Abstract:
A gusset preheating assembly and a method of using the same. The assembly includes a heating gun assembly mounted on a frame. Spreader rods open up a gap in a bag&#39;s gusset and nozzles blow warmed air into the gap. Orthogonally arranged first and second hydraulic members are operatively engaged with heating gun assembly and are activated to move the heating gun assembly vertically or horizontally. Hot air blowing into the gap from the nozzle relaxes the gusset. Pressure is applied to the relaxed gusset, thereby reducing the thickness of the gusset region of the bag. The reduction in thickness makes it possible to increase the number of gusseted bags that are packaged in a container or on a roll.

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
       [0001]    The present disclosure relates generally to a system for fabricating polypropylene (plastic) bags, particularly biaxially oriented polypropylene (BOPP) bags. Specifically, the present disclosure is directed to a system and machine for fabricating polypropylene bags that includes a gusset preheating assembly provided on either side of an area where the bags are fabricated; the preheating assembly includes heating gun assemblies that blow warmed air into gussets on the bags thereby relaxing those gussets, and rollers that apply pressure thereto so that the so-formed gusseted bags take up less room when they are subsequently cut or rolled and then packaged. 
       Background Information 
       [0002]    Polypropylene bags may be fabricated by weaving and laminating extruded polypropylene, particularly BOPP threads into a sheet that is wound onto a roll. During production, the sheet is progressively unrolled from the roll and passes into machinery that folds regions of the sheet to form gussets and then heat seals the bottom and sides of the bag and then cuts individual bags from the sheet. Other steps such as printing on the exterior of the bags, forming handles etc. may also occur during this fabrication process. The cut bags may then be stacked and packaged together for subsequent shipping to a customer. In other instances, instead of cutting the individual bags from the roll, after gussets have been formed in sheet, the gusseted sheet may be wound onto a second roll for subsequent processing. 
         [0003]    Having gussets on a bag allows the bag to open wider so that it is able to hold more materials inside of it. However, having gussets also makes the thickness of a bag uneven across its width because the side portions of the bag are thicker than a central region thereof. Because of this increased thickness and stiffness on the sides of the bags, a stack of gusseted bags or a roll of gusseted bags tends to takes up more space than a stack or roll of ungusseted bags. 
       SUMMARY 
       [0004]    There is a need in the art to provide a process and assembly for fabricating gusseted bags and that decreases the overall thickness of the gusseted bags across their width and thereby reduces the overall space a stack or roll of gusseted bags will occupy. 
         [0005]    A gusset preheating assembly and a method of using the same is therefore disclosed herein The assembly includes a frame, a heating gun assembly mounted for movement with respect to the frame; said heating gun assembly including a nozzle that is used to heat a gusset of a bag that is fed through the gusset preheating assembly. The assembly also includes a first hydraulic member and a second hydraulic member mounted on the frame and being operatively engaged with each heating gun assembly. The first and second hydraulic members are oriented at right angles to each other and are selectively activated to move a portion of the heating gun assembly vertically or horizontally with respect to the frame. The movement of the heating gun assembly causes the nozzle to be inserted into a gap in a gusset or removed therefrom. Hot air is blown into the gap from the nozzle, the gusset is allowed to cool as it passes through press-rollers and this causes gusseted regions of the bag to relax and form a crisper crease, thereby reducing in thickness and tending to reduce the sign of the gap between the layers of the gussets. The relaxation of the gussets and possible reduction in thickness makes it possible to increase the number of gusseted bags that are packaged in a container or on a roll. 
         [0006]    In one aspect the invention may provide a gusset preheating assembly comprising a frame; and a heating gun assembly including a nozzle that is adapted to heat a gusset of a bag that is fed through the gusset preheating assembly. The nozzle may be mounted for movement with respect to the frame. 
         [0007]    In another aspect, the invention may provide a gusset preheating assembly that further includes a first hydraulic member mounted on the frame and being engaged with the heating gun assembly; said first hydraulic member being selectively operable to move at least a portion of the heating gun assembly in a first direction towards the gusset or in a second direction away from the gusset; and a second hydraulic member mounted on the frame and being engaged with the heating gun assembly, said second hydraulic member being selectively operable to move at least a portion of the heating gun assembly in a first direction toward the gusset or in a second direction away from the gusset; and where the first hydraulic member and the second hydraulic member are oriented at right angles relative to each other and are operable to move the heating gun assembly in directions that are at right angles to each other. 
         [0008]    In yet another aspect, the invention may provide a method of producing plastic bags, said method comprising the steps of forming a gusset in each of two opposing sides of a plastic sheet; passing the gusseted sheet into a gusset preheating assembly; heating the gussets with a heating gun assembly; relaxing the gussets; and feeding the sheet with the relaxed gussets into a cutting operation or into a rolling operation. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    A sample embodiment of the invention is set forth in the following description, is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims. 
           [0010]      FIG. 1  is a schematic representation of a portion of a process or system for forming a roll or stack of gusseted polypropylene bags; 
           [0011]      FIG. 2  is a side elevation view of a gusset preheating assembly that comprises part of the system of  FIG. 1 ; 
           [0012]      FIG. 3  is a top plan view of the gusset preheating assembly of  FIG. 2 ; 
           [0013]      FIG. 4  is a front elevation view of the gusset preheating assembly; 
           [0014]      FIG. 5  is a cross-sectional view of one gusset on a polypropylene sheet prior to passing through the gusset preheating assembly for preheating, with the cross-section taken along line  5 - 5  of  FIG. 2 ; 
           [0015]      FIG. 6  is a cross-sectional view of one gusset on the polypropylene sheet shown during gusset heating, with the cross-section taken along line  6 - 6  of  FIG. 2 ; 
           [0016]      FIG. 7  is a cross-sectional view of one gusset on the polypropylene sheet shown after passing through the gusset preheating assembly and after being heated; with the cross-section taken along line  7 - 7  of  FIG. 2 ; 
           [0017]      FIG. 8  is a front elevational view of the gusset preheating assembly when a horizontal hydraulic system on the assembly is actuated; 
           [0018]      FIG. 9  is a front elevational view of the gusset preheating assembly when a vertical hydraulic system on the assembly is actuated; 
           [0019]      FIG. 10A  is a schematic view of a stack of gusseted polypropylene bags and a roll of gusseted polypropylene bags where the bags have not passed through the gusset preheating assembly in accordance with an aspect of the present invention; and 
           [0020]      FIG. 10B  is a schematic view of a stack of gussets polypropylene bags and a roll of gusseted polypropylene bag where the bags have passed through the gusset preheating assembly in accordance with an aspect of the present invention. 
       
    
    
       [0021]    Similar numbers refer to similar parts throughout the drawings. 
       DETAILED DESCRIPTION 
       [0022]    Referring to  FIGS. 1-10B  there is disclosed part of a system for forming polypropylene bags, particularly gusseted polypropylene bags. The part of the system shown herein relates to the portion of the process after the polypropylene granules have been melted and extruded into threads, they are woven and laminated to form a polypropylene sheet that has been wound into a roll around a spindle.  FIG. 1  shows an elongate sheet  10  of polypropylene wound around a spindle  12  to form a roll of polypropylene. 
         [0023]    Sheet  10  is progressively wound off spindle  12  and travels through a process  14  in the direction of arrow “A” ( FIG. 1 ). Process  14  may include a variety of steps that include but not limited to folding  16  regions of the sheet  10  as it feeds off spindle  12  and thereby forming gussets  17 , heat welding  18  one or more seams in the sheet, cutting  20  individual bags from the sheet or rolling  22  the uncut individual bags onto a second roll and ultimately packaging or further processing  24  of the cut or rolled bags. The cutting operation  20  may also include simultaneous welding of a bottom seam on the individual bags. The order of some of the steps set out above may be changed, depending on the type of bag that is being produced. 
         [0024]    It will be understood that additional steps to those discussed above may be undertaken during fabrication of the individual bags. Such additional steps may include but are not limited to heat welding a bottom seam or side seams or other seams prior to the cutting operation  20  or rolling operation  22 ; printing on the sheet  10  either before or after the individual bags are formed; cutting apertures for handles, applying zipper mechanisms etc. It should be noted that the steps of folding  16 , heat welding  18 , forming gussets  17 , cutting individual bags  20  or rolling  22  the uncut bags onto a second roll, and the step of packaging  24  or further processing of the cut or rolled bags is known in the art. 
         [0025]    Process  14  as illustrated in  FIG. 1 , however, includes one additional step that is unknown in the art. This additional step is represented in  FIG. 1  by the reference number  26  and comprises the steps of preheating the gussets formed in the sheet  10  and then applying pressure  19  ( FIG. 1 ) to the preheated sheet  10 . The preheating step  26  is performed on a gusset preheating assembly  28  that is illustrated in  FIGS. 2-9 . Gusset preheating assembly  28  and its method of use is described below. 
         [0026]    In the process  14  depicted in  FIG. 1 , polypropylene sheet  10  is initially wound onto spindle  12 . As process  14  begins, a length of the polypropylene sheet  10  unwinds from spindle  12  and is moved through the folding process  16 , a heat welding process  18  and a gusset forming process  17 . In the gusset forming process  17  a wheel may engage each side of sheet  10  and form a fold or gusset  30  ( FIGS. 5-7 ) therein. The two gussets  30  so formed are depicted in  FIGS. 4, 8 and 9  and one of the gussets  30  is shown in greater detail in  FIGS. 5-7 . The gusseted sheet is fed into preheating assembly  28  and the process that occurs therein will be further described below. Sheet  10  passing out of preheating assembly  28  either moves into cutting operation  20  where separate, individual bags are cut off the length of the sheet and are stacked one on top of the other in a stack that may be placed in a box (or some other container), as depicted in  FIG. 10B  by the reference number  32 . Alternatively, individual bags may remain connected to each other and therefore remain as part of sheet  10  moving through process  14 . These still-connected individual bags may be rolled onto another roll, identified in  FIG. 10B  by reference number  34 . The packaged  24  box  32  or roll  34  may be sent on to a customer or may be sent within the same plant for further processing. 
         [0027]    As shown in  FIG. 2 , preheating assembly  28  comprises a frame  36  made up at least from a plurality of spaced-apart horizontal frame members  36   a ,  36   b  and a plurality of spaced-apart vertical frame members  36   c ; and a plurality of cross-plates  36   d  ( FIG. 4 ). 
         [0028]    At least two heating gun assemblies  38  are mounted on frame  36 . Gun assemblies  38  may be laterally aligned with each other and are spaced laterally apart from each other. As shown in  FIGS. 3 and 4 , each heating gun assembly  38  includes a mounting assembly  40 , a first hydraulic member  42  and a second hydraulic member  44 . (First hydraulic member  42  and second hydraulic member  44  are oriented at right angles to each other and are operable to move at least a portion of heating gun assembly  38  in directions that are at right angles to each other, as will be later described herein.) 
         [0029]    Mounting assembly  40  includes two pairs of laterally and vertically spaced-apart guide tracks  40   a  that are fixedly secured to cross-plates  36   d , one pair of guide tracks  40   a  for each heating gun assembly  38 . Each track may be substantially U-shaped in cross-section. Mounting assembly  40  further includes a housing  40   b  that has a corresponding number of rails  40   c  provided on a rear wall  40   d  ( FIG. 3 ) thereof. Each rail  40   c  is shaped, sized and arranged to be complementary to and interlockingly engaged with one of tracks  40   a . This can be seen in  FIG. 2 . The engagement between rails  40   c  and tracks  40   a  is such that rails  40   c  are able to slide along tracks  40   a  when a force is applied thereto, as will be described hereafter. 
         [0030]    Each first hydraulic member  42  includes a cylinder  42   a  and a piston  42   b  that are engaged with each other as shown in  FIG. 3 . One end of each cylinder  42   a  is pivotally anchored to a bracket  42   c  mounted on cross-plate  36   d  and one end of each piston  42   b  is pivotally anchored to rear wall  40   d  of a different one of the housings  40   b . When first hydraulic members  42  are activated such that pistons  42   b  are extended outwardly from the associated cylinders in the direction of arrow “B” (as is shown in  FIG. 8 ), a force is brought to bear upon the associated rear wall  40   d  by the activated first hydraulic members  42 . Rear wall  40   d  is thereby caused to slide along horizontally-oriented tracks  40   a  in the direction of arrow “B”. When pistons  42   b  are retracted into cylinders  42   a , the associated rear walls  40   d  will be drawn toward the anchored cylinders  42   a  in the opposite direction of arrow “B”. Because of the orientation of tracks  40   a  and first hydraulic members  42 , the movements of housings  40   b  in response to activation of first hydraulic members  42  are movements in a horizontal or lateral orientation. 
         [0031]    Each second hydraulic member  44  includes a cylinder  44   a  and a piston  44   b  that are engaged with each other as shown in  FIG. 3 , One end of each cylinder  44   a  is engaged by way of a mounting bracket  40   e  ( FIG. 4 ) with an angled wall of housing  40   b . The end of piston  44   b  remote from its associated cylinder  44   a  is engaged with one of a plurality of heating guns  46  via a mounting  46   a  ( FIG. 4 ). A vertically-oriented guide track  40   f  is provided along a side of housing  40   b  adjacent heating gun  46  and a cooperating and complementary rail  46   b  is provided on heating gun  46 . Track  40   f  and rail  46   b  interlock in such a way that heating gun  46  is able to slide relative to housing  40   b . This sliding motion is generated by activation of second hydraulic member  44 . If piston  44   b  is retracted inwardly into cylinder  44   a  in the direction of arrow “C” ( FIG. 9 ), the heating gun  46  slides along guide track  40   f  in the direction of arrow “C”. If piston  44   b  is extended outwardly from cylinder  44   a  in the opposite direction of arrow “C”, then a force is exerted on or is brought to bear upon heating gun  46  by second hydraulic members  44  and heating gun  46  slides along guide track  40   f  in the opposite direction to arrow “C”. This motion of heating gun  46  in the direction of arrow “C” is a vertically oriented motion. Thus, first hydraulic members  42  are capable of moving housing  40   b  and therefore the heating gun  46  interlocked with housing  40   b , in a generally horizontal orientation. Second hydraulic members  44  are capable of moving housing  40   b  and therefore heating gun  46  in a generally vertical orientation. 
         [0032]    A nozzle  46   c  extends outwardly from an uppermost end of each heating gun  46 . This is shown in  FIG. 9  and  FIG. 4 . Nozzle  46   c  moves in unison with heating gun  46 . Consequently, as heating gun  46  is moved horizontally (in the direction of arrow “B” or in the direction opposite to arrow “B”) or vertically (in the direction of arrow “C” or in the direction opposite to arrow “C”), nozzle  46   c  is moved in like manner. 
         [0033]    As shown in  FIGS. 5-6 , when gusset preheating assembly  28  is to be used during a production run, the nozzle  46   c  is moved horizontally and vertically into a position where the nozzle  46   c  is in the correct position for blowing heated air into gap  30   a  defined between the folded layers  30   b  and  30   c  of gusset  30 . Heated air is also blown from nozzle  46   c  toward the folded ends of layers  30   b  and  30   c . The folded end of layer  30   b  defines a gap  30   d  therein and the folded end of layer  30   c  defines a gap  30   e  therein. When the run is completed, nozzle  46   c  is retracted so that it will not come into contact with sheet  10  and melt the same. 
         [0034]    A plurality of spreader rods  48  are mounted on each side of frame  36  by mounting brackets  50 . Each rod  48  is positioned adjacent one of the heating gun assemblies  38  and may be positioned close to where one of the nozzles  46   c  will be located when that associated nozzle  46   c  is moved upwardly (in the direction opposite to arrow “C”) and inwardly (in the opposite direction to arrow A″). Rods  48  may have a hemispherical tip  48   a  ( FIG. 6 ) that has a diameter that is equal to or greater than a diameter of nozzle  46   c . Tip  48   a  and rod  48  therefore expands or increases the size of the gap  30   a  defined in gusset  30  so that nozzle  46   c  is able to be inserted into gap  30   a  or removed from gap  30   a  without coming into contact with the layers of sheet  10  that have been folded to form gusset  30 . Rods  48  thus permit the insertion of nozzles  46   c  into gap  30   a.    
         [0035]    A plurality of feed rollers  52 ,  54 , and press-rollers  56 ,  58  is mounted on frame  36 . Sheet  10  is fed through rollers  52 - 58  in the manner illustrated in  FIG. 2 . The direction of the feed is identified by arrow “D” in  FIG. 2 .  FIG. 5  shows that prior to being fed through feed roller  52 , sheet  10  includes a gusset  30  (at either end—but only one end is shown in this figure). The maximum thickness of the gusset  30  is indicated as thickness “T 1 ” and thickness “T 1 ” is substantially greater than the thickness “T” of the central region of sheet  10 . 
         [0036]    After being fed over roller  54 , both gussets  30  are spread open and kept open by the first spreader rods  48  that are positioned opposite each other across the width of sheet  10 . Because of the gentle curvature of tip  48   a  of spreader rod  48 , sheet  10  is not torn or otherwise damaged by engaging tip  48   a . Immediately after being spread open by the spreader rod  48  closest to feed roller  54 , nozzle  46   c  is introduced into the gap  30   a  ( FIG. 6 ) created in gusset  30  by spreader rod  48 . Heating gun  46  and thereby nozzle  46   c  is raised vertically by activating second hydraulic members  44  and is moved horizontally inwardly into the gap  30   a  defined by the spread-apart gusset  30  by activating the first hydraulic members  42 . (It should be noted that the system for moving the heating gun assemblies, particularly for moving the nozzles thereon, may be omitted and the nozzle may remain in a fixed position relative to the frame during processing of the bags.) 
         [0037]    Once tip  46   d  of nozzle  46   c  is physically located in the gap  30   a , air flowing through heating gun assembly  40  is heated and then this heated air  55  is blown into gap  30   a  by nozzle  46   c  and is directed toward the folded ends of layers  30   b ,  30   c  where gaps  30   d  and  30   e , respectively, are defined. The heat from the heated air  55  warms layers  30   b ,  30   c  and the gaps  30   a ,  30   d ,  30   e . The air may be heated by heating gun assembly  28  to a temperature of around 400° C.; this temperature being sufficient to warm but not melt the polypropylene layers  30   b ,  30   c . As the sheet continues to move through the process, a second blast of hot air may be introduced into gap  30   a  by the second nozzle  46   c  on the same side of gusset preheating assembly  28 , i.e., that second nozzle being the nozzle closest to the second spreader rod  48  and the press rollers  56 ,  58 . 
         [0038]    It should be noted that each nozzle  46   c  may be located before or after the associated spreader rod  48 ; whichever position is most desirable. It will also be understood that only a single nozzle  46   c  and associated heating gun  46 , may be provided along one side of gusset preheating assembly  28  or two or more nozzles  46   c  with associated heating gun assemblies  46  may be provided on each side of gusset preheating assembly  28 . Additionally, only one spreader rod  48  may be utilized on each side of gusset preheating assembly  28  or two or more such spreader rods  38  may be provided on each side of assembly  28 . 
         [0039]    After being fed past the second spreader rod  48 , the gusset  30  is no longer held open by any additional spreader rods  48  and the gusset  30  tends to relax and cool. The relaxation of gusset  30  may tend to make the folded layers  30   b ,  30   c  of the gusset  30  collapse inwardly toward each other. The sheet  10  cools and is passed through S-wrap press rollers  56 ,  58 . Rollers  46 ,  58  are positioned and configured to apply pressure  19  ( FIG. 1 ) to the sheet  10 . This application of pressure causes the gaps  30   a ,  30   d ,  30   e  between and in the heated layers  30   b ,  30   c  to collapse and become reduced in size. As shown in  FIGS. 5 and 7 , the gap  30   a  may be reduced to gap  30   a ′, the gap  30   d  may be reduced to gap  30   d ′ and the gap  30   e  may be reduced to gap  30   e ′. The gaps  30   a ,  30   d ,  30   e  may therefore effectively disappear (see  FIG. 7  from between the layers  30   b ,  30   c . The folds in the gusset  30  consequently become less rounded and open and, instead the folds or creases in gusset  30  become crisper or sharper than would be possible if sheet  10  was not passed through gusset preheating assembly  26  ( FIG. 1 ). After passing through press rollers  56 ,  58 , the gusset  30  can be seen to have a maximum thickness indicated by the reference character “T 2 ” in  FIG. 7 . This thickness “T 2 ” is relatively comparable to the thickness “T” of the central part of sheet  10  and is much thinner than the thickness “T 1 ” prior to entering preheating assembly  28 . The sheet is subsequently fed into a cutting and stacking process  20  ( FIG. 1 ) or is fed into a rolling operation  22 . After cutting  20  or rolling  22 , the bags formed from sheet  10  may be packaged or further processed  24  as indicated in  FIG. 1 . 
         [0040]      FIG. 10A  shows a box  60  that schematically illustrates a plurality of bags  62  stacked one on top of the other inside box  60  and where the total height of the stack is indicated by the reference number “H”. Bags  62  are used to illustrate a number of bags that have not passed through preheating assembly  28 . Similarly, a roll that has not passed through preheating assembly  28  is shown schematically in  FIG. 10A  and is identified by the reference number  64 . Roll  64  is illustrated as having a diameter “D” and has several layers  66  of gusseted sheet rolled thereon. 
         [0041]      FIG. 10B  shows a box  32  that schematically illustrates a plurality of bags  68  stacked one on top of the other in a box  32 . Even though the height of the box  32  is the same height “H” as in  FIG. 10A  the number of bags  68  inside the box  32  has increased dramatically relative to the number of bags  62  in box  60 . The reason for the increased number of bags  68  in box  32  is that these bags  68  went through preheating assembly  28  and the thickness of the gussets  30  on these bags  68  has been reduced from the thickness “T 1 ” ( FIG. 5 ) to the thickness “T 2 ” in  FIG. 7 . Similarly, roll  34  illustrates a scenario where sheet  10  has been treated in preheating assembly  28 . The resultant roll  34  is of the same diameter “D” as roll  64  but there are substantially more layers  70  of sheet wound onto roll  34  than was the case with roll  64 . 
         [0042]    It has been found that by passing sheet  10  through preheating assembly  28  to decrease the thickness and stiffness of gussets  30  thereon, about 40% more bags  68  may be stacked in a stack or box  32  relative to sheet that has not passed through preheating assembly  28 . Similarly, about 40% more sheet layers  70  may be wound onto a roll  34  relative to a sheet that has not passed through a preheating assembly  28 . It is therefore possible to package about 40% more bags or layers in the same box or on the same roll than was possible before the development of preheating assembly  28  and the process of utilizing the same. 
         [0043]    In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. 
         [0044]    Moreover, the description and illustration set out herein are an example and the invention is not limited to the exact details shown or described.