Rotary printing press drying assembly roller

A roller for a rotary printing press drying assembly, comprising, near each printing unit, a drying assembly including a plurality of parallel rollers, each roller being circumferentially provided with a plurality of equispaced slots which are arranged parallel to the longitudinal axis of the cylinder.

BACKGROUND OF THE INVENTION
 The present invention relates to a roller for a rotary printing press
 drying assembly.
 As is known, e.g. in printing paper material bands, a plurality of printing
 units including known ink applying devices are generally used.
 Said printing units comprise drying assemblies, including a plurality of
 parallel rollers which, immediately after the printing cylinder of the
 printing unit, extend upward, and then downward, to convey the paper band
 toward a following printing unit.
 The above mentioned drying assemblies operate to remove from the paper band
 the solvents of the just applied ink, while simultaneously drying said
 ink.
 Since the bands to be printed, generally made of a paper material, are
 greatly hygroscopic, they, upon contacting the printing cylinder, absorb a
 comparatively great amount of ink and solvent particles, thereby causing
 the paper band to greatly expand.
 Moreover, since the paper band is mainly stressed, as it is conveyed, by a
 pulling force, the longitudinal expansions are integrally compensated for,
 whereas the cross expansions of the paper band cannot be compensated for
 and, accordingly, as the paper band passes through the series of parallel
 rollers of the ventilating assembly, a plurality of comparatively narrow
 creases extending in the band feeding direction are formed.
 In a finished product, said creases would constitute a waste generating
 defect, with a consequent yield decrease.
 SUMMARY OF THE INVENTION
 Accordingly, the object of the present invention is to overcome the prior
 art drawbacks, and provide a particular type of roller, to be used in a
 drying assembly, which allows to safely prevent longitudinal creases from
 being formed within a printed paper band.
 According to the invention, the above object is achieved by a roller to be
 arranged in a roller series in a drying assembly, said roller being
 circumferentially provided with a plurality of equispaced slots which are
 arranged parallel to the longitudinal axis of the roller and are delimited
 by projecting ribs.
 Thus, about the circumference of each roller a plurality of slots allowing
 the movable band, partially contacting longitudinal ridges delimiting a
 related slot, to be extended in a cross direction, thereby eliminating
 possible paper creases, and allowing the paper band to extend in the width
 direction thereof are defined.
 Advantageously, the valleys and ridges define circle sectors, each of which
 encompasses an angle of approximatively 15.degree. to 35.degree..
 Moreover, the slots and ridges are formed with an arch length of about 30
 mm.
 Owing to the interruption of the continuous circumference of each roller,
 by providing valleys in the form of broad slots alternating with ridges or
 ribs, the paper band can be moved and extended in the width direction
 thereof as it passes through the free space formed by said slots, thereby
 preventing or compensating for any permanent formations of undesired
 creases in the printed band.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 As is known, the drying assemblies arranged near each printing unit, for
 example in a rotary printing press, comprise a plurality of parallel
 rotary rollers. A detail of a roller is shown in FIG. 1 and generally
 indicated by 1.
 The rotary rollers 1 operate to support and convey the just printed paper
 band 2, which is driven at a comparatively high speed in the direction
 indicated by the arrow f.
 The ventilating or drying assemblies are usually provided with rollers
 having a fully smooth circumference and, accordingly, as the band 2 is
 conveyed through a said drying assembly, undesired longitudinally
 extending creases and wrinkles are formed therein.
 More specifically, said creases are formed in said band since the paper
 band 2 being pulled cannot be extended in its width direction.
 One of the above mentioned creases 3 is indicated, by way of an example, by
 a dash and dot line in FIG. 3.
 The invention proposes now to interrupt the closed circumference of a prior
 roller used in prior ventilating assemblies, by forming slots equispaced
 from one another and extending parallel to the longitudinal axis of the
 roller 1, and alternating a slot 4 forming a recessed zone with a
 projection or ridge defining a rib 5. Thus, the slots 4 and ribs 5 extend
 parallel with to the roller 1 axis X and about the circumference of said
 roller.
 FIG. 2, which is a front view of the cylinder or roller 1, shows that the
 paper band 2 bears, as it is driven in the direction of the arrow f, only
 and exclusively on the ribs 5 of the cylinder 1. Thus, the paper band 2 is
 not hindered, and is suspended without bearing as it passes, on the rotary
 roller 1, through the free space defined by a slot 4.
 Accordingly, the paper band 2 will alternatively abut on a projecting rib
 5, but it will be free of moving in a cross direction in passing through
 the roller 1 zone defined by the slot 4.
 As shown in FIG. 3, the projecting ribs are evenly alternated with
 corresponding slots 4.
 From the cylinder 1 axis X a plurality of imaginary circle sectors,
 schematically indicated by S, extend, said sectors S ending at the ribs 5,
 respectively the slots 4, and advantageously defining an angle a of
 approximatively 15.degree. to 35.degree..
 The angle a would be selected depending on the diameter of the cylinder or
 roller 1, the depth of the slots 4 also depending on said roller diameter.
 It is important to assure that the "non contacting" zone of the paper band
 2 and roller 1 be such as to allow the paper 2 to be distended.
 Accordingly, the precise value of the angle a and, consequently, the size
 of the arch defining the ribs 5, respectively the slots 4, depends on the
 printing speed, the paper weight as well as the physic characteristics of
 the paper material forming said band 2; accordingly, the angle .alpha. can
 be changed depending on technical requirements.
 Actually performed tests have demonstrated that it would be advantageous to
 provide the ventilating assembly roller 1 with 6-10 projecting ribs
 alternating with six recessed slots, i.e. recessed with respect to the
 roller 1 circumference.
 As the paper band moves away from the printing assembly, the distance of
 the drying roller 1 will increase.