Calender roller having a cylindrical base body

A calender roller includes a cylindrical base body. The base body has a thin circumferential wall, which is not self-supporting, and a support structure made of a thin-wall cellular material is disposed inside of the circumferential wall. At least a part of the walls which form the cells extend approximately in a radial direction, to provide a strong and light calender roller.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a calender roller having a cylindrical 
base body. More specifically, the present invention relates to a calender 
roller having a cylindrical base body and a flexible outer covering. 
2. Discussion of the Related Art 
Rollers that are used in calenders for treating a web of paper are known. 
The calender typically has at least one roller stack that can be loaded by 
a force acting on one of the ends of the stack. The calender rollers 
affect the surface structure of the paper web, such as the smoothness, 
gloss, thickness and the bulk. However, calenders can also be used to 
treat other materials, such as plastic films, webs of textiles, etc. A 
working nip is formed between the juncture of one hard roller and one soft 
roller. A soft roller has a flexible outer covering and primarily provides 
for uniform compression of the paper. A hard roller has a hard outer 
surface and is primarily responsible for affecting the surface structure. 
Known calender soft rollers have a base body in the form of a solid or 
hollow cylinder which is designed to be strong enough to absorb the forces 
that arise during calendering operations. Such a conventional roller is 
very heavy, which is undesirable for a variety of reasons. For example, 
problems arise due to the roller weight during transport and because of 
the high material costs. In addition, in a calender having a roller stack, 
the line load in the working nips increases from the top to the bottom 
because of the weight of the rollers lying above the nip. Therefore, the 
upper nips have a lower line load than the lower nips. Of course, it is 
desirable for the line load in the upper nips to closely approximate the 
line loads in the lower nips. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a calender roller that 
has sufficient strength yet is at a lower weight than conventional 
rollers. 
In accordance with a preferred embodiment demonstrating further objects, 
features and advantages of the present invention, the roller has a base 
body having a thin circumferential wall which is not, by itself, 
self-supporting. A support structure is connected to the inside of the 
circumferential wall to support the circumferential wall. The support 
structure is made of a thin wall cellular material. At least a portion of 
the walls that form the cells extend in an approximate radial direction. 
The circumferential wall, which has been stiffened by the support 
structure, is able to absorb the forces that arise during the operation of 
a calender roller. This is especially true for radial forces, which are 
transmitted by the walls and are applied in an approximately radial 
direction. Such a structure provides a very strong calender roller that 
has a very low weight and is therefore particularly suitable for use in a 
calender roller stack. 
The cells are preferably formed by a pair of side walls, which extend in 
the same direction. The side walls are connected, at least on one end, to 
a cover wall. Therefore, the cells are substantially completely closed. 
The cells are extraordinarily stiff because they are fixed in place at 
their ends by the cover wall. In addition, the cells are prevented from 
deforming due to their connection to adjacent walls. 
The support structure preferably has a large number of individual elements 
which are fixedly connected to each other. Because the elements are 
divided up into a plurality of individual elements, it is possible to 
vary, from one element to the next, the direction that the side walls 
extend. Therefore, the support structure is especially well adapted to 
absorb forces that arise during calendering operation. 
The present invention permits the cells to be smaller and, therefore, 
stiffer. The elements are preferably a plurality of round blanks. Each of 
the cells are disposed between two end walls which extend in radial 
planes. The end walls are held at a distance from one another by the cells 
and absorb the radial forces that act on a calender roller. The side walls 
of the cells also absorb radial forces. Tensile and compressive forces, 
which act in an axial direction of the roller, are absorbed by the 
circumferential wall, and by the components of the side walls of the cells 
which extend in the axial direction. Tensile compressive forces can also 
be absorbed by additional interior walls that are concentric to the 
circumferential wall. 
The cells of the individual elements preferably extend parallel to each 
other and to the end walls. Adjacent round blanks are offset at an angle 
with respect to each other so that the directions of the cells are offset 
at the same angle with respect to each other. In other words, the cells of 
one element extend in a direction that is disposed at a predetermined 
angle with respect to the direction that the cells of the adjacent element 
extend. The use of the angular offset in the elements provides essentially 
uniform result in the roller's ability to absorb radial forces over the 
circumference of the roller. 
In another embodiment, the side walls of the cells of the individual 
elements extend perpendicularly with respect to the end walls to provide 
an especially good stiffening effect on the round blanks'axial end walls. 
The end walls are held at a distance from each other by the side walls of 
the cells. 
The round blanks are preferably provided with a center hole so that a 
roller axle can be inserted into the support structure. The roller axle 
does not need to contribute to the stiffness of the roller, and can, 
therefore, be made with a relatively small diameter and a corresponding 
light weight. 
In another preferred embodiment of the present invention, at least one 
cylindrical (i.e., annular) layer is disposed between the roller axle and 
the circumferential wall. The layer is made of individual elements, 
adjacent elements of which are offset in the axial direction. Each element 
is formed by the cells' side walls, which extend in an approximately 
radial direction. Therefore, the cells, or more specifically, their side 
walls, absorb the entire radial loading of the calender roller. The 
position of the side walls can be matched to any particular 
circumferential region as is required because of the division of the layer 
into individual elements. Compressive and tensile forces can be absorbed 
by the circumferential wall, by additional walls that are concentric to 
the circumferential wall and by the axial components of the cells' side 
walls. 
The individual elements, which are adjacent to each other in the 
circumferential direction, are preferably offset from each other in the 
axial direction. Therefore, problem locations, which could otherwise arise 
from the individual elements bumping into each other, are eliminated. 
The cells preferably have a honeycomb-like shape. The cells have a 
hexagonal cross-section which, in combination with the adjacent cells and 
the covering at the ends of the cells, creates an extraordinarily stiff 
body. Such a honeycomb material is easy to manufacture because it can be 
comprised of webs which are alternately combined with adjacent webs. 
Alternatively, the cells may have a corrugated cardboard-like shape. This 
shape also provides sufficient stiffness and is inexpensive to 
manufacture. 
The cells are preferably made of a fiber-reinforced plastic. If carbon 
fibers are used, very high stiffness results together with the lowest 
possible weight. 
The cells are preferably made of an aramid material. In practice, however, 
other materials, such as paper, cardboard or sheet metal, for example, 
aluminum sheet, may be used as the cell material. The walls can be 
connected to one another and to the cover walls, end walls and the 
circumferential wall by various methods depending upon the material that 
is being used. In a preferred embodiment, the walls are bonded together. 
However, the walls may be connected by other processes, such as welding, 
soldering, and the like. 
The circumferential wall is preferably formed by a thin-wall, continuous 
tube. A continuous tube, by definition, does not have any seams, which 
results in a smooth, cylindrical surface. In addition, the support 
structure can be installed into the circumferential wall under prestressed 
conditions to increase the stiffness of the roller. 
In a preferred embodiment, the flexible covering forms the circumferential 
wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, a roller 1, for use in a calender is illustrated. 
Roller 1 includes a base body 2 and a covering 3, which is placed about 
the base body 2. Covering 3 is preferably shrink-fitted onto the base 
body. Covering 3 is made of flexible plastic, for example, silicone rubber 
or epoxy resin. The base body 2 has a circumferential wall 4 which is so 
thin that it is not, by itself, self-supporting. In other words, wall 4 
would deform under the forces which occur during normal calender operation 
if it were not stiffened by a support structure 5, which is placed in the 
interior of wall 4. Support structure 5 comprises of a number of 
individual elements 6, in the form of circular round blanks, which each 
have a central hole 7. A roller axle 8 is placed through the holes 7 of 
the elements 6. Roller axle 8 connects the two bearing journals 9 and 10 
of the calender roller to one another. Roller axle 8 also bears against 
two thrust pieces 11 and 12. Circumferential wall 4 is a cylindrical tube 
that is bonded to the support structure 5. Roller axle 8 can also be 
bonded to the support structure 5. 
Referring now to FIGS. 2-4, each round blank 6 has two end walls 13, 14. 
Side walls 15 are disposed between the two end walls 13, 14. Cells 16 are 
defined by the side walls 15. The cells 16 for each round blank 6 all 
extend in the same direction, as can be seen in FIG. 2. The center cell 16 
that would extend through a center of the round blank if not for the 
center hole 7, extends in a radial direction, and the remaining cells of 
the round blank all extend in a direction that is parallel to the center 
cell. Therefore, the remaining cells effectively form parallel chords of 
the circular round blank. 
The ends 17 of the cells 16 are bonded to a cover wall 18. In a preferred 
embodiment the cover wall 18 is formed by the circumferential wall 4. 
Because circumferential wall 4 surrounds the round blank 6 in a 
cylindrical fashion, at end 17 (whose cell extends closer to the center), 
a relatively small surface area is covered by wall 4, while at an end 17a 
(whose cell extends further away from the center) a relatively large 
surface area of the cell 16 is covered (See FIG. 2). A larger surface area 
of end 17a is covered because of the inclined position of its respective 
cell end relative to wall 18. Cells 16 extend parallel with respect to 
each other and to the end walls 13, 14. 
Adjacent round blanks 6 and 6a are offset at an angle with respect to one 
another so that the directions of their respective cells 16 are offset at 
the same angle with respect to each other. As illustrated in FIG. 2, as a 
result of a uniform angular offset, the effect of the positioning of the 
cells can be distributed evenly. The end walls of the individual round 
blanks, which lie against each other as illustrated in FIG. 1, are bonded 
to each other. During operation, the radial loading is absorbed by the end 
walls 13 and 14. The radial loading is also absorbed, in part, by the side 
walls 15 of the cells 16. Compressive or tensile forces that are acting in 
the axial direction are absorbed by the components of the side walls 15 
which extend in the axial direction. 
As FIG. 4 schematically shows, the side walls 15 are manufactured from 
trapezoidally formed webs which form a bonded joint 19 or 19a at every 
place where they lie against an adjacent side or end wall, respectively. 
While FIG. 4 shows a honeycomb-like cellular material, FIG. 5 shows a 
corrugated cardboard-like cellular material. Reference numbers have been 
increased by 100 in FIG. 5 from like reference numbers in FIGS. 1-4 with 
like elements. In essence, the difference between FIG. 4 and FIG. 5 is 
that the side walls 115 are shaped in a wave-like manners, not 
trapezoidally as are side walls 15. In addition, a side wall 115a, which 
is parallel to the end walls 113, 114, is disposed between the side walls 
115. Of course, numerous other differences in the cross-sectional shape of 
the cellular material are possible. For example, the cells could have a 
square cross-sectional shape. 
FIG. 6 illustrates an additional embodiment of the present invention. In 
this embodiment, the reference numbers have been increased by 200 from 
like reference numbers in FIGS. 1-4 with like elements. FIG. 6 shows a 
segment of a round blank 206 that has side walls 215 disposed between two 
end walls 213, 214. Side walls 215 are perpendicular to the end walls 213, 
214. The side walls 215 form hexagonal cells 216 which are bonded at both 
ends 217 to the end walls 213, 214. The end walls 213, 214 absorb the 
radial forces. The compressive and tensile forces which are acting axially 
are absorbed by the side walls 215 and by the circumferential wall, which 
for the sake of clarity in this drawing figure is not shown. 
FIGS. 7 and 8 illustrate a further embodiment of the present invention, in 
which the reference numbers have been increased by 300 from like reference 
numbers in FIGS. 1-4 with like elements. The support structure 305 built 
up between the roller axle 8 and the circumferential wall 4 consists of 
individual elements 306. Elements 306 are placed in several annular 
layers, one above the other, only three layers of which are shown in FIG. 
7. In a preferred embodiment, each of the individual elements 306 has an 
axial length of 50 to 100 cm and extends for an angle of from 10.degree. 
to 20.degree. in the circumferential direction. Each individual element 
306 has its side walls 315 of the individual cells 316 extending 
approximately radially. The ends of the cells 316 are covered by means of 
an inner cover wall 318 and an outer cover wall 318a. The cover walls are 
bonded in a fixed fashion with the adjacent cover wall of the layer that 
is located above or below it. Individual elements 306 and 306a, which are 
adjacent to one another in the circumferential direction, are offset with 
respect to each other in the axial direction (see FIG. 8). 
An example of the embodiment illustrated in FIGS. 7 and 8 had a base body 2 
having a diameter of 700 mm. A roller axle 8 had a diameter of 200 mm. The 
support structure had ten layers of elements, with each layer having a 
radial thickness D=25 mm. The outside radii of the layers, from outside to 
inside, was: 
R1=350 mm 
R2=325 mm 
R3=300 mm 
R4=275 mm, etc. 
Of course, the cover walls 318 and 318a were curved in accordance with the 
radii. 
The use of the base body 2, in conjunction with a flexible covering 3, has 
the advantage that minor irregularities on the surface of the base body 2 
are permissible because the flexible material compensates for these 
imperfections. In an alternative embodiment, the base body can also be 
used as a carrier for an outer metal layer, so that it is also possible to 
produce a hard roller having a relatively low weight. 
In a preferred embodiment, a plastic, such as an epoxy resin, which is 
reinforced with glass fibers or, more preferably, with carbon fibers, may 
be used for the cell material. The preferred ratio of fibers to plastic is 
65% to 35%. Alternatively, the cellular material could be made of a 
fibrous material. The fibrous material is preferably made of an aramid, 
such as a para-aramid (e.g., KEVLAR.TM.), or a meta-aramid (e.g., 
NOMEX.TM.), both of which are sold by Du Pont. The sheet material that is 
used as the starting material preferably consists of between 87% and 99% 
aramid fiber. Both materials have a relatively high resistance to heat for 
plastic. As a result, their physical properties are retained even under 
severe conditions. 
The stressed base body has an extremely low weight, extraordinary stiffness 
and high compressive strength, which provides the following advantages 
when it is being used as a calender roller. Because of the low weight of 
the roller package, a steeper curve for the pressure characteristic is 
achieved in the roller stack of the calender, which results in a lower 
roller load and lower power requirements. The stiffness prevents any 
movement of the roller body as a result of tangential forces. The high 
thermal resistance permits full use of the plastic's physical properties 
up to temperatures above 300.degree. C. Because a heavy, thick roller axle 
is not necessary, the weight of the axle is reduced. When the flexible 
covering is being replaced, only a new, prefabricated covering, in the 
form of an outer jacket, has to be replaced. The base bodies are 
maintenance free. The low weight makes handling easier and reduces 
transport costs. 
Having described the presently preferred exemplary embodiment of a calender 
roller having a cylindrical base body in accordance with the present 
invention, it is believed that other modifications, variations and changes 
will be suggested to those skilled in the art in view of the teachings set 
forth herein. It is, therefore, to be understood that all such 
modifications, variations, and changes are believed to fall within the 
scope of the present invention as defined by the appended claims.