TECHNICAL FIELD This invention relates to a printing roll core for a printing roll comprising such a core and one or more sleeves which are provided to be mounted on the core from one end thereof and to be displaced along the core to and from working positions on the core by causing compressed air to flow out through passages terminating in outlets distributed along the outer surface of the core, so that the sleeve from a state in which the sleeve tightly fits the core, when compressed air is not caused to flow through said outlets, may be expanded by causing air to flow through said outlets, so that the sleeve may be displaced along the core.

BACKGROUND OF THE INVENTION

Printing roll cores of the above mentioned type are known since long and are extensively used within the graphic industry. For example may be mentioned those printing roll core designs which are described in US-A-3 146 709 and G-A-l 581 232. A drawback of these known printing roll cores is that compressed air is flowing out through all the outlets in the surface of the core when the sleeve is being mounted on the core or is being removed from it. In order that this known system shall function it has therefore been necessary to concentrate the majority of the outlets to a region of the surface of the core adjacent to that end of the core where the mounting operation is initiated, while only one single outlet is located at the central part of the surface of the core. The reason for this that the sleeve already initially shall be caused to cover the majority of the outlets through which compressed air is caused to flow out since the fall of pressure otherwise would be so large that the sleeve would not be able to be sufficiently expanded. This compromise, however, means that a plurality of sleeves cannot be mounted side by side on one and the same core, which is a serious limitation since it is often desirable to make a plurality of printings side by side in one and the same printing unit. Another drawback is that a sleeve which by mistake has

been displaced so far along the core that it has passed the central outlet will be locked on the core without any possibility to be released.

BRIEF DISCLOSURE OF THE INVENTION

The purpose of the invention is to provide an improved printing roll core, in which the above mentioned drawbacks and limitations have been eliminated in a simple way. These and other objectives may be achieved therein that the invention is characterized by what is stated in the appending claims.

Further characteristic features, aspects and advantages of the inven¬ tion will be apparent from the following description of a preferred embodiment.

BRIEF DESCRIPTION OF DRAWINGS

In the following description of a preferred embodiment reference will be made to the accompanying drawings, in which

Fig. 1 is a longitudinal sectional view through a printing roll core according to the invention;

Fig. 1A shows an encircled detail of Fig. 1 at a larger scale;

Fig. 2 shows the same printing roll core as in Fig. 1 with a sleeve partly mounted on the core; and

Fig. 3 shows a printing roll core with a plurality of sleeves mounted side by side on the core.

DESCRIPTION OF PREFERRED EMBODIMENT

A printing roll core has been generally designated 1. It consists according to the embodiment of a cylindrical shell 2 (also a slightly tapered core may be conceived) and two end portions 3 and 4 provided with axle bars 5 and 6. The cylindrical outer surface of the shell 2 has been designated 7. Compressed air can be supplied from a source of

compressed air through a compressed air hose 9 via a connection nozzle 8 in axle bar 5. In hose 9 there may optionally be provided a valve for opening and closing the connection. The supply of compressed air may be effected either by opening the valve 10 or by connecting the mouth piece 11 of hose 9 to the connection nozzle 8 of the axle bar 5. When closing the supply the operation is reverse. In the interior of the printing roll core 1 is a fill body 12 of rigid cellular plastic material which reduces the air volume in the interior of the core to the thin gaps between on one side the shell 2 and the end portions 3 and 4, and on the other side the said fill body 12.

In the shell 2 there are in a manner known per se provided a number of passages 13a, 13b ... 13h. In each such passage is a nonreturn valve 14. More particularly the valve 14 is a ball valve of well known type, as is shown in Fig. 1A. In the passage 13a there is provided a valve seat 15 having an outer annular border line which essentially coincides with the outer surface 7 of the shell. A steel ball 17 is pressed towards the seat 15 by means of a spring 18. In the closing position of the valve the ball 17 extends beyond the outmost part of the valve seat 15 and also beyond the outer surface of the shell 2 by an outer portion 19 which has the shape of a spherical calotte.

The sleeve - or the sleeves - which shall be mounted on the printing roll core 1 may be designed in a manner per se and consist of an inner shell 20 of reinforced plastics and an outer tube 21 of rubber with an exterior cliche. The sleeve has been generally designated 22, Fig. 2. When the sleeve 22 shall be mounted on the core 2 the compressed air hose 9 is connected to the nozzle 8, and the valve 10 is opened so that the interior of the core is subjected to an overpressure. No air, however, can flow through the passages 13a-13h as the valves 14 are closed. The sleeve 22 is mounted, starting in the right hand portion of the core 2, which portion in this case is the initial mounting end. The end portion 23 therefore suitably is somewhat tapered in order to facilitate the initial mechanical mounting operation. When the sleeve 22 thus has been mounted so far that it has passed the tapered portion 23, the sleeve 22 will with its interior side press the balls 17 of

the valves 14 into the passages 13a under compression of spring 18. Herein the valves are opened in a manner known per se and air flows out through the outlets of these first passages 13a such that the sleeve 22 will be expanded to a sufficient degree in order that it readily may be further moved over the core 2. The other valves 14, i.e. the valves in passages 13b-13h, are still closed but they will successively be opened as they are covered by the sleeve 22 during the continued movement of the sleeve along the core 2.

Fig. 3 illustrates the case when a plurality of sleeves 22a, 22b, 22c, and 22d are mounted on a core 1. This may be made without problems according to the invention as the shell 2 of the core 1 may be pro¬ vided with a plurality of valve provided passages 13a-13h. These has been indicated in Fig. 1 only by an X. It is also possible according to the invention to provide only one or a couple of comparatively short sleeves on a comparatively long core 1, so that the sleeves only will cover a minor portion of the core, a possibility which sometimes is worthwhile.