The invention relates to web processing machinery and in particular to web spreader roll.

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.

There are innumerable types of web spreader roll, for satisfying specific requirements of the particular web material to be handled.

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.

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.

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.

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.

WO 97/00826 discloses a bearing arrangement and a coupling element of a spreading roll. The spreading roll comprises segments that are interconnected by coupling elements to rotate around a shaft. The fastening on the shaft is realized with one or more bearings that are positioned in place by means of an outer casing and a sleeve. The coupling elements that are reinforced with an inner sleeve replace the support previously supplied by the bearings.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The invention is defined in the annexed claims.

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.

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.

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.

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.

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.

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.

In this way, a sensible overall weight reduction of the complete web spreader roll can be achieved.

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.

The machining requirements of the inner cylindrical surface of the roll segments are also minimized.

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.

An even more effective construction towards minimization of inertia and frictional resistances is depicted in Figure 3.

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 axle 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.

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.

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.

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.

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.

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.