US3620884A

US3620884A - Sealing unit for sealing gusset bottom bags

Info

Publication number: US3620884A
Authority: US
Inventors: Donald T Peterson
Original assignee: Riegel Paper Corp
Current assignee: Riegel Paper Corp
Priority date: 1969-12-22
Filing date: 1969-12-22
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16

Abstract

A sealing unit for sealing together face-to-face strips of flexible material joined along their bottoms by a fold which is tucked upwardly to form a gusset of W-shaped cross section along the fold, the strips being advanced lengthwise and in upright planes along a predetermined path. The sealing unit comprises a primary rectangular seal bar and, spaced downstream therefrom, a gusset seal bar and a secondary rectangular seal bar, the seal bars being operable to seal the strips in such a manner as to form a series of gusset bottom bags. To enable the sealing of strips of various heights with only minor changes in the sealing unit, the primary rectangular seal bar seals the strips through a protective curtain which covers the strips except for the gusset and which allows the primary rectangular seal bar to extend downwardly alongside the gusset without pressably engaging the latter while sealing crosswise of the remainder of the strips. In order to enable the sealing of strips of various thicknesses, the gusset seal bar is mounted for adjustment laterally of the strips and relative to the secondary rectangular seal bar.

Description

United States Patent 1 3,620,884

[ 72] inventor Donald T. Peterson Primary Examiner-Benjamin A. Borchelt Rockford, Ill. Assistant Examiner-James M. Hanley [21] Appl. No. 886,980 Attorney-Wolfe, Hubbard, Leydig, Voit and Osann, Ltd.

[22] Filed Dec. 22, 1969 [45] Patented Nov. 16, 1971 [73] Assignee Riegel Paper Corporation ABSTRACT: A sealing unit for sealing together face-to-face New York strips of flexible material joined along their bottoms by a fold which is tucked upwardly to form a gusset of W-shaped cross [54] SEALING UNIT FOR SEALING GUSSET BOTTOM section along the fold, the strips being advanced lengthwise and in upright planes along a predetermined path. The sealln BAGS g 4Chims9Dmwing Figs unit comprises a primary rectangular seal bar and, spaced downstream therefrom, a gusset seal bar and a secondary [52] US. 156/553 rectangular seal bar, the seal bars being operable to seal the 156/251 156/515 strips in such a manner as to form a series of gusset bottom [51] Int. Cl bags To enable the ealing of strips of various heights 1332b 31/08 only minor changes in the sealing unit, the primary rectangu- [50] Field ofSearch 156/251, |ar seal bar seals the Strips through a protective curtain which 515, 583, 93/DIG 1 covers the strips except for the gusset and which allows the primary rectangular seal bar to extend downwardly alongside [56] References Cited the gusset without prcssably engaging the latter while sealing UN T STATES PATENT 5 crosswise of the remainder of the strips. In order to enable the 3,531,359 9/l970 Jones et al. 156/515 sealing of strips of various thicknesses, the gusset seal bar is 3,395,622 8/1968 Kugler 93/35 mounted for adjustment laterally of the strips and relative to 3,047,05l 7/1962 Matveeff 156/539 the secondary rectangular seal bar.

.-I ll I 4/ i 5 5 a I =--f= ll 1/ 1% 5 5 E T l 17 g 1/ i l" :2

PATENTEDuuv 1s nan SHEET 1 OF 2 SEALING UNIT FOR SEALING GUSSET BO'I'I'OM BAGS BACKGROUND OF THE INVENTION This invention relates to a sealing unit for sealing together face-to-face strips of flexible material joined by a fold which is tucked inwardly to form a gusset of W-shaped cross section along the fold. The strips are advanced along a predetermined path, and the sealing unit is operable to seal the strips crosswise at spaced intervals to form a series of connected gusset bottom bags. The sealing unit seals the strips with a generally rectangular seal tenninating at the gusset and with a generally triangular seal located on the gusset.

SUMMARY OF THE INVENTION The primary aim of the present invention is to provide a new and improved sealing unit for convening strips into gusset bottom bags and capable of sealing strips which may vary in height from run-to-run while requiring fewer and less expensive changes between runs than prior sealing units of the same general character.

A more detailed object is to achieve the foregoing by providing a unique sealing unit having a first sealing bar for forming at least the major part of each rectangular seal and having a second sealing bar spaced along the path of the strips from the first and operable to form the triangular seals on the gussets of the strips.

A further object is to take advantage of a protective curtain, which keeps the rectangular sealing bar from sticking to the strips, for also making only a selected length of such bar effective to seal the strips so that the same bar can be used to seal strips of various heights.

Another important object of the invention is to provide a sealing unit which, as compared with prior devices of the same general type, requires fewer and simpler modifications between runs in order to seal strips of different thicknesses. This is accomplished by mounting the second or gusset sealing bar for adjustment laterally of the strips and relative to the rectangular sealing bar.

The invention also resides in the novel provision of a secondary rectangular sealing bar which is associated with the gusset sealing bar to insure that the strips will be sealed in the area between the triangular seal and the seal formed by the primary rectangular seal bar, the adjustability of the gusset sealing bar enabling efiective sealing by the secondary bar regardless of the thickness of the strips.

Other objects and advantages of the invention will become apparent from the following detailed description when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view of a partially open gusset bottom bag. v

FIG. 2 is a fragmentary front elevation of the bag of FIG. 1 but showing the bag unopened.

FIG. 3 is an enlarged, fragmentary cross section taken substantially along the line 3-3 of FIG. 2 and showing the bag slightly open.

FIG. 4 is a fragmentary elevation of a sealing unit embodying the novel features of the present invention.

FIG. 5 is an enlarged, fragmentary cross section taken substantially along the line 5-5 of FIG. 4.

FIG. 6 is an enlarged cross section taken substantially along the line 6-6 of FIG. 4.

FIG. 7 is a perspective view of a portion of a backing mechanism shown in FIG. 6.

FIG. 8 is a perspective view of the gusset seal bar, secondary seal bar, and a support member.

FIG. 9 is a fragmentary cross section taken substantially along the line 99 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is embodied in a packaging machine having a heat sealing unit 10 (FIG. 4) for sealing together face-to-face strips 11 of flexible material to form gusset bottomed bags 12 (one bag being shown in FIG. I). The completed bag comprises front and back panels 13 (FIG. 3) joined together along the major length of their side edges by a narrow rectangular side seal 14 (FIG. 2). Along their bottoms, the panels 13 are joined by a bellowslike fold which is formed by two outer folds 15 (FIG. 3) and an intermediate and inwardly tucked reverse fold 16, thus resulting in the formation at the bottom of the bag of a gusset 17 of W-shaped cross section. The gusset extends along the lower edge portions of the side panels (and the strips 11 from which the panels are formed) with each adjacent pair of legs of the W constituting a double-walled flap 18.

The inner and

outer walls

19 and 20 at each end of each flap 18 are joined together by a seal 21 (FIG. 2) which extends over a generally triangular area including the flap comer and which terminates at an inner edge 22. The latter starts at the intersection 23 of the inner or upper end of the fold I6 and the inner edge of the side seal 14 and extends diagonally downwardly at an angle of about 45 degrees to the lower flap edge or fold 15.

When the bag 12 is opened, the \V-shaped gusset I7 is flattened out by unfolding of the flaps I8 so that the inner walls 19 of the two flaps lie substantially in the same horizontal plane to form a generally flat and rectangular bottom wall 24 as shown in FIG. I, the outer walls 20 of the flaps becoming part of the upright front and rear sides of the bag. Due to the triangular shape of the seals 21, the joined end portions of the flaps 18 ultimately turn up about a fold line 25 as the bag is opened, and the unsealed triangular portions 26 of the flaps between the seals are bent upwardly and become part of the end walls of the bag. Reference may be had to Morgan US. Pat. No. 2,821,337 for a more detailed description of a bag similar to the bag 12.

To make the bags 12, the packaging machine includes a plow (not shown) which folds or doubles an initially horizontal web of flexible material along its longitudinal center to form the face-to-face strips 11, the machine advancing the strips step-by-step and in upright positions along a predetermined path. During such advance, the lower fold connecting the strips is tucked upwardly between the strips to form the W- shaped gusset 17 along the lower margins of the strips. After the gusset had been formed, the sealing unit 10 seals the strips together at longitudinally spaced intervals, the sealing being effected as the strips dwell between successive steps. As the strips advance past the sealing unit, their upper margins straddle and slide along a stationary splitter bar 28 (FIG. 4) which is disposed above the strips to keep the extreme upper margins of the strips spread apart and thus enable easy opening of the bags at stations downstream of the sealing unit.

As shown most clearly in FIG. 4, the sealing unit I0 is operable to seal the strips 11 together with a generally rectangular seal 29 and with a generally triangular seal 30, the latter seal being formed on the gusset 17 or lower margins of the strips. The rectangular seal 29 extends upwardly along the strips from the top of the triangular gusset seal 30 to an elevation which is level with the lower edge of the splitter bar 28. For brevity, the portions of the strips which extend from the top of the gusset seals 30 upwardly and which are sealed by the rectangular seals 29 will hereinafter be referred to as panels" 31 since these portions correspond generally to the panels I3 of the ultimate bags I2.

After the strips 11 are sealed and advanced beyond the sealing unit 10, a knife (not shown) cuts the strips along the vertical centerlines of the seals 29 to separate the strips into individual bags 12. Being thus cut, each rectangular seal 29 forms the adjacent side seals I4 of adjacent bags, and each triangular gusset scal 30 forms the adjacent seals 21 on the gussets of adjacent bags.

In many instances, the same packaging machine may be used to make various lengths or heights of bags 12. That is, the machine may be used to run a series of bags of l height for a period of time and then changed over to run longer or shorter bags. This is accomplished by loading the machine with a wider or narrower web of bag material such that, when the web is folded, the resulting strips 1 1 are longer or shorter (in a vertical sense) than those fonned during a previous run with a web of a given intermediate width. With some machines capable of making bags of various heights, a so-called constant top datum line concept is employed wherein the upper edges of all strips, regardless of their height, proceed along the same horizontal top datum line during advancement of the strips. The vertical position of the splitter bar 28 thus need not be adjusted when the machine is changed over. When this concept is used, however, the bottom edges of the strips of 1 height will advance along a different lower horizontal line that the bottom edges of strips of a different height.

Other packaging machines rely upon a so-called constant bottom datum line concept. Thus, the lower edges of strips 11 of all heights advance along the same horizontal bottom datum line but, when the machine is changed over to run bags of a different height, the upper edges of the strips proceed along a different top horizontal line that the upper edges of the strips of the preceding run. In this case, the elevation of the splitter bar 28 must be changed when the packaging machine is set up to run bags 12 of a new height.

Regardless of which datum line concept is employed, certain changes must be made to the sealing unit lwhen the packaging machine is changed over to run bags 12 which differ in height from those of a preceding run. in other words, if the common top datum line concept is followed, the elevation of the gusset seals 30 on one run of bags will be difi'erent than the elevation of the gusset seals on the bags of the next run. The sealing unit thus must be modified to accommodate the different elevation of the gusset seals. Similarly, if the common bottom datum line concept is employed, the changing of the elevation of the splitter bar 28 makes necessary certain modifications in the sealing unit.

In accordance with the primary aspect of the present invention, the sealing unit is made up by a first sealing mechanism 33 for forming at least the major length of the rectangular seals 29, and by a second sealing mechanism 34, spaced along the bag path from the first, for forming the gusset seals 30. The use of separate sealing mechanisms for forming the two types of seals simplifies the changes needed to be made to the sealing unit when the packaging machine is changed over to form bags 12 of a different height and, in addition, all of the more complex and expensive parts of the sealing unit can be used regardless of the height of the bags being run and none need be replaced with parts of a different size when the machine is changed over.

Herein, the first or primary sealing mechanism 33 (FIGS. 4 and 9) for forming the major length of the rectangular seals 29 is located upstream of the second or gusset sealing mechanism 34 and comprises a front, vertically extending sealing bar 35 and a rear, vertically extending backing bar 36, the two bars being disposed directly across from one another on opposite side of the strips 11. Each bar is equal in width to the width of the rectangular seal 29 and is of a height which is equal to or greater than the height of the panels 31 of the tallest strips which the packaging machine will handle. The bars are carried on the upper end portions of swingable arms 37 and are mounted for vertical adjustment on the arms by means of bolts 38 which extend through vertically elongated slots 39 formed in the upper end portions of the arms.

Formation of each rectangular seal 29 is effected by swinging the sealing and backing bars 35 and 36 toward one another in unison (by swinging the arms 37) while the strips 11 are dwelling and by pressing the strips between the bars and simultaneously heating the strips with the bars. The inside faces only of the strips are coated with a thermoplastic material which, when heated and pressed by the bars, serves to seal the strips together in the areas located between the bars. Heat is applied to the bars by electric heaters 40 (FIG. 9) which are embedded in the upper end portions of the arms, the heat being conducted to the bars through the arms.

To prevent the hot sealing and backing bars 35 and 36 from sticking to the outer faces of the strips 11, a protective curtain 41 (FIGS. 4 and 9) of slick, heat conductive material is draped over the splitter bar 28 adjacent the tow bars and straddles the strips in such a position that, during sealing, one panel of the curtain is sandwiched between the sealing bar and the front strip while the other panel of the curtain is sandwiched between the backing bar and the rear strip. Preferably, the curtain is made of fibrous material impregnated with Teflon and conducts the heat of the bars to the strips. Thus, the strips are sealed by the bars through the curtain, the latter preventing direct contact of the bars with the strips to eliminate any danger of the bars sticking to the strips.

ln carrying out the invention, the curtain 41 is employed to advantage to enable the use of the same sealing and backing bars 35 and 36 regardless of the height of the strips 11 and to avoid the need of using bars of a different length each time the packaging machine is changed over to run strips of a different height. For the most part, these ends are achieved by using the curtain to make only a desired portion of the total length of each bar effective to actually seal the strips.

The foregoing may be best explained by first referring to FIGS. 5 and 9 wherein it will be seen that the panels 31 of the strips 11 are equal in thickness to the thickness of two individual strips while the gusset 17 is equal in thickness to thickness of four individual strips, this being due to the folded material in the gusset. Now, the bars 35 and 36 must not be permitted to press against the relatively thick gusset to any appreciable degree because, if this occurred, the gusset would either prevent inward movement of the bars to the extent necessary to seal the panels (which are of lesser thickness than the gusset) or would cause the bars to approach the panels at an angle, thus resulting in nonuniform sealing along the height of the panels. Also, regardless of the height of the strips and the elevation of the splitter 28, the upper ends of the bars always must be positioned just below, and must not extend above, the lower edge of the splitter so that the bars will be free to move inwardly to press the panels together without the inward movement of the bars being limited or influenced by the splitter.

The curtain 41 is employed to enable these criteria to be maintained while permitting the use of the same bars 35 and 36 regardless of the height of the strips 11. For purposes of explanation, let it be assumed that the strips shown in FIG. 9 are the shortest which will be handled by the packaging machine. Now, the bars, being at least as long as the height of the panels 31 of the tallest strips handled by the machine, are positioned with their upper ends below the lower edge of the splitter 28 and thus their lower end portions extend downwardly alongside the gusset 17. To keep the lower end portions of the bars from engaging the gusset and preventing the upper end portions from effectually sealing the panels 31, the curtain 41 is draped over the splitter in such a manner that the lower edges of the curtain panels terminate at or just short of the upper margin of the gusset.

Each panel of the curtain 41 is at least equal in thickness to the thickness of one individual strip 11. Accordingly, when positioned as shown in FIG. 9, the curtain panels keep the lower end portions of the bars 35 and 36 from pressing against the gusset 17 but still transmit to the strip panels 31 the heat and pressure of the upper end portions of the bars so that the panels 31 are sealed together to form the rectangular seals 29. Thus, even though the bars are considerably longer than the panels 31, the curtain causes the bars to seal only the panels 31 and enables such sealing to be effected uniformly since, with the curtain in position, all of the material engaged by the face of each bar lies in a common upright plane.

it the common top datum line concept is employed and the packaging machine changed over to run strips ll having a greater height than those shown in FlG. 9, it is necessary only to change the curtain 41 in such a manner that the lower edges of the curtain panels terminate at the upper margin of the gusset 17 of the taller strips, the gusset of such strips being disposed at a lower elevation that the gusset of the shorter strips of the preceding run. Most desirably, the curtain is simply replaced with one having longer panels capable of extending downwardly to the gusset of the taller strips. No further changes to the sealing mechanism 33 are necessary.

If the packaging machine employs the common bottom datum line concept and is changed over to run strips 11 of greater height than those shown in FIG. 9, the elevation of the splitter 28 is adjusted to correspond to the elevation of the upper edges of the taller strips and, in addition, the elevation of the bars 35 and 36 is changed (by loosening the bolts 38) so as to position the upper ends of the bars just below the lower edge of the splitter. Also, the curtain 41 is replaced with one having panel corresponding generally in length to the panels 31 of the taller strips.

Accordingly, regardless of which datum line concept is used, only the relatively inexpensive curtain 41 of the sealing mechanism 33 need be replaced when the packaging machine is changed over to form bags 12 of a different height. At most, the bars 35 and 36 need only be adjusted and need not be replaced with bars of a difierent length.

The gusset sealing mechanism 34, which is located downstream from the sealing and backing bars 35 and 36 as shown in FIG. 4, comprises a front gusset seal bar 45 (FIG. 5) and a rear gusset backing bar 46 (FIG. 7), the two bars being disposed directly across from one another on opposite sides of the strips 11. Each bar is formed in the shape of a truncated triangle the size of the gusset seal 30. The bars are mounted on front and back support blocks 47 and 48 which arecarr ied on; the upper end portions of paired

swingable rods

49 and 50, respectively.

Formation of each gusset seal 30 is effected by swinging the gusset sealing bar 45 and the gusset backing bar 46 toward one another in unison (by swinging the rods 49, 50) while the strips 11 are dwelling and by pressing the strips between the bars and simultaneously heating the strips with the bars. Heat is applied to the bars by electric heaters 51 (FIG. 6) which are embedded in the support blocks 47 and 48, the heat being conducted to the bars through the blocks.

To prevent the hot gusset sealing and backing bars 45 and 46 from sticking to the outer faces of the strips 11, a protective curtain 52 (FIGS. 4 and 5) of the same material as the curtain 41 is draped over the splitter 28 adjacent the two bars and straddles the strips. As shown in FIG. 4, the curtain extends downwardly from the splitter to a level below the bottomOon one panel of the curtain being sandwiched between the gusset sealing bar and the front face of the gusset 17 while the other panel of the curtain is sandwiched between the backing bar and the rear face of the gusset. As with the panels 31, the gusset is sealed through the curtain while the latter prevents direct contact of the sealing bars with the portion of the strips forming the gusset to prevent the bars from sticking to the gusset.

To enable vertical adjustment of the gusset sealing bar 45 and the gusset backing bar 46, the mounting

blocks

47 and 48 are adjustably mounted on their respective pair of

rods

49, 50 for sliding along the rods. For this purpose, the rods are clamped between the back surfaces 52 (FIG. 6) of the blocks and clamping plates 53. Each clamping plate is mounted on its respective block by a screw 54 which extends through the center of the plate, between the rods, and is threaded into the block. After each bar is positioned, each screw is turned to force its respective clamping plate toward its respective block thus clamping the block on the respective rods.

If the common top datum line concept is employed and the packaging machine is changed over to run strips 11 having a greater height than those shown in FIG. 5, it is necessary only to lower the gusset bars 45 and 46 by sliding the

blocks

47 and 48 downwardly on the

rods

49 and 50. If the common bottom datum line concept is employed, no change in the elevation of the gusset bars is required when the packaging machine is changed over to run strips of a greater height. Thus, like the upstream sealing mechanism 33, only relatively simple adjustments, if any, need be made to the gusset sealing mechanism 34 when the machine is changed over.

Herein, the rectangular sealing bar 35 and the rectangular backing bar 36 may not always seal the area on the panels 31 directly above the top of the gusset 17. This is true because pressure is exerted on the panels only in the area where the bars engage the curtain 41, and the latter often may not ex tend completely down to the top of the gusset. To insure that the rectangular seal 29 will be continuous from just below the splitter 28 to the top of the gusset, a secondary rectangular sealing bar 56 (FIG. 5) is carried on the front support block 47 above the gusset sealing bar 45 and a secondary rectangular backing bar 57 (FIG. 7) is carried on the back support block 48 above the gusset backing bar 46. As shown in FIG. 4, this arrangement results in an overlap of the seal formed by the rectangular sealing bar 35 and the seal formed by the secondary rectangular sealing bar 56 and insures the formation of a complete seal 29 along the height of the panels 31.

Because the gusset 17 is four strips 11 thick while the area of the panels 31 is only two strips thick, the spacing between the gusset sealing bar 45 and the gusset backing bar 46 must be greater during sealing than the spacing between the secondary rectangular sealing bar 56 and the secondary rectangular backing bar 57. In this instance, the gusset backing bar 46 and the secondary rectangular backing bar 57 are formed as an integral part of the back support block 48, and their sealing faces lie in a common plane (see FIG. 7). As best shown in FIG. 5, the sealing face of the gusset sealing bar 45 is closer to {the face 58 of the front support block 47 than is the sealing.

face of the secondary rectangular sealing bar 56 thereby to provide the necessary spacing difference during sealing. Herein, the secondary rectangular sealing bar 56 is formed as an integral part of the front support block 47.

In many instances, the same packaging machine may be used to make bags 12 from strips 11 which vary in thickness from run-to-run. That is, the machine may be used to run a series of bags with strips of one thickness for a period of time and then changed over to run bags from strips of a greater or lesser thickness.

In accordance with another aspect of the invention, the sealing unit 10 may be changed over to seal strips 11 which vary in thickness from run-to-run by making a simple adjustment to the gusset sealing bar 45 and without the necessity of replacing a major component of the sealing unit. For this purpose, the gusset sealing bar is adjustably mounted on the front support block 47 for movement laterally of the secondary rectangular sealing bar 56 and laterally with respect to the sealing position of primary rectangular sealing bar 35 and the path of the strips. With this arrangement, the gusset sealing bar 45 can be adjusted to compensate for the change in relative thickness between the panels 31 and the gusset 17 caused by the gusset being four strips thick and the panels being only two strips thick thus insuring that both the gusset sealing bar 45 and the secondary rectangular sealing bar 56 will be effective to press against and seal the strips.

When the thickness of the strips 11 is increased from one run to the next, the spacing between the sealing faces of the gusset sealing bar 45 and the gusset backing bar 46 in their sealing positions must be increased a distance twice as great as the increase in spacing between the sealing faces of the secondary rectangular sealing bar 56 and the secondary backing bar 57 in their sealing positions. Likewise, when thinner strips are run, the spacing between the gusset sealing and backing bars 45 and 46 must be decreased a distance twice as great as the decrease in spacing between the secondary rectangular sealing and backing bars 56 and 57. These relative changes must be made so that the strips will be pressed uniformly between the bars during sealing. Such relative changes in spacing are accomplished by adjusting the gusset sealing bar 45 laterally with respect to the secondary rectangular sealing bar 56. With the sealing faces of the gusset backing bar 46 and the secondary rectangular backing bar 57 lying in the same plane, the lateral spacing between the sealing faces of the gusset sealing bar 45 and the secondary rectangular sealing bar 56 should always be kept equal to the thickness of the two strips 11.

In this instance, the lateral spacing between the sealing faces of the

bars

45 and 56 is made adjustable by mounting the gusset sealing bar 45 releasably on the front support block 47 with two' screws 59 (FIG. 8) and by spacing the bar 45 from the block with a shim 60. When the thickness of the strips 11 is to be increased, the shim is replaced by a thinner shim to keep the sealing faces of the gusset sealing bar 45 and the secondary rectangular sealing bar 56 spaced two strip thicknesses apart. A thicker shim is used as a replacement when thinner strips are to be run.

It will be observed that the use of

separate sealing mechanisms

33, 34 for fonning the major portion of the rectangular seals 29 and the gusset seals 30 is particularly advantageous. This is true because, when the packaging machine is changed over to run bags 12 of a greater or lesser height,

. only very minor and inexpensive changes need to be made to the sealing mechanisms regardless of whether the top datum line concept or the bottom datum line concept is employed in the machine. The utilization of the protective curtain 41 between the panels 31 and the backing bar 35 and between the panels 31 and the backing bar 36 and terminating short of the gusset 17 is particularly advantageous because the curtain causes the bars to seal only above the gusset while allowing the lower end portions of the bars to extend downwardly alongside the gusset. Another advantageous feature is the mounting of the gusset sealing bar 45 for adjustment laterally of the secondary rectangular sealing bar 56 so that the sealing unit can be used to form bags from strips 11 which vary in thickness from run-to-run without replacing expensive major pans.

I claim as my invention:

1. A sealing unit for sealing together face-to-face strips of flexible material having panels joined by a fold which is tucked inwardly to form a gusset of W-shaped cross section along the fold and adjacent the panels, the strips being advanced along a predetermined path and the sealing unit being operable to seal the strips crosswise at spaced intervals, said sealing unit comprising a first sealer having a backer bar mounted adjacent one side of said path and extending crosswise of said strips, a generally rectangular heat sealing bar located on the other side of said path opposite said backer bar and extending crosswise of said strips, means disposed between said panels and said sealing bar and tenninating short of said gusset to keep said sealing bar from pressably engaging said gusset while conducting heat from said sealing bar to said panels, and mechanism for periodically moving one of said bars laterally of said path to press said panels against the other of said bars to seal the panels together, said sealing unit also comprising a second sealer spaced along said path from said first sealer, said second sealer having backing means mounted adjacent one side of said path alongside said gusset and having a heated gusset seal bar mounted on the other side of said path opposite said backing means, and mechanism for periodically moving said gusset seal bar relative to said backing means and laterally of said path to press said gusset against said backing means to form a gusset seal along the fold whereby the strips are formed into a series of connected gusset bottom bags.

2. The sealing unit of claim 1 in which said means comprises a sheet of heat conductive protective material having a thickness equal to or greater than the thickness of an individual strip, said sheet being between the strips and the sealing bar of said first sealer in a position to cover the area of the panel opposite such bar while leaving the gusset exposed.

3. A sealing unit as defined in claim 2 for sealing strips whose panels may, from run-to-run, vary in crosswise dimension within a predetermined range of dimensions, said bars of said first sealer being at least as long as the panels of greatest crosswise dimension within said ran e, and said sheet being changeable to keep the sheet corre ated in length mm the crosswise dimension of the panels of the strips being sealed while leaving the gusset of such strips exposed.

4. The sealing unit of claim 1 in which said second sealer further includes a secondary rectangular seal bar movable with and located adjacent said gusset seal bar, and said gusset seal bar being adjustably mounted for movement laterally of said path and relative to said secondary rectangular seal bar whereby said sealing unit may be adjusted to form bags from strips which, from run-to-run, may vary in thickness within a predetermined range of thicknesses.

Claims

2. The sealing unit of claim 1 in which said means comprises a sheet of heat conductive protective material having a thickness equal to or greater than the thickness of an individual strip, said sheet being between the strips and the sealing bar of said first sealer in a position to cover the area of the panel opposite such bar while leaving the gusset exposed.
3. A sealing unit as defined in claim 2 for sealing strips whose panels may, from run-to-run, vary in crosswise dimension within a predetermined range of dimensions, said bars of said first sealer being at least as long as the panels of greatest crosswise dimension within said range, and said sheet being changeable to keep the sheet correlated in length with the crosswise dimension of the panels of the strips being sealed while leaving the gusset of such strips exposed.
4. The sealing unit of claim 1 in which said second sealer further includes a secondary rectangular seal bar movable with and located adjacent said gusset seal bar, and said gusset seal bar being adjustably mounted for movement laterally of said path and relative to said secondary rectangular seal bar whereby said sealing unit may be adjusted to form bags from strips which, from run-to-run, may vary in thickness within a predetermined range of thicknesses.