DESCRIPTION

The present invention refers to a chill roll with recirculation of water or other suitable fluid used in printing machines, such as in particular rotogravure printing machines.

As known, in printing machines of the above mentioned type a plurality of printing units or printing stages follow one another. Once a first printing stage is over, before entering the subsequent one the printing support undergoes a drying treatment, pursuant to which the support is directed, via a set of deviation rolls, to the subsequent printing stage. One or more of these deviation rolls is an idle one and is water-cooled.

This cooled roll, known as chill roll, is presently the source of some unsolved problems.

In particular, being it idle, it is important that the roller opposes a minimum resistance to the printing support, otherwise the differences in speed between the printing support and the roller may result in the support being warped, being it not perfectly adherent to the roller.

However, minimizing the friction is a serious problem with the presently known chill rolls.

The rolls that are currently subject to a widespread use in the field are of two different types. A first type of know chill roll comprises a hollow sleeve into which a water jet is injected. The water, being poured over the inner surface of the sleeve, carries out the cooling of the outer surface contacting the printing support, by way of thermal conduction. The water jet falls then out of the sleeve due to simple gravity. This type of chill roll presents specific drawbacks. In particular, making it use of an open circuit, i.e. with an open water discharge, the water becomes oxygenated and this causes significant corrosion effects over the metal wall forming the sleeve. Moreover, the oxygen fosters the proliferation of microorganisms such as algae and fungi. This implies therefore that the maintenance of this type of chill roll and the relative water circulation system is demanding and troublesome. Another problem that ensues from this type of roll is that, by effect of the centrifugal force caused by the rotation of the roller, the water injected inside the sleeve gains a certain speed that hinders the idle rotation of the same roller, due to the dynamic friction between the water and the sleeve. This clearly contributes to an increased resistance between the printing support and the roller, and thus to cause the above mentioned defects (incorrect adhesion between the support and the roll, warping of the support).

A second type of known chill roll provides for, instead of an open water discharge as the one described above, a forced discharge. Therefore, the hydraulic circuit arranged within the roller is of a closed type. This implies that the oxygenation of the water is reduced, thus solving, with this roller, the above explained problems in connection with the corrosion and the formation of algae and other microorganisms. However, the forced discharge, carried out through a pressurized mechanical seal, causes a remarkable increase of the friction force opposing the rotation. This known roll is thus particularly unsatisfactory as far as the occurrence of friction is concerned, and then the correct interaction between the same roller and the printing support.

It is therefore an object of the present invention to solve the above mentioned problems.

A particular object of the present invention is to provide a water-cooled chill roll that solves the problem of friction and that does not need a frequent and demanding maintenance.

These objects are achieved with the water recirculation chill roll the essential features of which are defined by the first of the appended claims.

The characteristics and advantages of the chill roll according to the invention will become apparent from the following description of an embodiment thereof, provided by way of example and not limitative, with reference to the attached drawings wherein :

- figure 1 is a perspective view of a water recirculation chill roll according to the invention ;

- figure 2 is a longitudinal section of the roll of figure 1 , i.e. carried out by a sectional plane passing through the rotation axis of the same roll ;

- figure 3 is an enlarged view of an end portion of the roll, as marked in figure 2; and

- figure 4 is a broken view of the roll end portion of figure 3, taken according to sectional planes including longitudinal planes such as those of figure 2 and a cross-wise plane perpendicular to the longitudinal plane. With reference to the above figures, a chill roll adapted to be mounted in a printing machine such as in particular a rotogravure printing machine, comprises a cylindrical body 1 , elongated according to a longitudinal axis X. Two shaft pieces 2 project axially from respective end sections of the body; through the shafts the cylindrical body can be pivotally supported around the axis X by a fixed frame (not shown) of the printing machine.

Within the roller a cooling circuit 3 evolves, for the circulation of a cooling fluid, such as for instance, but this is not limitative, water; the circulation of the fluid in the cooling circuit causes a cooling of the roll, and in particular of an outer surface 1 0 thereof, which is adapted, when the roll is mounted in the printing machine, to be contacted by a printing support. The cooling circuit develops not only in the cylindrical body 1 , but also in a first piece 20 of the two shaft pieces 2. In particular, an inlet 30 to the cooling circuit is arranged on the first shaft piece 20, as clarified hereafter.

This inlet 30 opens in a first chamber 40, defined by a hydraulic seal element 4 that rotatably engages, in the fashion of a cap, on the first shaft piece 20. An access 41 for the inlet of the cooling fluid from the outside the chamber 40 also opens in the chamber 40.

The seal element 4 further comprises a second chamber 42, hydraulically separated from the first chamber 40. This second chamber 42 is communicated with a drain passage 420 for draining outside the cooling fluid coming from the circuit.

Close to its end the first shaft piece 20 supports auxiliary rotation drive means 5 arranged so as to be housed in the first chamber 40 and to be hit by the flow of cooling fluid entering the chamber to be supplied to the cooling circuit; as a result, the auxiliary drive means 5 are such to impart a rotational drive around the longitudinal axis X to the relevant shaft piece and consequently to the cylindrical body.

More in detail, the auxiliary drive means 5 comprise a turbine, and namely a polar array of fixed blades 50 around the end of the first shaft piece 20. The inlet access 41 is arranged tangentially, taking as a reference the outer circumference defined by the outmost potions of the blades, so that the entering flow hits the effective surface of the blades, propelling the rotation of the turbine, and as a consequence of the shaft, around the X axis. Furthermore the first shaft piece 20 comprises two sleeves coaxially arranged one inside the other (with a fixed relationship, that is with no relative motion), and namely an outer sleeve 200 and an inner sleeve 201 .

The inner sleeve 201 axially projects with an end portion 201 a from the outer sleeve, and it is on this end portion 201 a that the drive means 5 are arranged.

The hydraulic seal element 4 is coupled in the fashion of a cap around the end 201 a and engages over the outer periphery of the outer sleeve 200. The hydraulic seal element is mounted in a fixed relationship with the frame of the printing machine, that is to say with no relative motion with respect to it. The outer sleeve 200 and the inside of the seal element 4 are mutually connected in a pivotal arrangement around the X axis, via a bearing arrangement. Therefore, the outer sleeve and thus the shaft piece (and consequently the cylindrical body) are free to rotate with respect to the hydraulic seal element 4.

The two sleeves include part of the cooling circuit, in that they define intake and discharge segments of the same circuit. In particular, the inner sleeve 201 forms an inner duct 210, extending along the X axis, which represents a first intake segment 3a of the circuit 3.

The spout of the intake segment 3a at the end 201 a of the first shaft, that is the end where the drive means 5 are mounted, is the inlet 30 to the cooling circuit.

An annulus gap 201 between the inner sleeve 201 and the outer sleeve 200 extends in turn along the X axis and defines a final, discharge segment 3b of the cooling circuit. The open end 21 1 a of the annulus gap 21 1 is the outlet of the cooling circuit and opens in the second chamber 42, so that the flow coming from the circuit is collected in the second chamber 42 and discharged from it through the drain passage 420.

The cylindrical body 1 , in a preferred embodiment shown by the figures, comprises a tubular drum 1 1 the ends of which are shut by end plugs 12, to which the shaft pieces are fixed. The cooling circuit develops throughout both the end plugs and the thickness of the tubular drum 1 1 . In particular, within the thickness of the tubular drum a plurality of channels 1 1 0 are formed, extending along the X axis and consecutively arranged throughout the circumference of the drum, as visible in figure 4. In an alternate fashion following the circumference of the drum, among the channels one can distinguish flow supply channels 1 1 0' and flow return channels 1 1 0" that communicate respectively with the first intake segment 3a and the final discharge segment 3b, thereby the cooling fluid flows along the drum in a direction or the other (depending on the direction having a consequently different temperature) in an orderly alternate arrangement. Indeed, the temperature of the fluid in the supply direction is lower than that in the return direction, considering the progressive thermal exchange which it undergoes with the outer wall portion of the drum. Therefore, by alternating supply channels and return channels, and concurrently providing the inlet 41 and the drain/outlet 420 of the circuit in correspondence with the same end of the drum, the overall average temperature over the drum, and in in particular over its outer surface remains substantially constant, or at least prevents the rise of excessive thermal gradients.

Once installed in the printing machine, the chill roll according to the invention operates as follows. As mentioned, the seal element 4 is fixed to the frame of the machine. On the contrary, the cylindrical body rotates with respect to the fixed frame. As a result of the tangential engagement by the printing support and its advancement, the idle cylindrical body is set into rotation. The water flow injected into the first chamber 40 hits the turbine 5 imparting a rotation thereto, around the X axis; as a result, an auxiliary torque is supplied to the same body, opposing the frictional resistance due e.g. and in particular to the contact between the outer face of the roll and the printing support. This assists to achieve a desirable consistency between the rotation speed of the roll and the speed of the printing support, with no mutual resistances that can be responsible for defects like warps or tensions in the printing support.

The cooling fluid flows then from the first chamber 40 to the first intake segment 3a and from it to the drum through the flow supply channels 1 10'. After running along the drum for all its elongation, the fluid enters the return channels 1 10" and then the final discharge segment 3b, to be discharged thorough the second chamber 42 and eventually the drain passage 420. As mentioned, this internal construction accomplishes an optimum distribution of the cooling action over the whole width of the printing support.

The amount of fluid fed to the roll, and the pressure thereof, are such as to generate a torque that is sufficient to win the friction almost totally, so that the roll is rotated by the drawing power of the printing support with a negligible opposing force. As mentioned, the fluid can be water; being the circuit inside the roll actually a close one, the water does not become oxygenated, thus avoiding corrosion phenomena and formations of algae or other microorganisms.

The present invention has been described with reference to a preferred embodiment thereof. It should be understood that there can be other embodiments that belong to the same inventive concept, inasmuch as they fall within the scope of protection of the following claims.