GB2179590A - Apparatus for folding a flexible tubing to form sack bottoms, and for welding the bottom seams - Google Patents

Abstract

Apparatus for folding a flexible tubing to form sack bottoms (60) (Figure 2) and for welding the bottom seams comprises a deck (1) Figure 1 having a central slot means (50, 51) for longitudinally transporting the tubing through the slot over a distance which is sufficient to permit the bottom to be formed, an arm or stirrup (70, 71) which is pivoted to the deck and drive, means (69, 78, 79) provided for pivotally moving said arm or stirrup through about 180 DEG between the mutually opposite sides of the deck, so that suckers provided on the mutually opposite opening-defining edges of the flexible tubing at locations which are centrally disposed between the side folds of the tubing section open the flexible tubing which protrudes beyond the slot to form a complete square bottom (60) and a strip-shaped tubing portion, which is formed in the tubing section as a continuation of the inner edges of the infolded triangular portions. Stretching pins (82, 90) See Figure 11 are provided, which serve to stretch the square bottom and to flatten the strip-shaped tubing portion and cooperate with those portions of the deck and of the pivoted stirrup in which the suckers are disposed. Welding bars 40, 41 Figure 2 are provided which seam the strip-shaped tubing portions together. <IMAGE>

Description

SPECIFICATION Apparatus for folding a flexible tubing to form sack bottoms in the manufacture of sacks and for welding the bottom seams This invention relatestoapparatusforfoldingflexible tubing to form sack bottoms in the manufacture of block bottom sacks and for welding the bottom seams, which apparatus comprises suckers, which are disposed on opposite sides of the tubing and serve to open the tubing at one end thereof, a deck having a central slot, means for longitudinallytransporting the tubing through the slot over a distance which is sufficient to permit the bottom to be formed, and gripping and/or holding and stretching means, which are adapted to engage mutually opposite opening-defining edges of the tubing at the centre between the side foldsofthetubing,wherein one ofsaid gripping and/or holding and stretching means is mounted on the frame oron the deck and the other is mounted on an arm or stirrup, which is pivotedtothe frame, and drive means are provided for pivotally moving said arm orstirrupthrough about 1800 between the mutually opposite sides of the deck.

An apparatus ofthat kind is hnown from German Patent Specification 2931 607 and serves to form square bottoms by a folding offlexible tubing in the manufacture of large sacks. In that known apparatus the flexible tubing which has been folded to form the square bottoms are prov ided in succeeding processing stations with the welded or adhesive seams by which the bottom is closed. The square bottoms which have been formed by means of that known folding apparatus have triangular portions, which have been stretched apart and infolded by separate stretching means.The confronting inner edges of said infolded portions are spaced apart so that the square bottom has the shape of a double trapezium and the strip-shaped opening in the square bottom must be closed by the application of a so-called inner sealing strip, which is joined by welding or sticking, before the bottom can be completed in that the side portions are infolded to overlap each other and the bottom is closed by means of a bottom patch, which is welded or stuck onto said infolded side portions.

It is an object of the invention to provide an appar atus which is of the kind described first hereinbefore and which can be operated to perform in one station the operations offolding an end portion of flexible tubing in the manufacture of large sacks and of forming the seam welds for sealing the bottom whereas the need for inner sealing stripsforsealing the square bottoms is eiiminated.

In an apparatus of the kind described first hereinbefore that object is accomplished in that at least one sucker is provided on the deck and at least one sucker is provided on the pivoted stirrup, said suckers are provided on the mutually opposite opening-defining edgesoftheflexibletubing at locations which are centrally disposed between the side folds of the tubing, the tubing protrudes beyond the slot in a length which corresponds to the formation of a complete square bottom and of a strip-shaped tubing portion,which is formed in the tubing as a continuation ofthe inner edges ofthe infolded triangular portions, stretching pins are provided,whichservetostretchthe square bottom and to flatten the strip-shaped tubing portion and cooperate like pliers with those portions of the deck and of the pivoted stirrup in which the suckers are disposed, said stretching pins are moved or swung inwardly afterthe openingdefining edges have been moved apart, one of said stretching pins stands on the deck approximately at right angles thereto and clamps the lower edge ofthe tubing against the deck, and the other of said pins is pivoted to the pivoted stirrup in such a mannerthat a turning drive is operableto move said other stretching pin and the associated suckerfrom a clamping position, in which saidotherpinextendsatan acuteangleto the deck, to a stretching position, in which said other pin is also approximately at rightanglesto the deck, and welding bars which are movable to wards each other are disposed laterally ofthe strip-shaped tubing portion when the same has been stretched flat by the stretching pins and are operable to close the strip-shaped tubing portion by at least one bottom seam weld when the stretching pins have been moved out of said stripshaped tubing portion.

The apparatus in accordance with the invention is structurally simple and permits the bottom to be sealed by a single seam weld immediately afterthe tubing has been folded to form the square bottom, whereas it is not necessaryto provide the bottom with an additional sealing strip orto movethetubing into a succeeding processing station. The suckers respectively provided on the deck and at the centre of the pivoted stirrup serve initiallyonlyfora preliminary opening ofthe tubing at its end so that the stretching pins used to stretch the square bottom can move into the edge portion of the tubing at its end.The stretching pinsclamptheterminal edge portion ofthe tubing directly against the sucker, which engages that edge portion on the outside, or if there is a risk of damage to the sucker, the stretching pins may clamptheterminal edge portion againstthe backing surface adjacentto the sucker. Asthe pivoted stirrup isswungtofoldthetubingsoasto form the square bottom, the stretching pins stretch a cufflike strip-shaped portion of the tubing, which strip-shaped portion is a continuation of the inner edges of the infolded triangular portion.

The width of said stri p-shaped tubing portion is approximately as large as the depth to which the stretching pins move into the end portion of thetub- ing.Whenthetubing has been folded to form the square bottom, the strip-shaped tubing portion is held taut by the stretching pins. When the stretching pins have been moved and pivotally moved, respectively, out of the tubing, the bottom can be completely closed by transverse seam welds formed on said strip-shaped tubing portion.

The pivoted sucker is suitably secured to a yoke of the pivoted stirrup and said yoke is pivoted to the end portions of the legs of the stirrup and is pivotally movable relative to said legs by a turning drive. That turning drive may consist of a chain drive, which comprises a chain sprocket secu red to the pivot connecting the yoke to the legs ofthe stirrup at one end of said legs, and another chain sprocket, which is secured to the pivot at the other end ofthe legs ofthe stirrup, which latter pivot is secured to the frame.

To ensure that the stretching pin can perform a pivotal clamping movement relative to the pivoted sucker, the stretching pin is suitably secured to a shaft, which is rotatably mounted in bearing brackets ofthe yoke and which is pivotally movable by a fluid-operable piston-cylinder unit, which is connected to a leverthat is connected to said shaft.

In accordance with a fu rther preferred featu re the welding bars are provided with protruding pressure-applying bars or members, which are adapted to be forced back against spring force and to grip the strip-shaped tubing portion between the stretching pins ata location in front of the welding bars. By means of said pressure-applying bars or members the strip-shaped tubing portion to be provided with the bottom seam is held taut so that the stretching pins can be moved or swung out of the tubing and will not interfere with the formation ofthe bottom seam.

The welding bars may be mounted in a carriage for a movement towards and away from each other and said carriage may be movable by means of posts along tracks ofthe frame, which tracks are parallel to the deck. When the tubing has been folded to form the square bottom and the bottom seam weld has been formed, the strip-shaped tubing portion may still be gripped between the welding bars and/orthe pressure-applying or gripping bars so that the carriage can then be moved to pull ahead that portion of the tubing which forms the walls of the sack, until said tubing portion is in a position in which it can be severed from the remainder ofthe tubing, The carriage may be moved by a drive, preferably a chain drive.

In accordance with a further preferred feature ofthe invention the welding bars are transversely displaceably mounted by means of slide bushes on tracks oftheframe and said slide bushings are driven by a fluid-operable piston-cylinder unit through the intermediary of a transmission comprising gear segments and links.

The slot formed in the deck can suitably be closed by a flap, which clamps thetubing below that portion which is required forthe formation ofthe bottom. That edge of the deck about which the tubularfilm is pulled in the shape of a loop is suitably spring-cushioned. The spring-cushioned edge will permit a compensation of possible varia- tions ofthewidth ofthetubing.

That end portion ofthe tubing web which is to be provided with a bottom is suitably pulled forward by means of a feed roller, which is provided with a freewheel. In accordance with a further preferred feature of the invention the free-wheel is provided with a swingable lateral extension, which causes the feed roller to be turned back after each advancing operation and which has a forked end, which receives and defines a clearance with a stop, which is secured to the frame. That turning back ofthe feed roller will preventan unde sired looping of the tubing between the feed roller and the gap in the deck.

The deck may be provided with a knife, which is movable in a transversely extending slot and serves to trim to the correct length that end portion of thetubing which has been pulledto lie on the deck, and to severthe sack when it has been provided with a bottom from the remainder ofthe tubing.

An illustrative embodiment of the invention will now be explained more in detail with reference to the drawing, in which Figure lisa side elevation showing a bottomforming folding and welding station.

Figure 2is a top plan view showing the bottomforming folding and welding station, Figure 3 is a fragmentary elevation showing a portion ofthe apparatus of Figure 2 on a larger scale.

Figure 4 shows on a still larger scale the pivoted arm of Figure 2 in an initial position.

Figures a perspective view showing the pivoted which is arm surroundet by a circle in Figure 2.

Figure 6shows a portion of the deck with a slot serving as a passagefortheflexibletubing.

Figure 7is a perspective view showing a pressureapplying and welding bar.

Figure 8is a side elevation showing a feed roller provided with a freewheel.

Figure9is a sectionalviewtaken on lineVIII-VIII in Figure 8 and showing the feed roller.

Figure 10isasectionalviewtakenon lineX-Xin Figure 1.

Figure 11 is a sack, which has been made from a foldedflexibletubing and has distinctly apparent, vertically upstanding wall portions which are to be welded.

A deck 1 which is composed of a plurality of parts is connected by angle brackets 2, not shown in detail, to side frame 3 and 4. Two parallel track rods 5 are disposed under the table top 1 and are secured to brackets 6, which are joined to the side frames 3 and 4 by means which are notshown.

Two sectional posts 7,8 are slidably mounted on each track rod and are interconnected attheirtop ends by a framelike carriage 9. As is particularlyappa- rentfrom Figures 1 and 2,thesectional posts 7,8 are connected to two chains 10 and 11 ,which are adapted to be driven by a reversible motor 16 by means of an additional chain 15, a shaft 14, and chain sprockets 12 and 13 connected by the shaft 14.

ltisapparentfrom Figure 3 that brackets 17 are welded to the carriage sections 9a and 9b. The two brackets 17 of each pairthereof carry an axle 18, on which two sliders 19 and 20 are slidably mounted, which are pivoted to respective links 21, only one of which is shown, forthe sake of simplicity. Said links 21 are pivoted at their free ends to gear segments 22,23,24,25, which are rotatably mounted on vertical axles 26,27,28 and 29.

The axles 26 and 27 are secured to the carriage section 9b and the axles 28 and 29 are se cured to the carriage section 9a. The gear segments 22 and 25 are interconnected by a tie rod 30. When the piston-cylinder unit 31 is oper- ated to retract its piston rod 32, which is pivoted to the gear segment 25, the gear segments 24 and 22 will rotate in a clockwise sense and the gear seg ments 23 and 25will rotate in the counterclose- wise sense so that the two sliders 19 and the two sliders 20, respectively, will move towards each other. Thetwo gearsegments 22 and 23 are in mesh with each other and the two gear segments 24 and 25 are also in mesh with each other. This is clearly apparent from Figure 3 and need not be described in detail.

The sliders 19 and 20 of each pair thereof are inter connected by a section menber 33 or 34. Each section member 33 or34 is provided with two short depending brackets 35,36 or 37,38. Those ends of the brackets which are remote from the section member 33 or 34 are welded to connecting plates 39. Each ofthe connecting plates 39 is associated with one ofthe section members 33 and 34 and carries a combined gripping and welding bar 40 or41. One of said combined welding and gripping bars is shown in perspective in Figure 7.

It is apparentfrom Figure 7 thatthe connecting plate 39 is fixedly screw-connected to a welding beam carrier 42. Two parallel welding beams44are mounted by means of spaced apart bolts 43 and carrythewelding bars 45. A plurality of spaced apart gripping jaws 46, which are U-shaped in cross-section, em brace the carrier 42 for the welding beams and are urged againstthewelding beam carrier42 by a tension spring 47. One end ofthe tension spring 47 embraces a pin 47', which is provided in the gripping jaw 46. The other end of the tension spring 47 embraces a pin 48, which is fixed to the welding beam 44 and protrudes out wardlythrough a slot 49 formed in the gripping jaw.When the two combined gripping and welding bars 40 and 41 are moved towards each other by means ofthe gearsegments42to 45,the mutually opposite gripping jaws 40 will first engage each other to grip the material disposed between them. As the movement is continued the mut uallyoppositewelding bars 45 of the two combined welding and gripping bars 41 and 40 will en sce each other and the tension springs 47 will be s .As a result, the tubularfilm dis tween said combined welding and gripping t welded. in order to ensure that thet.i1 will be gripped before it is welded, the two free legs ofthe gripping jaws 46 must protrude from the welding bars 45 in a position of rest.

The motor 16 for driving the chain 11 drives also a pairoffeed rollers 50,51, one of which, 50, is prow; zd d with a freewheel 52. By means of said pair of feed X ullers, a continuous woven-fabric flexible tubing 53 is withdrawn from a roll and is moved through theslot54 in the deck 1 until the leading end oftheflexibletubing is disposed overa knife 55, which can be moved by means ofa piston-cylinderunits6 in a direction which is trans- verse to the deck. A piston-cylinder unit 58 is then operated to pivotally raise a flap 57 so thatthe slot 54 is closed and the tubing is gripped.

A plurality of suction openings 59 are disposed one beside the other adjacent to the knife 55 and retain the wall oftheflexibletubing which facesthe deck 1. The upper wall is now pivotally moved in the counterclockwise sense so that a bottom 60 is formed, which is indicated in phantom in Figure 2. For that purpose, a shaft 63 is rotatably mounted in hubs 61 and 62, which are fixed tothe sideframes3 and 4. Two chain sprockets 64 and 65of equal size are secured to the shaft 63 adjacent to the hubs 61 and 62 and are connected by respective drive chains 65' to two small chain sprockets 66 and 67, which are secured to the output shaft 68 of a gearmotor 69. The output shaft 68 is rotatably mounted in the motor 60 and attwo additional points.The bearings used for that purpose are not shown for the sake of simplicity. Two pivoted arms 70 and 71 are fixed to the two protruding end portions of the shaft 63 and at that end which is remote from the end portions of the shaft 63 each ofthe arms 70 and 71 carries a shaft 72 or 73, which protrudes at both ends from the pivoted arm 71 or72. Chain sprockets 74and 75 are secured to the inwardly protruding shaft ends. Aframe member 77 is pivotally carried by means of brackets 76 at those ends of the shafts 72 and 73 which are remote from each other. To permit a rotation oftheframe member77 relative to the pivoted arms 70 and 71, the chain sprockets 74 and 75 are in mesh with chains, which is non-detachably welded to the frame member 77.

When it is desired to startthe machine, theflexible tubing 53 is withdrawn by means ofthe pair of pinch rollers 50,51 (Figure 1) and is passed through the slot 54 and placed on the deck in such a length that the leading edge ofthe tubing is disposed adjacent to the knife 55. The lowerwall of the tubing is then held in position at its centre bythe sucker 59 whereas the upperwall is held bythe suckers 81 (see Figure 5). Atthattime, the pivoted arms 70,71 are in the position indicated in solid lines in Figure 4. Forthis purposethe deck 1 is formed with a bore, through which the clamping finger 82 can protrude downwardly. The motor 69 is then started to pivotally move the pivoted arms 70,71 in the sense ofthe arrow A. During that movement the piston-cylinder unit 88 forces the clamping finger 82 against the suckers which are provided on the middle tine 86" so that the upperwall ofthetubing is gripped between the suck ers81 andtheclampingfinger82(seethe position of the pivoted arms indicated by dotted lines in Figure4).Asthepivotal movementofthe two pivoted arms 70 and 71 is continued, the frame member 77 is pivotally moved relative to the pivoted arms to such an extentthattheframe memberwhich has reached its final position shown in Figure 2 will be in the position shown in Figure 5 relative to the pivoted arms 70 and 71.

Figure 11 showsthe bottom andthe clamping finger 82 for holding the bottom in position.

Figure 11 shows also a retaining rod 90, which is disposed beside the clamping finger 82 and in cooperation with the sucker59 prevents a detaching ofthelowerwall ofthetubingfromthesucker 59 during the formation of a sack bottom. Forthat purpose the retaining rod 90 is secured to a horizontal arm 91 (see Figure 1), which atthatendthat is remote from the retaining rod is secured to a vertically extending tube 92, wich is guided by a bearing 93 and a baseplate 94. The bearing 93 is fixedly connected by a holder 95to a base-plate 94.

The baseplate 94 is carried by two pistoncylinder units 96 and 97, which are operable indepen dentiy of each other. As is apparent from Figure 1 a turning lever 98 is connected to the tube 92 and to the piston rod of a piston-cylinder unit 99. The latter is pivoted to a lug 100, which is fixed to the baseplate 94. In the position shown in Figure 1 the retaining rod 90 forces the lowerwall of the sackforming tubing against the sucker 59.

After the folding operation, the piston-cylinder unit 31 (Figure3) is operated to movethetwo combined gripping and welding bars 40,41 towards each other so thatthegripping jaws 46 first engage each other to grip the raised position of the folded bottom shown in Figure 1. The gripping jaws are so arranged that the clamping finger 82 and the retaining rod 90 will not interfere with the gripping operation.

Afterthat operation the clamping finger is slightly moved in the counterclockwise sense so that that finger can be disengaged from the sack in thatthe two pivoted arms70 and 71 are pivotally moved in the clockwise sense.

To facilitate the lifting ofthe retaining rod 90, the piston-cylinder unit 79 is initially operated to extend its piston rod sothatthebaseplate94assumes such an inclination that a force is no longer exerted between the retaining rod 90 and the vertical portion of the folded bottom. The two piston-cylinder units 96 and 97 are subsequently op erased to extend their piston rods so thatthe retaining rod 90 is raised from the vertical part ofthe bottom.When this has been accomplished, the piston rod ofthe piston-cylinder unit 99 is retracted so thatthe retaining rod 90 and the tube 92 are pivotally moved through 180'. Thereafter the piston rods ofthe two piston-cylinder units 96 and 97 are entirely retracted so that the retaining rod 90 and the horizontal arm 91 are lowered through the longitudinal slot 101 in the deck.

Throughout that sequence of operations the welding beam carriers 42 have been moved towards each otherto such an extentthatthevertical portions ofthefolded bottom have been joined bywelding.

Thereafterthe motor 16 is started to move the posts 7,8 and with them the entire gripping and welding means in the direction of the arrow B in Figure 1. That movement is continued until the sack has been pulled to the desired length. Atubing section which has been provided with the bottom is now severed from the tubing 53 by an operation of the knife 55. The combined gripping and welding bars40,41 are moved apart andthereaf- terthewelding and gripping means are returned to the initial position shown in Figure 1. The cycle is then repeated in the same manner.

To permit a compensation of slightdifferences which are duetoavariation ofthewidthsofthe tubing, the deck may have adjacent to the slot 54the design shown in Figure 6. It is apparentfrom Figure 6 that the deck 1 is provided adjacent to the flap 57 with a resilient bar 102,which will compensate slight length differences of the tubing.

During a processing of a tubing which isthicker than specified over a substantial length, the feed rollers 50 and 51 will advance more material than is desired. This may result in a formation of loops between the slot 54 and the feed rollers 50 and 51 This is prevented in that the freewheel of the feed roller50 is so designed that the feed roller 50 can turn back to a small extent when the motor 16 has been turned offsothatthetubingwill always held tight between the slot 54 and the pairoffeed rollers 50 and 51.

The specific design ofthefreewheel is shown in Figures 8 and 9. the chain sprocket 52 and the inner race 103 ofthefreewheel 104 are fixed to the shaft ofthe feed roller 50. The outer race ofthe freewheel 106 carries a forked member 107. A stop 108 secured to the side frame 3 protrudes into the space between the prongs of the fork and in said space defines a clearance with the adjusting screw 109. In the position shown in Figure 9, an operation of the motor 16 causes the feed roller 50 to rotate in the sense in which the flexible tubing is withdrawn. When the flexible tubing has been withdrawn in an adequate length, the motor 16 is turned off and the stress ofthe tubing will then impart a rotation to the feed roller 50 in the counterc- lockwise sense until the adjusting screw 109 engages the stop 108.

Claims (15)

1. Apparatusforfolding a flexible tubing to form sack bottoms in the manufacture of block bottom sacks and for welding the bottom seams, which apparatus comprises suckers, which are disposed on opposite sides ofthe tubing and serve to openthetubing atone end thereof,adeck having a central slot, means for longitudinally trans- portingthetubingthroughtheslotovera distance which is sufficient to perm it the bottom to be formed, and gripping and/or holding and stretching means, which are adapted to engage mutually opposite opening-defining edges ofthe tubing at the centre between the side folds of the tubing, wherein one of said gripping and/or holding and stretching means is mounted on the frame or on the deck and the other is mounted on an arm or stirrup, which is pivoted to the frame, and drive means are provided for pivotally moving said arm or stirrup through about 1800 between the mutually opposite sides of the deck, wherein at least one sucker is provided on the deck and at least one sucker is provided on the pivoted stirrup, said suckers are provided on the mutually opposite opening-defining edges of the flexible tubing at location which are centrally disposed between the side folds of the tubing, the tubing protrudes beyond the slot in a length which corresponds to the formation of a complete square bottom and of a strip-shaped tubing portion, which is formed in the tubing section as a continuation ofthe inner edges of the infolded triangular portions, stretching pins are provided, which serve to stretch the square bottom and to flatten the strip shaped tubing portion and cooperate like pliers with those portions of the deck and of the pivoted stirrup in which the suckers are disposed, said stretching pins are moved or swung inwardly after the opening-defining edges have been moved apart, one of said stretching pins stands on the deck approximately at right angles thereto and clamps the lower edge ofthetubing against the deck, and the other of said pins is pivoted to the pivoted stirrup in such a mannerthat a turning drive is operable to move said other stretching pin and the associated sucker from a clamping position, in which said other pin extends at an acute angle to the deck, to a stretching position, in which said other pin is also approximately at right angles to the deck and welding barswhicharemov- able towards each other are disposed laterally of the strip-shaped tubing portion when the same has been stretched flat by the stretching pins and are operable to ciose the strip-shaped tubing portion by at least one bottom seam weld when the stretching pins have been moved out of said stripshaped tubing portion.

2. Apparatus according to claim 1, wherein the pivoted sucker is a yoke of the pivoted stirrup and said yoke is pivoted to the end portions ofthe legs ofthe stirrup and is pivotally movable relative to said legs byaturning drive.

3. Apparatus according to claim 2, wherein the turning drive of a chain drive, which comprises a chain sprocket secured to the pivot connecting the yoke to the legs of the stirrup at one end of said legs, and another chain sprocket, which is secured to the pivot at the other end of the legs of the stirrup, which latter pivot is secured to the frame.

4. Apparatus according to any of claims 1 to 3, wherein the stretching pin is secured to a shaft, which is rotatably mounted in bearing brackets ofthe yoke and which is pivotally movable by a fluid-operable piston-cylinder unit, which is connected to a leverthat is connected to said shaft.

5. Apparatus according to any of claims 1 to 4, wherein the welding bars are provided with protruding pressure-applying bars or members, which are adapted to be forced back against spring force and to grip the strip-shaped tubing portion between the stretching pins at a location in front ofthe welding bars.

6. Apparatus according to any of claims 1 to 5, wherein the welding bars are mounted in a carriage for a movement towards and awayfrom each other and said carriage is movable by means of posts along tracks ofthe frame, which tracks are parallel to the deck.

7. Apparatus according to claim 6, wherein the posts are movable on their tracks by drive means, preferably by a chain drive.

8. Apparatus according to any of claims 1 to 7, wherein the welding bars are transversely displaceably mounted by means of slide bushes on tracks oftheframe and said slide bushings are driven by a fluid-operable piston-cylinder unit through the intermediary of a transmission comprising gear segments and links.

9. Apparatus according to any of claims 1 to 8, wherein the slot formed in the deck is adapted to be closed by a flap.

10. Apparatus according to any of claims 1 to 9, wherein that edge of the deck about which the tubing is pulled in the shape of a loop is springcushioned.

11. Apparatus according to any of claims 1 to 10, wherein the feed roller for advancing the flexibletubing is provided with a freewheel.

12. Apparatus according to claim 11,wherein the freewheel is provided with a swingable lateral extension, which causes the feed rollerto be turned back after each advancing operation and which has a forked end, which receives and defines a clearance with a stop, which is fixed to the frame.

13. Apparatus according to any of claims 1 to 12, wherein the deck is provided with a knife, which is movable in a transversely extending slot and serves to trim to the correct length that end portion ofthetubing which has been pulled to lie on the deck, and to severthe sackwhen it has been provided with a bottom from the remainder of the tubing.

14. Apparatus according to claims 1 to 13, wherein the retaining rod is securedto a yoke,which is similarto a gallows and which is provided with drive meansforturning said rod andfor lowering it into a slot formed in the deck.

15. Apparatus for folding a flexible tubing to form a bottom in the manufacture of block bottom sacks and for welding the bottom seams, substantially as described herein before with reference to and as shown in the accompanying drawings.