WO2015181242A1

WO2015181242A1 - Machine for filling thermoplastic bags

Info

Publication number: WO2015181242A1
Application number: PCT/EP2015/061730
Authority: WO
Inventors: Luciano Salda; Georgi Dimitrov Todorov; Tihomirov Ivanov TSVETOZAR; Angelo Cappi
Original assignee: C.M.S. S.P.A.
Priority date: 2014-05-29
Filing date: 2015-05-27
Publication date: 2015-12-03

Abstract

Machine for filling bags, wherein the mouth of the first bag (S) is gripped on the larger, transverse sides by two parallel suction bars (9 and 9') that are subsequently moved along an upward path of progressive reciprocal separation, to raise and simultaneously open the bag and to bring its mouth underneath the feed mouth of filling means (14). When filling of the bag is complete, the two suction bars (9 and 9') are made to perform a movement of at least reciprocal approach and preferably also of rising up to be opportunely arranged above the product filling level, to close the bag's mouth, which has already been returned to the original gusseted shape by suitable means (33, 33'), to prepare it for sealing by the opposed heat-sealing bars (11 and 11'), after which the top of the bag is left free and the filled and sealed bag (S') offloaded, while its bottom heat-sealed portion (W) is separated by tearing it off from the mouth of the next bag below, which is placed in an area such that when said filled and closed bag (S') has been removed, the mouth of the new bag (S) can be gripped by said two said suction bars (9 and 9') that, with an opposite movement to the previous one, are returned to the cycle start position to grip the mouth of the new bag and repeat a new work cycle. Said heat-sealing bars, which apply the top heat seal (W) to seal the filled bag, can be advantageously associated with said two suction bars (9 and 9'), to exploit the work movements.

Description

TITLE

MACHINE FOR FILLING THERMOPLASTIC BAGS DESCRIPTION

The invention concerns a machine for putting loose products into bags of a heat-sealable material, usually polyethylene, especially in machines that obtain the bags from a continuous chain of flattened bags wound on a reel, preferably provided with side gussets, closed at the bottom and interconnected by a transversely weakened area that can be torn apart to separate one bag from the next and to open the mouth of the next bag, or that can be derived from a flexible tube of polyethylene, flattened and wound on a reel and which after unwinding is provided, at set lengths, with: said transverse weakened areas for separation by tearing off; side gussets; transverse heat seal(s) to close the bottom of the various bags, which are then fed to the parts of the bagging machine that grip the bag by the mouth, open it and position it vertically below the discharge mouth of filling means, subsequently close the upper mouth of the filled bag, seal this upper mouth with at least one transverse heat seal and, finally, remove the filled and closed bag, separating it from the next bag if this operation has not already been performed and then gripping the mouth of the next bag to repeat a new work cycle.

For this type of machine, which falls within the international classification

B65B43/00, the invention proposes a particularly simple device of high technological reliability for gripping the first bag from the feed reel, opening the mouth, placing it vertically beneath the filling means, closing it, sealing it at the top, offloading it, separating it from the bag chain from which it has been derived and then repeating a new work cycle.

Prior documents US 4,833,867 with priority date in 1987 and US 4,835,948 with priority date in 1988 are cited as the state of the known art. The first of these documents describes a machine that after having formed the bags with the bottom heat seal and providing weakening for the transverse tearing off, opens the bags at the tear-off, but only tears off one side from the opposite side, so that the bags remain interconnected by a single side. The open bags are positioned vertically, with the mouth facing upwards, the mouth being initially opened by a jet of air and then a fork, which enters top down and widens until the filling means can be inserted in the mouth of the bag, held by lower support means. At the right moment, said fork and said filling means are extracted and the upper mouth of the filled bag is closed with a heat-sealing operation and then the filled and closed bag is released from the support means to allow tear-off separation from the next bag, which it then advanced and positioned for repeating a new work cycle. In this machine, which enables producing bags of length and capacity as needed each time according to requirements, in the filling step, one side of the bag's mouth is connected to the corresponding side of the next bag by a tear line, while the other side of the bag's mouth is completely free in the filling step. It is intuitable that in these conditions the bag must be filled slowly and without triggering longitudinal tension on its sides as otherwise the bag might become detached from the next bag and no longer be controlled by the means of filling and subsequent top sealing.

The second document describes a machine of the same type under discussion, in which the first bag of the bag chain derived from a reel of a tubular sheet of plastic material, is guided along an upward vertical path, so as to have the open mouth at the top, due to the restraining of the longitudinal ends of one surface of the bag, which define the gusseted sides of the bag, by part of the straight overlapping arms of synchronized pairs of looped transport belts and while the first bag is being filled, it is supported at the bottom and sides by suitable means. In this solution, both the main transverse sides of the bag are left free in the filling step, with the problems that ensue as, due to the effect of the weight of the product being bagged, said transverse sides can become ruffled and render their subsequent closure via a transverse heat seal problematic.

The invention intends to overcome the limits of the known art with the solution set forth in appended claim 1 , which exploits the following inventive solution: The mouth of the first bag is gripped on the larger, transverse sides by two horizontal and parallel suction bars, which are subsequently moved along an upward path with progressive reciprocal separation to raise and simultaneously open the bag and position the mouth beneath the feed mouth of means that, when commanded, fill the bag with a predetermine quantity of product, provision being made in this step for supporting the mouth of the bag with supplementary means, possibly associated or cooperating with said discharge mouth. When the bag has been filled and said feed mouth removed, the two suction bars that support the opposite sides of the bag's mouth are made to perform a movement of at least reciprocal approach and preferably also of rising up to be opportunely arranged above the product filling level, to close the bag's mouth, which has already been returned to the original gusseted shape by suitable means, to prepare it for sealing by the opposed heat-sealing bars, after which the top of the bag is left free and the filled bag offloaded, while the bottom heat-seal portion is separated by tearing it off from the mouth of the next bag below, which is placed in an area such that when said filled and closed bag has been removed, the mouth of the new bag can be gripped by said two suction bars that, with an opposite movement to the previous one, are returned to the cycle start position to grip the mouth of the new bag and repeat a new work cycle with the latter. The heat-sealing means that apply the top seal on the filled bag can be advantageously associated with said two suction bars to exploit the work movements.

Further characteristics of the invention and the resultant advantages will appear clearer from the following description of a preferred embodiment thereof, shown by way of non-limitative example in the figures of the attached seven pages of drawings, in which:

^¾ Fig. 1 shows, lying flat, a continuous chain of preformed bags of a plastic material usable in the bagging machine under consideration;

^¾ Fig. 2 shows details of the bags in Fig. 1 in cross-section;

^¾ Fig. 3 shows, lying flat, a flexible tube of a plastic material from which bags as in the previous figures can formed in the machine;

^¾ Fig. 4 shows the tubular material in Fig. 3 in cross-section;

¾ Fig. 5 is a top view of the main parts of the bagging machine under consideration;

- Fig. 6 shows other details of the machine found along section VI-VI of Fig. 5; ¾ Fig. 7 shows, in perspective and with the related upper guide grid, one of the motorized parallel rollers that handle the feeding of the bags in the machine according to the invention;

¾ Fig. 8 is a side elevation view of the gripper bars for the mouth of the bag in an initial step of the work cycle of the bagging machine;

¾ Fig. 9 shows, from the side and on a larger scale, the same gripper bars for the mouth of the bag in a work step following that of Fig. 8;

¾ Fig. 10 shows, in side elevation, the gripper bars for the mouth of the bag in the intermediate step of opening and positioning of the same open mouth with regard to the discharge mouth of a hopper for filling the bag;

¾ Fig. 1 1 shows, with parts in cross-section along line XI-XI of Fig. 10, details of the machine in the bag filling step;

¾ Figs. 12 and 13 show, in side elevation, the gripper bars for the mouth of the bag in the final steps of closing, sealing and expulsion of the filled and sealed bag;

^¾ Fig. 14 shows details found along section XIV-XIV of Fig. 12 and regarding the action of lateral gusset folders before the step of closing and sealing the upper mouth of the filled bag;

¾ Fig. 15 shows, from the side and on a larger scale, the lower bag feed roller in one of the last work steps;

¾ Fig. 16 shows, from the side, a possible location on the bagging machine of the heat-sealing and transverse cutting means that enable the use of tubular material as in Figures 3 and 4 and the production of a continuous chain of bags, as in Figures 1 and 2, on the machine.

According to a simplified implementation, the bagging machine under consideration can use preformed bags of a plastic material S as in Figures 1 and 2, longitudinally provided with side gussets G and G', provided with at least one transverse bottom heat seal W and connected to each other to form a continuous chain C, with a transverse line of weakening P, usually perforated, positioned downstream and at a sufficient distance from said bottom heat seal, considering the feed direction F of the chain C, all so that the continuous chain of bags S can be wound and supplied in the form of a reel 6 (Fig. 8) and so that the tear-off separation of a first bag of said chain C corresponds to the opening of the mouth of the next bag. According to a more complex implementation, the bagging machine can be fitted with onboard means for producing the bags as in Figures 1 and 2, starting from a reel 6 of tubular material T as in Figures 3 and 4, which after unwinding from the reel is subjected to operations of longitudinal gusseting G and G', perforation P and transverse heat sealing W, with known means and, for example, of the type described in the prior documents cited as known art in the introduction. The more complex variant that contemplates the forming of bags on the machine, also with at least one longitudinal heat welding operation and starting from a reel of a continuous sheer of a plastic material also falls within the scope of the invention.

With reference to Figures 5 to 8, it can be seen that the machine comprises a box-shaped base structure 1 provided with a horizontal bottom surface 2, also of a composite type and with a transverse opening 3 of the same or slightly larger width than that of the bags S in Fig. 1 , under which a pair of guide and drive rollers 4 is position in parallel, rotatably supported by said structure 1 and between which the continuous chain C of bags S transferred on idle rollers 5 and 5' is inserted from below and unwound from a reel 6 rotatably supported by a pair of rollers 7, which like rollers 4 can be powered by means known to a person skilled in the art and are not shown (see below), to unwind the chain of bags S from the reel 6 and to correspondingly feed it upwards through said transverse opening 3, where the top of the bag is guided to slide between a pair of combs 102 and 102' as shown in detail in Fig. 7, integrated in the bottom surface 2. The teeth of the combs 102 and 102' point downwards and tangentially touch rollers 4 to perform said function of supporting and guiding the head of the chain of bags S in the best possible way and ensuring that it passes through the free spaces 8 present between the comb teeth, can upon command be inserted with their complementary shapes into the combs 109 and 109' of the straight bars 9 and 9' positioned above the opening 3, which are parallel to each other and to the opening 3, and have dimensions such as to affect the bag S substantially for its entire width and that on protruding parts destined to make contact with the bag are fitted with suckers 10 and 10' that can be connected upon command to suction means, not shown, via ducts 1 10 and 1 10'. The suckers 10 and 10' are preferably staggered from one another to not alter the planarity of the portion of the mouth of the bag that each sucker is destined to grip.

Above the suction combs 109 and 10, and 109' and 10', bars 9 and 9' carry a pair of parallel and complementary heat sealers 1 1 and 1 1 ' that can be connected upon command to a source of electric power via respective circuits 12 and 12'.

At the beginning of the work cycle, bars 9 and 9' are in the position indicated with an unbroken line in Fig. 8, partially inserted with their combs 109 and 10, and 109' and 10' between combs 102 and 102', but with an arrangement whereby the top of bag S can slide between them and be guided upwards for a certain length by the powered rollers 4, which automatically stop when the top of the bag S has gone past the currently inactive heat sealers 1 1 and 1 1 '. When this condition occurs, bars 9 and 9' are reciprocally moved closer together until the suckers 10 and 10' touch the opposite faces of the bag, as indicated by K1 in Fig. 9, after which the suckers 10 and 10' are activated to firmly grip the transverse opposite sides of the top of the bag and, in these conditions, bars 9 and 9' are raised and reciprocally moved apart with a symmetrical movement, while the rollers 4 and 7 are activated at the right moment to feed a corresponding section of bag everything stopping when the bag S is open and bars 9 and 9' reach position K2 in Fig. 10. In this condition, it is preferable that the tear line P of the open bag is situated below the currently stationary powered rollers 4, so that the bag is firmly supported on the lower part by these rollers as well as by the bottom surface 2. In the condition shown in Fig. 10, it is contemplated that the bottom part 13 of a hopper 14 is inserted into the mouth of the open bag S, supported by bars 9 and 9' with the associated suction combs 109 and 10, and 109' and 10', and that upon command, the hopper 14 opens and introduces a predetermined quantity of product Z into the bag S, while the bag itself is held at the mouth by the suction bars 9, 109, 10, 9', 109' and 10' and, if necessary, can be supported at the otherwise free sides of the mouth, formed by the gussets G and G' as shown in Figures 1 and 2, currently outstretched by external pressure means 15 and 15' (Fig. 1 1 ) that can block the bag against said bottom part 13 of the hopper 14. When the bag S has been filled, the bottom part 13 of the hopper 14 closes and moves away from the bag, as shown in Fig. 12, to free space above bars 9 and 9' that, through associated motion handling means described further on, are reciprocally moved towards each other and slightly upwards with symmetrical movements, passing from position K2, indicated in Fig. 12 with a broken line, to that of K3, indicated with an unbroken line, while the rollers 4 and 7 are activated at the right moment to move the bottom tear line P of the filled bag above rollers 4, into the space between combs 102 and 102' or just a little above them, as shown in Fig. 15. In this step of slightly raising the bag, the product drops down and conveniently moves away from the mouth of the bag, so as not to interfere with it and leave it free. During said step of lifting and closing the upper mouth of the bag, provision is made for the operation of folders 33 and 33', of the oscillating type for example, as in Fig. 14, which act in the same direction as the means indicated by reference numeral 15 in Fig. 1 1 , to return the gusseted sides G of the bag inside those supported by the bars 9 and 9', so that at the end of the step in Fig. 1 2, the top end of the bag returns to the same closed and gusseted condition in which it was taken at the beginning of the cycle by the bars 9 and 9' at combs 102 and 102'. At the end of the step in Fig. 12, the heat sealers 1 1 and 1 1 ' are activated to make at least one transverse heat seal W on the mouth of the bag to close and seal the bag (see Fig. 13).

It is not excluded that the bars 9 and 9' could be equipped with circuits and supplementary nozzles to deliver upwardly directed compressed air upon command or, alternatively, that circuits 1 10 and 1 10' of the suckers 10 and 10' could be alternatively connected to a suction circuit for the already mentioned functions or to a compressed air supply circuit to supply a jet of air through the suckers useful for cooling the top heat seal W and also useful in the initial step for forming air cushions between bars 9 and 9' that aid the sliding of the top of the bag between said bars 9 and 9' when they are in the cycle start position described with reference to Fig. 8. After the filled bag has been closed and sealed, while bars 9 and 9' are slightly separated from each other to leave the closed top end of the filled bag free, as shown in Fig. 13, a pusher 16 is operated, which at rest is located beneath the reel 6 (Fig. 8) and that, upon command, is made to move horizontally to push the filled and closed bag S' and offload it from the support surface 2, which for this purpose could be equipped with idle or driven rollers or belts. It may be appreciated how in the step of offloading the bag S', it can safely slide on combs 102 and 102' due to their rounded shape at the top. Unlike that shown, the bottom surface 2 and combs 102 and 102' could be made of a plastic material with a low coefficient of friction, for example Nylon or Polizene, and could rest on the drive rollers 4 so as not to be deformed at all by the weight of the bag in said steps of filling and final offloading. During the step of offloading the bag S' via the pusher 16, the bottom tear line P of the bag S' tears open and the new top of the next bag remains trapped between combs 102 and 102' and between the stationary and locked rollers 4, in a position suitable for repeating the next work cycle, after the pusher 16 has returned to the rest position and after the bars 9 and 9' have been lowered and re-joined above combs 102 and 102'.

From Fig. 5, it may be noted that in a first implementable solution, the motion handling means for bars 9 and 9' are all located on one side of the base 1 , inside a housing 101 and comprise pairs of parallel closed-loop chains 17 and 17', and 18 and 18', which driven on respective pairs of pinions 20 and 20', 21 and 21 ', and 22 and 22' placed at the vertices of the regular quadrilateral in Fig. 6 and having two upwardly diverging lower branches and two upwardly converging successive branches, move bars 9 and 9' with synchronous movements, taking them from the lowered position indicated by K1 of gripping the top of the bag, to the intermediate position K2 of raising the bag and opening its upper mouth for the filling step, and to the final position K3 of lifting slightly further and closing and sealing the mouth of the filled bag. With opposite movements to those first considered, the chains 17 and 17', and 18 and 18' return bars 9 and 9' to the lowered position K1 for repeating a new work cycle and in the intermediate positions mentioned with reference to the Figures

8 and 13. After being driven by the upper pair of pinions 22 and 22', the pair of chains 17 and 17', and 18 and 18' are driven by the pair of return pinions 23 and 23', and 24 and 24', the latter being fitted on a common shaft 25 driven by a motor reducer 19 with a motor having two directions of rotation, which with clockwise rotation when looking at Fig. 6, lowers bars 9 and 9', while with anticlockwise rotation raises bars 9 and 9'. The various pairs of pinions are rotatably supported by respective shafts 26, 27, 27', 28 and 29, in turn supported by the base housing 101 and by the lateral wall next to the base 1 , which has slots for the passage of an end of robust cross-beams 30 and 30' fastened to the pairs of chains 17 and 17', and 18 and 18' in an arrangement parallel to the support shafts of the pinions of the chains and said bars

9 and 9' that perform said functions of gripping and heat sealing the upper mouth of the bag are cantilever fastened to these cross-beams and longitudinally aligned with them. If bars 9 and 9' are very long, such that they are difficult to control with precision with the support and said cantilever motion handling, especially in the initial step of gripping the bag and the final one of sealing the mouth of the filled bag, at least at the side of the base 1 opposite that occupied by the motion handling housing 101 , an auxiliary unit 32 equipped with servo controls (not shown) could be provided to reciprocally move the cantilevered and otherwise free ends of bars 9 and 9' together and to secure them in said two positions of closure at the beginning and end of the cycle. As an alternative to these solutions, provision could be made to place only chains 17 and 18 of the solution in Fig. 5 in housing 101 and place chains 17' and 18' in the opposite auxiliary unit 32, which in this way, with chains 17 and 18 can directly support bars 9 and 9' at the opposite ends, as these chains are driven by a single motor reducer through a transverse synchronization shaft that passes under the bottom surface 2 in Fig. 6 and so does not interfere with the bag S in the opening and closing steps.

If a tubular material T as in Figures 3 is used to form the bags, the various operations of gusseting, perforation and transverse heat sealing to obtain the continuous chain of bags S as in Figures 1 and 2 from the same material T, are performed by known means located upstream of the feed rollers 4, so that the same chain of bags can be used substantially as in the previously described solution. In this last case, the means 31 for making the bottom heat seal W and tear line P on the bag chain can be located just before the pair of feed rollers 4 and can be active during the step of filling the bag, so as not to introduce idle times in the machine's work cycle. It is understood that the description refers to a preferred embodiment and operation of the machine, to which numerous variants and constructional modifications may be applied, which could, for example, refer to the fact that bars 9 and 9' are equipped only with means for gripping the bag and not the heat-sealing bars 1 1 and 1 1 ', which could be located with the associated motion handling means on the upper part of the machine and could be set up to operate on a portion of the closed bag preferably positioned beneath bars 9 and 9'. Further variants might refer to the fact that the lifting travel of the bars 9 and 9' for the step of opening the bag could have stop positions at variable heights, to form bags of variable height and adapted each time to different bagging requirements, especially when a continuous, tubular, bagging material T is used, as mentioned with reference to Figures 3 and 4. In this case, the chains 17 and 17', and 18 and 18' could be driven on supplementary pinions, whereby the first upward branches of the chains have a disjointed shape, with inclined and divergent first branches followed by substantially vertical sections along which bars 9 and 9' can be stopped at different heights. According to this variant, the bags could be separated at the bottom by tearing off from the next bag before or during the filling step, so that during the latter step it is possible to have the entire longitudinal extension of the bag available, proportioned to the volume requirements of the product to be bagged.

Other modifications could refer to the feed rollers 4, which might not be powered as the advancement of the bags could be determined by movement of the gripper bars 9 and 9' and these rollers 4 might be controlled by braking means to cause the tear-off separation of cyclically refilled bags. According to a further variant, rollers 4 might be provided with lateral annular recesses engaged by comb teeth 102 and 102'. These and all of those modifications or equivalent ones within the capabilities of a person skilled in the art, remain within the scope of the invention, as described and illustrated and as hereinafter claimed. In the claims, the references specified in parentheses are purely indicative and not limitative to the scope of the claims.

Claims

1 . A machine for filling bags of thermoplastic material, which may be used with a continuous chain (C) of bags (S) with lateral gussets (G, G') where each bag is defined by at least one transversal bottom's weld (W) and by a transversal perforation and tearing line (P) placed behind and at a short distance from said bottom's weld (W), to allow the tear separation of one bag from the next one and to form the mouth of each bag, wherein the machine includes a reel, wherein in use of the machine said continuous chain (C) of bags (S) is wound on the reel, and wherein the machine comprises means for gripping the mouth of the bag, means for cyclically feeding the leading bag of said continuous chain © of bags to said means for gripping the mouth of the bag and filling means (14), wherein the means for gripping the mouth of the bag are configured to open the bag with the mouth oriented upwards and to position the said mouth below the filling means (14), wherein the filling means are configured to introduce, on command, the product (Z) to be bagged into the bag and wherein the means for gripping the mouth of the bag are configured to close the mouth of the bag after the filling step, wherein the machine comprises sealing means for sealing the mouth of the bag with at least one transversal weld, wherein the machine comprises separating and tearing means for separating by tearing the filled and closed bag (S') in correct phase from the empty bag (S) of said continuous chain (C) of bags, wherein the machine comprises ejecting means for ejecting the machine from said filled and sealed bag (S'), and wherein the machine is configured to allow the repetition of a new working cycle with the next bag (S) of said continuous chain (C), characterized in that it comprises unwinding and feeding means (7, 5, 5') driving and longitudinal drag means (4), a pair of parallel comb shaped guides (102, 102') and parallel bars (9,9') with complementary teeth (109, 109') for gripping the bag, wherein the unwinding and feeding means (7, 5, 5') are configured to unwind the bagging material from said reel (6) and to feed in the form of a continuous and flat chain (C) of bags (S) interconnected by the transversal bottom weld (W), a leading end of each bag and said interposed transversal tear line (P), to the driving and longitudinal drag means (4) that carry the leading bag of said chain (C) in an ascending path between the pair of parallel comb shaped guides (102, 102'), provided with guide teeth intercalated with opposed and mutually aligned openings (8), wherein the openings (8) are so configured that portions of the leading end of a bag located between the pair of parallel comb shaped guides (102, 102') are left free by the aligned openings (8) such that the portions of the leading end of the bag on command can be gripped by the comb shaped complementary teeth (109, 109') corresponding to the openings (8) wherein the pair of parallel bars (9, 9') with the comb shaped complementary teeth (109, 109') is of such dimensions as to grip the bag (S) substantially across its entire width, wherein the machine further comprises suction means wherein the bars (9,9') on the front of their teeth intended to come in contact with the bag, are provided with suction cups (10, 10') that through conduits (1 10, 1 10') can on command be connected with the suction means to ensure that the transversal and opposite walls of the mouth of the bag are gripped firmly by these bars (9, 9'), wherein the bars (9, 9') are connected toO support and displacement means wherein the support and displacement means are configured to keep the bars (9, 9') always parallel to each other and on command to cause them to move along first ascending and diverging paths, for lifting the bag, for opening its upper mouth and for placing the same open mouth against said filling means (14), wherein the machine comprises gusset configuration means (33, 33') for returning the mouth into the gusseted configuration, and wherein the support and displacement means are configured to cause the bars (9, 9') to move along a further convergent path, for closing the mouth of the filled bag after the mouth has been returned in the gusseted configuration by the gusset configuration means (33, 33') and received between said bars (9, 9'), wherein the machine comprises welding bars (1 1 , 1 1 ') that are configurated to subsequently form on the closed mouth of the bag at least one transversal sealing thermo weld (W), wherein the machine is configured such that with the variation of the positions in altitude of the bars (9, 9') the driving and longitudinal drag means (4) are activated for driving and for dragging the bags, to ensure that when said upper thermo weld (W) has been executed, the bottom tear line (P) of the full bag appears above said driving and longitudinal drag means (4) and the corresponding pair of parallel comb shaped guides (102, 102') so that when the head of the full and sealed bag (S') is set free by said support bars (9, 9') and by said top welding bars (1 1 , 1 1 ') and when the means (16) for ejecting the full and sealed bag (S') are activated, the tear separation of the bag (S') from the next one whose leading end is retained between the now stopped driving and longitudinal drag means (4) and between the pair of parallel comb shaped guides (102, 102') is effected, so that said leading end can then be gripped by said bars (9, 9') when the same are carried again in the low position to start a new cycle.

2. The machine according to claim 1 , wherein said support and motion handling bars (9, 9') for the bag (S) are cantilever supported by the ends of cross-beams (30,

30') fastened to pairs of closed-loop chains (17, 17'; 18, 18'), driven on pinions (20, 20', 21 , 21 ', 22, 22', 23, 23' 24, 24') and operated by a synchronization shaft (25) and a centralized motor reducer (19) with two directions of rotation.

3. The machine according to claims 2, characterized by comprising servo controls in static positions to close the free, cantilevered ends of said bars (9, 9') when they are in the initial positions (K1 ) in which they are gripping the bag (S) and in the final one (K3) in which they are closing and sealing the upper mouth of said bag (S).

4. The machine according to claim 1 , wherein said bars (9, 9') ae supported at opposite ends by respective pairs of closed-loop chains (17, 17', and 18, 18') driven on pinions (20, 20', 21 , 21 ', 22, 22', 23, 23', 24, 24') operated by a common motor reducer (19) with two directions of rotation and synchronized by a transversal drive shaft, which passes under the surface (2) with the comb guides (102, 102') which are guiding the bags (S), in order not to interfere with the bags during the opening, filling, closing, top sealing, and final offloading steps.

5. The machine according to one or more of the preceding claims, wherein the lifting travel of said bars (9, 9') for the opening step of the bag (S) can have stop positions (K2) at variable heights, to form bags of variable height and adapted each time to different bagging requirements, especially when a continuous, tubular, bagging material (T) is used, in which case provision can be made that said pairs of chains (17, 17'; 18, 18') be driven on supplementary pinions, whereby the first ascending branches of said chains have a disjointed shape, with inclined and divergent first branches followed by substantially vertical sections along which said bars (9, 9') can be stopped at different heights.

6. The machine according to claim 1 , wherein said top welding bars (1 1 , 1 1 ') are associated with said bag support and motion handling bars (9, 9'), and are placed above said support and motion handling bars (9, 9') in order to not obstruct the gripping function of the said bars (9, 9').

7. The machine according to claim 1 , wherein said top welding bars (1 1 , 1 1 ') are placed in a static upper position, are controlled by their own guide, closing and opening means and are set up to operate on a transverse portion of the closed gusseted mouth of the filled bag (S'), located beneath said bag gripping and motion handling bars (9, 9').

8. The machine according to claim 1 , wherein said comb guides (102, 102') have their teeth pointing downwards and tangentially cooperating with the annularly grooved side surface of a pair of parallel powered rollers (4), between which the continuous chain (C) of plastic bags (S) advances upwards, in such a manner that the comb guides (102, 102') have characteristics suitable to permit to the bottom of the filled bag (S') to rest and slide thereon during the final step of offloading the bag (S').

9. The machine according to claim 1 , wherein said support and motion handling bars (9, 9') for the bag (S) can be fitted with supplementary means apt to supply jets of air, useful for cooling the top weld (W) closing the bag, made by said top welding bars (1 1 , 1 1 '), and also to aid the sliding movement of the top of the bag during the initial step of positioning between said guide combs (102 and 102').

1 0. The machine according to claim 9, characterized by comprising means to ensure that the bags (S) can be separated at the their bottom by tearing off from the next bag, before or during the filling step of the bags (S), in order that during the latter step the bag be available with a predetermined height correlated to the volume of product to be bagged.