Method and apparatus for calendering paper

The invention relates to a method and an apparatus calendering a fiber web, wherein the fiber web passes through an extended and heated nip, said nip being formed on one side by a cylindrical heated roll and on the other side by a flexible tubular jacket which is pressed against the heated roll by means of a concave load shoe, said tubular jacket surrounding a stationary support beam which supports at least one actuator which may urge said load shoe and said flexible tubular jacket against said heated roll, and wherein the extension of the load shoe in the axial extension is less than the axial extension of the jacket and the heated roll such that when the load shoe is urged against the heated roll there will be formed tapered sections at each side end of the jacket within the nip characterised in that said tapered section are substantially covered by said fiber web such that a small strips of the fiber web at each edge is not calendered in said extended nip.

TECHNICAL FIELD 
This invention relates to a method and apparatus for performing calendering 
of a fiber web, preferably using an enclosed shoe roll. 
PRIOR ART AND PROBLEMS 
Calendering of paper is performed in order to achieve a smooth surface of a 
fiber web, e.g. paper. Traditionally this is achieved by using two 
counter-acting rolls forming a nip within which a high pressure is applied 
to the paper surface in order to even out irregularities of the paper 
surface so as to form a smooth surface. A disadvantage by using the above 
mentioned method is that the high pressure acting on the web may cause 
excessive compaction of the web. As a result the thickness of the paper 
will be significantly reduced leading to relatively poor stiffness of the 
web after the calendering. 
The above mentioned disadvantage can be reduced by using heat in 
combination with a relatively moderate pressure. The reason for this is 
that the fibers of the paper are plasticized if the temperature is 
sufficiently high (The temperature of plastification is normally about 
170-210.degree. C., i.e. depending on the moisture content and the 
properties of the fibers.) Accordingly if a sufficiently heated roll, e.g. 
250.degree. C., is used and sufficient heat transfer is achieved to the 
surface of the web passing the roll, a web may be produced having a smooth 
surface and relatively large thickness, which results in a much stiffer 
product than if a high pressure nip without heat would have been used. 
For the above reason there are many applications where heat calendering is 
desired for the calendering process. A relatively recent problem in 
relation to heat calendering is the achievement of sufficient heat 
transfer, due to the trend towards higher and higher speed of the web. The 
faster the web moves through the nip the shorter time there will be for 
the transfer, i.e. shorter retention time. In U.S. Pat. No. 5,163,364 
there is shown a method for solving the latter problem. U.S. Pat. No. 
5,163,364 describes the use of an extended nip for obtaining sufficient 
retention time to ensure sufficient heating of the web surface during its 
travel through the nip. As shown in U.S. Pat. No. 5,163,364 the 
calendering zone is made up by a heated roll pressing from one side and an 
endless flexible belt which is pressed by means of a concave press shoe 
against the heated roll. 
The endless flexible belt is preferably made of a material that comprises 
polymers, resulting in relatively poor heat resistance, i.e. if the heat 
exceeds a certain temperature, normally about 100.degree. C., the flexible 
belt will be destroyed. Since the cost of such a belt is considerably high 
any over heating of the flexible belt must be avoided. This can be 
achieved by the paper web absorbing most of the heat in combination with a 
cooling of the flexible belt after having passed through the nip. However, 
if the paper web is broken, an arrangement as shown in U.S. Pat. No. 
5,163,364 in combination with the use of a flexible belt comprising 
polymers (not mentioned in U.S. Pat. No. 5,163,364) would lead to the 
destruction of the flexible belt due to overheating, since the heated roll 
would then act directly on the flexible belt. This problem would be even 
worse if an enclosed shoe roll would have been used, since the cooling of 
an open flexible belt is easier to achieve than in a closed roll, i.e. an 
enclosed shoe roll. Furthermore, the use of an enclosed shoe roll requires 
that the flexible jacket is longer than the load shoe, i.e. it extends 
outside the nip on each side. Accordingly there will exist portions of the 
jacket which normally would not be covered by the web, since these 
portions do not participate in the calendering within the nip. This would 
result in a direct heat radiation from the heated roll to these portions, 
which might lead to over heating of the jacket and premature destruction. 
Another related problem is the start-up process. Normally, the jacket of an 
enclosed shoe-roll is not driven by itself, but by means of friction once 
in contact with the fiber web. It is evident for the skilled person that 
the web will be negatively affected by such a starting-up process. 
Furthermore, such a start-up process also presents a possible risk of 
overheating of the belt at the moment of the start-up, since the belt does 
not move during the first contact with the web within the heated nip, i.e. 
an extreme heat transfer to the belt will occur. 
Another related problem is how to avoid undesired wear of a flexible 
belt/jacket. 
SOLUTION AND ADVANTAGES 
The object of the invention is to provide a process and apparatus which 
eliminates or at least minimizes some of the disadvantages mentioned 
above. This is achieved according to one aspect of the invention; 
By a method for calendering a fiber web, wherein the fiber web passes 
through an extended and heated nip, said nip being formed on one side by a 
cylindrical heated roll and on the other side by a flexible tubular jacket 
which is pressed against the heated roll by means of a concave load shoe, 
said tubular jacket surrounding a stationary support beam, which supports 
at least one actuator which may urge said load shoe and said flexible 
tubular jacket against said heated roll, and wherein the extension of the 
load shoe in the axial extension is less than the axial extension of the 
jacket and the heated roll such that when the load shoe is urged against 
the heated roll there will be formed tapered sections, at each side end of 
the jacket within the nip characterised in that said tapered section are 
substantially covered by said fiber web such that a small strip of the 
fiber web at each edge is not calendered in said extended nip. 
By the solution according to the invention the jacket is protected from 
over heating also at the end portions by means of covering them with the 
web. This leads to big cost savings, because of prolonging the lifetime of 
the jacket. The uncalendered strips may be cut off at a later stage, but 
according to a preferred aspect said small strips are calendered in a 
preceding or in a subsequent nip, which results in unproblematic rolling 
up of the produced web and possibly also obtaining a larger amount of the 
fiber web as a final product, which increases the income for the producer. 
According to further aspects related to the invention, 
said flexible tubular jacket forms a part of an enclosed shoe roll such 
that the ends of said jacket has end walls mounted thereto, which end 
walls are rotatably mounted in relation to said support beam to form a 
sealed space together with said jacket, and in that at least one of said 
end walls is driven by means of a drive arrangement which drive 
arrangement may be activated to drive the end walls and thereby also the 
jacket independently of its position in relation to the fiber web or the 
heated roll. 
said driving means is activated before the nip is closed in order to ensure 
a desired speed of the jacket at the moment of closure of the nip. 
the speed of the web is measured and that the speed of the belt is 
synchronized with said speed of the web before it is brought into contact 
with it. 
a detecting means which detects if the paper web is broken and a control 
system interconnected with said detecting means in such a manner that said 
driving means is activated if the web is broken and also at the same time 
that the jacket is moved away out of contact with the heated roll. 
the speed of the web exceeds 600 m/min, preferably exceeds 800 m/min, and 
more preferably exceeds 1000 m/min. 
the web being produced is paper whereby the speed of the web exceeds 1000 
m/min, preferably exceeds 1500 m/min, and more preferably exceeds 1800 
m/min. 
the temperature of the surface of said heated roll exceeds 150 C., 
preferably exceeds 170 C., and more preferably is about 200-250 C. 
the linear load within the nip is less than 500 kN/m, preferably less than 
400 kN/m, and more preferably about 320-380 kN/m. 
the linear maximum pressure within the nip is less than 15 MPa, preferably 
less than 13 MPa, and more preferably about 8-12 MPa. 
the force transmission from the drive arrangement to at least one of said 
end walls is achieved by means of friction. 
the force transmission from the drive arrangement to at least one of said 
end walls is achieved by means of a positively gripping drive arrangement. 
at least one of the end walls is axially displaceable such that the tension 
of the flexible jacket may be varied also during operation of the enclosed 
shoe roll. 
the last step of achieving the nip involves urging the jacket out and above 
its unloaded position by means of the load shoe to press against the 
heated roll. 
the jacket is moved out of contact with the heated roll by means of 
unloading the load shoe. 
The advantages according to the above further aspects of the invention are 
several. The drive arrangement according to the invention enables opening 
and closing of the nip during operation without the risk of destroying the 
jacket due to overheating or damaging the flexible jacket, which results 
in cost savings and less down-time of the machine. Furthermore since the 
force transmitting device of the drive arrangement is attached to the end 
walls of the enclosed shoe roll, and both end walls are rotated at the 
same rotational speed, the flexible jacket will not be affected by the 
driving of the enclosed shoe roll, neither by wear on the jacket surface 
nor by tensional forces on the jacket itself. Moreover, by the possibility 
of axially displacing the end walls, the position and/or tension of the 
flexible jacket in an axial direction may be adjusted during operation, 
and thereby reducing the wear of the jacket due to local stress of the 
jacket in different directions. 
A further aspect of the invention relates to a set of calenders for 
calendering a fiber web, comprising a first calender having a cylindrical 
roll and an enclosed shoe roll, said shoe roll comprising a flexible 
tubular jacket surrounding a stationary support beam, a load shoe which is 
movable by means of at least one actuator which is mounted on said 
stationary support beam, characterized in a second calender comprising a 
heated roll mounted for interaction with at least one small roll whose 
width is substantially smaller than the width of the fiber web. 
According to further aspects related to the invention, 
the width of said small roll is between 50-500 mm, preferably 100-300 mm. 
said small roll is arranged on at least one pivot arm which is pivotally 
attached to a support member and powered by an assembly, preferably a 
hydraulic piston assembly. 
there are two pivot arms between which the small roll is arranged, in order 
to obtain a rigid structure for good control of the action of the small 
roll within the nip. 
said small roll is powered by a separate drive. 
These and further aspects of the invention and the advantages with the 
invention will become apparent from the detailed description and from the 
attached claims.

DETAILED DESCRIPTION OF EMBODIMENTS 
In FIG. 1 there is shown a fiber web 80 passing through an extended and 
heated nip 1. The nip 1 is formed by an enclosed shoe roll 10 positioned 
on the lower side in relation to the fiber web 80. On the upper side of 
the fiber web 80 there is shown a heated roll 22. The enclosed shoe roll 
10 comprises a liquid impermeable flexible jacket 12, e.g. of a 
conventional type consisting of reinforced polyurethane. A stationary 
non-rotatable support beam 14 supports at least one load shoe 18. Between 
the load shoe 18 and the support beam 14 there is an actuator 20, in the 
preferred embodiment hydraulic pistons, for urging the concave load shoe 
18 and thereby also the flexible jacket against the counter-roll 22. It 
should be noted that (contrary to what is "normal practice") the jacket is 
urged out of its unloaded position in a direction away from the center of 
the enclosed shoe roll. (In known shoe type presses the counter roll 
depresses the jacket inwardly.) The jacket 12 is attached to the outer 
periphery of two circular end walls 24, 26, such that a sealed compartment 
13 (see FIG. 2) is obtained within the enclosed shoe roll. As also shown 
in FIG. 1, at least one detecting device 99 is arranged adjacent the fiber 
web 80, in order to detect if the web is broken. This detecting device 99 
is connected to a control device 98 for controlling the operation of the 
calendering process in dependence of the fiber web 80 being broken or not. 
As schematically shown in FIG. 1 the heated counter-roll 22 is arranged on 
a movable lever 95 having a pivot point 96 and a hydraulic piston 
arrangement 94 for providing the possibility of moving the heated roll 22 
into and away from the nip 1, which forms a part of a so called separating 
mechanism. In the preferred embodiment the separating mechanism comprises 
two mechanisms, a first mechanism for the movement of the load shoe 18 
(the position of the jacket after unloading of the shoe is marked with 
reference numeral 11 in FIG. 1A) and a second mechanism for the movement 
of the counter-roll 22. At least one of the separating mechanisms is 
controlled by the above mentioned control circuit 98, such that the jacket 
is moved out of contact with the heated roll 22 as soon as the detecting 
device 99 detects a break of the fiber web. However, the movement of any 
separating mechanism shall also be operational by manual control, e.g. in 
connection with inspection of the nip 1. 
In FIG. 2A it is shown that the end walls 24, 26 are rotatably mounted on 
stub shafts 16, 17 of the support beam 14. (The end walls are preferably 
not integral but divided into a static and a rotating parts as shown in 
FIG. 2B.). On one end of the stub shaft, a cylindrical shaft 32 is 
arranged rotatably via bearings 34. The support column 36 is arranged to 
the cylindrical shaft via self-aligning bearings 38, which allow spherical 
movement to allow the deformation/bending of the support beam 14 when 
heavily loaded. One of the end walls 24 is fixedly attached to the 
cylindrical shaft. A drive transmission 40 is fixedly attached to the 
cylindrical shaft 32 outside the end wall, in the shown embodiment a cog 
wheel. The cog wheel is connected to a transmission 42 and in turn a drive 
44. A cog wheel 46 is fixedly attached to the cylindrical shaft inside the 
end wall. A drive shaft 48 is arranged inside the jacket and parallel to 
the support shaft. The drive shaft is supported by bearings 50 arranged in 
bearing houses 52 attached to the support beam. At each end of the drive 
shaft, cog wheels 54, 55 are arranged. Preferably these cog wheels have a 
prolonged toothed portion to allow axial movement of the intermeshing cog 
wheel which is attached to the end wall. A further cog wheel 56 is fixedly 
attached to the second end wall 26 inside the jacket. Both cog wheels 
inside the jacket mesh with the corresponding cog wheel on the drive 
shaft. The second end wall 26 is rotatably arranged on the second stub 
shaft 17. The second stub shaft is in turn fixedly attached to a second 
support column 58. 
The function is as follows. During normal operation, the driven heated roll 
22 interacts with the fiber web and the flexible jacket 12 by means of a 
desired pressure being exerted by the load shoe 18, thereby causing a 
friction based drive of both the fiber web and the flexible jacket. 
Accordingly, during normal operation the forces exerted in the nip provide 
for rotation of the enclosed shoe roll. 
Merely during specific occasions there will normally be desired to operate 
the independent drive of the enclosed shoe roll 10. For instance, when 
starting-up of the calender is to be performed. If the calender should be 
started without first having speeded up the flexible jacket 12, this would 
inevitably cause damage to the flexible jacket due to overheating. 
Furthermore, it would also be deteriorating for the fiber web, since at 
the moment of start it would cause exceptional tension forces in the fiber 
web. Accordingly, the independent drive arrangement of the enclosed shoe 
roll is to be used for instance at the start-up of the calendering 
surface. At the start, the nip gap is not closed, but the roll 22 has been 
moved out of contact with the nip 1. Before moving the heated counter-roll 
22 into the nip, the drive arrangement 44 of the enclosed shoe roll 10 is 
activated to accelerate the first end wall 24 via transmissions. The 
rotation of the end wall causes the inner first cog wheel 46 to rotate, 
and subsequently the drive shaft 48. The drive shaft transmits the 
rotation to the second end wall 26 via the second inner cog wheel 56. The 
both end walls are thus accelerated and rotate at the same speed until a 
peripheral speed is obtained which is desired, normally equal to the speed 
of the fiber web. The nip is closed by activating the hydraulic piston 94 
to pivot the lever 95 and thereby moving the counter-roll 22 into the nip 
and subsequently the load shoe 18 is urged against heated roll 22 by means 
of its actuators 20. Once the calender functions in the desired manner, 
the drive arrangement of the enclosed shoe roll can be deactivated and the 
press roll driven in a conventional manner by means of friction within the 
nip 1. 
Also for inspection of the enclosed shoe roll the operation in accordance 
with the above is desired since this will avoid closing down the whole 
machine. After inspection and possible adjustments or replacements of 
components with the paper web just moving through the gap between the 
rolls, the press roll is accelerated in the above manner, the nip is 
closed and the process continues without a risk of breaking or ripping the 
web. 
It is to be understood that both end walls have to be driven and rotated 
with the same speed, since the flexible jacket cannot transmit any 
torsional forces. 
In FIG. 2B there is shown an alternative embodiment of the drive 
arrangement for an enclosed shoe roll as shown in FIG. 1 (not using a 
positively gripping drive arrangement as shown in FIG. 2) This embodiment 
uses friction for transmission of rotational force. 
FIG. 2B also shows a more preferred design of arranging the support beam 
and the end walls. The end walls are divided into a static inner part 24A; 
26A, a rotational part 24B; 26B and a bearing 24C; 26C therebetween. Both 
of the static parts 24A; 26A are secured to the support column 14 such 
that they cannot rotate. However, preferably they are arranged such that 
they can be axially displaced, as is known per se and described in U.S. 
Pat. No. 5,084,137, in order to provide for movement and/or tensioning of 
the jacket, if desired. The support beam 14 is at its ends arranged with 
self-aligning bearings 23, 25 to allow the beam 14 to flex. 
There is shown a drive 44 having a shaft 19B. On the shaft 19B there is 
arranged a disc 19 having a rubber layer at its peripheral end 19A. The 
outer ends 12B of the flexible jacket 12 are fixedly attached between an 
annular ring 15 (acting as a kind of force transmitting device 15 which 
can be exchanged after excessive wear) and the periphery of each end wall 
24. The annular ring 15, which may be segmented, is fixedly attached to 
the end wall 24 in any appropriate manner, e.g. by screws. (It is evident 
that the jacket can be secured to the end walls in many other ways, e.g. 
by a support (not shown) attached to the inner side of the end walls, 
which leads to a design where the frictional driving force preferably is 
transmitted directly to the outer surface of the end wall, i.e. the force 
transmitting device is integral with the end wall. It is of course also 
possible to attach a separate force transmitting device at the outer side 
of an end wall.) On the inside of the rotational part 24B, 26B of each end 
wall there is fixedly attached a cog wheel 46; 56, having annular form. 
The drive arrangement 44, 19 is movable in or out of contact with said 
force transmitting device 15. Accordingly, when it is desired to 
accelerate the enclosed shoe roll 10, the drive arrangement is moved such 
that the rubber layer 19A comes into frictional engagement with the force 
transmitting ring 15. The cog wheel 46 and the drive shaft 48 will 
transfer the rotation of the end wall 24 to the other end wall 26 by means 
of the cog wheels 54, 55 and 56, which at the same time fulfils the 
function of a synchronizing device. Hence, this will cause both end walls 
24, 26 to be operated in a corresponding manner as described above in 
relation to FIG. 2A. If needed there may be a drive on each side of the 
roll 10 interacting with each one of the end walls, whereby the 
transmission substantially merely acts as synchronizing device. In FIG. 2B 
it is also shown a schematic view of a preferred embodiment of the action 
of the load shoe 18. (Normally the load shoe 18 would not be positioned 
diametrically in relation to drive shaft 48, but perpendicularly as is 
shown in FIG. 1). The load shoe is urged to push the flexible jacket 12 
radially outwardly away from its normal resting position, to form the nip 
with the heated roll 22, as is explained more in detail below in relation 
to FIGS. 3A and 3B. 
From FIGS. 3A and 3B it is evident that the load shoe 18 does not extend 
all the way between the end walls 24, 26. This is an arrangement needed 
for not endangering ripping of the flexible jacket 12, due to the load of 
the load shoe at its edges. Furthermore it is shown that also the heated 
roll 22 extends longer than the load shoe, which is needed to ensure 
optimal heat distribution/transfer within the nip and also to avoid heat 
expansion problems. Preferably heated oil is used to heat the roll. A 
desired temperature would normally be about 200-220.degree. C. at the 
surface of the heated roll 22. The heated oil is supplied at the axial 
ends of the heated roll 22 which accordingly will have a higher 
temperature and therefore expand more. (Of course also other ways of 
heating are possible, e.g. heating by induction, steam or gas burners. 
However also using these alternative heating methods lead to similar heat 
distribution problems, which are reduced by making the roll longer than 
the shoe.) Furthermore it is shown that the heated roll 22 is positioned 
at a distance from the jacket 12, if the load shoe is in an unloaded 
state. To create a nip the load shoe 18 therefore has to press the jacket 
12 outwardly, as shown in FIG. 3A which also shows that the web 80 has a 
wider extension than the load shoe. The movement of the load shoe into the 
nip is achieved by an actuator 20, which in the preferred embodiment 
comprises a number of double-acting hydraulic piston assemblies 181 
wherein the piston end is secured to the load shoe 18. The hydraulic fluid 
is schematically shown to be supplied and withdrawn by means of two pipes 
186, 187 arranged within the enclosed shoe roll. In FIG. 3A it is shown 
that the upper pipe 186 is pressurized, the lower pipe 187 being 
unpressurized, such that the branch pipe leading to the lower side piston 
assembly is pressurised, which urges the piston 181 and the load shoe 18 
upwardly to form the nip with the heated roll 22. Normally the distance 
which the jacket is moved out of its unloaded position would be about 5-10 
mm. Accordingly, in the loaded state there exist two tapered zones 12A, 
12C adjacent the nip, where no contact will exist between the jacket/web 
and the heated counter-roll 22, and which tapered zones will be 
substantially covered by the web 80 to protect the jacket from the heat of 
the heated roll 22. 
In FIG. 3B the lower pipe 187 is pressurized, the upper pipe 186 being 
unpressurized, such that the branch pipe leading to the upper side of the 
piston assembly is pressurized, which urges the piston 181 and the load 
shoe 18 to move down to form a gap with the heated roll 22. Accordingly 
for this preferred kind of calender the separating mechanism comprises two 
mechanisms. Firstly, the actuator 20 moving the load shoe 18 and secondly 
the lever arm mechanism 94,95,96 moving the heated roll 22. Also for this 
embodiment the separating mechanism is controlled by the above mentioned 
control circuit 98, such that a gap is formed as soon as the detecting 
device 99 detects a break of the fiber web. However here firstly the load 
shoe is moved as explained above, such that the load shoe is allowed to 
quickly move back to its resting position and thereby creating a gap 
corresponding to the distance between the unloaded jacket and the heated 
roll, i.e. normally about 7 mm. This distance is sufficient for reducing 
the heat transfer to acceptable levels, especially if the jacket is 
rotated at the same time in accordance with the invention. Thereafter the 
second part of the separating mechanism is separated in order to allow a 
sufficiently large gap (normally at least 40 mm, but less than 100 mm) to 
allow a new web to be introduced into the gap. As mentioned above both 
rolls are rotating at the desired speed once the new web is introduced 
into the gap. Subsequently the lever arm is moved to position the heated 
roll in its "nip position" and finally the load shoe is activated to urge 
the jacket against the heated roll to close the nip. It is evident that it 
is much easier to make a quick move of the load shoe than of the much 
heavier heated roll. Accordingly this embodiment is a very effective 
solution of the problem of avoiding over heating of the flexible belt. 
As explained above, in order not to have an excessive heat transfer from 
the counter-roll 22 the tapered jacket zones, outside the nip, 12A, 12C 
have to be at least partially covered by the fiber web during operation. 
As a consequence there will exist two non-calendered strips 80A, 80B at 
each end of the fiber web. The thickness of these strips is then of course 
larger than the thickness of the rest of the web. Accordingly, such a 
fiber web could not be rolled up without problems. 
This latter problem may be solved in different ways. The first way of 
solving it is to arrange a further calendering subsequently after the nip 
1 (or optionally also before) wherein merely these strips 80A, 80B are 
calendered. Alternatively, the strips may be cut away before the fiber web 
is rolled up. 
In FIG. 4 there is shown a side view of a preferred embodiment of arranging 
the direct drive of the enclosed shoe roll 10, by means of frictional 
engagement (the same principle as shown in FIG. 2B). Accordingly, there is 
shown a torque transmitting wheel 19 having an outer rubber layer 19A, 
which is intended for interaction with the surface 15 of each end wall 24, 
26. Hence, there are two drive arrangements of the same kind, one arranged 
at each side of the enclosed shoe roll for transmitting force to each end 
wall 24, 26. The synchronization is achieved by having one drive being a 
master and the other being the slave. During an acceleration the master is 
supplied with a substantially larger torque than the slave, normally 2/1. 
A control circuit controls the speed of the wheels. If one wheel has a 
speed that differs from the speed of the other wheel, this means that one 
wheel is slipping and the power supply will then be adjusted accordingly 
such that slipping is eliminated. When two drives are synchronized in this 
way, the drive shaft 48 of the embodiment disclosed in FIG. 2B becomes 
redundant and can be eliminated. 
The drive wheel 19 is fixedly attached to a first shaft 102, which is 
rotatably mounted within two support levers 104 and 106. At the end of the 
shaft 102 there is mounted a toothed wheel 108. The toothed wheel 108 is 
powered by means of a flexible toothed belt 110, which in turn is powered 
by a second toothed wheel 112 fixedly attached to the end of a drive shaft 
114, which is powered by an induction motor 44. The drive shaft 114 is 
rotatably arranged within a casing 116. The casing in turn is rotatably 
mounted to a support structure 118, which is secured to a support beam 
120. At the first end of said casing 116, the support levers 104, 106 are 
fixedly attached thereto. At the other end of said casing 116 there is 
fixedly attached a lever arm 122, which at its end is mounted to a 
hydraulic piston assembly 124. The engine 44 is mounted on a separate 
support structure 126, which also is attached to the support beam 120. The 
drive shaft 119 protruding from the engine 44 is interconnected with said 
other drive shaft 114 by means of a coupling device 128. 
FIG. 4A is a side view of the enclosed shoe roll 10 according to invention 
showing how the drive arrangement according to FIG. 4 interacts with the 
roll. The view is a cross section along lines 4A--4A of FIG. 4. As can be 
seen, the hydraulic piston assembly 124 is adjustably secured to a support 
structure, preferably forming an integral part with the support beam 120. 
As is evident from FIG. 4A, the driving wheel 19 can be moved in or out of 
contact with an end wall 24, 26, by means of moving the hydraulic piston 
124 such that the lever arm 122 is pivoted about the drive shaft axis 114. 
As a consequence of the pivoting of the lever arm 122, also the support 
levers 104, 106 carrying the drive wheel 19 will be moved. If the engine 
44 is in operation, the toothed wheel 112 will pull the toothed belt 110 
to rotate the second toothed wheel 108 which causes the shaft 102 and also 
the driving wheel 19 to rotate. 
FIG. 4B is a cross section along the line 4B--4B of FIG. 4, which shows an 
adjustment device for adjusting the tension of the toothed belt 110. A 
support wheel 130 is adjustably attached to the outer support lever 106, 
such that it can be positioned to exert the desired pressure on the 
toothed belt. 
In FIGS. 5A, B and C there is shown an alternative manner of driving an 
enclosed shoe roll principally functioning as the embodiment shown in FIG. 
2B. Accordingly, also this embodiment has a central support beam 14 
passing through the roll, which forms the basic support for the rotating 
end walls carrying the flexible jacket 12. To the static part 24A of the 
end wall 24 there is fixedly secured a support structure 142. To said 
support structure 142 there are arranged a first toothed wheel 144 and a 
second toothed wheel 146. In sealing engagement with the static part of 
the end wall 24A there is a rotating part 24B of the end wall. To this 
rotatable end part 24B there is securely attached a toothed wheel 150. A 
toothed belt 152 is arranged to partly encircle the toothed wheel 150 and 
also the driving toothed wheel 146. The first toothed wheel 144 is 
arranged to apply an optimal pressure to the toothed belt. Also on the 
other side of the roll there may be exactly the same arrangement 
positioned according to a mirror image of the first arrangement. The 
drives (not shown) of both sides are synchronized to drive each side with 
exactly the same speed, either mechanically or by computer control. 
By driving the first toothed wheel 146 the toothed belt 152 will make the 
toothed wheel 150 to rotate and thereby causing the jacket 12 which is 
fixedly attached to the rotating part 148 of the end wall to rotate. 
FIGS. 6 and 7 show different variants of the present invention of driving 
the enclosed shoe roll. In FIG. 6 the drive 44 is placed inside the shoe 
roll driving two drive shafts 48 arranged with cog wheels 46 which in turn 
mesh with cog wheels 56 attached to the inside of the end walls. 
The embodiment of FIG. 7 is similar to the one of FIG. 6 but with the 
difference that it is arranged with two drives 44 acting directly on the 
respective cog wheel of the end walls. 
In FIGS. 8 to 10 there is shown different embodiments of how to include the 
function of having the end walls displaceable in a design as shown in FIG. 
2A. Such a device is known per se and described in U.S. Pat. No. 
5,084,137, (which document is herewith incorporated for reference.) 
According to said prior art document an hydraulic unit is arranged 
displacing both end walls in an axial direction by in fact displacing the 
inner bearing ring of each end wall support bearing, as in the preferred 
mode of this invention. 
According to the embodiment shown in FIG. 2A, however, the end wall is not 
divided as in FIG. 2B but is rotatably attached to rotate with the 
cylindrical shaft, i.e. it is necessary to keep the rotational connection. 
FIGS. 8-10 show different possible cross sections of the stub shaft, the 
cylindrical shaft and the end wall enabling an axial displacement of the 
end wall relative to the cylindrical shaft while maintaining the 
rotational connection. The end wall is provided with a through-hole with a 
certain profile and the cylindrical shaft is provided with a corresponding 
profile, with some clearance between them, enabling the end wall to slide 
along the cylindrical shaft. The hydraulic unit acts on the end walls to 
displace it along the shaft, thereby controlling its position and the 
tensioning of the jacket. For operation reference is made to U.S. Pat. No. 
5,084,137. 
In FIG. 11A there is shown a side view of a preferred device for a 
preceding step for merely calendering the strips 80A, 80C which are not 
treated within the extended nip 1. A roll 200 preceding the extended nip 1 
is mounted within in a conventional basic structure (not shown). 
Counteracting the roll 200 there is a small roll 201, having a width of 
about the same as distance between the side edge of the load shoe and the 
inner face of the end wall, which in the shown embodiment is about 150 mm. 
The small roll 201 is rotatably mounted within a support structure having 
two parallel pivot arms 205, 210. These arms 205,210 are pivotally 
attached to a fixed support member 204, by means of a shaft 207. The 
position of the arms 205, 210 are controlled by hydraulic piston assembly 
206, which is attached to said arms 205,210 via plates 203 at one end and 
to said support member 204 at the other end. Normally the roll is not 
powered but driven by means of friction when in contact with the fiber web 
80. Optionally it may be powered by a separate drive 209 as indicated in 
FIG. 11B. The function of the calender is basically the same as described 
above. Once the web 80 is in place on the roll 200 the hydraulic piston is 
activated to move the small roll 201 in contact with the web and to exert 
a desired pressure against a strip at the edge of the web. The roll 200 
passes along the whole width of the web and at the other end of the web 
there is also positioned a corresponding arrangement with a second small 
roll calendering the other strip. Afterwards the web will have a 
substantially equal thickness all over such that it may be rolled up 
without any problems. 
It is to be understood that the present invention is not limited to the 
embodiments and shown in the drawings, but may be modified within the 
scope of the claims. For instance, instead of having pair-wise hydraulic 
pistons 20 as shown in FIG. 1 only one row of hydraulic piston may be 
used. Furthermore, it is evident for a skilled person that said end walls 
24, 26 may have a design that differs from what is shown above. For 
instance, if a friction drive acts directly on the end wall, it may be 
advantageous to have an outer segmented periphery which can be easily 
exchanged after a certain time of wear. Moreover, the skilled person 
realizes that if a separate force transmitting device is used, this force 
transmitting device 15 for transmitting the frictional force may be 
attached to the end wall in many different ways, for instance by means of 
screws, welding, gluing, etc. Also the material of said device 15 may 
vary, although some kind of stainless steel is preferred. Alternatively 
the force transmitting device may be built into the jacket, e.g. a 
reinforced extra thick layer for interaction with a friction based drive. 
The drive has mostly been schematically shown, but would in the preferred 
case be provided by means of an electrically powered engine, preferably a 
frequency controlled induction motor. However, also e.g. hydraulic drive 
units or drive units powered by fuel may of course be used. The manner of 
achieving the movement of the heated roll out of or into the nip as well 
as also the movement of the independent drive of the enclosed shoe roll 
may also be provided for by many different means, although hydraulically 
powered systems would be preferred. It is further evident that any 
existing different solutions may be used for achieving the detecting 
device 99, for detecting if the fiber web 80 is broken, e.g. optical 
sensors, electric-magnetic sensors etc. Further, instead of having one 
stationary support beam, two or more may be used, in order to obtain the 
desired supporting structure of the enclosed shoe roll. Moreover, the 
skilled person realizes that the separating mechanism exemplified above 
may be achieved in many other ways, e.g. by means of having one or both 
rolls slidingly arranged at its/their ends, by the use of screw jackets 
instead of hydraulic units, etc. It is also understood that the separate 
driving mechanism for the enclosed shoe roll might be disconnected once 
the calender is in operation, but in some cases it might be preferable to 
have it connected also during operation, since it eliminates the need of a 
disconnecting mechanism, it also reduces the power consumption of the main 
drive and also eliminates any disadvantage that could arise (e.g. drag in 
jacket) during acceleration of the separate drive. Moreover it should be 
noted that the invention is not limited to the temperatures defined above, 
but may vary in dependence of specific needs. It is also understood that 
the invention is not limited to the use in connection with enclosed 
shoe-rolls but may, at least in parts, also be applied in connection with 
shoe press units using open ended belts, i.e. imparting movement directly 
to the flexible belt (without using end walls) especially in relation to 
the basic principle of operating a calender according to the invention. 
Finally it is evident that the invention may be used in connection with 
different kind of flexible belts, e.g. also belts not only being flexible 
but also elastic, e.g. rubber type belts.