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[0001] The present invention relates to the field of machines for converting paper and similar products, and in particular it relates to a paper conveying roller for machines working in this field such as in particular winding, rewinding, interfolding machines.
[0002] In particular, the invention relates to a paper conveying roller having circumferentially a plurality of holes which, connected to a vacuum system, allow the sheet or web of paper to adhere on their surface.
[0003] As known, many machines used in the paper converting field, for example rewinding and interfolding machines, are equipped on the surface of their rollers with systems for capturing the web or the sheet of processed paper, in certain operative phases, in order to cause the paper to follow a predetermined path.
[0004] In particular, such systems are used to provide the main operations of cutting the paper, of transferring it quickly from a roller to another, of final folding the paper same. To this object, the machines are normally equipped either with mechanical clamps or with pneumatic suction means.
[0005] In the latter case, the air suction systems, owing to a certain vacuum grade created within the rollers, cause the processed paper to adhere on the roller surface by means of rows of suction holes.
[0006] In more detail, as shown diagrammatically in
[0007] In particular, the paper conveying roller is normally coupled, at an end thereof, to a bell-shaped vacuum distributor element
[0008] With this system, channels
[0009] A not efficient suction by the holes, on the other hand, can affect the successive operations of the machine causing paper jamming and stop of production.
[0010] In any case, the maximum air flow rate is limited.
[0011] In order to limit this drawback it is therefore necessary:
[0012] to limit the length of the roller and then the volume of the chambers in it; this causes a subsequent limitation in the maximum width of the paper that can be processed and then reduces productivity of the machines that have such rollers;
[0013] starting/stopping the suction of the air channel with a vacuum advance, so that the suction in all the holes starts/stops at a predetermined moment; with a vacuum advance, it is necessary to change the vacuum timing as varies the speed of operation of the machine;
[0014] working with a high vacuum grade for reducing the time necessary for a row of suction holes to be fully operative.
[0015] As described in U.S. Pat. No. 4,207,998 paper dragging rollers also exist formed by a fixed cylinder that form a longitudinal chamber, about which a concentric roller rotates formed by a inner stiff tubular shell having a plurality of holes, and an outer resilient tubular shell, having a plurality of deformable holes. When contacting the paper the deformable holes are open and bring into communication the paper with the holes of the inner shell and the suction chamber, preventing the roller from sliding with respect to the paper. The sealing ability of the holes, however is limited to the contact with a web of paper and with a certain pressure, whereby this type of roller is unsuitable for applications with sheets of paper. Furthermore, it is suitable only for narrow fields of suction.
[0016] It is an object of the present invention to provide a roller equipped with suction points for conveying a web or sheet of paper in paper converting machines, such as in particular rewinding, winding, interfolding machines, which allows to provide a high production rate even with a low vacuum grade and then not much expensive with respect to the prior art.
[0017] It is another object of the present invention to provide such a paper conveying roller for increasing productivity and flexibility of the machine on which it is mounted, in order to work webs or sheets of paper of different type and wide enough without affecting the efficiency of the process.
[0018] It is a particular object of the present invention to provide a method for conveying the paper that uses this roller.
[0019] These and other objects are achieved by the roller for conveying a web or sheet of paper in paper converting machines, such as rewinding, winding, interfolding machines, comprising a first cylindrical tubular body, equipped with a plurality of radial holes arranged according to substantially longitudinal rows, capable of rotating with respect to a second inner fixed co-axial body. The roller provides inside at least one chamber connected to a suction system, defined between the first and the second body by means of sliding sealing elements, suitable for being brought selectively in communication with at least one of said row of holes during the relative rotation of the bodies. This way, maintaining a fixed vacuum grade in the chamber, the holes that communicate with it are immediately available as elements for capturing the paper on the external roller surface.
[0020] In other words, a web or sheet of paper adheres to the external surface of the first body only in the portion of surface set between rows of holes that communicates with the suction chamber. The fact that a determined vacuum grade is steadily maintained allows to enable directly for suction the holes located in the portion of surface overlapping the suction chamber.
[0021] Therefore, it is possible to provide rollers of much more length and then of increasing the flexibility and productivity of the machines that use them.
[0022] Advantageously, also the second body is tubular cylindrical and the sliding sealing capability is obtained with two radial boards, between which at least one opening is present, which extends between the first and the second tubular body for all the length of the roller in order to define the suction chamber.
[0023] Preferably, to increase the outlet speed of the air through the suction chamber, a plurality is provided of apertures arranged longitudinally along the second cylindrical tubular body and within the portion thereof defined by the radial boards.
[0024] In particular, to assure a high sealing capability, the ends which in the suction chamber contact the inner surface of the first body can provide plastic inserts, for example of polymeric resin, which slide on the smooth inner surface of the first tubular body.
[0025] Preferably, the sealing capability of the suction chamber is achieved forcing elastically the radial boards against the inner surface of the first cylindrical tubular body. This way, the necessary side sealing conditions of the suction chamber are guaranteed without that the radial boards effect a high resistance against the relative rotation of the two cylindrical tubular bodies.
[0026] In a preferred embodiment each radial board can comprise a fixed portion, forming a guide arranged longitudinally with respect to the conveying roller, within which a bar can slide radially forced elastically against the inner surface of the first cylindrical tubular body.
[0027] According to a particular aspect of the invention a paper converting machine, such as a rewinding machine, a winder or an interfolding machine, comprises at least one paper conveying roller as above described.
[0028] According to another aspect of the invention a method for moving a sheet or a web of paper in paper converting machines, such as rewinding machines, winders, interfolding machines, uses a paper conveying roller comprising a first cylindrical tubular body equipped with a plurality of radial holes arranged according to substantially longitudinal rows. The method has the feature that the holes are selectively enabled for suction or for not suction by the relative rotation between the first cylindrical tubular body and a second inner fixed co-axial body connected to a suction system through at least one opening. The relative rotation between the two bodies brings selectively in communication a suction chamber, defined between the first and the second body, with at least one of said row of holes, the chamber being defined by means of sliding sealing elements arranged between the first and the second body.
[0029] Preferably, the sealing capability of the suction chamber is achieved forcing elastically the sliding sealing elements, which belong to the second fixed co-axial body, against the inner surface of the first cylindrical tubular body.
[0030] In the drawings,
[0031]
[0032]
[0033] Further characteristics and the advantages of the roller according to the present invention, equipped with suction points for conveying a web or sheet of paper in paper converting machines, will be made clearer with the following description of an embodiment thereof exemplifying but not limitative, with reference to the attached drawings wherein:
[0034]
[0035]
[0036] In
[0037] The inner surface of first cylindrical tubular body
[0038] The apertures
[0039] In particular, radial boards
[0040] This way, it is possible to define with high precision the portion of the roller surface
[0041] This is for example effected in case of an interfolding unit shown diagrammatically in
[0042] Therefore, rollers
[0043] the sheet is captured by roller
[0044] the passage of a sheet from an interfolding roller
[0045] Obviously, a roller can be made that enables to suction three couples of rows of holes all with a system according to the invention. For example, the inner second body may have three radial boards, forming three chambers, one not enabled to suction and two enabled to suction with a different vacuum grade.
[0046] The present invention is applicable at a desired interfolding, rewinding or winding machine which uses a roller according to the invention.
[0047] The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.