Transport roller, especially for transporting paper

A transport roller, especially for transporting sheet material such as sheets of paper, has a rigid core surrounded by a friction increasing jacket of elastic material. At least one member is inserted between the jacket and the roller for preventing a relative axial displacement between the core and the jacket. Such member is an endless helical spring partially embedded in the jacket and projecting into a ring groove in the core, whereby the jacket is firmly held in place on the core against any relative axial displacement.

FIELD OF THE INVENTION 
The invention relates to a transport roller, especially for transporting 
paper such as sheets of paper. Such rollers have a solid roller core 
surrounded by an elastic roller jacket. The roller jacket has a radially 
inner surface in contact with a radially outer surface of the solid roller 
core, whereby the roller jacket is held in place by a biasing force 
effective radially inwardly. 
DESCRIPTION OF THE PRIOR ART 
Such rollers are well known and are used, for example, for transporting 
paper such as sheets of paper. By using different materials for the solid 
core and the elastic roller jacket, the advantage is obtained that it is 
not necessary to exchange a roller completely when the jacket surface is 
no longer fully functional due to wear and tear. 
However, known rollers having a separate core and a separate roller jacket 
have the disadvantage that keeping the roller jacket on the roller core 
poses a problem, especially when the elasticity of the jacket material 
increases, whereby the roller jacket has the tendency to travel in an 
axial direction along the roller core. On the other hand it is desirable 
to make the roller jacket of a material having a high elasticity because 
such material provides the necessary friction for the transport purposes. 
Thus, heretofore, it has been customary to produce rollers having the 
required good surface friction as a unitary, integral component in which 
the elastic material forms the core and the outer surface of the core as a 
single piece. Accordingly, such rollers must be replaced entirely when a 
certain degree of wear and tear has been reached. In other words, such 
rollers even require the replacement of the bearing sleeve on which the 
roller body has been attached by a vulcanizing process. 
OBJECTS OF THE INVENTION 
In view of the foregoing it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide a transport roller which has an exchangeable roller jacket of 
elastic material properly held on a roller core against axial displacement 
between the roller core and the roller jacket, while still providing the 
required friction; 
to secure the roller jacket of elastic material to the solid roller core in 
such a manner that the securing prevents the relative axial movement 
between the roller core and the roller jacket while simultaneously 
permitting the easy exchange of the roller jacket on a still useful roller 
core; and 
to prevent an axial stretching as well as an axial contraction of the 
elastic roller jacket material. 
SUMMARY OF THE INVENTION 
According to the invention there is provided a transport roller having a 
solid roller core and an elastic roller jacket surrounding the solid 
roller core, wherein at least one helical spring, connected at its ends to 
form an endless ring, is embedded in the roller jacket in such a manner 
that the spring projects radially inwardly from the radially inner surface 
of the roller jacket, whereby this projecting portion of the endless 
helical spring engages in a radially outwardly facing ring groove in the 
outer surface of the roller core. Due to the provision of at least one 
such endless helical spring which engages both the roller core and the 
highly elastic roller jacket, the latter is prevented from travelling 
axially relative to the roller core. Preferably, the endless helical 
spring engages the ring groove in the roller core with a radially inwardly 
directed biasing force, whereby the spring holds the roller jacket tightly 
on the roller core due to the solid connection between the spring and the 
roller jacket.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
FIG. 1 shows a roller shaft 1 shown partly broken away and carrying a solid 
roller core 2 conventionally secured to the shaft 1 which may be provided 
with rifling 1' for a secure attachment of the core 2 to the shaft 1. The 
outer surface of the core 2 is surrounded by a jacket 3 made of an 
elastical, flexible material. According to the invention an endless 
helical spring 5 is partially embedded in the inwardly facing surface 4 of 
the jacket 3. The endless helical spring 5 is located centrally between 
the ends of the jacket 3. The spring 5 is so embedded in the material of 
the jacket 3 that at least a cross-sectional portion of the spring 5 
projects radially inwardly from the inner surface 4 of the jacket 3. The 
ends of the springs 5 are connected to each other so as to provide an 
endless spring which reaches radially inwardly into a groove 6 which is 
open radially outwardly in the surface of the core 2. By making the bottom 
of the groove 6 narrower in the axial direction than the axial width of 
the projecting helical spring 5, it is assured that the spring 5 is wedged 
into the groove 6, whereby any axial play between the spring 5 and the 
groove 6 is avoided in a simple, yet effective manner. This wedging action 
is further enhanced by making the radial depth D of the groove 6 larger 
than the radial projection P of the helical spring 5. 
Further, the helical spring 5 is so dimensioned that it generates a 
radially inwardly directed biasing force so that this biasing force tends 
to press the helical spring 5 into the groove 6 in such a manner that any 
axial play between the groove and the spring is avoided. This feature 
simultaneously assures a reduction in the wear and tear because it 
positively prevents any back and forth movement of the spring and thus 
also of the roller jacket 3. Such movement would enhance wear and tear. 
It has been found that even highly elastic material such as rubber forming 
the jacket 3 can be held in place on a solid, rigid roller core 2 by just 
one helical, endless spring 5 embedded in the jacket material. If only one 
spring is used it is preferable to place it centrally between the ends of 
the roller. 
It has been found that even for transport rollers having a substantial 
axial length, one helical spring is sufficient. However, it may be 
desirable to use two endless helical springs 5' as shown in FIG. 2. These 
springs 5' are embedded in the radially inner surface 4' of the outer 
jacket 3' of elastic material near the edges of the jacket 3'. The rigid 
or solid core 2' solidly secured to the shaft 1 is provided 
correspondingly with two grooves 6' also preferably having a trapezoidal 
cross-section as shown in FIGS. 1, 2. By using one helical spring 5' 
adjacent each edge of the jacket it is possible to prevent an axial 
expansion and an axial contraction of the elastic roller jacket material 
in addition to any relatively axial movement between the jacket 3' and the 
core 2'. It has been found to be quite effective to embed the helical 
springs 5, 5' to such an extent that the windings of the helical springs 
are enveloped by the elastically deformable material of the roller jackets 
3, 3' to an embedding depth R' which is a portion of the spring coil 
diameter R shown in FIG. 3. For example, the embedding depth R' of the 
springs 5, 5' reaches radially inwardly up to about the radius of the 
helical spring coil. 
Due to the substantially rigid connection of the roller jacket 3, 3' on the 
roller core 2, 2' it is now possible to make the roller jacket 3, 3' of an 
elastically deformable material having a Shore hardness of less than 40. 
Such material is known under the name LIM (Liquid Injection Moulding). 
Such material is suitable for liquid injection molding purposes. Without 
the attachment features taught by the present invention it would not be 
possible to use such a material as a jacket on a transport roller. 
Numerous tests have shown that such a material exhibits a tendency to 
travel axially off the roller core. Such axial travel, without the 
features of the invention, takes place already after a short time and 
under small load conditions. Nevertheless, this material exhibits 
extraordinarily good friction characteristics so that it would be ideally 
suitable for making the jackets of transport rollers and the invention 
makes this possible. 
By embedding the individual windings of the endless helical springs 5, 5' 
in the material of the jacket 3, 3' an intimate bond between the spring 
and the roller jacket is assured so that the danger of separation between 
the helical spring and the roller jacket due to a fulling motion is 
avoided. 
It is also within the present teaching to cover the individual windings of 
the helical springs 5, 5', for example, with a brass coating or a bonding 
agent. Such coatings may be accomplished, for example, by an immersion 
method or by electroplating. The primary purpose of such coatings is to 
improve the bonding between the material of the roller jacket 3, 3' and 
the surface of the helical springs 5, 5'. It has been found to be 
advantageous to initially dimension the helical springs 5, 5' in such a 
manner that upon connection of the spring ends to each other, the windings 
touch each other and that after attaching the springs 5, 5' to the grooves 
6, 6' there is a certain radially inwardly effective biasing force which 
causes the individual windings to be slightly spaced from each other. The 
spacings then permit the material of the roller jacket to even enter into 
the space confined inside of the helical spring or springs, whereby an 
especially intimate bonding between the jacket material and the spring is 
achieved. If desired, the hollow space inside the spring or springs may be 
completely filled by the jacket material. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.