[0001] The invention relates to web processing machinery and in particular to web spreader
roll.
DISCUSSION OF PRIOR ART
[0002] So-called web spreader, expander or widener rolls are rotary parts that are extensively
employed in machinery for the fabrication and/or for successive processing of continuous
ribbons of materials of innumerable types. Machinery used in paper, plastic foil,
printing and textile industries generally require the use of numerous spreader rolls.
[0003] There are innumerable types of web spreader roll, for satisfying specific requirements
of the particular web material to be handled.
[0004] WO 02/092293 A1 discloses a web spreader roll and method for spreading webs of materials wherein
the spreader roll has a tapered diameter starting from a maximum diameter at the middle
of the roll wherein the taper may have a straight, a parabolic or other profile.
[0005] JP 2004189412 discloses a bow adjustment mechanism and relative method for a segmented spreader
roll made by a plurality of juxtaposed segments each independently supported at certain
elevation from a planar support.
[0006] WO 2005/115894 A1 discloses a spreader roll composed by a tapered stationary axle and a one-piece tubular
outer sleeve rotable about the axle and elastically flexible such to be able to bend.
[0007] WO 2006/045882 A1 discloses a spreader roll having a curved axle on which a plurality of roll segments
are mounted, each on a sustaining roller bearing, and wherein flexible connector members
connect juxtaposed ends of adjacent roll segments such that a terminal roll segment
may be driven to rotate all the roll segments around the axle.
[0008] US 2006/0183613 A1 discloses a spreader roll having a tubular one-piece sleeve supported by a plurality
of spools and the curvature of which is adjustable.
[0009] By adjusting the relative position of common inlet and outlet guide rollers and of
the orientation of the bowed spreader roll there between, the inlet angle of incidence,
the outlet angle of incidence and consequently the arc of contact of the running web
on a certain portion of the convex side of the spreader roll, a most effective transversal
stretching of the web material is produced by the spreader roll for eliminating any
weaving or creases that may be present in the central portion and/or along the edges
of the web, as well known to the skilled person.
[0010] A typical web spreader roll construction is shown in Figure 1. The depicted spreader
roll is shown provided also with the often unnecessary, optional means of independent
driving of the roll through a common belt transmission.
[0011] The drawing depicts only one end portion of the rotable part of the spreader roll
that is composed by a plurality of roll segments 2, mounted on an bowed axle 1. Each
roll segment 2 has a ball bearing 3 installed at the middle of the segment, commonly
retained by a pair of Seeger rings 4. For the belt driven embodiment shown in Figure
1, the first roll segment, at one side end of the plurality of segments that form
the rotable sleeve of the spreader roll, has a modified termination sustained by a
second ball bearing 3' for solidly carrying a cantilever pulley P on which a common
trapezoidal cross-sectional drive belt may run.
[0012] The plurality of roll segments 2 are slipped over the axle 1 in succession, inserting
also O-rings 5 of an elastically deformable material (elastomer) and tubular spacers
6 that elastically compress the O-rings 5 at the corner between the side surface of
the inner raceway rings 7 of the ball bearings 3 and the cylindrical surface of the
axle 1, such to hold fast the inner raceway ring 7 onto the stationary axle 1.
[0013] The outer raceway ring 8 of the ball bearings supports the respective roll segment
2. The juxtaposed spaced ends of two adjacent roll segments are joined by a flexible
connector 9, typically of an elastomer. Therefore, the plurality of centrally supported
rotable roll segments 2 revolves as a single-piece outer sleeve of the web expander
roll.
[0014] Considering that a basic parameter of a web expander roll is the diameter of its
rotable outer sleeve that, in combination with the spatial orientation of the convex
part of the bowed roll and the arc of circumference engaged by the running web determines
the transversal stretching action on the running web material, according to a common
roll structure as the one depicted in Figure 1, a certain outer diameter of the working
surface of the spreader roll, generally commands the choice of the diameter of the
stationary axle 1 and of the roller bearings used for supporting the roll segments
2 with minimum mechanical clearances in order to minimize vibrations and allow a high
rotational speed. This implies a considerable increment of overall weight of the structure
that generally goes well beyond what would required for satisfying only a stiffness
requisite.
[0015] The construction generally requires a relatively expensive machining of the inner
cylindrical surface of each roll segment to form the seats of the supporting roller
bearing and of the retaining Seeger rings 4 as well as abutment steps at the two ends
for installing the elastic spacing connectors 9. The use of ball bearings of relatively
large diameter, beside their proportionately higher cost and weight, also implies
greater resistant torques compared to ball bearings of smaller diameter.
[0016] In many cases, the continuous web of paper, film or fabric being handled may have
a width and mechanical strength characteristics such to be perfectly adequate to bring
and keep in rotation the free-wheeling roll segments that are usually connected together
to act as a free-wheeling sleeve of the spreader roll on which it runs. In other applications,
or when the web characteristics are not adequate to reliably rotate the free wheeling
array of roll segments of the spreader roll, a common belt transmission (as depicted
in Fig. 1) must be used to drive in rotation a first roll segment at one side end
of the spreader roll. In some applications, instead of connecting together the roll
segments by elastomer joints, an outer tubular sleeve of a elastic material is forcibly
pulled over the plurality of bearing supported roll segments for providing a single
piece outer surfacing member of the spreader roll.
[0017] Vibratory characteristics of spreader rolls are extremely important; usually critical
speed parameters are defined for every roll model in order to set appropriate safe
speed ranges of operation.
[0018] Regardless of the type and destination use of a spreader roll, there are evident
advantages, both in terms of cost reduction and of performances in:
- reducing the overall weight of the roll;
- reducing resisting torques acting during accelerations in order to make more reliable
the dragging into rotation of the roll by the running web to avoid the need of independently
driving the spreader roll;
- minimizing roller resistance in the bearings and enhancing their operating life without
requiring expensive special constructions of the bearings;
- increasing the maximum tolerable speed through a reduction of the diameter of the
roller bearings required for supporting the roll segments.
SUMMARY OF THE INVENTION
[0019] In searching for a way of more effectively satisfying above recalled general requirements
than it has so far been possible according to existing technologies and construction
approaches, the applicant has found an outstandingly effective construction of a web
spreader roll that achieves significant advances in satisfying the above noted requirements
and that at the same time simplifies and reduces the precision requisites of machining
of the curved axle, simplifies and makes quicker assembling the various components
to produce the finished spreader roll.
[0020] Basically, according to the novel structure of the applicant, each roll segment (or
spool) of the spreader roll is sustained at both its ends on two bearing assemblies
each comprising an outer crown portion of elastomer that engagingly sustains the two
juxtaposed end portions of two adjacent roll segments.
[0021] Compared to the traditional approach depicted in Figure 1 of providing each roll
segment with a roller bearing supporting it at its middle and of connecting together
the two spacingly juxtaposed ends of two adjacent roll segments with an elastic connector,
the novel structure ensures an enhanced vibration-free support of each roll segment
when rotating at high speed and subject to abrupt disuniformities of the load exerted
on the segments by the running web.
[0022] Moreover, it has been found that by increasing radial extension of the sustaining
bearing assemblies by including an outer crown portion of elastomer, the diameter
of the bowed axle as well as of the inner and outer raceway rings of the bearings
can be sensibly reduced without impairing stiffness characteristics of the spreader
roll. This allows to achieve a significant weight reduction while preserving the same
usable range of arc of contact with the running web, in other words allowing to significantly
reduce the ratio between the diameter of the stationary axle and the outer diameter
of the rotating "sleeve" of the spreader roll.
[0023] The invention is defined in the annexed claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The various aspects, features and advantages of the novel construction of this invention
will be discussed in detail in the following description of preferred embodiments
of this invention, with reference to the attached drawings, wherein:
Figure 1 is a partial cross-sectional view of a web spreader roll according to prior art;
Figure 2 is a partial cross-sectional view of a web spreader roll according to a first embodiment
of this invention;
Figure 3 is a partial cross-sectional view of a preferred alternative embodiment.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0025] Figure 2 illustrates a first embodiment of the novel structure of this invention
of basic geometrical parameters equivalent to those of the comparable prior art structure
of Figure 1. For a more immediate comparison, functionally similar parts are identified
with the same numerals in all the figures. A drive pulley P is associated to the first
roll segment as in the example of prior structure of Figure 1, in the assumption that
the type of application of the spreader roll requires it.
[0026] Differently from known constructions, each roll segment 2 is sustained at both its
ends on bearing assemblies, each comprising an outer crown portion 10 of elastomer
that engagingly sustains the spaced juxtaposed end portions of two adjacent roll segments.
[0027] The spacing between juxtaposed ends of the sustained roll segments may be in the
order of few millimeters, depending on outer diameter and bow of the expander roll,
in any case sufficient to prevent the rims of adjacent segments from touching each
other when rotating about the concave part of the bowed structure, as it is well known
to the skilled person.
[0028] The bearing assembly comprises a fixed bush 11 that is fastened onto the stationary
axle 1 by a set screw. A common ball bearing 3 is installed on the fixed bush 11,
in a confinement space defined by the fixed bush 11 and by an inner metal portion
12 of the radially extending composite rotable crown composed of said outer portion
of elastomer 10 and an inner metal portion 12. The bearing 3 is held by an elastic
washer 13 and Seeger ring 14 against abutment steps 15 and 16 of said fixed sleeve
11 and of the metal inner portion of the crown 12, respectively.
[0029] It has been demonstrated that by sustaining each roll segment at both its ends on
an elastomer crown portion, the roll segments are able to run more stably with reduced
vibrations notwithstanding the fact that the diameter of the axle 1 is substantially
reduced and similarly reduced is the diameter of the roller bearings used for supporting
the rotating roll segments. The supporting crown portion of elastomer appears to be
instrumental in significantly reducing/dampening vibrations.
[0030] In this way, a sensible overall weight reduction of the complete web spreader roll
can be achieved.
[0031] Moreover, by supporting each roll segment at both its ends, the stiffness of the
roll segment itself, or in other words its wall thickness may be reduced for contributing
to the reduction of the mass (inertia) of the rotating part of the spreader roll,
which is enhanced also by the possibility of employing bearings of relatively small
diameter.
[0032] The machining requirements of the inner cylindrical surface of the roll segments
are also minimized.
[0033] The use of relatively lighter tubular roll segments of a fiber reinforced plastic
2', optionally provided with an outer surfacing layer 2" of an appropriate material
for the type of web material to be handled, enhances the possibility of further reducing
overall inertia of rotating parts, in many cases, up to the point of making viable
a direct dragging into rotation of free-wheeling roll segments by the running web
material for web spreader roll dimensions that would have required a forced driving
of the roll, in case of a classical construction as the one depicted in Figure 1.
[0034] An even more effective construction towards minimization of inertia and frictional
resistances is depicted in Figure 3.
[0035] According to this particularly preferred embodiment, each bearing assembly is a pre-fabricated
one-piece composite formed by a ball bearing 3, the inner raceway ring 7 of which
is directly bonded onto the cylindrical surface of the bowed shaft 1. The outer raceway
ring 8 of the bearing has a crown 10 of elastomer bonded or molded thereon such to
form a single composite part.
[0036] It is remarked that the outermost surface of the crown of elastomer 10 has a narrow
circular trench 17 on a sectional plane that extends into the elastomer to a depth
sufficient to substantially de-couple the two outermost portions of the ealstomer
crown 10, in terms of lateral swayings. Each of two outermost portions of the partly
spit body of the elastomer crown 10 engages with and sustains the end portion of a
respective roll segment 2, swaying to one side and to the other in revolving about
the bowed axle 1, in opposite directions to the swaying of the other portion that
engages and supports the end of the adjacent roll segment.
[0037] Adequate engagement between the end portion of a tubular roll segment with the elastomer
crown portion may be established in many different ways. For example, a moderate compression
of a machined or precisely molded crown of elastomer 10, upon forcibly installing
thereon the ends of the tubular roll segments can establish a secure interference-engagement
of the parts that makes them to rotate as one piece. Glueing the end of the tubular
roll segment onto the outermost surface on the elastomer crown is another viable technique.
Forming matching projections and recesses on the inner end surface of the tubular
roll segment and on the surface of the supporting elastomer crown portion to be brought
into a secure engagement upon installing the tubular segments onto the rotable bearing
assemblies pre-installed onto the stationary bowed axle, is yet another effective
technique.
[0038] The inner raceway rings 7 of the roller bearings may be bonded to the axle 1 by an
adhesive, for example a powder loaded epoxy resin adhesive, a silicone based adhesive
and alikes, in order to prevent rotation of the raceway rings around the stationary
axle 1.
[0039] The elastic characteristics of the radially extending elastomer crown portion 10
may be established in the design phase, in function of dimensions, characteristics
of the web material, speed specifications, type, weight and mechanical characteristics
of the tubular roll segments.
[0040] Generally the elastomer is a natural or synthetic rubber having physical properties
such as chemical and temperature resistance and hardness suited for the contemplated
use or application of the expander roll.
1. A web spreader roll comprising a plurality of roll segments or spools each supported
on a outer raceway ring of a bearing, the inner raceway ring of which is fastened
onto an outer cylindrical surface of a stationary bowed axle of the spreader roll,
flexible connecting means of juxtaposed ends of adjacent roll segments, characterized in that
each roll segment is sustained at both its ends on two bearing assemblies each comprising
a crown portion of elastomer engagingly sustaining two spacingly juxtaposed end portions
of two adjacent roll segments.
2. The web spreader roll of claim 1, characterized in that each bearing assembly comprises
a fixed bush fastened on the bowed axle;
a bearing on said fixed bush, having an inner raceway ring held fast onto the bush
and an outer raceway ring;
a composite crown connected to said outer raceway ring of the bearing and defining,
together with said fixed bush, a confinement space of said bearing held against abutment
steps of said fixed bush and of said crown;
said composite crown having an inner metal portion and an outer portion of elastomer.
3. The web spreader roll of claim 1, wherein each bearing assembly is a preformed one-piece
composite including a bearing, the inner raceway ring of which is directly bonded
onto the cylindrical surface of the bowed shaft and the outer raceway ring of which
has a crown of elastomer bonded thereon; the outermost surface of the crown of elastomer
has a narrow circular trench that extends in the elastomer to a certain depth sufficient
to de-couple the two outermost portions of the ealstomer crown supporting said juxtaposed
ends of adjacent roll segments, respectively.
4. The web spreader roll of claim 3, wherein said crown of elastomer is bonded or molded
on a metal outer raceway ring of a ball bearing.
5. The web spreader roll of claim 3, wherein said inner raceway ring of the bearing is
bonded to the surface of the bowed axle by an adhesive.
6. The web spreader roll according to claim 1, wherein each roll segment is a tubular
segment having a cylindrical outer surface of a metallic or reinforced plastic material.
7. The web spreader roll according to claim 6, wherein each roll segment has an outer
surfacing layer of a material belonging to the group composed of natural and synthetic
rubbers, polyurethane , tungsten carbide.
8. The web spreader roll according to any of the preceding claims, further comprising
a drive pulley mechanically connected to an end portion of a first roll segment at
one side end of the spreader roll.