Paper machine drying section

A paper machine dryer group has a plurality of rolls, including a guide roll and a tension roll, and a carrier belt traveling over the rolls and forming a continuous loop. The guide roll can be displaced to a location parallel to its axis as well as at an angle to the direction of movement of the carrier belt. The guide roll and the tension roll are coupled to each other in such a way that, when the guide roll is displaced, the tension roll is simultaneously displaced in such a direction and to such an extent that the carrier belt tension remains at least approximately constant.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to paper machine components and in particular to 
paper machine dry sections having a plurality of drying cylinders and 
guide rolls looped about by an endless carrier belt. 
2. Description of Related Technology 
Dryer sections of paper machines are disclosed, for example, in Kade et 
al., U.S. Pat. No. 5,050,317 and Preisetanz et al., U.S. Pat. No. 
5,177,880. These patents disclose dryer sections with single-row dryer 
groups in which a plurality of dryer cylinders are disposed in a row and a 
suction-deflection roll is provided between two neighboring dryer 
cylinders. An endless carrier or support belt, also known as a dryer wire, 
loops in alternating fashion around the suction-deflection rolls and the 
dryer cylinders. During operation, a paper web to be dried is guided by 
the carrier belt as the paper and the belt travel about a dryer cylinder. 
The paper web is sandwiched between the surface of the dryer cylinder and 
the carrier belt. 
Normally, a dryer section contains several dryer groups so that a paper web 
is transferred from one dryer group to the next during its passage through 
the paper machine. 
At an initial region of the dryer section, the paper web has a relatively 
high water content and thus a relatively low strength. Therefore, the 
paper web is always supported by the carrier belt of a particular dryer 
group. The dryer groups are arranged such that the paper web is fully 
supported at transfer regions between the dryer groups. In such a transfer 
region, the web comes into contact with a carrier belt of a next dryer 
group positioned directly downstream with respect to a direction of travel 
of a paper web through the paper machine, but at the same time remains in 
contact for a small distance with the carrier belt of the previous (i.e., 
upstream) dryer group. Thus, the paper web is sandwiched between the two 
carrier belts for a short time. 
However, due to the paper web low strength mentioned above, tearing of the 
paper web often occurs. Also, large amounts of waste may be produced 
within a short time due to the high velocity of travel of the paper web 
through the paper machine. The waste must be removed as fast as possible 
so that it does not cause damage to the guide rolls, dryer cylinders or 
dryer screens. 
In order to be able to remove paper jam as fast as possible, the transfer 
region between dryer groups is preferably designed so that it can be 
"opened" rapidly. This is achieved, for example, by moving a dryer wire of 
a first dryer group away from a guide roll of a neighboring dryer group 
via corresponding displacement of a guide roll in the transfer region, so 
that the waste can fall into a machine cellar. The guide roll can be a 
suction roll which is located during normal operation within the wire loop 
of the neighboring dryer group and which is disposed near a last dryer 
cylinder of the previous (i.e., upstream) dryer group. See, for example, 
FIG. 1 of U.S. Pat. No. 5,177,880 which shows a suction guide roll near a 
dryer cylinder 13. FIG. 2 of U.S. Pat. No. 5,050,317 shows a dryer section 
arrangement in which a guide roll 194 can be displaced so that a dryer 
wire 174 of a dryer group can be moved away from a dryer wire 175 of the 
next (i.e. downstream with respect to a direction of travel of a web 
through the dryer groups) dryer group. 
Displacement of guide rolls generally results in a change of the tension of 
a cooperating dryer wire. To keep the tension constant, tension rolls may 
be provided within each dryer wire loop. The tension rolls receive signals 
from tension sensors which first record a change in wire tension and then 
give an appropriate command to the tension roll. However, as described 
above, a dryer wire becomes displaced during an "opening" process of a 
transfer region between dryer groups, as well as during a corresponding 
closing process of the region, which can lead to significant interruption 
of the operation of the dryer section and also to continual tearing of the 
paper web. 
In dryer sections known in the art described herein, application of tension 
to a dryer wire, after it becomes slack, does not take place fast enough. 
This is due to a certain inertia of the tension roll sensor system and of 
the tension roll control system. 
SUMMARY OF THE INVENTION 
It is an object of the invention to overcome one or more of the problems 
described above. It is also an object of the invention to provide a 
component of a paper machine, especially a dryer group of a dryer section 
of a paper machine wherein the tension of an endless belt that loops about 
the dryer group always remains the same, even during the opening and 
closing processes of a transfer region between dryer groups, and does not 
change even for short time periods. 
According to the invention, a paper machine dryer group has a plurality of 
rolls, including a guide roll and a tension roll, and a carrier belt 
traveling over the rolls and forming a continuous loop. The guide roll can 
be displaced to a location parallel to its axis and at an angle to the 
direction of movement of the carrier belt. The guide roll and the tension 
roll are coupled to each other in such a way that, when the guide roll is 
displaced, the tension roll is simultaneously displaced in such a 
direction and to such an extent that the carrier belt tension remains at 
least approximately constant.

DETAILED DESCRIPTION OF THE INVENTION 
According to the invention, a dryer group includes a guide roll and a 
tension roll coupled to each other such that when the guide roll is 
displaced, the tension roll is also displaced simultaneously in such a 
direction and to such an extent that the tension of the endless belt 
cooperating with the guide and tension rolls remains approximately 
constant. Although U.S. Pat. No. 5,050,317 describes a displaceable guide 
roll 192 or 194 supported on a common frame together with a tension roll 
170 (column 7, lines 29-34, in connection with FIG. 2), it does not follow 
from this disclosure that the two rolls are coupled with each other so 
that simultaneous displacement of the rolls occurs. 
The invention is explained in more detail in the drawings. FIG. 1 shows a 
portion of a dryer section of a paper machine. A paper web loops in 
succession about dryer components or groups generally designated A and B. 
The dryer group A includes three dryer cylinders 2, 3, and 4, disposed in 
succession and neighboring suction guide rolls 5, 6, 7, and 8. The dryer 
group A also includes a series of guide rolls 30, 31, 32, 33, 34, and 35. 
An endless support belt or dryer wire 9 travels over the cylinders 2, 3, 
and 4 and the rolls 30, 31, 32, 33, 34, and 35 in a continuous loop and 
moves in a direction indicated by an arrow 11. 
Similar to the dryer group A, the dryer group B has three dryer cylinders 
12, 13, and 14, three suction guide rolls 15, 16, and 17, five guide rolls 
40, 41, 42, 43, and 44, and a continuous belt or dryer wire 10 looped 
thereabout. The wire 10 moves around the cylinders and rolls in a 
direction indicated by an arrow 20. 
As shown in FIG. 1, a connecting line running through the dryer cylinders 
of the first dryer group A forms a V with a connecting line running 
through the dryer cylinders of the second dryer group B. 
A rocker 50 supports the suction guide roll 8, and the guide rolls 30 and 
31. The rolls 8, 30 and 31 assist in maintaining the wire 9 under tension, 
and thus also function as tension rolls. The rocker 50 can be swiveled 
around an axis 51 thereof. The axis 51 is parallel to longitudinal axes of 
the dryer cylinders as well as to longitudinal axes of the other rolls. 
The position of the rocker 50 shown by a solid line in FIG. 1 is a working 
position of the rocker 50. 
Another dryer component or group (not shown) is connected before the dryer 
group A, i.e., upstream of the dryer group A with respect to a direction 
of travel of a paper web through the paper machine, and a further dryer 
group (not shown) is connected downstream of the dryer group B with 
respect to a direction of travel of a paper web through the paper machine. 
However, such dryer groups are not further discussed herein. Other types 
of paper machine components or units can be disposed upstream and 
downstream of dryer groups A and B. For example, a press part may be 
disposed upstream of the dryer group A. 
The two dryer groups A and B operate as follows: The dryer group A takes 
over a paper web (not shown here in detail) from an upstream paper machine 
unit by transfer of the web with the aid of the dryer wire 9 and the 
suction guide roll 5. As the paper web loops about the suction guide roll 
5, the paper web is disposed outside of the dryer wire 9. Then, together 
with the dryer wire 9, the paper web is conveyed to the dryer cylinder 2, 
during the conveyance of which the web is sandwiched between a surface of 
the dryer cylinder 2 and the dryer wire 9. Thereafter, the paper web is 
further transported in succession to the suction guide roll 6, the dryer 
cylinder 3, the suction guide roll 7, the dryer cylinder 4, and the 
suction guide roll 8. In the region of the suction guide roll 8 which is a 
transfer region between the dryer groups A and B, the paper web is 
transferred from the dryer group A to the dryer group B by conveyance of 
the paper web from the dryer wire 9 to a surface of the dryer cylinder 12. 
In the transfer region between dryer groups A and B, the paper web is 
sandwiched for a short time between the dryer wire 9 and the surface of 
the dryer cylinder 12. The paper web then follows the surface of the dryer 
cylinder 12 and becomes sandwiched between the cylinder 12 and the dryer 
wire 10 of the dryer group B. 
If the paper web tears, the rocker 50 is swiveled to a position shown by a 
dashed line in FIG. 1. During this swiveling, the portion of the dryer 
wire 9 which is between the suction roll 8 and the guide/tension roll 30 
is moved away from the surface of the dryer cylinder 12. As a result, the 
path of the paper web is opened so that the paper web can fall down 
through an open gap into a machine cellar for recycling. The swiveling of 
the rocker 50 occurs about the axis 51 in a direction indicated by an 
arrow 60. 
During the swiveling of the rocker 50 the total path of the dryer wire 9 is 
shortened. However, at the same time, the guide/tension roll 31 acts as a 
tension roll as it is swiveled in a direction indicated by an arrow 61. 
The swiveling movements of the rolls 8, 30, and 31 carried by the rocker 
50 are necessarily coupled to one another, so that the tension of the 
dryer wire 9 remains the same at all times and displacement of the dryer 
wire 9 cannot occur. 
FIG. 2 also shows two dryer groups disposed in succession. A guide roll 30' 
can be displaced in a direction indicated by an arrow 60' to provide an 
opening at a transfer region between two dryer wires 9' and 10'. A 
neighboring tension roll 31' is rigidly coupled to the guide roll 30' by a 
rod 70' so that when the guide roll 30' is displaced, the tension roll 31' 
is simultaneously displaced with positive locking. The slackening of the 
dryer wire 9' due to the displacement of the guide roll 30' is compensated 
for instantly by tightening of the wire 9' due to the controlled 
displacement of the tension roll 31'. 
Modifications of embodiments according to the invention described herein 
are also possible. In the embodiment shown in FIG. 1, it is possible to 
support only the guide/tension roll 30 and the guide/tension roll 31 on 
the rocker 50, but not the suction guide roll 8. Furthermore, the 
guide/tension roll 30 and the roll 8 can be displaced together, while 
allowing the roll 31 to remain stationary. Also, various participating 
rolls, for example, the guide roll 31, can be supported rigidly or 
flexibly. 
Finally, the invention can be applied independently of whether the transfer 
region is between two bottom felt groups, between a bottom and a top felt 
group or between a top felt group and a bottom felt group. 
The foregoing detailed description is given for clearness of understanding 
only, and no unnecessary limitations should be understood therefrom, as 
modifications within the scope of the invention will be apparent to those 
skilled in the art.