Wrapping machine for single or grouped and/or stacked products, in packs of thermoplastic material obtained from film unwound from a reel and related operating method

Abstract

There is described a machine for packaging products in tubular wrappings of thermoplastic material obtained from continuous film unwound from a reel, equipped with a double transverse heat-sealing and intermediate cutting assembly that, with a horizontal translation movement, accompanies the pack that the assembly is closing the trailing end of to be unloaded while it is simultaneously closing the leading end of the tubular wrapper of the future pack that the heat-sealing and cutting assembly, also due to the presence thereon of pressers and counter-pressers, extracts from a tube-forming and longitudinal heat-sealing mandrel and that, by the same assembly, is separated from the pack upstream with a transverse cut. At the end of its active movement, the transverse heat-sealing and cutting assembly opens and with a horizontal movement in the opposite direction to and at a higher speed than the preceding one returns to the cycle start position, upstream of a new pack already filled and ready to be heat sealed at the trailing end and accompanied to be unloaded, repeating the cycle described. The transverse heat-sealing and cutting assembly is aided by a conveyor that supports and advances the packs being formed and those finished and separated, and that is equipped with a gap with variable geometry, which opens during the active horizontal movement of the same assembly and closes during the reverse horizontal movement of the same assembly.

1 . A wrapping machine for wrapping individual or grouped and/or stacked products, in packs of thermoplastic material of the type comprising a hollow horizontal mandrel to the loading end of which there is fed a continuous film of thermoplastic material, unwound from a reel, which proceeding towards the unloading end of this mandrel, is formed in a tube with overlapping and mutual heat-sealing of its longitudinal edges by heat-sealing means and which exits from the same mandrel in the form of a tubular wrapping, which is closed transversely by an assembly positioned downstream of the same mandrel and which, on the portion of the tubular wrapping previously gusseted by folders, carries out two transverse heat seals and an intermediate cut, filled and formed in the previous cycle, to close the leading end of the following pack and to separate the completed pack from the one being formed, and which comprises upstream of said mandrel and aligned longitudinally therewith, a loading station of the products to be packaged, grouped and/or stacked and compressed in transverse direction and which upstream of this station comprises aligned longitudinally, a pusher that, on command, transfers the product or products from the loading station into the tubular pack produced by said mandrel, passing through this latter for the whole of its length and beyond, characterised in that the parallel and opposed elements that form said assembly for carrying out the double transverse heat seal and the intermediate cut, are equipped upstream with respective pressers and counter-pressers to firmly clamp in transverse direction the portion of gusseted wrapping on which this assembly, on command, is closed, the same assembly being mounted on a main carriage with horizontal movement and operated by motion means to be able in correct phase to be moved away from the tube-forming mandrel to follow the completed pack during heat sealing of the trailing end and to extract from the mandrel a new portion of tubular wrapping into which in correct phase said pusher inserts a product to form said subsequent pack, there being provided means such that said main carriage is returned rapidly to the initial position moved towards the mandrel, to be arranged downstream of the new pack already filled and to be closed at the trailing end, a motorized conveyor being provided to support the packs being formed downstream of said mandrel and the upper branch of this conveyor being guided on parallel rollers supported rotatingly by said main carriage and being guided in a zigzag path on further rollers supported by a secondary carriage sliding horizontally on command on the same main carriage, all so as to form at said double transverse heat-sealing and intermediate cutting assembly a gap inside which the lower element of said assembly is normally housed and this gap being opened by the movement in one direction of said secondary carriage, to allow freedom of action of this lower element and the same gap, when engaged by said lower element, being closed by the movement of said secondary carriage in the opposite direction, so that said conveyor correctly supports the packs being formed during the return movement of said main carriage. 
     
     
         2 . The wrapping machine according to claim  14 , wherein the main carriage that carries said double transverse heat-sealing and cutting assembly, is equipped laterally with slides that slide on pairs of rectilinear and horizontal guides fixed longitudinally to the side panels of the portion of base plate of the same machine and these side panels also support, parallel to said pairs of guides, toothed belts closed in a loop and guided on respective end pulleys, a pair of which is interconnected by a transverse shaft in turn connected to a motion assembly with electric motor that rotates in two directions and of the type with electronic speed and phase control, the two side panels of the main carriage being connected to a branch of said two toothed belts, by means of clamps, to receive therefrom the necessary rectilinear reciprocating movement with the necessary acceleration and deceleration ramps. 
     
     
         3 . The wrapping machine according to  claim 1 , wherein the support means of the two parallel and opposed elements that form said double transverse heat-sealing and cutting assembly, are mounted on respective vertical slides positioned inside the side panels of the main carriage that support said slides with guide means, each slide being equipped with a protruding intermediate appendage, with a lead screw that cooperates with a vertical screw, in turn connected to a three-way bevel gearbox, the vertical way of which acts on said screw, while one of the horizontal ways connects the same screw of a slide to that of the slide of the opposite side, which will be served by a two-way bevel gearbox, while the third horizontal way of said gearbox is connected to a motion assembly, with electric motor that rotates in two directions and preferably of the type with electronic speed and phase control, to allow the automatic or semi-automatic adjustment of the position in height of the transverse heat-sealing and cutting assembly when the height of the packs to be produced varies. 
     
     
         4 . The wrapping machine according to claim  34 , wherein fixed to the inner sides of said vertical slides with supports that respectively support them by the lower end and by an intermediate area, are vertical guide rods, with a round section, sliding on which, with the interposition of recirculating ball bearings, are sleeves if the lower of which slides between said supports and supports the end of the lower transverse heat-sealing and cutting element, while the upper sleeves slide above the upper supports of the respective rods and support the ends of the upper transverse heat-sealing and cutting element, the sleeves of each said rod being fixed by means of respective clamps to the opposite branches of toothed belts guided on a pulley supported adjustably by the upper end of each rod and on a toothed pulley supported by the lower end of each said vertical slide and the same lower pulleys are connected to each other by a synchronizer shaft, in turn connected to a motion assembly with electric motor that rotates in two directions and preferably of the type with electronic speed and phase control, which transmits to the opposed elements of the transverse heat-sealing and cutting assembly the movements for total or partial closing or total or partial opening, with the necessary acceleration and deceleration ramps. 
     
     
         5 . The wrapping machine according to  claim 1 , wherein the pressers positioned upstream and downstream of the upper element of the double transverse heat-sealing and cutting assembly, are stressed in downward extension by respective counter springs so that when they are at rest, the lower edges with rounded profile of the same pressers are suitably spaced from each other by the lower operating surface of the same upper element while the lower element of the same assembly comprises with arrangement on a common horizontal ideal plane, counter means opposite said upper pressers which, similarly to these counter means are produced or machined so as to have a high coefficient of friction in contact with the tubular wrapping of film that forms the packs and that exits from said tube-forming mandrel, all so that, also in combination with the action of said counter springs said wrapping of film is able to be firmly clamped between these pressers and the respective counter means both when said elements are thrust against each other to carry out the two transverse heat seals and the intermediate cut for which they are responsible, and when these elements are close to each other but with the transverse heat-sealing and intermediate cutting means raised by the respective counter means, to free and cool the heat sealed and cut portions of wrapping. 
     
     
         6 . The wrapping machine according to  claim 2 , wherein said secondary carriage that supports the zigzag guide rollers of the upper branch of the conveyor, is equipped laterally with horizontal and longitudinal guides sliding on slides fixed on the top of a cross member, in turn fixed with its ends to the side panels of the main carriage, this cross member supporting rotatingly and in a cantilever fashion, a pair of screws parallel to each other and to said guides and these screws cooperate with respective lead screws, integral with appendages of the secondary carriage, and these screws being operated by a motion assembly flanged to said cross member and operated by an electric motor that rotates in two directions and optionally also of the type with electronic phase control. 
     
     
         7 . A method for wrapping single or grouped and/or stacked products, in packs of thermoplastic material obtained from film unwound from a reel, with a machine according to  claim 1 , with a transverse heat-sealing and cutting assembly equipped with pressers and counter pressers upstream and downstream of the transverse heat-sealing and cutting means, to be able to firmly clamp the tubular pack of film during the step of carrying out the transverse heat seals and in which the same transverse heat-sealing and cutting assembly is movable in the pack forming direction, first closed and moving away from the tube-forming mandrel and then open and in the opposite direction, to return to the cycle start position for repetition of a subsequent operating cycle, all so that advance of the tubular wrapping along the tube-forming mandrel can take place drawn by the same double transverse heat-sealing and cutting assembly with pressers, characterised in that with this assembly it is possible to carry out in the forming and filling step of each subsequent tubular pack, while the transverse heat-sealing and cutting assembly is closed and moves away from the mandrel and also characterised in that the return movement to the cycle start position of the transverse heat-sealing and cutting assembly, after it has been opened, overlaps the return movement at the same speed of the pusher for bagging the product and, after this return step, a pack filled and ready for closing of the trailing end is already positioned downstream of the transverse heat-sealing and cutting assembly. 
     
     
         8 . The method according to  claim 7 , characterised in that while the new tubular pack advances and is drawn by the transverse heat-sealing and cutting assembly with pressers, which heat seals the leading end of this new pack, closes the trailing end of the pack of the previous cycle and is accompanying this latter to be unloaded, the same new pack can be filled rapidly by the designated pusher, as the presser downstream of this transverse heat-sealing and cutting assembly, mechanically isolates the transverse heat seal of the leading end carried out on the new pack, so that this transverse heat seal is not stressed by insertion of the product into the new tubular pack and by thrust of the air trapped in the same new pack and positioned in front of the product, also as in this step it is possible for the pusher to insert the product into the new pack with a relative speed that allows slow and progressive backward discharge of the air that is compressed upstream of the same product and against the leading end of the new pack. 
     
     
         9 . The method according to  claim 7 , wherein during the active movement away from the tube-forming mandrel, the double transverse heat-sealing and cutting assembly, is given all the time required to carry out its main heat sealing and cutting operations and, in the last part of the same active movement, to open the heat sealers and the cutting means slightly to free the transverse heat seals and allow action of the means for natural or forced cooling of these heat seals, while the wrapping of the packs upstream and downstream is held at all times by the pressers, which prevent even minimum stress on said transverse heat seals. 
     
     
         10 . The method according to  claim 7 , characterised in that in the initial step of its operating cycle, the double transverse heat-sealing and cutting assembly can be closed only partially on the gusseted tubular wrapping and in this partially closed condition can be moved slowly away from the tube-forming mandrel so as to move towards the pack downstream and compress it longitudinally, after which the same assembly is fully closed and increases its speed of movement to carry out the double transverse heat sealing and intermediate cutting steps for which it is responsible.