Abstract:
The present invention refers to a folding unit of a high-speed folding machine, for folding sheet-like products (S) made of tissue paper or the like. Such a unit comprises a first folding cylinder ( 3 ) with pneumatic means ( 5, 6, 5′, 6′ ) adapted to promote an orderly and precise release of the material in the folding step even at high speed.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention concerns the field of apparatuses for the production of paper products such as tissue paper, napkins or other products in general with high speed folding machines operating with a vacuum system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Such machines normally comprise two or more mutually cooperating folding cylinders, according to the type of product to be made. Work speed, and consequently productivity limitations, substantially depend upon the system for holding the material to be folded over the cylinders along the direction that is transverse with respect to the advancing direction. For such a purpose according to the prior art it is foreseen for there to be holes or slots along the periphery of the folding cylinders, which are connected to a vacuum source and are normally driven by sequential valves that are arranged at the axial end(s) of the cylinders themselves. 
         [0003]    The most critical step is that in which the paper segments pass from a first cylinder, which normally provides also for a transversal cut of the paper, to a second cylinder so as to indeed execute the first transversal folding line. It is in this step that at the high speed at which such machines operate, there is the difficulty of ensuring a correct movement of the product from the condition in which it adheres to the first cylinder to that in which it adheres to the second cylinder. In order to minimise the risk of defects or malfunctioning it is necessary for the work speed to not exceed a set limit. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention is to provide a system that solves such a problem, by providing a cross-wise folding unit for folding the product that makes it possible to increase production speed beyond the current production limits, obtaining at the same time a high quality product, i.e. without the defects caused today by the passage of the product through the folding cylinders. 
         [0005]    According to the invention, such an object is achieved with the folding unit as defined in the first of the attached claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The characteristics and advantages of the folding unit according to the present invention shall become apparent from the following description of its embodiments, which are described as an example and not for limiting purposes, with reference to the attached drawings, in which: 
           [0007]      FIG. 1  is a schematic side view of a folding unit according to the invention, with parts that have been removed for the sake of clarity; 
           [0008]      FIG. 2  is a side view of a first folding cylinder; 
           [0009]      FIG. 3  is a sectional view of the first cylinder according to the arrows Ill of  FIG. 2 ; 
           [0010]      FIGS. 4 and 5  are a side view and a sectional view according to the arrows V-V, respectively, of a first sequential valve, which is arranged on a first side (left side according to the view of  FIG. 3 ) of the first folding cylinder; 
           [0011]      FIGS. 6 and 7  are a side view and a sectional view according to the arrows VII-VII, respectively, of a second sequential valve that is arranged on a second side (right side according to the view of  FIG. 3 ) of the first folding cylinder; and 
           [0012]      FIGS. 8 and 9  are a side view and a sectional view according to the arrows IX-IX, respectively, of a single sequential valve that, according to an embodiment that is different from those of  FIGS. 4 to 7 , is arranged on one side of the first folding cylinder. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    With reference to the above figures, a folding unit according to the present invention can advantageously provide for one or more adjacent channels which operate in parallel and it is fed with continuous bands of paper  1 , having one or more layers (plies), with or without longitudinal folds with respect to the advancing direction. 
         [0014]    The unit according to the present invention comprises, as known, a cutting cylinder  2  which cooperates with a first folding cylinder  3  so as to provide for cutting the product into segments with two blades  16  that are diametrically opposite one another (on the cutting cylinder  2 ) and two corresponding anvil grooves or counter-blades  17  (on the first folding cylinder  3 ), starting from a single band of paper  1 . Subsequently, the same first folding cylinder  3  and a second folding cylinder  4  that counter-rotates with respect to the first cooperate in a tangential manner, at a pinch point in which the material is held by the second cylinder, so as to provide for folding the paper S obtained from the band  1  by means of cutting. 
         [0015]    The first folding cylinder  3  comprises suction channels  5 ,  5 ′ which extend axially near to the work surface  3   a , for the passage of a vacuum that is suitable for keeping the band or segments of paper over such a surface. For such a purpose the channels  5 ,  5 ′ continuously cover the entire circumferential development of the cylinder, opening up on the surface  3   a  through holes  6 ,  6 ′. The band of paper  1  is held in this way during cutting and thereafter the cut segment S is also held up to a release point from the first cylinder  3 , with a vacuum of a sufficient strength, which is regulated through two sequential valves  7 ,  13  (not represented/visible in  FIG. 1  but shown isolated in  FIGS. 4 to 7 ) that are alongside one another and in contact on respective axial ends (or sides) of the aforementioned first cylinder. 
         [0016]    Each valve is in practice a full fixed disc that blocks the ends of the channels  5  except for at suitably designated slots  9 ,  11 ,  14 , which will be described in greater detail hereafter, which over certain set arcs of rotation make it possible for the vacuum flow to pass, said flow being generated and supplied by vacuum-generating devices that are arranged outside and are not represented. In any case, it should be noted that in  FIGS. 5 and 7  intakes  8 ,  12 ,  15  for pneumatically connecting the slots to the vacuum-generating devices placed upstream. 
         [0017]    The suction channels extensively involve the work surface  3   a , since they are spaced apart with a suitable density with respect to the evolution of the circumference. The majority of the channels, indicated with reference numeral  5 , are open on the end side facing the first sequential valve  7  and are closed on the opposite side, so that the pneumatic circulation inside the aforementioned channels  5  is only determined by the first valve. Some channels, on the other hand, in particular two channels  5 ′ that are diametrically opposite one another in an immediately adjacent position with respect to the counter-blades  17  (upstream considering the rotation direction of the first cylinder) are open on the end side facing the second sequential valve  13  and are closed on the side of the first valve, so that the pneumatic circulation inside the (two) channels  5 ′ is determined only by the interference with the second valve  13 . 
         [0018]    The tangential cooperation point between the first and the second folding cylinder is that in which the segment S of paper is released from the first cylinder  3 , through gripping of the second cylinder  4  along a transversal intermediate line; consequently the paper becomes folded along such a line on the second cylinder  4 . For such a purpose it is foreseen for there to be, in a suitable position on respective portions of the second folding cylinder  4 , sets of axial channels  20  and holes  21  which open radially on the work surface  4   a  of the cylinder, which are capable of providing for gripping or pinching the sheet through suction. 
         [0019]    Returning now to the two sequential valves  7 ,  13  and to the relative slots, the first sequential valve  7  has two consecutive slots  9 ,  11 , which are separated by an interruption, i.e. by a solid separating wall  10 , that overall extend for an arc of rotation of around 270°. A first slot  9  occupies around 180° of rotation and, in it, through the intake  8 , a high vacuum is generated, which results through the channels  5  and the holes  6  in a suction by the work surface  3   a  on the paper S. 
         [0020]    The subsequent slot  11  that extends for an arc of rotation of around 90° (following the passing on the pinch point by the second cylinder  4 ) is, on the other hand, fed through the intake  12  with a rough vacuum or no vacuum (according to the characteristics of the material being processed), so as to transmit, again through the channels  5  and the holes  6 , low or null suction that promotes the release of the paper. 
         [0021]    Instead, as far as the second sequential valve  13  is concerned, only one slot  14  is provided, for the generation of high vacuum that is transmitted through the two channels  5 ′ and relative holes  6 ′. This slot  14  extends by covering the same 180° of the first slot  9  of the first valve, and further on develops over a substantial part of the 90° of the second slot  11 . With respect to the latter, the slot  14  ends with an advance of a certain angle (typically between 15° and 30°, thus corresponding to a rotation angle downstream of the release point comprised between 60° and 75°). 
         [0022]    In such a way, through the holes  6 ′ that are immediately adjacent to the cut performed at the counter-blade  17 , and thus in the immediate proximity of the head or frontal edge of the segment S (i.e. the edge that advances at the front when using the rotational advance direction as a reference), a suction is exerted which firmly holds such edge over the first cylinder (see indeed the operation step depicted by  FIG. 1 ) for the entire displacement, also downstream of the folding point and also and especially in the step of incipient folding, when on the remaining part of the segment there is progressively less suction so as to promote the release (effect of the second groove  11  of the first aforementioned valve  7 ). 
         [0023]    The operational behaviour of the unit according to the invention is then immediately clear to a man skilled in the art, considering that anything that was not been specifically described is indeed analogous to what is well known in the conventional units. Thanks to the feature introduced by the second sequential valve, in a structurally very simple manner, there is the possibility of avoiding deformations of the front edge even at high production speed, with consequently lower wastes and an increase in the quality of the product. 
         [0024]    According to  FIGS. 8 and 9 , in a possible different embodiment the functions of the second sequential valve can be integrated on a single valve  107  thorough a double array of slots, which are radially offset to a greater or lesser extent. In such figures the slots  109  and  111 , with the relative suction intakes, correspond to the previous slots  9  and  11  of the first embodiment, whereas a double slot  114   a ,  114   b  operationally corresponds to the slot  14  of the first example. Two consecutive and separated segments  114   a ,  114   b  are used in this case for a possible differentiation of suction (higher or lower vacuum) in two respective advancing steps upstream and downstream of the release/pinch point, respectively, also in connection with the hold at the front edge. Such a differentiation, which can be useful according to the type of material being treated, can also be obtained in the first embodiment by separating the groove  14  into two distinct segments. 
         [0025]    Obviously, the structure of the first folding cylinder (not shown) must be correspondingly adapted, since in this case the two channels corresponding to the channels  5 ′ of the first embodiment, i.e. the channels that are suitable for holding the front edge of the segment and for communicating with the slots  114   a ,  114   b , are made in a position that is radially more centred with respect to the other normal peripheral channels which correspond to the channels  5  of the first embodiment and in which there is the pneumatic opening/closing action of the slots  109  and  111 . 
         [0026]    It is worth underlining that by high vacuum, in the present description, it is meant a high vacuum, ultra high vacuum or extremely high vacuum according to the definitions that are commonly and conventionally used in the field. 
         [0027]    The present invention has been described with reference to preferred embodiments thereof. It should be understood that there can be other embodiments that belong to the same inventive core, within the scope of protection defined by the appended claims.