DE1208871B - Process for the continuous manufacture of bags from a long, flat plastic tube - Google Patents

Description

Process for the continuous manufacture of bags from a long flat hose made of plastic The invention relates to a method for continuous production of bags from a long, flat plastic tube, wherein the hose is welded at a first work site in the transverse direction and the bag formed is cut off at a second, downstream work station will.

Plastic sacks and bags for packaging a wide variety of articles are made in large quantities from films made of polyethylene, vinyl polymers or others heat-sealable thermoplastic masses produced in the form of webs or tubes. The processing is usually carried out in the form of simple and intermediate pieces Sacks and bags with sizes between 7.5 x 7.5 cm and 120 x 150 cm and thicknesses from 25 to 150. These sacks and bags can be made from tubular film with a smooth, embossed finish and printed surface. The seam that runs the bottom of the bag forms, can be straight (transverse to the direction of the web) or curved in various ways Shapes that are appropriate for the item in question are designed.

Vinyl films, e.g. B. made of polyvinyl chloride, and polyethylene films for the production of sacks and bags for the tight wrapping and packaging of A wide variety of meat items are used, which have an arched bottom of the bag and a straight cut top open end.

These elastic bags are filled by first using the The open end is pushed over several curved metal fingers lying close together will. The fingers are then spread apart, lifting the pouch in a transverse direction stretch so far that the meat article can be inserted. The meat item is placed in the expanded bag and pushed close to the bottom, whereupon the bag is peeled off by the reuniting fingers. That The open end of the bag is then stretched, for example by pulling it tightly over the Meat item is pulled, gathered or folded and subjected to heat or mechanically sealed. The elastic bag then strives to to contract to its original size, and thus envelops, tightly, the packaged meat item. So that the packaging fits snugly, the size of the bag for a certain type of meat article is chosen so that its size when flaccid is smaller than the circumference of the meat item.

The production of bags from heat-shrinkable polyethylene is also and polyvinylidene chloride films are known. These pouches are usually bow-shaped Bottom seal are produced, are produced as shrink packs as follows: The meat item to be packaged is loosely wrapped and then the bag is tightly covered pulled it, for example by gathering or folding the open end.

After evacuating the air from the bag, it is closed, for example by heat or by mechanical means. Then the bag completely immersed in a liquid held at a temperature in which the film is firmly shrunk onto the meat item and adheres to it applies.

As a result of the different operations that the hose during is subjected to manufacture, individual hose parts are different tense. There were changes in length from 5 to 10010 between the stretched and slackened state before and immediately after welding. Leading however, to the fact that the finished seam is weakened or even separated. These Difficulty is increased by the fact that the bag weld seam has a curved course must have. Although a device is already known that a thermoplastic Plastic tape is continuously conveyed and automatically to bags cuts. In this case, however, the hose becomes a welding device in the tensioned state promoted. The weld seams themselves are straight.

The invention is based on the knowledge that the feeding of the Hose to the welding device in the relaxed state should be done to the formation to facilitate a curved weld. Here, however, is aggravating that the tubular film is very thin.

The method according to the invention enables relaxed feeding of the hose to the welding work site in that the hose with increased speed between the welding plates of the first job, but is removed from it at a reduced speed, so that the hose is welded in the relaxed state. This ensures that the formation curved weld seams even with thin plastic films in a continuous, safer way Way, so that you can tightly packed bags in a steady, rapid workflow receives. A break in the seam or considerable different tensions in the seam are better avoided than before.

In a further embodiment of the invention it is proposed that the Hose along an outer line adjacent to the weld seam at the same time the weld seam formation is perforated, the perforation at the second work site adjusted and then torn off the bag at the perforation point from the tube and next to the perforation point is cut from the tube. Through this simultaneous Attachment of the weld seam as well as the perforation will create centers of tension better avoided in the weld seam.

To carry out the method according to the invention, a device proposed the one between a backup roller and a pull roller as a pair of rollers running, elastically resilient transversely to its longitudinal direction, transporting the hose Tape provides. The thickness of the tape is preferably a multiple of that of the hose or is relatively large compared to the radius of the support roller. Under Consideration of these conditions becomes the relaxed one with relatively little construction effort The condition of the hose on the welding jaws is ensured. In further development The invention provides that the one curved welding jaw and next to it a Perforation knife having welding head is arranged next to the draw roller. Through this will cause that this relaxed state may be lost. aside from that the perforation can also be carried out on the relaxed tube.

Another embodiment of the device provides that the location adapted to the perforation, they through urgent switching contacts at the second job are present, which are in an electrical control circuit, by the gripper and knives are controllable. Simple, convenient control is achieved.

Furthermore, this arrangement enables compliance with a necessary Time to cool the seam before the rest is cut off. Another embodiment the invention provides that the first job with a photoelectric Cell for scanning a register mark is provided on the tube and one with the circuit of the photoelectric cell in front of tied delay circuit, which renders the circuit ineffective outside the marking area, and that the delay circuit actuation term devices to stop the movement of the hose are available at the first job. Through this design will be in detail the necessary spatial or temporal distance between welding and cutting off. The one through the perforated tube extending switching contact is preferably designed as a spark electrode.

In the drawings, F i g. 1 is a partial view of a flat tube in a typical workflow for making bags for shrink packs according to the invention; F i g. Figure 2 is a perspective view of a typical package; 3 is a schematic side view of an automatic device according to FIG the invention; Fig. 4 shows, in side elevation, an enlarged partial view of the relaxation device; F i g. Figure 5 is a partial top plan view of the sealing and perforating device; F. i g. 6 is a cross section taken along line 66 of FIG. 5, and FIG. 7 shows im On an enlarged scale, a detail in cross section along the line 7-7 of Fig. S.

As shown in FIG. 1 can be seen, the hose 10 is also printed Registration marks 12 for identifying the relative position of the weld seam 14 and the marking area 16 provided. The welding process is carried out by an optical Switching system triggered when the tubular film is at rest.

Time, temperature and pressure of the welding process are precisely controlled, As shown in FIG. 3, a flat tube 10 is passed through from a roller 24 a drawing roller 26, which is made of soft rubber and supported by several support rollers 28, 29 and 30 running belt 27 interacts intermittently in the machine M drawn. A photoelectric cell 31 arranged under the hose 10 and which is opposite a light source 32 above the hose, is used for scanning of the marks 12 printed on the tube when processing a printed tube film will.

If unprinted tubes are used, a correspondingly long Piece pulled into the machine by a control system.

A welding and perforation head 34 (first job. Job position) is Immediately after the pull roller 26 whether it is arranged balb of the belt 27. The head 34 is controlled by a vertical control device 35 in a time, pressure and Heat cycle actuated when the intermittently moving hose 10 stopped has come. As shown in FIG. 5 to 7, the head 34 is electrically connected heated arc-shaped welding jaw 36 and the perforation gauge? 38 provided. These two parts work with the padded belt 27 and the belt support plate 33 together in the formation of the bottom closure 14 of each bag. The perforation knife lies directly next to the welding jaw and is used to make a line of short cuts, for example of 5.5 mm length, at a distance of 6 mm through the imperforate To guide the hose so that it is possible to pass it through the cohesive form subsequent ~ workplaces of the machine.

On each side of a hole punching device, the hose is pulled over Deflection rollers 40 or 41 out, which are adjustable and allow the length the hose parts located between the welding, punching and cutting stations adjusted so that there are several bag lengths between them. Subsequently to the supply roll 41 are intermittent working pull rollers 44, which cooperate with a knife 46, and a stacking mechanism provided with gripping bars 48 provided. This mechanism separates the tube into the individual bags, by pulling on the perforationcliniç acseina.zder, the knife 46 cuts then the rest off, which is scrap.

Since between the welding head and the cutting device three to twelve Can be bag lengths, a sensing device is provided, which is on a suitable Responds to the reference point on the hose and the movement of the pull rollers 44 synchronized with the trean and cutting processes and controls.

An electrode arrangement with a lower, smooth, rounded switch contact 50, on the constantly about 4000 V direct current voltage lying, an upper switching contact 52, which can be designed as a metal brush, is located just above the lower switch contact at a distance of, for example up to 3 mm.

The hose runs through the middle between the switch contacts and isolates these electrode contacts. However, a hose perforation wanders between through them, a spark discharge takes place, which triggers an impulse, which in turn A relay is actuated via a delay circuit 54. This relay establishes the connection between a control mechanism and an electric clutch and brake assembly 55 that the shafts 80 and 57 that drive the mechanism of the hose 10 intermittently moving pull rollers 44 represent, connects to one another. The wave 80 is driven by an adjustable reduction gear. The delay circle 54 is adjustable and causes each line of perforations to be at the line separating the Tube remains in a suitable place in the individual bag 21. At this moment, in which the hose is stopped by the pull roller 44 becomes the one with the web connected bags 21 gripped by movable grippers of the stacking device 48, stretched, torn off the hose at the perforations and placed on a conveyor belt 56 filed. Immediately thereafter, the knife 46 is automatically actuated to cut off the remaining piece 22. The reduction gear 58 is driven by a motor 59 powered.

A camshaft 61 is also provided by the reduction gear powered, The electromechanical working cycle in which a bag is manufactured starts operation of a trip switch 62 on shaft 61. This switch is activated once per manufactured bag. As shown in FIG. 3 it can be seen that it is operated mechanically by the shaft 61, each manufactured Bag makes one turn. This mechanism also operates the hole punching mechanism 42, the knife 46 and the stacking device 48. The trigger switch 62 actuates two scanning circles simultaneously, namely one responsive to the marking area photoelectric circuit consisting of the delay circuit 67 and individual circuits 63, 78, 68 and the circuit 54 responsive to the perforation.

The operational sequence of the person used to scan the registration mark Circuit is as follows: By closing the trigger switch 62, the hose set in motion by releasing the brakes and engaging both clutches 55 and 64 will. As a result, the pull rollers 44 arranged in front of the knife and the belt 27 powered.

This belt is connected to the roller 29 which is passed through the reduction gear is driven via shaft 65, clutch 64 and shaft 66.

At the same time, the delay circuit 67 begins to control. This Circle has the task of keeping cell 31 out of order until a hose mark is reached the light beam has passed through it, but has to reactivate before it hits the web printed registration bar 12 migrates into the light beam. This time is in Set depending on the length of the area 16 to be cut out. When a Switching clock of the delay circuit 67 is completed, the cell 3; 1 ready for use, to capture the next registration bar 12. The interruption of the light beam The switching device controlling the welding is set through this registration bar 68 in progress. This device, which is located in front of the welding station, is set in such a way that that the welding area can advance to station 69 and stop there. When the switching cycle of the device 68 has expired, the tape is simultaneously 27 shut down for the hose by disengaging the coupling 64 and breaking it and the welding head 34 is actuated.

The switch 62, which triggered this workflow, is the for sensing the perforation serving circuit 54 closed. At this moment, when the trigger switch sets the hose in motion, the switching contacts are activated 51, 51, 52 ready to detect the next perforation.

A spark jumping through the perforation is triggered by the Circuit 54 an excitation of the clutch and end with an adjustable time delay Brake assembly 55 triggered and the film with the bag 21 at the station 70 for Brought to a standstill. The speed at which the pull rollers 44 at the station 70 feed the hose is higher than that of the pulling rollers 26; 27, 28, 29 at the Station 69, so that the pull rollers 44 normally a fraction of a second before the Pull rollers 26, 27, 28, 29 come to a standstill. This difference in running speed of the hose is balanced by a pendulum roller 71. This makes it possible to guide the hose through the machine M with minimal tension, while the Sampling at two separate stations 69 and 70 is maintained.

Immediately after the film has stopped at both scanning points At stations 69 and 70 the welding head 34 touches the hose on the belt 27. It actuates also a switch 72 and releases the timer 35 at the first job which controls the time while the welding head remains in the down position. This time can be set on the timer. After this Welding the head 34 goes up and the circuits of the switching devices are up interrupted until the trigger switch 62 again the same operations for the next bag triggers.

The l> i cams 73 and 74 on the shaft 61 are set so that that the punching device and the knife 46 are actuated while the hose is in rest position.

The stacking mechanism 48 is mechanical through the change gear 75 controlled, which drives the shaft 61 and through this the shaft 76. Through this If the tube is separated along the perforation, the separated bag is gripped and placed on the belt 56.

According to the invention, the band 27 on which welding is carried out consists preferably from proportionately thick, resilient material. The tape runs around support rollers 28-30 and is at a clamping point 77 by the revolving draw roller 26 compressed. The tube 10 becomes the curved ob er surface of the elastic belt 27 and fed from there to the nip. The curved one The outside of the thick upholstery tape has a larger radius than the support roller, so that the curved surface of the belt travels at a higher surface speed than the straight surface of the belt (between the support rollers). This will make the Hose fed to the straight part of the upholstery tape in excess.

The hose enters the nip 77 under tension, where it becomes stuck taken and thus with the running speed of the belt surface in contact area is given through the gap on the tape.

The outside of the upholstery tape moves in its curved part itself faster than the tape in its straight part; namely by a factor d X, d. i.e., a length X on the straight dough of the ribbon increases by d X on the curved outside.

This difference has in the surface speed of the belt as a result, the speed at which the hose passes the straight part of the belt is higher than that of the belt surface.

This results in a relaxed film of sufficient length to to compensate for the shrinkage.

A very serious difficulty that has hitherto occurred in experiments, stretchable This overcomes the automatic processing of plastic foils.

It is true that the method described here uses intermittent Movement worked, but the process can easily be continuous design.

Claims (8)

Claims: 1. Process for the continuous production of Bags made from a long, flat tube made of plastic, with the tube attached to a first job welded in the transverse direction and the bag formed on one second, subordinate job is cut off, which is indicated by d u r c h, that the hose at increased speed between the welding jaws of the first Job introduced, but removed from here at a reduced speed so that the hose is welded in the relaxed state. 2. The method according to claim 1, characterized in that the hose along an outer line adjacent to the weld seam simultaneously with the weld seam formation is perforated, the perforation is adjusted at the second work station and then the bag torn from the tube at the perforation point and next to the perforation point is cut off from the hose. 3; Apparatus for carrying out the method according to claim 1 or 2, characterized by a between a support roller (28) and a pull roller (26) running as a pair of rollers, elastically resilient transversely to its longitudinal direction, the Hose transporting belt (27). 4. Apparatus according to claim3, characterized in that the thickness of the band (27) is a multiple of that of the hose (10) or relatively is large compared to the radius of the support roller (28). 5. Apparatus according to claim 3 or 4, characterized in that the one having a curved welding jaw (36) and next to it a perforation knife (38) Welding head (34) is arranged next to the draw roller (26). 6. Device according to one of claims 3 to 5, characterized in that that the position of the perforation adapted, penetrating switching contacts (50, 52) at the second job in an electrical control circuit by which the gripper (48) and knife (46) can be controlled: 7. Device according to one of claims 3 to 5, characterized in that the first job (34, 33, 72) with a photoelectric cell (31) for scanning a registration mark is provided on the hose (10) and one with the circuit of the photo electrical Cell connected delay circuit (67), which the circuit outside of the marking area (16) makes ineffective, and that the delay circuit actuating Devices (68) for stopping the movement of the hose (10) at the first Job are available. 8. Apparatus according to claim 6, characterized in that the through The switching contact formed through the perforated tube is designed as a spark electrode is. References considered: U.S. Patent No. 2444 685.