WO2012131613A1

WO2012131613A1 - A folding unit for sheet-like products

Info

Publication number: WO2012131613A1
Application number: PCT/IB2012/051512
Authority: WO
Inventors: Renzo Tommasi
Original assignee: Rent S.R.L.
Priority date: 2011-03-30
Filing date: 2012-03-29
Publication date: 2012-10-04
Also published as: ITFI20110048A1

Abstract

The present invention concerns a folding unit of high-speed folding machine for folding tissue products (7) or the like. The unit comprises a first folding cylinder (3) with air ejection means assisting the detachment of the material and its hold by a second folding cylinder (4).

Description

A FOLDING UNIT FOR SHEET-LIKE PRODUCTS

DESCRIPTION

Field of the invention

The present invention relates to the field of apparatus for the production of paper products such as tissue, napkins or other similar products with high speed folding machines operating with a vacuum system.

Background of the invention

In such machines there are normally provided two or more mutually cooperating folding cylinders, as a function of the type of product to be realized. The limits to the working speed and, consequently, to productivity, are substantially related with the system that keeps the products to be folded in adherence to the cylinders along a crosswise line (i.e. crossing the feeding direction of the material). To this purpose, according to the known art, holes or slots are formed in the periphery of the cylinders, communicated with a vacuum source and controlled by sequential valves arranged at one or both axial ends of the same cylinders.

The most critical step is that in which the tissues pass from a first cylinder (normally providing also for a crosswise cut of the feeding material) to a second cylinder for actually carrying out a first crosswise line fold. It is in this step that, at the high working speeds of these machines, the material tends to detach from the folding cylinders, as a result of the pressure gradient on the two faces of the tissue while the same tissue is displaced from a condition of adherence to the first cylinder to a condition of adherence to the second cylinder. In order to minimize the risk of defects and malfunctioning, it is necessary to keep the working speed under a certain safety limit.

Summary of the invention

It is the object of the present invention to provide a system that solves the above problem, with a unit for carrying out crosswise folds of the product allowing for an increase of the productive speed over the present limits, obtaining at the same time a high quality product, that is a product without the defects now caused by the passage of the tissues between the folding cylinders.

According to the invention, this object is achieved with a folding unit as defined in the first of the appended claims.

The main advantage of the present invention is given by the fact that, ejecting high-pressure air between the work surface of the first folding cylinder and the tissue product piece in the release step towards the second folding cylinder, pressure is increased in the region so defined, assisting the displacement and the folding of the product. Preferably, and still with the same result, a depression is also carried out through a chamber arranged on the external side of the product, for decreasing the external pressure in the release area, with respect to ambient pressure that normally hinders the progress of the material. In this way, the risk of a loss of the hold by the second folding cylinder on the material, or in any case of an inaccurate hold with consequent undesired defects and warps on the folded products, is further reduced.

Brief description of the drawings

Further characteristics and advantages of the folding unit according to the invention will become clearer from the following description of an embodiment thereof, given as a non-limiting example, with reference to the attached drawings, in which:

- figure 1 is a schematic side view of a folding unit according to the invention, with the cylinders in a rotation position taken as a conventional reference as zero position;

- figure 2 represents a cross section of the unit taken along line ll-ll of figure 1 ;

- figure 3 shows a detail of the unit as in figure 1 in a material feeding step following a rotation of the cylinders of 20° with respect to the zero position of figure 1 ;

- figures 4 and 5 are analogous to figure 3, but with a rotation of the cylinders respectively of 40° and 60°;

- figure 6 is a top plan view of the unit of figure 1 ;

- figures 7 and 8 are respectively a side view and a cross section view taken along line VIII-VIII of a sequential valve of a first folding cylinder; and

- figure 9 is an enlarged side view of the first folding cylinder.

Detailed description of the invention

With reference to the above figures, a folding unit according to the present invention can advantageously provide for one or more production lines working in parallel (as represented in figure 6 where two side by side lines are defined by a single cylinder assembly) and is fed with continuous paper bands 2, having one or more tissue layers (plies), with or without longitudinal folds extending along the feeding direction.

The unit according to the invention comprises, as known, a cutting cylinder 1 cooperating with a first folding cylinder 3 for cutting the product in pieces with two diametrically opposed blades 7 (in the cutting cylinder 1 ) and two matching anvil grooves or counter-blades 8 (in the first folding cylinder 3), starting from a continuous paper band 2. Subsequently, the same first folding cylinder 3 and a counter-rotating (with respect to the first) second folding cylinder 4 tangentially cooperate to fold the paper product or segment S obtained from the band 2 as a result of the cut.

The first folding cylinder 3 comprises suction channels 5 extending parallel with the axis of the cylinder in the proximity of a work surface 3a of the same cylinder, permitting the passage of a depression adapted to hold the paper band or the segments in adhesion to such surface. To this purpose the channels 5 are extensively distributed over the whole circumferential development of the cylinder, being opened on the work surface 3a through holes 6. Such holding action is kept on the paper band during the cut and subsequently on the cut segment S up to a point of release from the first cylinder 3, with a sufficiently strong depression, controlled and adjusted by means of sequential valves 50 (figure 7) contacting sideways respective axial ends of the first cylinder. Each valve consists of a fixed disc that shuts the ends of the channels 5 but in correspondence with a passage 51 , that along a predetermined rotation angle leaves way to the depression flow, created by and supplied from suction means arranged outside, not shown.

Further displaced towards the inside of the same first folding cylinder 3, avoiding intersections with the channels 5, air ejection channels 10 are formed, in turn opened on the work surface through radial holes 1 1 . Via the channels 10 and the holes 1 1 high-pressure air is ejected from the work surface 3a, the flow of which is controlled by a further arc shaped passage 52, or ejection passage, formed in a suitable position, downstream of the depression passage 51 , on each sequential valve 50. The ejection channels 10 are in this case arranged according to two pairs of side by side channels, the two pairs being, still in the present embodiment, at mutually opposed (poles apart) regions, in intermediate position with respect to the counter- blades 8 (staggered by 90°) and then in correspondence to the folding line of the paper segment S.

An group of depression chambers 30, communicated with the depression feeding system or vacuum source through ducts 31 , is arranged so as to carry out a suction in the tangential cooperation area (release point 13) between first and second folding cylinder, an area in which the tissue segment S is pinched by the second cylinder 4 and thus released from the first cylinder 3 along an intermediate crosswise line, to become folded along said line over the second cylinder 4. To this purpose, the second folding cylinder 4 provides, in suitable positions at respective release portions, axial channels 14 and holes 9 opening on a work surface 4a of the cylinder, adapted to pinch the paper by suction. The passage of the channels 14 in the release and pinch point or area 13 is synchronized with the passage in the same area of the channels 10 of the first cylinder 1.

Turning back to the depression chamber 30, two in the example, one for each working line, according to an advantageous solution they consist of funnel-shaped box-like frames, each comprising a base wall 30a, to which the duct 31 is connected, arranged substantially over a common tangential plane of the two folding cylinders, and curved side walls 30b that follow the work surfaces of the cylinders, in close proximity thereto. The curved side walls 30b define an end suction mouth 30c facing precisely the release point 13. The provision of the depression chambers results indeed in isolating, and least partially, from the outside, the product release area towards the second folding cylinder, establishing, in the isolated area, a pressure lower than the ambient pressure.

Furthermore, it can be noticed in each sequential valve 50 a second passage 53 for a flow of a suction, in this case at lower power than the previous cases and with a purpose that will result clearer hereafter, formed along an arch of the same diameter and subsequently to the first above mentioned depression passage 51 .

The unit according to the invention works in the following manner. In a working cycle the paper band 2, once cut at its head (corresponding to a tail cut of a previously processed segment) at an inlet or cut point 12 - that is the point of tangential cooperation with the cutting cylinder 1 along a common generatrix - advances being held by the first folding cylinder 3 at the same peripheral speed of the same cylinder. The material is held on the work surface 3a tank to the holes 6 along an angle of rotation between the above mentioned inlet point 12 and the release point 13, that is the point of tangential cooperation with the second folding cylinder 4 along a common generatrix. In the depicted embodiment, and typically, said points are angularly spaced by a rotation of 180°, as also shown by the angular extension of the holding depression passage 51 in the sequential valve 50. The two points are in fact represented in figure 7 by ends P1 and P2 of said passage 51 .

Once the release point 13 is overcome, as a result of the subsequent passage or slot 53 and still via channels 5 and holes 6, a depression is applied through the work surface 3a, between two points indicated at P3 and P4 and corresponding to the end points of the same slot. Such depression has however a lower power than the previous holding depression, for instance and preferably having a value of about one third of the vacuum fed between the points P1 and P2. In this way a certain holding power on the paper product, although reduced, is in any case maintained, this being useful to permit the advancement of the material along the peripheral work surface of the first cylinder 3, without hindering and thus jeopardizing the release to the second folding cylinder 4. The angle between P3 and P4 is advantageously of 90°.

A tail cut of the segment S has been in the meantime carried out when the head of the same segment has reached the point P2. The position of figure 1 , that can be taken as a reference of a "zero rotation" position, corresponds to a segment that is about to be pinched by the second cylinder 4, and then with the head end of the tissue segment that has reached the point P4. In this condition, in the present and most common embodiment, the fold is at the centre of the length of the segment.

At this stage, once also point P4 has been overcome, any holding action on the material by the channels 5 is completely stopped, and a depression is switched on in the channels 14 of the second folding cylinder 4, by means of a sequential valve analogous to the previous one and not shown in the drawings. The second cylinder 4 takes hold of the segment S, which is released from the first cylinder 3 (figure 3). In order to assist this high-speed working step, high pressure air is ejected through the channels 10 and relative holes 1 1 controlled by the passage 52 of the valve 50.

Figure 3 precisely shows the folding step, the first folding cylinder 3 having further rotated of an angle a' of 20° with respect to the zero position of figure 1 , while figures 4 and 5 show subsequent steps, in which it is clear the progression of the folding operation of the segment S, corresponding to rotations respectively of angles a" e a'" of 40° and 60°. The volume delimited between the segment S being released (a flap of the segment being progressively held by the second cylinder 4) and the work surface 3a of the first folding cylinder, indicated in the three just cited figures respectively with V1 , V2, and V3, progressively increases. In this stage the ejection channels 10 and the holes 1 1 keep on feeding high pressure air into said volume, with the effect of significantly reducing the pinch demanded to the second folding cylinder 4, that is to its suction system comprising the channels 14 and the holes 9.

During the whole release and folding step of the segment S, also the depression chamber 30 is turned on, creating in the region involved a depression of variable strength depend ing on the working speed. This contributes to decreasing the resistance opposing the release movement of the segment S, with respect to the resistance occurring at ambient pressure, with a further assistance to the orderly transfer of the folded product to the second folding cylinder.

It is then provided a folding unit that offers a remarkable increase in working speed and accuracy, having the further advantage of permitting also operation with depression power exerted by the pinch/hold means of the second folding cylinder 4 (channels 14 and holes 9) considerably lower than in the traditional units, with a resulting significant power saving.

Obviously, the number and position of the air ejection means (such as the channels 10) may vary depending on the design features of the unit.

The present invention has been described with reference to its preferred embodiments. It should be understood that there can be other embodiments that take advantage of the same inventive core within the scope of protection defined by the appended claims.

Claims

1 . A folding unit for folding sheet-like products (S) made of tissue paper or the like, comprising a first folding cylinder (3) and a second folding cylinder (4) mutually counter-rotating and tangentially cooperating in a release and pinch area to carry out the folding of said products (S), said first folding cylinder (3) comprising a work surface (3a) and vacuum means (5, 6) adapted to hold said products over said work surface (3a), at least a release portion being defined on said work surface (3a), said portion being adapted to pass in said release and pinch area in synchrony with a corresponding pinch portion of a work surface (4a) of said second folding cylinder (4), the unit being characterized in that said first folding cylinder (3) comprises air ejection means (1 0, 1 1 ) for ejecting pressurized air from said work surface (3a), said air ejection means (10, 1 1 ) being arranged at least in said release portion.

2. The unit according to claim 1 , comprising selective operation means of said air ejection means (10, 1 1 ), adapted to command the ejection of air along a limited arc of rotation of said first folding cylinder (3) starting from, and downstream of, said release and pinch area.

3. The unit according to claim 2, wherein said air ejection means comprise for each release portion at least one axial channel (1 0) communicating with an external vacuum source and opened to said work surface via a distribution of radial holes (1 1 ).

4. The unit according to claim 3, comprising at least one axial channel (10) on each of two diametrically opposed release portions of said work surface (3a) of said folding cylinder (3).

5. The unit according to claim 4, comprising for each release portion a couple of axial channels (10) with respective distributions of radial holes (1 1 ).

6. The unit according to any of the claims from 3 to 5, wherein said selective operation means comprise at least a sequential valve (50) comprising a disc arranged on an axial end side of said first folding cylinder (3) and adapted to close said at least one axial channel (10), an arc-shaped air ejection passage (52) being formed in said disc for corresponding with said channel (10), so that pressurized air coming from an external source is fed to said channel (10) in said limited arc of rotation of said first folding cylinder downstream of said release and pinch area.

7. The unit according to claim 6, wherein said vacuum means of said first folding cylinder (3) comprise a number of axial channel (5) opening on said work surface (3a) via respective distribution of radial holes (6), said at least one air ejection axial channel (10) being formed at a position displaced towards the centre with respect to the vacuum channels (5), said valve comprising a first arc-shaped vacuum passage (51 ), adapted to correspond with said vacuum channels (5) to permit the passage of a suction flow driven by an external vacuum source, said first vacuum passage (51 ) being formed upstream of, and in more peripheral position than, said air ejection passage (52).

8. The unit according to claim 7, wherein said valve further comprises a second arc- shaped vacuum passage (53) adapted to correspond with said vacuum channels (5), arranged downstream of said first vacuum passage (51 ) and running sideways with said air ejection passage (52) for at least part of its circumferential development, said second arc-shaped vacuum passage (53) being adapted to permit the passage of a suction flow driven by an external vacuum source, at a lower power than the suction driven through said first vacuum passage (51 ).

9. The unit according to claim 8, wherein the value of said lower power suction driven through said second vacuum passage (53) is of about one third the value of the suction driven through said first vacuum passage (51 ).

10. The unit according to any of the previous claims, comprising external vacuum means (30) arranged so as to face said release and pinch area between the first (3) and the second (4) folding cylinder to isolate from the outside, at least partially, the release and pinch area and permitting the establishment, in the space delimited by said cylinders (3, 4) and said external vacuum means (30), of a pressure lower than the ambient pressure.

1 1 . The unit according to claim 1 0, wherein said external vacuum means (30) comprise at least one vacuum chamber (30) comprising a reversed funnel box-shaped frame defined by a base wall (30a), in which a duct (31 ) opens, said duct being communicated with a vacuum source, said wall (30a) being arranged substantially over a common tangential plane of the two folding cylinders, the chamber (30) further comprising curved side walls (30b) that follow respective work surfaces of the cylinders, adjacent with the same, said curved side walls (30b) delimiting an end suction port (30c) facing the release and pinch area.

12. A method for folding sheet-like products (S) made of tissue paper or the like by means of a first folding cylinder (3) and a second folding cylinder (4) mutually counter- rotating and tangentially cooperating in a release and pinch area to carry out the folding of said products (S), the method comprising: exerting a vacuum over a work surface (3a) of the first folding cylinder (3) to hold said products over said work surface (3a); and pinching said products by said second folding cylinder (4) when a release portion of said work surface (3a) passes in said release and pinch area, in synchrony with a corresponding pinch portion of a work surface (4a) of said second folding cylinder (4), the method being characterized in that pressurized air is ejected from said work surface (3a) to assist the release of the products from said surface when said release portion of said work surface (3a) passes in correspondence to said release and pinch area.

13. The method according to claim 12, wherein said ejection of air is operated over a limited arc of rotation of said first folding cylinder (3) starting from, and downstream of, said release and pinch area.

14. The method according to claim 12 or 13, wherein said ejection of air is operated as each of two diametrically opposed release portions of said work surface (3a) of said first folding cylinder (3) pass in said release and pinch area.

15. The method according to any of the claims from 12 to 14, wherein said ejection of air is operated in a coordinated manner with a stop of the vacuum exerted by said work surface (3a) upstream of said release portion and with a reduction of the vacuum exerted by said work surface downstream of said release portion.

16. The method according to claim 15, wherein the reduced vacuum has a value of about one third of the vacuum exerted by said work surface (3a) upstream of said release portion.

17. The method according to any of the claims from 12 to 16, wherein an external vacuum is exerted so as to involve said release and pinch area between the first (3) and the second (4) folding cylinder so as to isolate from the outside, at least partially, the release and pinch area and to establish in said area a pressure lower than the ambient pressure.

18. A folding cylinder such as the first folding cylinder (3) of the unit according to any of the claims from 1 to 1 1.