Abstract:
A method and apparatus for grasping and advancing adjacent layers of thermoplastic film through the side sealing mechanism of a packaging machine includes a plurality of belts which travel about two sets of cooperating pulleys. Each pulley has two circumferential belt grooves defined within it, each belt groove being functionally adapted to allow the travel of a belt along it. A first line of travel is defined along a path which is parallel with the line of travel for articles moving along the wrapping machine. The second line of travel diverges away at a slight angle. The belts are truncated V-belts, the “truncated V” portion of the belts being disposed outwardly of the pulleys. Each set of pulleys is offset such that the belts cooperate in tooth-meshing fashion. A tail pulley of each set is mounted in an offset cam fashion and is spring loaded to apply tension to the belts. Disposed between the belt paths is a hot wire assembly having a similarly longitudinally diverging hot wire. The hot wire assembly utilizes one mounting block which is stationary and another which is rotatable. The mounting blocks are provided with means for allowing insertion of hot wire end connectors at a predetermined depth. An end sealing apparatus includes means for adjusting the end seal location relative to the vertical height of the article to be wrapped.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to automatic package or article wrapping methods and devices. More particularly, it relates to a method and apparatus for heat sealing articles within a thermoplastic film as the articles move at a high rate of speed through an article wrapping machine. 
     BACKGROUND OF THE INVENTION 
     Machines for wrapping articles and packages with a heat sealable thermoplastic film are known art. Indeed, such machines have been utilized commercially for several decades. In a typical configuration, the package wrapping machine advances a steady stream of articles along a conveyer belt and towards a plastic envelope. This plastic envelope is formed by providing a roll of center-folded thermoplastic film which is situated to one side or the other of the conveyer. A continuous sheet of center-folded plastic film is pulled from the roll and is presented along a line which is typically perpendicular to the conveyer and perpendicular to the path of the articles which are moving along that conveyer. Means for separating the adjacent layers of film in the center-folded configuration is provided by use of a film inverter. The film inverter separates and opens the film envelope and reverse folds, or inverts, the film envelope such that the advancing articles are effectively captured by the film envelope and interposed between the adjacent film layers. As the enveloped articles continue their advance, leaving the film inverting area of the machine, one continuous side or edge of the film envelope remains open. A side sealing mechanism is provided for effectively welding or sealing the continuous side or edge of the adjacent and open film layers. Once side sealed, this mechanism provides a generally tube-like thermoplastic envelope for the articles. As the articles and the continuous side sealed plastic film envelope which covers them continue to advance along the machine, an end sealer effectively welds or seals a leading edge of the envelope and then reciprocates to the rear of the article, or simply allows the article to advance, to then weld or seal the trailing edge of the envelope. In this fashion, the leading edge of the next-in-line article is also sealed and the process is repeated. 
     In the experience of these inventors, one problem which is inherent to the side-sealing action of presently used packaging machines is that incomplete seams or welds often result in the side sealer portion of the machine. This is particularly true if the film tensions are not adequately maintained within the side-sealing portion of the machine as the film is advanced. That is, thermoplastic film which is not properly or adequately grasped within, or advanced by, the side sealer mechanism can result in adjacent film layers which are misaligned or simply not maintained in close enough proximity to one another to form a proper weld or seal as the layers are drawn into the vicinity of a hot wire or weld element. Similarly, adjacent film layers which are not maintained in proper alignment may result in welds which not only appear crumpled or wrinkled, but which are effectively incomplete. If adjacent film layers cannot be brought close enough together during the side-sealing process, it may be necessary to make other adjustments such as increasing the temperature of the weld element, or increasing the time that any given portion of the continuous film layers must remain in welding vicinity to the weld element. This latter adjustment essentially amounts to a slowing down of the packaging process and a net reduction in production. 
     Another problem which arises is the need to replace the “consumables” of the packaging machine. In the experience of these inventors, the consumables take two forms—the drive belts of the side sealer mechanism which are functionally intended to grasp and advance the thermoplastic film—and the weld element itself. In the case of any particular packaging project, drive belt breakage and weld element burn-out are recognized, though unwelcomed, inconveniences. Once broken, drive belt replacement is absolutely necessary for the continued successful operation of the machine. And, suffice it to say that no welds will be made without a properly functioning weld element. The replacement of such consumables, however, is often easier said than done. The reality being that production must come to a halt and, in the case of a broken belt, the belt drive and tail pulleys must be untensioned by use of the proper tools to allow a new belt to be stretched over them and properly seated back into place. In the case of the malfunctioning or shorted out weld element, it too must be replaced by untensioning the weld element fastening means to either end of the weld element by use of the proper tools and by resetting the newly placed weld element to the proper depth and taper so as to allow optimum performance of the weld element. All of this often requires the use of several tools, is time consuming and is surely not something that the production manager looks forward to. 
     Further in the experience of these inventors, the weld or heat element of the present generation of side sealer mechanisms which are incorporated into packaging machines may also have a tendency to degrade a weld which is, at least initially, completely and acceptably formed. That is, the weld which is formed within the side sealer may leave the welding area in perfect or near perfect condition. If the weld is overexposed to the heat of the hot wire or weld element, by spending too much time near or traveling too close to the wire or element after the weld is formed, the weld quality will be compromised. In extreme cases, the weld may actually be reopened. This too is an unacceptable result in the overall quality of production. 
     Another problem associated with present packaging machines is that the end sealing mechanisms incorporated in such machines create end seals which may also display weld inconsistencies. One explanation for this, in the view of these inventors, is that the article which is enveloped within the so-called plastic film “tube” typically has some height or thickness to it. While some articles are very thin, others are more bulky. For articles with any substantial girth, sealing of the film should optimally occur at or very near to the horizontal midline of the article. In this fashion, an equal amount of film is pulled down around the article from the top film layer as is pulled up around the article from the bottom film layer. This is not, however, how most articles are typically end sealed using machines that are available today. To the contrary, the surface upon which the article rests typically provides the horizontal reference point at which the article is sealed instead. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes these problems and disadvantages. It provides a new and useful method and apparatus for securely grasping and advancing the adjacent layers of thermoplastic film through the side sealing mechanism of a packaging machine. It also provides a new and useful method and apparatus for maintaining integrity of the heat-induced weld which is created at the side sealing mechanism and at the end sealing mechanism of the packaging machine. It also provides a new and useful method and apparatus which accomplishes all of this while making the side sealing mechanism an apparatus in which the consumables utilized within the mechanism can be maintained or replaced by the user without the need for tools or special adjustments. 
     The present invention accomplishes this by providing a plurality of film grasping belts which travel about two sets of cooperating pulleys, each pulley set including a drive pulley, a tail pulley and a number of idler pulleys disposed between the drive pulley and the tail pulley. Each pulley—drive, tail and idler—has two circumferential belt grooves defined within it, each belt groove being functionally adapted to allow the travel of a belt along it as the pulley is rotated about a central axis. A first line of travel about the pulleys is defined within the cooperating pulleys along a path which is substantially parallel with the line of travel of an article which is being advanced by the wrapping machine. The second pulley line of travel is defined within the cooperating pulleys along a path which diverges away at a slight angle relative to that path of travel. The grooves or pathways of the cooperating drive and tail pulleys of each set are cooperatively tapered or beveled so as to allow this divergence and to prevent the belt from “walking” out of the grooves. The belts which are used in the method and apparatus of the present invention are V-ribbed belts, the “V-ribbed” portion of the belts being disposed outwardly of the pulleys and the flat belt portion being immediately adjacent the pulleys. Each pair of cooperating pulleys is offset by an amount which is equal to one-half of the pitch of one rib and groove of each V-ribbed belt such that the belts engage each other in tooth-meshing fashion. This meshing action is functionally adapted to firmly grasp a pair of thermoplastic film layers therebetween and to prevent slippage therefrom. It should also be noted that the contour of the belt may be varied without deviating from the scope of this invention. 
     The tail pulley of each pulley assembly is, in the preferred embodiment, mounted in an offset cam fashion and is spring loaded to apply tension to the belts. A rotational handle is also provided. This feature allows torsional pressure to be applied to the tail pulley by the user for quick and tool-less removal of a damaged or broken belt. 
     Disposed between the divergent belt paths is a hot wire assembly which is functionally adapted to weld the thermoplastic layers together as the plastic film passes near the hot wire. This hot wire assembly is constructed such that the hot wire itself drops down along a line which is at a slight angle relative to the horizontal. It is also constructed such that the hot wire itself is divergent away from the path of travel of the article being sealed. This feature prevents over-exposure of the weld to the hot wire thereby maintaining weld integrity. The hot wire assembly, in the preferred embodiment, utilizes a first wire mounting block which is stationary and a second wire mounting block which is rotatable. A rotational handle is provided. This feature allows torsional pressure to be applied to the rotatable mounting block by the user for quick and tool-less removal of a damaged or burned out hot wire. The mounting blocks of the hot wire assembly are also provided with means for allowing insertion of the hot wire end connectors at a predetermined depth which preserves the preset angle relative to the horizontal and which does away with any need to measure or manually adjust wire depth or angle. 
     Following the side sealing apparatus of the present invention is an end sealing apparatus which includes an elevation screw for adjusting the end seal location at a point which lies at the middle of the vertical height of the article to be wrapped. The elevation screw has a elevation screw nut which is attached to it, which is in turn attached to a rocker assembly for moving a horizontally disposed and vertically moving top seal bar downwardly and a cooperating bottom seal bar, likewise horizontally disposed and vertically movable, upwardly such that the top and bottom seal bars meet at the vertical center of the article. 
     In summary, the advantages of the invention are that it provides a method and apparatus for securely grasping and advancing the adjacent layers of thermoplastic film through the side sealing mechanism of a packaging machine; that it maintains integrity of the heat-induced weld which is created at the side sealing mechanism and at the end sealing mechanism; and which makes the side sealing mechanism an apparatus in which the consumables utilized by it can be quickly and easily maintained without the need for tools or readjustment. 
     The foregoing and other advantages of the method and apparatus of the present invention will be apparent from the description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a packaging machine having a side sealing apparatus and an end sealing apparatus, both of which are constructed in accordance with the present invention. 
     FIG. 2 is an enlarged front and right side perspective view of the side sealing apparatus of the present invention. 
     FIG. 2A is a greatly enlarged right side elevational view of the cooperating belts shown in the side sealing apparatus shown in FIG.  2 . 
     FIG. 2B is another greatly enlarged right side elevational view showing a weld created along adjacent layers of thermoplastic material as they pass through the side sealing apparatus shown in FIG.  2 . 
     FIG. 3 is a rear and left side exploded perspective view of one subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 4 is a rear and left side exploded perspective view of another subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 5 is a further enlarged front right side exploded perspective view of another subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 6 is a partial and cross-sectioned right side elevational view of the side sealing apparatus shown in FIG.  2 . 
     FIG. 7 is an exploded front and right side perspective view of a tail pulley subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 8 is an enlarged cross-sectioned view of the tail pulley subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 9 is an enlarged cross-sectioned right side elevational view of a drive pulley subassembly of the apparatus shown in FIG.  2 . 
     FIG. 10 is an enlarged exploded front and right side perspective view of an idler pulley subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 11 is a further enlarged cross-sectioned right side elevational view of the idler pulley subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 12 is a top plan view of one set of idler pulleys shown in FIG.  2 . 
     FIG. 13 is an enlarged and exploded front and right side perspective view of a hot wire subassembly of the side sealing apparatus shown in FIG.  2 . 
     FIG. 14 is a further enlarged cross-sectioned right side elevational view of the stationary attachment portion of the hot wire subassembly shown in FIG.  13 . 
     FIG. 15 is a further enlarged cross-sectioned right side elevational view of the pivoting attachment portion of the hot wire subassembly shown in FIG.  13 . 
     FIG. 16 is a partial cross-sectioned and front elevational view of the hot wire subassembly shown in FIGS. 2 and 13. 
     FIG. 17 is a further enlarged and partial cross-sectioned top plan view of the hot wire and pulley subassemblies of the side sealing apparatus shown in FIG.  2 . 
     FIG. 18 is a left side elevational view of the end sealing apparatus of the present invention. 
     FIG. 19 is a partially cross-sectioned rear elevational view of the end sealing apparatus taken along line  19 — 19  of FIG.  18 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings in detail, FIG. 1 illustrates a preferred embodiment of an apparatus utilizing the method of the present invention. The packaging machine, generally identified  10 , includes a main table portion  11 , a package conveyer belt  12 , a plastic film inverter  13 , and a discharge belt  15 . The packaging machine  10  also includes a side seal assembly, generally identified  20 , and an end seal assembly, generally identified  30 . An intermediate belt  14  is situated immediately adjacent the side seal assembly  20 . 
     As an article  8  to be wrapped approaches the film inverter  13 , the article  8  enters an envelope which is created by a center folded sheet of thermoplastic film  1 . The supply of film  1  is continuous and is fed from a roll (not shown) located to one side of the machine  10 . As the article  8  passes through the inverter  13 , there is a first layer  2  of thermoplastic film  1  which is disposed over the article  8 , and a second layer  3  disposed beneath the article  8  such that the article  8  will continue to be carried along the table  11  atop the second film layer  3  and into the vicinity of the side sealer assembly  20 . As the article  8  continues on its way, a continuous and open side  6  of the film envelope formed by the adjacent edges  4 ,  5  of the film  1  remains. The side sealer assembly  20  captures this open side or edge  6  and effectively welds or seals it thereby creating a generally tube-like plastic film envelope which effectively encircles the article  8 . See FIG.  2 . 
     The side sealer assembly  20  is mounted to one side of the packaging machine  10  by means of a side seal bottom base plate  22  and a side seal top plate  21 . See FIG.  3 . The side seal base plate  22  and the side seal top plate  21  are separated by a pair of tubular column spacers  23  which are placed in tension by means of a rod  24  which is disposed to the inside of each spacer  23  by virtue of nuts  25  which are threaded onto the ends of the rods  24 . Also disposed between the side seal base plate  22  and the side seal top plate  21  is a first linear bearing shaft  26  and a second linear bearing shaft  27 . The first and second bearing shafts  26 ,  27 , respectively, are each attached to the side seal top and base plates  21 ,  22 , respectively, by means of a number of fasteners  28 . The first linear bearing shaft  26  is functionally adapted to slidably receive a top seal frame bearing  98  and a bottom seal bearing  99 . See FIG.  4 . Similarly, the second linear bearing shaft  27  is functionally adapted to slidably receive a second top seal frame bearing  96  and second bottom seal bearing  97 . The first and second top seal frame bearings  98 ,  96 , respectively, are attachable to a seal frame upper back plate  90 . Similarly, the first and second bottom seal frame bearings  99 ,  97 , respectively, are attached to a seal frame lower back plate  91 . A seal frame upper face plate  92  is provided as is a seal frame lower face plate  93 . The upper seal frame face and back plates  92 ,  90 , respectively, are attached to each other by means of a plurality of bolts  89  and with a seal frame head spacer and seal frame tail spacer  94 ,  95 , respectively, interposed between them. Similarly, the lower seal frame face and back plates,  93 ,  91 , respectively, are attached to each other with the head and tail spacers  94 ,  95  situated between them as well. It should be noted here that the bottom seal frame bearings  97 ,  99  are, in the preferred embodiment, machined to be 0.046 in. thinner than their top seal frame counterparts  96 ,  98 . The purpose for this is to mount the top face plate  92  in a plane which is 0.046 in. forward of a plane which defines the bottom face plate  93 . This detail will be discussed further later in this detailed description. It is also to be noted that the back plates and face plates,  90 ,  91 ,  92 ,  93 , respectively, of the side sealer assembly  20  are shown attached to the packaging machine  10  in a given location. This location is determined by a number of factors, including which side of the machine  10  that the open side  6  of the film  1  is presented on and what direction the article  8  is to travel in. It is to be understood that, in the preferred embodiment, both top plates  90 ,  92  and both bottom plates  91 ,  93  could be interchanged so as to allow the article direction to change, and the side at which the film envelope edge  6  presents itself, as such is desired or required. In other words, the back and face plates,  90 ,  91 ,  92 ,  93 , respectively, are functionally adapted to be assembled in another way and still come within the scope of the method and apparatus of the present invention. This is an advantage to the manufacturer, to production people and to end users alike. 
     Disposed outwardly of the upper and lower face plates,  92 ,  93 , respectively, are a number of pulleys. Specifically, the preferred embodiment contemplates of use of a tail pulley  55 , a front drive pulley  75  and a plurality of belt idler pulleys  65 , the idler pulleys  65  being linearly disposed between the tail pulley  55  and the front drive pulley  75 . See FIG.  2 . Two sets of pulleys are provided, one set disposed immediately above the other. Each idler pulley  65 , though identical in function, is configured slightly differently from the others as will become further apparent later in this detailed description. 
     The tail pulley  55  is mounted to the leading rod portion  51  of a tail pulley eccentric  50 . See FIG.  7 . The tail pulley  55  is mounted to the rod portion  51  by means of two bearings  54  and a tension pin  61 . The tail pulley eccentric  50  includes an offset rod portion  52  which projects opposite the forward rod portion  51  of the tail pulley eccentric  50 . The purpose of the tail pulley eccentric  50  is to provide the user of the packaging machine  10  with the ability to quickly and easily move the tail pulley  55  relative to the side seal assembly  20 , one tail pulley  55  being mounted to one side of the upper face plate  92  and another being mounted to the same side of the lower face plate  93 . See FIGS. 2 and 8. The tail pulley eccentric  50  is spring-loaded by virtue of a torsion spring  58  and a tail pulley clip  59 . The tail pulley eccentric  50  is moveable by means of a tail pulley knob assembly  53  which is disposed to the back side of either the top or bottom back plates  90 ,  91 , with a collar  62  disposed therebetween. The tail pulley  55  also includes a first belt recess  57  and a second belt recess  56 , the latter of which is tapered. 
     The side sealer assembly  20  includes a front drive pulley  75  which is similarly mounted to and through the seal frame upper plates  90 ,  92  and another drive pulley  75  mounted to the lower plates  91 ,  93  by means of a drive shaft  71 . The drive shaft  71  and the drive pulley are each keyed to receive a drive line key  72  therewithin. See FIGS. 2 and 9. To the rear, or backside, of the upper and lower back plates  92 ,  93 , respectively, the drive shaft  71  is configured with a pair of drive sprockets  78 ,  79 , each of which is also keyed for receiving a second drive line key  74 . While the preferred embodiment contemplates the use of a conventional chain for engagement with and driving of the sprockets  78 ,  79 , such is not a limitation of the present invention and the precise drive mechanism can be varied without deviating from the scope of the invention. The drive pulley  75  includes a first belt recess  77  and a second tapered belt recess  76 . It should be noted that the taper of the belt recess  76  of the drive pulley  75  is opposite that taper which is machined into the second belt recess  56  of the tail pulley  55 . The purpose of this will become further apparent later. 
     Linearly disposed between each front drive pulley  75  and each tail pulley  55  are a number of similarly configured belt idler pulleys  65 . In the preferred embodiment, five such idler pulleys  65  are provided. See FIG.  2 . Each idler pulley  65  includes a first belt recess  67 , a second belt recess  66  and a central hot wire clearance recess  69 . See FIGS. 10 and 11. This central recess  69  is cut relatively deeper into the idler pulley  65  than are the other belt recesses  66 ,  67 . The purpose of this is to allow each idler pulley  65  to clear the hot wire  40  which lies between the traveling belts. See FIG.  17 . Each idler pulley  65  is rotatable about and mounted on a shoulder screw  60  by means of a pair of bearings  63 . Disposed between those bearings  63  and the belt idler pulley  65  are a pair of idler pulley insulators  64 . The idler pulley insulators  64  are electrically nonconductive, the purpose of which is to prevent a short to the side seal assembly  20  in flue event of unintentional contact between the hot wire  40  and any one or more of the idler pulleys  65 . The shoulder screw  60  is secured to the rear of the seal frame back plates  90 ,  91  and the idler pulley is spaced away from the front of the face plates  92 ,  93  by use of a bushing  68 . In the preferred embodiment, the first belt recess  67  of each idler pulley  65  is colinear. That is, a continuous belt  80  traveling along one side of them is held in a straight line and the continuous belt  80  overall is held, in the shape of an elongated oval, in a vertical plane. Such is not the case with the second belt recess  66  of each idler pulley  65 . In the preferred embodiment, the pulleys  65  are collinear and the path formed by the second belt recesses  66  is also collinear, but the plane of the belt  81 , though vertical, diverges away from the plane formed by the belt  80  held within the first belt recess  67  at an angle B as shown in FIG.  12 . Similarly, the distance from the innermost edge of the second belt recess  67  to the innermost edge of the idler pulley  65  decreases from X to Y along the continuum shown in FIG. 12 as well. In this regard, see also FIG. 17 which shows the divergence between the belts  80 ,  81  as described above. 
     The side sealer assembly  20  of the present invention also includes a hot wire  40  which is functionally adapted to cut and weld adjacent layers of thermoplastic film  1  as they pass by it. A stationary wire mounting block  37  and a pivoting wire mounting block  38  are provided. The stationary wire mounting block  37  is mounted above and just inside the tail pulley  55  along the seal frame upper face plate  92 . Similarly, the pivoting wire mounting block  38  is pivotally mounted to the seal frame upper face plate  92  above and just inside the front drive pulley  75 . In the preferred embodiment, the direction of article  8  travel relative to the side sealer assembly  20  is from the direction of the stationary wire mounting block  37  and towards the pivoting wire mounting block  38  for reasons which will be explained later. The stationary wire mounting block  37  is electrically isolated from a charge which is provided by an electrical wire  31  connected to an internal wire assembly clamp  44  by means of a phenolic insulating sleeve  33 . The bottommost portion of the wire assembly clamp  44  is further electrically isolated by virtue of a phenolic washer  43 . The wire assembly clamp  44  includes an internal bore  46  which is machined at a predetermined depth. The internal bore  46  is functionally adapted to receive one lead end  41  of the hot wire  40 . See FIG.  14 . Similarly, the pivoting wire mounting block  38  is electrically isolated from a charge which is provided by an electrical wire  31  connected to an internal wire assembly clamp  45  by means of a phenolic insulating sleeve  33 . The bottommost portion of the wire assembly clamp  45  is further electrically isolated by virtue of a phenolic washer  43 . The wire assembly clamp  45  includes an internal bore  47  which is machined at a predetermined depth and is functionally adapted to receive a second lead end  42  of the hot wire  40 . See FIG.  15 . In the preferred embodiment, the depth of the bore  46  of the stationary wire clamp  44  is 1.00 in. whereas the depth of the bore  47  of the pivotal wire clamp  45  is 0.75 in. In this fashion, a stock wire  40  having lead ends  41 ,  42  which are 2.50 in. long drops about 0.25 in. in a run of about 8.125 in., or at an angle WV as shown in FIG.  16 . Fine adjustment of the wire ends  41 , 42  may be accomplished by use of side bolts  49 . See 
     FIG.  13 . Also in the preferred embodiment, the wire  40  diverges at an angle WH as shown in FIG. 17, which divergence is about 0.32 in. over the 8.125 in. run mentioned above. This divergence is at an angle WV relative to the path of the forwardly disposed belts  80 ,  82  shown in FIG.  2 B. 
     The pivoting mounting block  38  is spring-loaded by virtue of a torsion spring  36  and a wire tensioner collar  35 , both of which are disposed between the seal frame upper back and face plates  90 ,  92 , respectively. The mounting block  38  is movable by means of a knob assembly  39  which is attached to one side of the block  38 . In this fashion, rotation of the block  38  releases tension of the wire  40  and allows quick and easy removal of the wire ends  41 , 42  from the wire assembly clamps  44 , 45 . 
     As previously alluded to, the arrangement of a front drive pulley  75 , a tail pulley  55  and the belt idler pulleys  65  which are disposed between them is duplicated along the lower face plate  93  of the side sealer assembly  20 . The size, shape and configuration of each pulley is effectively mirrored in substantially vertical alignment with its upper face plate counterpart. The pulleys may also be slightly offset to effectively create a greater area of belt surface contact between upper and lower cooperating pulleys. As they lie in a vertical plane extending from the front drive pulley  75  to the tail pulley  55 , the pulleys  55 ,  65 ,  75  which are attached to the seal frame upper face plate  92  are slightly disposed outwardly relative to their counterparts in the seal frame lower face plate  93 . As discussed earlier, this is the result of machining to the bottom seal frame bearings  97 ,  99  by 0.046 in. This is a very important distinctive feature over prior art in that it allows the cooperating V belts  80 ,  82  and  81 ,  83  which have a meshing-teeth configuration to engage each other in a meshing fashion. More specifically, this feature allows the cooperating V belts  80 ,  82  and  81 ,  83  to firmly grasp the edge  6  of the thermoplastic film  1 . See FIG.  2 A. Slippage is completely eliminated and distortion of the film  1  is minimized. This results in an extremely smooth and consistent weld along the film edge  6 . See FIG.  2 B. The divergence of the belt paths, i.e. top inner belt  81  away from top outer belt  80  and bottom inner belt  83  away from bottom outer belt  82 , also results in a positive  16  withdrawal of the trimmed post-welding edge away from the side sealed article  8 . Vertical movement of each set of pulleys towards or away from each other is accomplished by use of an air cylinder  16 . See FIGS. 5 and 6. In the preferred embodiment, the bottom set of pulleys which are attached to the seal frame lower plates  91 ,  93  are moveable vertically by means of an elevational screw  18  which sets the height of the seal assembly  20  for optimum position relative to the size of the article  8 . Actuation of the air cylinder  16  one way separates the upper and lower pulley and belt assemblies so as to allow the leading edge  6  of the film to be inserted between the belts  80 ,  81 ,  82 ,  83 . Actuation of the air cylinder  16  another way closes the belts  80 ,  81 ,  82 ,  83  towards one another, the force of the cylinder  16  being dampened by means of a dampening spring  17 . 
     Referring now to FIGS. 18 and 19, the details of the end sealer, generally identified  30 , are illustrated. In particular, an end sealer frame  7  is provided which supports a pair of vertically disposed elevation screws  35 . Each elevation screw  35  is rotatable about a vertical axis by means of a drive wheel  29  which, when rotated, turns a horizontally disposed drive bar  32  and a pair of elevation drive gear assemblies  34 . A rocker pivot  36  is movable along the vertical flight of the elevation screw  35  so as to orient a rocker pivot  36  at the desired center point of the assembly  30  relative to the article  8  to be sealed. A rocker  16  is rotatably attached to the rocker pivot  36  and an upper arm  17  and a lower arm  18  are also provided. The upper and lower arms  17 ,  18 , respectively, are likewise rotatably mounted at one end to the rocker  16 . The opposite end of the upper arm  17  is rotatably attached to a top seal bar assembly  47 . Similarly, the opposite end of the lower arm  18  is rotatably attached to a bottom seal bar assembly  87 . The top seal bar assembly  47  includes a top seal bar  48  and the bottom seal bar assembly  87  includes a bottom seal bar  88 , the top and bottom seal bars  48 ,  88 , respectively, being functionally adapted to cooperate in the end sealing of the leading edge of the thermoplastic film  1  which approaches the end seal assembly  30 . The bottom seal bar assembly  87  is movable actuated by means of an air cylinder  9  which is mounted within the frame  7 . 
     In operation, the position of the side sealer assembly  20  and of the end sealer assembly  30  are adjusted to accommodate the size of the article  8  which is to be packaged. The article  8  enters the film envelope  1  with the adjacent film edges  4 ,  5  overlaying one another. The film edges  4 ,  5  enter the side sealer assembly  20  at the point where the cooperating tail pulleys  55  are situated. Note that the tail pulleys  55  are somewhat separated to allow for some fluctuation in the film  1  positioning. See FIG.  2 . As the film  1  advances, the adjacent film edges  45  are firmly grasped within the teeth  86  and grooves  85  of the outwardly disposed belts  80 ,  82  and the inwardly disposed belts  81 ,  83  of the side sealer assembly  20 . See FIG.  2 A. As the film  1  continues to be advanced, the diverging sets of belts  80 ,  82  and  81 ,  83  pull and stretch the film  1  therebetween. As this is occurring, the film begins to enter the fusion area F of the hot wire  40 . See FIG.  16 . This fusion area F is the point generally at which the wire  40  descends below the horizontal plane of film  1  which is belt captured. The heat from the hot wire  40  creates a weld  19  along the film edge closest to the outwardly disposed belts  80 ,  82 , which weld  19  is the final side weld for the article  8 . A second weld  39  is created along the film edge closest to the inwardly disposed belts  81 ,  83  and which is being pulled away from the first weld  19  by virtue of the divergence of the belts previously described. The quality of the final weld  19  which travels along with the article  8  is preserved by virtue of the divergence of the wire  40  away from the weld  19  also as previously described. As the side sealed article  8  continues, the air cylinder  9  of the end sealer assembly  30  is actuated to move the bottom seal bar assembly  87  upwardly and, by virtue of the rocker  16  and rocker arms  17 ,  18 , the top seal bar assembly  47  downwardly to effect an end seal between the top and bottom seal bars  47 ,  87 , respectively. The article  8  continues to advance and the end sealer assembly  30  is again actuated to end seal the trailing edge of the plastic encased article  8 . If, during this process, a belt  80 ,  81 ,  82 ,  83  or wire  40  needs to be replaced, the non-tool movement of one of the tail pulleys  55  or the non-tool pivoting of the wire mounting block  38  quickly and easily allows the insertion of the replacement part without any need to readjust or realign the side sealer assembly  20 . 
     From the foregoing description of the illustrative embodiment of the invention set forth herein, it will be apparent that there has been provided a new and useful method and apparatus for securely grasping and advancing the adjacent layers of thermoplastic film through the side sealing mechanism of a packaging machine; which maintains the integrity of the heat-induced weld which is created at the side sealing mechanism and at the end sealing mechanism of the packaging machine; and which makes the side sealing mechanism an apparatus in which the consumables utilized within the side sealing mechanism can be maintained or replaced by the user without the need for tools or special post-replacement adjustments.