US3070897A

US3070897A - Automatic oven air balancing system

Info

Publication number: US3070897A
Application number: US702120A
Authority: US
Inventors: Donald J Lowe
Original assignee: YOUNG BROTHERS CO
Current assignee: YOUNG BROTHERS CO
Priority date: 1957-12-11
Filing date: 1957-12-11
Publication date: 1963-01-01
Anticipated expiration: 1980-01-01

Description

5 Sheets-Sheet 1 Jan. 1, 1963 D. JA, LOWE AUTOMATIC ovEN AIR BALANc-ING SYSTEM Filed Dc. 11, 1957 ATTORNEYS Jan. l, 1963 D. J. LOWE 3,070,897

l AUTOMATIC OVEN AIR BALANCING SYSTEM Filed Dec. 11, 1957 5 Sheets-Sheet 2 I OPEN e e G I No VOLATILES I i e e e e e g i Pm'lAl. voLrlLEJcoNDITIoN g i INVENTOR. DONALD J. Lowa ATTORNEYS D. J. LOWE AUTOMATIC OVEN AIR BALANCING SYSTEM Jan. 1, 1963 5 Sheets-Sheet 5 I Filed Dec. 11, 1957 INVENTOR. DONALD J. LOWE ATTORNEYS Jan. 1, 1963 D. J. LowE AUTOMATIC OVEN AIR BALANCING SYSTEM 5 Sheets-Sheet 4 Filedv D ec. 1l, 195'?" T INVENTOR. DQNALD` J. |.owl-2l ATTORNEYS Jan. l, 1963 D. J. LowE 3,070,897

AUTOMATIC OVEN AIR BALNCING SYSTEM Filed' Dec. ll, 1957 5 Sheets-Sheet 5 j E l z s 3k z i Eig-B i I e s f# i I L i N A H 3g INVENTOR.

DONALD J. LOWE BY United States Patent O 3,070,897 AUTOMATIC OVEN AIR BALANCING SYSTEM Donald J. Lowe, Northfield Center, Ohio, assgnor t Young Brothers Company, Cleveland, Ohio, a corporation of Michigan Filed Dec. 11, 1957, Ser. No. 702,120 Claims. (Cl. 34-46) This invention relates to automatic control of the exhaust in an industrial oven of a type in which heated air is caused to ow over the work and at least a portion of such airis desirably recovered for recirculation.

The eiciency and economy of operation of such an oven is obviously affected by .the volume of warm air coming from the work which may thus be re-used, with of course due regard to the moisture content of the recovered air and, in many cases, to the character of the entrained vapor and gases where the process carried out involves more than the simple extraction of water from the work. For example, resinous coatings applied to tin plates are baked in metal decorating ovens and such coatings usually comprise volatile solvents driven olf in the heating and resulting in a flammable exhaust. Safety specifications require that the atmosphere in such an oven :be maintained below a particular level of concentration of the volatile gas and, accordingly, the consideration of recirculation for maximum economy is limited in this respect, as Well as by the usual effect of the moisture content on the efficiency of drying.

The amount of air which is exhausted is known as the exhaust overlap and, in ovens designed for treating decorated metal particularly, the prior practice has .been to size the exhaust overlap to satisfy the volatile gas concentration limit for the maximum solvent load which may be encountered in the oven. Accordingly, more make-up air than is needed is taken in during operation at lesser loads, with a corresponding excess in the fuel consumed as compared yto operation with that exhaust and recirculation condition actually effective to provide a safe and proper atmosphere for the particular load being handled.

It is accordingly a primary object of my invention to provide a variable exhaust system forrsuch an oven in which a .portion of the ow from the work is variably divided between recirculation and exhaust automatically in accordance with regulation of the fresh air supply and venting of the oven, whereby oven balance or pres-v sure can be maintained with the degree of recirculation controlled to afford the most economical and efficient condition thereof.

Another object is to provide such a variable exhaust control, including automatically regulated recirculation, in which the system is responsive to the presence and concentration of combustible matter in the oven atmosphere and effective to hold the level thereof below a predetermined safe limit.

It is also an object of the invention to provide practical and reliable structure constituting an oven control characterized by the operational features noted in `the above.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the lforegoing and related ends, the invention, then, comprisesthe features hereinafter fully described and particularly pointed out inv the claims, the following description and the annexed drawings setting forth in detail certain illustrative emq bodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Patented Jan. 1, 1963 ICC In said annexed drawings:

FIG. l is a side elevational view, partly in section, of the first operative zone of a continuous conveyor oven equipped with control means in accordance with the present invention;

FIG. 2 is a transverse sectional view taken on the plane of the line 2-2 in FIG. l;

FIG. 3 is a semi-diagrammatic view illustrating the major components of such system;

FIG. 4 is a table which illustrates diagrammatically various conditions of adjustment of the system;

FIG. 5 is a fragmentary elevational view showing the control means used with the exhaust damper of the system;

FIG. 6 is a sectional view taken on the plane of the line 6-6 in FIG. 5;

FIG. 7 is a further section taken along the line 7-7 in FIG. 6; and

FIG. 8 is a wiring diagram showing the electric circuits used for automatic control of the system operation.

Referring now to the drawings in detail, the metal decorating oven shown partially in FIG. 1-conventionally comprises a .tunnel housing 1 through which an endless wicket-type conveyor, designated generally at 2 and driven by electric motor 3, carries the tin plates for baking of the coatings thereon. Since the volatile solvents in such coatings are driven off in the iirst heating zone 4 of the oven, and my new control is concerned with exhaust of the same, only this initial zone has been illustrated, the sheets or plates being loaded on the wickets at the right end and being moved through the oven in the direction of the arrow. For obvious convenience and clarity, the conveyor is not fully shown.

The source of heat for this zone is a burner S in which by an electric motor 9, connected to the shaft 10 thereof through a belt 11, and propels the heated air -from the burner downwardly through a supply boot 12 which extends along the outer side of the oven housing to a At 'i such region, the boot is connected to a distributor pan region below the upper course of the conveyor.

13 in the oven which is longitudinally enlarged and bridged transversely at its upper periphery by a number of cross pieces 14 in spaced apart parallel relation. The

separation of such pieces of course forms transverse slots through which lthe heated air currents are discharged' from the pan or manifold for flow upwardly through the conveyor bearing the metal sheets and hence across the coated surfaces of the latter. I

A recirculatin'g duct 15 of inverted U-shape, as shown most clearly in FIG. 2, extends along the top portion of the oven heating chamber from a point adjacent the end wall 16, above the entrance hood 17, to a point beneath the burner 5 where it terminates in a slightly enlarged open end section 18. Adjacent the end wall 16, the duct is provided with a top opening 19 and above the same the oven has a vertical extension 20 leading to an exhaust Ablower 21. The latter is driven by an electric motor 22 through a belt drive 23 to the shaft 24 of the same and creates a forced draft upwardly through a suitable stack, a portion of which is shown at 25.

As indicated, such oven construction is generally conventional and it will be understood that there are successive heating zones for carrying out the complete baking process. The recirculating duct 15 does not extend over the complete length of the .lower supply manifold 13 but terminates short of the inner end of the latter, whereby the air currents discharged over a predetermined extent at this end are ordinarily unimpeded in return flow to the burner 5.` Such flow must .proceed through a series of transverse ports 26 above the conveyor which yare adjustable by virtue of being defined by slide members 27.. Over the remaining, and greater, length of this first heating zone the air proceeding from the work ows into the rie-circulating duct through slots formed by longitudinally spaced apart cross members I28 bridging the open bottom of the duct. Such members are hollow, for a purpose to be described.

In order to provide a variable exhaust, this oven is equipped with an exhaust damper 29 in its vertical end portion 20 and a fresh air damper 30 in the intake 6 of the burner, these two dampers of course being intended to vary the intake and exhaust in relation to one another. To maintain proper pressure or balance in the oven with such variable exhaust, I provide a plurality of overlap dampers 31-36, respectively, in the recirculating duct 15, ywith the damper 31 of such series being Alocated at and adapted to close the inner end 18 of the duct beneath the burner chamber and the other dampers spaced longitudinally along the duct and capable, when moved to vertical closed condition, of variably dividing the same longitudinally to regulate the exhaust overlap or the division of the air flow from the duct between the burner and the exhaust stack 25. The effective length of the duct is determined by the dampers 31, at one end, and 36, at the other end. I have shown six such overlap dampers, but it will be understood that this number can be varied as required to meet best particular conditions of operation .and dimensions of the oven.

For convenience of illustration, the fresh air damper 30 is shown in the schematic diagram of FIG. 3 on a horizontal shaft so as to correspond with the other control dampers which are actually pivoted on horizontal axes. The damper arrangement shown in FIGS. l and 3 and in block A of the FIG. 4 table is thus the same and provides one condition of operation wherein the intake and exhaust dampers are fully open, the innermost overlap damper 31 is closed, and theremaining overlap dampers 32-36 are open. In such condition, it will be clear that. all the air flowing into the recirculating duct 15 from the work is exhausted, i.e., that there is maximum exhaust overlap. Block B of the FIG. 4 table illustrates the damper positions at the opposite lim'it, for maximum recirculation, with the intake and exhaust dampers being completely closed, overlap damper` 36 at the otherA end of the recirculating duct closed,` and the remaining overlap dampers 31-35 open. Block C ofthe table illustratesan intermediate condition in which thevintake and exhaust dampers are partially and cor- 4respondingly open, overlap damper 34 is closed, and they In this last noted` other overlap dampers are open. intermediate condition, the closed overlapv damper 34 forms a longitudinal divider in the duct 15, with the air entering the same at the right of such damper being exhausted and air in the duct to the left of the damper being returned to the burner 5 for recirculation. Other intermediate conditions are established by closing dif-v ferent ones of the overlap dampers to vary such longitudinal division and hence proportioning of the air coming from the work lbetween exhaust and recirculation.

By properly relating the division effected by the over-1 lap dampers to the settings of the intake and exhaust dampers, maximum recirculation permissible for safe and eicient operation can be had with different loads in the oven. Operation of the system is desirably automatic and in the preferred embodiment of the invention, the concentration of volatile gas in the exhaust is used as the condition to which the system operation responds.

In such embodiment,l the fresh air damper 30 is op.

erated by a proportional air motor 37, such as a Taylor lever motor, adapted to be connected to a controlled air -supply through a three-way solenoid air valve AVI (c g. an Asco valve) operative as a safety dev-ice in a manner to be described hereinbelow, said valve having an inlet 38 for connection to the air supply of the motor 37 and an exhaust 39. Exhaust damper 29 is .moved by a similar air motor 40 preferably connected to the same controlled source as motor 37, a further safety valve AVZ included in like association with the motor 40. rPhe overlap dampers are actuated by spning-return air cylinders il-d6 controlled by solenoid operated air valves AV4-AV9, with the usual supply and exhaust connections. The air cylinders t1-46 and air valves AV4-AV9 are constructed and operate in identical manner, the air cylinder 46 and the air valve AVlt being cross sectioned in FIG. 8 for illustrative purposes. The air cylinders and air valves are conventional and form no part of the instant invention. Referring briefly to FIG. 8 it will be seen that when the solenoid actuated valve AV4- is deenergized, the supply inlet to said valve is closed whereby damper 36 is under the control of the spring in the air cylinder 46. When the solenoid in valve AV4 is energized, the inlet port is uncovered thereby allowing the pressurized air to flow through said valve into the bottom of the air cylinder 46, thus rotating the damper .36. The intake and

exhaust dampers

29 and 30, respectively, are thus proportionally adjustable by their air motors, whereas the overlap dampers operate between full open and closed positions. With regard to the overlap dampers, the spring of cylinder 41 holds damper-3l normally closed and the other such dampers are spring-biased open by their respective operating cylinders.

Operation of the overlap dampers can be made dependent on the setting of either of the exhaust and fresh air dampers, and I have illustrated an arrangement whereby movement of the former determines such operation. As shown in FIGS. 5 to 7, the shaft 47 on which the exhaust damper 29 is mounted projects through a bearing 48 held in the rear wall 49 of a box-like housing 50 secured to the outer wall 51 of the oven, the shaft extending through this housing and outwardly thereof being connected to the arm 52 of the air motor 40 supported on such wall by a bracket 53. Within the housing 50, a cam plate 54 is fixed onthe shaft and a series of limit switches Sl-SS are mounted on brackets 55 holding the actuators of these switches adjacent the periphery of the cam plate. The latter is divided into quadrants at alternating radii, whereby there are two raised cam surfaces 56 diametrically opposite and each approximately in extent; the remaining intermediatedepressed surfaces 57 provide loss of contact between the plate and the switch actuators. Switch S2 is spaced with its actuator 120 from top center, switch S4 at 150, switch S1 at 285, switch S3 at 315, and switch S5 at 345. The cam is here shown in its position corresponding to the exhaust damper 29 in its normal full open position and it will be clear that turning of the damper causes actuation of the switches individually in sequence.

The movement of the intake and exhaust dampers is controlled by an exhaust gas analyzer and control assembly of commercially available type, such as made by Davis Instruments, such assembly being operative to measure the combustibility of the exhaust gas, and to provide a signal proportional to the volatile gas or vapor present. The analyzer and control assembly includes an analyzer which isindicated in the wiring diagram of FIG. 8 by reference numeral 58, the same being connected between conductors L1 and L2 of an ordinary 1l() volt supply through a manual switch 59. The usual alarm horn 60 for emergency condition, also provided by Davis Instruments, is shown connected throughA a normally open switch 61 and an interlock relay R is connected between L1 and L2 through switch 59 and through a normally closed switch 62.

The analyzer and control assembly supplied by Davis Instruments also includes a detector D, over which gas is passed and burned on a platinum wire, the temperature thereof being measured by a thermocouple T to provide the control signal. The detector unit D of the analyzer assembly is preferably located in an appropriate location in the oven to sample the atmosphere in the same, for example, in the exhaust extension 20 as shown in FIG. l. The control signal from the thermocouple T is applied to a proportioning potentiometer-type pneumatic controller M, also supplied by Davis Instruments and forming part of the analyzer and control assembly. This controller is connected, as shown, in the supply line 38 to the

air motors

37 and 40, the branched outlet from the controller leading to the two valves AV1 and AV2. The controller M is well known in the art and comprises a pressure regulating valve which is responsive to the control signal produced by the thermocouple T. The pressure regulating valve regulates the pressure of air supplied to the

motors

37 and 40 through supply line 38. Such regulation results in a variable positioning of

dampers

30 and 29, respectively, such variable positioning depending as will be apparent, on the pressure of the air supplied to the

motors

37 and 40. As clearly set forth above, the analyzer and control assembly is commercially obtainable from Davis Instruments and thus forms no part of the instant invention. I have accordingly indicated such conventional structure in FIG. 8 by enclosing the same within a dotted line enclosure.

As will be understood, when the combustible gas in the exhaust increases, the analyzer 58, detector D, and thermocouple T will respond to such increase by way of changing the control signal to the controller M whereby the pressure regulating valve therein effects a decrease in the pressure of air flowing therethrough, thus moving

dampers

29 and 30 toward fully open position.

The safety valves AV1 and AV2 serve only as safety devices and function, in the event of an electric power failure, to cause the

air motors

37 and 40, respectively, to move the

dampers

30 and 29 to their full open position whereby gas is completely exhausted from the system. There is thus provided a fail safe feature which insures the exhausting of all gases in the event of power failure, thereby eliminating the possibility of ignition of any combustible gases. It should also be noted that, as set forth above, the springs of the overlap damper cylinders 41 to 46, in the non-actuated condition of such cylinders move these dampers to the positions shown in FIG. 3, so thatv maximum exhaust overlap obtains upon failure of the power supply. During normal operation of the system, i.e., in the presence of a power supply, the supply of air ows directly through valves AVI and AV2 to the

motors

37 and 40 respectively, the latter valves not affecting theA tiow in any manner. Under such conditions, the air supply to the

air motors

37 and 40 is under the control of' the regulating valve of controller M, which functions as explained above. Referring to the operation of valves AV4-AV9, of which valve AV4 has been selected for illustrative purposes l(FIG. 8), when valve AV4 is in a deenergized state, the' piston rod and heads move downwardly due to gravity, the downward movement being cushioned by the spring mounted in the bottom of the cylinder, whereby the supply line 38' is closed and the exhaust line 39 open. When the solenoid is actuated, the pistons in the cylinder of AV4 move upwardly thereby closing the exhaust line and opening the supply line. Air is thus supplied to the bottom of the piston in cylinder 46 thereby forcing the piston rod upwardly, thereby pivoting damper 36 about its stationary, horizontal axis and closing said damper. When valve AV4 is deenergized, the spring in cylinder 46 will force the air below the piston outwardly of the cylinder 46 and through the exhaust line in valve AV4.

, The Valves AV4-AV9 which control the several overlap dampers are connected in parallel between the supply lines L1 and L2 through the main manual switch 59 and the several limit switches S1-S5. Each limit switch, except switch S1, as illustrated in FIG. 8, is operative in two of the valve circuits simultaneously to open one and close the other. Switch S1 is either opened or closed in both the branch circuits of valves AV4 and AVS simultaneously.

In the open position of dampers 32-36 and closed position of damper 31, whereat full exhaust occurs, switch S1 is closed in the branch circuits of control valve AV4 and control valve AVS; switch S2 is closed in the circuit of valve AVS, and open in the circuit of control valve AV6; switches S3 and S4 are similarly arranged and operative in the succeeding valve circuits, being open in one circuit and closed in another. The last switch S5 during full exhaust is closed in the circuit of valve AV8 and open in the circuit of control valve AV9. Such overlapping connections provide sequential operation of the dampers in a manner to be described.

When the main switch 59 is moved to on position, this position being shown in the FIG. 8 diagram, and the analyzer does not detect any combustible gas in the exhaust, the controller M causes the

motors

37 and 40 to move the inlet and

exhaust dampers

30 and 29, respectively, to fully closed position. The damper 29, in moving from a fully open to a fully closed position, rotates in a counterclockwise direction about its horizontal axis, as depicted in FIG. 3. This counterclockwise rotation, shown by the solid line arrow in FIG. 3, will close, in sequence, switches S5, S4, S3, S2 and S1 through raised cam surfaces 56 of cam plate S4, referring to FIG. 6. At the end of the counterclockwise rotation of damper 29, the overlap damper 31 will be open and the damper 36 will be closed, through energization of valves AV9 and AV4, respectively, and the dampers 32-35 will be in their open position, the valves AV8, AV7, AV6 and AVS, respectively, having been first energized and then deenergized during the 90 counterclockwise rotative movement of damper 29. This fully closed condition of

dampers

29 and 30 is illustrated in block B of FIG. 4. When

dampers

29 and 30 are fully closed the entire amount of the exhaust gas is recirculated.

It will be understood that if the analyzer and control assembly detects an excess of volatiles in the exhaust before the

dampers

29 and 30 reach their fully closed position, controller M will cause the

dampers

29 and 30, through the

air motors

37 and 40, and, more specifically, through the pressure regulating valve in controller M, to remain in a partially and variably open position as long as the excess volatiles are present in the exhaust, such a partially open position being shown in FIG. 4C. As shown therein, when the

dampers

29 and 30 are in a partially open position, one of the intermediate overlap dampers will be cosed, damper 34 in block C of FIG. 4 being shown in such closed position. It will be apparent that the particular intermediate damper in closed position will depend upon the degree of rotation of damper 29, as shown in FIG. 3. The closing of damper 34 indicates that damper 29, and cam plate 54 operatively connected thereto, will have rotated to a position wherein cam surface 56 has closed switch S2 in the branch circuit of valve AV6 thereby energizing valve AV6. In this partially open position of

dampers

29 and 30 it will be understood that a portion of the exhaust gas is caused to recirculate subsequent to combination thereof with fresh air, and the remaining portion of the exhaust gas is exhausted.

If, after the damper 29 has reached a closed position whereby maximum recirculation is effected, the analyzer and control assembly senses an excess of volatiles in the recirculated air, the controller M, which is responsive to the thermocouple T, moves

dampers

29 and 30 to a partially open position, in a clockwise direction as shown by the dotted line arrow in FIG. 3, thereby exhausting a portion of the air entering the circulation duct 15 and diluting with fresh air the remaining, recirculated air portion, as explained above. Movement of the

dampers

29 and 30, through the

air motors

40 and 37, respectively, via the controller M, as stated above, is in a clockwise direction from their closed position. As the damper 29 rotates in a clockwise direction, the switches S1, S2, S3, S4 and S5, in sequence and in that order, come out of contact with the raised cam surfaces 56, as will be apparent from FIG. 6, such clockwise movement being shown therein by a dotted, curved arrow line. Thus, when switch S1 comes out of contact with cam surface 56, the circuit through control valve AV4 is closed thereby returning the damper 36 to its horizontal position. The closing of switch S1 also completes the branch circuit through the control valve AVS whereby the same is energized to move the overlap damper 35 to a closed position, whereby a portion of the air entering the recirculating duct is exhausted. When switch SZ is opened, damper 35 assumes its open, horizontal position and damper 34 becomes closed, whereby a greater proportion of air entering the recirculating duct is exhausted. The operation proceeds in this manner until the maximum exhaust condition is reached. At maximum exhaust, as will be understood, the exhaust gas is completely exhausted from the system and fresh air is supplied to said system through the air inlet opening 6. It will be understood that if the proper volatile content of the air can be obtained with partial exhaust and partial dilution with fresh air, the damper 29 will not reach the vertical, bock A, full exhaust FIG. 4 position but will assume the block C, FIG. 4 position and remain there until the volatile content of the air either increases or decreases, whereupon controller M will cause the

air motors

37 and 40 to correspondingly move the

dampers

30 and 29, respectively, in the proper direct'on to achieve optimum recirculation and exhaust conditions.

It is preferable that the oven Ibe provided with means precluding condensation of vapor on the surfaces of the recirculating duct assembly, and for such purpose, the duct walls are spaced from the oven walls as `shown in FIG. 2. Heated air can thereby circulate about the outer surface of the duct to prevent condensation of solvent in the exhaust thereon. Furthermore, the hollow cross members 2S are connected at their ends to two longitudinally extending side ducts ed and have a series of apertures 65 along the tops of the same. Duets 64 are connected through conduits 66 to an auxiliary gas burner 67 (FIG. 1) for circulation of heated air currents through the cross pieces, and two further ducts 68 lead from the burner 67 to the space betweenthe oven and recirculating duct near the work-entering endof. the roven where maximum solvent evaporation takes place, it being clear from FIG. 2 that the topand side walls of the recirculating duct are spaced inwardly of the oven.

It will accordingly be seen that the construction illustrated and described provides return of a relatively fixed, but adjustable, amount of the ow proceeding from the work zone to the furnace or heat source at the inner end of the same where there is in normal operation negligible evaporation of volatile matter. Likewise independent of the recirculating ductjmeans, a certain amount of the flow is exhausted at the work entrance end, the high evaporation area, under control of the exhaust damper. The latter and the fresh air damper are thus regulable to establish various exhaust settings for the oven.

The remaining major portion of the ow leaving the work enters the recirculating duct means to afford control over the same, i.e., in the division thereof between the burner 5 and the exhaust, and such control is tied to the regulation of the oven exhaust setting. In such manner, the system provides a variable exhaust with automatically related variation in the degree of recirculation to maintain balance of the oven air, and by making the exhaust adjustment responsive to the combustibility of the oven gases, as disclosed, it is possible to meet all safety requirements of the nature discussed without excessive exhaust E overlap and without the excess consumption of fuel resulting from the same.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I, therefore, particularly point out and distinctly claim as my invention:

l. An oven comprising walls defining a work-receiving chamber, means for discharging heated air in a lower por.- tion of said chamber for ow upwardly therethrough, a collector duct in an upper portion of the chamber having top and side walls in spaced relation to the chamber Walls, whereby oven air is free to circulate about said duct, the bottom of the duct being partially closed by a series of transversely extending members spaced-apart to form inlets for the entry of air to the duct, said members being hollow, a source of heated air currents, and conduit means connecting said. members to said source for flow of heated air through the former.

2. An oven as set forth in claim l characterized further in that such hollow members are provided with apertures for discharge of the heated air supplied to the same into the collector duct.

3. An oven comprising Walls defining a work-receiving chamber, a heat source, means for flowing heated air from said heat source upwardly through said work-receiving chamber, vent means for exhausting air from the chamber, an elongated collector duct means in an upper portion of said chamber and open at the bottom for entry of air thereinto, said duct means at one end communicating with said heat source and at its other end with said vent means, barrier means transversely within the duct means intermediate the ends thereof, said barrier means forming a transverse partition in the duct means to divide the ow of said heated air entering the same between the heat source for recirculation and the vent means for exhaust, and means for adjusting the barrier means to vary the effective longitudinal position of the transverse partition formed by the same in the duct means, thereby to provide different degreesof recirculation and exhaust of the air which enters the duct means.

4. An oven as set forth in claim 3 wherein said barrier means comprises a series of dampers in longitudinally spacedrelation within the duct means, said dampers being selectively movable by said barrier adjusting means lfrom a horizontal open position to a vertical closed position and return so that only one damper at any time is vertical, thel others being horizontal, whereby the flow of air entering the duct means is divided between recirculation and exhaust.

5. An oven comprising walls defining a work-receiving chamber, aheat source, an adjustable fresh air intake for said heat source, means for owing heatedair from said heat source upwardly through said work-receiving chamber, adjustable vent means for exhausting air from the chamber, collector duct means in an upper portion of.

said chamber and open at the bottom for entry of air thereinto, said duct means at one end communicating with said heat source and at its other end with said vent means, regulating means for adjusting said fresh air intake and said vent means to establish different exhaust settings for the chamber, barrier means transversely within the duct means intermediate the ends thereof, said barrier means 4forming a transverse partition in the duct means -rtoV divide the flow of air entering the same between the heat source for recirculation and the vent means for exhaust, barrier-adjusting means for varying the effective longitudinal position formed by the barrier means in the duct means, thereby to provide different degrees of recirculation and exhaust of the said heated air which enters the duct'means, and control means for operating said barrier-adjusting means to increase the amount of air proceeding from the `ductmeansto .the vent rneanszwi-thl increase in the combustible mixture in Ithe exhaust of the chamber.

6. An oven as set forth in claim wherein said barrier means comprises a series of dampers in longitudinally spaced relation within the duct means, said dampers being selectively movable by said barrier adjusting means from a horizontal open position to a vertical closed posi- -tion and return so that only one damper at any time is vertical, the others being horizontal.

7. An oven comprising walls defining a work-receiving chamber, a heat source, means for flowing heated air from said heat source upwardly through said work-receiving chamber, means for returning a first portion of the heated air flow through the chamber to the heat source for recirculation, vent means for exhausting air from the chamber, means for directing a second portion of the heated air flow through the chamber substantially directly to the vent means for exhaust thereof, collector duct means in an upper portion of the chamber and open at the bottom for entry of the remaining portion of the ow, said duct means at one end communicating with said heat source and at its other end with said vent means, barrier means transversely within the duct means intermediate the ends thereof, said barrier means forming a transverse partition in the duct means to divide said remaining portion of the ow between the heat source for recirculation and the vent means for exhaust, and means for adjusting Ithe barrier means to vary the effective longitudinal position of the transverse partition formed by the same in the duct means, thereby to provide different degrees of recirculation and exhaust of the remaining portion of the ow which enters the duct means.

8. An oven comprising walls defining an elongated work-receiving chamber, conveyor means for carrying work longitudinally through said chamber, a heat source, means for owing heated air from said heat source upwardly through the chamber, a vent for exhausting air from the chamber, a duct extending along the interior of the chamber above the conveyor means, said duct being open at the bottom for said heated air flow into the same, with the duct at one end communicating with the heat source and at its other end with said vent, barrier means within the duct forming a transverse partition in the same, so that said heated air entering the duct at the same side of the barrier means as the end of the duct communicating with the heat source proceeds from the duct to said source and said heated air entering the duct at the other side of the barrier means proceeds to said vent, the flow of air which enters the duet thereby being divided between recirculation and exhaust, and means for adjusting the effective longitudinal position of the barrier means to vary .the division of the said heated air ow which enters the duct between the heat source and the vent.

9. An oven comprising walls defining an elongated work-receiving chamber having an entrance for the work at one end and an exit therefor `at the other end, conveyor means for carrying work longitudinally through the chamber from the entrance to the exit of the same,

a heat source, means for discharging heated air from said source in the chamber beneath the conveyor means for upward How through the chamber, a vent for the chamber adjacent the entrance end of the same, a collector duct extending along the interior of the chamber above the conveyor means and being open at the bottom for entry of said heated air to the same, said duct communicating at one of its ends with the heat source and at its other end with the vent, means for conducting a portion of the upward flow of said heated air adjacent the entrance end of the chamber substantially directly to the vent, means for conducting another portion of the upward flow to the heat source from an inner region of the chamber independently of the duct, the remaining portion of the flow entering the duct, barrier means in the duct forming a transverse partition therein to divide the duct into first and second longitudinal sections respectively communicating at the duct ends with the vent and the heat source, and means for shifting the effective longitudinal position of the barrier means in the duct to vary the relative size of said first and second sections thereof.

10. An oven for the heat treatment of 'work the heating of which causes volatiles to be released, comprising walls defining a work-receiving chamber, a heat source, means for liowing heating air from said heat source upwardly through said work-receiving chamber, vent means for exhausting air from the chamber, collector duct means in an upper portion of said chamber and open at the bottom for entry of air thereinto, said duct means at one end communicating with said heat source and at its other end with said vent means, barrier means transversely within the duct means intermediate the ends thereof, said barrier means forming a transverse partition in the duct means to divide the flow of air entering the same between the heat source for recirculation and the vent means for exhaust, barrier-adjusting means for shifting the effective longitudinal position of the barrier means in the duct means to provide different degrees of recirculation and exhaust of the air which enters the duct means, means for measuring the concentration of volatiles in the ow through the vent means, and control means responsive to said measuring means for operating the barrieradjusting means to increase and decrease the exhaust from the duct means respectively with increase and decrease in the thus measured concentration of volatiles.

References Cited in the le of this patent UNITED STATES PATENTS 1,431,145 Bolling Oct. 10, 1922 1,779,569 Thompson Oct. 28, 1930 1,779,622 Drelein Oct. 28, 1930 1,888,573 Sadwith Nov. 22, 1932 2,073,825 Beck et al. Mar. 16, 1937 2,134,906 Byron Nov. 1, 1938 2,135,512 Holven Nov. 8, 1938 2,671,969 Mayer Mar. 16, 1954 2,850,086 Sanscrainte Sept. 2, 1958

Claims

5. AN OVEN COMPRISING WALLS DEFINING A WORK-RECEIVING CHAMBER, A HEAT SOURCE, AN ADJUSTABLE FRESH AIR INTAKE FOR SAID HEAT SOURCE, MEANS FOR FLOWING HEATED AIR FROM SAID HEAT SOURCE UPWARDLY THROUGH SAID WORK-RECEIVING CHAMBER, ADJUSTABLE VENT MEANS FOR EXHAUSTING AIR FROM THE CHAMBER, COLLECTOR DUCT MEANS IN AN UPPER PORTION OF SAID CHAMBER AND OPEN AT THE BOTTOM FOR ENTRY OF AIR THEREINTO, SAID DUCT MEANS AT ONE END COMMUNICATING WITH SAID HEAT SOURCE AND AT ITS OTHER END WITH SAID VENT MEANS, REGULATING MEANS FOR ADJUSTING SAID FRESH AIR INTAKE AND SAID VENT MEANS TO ESTABLISH DIFFERENT EXHAUST SETTINGS FOR THE CHAMBER, BARRIER MEANS TRANSVERSELY WITHIN THE DUCT MEANS INTERMEDIATE THE ENDS THEREOF, SAID BARRIER MEANS FORMING A TRANSVERSE PARTITION IN THE DUCT MEANS TO DIVIDE THE FLOW OF AIR ENTERING THE SAME BETWEEN THE HEAT SOURCE FOR RECIRCULATION AND THE VENT MEANS FOR EXHAUST, BARRIER-ADJUSTING MEANS FOR VARYING THE EFFECTIVE LONGITUDINAL POSITION FORMED BY THE BARRIER MEANS IN THE DUCT MEANS, THEREBY TO PROVIDE DIFFERENT DEGREES OF RECIRCULATION AND EXHAUST OF THE SAID HEATED AIR WHICH ENTERS THE DUCT MEANS, AND CONTROL MEANS FOR OPERATING SAID BARRIER-ADJUSTING MEANS TO INCREASE THE AMOUNT OF AIR PROCEEDING FROM THE DUCT MEANS TO THE VENT MEANS WITH INCREASE IN THE COMBUSTIBLE MIXTURE IN THE EXHAUST OF THE CHAMBER.