CA2077295A1

CA2077295A1 - Method for making, filling and sealing sacks

Info

Publication number: CA2077295A1
Application number: CA002077295A
Authority: CA
Inventors: Konrad Tetenborg
Original assignee: Konrad Tetenborg; Windmoller & Holscher
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1991-09-23
Filing date: 1992-09-01
Publication date: 1993-03-24
Also published as: EP0534062A1; DE59207488D1; DE4131646A1; BR9203678A; JPH05278703A; ES2093142T3; EP0534062B1; JP3330646B2; ATE144950T1

Abstract

METHOD FOR MAKING, FILLING AND SEALING SACKS

ABSTRACT

The invention relates to a method for making, filling and sealing sacks or bags from a tubular film web of thermoplastic material preferably provided with side folds and printed in format print. The leading end of the tubular film web is provided with a transverse weld; a section constituting an open sack is cut off from the tubular film web; the sack is then filled; and the open end of the sack is sealed by a transverse weld. The invention seeks to provide a method where the sacks produced are always an appropriate size to be filled tight and full. It is provided that the length of the formed tubular web section is varied, corresponding to the filling level of the sack. After making the transverse weld forming the sack, the tubular film web is advanced up to a printed mark. The section constituting the sack is cut off by means of a separating cut without at the same time forming the transverse weld sealing the leading end of the tubular film web, then the web is again advanced by a comparatively short adjustable length, and the excess section of tubing is cut off and at the same time a transverse weld is formed.

Description

1090~11

2~2~c~3 ~ETE~OD FOR MP.KING, FIL~ING AND SEALING SACKS

This invention relates to a method for making, filling and sealing sacks or bags from a tubular film web of thermoplastic material, preferably provided wi-th side folds, and printed in format print. The leading end of the tubular film web is provided with a transverse weld, and the section forming an open sack is cut off. The sack is then filled, and the open end of the sack is closed by an additional transverse weld.

Such methods are largely known in the prior ar-t. For instance, the sections that will later constitute the sack are withdrawn from a tubular web in accordance with a known method.
The tubular web is perforated at predetermined distances, so that the sections correspondin~ -to the future sacks can be torn off along the perforations. After forming a transverse bottom weld, the individual sack sections are supplied to the charging hopper for filling, for instance with granular material. When a predetermined quanti-ty of the material has been filled into the sack, the open sack is removed, pulled taut at the open end, and sealed in a special trimming means.

However, the method can also be performed by means of an appara-tus in accordance with -the DE-OS 37 15 685. This apparatus comprises sliding and advancing rollers, by means of which the leading end of the tubular film web provided with a transverse weld is moved in a vertical direction while freely hanging down, advancing intermittent].y one length of bag or sack at a time, between -the welding jaws of a welding device. The welding device jaws open and close in a horizontal plane. Below the welding jaws a transverse cutting means is disposed, and below the transverse cutting means grippers arranged in pairs on a transport means are provided, which supply the hanging bags or sacks via a cooling line (for cooling the transverse weldsl to a transfer means transporting them to a filling station. The transport means consists of a hub-like supporting member, which 2 ~ r~rj is pivotally mounted about a vertical axis, with radial arms whose free ends are provided with grippers arranged in pairs.
The cooling line consists oE a cooling carrousel, which carries the sack workpieces, provided with transverse welds and cut off from the tubular web, from-the welding stat.ion on a circular path to a means for transferring the sack workpieces -to the Pilling station. When this appara-tus comprises, for ins-tance, four radial arms, there is provided above-the ~irs~ station a welding means as well as a cutting means. In accordance with this prior art each cycle of making a sack comprises the steps of introducing from the top a-tubular film web already provided with a transverse weld into the first pair of open grippers, and seizing and cutting off the tubular film web after it has been advanced by the length of one sack. Then, a new transverse weld is formed at the end of the tubular web, while the cooling carrousel intermittently rotates about an angle of 90 and remains in this position until a fur-ther sack provided with a -transverse weld has been introduced in the succeeding station.
In a four-arm cooling carrousel this is repeated until the first station has rotated by 270 in three cycles. At this point the transverse weld has cooled and -the sack is transferred to a transfer means for transporting the sack -to a filling station, where, after filling the sack and pulling the open end of the sack taut, a further transverse weld is made for sealing the filled sack.

In the filling station -the sack is filled with a predetermined quantity oE Eilling material, generally measured as a predetermined weight of material. However, the filling material, for instance a granular material, often has a variable bulk volume for the same weight. This is, for instance, due to a difEerent moisture content of the bulk material. Due to the different volumes it can occur that the sack, after it has been filled and sealed, has an undesired free space between the weld and the filling material. This means that the sacks are not Eilled tight, which in particular, is disadvantageous in the further handling oE the sacks.

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When carrying out -the method by means of an apparatus in accordance with the DE-OS 37 15 6~5 -there is an addi-tional problem, in that no adjustmen-t oE the trlmmlng means disposed ln the same apparatus is provided, so -that depending on the bulk density of the filling material the sacks can be either filled tight, or are filled with an undesired amount of excess air between the filling material and the sealing transverse weld.

The present invention seeks to provide a method such that it is ensured that all sacks can be filled tight and full, without undesired dead volume.

In accordance with the invention, the length of the formed tubular film web sec-tions is varied corresponding to the filling level of the sack.

After forming a first transverse weld the tubular film web is intermittently advanced up to a preprinted mark. The section constituting the sack is cut off by means of a separating cut without simultaneous formation of an additional transverse weld. The tubular film web then is advanced by a comparatively short adjustable length, the advanced section of the tubular film web is cut off, and the transverse weld sealing the succeeding tubular section is formed. This invention is based on the knowledge tha-t the bulk properties of the filling ma-terial do not change abruptly. When it is detected that, due -to a change of the bulk density, the bulk volume of the filling material has changed, the length of the formed tubular film web sections can be varied by a corresponding adjustment of the sliding and advancing rollers of the apparatus advancing the tubular film web, and thereby adapt the length oE the sack to the changed filling level of the filling material in the sack. By means of the method in accordance with the :invention, the length of each formed section can be varied without cutt:ing the tubular film web at a preprinted point. It is essential that the tubular film web is always advanced up to a preprinted mark at the opening edge of the sack to be cut oEf, that it is cut off then, and ~hat in 2~r~r~
accordance wlth the length of the sack to be formed the position of the bottom weld of the succeedillg section is varied in accordance with the required filling level. Depending on the filling level of the filling material there is formed a tubular film web section a few centimeters long which can be collected separately and can be recycled. Alternatively, said tubular film web section, in particular when it only has a very small length, can remain on the sack as excess.

In accordance with a further embodirnent of the invention the above-described intermedia-te advance of the tubular film web after cutting off -the sack section can be set at zero for the case when the bulk material reaches its minimum density to be expected and thus a maximum bulk level. This is the case, for instance, in the comple-tely dry condition of a granular material to be filled. In this case, when cutting off the leading sack section the transverse weld o~ the succeeding sack section can be formed at the same time, utilizing the maximum available leng-th of the tubular film web sec-tion.

When during the cutting off and Eorming of the transverse welds corners are welded ofE a-t the same time, as is known from the EP-A 00 21 463, it should be considered tha-t in this case the corners of the opening edge of the leading bag and the corners at the bottom weld of the succeeding bag section cannot simultaneously be formed by means of a single tool, as this would for instance be easily possible in a tubular Eilm web with scattered print. Therefore, in accorclance with a further advantageous embodiment oE the present invention khe welding of corners at the opening edge oE the sack section and at the bottom seam is made by means oE separate corner welding tools.
Corresponding to -the length oE the :Lnterrnediate section, the section can then manually or automatically be readjusted between the separate corner welding tools. ~dvantageously, all corner welds can be formed-together with the transverse weld sealing the succeeding tubular section.

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Alternatively, the welding of corners at the opening edge of the sack section can be made together wlth the separating cut, and the welding of corners at the bottom seam can be made together with the formation of the transverse weld. In this method variant it is, however, accepted that the duration of the method sequence is compara-tively longer.

The speed is now no longer determined by the time required for cutting the web, but by the time required for welding the corners. In the case where the intermediate advance is set at zero, both tools are advanced to the tubular film web at the same time.

An embodiment of the invention will subsequently be described in detail by means of the drawings, wherein:
Figure 1 shows an apparatus for carrying out the method in accordance with the invention for making bags or sacks comprising a cooling carrousel in a schematic side view, Figure 2 shows a section through the apparatus along line II-II in Figure 1, Figure 3 shows the por-tion circled in Figure 1 with a dash-dotted line in an enlarged representation, Figure 4 shows a central portion of the apparatus of Figure 1 on a greater scale, and Figure 5 is a plan view of the locking plate apparent in Figure 9.

Referriny now to the drawings frame 1 comprlses side walls 2 and 3, which are indicated i.n Eigure 2. Both side walls 2, 3 are connected with each other by a crossbar 9 (which is cut away for clari.ty in Figure 2). The crossbar 9 is provided with a downwardly extending fixed shaft 2:L, on which in the vicinity of the crossbar 9 a swivel arm 5 is mountecl, which by a fluid piston cylinder unit 6, which :is rigiclly supported, can be rnoved to either of two possible end positions.

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In Figure 5 it can be seen that the swivel arm 5 designed as an angle lever carries a molding 5' at its free end, and in its angle sector is provided with a retaining roller 7.
The function of these parts will be discussed Eurther below.

A further ver-tical axis 8 is at-tached to the crossbar ~, which below the swivel arm 5 carries a four-arm rotary table 9, which by means of a toothed belt 10 can be intermittently rotated by a motor 11 in steps of 90~. The direction of rotation of the rotary table 9 is indicated in Figure 2 by the arrow A.

From Figure 2 it can be seen that the freely protruding arms 9a of the ro-tary table 9 constituting a hub, comprise moldings 12 each provided with two upwardly projecting pins 13.
Pivotally mounted about each pin 13 is a lever 14, which at its free end consti-tutes a gripper 15. Each of the grippers 15 is urged against an abutment surface 17 by the force of the springs 16, wi-th each molding 12 being provided with -two abutment surfaces 17. The levers 1~ facing each other of -two adjacent arms 9a are functionally connected with each other by connecting rod 18, so that the two associated grippers 15 open or close simultaneously, so as to be able, for ins-tance, to seize and hold a sack 19'.

The grippers 15 are opened by the wedge- or curve-shaped cam surfaces of the molding 5' oE the supporting arm 5.
When the supporting arm 5 is swivelled by extending the piston rod of the fluid piston cylinder unit 6, the molding 5' urges apart the pressure rollers 20 oE the molding 12 connected with the levers 14, so that the grippers 15 swivel about the pins 13 and move away Erorn the associated abutmerlt surEaces 17. By means of the connecting rocls 18 the grippers :L5 oE adjacent rnoldings are released at the same time.

To ensure that in the case of an undesired starting of the motor 11 no damage occurs, from the molding 5', the retaining roller 7 mounted in the angle sector of the swivel arm 5 moves in a guiding groove 22 of a loc]cing plate 23 when the swivel arm is swivelled to open the grippers. The locking plate 23 is firmly connected to -the rotary table 9 by means 24 such as bolts, so that the rotary table is prevented from rotating by-the retaining roller 7 of the swivel arm 5, as long as the molding 5' is present between the rollers 20 of the molding 12.

From Yigure 1 it can be seen that from a roller 25 a tubular web 26 moves into an inle-t station 27. The inlet station 27 is rigidly connected with the frame 1 and is represented in detail in Figure 3. Figure 3 shows the central axis 8 of the cooling carrousel and a part of the rotary table 9. Clamped between the grippers 15 and the abutment surfaces 17 of the rotary table 9 is a section 19' of-the tubular web provided with a bottom seam, which is, however, still connected with the tubular web 26. Above the grippers 15 and 17 there is provided a coupling rod 28 guided in parallel on connecting rods 2~' which, at its end adjacent the web 26 carries a clamping bar 29, which cooperates with a mating bar 31 fixed in a s-tationary support 30. In addition to the mating bar 31, the support 30 includes a knife recei.ving groove 32 as well as a welding jaw 33.
For cutting off the sack 19' from the -tubular web 26 a knife 39 enters the knife receiving groove 32, while a second welding jaw 35 cooperates with the welding jaw 33, so as to provide the leading end of the tubular web 26 with a transverse weld.

The tubular web 26 is printed in format print. In this case it is important that the print is not cut through when the sack sections are formed. Therefore, the advance o the tubular web is gauged intermittently by means of a printed mark provided at the opening edge of the respective sack. Changing the length of the sack section is now effected by varying the length of the strip which :is cut off between the opening edge of the bag section and the bottom weld of the succeeding sack section.
These intermediate sections can then be collected and recycled.
When making the separating cut at the opening edge the knife 39 is applied to the tubular web 26 without the welding jaw 33.

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Having advanced the web by the intermediate section to be cut off, the knife 3~ is again applled to -the tubular web 26, but this -time together with the welding jaw 33. Thus, the cut for separating the lntermediate section and the formation of the transverse weld of the succeediny sack section are efected at the same -time.

Above the welding jaws 33 and 35 a further clamping means is provided for clamping the tubular web 26. The clamping means consists of a pivoting lever 39 provided wi~h a clamping strip 38, which can be moved by means of a fluid piston cylinder unit 40. Firmly connected with the pivoting lever 39 is an arm 42 bearing a roller 41, where the roller 41 in the clamping position of the pivoting lever 39 is disposed at a distance,from a guide member 43. The guide member 43 is connected with a lever 44, which is held in engagement with a stop 46 by means of a spring 45. The pivot of the lever 49 lies on the axis of the advancing roller 47. It has a downwardly pointing projection 48, which constitutes a counterpart for the clamping strip 38. For releasing the clamping, after forming a bottom seam and making a separating cut, the fluid pis-ton cylinder units 37 and 40 are first of all actuated, and as a result the coupling rods 28, 36 as well as the lever 39 are withdrawn. During this movement the roller 41 comes into contact with the cam surface of the guide member 43. This leads to a pivoting of the projection 48 in the direction of arrow C, so that the end of the web 26 freely hanging down is deflected and moved clear of the welding jaw 33.
Due to this deflection it is ensured -that in the next cycle the web does not collide with the support 30, when it is advanced one sack length by the rollers 4'1 and 51.

To furl,her prevent the web 26 from wrapping around the advancing rollers 97 and 51, t,he advanc:ing rollers are provided with annular grooves 49, 50 which engage str:ipping fingers 52 and 53. The fingers 52 are held to block 59 and the fingers 53 are attached to the projection 98 as stripping rakes.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for producing sacks or bags from a tubular film web of thermoplastic material where corresponding to the desired filling level of the sack, the length of the tubular film web sections formed is varied comprising the steps wherein the leading end of the web of tubular film is provided with a first transverse weld seam with a welding tool;
the tubular film web is intermittently advanced to a printed mark;
the section constituting the sack is cut off;
the tubular film web is advanced again by a comparatively short adjustable length and cut off; and a transverse weld sealing the succeeding leading end of the tubular web is formed.

2. A method according to Claim 1 wherein the tubular film web of thermoplastic material is printed in format print.

3. A method according to Claim 1 wherein the tubular film web of thermoplastic material is provided with side folds.

4. The method according to Claim 1 wherein after cutting off the sack section the intermediate advance of the tubular film web can be set at zero; and when the sack section is cut off, the transverse weld of the succeeding sack section is made at the same time.

5. The method according to Claim 1 including the additional step of welding of corners at the opening edge of the sack section and at the bottom seam by means of separate corner welding tools.

6. The method according to Claim 5 wherein the distance between the separate corner welding tools is readjusted automatically.

7. The method according to Claim 5 wherein all corner welds are made at the same time as the transverse weld sealing the succeeding leading end of the tubular web.

8. The method according to Claim 5 wherein the welding of corners at the opening edge of the sack is made together with the separating cut, and the welding of corners at the bottom seam is made together with the transverse weld.