This invention relates to the use of a combustion gas heater for generating significant heat that is uniformly directed across the underside or other regions of a conveyor system, and incorporating a heated air circulation system, for use with shrink wrapping operations for applying polyethylene film about packaged goods, as a protection during shipment.
Heat-shrink conveyor systems are utilized in the packaging industry to replace cardboard cartons with, in many cases, a cardboard tray and a thin film of plastic material which when heated forms around the containers to physically hold the product in place. Examples of such products include water, soda, and other flavored drink bottles or can products from soda to soup or vegetables. Electric operated heaters have been utilized to provide the elevated air temperature required to activate the “shrink” feature of the thin-film plastic material. The electric heaters normally have difficulty in sustaining a constant and uniformly disseminated elevated heat to achieve the shrink wrapping operations, and secondly, does not accommodate uniformity of circulation of the heat to assure that all aspects of the shrink wrap film is constantly exposed to the same temperature, to assure consistent and uniform shrinkage of the film during its packaging of the desired goods.
The conveyor system includes an enclosure above a moving conveyor which forms a tunnel to contain the heated air around the product passing through the chamber. The heated air passes from the chamber back across the electric heater elements and then into the re-circulating fan where it discharges back into the chamber in a re-circulating manner. Drawing air across an electrical heating bank that spans the width of the tunnel attempts to create an even temperature distribution in the chamber where the plastic material shrinkage is to take place. It is very important that the temperature in the chamber be uniform so that the plastic material shrinks evenly against the packaged product.
The operating temperature needed to accomplish the proper shrink effect in a tunnel requires that temperatures to be in excess of 350° F., however, the speed of the product moving through the tunnel may require the chamber temperature to reach temperatures approaching 450° F. The specified temperature must also be held at the set-point within very close tolerances generally within plus or minus 1%. This is important should the volume of product flowing through the tunnel change abruptly. Thus the need for a fast responding modulation controls system along with the requirement for a high turn down ratio of the heating system.
The above system temperature requirements make it difficult to address with indirect gas-fired burner/heat exchanger systems. Space for the heater section is generally limited which creates a problem for a heat exchanger that has to be de-rated at these operating temperatures to keep from exceeding the temperature limit of the material and to maintain the thermal efficiency near 80%. The lower efficiency of the heat exchanger makes it more difficult to compete against the cost of electricity in most parts of the country.
Attempting to apply a direct fired-gas burner system to such an application would have an advantage over an indirect approach because it has a 100% thermal efficiency by its very nature, however, it has been problematic because the heat source is much closer to a point source than distributed as a plane section source as is accomplished by the electric heater bank. The airflow pattern in the tunnel acts to keep the heat flow from a point source burner from reaching the far side of the tunnel, so one cannot mount a burner on one side of the chamber and expect that the temperatures will eventually equalize. Furthermore, the confines of the conveyor cabinet limits the amount of air mixing devices that can be added to match the uniform temperature profile produced from the electric heating system. A solution to this condition is therefore the basis for this patent application.
The operating cost difference between electrical power cost and the cost of natural gas operating at a thermal efficiency of 100% more than justifies a solution to overcome the obstacles that had thus far blocked the entry of a direct gas-fired system from breaking through as a viable alternative to the electric heater in this market.
It becomes obvious that other specialized-heating applications that have similar issues as are encountered with the shrink-wrap conveyer systems as described above would benefit from the solutions offered by this invention. This is a common problem when the heat source tends to act as a point source rather than a distributed output such as a planer source like a heating element bank when the airflow is perpendicular to the heat source. A similar problem exists when a point heat source is small in comparison to the plane of the airflow pattern when the airflow is in the same directions as the heat output. The velocity of the system fan tends to keep the high temperature air from mixing evenly.
This invention contemplates the usage of a direct gas-fired burner to furnish elevated and uniform heat for application in an effective shrink wrapping operation that uses polymer to wrap goods for shipment and/or storage.
A direct gas-fired burner with an embedded combustion air fan is employed as a point heat source that is firing through the sidewall of a shrink-wrap conveyor where the internal airflow is flowing from left to right. An insulation box provides the wall interface for mounting the assembly to the conveyor chamber wall. The outlet of the burner penetrates through the insulation box and into the chamber itself. A heat box captures all of the hot air leaving the burner outlet which in turn pressurizes the heat box by the airflow associated with the combustion air fan. The heat box protects the heat leaving the burner from any disturbance by the circulating airflow of the conveyor fan while the heated air remains inside the heat box.
The key to providing a solution for distributing the heat evenly across the width of the conveyor and within the limited area or confines of the assembly is to have the heat box itself traverse across the width of the chamber and then allow the heated air to escape evenly through a linear slot along its length or a series of punched holes. In the present invention, a partially open outlet slot applies a back pressure on the heated air within the heat box cavity which serves to equalize the air velocity leaving the heat box through such linear slot. A baffle has been installed under the linear slot to block flame from directly entering the linear slot. The baffle assembly provides a path around the bottom baffle with slot openings on each side, below the linear slot to lengthen the heated air path for better mixing and minimize the possibility of flame escaping or passing through the linear slot.
As mentioned earlier, it is acknowledged that, in lieu of a slot configuration, a series of properly sized perforated holes in the heat box could accomplish the same end result and therefore should be recognized by those skilled in the art that adequate results could be achieved with an alternate method of obtaining an even airflow of a mixed heated air output from a heat box.
The heat box is surrounded by a hot air envelop designed to direct the circulating air over the surfaces of the heat box with the larger air volume from the circulating fan passing through the heated air leaving the heat box through the linear slot. The circulating fan airflow dilutes the heated air leaving the heat box. The volume relationship of the circulating fan to that of the combustion air fan is generally 15 to 30 times as much flow, therefore the dilution effect of the circulating airflow effectively decreases the overall temperature of the heated air leaving the linear slot to significantly closely approach the desired chamber temperature. The top surface of the hot air envelop is solid to act as a hit zone for the heated air so as to absorb any hot spots that are not thoroughly distributed by the circulating fan of the chamber including the possibility of flame tips.
It is also recognized that this solution of linearizing the output of a point source heat generating device would apply to other types of heat generating equipment besides the gas burner that was the bases for this patent protection submission. Theoretically, an electric hair dryer could be used as a point source heat generating device.
From empirical data, it was found that a slot block-off which is located above the end point of the burner was necessary to equalize the air temperature inside of the conveyor chamber to maintain the temperature variance tolerance desired. This slot block-off was utilized to address a hot spot area associated at the point where flames were exiting the burner.
A significant benefit of capturing the burner heat output in a heat box as described is that it eliminates the possibility of flame impingement by the airflow from the circulating fan. Testing conducted prior to incorporating the heat box in the design resulted in significantly higher levels of combustion products such as carbon monoxide (CO) and nitrogen oxides (NO, NO2, and NOx). The shielding of the flames and capturing of the heat in the confines of the heat box before discharging the heated air out of the linear slot was absolutely necessary to attain acceptance by the end user desirous of utilizing the gas heat solution.
It is, therefore, a principle object of the current invention to provide a direct gas-fired burner assembly for generating significant heat that is uniformly distributed and dispersed within the circulating air that is applied to furnish shrink wrapping of polymer film about packaged goods.
Another object of this invention is to provide a gas-fired burner that can significantly elevate the generated temperature of a shrink wrap chamber to attain uniformity of shrinkage of the polymer film applied about packaged goods.
Still another object of this invention is to provide a gas-fired burner that may be used directly in proximity with the conveyor carrying polymer wrapped goods through a heat chamber to attain uniformity of shrinkage of the polymer film during packaging.
Still another object of this invention is to provide a direct gas-fired burner that operates in conjunction with a heat box, and a hot air envelop that provides for uniformity of circulation of heated air within a shrink wrap operation.
Still another object of this invention is to provide a gas-fired burner and its operative assemblies that incorporate components that assure the uniform dissemination of heat, from the burner, as it circulates within the chamber of a shrink wrapping assembly.
These and other objects may become more apparent to those skilled in the art upon review of the summary of the invention as provided herein, and upon undertaking a study of the description of its preferred embodiments, in view of the drawings.
In referring to the drawings,
In referring to the drawings, and in particular
The heat box 5 (see
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As can be noted in the schematics of
Variations or modifications to the subject matter of this invention may occur to those skilled in the art upon review of the development as described herein. Such variations, if within the spirit of this invention, are intended to be encompassed within the scope any claims to patent protection issuing hereon. The summary of the invention herein, its depiction in the drawings, and description in the preferred embodiment, are intended for illustrative purposes only.
This non-provisional patent application claims priority to provisional patent application having Ser. No. 61/464,850, filed on Mar. 10, 2011.
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Number | Date | Country | |
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20120227727 A1 | Sep 2012 | US |
Number | Date | Country | |
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61464850 | Mar 2011 | US |