US3512456A - Method and apparatus for mechanically producing string-tied bags - Google Patents

Description

- May 19, 1970 A. MEYER A I 1 METHOD AND APPARATUS FOR MECHANICALLY PRODUCING STRING-TIED BAGS Filed May 4, 1966 4 Sheets-Sheet 1 INVENTOR MW 'BY h /M [1 f ATTORNEY May 19, 1970 I A.-M'E'YER 3,512,456

METHOD AND APPARATUS FOR MECHANICALLY PRODUCING STRING-TIED BAGS Filed May 4, 1966 4 Shee tsSheet 2 42a 42b 24b ma --41b INVENTOR BY juk "L" Li f s [7, [IQ-C1,.

ATTORNEY May 19,1970. A. MEYER 3 12, 56

METHOD AND APPARATUS FOR MECHANICALLY PRODUCING STRING-TIED BAGS Filed May 4, 1966 a 4 Sheets-Sheet 5 INVENTOR BY 1 143. 1g jriv/ ATTORNEY May 19, 1970 A. MEYER METHOD AND APPARATUS FOR MECHANICALLY PRODUCING STRING-TIED BAGS Filed May 4, 1966 4 Sheets-Sheet 4 ATTORNEY United States Patent 3,512,456 METHOD AND APPARATUS FOR MECHANICALLY PRODUCING STRING-TIED BAGS Alfons Meyer, 40 Donauschwabenstrasse, 705 Waiblingen, Germany Filed May 4, 1966, Ser. No. 547,567 Claims priority, application Germany, May 8, 1965, M 65,170; Jan. 12, 1966, M 67,977 Int. Cl. B31b 1/90, 49/04; B65]: 61/14 US. Cl. 93-8 26 Claims ABSTRACT OF THE DISCLOSURE A web of superimposed layers is continuously transported and supplied with two pairs of strings which are placed in folded over tubular hems and drawn from supply bobbins when bag sections are severed, welded, and then transported at a higher speed than the web whereby each bag has strings longer than the width of each bag, which strings are tied to form two draw string loops.

The present invention relates to a method and appartus for mechanically producing string-tied bags which are made of superimposed layers of a plastic or similar sheet material, and especially of a tubular sheet of such a material, and wherein the border at the mouth of each bag is folded over outwardly or inwardly to form a hem for receiving the string for closing the mouth of the bag.

For this purpose it is known to stamp individual apertures for the passage of the strings into the border which is to be hemmed and to insert the strings either before the hemming or after the completed bag has been cut off. Such a method requires, however, a complicated threading of the strings into the hemmed or unhemmed border. Furthermore, after each bag has been cut off, it is necessary to pull the ends of the strings out of the bag so as to permit them to be manipulated.

It is an object of the present invention to provide a method of producing string-tied bags which is much more simple than the methods which were previously employed, and which permits the entire bags including the complete string assembly for each individual bag to be produced mechanically or fully automatically within a single continuous operation. The inventive method essentially consists of continuously applying two strings upon one lateral border of each of the two traveling superimposed layers of the plastic or similar sheet material and folding the borders over the strings and hemming the borders with the strings therein, of then severing a from section of the stringed layers by a transverse cut from the uncut layers behind so as to have a width in accordance with the width of the desired bag, but without severing the strings, of then advancing the severed bag section together with the strings at a speed of travel higher thanthe speed of the layers behind until this section is separated from the front edge of these layers at a distance equal to the desired length of the strings of this bag, and of then severing these strings between the severed bag section and the layers behind so as to have the desired length.

Another advantageous feature of the invention consists in combining the operations of severing the bag section from the continuous layers behind and welding together ice the edges of the two layers directly adjacent to and in front of the transverse cut which then form the lateral rear edge of the severed bag and the edges of the two layers behind the transverse cut which then form the lateral front edge of the bag which is subsequently formed. According to the invention, these severing and welding operations may therefore be carried out simultanously and by the same step.

A further advantageous feature of the invention consists in passing two strings through the hemmed border or hem on each layer and in knotting the two corresponding strings of both borders together, and in making the outlet openings for the strings of such a small size, for example, by reducing their size when making the lateral welds, so that, while the strings may be easily pulled through the hems, one knot on each pair of strings will press from the outside against the mouth of the respective outlet opening and will be prevented from slipping through this outlet opening into the hem.

The two pairs of strings may be cut off and the knots may be tied thereon in positions which are longitudinally offset relative to each other in the direction of travel of the bag section through the apparatus so that in the finished bag one knotted end of each pair of strings may be pulled out at one side of the bag in the opposite direction to the corresponding knotted end of the other pair of strings at the other side of the bag, while the knot at the other end of each pair of strings then presses against the mouth of the respective outlet opening so as to close the bag. Consequently, each knot on both pairs of strings may therefore serve as a handle to facilitate the respective pair of strings to be pulled outwardly in one direction or as an abutment to press against the mouth of the outlet opening when this pair of strings is pulled outwardly at the other end in the opposite direction.

Another feature of the invention consists in the formation of knots which may be produced at a high rate of production of the apparatus and in a mechanically relatively simple manner without causing any appreciable waste of string material. For this purpose, the invention provides that the strings are severed between each preceding and subsequent bag and are then knotted together under tension at both sides of the cut between them by means of tying tongs or similar tools which are rotated in accordance with the other operations of the apparatus.

The method according to the present invention has the advantage over the methods which were previously known that a pair of knots is simultaneously produced and that the tying or knotting device and the severing means for the strings may be easily adjusted so as to be located in such a position that the remaining free ends of the strings may be tied into the desired knots without being required to be of any particular length.

For this purpose, the pair of strings which passes over the tying tongs is preferably gripped by the opened tong mouth when the tongs are turned, and is thereby looped around the tongs, and the two sections adjacent to the loop are then looped through each other whereupon while the strings are under tension the loop is pushed off the tong claws and tightened so as to form a knot. The length of the pair of strings between its cutting point and tying point may then be made equal to the length of the strings whichis required for producing the knot.

Another feature of the invention consists in holding the pair of strings which is to be knotted together so that the section thereof which is located adjacent to the cutting point is slidable under tension, preferably under spring tension, while the opposite section adjacent to the bag is tightly gripped during the knotting operation.

The present invention further relates to the details of the method and of the apparatus for producing the knots. This apparatus especially comprises slide members each of which is adapted to clamp the strings between it and an opposite member. The strings which are layed over the tying tongs are then drawn in the transverse direction and will be gripped by and looped around the tying tongs during the subsequent rotation of the latter for the formation of the knot. By the provision of an ejector, the loop which is previously formed on each pair of strings is then tightened into a knot by drawing the 'strings oif the tying tongs.

The operations of severing the bags and drawing them apart together with the hemmed-in strings which are still uncut are preferably preceded by the operations of folding over and hemming the borders adjacent to the slot which forms the mouth of the bag. The method according to the invention therefore preferably consists of the steps of conveying a fiat tubular sheet of plastic or similar material in one direction, preferably by an intermittent movement because of the required welding operations, of first slitting one edge of this tubular sheet in a conventional manner so as to form a slot which subsequently forms the mouth of the bag, of then supplying two strings to each layer of this sheet and applying them thereon in positions parallel to and near the slit edge and conveying them together with the two layers, of then folding the border of each layer adjacent to the slit edge over the respective pair of strings and thereafter hemming the borders, for example, by welding, so as to enclose the strings within each hem, and of then cutting the two layers transversely so as to form a bag section of the desired width, and at the same time and by the same operation welding together the rear edges of this bag section and the front edges of the following as yet unsevered section at both sides of the cut. Either before or after the borders of the two layers are hemmed, another welding operation is preferably carried out between the two strings within each hemmed border so as to form separate channels for each string.

The various features and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which:

FIG. 1 shows a diagrammatic perspective view of an apparatus for carrying out the method according to the invention;

FIG. 2 shows a plan view of the finished bag;

FIG. 3 shows a cross section which is taken along the line 33 of FIG. 2;

FIG. 4 shows a diagrammatic perspective view of a twin knotter according to the invention in two different positions at the left and right sides of the drawing, in which for the sake of clarity some elements of the apparatus are partly broken away or omitted; while FIGS. 5 to show perspective views on one of the tying devices in different positions of its operation for producing a knot.

As illustrated in FIG. 1 of the drawings, the two superimposed layers 10 of plastic or other suitable sheet material which are required for producing the bags and may, for example, be connected to each other along their lateral edges so as to form a tubular sheet are wound up on a supply roll 11 from which they are drawn when the conveying mechanism is operated. These two layers 10 are at first passed over a guide roller 12 to a blade 13 which slits apart one of their connecting edges 10a while they are traveling in the direction of the arrow.

The two layers 10 are then passed through the conveying or pressure rollers 14, andthereafter the parts adjacent to the edges 10a are spread apart by a wedge-shaped member 15. One pair of strings 17 and 18 is then supplied from a pair of bobbins 16 to an upper inlet guide 21 which is located closely above the upper layer 10, and another pair of strings 19 and 20 is supplied from another pair of bobbins 16 to a lower inlet guide 22 which is located closely underneath the lower layer 10. From these inlet guides 21 and 22 the strings are then conveyed together with the layers 10 in the direction of travel of the latter as indicated by the arrow X. One pair of strings 17, 18 then engages upon the upper side of the upper layer 10 and the other pair of strings 19, 20 engages upon the lower side of the lower layer 10, and all of these strings extend parallel to and at a certain distance from the slit edge 10a of the two layers 10.

At a short distance from the inlet guides 21 and 22 a folding device 23 is provided for folding over the border of each layer 10 adjacent to the slit edge 10a and for thus forming a hem 24. This device 23 which may be of a conventional type folds over the border of the upper layer 10 in the upward direction and the border of the lower layer 10 in the downward direction so that the strings 17 and 18 will be hemmed in by the hem of the upper layer 10 and the strings 19 and 20 by the hem of the lower layer 10.

Shortly after the borders of the two layers 10 have been folded over to form the hems 24, the layers are passed to a pair of pressure rollers 25 and thereafter to the longitudinal welding bars 26 and 27. Welding bars 26 serve for producing separating welds between each pair of strings by welding parts of each hem 24 between the strings 17 and 18 and between the strings 19 and 20 together with the upper and lower layer, respectively, while the longitudinal welding bars 27 serve for closing the hems by welding the previously cut edges together with the inner sides of the folds. Welding bars 26 are preferably made of a short length so that the separating welds will extend only along a small part of the 'width of each bag.

After passing through another pair of pressure rollers 28 which like the rollers 25 are preferably provided with shallow recesses in alignment with the strings in order to prevent the latter from adhering when they are pulled relative to the layers 10, these layers are passed to a severing device 29 which consists of a roller 30 and a transverse welding bar 31 which is adapted to produce a central cutting weld and at the same time a lateral sealing weld on each side of this cutting weld whenever a section of the double layer 10 of the desired width of the bags has passed underneath the Welding bar 31. This seciton is thus severed from the strip behind in the direction transverse to the direction of travel X, and the rear edges of the two layers of this severed section which forms one bag, as well as the adjacent front edges of the layers for producing the next bag are at the same time welded together so as to form the closed lateral edges of these bags.

The bag section which has been severed by means of the welding bar 31 then passes the accelerating and cord drawing mechanism 32 which, according to the partlcular embodiment of the invention as illustrated in FIG. 1, consists of a pair of drawing rollers 33, a further pair of rollers 34, and the conveyor belts 35 which connect the two pairs of rollers 33 and 34 to each other so as to drive the same and which may also serve for conveying the severed bags from the pair of rollers 33 to the pair of rollers 34 and beyond the latter. The pair of rollers 33 is spaced from the roller 30 and the welding bar 31 at a distance b which corresponds approximately to the desired width b of each bag and is preferably adjustable.

Rollers 33 or more preferably the rollers 34 are driven at a peripheral speed higher than the speed of travel of the layers within the apparatus as previously described, so that at the moment when one bag section is severed by the welding bar 31, it will be gripped by the accelerating mechanism 32 and be separated and drawn away from the adjacent section which still forms a part of the strip of layers 10. These individual bags or bag sections which are designated in FIG. 1 by the numeral 36 and have a width b will then be conveyed in the direction of the arrow X at a distance a from each other.

Together with the bags or bag sections 38 the strings 17, 18 and 19, which are not cut apart by the welding bar 31 are drawn along and pulled out of the bag sections for a length in accordance with the distance a. This distance a is made of such a size that the free length of strings 17, 18 and 19, 20 will correspond to the desired length to which the strings should project from each bag. Strings 17, 18 and strings 19, 20 (not shown) are then cut apart by suitable cutting means as indicated diagrammatically at 37. These cutting means, for example, in the form of shears, are preferably offset relative to each other in the direction of travel X so that one set of shears will cut the strings 17 and 18 near one bag at 37a and the other shears will cut the strings 19 and 20 near the other bag, for example, at 37b. It is, however, also possible to cut all of the strings at the same point, and the strings may then be drawn out subsequently to the desired length, for example, if they are tied together by hand.

If the shears are offset relative to each other, they may also be associated with a tying device which knots the severed ends of the respective strings at 37a and at 37 b mechanically to each other.

The bags after being thus completed are then passed to the point 38 where they are sucessively deposited on top of each other so as to form a stack 39.

FIGS. 2 and 3 illustrate a side view and a cross section of one of the finished bags 36 which consists of the two layers 36a and 36b which are connected to each other along the lower edge 40 by the fold of the tubular sheet material and along the lateral edges 41a and 41b by the welds which are formed by the welding bar 29.

The upper edges of the two layers 36a and 36b are folded over to form the henis 24a and 24b and each of them is connected substantially centrally of its width to the end of the layer 36a or 36b of the tubular sheet by an intermediate or spacing weld 42a or 42b which is produced by the Welding device 26, while the lower edge of each fold is connected to the layer 36a or 36b, respectively, by a line of weld 43a or 43b which forms a hem seam and is produced by the welding device 27. Strings 17 and 19 are thus loosely hemmed-in between the hem seam 43a or 4311 and the spacing weld 42a or 42b, respectively, while strings 18 and 20 are loosely hemmedin between the spacing welds 42 and 42b and the upper folded edges of the layers. The free ends of strings 17 to 20 then extend at both sides from the bag 36 for a length which depends upon the selected distance a and the location of the cutting means 37, for example, at 3711 or 3711, respectively, as indicated in FIG. 1. By means of the tying device, the strings of each pair may be tied together in the manner as illustrated by the knots 44, and 46 and 47, respectively. The openings 44a, 45a, 46a, 47a where the strings pass from the bag at the edges 41a and 41b thereof to the outside are preferably closed to such an extent by the separating weld that the strings 17 to 20 may just be drawn through without interference. If the strings are then pulled outwardly on the knots 45 or 46 in the opposite directions, as indicated by the arrows Z1 and 2 the knots 44 and 47 Will press against the mouths of the openings 44a and 47a and thereby draw together and close the mouth of the bag.

FIGS. 4 to 10 illustrate by way of example an apparatus for mechanically knotting the strings together in accordance with the present invention.

FIG. 4 illustrates a stationary frame 110 to which a pair of string supports 111 are rigidly secured, and on which the shaft 112a of the driving lever 112 is mounted so as to be pivotable about the axis X of this shaft. This driving lever 112 is controlled by a drive shaft (not shown) by means of a cam plate of a suitable design. By means of an intermediate plate 113 which is rigidly connected to and pivotable about the axis Y of a shaft 113a and provided with an adjustable roller 114, the driving lever 112 is operatively associated with three levers 116, 117, and 118, each of which is provided with an adjustable control roller 115 (only one being shown in FIG. 4). Levers 116 and 177 are adapted to actuate the holding brackets 119 and 120 so as to move the latter either downwardly in the direction of the arrow f until they engage, preferably resiliently, with the string support 111, or upwardly in the direction of the arrow f Lever 118 is adapted to actuate a cutting blade 121 so as to move the same likewise in the upward and downward directions in accordance with the arrows f and f This cutting blade 121 may enter into the gap 122 which is provided between the two string supports 111.

At both sides of frame 110 a pair of clamping slide members 123 and 124 are mounted which are movable back and forth in a horizontal direction are guided by bolts 125 and 126 which are movable within slots 127 and 128. These slide members 123 and 124 are operatively associated with arms 129 and 130 and each of them is for this purpose provided with a recess 131 which is open toward the front and defined at its lower side by a fingerlike projection 132 which serves as a support for the strings and at its upper side by a projection 132a, the upper side of which is provided with an inclined or rounded surface 133. Each arm 129 and 130 is provided at its front end with a horn-shaped projection 134 which extends upwardly and is located at a certain distance from the stop surface 135 on slide member 123 when the apparatus is in its inactive position, as shown at the left side of FIG. 4, so that an opening 136 for the passage of the strings is then formed. The size of this opening 136 may be reduced to zero or nearly zero when the slide member 123 is shifted forwardly in the direction of the arrow f Slide members 123 and 124 are further operatively associated with pawls 137 and 138 which are pivotally mounted on frame 110 and may be pivoted in the clockwise direction by setscrews 140 on the ends of arms 141 on the levers 142 which are rigidly connected to the shaft 113a and by the latter to the intermediate plate 113. By this pivoting movement of pawls 137 and 138, the locking surfaces 143 thereof will disengage from the associated upwardly projecting locking surfaces 144 on slide member 123 or 124 so that the latter will then be moved forwardly in the direction of the arrow f;, by the action of a spring (not shown).

Each of the string supports 111 carries a string guide 145 which is provided with a slot 146 and an inclined edge 147 along which the strings to be guided may slide into the slot 146.

Between the slide members 123, 124 and the string guides 145 the apparatus is further provided with tying tongs 148 and 149 which are of the same shape and design. Each of these tying tongs is driven by a worm shaft 150 which is rotated by the opposite edges 151 of driving lever 112 in such a manner that the edge 151 engages with the flattened helical surfaces 152, 152a of 'worrnshaft 150 so that, when the driving lever 112 is moved in the direction of the arrow g, the worm shaft will be turned in accordance with its winding.

The two tying tongs 148 and 149 are controlled in a manner known as such by means of control cams, for example, eccentrics 153, so that when the Worm shafts 150 and thus the associated tying tongs are rotated, the rear claw 154 of each tong assembly will move away from the two front claws 154, each of which is, for example, rigidly connected to one of the worm shafts 150, so that the mouth 156 between the claws will be opened, and will thereafter move again toward the front claws 154 so that the month 156 will be closed. These operations will subsequently be further described in detail with reference to FIGS. to 10.

Levers 142 further carry the shafts 157 and 158 of the string guide rollers 159 and 160. For illustrating the structure more clearly, guide rollers 159 and 160 are only shown at the right side of FIG. 4 together with short pieces of the shafts 157 and 158, while at the left side of FIG. 4 only the ends of these shafts on the lever 142 are shown. These guide rollers 159 and 160 serve for conveying the pair of strings 162 which extend parallel to the conveyor belts 161 and are indicated at the left side of FIG. 4 in the upper position 162a and in the lower position 162b. The conveyor belts 161 are driven by the machine so as to rotate the rollers 159, 160 which are pressed against each other by springs, not shown.

Frame 110 further supports the ejector 163 which is pivotally mounted on the pivot bolts 126 and provided with two upwardly extending ejector arms 164 and a control arm 165 which is driven by the driving lever 112 by means of a roller 165a or the like. Control arm 165 is supported on driving lever 112 at a point intermediate the axis X and the axis of pivot bolt 126 when the driving lever is pivoted beyond a certain position in the direction of the arrow g.

The mode of operation of the apparatus as previously described is as follows:

The left half of the apparatus as shown in FIG. 4 illustrates this apparatus in its position prior to the insertion of the strings, that is, when the strings are in the position 162a, and after the insertion of the strings, that is, when they are in the position 162b, while the right side of the apparatus as shown in FIG. 4 illustrates the latter in its position after the knotting operation has been completed. Of course, in the actual operation of the apparatus both sides thereof are symmetrical and are actuated simultaneously in the same manner.

The pair of strings 162 which is inserted into the hem of one of the layers of the tubular sheet according to FIG. 1 is passed into the apparatus by the left pair of rollers 159, 160 (not shown) and then over the slide members 123, 124, the tying tongs 148, 149 and the string guides 145 and string supports 111, and then out of the apparatus by the right pair of guide rollers 159, 160. The adjacent bags, the string ends of which are to be tied together so as to form knots, are hereby drawn apart by means of the conveyor belts 161 so as to be spaced at a distance a from each other, as shown in FIG. 1. The bags then hang over the front end of the apparatus. The bags and strings are conveyed by means of the endless conveyor belts 16-1, the lower parts of which may run, for example, over the driving guide roller 166 and the further guide rollers 167.

For producing the knots, the driving lever 112 as well as the intermediate plate 113 which is applied under sp ing pressure against this lever, and also the levers 142 which are connected to plate 113 and carry the string guiding rollers 159 and 160 are pivoted by the driving means of the machine in the direction of the arrow g. As the result of this movement of driving lever 112 and of the guide rollers 159 and 160, strings 162 are lowered from the position 162a to the position 162b, while at the same time the holding brackets 119 and 120 are also pressed resiliently upon the support 111. Strings 162 then slide downwardly along the inclined surfaces 133 on slide members 123 and 124 and along the inclined edges 147 of the string guides 145 until they rest on the fingerlike projections 132 and are inserted into the slots 146. The holding brackets 119 and 120 then hold the strings with such a spring force on the supports 111 that they can be moved in the longitudinal direction only against a certain frictional resistance.

During the downward movement of the strings, they engage upon the bottom of the recesses 148a and 1490 of the tying tongs and the string guides 145, as illustrated at the lower string position 162b in FIG. 4.

As soon as the pair of strings is pressed by the holding brackets 119 and against the supports 111, it is cut apart between these two brackets within the slot 122 between the two supports 111 by the cutting blade 121 which then moves downwardly in the direction of the arrow f and is preferably likewise acted upon by a spring.

During the further movement of driving lever 112 in the direction of the arrow g the pawls 137 and 138 will be pivoted upwardly by the arms 141 and the setscrews from the locking position, as illustrated by the left pawl 137, in which the locking surfaces 143 and 144 are in engagement with each other, so that they will then be in the position of the right pawl 138. The slide members 123 and 124 which are acted upon by springs will thereby be released and moved rapidly in the forward direction as indicated by the arrow f until the rollers 144a again engage upon the driving lever 112. When this lever 112 is then further moved in the direction of the arrow g, slide members 123 and 124 will be further shifted in the direction of the arrow f until the stop surfaces 135 abut against the horn-shaped projections 134 on the arms 129 and 130, as illustrated by the slide member 124 and the arm 130 at the right side of the apparatus according to FIG. 4. Strings 162 will thereby be clamped in the position 16% on the projection 134 and be moved forwardly beyond claw 154. This position of the apparatus and of the pair of strings 162 is illustrated in detail in FIG. 5.

During the further movement of driving lever 112 in the direction of arrow g the tying tongs 148 and 149 are rotated by the worm shaft 150 since one edge 151 of lever 112 then slides along the spirally-shaped surface 152 of the associated worm shaft 150 and thereby turns the respective tying tongs accordingly. When the tying tongs 148, the stationary claws 154 and moveable claw 155 of which are mounted essentrically within the control cam 153, are moved in the direction of rotation as indicated by the arrow z from the position according to FIG. 5 via the positions according to FIGS. 6 and 7 to the position according to FIG. 8, the loop for the knot will be for-med in strings 162. When the tying tongs, for example, tongs 148, are turned from the position according to FIG. 6 to the position according to FIG. 7, strings 162 which are bent forwardly are layed around the tong claws. When the opened tongs are then further turned past the string guide 145, the strings will be gripped by the tongs within their opened mouth 156, as shown in FIG. 8, and, when the tongs which are then closed by the control cam 153 are then further turned, the strings will be drawn out from its position underneath the holding brackets 119 or 120 and be clamped by the claws 155, 156 while the loop 168 is formed, as shown in FIG. 9.

Tying tongs 148 or 149 then remain in a vertical position, as illustrated in FIG. 9, while the driving lever 112 moves further in the direction of the arrow g so that the edge 151 slides along the plane surface 152a of worm shaft 150 and causes the ejector 163 to be moved upwardly from the position as shown at the left of FIG. 4 to the position as shown at the right by means of the rollers 165a and arm 165. By means of one of the ejector arms 164 acting upon the end of the pair of strings which is held by the claws 154 and 155 of tongs 148, loop 168 is thereby drawn off the claws in the direction of arrow k as shown in FIG. 9, and, since the strings are then held at one side by the slide members 123, 124 and at the other side by the claws 154, 155 of tongs 148, the loop 168 is drawn tight to form the knot 169, as shown in FIG. 10.

During the return movement of driving lever 112 about the axis X, at first the ejector 163 will be pivoted back in the direction of the arrow I1 for example, by the action of a spring. At the same time, the tying tongs 148, 149 are turned back and the slide members 123, 124 are withdrawn by the pins 144a from driving lever 112 9 until they are in the position as shown in FIG. 4 by the left slide member 123, in which they will be locked by pawl 137 or 138 by means of the locking surfaces 143, 144. This locking action may be produced by the weight of the pawl or by a spring which acts upon the pawl. Finally, the cutting blade 121 and the holding brackets 119, 120 will be lifted by means of the levers 118 or 116,

117 and the string guiding rollers 159, 160 by means of the levers 142.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no way limited to the details of such embodiment but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim is:

1. In combination with an apparatus for successively producing string-tied bags from two superimposed layers of a sheet plastic, including means for feeding said layers at a certain speed in one direction together with at least one string loosely contained within a hem along one edge of each layer, means for severing said layers in a direction transverse to their direction of travel so as to obtain a front section of the desired width of a bag but without severing said strings, means for welding together the rear edges of the layer parts of said section and the front edges of the layers behind said section, means for conveying said section with said strings therein in said feeding direction at a speed higher than said feeding speed so as to draw said section away from the front edge of said layers behind said section and thereby to draw said strings through said hems of said layers behind said section so as to form free strings, means for cutting said free strings so as to form two string parts projecting from the rear edge of said section and from the ends of the two hems thereon and two string parts projecting from the front edge of said layers behind said section and from the ends of the hems thereon for lengths substantially equal to the desired lengths of the projecting string parts on each finished bag, and tying means for knotting together the ends of the corresponding string parts substantially simultaneously with said cutting at both sides of the cut, said tying means comprising two sets of tying tongs spaced from each other in said feeding direction, means for rotating said tongs, and string holding means in front of and behind each set, said cutting means comprising a cutting blade between said two sets of tongs, and means for driving said holding means, said cutting blade, said tongs, and said conveying means in a timed relation to each other.

2. An apparatus as defined in claim 1, further comprising an ejector associated with each set of tongs for sliding a completed loop off the tong claws of each set and for tightening the loop, and means for moving said ejectors in a timed relation to said driving means of said tongs.

3. An apparatus as defined in claim 2, further comprising guide rollers in front of and behind both sets of tongs, and means for lifting and lowering said guide rollers.

4. An apparatus as defined in claim 3, further comprising a'frame for supporting said tying tongs and .their associated means, said driving means being adapted to lift and lower said guide rollers, said string holding means, said cutting blade, and said ejectors relative to said frame and to rotate said tying tongs, and main driving means for driving all of the individual driving means of said apparatus.

5. An apparatus as defined in claim 4, in which said string holding means comprise clamping means at one side of each set of tongs and having a movable part adapted to move at right angles to the lifting and lowering movement of said string guiding means for drawing the strings in the axial direction of said tongs.

6. An apparatus as defined in claim 5, in which said string guiding and holding means are designed so as to draw the string sections leading to and from each set of tongs and lying on the neck thereof in the forward direction against the tong head when said string holding means are closed for thereby gripping the strings and forming loops thereon.

7. An apparatus as defined in claim 6, in which the movable parts of said string holding means in front of and behind each set of tongs are movable at right angles to each other within planes extending at right angles to the direction of the strings.

8. An apparatus as defined in claim 6, in which the string holding means which are movable at right angles to the exis of rotation of each set of tongs are operatively associated with a relatively stationary inclined guide sur face for the strings so that by the movement of the movable part of said holding means the string section passing over the inclined surface carries out a downward movement into the neck of the tongs and also a forward movement in the direction toward the head of the tongs into a clamping slot, and in which the part of the string holding means which is movable in the axial direction of the tongs and has an inclined guide surface along which the strings can slide while being lowered upon a receiv ing surface forms a clamping slide member which while moving forwardly clamps the strings between it and a relatively stationary member.

9. An apparatus as defined in claim 8, in which said holding means are resiliently held in their clamping position.

10. An apparatus as defined in claim 8, in which the movable part of at least one of said holding means is held in its inactive position by a locking device and is released shortly before the string is knotted and quickly moved by spring action into the clamping position.

11. An apparatus as defined in claim 1, in which each set of tongs is rotatably mounted within an eccentric guide which during the rotation of said tongs produces a movement of the tong claws relative to each other for opening and closing the tong mouth.

12. An apparatus as defined in claim 1, in which said driving means for said tongs comprise a worm shaft connected to each set of tongs, a member engaging into the worms of the worm shafts of both tong sets, and a con trol shaft for rotating said member and for thereby simutaneously rotating both tong sets.

13. An apparatus as defined in claim 12, in which said member comprises a lever connected to said control shaft and adapted to be pivoted about the axis of said control shaft in a direction parallel to the axes of said worm shafts and having lateral edges engaging into the worms of said worm shafts so as to rotate the same when said lever is pivoted by said control shaft.

14. An apparatus as defined in claim 5, in which said driving means comprise a worm shaft connected to each set of tongs, a lever connected to said control shaft and adapted to be pivoted about the axis of said control shaft in a direction parallel to the axes of said worm shafts and having lateral edges engaging into the worms of said worm shafts so as to rotate the same when said lever is pivoted by said control shaft, another lever connected to and adapted to be pivoted by said control shaft, said other lever carrying said guide rollers for lifting and lowering the same, and arms on said leverfor moving said movable parts of said clamping means.

15. An apparatus as defined in claim 14, in which said clamping means comprise a clamping slide member, locking means for acting upon said slide member for locking it in an inactive position, and means for releasing said locking means.

16. An apparatus for producing double string-tied bags comprising means for transporting two superimposed layers of a sheet material at a predetermined speed in one direction, supply means for continuously supplying one pair of strings to each of said layers and for applying said strings thereon so as to extend along lines near and substantially parallel to one edge of the respective layer, means for folding the marginal parts of said layers adjacent to said edges over each pair of said strings so that the same extend substantially parallel to each other within each of the folded marginal parts, means for joining said edges to said layers so as to form a tubular hem on each layer in which said pairs of two strings are, respectively, loosely enveloped, means for severing said layers in a direction transverse to said one direction so as to obtain a severed leading section of a width equal to the desired width of a bag but without severing said strings, means for moving said severed leading section at a speed greater than said predetermined speed of said unsevered layers so as to draw the unsevered pairs of strings at said speed greater than said predetermined speed through the tubular hems of the unsevered layers from said supply means and to form thereby free parts of said strings between said severed leading section and said unsevered layers located outside of said hems, means for cutting the free parts of said strings so as to form string portions projecting from the ends of the two tubular hems of said leading section for lengths substantially equal to the length desired on each finished bag, and means for joining the ends of the string portions of each of said pairs of string to the corresponding ends of the corresponding string portions of the other of said pairs.

17. An apparatus for producing double string-tied bags comprising means for transporting two superimposed layers of a sheet material at a predetermined speed in one direction; supply means for continuously supplying one pair of strings to each of said layers and for applying said strings along lines near and substantially parallel to one pair of superimposed longitudinal edges of said superimposed layers; means for folding the marginal parts of said layers adjacent said one pair of longitudinal edges over each pair of said strings so that the same extend substantially parallel to each other within each of the folded marginal parts; means for joining said longitudinal edges to said layers, respectively to form a tubular hem on each layer in which said pairs of twostrings are, respectively, loosely enveloped; means for joining at least a part of each folded marginal part of said hem of said superimposed layers to the associated layer substantially centrally between the strings of the respective pair of strings within each tubular hem for dividing at least a part of each tubular hem into two coextensive tubular hem parts containing and guiding one string, respectively; means for severing said layers in a direction transverse to said one direction without severing said strings so as to obtain a severed leading section of a Width equal to the desired width of a bag; means for joining together the transverse edges of said layers without closing said tubular hems so as to obtain a separate bag section; means for drawing the unsevered strings of said pairs of strings through said tubular hem parts, respectively, of the unsevered layers, and from said supply means so as to form free parts of said strings located outside of said hems; means for cutting the free parts of said strings so as to form string portions projecting from the ends of said tubular hem portions of said leading section for lengths substantially equal to the length desired on each finished bag, and means for joining the ends of each of said pairs of strings to the corresponding ends of the corresponding string portion of the other of said pairs.

18. An apparatus as defined in claim 17, wherein said means for joining part of each folded marginal part of said hems to the associated layer, is located adjacent said transverse edges so that said tubular hem parts are located at the open ends of said hems, respectively.

19. An apparatus as defined in claim 17, in which said means for drawing said strings comprise conveying means for conveying said severed leading section with said pairs of strings therein in said one direction at a speed higher than said predetermined speed of said layers so as to move said severed leading section away from the front edge of said unsevered layers behind said severed leading section.

20. An apparatus as defined in claim 19, in which said conveying means comprise at least one pair of rollers acting upon the opposite sides of said severed leading section and being spaced from said severing means at a distance substantially equal to the width of the desired bag so that said section will be gripped by said rollers substantially simultaneously with being severed from the said superimposed layers, and means for driving it least one of said rollers.

21. An apparatus as defined in claim 20, further comprising means for adjusting said rollers so as to vary the distance of the same from said severing means.

22. An apparatus for producing double string-tied bags comprising means for transporting two superimposed layers of a flat tubular sheet of plastic which are connected along their lateral edges at a predetermined speed in one direction, means for cutting open one of said lateral edges, supply means for continuously supplying a pair of strings to each of said layers and for applying said strings thereon so as to extend along lines near and substantially parallel to said cut edge of the respective layer, means for folding the marginal parts adjacent to said out edges over said strings, welding means for welding said edges to said layer so as to form a tubular hem on each layer in which said pairs of strings are, respectively, loosely enveloped, means for severing said layers in a direction transverse to said one direction so as to obtain a severed leading section of the desired width of a bag but without severing said strings, means combined with said severing means for welding together the rear edges of the layer parts of said leading section and the front edges of said superimposed layers behind said leading section substantially simultaneously with the severing of said leading section, means for conveying said severed leading section with said strings therein in said one direction at a speed higher than said predetermined speed of said layers so as to draw said severed section away from the front edges of the superimposed layers behind said severed sectionand there-by to draw said unsevered strings from said supply means through the tub ular hems of the unsevered superimposed layers and from the front edges of said unservered superimposed layers so as to form free parts of said strings, means for cutting said free parts of said strings so as to form string portions projecting from the rear edge of said severed section and from the ends of the two hem portions thereon, and other string portions projecting from the front edges of said superimposed layers behind said section and from the ends of the tubular hems thereon, and means for joining the ends of the corresponding string portions substantially simultaneously with said cutting at both sides of the cut.

23. An apparatus as defined in claim 22, further comprising additional conveying means intermediate said supply means and severing means and comprising at least one pair of pressure rollers acting upon the opposite sides of said superimposed layers, and means for driving at least one roller of said pair.

24. An apparatus as defined in. claim 22, said welding means comprising means for welding at least a part of each folded marginal part to the associated layer substantially centrally between said pair of strings 'within said tubular hems for dividing at least a part of each tubular hem into two tubular coextensive parts each containing and guiding one string.

25. An apparatus as defined in claim 24, in which said welding means comprise two pairs of welding bars extending behind each other in said one direction of said layers and being adapted to act upon the outer side of each layer.

13 14 26. An apparatus as defined in claim 17, in which said 2,897,729 8/1959 Ashton. welding means comprise at least one pair of welding bars 2,993,455 7/1961 Baize. extending in said one direction of said layers and having 3,058,402 10/1962 Kugler. parallel welding surfaces laterally adjacent to each other 3,058,403 10/ 1962 Kugler.

for substantially simultaneously welding said edges and 3,079,844 3/1963 Kugler. forming the separating welds on said hems and adapted to act upon the outer side of each layer. FOREIGN PATENTS 1,084,473 6/1960 Germany.

References Cited UNITED STATES PATENTS 10 WAYNE A. MORSE, JR., Primary Examiner 3,406,610 10/1968 Golden. 1,125,666 1/1915 Dalton 93-91 X 2,777,491 1 1957 Ashton, 93-35, 91; 53-435

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