The invention also relates to a winding method to produce logs of web material about cylindrical winding cores.

State of the art To produce logs of web material about cylindrical or tubular winding cores so-called peripheral rewinding machines are usually employed, wherein the winding core is made to pass-rotating about itself-through a nip between two rotating winding rollers, which define alone or in combination with other members (typically a third winding roller with a movable axis) a winding cradle wherein the log is formed and for this purpose maintained in rotation through the effect of friction exerted by the winding rotters on its periphery. The web material to be wound is fed about one of the two winding rollers that form the nip through which the winding core and the web material pass. At the moment it passes through the nip a certain quantity of web material may have already been wound about the core.

Examples of peripheral rewinding machines of this type are described in the US patent n. 4,487, 377, in the British patent GB-B-2150536, in the European patent EP-B-524158, in the US patent 5,979, 818 and in numerous other patents. in the same technological sector.

Usually, the winding core is constituted by a tube made of flexible material, typically cardboard, with relatively thin wall. The diameter thereof is slightly greater than the minimum dimension of the nip between the two winding rollers, through which the core must pass. This guarantees that the rollers grip the core and that winding therefore takes place correctly. The pressure allows an adequate friction force to be applied, by means of the winding rollers, to the core to accelerate it to the angular velocity required for winding.

The pressure applied on the core causes some drawbacks. In fact, the core normally produced with helically wound and glued strips of cardboard,

may be damaged irreparably due to the pressure applied and the consequent deformation, especially if the gluing between the strips of cardboard forming the core is not high quality.

The use of flexible cardboard cores decreases the possibility of using very long cores, able to wind wide sheets of web material. This is due to the difficulty in handling cores subject to noteworthy bending deformations.

Therefore, it would be advisable to utilize cores of noteworthy consistency and resistance to bending deformation, in contrast with the need to be radially yielding in order to penetrate a nip with smaller dimensions to the dimension of the diameter of said core.

Usually, the core remains inside the log formed and is cut crosswise together with the material wound thereon when the log is divided into rolls of the final dimension destined for distribution.

On the other hand, in some rewinding machines the winding core is removed after winding and recycled. The log produced therefore has no tubular winding core. This technique has some advantages known to those skilled in the art. Examples of machines that operate with removable and recyclable winding mandrels or winding cores are described in WO-A- 0172620 and in WO-A-0068129.

Objects and summary of the invention The object of the present invention is to produce a machine to wind logs that allows the use of winding cores with characteristics differing from those utilized traditionally and more suitable to be removed from the finished log and recycled, and also to overcome or reduce the drawbacks deriving from excessive bending of the core and/or from the possibility of it breaking or being damaged when it is pressed radially.

According to a different aspect, the object of the present invention is to produce a method that makes use of a different type of winding cores, and simplifies the operation to remove the mandrel or winding core from the finished log.

In substance, according to the invention a peripheral rewinding machine is provided, including a first winding roller and a second winding roller defining a nip through which a web material to be wound passes and winding cores about which pre-established quantities of said web material are wound.

Characteristically, according to the invention at least one of said winding rollers is associated with an elastically deformable element, to temporarily increase the dimension of said nip when said winding cores pass through.

In principle, the elastic element may be constituted by an elastic support that allows the two rollers to be moved reciprocally away from each other with consequent widening of the nip through which the core passes. However, the deformable element is preferably constituted by an elastically yielding coating of the roller. This solution is particularly simple and reliable.

In practice, the invention is based on the idea of making the dimension of the nip temporarily variable (through elastic deformation of a mechanical member) to-allow a winding core that may even be essentially incompressible, or in substance non-deformable both axially and radially, to pass through it. With a configuration of this type the winding cores may for example be made of metal, carbon fiber, glass fiber, resin or another rigid material, tubular or even solid. Typically, they may be constituted by an aluminum tube. This makes them easy to remove from the formed log, without the risk of breakage and easy to recycle, also with washing if required to eliminate any glue or other residues that may deposit thereon.

According to a different aspect, the invention relates to a method to produce logs of web material wound about winding cores, comprising the steps of: providing at least a first winding roller and a second winding roller defining between them a nip through which the web material and the winding cores pass; -feeding the web material continuously through said nip; winding a pre-established quantity of web material about a first winding core forming a first log of web material; at the end of winding said first log, severing the web material and starting to wind a second log about a second winding core, said second winding core being made to pass through said nip; characterized in that said nip is widened by means of elastic deformation of an elastically deformable element (typically the coating of the roller) when said second core passes through.

Further advantageous characteristics and embodiments of the invention

are described hereunder and indicated in the appended dependent claims.

Brief description of the drawings The invention shall be better understood with reference to the description and the accompanying drawing, showing a non-limiting practical embodiment of the invention. In the drawing, where equivalent or corresponding parts are indicated with the same reference numerals : Figures 1 to 3 show a sequence to insert the new winding core into the winding cradle.

Detailed description of an embodiment of the invention The attached drawing schematically shows a rewinding machine of a type analogous to the one described in EP-B-524158, to which the present invention is applied. The drawing only shows the elements required to understand the present invention. It must be understood that the same inventive concept may be applied to other rewinding machines of the type defined in the appended claims.

The rewinding machine comprises a first winding roller 1 and a second winding roller 3 which between them define a nip 5. The web material N to be wound on cylindrical or tubular winding cores A1, A2, made for example of metal and essentially incompressible, passes through the nip 5.

The rollers 1 and 3 form, together with a third winding roller 7, a winding cradle 9 wherein logs R of web material N wound about the cores A1, A2, are formed in succession. At the end of winding a log R about a core A1, this is unloaded from the winding cradle 9 onto a chute 10 and a new core A2 is inserted through the nip 5 into the winding cradle 9 to form a new log R2. For this purpose an oscillating taker-in 11 is provided to pick up the core from a conveyor, schematically indicated with 13 (Figure 3), and push it into the nip 5 between the rollers 1 and 3.

The dimension of the diameter of the cores A1, A2, A3 is greater than the minimum dimension of the nip. The passage therethrough is permitted by the fact that the winding roller 3 is coated with a layer 3A of elastically yielding material, typically rubber or an elastomer. As can be seen in the sequence in Figures 1 to 3, when the core A2 is pushed into the nip 5, the coating 3A of the roller 3 is compressed locally, in substance causing temporary dilation of the nip 5 to allow the core A2 to pass through towards the cradle 5.

Severing of the web material N, unloading of the log R1 and starting winding on the new core A2 may take place in any of the known ways and not described herein. In particular, the start of winding may take place with the aid of jets of air, electrostatically charging the winding core (for example if it is made of plastic rather than metal), by applying a glue or a liquid (even simply water) to the surface of the core or in another appropriate way. If a glue is employed the cores may be washed if needed-in a per se known way- before reuse.

The invention has been described herein with reference to a machine wherein winding starts when the core has already passed through the nip 5.

Nonetheless, it must be understood that the same concept may also be utilized on machines wherein winding starts upstream of the nip and cores on which one or more turns of web material have already been wound pass through said nip. A rewinding machine of this type is described for example in WO-A-9421545.

It is understood that the drawing merely shows a possible embodiment of the invention, which may vary in forms and layouts without however departing from the scope of the concept on which the invention is based. Any reference numerals in the appended claims are provided purely to facilitate reading in the light of the description hereinbefore and of the accompanying drawings, and do not limit the scope of protection whatsoever.