US3853664A

US3853664A - Bag making machine and method

Info

Publication number: US3853664A
Application number: US00384611A
Authority: US
Inventors: A Lafleur
Original assignee: Square Bag-It Corp
Current assignee: Viskase Corp; Square Bag-It Corp
Priority date: 1973-08-01
Filing date: 1973-08-01
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10

Abstract

A machine for processing plastic web stock in a continuous manner for making bags. The bags have one or more gusseted portions with diagonal seals at corners thereof. The machine for applying the diagonal seals on the web stock includes a guide structure which is mounted for free floating movement in a direction transverse to the direction of travel of the stock through the machine. The guide structure engages the inner fold of each gusseted portion so as to shift laterally in response to lateral weaving of the stock as it travels through the machine. The mechanism for applying the diagonal seals is mounted to shift laterally as a unit with the guide structure so that the seals will be precisely located relative to the inner fold lines of the gusseted portions.

Description

Uni I tates LaFleur 1451 Dec. 10, 1974 [73] Assignee: Square Bag-It Corp, Manistee,

Mich.

[22] Filed: Aug. 1, 1973 [21] Appl. No.: 384,611

52 us. (:1 156/306, 83/368, 83/428, 93/DIG. 1, 93/35 813, 156/252, 156/515.

51 1m. (:1. 1309 5/00, 133213 31/00, 33% 15/34 [58] Field 01 Search 156/242-244,

156/251, 252, 255, 306, 384, 494-496, 500, 504, 515,530, 583; 93/D1G. 1, l4,17-20, 33 H, 35 R, 35 SB; 229/53, 5760; 83/368, 428

Wech 156/515 3,776,804 12/1973 Monahan et all 156/515 Primary Examiner-Clift0n B. Cosby Assistant ExaminerJohn E. Kittle Attorney, Agent, or FirmBarnes, Kisselle, Raisch & Choate [5 7] ABSTRACT A machine for processing plastic web stock in a continuous manner for making bags. The bags have one or more gusseted portions with diagonal seals at corners thereof. The machine for applying the diagonal seals on the web stock includes a guide structure which is mounted for free floating movement in a direction transverse to the direction of travel of the stock through the machine. The guide structure engages the inner fold of each gusseted portion so as to shift laterally in response to lateral weaving of the stock as it travels through the machine. The mechanism for applying the diagonal seals is mounted to shift laterally as a unit with the guide structure so that the seals will be precisely located relative to the inner fold lines of the gusseted portions.

26 Claims, 19 Drawing Figures 3@3 ,66&

PATENTB, DEC? 019M llllltiillllllllnllllv BAG MAKING MACHINE AND METHOD This invention relates to a bag making machine and method and more generally to a machine for performeration of the machine that the invention is admirably suited for performing a variety of operations on a travelling plastic web having a lengthwise extending fold line therein.

In the manufacture of many plastic articles from tubular or folded plastic webs it is necessary to perform some operation on the web at a predetermined location in relation to the side edges or a fold line in the web material as the stock is fed from a source of supply to a wind-up roll or to a cutting and stacking device. When such web stock is fed in a more or less continuous manner (with or without intermittent interruptions in the feed cycle) there is usually a tendency for the web to weave or shift laterally of its direction of travel at least slightly as it progresses through the machine. Several elaborate and expensive web guiding arrangements have been developed heretofore to maintain the alignment of the travelling web within relatively close tolerances so that any auxiliary processing operations performed on the web (such as sealing, slitting, printing, etc.) will be accurately located in relation to the side edges or a fold line on the web. In such machines the apparatus for performing the auxiliary operation on the web, is normally in a fixed position and the web is shifted laterally as required by the web guiding mechanism while it is being fed through the machine in order to properly align the web with the mechanism for performing the auxiliary operation thereon.

The present invention has for its primary object the provision of a machine of the type described wherein the apparatus for performing the auxiliary operation on the web is mounted on the machine in a manner permitting it to float or shift transversely of the path of travel of the web and a fold or gusset in the travelling web is utilized to shift this apparatus transversely of the path of travel of the web as required so that the auxiliary operation will be performed on the web at a location accurately aligned relative to the fold line or gusset in the web.

The machine disclosed herein is illustrated for the manufacture of plastic bags of the type shown, for example, in my prior US. Pat. No. 3,143,277 wherein the bag is provided with an inwardly extending gusset on each side thereof and diagonally extending seals are provided in the gusseted portions of the bag. With bags of this general type it is important that the diagonally extending seals terminate at their inner ends closely adjacent the apex of the V-shaped gusset in order to prevent leakage from the bag and so that when the bag is filled it is properly reinforced by the gusset seals. Accordingly, in the form of machine illustrated herein a sealing mechanism is mounted on the machine frame by means of rollers or the like which permit the sealing mechanism to shift laterally in relation to the path of travel of the gusseted web through the machine. The

sealing mechanism includes guide members which extend laterally inwardly from opposite side edges of the web into the gussets and engage the fold line of the gus set so that the entire guide and sealing assembly shifts laterally in response to lateral shifting of the web and thus produces seals which are accurately located in relation to the gussets along each side of the web. In addition, in order to insure proper guiding of the sealing mechanism it is important that the webbe maintained in a lengthwise tensioned condition at the section thereof engaged by the guides so that any slight lateral shifting of the web will result in a corresponding lateral shifting of the guide and sealing mechanism.

Other objects and advantages of the present inven-. tion will become apparent from the following description and accompanying drawings, in which:

FIG. 1 is a side elevational view, partly in section, of a machine embodying the present invention;

FIG. 2 is a fragmentary elevational view in the direction of arrow 2 in FIG. 1;

FIG. 3 is a fragmentary sectional view along line 33 in FIG. 2;

FIG. 4 shows a portion of the assembly illustrated in FIG. 2 on an enlarged scale;

FIG. 5 shows the opposite side of the assembly shown in FIG. 4;

FIG. 6 is a fragmentary sectional view taken along line 6-6 in FIG. 5; i

FIG. 7 is a fragmentary cross sectional view of a portion of the sealing and guide mechanism;

FIG. 8 is a fragmentary elevational view of a modified form of sealing and guide mechanism,

FIG. 9 is a top view of the arrangement shown in FIG. 8.

FIG. 10 is a fragmentary view of a further modified FIG. 15 is a perspective view of'a bag formed from the stock shown in FIG. 14;

FIG. I6 is a fragmentary plan view of plastic stock with the seal pattern produced in accordance with the modification shown in FIG. 10 andFIG. 17 shows the bag formed thereby;

FIG. 18 is a fragmentary plan view of the plastic web as processed by the arrangement shown in FIG. 11;

FIG. 19 illustrates a bag formed from the web stock shown in FIG. 18.

Referring first to FIGS. 1 through 7, the machine illustrated includes a frame, generally designated 10, having means for supporting a supply roll 12 of tubular plastic web, a wind-up roll 14 for the processed web and means intermediate rolls 12 and .l4 foradvancing the tubular stock through the machine. The latter means includes two sets of intermittently driven pull rolls 16 adjacent the wind-up roll I4 and between which is arranged a transverse sealing and perforating mechanism 18. The tubular stock is wound on roll 12 in a flattened condition as it emerges from an extruder,

the stock being provided with inwardly extending gussets 20 along opposite edges thereof. The inner edges of the gussets are defined by fold lines 22. As the stock, generally designated 24, is unwound from roll 12 it is caused to travel around a pair of dancing rolls 26 and idler rolls 28 in a conventional zig-zag fashion and then past a snubbing device 30 which engages the stock to prevent reverse movement thereof as might otherwise be produced by the freely vertically movable dancing rolls 26. As the stock travels past snubber 30 it wraps around a continuously driven roll 32 against which it is maintained in frictional engagement by idler rolls 34, 34a. The web then travels vertically upwardly through a sealing mechanism, generally designated 36, around a vertically shiftable web relaxing roll 38 and then around a vertically adjustable top roll 40. The web is then directed in a downwardly direction between

friction rolls

42, 44, through another sealing mechanism 46 and then upwardly around an idler roll 48. It then travels over a second vertically adjustable roll 50 to the intermittently driven pull rolls 16. Wind-up roll 14 is suitably driven to wind up the web as it is fed by pull rolls 16. A conventional drive is utilized for this purpose. Likewise, a conventional drive is utilized for rotating pull rolls 16 intermittently.

A shaft 52 on which is fixed a cam 54 is driven continuously at a predetermined speed in relation to the speed of rotation of pull rolls 1'6. Sealing mechanism 18 includes a vertically reciprocable heating and perforating element 56 which is actuated by a cam follower 58 engaging cam 54 such that, when the rotation of pull rolls 16 is arrested, the heat sealing element 56 is lowered into contact with the web stock to form a transverse seal therein as indicated at 60 in FIGS. 14, 16 and 18. Element 56 is also designed to form a transverse perforation line 61 (FIG. 14).

Shaft 52 also has a drive pulley oragear 62 mounted thereon which is connected as by a chain or belt 64 with a driven gear or pulley 66 on a second shaft 68 journalled on frame 10. Two cams 70, .72 are keyed to shaft 68. Cam 70 is engaged by a cam follower 71 to vertically reciprocate a link 74 connected to a lever 76 which supports roller 38 at one end. The opposite end of lever 76 has a fixed pivotal connection as at 78 on frame 10. When lever 76 is raised to the solid line position shown in FIG. 1 it cooperates with dancing rolls 26 to maintain the web stock in a tensioned condition between supply roll 12 and the first set of pull rolls 16. When the cam follower 71 at the lower end of link 74 engages the recessed portion of cam 72 lever 76 swings downwardly to the broken line position and relaxes the tension in the web between snubber 30 and the pull rolls 16. The rotation of pull rolls 16 is coordinated with the rotation of cam 72 such that their rotation is arrested while cam follower 71 is in engagement with the recessed portion of cam 72. Thus, the stock is fed intermittently through the machine and, when its forward movement is arrested, the tension in the web is relaxed.

An auxiliary frame 80 is guided for horizontal movement on frame by a plurality of guide rollers 82. Frame 80 is biased in a direction toward the right as viewed in FIG. 1 by a compression spring 84. A cam follower 86 on frame 80 engages the periphery of cam 70 to normally maintain spring 84 compressed, but at regularly spaced intervals, to permit frame 80 to shift in a direction toward the right. It will be observed that the recessed portion 88 of cam is related in a circumferential direction to the recessed portion 90 of cam 72 such that frame 80 shifts to the right when roller 38 is in the lowered position and the tension on the web is relieved.

The two sealing

mechanisms

36, 46 are adapted to form diagonal seals on the gusseted portions of the tubular stock, such as indicated at 92 in FIG. 14. Both of these sealing mechanisms are of generally the same construction. Each of these sealing mechanisms comprises a pair of separate rigid upright struts 94, each having an angularly inclined bracket 96 at its upper end on which is journalled a roller 98. Each roller 98 is supported on a shoulder of a horizontally extending angle member on'frame 10. The angle member associated with sealing mechanism 36 is designated as 100a and the angle member associated with sealing mechanism 46 is designated as 10%. A second roller 102 is journalled at the lower end of each strut 94 for rotation about a vertical axis. Each roller 102 is adapted to engage one leg of a horizontally extending guide channel on frame 10. The guide channel associated with sealing mechanism 36 is designated as 104a and the guide channel associated with sealing mechanism 46 is designated as 104b.

Each strut 94 is also provided with a shallow yoke 106 which is securely attached thereto and which is shaped to'receive a tie bar 108. A locking thumb screw 110 is threaded into each yoke 106 for rigidly interconnecting the two struts 94 in a fixed, laterally spaced relation by means of tie bar 108. Thus, the two struts 94 can be spaced further apart or closer together, as desired, by means of tie bar 108. Each strut 94 has a horizontally extending support arm 112 extending laterally outwardly therefrom. To the outer end of each arm 1 12 there is rigidly mounted a tubular brace 114. There is associated with each strut 94 a guide plate 116, the laterally outer edge of which is reinforced by an angle 118. Each guide plate 116 is rigidly connected to tubular brace 114 so as to extend vertically in spaced relation to strut 94 (see FIG. 6).

The adjustable tie bar construction described enables the two guide plates 116 on each sealing mechanism to be spaced apart so that their vertically extending, inwardly opposed edges 120 (FIG. 5) can be spaced horizontally apart to correspond with the horizontal dimension between the two fold lines 22 of gussets 20 on the tubular stock 24. This is illustrated in FIG. 3. With the guide plates 116 so adjusted and extending into the gussets 20 it will be appreciated that the mechanism supported on each set of

rollers

98, 102 is free to shift laterally as the web stock 24 weaves sidewise relative to its path of travel.

More specificially, with reference to scaling mechanism 36 it will be observed that, since the web stock wraps around roller 34 and around roller 38, when it is in a tensioned condition the frictional engagement of the travelling web with

rollers

34 and 38 will maintain the portion of the web between these rollers in a relatively taut condition. By reason of the manner in which the tubular stock is manufactured and the gussets 20 formed therein, the distance d between the fold lines 22 is very uniform. When the guide plates 116 are adjusted so that their inner edges are spaced apart corresponding to the distance d and since the web is relatively taut between

rollers

34 and 38 when roller 38 is in the raised position, it follows that as the web shifts laterally the roller supported guide plates 116 likewise shift lattendency for the web to flex laterally in response to the lateral force applied thereto by guide plates 116 is minimized by the fact that the web is in a tensioned condition and frictionally engaged adjacent the upstream and downstream ends of sealing

mechanisms

36, 46. This is an important feature of the present invention since the sealing mechanisms are supported by the structure which supports guide plates 116. Thus, each vertical strut 94 and the components supported thereby can be considered as a carriage which is free to shift laterally on frame to correspond with the lateral shift ing or weaving of web 24 between

rollers

34 and 38. With respect to sealing mechanism 46 on the opposite side of frame 10, the function of

rollers

34 and 38 insofar as frictional engagement with the web is concerned is performed by rollers 48 and 44, respectively.

Referring now to FIGS. 5 through 7, it will be observed that on one side of guide plate 116 and spaced parallel thereto there is rigidly attached to tubular brace 114 a tubular arm 122. Each arm 122 has a pair of tubular brackets 124 rigidly mounted thereon in vertically staggered relation (FIG. 5). A heat sealing bar 126 having an electrically energized heater 128 mounted thereon extends generally diagonally of each guide plate 116. Each heat sealing bar 126 has a tubular member 130 fixedly attached thereto. A pair of horizontally extending pins 132 are fixedly mounted on tubular member 130 and extend horizontally through tubular brackets 124 to enable heat sealing bar 126 to be shifted horizontally toward and away from its respective guide plate 116. Springs 134 normally bias heat sealing bars 126 to a retracted position spaced from its respective guide plate 116. Horizontally movable frame 80 has a pair of flattened tubes 136 fixedly attached thereto and horizontally positioned to register with the guide pins 132 of sealing

mechanisms

36 and 46. Thus, when the cam follower 86 encounters the recessed portion 88 of cam 70, frame 80 shifts to the right under the influence of compression spring 84 so that the tubes 136 engage guide pins 132 and shift both heat sealing bars 126 toward the respective guide plates 116.

Referring now to FIGS. 4 and 6, it will be observed that on the side of each guide plate 116 opposite the heat sealing bar 126 there is a back-up bar 138. Each back-up bar 138 is rigidly connected to strut 94 by a rigid strap 140. Each back-up bar 138 registers with its respective diagonally inclined heat sealing bar 126.

Referring now to FIG. 5, it will be observed that each guide plate 116 has a diagonally extending slot 142 therein which registers with the heat sealing edge portion 144 of each heat sealing bar 126. Edge portion 144 of each heat sealing bar extends over each slot 142 to the inner edge 120 of each guide plate 116. Each slot 142 extends diagonally downwardly from the inner edge 120 of each guide plate 116 to adjacent the outer edge of the guide plate as shown in FIG. 5. A Teflon web 146 loosely spans slot 142 throughout the length thereof and is attached to the face of guide plate 116 which is adjacent the heat sealing bar 126 as shown in FIG. 7. Edge portion 144 of heat sealing bar 126 also has a strip of Teflon 148 attached thereto. FIG. 7 also illustrates the fact that back-up bar 138 is likewise axially'aligned with slot 142 opposite heat sealing bar 126. Onthe face thereof adjacent guide plate 116 back-up bar 138 is provided with a cushion 150 and the entire assembly is wrapped with a Teflon covering 152.

As mentioned previously, sealing mechanism 46 is generally the same as sealing mechanism 36. However, it will be appreciated that, when the web stock 24 is threaded through the machine and guide plates 116 in the manner shown in FIG. 3, heat sealing bar 126 of heat sealing mechanism 36 is designed to act upon the two overlying plies of the web at one face thereof and the heat sealing bar 126 of heat sealing mechanism 46 is adapted to act upon the two overlying plies of the web at the other side thereof. Referring to FIG. 7, the heat supplied to heat sealing bar 126 through heater 128 is controlled such that, when the heat sealing bar 126 is shifted to the right to apply pressure to all four plies of the web between the heat sealing edge portion 144 and cushion 150, the heat is only sufficient to form a weld joint between the two plies of the web at the left of the guide plate 116. The

Teflon members

146, 148 and 152 prevent the heated plastic web from sticking to the opposed members by means of which heat sealing pressure is applied to the web. Since the heat sealing bars 126 are caused to contact the web when the web is in a relaxed position, the two

heat sealing mechanisms

36, 46 produce the weld seams 92 shown in FIG. 14 on each of the four sets of two plies at opposite edge portions of the web. The tension in the web is relaxed and the feed is arrested for a period of time to allow the weld seam to solidify and withstand the tension subsequently applied thereto when roll 38 is again raised and rotation of pull rolls 16 is resumed. Furthermore, it will be observed that the slots 142 in each guide plate 116 enables the plies of the web to be sealed from the outer side edge portions thereof directly to the fold lines 22. This results not only in a bag 154 (FIG. 15) having a reinforced bottom corners, but also in a bag the square bottom of which is absolutely leakproof and adapted to contain lliquids or other free flowing materials. If the seals 92 did not extend directly to the fold lines 22, but instead terminated short thereof, a small opening would be formed in the bottom of the bag at the joints between the fold lines 22 and the seals 92. If seals 92 extended beyond fold lines 22, when the individual bags are severed from the stock the upper ends thereof would have unwanted localized seams therein.

It will be appreciated that roller 40 is vertically adjustable so that the heat sealed seams 92 at one side of the bag will register accurately with the heat sealed seams 92 at the opposite side of the bag. Likewise it will be appreciated that roll 50 is vertically adjustable so that the transversely extending seam 60 and/or the perforation line 61 produced by the mechanism 18 will register accurately with the inner ends of seams 92.

In the modification illustrated in FIGS. 8 and 9 the two heat sealing assemblies are mounted in directly opposed relation on opposite sides of the same guide plates. Thus, in this modification the two

guide plates

156, 158 are mounted on two

carriages

160, 162. The two

carriages

160, 162 are adjustably interconnected in spaced relation by means of tie bars 164, 166. The carriages are provided with rollers 168, which enable the two carriages to shift as a unit freely on horizontally extending

rails

172, 174 on the frame of the machine. The two

guide plates

156, 158 are constructed similarly to guide plates 116 shown in FIG. 7 with the Teflon I web 146 extending across the diagonal slot in the guide plate. However, the heat sealing bars 176, 178 are arranged on opposite sides of

guide plates

156, 158 in alignment with the slots therein. In the arrangement illustrated in FIGS. 8 and 9 the two sets of heat sealing bars 176, 178 are simultaneously actuated by air cylinders or solenoids 180 to form all four diagonal seals 92 in the plastic web at the same time. In this arrangement the Teflon web corresponding to that shown at 146 in FIG. 7 prevents the two plies adjacent one face of the web from sticking to the two plies at the opposite face of the web. In most other respects the arrangement shown in FIGS. 8 and 9 is substantially the same as that shown in FIGS. 1 through 7. However, since heat sealing bars 176, 178 are in opposed relation, a back-up bar (such as shown at 138 in FIG. 7) is not required. Likewise, in the modification shown in FIGS. 8 and 9 the machine does not require a horizontally movable frame such as shown at 80 in FIG. 1; instead a cam corresponding in function to cam 70 may be utilized for triggering elements 180.

The arrangement shown in FIG. 10 is used in conjunction with plastic web stock 182 having a single gusset 184 at only one edge thereof. The guide plate 186, which extends inwardly of gusset 184 with its inner edge engaging the fold line 188, is guided for horizontal movement between rollers 190 on a stationary portion 192 of the machine frame. Guide plate 186 is urged in a direction inwardly of gusset 184 with a very light pressure by a very light counterweight 194. Obviously a very light spring could be used in place of counterweight 194. The two heat sealing bars 196 are mounted by structure (not shown) to move horizontally with guide plate 186 and are caused to advance toward each other intermittently to form the two diagonally extending

seals

198, 200 on the gusseted portion 184 of the web 182 (FIG. 16). When the web 182 is severed through the transversely extending seals 60 a bag 202 is provided wherein the gusseted portion 184 forms the bottom 204 of the bag. In this embodiment seals 60 are of sufficient width so that a line of perforations can be applied therethrough without disturbing the seal on each side thereof and thus provide successive bags with the seals 60 extending along the end edges thereof.

A further modification of the present invention is shown in FIGS. 11 through 13. In this arrangement the plastic web stock, generally designated 206, is of flattened tubular cross section with inwardly extending gussets 208 along opposite edges thereof similar to that shown in FIG. 3. In this arrangement two guide plates 210 are interconnected in adjustably spaced relation by a tie bar 212. Guide plates 210 are spaced apart such that their inner edges 214 engage the fold lines 216 of the two gussets 208. The two guide plates 210 interconnected bythe tie bar 212 act as a carriage which is movable freely in a horizontal direction on the frame of the machine by means of guiding rollers 218. Intermediate the upper and lower edges thereof each guide plate 210 is formed along its inner edge with a rectangularly-shaped recess 220. A V-shaped heating element 222 is mounted on each guide plate 210 and is preferably bent as shown in FIG. 12 so that it extends into recess 220 in the plane of its respective guide plate 210. The apex 224 of each heater 222 is axially aligned with the guiding edge 214 of its respective guide plate 210. A Teflon web 226 is wrapped around the inner edges of guide plates 210 so as to overlie the opposite faces of heater 222. At the side of each guide plate 210 opposite tie bar 212 there is arranged on the machine a pair of movable platens 228 which overlie the V-shapecl heaters 222. The operating faces of platens 228 and tie bar 212 adjacent the gusset 208 are coated with Teflon or other suitable material which prevents the heated plastic web from sticking thereon when the platens are actuated to apply pressure to the gusseted portions of the web stock 206 while heaters 222 are energized. Heaters 222 are preferably of the impulse type which cool immediately after a short heating cycle. This results in a rapid cooling of the heat seals so that they can withstand the required tension when the stock is fed again immediately following a heat sealing operation. Rapid cooling of the seals is required for high production rates when all four seals are formed simultaneously.

The modification shown in FIGS. 11 through 13 produces a finished web of the type shown in FIG. 18. In this arrangement two V-shaped seals 230 are simultaneously formed at the gusseted portions 208 at each side of the plastic web 206. A slitting knife (not shown) is mounted on the horizontally movable carriage structure (guide plates 210 or tie bar 212) so as to slit the web lengthwise centrally between the inner fold lines of the gusseted portions as indicated at 232 in FIG. 18. Thus, the arrangement shown in FIGS. 11 through 13 is adapted to form two sets of bags simultaneously, one of which is shown at 234 in FIG. 19. From the standpoint of its construction bag 234 is similar to bag 202 illustrated in FIG. 17.

In each of the embodiments illustrated it will be observed that a freely floating guide structure is provided which engages within a fold or gusset in the web stock being fed so as to shift horizontally in accordance with the lateral weaving or shifting of the web. While the web is being fed, it is maintained in a tensioned condition and the portion of the web being acted upon by the guide structure is prevented from flexing laterally in response to the lateral forces applied thereto by the guide structure. This results from the fact that on the upstream and downstream sides of the guide structure the tensioned web is frictionally engaged (such as by

rollers

34, 38 and 44, 48). This frictional engagement prevents .the web from shifting sidewise on the rolls while in a tensioned condition.

In each instance the apparatus for performing an operation on the web (the heat sealing mechanisms in the embodiments illustrated) is mounted to shift laterally with the guide structure so that the operation performed on the web is always in a predetermined position in relation to the fold line engaged by the guide structure. Thus, if the web weaves slightly from side to side as it travels through the machine (and this invariably occurs), the operation performed on the web is always precisely located with reference to the fold lines on the web engaged by the guide structure. While the embodiments illustrated show the forming of heat sealed seams on the web, it will be appreciated that the appartus operating on the web could also be or include a printing device, a punching or slitting device, or any other type of apparatus which might be utilized for performing an auxiliary operation on the travelling web. In order to prevent the web from tearing at the heated seals, the tension on the web is relaxed while the heat sealing operation is being performed.

I claim:

1. In a machine for performing an auxiliary operation, such as sealing, slitting, printing or the like, on a continuous length of a flexible plastic web having a longitudinally extending fold therein the combination comprising, a frame, means on said frame for feeding said web in a lengthwise direction, means on said frame at one zone in the path of travel of the web for maintaining the web in a lengthwise tensioned condition so that the line of folding follows a generally straight path, carriage means on said frame at said zone mounted for relatively free movement in a direction transversely to the path of travel of the web and in a plane generally parallel to the plane of the web, guide means on said carriage means adapted to extend into and between the folded plies of the web and engage the web at the fold line for causing the carriage to shift laterally on said frame in response to lateral weaving of the fold line of the web as the web travels through said zone, and means carried by and movable with said carriage means for performing said operation on the portion of the web travelling through said zone, said operation performing means being disposed adjacent said guide means so that the operation performing means acts on said web adjacent the portion thereof engaged by the guide means.

2. The combination called for in claim 1 including means at the inlet and outlet ends of said zone frictionally engaging said web and resisting lateral flexing thereof in response to lateral forces applied to the web by said guide means as the tensioned web travels through said zone.

3. The combination called for in claim 1 including a roller at the inlet end of said zone around which the web is caused to travel in a tensioned condition, and means for directing the web to said roller such that the web approaches the roller in a plane inclined to the plane of the web as it travels through said zone, said tensioning means causing the web to frictionally engage said roller to minimize the tendency of the web to flex laterally in response to lateral forces applied to the web by said guide means. 1

4. The combination called for in claim 1 including a roller adjacent each of the opposite ends of said zone, said rollers extending transversely of the path of travel of the web, said two rollers directing said web in a rectilinear path therebetween so that the web assumes a flat plane at the portion thereof extending between the rollers, said web being directed to one of said rollers and away from the other roller at angles inclined to said flat plane so that the tensioning means causes the web to frictionally engage the periphery of said rollers and thus minimize the tendency for the web to flex laterally in response to lateral forces applied thereto by the guide means as the web travels through said zone.

5. The combination called for in claim 41 wherein said guide means are disposed intermediate said two rollers in the path of travel of the web.

6. The combination called for in claim I wherein said operation performing means comprises a heat sealing member for applying a welded seam to the plastic web in a predetermined position relative to the fold line therein.

7. The combination called for in claim 1 wherein said web is formed with a V-shaped gusset extending inwardly from a side edge thereof and said guide means extend laterally inwardly of said side edge and engage the fold line defining the apex of the V-shaped gusset.

8. The combination called for in claim 7 wherein the gusseted portion of the web defines four plies of said web adjacent said one edge and said operation performing means acts upon two of the plies at one side of the guide means.

9. The combination called for in claim 7 wherein the gusseted portion of the web defines four plies of said web adjacent said side edge, said guide means engaging the fold line of said gusset at two longitudinally spaced portions thereof, said operation performing means being disposed between said longitudinally spaced portions and between the two inner plies of said web.

10. The combination called for in claim 9 wherein said operation performing means comprises heat sealing means adapted to form a welded seam on the gusseted portion of the web extending inwardly to said fold line in a direction inclined at an acute angle to the path of travel of the web.

11. The combination called for in claim 1 wherein said web comprises a flattened tubular member having a V-shaped gusset extending laterally inwardly from each side thereof, said guide means comprising a pair of laterally spaced co-planar members extending laterally inwardly from each side edge of the web with the opposite inner edges engaging the opposed vertices of said V-shaped gussets.

12. The combination called for in claim 11 wherein said carriage means comprises two carriages, one for each guide means, and means for maintaining said guide means in adjustably fixed laterally spaced rela-' tion so that the inner opposed edges thereof can be spaced apart in fixed relation to correspond with the lateral spacing between the vertices of webs having differently sized gussets.

13. The combination called for in claim 12 wherein said last-mentioned means comprises a tie bar interconnecting the two guide means, the interconnection between the tie bar and at least one of said guide means being laterally adjustable.

14. The combination called for in claim 12 wherein said operation performing means comprises a heat sealing member and a back-up member disposed on opposite sides of said guide means in spaced relation to the opposed outer plies of said web and means for relatively moving the heat sealing member and the back-up member toward each other to form a welded seam on the gusseted portion of the web.

15. The combination called for in claim 1 wherein the guide means comprises a guide plate extending laterally inwardly between the plies of the web and having an inner guiding edge engaging said fold line, said guiding edge having a recess therein, said operation performing means comprising a heat sealing member, said heat sealing member registering with said recess in the guide plate and extending laterally inwardly to said fold line so that, when the heat sealing member is actuated, it is adapted to form a heat seal extending inwardly from the side edge of the web directly to the fold line.

16. The combination called for in claim 15 wherein said recess is located in said guide edge intermediate the ends thereof.

17. The combination called for in. claim 16 including a sheet of material overlying said recess, said material lll being of the type to which said plastic web stock will not readily adhere when in a heated condition.

18. The combination called for in claim 1 wherein the machine includes a second zone having a similar. carriage means, guide means and operation performing means at said second zone, said web stock being of flat tubular cross section and having a laterally inwardly extending V-shaped gusset at each side thereof, said guide means at each of said zones engaging the fold lines comprising the vertices of said two gussets, said operation performing means being disposed adjacent one face of the web stock at one of said zones and adjacent the opposite face of the web stock at the other zone.

19. The combination called for in claim 18 wherein said operation performing means comprises a heat sealing member at each of said zones which when actuated is adapted to form diagonal seals through two plies of the stock at said gussets which extend from the outer side edges of the stock inwardly to the vertices of the gussets.

20. The combination called for in claim 19 wherein said two zones are spaced apart in the direction of travel of the stock so that the diagonal seals formed be-' tween two plies of the stock at one zone register with the diagonal seals formed between the other two plies of the stock at the other zone.

21. The combination called for in claim 17 wherein said heat sealing member is mounted on said guide plate at said recess and said material overlies opposite faces of the heat sealing member.

22. The method of aligning a moving web of plastic material having a fold line extending lengthwise thereof in the direction of travel of the web with an apparatus for performing an operation on the web, such as sealing, slitting, printing and the like, comprising the steps of moving the web lengthwise on a support structure in a tensioned condition and in a rectilinear path between two longitudinally spaced points on said support structure, frictionally engaging the web at said two points to minimize the tendency for the web to flex laterally of its direction of travel in response to lateral forces applied to the web between said two points, engaging the fold line of the web with a guide means positioned between said two points, permitting the guide means to shift freely in a lateral direction on said support structure in accordance with lateral movement of the travel of the web between said two points, and supporting said apparatus for free lateral movement with said guide means so that said apparatus is always located laterally in a predetermined position relative to said fold line.

23. The method according to claim 22 wherein said two points are located on said support structure closely adjacent said guide means on the upstream and downstream sides thereof.

24. The method according to claim 22 wherein said web is of flat tubular cross section with an inwardly extending V-shaped gusset at each side thereof and said guide means comprises a pair of laterally interconnected guide members extending into said gussets from opposite sideedges of the web and engaging the fold lines defined by the apices of the two gussets.

25. The method according to claim 22 wherein said web comprises a heat sealable plastic film and said apparatus for performing an operation thereon comprisesa heat sealing means and including the steps of intermittently arresting thelengthwise movement of said web, relaxing the tension in the web when its lengthwise movement is arrested and causing the heat sealing means to engage the web while the web is in said relaxed condition.

26. The method according to claim 25 wherein the web is flattened tubular cross section with an inwardly extending V-shaped gusset at each side edge thereof, said guide means comprising a pair of laterally interconnected guide members extending into said gussets from opposite side edges of the web and engaging the fold lines defined by the apices of the V-shaped gussets and wherein said heat sealing means are caused to engage the gusset portions of the web to form diagonal seals therein extending inwardly from the opposite side edges of the web and terminating at said fold lines.

Claims

3. The combination called for in claim 1 including a roller at the inlet end of said zone around which the web is caused to travel in a tensioned condition, and means for directing the web to said roller such that the web approaches the roller in a plane inclined to the plane of the web as it travels through said zone, said tensioning means causing the web to frictionally engage said roller to minimize the tendency of the web to flex laterally in response to lateral forces applied to the web by said guide means.

5. The combination called for in claim 4 wherein said guide means are disposed intermediate said two rollers in the path of travel of the web.

6. The combination called for in claim 1 wherein said operation performing means comprises a heat sealing member for applying a welded seam to the plastic web in a predetermined position relative to the fold line therein.

12. The combination called for in claim 11 wherein said carriage means comprises two carriages, one for each guide means, and means for maintaining said guide means in adjustably fixed laterally spaced relation so that the inner opposed edges thereof can be spaced apart in fixed relation to correspond with the lateral spacing between the vertices of webs having differently sized gussets.

17. The combination called for in claim 16 including a sheet of material overlying said recess, said material being of the type to which said plastic web stock will not readily adhere when in a heated condition.

18. The combination called for in claim 1 wherein the machine includes a second zone having a similar carriage means, guide means and operation performing means at said second zone, said web stock being of flat tubular cross section and having a laterally inwardly extending V-shaped gusset at each side thereof, said guide means at each of said zones engaging the fold lines comprising the vertices of said two gussets, said operation performing means being disposed adjacent one face of the web stock at one of said zones and adjacent the opposite face of the web stock at the other zone.

20. The combination called for in claim 19 wherein said two zones are spaced apart in the direction of travel of the stock so that the diagonal seals formed between two plies of the stock at one zone register with the diagonal seals formed between the other two plies of the stock at the other zone.

24. The method according to claim 22 wherein said web is of flat tubular cross section with an inwardly extending V-shaped gusset at each side thereof and said guide means comprises a pair of laterally interconnected guide members extending into said gussets from opposite side edges of the web and engaging the fold lines defined by the apices of the two gussets.

25. The method according to claim 22 wherein said web comprises a heat sealable plastic film and said apparatus for performing an operation thereon comprises a heat sealing means and including the steps of intermittently arresting the lengthwise movement of said web, relaxing the tension in the web when its lengthwise movement is arrested and causing the heat sealing means to engage the web while the web is in said relaxed condition.