Longitudinal welding equipment in a packer machine

Abstract: Longitudinal welding equipment in a machine for packaging products fed on a conveyor belt inside a continuous film of plastic material wrapped around said products with overlapping longitudinal side edges, comprising a longitudinal welding means positioned above said edges on means generating an oscillatory rotary-­ translational motion on a vertical plane, furthermore provided being at least one pressure and accompanying belt atop said products wrapped inside said film, said welding means and said pressure belt being operatively driven by a same central motor means which actuates said conveyor belt, said welding means being equipped with means for temperature control operatively connected to the packaging speed.

Description: The present invention relates to a longitudinal welding equipment in a packer machine. In packer machines for products fed sequentially one after the other, which use continuous films of plastic sheet, whether of heat-shrinking type or not, wrapped around the products, it is known to weld such a sheet film, wrapped around the products, transversely to the feeding direction both of the products and of the film, so to accomplish an at least partially closed packing. However, the longitudinal overlapping edges of said film remain in any case free, so that it is possible to carry out an action on the accomplished packing, or to tamper it with. In view of such a fact, it is advantageous to weld the overlapping edges to each other, so to completely seal the package and to render completely impossible the tampering with the product contained inside the film. From US-A 4 546 595 is know a machine for packaging products fed on a conveyor belt driven by a motor-variator, wherein the products are wrapped inside a continuous film of plastic material having overlapping longitudinal side edges and wherein a longitudinal welding equipment provides for the continuous welding of said overlapping longitudinal side edges of the film so to completely seal the package, said equipment comprising a welder having a substantially circular welding surface lying in a longitudinal vertical plane and overlying said longitudinal side edges of the film and a pressure belt positioned atop said products wrapped inside said film. In the known equipment a stationary longitudinal welder is used, which continuously remains in contact with the material to be welded in one and the same point or zone of its welding surface. This construction has the drawback that if the welder is heated to the temperature normally required to produce a good seal, a reliable welding can be obtained only in the instant of first contact of the welding surface with the material to be welded, inasmuch as, due to heat transfer to the material, the contact point or zone of the welding surface instantaneously is cooled to a lower temperature and no secure continuous weld is obtainable. On the other hand, if the welder is heated to a higher temperature, in the instant of first contact the risk of fusing and perforating the material and of damaging the packaged products exist. It is therefore the purpose of the present invention to provide a longitudinal welding equipment which avoids the above mentioned drawback and which is able to produce a reliable continuous longitudinal welding of the overlapping side edges of the film wrapped around the products. This purpose is achieved according to the invention by the fact that the longitudinal welder is pivotally mounted on a pivot axis, that means to impart a reciprocatory rocking motion to said welder about its pivot axis and means to drive said pressure belt are operatively connected to said motor-variator, and that said pivot axis is shiftable by means of a lifting and lowering device between a lowered position when the packer machine is running, in which the welding surface of the welder contacts said overlapping longitudinal side edges of the film, and a lifted position when the packer machine is stopped, in which the welding surfacs of the welder is out of contact from said overlapping longitudinal side edges of the film, and the welding surface of the welder is constituted by an electrically heated bar, means being provided to control the temperature of said bar in dependence on the packaging speed. The structural and functional characteristics and the advantages of an equipment according to the present invention will be better understandable from the following exemplifying and not limitative disclosure referring to the related drawings, wherein: Fig. 1 is a schematic side view of the equipment according to the invention; Fig. 2 is a partial top view of the equipment of Fig. 1; Fig. 3 shows the electrical wiring diagram of the welding equipment according to the invention; and Fig. 4 is a chart exemplifying the temperature change of the welding element as a function of the packing speed. Referring to Figs. 1 and 2, a side wall 10 of a packer machine supports a longitudinal welding equipment according to the present invention, generally indicated with 11. The packer machine comprises essentially a conveyor belt 13 for the conveyance of a set of products 14 to be packed, which products are fed on the belt by means of pusher means schematically shown in 12. A central motor 15 actuates, by means of a belt transmission 16, an intermediate speed variator 17 which, via a chain transmission 18, installed in series, actuates a drive roller 19, around which said conveyor belt 13 is driven. In correspondence of the area into which the products 14 are fed, provided is a return roller 20 for the return of belt 13, towards which driven is a film of plastic material 21, which is unrolled from a spool 22 and gets interposed between the conveyor belt 13 and the products 14 to be packaged. In a known way, the continuous film 21 is completely wrapped around said products 14 with overlapping longitudinal side edges before coming to the longitudinal welding equipment 11 and to a transversal welding device schematically shown in 9. The equipment 11 comprises a pair of support side shoulders 23 which are positioned above the side wall 10 of the frame, vertically movable by a pressure handwheel 24 in dependence on varying thickness of products 14, so to cause the same products to engage a pressure belt 25. Said pressure belt 25 is positioned in closed loop supported on at least one pair of end rollers 26 rotatably supported by said pair of shoulders 23 and laterally provided with sprocket wheels 27, solid with said rollers 26, actuated by a chain transmission 28. A sprocket wheel 29 actuates said chain transmission 27 and is axially made solid with and coupled to a second sprocket wheel 30 having different diameter and different number of teeth, in its turn driven by a chain transmission 31. Two sprocket wheels 32 and 33, having different numbers of teeth, are laterally keyed onto said drive roller 19 and are respectively connected: the first one to the chain transmission 18 coming from the intermediate speed variator 17, and the second one to the chain transmission 31 actuating the longitudinal welding equipment 11. This latter chain transmission 31 is provided with a chain tightening lever 34, articulated in 37 relatively to the side wall 10 and kept in its operating position by an elastic element or spring 35, said lever bearing, hinged onto its free end, a small return idle sprocket wheel 36. The side shoulders 23 support, centrally hinged on a shaft 38, a bell crank 39 which is hinged at 40, at an upper end thereof, to an adjustable stem 41 of a cylinder 42 articulatedly fastened to the same shoulders. The bell crank 39 bears, at the other end thereof, a pivotal axis 43 on which is pivotally mounted a longitudinal welder 44 of rocking type with a welding surface constituted by a bar of circular shape, e.g., by a wire, arranged in the same direction of motion of the products, and such to accomplish a continuous weld 58. The body of the welder 44 extends in a rocker lever 45 pivoted to a connecting rod 46, the free end of said connecting rod being hinged in 47 to a crank-pinion 48, rotatably and axially supported in 49 onto at least one shoulder 23. The crank-pinion 48 is driven to rotate by the same chain transmission 28 which actuates the accompanying belt 25. The crank-pinion 48, together with the connecting rod 46 and the rocker lever 45 constitute the articulated quadrilateral which converts the continuous rotary motion of the crank-pinion 48 into the reciprocatory rocking motion of the rocker lever 45 and of the longitudinal welder 44 solid therewith. The bell crank 39 and the cylinder 42 constitute the device which lowers and lifts the longitudinal welder 44 at each start-up or shut-down of the packer machine. The use of a continuously operating hot-bar longitudinal welder 44 requires necessarily a suitable control of the welding temperature, which must depend, besides on the material to be welded, also on the variations in packing speed. To that purpose an adjustment element 50, e.g., a voltage adjuster (Fig. 3) is provided, which is properly set during the packer machine start-up step, so to have a certain input-output value on a transformer 51. This is determined by the use, e.g., of a first microswitch 52 engaged by a plate 53 connected to a distributor-box 54 actuated by the speed changes of the central motor 15. In fact, as soon as the speed exceeds a predetermined first value (Fig. 4), the distributor-box 54 is actuated to move, thus causing, by means of the plate 53, the engagement, besides the first microswitch 52, also of a second microswitch 55, which switch over of the input to transformer 51. Said switch over involves an increasing voltage lever (see Fig. 4) and consequently a related increase in temperature of the welder 44, so to compensate for the greater removal of heat from the welder, which acts on a greater number of products 14 being packed. The same effect of further increase of temperature is obtained by means of a third microswitch 56 which gets switched on when the packer machine comes close to the highest packing speed. In an equivalent way, the various microswitches are switched off when the packing speed of the machine decreases, so to accomplish means for adjusting the temperature with varying packaging speed. If, for example, the central motor 15 comprises a linear actuator such as a pump, the motion of the distributor-box 54 controlled by an electrovalve 57, besides varying the pump flow rate, switches on the various microswitches performing the adjustment of the temperature of the welder.

Claims: Longitudinal welding equipment in a machine for packaging products (14) fed on a conveyor belt (13) driven by a motor-variator (15, 17), wherein the products (14) are wrapped inside a continuous film (21) of plastic material having overlapping longitudinal edges, said equipment comprising a welder (44) having a circular welding surface lying in a longitudinal vertical plane and overlying said longitudinal side edges of the film (21) and at least one pressure belt (25) positioned atop said products (14) wrapped inside said film (21), characterized in that said welder (44) is pivotally mounted on a pivot axis (43), that means (45-48) to impart a reciprocatory rocking motion to said welder (44) about its pivot axis (43) and means (28-33) to drive said pressure belt (25) are operatively connected to said motor-variator (15, 17), and that said pivot axis (43) is shiftable by means of a lifting and lowering device (38-42) between a lowered position when the packer machine is running, in which the welding surface of the welder (44) contacts said overlapping longitudinal side edges of the film (21), and a lifted position when the packer machine is stopped, in which the welding surface of the welder (44) is out of contact form said overlapping longitudinal side edges of the film (21), and the welding surface of the welder (44) is constituted by an electrically heated bar, means (50-56) being provided to control the temperature of said bar in dependence on the packaging speed. Welding equipment according to claim 1, characterized in that a chain transmission (31) including chain tightening means (34-36) and starting from a drive roller (19) of the conveyor belt (13) by means of a sprocket wheel (29) actuates a further chain transmission (28) to drive said pressure belt (25), and that said further chain transmission (28) drives a crank-pinion (48) to which a connecting rod (46) is hinged, said connecting rod (46) being pivotally connected to a rocker lever (45) extending from the welder (44) to impart the reciprocatory rocking motion to said welder (44) about its pivot axis (43). Welding equipment according to claim 1, characterized in that the pivot axis (43) of the welder (44) is borne at one end of a bell crank (39) pivotally mounted on a fixed shaft (38), the other end of said bellcrank (39) being hinged to an adjustable stem (41) of a cylinder (42) to rotate said bell crank (39) about said shaft (38) and thereby lower or lift said pivot axis (43) and the welder (44). Welding equipment according to claims 2 and 3, characterized in that the shaft (38) on which the bell crank (39) bearing the pivot axis (43) of the welder (44) is pivotally mounted and that said pressure belt (25) with its driving chain transmission (28) and with said crank pinion (48) are supported by at least one side shoulder (23) positioned abouve a side wall (10) of the packer machine frame, means (24) being provided to vertically position said shoulder (23) in dependence on the thickness of the products (14) to be packaged. Welding equipment according to claim 1, characterized in that said temperature control means comprise a presettable voltage adjustment element (50), a transformer (51) and a set of microswitches (52, 55, 56) sequentially actuatable in dependence on the packaging speed to switch over the input-output voltage of said transformer (51).

Inventors: BALLESTRAZZI ARIS, TASSI LAMBERTO, BALLESTRAZZI, ARIS, TASSI, LAMBERTO
Applicants: SITMA SPA, SITMA S.P.A.
Application year: 1986
Main classification: B65B51
IPC codes: B65B51