Device for drying a web

Device for drying a web in a two-screen dryer section. The device may include a plurality of heatable dryer cylinders arranged in vertically spaced upper and lower cylinder rows, an upper endless screen associated with the upper cylinder row and a bottom endless screen associated with the bottom cylinder row, and a screen guide roll associated with one of the upper and lower endless screens. A shaft may be formed between adjacent cylinders in a cylinder row and bounded by one of the upper and lower endless screens guided around the adjacent cylinders and the screen guide roll. An air box and a blowing device may be positioned within the shaft, and the blowing device may be arranged in a region of separation between the screen and the screen guide roll to direct an air flow through the screen. The device may also include a longitudinal sealing strip coupled to a surface of the screen guide roll in a vicinity of the region of separation.

CROSS-REFERENCE TO RELATED APPLICATION 
The present application claims priority under 35 U.S.C. .sctn.119 of German 
Patent Application No. 296 13 809.6 filed Aug. 9, 1996, the disclosure of 
which is expressly incorporated by reference herein in its entirety. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a device for drying a web in a two-screen 
dryer section, e.g., in a paper manufacturing machine, and for discharging 
paper shreds and foreign objects entering a loop or shaft formed by the 
dryer screen. 
2. Discussion of Background Information 
In the prior art, several devices, e.g., U.S. Pat. No. 5,379,526 and German 
Patent Application No. DE 44 04 726, have been proposed for removing paper 
and foreign objects which fall through a dryer screen. 
The prior art documents discuss, in general, that upon leaving a dryer 
cylinder of a first cylinder row, the web to be dried is guided by the 
dryer screen until the web is lifted off at the screen guide roll. The web 
then runs, via a free draw in which the web is not supported, to a 
cylinder of the second cylinder row. This arrangement prevents the risk 
web flutter and web breaks. Thus, in regions in which the web and/or dryer 
screens are not running along a defined surface, such as a cylinder 
surface or guide roll surface, the web and dryer screens are able to steam 
out without interference. 
The dryer screen, after separating from the web, is guided around the 
screen guide roll to an adjacent dryer cylinder in the cylinder row. The 
screen forms a loop or shaft and an air box is located within the loop or 
shaft. A sealing element, supported by the air box, prevents the air 
boundary layer from being pulled into the shaft and feeds the air boundary 
layer through the screen running around the first cylinder. 
In a region in which the dryer screen loop is not covered with paper, a 
second air flow exists. The air flow is required to ventilate the 
"pocket," i.e., the region between the dryer screen and a portion of the 
web being guided onto the adjacent cylinder in the same row, through the 
dryer screen. The pocket ventilation is provided in DE '726 via a blowing 
device positioned in a "discharge wedge" between the screen guide roll and 
the discharge screen. The blowing device consists of a driving nozzle 
creating a vacuum to apply suction to the web leaving the first cylinder. 
However, the above-discussed methods of vacuum generation, i.e., in a first 
section of the shaft, and/or pocket ventilation have been shown to be 
inadequate. In recent years, the operating speed of modern paper 
manufacturing machines has increased significantly, i.e., in an order of 
magnitude of 1800 m/min and greater. Thus, an increased drying capacity 
per dryer cylinder and an increase in the dry air volume is required to 
remove steam. Therefore, more air must be pushed through the dryer screen 
into the pocket. Further, in spite of increased speed, the web runs must 
be maintained as quietly as possible. 
For this purpose, German Patent Application No. 195 27 289.7 discloses 
that, in keeping with the requirements of the system, an air flow at any 
pressure is fed separately to the blowing device so as to intensify the 
pocket ventilation, and that an independent second air flow is provided to 
enable the adjustment of the vacuum present in the shaft via a driving 
jet. For this purpose an air duct is provided between the air box and the 
blowing device, which starts out from a first part of the shaft. This 
advantageously provides a blowing device pressurized with any rate of air 
flow to randomly intensify the pocket ventilation. By subdividing the air 
supply system into two subsystems, partial functions can be affected 
individually. 
However, a disadvantage of the systems of DE '726 and DE '289 is that, in 
the region between the blowing device and the dryer screen discharged by 
the guide roll, there is a space limited by longitudinal seals in which 
paper shreds occasionally accumulate which are difficult to remove. 
Further, in the event of a web break, the paper shreds arrive at a "wrong" 
side of the dryer screen and are transported by the screen into the shaft 
and may be caught in the space. 
SUMMARY OF THE INVENTION 
The present invention overcomes the above-noted defects and drawbacks of 
the prior art device by automatically removing paper shreds or other 
foreign objects occasionally dropped into the shaft. The removal may be 
performed as soon after the paper shred or foreign object enters the shaft 
to prevent undesired accumulation of the shreds or foreign objects in the 
space. 
The present invention may be directed to a two-screen dryer section that 
includes a plurality of heatable dryer cylinders arranged in two 
substantially parallel and vertically displaced cylinder rows, an upper 
endless screen may be associated with an upper cylinder row and a bottom 
endless screen may be associated with a bottom cylinder row. Between 
adjacent cylinders of the cylinder rows, a loop or shaft may be formed by 
the endless screen as it is guided from one cylinder of a cylinder row to 
an adjacent cylinder in the cylinder row via a screen guide roll. An air 
box and a blowing device may be provided in the shaft. The blowing device 
may be arranged in the shaft to direct an air flow through the screen at a 
separation region of the screen and the screen guide roll. A longitudinal 
sealing strip, e.g., a blade, may be attached to a surface of the screen 
guide roll in a vicinity of the separation region. A blade-shaped 
longitudinal sealing strip may perform both a sealing function and ensure 
immediate removal of a foreign object, e.g., transported between the guide 
roll and the screen, from the shaft. The present invention is equally 
applicable in the upper row and the lower row of a double row, double 
screen dryer section. 
The present invention may also include an air control system subdivided 
into two individually controllable sections in a manner substantially 
similar to DE '289. 
Accordingly, the present invention may be directed to a device for drying a 
web in a two-screen dryer section. The device may include a plurality of 
heatable dryer cylinders arranged in vertically spaced upper and lower 
cylinder rows, an upper endless screen associated with the upper cylinder 
row and a bottom endless screen associated with the bottom cylinder row, 
and a screen guide roll associated with one of the upper and lower endless 
screens. A shaft may be formed between adjacent cylinders in a cylinder 
row and bounded by one of the upper and lower endless screens guided 
around the adjacent cylinders and the screen guide roll. An air box and a 
blowing device may be positioned within the shaft, and the blowing device 
may be arranged in a region of separation between the screen and the 
screen guide roll to direct an air flow through the screen. The device may 
also include a longitudinal sealing strip coupled to a surface of the 
screen guide roll in a vicinity of the region of separation. 
In accordance with another feature of the present invention, the 
longitudinal sealing strip may include a blade holder mounted on the 
blowing device and a blade. The blade holder may be coupled to the blade. 
In accordance with another feature of the present invention, the 
longitudinal sealing strip may include a side facing the screen having an 
essentially smooth surface. 
In accordance with still another feature of the present invention, the 
screen guide roll may be located between adjacent first and second 
cylinders of one of the upper and lower cylinder rows, and the web and the 
one endless screen may be guided together from the first cylinder to the 
screen guide roll. The web and the one endless screen may be separated at 
the screen guide roll and the web may be guided in a free draw to a 
cylinder of the other of the upper and lower cylinder rows. 
In accordance with a further feature of the present invention, the device 
may also include an air duct located between the air box and the blowing 
device, and at least one driving jet may be directed into the air duct to 
evacuate air from a first part of the shaft, thereby drawing the web onto 
the dryer screen. Further, blast air may interdependently pressurize the 
driving jet and the blowing device. 
The present invention may be directed to a device for guiding a web and for 
removing paper shreds that enter a shaft in a two-screen double row dryer 
section. The two-screen double row dryer section may include an upper and 
lower dryer cylinder row having a dryer screen with a screen guide roll 
positioned in a gap between adjacent first and second dryer cylinders of a 
same dryer cylinder row, a shaft formed by a portion of the dryer screen 
associated with one of the upper and lower dryer cylinder row in a region 
of separation from the first dryer cylinder, guided around the screen 
guide roll, and guided onto the second dryer cylinder. The device may 
include a sealing strip positioned within the shaft and adjacent the 
screen guide roll to remove paper shreds from the screen guide roll and a 
blower box positioned within the shaft and adjacent the screen guide roll. 
The blower box may direct an air flow and the paper shreds through the 
dryer screen in a direction substantially toward the second dryer 
cylinder. 
In accordance with another feature of the present invention, the device may 
include an air box having an air jet nozzle substantially directed toward 
the second dryer cylinder. Further, the air jet nozzle may create a 
suction to couple the web to a portion of the dryer screen located between 
the region of separation from the first dryer cylinder and the screen 
guide roll. Still further, the blower box may be coupled to an output of 
the air box to receive compressed air. 
In accordance with still another feature of the present invention, the 
device may include a first, second and third part. The first part may 
include a vacuum section to act on the web, the second part may be 
associated with the blower box, and the third part may include a blower 
for removing steam generated in the vacuum section. 
In accordance with a further feature of the present invention, the sealing 
strip may include a scraper having a scraper end coupled to the screen 
guide roll in a vicinity of a separation of the dryer screen. 
In accordance with still another feature of the present invention, the 
blower box may be coupled to a compressed air source. 
In accordance with a still further feature of the present invention, the 
compressed air source may include an air box. Further, the air box may 
include a first and second air duct, and the second air duct may be 
coupled to the blower box. Still further, the air box may include an 
internal partition separating a first and second air duct. The first air 
duct may be coupled to the blower box and the second air duct may form a 
vacuum to couple the web to a portion of the dryer screen. 
Other exemplary embodiments and advantages of the present invention may be 
ascertained by reviewing the present disclosure and the accompanying 
drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The particulars shown herein are by way of example and for purposes of 
illustrative discussion of the preferred embodiments of the present 
invention only and are presented in the cause of providing what is 
believed to be the most useful and readily understood description of the 
principles and conceptual aspects of the invention. In this regard, no 
attempt is made to show structural details of the invention in more detail 
than is necessary for the fundamental understanding of the invention, the 
description taken with the drawing figure making apparent to those skilled 
in the art how the invention may be embodied in practice. 
The Figure may illustrate a portion of a two-screen double row dryer 
section in which two adjacent dryer cylinders 4 and 5 of an upper row of 
the dryer section are shown. Further, a web 7 is shown being guided around 
dryer cylinder 4 by a dryer screen 8 to a screen guide roll 6. At screen 
guide roll 6, web 7 may be lifted off or separated from dryer screen 8 and 
guided to a dryer cylinder of the lower cylinder row (not shown). Dryer 
screen 8 may be guided around screen guide roll 6 and guided toward 
adjacent dryer cylinder 5 of the upper row to form a loop or shaft. Web 7 
is guided around the dryer cylinder of the lower dryer row and guided to 
dryer cylinder 5 of the upper cylinder row. Web 7 is then guided around 
dryer cylinder 5 by dryer screen 8. A boundary air layer 9, which may be 
carried along dryer cylinder 4 by a surface of dryer screen 8 opposite 
dryer cylinder 4, may be diverted by a seal 10 of an air box 11. The 
arrangement of the dryer screen and dryer cylinders for the lower cylinder 
row may be substantially the same, albeit inverted, as the Figure. 
An air box 11 may form and expel air as a driving jet 27. Driving jet 27 
may be formed by a supply line 18 and an air duct 13a of air box 11. 
Because driving jet 27 is directed into air duct 23, a flow may build up 
to form a vacuum in a region 1 of the shaft. Thus, in region 1, web 7 may 
be suctioned onto dryer screen 8 so that steam produced from the drying of 
the web and escaping from dryer screen 8 may also evacuated. These air 
flows may reach a region 3 through air duct 23, where they may be expelled 
without interference. Further, at least a portion of the expelled air may 
enter into a pocket T formed between dryer screen 8 between screen guide 
roll 6 and dryer cylinder 5 and web 7 between the lower cylinder row and 
dryer cylinder 5. 
The present invention may also include a blowing device 15, which may be 
separate from air box 11 with respect to ventilation. That is, blowing 
device 15 may be located in an immediate vicinity of screen guide roll 6, 
i.e., in a bottom region 2 of the shaft in the upper cylinder row and in a 
top region of the shaft in the lower cylinder row. Blowing device 15 may 
be provided with a plurality of blow openings directed through screen 8 
toward pocket T. Blowing device 15 may be supplied with compressed air via 
a supply line 19 and air ducts 13 and 14 of air box 11. Alternatively, the 
present invention also contemplates that blowing device 15 may be provided 
with a dedicated lateral compressed air connection. In the alternative 
embodiment, no connecting air ducts 14 would be necessary between the air 
box 11 and blowing device 15. 
A wedge-shaped region 2 of the shaft, i.e., formed between blowing device 
15, screen guide roll 6 and screen 8, may be further delimited by 
longitudinal sealing elements 16 and 17 extending substantially 
perpendicular or transverse to a screen travel direction. Longitudinal 
sealing strip 16 may extend along screen 8 immediately adjacent and 
downstream, with respect to the screen travel direction, of the plurality 
of blower openings of blowing device 15. Longitudinal strip 17 may extend 
along the outer surface of screen guide roll 6 to form a scraper blade. 
Longitudinal sealing strip 17 may include a blade holder 17a mounted on 
blowing device 15 and a blade 17b supported by blade holder 17a. In the 
view shown in the Figure, a free end of blade 17b may be placed on or 
adjacent the surface of screen guide roll 6 with little force. A side 20 
of blade 17b and blade holder 17a, which faces screen 8, should be as 
smooth as possible to ensure that any paper shreds or similar foreign 
objects do not hang on longitudinal seal strip 17. The free end of blade 
17b may extend as far as possible in a direction of the separation region 
of screen 8 of screen guide roll 6. In this manner, paper shreds or 
similar foreign objects may be forced to quickly move in a direction 
toward cylinder 5 and, thus, toward the outside. 
In an alternative to the preferred embodiment depicted in the Figure, air 
box 11, for example, may be provided with a pipe 12 as a supporting 
element, and an interior may be subdivided into two halves by an internal 
partition 22 to form air ducts 13 and 13a. Blowing device 15 may be 
rigidly coupled with pipe 12 via air ducts 14. 
It is noted that the foregoing examples have been provided merely for the 
purpose of explanation and are in no way to be construed as limiting of 
the present invention. While the invention has been described with 
reference to a preferred embodiment, it is understood that the words which 
have been used herein are words of description and illustration, rather 
than words of limitation. Changes may be made, within the purview of the 
appended claims, as presently stated and as amended, without departing 
from the scope and spirit of the invention in its aspects. Although the 
invention has been described herein with reference to particular means, 
materials and embodiments, the invention is not intended to be limited to 
the particulars disclosed herein; rather, the invention extends to all 
functionally equivalent structures, methods and uses, such as are within 
the scope of the appended claims.