Device for tensioning core tubes

A device for tensioning core tubes, especially core tubes for webs of paper or similar materials, consists of several tensioning segments in the shape of arcs of a hollow cylinder. The segments can be displaced radially inside a cage and are distributed around an arbor. Supports are positioned between the arbor and the tensioning segments in circumferential grooves on the surface of the arbor. The cross section of the arbor is an equilateral polygon in the vicinity of the grooves. The side of each support that faces a tensioning segment is spherical and is inserted into a corresponding hemispherical depression in the inner surface of the tensioning segment. The side of each support that faces the arbor has a contact surface that matches the cross-section of the floor of the groove.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for tensioning core tubes, 
especially core tubes for webs of paper or similar materials, and consists 
of several tensioning segments in the shape of arcs of a hollow cylinder 
that can be displaced radially inside a cage and that are distributed 
around an arbor, with supports positioned between the arbor and the 
tensioning segments in circumferential grooves on the surface of the 
arbor, whereby the cross section of the arbor is an equilateral polygon in 
the vicinity of the grooves. 
Tensioning devices of this type are known, from British Patent No. 917 978 
for instance. The supports in the known tensioning devices are cylindrical 
rollers. When a rotary motion is exerted on the arbor, the cylindrical 
rollers roll both against the floor of the circumferential grooves in the 
arbor and against the tubular interior surface of the tensioning segments, 
forcing the segments radially outward into the tensioning position or 
inward back into the initial position. 
One drawback of the known tensioning device is a high level of wear that 
results from powerful stress on the arbor, tensioning segments, and 
cylindrical supports. 
SUMMARY OF THE INVENTION 
The object of the present invention is to improve a tensioning device of 
the aforesaid generic type in such a way as to decrease the wear on the 
parts that move in relation to one another. 
This object is attained in accordance with the invention in a device for 
tensioning core tubes of the aforesaid generic type in that the side of 
each support that faces a tensioning segment is spherical and is inserted 
into a corresponding hemispherical depression in the inner surface of the 
tensioning segment and the side of each support that faces the arbor has a 
contact surface that matches the cross-section of the floor of the groove. 
The shape of the tensioning segments in accordance with the invention 
results in extensive contact between the supports and the tensioning 
segments and between the supports and the arbor. The parts that move 
against one another--the tensioning segments, supports, and arbor--do not, 
accordingly, contact each other along a line as in the known tensioning 
device, but over an area, so that the pressure per unit of area will be 
less and the wear will be lower. Furthermore, the design of the device for 
tensioning core tubes in accordance with the invention allows the core 
cross-section of the arbor to be expanded, increasing its strength. 
In one preferred embodiment of the invention the cross-section of the floor 
of each circumferential groove in the arbor is convex. The convexity makes 
the arbor thicker, which also contributes to its strength. 
In another preferred embodiment of the invention the longitudinal 
cross-section of the floors of the circumferential grooves in the arbor is 
concave. The concavity prevents the fatigue notching that can occur at 
sharp-edged transitions in the grooves and increases mating precision or 
allows compensation of slight manufacturing errors. 
Since the supports in the hemispherical depressions in the tensioning 
segments always support the segments at the same point, even while the 
arbor is turning, the segments will not tilt as easily as in the known 
device, wherein the supports can also become displaced in relation to the 
tensioning segments when the arbor turns. Still, the tensioning elements 
will continue to rock against the arbor to the same extent as a result of 
their ball-bearing type of coupling with the supports.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A device for tensioning core tubes consists as illustrated in FIGS. 1 and 2 
of flanging screws 1, of an annular spring 2, of a frontal ring 3, of 
tensioning segments 5 in the shape of segments of a hollow cylinder with 
serrated or corrugated outer surfaces 4, of supports 6, of another annular 
spring 8, of a cage 9, and of a cover plate 10 that is fastened to an 
arbor 7 by means of a screw 11 and that secures the axial position of the 
other parts, which are slid over the arbor. 
The floor 12 of the circumferential grooves 13 in the arbor 7 illustrated 
in FIG. 2 is concave. The surface of each support 6 that faces arbor 7 is 
accordingly shaped like the arc of a circle with a radius r.sub.2 (FIG. 
4). The circumferential grooves 13 are convex from the aspect of the 
cross-section of FIG. 1. The residual core cross-section of the arbor 7 is 
indicated in FIG. 1 by the hatched area. The surface of support 6 that 
faces arbor 7 accordingly matches the convexity of the floor 12 of 
circumferential groove 13 from the aspect of the cross-section of FIG. 1 
with a radius r.sub.3 (FIG. 3). The supports 6 in this embodiment contact 
the floors 12 of the circumferential grooves 13 in arbor 7 over an area, 
as will be evident from FIGS. 1 and 2. 
Tensioning segments 5 have hemispherical depressions 14 that are also fully 
contacted by the spherical surfaces of supports 6, which have a radius 
r.sub.1. Thus, supports 6 and tensioning segments 5 constitute a 
ball-bearing type of articulation that allows tensioning segments 5 to 
rock to a certain extent around the axis of arbor 7. 
The tensioning device is assembled by placing tensioning segments 5 in 
circumferential grooves 13 with supports 6 in between or the depressions 
14 in tensioning segments 5 over arbor 7 and securing them radially with 
annular springs 2 and 8. Cage 9 is then slid over arbor 7 and attached to 
it with cover plate 10 and screw 11. 
It is understood that the specification and examples are illustrative but 
not limitative of the present invention and that other embodiments within 
the spirit and scope of the invention will suggest themselves to those 
skilled in the art.