WRAPPING MACHINE

Abstract

A method and an apparatus (10) for wrapping a bundle on 5 of the 6 faces thereof comprises gripping fingers (44) for holding a sheath (S) from opposed lateral sides of the bundle while folding members (62, 64) pivot into the sheath to tuck in inner creases along the sides of the bundle also thereby forming two-ply outer creases. The two-ply outer creases are brought down against the inner creases by the gripping fingers (44) and a sealing unit (40) is presses against the sides of the bundle to seal the so formed three-ply folds.

Description

TECHNICAL FIELD

The application relates generally to an apparatus and a method for wrapping goods, such as bundles, with sheathing materials.

BACKGROUND OF THE ART

There is a need for a new apparatus and method for providing effective and convenient wrapping or sheathing of rigid wood products, such as wood joists with sheathing materials or the like.

SUMMARY

In one aspect, there is provided a method for wrapping a bundle into a sheath, the method comprising: drawing the sheath in front of the bundle, holding the sheath against a front face of the bundle, drawing the sheath over a top surface of the bundle while the sheath is being held at the front of the bundle, creating a three-ply fold in the sheath on each opposed lateral sides of a front end portion of the bundle, sealing the three-ply folds, drawing the sheath over a rear face of the bundle, holding the sheath against the rear face of the bundle, creating a three-ply fold in the sheath on each opposed lateral sides of a rear end portion of the bundle, and sealing the three-ply folds.

In accordance with a further aspect of the present invention, there is provided a method of bagging a bundle into a sheath having a bottom open face comprising covering the bundle with the sheath, creating a pleat at each corner of the sheath, each pleat being made by doubling the sheath over on itself to form a section of three thicknesses including an inner crease along a side of the bundle and a two-ply outer crease having two superposed sheath layers, and joining the two-ply outer crease of each pleat to the associated inner crease.

In accordance with still further aspect, there is provided an apparatus for wrapping a bundle, comprising a conveyor for carrying the bundle through the apparatus, a sheath dispensing unit for covering a top surface and the lateral sides of the bundle with a sheath, first and second pairs of gripping fingers for holding the sheath from opposed lateral sides of the bundle, folding members disposed on opposed lateral side of the conveyor to tuck in the sheath along the sides of the bundle at each end of the bundle while the sheath is held by said gripping fingers, thereby forming pleats at each corner of the sheath, each pleat comprising an inner crease lying against an underlying side surface of the bundle and a two-ply outer crease held by the gripping members, the first and second pairs of gripping members being movable to draw the two-ply outer creases over corresponding inner creases, and a joining unit engageable with the sheath to join the two-ply outer crease to the underlying inner crease at each pleat.

Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1a is a front perspective view of an embodiment of a wrapping machine;

FIG. 1b is a top perspective view of the wrapping machine shown in FIG. 1a;

FIG. 2 is a simplified front perspective view of the wrapping machine illustrating the relative positions of various components of the machine before the wrapping operation be initiated, some of the components being omitted for clarity purposes;

FIG. 3 is a simplified front perspective view of the wrapping machine illustrating how the sheath is first drawn in front of the bundle to be sheathed;

FIG. 4 is a simplified front perspective view of the wrapping machine illustrating how the sheath is held and maintained against the front face of the bundle;

FIG. 5 is a simplified front perspective view of the wrapping machine illustrating how the sheath is pulled rearwardly over the top face of the bundle;

FIG. 6 is a simplified front perspective view of the wrapping machine illustrating how the front sides of the sheath are gripped to permit the same to be subsequently folded over against the lateral sides of the front end portion of the bundle;

FIG. 7 is a simplified front perspective view of the wrapping machine illustrating the folding operation of the front corners of the sheath against the front sides of the bundle;

FIG. 8 is a simplified front perspective view of the wrapping machine illustrating the sealing of the folded front corners of the sheath;

FIG. 9 is a simplified front perspective view of the wrapping machine illustrating a partly wrapped bundle in the process of being move in the forward direction in order to bring the rear end of the bundle in alignment with the folding and sealing components of the machine;

FIG. 10 is a simplified front perspective view of the wrapping machine illustrating the lowering of a weighting component and guiding rods on top of the sheath in preparation of the subsequent cutting, folding and sealing operations at the rear end of the sheath;

FIG. 11 is a simplified front perspective view of the wrapping machine illustrating the sheath covering the rear face of the bundle after having been cut from the remainder of the roll of sheath;

FIG. 12 is a simplified front perspective view of the wrapping machine illustrating the formation of the folds against the sides of the rear end of the bundle;

FIG. 13 is a simplified front perspective view of the wrapping machine illustrating the sealing of the folded rear corners of the sheath; and

FIG. 14 is a simplified front perspective view of the wrapping machine illustrating the withdrawal of the folding and sealing component of the apparatus to permit the exit of the bundle once the wrapping operation has been completed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to the drawings, and in particular to FIGS. 1a and 1b, a wrapping apparatus 10 suited for sheathing, bagging or wrapping bundles B of varying height and length with a sheath S will be described. The apparatus 10 is suited for wrapping bundles on 5 of the 6 faces thereof (i.e. the four lateral sides and the top face) leaving the bottom face uncovered. The apparatus 10 is particularly suited for wrapping bundles B having non-uniform or uneven lateral sides. In the illustrated example, the bundle is composed of a number of elongated I-shaped wood beams or joists. The I-shaped cross-section of the beams provides for elongated recessed lateral surfaces along the opposed longitudinal sides of the bundle. Wrapping that type of bundles is challenging because the lateral sides of the bundles do not provide uniform abutting surfaces to permit sealing of the sheath on the bundle.

The apparatus 10 generally comprises a motorized conveyor 12 for transporting successive bundles B through the apparatus 10. A pair of siderails 14 extends lengthwise along opposed longitudinal sides of the conveyor 12. A carrier 16 is mounted on the siderails 14 for axial forward and backward movement relative to the bundle B on the conveyor 12, as depicted by arrow 15 in FIG. 1b. An actuator 18, such a reversible electric motor, a pneumatic or hydraulic cylinder arrangement, is provided for displacing the carrier 16 back and forth along the siderails 14. A sheath dispensing unit including a roll of sheath material carried on an overhead supply reel 20 and two pairs of vertically aligned motorized indexing rollers 22 are mounted to the carrier 16. The supply reel 20 is supported above the conveyor 12 for rotation about a horizontal axis transversal to the conveyor 12, thereby providing for the dispensing of the sheath S in the longitudinal/feeding direction of the conveyor 12. As shown in FIG. 1a, the sheath S is provided in the form of a film or an elongated web of flexible, stretchable, resilient plastic material, rolled on the supply reel 20. It is understood that other types of bagging material could be used. For instance, the sheathing material could be provided as a pre-formed bag having one open end. The first and second pairs of indexing rollers 22 are mounted on a support 24 which is, in turn, mounted for vertical movement along two upstanding posts 28 forming part of the carrier 16. Actuators, such as pneumatic or hydraulic cylinders, are provided for selectively raising or lowering the indexing roller assembly along the posts 28. A pair of guide rods or rollers 30 are also carried by the support 24 in front of the indexing rollers 22 for engaging the sheath S while the same is being drawn over the top surface of the bundle B. Actuators 32, such as pneumatic or hydraulic cylinders, are provided for selectively raising or lowering the guide rollers 30 relative to the indexing rollers 22. The guide rollers 30 can be mounted at the distal end of respective arms pivotally mounted on each side of the support 24.

As can be appreciated from FIG. 1a, the sheath S is directed from the supply reel 20 to the first and second pairs of indexing rollers 22. Each pair of rollers 22 can be opened for receiving the sheath S therebetween and then closed against the sheath S for drawing the same from the reel 20. The first and second pairs of indexing rollers 22 can be driven at different speeds in order to pre-stretch the sheath S, thereby subsequently facilitating the full stretching thereof in the wrapping apparatus 10. Additional set of pre-stretching rollers driven at increased speed from one set to the next could be provided for pre-stretching the sheath S.

A bottom transversal rail 32 is provided at the front end of the apparatus 10. First and second pairs of elongated gripping fingers 34 are provided at opposed ends of the bottom transversal rail 32 for selectively holding the sheath S on opposed longitudinal sides of the bundle B. The first and second pairs of gripping fingers 34 are mounted at the upper end of respective vertically disposed Z-shaped arms 36. The Z-shaped arms 34 are linearly displaceable along opposed end portions of the rail 32 toward and away from each other between a retracted/outward position (FIG. 1a) and an operational/inward position (FIG. 4). An actuator 38, such as a pneumatic or hydraulic cylinder, is provided to reciprocate each Z-shaped arm 36 and the associated pair of gripping fingers 34 along the bottom transversal rail 32. Actuators are also provided to selectively open and close each pair of gripping fingers 34 in a horizontal plane.

First and second heat sealing members 40 are facing each other from opposed sides of the apparatus 10 for sealing the corners of the sheath S after the same have been folded over on opposed sides of the bundle B, as will be seen hereinafter. The sealing members 40 are reciprocable along transversal rail segments 42 mounted at the front end portion of the longitudinal side rails 14 behind the gripping fingers 34. Actuators (not shown) are provided for displacing the sealing members 40 from an outwardly retracted position (FIGS. 1a and 1b) to an inwardly extended position (FIG. 8) in a direction transversal to the longitudinal/feeding direction of the conveyor 12.

First and second pairs of pivotable gripping fingers 44 are facing each other from opposed longitudinal sides of the apparatus 10. The first and second pairs of pivotable gripping fingers 44 are mounted for reciprocating movement along respective pivotable ramps 46. Actuators 45, such as pneumatic or hydraulic cylinders, are provided for displacing the pairs of fingers 44 along the ramps 46. The ramps 46 are pivotally mounted to a rear facing side of rail segments 42 for upward/downward pivotal movements between a collapsed position (FIG. 1a) to clear the passage for the indexing rollers 22 and a raised position (FIG. 1b) in which the ramps 46 are inclined at 45 degrees from the horizontal plane of the apparatus 10. Actuators, such as pneumatic or hydraulic cylinders, are provided for raising and lowering the pivotable ramps 46. Referring to FIGS. 6 and 7, it can be seen that each pair of fingers 44 are also pivotable or swignable from a horizontally extending position (FIG. 6) to a vertically upwardly extending position (FIG. 7). Suitable actuators are provided for swinging the fingers 44 between their horizontal and vertical positions. The pivotable fingers 44 open and close in a vertical plane that is in a plane perpendicular to the opening and closing plane of the above described elongated fingers 34. Suitable actuators are provided for opening and closing the fingers 44.

As best seen in FIG. 1b, a pair of upstanding posts 48 are mounted for linear back and forth movements on front rail segments 50 provided at the front of the siderails 14. Actuators 52, such as pneumatic or hydraulic cylinders, are provided for reciprocating the posts 48 along the axially extending rail segments 50. A transversal weighting member 54 is mounted at opposed ends thereof to the posts 48 for upward and downward movement along the upper end portion of the posts 48. Actuators 56, such as pneumatic or hydraulic actuators, are provided for raising and lowering the weighting member 54.

As shown in FIG. 1a, a pair of anvil members 58 may be mounted at opposed ends of a bottom shaft 60 and are spaced by a distance sufficient to accommodate a bundle of predetermined width therebetween. The anvil members 58 are pivotable to an upstanding position in which the anvil members 58 lie vertically between the sheath S and the adjacent lateral surface of the bundle B (see FIGS. 5 to 8) in order to offer uniform abutting surfaces to the sealing members 40 during the sealing operation of the folded corners of the sheath S. In the illustrated example, the anvil members 58 palliate for the non-uniform lateral surfaces resulting from the I-shaped cross-section of the wood joists composing the bundle to be wrapped. Each anvil member 58 provides a flat and uniform surface on the inner side of the package against which the associated sealing member 40 can be pressed in order to obtain a strong and uniform seal in the sheath S. The use of the anvil members 58 is particularly optional when the items to be wrapped already have a uniform lateral surface against which the sealing members 40 could be pressed to form a seal in the sheath S. As shown in FIG. 14, each anvil member 58 can be pivoted forwardly downwardly to a rest position in which the anvil member lies horizontally below the bundle that has just been wrapped, thereby allowing the discharge of the wrapped bundle from the apparatus 10. The anvil members 58 rotate together with the bottom shaft 60. A reversible electric motor 65 can be provided for rotating the anvil members 58 together with the bottom shaft 60.

As shown in FIG. 1a, a pair of front and a pair of back sheath folding members 62 and 64 are also mounted to the opposed ends of the bottom transversal shaft 60 for independent pivotal movement thereabout. Each sheath folding member 62, 64 has its own actuator 66, 68. In the illustrated examples, the actuators 66 and 68 are provided in the form of pneumatic cylinders. The actuators 66 are operable to pivot the front folding members 62 from a forwardly horizontally extending position (FIG. 1a) to an upstanding position (FIG. 7) for folding the corners of the sheath S at the front end of the bundle. Likewise, the actuators 68 are operable to pivot the rear sheath folding members 64 from a rearwardly horizontally extending position (see folding member 64 on the left hand side of FIG. 1a) to an upstanding position (FIG. 12) for folding the corners of the sheath S at the rear end of the bundle B. The rear folding members 64 are further pivotable forwardly from their functional upstanding position together with the bottom shaft 60 and the anvil members 58 to a forwardly horizontally extending position (see folding member 64 on the right hand side of FIG. 1b and FIG. 14). Bushings or the like are provided between the shaft 60 and the front folding members 62 to allow the shaft 60 to rotate without driving the front folding member 62 in rotation and vice versa.

Each folding members 62,64 can be provided in the form of a two-piece part comprising a stem 62a, 64a pivotally mounted to the shaft 60 and a freely articulated arm 62b, 64b pivotally mounted to a distal end portion of the stem 62a, 64a. The operation and construction of the front and rear folding members 62, 64 are similar and, thus, will only be described in connection with one of the front folding members 62. As best seen in FIG. 6, when not in use, the articulated arm 62b lies over one side of the stem 62a. The articulated arm 62b and the stem 62a are partially longitudinally offset so that a distal end portion of the articulated arm 62b projects beyond the underlying stem 62a above the pivot between the arm 62b and the stem 62a, thereby providing a lever against which a force can be applied to pivot the arm 62b relative to the stem 62a. When the folding member 62 is pivoted to its upstanding functional position, as depicted by arrow 70 in FIG. 7, the articulated arm 62b is caused to pivot in the opposite direction, as shown by arrow 72, relative to the stem 62a under the force exerted by the sheath S on the distal upper end portion (i.e. the lever) of the arm 62b in reaction to the advancement of the folding member 62 in the sheath. The pivotal movement of the articulated arm 62b allows to roughly forming a 45 degrees fold in the sheaths S, as shown in FIG. 7.

As shown in FIGS. 1a, 1b, 2 and 4, a set of front heel members 74 are mounted on a transversal shaft 76 provided at the front discharged end of the conveyor 12. The front heel members 74 are jointly pivotable between a rest position (see FIGS. 1 a and 2) in which the heel members 74 extend in a horizontal plane slightly below a top surface of the conveyor 12 for allowing the passage of the bundle thereover, and a raised position (FIG. 4) for retaining the sheath S against the front face of the bundle B. An actuator (not shown) is provided for pivoting the front heel members 74 between their lowered and raised positions.

Likewise, as shown in FIG. 14, a set of back heel members 78 are mounted on a transversal shaft 80 provided at the inlet end of the machine 10. The back heel members 78 are pivotable between a lowered position (FIG. 11) for allowing the passage of the bundle B thereover and a raised position in which the back heel members 78 maintain the sheath S against the back face of the bundle B.

A cutting unit (not shown) is provided at the inlet end of the machine 10 for transversally cutting the sheath S at the back of the bundle B.

The operation of the machine and the various steps of the bundle wrapping process will now be described with reference to FIGS. 2 to 14. It is noted that some of the structural elements of the machine 10 have been omitted from FIGS. 2 to 14 in order to better illustrate the various sequences of the wrapping operation. For instance, only the right hand side parts are shown, the corresponding left hand side parts having the same mode of operation.

FIG. 2 shows the initial position of the parts of the machine. The front and back heel members 74 and 78 are lowered in order not to interfere with the advancement of the bundle B on the conveyor 12. The carrier 16, which supports the roll of sheath S and the indexing rollers 22, stands in its upstream most position relative to a feeding direction of the bundle B through the machine 10. The height of the indexing rollers 22 and guide rollers 30 on the posts 28 of the carrier 16 is adjusted according to the height of the bundle B to be wrapped. The pivotable ramps 46 are lowered to clear the passage of the indexing rollers 22 carried by the carrier 16. The elongated gripping fingers 34 and the sealing units 40 are retracted laterally outward to their rest positions. The anvil members 58 are raised in their upstanding position for receiving the bundle B therebetween. The front and back sheath folding members 62 and 64 are lowered to their rest positions. The weighting member 54 assumes its raised position and the posts 48 carrying the weighting member 54 stand in their upstream most position on the front rail segments 50 of the siderails 14.

First, a length of sheath S is unrolled from the supply reel 20 and engaged between the motorized indexing rollers 22 and the bundle B is advanced on the conveyor 12 between the raised anvil members 58 to a position wherein the front face of the bundle B is disposed slightly downstream of the anvil members 58, as shown in FIG. 2. The first and second pairs of motorized rollers 22 are driven at different speeds to pre-stretch the sheath S and draw the same in front of the bundle B, as shown by arrows 81 in FIG. 3.

As shown by arrows 83 in FIG. 4, the elongated gripping fingers 34 are displaced transversally inwardly along the bottom rail 32 towards the bundle B to grip the sheath S. At the same time, the front heel members 74 are pivoted upwardly against the front face of the bundle B to hold the sheath S thereagainst.

The carrier 16 supporting the supply reel 20 and the indexing rollers 22 is then displaced backward along the siderails 14 to draw a length of sheath S over the top surface of the bundle B, as represented by arrows 85 in FIG. 5. The guide rollers 30 are lowered to press the sheath S against the top surface of the bundle B while the carrier 16 is being displaced rearwardly. The carrier 16 is displaced to a position which is upstream from the pivotable ramps 46 relative to a feeding direction of the bundle through the machine.

As depicted by arrow 87 in FIG. 6, the ramps 46 are then pivoted upwardly to their operational position. In this position, the ramps 46 have a 45 degrees inclination. This allows the gripping fingers 44 to grip the sides of the sheath S on bundles of different height. As represented by arrow 89, the gripping fingers 44 are displaced downwardly along the inclined ramps 46 to an intermediate position where the gripping fingers 44 grab the sheath S on each longitudinal lateral sides of the bundle B.

Once the small gripping fingers 44 firmly holds the sheath S, the elongated gripping fingers 34 open and retract to their rest position, as represented by arrows 91 in FIG. 7. The front folding members 62 are then pivoted upwardly as depicted by arrow 70 to create a pleat at each side of the front end portion of the bundle. The pleat is defined by a 45 degree fold in the sheath made by doubling sheath over on itself to form a section of three thicknesses or layers including an inner crease along the side of the bundle and an outer crease having two superposed sheath layers, As depicted by arrow 93, the gripping fingers 44 then continue their stroke down the inclined ramp 46 and swing to their vertical orientation as shown by arrow 95, thereby pulling the double layer outer crease of the sheath S over the inner crease with the inner layer of the double layer outer crease lying against the outwardly facing surface of the inner crease previously tucked in by the front folding fingers 62. This provides for a three-layer folded corner on each side of the front end portion of the bundle B.

As shown in FIG. 8, the sealing members 40 are then displaced transversally inwardly against the opposed lateral longitudinal sides of the bundle B to seal the three-layer folded corners of the sheath S. The anvil members 58 on the inner side of the sheath S provides a uniform resting or backing surface against which the sealing members 40 can be pressed for sealing the front folded corner of the sheath S. The three-layer folded corners on opposed sides of the bundle are firmly held between the anvil members 58 and the sealing members 40 during the heat sealing process, there by providing for sturdy front seam at each side of the bundle B.

After the sealing operation, the gripping fingers 44 open and move further down the ramps 46 out of engagement from the sheath S. The gripping fingers 44 then swing back to their original horizontally extending position and move up the ramps 46 to their retracted position, as depicted by arrow 97 in FIG. 9. The sealing members 40 also retract to their rest position, as depicted by arrows 99. The conveyor 12 is then powered to abut the front face of the bundle B firmly against the front heel members 74. The carrier 16 supporting the roll of sheath is displaced backward to further taut the sheath S over the front end portion of the bundle B. Then, the front heel members 74 are pivoted forwardly to their horizontally lying position and the conveyor 12 is operated to displace the bundle forwardly together with the carrier 16 supporting the supply reel 20 and the indexing rollers 22. The front folding members 62 are pivoted back to their rest position, as depicted by the arrow 101. The conveyor 12 and the carrier 16 are synchronized to advance the bundle B, the supply reel 20 and the indexing rollers 22 at the same speed. The indexing rollers 22 are operated to unroll a length a sheath S in accordance with the length of the bundle B.

As depicted by arrows 105 in FIG. 10, the guide rollers 30 are lowered on top of the bundle B for positioning the sheath S for the gripping fingers 44. The conveyor 12 is stopped to immobilize the rear end portion of the bundle B in line with the anvil members 58. Then, as shown by arrows 107, the weighting member 54 is lowered on top of the bundle B to maintain the tension in the sheath S over the bundle B. The gripping fingers 44 are moved down the ramps 46 for gripping the sheath S, as represented by arrow 109. A cutter (not shown) is then operated to transversally cut the sheath at the rear of the bundle B.

After the sheath has been cut as shown in FIG. 11, the gripping fingers 44, move up a predetermined distance along the ramps 46 for tensioning the sheath S on the bundle B. Thereafter, the rear heel members 78 (see FIG. 11) are pivoted upwardly to maintain the rear flap of the sheath against the rear face of the bundle B. The rear folding members 64 are pivoted to their upward position to create the folds in the sheath S on both opposed lateral rear sides of the bundle B (see arrow 111 in FIG. 12). The gripping fingers 44 are displaced down the ramps 46 to an intermediate position and swung to their vertical orientation (see arrows 113 and 115 respectively) such as to pull the double-layer outer crease downwardly over the inner crease formed in the sheath S by the rear folding members 64.

As depicted by arrows 117, the sealing members 40 are displaced transversally inwardly against the anvil members 58 disposed between the sheath S and the bundle B. The three-layer folded sheath corners pressed between the anvil members 58 and the sealing members 40 are sealed, thereby forming the rear end of the sheath envelope about the bundle.

Finally, as shown in FIG. 14, the sealing members 40 and the gripping fingers 44 are retracted, the rear folding members 64 are pivoted forwardly together with the anvil members 58 to a substantially horizontally lying position and the weighting member 54 is raised from the bundle B. The conveyor 12 can then be operated to discharge the bundle B that has just been wrapped.

Once the wrapping cycle has been completed, the various parts of the machine are displaced back to their original position for receiving the next bundle to be wrapped.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the anvil members could for instance be omitted when the longitudinal lateral sides of the bundle are flat or free from any voids or recesses. The front and rear folding members 62 and 64 could have a one-piece construction. For example, they could be provided in the form of one-piece boomerang-shaped urethane members. The 45 degrees ramps 46 could be fixed. The indexing and the supply reel could move upwardly to provide the required clearance. Also the three-ply fold at the corners of the sheath could be secured by any suitable means (i.e. heat sealing being only one possible way of holding the folds in place). Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

Claims

1. A method for wrapping a bundle into a sheath, the method comprising:

drawing the sheath in front of the bundle, holding the sheath against a front face of the bundle, drawing the sheath over a top surface of the bundle while the sheath is being held at the front of the bundle, creating a three-ply fold in the sheath on each opposed lateral sides of a front end portion of the bundle, fastening the three-ply folds in place, drawing the sheath over a rear face of the bundle, holding the sheath against the rear face of the bundle, creating a three-ply fold in the sheath on each opposed lateral sides of a rear end portion of the bundle, and fastening the three-ply folds in place.

2. The method defined in claim 1, wherein the fastening steps comprise placing an anvil member between the sheath and the bundle and pressing the three-ply folds between the anvil member and a heat sealing member.

3. The method defined in claim 1, wherein creating a three-ply fold comprises moving a folding member on one side of the bundle into a laterally held portion of the sheath, the engagement of the folding member in the sheath forming a fold in the sheath, the fold defining an inner crease lying against an underlying side surface of the bundle and a two-ply outer crease in a remaining portion of the laterally held portion of the sheath, and drawing the two-ply outer crease over the inner crease, thereby forming a three-ply fold.

4. The method defined in claim 1, wherein creating a three-ply fold comprises holding a side portion of the sheath so as to create a foldable flap extending laterally outwardly from one end of the bundle, moving a folding member in the foldable flap to tuck in a first portion of the flap against one side of the bundle, thereby forming an inner crease, and pulling a remaining portion of the foldable flap over the first portion of the sheath.

5. The method defined in claim 3, wherein the folding member has a stem and a freely articulated arm pivotally mounted to a distal end potion of the stem, the freely articulated arm having a lever portion extending beyond the stem portion, and wherein continued advancement of the folding member in the laterally held portion of the sheath causes the articulated member to pivot relative to the stem under the force transmitted from the sheath to the lever portion of the articulated arm, thereby creating a fold line in the sheath.

6. The method defined in claim 4, wherein holding a side portion of the sheath comprises moving a pair of gripping fingers along a ramp having a 45 degrees inclination to an elevation corresponding generally to a top surface of the bundle, and then gripping the sheath with the gripping fingers.

7. The method defined in claim 6, wherein pulling a remaining portion of the foldable flap over the first portion of the sheath comprises moving the gripping fingers down the ramp and pivoting the gripping fingers from a horizontal orientation to a vertical orientation.

8. A method of bagging a bundle into a sheath having a bottom open face comprising covering the bundle with the sheath, creating a pleat at each corner of the sheath, each pleat being made by doubling the sheath over on itself to form a section of three thicknesses including an inner crease along a side of the bundle and a two-ply outer crease having two superposed sheath layers, and for each pleat, joining the two-ply outer crease to the inner crease.

9. The method defined in claim 8, wherein creating a pleat comprises moving a folding member on each side of the bundle into a laterally held portion of the sheath, the engagement of the folding member in the sheath forming a fold in the sheath, the fold defining the inner crease and the two-ply outer crease, and drawing the two-ply outer crease over the inner crease.

10. The method defined in claim 9, wherein the laterally held portion of the sheath is held by a pair of gripping fingers movable along a ramp having a 45 degrees inclination.

11. The method defined in claim 10, wherein drawing the two-ply outer crease over the inner crease comprises moving the gripping fingers down the ramp and pivoting the gripping fingers from a horizontal orientation to a vertical orientation.

12. An apparatus for wrapping a bundle, comprising a conveyor for carrying the bundle through the apparatus, a sheath dispensing unit for covering a top surface and the lateral sides of the bundle with a sheath, first and second pairs of gripping fingers for holding the sheath from opposed lateral sides of the bundle, folding members disposed on opposed lateral side of the conveyor to tuck in the sheath along the sides of the bundle at each end of the bundle while the sheath is held by said gripping fingers, thereby forming pleats at each corner of the sheath, each pleat comprising an inner crease lying against an underlying side surface of the bundle and a two-ply outer crease held by the gripping members, the first and second pairs of gripping members being movable to draw the two-ply outer creases over corresponding inner creases, and a joining unit engageable with the sheath to join the two-ply outer crease to the underlying inner crease at each pleat.

13. The apparatus defined in claim 12, wherein the sheath dispensing unit comprises an overhead supply reel mounted on a carrier axially displaceable back and forth relative to a feeding direction of the conveyor, and indexing rollers mounted to a support which is in turn mounted to the carrier for up and down movement with respect thereto.

14. The apparatus defined in claim 12, wherein the joining unit comprises first and second heat sealing members facing each other from opposed sides of the conveyor, the sealing members being movable towards and away from each other along an axis transversal to the conveyor.

15. The apparatus defined in claim 12, wherein the first and second pairs of gripping members are reciprocable along respective ramps, the ramps being oriented transversally to the conveyor and having an inclination of about 45 degrees.

16. The apparatus defined in claim 13, wherein the first and second pairs of gripping members are reciprocable along respective ramps, the ramps being oriented transversally to the conveyor and having an inclination of about 45 degrees when the gripping fingers are displaced to a sheath grabbing position, and wherein the ramps are pivotable to a collapsed position to clear the passage of the indexing rollers.

17. The apparatus defined in claim 12, wherein each pair of gripping fingers is pivotable from a horizontally extending position to a vertically extending position.

18. The apparatus defined in claim 14, further comprising a pair of anvil members mounted on opposed sides of the conveyor, the anvil members being displaceable between a collapsed position to an upstanding position in which the anvil members lie vertically between the sheath and an adjacent surface of the bundle in alignment with the first and second heat sealing members, the anvil members offering substantially uniform bearing surfaces against which the first and second heat sealing members can be pressed during the sealing operation.

19. The apparatus defined in claim 13, further comprising front and rear heel members pivotable between a collapsed position for clearing the passage of the bundle on the conveyor and a raised position for respectively retaining the sheath against the front and rear faces of the bundle while the carrier is displaced relative to the bundle.

20. The apparatus defined in claim 12, wherein the folding members are pivotable about an axis generally transversal to the conveyor for movement between an idle position in which the folding members lie in a generally horizontal plane and an upstanding position for tucking in the sheath along the sides of the bundle.

21. The apparatus defined in claim 12, wherein each of the folding members has a stem and a freely articulated arm pivotally mounted to a distal end portion of the stem, the articulated arm and the stem are partially longitudinally offset, the articulated arm having an end portion extending beyond the distal end portion of the stem to provide a lever for automatically causing the arm to pivot relative to the stem when a force is applied on the lever.