Heat sealer for stretch wrapping apparatus

A heat sealing device for sealing layers of plastic film together is provided. In a preferred embodiment, the heat sealing device is incorporated into a stretch wrapping apparatus for wrapping a load. The heat sealing device includes a heater element, an air compressor or blower, and a sealing head in fluid communication with the heater element to distribute the heated air. The sealing head is preferably flexible and includes a plurality of convection ports configured to apply heated air to a portion of the packaging material without being completely covered by the packaging material. At least one insulated film contact portion is provided to distance the convection ports from the plastic film.

DESCRIPTION OF THE INVENTION

1. Field of the Invention

The invention relates to wrapping a load with packaging material, and, more particularly, to stretch wrapping.

2. Background of the Invention

Stretch wrapping can be performed as an inline automated packaging technique which dispenses and wraps packaging material in a stretched condition around a load on a pallet to cover and contain the load. Pallet stretch wrapping, whether accomplished by turntable, overhead arm, or rotating ring typically covers the four vertical sides of the load with a stretchable film such as polyethylene film. After the sides of the load are covered, the web of film is cut and the tail is usually “wiped” to press it against the load. Most stretch wrap packaging films are manufactured with an element of tackiness to add to their layered stability and to provide a mechanism for closure of the ending film tail, however, wiping is not sufficient to ensure that the tail of the film will not come loose during shipping, resulting in loose or torn wrap. In addition, in certain circumstances, such as outside storage of loads, open truck transit where winds can cause unwinding of film, or where tacky film is undesirable or unavailable, merely wrapping the load will not protect it. To overcome these problems, the tail of the packaging material can be adhered to the wrapped load by heat sealing. Sealing plastic wrapping material with heat, however, poses another set of problems.

Many types of plastic films are effectively sealed for the purpose of making a bag, closing a bag, or completing the enclosure of a package wrapped in film. The most popular plastic films include high and low density polyethylene, irradiated polyethylene, polypropylene, PVC and EVA. Technology for sealing each of these films is well known in the art. Unlike most other packaging films, low-density polyethylene has a sealing temperature very close to its melt temperature. As a result, great care must be taken to insure there are no unsupported strains on the film while the film is substantially melted during the sealing process. Most successful sealing of polyethylene is accomplished by “conduction” of heat from contact with a heat source by placing a rigid or flexible heated element on top of the layers to be sealed with a supporting element below and applying a controlled temperature, pressure and time to complete the seal. Alternatively, carefully controlled hot slitting knives, and “convective” sealing with hot air is used for some applications such as the production of trash bags and closure of heavy wall chemical, fertilizer and bulk food bags. Radiant sealing is very rare for clear packaging films due to its relative resistance to absorbing radiant energy and the potential fire hazard of proximity to the high temperature elements required.

Virtually all pallet stretch wrapping film is a form of low density polyethylene, typically from 50 gauge to 120 gauge, and the film is wrapped in multiple layers around the product load. Virtually all heat sealing of the tail of the stretch wrap packaging material to the load is accomplished by “conduction” contact of a heated element. Multiple heated elements are typically arranged to place a series of seals aligned along the stretch direction to protect the seal from being pulled apart by the residual force on the film imparted during the wrapping process. Most of the heating elements include some type of coating or release material such as Teflon tape to prevent the molten film from sticking to the sealing element. The elements may be applied to the stationary film or may be rolled on the surface of the wrapped load.

In the environment where stretch wrappers operate, heat sealing has been very problematic. Pallet loads may contain a wide variety of “backing” materials to be sealed against, i.e., the material or products of the load form a backing against which the stretch wrap packaging material is pressed to seal it. Such materials include bulk beverage containers, corrugated containers, construction materials including brick, stone, and concrete, metal and plastic automotive parts, stacks of paper, and most difficult, irregular loads with substantial voids of product behind the film. As a result of these “backings”, the pressure of the heat sealer often “burns through” the stretch wrap packaging material, resulting in a hole with the potential for product damage from water or other contaminants. Loads often do not provide a vertically plumb side for the sealing element to contact, thereby preventing one or more of the sealing elements from actually contacting the film.

Release materials, such as Teflon, used to prevent the film from sticking to the sealing element eventually wear off and allow film to build up on the sealing element. The somewhat delicate heating element itself may take a beating by repeated contact with the above mentioned loads. This wrapping process can take place in refrigerated, unheated and even corrosive environments within plants or in the full range of outside conditions including temperature and wind. Although a convective sealing apparatus for stretch wrapping is shown in U.S. Pat. No. 4,993,209 to Haloila, the device has not experienced commercial success, most likely due to the types of problems discussed above.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method and apparatus for wrapping a load with packaging material which provides advantages over and obviates several problems associated with earlier methods and apparatus for heat sealing stretch wrap packaging material.

According to one aspect of the present invention, a heat sealing device for sealing plastic film is provided. The heat sealing device comprises a heater element; and a sealing head comprising a plurality of convection ports, and at least one insulated film contact portion positioned adjacent at least one of the convection ports and providing a set distance between the convection ports and the plastic film to be sealed when in contact with the plastic film.

According to another aspect of the present invention, a heat sealing device for sealing plastic film includes a heater element, and a sealing head comprising a structure having a plurality of convection ports, and an insulated film contact portion positioned adjacent to the structure and providing a set distance between the convection ports and the plastic film to be sealed when in contact with the plastic film.

According to yet another aspect of the present invention, an apparatus for wrapping a load is provided. The apparatus comprises a dispenser for dispensing plastic film, a heat sealing device including a heater element and a sealing head, the sealing head comprising a plurality of convection ports and at least one insulated film contact portion positioned adjacent at least one of the convection ports and providing a set distance between the convection ports and plastic film on a side of the load when in contact with the plastic film on the side of the load, and means for providing relative rotation between the dispenser and the load to wrap plastic film around the load.

According to a further aspect of the present invention, an apparatus for wrapping a load comprises a dispenser for dispensing plastic film, a heat sealing device including a heater element and a sealing head, the sealing head comprising a structure having a plurality of convection ports and an insulated film contact portion positioned adjacent to the structure and providing a set distance between the convection ports and plastic film to be sealed when in contact with the plastic film to be sealed, and means for providing relative rotation between the dispenser and the load to wrap plastic film around the load.

According to another aspect of the present invention, a method of wrapping a load with plastic film is provided. The method comprises placing a load on a load wrapping surface, providing relative rotation between the load and a plastic film dispenser to wrap plastic film around the load, pressing a portion of a top layer of the plastic film into a layer of plastic film below the top layer with at least a portion of a sealing head, and applying a stream of heated air to the portion of the top layer of the plastic film from a plurality of convection ports to seal the portion of the plastic film to layer of plastic film below it, wherein the convection ports are not completely covered by the portion of the plastic film.

According to yet another aspect of the present invention, a method of wrapping a load with plastic film comprises placing a load on a load wrapping surface, providing relative rotation between the load and a plastic film dispenser to wrap plastic film around the load, pressing a portion of a top layer of the plastic film into a layer of plastic film below the top layer with at least a portion of a sealing head, and applying a stream of heated air to the portion of the top layer of the plastic film from a plurality of convection ports to seal the portion of the plastic film to layer of plastic film below it while maintaining the convection ports a set distance from the portion of top layer of plastic film.

According to another aspect of the present invention, a method of wrapping a load with plastic film comprises placing a load on a load wrapping surface, providing relative rotation between the load and a plastic film dispenser to wrap plastic film around a top of the load and a bottom of the load wrapping surface, extending a top portion of a clamp assembly from below the load wrapping surface, overwrapping the top portion of the clamp assembly with a top layer of plastic film, pressing a portion of the top layer of the plastic film into a layer of plastic film below the top layer with at least a portion of a sealing head, and applying a stream of heated air to the portion of the top layer of the plastic film from a plurality of convection ports of the sealing head to seal the portion of the plastic film to layer of plastic film below it.

According to a further embodiment of the present invention, an apparatus for wrapping a load comprises means for dispensing plastic film, a heat sealing device including a heater element and a sealing head comprising a plurality of convection ports and means for providing a set distance between the convection ports and plastic film on a side of the load when in contact with the plastic film on the side of the load, and means for providing relative rotation between the dispenser and the load to wrap plastic film around the load.

DESCRIPTION OF THE EMBODIMENTS

The present invention provides a method and apparatus for wrapping a load. The apparatus provided substantially reduces the problems typically associated with heat sealing stretch wrap packaging material. In a preferred embodiment, the present invention allows at least a portion of a head of the heat sealer to conform to the shape of the load, overcoming the difficulties previously posed by irregular loads. In addition, the present invention uses convection and thus does not place the heating element in direct contact with the packaging material, thereby preventing the buildup of packaging material on the heating element. Portions of the head of the heat sealer are placed in contact with the packaging material to ensure good contact between the layers of packaging material to be sealed to one another. These portions of the heat sealer, defined herein as the “foot” of the heat sealer, are insulated to prevent them from becoming heated and sticking to the packaging material.

In accordance with one aspect of the present invention, an device is provided for sealing a trailing (tail) end of packaging material to a wrapped load. The device includes a sealing head, a heating element, and a support arm.

As embodied herein and shown inFIGS. 1,5A, and5B, a heat sealing apparatus100includes a heating element150. The heating element150is contained in a heater box152. Preferably, the heating element150is capable of reaching and maintaining a temperature of 700 degrees. An air compressor/blower160is connected to a first end of the heating box to blow air through the box152and over the heating element150. The box152may include baffle elements154to mix the air flow to ensure the air is evenly heated before it leaves the box152.

As shown inFIGS. 1,5A, and5B, heat sealing apparatus100includes a flexible sealing head110. As shown inFIGS. 1,5A, and5B, heat sealing head110includes a first flexible band112. First flexible band112includes a plurality of orifices120along its length. The first flexible band is preferably made of spring steel, although other materials of suitable strength and flexibility may be used. A first end of the first flexible band is attached to a support114and a second end of first flexible band112is attached to a second support116. Supports114and116may extend from heater box150. Alternatively, the ends of the band may be directly connected to heater box150. The first flexible band112is thus formed into a substantially oval-like shape. This oval shape allows flexible band112to flex as it contacts a surface of a load124. A back face118of the first flexible band112faces toward heater box such that each orifice120is oriented to receive a flexible hose126.

A plurality of flexible hoses126extend from an end of the heater box152and each flexible hose126is in fluid communication with heater box152so as to receive the heated air as it passes through baffles154and out of heater box152. Each flexible hose126is connected to an orifice120in first flexible band112. Preferably the hoses126are connected to flexible band112in orifices120by snap on pneumatic fittings with brass oval nozzles. Other suitable means of connection may be used. Preferably, all of the hoses126are approximately the same length, such that the distance to each orifice120from the heater box152is the same. This ensures that the temperature of the heated air flowing through each orifice120has substantially the same temperature. Preferably, the temperature of the air exiting each orifice is between 205 and 240 degrees, and most preferably, the temperature of the air is 225 degrees. The temperature of the air exiting the orifices may vary by approximately ±10 degrees.

As shown inFIGS. 1,5A, and5B, sealing head110includes a second flexible band130. Second flexible band130includes a plurality of orifices132and is attached to a plurality of standoff insulation elements134. Preferably, the second flexible band130is made of a very flexible material, such as high density polyethylene. Second flexible band130is positioned such that orifices132are aligned with orifices120in first flexible band112. Thus, together, orifices120and132form a vent to allow heated air to pass from the nozzles of hoses126. The flexibility of the sealing head110, imparted by flexible bands112,130, allows the sealing head to substantially conform to the shape of a surface it contacts, for example a side of the load.

In one embodiment, a standoff insulation element134positioned adjacent each orifice, such that the portions of flexible band130surrounding orifices132are in contact with standoff insulation elements134. The standoff insulation elements134are permanently attached to a back face of second flexible band130.

The purpose of standoff insulation elements134is twofold. First, standoff insulation elements134insulate the areas of second flexible band130which do not include an orifice132. Thus, when these areas are brought into contact with packaging material, standoff insulation elements134prevent these areas from becoming heated to the high temperatures associated with the convective heat sealing air flow and therefore prevents sticking of the insulated areas to the packaging material and thus prevents packaging material from building up on these areas. As used herein, the term “insulated” simply means that the insulated material is able to maintain a temperature significantly below that of the heated air temperature so as to prevent melting contact with the packaging material.

Secondly, standoff insulation elements134allow the formation of the “vents” between orifices120and132, i.e., elements134provide space for air flow between the nozzles in orifices120which are blowing hot air and the packaging material onto which the hot air is being blown. Because there is a distance between the nozzle (orifice120) through which the hot air is being blown and the packaging material being sealed, a low pressure air flow can be used, reducing the likelihood that damage will be done to the packaging material. In addition, the distance between the nozzle (orifice120) and the packaging material prevents the orifice120from being completely covered by packaging material. This is important because if the packaging material completely covers the orifice120, it will block air flow and prevent proper sealing of the packaging material. Thus, the standoff insulation elements are means for providing a set distance between the convection ports and plastic film.

Alternatively, if the packaging material covers the orifice, it will require a very high pressure to remove the packaging material from the orifice, and the pressure may actually puncture the packaging material. Thus, the standoff insulation element134should be made from a temperature resistant material, and a material that is fairly rigid to allow a distance to be maintained between the first and second flexible bands. An example of such a material is ultra-high molecular weight polyethylene (UHMWPE). If a more compressible material is used, the thickness of the element134should be increased to compensate for the compressibility and to maintain the desired distance between the first and second flexible bands.

Although the plurality of standoff insulation elements are shown as positioned between the slits120, other configurations of standoff insulation elements may be used as shown inFIGS. 13A-13F. For example, it is possible that the plurality of standoff insulation elements may be replaced with one or two insulation elements, positioned for example, on either end of the second flexible band130(FIGS. 13C and 13D). Alternatively, it is possible that the standoff insulation elements may form a frame or mask around a perimeter of the second flexible band130, enclosing all orifices120(FIGS. 13A and 13B). Other suitable designs for the standoff insulation element, e.g., designs that allow the standoff insulation element to provide a “cool” surface to press against the packaging material and press the layers of packaging material together, and prevent the orifices120from becoming blocked with the packaging material, may also be utilized.

As shown inFIGS. 1,5A, and5B, a front face of each standoff insulation element134is permanently attached to a back face of the second flexible band. Any suitable attachment means may be used. A back face of each standoff insulation element134includes a bracket like configuration to allow the standoff insulation elements134to slidingly engage a front face119of the first flexible band112, thereby connecting the first and second flexible bands112,130. In a preferred embodiment, one standoff insulation element134, preferably one located in a center of the sealing head110, is permanently connected to first flexible band112. By limiting the fixed connections between the two bands112,130, the flexibility of sealing head110is enhanced. Thus, the second flexible band130is connected to and aligned with the first band112such that the orifices120,132in the first and second bands112,130are aligned to form “vents”. Positioned between the first and second flexible bands112,130around the orifices120,132are the standoff insulation elements134.

The flexibility of the second flexible band130allows the band130to conform to the shape of a surface124aof the load124when the heat sealing head110is pressed into contact with packaging material on the surface124aof the load124during sealing. In addition, the standoff insulation elements134support the flexible band130and allow heat sealing head110to press the top layer of packaging material wrapped around the load into contact with a layer directly beneath the top layer. Because the layers are in contact, they can be sealed to one another via the application of hot air through the orifices120,132.

As embodied herein and shown inFIGS. 1,5A, and5B, the flexible heat sealing head110is mounted on an arm140. Arm140is movable from a retracted home position to an extended sealing position. Thus, in use, arm140extends toward load124until heat sealing head110is in contact with the packaging material on the side124aof the load124, and remains in contact with the packaging material on the side124aof the load124until heat sealing is performed. After heat sealing, arm140moves back to the retracted home position, removing heat sealing head110from contact with the packaging material on the load124.

As shown inFIGS. 5A and 5B, heat sealing apparatus100may include roller bar and hot wire assembly145. Roller bar and hot wire assembly145is preferably mounted on a separate arm142. Arm142is movable from a retracted home position to an extended sealing and cutting position. Roller bar and hot wire assembly145includes a roller bar146. Roller bar146is preferably mounted in a forward biased position on a bar holder147(seeFIG. 5B). Roller bar146is movable within bar holder147to a rear position. As shown inFIG. 5B, roller bar146is forwardly biased. However, by application of pressure, roller bar146can be moved back until it is in contact with bar holder147. Roller bar146is connected to bar holder147such that application of pressure on only one end of roller bar146will cause only that end to move back toward bar holder147, such that roller bar146would be at an angle with respect to bar holder147. In use, roller bar146is used to move the packaging material, after wrapping, to a packaging material holding clamp. Roller bar146is also used to push a trailing end of the packaging material into contact with the load in preparation for heat sealing. After the packaging material is heat sealed to the load, a hot wire148(FIG. 5A) is used to cut the packaging material.

According to another embodiment of the invention, the heat sealing head may comprise a flexible tube. As embodied herein and shown inFIG. 2, a heat sealing device200is provided with a flexible heat sealing head210. Many of the elements present in the previous embodiment are also shown inFIG. 1and where these elements are substantially the same, similar reference numerals have been used and no detailed description of the element has been provided.

Heat sealing device200includes a heater box252containing heater element250. Flexible heat sealing head210is mounted on an arm240and is movable between a retracted home position and an extended sealing position. A roller bar and hot wire assembly245is also provided.

Flexible heat sealing head210includes a flexible tube212. Preferably flexible tube212is made from a high temperature silicon or Teflon tubing. The tubing may be reinforced with overwound spring or spring steel. Flexible tube212is fluid communication with heater box252to receive the heated air. Flexible tube212includes slits or holes220spaced along its length. Preferably, slits220are oval in shape and are spaced approximately 1 and ½ inches apart from one another. Between slits220are standoff insulating elements234. Standoff insulating elements234may also be made from portions of a flexible tube. Other suitable materials and configurations of standoff elements may be used. The purpose of standoff insulating elements234is to provide “cold spots” between the seal points on the plastic packaging material, i.e., to provide places where the flexible sealing head210can contact the packaging material without heating it. By contacting the packaging material, the layers of packaging material to be sealed can be pressed together. Additionally, the standoff insulating elements provide distance between the slits220and the packaging material to be sealed, allowing room for air flow from the slits220to the surface of the load224.

According to another embodiment of the invention, the heat sealing head may not be flexible. As embodied herein and shown inFIG. 3, a heat sealing apparatus is provided with a heat sealing head310. Many of the elements present in the previous embodiment are also shown inFIG. 3and where these elements are substantially the same, similar reference numerals have been used and no detailed description of the element has been provided.

Sealing head310includes a rigid tube312. Preferably rigid tube312is made from a high temperature silicon or Teflon tubing. A sealing head310having a rigid tube312is useful in applications where the load being wrapped comprises a substantially plumb side or does not include irregular shapes. As an alternative to rigid tube312, a metal nozzle412may be used as shown inFIG. 4.

Rigid tube312is in fluid communication with heater box352via a tube313to receive heated air. Rigid tube312includes slits or holes320spaced along its length. Preferably, slits320are oval in shape and are spaced approximately 1 and ½ inches apart from one another. Between slits320are standoff insulating elements334. Standoff insulating elements334may also be made from portions of any type of heat resistant, substantially rigid material. The purpose of standoff insulating elements334is to provide “cold spots” between the seal points on the plastic packaging material, i.e., to provide places where the rigid sealing head310can contact the packaging material without heating it. By contacting the packaging material, the layers of packaging material to be sealed can be pressed together. Additionally, the standoff insulating elements334provide distance between the slits320and the packaging material to be sealed, allowing room for air flow from the slits320to the surface of the load.

As shown inFIG. 4, rigid sealing head310may comprise a metal nozzle412. Metal nozzle412is in fluid communication with heater box452via a tube413to receive heated air. Metal nozzle412preferably comprises sheet metal although other suitable materials may be used. Metal nozzle412includes baffles420for direct air distribution from heater box452to the load. Between baffles420are standoff insulating elements434. Standoff insulating elements434may also be made from portions of any type of heat resistant, substantially rigid material.

According to another embodiment of the invention, the heat sealing head may include a heat sealing element unconnected to a foot or standoff insulation element. As embodied herein and shown inFIGS. 6A and 6B, a heat sealing device500may be configured to be positioned underneath a load support surface or conveyor wrapping assembly. Heat sealing device500includes a heater box (not shown) containing a heater element (not shown) as described in previous embodiments.

The heat sealing device500includes a heat sealing head510. Sealing head510includes a heat sealing element such as a rigid tube512. Preferably, rigid tube512is made from high temperature silicon or Teflon tubing. Rigid tube512is in fluid communication with heater box (not shown) via a tube or other means (not shown) to receive heated air. Rigid tube512includes orifices520spaced along its length. Preferably, orifices520are oval in shape and are spaced approximately 1 and ½ inches apart from one another. Rigid tube512is positioned such that the orifices520are facing upward, toward the load support surface.

Rigid tube512is connected to and movable with an arm540. Rigid tube512and arm540are movable in a horizontal direction, between a retracted position and an extended position. Rigid tube512and arm540may also be movable in a vertical direction, between a lowered, disengaged position and a raised, engaged position.

As embodied herein, heat sealing device500also includes a foot or standoff insulation element534a. As embodied herein and shown inFIG. 6A, standoff insulation element534ais preferably not connected to rigid tube512. As shown inFIG. 6A, standoff insulation element534ais positioned adjacent to rigid tube512and is movable independently of rigid tube512. Standoff insulation element534ais mounted on a second arm540a, positioned adjacent to arm540. Standoff insulation element534aand second arm540aare movable in a horizontal direction, between a retracted position and an extended position. Standoff insulation element534aand second arm540amay also be movable in a vertical direction, between a lowered, disengaged position and a raised, engaged position.

Standoff insulation element534aand second arm540aare positioned below a wrapping conveyor assembly541and are positioned between the heat sealing element (rigid tube512) with arm540and a clamp assembly561. Clamp assembly561includes a top clamp portion561aand a bottom clamp portion561b. Clamp assembly561works in conjunction with heat sealing device500during the wrapping cycle to secure and sever the film, as described in detail below.

Alternatively, as shown inFIG. 6B, standoff insulation element534bmay be positioned above and movable with the heat sealing element (rigid tube512). As embodied herein, standoff insulation element534bmay form a frame or mask in which rigid tube512will apply heat to the plastic packaging material. In this embodiment, the standoff insulation element534bis not necessarily positioned between the orifices520of the rigid tube512, but instead may form a perimeter around the orifices520(FIGS. 13A,13B). Alternatively, standoff insulation element534bmay comprise a plurality of “bars” forming standoff portions between the orifices520or may comprise “bars” only at the ends of the rigid tube512(FIGS. 13E and 13F). Any configuration that is sufficient to maintain “cool” portions to contact and compress the layers of plastic packaging material together for heat sealing, while keeping the orifices520free of packaging material, is acceptable. These alternate configurations for the standoff insulation element, shown inFIGS. 13A-13Fand discussed with respect to the first embodiment of the heat sealing apparatus100may also be used with the other embodiments of the heat sealing device discussed previously.

According to another aspect of the invention, a stretch wrapping apparatus including a heat sealing device is provided. The apparatus1000includes the heat sealing apparatus100, a packaging material dispenser, and means for providing relative rotation between the dispenser and the load to wrap packaging material around the load.

As embodied herein and shown inFIGS. 7-9, the heat sealing apparatus100includes a sealing head110, a heating element150, and a support arm140as discussed above with respect toFIGS. 1,5A, and5B. In addition, a roller bar and hot wire assembly145is also preferably provided.

As embodied herein and shown inFIGS. 7-9, stretch wrapping apparatus1000includes a packaging material dispenser102. As shown inFIG. 7, packaging material dispenser102dispenses a sheet of packaging material106in a web form. Packaging material dispenser102includes a roll of packaging material contained within a roll carriage. Packaging material dispenser102may be mounted on a stationary mast105upon which the roll carriage can be vertically positioned to dispense packaging material from dispenser102to wrap load124as it rotates. Alternatively, the roll carriage of dispenser102may be vertically moveable on an arm to dispense packaging material106spirally about load124as the arm rotates about load124or dispenser102may be mounted on a wrapping ring to dispense packaging material106spirally about load124as dispenser102rotates around the ring and load124. In a preferred embodiment, stretch wrap packaging material is used, however, various other packaging materials such as bubble wrap, netting, strapping, banding, or tape can be used as well. The inventors have found that the present invention works particularly well when bubble wrap is used as the packaging material. As used herein, the terms “packaging material” and “film” are interchangeable.

According to one aspect of the invention, the apparatus1000includes means for providing relative rotation between the dispenser and the load to wrap packaging material around the load. As shown inFIG. 7, the means for providing relative rotation between the dispenser102and the load124may include a motor driven turntable180mounted on a base to rotate load124about a vertical axis. The turntable180includes a load support surface186upon which the load124is supported as it is wrapped. In addition, turntable180may include conveying means (not shown) for conveying load124into and out of the wrapping area. Alternatively, in an arrangement in which packaging material dispenser102revolves around load124, the dispenser may be carried by an arm or ring or other arrangement. In addition, conveyors184aand184bmay be provided to move the load to and from the wrapping area, respectively.

In operation, a method of wrapping a load according to the present invention is shown sequentially inFIGS. 7-9. The method includes placing the load124on a load support surface. Initiating relative rotation between the load124and a packaging material dispenser102to wrap the packaging material106around the load124while heat sealing device1000and roller bar and hot wire assembly145are in their retracted home positions (FIG. 7).

As the packaging material106is being wrapped around the load124, heater element150and air blower160of heat sealing device1000are actuated to allow the heater element150to heat up as the load is being wrapped and, by actuating the blower, allowing the heated air to pass through the heat sealer1000, warming up all components.

After the load124is wrapped, the heat sealing head110and roller bar with hot wire assembly145move out, for example, by extending or rotating, to contact and distend the packaging material106, moving the packaging material path such that the trailing end of the packaging material is positioned over a packaging material clamp (FIG. 8). Once the packaging material is positioned over the clamp, the clamp closes on the packaging material.

Next, the roller bar and hot wire assembly145, and heat sealing head110are extended toward the load124on arms142,140, respectively, until the roller bar146locates and contacts a side124aof the load124. (FIG. 9) The heat sealing head110continues to advance into the side124aof the load124until the second flexible band of the heat sealing head110is in contact with packaging material on the side124aof the load124, pushing the top layer of packaging material106into contact with the layer below it (FIG. 9). While the second flexible band130is in contact with the side124aof the load124, hot air is being blown through the orifices120,132of the heat sealing head110and onto the packaging material106that is on the load. The flexible second band remains in contact with the side124aof the load124for a heat sealing cycle, approximately 2-4 seconds. However, the heating cycle may be longer if necessary or desired.

After the heat sealing is complete, the hot wire cuts the packaging material, and the roller bar and hot wire assembly145and heat sealing head110are withdrawn from the side124aof the load, and then move back to the home position. The blower160and heater element150shut off after the heat sealing cycle is complete.

In an alternative embodiment of a stretch wrapping apparatus and according to one aspect of the invention, a wrapping conveyor707having a top load support surface and a bottom packaging material transfer surface is provided instead of a turntable.

As embodied herein and shown inFIGS. 10-12D, a ring stretch wrapping apparatus700is provided. Apparatus700includes a feed conveyor703, a wrap and load conveyor assembly707, a packaging material dispensing mechanism702with a cutting mechanism (not shown), a take off conveyor711, and a heat sealing device710(as described previously with respect toFIGS. 6A and 6B).

The load724is placed on an infeed conveyor703which includes an endless belt756mounted on a frame support758. The endless belt756is mounted on rollers760which are rotatably journaled by suitable bearing means and brackets which are secured to the frame support758. The infeed conveyor703carries the load724onto a wrapping station741including a packaging material dispensing apparatus702and a wrapping conveyor assembly707.

The wrapping assembly includes a frame762on which a steel donut or ring shaped packaging material support member764is rotatably mounted and supported on three planes by guide rollers766. If desired, the packaging material support member764can be constructed of aluminum. A plurality of guide rollers766project inward from the frame762on arms767and mounting plates768to engage the ring shaped member764so that it can be driven in a predetermined path. A friction drive wheel769is positioned adjacent the ring member764at its base and engages the member764to rotate the member764within the guide wheel rolling area. The friction drive wheel769is driven by a motor770having a shaft that is suitably connected with a drive reducer772. Material roll dispensing shaft774is rotatably secured to the ring member764for rotation on its axis and is adapted to receive and hold a roll of packaging material776.

The wrapping conveyor assembly707comprises two conveying surfaces782and784. The top load supporting and conveying surface782is a standard plate type conveyor well known in the art comprising a driven endless belt786mounted on a plurality of rollers790. The rollers790are supported by plates792secured in turn to a frame member (not shown) which holds the rollers in a rotatable position. The endless belt786is rotated in a direction which moves anything on the belt786through the wrapping device741in a direction forming from the infeed conveyor703toward the take-off conveyor711. Belt786is driven by a motor assembly794which is connected by gears796and linkages798in the form of chains or belts to drive the conveyor.

Lower packaging material transporting conveyor784is a non-driven conveyor and includes two sets of inline rollers794aand794bmounted to an outer surface of a rail (not shown) on either side of a conveying surface of conveyor782. These rollers are inline directly one behind the other to form two rows of rollers. Non-driven rollers794a,794bare preferably roller skate wheels, approximately two inches in diameter, aligned in an inline configuration. Other sizes or types of wheels may be used, however, currently preferred are roller skate wheels, which are inexpensive, easy to find, of the appropriate size, and commonly used in carton conveyors. Alternatively, more than two rows of rollers may be used, or only a single row of rollers may be used. In an alternative embodiment, the lower packaging material transporting conveyor784may be driven (motorized) by any suitable means, and the surface may comprise, for example, driven rollers or an endless driven belt.

This construction of the wrapping conveyor assembly707allows packaging material778to be wrapped around a load724which was carried from the infeed conveyor703onto the wrapping station741. The packaging material778is wrapped around the wrapping conveyor assembly707and the load724with both the load724and packaging material778being carried by the conveyor assembly707in the same direction. In all wrapping modes—full web, spiral and banding modes—the conveyor assembly707and wrapping ring764are stopped and the heat sealing device710and clamp apparatus761work together to clamp, heat seal, and sever the packaging material. The heat dispensing portion is mounted on an extendable arm740, and positioned near clamp assembly761. Between clamp assembly761and heat dispensing portion, standoff insulation element734ais mounted on extendable arm740a. The conveyor assembly707is activated carrying the load and wrap downstream to a takeoff conveyor711. When the load724encounters the takeoff conveyor711, the elongated stretched wrap778coming off the end of the conveyor assembly over last inset rollers794c,794dassumes its memory position M against the load in the space between the conveyor assembly707and takeoff conveyor711, allowing the contained load covered by stretch wrap to be carried away.

The wrapping conveyor assembly707leads from the infeed conveyor703to a takeoff conveyor711which is constructed like the infeed conveyor703and runs at the same speed as the infeed conveyor703. In order to control both conveyors at the same rate of speed, a suitable mechanical means not shown is set up to make the drive of both the infeed conveyor703and the takeoff conveyor711equal to reduction gearing assembly of the drive motor. Thus, if the motor slows down or speeds up to drive the wrapping mechanism at different speeds, the infeed and takeoff conveyors simultaneously speed up or slow down so that the load moves to conveyor assembly707and is taken away from the conveyor assembly707at consistent relative speeds.

A method for wrapping a load according to the second embodiment of the present invention will now be described. In the operation of the inventive wrapping apparatus, full web, spiral web, and banding modes of operation are substantially identical manner. In these modes, a feed conveyor703brings the load724onto the top load supporting and conveying surface782of wrapping conveyor assembly707. Load supporting and conveying surface782then carries the load to a predetermined wrap position within the packaging material dispensing path and the conveyor assembly stops leaving the load in a stationary position.

A leading edge777of the packaging material778is held in a clamping assembly761located beneath the conveyor assembly707as seen inFIGS. 10 and 11. After at least one wrap has been made around the load724and the clamp assembly761, the clamps761a,761bare rotated releasing edge777which is held by the web wrap. If the wrap is for a full web load or a banded load, a plurality of overlying layers of packaging material are wrapped around the load and the conveyor assembly707. In the spiral wrap mode, a plural number of wraps are wrapped around the downstream end of the load724in the same manner as the banding and the conveyor assembly is activated carrying the load downstream to a takeoff conveyor so that a spiral wrap is formed around the load.

When the load724reaches a station where the end is sensed by a feeler gauge, light sensing means, pressure sensor switch or other suitable sensing mechanism, both the takeoff conveyor711and the wrapping conveyor assembly707stop and a second band is placed around the upstream end of the load724in the same manner as if a band or full web wrap were being wrapping around the load724.

Before completion of the wrap cycle, a top clamp portion761aof the clamp assembly761extends outward from below conveyor assembly, allowing at least the last layers of the packaging material wrap to be supported between the edge of the conveyor assembly707and the top clamp portion761a(FIG. 12A). After top clamp portion761aextends out and is overwrapped by the packaging material, standoff insulation element734aand heat sealing element (rigid tube712with orifices720) of the heat sealing device710extend out from beneath the conveyor assembly707on arms740a,740, respectively. Standoff insulation element734aengages the packaging material778and pushes the last layer upward, into contact with the layers beneath it (FIG. 12B). Once the layers of packaging material are pushed into contact with one another, hot air is blown through rigid tube712and orifices520onto the layers of packaging material. The sealing cycle lasts for approximately 2-4 seconds, although it may be longer if necessary. After the sealing cycle and a short cooling period, approximately 2-5 seconds, the lower clamp portion761bof the clamp assembly761extends outward, clamping the packaging material web between the top and bottom clamp portions761a,761bof the clamp assembly761, cutting the packaging material web and clamping the leading edge of the packaging material for the next wrap cycle (FIG. 12C). The heat sealer device710then withdraws under the wrapping conveyor assembly as the load724exits the wrapping area (FIG. 12D).

Alternatively, when a heat sealing device710that does not include separately mounted standoff insulation and sealing elements (FIG. 6B), the method is substantially the same. After top clamp portion761aextends and is overwrapped, the heat sealing element712with the connected standoff insulation element734bextend out from beneath the wrapping conveyor assembly707in a lowered position. The heat sealing element712and standoff insulation element734bare then raised into the engaged position, such that the standoff insulation element734bcontacts the packaging material778and presses the layers of the packaging material together. The heating cycle is actuated, and after cooling, the lower clamp761bportion of the clamp assembly761extends out to clamp and cut the packaging material778. The heat sealing element712and standoff insulation element734bare lowered to the disengaged position and withdrawn while the load724exits the wrapping area.

The method and device for sealing plastic wrap taught herein can be used in processes other than stretch wrapping, where it is necessary to seal together layers of packaging material, especially when the layers of packaging material should be compressed prior to sealing. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.