Abstract:
A device for manufacturing, filling and sealing thermoplastic sacks comprises a station, which comprises a forward draw unit for intermittently pulling forward a web of thermoplastic blown film and for its suspended feed in a vertical direction through a cross welding and cross severing mechanism, which provides the leading end of the blown film web with a cross weld and severs from said web a tubular segment above a gripping and transport mechanism. In order to pass the leading end of the blown film web quickly and without limply withdrawing to one side through the cross weld and cross severing mechanism into a stretched hanging position, there is a wall parallel to the feed path of the blown film web, and above the wall there are in its top region blowing air nozzles, facing the feed direction, between the wall and the feed path.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device for manufacturing and preferably also for filling and sealing thermoplastic sacks. This device comprises a forward draw unit for intermittently pulling forward a thermoplastic blown film web and for its hanging feed in a vertical direction through a cross welding and cross severing mechanism, which provides the leading end of the blown film web with a cross weld and severs from said web a tubular segment above a gripping and transport mechanism. 
     2. Description of the Related Art 
     This class of device is known from the prior art in different designs. They serve the purpose of providing tubular segments with bottom welds. Preceding this step, the tubular segments were severed from a blown film web, which was wound on a supply roller. Then the welded tubular segments are filled with loose material; and the filled sacks are sealed with head welds and transported away. It is the desire of manufacturers to make such machines work more efficiently, i.e. at a high cycle rate. The output of such machines is also limited due to the fact that the leading end of the plastic web, provided with a bottom weld, must be passed in such a manner through the welding jaws, executing the bottom weld, and the cross cutter that the web is stretched. Furthermore, the freshly formed bottom weld must cool down in order to solidify before the segment, which was severed from the blown film web and now forms the a sack, can be filled with loose material. Pushing the leading end of the blown film web, provided with the bottom weld, in the direction of the transport plane of the sacks to be filled causes the problem that the freely advanced end segment tries to turn aside due to its limpness. Hence, it can move crossways and escape so that it takes additional time until the tubular segment to be severed has assumed its correct vertically hanging position. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the invention is to provide a device of the class described above, in which the leading end of the blown film web can be pushed quickly and without limply withdrawing to one side through the cross weld and cross severing mechanism into a stretched hanging position, in which the end sided bottom weld is in the area of the transport plane of the sacks to be filled. 
     The invention solves this problem in that there is a wall parallel to the feed path of the blown film web, and above the wall or in its top region there are blowing air nozzles, facing the feed direction, between the wall and the feed path. 
     The blowing air, blown through the blowing air nozzles into the gap between the web and the advanced end of the blown film web, flows in essence laminarly in the feed direction and takes with it the advancing end of the blown film web so that said web is stretched. In this manner a vacuum, which prevents the undesired flapping and turning aside of the fed in end of the blown film web, is generated between the blown film web and the wall. Preferably the blowing air nozzles comprise a row of blowing air nozzles or a elongated nozzle slit. 
     The blowing air, which serves to feed the end of the blown film web so as to be stretched, also cools the bottom weld. However, to reduce the cycle period for producing and filling the sacks even more, it is desirable to cool the bottom weld so that it will solidify even faster. Therefore, another embodiment of the invention provides that the end region of the feed path has jaws that cool the bottom weld. These jaws can comprise a stationary jaw and a jaw that interacts with the stationary jaw and can be swung like pliers. 
     Preferably at least one of the jaws is provided with blowing air nozzles aimed at the bottom weld. Preferably both jaws exhibits rows of blowing air nozzles that are aimed at the bottom weld. The jaws clamp the bottom weld preferably not between their jaws in order to prevent the jaws from adhering to said weld. 
     In devices of the kind disclosed in the invention, sacks of different sizes and length are usually produced and filled. Therefore, it is necessary to change the distance between the cross weld and cross cutting mechanism and the transport plane of the sacks to be filled and to adjust the distance to the varying lengths of the sacks. Therefore, the jaws that serve the cooling process are mounted expediently on the support of a conveyor belt that carries away the filled sacks and that is mounted and guided in the machine frame so that it can be raised and lowered in accordance with the change in size. 
     The pliers holding the severed sacks can be moved preferably transversely or swung relative to the machine frame so that they can convey the severed sacks by one station length in the direction of the fill station. 
     Preferably there is a second pair of cooling jaws, of which at least one jaw is cooled and which are spaced one station away from the cooling jaws. Preferably this second pair of cooling jaws is also fastened to the support of the conveyor belt or to a bracket connected to said support. 
     An especially preferred embodiment of the invention provides that the length of the wall can be adjusted to the height of the support of the conveyor belt, thus to the changed sack size. 
     To make the adjustment to the different sack sizes, the wall can be made of a flexible web, whose bottom end is fastened to the support or to a bracket connected to said support. In this respect the web is looped between an upper deflecting rod or deflecting edge and an attachment of its other end to the machine frame; and a weight, e.g. a rod, is inserted into the loop. When the support of the conveyor belt moves, the wall adjusts itself automatically to the different sizes in that the wall elongating web segments are pulled out of the loop or wall shortening web segments are pulled into the loop. 
     To make the adjustment to the different sizes, the wall can also comprise overlapping wall sections, of which the top section is fastened rigidly to the frame and the bottom section is fastened to the support. In this embodiment the wall sections are made of a rigid material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention is explained in detail with the reference to the drawings. 
     FIG. 1 is a side view of the device. 
     FIG. 2 is a top view of the device. 
     FIG. 3 is a schematic drawing of a side view of the device with its front wall removed. 
     FIG. 4 is an enlarged view from FIG. 3 of the gripping pliers carrying away the sack segments at a given cycle rate. 
     FIG. 5 is an enlarged view of the jaws cooling the bottom weld. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     The device shown in the drawings for producing, filling, sealing and transporting away thermoplastic sacks comprises a machine with a relatively short overall length. All of the processing stations are arranged in one single machine frame. 
     The machine frame comprises two side members  1 ,  2 , which are connected together with conventional traverses (not illustrated). The machine frame is encased with plates, doors and windows, so that it looks attractive. One end of the machine frame exhibits on the side members  1 ,  2  an unwinding unit  3  for the thermoplastic blown film web, wound into a supply roll. A blown film roller  4  is cradled in said unwinding unit. The blown film web  5 , hauled off the blown film roller  4 , is pulled forward at a given cycle rate over deflecting rollers by a pair of forward draw rollers  6 . Between the deflecting or guide rollers  10 ,  11  the blown film web, hauled off the supply roller  4 , is pulled by a pendulum roller  12  into a web loop, which forms a web storage. The blown film web, which is pulled forward at a given cycle rate, is hauled off the web storage, which fills again in the standstill phases of the blown film web in that the pendulum roller  12  draws such a large segment from the supply roller  4  that the loop obtains again its length, storing the segment length. The pendulum roller  12  is mounted between two levers  13 , which are mounted on the machine frame and which are swung at a given cycle rate by a pneumatic cylinder  14  out of its swung in state into its illustrated swung out state. 
     The pair of forward draw rollers  6  pulls the blown film web  5 , flowing off the deflecting roller  7 , out into a vertical direction and pushes it between a cross welding and cross severing mechanism  15 . This cross welding and cross severing station comprises a frame mounted jaw  16  and a swivelable jaw  17 , which is carried by guide arms  18  that are mounted stationarily on the frame and can be swung back and forth by a rod  19 , which is provided with a drive and hinged to a guide arm  18 . The top part of the jaws  16 ,  17  is designed as the welding jaws executing the bottom welds. Below the welding jaws the stationary jaw  16  is provided with a groove and the swivelable jaw is provided with a cutting blade  20 , which drops into the groove in synchronism with the tubular segments  21  to be cut off. 
     Preferably the blown film web is provided with side folds. 
     Mounted on guide arms  22 ,  23 , which are attached rigidly to the frame, is a support  24 , which forms a four joint system, thus a coupling. This support is connected to an inclined bracket  25 , to whose side below the opening rims of the tubular segments  21  there are gripping pliers  26 , which are indicated by the illustrated gripping jaws. Hinged to the guiding arm  23  is a connecting rod  27 , which can be moved back and forth by a crank  29 , driven by a gear motor  28 . In so doing, the swivel motion of the support  24  is so large that the gripping pliers  26 , enclosing the sack segment  21  below the cross welding and cross severing mechanism, move the sack segment by one station length along the arc  30  into a delivery station  31 , where the gripping pliers  26  deliver the sack section to grippers  32 , which grasp the opening rims from the top and convey the sack segment  21  to the filling station  33 . The grippers  32  are carried by levers  34 ,  35 , both of which are hinged to a thrust rod  36  and form with their hinged points on the thrust rod and the grippers a four joint system. The lever  35  is a two armed lever, whose top lever arm  37  is mounted rigidly on the frame in the manner illustrated. The thrust rod  36  is hinged to a two armed lever  38 , which is mounted stationarily on the frame and whose top lever arm is loaded by a return spring  39  in the manner illustrated. The crank  29  is designed in the illustrated manner as a cam plate. A cam roller  40 , which is mounted on the lower lever arm of the two armed lever  37 , rolls down this cam disk. The thrust rod  36  is driven in such a manner by its cam plate—lever—cam roller drive that the grippers  32  advance and transfer the sack segment to holding grippers, which grasps below the fill funnel  42  on the side of the opening areas of the sack segments. On the support  24  there is a second pair of grippers  43  that passes the opening rims of the filled sack that are pulled tight again, after filling, to a welding station  34 , where welding jaws (not illustrated) seal the tightly pulled opening rims of the sack with a cross weld. 
     Below the filling station  33  there is a conveyor belt  51 , which is provided with posts  50  and which runs over one sided drive and deflecting rollers  52 ,  53  and which conveys the filled sacks  54  away from the filling and welding stations in synchronism with their filling. The drive and deflecting rollers  52 ,  53  of the conveyor belt  51  are mounted on the ends of a horizontal support  55 , which can be raised and lowered by a spindle drive  57  in guides  56 , which are fastened to the frame. In this respect the spindle drive  57  can be driven by means of a gear motor  58 . 
     At this point the procedure for lowering the leading end of the blown film web  5 , which is provided with a bottom weld  60 , without flapping freely will be described in detail with reference to FIG.  5 . While the blown film web  5  is fed intermittently through the cross weld and cross cutting mechanism  15 , the jaw  17 , which can be swung back and forth in the direction of the arrow A, is raised by the jaw  16 , fastened rigidly to the frame. Below the jaw  17  in the machine frame there is a blowing air nozzle slit or a row of blowing air nozzles  61 , whose blowing air current is aimed vertically toward the bottom. Parallel to the feed path for the blown film web  5  or the sack segments  21 , severed from it, there is in the machine frame a wall  62 , which comprises a taut web of film or fabric. The lower end  63  of the web  62  is connected to the brackets  64 , which are connected to the support  55  of the conveyor belt  51  in the manner shown in FIG.  4 . The web  62  travels from its bottom attachment  63  via a top deflecting rod  65 , which is fastened rigidly to the frame, to its attachment  66 , which is fastened rigidly to the frame. Between the deflecting rod  65  and its attachment  66  the web  62  is pulled out so as to form a loop  67 . Inserted into the loop is a rod  68 , which holds the web  62  taut. If for the sake of adjustment the support  55  of the conveyor belt  51  is moved upwardly, the taut section  62  of the web adapts automatically to the size change of the sack so that the required length of web is pulled out of the loop  67  or moves into said loop. 
     A slit of suitable width  69  is formed between the wall, comprising the taut film web  62 , and the web segment  5 , fed by the forward draw rollers  6 . Above the wall  62  there are the blowing nozzles  61  or a blowing nozzle slit, from which blowing air is blown in the feed direction of the leading web segment  5  into the slit  69 . Due to the constriction in the slit the blowing air becomes laminar. This laminar flow exerts a suction effect on the leading web segment and thus prevents it from flapping and turning aside. Owing to the effect of the blowing air current  61 , which makes the web taut and attracts it through suction, the leading blown film segment  5  descends in the direction of the bracket  64  at a rate, specified by the pair of forward draw rollers  6 . 
     As soon as the front end of the blown film web  5  has dropped and is now in the region of the cooling jaws  70 , the pneumatic cylinder  71 , which is pivot mounted on the bracket  64 , swings the jaw  72  in the direction of the stationary jaw  70 . Both jaws  70 ,  72  are provided with blowing air nozzles  73 ,  74 , which blow cooling air on the weld  60 . In so doing, the jaw  72  approaches the stationary jaw  70  only to the extent that both jaws do not touch the weld  60 , thus preventing the jaws from adhering to said weld. 
     As soon as the segment  21  has been pushed in a taut state through the cross weld and cross cutting mechanism  15 , the grippers  26  grasp the segment on the side below the top opening rim, so that then the segment  21  is severed. At the same time the cross weld can be affixed to the freshly formed end of the blown film web  5 . The gripping pliers  26  convey the top segment end one station further so that in the delivery station  31  the pliers  32 , grasping from the top, can take over the segment. Through this transfer stroke the tubular segment is conveyed into the position, which is shown on the left in FIG.  5  and where the weld  60  stops before a stationary jaw  76 . This stationary jaw  76  is assigned a swivelable jaw  77 , which is swung against the stationary jaw  76  in synchronism with the machine by a pneumatic cylinder  78 . The stationary jaw  76  is penetrated by channels  79 , through which cooling air flows. During the short residence period of the sack segment  21  in the delivery station  31  the weld  60  continues to cool as the weld  60  is clamped between the jaws  76 ,  77 . 
     The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.