US3650873A

US3650873A - Bag making machine having heat sealer whose dwell time is adjustable

Info

Publication number: US3650873A
Application number: US765316A
Authority: US
Inventors: William E Smith; Edward P Primosch; John D Keenan Jr
Original assignee: Amsco Packaging Machinery Inc
Current assignee: Amsco Packaging Machinery Inc
Priority date: 1968-10-07
Filing date: 1968-10-07
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21

Abstract

The web from a roll of thermoplastic sheet material folded longitudinally, and the folded web passes around dancer rods, then between feed rollers and over a platen roller. A heated sealing and severing bar is alternately moved against the folded web to press it against the platen roller to heat seal and sever the folded web transversely, and away from the folded web, in timed relation with the speed of feed of web by the feed rollers to form bags of uniform width, each open at one end. The feed of the web is stopped each time the sealing bar presses against the folded web. The dwell time and pressure of the sealer can be adjusted. The width of the bags can be adjusted. The formed bags are delivered for stacking. When tension on the web slackens, the roll of the web material is correspondingly braked. Each time a predetermined number of bags are made, the feed rollers stop feeding and the sealing bar is held away from the web on the platen to permit each delivered stack of bags to be removed, before resuming the bag making operation.

Description

United States Patent Smith et al. Mar. 21, 1972 [54] BAG MAKING MACHINE HAVING 3,148,598 9/1964 Davis ..156/515 x HEAT SEALER WH S DWELL TIME 3,451,870 6/1969 Pearson ..156/515 x IS ADJUSTABLE Inventors: William E. Smith, Upper Saddle River, N.J.; Edward P. Primosch, Franklin Square, N.Y.; John D. Keenan, Jr., Caldwell, NJ.

Assignee: Amsco Packaging Machinery, Inc.

Filed: Oct. 7, 1968 Appl. No.: 765,316

References Cited UNITED STATES PATENTS Primary Examiner-Benjamin A. Borchelt Assistant Examiner-J. J. Devitt Att0mey-Breitenfeld & Levine [5 7] ABSTRACT The web from a roll of thermoplastic sheet material folded longitudinally, and the folded web passes around dancer rods, then between feed rollers and over a platen roller. A heated sealing and severing bar is alternately moved against the folded web to press it against the platen roller to heat seal and sever the folded web transversely, and away from the folded Web, in timed relation with the speed of feed of web by the feed rollers to form bags of uniform width, each open at one end. The feed of the web is stopped each time the sealing bar presses against the folded web. The dwell time and pressure of the sealer can be adjusted. The width of the bags can be adjusted. The formed bags are delivered for stacking. When tension on the web slackens, the roll of the web material is correspondingly braked. Each time a predetermined number of bags are made, the feed rollers stop feeding and the sealing bar is held away from the web on the platen to permit each delivered stack of bags to be removed, before resuming the bag making operation.

10 Claims, 12 Drawing Figures PATENTEDMARZI m2 SHEET 1 OF 7 TTORNEYS PATENTEDMARZ] m2 3,650,873

sum 2 [IF 7 H TTOIQ/VEYS PATENTEDMARZ] I972 SHEET 3 BF 7 INVENTORs':

PATENTEDMARZ] m2 SHEET U, UF 7 EDI/V489 E J k a D W m a J 1 Y PATENIEIJMARZI I972 3.650.873 sum S []F 7 S #2. w mfl 7M.m HEM W5 1. MM N.P 1E. Vllll all -1? --.-..i: M M: 0 M z WE; N W. L L 8 BAG MAKING MACHINE HAVING HEAT SEALER WHOSE DWELL TIME IS ADJUSTABLE This invention relates to machines for making bags from a web of thermoplastic film.

Machines for folding a web longitudinally and then sealing it transversely along longitudinally spaced apart lines, to form individual bags, are known.

An object of this invention is to provide in a bag making apparatus, means for adjusting the dwell time and pressure ofthe heated sealer bar against the platen roller, and means for adjusting the width of the formed bags. A further object of the invention is to provide in such apparatus, eccentric means to raise and lower the heat sealer bar, and clutch and brake controlled means for intermittently rotating one of the feed rollers and the platen roller in one direction only.

Still another object of this invention is to provide in a bag making apparatus, highly improved means to control the tension of the web, including an electrically operated brake controlled by movement of dancer bars engaged by the web.

Yet a further object of this invention is to provide in apparatus of the character described, means to automatically stop feed of the folded web at predetermined intervals and for predetermined periods to permit removal of stacks of finished bags before bag making is automatically resumed.

- Other objects of this invention will in part be obvious and in part hereinafter pointed out.

In the accompanying drawings, in which is shown an illustrative embodiment of this invention;

FIG. 1 is a perspective view illustrating part of a machine embodying the invention;

FIG. 2 is a perspective, partly exploded, view illustrating parts shown in FIG. 1 and other parts of the machine;

FIG. 3 is a partial, side elevational view of the machine;

FIG. 4 is a cross-sectional view taken on line 44 of FIG. 3;

FIG. 5 is a cross-sectional view taken on line 5--5 of FIG. 4;

FIG. 6 is a cross-sectional view taken on line 66 of FIG. 3;

FIG. 7 is a cross-sectional view taken on line 77 of FIGS. 3 and 9;

FIG. 8 is a cross-sectional view taken on line 8-8 of FIG. 7;

FIG. 9 is a cross-sectional view taken on line 9-9 of FIG. 7;

FIG. 10 is a cross-sectional view taken on line 1010 of FIG. 9;

FIG. 11 is a cross-sectional view taken on line 11-11 of FIG. 9; and

FIG. 12 is a schematic diagram of a portion of the electrical circuitry associated with the present machine.

Referring now in detail to the drawings, 10 designates a machine for making bags from a web 11 of thermoplastic film coming from a supply roll R. The machine 10 comprises a stand 12 (FIGS. 3 and 4) which may be mounted on a floor or supporting surface 13. The stand 12 comprises a pair of parallel, longitudinal channel shaped members 14 supported by legs 15. Fixed to channel members 14 are transverse parallel angle members 16 supporting pairs of

blocks

17 and 18. Mounted on blocks 18 are a pair of square tubular vertical posts or stanchions 20 supporting, adjacent their upper ends, a longitudinal horizontal round rod 21 (see also FIG. 1). Fixed to the upper ends of said stanchions 20 are upwardly and rearwardly extending tubular brackets 22 supporting a longitudinal horizontal round rod or roller 23. Fixed to intermediate portions of stanchions 20 are rearwardly extending horizontal brackets 24 rotatably supporting a longitudinal roller 25. Mounted one one of said stanchions 20 is an electromagnetic brake mechanism 26. Also mounted on the same stanchion 20, above brake 26, is a rheostat or potentiometer 27 including a horizontal rotatable control shaft 28. The rheostat 27 is connected to the coil of the electromagnetic brake 26 by wires 29. On shaft 28 is a gear 82 fixed for rotation therewith and enclosed in a bracket 28a. Rotation of the gear, in the manner hereinafter explained, controls the brake 26 for the purpose hereinafter appearing.

On roller is mounted the supply roll R of thermoplastic film, the roll R being shiftable to the right or left on roller 25. If desired, the roll R may be fixed to the roller 25, and the roller shiftable to the right or left in its bearings. The roll R is mounted for rotation with roller 25, the web 11 from roll R extending upwardly and around rod 23 then over rod 21. The web 11 is folded longitudinally as it unwinds from the roll R. To this end, there is fixed to rod 21, a V-shaped frame 34 (FIGS. 1, 3, 4, and 5) inclined downwardly and forwardly therefrom and terminating in an apex 35 above blocks 17. Frame 34 comprises

inclined rods

37 and 38 fixed at their upper ends to the rod 21 and converging to the apex 35.

Rods

37 and 38 are interconnected by a plate 40, and the later is connected by a reinforcing rod 41 to a longitudinal tube 42 mounted on blocks 18.

Mounted on and fixed to blocks 17 is longitudinal angle member 45. Rotatably mounted on angle member 45 and tube 42 is a transverse horizontal rod 46 located somewhat below the apex 35 and slightly offset to one side thereof (FIG. 5 On rod 46 is a roller 47. Fixed to angle member 45 and tube 42, are vertical, aligned

brackets

49 and 50, respectively, supporting a horizontal rod 51 carrying a roller 52 located to the right ofroller 47 and thereabove (looking at FIG. 3).

The web 11 passes down and over rod 21 and around

rods

37 and 38 whereby it is folded, and the folded together portions 11a, 11b (FIGS. 1 and 5) engage beneath roller 47 and pass up at an incline over roller 52, forming a longitudinal fold line 11c. It will be noted that the lower web portion 11b is wider than upper web portion 11a. This is accomplished by moving roll R to the right looking at FIG. 1 (or left looking at FIG. 3) so that a greater length of roll R is to one side of apex 35 than to the other side thereof.

Channels 14 extend beyond stanchions 20 to the right, looking at FIG. 3. Fixed to the ends of channels 14 are parallel vertical front and rear posts 60 to which are fixed lower front and rear longitudinal members 61 and upper front and rear longitudinal members 62.

Members

61 and 62 may be supported at their outer ends in any suitable manner. At the upper ends of posts 60 are vertical brackets 63. Fixed to posts 60 are brackets 64 to which are pivoted, as at 65, dancer arms 66 (see also FIGS. 1 and 2) projecting beyond posts 60 to the right, looking at FIG. 3, and located inside of the posts and inside of

members

61 and 62. The outer ends of dancer arms 66 are connected by coil tension springs 67, as at 68, to posts 60, below longitudinals 61, to bias said dancer arms for rotation in a clockwise direction, looking at FIG. 3, about pivots 65. Carried by upper members 62 are a plurality of horizontal transverse, equally spaced rods 70 on fixed axes and on which rollers 71 are rotatably mounted.

Mounted between the dancer arms 66 are horizontal, transverse, equally spaced rods 73 carrying rollers 74. The folded web 11a, 11b passes initially over the first roller 71 then down and beneath the first dancer roller 74, then up and over the second roller 71 and down and under the second dancer roller 74 and so forth until it reaches the last upper roller 71. From there the folded web passes under and around a pair of rollers 75 carried by rods 76 mounted one above the other on brackets 63. The folded web then passes to the right looking at FIG. 3.

Pivoted to one dancer arm 66 as at 80 is a rack 81 meshing with a gear 82 mounted on rheostat shaft 28. The teeth of rack 81 are held in engagement with the teeth of gear 82 by a strap 83 disposed within bracket 28a (FIG. 6).

Pivot pin 80 passes through slot 81a in rack 81 to allow normal movement of the dancer arms without effecting the rheostat. However, when the arms 66 swing up more than a certain extent, due to the web being consumed during bag making, the rack 81 moves up and rotates the rheostat shaft 28 to lessen the braking action of brake 26 and relieve tension, thereby permitting the springs 67 to pull the dancer arms down and draw more film from the supply roll R. As the dancer arms are pulled down the rack moves down and actuates the rheostat to increase the braking force of the electromagnetic brake on the roller 25, carrying the supply roll R, to increase tension on the web. Although the brake 26 is shown mounted on the roller 25, the brake could be separate from the roller and operatively connected to it, such as by gearing.

Another way of automatically adjusting the tension of the web is to provide the pivotally mounted end ofone dancer arm 66 with a cam, and arrange the cam to operate a microswitch for controlling the flow of current to the brake 26, Le, when the dancer arm moves up the switch is opened to eliminate braking, and when the arm is pulled down by springs 67 the switch is closed. An arm resting on the supply, and responsive to its change in diameter, may control, braking force via a potentiometer.

The folded web moves from rollers to and between a pair of feed rollers and 91 (FIGS. 1, 2, 7, and 8). Roller 91 is an idler and roller 90 is fixed to a shaft 92. Shaft 92 carries a gear 93 and is connected through an electrically operated combination clutch and brake mechanism 94 to a coaxial shaft 95 carrying a pinion 96.

Engaging the pinion 96 is a rack 97 pivoted, in the manner to be described, to a crank disc 98 fixed to crank shaft 99 parallel to shaft 92. Fixed to the outer side of disc 98 is a radially extending slotted member 100 (FIGS. 9 and 11) formed with flanges 101. Sliding in member 100 is block 102 having flanges 103 arranged beneath the flanges 101, and pivoted at 104 to the rack 97. One end of member 100 has an opening 105, and a rod 116, screwed at one end to block 102, passes through opening 105 and though an opening in a plate 107 fixed to the disc and extending at right angles thereto. On rod 106 are collars 108 disposed at opposite sides of said plate 107. A hex head 109 fixed to the outer end of rod 106 permits turning of the rod to adjust the position of block 102 radially ofthe disc 98. The position of block 102 determines the extent of movement of the rack 97 when disc 98 is rotated (in the manner hereinafter explained).

On shaft 99 is a sprocket wheel 110 (FIG. 2) connected by sprocket chain 111 to a sprocket wheel 112 on a horizontal drive shaft 113 supported between frame members 130 (FIG. 7). Shaft 113 is connected through a gear box 114 to a shaft 115 which extends at right angles to shaft 113. Shaft 115 carries a pulley 116 connected through belt 117 to a pulley 118 on a shaft 119 driven by electric motor 120. It will be understood that when motor 120 is energized, disc 98 will rotate to oscillate shaft 95. As rack 97 is moved to the left, looking at FIG. 2, shaft 95 will rotate in a counterclockwise direction and because ofclutch-brake mechanism 94 will not rotate shaft 92 (the clutch then being open) and said shaft 92 will at the same time be braked (the brake then being actuated). When the rack 97 moves to the right, looking at FIG. 2, shaft 95 will be rotated in a clockwise direction and will be clutched to shaft 92 to rotate the feed roller 90, while the brake is then released. In his manner the folded web is intermittently fed by the

feed rollers

90 and 92.

A platen roller 121 (FIGS. 1, 2, and 8) parallel to the feed rollers and spaced therefrom, is fixedly mounted on shaft 122 which carries a gear 123 meshing with an idler pinion 124 which in turn meshes with gear 93. Thus platen roller 121 rotates simultaneously with, and in the same direction as, but faster than, feed roller 90.

A frame 133 (FIG. 8) supports a vertical transverse cooling plate 134 interposed between roller 91 and roller 121, the plate 134 carrying conduits 1340 for cooling fluid. Carried by frame 133 are parallel,

horizontal bars

131 and 132 to which are fixed

guide fingers

131a and 132a, respectively, forming a throat through which the folded web passes to reach the

feed rollers

90 and 91.

Means is provided to heat seal the folded web transversely and to sever the web along the lines of sealing, to thereby form individual bags. To this end, there is pivoted to frame 133 (FIG. 8), as on pivot pins 135, a pair of arms 136 (see also FIG. 2) to the front ends of which is attached a transverse channel 137 supporting a plurality of vertical pins 138 provided with collars 139 disposed at opposite sides of the channel. At the lower ends of the pins 138 is mounted an electrically heated bar 140 from which a beveled heated knife 141 projects downwardly directly above the axis of platen roller 121. The folded web 11a, 11b passes over the top of platen roller 121, as shown in FIG. 8 of the drawing.

On shaft 113 is an eccentric circular disc 145 (FIGS. 2 and 9). Rotatably mounted on said disc is an annular ring 146 (see also FIG. 7) provided with a radial outwardly extending lug 147. Attached to said lug 147 is radial rod 148 (see also FIGS. 8 and 10). An intermediate portion of rod 148 is screw threaded as shown at 149. Screwed on threaded portion 149 is a nut 150 having a wrench engaging portion 151. Slidable on the rod 148 and above the nut 150, is a sleeve 152. Rod 148 carries a nut 153 at its upper end, and a coil compression spring 154 surrounding rod 148 is interposed between sleeve 152 and nut 153. Sleeve 152 is pivoted to a pair of parallel bars 155 by means of diametrically opposed coaxial pivot pins 156. A block 158 is interposed between the rear ends of bars 155, and a horizontal shaft 159 passes through suitable registering openings in the rear ends of bars 155 and block 158. Fixed to the shaft 159 are spaced arms 160 which in turn are pivoted at 161 to the lower ends of a pair of upstanding bars 162. Bars 162 have rearwardly and upwardly inclined upper extensions interconnected by a rod 163. The bars 162 have aligned notches 164 in their front edges, the notches accommodating projections 165 on arms 136 which carry the heated sealing and severing bar 141.

It will now be understood that as shaft 113 is rotated, rod 148 will be reciprocated, due to eccentric 145, to oscillate bars 155 and hence shaft 159. Oscillation of shaft 159 reciprocates the bars 162 up and down, and hence will also cause the sealing and severing bar 141 to reciprocate up and down in synchronization with the intermittent rotation of the feed rollers and platen roller 121. The bar 141 comes down to heat seal and sever the folded web each time the feed rollers and the platen roller stop rotating. Arms 136 may be raised manually, up to the dot-dash position of FIG. 8, if it is desired to hold them away so that the sealing bar is out of operation. Of course, to do this, bars 162 must first be disengaged from the rod 165.

PLastic films of different thicknesses require more or less contact time with the sealer 141, and greater or lesser pressure between sealer 141 and platen 121, to provide a seal and cut of optimum character. Hence, according to the invention the dwell time and pressure of the heat sealer against the platen roller 121 may be adjusted independently of each other. To reduce the dwell time, nut 150 is screwed upwardly on the rod 148. With the rod 148 stationary, movement of the nut 150 upwardly on the rod causes the sealer 141 to be raised via the bars 155, the arms 160, bars 162, and arms 136. Thus, the sealer 141 will contact the platen roller 121 later in each cycle and will leave the roller 121 sooner, i.e., the dwell time will be reduced. On the other hand, lowering the nut 150 along the rod increases the dwell time.

If the nut 153 is screwed downwardly along rod 148, the spring 154 is compressed and hence presses the sealer 141 against the platen roller 121 with greater force, via the bars and arms mentioned above. MOving the nut 153 upwardly along rod 148 reduces the sealing pressure.

It will also be understood that the width of the bags may be adjusted. Thus to provide for bags of less width, the pivot block 102 (FIGS. 9 and 11) is moved within the slotted member 100 closer to the center of disc 98 to shorten the stroke of the rack 97, and hence shorten the length of web fed by the feed rollers each time they rotate.

Means is provided to periodically prevent actuation of the sealing and severing of the folded web. To this end, locking bars (FIGS. 2 and 8) are mounted for reciprocation by means of solenoids 171. Bars 170 are so located that when solenoids 171 are energized, in the manner hereinafter appearing, locking bars 170 will be moved outwardly beneath bars 172 fixed to shaft 159, to prevent further rotation of said shaft and hence prevent movement of bars 162 downwardly sufficiently to allow the sealing and severing bar 141 to contact the folded web.

Rotatably mounted on the frame of the machine is a horizontal shaft 175 (FIG. 2) carrying a sprocket wheel 176 connected by a sprocket chain 177 to a sprocket wheel 178 on shaft 99. Fixed to shaft 175 are four

cams

180, 181, 182 183, controlling

switches

180a, 181a, 182a, 183a, respectively. Switch 180a controls the clutch portion of the clutch-brake mechanism 94. Switch 181a controls the brake portion of the clutch-brake mechanism 94. Switch 182a controls a hole puncher 185 (FIG. 1) to punch a pair of holes 186 in the portion of web part 11b which projects beyond the edge of web part 11a. With such construction each bag B will have a pair of punched holes 186 (FIG. 1). When the bags are stacked, the holes 186 in all the bags are aligned and the arms of a U- shaped wire wicket (not shown) are passed through the holes to maintain the registered orientation of the bags while the stack is transported to the location in which the bags will be filled. The switch 18311 is in an electric eye circuit (not shown) adapted to sense preprinted marks on the plastic web for the purpose of registering the printing of the web with the operation ofthe

feed rollers

90 and 91 and sealing bar 141.

Means is provided to stop the feed of the web, and the heat sealing and severing operation, at predetermined intervals, for predetermined periods. To this end shaft 99 (FIG. 2) carries a pinion 190 meshing with a gear 191 on a parallel shaft 192. On shaft 192 is a sprocket wheel 193 about which hangs a continuous sprocket chain 194. A plurality of adjacent links of the chain carry outwardly projecting switch actuators 195, adapted to open a normally closed switch 196 mounted close to the chain 194. As the chain is moved, the switch actuators 19S hold the switch open for a predetermined period, determined by the number of links carrying actuators 195. After the actuators 195 pass the switch, the latter is closed until the actuators 195 again come into engagement with the switch. As may be seen in FIG. 12, switch 196 is in series with the camoperated switches 180a and l81a-which control the electric clutch and brake portions, respectively, of the mechanism 94. Also in series with these three switches is the coil 205 of a relay. The relay includes a normally closed switch 205a in series with brake portion 94b, normally open switch 205b in series with clutch portion 940, and a normally open switch 205v shunted across

switches

180a and 196.

At the beginning of each cycle, and assuming the switch 196 is not actuated by actuators 195, the switches are as shown in FIG. 12, whereby the brake 94b is energized and the clutch 94c is deenergized. Rotation of cam shaft 175 causes the switch 180a to be closed instantaneously, and the switch 1810 to be closed for a major portion of the cycle. Consequently, relay coil 205 is energized, whereupon switch 205a opens, deenergizing brake 94b, and switch 20512 closes energizing clutch 940. Furthermore, switch 2050 closes and serves to maintain coil 205 energized although switch 180a opens almost immediately after closing. The machine then operates through a complete cycle, and finally switch 181a opens to deenergize coil 205, and cause brake 94b to be energized and clutch 94c to be deenergized. lf machine cycles are to be skipped, the switch 196 is opened by actuators 195 on chain 194. It will be appreciated that the machine operations should not be halted at the instant the switch 196 happens to open, but only at the end of a complete machine cycle. Therefore, should switch 196 open during the course of a machine cycle, there will be no reaction since the switch 196 is shunted by the relay switch 2050 which is closed throughout most of the cycle. However, after the cycle is completed, upon closing of the

switches

180a and 181a at the beginning of the next cycle, the coil 205 will not be energized since the switch 196 is open. Consequently, the brake 94b remains energized and clutch 94c deenergized. Thus, for a period determined by the number of links of chain 194 carrying actuators, no film is fed by the feed rollers and hence no bags are made, thereby giving the machine operator an opportunity to remove a complete stack of bags from a delivery tray, the delivery tray being fully described in our copending application filed the same date as this application.

Although, for the sake of simplicity, the switch 106 has been referred to above as if it were a single throw, normally closed switch, it is actually a double throw switch, and when it is actuated, it serves to close a circuit (not shown) for energizing the solenoid 171 to operate blocking bars 170. Therefore, during the period of inactivity of the feed rollers, the sealer 141 is held out of contact with the platen roller 121, so that the sealer does not burn or otherwise injure the platen roller, and so that the sealer does not remain in engagement with the leading edge of the film and thereby thicken and distort the leading edge of the next succeeding bag. It will be appreciated that the number of bags produced between inactive periods of feeding and scaling is determined by the length of chain 194, and hence the number of bags in a complete stack may be varied by altering the length of the chain.

The formed bags B pass from the platen roller to between a pair of delivery conveyors or belts 200,201 (FIG. 1) by means of which the bags are delivered to a stacking device. The upper conveyor belt 200 extends around parallel rollers 200a and 200b, and the lower belt 201 extends around parallel rollers 201a and 20lb. Shaft 20llb may be driven by any suitable motor actuated driving means.

As possible embodiments might be made of the above invention, and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings, is to be interpreted as illustrative only.

What is claimed is:

l. A bag making machine, comprising means for folding a web of heat-scalable material longitudinally, means for intermittently feeding the folded web in a longitudinal direction, a platen beneath the path of advancement of the folded web, heat sealing and severing means arranged transversely to the folded web and above the path of advancement of the folded web, and means for oscillating said heat sealing and severing means toward and away from said platen in synchronization with the intermittent feed ofthe web to press the web between said heat sealing and severing means and said platen during periods when the web is stationary, said oscillating means including a rotating shaft, a member arranged for oscillation by said rotating shaft, an element movable with said heat sealing and severing means, resilient means for transmitting the motion of said oscillating member to said element for moving said heat sealing and severing means toward said platen, and an abutment movable with said oscillating member and adapted to engage said element to move said heat sealing and serving means away from said platen, said abutment being adjustable into different positions with respect to said oscillating member so as to adjust the dwell periods during which said heat sealing and severing means engages said platen.

2. The combination of claim 1 including means operable at predetermined intervals for discontinuing the feed of the web during continued operation of said oscillating means.

3. The combination of claim 1 including means operable at predetermined intervals for preventing engagement between said heat sealing and severing means and said platen during continued operation of said oscillating meansv 4. The combination of claim 1 including a rotatable supply roll of web material, means for applying an adjustable retarding force to said roll to vary its freedom of rotation, and means responsive to the length of web material between said supply roll and said feeding means for controlling said adjustable retarding means.

5. The combination of claim 4 including a rotatable shaft for supporting said supply roll, and wherein said adjustable retarding means is an electric brake operatively connected to said shaft.

6. The combination ofclaim 1 including means for adjusting the contact pressure between the heat sealing and severing means and said platen.

7. The combination of claim 1 wherein said abutment is threadably mounted on said oscillating member whereby the position of said abutment on said member may be adjusted by rotating said abutment.

8. A bag making machine, comprising means for folding a web of heat-scalable material longitudinally, means for intermittently feeding the folded web in a longitudinal direction, a platen beneath the path of advancement of the folded web, heat sealing and severing means arranged transversely to the folded web and above the path of advancement of the folded web, means for oscillating said heat sealing and severing means toward and away from said platen in synchronization with the intermittent feed of the web to press the web between said heat sealing and severing means and said platen during periods when the web is stationary, said oscillating means including means for adjusting the dwell periods during which said heat sealing and severing means engages said platen, and means operable at predetermined intervals for discontinuing the feed of the web during continued operation of said oscillating means, said operable means including an electric circuit having a switch, a continuous chain adjacent to said switch, and means for continuously moving said chain during operation ofthe machine, only some of the links ofsaid chain carrying means for actuating said switch.

9. The combination of claim 8 including means for rendering said switch ineffective to discontinue the feed of said web until the completion ofa machine cycle.

10. A bag making machine, comprising means for folding a web of heat-scalable material longitudinally, means for intermittently feeding the folded web in a longitudinal direction, a platen beneath the path of advancement of the folded web, heat sealing and severing means arranged transversely to the folded web and above the path of advancement of the folded web, means for oscillating said heat sealing and severing means toward and away from said platen in synchronization with the intermittent feed ofthe web to press the web between said heat sealing and severing means and said platen during periods when the web is stationary, said oscillating means including means for adjusting the dwell periods during which said heat sealing and severing means engages said platen, means operable at predetermined intervals for preventing engagement between said heat sealing and severing means and said platen during continued operation of said oscillating means, and means movable with said heat sealing and severing means, and wherein said preventing means includes a solenoid operated block shiftable into the path of movement of said movable means.