Note: Descriptions are shown in the official language in which they were submitted.
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MOVEABLE WEB SLOT
BACKGROUND OF THE INVENTION
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The present invention relates to the reduction of web slot infiltration
which occurs during the drying of a web or the like in industrial drying
apparatus.
In drying a moving web of paper, film, or the like, it is desirable
that the web be contactlessly supported during thè drying operation, to avoid
damage to the web itself or to an ink or coating on the web. One common
arrangement for contactlessly supporting a web comprises upper and lower
sets of air bars extending along a substantially horizontal stretch of the
web. Air issuing from the lower set of air bars floatingly supports the
web. Air issuing from the upper set of air bars steadies the web to maintain
it substantially straight and at a substantially constant distance from the
air bars of both sets. The air blown from both sets of air bars is usually
heated to expedite web drying, and typically the air bar array is inside
an enclosure which is maintained at a slightly subatmospheric pressure by
an exhaust blower that draws off the volatiles emanating from the web.
I~eb dryers are used in many printing and graphics applications, such
as the processing of photographic film, web offset printing, and other types
of printing. In some applications, such as the processing of photographic
film, web dryers having very long lengths, often as long as 150 feet, are
commonly used. The greater the ratio of the length of the dryer to the width
of the `web (hereinafter referred to as the "length to width ratio"), the
more susceptible the web is to minor forces that can cause the web to weave
(move back and forth in a lateral direction) or shift ~move laterally from
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~he centerline and remain there). Also, some webs, such as thin plastic
films, naturally take on a "banana-shaped" curve when they are laid flat,
as in a dryer, thereby exacerbating the problems of web weave and shift.
Web sllifting and weaving may also resu:Lt when the web tension is low, and
when a lighter weight web, such as polyester film, is used.
When the traveling web exits the drying apparatus it is generally wrapped
around one or more rotating take-up members, such as chill rolls. When web
weave or shift takes place as the web travels through the dryer, the web
will correspondingly shift or weave as it contacts the rotating take-up
member. Unless the web can be brought back to a straight orientation with
respect to the centerline, the web will not fold properly and the press must
be shut down. This results in costly downtime and waste.
Other problems may result from web weave or shift, e.g. if the web moves
to one side or the other and stays in the new position it may not be centered
on the press, resulting in an unacceptable product; if the web weave or shift
is severe enough the web may break or tear, etc. These problems also force
a shut-down of the press and thus a loss of valuable production time.
In the past, attempts have been made to circumvent web weave and shift
by guiding the web using contact systems such as a series of rollers. These
systems are undesirable as they may cause damage to the ink or coating on
the web, and are therefore inefficient in situations where there is a high
length to width ratio.
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Co-pending U.S. Patent Application Serial No. 464,831 assig2~ ~o3 ~h
assignee of the instant invention concerns apparatus which both floatin~ly
supports a moving web and maintains the web in a substantially strai~ht path
as it travels through the d~yer. The apparatus includes a steerable air
bar assembly whereby air bars are adjusted or steered with respect to the
running web so as to correct any undesired web weave or web shift.
In order to accommodate web weave and shift, the web slot both at the
inlet and outlet of the dryer is appropriately dimensioned, so that if and
when the web moves from its desired location, physical contact with the
borders defining the slot is avoided. However, since the dimensions necessary
to so accommodate such web movement are larger than ~ould be necessary were
the web to remain in its desired location, substantial infiltration of ambient
air into the dryer results. Since any air taken into the web slot would
eventually need to be exhausted at temperatures as high as about 350F, fuel
wastes become substantial. For example, in a dryer operating at a negative
pressure of 0.2" w.c., A lO"x40" web slot would have an air flow of 4,172
cubic feet per minute. At the same negative pressure, if the web slot were
only l'lx40", the flow would be reduced to 497 cubic feet per minute. The
one inch slot would use approximately 0.15 million btu's/hr, while the ten
inch slot would use approximately 1.5 million btu's/hr, a 10 fold increase
in fuel usage.
In addition, web slot infiltration results in condensate build-up on
the air bars in the dryer that are closest to the web slots. This build-
j up occurs when the cooler ambient room temperature air outside of the dryer
enclosure is drawn into the web slots and meets the hot printing ink oil
.solvent laden inside the drver, thus dro~ & the t~mpcratur~ ~o thecondensation point. Too much build-up causes air bar nozzles to become
plugged, which results in adverse floatation problems. Drawing too much
air through the web slot can also cause floatation stability problems.
It is therefore an object of the present invention to reduce infiltration
through a web slot in drying apparatus.
SUMMARY OF THE INV~TION
The problems of the prior art have been solved by the present invention,
which provides a moveable web slot to reduce infiltration ineo the dryer
proper. In particular, the present :invention relates to a moveable or
rotatable web slot which moves according to the position of the web as it
moves through the dryer. The invention further relates to a dryer comprising
one or more moveable web slots.
Although it will be understood by those skilled in the art that the
adjustable web slot assembly of the present invention can be used
independently, in a preferred embodiment, the moveable web slot is in
mechanical communication with a steerable air bar steering mechanism. As
the steering mechanism operates to steer the web, the moveable web slot or
slots is caused to move to a position corresponding to the changing position
of the web. In this way, web contact with the boundaries of the web slot
is avoided without requiring over-sized web slots.
BRIEF DESCRIPTION OF THE DRAWINGS 2 ~ ~ ~ 9 ~ 3
Figure 1 is a front cross-sectional vi.ew of a dryer having an ad,justable
web inlet slot and an adjustable web outlet slot in accordance with the
present invention;
Figure 2 is a web entry-side view of a dryer having an ad,justable web
slot in accordance with the present invention;
Figure 3 is a perspective view of a steerable air bar assernbly that
can be used in conjunction with the adjustable web slot of the instant
invention;
Figure 4 is a multi-position schematic view of one embodiment of a
, steerable air bar assembly that can be used in conjunction with the adjustable
web slot of the instant invention;
Figure 5 is a top cross-sectional view of a vertical tracking spring
loaded guide roller assembly in accordance with the present invention;
Figure 6 is a perspective view of the vertical push rod assembly in
accordance with the present invention;
Figure 7 is a perspective view of one embodiment of a dryer in accordance
with the present invention;
Figure 8 is a side view of the "J" seal for use in an ad,justable web
slot in accordance with the present invention;
Figure 9 is an exploded side view of the adjustable web slot in
accordance with the present invention; and
I Figure 10 is a multi-position schematic view of one embodiment of a
steerable air bar assembly that can be used in conjunction with the adjustable
web slot of the present invention.
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DETAILED DESCRIP1'ION OF THE INVENTION 2 0 6 3 9 ~ 3
Turning now to Figure 1, there is shown a dryer 10 having a plurality
of air bars 38 affixed to upper and lower headers 44 and 42, respectively.
Air issuing from the air bars 38 floatin~ly guides web 11 through the dryer
while drying any solvent, etc. on the web surface(s), The upper and lower
air bars are transversely positioned across the web, and are in stag~ered,
spaced relation along the web with respect to each other such that the
floating web assumes a substantially sinusoidal path. Web 11 is shown being
guided through a web slot 13 having a pre-set constant or substantially
constant gap of approximately one inch and bein8 defined by adiustable "J"
seals 60, 61 (Figures 8 and 9), through slot 95 defined by web slot housing
frame 96, into the interior of the dryer, and out throu~h web exit slot 19.
For convenience, only the web entry slot will be referred to; however it
should be understood that similar features and functions are typical to web
exit slot 19 as well.
Vertical push rod 24 with attached guide block 25 guided in guide rail
98 (Figure 6) is generally shown and is affixed to the lower face plate 16
of dryer lO by suitable means. Upper spring loaded guide rod 20 is associated
with a collar clamp 21, bushing 22 and compression sprlng 23 for purposes
described hereinbelow with respect to Figure 2. Yertical push rod 24 is
driven by drive shaft 26 through miter gears 27 supported by bracket 28.
Drive shaft 26 is also coupled to screw jack 40 through reduction gears/header
stop assembly 31. The jack 40 driven by motor 32 is coupled to the
corresponding jack 40' for web slot 19 by shaft 26a having pillow block
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arings 30 (Figure 7~, and functions to adjust the position of the steerable
air bar assembly. The push rods disengage once the headers move greater than
about one inch so that the adjustable web slot assembly remains stationary
during web up, etc.
With particular reference to Figure 3, there is shown an example of
a steerable air bar assembly which for purposes of illustration, includes
three adjustable air bars 38 such as Coanda air bars supported by and in
air-receiving communication with upper and lower headers 44 and 42,
respectively. (The combinations of the two lower air bars and the lower
header, and the single upper air bar and upper header 44 will hereinafter
be referred to as the lower and upper air bar/header assemblies,
respectively). In the embodiment shown, the upper and lower air bar/header
assemblies are maintained in opposin~ spaced relation by spacer means
comprising header carriage 36 and support member 50, and upper and lower
headers 44 and 42 are each sealingly joined at one of their respective ends
to upper and lower flexible air ducts 46 and 48 (additional ducting not
shown). Header carriage 36 is connected at its lower ed8e to screw jack
40, and the lower air bar/header assembly engages on each side a pivot bearing
52, supported by a support member 54, bY means of a connectin~ rod 53. Thus,
when screw jack 40 is adjusted up or down, the ends of both air bar/header
assemblies adjacent screw jack 40 will correspondingly move up or down,
as shown schematically in Fig. 4. The angular adjustment of the air
bar/header assemblies is thus facilitated by a pivoting support means,
comprising pivot bearings 52 and connecting rods 53, and an angular adjustment
means, comprising screw jack 40, which allow the air bar/header assemblies
to be rotated about an axis A which is substantially parallel to the
longitudinal centerline of the running web, while being prevented from
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~ranslational or rotational movement in any other plane. The presence of
header carriages 36 and 50 and support member 54, allows this movement to
take place without the spatial relationship among the air bars being altered.
This simultaneous adjustment of the orientation of both the upper and lower
air bars is further facilitated by flexible air ducts 46 and 48, which allow
a sealing relationship to be maintained between upper and lower headers 44
and 42 and the air supply, regardless of the position of the headers. One
type of flexible air duct which may be used in the invention is described
in U.S. Patent No. 4,480,859, the disclosure of which is incorporated herein
by reference. The adjustment of the orientation of the surfaces of the air
bars with respect to the web may be accomplished manually by the dryer
operator, by computer, or by other suitable means.
The position of the edge of the running web can be monitored at one
or more locations within the dryer, usin~ conventional sensing means, such
as fiber optics. Based on these measurements of the position of the web
edge, the steerable air bars are adjusted, periodically or continuously,
such that they provide a force which adjusts the web into a substantially
straight path. Alternatively, instead of sensing the position of the web
as it travels through the dryer, computer-generated dsta may be used to
predetermine the desired web path and the anticipated web position, and to
compare these two positions. The steerable air bars may then be adjusted
based upon that comparison to adjust the position of the web to the desired
web path.
In an alternative embodiment, the upper header system 44 in Figure 7
(where all numerals correspond to those previously described) is stationary.
The lower header system 42 is supported by screw jacks 40 located on each
side of the web centerline. The screw jacks at opposite sides of the web
centerline move in opposite directions with respect to each other when
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2063903
ergized. This causes lower header system 42 to pivot about its centerline,
2s shown in Figure 10.
Turning now to Figure 2, where all numerals correspond to those
previously described, there is shown the web entry side of dryer 10 having
a moveable web slot sealing frame 12 with web 11 passing through the slot
13. Adjustable "J" seals 60, 61 define slot 13, and are affixed to the frame
12. As best seen in Figure 9, where all numerals correspond to those
previously described, the ~J~ seals minimize the web slot opening in order
to minimize the web slot infiltration of ambient air into the dryer through
the web slot opening. In addition, the "J" shape of the seal is such that
a snag free non-sharp sealing edge is created at the entry and/or exit of
the dryer web slot. Those skilled in the art will recognize that other shapes
could be used to achieve similar functions, such as "L" shaped seals where
the longer arm is in the direction of web travel. Sealing gaskets 62, 63,
such as Teflon-coated gaskets in gasket retention channel 99 welded to frame
12, seal frame 12 against the face of the dryer, as shown in Figures 1, 6
and 9. The web slot sealing frame 12, adjustable "J" seals 60, 61 and sealing
gaskets 62, 63 are considered to be the moveable web slot assembly. The
sealing frame 12, which is spring loaded which enables it to float in a
substantially vertical direction, sits on push rod roller 70, which functions
to move the frame up and down upon being driven by drive shaft 26. As the
web slot assembly is pushed upward, upper spring loaded guide rod 20 maintains
spring pressure against the frame 12 and guides the web slot assembly. A
collar clamp 21 and bushing 22 are located on the guide rod 20 so that as
vertical push rod 24 and push rod roller 70 is lowered, the collar clamp
21 meets bushing 22 and provides a stop.
Substantial vertical alignment of the moveable web slot assembly is
ma1ntained by vertical tracking spring loaded guide roller assemblies 75,
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76, 77 and 78 (Figures 2, 5 and 6). Reference will now be made to vertical
tracking spring loaded guide roller assembly 75, although it will be
understood that guide roller assembly 75 is typical of assemblies 76, 77
and 78 as well. Assembly 75 includes three rollers with bearings, or cam
followers. A bolt head 80 secures one cam follower 82. Substantially
perpendicular thereto is a second bolt head 81 and cam follower 83. A third
bolt head and cam follower is positioned behind the second and is therefore
not visible in Figure 5. The cam followers are located in a channel position
between the dryer front and the web slot sealing frame 12. The second and
third cam followers are spring loaded with compression spring 85 (compression
spring for the third cam follower not shown). Nut 86 and bushing 87 are fitted
on spring loaded stud 88 between slotted bracket 89, such that adjustment
of nut 86 adjusts the channel 90 to maintain a tight seal against the dryer.
As the steerable air bar assembly and, in particular, screw jacks
operate to steer the web, drive shaft 26 drives push rod 24 so that the web
slot assembly moves in unison with the web steering achieved by the steerable
air bar header system. Thus, as the steerable air bar header system corrects
or prevents web weave and/or web shift, a corresponding shifting of the web
slot assembly (eg., dryer operator side to dryer gear side) is achieved in
order to accomodate the new position of the web without altering the actual
dimensions of the web slot.
Having thus described the preferred embodiment of the present invention,
those skilled in the art will understand that various modifications can be
made without departing from the spirit and scope of the invention. For
example, although the moveable web slot has been described by way of
illustration as functioning in conjunction with a steerable air bar assembly,
the instant invention can be ùsed in any situation where web slot movement
is desirable.
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