Movable U-bar sealing device and a method for shrink wrapping a load with a flexible material

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. provisional application Ser. No. 60/592,895 filed Jul. 30, 2004 and entitled “SHRINK WRAP APPARATUS,” which is incorporated by reference herein.

FIELD OF THE INVENTION

The field of invention relates to a sleeve film wrapping device for shrink wrap apparatus and a method for wrapping a load with a flexible material, which is supplied as a film. More particularly the field of this invention relates to a device and a method for completely sealing a load optimally in a single operation at a high rate of speed. The inventive device features a movable heated “U-bar” sealing device comprising a heated cross-sealing bar and two perpendicular heated side sealing bars. The juncture of the heated cross-sealing bar and the two perpendicular heated side sealing bars is in the form of an arch and comprises a curved bracket. The juncture end of each heated side sealing perpendicular bar is curved accordingly to form a rounded surface in the curved shape of an arch. The arch-curvature of the heated U-bar sealing device conforms to the peripheral shape of the load. The curvature design of the curved bracket of the movable, heated U-bar sealing device between the heated cross-sealing bar and the two perpendicular heated side sealing bars controls bunching of the applied film.

The movable, heated U-bar sealing device typically is made from sheet metal. The movable, heated U-bar sealing device is provided with a suitable heating device, preferably an electric heating device. A significant advantage of the inventive movable, heated U-bar sealing device is that as the film wrap is completed and the applied film wrap is severed from the film roll, the movable, heated U-bar sealing device spreads the film evenly over the load and will advantageously spread the film evenly at the corners of the load. The movable, heated U-bar sealing device spreads the film particularly at the corners prior to sealing a load, thus avoiding film bunching at the corners. The prior art inventions have been unable to achieve this uniformity in a single operation and at high-speed. The instant invention provides for high-speed and continuous wrapping and binding a load with a flexible film. The problem addressed by the instant invention, and which has not been solved by the prior art inventions, involves the issue of film folding up at the corners of the package. This problem is increased if the wrapping and sealing of a product is conducted in a single operation and at high-speed. This invention has overcome the problem faced by the prior art wherein the film folds up at the corners of the package forming multiple layers of film. The film folding takes place in a small area in the corners making precise film cutting nearly impossible. The film is suitably selected from any material that is sealable on shrink wrap equipment. Suitable films, which are advantageous, include but are not limited to polyolefins such as high or low density polyethylene, polypropylene and related sealable polymers.

The novel movable, heated U-bar sealing device comprises: a heated cross-sealing perpendicular heating bar, heated two side sealing bars attached to the heated cross-sealing bar to simultaneously form the film sleeve, and seal the open sides of the film sleeve. The entire movable, heated U-bar sealing device moves back and forth with the load facilitating the creation of the film seal in a high-speed continuous manner. The movable, heated U-bar sealing device of this invention is suitably provided with a plurality of film rolls suitably at least two rolls of film, which are welded together by a separate heating device (not shown) to form a film curtain.

It is an object of this invention to provide a movable, heated U-bar sealing device wherein the movable, heated U-bar sealing device spreads the film curtain evenly over the product and facilitates the continuous operations of the shrink wrap apparatus at high-speed. The prior art formed multiple layers of the film, causing film cutting to be difficult and also wasting great quantities of film. The present invention has overcome these shortcomings of the prior art.

The movable, heated U-bar sealing device comprises:

• • (a) a heated cross-sealing bar,
  • (b) a perpendicular first heated side sealing bar having two ends, a proximate end and a distal end, the proximate end is in contact with the heated cross-sealing bar and is facing a conveyor device;
  • (c) said perpendicular first heated side sealing bar having two sides, an inner side and an outer side, the inner side facing the conveyor device;
  • (d) a second perpendicular heated side sealing bar having two ends, a proximate end and a distal end, the proximate end is in contact with the heated cross-sealing bar and is facing the conveyor device;
  • (e) said first perpendicular side sealing bar having two sides, an inner side and an outer side, the inner side facing the conveyor device;
  • (f) said first perpendicular heated side sealing bar comprising a heated bar having two ends, a first curved bracket end and a distal end, the first curved bracket end joined to heated cross-sealing bar and facing the conveyor device; and
  • (g) the second perpendicular heated side sealing bar comprising a heated bar having two ends, a second curved bracket end and a distal end, the second curved bracket end joined to the heated cross-sealing bar and is facing the conveyor device.

The inventive movable, heated U-bar sealing device is provided with a supply device for supplying film to a curtain welding device, the curtain welding device for welding film from a plurality of rolls and a conveyor device for transporting a load through the shrink wrap apparatus. The heated U-bar sealing device is also provided with a cutting device for severing the film curtain from the curtain welding device. To complete the shrink wrapping of the load, a shrink wrap tunnel apparatus is provided for shrinking the film on the load at elevated temperatures. A cooling device is provided for the shrink wrapped load.

A control device is connected to the movable, heated U-bar sealing device comprising a heated cross-sealing bar and two perpendicular heated side sealing bars. The control device also controls the supply rolls, the curtain welding device, the shrink wrap tunnel apparatus, and the cooling device.

The movable, heated U-bar sealing device adjusts to the peripheral side of the load and the temperature of the movable, heated U-bar sealing device is in the range of 200 to 600 degrees Fahrenheit, preferably 350 to 375 degrees Fahrenheit. The movable, heated U-bar sealing device of this invention comprises the heated cross-sealing bar and the conjoined two perpendicular movable heated sealing bars. The movable, heated U-bar sealing device is operationally programmed to move back and forth with the direction of the load to provide a uniform high-speed film sealing of the load.

On each of the sides of the perpendicular movable, heated sealing bars on the side facing the conveyor is an attached curved bracket. The curved end of each heated curved bracket is proximate to the heated cross-sealing bar. The two curved brackets are instrumental in spreading the film and controlling the bunching of the film at the corners of the load.

The curved brackets of the heated cross-sealing bar and two perpendicular, movable, heated side sealing bars comprising the movable, heated U-bar sealing device are suitably made of metal such as steel, tungsten and the like.

The shrink wrap apparatus also comprises a shrink wrap tunnel in which the shrink wrapping of the load is conducted after the sides of the load have been sealed, including:

• • (a) a tunnel having an exit port, an entrance port and opposed side walls,
  • (b) a conveyor device mounted in said tunnel between side walls for transporting loads from said entrance port to said exit port,
  • (c) a heat exchanger mounted adjacent said side walls and extending between said entrance and exit ports on either side of said conveyor device, said heat exchanger including an extended permeable surface with a plurality of electric surface heater elements fixed thereto,
  • (d) an air circulating system mounted adjacent said tunnel, said air circulating system including a blower having a blower input and a blower output, an intake duct work communicating with said blower input and said tunnel adjacent said exit port, and an output duct work communicating with said blower output and said tunnel in said heat exchanger. The shrink wrap tunnel is operated in the range of 200 to 600 degrees Fahrenheit, preferably in the range of 350 to 375 degrees Fahrenheit.

Suitable flexible films, included but are not limited to, are polyolefins such as a polyethylene or polypropylene. The suitable film thickness is about 1.5 to 10 mils, however the range can vary from 1.5 to 18 mils, the preferred range being 1.5 to 6 mils.

Another object of this invention is to provide a high-speed continuous method for wrapping and binding a load with a flexible film said process comprising:

• • (a) feeding the film from a plurality of sources to a curtain welding device,
  • (b) welding together the film from the plurality of film sources forming a curtain,
  • (c) passing the load through the film curtain and covering the load with the film curtain,
  • (d) spreading the curtain film over the load prior to sealing thus avoiding bunching at the corners of the load,
  • (e) sealing the film curtain to the load at a temperature in the range of 200 to 600 degrees Fahrenheit,
  • (f) shrink wrapping the film curtain to the load at a temperature in the range of 200 to 600 degrees Fahrenheit, preferably at a temperature in the range of 350 to 375 degrees Fahrenheit, and
  • (g) optionally cooling the shrink wrapped film.

DESCRIPTION OF THE PRIOR ART

Shrink wrap packaging systems are known in the prior art. Many methods and apparatus have been taught in the prior art for securing shrink wrap material around a product. The problem with the prior art processes has been that in high-speed applications the film will fold up at the corners of the product forming multiple layers of film in a small area, which makes clean film cutting difficult or even impossible.

U.S. Patent Application Publication No. 20020073661 to Nolan is directed to a heat sealing apparatus using a non-linear sealing bar. The Nolan application is directed to batch wise operations.

U.S. Pat. No. 4,365,456 to Ullman relates to packaging machines arranged in succession along a predetermined path. They include a first glue station, a turning station, a second glue station, a film disposing station, and a compression station.

The prior art has not developed an apparatus for high-speed film sealing a load such as a newspaper package in a total enclosure in a single operation. The prior art does not suggest or disclose the inventive movable, heated U-bar sealing device wherein the heated cross-sealing bar with two perpendicular heated side sealing bars form a “U”. The curved or “U” design facilitates the spreading of the film before sealing and that allows the film to be sealed at the point of intersection. The prior art apparatus and process have not been able to totally seal a product due to film bunching at the corners of the product.

SUMMARY OF THE INVENTION

The present invention comprises a heated, movable sealing device called a U-bar. This device comprises a heated cross-sealing bar and two perpendicular heated side sealing bars. The two perpendicular heated side sealing bars and the heated cross-sealing bar form a “U” and form a heated movable U-bar sealing device. This invention also comprises a high-speed, continuous method for wrapping and binding a load with a flexible film. This high-speed, continuous method comprises:

• • (a) feeding the film from a plurality of sources to a curtain welding device,
  • (b) welding together the film from a plurality of sources to form a film curtain,
  • (c) processing the load through the curtain and covering the load with the film curtain,
  • (d) spreading the film curtain over the load prior to sealing, thus avoiding bunching at the corners of the load,
  • (e) sealing the film curtain to the load at a temperature in the range of 200 to 600 degrees Fahrenheit,
  • (f) shrink wrapping the film curtain to the load at a temperature in the range of 200 to 600 degrees Fahrenheit, preferably at a temperature in the range of 350 to 375 degrees Fahrenheit, and
  • (g) optionally cooling the shrink wrapped film curtain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the conveyor with a side view of the movable, heated U-bar sealing device of this invention, including the related devices to conduct a continuous shrink wrapping of the load.

FIG. 2 is a top view of the movable, heated U-bar sealing device.

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring to FIG. 1, the movable, heated U-bar sealing device of this invention includes a frame 10 through which a conveyor 11 runs. On the conveyor 11 is placed the load 12. Supply rolls 13(a), 13(b) for supplying film 22a, 22b are attached to the frame 10. The flexible film is polyolefin such as polyethylene or polypropylene. The film has a thickness in the range of 1.5 to 18 mils, preferably 1.5 to 6 mils. The supply rolls comprise a plurality of rolls of flexible film 22a, 22b, preferably at least two rolls. The film 22a, 22b from supply rolls 13a and 13b is welded together by the curtain welding device 14 to form flexible film curtain 23. The load passes through the film curtain 23 and is covered with the film curtain 23. Cutting device 15 cuts the film curtain 23 from the curtain welding device 14. The load 12 encounters the curved brackets 18a and 18b attached to the heated cross-sealing bar 17 and the perpendicular heated side sealing bars 16a and 16b, and comprising the movable, heated U-bar sealing device, which spreads the film curtain 23 and controls the bunching of the film curtain 23. The spreading of the film curtain 23 over the load 12 prior to sealing avoids bunching of the film curtain 23 at the corners of the load 12. Control device 21 controls all the sealing operations.

The film is sealed to the load at a temperature in the range of 200 to 600 degrees Fahrenheit preferably at a temperature in the range of 350 to 375 degrees Fahrenheit using the movable, heated U-bar sealing device comprising a heated cross-sealing bar 17 and perpendicular heated side sealing bars 16a and 16b. After sealing, the load 12 is transferred by the conveyor device 11 to the shrink wrap tunnel 19, and then optionally the load 12 is moved by the conveyor device 11 to an air circulating system 20 to bring the temperature of the load 12 to ambient conditions. An air circulating system 20, after the shrink wrap tunnel 19, cools the shrink wrapped film to ambient temperatures.

The shrink wrapping of the film is conducted at a temperature in the range of 200 to 600 degrees Fahrenheit, preferably at a temperature in the range of 325 to 375 degrees Fahrenheit.

FIG. 2 is a side view of the movable, heated U-bar sealing device showing the interaction of the cross-sealing bar 17, perpendicular heated side sealing bars 16a and 16b, and the curved brackets 18a and 18b. This arrangement is critical to the invention and allows the wrapping of the load with the flexible film to be carried-out as a rapid continuous process. Prior art could not seal the film to the load in one step. Also, the prior art did not employ curved brackets 18a and 18b, which minimize the bunching of the film 27 bundles in the corners. The curved brackets are made of metal such as tungsten, copper or steel.

The heated cross-sealing bar 17 and the two perpendicular heated side sealing bars 16a and 16b are made of metal such as steel, tungsten and ceramics.

The full sequence of operations of the shrink wrapping apparatus, which incorporates the inventive movable, heated U-bar sealing device, are controlled by a controlling apparatus comprising a programmable logic controller, which is part of the present invention.

While the preferred form of controller is a programmed microprocessor, it should be understood that the invention is not limited thereto. Alternatively, the controller may be based upon relay logic, fluidics or discrete digital logic programmed specifically for operating the present invention.

A preferred form of a micro programmable logic controller (PLC) controller 21, which is suitably programmed to control the operations of the apparatus of this invention is a micro-programmable logic controller (PLC) system (such as one made by Rockwell Automation of Milwaukee, Wis.).

Various modifications of the invention are contemplated. It is to be understood, therefore, that within the scope of the appended claims, the invention may be practiced otherwise than specifically described.