Safe Infrared Radiation-emitting Apparatus

Abstract

An apparatus for safely emitting infrared radiation, as when the radiation source must be separated from an article being irradiated. One surface of an infrared radiation-transmissive sheet or wall confronts the radiation source, and the opposed surface of the radiation-transmissive sheet or wall is cooled by a coolant transported thereacross. In one embodiment, a gas-impermeable, radiation-transmissive wall separates a combustion chamber housing a fuel-fired source of infrared radiation from an enclosure housing a conveyor carrying an article to be irradiated in the path of the radiation. A radiation mask having open and closed positions closes in response to stoppage of the conveyor to prevent radiation from entering the conveyor enclosure, and a sensor senses the integrity of the radiation-transmissive wall and halts the flow of fuel to the radiation source if the integrity of the wall is lost. An article in association with an inflammable solvent may thus be heated safely to remove the solvent by a fuel-fired source of infrared radiation.

Description

BACKGROUND OF THE INVENTION

Although fuel-fired heaters have long been employed to heat homes and other buildings, such sources of heat have not found great utility in the heating of articles containing flammable solvents, such as solvent-cast plastic sheets and the like. The recurring problem in such use of fuel-fired heaters is the possibility that explosive mixtures of flammable solvent vapor and air may be ignited by the fuel-fired heater. Accordingly, those heaters which have employed a fuel-fired source of heat for drying flammable solvent-containing articles have ordinarily required wide separation of the heat source from the article being dried. This has been accomplished by having the heater heat air in a separate circulatory system, the heated air then being blown upon the articles to be dried. This system, it will be appreciated, requires a great deal of space for separation of the heat source from the solvent-containing articles and further requires a great deal of expensive duct work and the like for transporting heated air through a separate plenum from the heat source to the articles to be dried.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides an apparatus for safely emitting infrared radiation and which is useful in the drying of flammable solvent-laden articles. The apparatus comprises a source of infrared radiation, such as a gas-fired burner. An infrared transmissive sheet or wall having a surface confronting the radiation source is spaced from the source. The apparatus includes means for transporting a coolant across the opposed surface of the wall to cool the wall, whereby the radiation source is isolated from the coolant by the radiation-transmissive wall.

In a preferred embodiment, a fuel-fired source of infrared radiation is housed within a combustion chamber having a gas-tight infrared transmissive wall spacedly confronting the infrared source and having an exhaust aperture permitting combustion product gases to be exhausted from the chamber. The apparatus includes a conveyor for transporting an article to be irradiated exteriorly of the radiation-transmissive wall and in the path of radiation emitted therethrough, an enclosure housing the article during irradiation thereof, and means for transporting a coolant exteriorly of, but in cooling relationship to, the radiation-transmissive wall to cool the same. A mask having radiation-transmissive wall, and means are provided for affecting closure of the mask when movement of the conveyor ceases. A sensor is provided for sensing the integrity of the radiation-transmissive wall, and is adapted to shut off the fuel supply to the radiation source when integrity of the wall has been lost.

DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation view of the apparatus of the invention, shown in partial cross section and partially broken away; and

FIG. 2 is a broken away cross-sectional view of a portion of the apparatus showing the radiation-transmissive wall of the invention and a sensor for sensing the integrity of the wall.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the apparatus of the invention designated generally as 10 includes a combustion chamber 12 having an inclined upper wall 14, front and rear walls 16 and 18, and a radiation-transmissive lower wall 20. Front wall 16 has an aperture 16.1 for supplying air to the combustion chamber, and rear wall 18 has an exhaust aperture 18.1 positioned adjacent the superior end of upper wall 14 to exhaust combustion product gases from the combustion chamber. Air inlet aperture 16.1 may be provided with an adjustment (not shown) such as a damper for regulating the amount of air which is permitted to enter. Housed within the combustion chamber is a source of infrared radiation such as a series of gas burners 20.1, which may be Schwank type burners. Fuel, such as natural gas, is introduced under pressure into a gas pipe 20.2 exteriorly of the combustion chamber, and the gas burners 20.1 depend from the gas tube 20.2 so that the gas burners are substantially aligned with one another in a horizontal plane, each substantially equidistant from the radiation-transmissive lower wall 20 of the chamber. Regulator valve 20.3 is provided exteriorly of the combustion chamber for regulating the amount of fuel which is fed to the burners 20.1. The burners 20.1 include a ceramic element which, when heated, emits infrared radiation. Each burner is provided with one or more orifices (not shown) through which air entering the chamber through aperture 16.1 may pass and be mixed with the fuel to form a flammable mixture which is burned at the bottom of the burners. Since the atmosphere within the combustion chamber 12 is not permitted to contact an article to be irradiated, as will be explained more fully below, it is important from the standpoint of efficiency that a large proportion of the energy resulting from combustion of the fuel be transformed into infrared radiation emanating from the burners.

The inner surface of the combustion chamber may be made radiation reflective in whole or in part, as desired, so that a large proportion of the infrared radiation which is generated passes downwardly through the radiation-transmissive lower wall 20. The hot combustion product gases will normally rise to the upper wall 14 which preferably, but not necessarily, is inclined, and will then pass outwardly of the chamber through exhaust aperture 18.1 aided, if necessary, by means urging the flow of air through the chamber such as the powered exhaust stack 32. The upper wall 14 need not be inclined, of course, provided means are supplied for otherwise exhausting the combustion chamber.

The radiation-transmissive lower wall 20 of the combustion chamber is preferably a flexible plastic sheet which is supported about the lower periphery of the combustion chamber in a gas-tight manner to prevent the escape of combustion product gases through the lower wall from the chamber 12, and to prevent solvent vapors or the like emanating from an article being irradiated from passing upwardly through the lower wall into the combustion chamber. The lower periphery of the combustion chamber may be provided with a connector 20.4 which forces the edges of the radiation-transmissive wall 20 sealingly up against the bottom surface of a short, continuous flange 16.3 extending inwardly of the lower periphery of the chamber. The wall 20 may further be held in place by means of bolts 16.2 extending through the flange 16.3, the wall 20, and the connector 20.4, as shown in FIG. 2. The radiation-transmissive wall 20 is sufficiently flexible so that it tends to balloon downwardly slightly, as shown in FIG. 2, under the influence of a pressure differential across the wall, and ordinarily softens or melts below 1000.degree.F. Preferred materials for the radiation-transmissive wall 20 include polytetrafluoroethylene (Teflon "TFE," a trademarked product of E.I. DuPont DeNemours and Company, Inc.) which has an infrared transmissivity of approximately 0.88, poly(tetrafluoroethylene-hexafluoropropylene) (Teflon "FEP," the DuPont Company) and a polyester such as poly(ethylene-terephthalate), a product sold under the name Mylar by the DuPont Compony and which has an infrared transmissivity of approximately 0.77. Unusually high temperatures may be tolerated by poly (4,4'-diaminophenylether pyromellitimide) ("Kapton," a product of the DuPont Company). Teflon TFE film having a thickness of approximately 0.002 inches is preferred, since this material is flexible, is highly transmissive of infrared radiation, and is more resistent to high temperatures than most other thermoplastic materials.

A conveyor 22 is provided beneath the radiation-transmissive wall 20 to carry an article 24 into the path of infrared radiation emitted by the burners 20.1. For this purpose, a conveyor belt 22.1 is trained about rollers 22.2 and 22.3 at opposite ends of the combustion chamber, the last-mentioned roller being driven through a belt 22.4 which passes over and is driven by rotating pulley 22.5. The latter is driven by an electric motor (not shown) or the like which is housed within power housing 26. The conveyor belt is housed along at least a portion of its length by an enclosure 28 having openings 28.1, 28.2 at either end. The radiation-transmissive wall 20 forms a portion of the upper wall of the conveyor belt enclosure such that infrared radiation emitted downwardly from the burners 20.1 is transmitted through the wall 20 to impinge upon the article 24 carried by the belt. Articles to be irradiated may thus be placed on the belt adjacent roller 22.2 and may be removed adjacent roller 22.3. The belt 22.1 itself is preferably of infrared radiation-transmissive material, such as Teflon TFE. A reflector 30 is positioned beneath the belt in confronting relationship to the radiation emitted through the wall 20 so as to reflect infrared radiation upwardly against portions of the articles 24 which are not exposed to the downwardly directed radiation emitted by the burners, thereby permitting the articles to be more uniformly irradiated and thus more uniformly heated. Food products such as potato chips, cookies, and the like may thus be uniformly browned after having been baked by microwaves. If desired, one or more of the surfaces of the conveyor belt may be reflectorized, or the bottom surface 28.3 of the enclosure may have an upwardly facing reflectorized surface. To avoid reducing reflectance by accumulations of dirt and the like, however, a separate reflector positioned between the upper and lower runs of the conveyor belt 22.1, is preferred, as shown in FIG. 1.

Communicating with the combustion chamber through exhaust aperture 18.1 and with the conveyor enclosure 28 through opening 28.2 is an exhaust stack 32 having a powered blower 34 mounted at its upper end. The blower is adapted to provide a partial vacuum within the stack 32 for drawing combustion product gases from the combustion chamber 12 and for simultaneously drawing air into the opening 28.1 in one end of the conveyor enclosure 28 and from opening 28.2 in its other end. The air thus flowing through the conveyor enclosure is caused to pass across the lower surface of the radiation-transmissive wall 20 to cool the wall. Baffles (not shown) or other means may be provided to insure that the air drawn through the conveyor enclosure passes sufficiently close to the bottom surface of the wall 20 so that sufficient heat is transferred from the wall to the cooling air to prevent the wall from becoming too hot so as to soften, melt, or otherwise become distorted. A damper 32.1 is rotatably mounted in the exhaust stack 32 between its side walls to control the amounts of air issuing from the opening 28.2 in the conveyor enclosure. A second damper 32.2 is rotatably mounted between the side walls in the exhaust stack adjacent the exhaust aperture 18.1 leading from the combustion chamber to regulate the quantity of combustion product gases which are drawn through the exhaust aperture. The dampers 32.1 and 32.2 may be joined by a chain 32.3, or may be otherwise connected, so as to rotate in unison, whereby the reduction in the amount of air drawn from the conveyor enclosure results in a greater quantity of combustion product gases being drawn through the exhaust aperture 18.1, and vice versa. The dampers 32.1 and 32.2 are normally so adjusted that a greater partial vacuum is drawn in the conveyor enclosure than in the combustion chamber, thus causing large quantities of cooling air to pass beneath the radiation-transmissive wall 20 and further causing the wall to balloon downwardly slightly as shown in FIG. 2 under the influence of the pressure differential thus created between the combustion chamber 12 and the conveyor enclosure 28. It may in some cases be desirable to provide air under pressure into the aperture 16.1 in the combustion chamber and into the opening 28.1 at the front end of the conveyor enclosure, whereupon the blower 34 on top of the stack may be eliminated. In this embodiment, the relative quantities of air introduced through the aperture 16.1 and the opening 28.1 are such as to cause the pressure within the combustion chamber to be slightly higher than the pressure within the conveyor enclosure, thus causing the radiation-transmissive wall to balloon outwardly slightly from the combustion chamber. In any event, it will be understood that the pressure differential between the combustion chamber and the conveyor enclosure prevents flammable solvent vapors which may be produced in the enclosure from entering the combustion chamber.

A tension sensor 36 (FIG. 2) is mounted exteriorly of the combustion chamber and includes a downward projection 36.1 having a laterally extending sensing finger 36.2, the end 36.3 of the finger being biased gently upwardly against the outwardly ballooned radiation-transmissive wall 20. If the integrity of the wall 20 is lost (e.g., by rupturing or tearing or the like), the ballooning effect of the wall will be changed and this change is sensed by the finger 36.2. In response to movement of the finger in this fashion, sensor 36 provides a signal to the fuel regulator 20.3, causing the fuel supply to the burners 20.1 to be immediately halted. Since the relative pressures in the combustion chamber and conveyor enclosure will be substantially constant during steady-state operation of the apparatus, the sensing finger may be finely adjusted so that the sensor 36 responds to very slight fluctuations in the wall 20, so that small tears or rips occurring in the wall are detected. Pinholes or extremely small tears in the wall, however, are tolerated by the sensing finger. It will further be understood that any obstructions which develop which hinder the free flow of air through the conveyor enclosure or the combustion chamber will also be mirrored in a change in the pressure differential across the film, thus changing slightly the position of the outwardly ballooned wall 20 which results in the halting of gas flow to the burners 20.1. When softened by unduly high temperatures, moreover, the wall 20 will balloon outwardly to a greater degree, thus triggering the sensor 36.

A plurality of radiation opaque louvers 38 extend transversely in the combustion chamber spaced closely above the radiation-transmissive wall 20, and are rotatable about shafts 38.1 journaled into the side walls of the combustion chamber. Simultaneous rotation of the shafts 38.1 causes the louvers to move from a vertical position (solid lines in FIG. 1) which permits passage of radiation emitted from the burners, to a closed position (shown in dashed lines in FIG. 1) wherein radiation is prevented from reaching the wall 20. One end of each louver shaft 38.1 extends through the side wall of the combustion chamber, and an exterior, generally downwardly directed link 38.2 is rigidly mounted thereon. The bottom ends of the links 38.2 are in turn pivotally connected to an axially movable horizontal rod 38.3 such that axial movement of the rod causes the louvers to move between open and closed positions. The rearwardly extending end of the rod 38.3 enters the power housing 26 and therein is pivotally affixed to a rotatable link 26.1, rotation of which about its stationary pivotal connection 26.2 is governed through an appropriate controller 22.6 by rotation or non-rotation of the pulley 22.5 driving the conveyor belt 22.1 as sensed by motion sensor 22.7. When the conveyor belt ceases to move, the controller urges rotatable link 26.1 to the right (as shown in dashed lines in FIG. 1), thus drawing the rod 38.3 to the right to cause the louvers, acting through connecting links 38.2, to assume a substantially flat, closed position. A purpose of the louver mechanism thus described is to prevent articles carried by the conveyor from becoming overexposed to the radiation emitted through the wall 20 when the conveyor is momentarily stopped. When movement of the conveyor is resumed, the louvers are returned to their vertical position by the linkage elements thus described. When in their flat, closed position, the temperature of the louvers themselves may become increased due to absorption of infrared radiation. When raised again to their vertical position upon resumption of conveyor movement, the heated louvers are thus positioned away from the radiation-transmissive wall 20 so as not to cause overheating, and possible rupture, of the wall. The louvers may be provided with an infrared reflective surface to lessen the possibility of overheating.

In another embodiment, the radiation-transmissive wall or sheet may be in the form of a circular drum into which wet clothes or other articles to be dried may be placed, the combustion chamber extending in an annular fashion about the outer periphery of the radiation-transmissive wall and having fuel-fired sources of infrared radiation about the circumference of the chamber and spaced from the wall. In this embodiment, the the wet laundry is the coolant which is transported over the inner surface of the wall 20 by rotation of the wall about its axis, or by internally mounted paddles, or the like. Since water is considerably more absorptive of infrared radiation than are most fabrics, water from the wet laundry will be heated, vaporized, and exhausted through an appropriate exhaust stack which may also carry the combustion product gases from the combustion chamber. The relatively low infrared absorptivity of the clothes prevents overheating of the clothes which might damage temperature sensitive fabrics. In contrast, gas-fired clothes dryers of the type in popular, present-day use either pass combustion product gases through the clothes for drying, or require a separate plenum wherein air is heated and then passed through the clothes.

Manifestly, I have provided an apparatus for safely emitting infrared radiation in which articles to be irradiated are separated from the radiation source by an infrared radiation-transmissive wall having a surface which confronts the radiation source, the other surface of the wall being cooled by passage of a coolant thereacross. The wall provides a barrier to the communication of gases thereacross for reasons of safety and cleanliness. In preferred embodiments, the integrity of the infrared radiation-transmissive wall is continuously sensed, and the radiation source is deactivated should integrity of the wall be lost. A movable conveyor is provided for carrying articles in the path of the radiation emitted from the radiation source, and a mask is provided to prevent radiation from impinging upon articles to be irradiated when the conveyor ceases to move.

While I have described a preferred embodiment of the present invention, it should be understood that various changes, adaptations, and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

Claims

What is claimed is:

1. Apparatus for safely emitting infrared radiation comprising a source of infrared radiation, an infrared radiation-transmissive, flexible wall softenable at a temperature below 1,000.degree. F. and having a surface confronting the radiation source but spaced therefrom, means for transporting a coolant across the opposed surface of the wall to cool the latter, and means preventing access of the coolant to the radiation source.

2. The apparatus of claim 1 wherein the radiation source is fuel-fired.

3. Apparatus for safely emitting infrared radiation comprising a first chamber, a source of infrared radiation enclosed in the first chamber, a second chamber adjacent the first chamber and desposed in radiation-receiving position with respect to the infrared radiation source, an infrared radiation-transmissive flexible wall softenable at a temperature below 1,000.degree. F. and having one surface confronting the radiation source and an opposed surface confronting the second chamber, a coolant, and means for transporting the coolant across the opposed surface of the wall to cool the wall.

4. The apparatus of claim 3 wherein the coolant includes an article adapted to be heated within the second chamber by absorption of infrared radiation.

5. The apparatus of claim 3 including means for moving an article within the second chamber in a path permitting confrontation of the article with infrared radiation emitted from the infrared radiation source.

6. The apparatus of claim 3 wherein the source of infrared radiation is fuel-fired, and including means for exhausting combustion product gases from the first chamber.

7. The apparatus of claim 3 wherein the infrared radiation-transmissive wall forms a gas-tight wall of the first chamber confronting the second chamber.

8. Apparatus for safely emitting infrared radiation comprising a first chamber, a source of infrared radiation enclosed in the first chamber, a second chamber adjacent the first chamber and disposed in radiation-receiving position with respect to the infrared radiation source, an infrared radiation-transmissive gas-tight wall having one surface confronting the radiation source and an opposed surface confronting the second chamber, a coolant, means for transporting the coolant across the opposed surface of the wall, and a sensor for sensing the integrity of the infrared transmissive wall, the sensor including a controller responsive to the sensor and adapted to deactivate the infrared radiation source when non-integrity of the wall is sensed by the sensor.

9. The apparatus of claim 8 wherein the infrared transmissive wall forms a common wall of the first and second chambers.

10. Apparatus for safely emitting infrared radiation comprising a first chamber, a source of infrared radiation enclosed in the first chamber, a second chamber adjacent the first chamber and disposed in radiation-receiving position with respect to the infrared radiation source, means for moving an article within the second chamber in a path permitting confrontation of the article with infrared radiation emitted from the source, an infrared radiation-transmissive wall having one surface confronting the radiation source and an opposed surface confronting the second chamber, a coolant, means for transporting the coolant across the opposed surface of the wall, a mask confronting the wall and having an infrared radiation-transmissive open position and an infrared radiation opaque closed position, and including means responsive to the movement of an article within the second chamber and adapted to affect closure of the mask when the movement of the article ceases.

11. Apparatus for safely emitting infrared radiation comprising a first chamber, a fuel-fired source of infrared radiation enclosed in the first chamber, a second chamber adjacent the first chamber and disposed in radiation-receiving position with respect to the infrared radiation source, means for moving an article within the second chamber in a path permitting confrontation of the article with infrared radiation emitted from the source, an infrared radiation-transmissive wall having one surface confronting the radiation source and an opposed surface confronting the second chamber, a coolant, means for transporting the coolant across the opposed surface of the wall to cool the wall, and an exhaust stack communicating with the first and second chambers for exhausting combustion product gases and coolant simultaneously from the respective chambers.

12. The apparatus according to claim 5 including an infrared radiation reflector in the second chamber and positioned to receive infrared radiation emitted from the infrared source and to reflect the same against a portion of the article not confronting the infrared source.

13. Apparatus for safely irradiating an article with infrared radiation comprising:

a fuel-fired source of infrared radiation;

a combustion chamber housing the infrared radiation source and having a gas-tight, infrared radiation-transmissive flexible wall softenable at a temperature below 1,000.degree. F. and spacedly confronting the infrared radiation source, the combustion chamber further having an exhaust aperture permitting combustion product gases to be exhausted from the chamber;

a conveyor for transporting an article exteriorly of the infrared radiation-transmissive wall and in the path of infrared radiation emitted therethrough;

an enclosure housing the article during movement thereof in the path of the infrared radiation; and

means for transporting a coolant exteriorly of, but in cooling relationship to, the radiation-transmissive wall to cool the same.

14. The apparatus of claim 13 wherein the article enclosure is positioned beneath the combustion chamber and wherein the radiation-transmissive wall of the chamber forms an upper wall of the article enclosure.

15. Apparatus for safely irradiating an article with infrared radiation comprising:

a fuel-fired source of infrared radiation;

a combustion chamber housing the infrared radiation source and having a gas-tight, infrared radiation-transmissive lower wall spacedly confronting the infrared radiation source and having an exhaust aperture for exhaustion of combustion product gases;

a conveyor for transporting an article exteriorly of the infrared radiation-transmissive wall and in the path of radiation emitted through the wall;

an enclosure housing the article during movement of the latter in the path of the infrared radiation, said infrared radiation-transmissive lower wall of the combustion chamber forming an upper wall of the article enclosure;

a gaseous coolant; and

means for transporting the coolant comprising an exhaust stack communicating with the combustion chamber and with the article enclosure and adapted to simultaneously draw combustion product gases from the chamber and coolant gas from the enclosure, and to exhaust the same.

16. The apparatus of claim 15 including a sensor for sensing the integrity of the radiation-transmissive wall and adapted to halt fuel flow to the infrared radiation source in response to sensing non-integrity of the wall.

17. The apparatus according to claim 16 including a mask confronting the radiation-transmissive wall comprising parallel louvers movable between radiation transmissive open positions and radiation opaque closed positions, and including means responsive to the movement of articles within the second chamber and adapted to affect movement of the louvers to the closed position when the movement of articles cases.

18. Apparatus for irradiating moving objects with infrared radiation comprising:

a combustion chamber having an upper wall, a flexible, gas-tight, infrared radiation-transmissive lower wall, and side walls, the combustion chamber having an exhaust aperture positioned to draw combustion product gases from the chamber and having an inlet aperture permitting entry of air into the chamber;

a fuel-fired source of infrared radiation positioned within the combustion chamber and spaced from the radiation-transmissive lower wall;

a conveyor adapted to convey an article beneath the radiation-transmissive lower wall for exposure of the article to infrared radiation;

an enclosure housing the conveyor, the radiation-transmissive lower wall of the combustion chamber forming an upper wall of the conveyor enclosure, the enclosure having openings permitting the flow of air therethrough in cooling proximity to the radiation-transmissive lower wall; and

an exhaust stack communicating with the exhaust aperture of the combustion chamber and an opening of the conveyor enclosure to simultaneously draw combustion product gases from the combustion chamber and cooling air from the conveyor enclosure.

19. The apparatus of claim 18 including means providing a higher pressure in the chamber than in the enclosure, whereby the flexible radiation-transmissive lower wall is caused to balloon outwardly from the combustion chamber.

20. Apparatus of claim 18 including a series of louvers extending across the combustion chamber adjacent the radiation-transmissive lower wall, the louvers being movable between a radiation-transmissive open position and a radiation opaque closed position, the latter position substantially preventing transmittance of radiation from the source exteriorly of the combustion chamber, linkage elements connected to the louvers and adapted to move the latter between open and closed positions, a motion sensor for sensing movement of the conveyor, and a controller controlling movement of the linkage elements and responsive to the sensor and adapted to affect closure of the louvers when movement of the conveyor ceases.

21. The apparatus of claim 20 including a pressure control adapted to maintain combustion chamber pressure at a higher level than the conveyor enclosure pressure, wherein the radiation-transmissive lower wall of the chamber is sufficiently flexible as to balloon out slightly exteriorly of the chamber in response to the pressure differential between the chamber and the enclosure, and including an integrity sensor having a sensing finger touching said outwardly ballooned radiation-transmissive wall and adapted to sense the loss of integrity thereof, and a fuel controller responsive to the integrity sensor and adapted to shut off the supply of fuel to the infrared radiation source in response to the sensing of non-integrity of the radiation-transmissive lower wall of the chamber.