Roller for conveying a web or sheet of paper in paper converting machines and conveying method thus obtained

Abstract

An improved conveying roller for a web or a sheet in a paper converting machine comprises a first cylindrical tubular body having a plurality of radial holes arranged in substantially longitudinal rows, and a second fixed tubular body arranged coxially within the first cylindrical tubular body. The first cylindrical tubular body is capable of rotation relative to the second fixed tubular body. Slidable sealing elements are positioned between the first cylindrical body and the second fixed tubular body to define at least one suction or vacuum chamber. The chamber is suitable for being brought selectively in communication with at least one row of the radial holes during the relative rotation of the bodies.

Claims

1. A sheet folding unit comprising: two conveying rollers and two respective folding rollers working in cooperation with said conveying rollers, each of the folding rollers comprising first rows of holes connected to a first suction system by first suction channels and a first vacuum distributor, said first suction system having a first suction force, said first rows of holes arranged to capture from said conveying rollers a sheet of paper and to bring the sheet up to a point of contact between said two folding rollers, and each of the folding rollers comprising second rows of holes connected to a second suction system having a second suction force, wherein the second suction force of the second suction system is greater than the first suction force of the first suction system, said second rows of holes arranged for causing said sheet to pass from one folding roller to the other folding roller and to follow the other folding roller up to a folding point, each of the conveying rollers comprising a conveying system arranged for conveying said sheet to said point of contact and to release it to one of said folding rollers at one row of holes of said first rows of holes, said folding rollers further comprising: a first tubular body capable of rotating about an axis of rotation, said first tubular body having a plurality of couples of neighboring parallel rows of radial holes of said second rows of holes, a second tubular body within said first tubular body that extends for all length of said first tubular body and is always connected to a vacuum source, whereby said second tubular body is always under vacuum, an interposition means integral to said second tubular body and arranged between said second tubular body and said first tubular body for defining a suction chamber between said second tubular body and said first tubular body, said interposition means arranged in such a way that by the rotation of said first tubular body said interposition means selectively causes said suction chamber to connect with one row of holes at a time of said couples of neighboring parallel rows of radial holes of said second rows of holes at determined angular positions of said first tubular body and to provide the second suction force on a sheet captured by one row of holes of said first rows of holes and to cause said sheet to pass from one folding roller to the other folding roller and to follow the other folding roller between said positions up to said folding point.

2. A sheet folding unit according to claim 1, wherein said interposition means comprises sealing elements sliding against an inner surface of said first tubular body.

3. A sheet folding unit according to claim 2, wherein said sliding sealing elements are forced elastically against said inner surface of said first tubular body.

4. A sheet folding unit according to claim 1, wherein said interposition means provides two radial boards that radially extend from said second tubular body up to said first tubular body for all the length of said first and second tubular bodies to define said suction chamber, between said radial boards at least one opening being provided that brings in communication said chamber with an inner space within said second tubular body that in turn is connected to said vacuum source.

5. A sheet folding unit according to claim 4, wherein there is provided a plurality of apertures arranged longitudinally along said second cylindrical tubular body and within the portion thereof defined by said radial boards in said chamber.

6. A sheet folding unit according to claim 4, wherein each radial board comprises 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 forming a sliding element.

7. A sheet folding unit according to claim 4, wherein said first suction system, in order to capture from said conveying rollers a sheet of paper and to bring the sheet up to a point of contact between said two folding rollers, comprise a bell-shaped vacuum distributor arranged at an end of said folding roller and selectively communicating with the rotation of said first tubular body with longitudinal channels arranged in said first tubular body and with a respective row of holes of said first rows of holes.

8. A method of folding a sheet, said method comprising: conveying a sheet of paper from a conveying roller to a folding roller of a couple of folding rollers, each of the folding rollers comprising first rows of holes connected to a first suction system by first suction channels and a first vacuum distributor, said first suction system having a first suction force, wherein said first rows of holes are arranged to capture from said conveying rollers a sheet of paper and to bring the sheet up to a point of contact between said folding rollers, and each of the folding rollers comprising second rows of holes connected to a second suction system having a second suction force, wherein the second suction force of the second suction system is greater than the first suction force of the first suction system, said second rows of holes being arranged to cause said sheet to pass from one folding roller to the other folding roller and to follow the other folding roller up to a folding point, each of the conveying rollers comprising a conveying system arranged for conveying said sheet to and to release it to one of said folding rollers at one row of holes of said first rows of holes, said folding rollers further comprising: a first tubular body capable of rotating about an axis of rotation, said first tubular body having a plurality of couples of neighboring parallel rows of radial holes of said second rows of holes, a second tubular body within said first tubular body that extends for all length of said first tubular body and is always connected to a vacuum source, whereby said second tubular body is always under vacuum, an interposition means integral to said second tubular body and arranged between said second tubular body and said first tubular body for defining a suction chamber between said second tubular body and said first tubular body, wherein said interposition means is arranged between said second tubular body and said first tubular body in such a way that said angular positions are located between said point of contact and said folding point; wherein said interposition means arranged in such a way that by the rotation of said first tubular body said interposition means selectively causes said suction chamber to connect a row of holes at a time of said couples of neighboring parallel rows of radial holes of said second rows of holes at determined angular positions of said first tubular body and to provide the second suction force on a sheet captured by one row of holes of said first rows of holes and to cause said sheet to pass from one folding roller to the other folding roller and to follow the other folding roller between said positions up to said folding point.

9. A method according to claim 8, wherein said step of providing in said folding roller a first suction system arranged to capture from said conveying rollers a sheet of paper and to bring the sheet up to a point of contact between said folding rollers, comprises providing a bell-shaped vacuum distributor at an end of each of said folding rollers and selectively communicating with a vacuum source, by the rotation of said first tubular body, with longitudinal channels arranged in said first tubular body and with a respective couple of rows of holes of said first rows of holes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, FIGS. 1 and 2 already commented in the introductory part show the following:

(2) FIG. 1 is a perspective view of a paper conveying roller for paper converting machines and of the vacuum distributor to it associated, as known in the art;

(3) FIG. 2 shows a longitudinal cross section of a conveying roller according to the prior art coupled to a vacuum distributor.

(4) 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:

(5) FIGS. 3 and 4 show a cross sectional view of a paper conveying roller for paper converting machines, according to the present invention, in two relative different positions between the first and the second cylindrical tubular body, wherein said roller has a suction system as used in the sheet folding unit like that of FIG. 5;

(6) FIG. 5 shows a cross sectional view of a sheet folding unit of an interfolding machine that has conveying rollers according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) In FIGS. 3 and 4, a cross sectional view is shown of a roller 1 used for conveying a web or sheet of paper 20 for a sheet folding unit like that of FIG. 5.

(8) The roller 1 comprises a first outer cylindrical tubular body 2, equipped with a plurality of radial holes 3 arranged according to substantially longitudinal rows, capable of rotating with respect to a second inner fixed body 4, co-axial to the former and connected to a suction system not shown. The second body 4, which as shown in the embodiments of FIGS. 3 and 4 has tubular cylindrical geometry like first body 2, has a plurality of apertures 5 and two radial boards 7 at opposite sides with respect to apertures 5.

(9) The inner surface of first cylindrical tubular body 2, radial boards 7 and the external surface of second tubular body 4 define a suction chamber 6 that, during the relative rotation of the two bodies, brings selectively in communication some rows of holes 3 of first cylindrical tubular body 2 with the apertures 5 of second tubular body 4 and then with the suction system of the machine. Therefore, a web or sheet of paper 20 adheres to the external surface of first body 2 only in the portion P1P2 of the surface set between the rows of holes 3′ that communicate with the suction chamber (FIG. 4).

(10) The apertures 5 made on the surface of second tubular body 4 are arranged longitudinally and are enough to allow a quick outlet of the air present in holes 3′ that in turn overlap to the suction chamber 6. This is possible also because chamber 6 is fixedly kept at a determined vacuum grade.

(11) In particular, radial boards 7, between which the apertures 5 extend, are arranged radially for all the length of second cylindrical tubular body 4 and are have high sealing capability of the suction chamber from the remaining space comprised between bodies 2 and 4. This result is obtained with radial boards having a fixed portion 10, integral to second inner tubular body 4 and forming a longitudinal channel, and a movable portion 7 that engages with fixed portion 10 and pushes elastically against the inner surface of first tubular body 2 urged by springs 9. Springs 9 can be located, as in the case of FIGS. 3 and 4, about pins 11 which are constrained in a housing within fixed portion 10.

(12) This way, it is possible to define with high precision the portion of the roller surface 1 enabled for the suction of the paper and to make easier possible cutting operations, which can be made between two adjacent rows of holes 3.

(13) This is, for example, effected in case of a sheet folding unit of an interfolding unit shown diagrammatically in FIG. 5. In particular, conveying rollers 1 are provided as above described that work in cooperation with folding rollers 40. The unit works for example in the way described in EP0982255 or in EP0982256 in the name of the same applicant.

(14) More precisely, in a folding unit like FIG. 5, sheets 20 coming from conveying rollers 1 are captured by suction rows 103 (similar to FIG. 2) of respective folding rollers 40 and are then dragged up to the point of contact 41 between folding rollers 40.

(15) Therefore, contemporaneously, there are two sets of sheets coming from the left and from the right, which are shifted from each other. Suction rows 103 of folding rollers 40 capture the head of each sheet 1 and then they become inactive at point of contact 41.

(16) Suction rows 3′ become active at point of contact 41 and then become inactive at folding point 42.

(17) This way a sheet 20 coming from one folding roller 40 (in FIG. 5 coming from left folding roller) is captured at point of contact 41 by the rows 3′ of the other folding roller 40.

(18) In the meantime, a sheet 20 that was coming from the other folding roller 40 (right) and that had been captured at point of contact 41 has been brought up to folding point 42 by the other (left) folding roller 40.

(19) So, at folding point 42, the sheet is free to fold and form the stack 50.

(20) In particular, at contact point 42, there are two sheets overlapping, and the folding unit has to capture both.

(21) Therefore, suction row 103 is enough for capturing the sheet from the conveying roller 1 and to bring it to contact point 41. Instead, such a suction row 103 would be not precise and is not strong enough to pick up exactly at contact point 41 two sheets together, and to bring them together up to folding point 42.

(22) According to the invention, the suction force of suction rows 3′ is suddenly strong, and precise, because it is always under vacuum, and as soon as a suction row 3′ is at suction chamber, it is immediately active with a strong suction force, and can capture two overlapping sheets.

(23) With reference to the particular and not limiting embodiment of FIG. 5, differently from rollers 1, rollers 40 have six couples of rows, where three couples of rows of holes spaced 120° capture the end of a sheet, and other three couples of rows of holes spaced 120°, shifted 60° with respect to the former, capture through the central portions of a sheet, the end of a second overlapped sheet and ready for being interfolded. Therefore, the first three couples of holes are enabled for suction between two consecutive cuts, for a sector between the point of contact of rollers 1 with rollers 40 up to the contact between the two opposite rollers 1, whereas the other three couples of holes must be enabled for suction between the contact between the two rollers 40 and the point where the fold is made.

(24) Therefore, rollers 40 are shown in FIG. 5 having a “mixed” structure as a combination of a roller of prior art and a roller 1 according to the invention. More in detail: the sheet is captured by roller 1 up to the point of contact between two rollers 40 by means of a traditional suction system, namely a first suction system, with suction channel and bell-shaped vacuum distributor; in fact, for capturing and holding the sheet a light vacuum grade and a not high angular precision are enough and this system is sufficient; the passage of a sheet from an interfolding roller 40 to the other is made with a second suction system according to the invention, since higher angular precision and higher vacuum in suction are required.

(25) 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.

(26) The present invention is applicable at a desired interfolding, machine which uses a sheet folding unit according to the invention.

(27) 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.