Note: Descriptions are shown in the official language in which they were submitted.
~ ~4~
The present invention is particularly concerned with the
utilization of pressurized fluids in the paper making industry and
is particularly useful in drying and doctoring operations.
As is well known paper making in the past was as much an
art as it was a science. However, with the high speeds of present
day paper making the production of good quality paper can only be
enhanced if the paper maker himself is very talented. Computer
controls and improved technology are moving to decrease the down-
time of the paper machine and to make it more efficient and
effective. The paper maker thus is able to devote more of his time
to his "art". One ~ the problem areas which still has a good deal
; of downtime associated therewith is the creping operation which
involves the use of a doctor blade on the Yankee roll in the dryer
stage. Experience shows that there is considerable wear both to the
Yankee shell and the doctor blade although the doctor blade has more
wear associated therewith. Both the blade and the shell have to be
reground periodically to bring them back into dimensional congruity.
~he doctor blade regrinds can be carried out with little machine
d~sruption since they are replaced on the run every 20 to 120
minutes. But the Yankee regrinds ar time-consuming, frequent and
; costly, and, of course, both the doctor blade and the Yankee have
structural limits which determine the total amount of material that
can be ground off. Since the Yankee roll is pressurized it is
understood that as the shell thickness decreases so must the internal
pressure and/or the loading. This greatly limits the usefulness of
this very costly item, most Yankees now costing over one million
dollars to replace.
In many mills the bottleneck for increased speed potential
is the dryer section. ~he dryers, of course, may include the
Yankee mentioned above which is steam heated to vaporize moisture
from the paper web thexeon. In some instances dryer per~ormance is
~p ::
. . , , " ., . :
--~ 104 ~
- ~d by the provision of a peripheral hood which utilizes nozzles
and high velocity air jets. These high velocity hot air or gas
hoods or caps are placed over standard steam dryers to improve
the rate or uniformity of drying. Because there is a boundary
layer of moisture upon the web which impedes heat flow to and
moisture flow away from the sheet, high expenditures of energy
are required in order to obtain the hot gas velocities in the
region of 10,000 to 20,000 feet per minute that are needed to
decrease the boundary-layer effect. The temperatures of the heated
air used are in the range of, say 600F to 800~F. An attendant
problem with hot air caps is, of course, the removal of the vast
volumes of high temperature saturated air. The balance between air
flowing to the sheet and back pressure involved in removing the
moisture and air has always been a design compromise.
It has been known in the past to use doctor blades sup-
ported on a film of air. Minton in his Canadian Patent 223,760
; issued April 5, 1922 described and claimed such a device but it
never enjoyed any commercial success. In the Minton doctor a
relatively narrow structure was provided with a passage ending in
a port near the end of the toe portion. Air escaped at the
port in the form of a jet adjacent a ~~ylinder and the jet would
allegedly strip the web from the cylinder. A portion of the fluid
under pressure would back up to form a cushion between the toe and
the cylinder to preclude contact of the doctor with the cylinder.
It is noted in particular that the passage is in a plane perpendicu-
lar to the cylinder axis and hence the air jetting from the port
will be unstable and would tend to back up on either side of the
port and would not be organized. Thus the action of the doctor and
of the creped paper resulting from operation thereof would not be
consistent and predictable. In addition, no cleaning of the
cylinder surfaces either to the front or back of the toe portion
would be provided.
10~
The present invention is intendcd to overcomc the
problems of the prior art with respect to doctoring and drying,
The structure of the present invention is such that it can be used
as an air-supported doctor, as an element in a high-velocity
hot air dryer and as a sealing element in an air cap type dryer.
The present invention utilizes air exitting from a curved surface
positioned along the length of a cylinder to support the surface
away from thecylinder. The jetting air is angled obliquely rela-
tive to the cylinder axis so that its flow is organized and pre-
dictable. In addition a portion of the jettin~ air is used toeffectively seal the remainder of the jetting air from escaping in
an unwanted and hence inefficient flow pattern.
In its broadest as~ects the present invention contem-
plates apparatus for use in conjunction with a cylinder surface
rotatable about an axis. The apparatus comprises a foot portion
having an outer surface which substantially conforms to the curv-
ature of the cylinder surface and means for resiliently supporting
the apparatus in close juxtaposition to the cylinder surface
whereby a gap of thickness diminishing progressively towards
one longitudinal edge of the foot portion is formed between the
outer surface and the cylinder surface. At least two rows of
nozzles communicate through the foot portion to exit therefrom at
the outer surface. A source of pressurized fluid is connectable
to the nozzles, each of the nozzles being directed obliquely to
three orthogonal planes, one of which is parallel to the one edge
~, and another of which is tangent to the outer surface at the
juncture of the nozzle axis with the outer surface. Thus, fluid
which issues from the nozzles in the row farthest from the one
edge will coact with the fluid issuing from adjacent nozzles in
the same and adjoining rows to act as a seal to preclude fluid from
the rema~ning nozzles from passing thereb~.
~ he invention will now be described in greater detail and
with reference to the drawings wherein:
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Figure 1 is a view, generally in cross-section, showing
the basic structurc of the present invention.
Figure 2 is a perspective view showing the present
invention in place adjacent a c~linder.
Figure 3 is a view showing the flow pattern of air
issuing from the jets of the present invention.
Figures4 and 4a show a basic doctoring application of
the present invention.
Figures 5 and 5a show a more sophisticated version of
the doctoring application of the present invention.
Figures 6, 7 and 8 show three separate embodiments of
; a dryer application of the present invention.
Figures 1 and 2 are intended to depict the basic config-
uration for the present invention, without any particular Q~pl~c
such as doctor, dryer, or seal in mind. In some instances 1n
the Figures distances and separation have been exaggerated for
effect.
Figure 1 shows a cylinder 10 of radius R for rotation in ~ -
the direction of the arrow A. In close juxtaposition to the -~ -
- 20 cylinder surface 12 is the apparatus 14 of the present invention.
It is provided with a foot portion 16 having an outer surface 18.
Resilient and adjustable means 20, connected to a solid support
structure which, under load, maintains the juxtaposition referred
- to above so that the gap gdiminishes progressivesly towards one
` edge, such as 22, of the foot portion 16. At least two rows 24,26 --~
. i .
of nozzles 28 communicate through the foot portion 16 to exit aTt~
outer surface 18 thereof. A course (not shown) of pressurized
fluid , such as air, is connectable with the nozzles 28 through
hose 30 and plenum 32, the latter formedwithin housing 34 sealed
to foot portion 16. As is seen in Figure 1 and particularly in
Figure 2 each nozzle is directed obliquel~ to three orthogonal
plane~ P-l, P-~ P-3. Plane P~ parallel to the tangent at the
.
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~he cylinder surface at thc juncture of thc nozzle axis with the
cylinder surface. Plane P-2 is parallel to the edge 22 and, of
course, plane P-3 is perpendicular to the planes P-l and P-2.
As seen in Figure 2 the centerline of a nozzle 28 makes an
obli~ue angle ~ with plane P-l, an obli~ue angle ~ with plane
P-2 and an oblique angle ~ with plane P-3.
Referring to Figure 3, air exitting from the nozzles in
row 24 as flow 34 wlll thus issue in such a manner that it tends
to be directed towards edge 22 but at an angle oblique thereto.
The overall accumulated flow thus has components parallel to the
edge 22 as well as perpendicular thereto. The air exitting from
the nozzles in row 26 as flow 36 is initially directed in the same
general direction as that issuing from nozzles 24, However, the
air from nozzles 26 will encounter the air flow from the nozzles
in row 24 and this air flow from the nozzles in row 26 will tend
; to have a greater flow component parallel to the edge 22. In
effect this air is turned more towards a parallel flow direction
and it acts as a "skirt" or seal along the back portion of the
foot 16. This is very advantageous since the sealing air ensures
that there is no backward escape of air from the nozzles , even
~: -
when the cylinder is rotating toward edge 22 and this sealing air
also prevents the intrusion of dust and debris into the small gap
`; formed between the surface 18 and the surface 12. Needless to
say, the air and the flow thereof operating in the gap g maintains
the gap since the structure and its operation is analogous to the ~-
structure and operation of an air bearing or a skirtless air
cushion.
The flow pattern and the properties thereof as described
above can be put to practical use in the paper industry. The
structure described above can be used in the paper drying stage to
impinge high velocity air at the wet web from very close proximity;
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1~)4~459
chc sealing effect can bc used to prevent detrLmental escape of
the drying air from dryer hoods; and the very close juxtaposition
of the ~oot portion to the cylinder surface permits the structure
to be used ~s a doctor for the removal of paper from a rotating
cylinder, especially for the creping of the web from a Yankee
roll. This is particularly useful in the production of high bulk
tissue sheets which are formed and dried to high degrees of dryness
with minimum mechanical work being exerted on the paper web. Such
work is detrimental to softness and strength of the web but it has
been found that differential creping action is of benefit to
softness and strength properties.
These various applications of the present invention
will be depicted in Figures 4 to 8 and described hereinafter. It
is noted that most of these Figures show the application of the
present invention in essentially schematic or sectional form. It
is understood that the configuration is three-dimensional and, for
example, that the individual apparatus of the present invention
- would probably extend along the full length of any cylinder shown -
although sections of short length can be employed to remove trim ~
20 from the edges of the dryer cylinder without wear problems. --
Figures 4 and 4a show a very basic concept for use as a -~
doctDr fora Yankee, or other, cylinder 10 rotating in the direction --
of the arrow. The apparatus of the present invention is resiliently
mounted on a rotatable shaft 38 which is biased as by a torsion
spring, air bag or piston (not shown) tobring the foot portion 16
into close juxtaposition with the cylinder surface 12. A gap g -~
i8 formed between the surface 12 and the complementary curved -~ -
outer surface 18 of the foot portion, the gap g diminishing -~
progressively in thickness towards the edge 22 of the foot portion
16. The apparatus is provided with a plenum 32 which is continu-
ously supplied with a pressurized fluid, usually compressed air at
varlou~ pre~8ures, say 10 to 40 p.8.i. It is underRtood that
- 6 -
1~44459
`octoring applications re~uire highex loads and extremely
close juxtaposition to the web cylinder. The air is permitted
to escapc from the plenum through nozzles 28 in a pair of
parallel rows 24 and 26, the nozzles being oriented as depicted
in Figures 1 and 2 and havin~ a flow pattern as depicted in
Figure 3. The issuing air forms a thin wedge of fluid between
surfaces 12 and 18 as shown in Figure 4a, the thickness of the web
diminishing in the direction of projection, that is, towards edge
22. The nozzles are designed so that the air issued therefrom at
or near supersonic speeds and exits from the gap with sufficient
velocity and force to break the adhesion of the web of paper 40
to the cylinder surface 12. The action of the air-support
doctor is such as to impart a creping configuration to the doctor
web or to assist,in various degrees,mechanical action of the
~, leading edge of the blade, as shown in Figures 4 and 4a. It is
important to note that the air wedge formed between the surfaces
12 and 18 is sufficient to prevent con~act between the doctor
and the cylinder surface and the air exitting from the front
edge of the foot portion assists in varying the degree of contact ~-
20 between the paper and the doctor. Since there may be somewhat -
random intr~sions of pressurized fluid into the region bounded by
the paper, the cylinder surface 12 and the edge 22 the resultant
creping action can be considered to be differential along the
length of the edge 22 and, as pointed out above, this is a
desirable effect. Because of the orientation of the nozzles all
of the air is effectively used for support and creping interaction
as it all exits in a preferential direction. This flow can be
effective in cleaning doctoring surfaces of any fibre or lint
buildup. Doctoring is achieved over the full length of the doctor
and is readily controlled through variations in air pressure and
doctor loading. Because there is no contact between the doctor
and the cylinder there will be no wear and no chance of damage to
the sheet of paper by worn, chipped or damaged equipment.
104.~4S9
It is understood that the resultant radially outward
forces generated by the support wedge are counterl~alanced by --
the nozzle unit and support weight together with resilient mount-
ing and loadin~ systems of the apparatus on shaft 38 whereby the
gap g is properly maintained at equilibrium.
Figures 5 and 5a show a somewhat more sophisticated
version of the doctor apparatus of Figures 4 and 4a. As with the
previous embodiment the cylinder 10 rotates in the direction of
the arrow at its usual speed of roughly 4000 feet per minute,
carrying paper web or sheet 40 on its outer curved surface 12.
Foot portion 16 is resiliently biased towards cylinder surface 12
by resilient means 20, similar to that shown in Figure 1, and
L-shaped arm 42 is affixed to shaft 38 adjacent and parallel to
: cylinder 10. A plurality of spaced spring fingers 44 extend
` from the end of one leg 42a of arm 42 and are removably attached
to housing 34 of the doctor apparatus. Fingers 44 are spaced
along the length of the arm 42 and the doctor apparatus so as to
effectively bias the doctor therealong toward the cylinder.
Adjusting means 46, shown as a nut passing through finger 44 to ~-~
be received in a threaded hole 48 in leg 42b of arm 44 permits -
, . . . ~ ~
the load on finger 44 and hence the load on the doctor apparatus -~
to be adjusted. In this manner the gap g can be adjusted so that
it remains constant or it an be varied as required to account
for discrepancies in the surface smoothness or position of ~ -
cylinder 10.
The foot portion 16 is provided with parallel rows 24 ~
and 26 of nozzles 28 which are oriented and operate as previously ~ -
described. In addition, however, the surface 18 is stepped, as
at 50, in order to accomodate a blade 52 which is removably
pivoted to the foot portion as at 54 and which extends outwardly
towards and possibly beyond edge 22 along the lengthof the doctor.
b~/
.
1~444S9
~ third row of nozzles 56 communicates through foot portion 16
from plenum 32 in order to supply pressurized air to the space
betwecn blade 52 and the outer surface of the stepped portion 50
of surface 18 to thereby provide further resilience to the blade
support system.
In operation the diminishing gap g is maintained by the
air issuing from the nozzles in rows 24 and 26 and most of that
air exits from the front edge 58 of blade 52 to break the adhesion
of the paper 40 from surface 12 and to assist in giving it its
creped effect (see Figure Sa). The air from nozzles 56 exits
adjacent edge 22 from between stepped portion 50 and blade 52
and serves to provide a resilient support to the blade as well as
to create a source of pressurized air to deflect the creped paper
away from the doctor. Thus the chances of difficulties arising
from interference by the doctor support with the creped paper is
reduced and the creped paper is in a better position to be fed
to subsequent operations.
There are many variaties of mounting means for the
doctor apparatus, incorporating load adjustment, air feed pressures, ~-
etc. In fact it is possible by using an air bag in series with -
the plenum and the air supply to render the loading automatically
appropriate to the pressure conditions presentat the gap g. These
variations in the mounting means and other variations in the
doctor apparatus itself will be readily apparent to someone skilled
in the art who is faced with a custom installation of the apparatus
; for a specific cylinder. Needless to say, all mountings provide
a means of quickly releasing built up paperjams or clearing of the
drier or feeding of paper by pivoting away from the dr er for
maximum clearance. Opening of the hood of an air cap dr~er for
major cleaning of paper build-ups will be by various lifting
; systems or automatic opening arrangements now in use.
.. ':
_g _
1~4~45~
Figure 6 shows a dryer situation in which the present
invention can be utilized to achicve high efficiency drying of paper.
A standard press system, depicted by reference number 60 feeds a
sheet of partially dried paper 50 to the inlet 62 of a hot gas cap
dryer. The standard gas cap system is depicted by reference
number 64 and need not be considered in full herein. It suffices
` to say that in the configuration of Figure 6 a Yankee or similar
` dryer cylinder 10 having an outer surface 12 is supported for
rotation in the direction of the arrow and it is covered over at
least 50 percent of its surface by the cap 66. Exterior to cap
66 is a high pressure burner 68 fed by compressor 69 with air
extracted from the interior of the cap. The burner 68 provides
high pressure hot gases of sufficiently low relative humidity for
use in the dryer devices 72, four of which are shown. A conduit
70 leads from the burner to each dryer device 72, the free end of
each conduit comprising a resilient mounting means 74 analogous -~
to resilient means 20 of Figures 1 and 5. In fact, it might be
found that an intermediate position of the resilient mounting means
may permit the air exiting from the nozzles in devices 72 to assist
in threading thesheet over the cylinder surface.
~ Dryer devices 72 are completely analogous to the appara- -
tus 14 shown in Figure 1 and need not be described in detail.
It suffices to say that high velocity hot air issues from the
nozzles in each foot section to float the foot portion on a wedge
Of fiuid and to impinge on the paper sheet as it travels past.
The jetting air cracks the boundary layer of moisture on the
sheet due to the juxtaposition of the dryers from the sheet, in
the range of, say 1/8 to 1/4 of an inch, and the high velocity air.
~ests have shown with other imp in~ement devices that 35 to 40
per cent drying efficiency increases can be realized with jets
moved fxom 1 inch to 1/2 inch from dryer or web surfaces, Thus a
more efficient drying ~ystem is achLeved while at the same time
--10--
.
.
i~444~9
there is a reduction in the power required over existing systems.
The gap between the nozzles in existing air dryers and the
sheet must be be fixed at some comprcmise clearance for air
removal balance with turbulent and unorganized flows. This gap
is extremely large in relation to the gap achievable with the
present invention and this goes a long way to reducing the po~er
required to achieve the desired degree of drying. In the present
invention an optimum proximity can be achieved by automatic
balance of the incoming nozzle hot gases impinging on the sheet
with the required exhaust area required to release the hot air
and vaporize moisture from the sheet. The organized flow of
the angled jets will provide the best flow of hot gases with
optimum removal conditions. Also, since the dr~er cylinder is
reduced in diameter due to repeated grinding the present invention
automatically adjusts to the best new clearance position. It is
also worthwhile noting that with the relatively high velocities
of the nozzle jets as compared to the dryer surface speed, the
nozzles need not necessarily be directed in one direction or the
other with regard to the dr~er rotation or web direction.
In the embodiment shown in Figure 6 a doctor apparatus -~
76 is shown exterior of the dryer cap 66 to remove the dried
paper from the cylinder. The doctor apparatus 76 could take the
form shown in Figure 4 or Figure 5 or it could be custom
designed to the particular operation. Other s;milar doctors could
be used subsequent to doctor 76 to clean the cylinder surface of
extraneous fibres or debris. ~-
Figure 7 shows a second dryer embodiment which utilizes
the present invention in all of its modes of application, namely
drying, sealing and doctoring. The dryer of Figure 7 has an
insulated vacuum hood 78 extending around more than 50 percent of
the periphery of Yankee cylinder 10. At each endof the hood 78
a seal device 80 is resilientl~ mounted so as to direct pressurized
hot gas¢s or air against the paper sheet 40 at the entrance to the
:, -, , - ,
i~ 4~9
hood and at the exit of the hood thereby providing a dynamic
non-wearing seal for the interior of the hood. Each seal device
80 is analogous to the basic apparatus 14 in that it rides on a
wedge of pressurized air and it need not be further described
since there is no difference in the air flow. As with the
embodiment of Figure 6 the present embodiment is provided with an
air supported doctor device 76 which removes the dried sheet 40,
from the cylinder 10. ~
Within the vacuum hood ~is at least one, and prefer-
ably a`plurality of, dryer devices 82 resiliently mounted so that
a narrow gap diminishing in the direction of fluid projection is
established between each foot portion and the paper sheet 40.
No further discussion of the structure or mounting of devices 82
` is required in view of previous discussions. Each device 82 is
connected to a manifold 84 within hood 78 which acts as a source
of relatively hot and dry high pressure air. The inlet of the `
manifold is sealed to the hood as at 86 and the outlet of the hood -
is sealed to conduit 88. Because of the sealing provided by seals
80 the only airflow within the hood 78 can be from manifold 84,
through the nozzles in dryer devices 82 and hence through outlet
.
conduit 88. Since the outlet conduit is connected to a vacuum/
compressor pump 90 the interior of hood 78 can be maintained at a
partial vacuum and hence the rate of evaporation from the paper
sheet 40 can be considerably increased. Also, since the present --`
apparatus works under partial vacuum conditions the temperatures
" of the hot air can be reduced from the temperatures required in an
atmospheric system such as that shown in Figure 6. In order to
provide an essentially closed air system, showers 92 spray cooling
water into the conduit 88 to initially cool the air in and hence
remove moisture by condensation while providing the ~acuum pump
with sealing water and aid in the compression of the air. The com-
pressed moist air rom pump 90~ heated somewhat by compression
passes through separator 94 to remove the water drople~s and then
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1~4~S9
passes through hcat exchangcr 96 to heat and thus relatively dry
it even further. Thus thcre will be ver~ 1ittle air loss in the
system and efficiencies will increase. Itshould be noted that
gases heavier than air could be utilized to enchance drying by
increased gas densities or improved properties.
Figure 8 shows a third dryer configuration typical
of many specialty or paper board dryer cylinder configurations
except that in the present embodiment these dryers are enclosed
to provide a system which is recirculatory, thereby resulting in
enormous savings in energy. As with the previous embodiment the
present embodiment uses low temperature air combined with a vacuum
condition to achieve high dryer efficiencies. The paper sheet 40
is fed from the paper machine press section 60 around an input
cylinder 98 at the entrance to the dryer. A pair of air supported
seal devices, similar to devices 80 alre~dy described for the -
embodiment of Figure 6, are provided. The dryer has a vacuum
hood 102, interrupted only by the paper input at cylinder 98, the
paper output at cylinder 104 (sealed by air-supported seal
devices 100 as well) and the air outlet 106. The air outlet 106
, 20 is connected to conduit 108 which has cooling water spray 110
associated therewith and in turn is connected to vacuum/compressor
pump 112. The moist air is compressed and fed to a separator 114
where the moisture (water) is removed. The compressed air is then
fed to manifold 116 from which it is distributed to the seal
devices 100 and the dryer devices 118 (distribution being ,
schematically shown by the arrows leaving manifold 116).
As is shown in Figure 8 the dryer devices are dis-
tributed about the portions of rolls 120 which support the paper
8heet 40. As the sheet passes around a roll 120 it is subjected
to high velocity impingement of air issuing from the dryer devices
118. With the air from the dryer devices being exhausted through
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vacuum/compressor pump 112 a partial vacuum is obtained within the
dryer hood and evaporation of moisture from thc paper sheet is
enhanced, The fluid exhausted is cooled, dried, recompressed and
recycled to the drier devices via manifold 116. Thus there is
very little loss of fluid and the energy input is extremely small
in comparison to existing dryers. After exitting the dryer hood
around the exit cylinder 104 the sheet is fed to the reel section
122 where it is wound for subse~uent finishing.
As can be seen from the examples of particular
applications described herein the apparatus of the present
invention is extremely versatile. It can be used to enchance the -
efficiency of regular dryers; it can be used to seal the inlet and
exit ends of a vacuum dryer efficiently; it can be used to doctor
a paper sheet from a rotating cylinder; it can be used in indus-
tries other than the paper industry for similar applications; and,
in fact, it can perform multiple duty as, for example, a dryer
and a seal device. This last function is performed of course by
the two devices 100 which face the paper sheet, one at the inlet
roll 98, the other at the outlet roll 104 (Figure 8). The present
invention therefore, while appearing to be relatively straight
forward in basic structure, is capable of alleviating many
problems associated with the paper industry, espcially at the
dryer end of the paper machine and it does provide an additional
new field of utilizing fluids heavier than air to provide energy -
savings unheard of at the present time where systems are ,
llmited to air.
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