The invention also relates to a method for producing tubular products by means of helically winding strips of web material, in particular strips of cardboard or paper, around a spindle, preferably fixed.

State of the art In many industrial fields continuous materials in sheets or in webs are required to be wound to form logs or reels. For example, in the production of logs of plastic film, non-woven fabric, adhesive tape, paper, tissue paper and other continuous materials in sheets, the web material to be wound is coiled around tubular cores produced by spirally or helically winding strips of card or paper. Two or more continuous strips of paper ! or cardboard are fed continuously to a production machine, called"core winder", wherein the strips are partially overlapped with a helical pattern around a forming spindle. A glue is applied to make the strips forming the tubular product adhere to one another. The procedure is continuous and tubes or tubular cores are produced starting from a continuous tubular semi-finished product that is cut into lengths by specific knives that work in synchronism with a forward movement of the semi-finished product being formed around the spindle.

Examples of machines of this type are described in US patents 3.150. 575; 3.220. 320; 3.636. 827; 3.942. 418; 5.468. 207 and 5.873. 806.

These machines are disposed beside production lines, for example in production lines for tissue paper logs. They are subject to frequent stops, for example caused by downstream machines stopping. When a rewinding machine that receives cardboard tubes produced by the tube-forming machine stops, for example to replace the feed reel of the web material to be wound into logs, or simply slows down for various reasons, it may be necessary to stop production of the cardboard tubes. This occurs, for example, when it is no longer possible to

store the tubular cores in an intermediate storage unit, between the core winder and the web production line.

The core winder must also be stopped, for example, at the end of the work shift if the line does not work in a continuous cycle.

As known to those skilled in the art, stopping the core winder causes some drawbacks which cause the need to reject the first meters of tube produced after starting up again. In practice, it has been found that to attain the standard of quality required in the production of tubes produced by these machines they must reach the normal operating temperature through the effect of friction with the tubular product being formed and of the glue, which is normally heated before being applied. This causes a waste of material as the first meters of the tubular product produced must be scrapped or in any case are of poor quality. Moreover, there are other drawbacks resulting from loss of time with consequent negative effects in terms of productivity, also in view of the time required to return to optimal operating speed.

Objects and summary of the invention The object of the present invention is to produce a machine of the type mentioned above that allows the drawbacks of traditional machines to be overcome. In particular, the object of the present invention is to produce a machine that overcomes the drawbacks that occur in traditional machines when starting up again after a more or less prolonged stop and due to the need to return the machine to the normal operating temperature.

This, and other objects and advantages, which shall be apparent to those skilled in the art from reading the text hereunder, are obtained in substance with a machine of the type mentioned, wherein the temperature of the spindle around which the strips of web material are wound is controlled, by means of suitable control means, which may supply and/or remove heat.

In practice, although temperature may be controlled by external means, it is preferable and advantageous for the spindle to include temperature control members that act from inside the spindle, supplying or removing heat from inside it. This essentially simplifies the arrangement of the machine and allows to thermally control the spindle in a particularly efficient way and with a rapid thermal response, without influencing or modifying the temperature of other elements around it.

The temperature control system is firstly used to heat the spindle to the normal operating temperature when the machine is started up. This first function may also be implemented by means that allow only heating of the spindle, for example an electrical resistance or the circulation of saturated or overheated steam inside the spindle.

However, in certain situations it was found to be desirable to remove heat from the spindle to avoid overheating, for example due to excessive heat developing through friction and/or due to excessive heat being supplied by the glue used. In this case the temperature control system may also be used to cool the spindle with suitable heat removal. Also in this case, removal of heat preferably takes place from inside the spindle.

When it is desirable for the temperature control system not only to heat but also-if necessary-to cool the spindle, its temperature may be controlled by a convective fluid, such as water, oil, or another suitable fluid. A thermostat may be provided to regulate the supply or removal of heat in a specific heat exchanger that regulates the temperature of the convective fluid. A convective fluid of this type may also be used if the spindle is only to be heated and not cooled.

In the solution with temperature control through a convective fluid the use of oil and in particular of a diathermic oil is preferable, on the basis of considerations of a thermodynamic nature to avoid problems of corrosion.

Temperature control of the spindle and in particular the possibility of heating it quickly allows various advantages to be attained, including the use of a glue that is activated thermally thanks to the temperature of the spindle and therefore of the strips of web material and the glue during winding. In particular, a cold glue may be used, that can be thermally activated by heating obtained through the heat supplied by the spindle.

When the temperature of the spindle is controlled by a convective fluid, the inside of the spindle may advantageously be hollow and associated with members for the circulation of the convective fluid inside it. The fluid may for example be made to circulate in the spindle by introducing and removing it from the same end of the spindle, at which it is cantieverly supported by the structure of the machine.

According to a possible embodiment of the invention, the spindle may be provided with an axial internal cavity, inside which a duct to introduce the convective fluid extends (coaxially to the spindle). This duct has for example a first

end connected to a corresponding first end of the spindle and to the supporting structure from which the spindle is cantileverly supported. The second end leads into the axial cavity of the spindle in proximity to the end of the spindle opposite the zone connected to the load-bearing structure. In this way, the internal cavity and the duct define a circuit for the convective fluid extending from the first end of the spindle towards the second end and from here back towards the first end.

According to an advantageous embodiment the spindle and the duct for introducing the convective fluid may be connected to each other by means of a connecting member comprising a first passage for introducing the convective fluid to the duct coaxial to the spindle and a second passage for removing the convective fluid from the axial cavity of the spindle.

As shall be apparent from the description below with reference to an example of embodiment, in this way the traditional spindle may be replaced with a temperature controlled spindle without acting in any way on the remaining structure of the machine.

According to a different aspect, the invention relates to a method for producing a tubular product formed of a helically wound web material, wherein at least two strips of web material are fed in an essentially continuous way and wound overlapping and staggered in respect of each other around a spindle, a glue being applied to make said strips adhere to each other, characterized in that the spindle is thermally controlled during winding.

By controlling the temperature of the spindle it is possible both to overcome the drawbacks deriving from the need to bring the tube-forming machine to normal operating temperature, and for example to use a heat-sensitive glue, which can provide faster and more stable gluing of the strips of web material wound helically to form the tubular product.

Further advantageous characteristics and embodiments of the method and of the machine according to the invention are indicated in the attached dependent claims and shall be described in greater detail with reference to an embodiment of the machine.

Brief description of the drawings The invention shall be better understood by referring to the description hereunder and to the accompanying drawings which show a non-limiting practical embodiment of the invention. In the drawings:

Figure 1 is an overall schematic side view of the machine; Figure 2 is a longitudinal section of the spindle according to II-II in Figure 3; and Figure 3 is a cross section according to III-III in Figure 2.

Detailed description of the preferred embodiment of the invention Figure 1 shows as a whole a core winder to which the present invention has been applied. The machine shown has a structure essentially the same as the one described in the patent USA 5.873. 806, which should be referred to for a detailed description of the components of the machine, which are not of interest in the description of the present invention. It must however be understood that the invention may also be applied to machines with a different structure, as long as they are provided with a forming spindle to form tubes, which may either be fixed or rotating around its axis.

Hereunder reference will be made in particular to the possibility to heat the spindle by circulation of a convective fluid. It must however be understood that the same fluid may be used more generally to perform temperature control of the spindle, and therefore also to remove heat rather than supply it.

Briefly, and limited to the matters of interest for the present description, the machine in Figure 1, generically indicated with 1, comprises a supporting structure 3 from which a spindle 4 is supported projectingly, a first end of which, indicated with 6, is connected to the supporting structure 3 by means of a coupling 8. The opposite end of the spindle 4, indicated with 10, is connected to an auxiliary spindle 12 supported idle that extends to a cutting unit 14 that divides the tube (T), formed continuously as described hereunder around the spindle 4, in several lengths of the required axial length.

To form the tube T, two strips of cardboard or other web material, indicated with S1 and S2, are fed to the core winder 1. These are wound helically around the spindle 4 with the aid of a continuous belt 7 that has two branches 7A and 7B, driven around two pulleys 9 and 17, the respective axes of rotation of which are indicated with 9A and 17A. The branch 7A forms a helical turn around the spindle 4 and the strips of web material S1 and S2 during the winding phase. A motor 19 draws the driving pulley 17 in rotation, producing movement of the belt 7.

The spindle 4 has an axial internal cavity 21 closed at the front by a closing cap 23, integral with which is a pin 25 that forms a seat of a bearing 26 supporting

an auxiliary spindle 12. Inside the cavity 21 and coaxial to the spindle 4 a duct 27 extends, terminating with one of its ends 27A at a distance from the cap 23. The opposite end, indicated with 27B, of the duct 27 is integral with a connecting member 29 and welded to it.

The connecting member 29 has a cylindrical external surface 31 flush with the cylindrical external surface 6A of the end 6 of the spindle 4 connected to the supporting structure 3. In this way the external surface 31 of the connecting member 29 and the cylindrical surface 6A of the end of the spindle 4 form a continuous cylindrical surface which allows the spindle 4 to be clamped to the supporting structure 3 by the coupling 8. The connecting member 29 is connected to the end 6 of the spindle 4 (which has a larger diameter to the main body of the spindle) by screws 33 passing through holes 35 produced in the connecting member 29.

Two radial holes 37 and 39 are produced in the connecting member 29 staggered angularly around the axis A of the spindle (coinciding with the axis of the connecting member 29) for introducing the convective fluid and removing it from inside the spindle 4. The hole 37 is in fluid connection with an axial hole 41 aligned with the duct 27 and connected to it. It is therefore possible to introduce the convective fluid (coming from a specific heat exchanger or the like through a flexible tube) through the hole 37 into the spindle 4. The convective fluid flows out from the free end 27A of the duct 27 and into the cavity 21 of the spindle 4 filling the empty space between the cylindrical internal wall of the cavity 21 and the external wall of the duct 27.

From the cavity 21 the convective fluid, which has yielded at least part of its heat through the wall of the spindle 4 towards the outside of the latter, reaches, through a hole 47 parallel to the axial hole 41 produced in the connecting member 29, the second radial hole 39 to which a second flexible tube, not shown, can be connected for recirculation of the convective fluid.

With the layout shown the spindle 4 can be taken to, and maintained at, a normal operating temperature to produce tubes by helically winding the strips of web material S1, S2. The temperature to which the spindle can be taken may even be substantially higher than the ambient temperature, so that heat sensitive glues can be used to improve the quality of the product.

Moreover, the particular arrangement of the connecting member 29 and the

fact that its head is clamped with screws 33 to the end 6 of the spindle 4 with the larger diameter allows the immediate replacement of traditional spindles with spindles with thermostatic or generic temperature control, produced as described without performing any operations whatsoever on the layout of the machine.

It is understood that the drawing purely shows a practical embodiment of the invention, the forms and layouts of which may vary without however departing from the scope of the concept on which the invention is based. The presence of any reference numbers in the accompanying claims has the sole purpose of facilitating their reading in the light of the description hereinbefore and the accompanying drawings and does not in any way limit the scope of protection defined by the claims.