WINDING SPINDLE

The present invention relates to a winding spindle for the manufacturing of reels without a core or supporting member. In the field of the manufacturing of packaging materials, films of extruded and blown plastic materials are generally wound in reels having a hollow central cylindrical support called core. During the winding step the core is supported and rotated by inserting an expandable spindle or, alternatively, by means of tailstocks inserted at its ends. Generally, the core is made of cardboard, plastic or metal and must be able to withstand the radial pressures exerted by the wound film.

A new technology allowing to wind plastic films to form reels without a core, also called "coreless" reels, has recently been developed, which coreless reels, due to the elimination of the supporting member, are much cheaper than the traditional ones.

Coreless reels are made by winding a film directly on a spindle, which must be extracted once winding is complete. The extraction of the spindle is a rather complex operation because the wound film exerts on the spindle surface pressures in the order of

MPa. These pressures mainly depend on the winding tension of the film, the winding speed as well as the curvature and the quality of the surface of the spindle itself.

In order to try to make the operation of extracting a spindle easier, coreless reels are prepared by trying to keep the tension of the film down to values close to zero, which, during winding, results in a lot of air being included between one and another layer of the wound film. Therefore, on equal length and thickness of the wound film, the volume of a coreless reel is from 2,5 to 4 times larger than the volume of reels having a core. Moreover, still due to the air included during the winding, the general aspect of coreless reels is rather poor in terms of cylindrical shape and flatness.

In order to try to overcome these drawbacks, spindles for winding coreless reels have been developed that are expanded during the winding step and then collapsed, thus regaining their initial diameter in order to allow to extract the finished reel.

JP 20021377856 describes, for example, a spindle for the winding of coreless reels made up of a cylindrical body having a cut throughout its length, which allows it to be radially expanded and collapsed in order to allow the winding and the extraction

of a reel, respectively. In order to maintain the homogeneity of the cylindrical surface of the spindle, the cut line is zigzag- or sawtooth-shaped or the like, such as to ensure continuity of the cylindrical surface in the axial direction and homogeneity of the wound film. JP2003252532 describes an expandable spindle that is similar to the previous one, wherein the cylindrical body has a cut along the axial direction throughout its length. The spindle is radially expanded by inserting an annular member having a larger diameter, which is removed at the end of the winding in order to bring the diameter back to the original size, thus allowing the extraction of the reel. Elastically expandable spindles of the above-described type have the drawback that the spindle surface is discontinuous due to the presence of the cut line allowing its expansion. This discontinuity, although having a small size, causes vibrations that limit the maximum winding speed. Moreover, the cut line can pinch and damage the film either during the winding or the extraction step and facilitates the inclusion of air, thus causing an undesired increase in the volume of the finished reel.

Expandable spindles are also known which are provided with a plurality of radially movable cylindrical sectors that allow to engage and/or disengage the reel core. WO 9919241 describes, for instance, a spindle for the winding of coreless reels comprising a cylindrical body provided with two members that are radially expandable by means of a pneumatic drive. The radial outward movement of the expandable members allows to grip a tail of the film to be wound as well as to engage the reel core during the winding step. The movement of the expandable members in the opposite direction allows to free the reel once finished.

EP 731770 describes an expandable spindle provided with a plurality of radial openings from which blade members, rod members or the like protrude. The movement of these members allows to obtain a variation of the spindle diameter.

Expandable spindles provided with radially movable members have the drawback of providing a wound reel having a polygonal aspect and in addition the discontinuous contact between the film under winding and the radial sectors in the expanded state results in problems of vibrations and inclusion of air, which may be limited only by reducing the winding speed.

It is therefore an object of the present invention to provide a winding spindle for coreless reels allowing to overcome these disadvantages. Said object is achieved with a winding spindle, whose main features are disclosed in the first claim, while other features are disclosed in the remaining claims. The winding spindle according to the present invention is made up of a cylindrical body having a circular cross-section that comprises a plurality of radial cylindrical sectors. The surface of the cylindrical body is homogeneous and compact and the sectors form a kinematic chain in which at least one cylindrical sector is radially movable. A movement of this cylindrical sector radially inwards causes a movement of the other cylindrical sectors adjacent thereto towards the spindle axis and a reduction in the external diameter of the spindle.

The main advantage offered by the present invention is that the surface of the winding spindle is homogeneous and compact, i.e. free from discontinuities, thus allowing to obtain reels having an even cylindrical shape while avoiding vibration problems and risks of pinching the film.

The choice of collapsing the spindle in other to allow the extraction of a reel is also highly advantageous, because, contrary to known winding spindles, this allows to maintain the compactness and the homogeneity of the surface during the whole winding step. Another advantage offered by invention is that, still due to the homogeneity and the compactness of the spindle surface, the winding step is substantially free from the problems of inclusion of air, which are typical of the spindles of the prior art, thus allowing to substantially work at the same winding speeds used for traditional reels.

Another advantage offered by the invention is that the winding spindle has a structure suitable to withstand traction and compression forces in the radial direction, thus also allowing the winding of a pre-tensioned material. Consequently, the coreless reels obtainable by means of the spindle of the invention have a volume substantially corresponding to the volume of reels provided with a supporting member.

Moreover, thanks to its particular structure, the winding spindle according to the present invention is suitable for the winding not only of packaging films, but also of other materials such as paper and wo ven-non- woven fabrics.

Further advantages and features of the winding spindle according to the present invention will become clear to those skilled in the art from the following detailed and non-limiting description of an embodiment thereof with reference to the attached drawings, wherein: - figure 1 shows a perspective view of the spindle according to the present invention in a winding configuration; figure 2 shows a perspective view of the spindle of figure 1 in an extraction configuration; figure 3 shows an exploded perspective view of the spindle of figure 1; - figure 4 shows section IV-IV of figure 1; figures 5 and 6 show sections V-V and VI-VI of the spindle of figure 4; figure 7 shows a longitudinal section of the spindle in the extraction configuration; and figure 8 and 9 show sections VIII-VIII and IX-IX of the spindle of figure 7. Referring to figures 1, 2 and 3, the winding spindle according to the present invention is made up of a cylindrical body having a circular cross-section and comprising a plurality of radial cylindrical sectors. In the illustrated embodiment, the spindle comprises a first cylindrical sector 1, a second and a third cylindrical sectors 2, 3, equal to each other and symmetrically arranged with respect to the first cylindrical sector, and a fourth cylindrical sector 4 arranged between the second and the third cylindrical sectors 2, 3. At the ends of the cylindrical body of the spindle two heads 5, 6 allowing to mount and rotate the spindle on a winding machine are arranged.

According to the inventive concept underlying the present invention, the cylindrical surface of the spindle resulting from the composition of the adjacent cylindrical sectors is homogeneous and compact and thus free from the discontinuities typical of the prior art spindles.

Moreover, the cylindrical sectors of the spindle form a kinematic chain in which at least one cylindrical sector is radially movable. The radial inward movement of this cylindrical sector causes a movement of the cylindrical sectors adjacent thereto towards the axis of the spindle. Consequently, the spindle collapses starting from a winding configuration, thus reducing its diameter in order to allow the extraction of a reel.

As it may be seen by comparing figures 1 and 2, in the illustrated embodiment the sector which can radially moved inwards is the fourth cylindrical sector 4, i.e. the sector arranged between the symmetrical cylindrical sectors 2, 3, which, when the spindle is in a collapsed configuration, remains hidden under the symmetrical cylindrical sectors 2, 3.

As shown in figure 3, the first cylindrical sector 1 is connected to the second and the third cylindrical sectors 2, 3 by means of hinge members comprising a plurality of protrusions 7 formed on the cylindrical sectors 2, 3 and axially bored, which are engaged with corresponding recesses 8 formed at the sides of the first cylindrical sector 1 by inserting a pin 9.

The first cylindrical sector 1 is further provided at its upper portion with a longitudinal guide 10 suitable to slidably receive a bar 11 to which a plurality of maneuvering rods 12 are pivoted.

The fourth cylindrical sector 4 is provided at its lower portion with a number of protrusions 13 corresponding to the number of the maneuvering rods 12 and suitable to engage with their free ends.

Therefore, the fourth cylindrical sector 4 is restrained to the first cylindrical sector 1 in the radial direction through the maneuvering rods 12. Protrusions 13 are symmetrical with respect to a mid plane of the fourth cylindrical sector 4, so to engage with rods 12 at both sides.

A plurality of connecting rods 14, which are connected to the second and third cylindrical sectors 2, 3 by means of a pin 15, are pivotally mounted at the free ends of these sectors. The connecting rods 14 are further pivoted by means of a pin 16 to protrusions 13 symmetrically formed on the fourth cylindrical sector 4. Therefore, the fourth cylindrical sector 4 is also restrained to sectors 2 and 3, which are adjacent thereto.

The kinematic chain made up of the different cylindrical sectors forming the spindle body and of their connecting members can be schematized as a six-sided articulated polygon, in which the base is the first cylindrical sector 1 and the second and third cylindrical sectors 2, 3 are a pair of symmetrical cranks connected to the base; the free ends of the cranks are connected to each other through a three-rod system, in which

the central rod is the fourth cylindrical sector 4 and the side rods are the connecting rods 14.

Due to the constraint in the radial direction between the fourth cylindrical sector 4 and the first cylindrical sector 1, the kinematic chain in the form of a six-sided articulated polygon has one degree of freedom only, corresponding to the movement of the fourth cylindrical sector 4 in the radial direction.

When the spindle is in a winding configuration, shown in figures 4 to 6, the maneuvering rods 12 are in a substantially vertical position and the fourth cylindrical sector 4 is inserted between the second and the third cylindrical sectors 2, 3, thus making the cylindrical surface of the spindle perfectly homogeneous and compact.

Moreover, in this position the connecting rods 14 are in a substantially horizontal position, whereby the kinematic chain is in a stuck configuration that can withstand both the radial compressing actions exerted by the film under winding on the spindle and the centrifugal forces acting on the spindle, which would tend to expand the different cylindrical sectors.

Once finished the winding step, in order to allow to extract the spindle from the reel, bar 11 is axially moved along the direction shown by arrow S in figure 7. Consequently, the maneuvering rods 12 rotate towards bar 11, thus withdrawing the fourth cylindrical sector 4 radially inwards. This movement of the fourth cylindrical sector 4 causes, through the connecting rods 14, a movement of the second and third cylindrical sectors 2, 3 towards the axis of the spindle. In particular, the second and third cylindrical sectors 2, 3 rotate towards each other nearly up to touch each other with their free ends.

Thus, the spindle passes from the winding configuration, wherein it has an homogeneous and compact external cylindrical surface having a substantially circular cross-section, to an extraction configuration, wherein the structure is collapsed and has an external surface that is no longer homogeneous, but has a discontinuity at the contact point between the free ends of the second and third cylindrical sectors 2, 3. In the extraction configuration, the cross-section of the spindle has a diameter that is smaller than the diameter of the cross-section during the winding step. The diameter reduction of the cross-section between the winding and the extraction configurations is so

designed to be always higher than the diameter reduction of the reel core, which occurs due to the winding tension of the film, thus ensuring the possibility of extracting the reel.

For instance, in the case of a pre-tensioned packaging film, the diameter reduction of the reel is generally comprised between 1 and 4% of the winding diameter. Therefore, the winding spindle will be so sized that the diameter reduction between winding and the extraction configurations is not lower than 5%.

In order to allow the movement along the axial direction, bar 11 is provided at one end with a threaded member 17 engaging with a maneuvering ring nut 18 that is axially restrained to one of the spindle heads, e.g. head 6. This solution is simply to achieve and allows to adapt the spindle to any type of winding machine.

Alternatively, the drive of bar 11 in the axial direction might be carried out by means of a spring, pneumatic or hydraulic drive. Moreover, the maneuvering rods 12 enabling the movement of the fourth cylindrical sector 4 along the radial direction could be replaced by cam profiles arranged at or formed on bar 11, or directly arranged at or formed on the fourth cylindrical sector 4.

Possible modifications and/or additions may be made by those skilled in the art to the hereinabove disclosed and illustrated embodiment of the invention while remaining within the scope of the following claims.