general object of the present in-
vention to provide a method and apparatus in a size press and sub-
sequent web treatment in which the drawbacks mentioned above are
eliminated.
More particularly, it is an object of the present invention
to provide a method and apEaratus in a size press and subsequent web
treatment wherein even thin webs and/or relatively weak webs con-
taining groundwood and/or fillers and/or of short fibre pulp stock,
~ be treated at high running speeds without an excessive risk of
web breakage.
It is a further object of the present invention to provide
a method and apparatus in a size press and subsequent web treatment
wherein in the web treatment step following the surface siæing, the
web can be run with a lower tension allowing the web to be deformed
in a transverse direction, e.g., spread, to a desireable extent.
:, --1 1-- ,
1221~i9
Briefly, in accordance with ~h~ present invention, th~se
and other objects are attained by providing a method wherein the
web, arriving from a prior drying section of the paper machine, is
surface-sized on both sides thereof in at least one size press nip,
conducting the web after the surface-sizing step, either directly
or by way of a non-contact turning, supporting and/or spreading
means, to a stabilizer means which acts to support the web in a
non-contacting manner and whereby the run of the web is stabilized,
thereafter conducting the web, either directly or over a non-contact-
ing turning, supporting and/or spreading means, or spreading roll,
to a subsequent drying section of the paper machine, and wherein
the non-contacting stabilizer means and additional web conducting
means, if any, are so disposed that the free draws of the web run
will be not be unduly long considering the possibility of free
fluttering of the web, and so that the web is allowed to spread
out in its transverse direction.
The apparatus of the invention is essentiall~ character-
ized in that it comprises a stabilizer means which acts on the web
from both sides thereof utilizing gas flows and which is situated
after the size press and before the subsequent drying section of
the paper machine. Moreover, the paper product o~ the present in-
vention is mainly characterized in that the paper is newsprint or
the like, the printability propertiesof which have been achieved
essentially by a two-sided surface sizing of the web.
The method and apparatus of the present invention provide
advantages which are important in practice and, moreover, climinate
a number of drawbacks inherent in conventional apparatus. The most
important advantage obtained is that thinner and weaker wcbs can berun
ina more stabilized, flutter-free mannerthan has been possible here-
tofore and, therefore, with the risk of wcb breakage at higher speeds
-12-
~ ZZ~ifi9
being significantly reduced. Moreover, af ter tl-e surfacc-sizing,
the web can be treated in a manner such that the web can be conducted
to a standard multiple cylinder dryer section in which it is possible
to utilize a felt fabric conduction and which is operated at full
efficiency, i.e., at increased temperature levels.
It is a significant advantage of the present invention
that completely new types of paper can be manufactured on modern
fast-running paper machines such, in particular, as newsprint paper
machines. The present invention therefore makes possible the manu-
facture of surface-sized newsprint from more versatile and advanta-
geous raw materials than has been possible heretofore and, addition-
ally, with better printabi~ity characteristics by virtue of the
two-sided surface-sizing. Furthermore, the runability of the paper
machine is improved. The desirability of such paper is readily
apparent, for example, in view of advertisements and multiple color
printing in newspapers.
By the method of the present invention, a so-called
synergistic effect is obtained since a contact-free and stabilized
guidance and support of the web is achieved with fluttering and web
breakage prevented while, additionally, the web is provided with
sufficient time and travelling distance between the size press and
subsequent drying section to allow the same to expand and spread in
a lateral direction and, if required, be positively spread out in a
transverse direction. This latter action is particularly advantageous
since in this manner the length of the web draw between the surface-
sizing operation and the subsequent drying section can be reduced.
According to the present invention, stabilizer means are advantageously
utilized to guide the web in a contact-free manner on both sides
thereof so that through the effect of gas, such as air,being directed
from consecutively arranged nozzles of the stabilizer means, the web
-13-
~22~;6~
runs with a substantially sinusoidal and controlled wave motion in
its longitudinal direction. By such controlled wave motion, the
free and uncontrolled fluttering of the web is preventcd while
wrinkles which extend longitudinally in the web are removed or
their formatîon prcvented. Heated gases may be used in the stabilizer
means so that both sides of the surface-sized web are dried to a
moisture content which is suitable with a view toward normal sub-
sequent drying steps. The use of such drying is, however, not
necessary in all cases.
It is further possible utilizing the apparatus of the
present invention to optimize the run of the web between the size
press and the subsequent drying section. Since the web on its run
between the surface-sizing steps and the subsequent drying section
can change direction in accordance with the present invention, it
now becomes possible to accommodate a sufficiently long contact-free
run of the web, such as to enable a transverse spreading thereof,
within a relatively short space in the paper machine hall.
DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily appreciated
as the same becomes better understood by reference to the following
detailed description when considered in connection with the accompany-
ing drawings in which:
FIG. 1 is a schematic elevational view of apparatus for
performing the method of the present invention and comprising a
three-roll, two-nip size press followed by a contact-free means for
turning and spreading the web, and followed by a contact-ree
stabilizer means;
FIG. 2 is a schematic elevational view of apparatus for
performing the method of the present invcntion and comprising a
- 1 ~ .
i2Zl~i9
three-roll, two-nip siæe press followed by a contact-free stabilizer
means, which operates utilizing heated drying gases;
FIG. 3 is a schematic elevational view of apparatus for
performing the method of the present invention and comprising a
two-roll, single-nip size press, followed by a contact-free stabilizer
means, which is followed by a contact-free web spreading and/or return
means;
FIG. 4 is a schematic elevational view of apparatus for
performing the method of the present invention and comprising a
two-roll, single-nip size press and wherein the web is conducted in
a straight draw to a contact-free turning and spreading means, which
is followed by a contact-free stabilizer means;
FIG. 5 is a schematic elevational view of an embodiment
of stabilizer means in accordance with the present invention;
FIG. 6 is an elevational view in section of a portion of
a nozzle utilized in the stabilizer means illustrated in FIG. 5;
FIG. 7 is a perspective view of a nozzle for use in the
stabilizer means of FIG. 5:
FIG. 8 is a more detailed view of an embodiment of the
web turning and spreading means for use in connection with the
present invention; and
FIG. 9 is a detailed view showing the carrying surface
of the turning means illustrated in FIG. 8 on a larger scale.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like reference
characters designate identical or corresponding parts throughout the
several views, and more particularly to FIGS. 1 and 2, the size
press 100, 100' comprises a web gui~croll 10 and the actual size
press rolls 11, 12 and 13, the rolls being mounted in a conventional
--15-
1221~6~
frame (not shown) along with other conventional components of a si~c
press. The web arriving from the paper machine at the size press for
treatment therein is designated by Win. The web leaving the size pre~s
after having been treated on hoth sides with a coating substance, such
as sizing, is designated Wl. The passage of the web through the size
press is designated by dashed lines in FIG. 1.
Guide roll 10 constitutes the first of the rolls belonging to
the size press in the direction of travel of web W. The first coating
nip Nl is defined by rolls 11 and 12, the roll 12 constituting a cen-
tral roll of the size press and of course is rotatably carried such,
for example, as in stationary bearing stands (not shown). The second
coating nip N2 is defined by the central roll 12 and the third or
lowermosk roll 13.
Two pools Ll and L2 f the coating suspension or size solu-
tion are formed in the size press 100, 100'. Thus, coating or size
substance is supplied to the first pool Ll through a sizing supply
tube 17 which extends over the entire breadth of the web W. The tube
17 carries a plurality of parallely disposed nozzle tubes 17a, or may
alternatively be provlded with an equivalent continuous nozzle slit.
The first sizing pool Ll is defined in the throat or cleft region
defined by the central roll 21 and the web W prior to the first nip
Nl. The sizing or other coating substance is absorbed into the first
side or surface of the web W whereupon the sizing is pressed into the
web W as the same passes through the nip Nl.
The size press 100 comprises a second sizing supply tube 18
for supplying the sizing material to the second pool L2. The sizing
supply tube 18 is disposed in conjunction with the third coating
roll 13 and dispenses sizing material through a set of sizing
supply nozzles 18a or through an equivalent nozzle slit. In this
manner, a second sizing pool L2 is formed before the nip N2 and the
-lG-
~ 22~56~
second, opposite side of the web W is treated and impreqnated with the
sizing material in pool L2. After passing through the second sizing nip
N2, the web W remains adhered to and follows the surface of the central
roll 12 over a sector(~ 3, after which the web W is separated from
the roll 12 and conducted to subsequent wet web treatment steps in
accordance with the present invention, described below.
As seen in FIG. 1, the web W laps the first press roll 11
over a suitable angle ~ 1 before entering into the nip Nl. This
arrangement is important since in this manner the web W is backed up
by the surface of the roll 11 in the region of the sizing pool Ll.
The angle ~ 1 has a magnitude preferably about 45. The geometry
of the rolls of the size press 100, 100' is such that the middle
roll 12 in the vertical direction constitutes the central rol7 while
the outer rolls 11 and 13 are so disposed that the first nip Nl and
the second nip N2 are substantially symmetrically disposed with
respect to the horizontal plane which passes through the central
axis of roll 12. The angle ~ 2 on the central roll 12 between the
nips Nl and N2 is preferably about 90.
It is known from experience that it is advantageous to
define a size press nip by situating a hard roll an~ a soft roll
against each other since when a pair of hard rolls define such a
nip, a tendency exists for holes to be formed in the paper. For
example, the central roll 12, which constitutes the hardest roll of
the size press, may have a so-called "micro rock" covering which has
a hardness in the range of about 0 to 1 P&J hardness degrees. The
roll 11 which defines the first size press nip Nl with roll 12 may
have a softer "micro mate" covering whose surface has a hardness,
for example, in the range of about 20 to 30 P&J degrees. Second
press nip N2 is defined by the central roll 12 and the other outer
roll 13 which may have a surface similar to that of roll 11.
1221569
In the emhodiment discussed above, the abovc-stated
criteria for a size press is realized in that a hard roll and a
soft roll define both nips Nl and N2 in a manner such that the
central roll 12 is the hardest roll and against which are urged
two softer rolls 11 and 13. Of course, the same end result can be
accomplished by providing the central roll 12 with a soft covering
and arranging two harder rolls against it.
The moisture content of the paper web W arriving at the
size press, such as from a prior drying section, is about 3 to ~/~.
Paper having a moisture content lower than about 3% is considered
brittle and presents poor aborptivity. If the moisture content is
greater than about ~/~, such moisture will generally be distributed
in a non-uniform manner and the absorptivity of the paper will be
too high. The lineal pressure in the nips Nl and N2 is generally
between 10 and 50 ~N/m and preferably in the range of about 30 to
40 ~N/m. Usually, at least two of the three size press rolls 11,
12 and 13 will require deflection compensation, certainly in the
case of a size press through which various types of paper are run.
It is also known that deflection compensation is more urgently in-
dicated on wider machines than on narrower machines. Although the
diameters 2 Rl , Z R2 and 2 R3 of the rolls 11, 12 and 13 may be
selected so as to be equal to each other with a view towards facili-
tating maintenance thereof, the roll 11 is selected in the illustrated
embodiment ts have a smaller diameter than the rolls 12 and 13. As
noted above, in both nips Nl and N2, one of the two rolls should be
a soft roll in order to enable the pressure area or zone of the nips
to have a sufficiently large width. Each of the three rolls 11, 12
and 13 is provided with its own controllable drive 14, lS and 16
respectively and the peripheral velocities of the rolls are sub-
stantially equal to the velocity of the web running through the size
,, --18--
press.
Referring to FIG. ~ a~er the web W has be~n surfacc sized on
both of its sides in the nips Nl and N2, the web follows along with the
central roll 12 of the size press through a small angle C~ 3 as noted
above. The web is thereafter carried in a substantially straight draw
Wl to the turning means 20 in the region of which the web W changes
direction, i.e., the web W turns over an angle ~ to an upper direction.
As described in greater detail below, the web W2 is carried in a non-
contact or contact free manner on a cushion of air which flows be-
tween the carrying surface of the turning means and the web. As des-
cribed below, the air (or other gas) is ccnducted into the gap between
the carrying surface and the web through nozzle slits which extend
transversely in their longitudinal direction to the direction of travel
of the web W2.
The web W2 may also be spread out in the transverse direc-
tion as it travels over the turning means 20. Indeed, a preferred
embodiment of the turning means 20 described below, is characterized in
that the air jets operating in the region of the carrying surface
thereof actually positively acts to spread the web in the transverse
direction thereby preventing the formation of wrinkles and eliminating
previously formed wrinkles, all while insuring a contact-free conduction
of the web.
After passing over the turning means 20, the web W2 is car-
ried in a substantially straight draw, designated W3, to stabilizer
means constituted by a pair of mutually opposed components 40 and 41,
each of which is provided with nozzles 50. The web W4 in the region of
the stabilizer means 40,41 is carried through it in a contact-free man-
ner and, according to the invention, is guided in a stabilized fashion
by air jets discharging from the nozzles 50. The air may be heated. In
this manner, the web discharging from the stabilizing means 40, 41
designated WOUt~ may be conducted directly to a standard drying
--19--
~ L221569
cylinder 61 where a drying felt, either in a single-felt or in a
double-felt coslduction, may be employed~
It is seen from the foregoing that the web throughout its
entire run from the last size press nip N2 and from the size press roll
12 to the first drying cylinder 61, i.e., web Wl-W2-W3-Wout, has a
stabilized run while being subjected to a contact-free supporting
action. The drying section consisting of several dryer cylinders and
felt means has not been shown in its entirety. In this manner, ~he
web may be freely spread out in a lateral or transverse direction or
may be positively transversely spread and, moreover, the run W1-WOut
of the web has no excessively long free draw wherein a free, indefinite
and uncontrolled high-amplitude fluttering can occur.
~ Referring to FIG. 2, the size press 100' is substantially the
same as that illustrated in FIG. 1. However, in the case of the embodi-
ment illustrated in FIG. 2, after leaving the last size press nip N2
of press 100', the web Wl follows along with the central roll 12
thxough the angle C~'3 after which the web is conducted in a sub-
stantially horizontal direction directly to the stabilizer means 40',
41' in the region of which the web W'4 is supported in a contact-free
manner. Additionally, heated air, is directed through the nozzles 50
of the stabilizer means 40', 41' so that the web W'4 is dried acquiring
a sufficiently high dry matter content. It is noted that it is also
possible to apply radiation dryin~ designa~ed H,to the web W'4 as it
passes through the stabilizing means 40', 41'. The web WOUt leaving
the stabilizing means is conducted over a guide roll or spreading roll
42 to a multiple cylinder dryer which being known in the art is only
schematically shown and presented by cylinders 61' and G2'. Normal
drying temperatures can be utilized in the drying cylinders 61' and
62' thercby obtaining the advantages discussed above not found in con-
ventional arrangements. Various dryer felt run arrangements known in
.. ~ .
~ 2Z1569
the art can be used.In this connection reference is made to appli-
cant's U.S. Patents No~ 4,075,056; 4,172,007 and 4,202,113.
Another embodiment of the present invention is illustrated
in FIG. 3 wherein an oblique size press lOOa is constituted by a pair
of rolls lla and 12a so as to define a single nip Nla. This type of
oblique size press lOOa is known in the art and is commonly utilized
in connection with fast-running machines since it provides for an
easy passage of the paper web therethrough. The top or upper roll
lla of the lOOa is a hard-surface roll so that the web Wl will follow
along with the top roll lla through the angle ~ a. After leaving
the size press lOOa, the web Wl has a substantially horizontal run
and is conducted to stabilizer means 40a, 41a. The web W4 running
within the stabilizer means 40a, 41a is supported in a non-contact
manner by means of air blown through the nozzles 50 and the run of
the web W4 is stabilized in a manner described in greater detail below.
A turning means 20a follows the stabilizer means 40a, 41a and the web
leaving the stabilizing means is supported by the turning means 20a
in a non-contact manner. The web WOUt which has been turned in di-
xection in the turning means 20a is then conducted to a conventional
multiple cylinder dryer section, the first ones of its cylinders 61a
and 62a being illustrated in FIG. 3.
Turning now to the embodiment illustrated in FIG. 4, the
conduction of a surface-sized web is substantially similar to that
described above in connection with FIG. 1 except that a single-nip,
oblique size press lOOb, similar to that illustrated in FIG. 3, is
employed. The sole nip Nlb is defined between a hard roll llb and
a rubber-coated lower roll 12b. After the surface sizing nip Nlb,
t~e web Wl is carried to turning means 20b and then to stabilizer
means 40b, 41b from which the web WOut is conducted to a conventional
multiple cylinder dryer 61b, 62b. The dryer felts or fabrics used and
known in the art, are not shown, nor are their guide rolls.
,
-21-
~2Z~;69
Turning now to FIG. 5, a more d~tailed ill~istration of the
constr~ction of the stabilizer means 40, 41 and of the passagc of the
web therethrough is shown. The stabilizer means are constituted by two
mutually opposed housings 46 and 47 into the interior of which gas, such
as air, is directed through tubes 45. ~he housings 46 and 47 extend
across the web W in its transverse direction. The housings 46 and 47
include inwardly facing opposed walls 48 which carry nozzles 50, each
of which extends transversely over the entire breadth of the web.
Moreover, the position of the nozæles 50 fixed on the opposed walls 48
are alternate with respect to each other so that the nozzles fixed to
one of the walls 48 will lie between the nozzles fixed to the other
opposed wall 48. In this manner, the web W4 will pass in a stabilized
manner and with a substantially sinusoidal wave motion supported by
the air flows which are discharged through the nozzles 50.
It is important from the standpoint of the present invention
that the web run in a wavy fashion in the stahilizer means 40, 41.
The wavelength ~ of the undulation of web W4, which equals the center-
to-center spacing of the nozzles on one side of the web, is preferably
within the range of between 200 to 800mm, and most preferably in the
range of from about 400 to 500 mm. The distance ~ between the sur-
faces of the nozzles 50 facing the undulating web, is preferably within
the range of about 15 to 50 mm, and most preferably between 20 to 30mm.
The distance ~ is substantially larger than the corresponding dimension
used in conventional floater dryers presently in use. In this manner,
the amplitude of the wave motion undergone by the web W4 is sufficiently
large to establish the stabilizing effect required by the invention
and, moreover, reduces any risk of the web W4 contacting the surfaces
of the nozzles S0. Thus, in conventional floater dryers, such as
are used in off-machine coaters or in connection with the manufacturing
of e.g. paper grades having good stretch properties, the corrcsponding
~ 22~569
value of ~ is at most about lOmm. Of course, it is understood tl~at in
such a case the aim is primarily to achieve an efficient drying actior
rather than obtaining the stabilizing action which is one of the ob-
jects of the present invention.
The guided and controlled wave motion of the web W4 elimi-
nates or precludes the formation of wrinkles extending longitudinally
in the web. Moreover, the controlled wave motion efficiently elimi-
nates any free and uncontrolled fluttering of the web which, as noted
above, is detrimental to the process. The gas jets directed through
the nozzles 50 of the stabilizer 40, 41 also tend to spread the web
out in a transverse direction to thereby straighten any longitudinal
wrinkles which might have occurred in the web and further result in
that the transversal expansion of the web resulting from its wetting
does not consume an undue amount of time.
The particular construction of the stabilizer and its nozzles
50 in accordance with the present invention, described in detail below,
is such that the spacing ~ between the opposed nozzles 50 is larger
than the spacing between opposed nozzles in conventional floater dryers.
Moreover, the construction of the nozzle means 50 permit a larger var-
iation in the angle at which the web W3 enters into the stabilizing
means. This is advantageous in case the web W being conducted in
accordance with the present invention will have a relatively low ten-
sion and, accordingly, the point at which the web Wl is detached from
the central roll 12 of the three-roll size press, or from the top roll
lla, llb of an oblique size press, is variable. Similar advantages
are obtained by the turning means 20, 20a, 20b according to the in-
vention as described below in greater detail.
Returning to FIG. l, a schematically illustrated means 20''
is provided before the turning means 20. This means 20'' having a
carryin~ surface provided with nozzles permits the dircction in which
the wcb W enters the turning means 20 or, in other words, the extcnt
:
-23-
~ 221~69
of anglc ~ 3, ~o vary. It i~ un~crstood that throat-likc mcans,
equivalent to the illustrated means 20', may also be used at the
entry region of the stabilizer means 40, 41.
Referring now to FIGS. 5, 6 and 7 a preferred embodiment of
the nozzles 50 formin~ a part of the stabilizer 40, 41 will be des-
cribed. The nozzle means are of the same type which is disclosed in
the Applicant's Finnish Patent No. 60261
Each nozzle 50 comprises a nozzle box which~ as noted above,
extends across the breadth of the web. The gas to be discharged from
the nozzle means is conducted into the nozzle box between inner walls
54 and 55 by supply tubes 45 whereupon the gas is conducted into side
volumes 52 and 53 defined between inner walls 54 and 55 and outer
walls 60 and 61 through apertures 51 formed in the inner walls 54 and
55. The inner walls 54 and 55 merge into each other to define an
upper surface 56 facing the web. The web facing surface 56 curves,
for example, substantially in the shape of circular arc having a radius
R2, toward the interior volume of the nozzle box in a smooth and con-
tinuous arc. The wet web W4 passes over the web facing surface 56
being spaced at a minimum distance ~ 1 therefrom.
The outer walls 60 and 61 of nozzle 50 have upper planar
portions 62, 63 respectively which extend upwardly towards each other.
Moreover, the inner walls 54 and 55 of the nozzle box have outer
regions which include curved portions (having radii Rl) and the planar
portions 62 and 63 of the outer nozzle walls define together with the
curved portions of the inner walls 54 and 55 a pair of nozzle slits 57
and 58, which are preferably located on the curved portions of the
walls 54 and 55.
The nozzle slits are located in the region of an angle C~ O
which is the angle subtended by the initial direction Sl of the gas
-24-
~ 22156~
jets disch~rging t?lrough the slits 57 and 5~ and tllc plane of thc wcb
W4 and which equals the angle at which the gas-jet gulding surface
curves starting at the mouth of the nozzle slits 57 and 58 and ex-
tending up to the plane L-L. The imaginary plane L-L at the same time
defines a depression 59 between it and the carrying surface 56. The
depression 59 serves as a "calming" volume wherein the gas jets vl,
which flow in opposite directions from respective nozzle slits, meet
to form an air cushion supporting the web W4 and extending a consid-
erable distance in the direction of travel of the web W4. The radius
of curvature of the web facing surface 56, namely R2, is preferably
substantially larger than the radius of curvature Rl of the curved
guiding surfaces in a region adjacent to the depression 59.
~ The angle ~ 0 is advantageously selected in a manner so that
no separation of the gas flows from the curved web facing surface
56 occurs before the jets vl have been deflected so as to be sub-
stantially parallel with the web W4. As noted above, in this manner
the jets vl will flow against each other in the region of the
depression 59 where they meet so that a relatively extensive air
cushion for supporting the web W4 is established. Should the nozzle
means 50 be used in conjunction with drying the web, it is significant
to note that the heat transfer coefficient will be relatively good as
a result of the vortex produced adjacent to the depression 59 and in
the region between the nozzle slits 57 and 58. In order to accomplish
the foregoing, the angle O~ associated with the curved guiding sur-
faces (Rl) has a maximum value of about 70 and is preferably in the
range of about 40 to 60.
The construction of the nozzle 50 illustrated in FIGS. 6
and 7 is symmetrical with respect to a vertical center-plane A-A
(FIG. 6) which passes through the bottom of the depression 59 formed
-25-
12Z~569
in t]lC web iacing surface 56. It is undcrstood, howovcr, that the
nozzles 50 may be c~nstructed having assymetric designs.
Referring to FIGS. 8 and 9, a more detailed illustration
of a preferred embodiment of the web turning and spreading means 20
employed in certain embodiments of the invention is shown. m is
type of web turning means has been disclosed in applicants Finnish
patent application No. 81 1402.
The contact-free turning and spreading means 20 which acts
n the web W as shown in ~IGS. 8 and 9 comprises a curved carrylng
surface structure 32 over which the web W runs. As seen in FIGS. 8
and 9, planar side walls 24 (only one shown) and end walls 26 define
an interior volume 20' together with the carrying surface 32. The
treatment or supporting gas, such as air, is admitted through a
passage 25 and then through a curved, perforated wall 23 into the
interior volume 20' from where it is further conducted through a
plurality of nozzle slits 36 to provide support for the web W in a
manner described below.
As sc-en in FIG. 8, the direction of the web W changes
over an angle ~ as i~ travels on the carrying surface 32, the
angle ~ at the same time defining the sector of the curved carrying
surface 32, which preferably has a constant radius of curvature, ex-
tends. The arrying surface 32 is constituted by a plurality of
pressure surface laths 34 which alternate with a plurality of spacer
surface laths 35 and which define the nozzle slits 36 between them-
selves. ~he gas is directed through the nozzle slits towards the
web W from the interior volume 20' into which it is introduced by
means of a blower or the like (not shown) in a manner such that the
web W is carried at an appropriate distance M from the carrying
surface 32.
More particularly, the pressure surface laths 34 are each
constructed to include a substantially planar prcssure surface 37
-26-
~ 2Z~S~i9
which merges at its rcspcctive cnds with Lcspcctive curved s~lrfaces
38 which are angled inwardly and having a radius R. The spacer sur-
face laths 35 are each constructed to include a spacer surface 39
which joins at its ends with a respective pair of inwardly extending
planar portions 22, the planar portions 22 meeting the spacer sur-
face 39 at respective sharp edges 21. The planar portions 22 termi-
nating at the sharp edges 21 are arranged in a certain proximate
relationship to respective curved surfaces 38 of the pressure surface
laths 34 to define the nozzle slits 36, the planar portions 22 and
curved surfaces 38 being configured so as to impart a starting
direction to the gas being directed from the nozzle slits which de-
fine an angle ~ 1 with the web W2 in the region of the nozzle slit.
Moreover, the nozzle slits are configured in a manner such
that the gas jets S being directed therefrom follow the curved sur-
faces 3~3 without separating therefrom up to the pressure surface 37
so that an efficient and stable support of the web W2 is obtained.
In this connection, the width a of the nozzle slit, the radius of
curvature R sf the curved surfaces 38 and the angle ~ 1 are
dimensioned with specific consideration being given to achieve the
non-separating flow described above. Reference is made in this
connection to the article "Experiments On The Separation Of A Fluid
~et From A Curved Surface" by D.W. McGlaughlin and J. Greber,
American Society Of Mechanical Engineers, Advances in Fluids, 1976,
pages 14-29. It is disclosed in this article that at the relevant
flow velocities, the gas jet will follow the curved surfaces 38
through an angle in the range of about 45 to 70. The sharp edges
21 of the spacer surface laths 35 are so positioned with respect to
the curved surfaces 38 at the angle of a line connecting an edge 21
and the center of the associated curved surface 38 and the direction
of travel of the web does not exceed about 70. The lengths L and
_~7-
~ Z2~6g
L of the pressure and spacer surfaces 37, 39, respectively, are
preferably chosen such that the ratio o~ their combined length L
plus L2 and the width a of the nozzle apertures 36 is between about
20 and 200.
As seen in FIG. 9, the spacer surfaces 39 lie substantially
in the same plane as the pressure surfaces 37 which are adjacent to
them. The sharp edges 21 of the spacer surface laths 35 act to
prevent the gas jets which are discharged through the nozzle slits
36 from turning inwardly over the spacer surfaces 39. In fact, the
so-called Coanda effect which causes the gas jets to follow the
curved guiding surfaces 38 without separating therefrom as disclosed
in the above-mentioned article is so strong that the direction of
flow of the gas will not be affected even by the moving web.
Since the curved guiding surfaces 38 and pressure and spacer
surfaces 37 and 39 block all other exit passages, the gas jets ~s-
charging from the nozzle slits 36 are only able to escape by moving
past the sides of the web W2, i.e., the gas jets being directed from
the nozzle slits 36 must move transversely towards the lateral sides
of the web. Thus, the gas flow between the carrying surface structure
32 in the web towards the sides of the web produces a positive
spreading action which tends to spread the web W2 in a transverse
direction. Such spreading action is important in that, for example,
the same prevents wrinkling of the web which has been wetted in the
surface-sizing step.
It is seen from the foregoing that the web supporting and
turning means 20, which tends to spread the web in a transverse
direction, provides an extremely stable carrying force requiring a
relatively low consumption of energy and is especially suitabl~ for
tr¢ating webs of widely diverse types. As noted above, as the gas
escapes from between the web and the curved carrying surface structure
-28-
~2215~9
32 over the sides of the web, an advantageious force which tends to
spread the web W in a transverse direction is obtained which is
extremely advantageous in many respects.
In this connection there are reasons to discuss and
summarize the advantages of the method and device according to the
present application against the theoretical background of the sur-
face sizing and coating process.
Treating of the web in the size press is a physico-
chemical process in which certain material5 by making use of water
are brought onto the surface of the web and partly into its internal
structure to improve the properties of a finished web. The effect
of water on the running web has a decisive role in manyrespects
in connection with the surface sizing process.
As the fibres get moistened or wet, they will swell. This
results in an increase in the thic~ness and width of the web. The
change in the web thickness is hardly noticeable, but the width
grows to such an extent that it has to be taken into consideration
in the design of the parts and components of a paper machine
following the size press. The web must be allowed to expand freely,
otherwise longitudinal wrinkles are formed in the web, which as such,
impair the paper quality, but may also disturb the paper drive
operation.
Swelling of the fibres and the resulting extension of the
web do not occur in an instant but demand a certain time which de-
pends on the fibre type and on the basis weight of the web. To give
sufficient time for the transformation of the web the distance or
space between the size press and the subsequent drying section has
to be correspondingly long enough. In case this space forms an
-29-
i22~56~
open draw, the result will be, as explained, excessive fluttering
of the web and breaks will occur to such an extent that the pro-
duction of the paper machine falls down.
The apparatus and concept according to the present in-
vention offers as a combination the following advantages to elimi-
nate the said difficulties:
- The expansion of the web (i.e. increase of the web ~idth)
resulting from the phisio~chemical swelling of the paper
fibres caused by water is "mechanically" assisted. This
means that a blowing effect is directed to the web aiding
the extension thereof in its width.
- , The means creating the said blowing effect stabilize
simultaneously the web run so that the "dangerous"
fluttering can be prevented or at least substantially
controlled.
- Due to the said blowing action extending the web and
stabilizing its run, the web is simulta-
neously dried to such an extent that when it becomes
subjected to the contact drying taking place against the
cylinder surface no wrinkling problems are created any more.
- ~ue to the combination of means according to the invention
the dry content of the web is so high that a normal drying
cylinder can be used as the first cylinder following the
size press without the risk that the web would stick to
the cylinder surface.
- By means of the equipment according to the invention the
-30-
travelling distance o~ ~e web ~ecomes longcr than what
is the straight geometrical space between the size press
and the subsequent drying section and thus the web will
stay on this space correspondingly so long that the re-
quired dry content is achieved.
All this means that the provision of the non-contact web
stabilizing means between the size press and the subsequent drying
section results in obtaining a synergistic effect in that the
fluttering of the web is eliminated and the possibility of web
breakage reduced while simultaneously increasing the time for the
web to expand and spread in a lateral direction.
Still further, the use of the web stabilizing means 40, 41
illustrated in FIGS. 5-7 and the particular structure of the nozzles
50 prevents the separation of the gas jets from curved surface and
falling down to the suction side which would decrease tlle heat trans-
fer coefficient between the nozzles. Thus, the nozzle slits 57, 58
of the web stabilizing means are so disposed on the curved nozzle
surface that the jets v , v do not separate from the nozzle surface
56~ By providing.the web facing surface 56 with a curved shape
forming a depression 59 between the nozzle slits 57 and 58, a
"calming" region is obtained in which the gas jets v and v which
are flowing in opposite directions will meet to form an air cushion
extending for a substantial distance in the 3.ongitudinal direction
of the web W to support the same. The heat transfer coefficient
can have favorable values even in the area between the nozzle slits
57 and 58 according to the invention. Since the gas jets will not
sharply impinge on the web W and since too early separation and
falling down of the jets v and v is prevented through appropriate
alignments, the travel of the
-31-
~2~;69
web W4 will be extrelllely smooth and flutter-free when the nozzles 50
in accordance with the present invention are employed. This is of
essential significance with a view towards achieving the objects of
the present invention.
The components of the apparatus of the present invention
including a size press, preferably comprising a three-roll and two-
nip size press, and the subsequent contact-free stabilizing and
guiding means,are preferably situated in the drying section of the
paper machine so that about two thirds of the drying cylinders
operate prior to this apparatus and one third of the drying cylinders
operate subsequent thereto.
It has been found preferable to have the web W4 pass
through the stabiling means 40, 41 in as nearly a vertical direction
as possible since the removal of broke from between the noæzles 50
is facilitated relative to the case where the web passes horizontally
through the stabilizing means.
Obviously, numerous modification and variations of the
present invention are possible in the light of the above teachings.
It is therefore to be understood that within the scope ofthe claims
appended hereto, the invention may be practiced otherwise than as
specifically disclosed herein.
