Title:
Apparatus and method for covering a load on a pallet
United States Patent 3897671
Abstract:
A load on a pallet covered with an inverted bag with heat shrinkable film is moved through a shrink tunnel. Air is withdrawn from the bag by a venting system that follows the movements of the bag in the tunnel. The air is withdrawn from the bag with sufficient negative pressures to cause the lateral skirts of the bag, which depend below the pallet, to fold against the pallet bottom for heat shrinkage in that position so as to anchor the bag to the pallet.
US Patent References:
METHOD AND APPARATUS FOR COVERING A LOAD ON A PALLET
Myers - April 1970 - 3508375
METHOD OF ENVELOPING A LOADED PALLET IN A CONFORMING PLASTIC FILM
Kaliwoda et al. - August 1970 - 3522688
PACKAGE AND METHOD OF MAKING
Begnaud et al. - June 1971 - 3589510
/3621588.html
Grocke - November 1971 - 3621588
METHOD AND APPARATUS FOR A PALLET LOAD
Zelnick - February 1972 - 3640048
METHOD AND APPARATUS FOR COVERING A LOAD ON A PALLET
Myers - April 1970 - 3508375
METHOD OF ENVELOPING A LOADED PALLET IN A CONFORMING PLASTIC FILM
Kaliwoda et al. - August 1970 - 3522688
PACKAGE AND METHOD OF MAKING
Begnaud et al. - June 1971 - 3589510
/3621588.html
Grocke - November 1971 - 3621588
METHOD AND APPARATUS FOR A PALLET LOAD
Zelnick - February 1972 - 3640048
Application Number:
05/393608
Publication Date:
08/05/1975
Filing Date:
08/31/1973
View Patent Images:
Export Citation:
Assignee:
Comptex, Inc. (Chicago, IL)
Primary Class:
Other Classes:
34/222, 34/229, 34/225, 34/235, 53/557
International Classes:
B65B53/06; B65B53/00; B65B53/06
Field of Search:
53/22R,22B,112R,112B,3S,184S 34/212,216,217,222,225,229,230,235 219/385,388
US Patent References:
Primary Examiner:
Spruill, Robert L.
Attorney, Agent or Firm:
Quarton, Esq. Charles E.
Claims:
I claim
1. A method of covering a load on a pallet comprising the steps of:
2. The method of claim 1 which further includes the step of folding the depending skirt at the front end under the pallet and holding the front end skirt in folded position through at least a portion of the heat shrinking operation in order to form such securement.
3. The method of claim 1 which further includes the step of folding the depending skirt at the rear end under the pallet and holding the rear end skirt in folded condition during at least a portion of the heat shrinking operation in order to form such securement.
4. The method of claim 1 in which said withdrawal of air from the bag continues during movement of the pallet during at least a portion of the heat shrinking operation.
5. The method of claim 1 wherein the withdrawal of air from the bag occurs before the bag of heat-shrinkable film reaches a weld temperature to collapse the bag.
6. A method of covering a load on a pallet with heat-shrinkable film, the steps comprising:
7. The method of claim 6 wherein the bag of film has a skirt depending below the pallet and air is withdrawn from the bag so that the side flaps of said skirt are folded below the pallet bottom with air pressures.
8. The method of claim 7 wherein at least one end flap is folded below the pallet bottom and the side flaps are fused to said end flap during the heating shrinking operation.
9. The method of claim 7 wherein the venting of the inverted bag occurs before the heat-shrinkable film reaches a weld temperature.
10. Apparatus for shrinking an inverted bag of heat-shrinkable film upon a loaded pallet comprising:
1. A method of covering a load on a pallet comprising the steps of:
2. The method of claim 1 which further includes the step of folding the depending skirt at the front end under the pallet and holding the front end skirt in folded position through at least a portion of the heat shrinking operation in order to form such securement.
3. The method of claim 1 which further includes the step of folding the depending skirt at the rear end under the pallet and holding the rear end skirt in folded condition during at least a portion of the heat shrinking operation in order to form such securement.
4. The method of claim 1 in which said withdrawal of air from the bag continues during movement of the pallet during at least a portion of the heat shrinking operation.
5. The method of claim 1 wherein the withdrawal of air from the bag occurs before the bag of heat-shrinkable film reaches a weld temperature to collapse the bag.
6. A method of covering a load on a pallet with heat-shrinkable film, the steps comprising:
7. The method of claim 6 wherein the bag of film has a skirt depending below the pallet and air is withdrawn from the bag so that the side flaps of said skirt are folded below the pallet bottom with air pressures.
8. The method of claim 7 wherein at least one end flap is folded below the pallet bottom and the side flaps are fused to said end flap during the heating shrinking operation.
9. The method of claim 7 wherein the venting of the inverted bag occurs before the heat-shrinkable film reaches a weld temperature.
10. Apparatus for shrinking an inverted bag of heat-shrinkable film upon a loaded pallet comprising:
Description:
BACKGROUND OF THE INVENTION
It is a well-known practice to store or handle articles supported on pallets. When the pallets are to be outdoors or otherwise surrounded by an atmosphere which may damage the articles, plastic covers have been employed heretofore for protection. Moreover, the plastic covers reduce pilferage, stabilize the loads so the articles are not dislodged, and protect against dust and moisture.
Problems have arisen in covering pallet loads with plastic. Most pallet loads are irregular and it is difficult to produce a packae that will conform to the shape of the load. One approach is disclosed in Meyers U.S. Pat. No. 3,508,375 in which heat-shrinkable film in the form of an inverted bag is placed over the load and air withdrawn from the bottom of the bag while heating occurs. In such an arrangement, the pallet load must be stationary because of the fixed position of the heating duct, and this does not lend itself to high volume production.
Another problem arises in attempting to fasten the lower end of the inverted bag to the pallet. Staples, adhesive, and various folding techniques have been used, but these techniques are time consuming and do not lend themselves to automatic procedures.
SUMMARY OF THE INVENTION
A general object of the invention is to provide a effective and reliable method and apparatus for covering a load on a pallet with heat shrinkable film.
It is another object of the invention to provide a system for securing heat shrinkable film to the pallet by folding flaps or skirts under the pallet bottom.
It is yet another object of the invention to provide a system for withdrawal of air from an inverted bag of heat shrinkable film covering a load on a pallet while moving.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the heat shrink tunnel illustrating diagrammatically the method of placement of the bag of heat shrink film over the load on the pallet.
FIG. 2 is longitudinal section taken along line 2--2 of FIG. 1, and diagrammatically illustrating a load on a pallet covered with heat shrink film in the tunnel.
FIG. 2A is an enlarged view of a movable vane of the type employed in the shrink tunnel.
FIG. 3 is a perspective view of the heat shrink tunnel in part broken away to illustrate the heating system.
FIG. 3a is a view taken along line 3a--3a of FIG. 3 illustrating an air flow control.
FIG. 3b is a view taken along line 3b--3b of FIG. 3 illustrating the inlet ducts at the top of the tunnel.
FIG. 4 is a fragmentary view of the bottom vent for withdrawal of air from the bag and associated linkage for controlling the movable vanes.
FIG. 5 is a cross-sectional view through the tunnel diagrammatically illustrating the manner in which the inverted bag of heat shrink film covers the load on the pallet.
FIG. 6 is a diagrammatic view showing in phantom lines the system for folding the flap or skirt under the front end of the pallet, and illustrating the vent opening below the pallet for withdrawal of air from the inverted bag.
FIG. 6a is a diagrammatic view showing in phantom lines the system for folding the flap or skirt under the rear end of the pallet, and illustrating the manner in which the vent opening follows the movement of the pallet so that air is withdrawn from the inverted bag while the pallet is moving.
FIG. 7 is a bottom view of the pallet load showing the flaps folded beneath the pallet.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly stated, the present invention is directed to removing the air from an inverted bag of heat shrink film covering a load on a pallet while the pallet is moving. The air is removed with sufficient negative pressures to cause the depending lateral skirts or flaps to fold under the bottom of the pallet at which location they are welded and fused to assist in anchoring the bag to the pallet.
Referring now to FIG. 1, a loosely fitting bag 10 made of heat shrinkable film is placed over a load 11 on pallet 12. The inverted bag may be placed over the load as indicated by the arrow either manually or by automatic equipment. The load on the pallet covered with the inverted bag is then moved through the tunnel 30 by suitable conveying means. After passing through the heat shrink tunnel the heat shrinkable bag tightly encases the load and pallet, as illustrated at the right side of FIG. 1.
The inverted bag should have a height greater than the combined height of the load and pallet so that the lower edges of the bag form a skirt or flap which depends below the pallet and which can be folded under the pallet bottom to secure the bag. Referring to FIG. 7, which shows the bottom of the pallet after emerging from the tunnel, there is illustrated flaps 10A, 10B, 10C, and 10C which have been folded under the pallet bottom and secured in place by fusion or welding of the heat shrinkable plastic at the overlapping corners. The flaps are fused at the corners form a frame which encloses the marginal portions of the pallet bottom.
The manner in which the flaps are folded under the pallets will now be described. The front end flap 10A is folded as shown in FIG. 6, as the pallet is transferred to conveyor 20 for movement through the tunnel 30. As illustrated, the pallet is transferred from conveyor 25 to conveyor 20, and the front flap 10A is folded during the transfer from one conveyor to the other.
The folding of rear end flap 10B is illustrated in FIG. 6a. The conveyor 25 is provided with transverse roller bars 26 which rotate freely about their transverse axes. The conveyor 25, at the time of the movement of the rear end of the pallet to conveyor 20, rotates at an increased speed which has a longitudinal velocity greater than the movement of the pallet and conveyor 20. The greater speed of conveyor 25 and bars 26 acts to push flap 10B below the pallet as it moves on to conveyor 20 as depicted in FIG. 6a.
The side flaps 10C and 10D are folded under the pallet by air pressure differentials between the exterior and interior of the bag as will now be described. Referring to FIGS. 1, 2 and 5, it will be noted that the pallet 12 has a greater width than the conveyors 20 and 25. This allows the flaps at the sides of the pallet to hang freely below the pallet bottom as the pallet enters the tunnel 30.
Referring now to FIG. 5, there is shown an air return duct 40 located below the conveyor 20 and below the center portion of the pallet 12. The duct extends substantially the entire length of the path of travel of the pallet through the tunnel, although the desired length can be varied as circumstances warrant. Duct 40 creates a negative air pressure in the bag 10 in sufficient amounts to cause the flaps 10C and 10D to fold under the bottom of the pallet as illustrated in FIG. 5.
The heat within the tunnel welds and fuses the overlapping plastic at the corners of the flaps 10C to 10D so that an under-frame of film for the bag 10 is created as depicted in FIG. 7. It will be realized that an effective frame for holding the plastic bag can be formed with only three flaps, for example, 10A, 10C and 10D, and the present invention contemplates three folds, as well as the four folds as described hereinabove.
It has been discovered that the negataive air pressure should be applied to the inverted bag 10 of heat shrink film before the film reaches the weld temperature. In this way, the inverted bag 10 will be collapsed around the load 11 and pallet 12 and overlapping folds of the heat shrink film both around the load 11 and underneath the pallet 12 will become fused before significant shrinkage of the film occurs. Subsequent shrinkage of the heat shrink film after fusion will draw the heat shrink film taut around the load and pallet. Thus, the initial application of negative air pressure serves to collapse the inverted bag 10 of heat shrink film and conserve the shrink energy in the film for use in drawing the film taut over the loaded pallet.
The duct 40 is provided with a moving vent 41 that follows the pallet as it moves through the tunnel. Referring to FIG. 6, it will be noted that the pallet 12 is at the beginning of the tunnel 30, and the duct 40 has vent openings 41 below the pallet while the vent openings at the opposite end of the duct 40 are closed. Referring to FIG. 6a, it will be noted that the pallet 12 is at the end of the tunnel 30, and the vent openings 41 at the end of the duct 40 are open while those at the beginning of the duct 40 are closed. Thus, the vent openings follow the pallet 12 as it travels through the tunnel. Moreover, it wil be noted that the vent openings 41 are closed by slats 45 which move relative to the vent openings.
Referring now to FIG. 3, it will be seen that the slats 45 are secured to a frame 46 which is slidable on the duct 40 by pneumatically operated piston 48. The piston is operated by a control system (not shown) that controls the movement of the slats to open the vents below the pallet as it traverses the tunnel.
The heating system for the tunnel 30 will now be described. Motor driven blower 50 is the source of a forced air in a closed system which follows the air path indicated by the arrows in FIG. 3. The air is first heated by heating elements 52 in furnace 54, then driven by blower 50 into the top and sides of the tunnel and then returned by duct 40 to furnace 54 for recirculation. At the entrance to the tunnel, the air is directed by longitudinally extending nozzles 60 directed toward the bottom of the pallet in order to assist in the folding of the side flaps 10C and 10D and the heat shrinkage of plastic film at the bottom of the bag. Following the nozzles 60, the entire sides and top of the bag is heated. The hot air enters the top of the tunnel through inlet ducts 62, and the sides of tunnel through inlet ducts 64. Vanes 66 are pivotally mounted for directing the air discharged by ducts 64 toward the moving load and pallet as it continues through the tunnel.
Referring to FIG. 2A, which illustrates one vane, the vane 66 is secured to a vertical pivotal rod 67 so that the vane can pivot to the positions indicated by the dotted lines in order to direct the hot air projected through the duct 64 toward the moving load.
The vanes are operated by a linkage mechanism connected to sliding frame 46 as shown in FIGS. 2 and 4. Referring to FIG. 4, the vertical rods 67 for the vanes are pivotally mounted in a movable bars 68 which are connected through link 69 and rod 70 to the slidable frame 46. Thus, as the frame 46 is moved to follow the moving pallet, not only are the slats 45 moved to open the vents 41 to provide a moving vent for withdrawal of air that follows the bottom of the bag 10, but also the vanes 66 are moved to direct hot air against the sides of the covered load as it progresses through the tunnel.
Referring now to FIG. 3a, there is shown a device for controlling the air flow. A divider valve in the form of a hinged plate 80 proportions the relative amounts of forced hot air from blower 50 between the sides and top of the shrink tunnel. The adjustment of plate 80 is conveniently made by threaded supporting rods 81 that extend outside the top of the furnace 54. By simply turning the nuts 82 on rods 81, adjustments to the plate 80 are made to control the air flow.
From the foregoing, it is believed that operation of the invention will be apparent. An inverted bag 10 of heat shrink film is placed over the load as indicated in FIG. 1. The bag is of a height size sufficient for flaps or skirts to depend below the bottom of the pallet 12. The flap 10A at the front of the pallet is folded under the pallet bottom as the pallet is placed on the conveyor 20 for the tunnel, as shown in FIG. 6. The flap 10B is folded as the rear of the pallet moves on to the conveyor 20, as shown in FIG. 6. The flaps 10C and 10D at the sides of the pallet are folded under the pallet bottom and the bag 10 is collapsed around the load 11 by negative air pressures created within the bag 10 by vent 40. The overlapping corners of the flaps are fused and welded together in the tunnel to form a frame for securing the bag to the load and the pallet. The frame may be formed with only three flaps 10A, 10C and 10D, and in some circumstances it may be the simplest and most convenient method for anchoring the bag to the load and pallet. Also, any overlapping portions of the bag collapsed around the load are fused and welded together.
The vent for withdrawing air from the bag moves with the pallet so as to apply a continuous negative air pressure to the bag while it traverses the tunnel. The vent is moved by operating slats 45.
The advantages of the invention should be apparent. An under-frame is provided by the flaps below the bottom of the pallet. The under-frame may consist of three or four flaps depending upon the circumstances. The side flaps in any case are readily folded under the pallet bottom in the tunnel to be fused at their corners with front and/or rear flaps by air pressures.
In the drawing and specification, there has been set forth preferred embodiments of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for purpose of limitation. Changes in form and proportion of parts, as well as substitution of equivalents are contemplated, as circumstances may suggest or render expedient, without departing from the spirit or scope of this invention, as further defined in the following claims.
It is a well-known practice to store or handle articles supported on pallets. When the pallets are to be outdoors or otherwise surrounded by an atmosphere which may damage the articles, plastic covers have been employed heretofore for protection. Moreover, the plastic covers reduce pilferage, stabilize the loads so the articles are not dislodged, and protect against dust and moisture.
Problems have arisen in covering pallet loads with plastic. Most pallet loads are irregular and it is difficult to produce a packae that will conform to the shape of the load. One approach is disclosed in Meyers U.S. Pat. No. 3,508,375 in which heat-shrinkable film in the form of an inverted bag is placed over the load and air withdrawn from the bottom of the bag while heating occurs. In such an arrangement, the pallet load must be stationary because of the fixed position of the heating duct, and this does not lend itself to high volume production.
Another problem arises in attempting to fasten the lower end of the inverted bag to the pallet. Staples, adhesive, and various folding techniques have been used, but these techniques are time consuming and do not lend themselves to automatic procedures.
SUMMARY OF THE INVENTION
A general object of the invention is to provide a effective and reliable method and apparatus for covering a load on a pallet with heat shrinkable film.
It is another object of the invention to provide a system for securing heat shrinkable film to the pallet by folding flaps or skirts under the pallet bottom.
It is yet another object of the invention to provide a system for withdrawal of air from an inverted bag of heat shrinkable film covering a load on a pallet while moving.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the heat shrink tunnel illustrating diagrammatically the method of placement of the bag of heat shrink film over the load on the pallet.
FIG. 2 is longitudinal section taken along line 2--2 of FIG. 1, and diagrammatically illustrating a load on a pallet covered with heat shrink film in the tunnel.
FIG. 2A is an enlarged view of a movable vane of the type employed in the shrink tunnel.
FIG. 3 is a perspective view of the heat shrink tunnel in part broken away to illustrate the heating system.
FIG. 3a is a view taken along line 3a--3a of FIG. 3 illustrating an air flow control.
FIG. 3b is a view taken along line 3b--3b of FIG. 3 illustrating the inlet ducts at the top of the tunnel.
FIG. 4 is a fragmentary view of the bottom vent for withdrawal of air from the bag and associated linkage for controlling the movable vanes.
FIG. 5 is a cross-sectional view through the tunnel diagrammatically illustrating the manner in which the inverted bag of heat shrink film covers the load on the pallet.
FIG. 6 is a diagrammatic view showing in phantom lines the system for folding the flap or skirt under the front end of the pallet, and illustrating the vent opening below the pallet for withdrawal of air from the inverted bag.
FIG. 6a is a diagrammatic view showing in phantom lines the system for folding the flap or skirt under the rear end of the pallet, and illustrating the manner in which the vent opening follows the movement of the pallet so that air is withdrawn from the inverted bag while the pallet is moving.
FIG. 7 is a bottom view of the pallet load showing the flaps folded beneath the pallet.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Briefly stated, the present invention is directed to removing the air from an inverted bag of heat shrink film covering a load on a pallet while the pallet is moving. The air is removed with sufficient negative pressures to cause the depending lateral skirts or flaps to fold under the bottom of the pallet at which location they are welded and fused to assist in anchoring the bag to the pallet.
Referring now to FIG. 1, a loosely fitting bag 10 made of heat shrinkable film is placed over a load 11 on pallet 12. The inverted bag may be placed over the load as indicated by the arrow either manually or by automatic equipment. The load on the pallet covered with the inverted bag is then moved through the tunnel 30 by suitable conveying means. After passing through the heat shrink tunnel the heat shrinkable bag tightly encases the load and pallet, as illustrated at the right side of FIG. 1.
The inverted bag should have a height greater than the combined height of the load and pallet so that the lower edges of the bag form a skirt or flap which depends below the pallet and which can be folded under the pallet bottom to secure the bag. Referring to FIG. 7, which shows the bottom of the pallet after emerging from the tunnel, there is illustrated flaps 10A, 10B, 10C, and 10C which have been folded under the pallet bottom and secured in place by fusion or welding of the heat shrinkable plastic at the overlapping corners. The flaps are fused at the corners form a frame which encloses the marginal portions of the pallet bottom.
The manner in which the flaps are folded under the pallets will now be described. The front end flap 10A is folded as shown in FIG. 6, as the pallet is transferred to conveyor 20 for movement through the tunnel 30. As illustrated, the pallet is transferred from conveyor 25 to conveyor 20, and the front flap 10A is folded during the transfer from one conveyor to the other.
The folding of rear end flap 10B is illustrated in FIG. 6a. The conveyor 25 is provided with transverse roller bars 26 which rotate freely about their transverse axes. The conveyor 25, at the time of the movement of the rear end of the pallet to conveyor 20, rotates at an increased speed which has a longitudinal velocity greater than the movement of the pallet and conveyor 20. The greater speed of conveyor 25 and bars 26 acts to push flap 10B below the pallet as it moves on to conveyor 20 as depicted in FIG. 6a.
The side flaps 10C and 10D are folded under the pallet by air pressure differentials between the exterior and interior of the bag as will now be described. Referring to FIGS. 1, 2 and 5, it will be noted that the pallet 12 has a greater width than the conveyors 20 and 25. This allows the flaps at the sides of the pallet to hang freely below the pallet bottom as the pallet enters the tunnel 30.
Referring now to FIG. 5, there is shown an air return duct 40 located below the conveyor 20 and below the center portion of the pallet 12. The duct extends substantially the entire length of the path of travel of the pallet through the tunnel, although the desired length can be varied as circumstances warrant. Duct 40 creates a negative air pressure in the bag 10 in sufficient amounts to cause the flaps 10C and 10D to fold under the bottom of the pallet as illustrated in FIG. 5.
The heat within the tunnel welds and fuses the overlapping plastic at the corners of the flaps 10C to 10D so that an under-frame of film for the bag 10 is created as depicted in FIG. 7. It will be realized that an effective frame for holding the plastic bag can be formed with only three flaps, for example, 10A, 10C and 10D, and the present invention contemplates three folds, as well as the four folds as described hereinabove.
It has been discovered that the negataive air pressure should be applied to the inverted bag 10 of heat shrink film before the film reaches the weld temperature. In this way, the inverted bag 10 will be collapsed around the load 11 and pallet 12 and overlapping folds of the heat shrink film both around the load 11 and underneath the pallet 12 will become fused before significant shrinkage of the film occurs. Subsequent shrinkage of the heat shrink film after fusion will draw the heat shrink film taut around the load and pallet. Thus, the initial application of negative air pressure serves to collapse the inverted bag 10 of heat shrink film and conserve the shrink energy in the film for use in drawing the film taut over the loaded pallet.
The duct 40 is provided with a moving vent 41 that follows the pallet as it moves through the tunnel. Referring to FIG. 6, it will be noted that the pallet 12 is at the beginning of the tunnel 30, and the duct 40 has vent openings 41 below the pallet while the vent openings at the opposite end of the duct 40 are closed. Referring to FIG. 6a, it will be noted that the pallet 12 is at the end of the tunnel 30, and the vent openings 41 at the end of the duct 40 are open while those at the beginning of the duct 40 are closed. Thus, the vent openings follow the pallet 12 as it travels through the tunnel. Moreover, it wil be noted that the vent openings 41 are closed by slats 45 which move relative to the vent openings.
Referring now to FIG. 3, it will be seen that the slats 45 are secured to a frame 46 which is slidable on the duct 40 by pneumatically operated piston 48. The piston is operated by a control system (not shown) that controls the movement of the slats to open the vents below the pallet as it traverses the tunnel.
The heating system for the tunnel 30 will now be described. Motor driven blower 50 is the source of a forced air in a closed system which follows the air path indicated by the arrows in FIG. 3. The air is first heated by heating elements 52 in furnace 54, then driven by blower 50 into the top and sides of the tunnel and then returned by duct 40 to furnace 54 for recirculation. At the entrance to the tunnel, the air is directed by longitudinally extending nozzles 60 directed toward the bottom of the pallet in order to assist in the folding of the side flaps 10C and 10D and the heat shrinkage of plastic film at the bottom of the bag. Following the nozzles 60, the entire sides and top of the bag is heated. The hot air enters the top of the tunnel through inlet ducts 62, and the sides of tunnel through inlet ducts 64. Vanes 66 are pivotally mounted for directing the air discharged by ducts 64 toward the moving load and pallet as it continues through the tunnel.
Referring to FIG. 2A, which illustrates one vane, the vane 66 is secured to a vertical pivotal rod 67 so that the vane can pivot to the positions indicated by the dotted lines in order to direct the hot air projected through the duct 64 toward the moving load.
The vanes are operated by a linkage mechanism connected to sliding frame 46 as shown in FIGS. 2 and 4. Referring to FIG. 4, the vertical rods 67 for the vanes are pivotally mounted in a movable bars 68 which are connected through link 69 and rod 70 to the slidable frame 46. Thus, as the frame 46 is moved to follow the moving pallet, not only are the slats 45 moved to open the vents 41 to provide a moving vent for withdrawal of air that follows the bottom of the bag 10, but also the vanes 66 are moved to direct hot air against the sides of the covered load as it progresses through the tunnel.
Referring now to FIG. 3a, there is shown a device for controlling the air flow. A divider valve in the form of a hinged plate 80 proportions the relative amounts of forced hot air from blower 50 between the sides and top of the shrink tunnel. The adjustment of plate 80 is conveniently made by threaded supporting rods 81 that extend outside the top of the furnace 54. By simply turning the nuts 82 on rods 81, adjustments to the plate 80 are made to control the air flow.
From the foregoing, it is believed that operation of the invention will be apparent. An inverted bag 10 of heat shrink film is placed over the load as indicated in FIG. 1. The bag is of a height size sufficient for flaps or skirts to depend below the bottom of the pallet 12. The flap 10A at the front of the pallet is folded under the pallet bottom as the pallet is placed on the conveyor 20 for the tunnel, as shown in FIG. 6. The flap 10B is folded as the rear of the pallet moves on to the conveyor 20, as shown in FIG. 6. The flaps 10C and 10D at the sides of the pallet are folded under the pallet bottom and the bag 10 is collapsed around the load 11 by negative air pressures created within the bag 10 by vent 40. The overlapping corners of the flaps are fused and welded together in the tunnel to form a frame for securing the bag to the load and the pallet. The frame may be formed with only three flaps 10A, 10C and 10D, and in some circumstances it may be the simplest and most convenient method for anchoring the bag to the load and pallet. Also, any overlapping portions of the bag collapsed around the load are fused and welded together.
The vent for withdrawing air from the bag moves with the pallet so as to apply a continuous negative air pressure to the bag while it traverses the tunnel. The vent is moved by operating slats 45.
The advantages of the invention should be apparent. An under-frame is provided by the flaps below the bottom of the pallet. The under-frame may consist of three or four flaps depending upon the circumstances. The side flaps in any case are readily folded under the pallet bottom in the tunnel to be fused at their corners with front and/or rear flaps by air pressures.
In the drawing and specification, there has been set forth preferred embodiments of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for purpose of limitation. Changes in form and proportion of parts, as well as substitution of equivalents are contemplated, as circumstances may suggest or render expedient, without departing from the spirit or scope of this invention, as further defined in the following claims.