US2921778A - Re-circulating oven - Google Patents

Description

1311- 1960 R. J. RUFF RE-CIRCULAT'ING OVEN 3 Sheets-Sheet .1

Filed April 19, 1957 v INVENTOR ATTORNEY R/cHARnJ. RUFF Jan. 19, 1960 R, J, R FF RE-CIRCULATING OVEN 3 Sheets-Sheet 2 Filed A ril 19, 1957 INVENTOR RICHARD J RUFF ATTORNEY R. J. RUFF RE -CIRCULATING OVEN Jan. 19, 1960 3 Sheets-Sheet 3 Filed April 19, 1957 CURRENT SOURCE INVENT OR RICHARD J RUFF ATTORNEY United States Patent RE-CIRCULATING OVEN Richard J. Rutf, Detroit, Mich., assignor to Catalytic Combustion Corporation, Detroit, Mich., a corporation of Michigan Application April 19, 1957, Serial No. 653,783 11 Claims. c1. 2633) This invention relates to the heat treatment of coated materials and more particularly to an apparatus for heat treating coated materials to evaporate the solvents or other volatile components in the coatings to dry and bake such coatings on the materials to which they are applied.

The apparatus of this invention may be utilized to heat treat many difierent types of coatings on many difierent articles or materials, but is primarily intended to heat treat enamel coatings applied to wire for insulating purposes and, accordingly, the invention will be described in connection with the enamel coating of Wires, but it is to be understood that this is for illustrative purposes only and that the apparatus is in no way limited to such use.

Heretofore, ovens for heat treating enamel coated wire have been either of the horizontal or vertical type, but the majority of such ovens have been of the vertical type, that is, in which the plane of travel of the wire is in a vertical direction, since for wire of intermediate or large diameters, this type of oven provides a uniform concentricity of the coating, whereas in the horizontal type oven there is a tendency for the coating to run or sag toward the lower side of the wire.

The use of vertical ovens for this purpose has presented considerable difiiculty, due to the fact that it is necessary to provide a vertical treating chamber having openings at the bottom and top for feeding wire thereto and removing the same from the chamber, with the result that a rather pronounced stack elfect or thermal head is introduced which causes entrance of cold air at the bottom and the discharge of heated vapor or fume laden air at the top. The fumes created during operation of an oven of this type are odorous and noxious in character, as well as inflammable and furthermore, the entrance of cold air at the bottom of the heating chamber increases the heat requirements and also adversely effects the drying and baking process and at the same time, may result in excessive condensation of the solvent vapors thereby creating a fire hazard and necessitating frequent cleaning of the ovens.

Forced re-circulation of air within the oven has heretofore been attempted in order to provide more efiicient utilization of heat and more uniform temperatures in the treating chamber. This has been only partially successful, since in attempting to overcome the stack effect, the air was forced downwardly in the treating chamber which permits adequate temperature control throughout the treating zone, but also imposes a positive pressure at the upper end of the treating chamber which added to the stack effect tends to force vapors or fume laden gases out of the top opening of the chamber. To prevent this, excess ventilation has been employed which materially increases the operating cost of the oven due to the increased heat input requirements.

Attempts have been made to prevent the discharge of fume laden gases from the top opening of the treating chamber by utilizing the motion of the heated air to produce a Venttui efiect at the top opening thereby drawing in outside air at this point, but this has been difiicult to accomplish in that, the efllectwas not uniform across the entire top opening. This resulted in unpredictable temperature difierences in difierent zones of the treating chamber thereby producing an inferior product and furthermore, in this system, it is necessary to connect the intake of the circulating fan to the lower end of the treating chamber thereby increasing the flow of fresh air through the lower or bottom opening of the chamber which, of course, adds to the heat input requirements and increases the cost of operation.

It is therefore desirable to provide a heat treating apparatus of the character under consideration which will eliminate all discharge of vapor or fume laden air and furthermore, since the fumes or vapors from the solvents of the coatings may be oxidized through catalytic action, the heat available from such oxidation would normally be adequate to supply the total heat requirement of the oven and the apparatus of the instant invention is designed to accomplish this result.

It is accordingly an object of the invention to provide a heat treating apparatus for coated materials utilizing a vertically disposed treating chamber and incorporating means to control the infiltration of air at the entry and exit openings of the chamber.

A further object of the invention is the provision of a heat treating apparatus for coated materials incorporating a vertically disposed heat treating chamber in which the stacked or thermal head effect is balanced by introducing heated air to the chamber in a downward'direction at a plurality of vertically spaced locations.

A still further object of the invention is the provision of a heat treating apparatus for coated materials incorporating a vertically disposed heat treating chamber in which the temperatures in difierent vertically spaced zones of the chamber may be controlled over wide limits or held substantially constant in one zone in order to properly dry and bake various types of coatings.

Another object of the invention is the provision of a heat treating apparatus for coated materials, including a vertically disposed heat treating chamber having bottom and top openings and in which the infiltration of air at the bottom opening may be controlled as desired.

A further object of the invention is the provision of a heat treating apparatus, including a vertically disposed heat treating chamber having bottom and top openings in which air is withdrawn from the chamber adjacent the top thereby causing infiltration of air through the top opening which prevents discharge of fume laden air through the top opening, but does not adversely effect the temperature conditions in the treating portions of the chamber.

A still further object of the invention is the provision of a heat treating apparatus for coated materials, including a vertically disposed heat treating chamber and power driven means for withdrawing heated air from the top of the chamber, circulating the same through a firebox having burners therein, through a catalytic oxidizing unit and thereafter re-introducing such air to the treating chamber in a downward direction at a plurality of vertically spaced locations.

Another object of the invention is the provision of a re-circulating type heat treating apparatus for coated materials incorporating a vertically disposed heat treating chamber in which means is provided for controlling the relative quantity of re-circulated heated air introduced into the chamber at a plurality of vertically spaced locations.

A further object of the invention is the provision of a re-circulating type heat treating apparatus for coated materials incorporating a vertically disposed heat treating chamber in which means is provided for introducing a controlled amount of fresh air and in which means is 3. V provided for exhausting a controlled amount of fume free air.

A still further object of the invention is the provision ,of a re-circulating type heat treating apparatusfor coated mate rialsincorporating a vertically disposed he'at' treating chamber in which a variable speed power driven fan utilizednto withdraw and re-circulate air through the treating chamber. 'Another' object. of the invention isthe provision ofa .re-circ'ulating'f typej heat treating apparatus for .coated .materials incorporatinga vertically disposed heat treating chamber and in. which heat may be supplied by burners, by catalytic oxidation of the fumes withdrawn from the treating chamber, by a combination of :the.

two and. including control means for the fuelsupply to the burners'operatingin'response to the temperature "conditions required. T f 7 A further object of the invention is the provision of a re-circulating type heat treating apparatus for coated materials incorporating a vertically disposed heat treating chamber and having a catalytic'vapor incinerator disposed in the path of flow of the vapor or fume laden air, there being a fresh air inlet onthe downstream side of the incinerator whereby dilution ofthe fume laden air prior to incineration is prevented. A still further object ofthe invention is the provision of a re-circulating type heat treating apparatus for coated materials incorporatinga vertically disposed heattrea't- .ing chamber, there being heating burners and a catalytic vapor incinerator disposed in the path of flow of air from the treating chamber, such apparatus also having a fresh air inlet and an exhaust outlet on the downstream side of the incinerator, there being automatic control means for the supply of fuelto the burners, as' well as automatic control means for the fresh air inlet and exhaust outlet operating in response to the temperature requirements and the heat output of the incinerator.

'Yetanother object of the invention is the provision of 'a re-circulating type heat treating apparatus with or with- "out a catalytic fume incinerator or one in which the catalytic fume incinerator may be completely 'by-passed by pivoting the same or one in which the catalytic incinerator may be partially by-passed by mounting a damper in co-planar relationship therewith.

Further objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawing wherein:

Fig. 1 is an elevational view of a catalytic re-circulating heat treating apparatus constructed in accordance with thisinvention; V

Fig. 2 is a sectional view taken substantially on the line 22 ofFig. 1; a 'Fig. 3 is a sectional of the invention; and, a

Fig. 4 is a partial sectional view similar to the upper right hand part of Fig. 3 of a still further modification 'of the invention. a 7

With continued reference to the drawing, there is shown in Figs. 1 and 2 a heat treating apparatus for coated materials constructed in accordance with this invention and which may well comprise a frame 10 formed by suitable corner posts 11 of angle iron or'other suitable structural shapes, which frame serves to support a generally rectangular housing 12 having front and back walls 13 and 14, sidewalls 15 and 16 and top and bottom walls 17 and 18. A vertical partition 19 is provided between view of a slightly modified form J the top and bottom walls 17 and 18 and spaced inwardly from the front wall 13 to provide a vertically disposed treating. chamber 20 for receiving coated materials, such as one or more wires 21 having an enamel. or other coating thereon passing upwardly through an entrance opening 22 in the lower end of the chamber 20 and leaving the chamber through an exit opening 23 in the upper end thereof. V w

p A circulating fan 24 is disposed in the housing 12 and is provided with an intake opening 25 and a discharge opening 26. The fan 24 is mounted on' a shaft 27 extending exteriorly of the housing 12 and rotatably mounted in bearings 28 supported on a suitable bracket 29 carried by the frame 10. A pulley 30 is fixed to the shaft 27 and serves to engage a belt 31 which in turn engages a variable speed type pulley 32 mounted on the drive shaft of a motor 33. The motor 33 is carried by a slidable base 34 supported by the frame 10 and the base 34 may be moved toward or away from the shaft 27 of the fan 24 by means of a screw threaded adjusting member 35 having a hand wheel 36 mounted thereon. Such movement of the base 34 and motor 33 results in increasingror decreasing the effective diameter of the pulley 32 thereby varying the speed of rotation of the fan 24.'

A discharge conduit 37 is connected to the discharge opening 26 of the fan 24, the conduit 37 extending downwardly to .a point adjacent the bottom .of the treating chamber 20 and thereafter upwardly to a point above the midpoint of the chamber 20. The upwardly extending portion 38 of the conduit 37' is provided with partitions 39 and 40 dividing the same into'three ducts. 41, 42 and 43, the duct 41 terminating in a downwardly directed discharge passage 44 opening into the treating chamber 20 at a point spaced above the bottom thereof. The duct 42 terminates in a downwardly directed discharge passage 45 opening into the treating chamber 2% above the opening of the dischargepassage 44 to provide an intermediate discharge opening and the duct 43 terminates in a downwardly directed discharge passage 46 opening into the treating chamber 20 at a point above the intermediate discharge opening and slightly above the midpoint of the treating chamber 20. While three ductsand discharge openings have been shown and described, it is to be understood, that any desired number and'spacing thereof may be employed in order to produce the desired distribution. of heated air within the treating chamber 29. A damper 47 is provided at the lower endof the partition 39 and such damper may be provided with an actuating lever 48 disposed exteriorly of the housing-12 to permit convenient operation of the same and the damper 47 may be utilized to direct the entire flow of air from the conduit 37 into the duct 41 and discharge passage 44,. to direct a portion of the flow of air to the duct 41 and the remainder to the ducts 42 and 43 or to direct the entire flow to the ducts 42 and 43. It is to be noted, that the partition 40 terminates above the lower end of the partition 39 and disposed at the lower end of the partition 40 is a damper 49 having anactuating lever 50 exteriorly of-the housing 12 to permit convenient operation thereof. Thedamper 49 may be utilized to regulate the flow of air from theconduit 37 through the ducts 42 and 43 and the discharge passages 45 and 46. A A firebox '51 is located in thehousing =12'above the fan 24 and disposed in the firebox' 51 are burners 52 which may utilize gaseous orliquid fueland'a control valve 53 is provided. for the control. of 'such fuelinput to the burners 52. A passage 54 is provided between the upper end of vthe treating chamber, 20 adjacent the outlet opening 23. and a damper 55 may be provided in thepassage 54 for controlling the flow of fume laden air or vapor'from the chamber 20 into I the fire box 51. A catalytic fume incinerator unit 56 is disposed in the path of flow of-air from theburners 52 to the fan 24 and is positioned in such a manner. that the entire flow of such is through the incinerator to the fan. The catalytic fume incinerator 56 maybe of the type disclosed in patent to Suter et 21., #2,658,742, dated November 10, 1953, or may be of any other suitable type andno detailed description ofthis incinerator is believed necessary or desirable, reference being made to the. above patent for this purpose. Since the incinerator 56 is located directly in theflow of fume laden vapors from the burners 52, there is, no, dilution thereof prior. to contact with the catalyst and consequently, suchcataly'st may operate at peak efliciency.

A passage 57 leads from the outlet side of the catalytic incinerator 56 to the inlet opening 25 of the fan 24 and a fresh air inlet duct 58 connects'with the passage 57 and extends exteriorly of the housing 12. The outer end of the fresh air inlet duct 58 may be provided with a manually operable damper 59 for controlling the flow of fresh air into the duct 58.

An exhaust duct 60 communicates with the discharge conduit 37 and extends exteriorly of the housing 12. One or more dampers 61 may be disposed in the exhaust duct 60 to control the flow or air therethrough. and the damper 61 may be operated through a suitable linkage mechanisr'n 62 connected to a damper actuating motor 63. While the motor 63 is shown in Fig. l as being of'the fluid pressure operated type, it is to be understood, that an electric motor or any other suitable damper actuating motor may be employed.

An inspection or cleaning opening 64 may be provided in the rear wall 14 of the housing 12 and such opening may normally be closed by a door 65. Other inspection or cleaning openings may, of course, be provided Where ever desired.

It is, of course, to be understood, that the above described oven may be manufactured in various shapes, sizes and forms and furthermore, suitable heat insulation will be provided to prevent undue loss of heat and maintain operating efliciency at a maximum.

In operation and starting with the furnace cold, the burners 52 will be ignited and will operate at full capacity to provide heated air to be circulated by the fan 24 through the treating chamber 20. When the temperature in the chamber reaches the desired value, coated materials, such as one or more wires 21 will be fed into the chamber 29 through the bottom opening 22 and the quantity of heated air flowing through the lowermost discharge passage 44 into the chamber 20 will be adjusted by the damper 47 in such a manner as to either entirely prevent or set at the desired value, the quantity of air flowing into the chamber 20 through the bottom opening 22. The heated air flowing from the lowermost discharge passage 44 serves to evaporate the solvents and other volatile components of the enamel or other coating on the coated materia s or wires 21 and the heated air flowing into the chamber 20 through the intermediate discharge passage 45 and uppermost discharge passage 46 as controlled by the damper 49 serves to counter-balance the stack effect or thermal head in the chamber 20 and to bake the coating to the desired hardness. The fume laden air or vapors are withdrawn from the treating chamber 20 through thepassage 54 into the firebox 5'1 and through the burners 52 until such vapors contact the catalytic incinerating unit 56. At this time, such unit operates to oxidize the solvents in the air and in so doing, to release additional heat into the air stream flowing from the incinerator unit 56 to the intake opening of the fan 24.

As the oven reaches the desired temperature, the rate of feeding of the coated materials to the treating chamber 20 is increased with the result that additional solvents are evaporated and since such solvents are also oxidized by the catalytic incinerator 56, the heat liberated thereby is increased to a point Where the entire heat requirement of the oven is supplied by the oxidation of solvents in the catalytic incinerator 56. During this process, the control means for the fuel supply to the burners 52 has operated in response to the temperature conditions in the treating chamber 25 and as the heat liberated by the incinerator 56 increases, the fuel supply to the burners 52 is automatically reduced until such burners are completely shutoff and the entire heat input for the oven is supplied by the incinerator unit 56.

Since under certain conditions, the heat liberated by the incinerator unit 5 6 be in excess of that required 6 by the oven, this may be compensated for by adjustment of the damper 59 controlling the flow of fresh air through the duct 58 to the inlet 25 of the fan 24 and by controlling the damper 61 in the exhaust duct to regulate the quantity of heated air exhausted from the oven. Since the fresh air inlet duct 58 is located downstream from the catalytic incinerator unit 56, no dilution of the vapors flowing therethrough will occur and such unit will operate at maximum efliciency and furthermore, since the exhaust duct 60 communicates with the discharge conduit from the fan 24, all air exhausted from the oven will be free of solvent or other fumes.

It is to be noted, that due to the Withdrawal of fume laden air from the chamber 20 through the passage 54 at the upper end of the chamber 20 and adjacent the-outlet opening 23 that there will be some infiltration of air through the top opening 23 thereby preventing flow of fume laden air through the opening 23 and obviously, such infiltrating air will not flow downwardly into the treating zone of the chamber 20, but will mingle with the air flowing through the passage 54 into the firebox 51.

It is, of course, to be understood, that any desired control circuit or mechanism may be utilized to control the operation of the exhaust damper motor 63 and the valve '53 controlling the fuel input to the burners 52. Also, if desired, the dampers 47 and 49 may be automatically controlled by any suitable conventional control circuit and mechanism, and one or more temperature responsive elements, not shown, maybe located at desired points in the air circulating passages or ducts or in the treating chamber 20.

The modified form of the invention shown in Fig. 3 difiers from that above described only as to the arrangement and operation of the dampers for the fresh air intake duct 58 and the exhaust duct 60 and the pivotal mounting of the catalytic element. The fresh air intake duct 58 is provided with a damper 66 and the exhaust duct 60 is provided with a damper 67. Dampers 66 and 67 are connected by a suitable linkage 68 which in turn is connected to a damper actuating motor 69 which may be of any desired type, but for convenience of illustration is shown as electrically operated. An actuating motor 70 operates the control valve 53 for controlling the supply of fuel to the burners 52, and the motor 69 connected through a suitable relay 71 and the motor 70 are connected to a proportioning temperature controller 72 which operates in response to a thermostat or temperature responsive element 73 disposed in the discharge duct 37 or at any other desired location in the oven.

In the operation of this form of the invention when starting the oven, it is assumed that the burners 52 will be operating at full capacity, and as the incinerator unit 5612 begins to liberate heat, this will be detected by the temperature responsive element 73 which through the proportioning controller 72 to the valve actuating motor 70 will gradually reduce the supply of fuel to the burners 52 until such time as these burners are completely shut down as a result of the entire heat requirement being supplied by the incinerator unit 56. At this time, control of the temperature conditions in the treating chamber 20 will be completely through the proportioning controller 72, the relay 71 and the damper actuating motor 69 which will actuate the dampers 66 and 67 in synchronism to control the intake of fresh air to the oven and the exhaust of fume free air therefrom. This system will operate to maintain the desired temperature conditions in the treating chamber 20,v even though the heat released by the incinerator unit 56 is in excess of the heat requirements in the treating chamber 20.

It will be noted that in Fig. 2 the catalytic fume incinerator 56 is mounted so as to prevent the by-pass of any of the heated air from coming from the chamber 20 and passing through the fire-box. In Fig. 3 the catalytic fume incinerator 56b is pivotally mounted so as to swing about'the axis'sd and'scat againsttheangle irons 84- 'portance and not mandatory. It is believed to be obvious that as the catalytic damper begins to open some of the fume-laden gases will continue to pass through thecatalyst'bed and here a floating control or an on-otf controller might well be employed.

Referring now to Fig; .4, in this modification the catalytic fume incinerator 56a extends partially across the passage between the fire-box and the inlet of the fan. The catalytic element 56a is mounted upon angle irons 81 and 82. The remaining cross-sectional area of such passage may be completely closed by a damper 80 or, if desired, the damper 80 may be opened fully so as to permit partial by-passing of the fume-laden gases.

In this arrangement the temperature controller is connected to the externally extended rod of the damper 80. During starting operations or even for continuous operation with light solvent loads having heatrelease insufiicient for the thermal demands of the oven, the damper 80 would be in a fully closed position. In this case the oven temperature would be maintained by means of the controller on the burner.' As higher solvent loads are experienced, that is'those beyond the thermal demands of the ovens, the burners v52 are reduced to pilot position and control is then maintained by thermostatically opening the by-pass damper. 80. Undernormal' fullflow conditions the pressure drop through the catalyst bed 56a is on the .order of 0.4" wg. As the damper assumes a partially open position, there will be a tendency for the air to bypass the'catalyst bed 56a or at least partially so that part of the air passes through the bed 56:: and heat is released for maintaining oven tem perature. At the same time the excess is by-passed 'to the re-circulating fan. On the next're-circulating pass any of the unconsumed gases will pass the burners 52, and they may well pass through the bed 56a instead of passing around it, The net effect of this form of the invention is a raising of the latent energy from the fumes throughout the oven, and the exhaust gases will carry out this excess latent energy. i l i It will be seen that by the above described invention there has been provided a relatively simple, yet highly efficient, heat 1 treating apparatus for coated materials which permits the movement'of such coated materials 'in a vertical path, thereby maintaining concentricity of the coating; and'by reason of the particular design the stack efiect or thermal head in the treating chamber is counter-balanced in such a manner that entrance of outside air at the bottom of the chamber is controlled and the discharge of fume laden air at the top of the chamber'is prevented. This arrangement serves to prevent dilution of the fume laden air, thereby maintaining the efiiciency'of operation of the catalytic incinerator unit and, furthermore, prevents the infiltration of relatively cold air into the treating zone of the treating chamber. For'this reason, condensation of the vaporized solvents with a consequent fire hazard and cleaning problem is prevented, and since the oven may be operated at slightly Thus, the oven 'willfalso have application in areas when air pollution is not a critical factor. 7

' It will be obvious to'those skilled in the art that various changes may be made inthe invention without departing from the spirit and scope thereof and therefore the invention is not limited by that which'is shown in the drawing and described in the specification, but only as indicated in the appended claims.

What is claimed is:

1. A catalytic're-circulating oven comprising a frame, a generally rectangular housing carried by said frame and having front, back, side, top and bottom Walls, a partition between said top and bottom walls spaced inwardly from said front wall to provide a vertically disposed treating chamber for receiving coated materials passing therethrough, an entrance opening at the bottom of said chamber for feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan in said housing havingv intake and discharge openings, a variable speed drive for said fan, a discharge conduit connected to the discharge opening of said fan, a portion of said conduit extending upwardly from adjacent the bottom of said chamber to a point above the midpoint thereof, partitions dividing said portion of said conduit into three ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for controlling the flow of air from said conduit to the first duct and lowermost first discharge passage'and to the second and third ducts, a second damper for controlling the relativeflow of air in said second and third ducts to the intermediate second discharge passage and to the upper third discharge passage whereby the relative flow of air into said chamber at vertically spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in the upper portion of said housing, burners disposed in said firebox adjacent the upper portion thereof, a passage between the upper portion of said chamber and said firebox and means to control the flow of vapors from said chamber into said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh'air inlet duct connected to said last named passage and-extending exteriorly of said housing, means for controlling the flow of air into said fresh air inlet duct, a catalytic vapor incinerator disposed in said firebox in the path of vapors flowing from said burners to said fan, automatically operated damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with theheat required in said chamber.

2. A catalytic re-circulating oven comprising a generally rectangular housing having front, back, side, top and bottom walls, a partition between said top and bottom walls spaced inwardly from said front Wall to provide a vertically disposed treating chamber for receiving coatedmaterials, passing therethrough, an entrance opening at the bottom of said chamber for the feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan in said housing having intake and discharge openings, means for driving said fan, a discharge conduit connected to the discharge opening of said fan, partitions dividing said conduit into'three ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for controlling the flow of air from said conduit to the first duct and lowermost first discharge passage and to the second and third ducts, a second damper for controlling the ass-1 erssaidhousing, burners disposed in saidfireb'ox,a passage between the upper portion of said chamber and said fire? box, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said last named passage and extending exteriorly of said housing, means for controlling the flo'w of air into said fresh air inlet duct, a catalytic vapor incinerator disposed in said housing in the path of vapors flowing from said burners to said fan, automatically operated damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with the heat required in said chamber.

3. A catalytic re-circulating oven comprising a generally rectangular housing having front, back, side, top and bot torn Walls, a partition between said top and bottom walls spaced inwardly from said front wall to provide a vertically disposed treating chamber for receiving coated materials passing therethrough, an entrance opening at the bottom of said chamber for the feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan having intake and discharge openings, means for driving said fan, a discharge conduit connected to the-discharge opening of said fan, partitions dividing said conduit into three ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for controlling the flow of air from said conduit to the first duct and lowermost first discharge passage and to the second and third ducts, a second damper for controlling the relative flow of air in said second and third ducts to the intermediate second discharge passage and to the upper third discharge passage whereby the relative flow of air into said chamber in vertically spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners disposed in s'aid firebox, a passage between the upper portion of said chamher and said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said last named passage and extending exteriorly of said housing, means for controlling the flow of air into said fresh air inlet duct, a catalytic'vapor incinerator disposed in said housing in the path of vapors flowing from said burners to said fan, automatically operated damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with the heat required in said chamber.

4. A catalytic re-circulating oven comprising a generally rectangular housing having front, back, side, top and bottom walls, a partition in said housing providing a vertically disposed treating chamber for receiving coated materials passing therethrough, an entrance opening at the bottom of said chamber for the feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan having intake and discharge openings, means for driving said fan, a discharge conduit connected to the discharge opening of said fan, partitions dividing said conduit into three ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for controlling the flow of air from said conduit to the first duct and lowermost first discharge passage and to the second and third ducts, a second damper for controlling the relative flow of air in said second and third ducts to the intermediate second discharge passage and do the upper third discharge passage whereby the relative flow of air into said chamber at vertically spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners disposed in said firebox, a passage between the upper portion of said chamber and said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said I' 16 last named passage and extending exteriorly of said lions? ing, means for controlling the flow of air into said fresh inletduct, a catalytic vapor incinerator disposed in said housing in the path of vapors flowing from said burners to said fan, automatically operated damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with the heat required in said chamber.

5. A catalytic re-ci'rculating oven comprising a housing, means in said housing providing a vertically disposed treating chamber for receiving coated materials passing therethrough, an entrance opening at the bottom of said cham-' her for the feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan having intake and dis-' charge openings, means for driving said fan, a dischargeconduit connected to the discharge opening of said fan, partitions dividing said conduit into three ducts termi nating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for con trolling the flo-w of air from said conduit to the first duct and lowermost first discharge passage and to the second and third duct, a second damper for controlling the relative flow of air in said second and third ducts to the inter mediate second discharge passage and to the upper third discharge passage whereby the relative flow of air into said chamber at vertically spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners disposed in said firebox, a passage be= tween the upper portion of said chamber and said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said last named passage and extending exteriorly of said housing, means for controlling the flow of air into said fresh air inlet duct, a catalytic vapor incinerator disposed in said housing in the path of vapors flowing from said burners tosaid fan, automatically operated damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with the heat required in said chamber.

6. A catalytic re-circulating oven comprising a housing, means in said housing providing a vertically disposed treating chamber for receiving coated materials passing therethrough, an entrance opening-at the bottom of said chamber for the feeding of said coated materials, an exit opening at the top of said chamber for the discharge of said coated materials, a circulating fan having intake and discharge openings, means for driving said fan, a discharge conduit connected to the discharge opening of said fan, partitions dividing said conduit into three ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a damper for controlling the fiow of air from said conduit to the first duct and lowermost first discharge passage and to the second and third ducts, a second damper for controlling the relative flow of air in said second and third ducts to the intermediate second discharge passage and to the upper third discharge passage whereby the relative flow of air into said chamber at vertically spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners disposed in said firebox, a passage between said chamber and said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said last named passage and extending exteriorly of said housing, means for controlling the flow of air into said fresh air inlet duct, a catalytic vapor incinerator disposed in 'said housing in the path of vapors flowing from said burners to said fan, damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the supply of fuel to said burners in accordance with the heat required insaidchambern .17. A catalytic re-circulating oven comprising a housing, means in saidhousing providingia vertically" disposed treating chamber for receiving coated materials passing therethrough, an entrance opening at the bottom of said chamber for the feeding of said coated materials, an exit opening at the top ofsaid chamber for the discharge of said coated'materials, a circulating fan having intake and discharge openings, means for driving said fan, a discharge conduit connected to the discharge opening of said fan, partitions dividing said conduit into a plurality of ducts terminating in vertically spaced downwardly directed discharge passages opening into said chamber, a

, damper for: controlling the'fiow of air from said conduit to the first duct and lowermost first discharge passage and to the remaining ducts, means for controlling the relative flow of air in the remaining ducts to the remaining discharge passages whereby the relative flow of air into said chamber at vertically spaced locations maybe con trolled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners disposed in said firebox, a passage be tween said chamber and said firebox, a passage connecting said firebox and the intake opening of said fan and a fresh air inlet duct connected to said last named passage and extending exteriorly of said housing, means for controlling the flow of air into said fresh air inlet duct, a

catalytic vapor incinerator disposed in said housing in the path of vapors flowing from said burners to said fan,

damper means for controlling the flow of air from said exhaust duct and automatic means for controlling the ber for the feeding of said coated materials, an exit opening in the top of said chamber for the discharge of said coated materials, a circulating fan having intake and discharge openings, means for driving said fan, a discharge conduit connected to the discharge opening of said fan, partitions dividing said discharge conduit into a 12 a plurality of'ducts terminating in-vertically'spaced down: wardly directed discharge passages opening into said chamber, a damper for controlling. the flow of air from said conduit to' said first duct and lowermost first discharge passage andto the remaining ducts, damper'means for-"controlling the relative flow of air in theremaining ducts to the remaining discharge passages whereby the relative flow of air into said chamber at vertically'spaced locations may be controlled, an exhaust duct connected to said conduit and extending exteriorly of said housing, a firebox in said housing, burners .disposed in said firebox, apassage between said chamber and said firebox, a passage connecting said firebox and said intakeopening of said fan and a fresh air inlet duct connected to said last-named: passage and extending exteriorly -of said housingfmeans .for controlling the flow of air into said fresh air inlet duct, damper means for controlling the flow of air from said exhaust duct, and automatic means for controlling the supply of fuel to said firebox in accordance with the heat supplied to said chamber.

9. An apparatus 'as defined in claim 8, in which said fresh air inlet duct and exhaust .duct are provided with automatically operated inter-connected dampers for controlling the intake and exhaust of air from said oven;

10."An apparatus as defined in claim 9, in which said inter-connected dampers and said fuel supply control means are connected in a control circuit operating in response to a temperature responsive element disposed in said conduit to control the supply of heated air to said chamber and to control the'supply of fuel to said burners.

11. An apparatus as defined in claim 9, in which said inter-connected dampers and said] fuel supply control means are connected in a control circuit operating in response to a temperature responsive element to control the supply of, heated air to said chamber and to control the supply .of fuel to said burners.

References Cited in the file of this patent vUNITED STATES PATENTS 1,755,755 Winder Apr. 22, 1930 2,133,330 Often Oct. 18, 1938 2,658,742 Suter et a1. Nov. 10, 1953 2,795,054 Bowen Iunell, 1957

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