US2752147A - Metallurgical furnace and method of treatment of work - Google Patents

Description

June 26, 1956 w. BESSELMAN EI'AL 2,752,147

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21, 1950 4 Sheets-Sheet 1 g Q INVENTORS b WAYNE LEO BESSELMAN t JAMES HENRY SOMERSET 5 GUSTAVE M. TAUBER W ZMM ATTO R N EYS June 26, 1956 w. L. BESSELMAN EI'AL 2,752,147

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21, 1950 4 sheets sheet 3 Controller L 63 L, L2

60 Inlet 56 EAux.|n|et E V V 52 A 76 2 77 58 65 Motor B Pump 6 Furnace P as i 33 31 INVENTORS. WAYNE LEO BESSELMAN JAMES HENRY SOMERSET GUSTAVE M. TAUBER June 26, 1956- w. L. BESSELMAN ETAL 2,

METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Filed Dec. 21, 1950 4 Sheets-Sheet 4 I N VEN TORS' WAYNE LEO BESSELMAN JAMES HENRY SOMERSET GUSTAVE M. TAUBER ATTORNEYS United States l' atent F METALLURGICAL FURNACE AND METHOD OF TREATMENT OF WORK Wayne Leo Besselman, Philadelphia, James Henry Somerset, Glenside, and Gustave M. Tauber, Phiiadeiphia, Pa., assignors to Leeds and Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Application December 21, 1950, Serial No. 201,906

14 Claims. (Cl. 266-4) This invention relates to methods of and apparatus for heat-treating work and is particularly applicable where it is desired to maintain the work under atmosphere control both during, and after completion of, the heating part of the cycle.

The present invention is particularly applicable to annealing, normalizing, hardening, case carburizing, carbon restoration, and to homogeneous carburizing, and the heat-treating apparatus has the capability of treating Work over the full range of normal heat-treating temperatures heretofore utilized.

Heretofore, efforts have been made to prevent formation of oxide or scale on the surfaces during the heat treatment of the work. To this end it has been proposed that during the heating of the work, a non-oxidizing atmosphere be maintained, as for example one with a carbon content, and that such protective atmosphere further be maintained during transfer of the work from the heating chamber to the quenching chamber. However, prior to the invention made by one of applicants and his co-inventor, United States Letters Patent No. 2,541,857, entitled Control of Constituent-Potentials, continuous control of the constituent-potential within a heating chamber had not been satisfactorily attained. Advantage is taken in the present invention of certain features of said joint invention disclosed in said patent application to the end that there is not only achieved uniformity of atmosphere within the heating chamber as regards the transference of a constituent thereof to and from the work, but also an atmosphere of known and predetermined composition is maintained within a vestibule or loading chamber associated with the heating chamber, control of said atmosphere within the vestibule being regulated by the constituent-controlling means of the heating chamber.

Further in accordance with the present invention, whenever a door of the heating chamber is opened, there is established an auxiliary supply to the heating chamber of constituent material which compensates for any dilution of the atmosphere of the heating chamber; but the introduction of the added constituent material may not increase the constituent-potential of the furnace atmosphere materially above its preselected value since the constituent-controlling means acts to decrease the supply thereof as soon as the constituent-potential within the heating chamber tends to rise above its selected value.

After completion of the heating step of the heat-treating cycle, the work is withdrawn through an open door of the chamber into the vestibule or discharge chamber without encountering a change in the character of the atmosphere within the vestibule, which is solely dependent upon that of the heating chamber. The work is automatically brought to rest on an elevator in position to be directly lowered into a quench tank. Where air-temperature quenching is desired, the elevator need not be used, but where oil or other liquid quenching is desired, the work is immediately lowered to a predetermined level where the elevator platform cooperates with stationary structure 2,752,147 Patented June 26, 1956 to localize the flow of the quenching liquid in the region of the work. More particularly, a circulating pump is provided having one connection on one side of the platform support and the other connection on the opposite side, preferably the suction side of the pump being below the stationary work support for positive forced circulation of quenching liquid intimately about the work uniformly to lower the temperature thereof at the desired rate.

Further in accordance with the invention, there is provided a metallurgical furnace of rugged construction of relatively simple design having great flexibility in its operation and applications, and which has many features which may be usefully employed with and without other features thereof.

For further objects and advantages of the invention, reference should be had to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a side elevation partly in section of a typical metallurgical furnace embodying the invention, with certain associated apparatus omitted;

Fig. 2 is a front elevation of the manually operable control valve and mechanically interlocking actuating elements thereof;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1;

Fig. 4 diagrammatically illustrates in one position a manually operable control valve and associated elements of the furnace;

Fig. 5 diagrammatically illustrates the control valve of Fig. 4 in its other control position;

Fig. 6 diagrammatically illustrates a control system of a metallurgical furnace as shown in Figs. 1 and 2; and

Fig. 7 diagrammatically illustrates the foot treadle controller of Fig. 2 in conjunction with the associated piping for the actuating cylinders 32 and 80.

Referring to the drawings, the invention in one form has been shown applied to a metallurgical furnace 10 having a heating chamber 11, a vestibule or entrance chamber 12, and a quench tank 13 having a localized quenching zone 13a. It is believed the invention will be readily understood by an immediate explanation of the manner in which the furnace is used for the treatment of work. Accordingly, it will be assumed that the furnace is in readiness for the treatment of work, that is to say, it is up to temperature, the desired atmosphere has been established in the heating chamber 11 and in the vestibule 12. An exhaust flame 14, ignited by a pilot burner 15, consumes the gases from the vestibule.

The metallurgical furnace of Figs. 1 and 3 is designed for use with trays for carrying the work, one such tray 16 being shown within the heating chamber 11. Such a tray loaded with work is first deposited on a rack 17 disposed to one side of the path of a door 18 of the vestibule 12, which door is supported on angle brackets 18a. In Fig. 1 the door 18 is illustrated in the closed position. When swung about its pivotal mounting means or shaft 19 in a counterclockwise direction, as by handle 1812, it lies between the loading rack 17 and a discharge rack 20. Thus, a tray of work can be slid directly from the loading rack 17 onto the door which thus serves as a transfer support for the tray as it is moved into the vestibule 12. While in Figs. 1 and 3 there is illustrated a stop element or abutment 21 in the path of the tray, such stop or abutment is, by the opening of door 18, moved out of the path of the tray by means of a bifurcated link 22 rotated by shaft 19 which operates through a link 23 and a link 24 to lower the abutment out of the path of the tray. The link 24 is guided in its vertical movement by one or more U-shaped clips 25. Upon opening of the door 18, the exhaust flame 14, is extinguished.

After the tray 16 and the work carried thereby is pushed into the vestibule 12, the door 18, of course, is immediately closed.

Referring to Fig. 3, it will-be seen that the shaft 19 has connected to it an actuating arm 27 which upon opening the door closes a valve 28 disposed in a conduit forming a flow passage 29 interconnecting the heating chambe: 11 and the vestibule 12. Thus, while the door 18 is in the open position, there is avoided loss of protective atmosphere within the heating chamber 11. However,

upon closure of door 18, the valve '28 is opened to es-' tablish forced flow of gases from the heating chamber 11 to the vestibule 12. The manner of producing the forced flow will be fully explained hereinafter.

Preferably, after the exhaust flame 14 is reestablished, indicating the presence in the vestibule of the protective atmosphere, an operator actuates a foot treadle 39 connected to a valve 31, from the position shown in Fig. 7 to the position shown in Fig. 2'to admit fluid under pressure to an actuating cylinder 32, Figs. 1, 4 and 7 to elevate the fire door 33 illustrated in Fig. l in the closed position between the heating chamber 11 and the vestibule 12. As soon as the door 33 is in its open position, a push rod may be inserted through a relatively small opening 34 in the door 18, normally'closed by a pivoted cover plate 180, to push the tray from the position illustrated by broken lines on elevator platform 35 in the vestibule 12 to the position illustrated in the fire chamber 11 on the tray support 36.

It is to be observed, Figs. 2 and 7, that upon operation of the treadle 30 to the position shown in Fig. 2, an,

end thereof is moved downwardly against an end of in terlock lever 37 pivoted at 38 to complete a mechanical connection between treadle 30 and treadle 40 disposed for actuation of control'valve 41 for the elevator mechanism, shown as pneumatic cylinder 80, of platform 35.

If, with treadle 36 in the actuated position to raise door 33; the operator were to rotate treadle 40 in a. counterclockwise direction, the lever 37 would immediately actuate treadle 30 to close door 33, or if the operator were pressing down on treadle 30 to position shown in Fig. 2, the treadle 40 could not then be rotated. An advantage of the interlocking lever 37 is that it does not interfere with the operation of treadle 30 with the parts in the positions illustrated in Fig. 2, and neither does it interfere with the operation of treadle 40 with treadle 30 in the close-door position, but it is effective to prevent operation of the elevator mechanism at any time the valve 31 of actuator 32 has been actuated to the door-opening position. 7

After the work and tray 16 is in position on the tray support 36, the door 33 is closed by actuation of the treadle 30 from the position illustrated in Fig. 2. As

'it is lowered, the door 33 is pressed against the outer wall 'of the fire chamber by means of cams 42 and 43 which engage pins 44 and 45 extending outwardly from the sides of thedoor. As best seen in Fig. 3, the fire door 33 overlaps the opening into the heating chamber 11, and as best seen in Fig. 1, the lower face of the door 33 rests upon an extension of the floor of fire chamber 11. Thus the door forms a substantially gas-tight seal for the fire chamber 11. After the work has been retained in the heating chamber 11 for a desired length of time, determined by the nature of the treatment to which it is to be subjected, it is removed therefrom. While in the heating chamber 11, the temperature is under the control of a thermocouple 46 mounted within a thermowell 47, the thermocouple 46 being shown in Fig. 6 as connected to a temperature controller 48 which, through control of operation of a circuit-breaker 49, opens and closes a circuit from suitable supply lines 50 to control the energization of heater coils 51 disposed within the heating chamber 11. The temperature controller 48 may be of the type fully disclosed in United States Patent No. 2,325,232, Davis.

While electrical heating of the chamin Fig. 6 as under the control of contacts 62 actuated by her 11 has been illustrated, it is to be understood that controlled gas heating or any other suitable type ofheating can be utilized with full advantage taken of the features of the present invention.

It is to be observed that the heating chamber 11 is of considerably greater length than the length of the work supporting tray '16. Preferably, it is at least half as long again as the length of the tray 16. It has been found that by arranging the radiant heat-producing means, as the heater coils 51, along the opposite side walls of the chamber 11, both in positions opposite tray 16 and above and below it, as diagrammatically shown in- Fig. 1, radiant heat will be transferred to the work in the tray with a surprising degree of uniformity. In accordance with the present invention, it has been found unnecessary to provide heat-generating devices such as electrical heating coils along either the front wall, the rear wall, the roof or n e fioor of the heating-chamber. Thus, there is'a'substantial saving in the cost and maintenance of theheatingdevices by minimizing the number required, the savings'morethan offsetting the cost'of the slightly larger size, particularly as regards length, of the heating chamber.

For a great many heat-treating operations, it is highly desirable to maintain under accurate control the character of the atmosphere within the heating chamber. In accordance with the present invention, constituent forming material is supplied by way of inlet 52 for distribution through openings 53 and a distributing plate 54'within chamber 11.

More particularly, Fig. 6, a carburizing agent may be introduced through inlet 52 under the control of valves 55 and 56. In practice, a motor 57 driving a pump 58, preferably of the constant-head type, supplies the carburizing agent which, when valve 56 is opened as by the coil 60, flows through throttling valve 55 and a flow indicator 61 to the inlet line 52. While the throttling valve 55 is not deemed essential, it is desirable to include-it to separate the function of regulating, as by valve 55, the

supply of carburizing agent from the function of valve 56 in turning the flow on and off. a

The energization of the valve-operating coil is shown a controller 63 which may be of the form disclosed in said Patent No. 2,541,857. Briefly, the controller may include a Wheatstone bridge, in one arm of which there 7 is provided the constituent-potential sensitive element disposed within the furnace 10 in a position to be subjected to the furnace atmosphere. The controller, in response to unbalance of the bridge due to change in the constituent-potential from a predetermined:selectedvalue,

functions to open and close the contacts 62 to regulate a the flow of the constituent-forming-material, such as a carburizlng agent, through inlet 52 to the furnace 10.

In practice, systems will be used of the type disclosed in United States Letters Patent No. 2,698,222, granted uponapplication Serial No. 122,946, filed October 22, 1949,

.Patent No. 2,698,222, by Raymond L. Davis II,"for

Methods of and Apparatus, for Calibrating Measuring Systems for Constituent Potentials, a co-employee of ours. Pursuant to said Patent No. 2,698,222, the sensitive element 65 may comprise a wire having a composition capable of reversible transference of the constituent to be maintained at a predetermined value in. the furnace atmosphere, as carbon or nitrogen. More particularly, the wire may comprise a length of #40 A. W. G. iron wire,

preferably the ferrous alloy described in United Patent" No. 2,325,759, Finch. The. detector and controller 63 may be either of the galvanometer and mechanical relay type such as shown in United States Patent No. 1,935,732, Squibb, or it may be of the electronic type as shown in United States Patents Nos. 2,113,164 and 2,3 67,746, Williams. If measuring instruments of the foregoing typesare utilized, their scales may be calibrated in terms: of. the constituentrpotential of the furnace atmosphere, that;

is, the transference and the possibility of transference of a constituent of the furnace atmosphere and the work subjected thereto, which transference varies the composition of the case or near-surface region of the work primarily affected by said transference.

The length of time that the tray or basket 16 and the work contained therein remains in the heating chamber 11 and the nature of the atmosphere maintained therein will depend entirely upon the nature of the treating operation desired. If the treatment is solely for hardending, annealing or normalizing the controller will be set to maintain a carbon atmosphere having a carbon potential corresponding with that of the work. Thus, there will be avoided an increase or decrease in the carbon content of the work, and assurance will be had that in the quenching the hardness acquired will be related to a known value of carbon content. In the event some carbon is to be added to the work, the constituent-potential will be made somewhat higher to increase the carbon potential of the furnace atmosphere for transference of carbon to the work for added carburization thereof. If there has been carbon depletion of work, obviously it can be restored during treatment within the heating chamber 11. Variable carbon content of work can be made homogeneous. A further important advantage of the present invention is that the carbon content can be maintained over the full range of heat-treating temperatures utilized for a wide variety of ferrous work.

It will now be assumed that the work has been in the heating chamber 11 for the requisite period of time under selected carburizing condition and that the work is to be quenched. Accordingly, an operator depresses the treadle 30 to its position shown in Fig. 2 to raise the fire door 33 by means of the pneumatic device 32. Rotation of treadle 30 positions valve 31 as shown in Fig. 4 to connect a source of compressed air 66 by way of a throttling valve 67 to the lower side of a piston 68 of the pneumatic device 32. The valve 31 also connects the upper side of piston 68 through a throttling valve 69 to atmosphere as through the discharge opening 70. The piston 68 is actuated to raise the door 33. At the same time it will be observed that air under pressure is applied as by pipe 71 to a pressure-responsive device shown as a Sylphon bellows 72 which expands to close an electrical circuit through contacts 73 which increases the supply of constituent material to the chamber 11.

As shown in Fig. 6, an energizing circuit is completed from supply lines L1 and L2 by the switch 73 for the operating coil 74 of a valve 75. The valve 75 controls the flow of constituent material, as the carburizing agent, supplied under pressure by the pump 58 to a pipe 76, through the throttling valve 77, a flow indicator 78, and thence by way of inlet pipe 52 to the furnace 10. The relative rates of flow of the two streams of constituentforming material are established by the setting of the throttling valves 55 and 77. In most cases, the stream through valve 55 will be small, as for example, about three pints of a carburizing liquid per hour, whereas the valve 77 will be set for a higher flow, as for example, twenty pints of carburizing liquid per hour. Thus, the increased supply of the carburizing agent will immediately increase the carbon potential within the heating chamber 11 in compensation for ingress into the vestibule of air due to leakage upon the opening of the closure 180. However, the carbon potential within heating chamber 11 is not likely to exceed the selected value by a substantial amount for the reason that during the time the door 33 is in open position, the sensitive element 65 and associated control continue to function; and when.

the constituent-potential rises above the selected value, the controller 63 will close the valve 56 to terminate flow of the carburizing fluid by way of the flow indicator 61. By suitably adjusting the ratio of flow of the two streams, the carbon or constituent-potential of the furnace at.- mosphere with the door 33 open or closed may be maintained at a substantially constant value, for example,

6 within twenty to thirty points of carbon (0.2. to 0.3 per cent carbon) in contrast with wide changes in carbon potential heretofore experienced in furnaces to which the present invention has not been applied.

With the door 33 in the open position, a hook inserted through the opening 34 of door 18 is inserted into the opening in a handle 16a of tray 16 for withdrawal past the door 33. Since the door 18 is in closed position, the stop 21 will be elevated as shown in Fig. 1. Accordingly, the tray 16 may be rapidly moved until it abuts against the stop 21. At this time the operator may operate treadle 30 to lower the door 33. Operation of treadle 30 from the illustrated position in Fig. 2 to that in Fig. 7 completes connections through the valve 31 as shown in Fig. 5, admitting compressed air from the supply pipe 66 by way of valve 69 to the upper part of the cylinder of pneumatic device 32, the under side of the cylinder within which the piston 68 is disposed then being connected by way of valve 67 to the outlet 70. At the same time the decreased pressure within bellows 72 opens the contacts 73 to terminate the flow of the auxiliary stream of constituent-forming material by way of supply pipe 76.

As soon as the door 33 is lowered, the operator will depress treadle 40 from the illustrated position, Fig. 7, to admit air to the upper portion of a pneumatic actuator or cylinder to lower the piston rod 81 which supports the platform 35, Fig. l, as by the structural members 82 and 83, disposed on opposite sides of guides 85 and 86, Fig. 3. The valve 41 is of the same construction as valve 31 and the pneumatic actuator 80 is of the same construction as actuator 32. Thus, Figs. 4 and 5 also diagrammatically illustrate operation of valve 41 and of actuator 80, with an assumed omission of bellows 72. The pneumatic actuator 80 for the platform 35 is designed to lower the tray 16 until it rests upon a stationary support 84 shown in the lower portion of the quenching zone 13:: within the tank 13. The bottom of the tray 16, shown in broken lines at the bottom of the quenching zone 13a, rests upon the stationary support 84 to localize the flow of the quench oil through the supporting ribs 16b of the tray. More particularly, a pump driven by motor 87 has its inlet 91, Fig. 1, connected to the quenching zone 13a below the stationary support 84 and a screen 92. A valve 89, Fig. 3, in outlet 88 serves to regulate the rate of flow of the quench oil or other liquid which may be utilized for quenching purposes. The pump 90 by withdrawing quench oil from below the screen 92, Fig. 1, produces forced and uniform downward flow of quench oil as indicated by the arrows over and about the work supported on the tray 16, uniformly and rapidly to lower its temperature for the hardening of thework. The discharge of the pump is by way of line 88 and valve 89 to a cooler 94 disposed within quench tank 13 outside of the quenching zone 13a. Oil is discharged from an open end of cooler 94 into the body of quench oil, the oil level 95 being somewhat higher in the cooling zone in which the cooler 94 is located than the oil level 96 in the quenching zone, the latter being lower by reason of the suction developed by the circulating pump 90. It is to be observed that the quenching zone is defined by a rear wall 97 common to both zones. Separate side Walls 98 and 99 extend to the bottom of the tank on opposite sides of the platform 35, and a front wall 100 completes the wall structure of the quenching zone. The side walls are provided with openings 96a and 96b for flow of quench oil into the quenching zone and downwardly about the work, the slot in wall 100 through which rod 24 extends also forming an additional flow-path. Valve 93 is a shut-01f valve, Fig. 3.

The cooler 94 is of conventional construction well known to those skilled in the art, provision being made for the circulation through cooling coils of a cooling fluid,

such as water, admitted through a supply line under work.

the control. of a, valve 111 operablebya coilor solenoid 112; The solenoid 11-2.may'be energizediunder thereon. trol of a-controller 115 whichalsocontrols the operation ofa circuit breaker 116 which controls the energization of an. immersion heater 117. Such-acombined control system. maybe of the type fully described in United States Patent No. 2,530,326, Davis. The coolingv liquid from the cooler 94 is discharged by wayofoutletpipell'll;

Under the control of aresistancethermometer 114 or other type oftemperature sensitive device extendinginto well 114:: of pump intake Iine=9 1, the controller 115 of the type shown in saidDavis Patent- 2,'530,326, functions to maintain the temperaturcof thequenchi'ngliquid, as oil, at a predetermined value. For example, when it is below a selected temperature, current'from supply lines Lt 1nd Lz issupplied by controller 115 to the circuit breaker 316 and to the immersion heater 11-? to raise the temperature of the'quenching-liquid to its selected'value;

However, when theheat-of the work elevates the temperature of the quenching liquid above the selected value,

the controller 115 by way of lines 118 energizesthe coil 15.2 toopenvalve 111 for admission of cooling liquid-to the cooler 94.

After completion of the quenching of the work, the operator will depress the treadle 40'to moveit to the position shown in Fig. 2 to raise the elevator preparatoryto discharge of the Work from the vestibule 12. It is to be observed the operator could not raise'the door 33 during the time the elevator or'plat-form 35- was in its lowermost position by reason of the interlock lever 37 which would have prevented that operation.

With the elevator inthe raised position, the door 18 is opened, the stop- 21 then being moved outof the path of tray 16 and it is then withdrawn through the door and slid to the discharge rack 20. The rack 20 is elevated somewhat above a drip pan 101 having openings 101a leading into the quench tank. Thus, oil draining from the tray and the work isreturned to the quench tank.

it is to be understood the foregoing operations will be repeated for successive charges of work and that the output of the furnace will remain at a high level of chiciency due to the fact that no substantialtime; is lost in maintaining the needed protective atmosphere for the In particular, the carbon potential of-the heating chamber 11 is maintained at substantiallyitsdesired value at all times. The auxiliary supply of constituent-forming material initiated each time the door 33 is opened insures a rise in the constituent-potential of the gases within the heating chamber 11, andthus during the charging of the fire chamber, as by transfer of the work tray 16 either from the loading platform directly to the fire chamber or by transfer first to the vestibule and later to the fire chamber, assurance is'had that the work will be under a protective atmosphere, an atmosphere which Will'at all times be near the selected value of constituent-potential. A further important function of the auxiliary supply of constituent-formingmaterihl is the protection of the sensitive element 65- which, it will be recalled, is of relatively fine wire. Hence, its cross-sectional area must not be changed as would occur if it were subject to oxidizing conditions. The resulting change in resistance would greatly interfere with its operation in the control of the constituent-potential. However, by maintaining the eonstituent-potentia-l within the heating, chamber at a relatively high level, the sensitive element 65 is protected and it continues to function during run after run with great accuracy.

While a separate fan or air pump may be utilized to withdraw gases from the heating chamber 11', and ad'- vantage taken of certain features of the present invention, considerable savings may result by utilizingthe fan 102 located within thefire chamber 11 and driven by a motor 193 located outside that chamber, It is preferred that the fan lit-2 be disposed within a housing which includes a plurality of vanes extending substantially tangent to the the work supported in the tray 16.

A detailed disclosure of the fan and the preferred associated vanes is set forth in United States Letters Patent No. 2,686,665 granted upon copending application Serial No. 190,152, filed October 14, 1950, by one of us and .l. J. Schultz," a co-employee of ours, for'Heat-Treating Furnace.

Advantage is taken of the fact that zones of high pressure. are produced by a fan, as. at certain of the adjacent directing vanes, that'is, pressures higher than in other portions of the heating chamber 1-1. By disposingvthe inlet 29a of recirculating pipe/29 in a high pressure zone: adjacent the fan 102, there will be forced circulation of gases from the heating chamber 11 into the vestibuleof loading chamber izso long as the door 13 isclosed, the

condition required for the valve 28 to be in the open position. In this manner thereis. avoided the need of an additional motor and fan for withdrawing the gases from the heating zone for supply to the vestibule-12. In this. connection, it is to be observed that gases from the heating chamber 11 are not returned thereto but form the supply of the gases for the exhaust flame 14. As shown,

the inlet 29a is in the form of a scoop, this being preferredwhere the directing vanes are notprovided.

While'a preferred embodiment of the invention has been set forth, it is to beunderstood that modifications may bemade, certain features used without other features, and that other modifications may be made within the scope of the appended claims.

What is claimed is:

l. A heat-treating furnace having a heating chamber and a vestibulefor receiving work preparatory to' delivery into said heating chamber, a fan disposed within said heating chamber having a high-pressure zone for forced circulation of gases withi-n'said heating chamber, walls forming a flow passage extending between said heating chamber and said vestibule with an entrance portion extending into said'heati-ng chamber to a point within saidhigh-pressu-re zone and adjacent said fan portion extending into said heating chamber to a point for forced flowinto said heating chamber and for receiving the. work said vestibule to form an atmosphere in said. vestibule and extending to the liquid level of said tank, said atmosphere having substantially the same'constituent quality as that within said heating chamber, and means including a constituent-sensitive device exposedjto the atmosphere of'said.

. heating chamber for controlling the constituent concentration in said heating chamber and of the atmosphere in said vestibule formed by the gases transferred thereto from said chamber.

3. A heat-treating furnace having a heating chamber and a vestibule for receiving work preparatory to delivery 9 into said heating chamber, a door between said chamber and said vestibule, a fan disposed to circulate gases within said heating chamber, a flow passage between said heating chamber and said vestibule for transfer of gases from said heating chamber to said vestibule with said door in open or in closed position to form an atmosphere in said vestibule having substantially the same constituent quality as that within said heating chamber, the inlet to said passage being disposed inwardly of said chamber and within a hi h-pressure zone adjacent to, and produced by, said fan, a valve in said flow passage for regulating the rate of flow of gases therein, means including a constituent-sensitive device exposed to the atmosphere of said heating chamber for controlling the constituent concentration in said heating chamber and of the atmosphere in said vestibule formed by the gases transferred thereto from said chamber, said vestibule having an access door movable between closed and open positions for placing work within said vestibule, and means operable upon movement of said access door towards open position to close said valve at times when said first-named door is in closed position.

4. In combination, a heat-treating furnace having a heating chamber, a normally closed vestibule adjacent said heating chamber, a door movable between open and closed positions to establish communication between said vestibule and said heating chamber, supply means for delivering to said heating chamber a constituent material for maintaining the constituent-potential of the atmosphere within said heating chamber at a predetermined value, means responsive to change in the constituentpotential of said atmosphere for regulating control of said constituent supply means to maintain said constituentpotential at said predetermined value, means forcibly circulating gases from said heating chamber to said vestibule to maintain therein an atmosphere whose constituent content is under the control of said constituent-potential responsive means, and means operable upon opening of said door of said heating chamber for establishing an auxiliary supply of said constituent material to said heating chamber.

5. in combination, a heat-treating furnace having a heating chamber, a normally closed vestibule adjacent said heating chamber, a door movable between open and closed positions to establish communication between said vestibule and said heating chamber, supply means for delivering to said heating chamber a constituent material for maintaining the constituent-potential of the atmosphere within said heating chamber at a predetermined value, means responsive to change in the constituentpotential of said atmosphere for regulating control of said constituent supply means to maintain said constituent-potential at said predetermined value, means forcibly circulating gases from said heating chamber to said vestibule to maintain therein an atmosphere formed by gases transferred from said chamber whose constituent content is under the control of said constituent-potential responsive means, and means operable upon opening of said door of said heating chamber for establishing an auxiliary supply of said constituent material to said heating chamber while said door is in its open position, said constituent-potential responsive means functioning to decrease delivery of said constituent material by said supply means when the constituent-potential within said furnace exceeds said predetermined value.

6. In combination, a heat-treating furnace having a heating chamber, a vestibule adjacent said heating chamber, a door movable between open and closed positions to establish communication between said vestibule and said heating chamber, supply means for delivering to said heating chamber a constituent material for maintaining the constituent-potential of the atmosphere within said heating chamber at a predetermined value, means responsive to change in the constituent-potential of said atmosphere for regulating control of said constituent supply means to maintain said constituent-potential at said predetermined value, means forcibly circulating gases from said heating chamber to said vestibule to maintain therein an atmosphere formed by gases transferred from said chamber whose constituent content is under the control of said constituent-potential responsive means, means operable upon opening of said door of said heating chamber for establishing an auxiliary supply of said constituent material to said heating chamber while said door is in its open position, said constituent-potential responsive means functioning to decrease delivery of said constituent material by said supply means when the constituentpotential within said furnace exceeds said predetermined value, and flow regulating means for regulating the maximum rates of flow from said supply means and from said auxiliary supply to establish maximum predetermined rates of flow when said door is in said open position.

7. The method of maintaining substantially constant the constituent concentration within a heating chamber during the transfer of work to and from the chamber, which comprises regulating the flow to the chamber of a first stream of constituent-forming material to maintain the constituent-potential within the chamber at a selected substantially constant value, increasing the supply of said constituent-forming material by initiating flow of a second stream of said material during transfer of work to and from the heating chamber, and decreasing the flow of said first stream of constituent-forming material when said second stream increases the constituent-potential of the atmosphere above said selected value.

8. The method of maintaining substantially constant the constituent concentration within a heating chamber and within a vestibule during the transfer of work between said vestibuie and said heating chamber, which comprises regulating the flow to the chamber of a first stream of constituent-forming material to maintain the constituent-potential within the chamber at a selected value, forcibly flowing a stream of gases from said chamber to said vestibule for producing therein an atmosphere having the constituent concentration therein in correspondence with that of said chamber, increasing the supply of said constituent-forming material by initiating the flow into said chamber of a second stream of said material during transfer of work to and from the heating chamber, and decreasing the flow of said first stream of constituent-forming material when the constituent-potential of the atmosphere within said heating chamber rises above said selected value.

9. The method of heat-treating work under conditions of a controlled constituent concentration of an atmosphere with transfer of said work to a quenching medium While under the protection of said atmosphere, which comprises heating the work within a heating chamber, supplying to the chamber a constituent material to establish an atmosphere having a selected concentration of said constituent therein, regulating the supply of said material in response to change of the constituent-potential of said atmosphere from a predetermined selected value, forcibly removing gases from said heating chamber to maintain within a discharge chamber an atmosphere having a constituent concentration dependent solely upon that maintained with in said heating chamber, during transfer of said work from said heating chamber to said discharge chamber establishing an auxiliary supply of the constituent-forming material to the heating chamber, and decreasing the first-mentioned supply of said material when said constituent-potential within said heating chamber exceeds said selected value.

10. A heat-treating furnace having a heating chamber and a vestibule for receiving work preparatory to delivery into said heating chamber, a fan disposed adjacent the floor of said chamber to produce a region of pressure at the periphery higher than at the central part to circulate gases forcibly in a closed path within said heating chamber, a conduit forming a flow passage having an inlet, opening intosaidv peripheral zone and adjacent thereto and eXtend-ingbetween and in-part outside of said heating; chamber and of said vestibule with an inlet opening into saidxvestibule for forcible transfer of gases from saidheating chamber to said vestibule to form an atmosphere therein having substantially the same quality as that within said heating chamber, and a Work support within said vestibulebelow the zone of entry of said gases.

1]. In combination, a heat-treating furnace having a heating; chamber, a door providing access to said heating chamber, a vestibuleadjacent said door forming a closed loading; chamber, a closure for said vestibule movable between open and closed positions, a quench tank disposed below saidvestibule, an elevator for supporting work within said vestibule for transfer to and from said heating chamber, elements disposed within the path of work moved-from said chamber to said vestibule to position' said Work on: said elevator When, said closure is in its, closed position and operable out of the path of said work when'said closure is in its open position.

12. Aiheat-treating furnace having a heating chamber and a vestibule for receiving Work preparatory to delivery into said heating chamber, a door between said vestibule and said chamber, afan disposed to circulate gases within said heating chamber, a flow passage between said heating chamber and said vestibule for transfer of gases from said heating; chamber to said vestibule with said door in open or in closed position to form an atmosphere in said vestibulehaving substantially the same constituent quality as that within said heating chamber, a valve in said flow passage for regulating therate of flow of gases therein, said vestibule having an access door movable between closed and open positions for placing Work within said vestibule, and means operable upon movement of said access door towards open position to close said valve to prevent flow of furnace gases'to said vestibule from said furnace while said access door is open and said firstnamed door is closed,

13. A metallurgical furnace comprising a heating chamber,a vestibule for receiving work moved into and out of, said heatingtchamber, a quench tank disposed below said vestibule, an elevator for lowering Work into and out of said, quench tank, a door for said heating chamber, actuating mechanism for said door and for said elevator,

' means for controlling, said actuating mechanism to raise and lower said elevator at will while said door is closed, means for controlling said actuating mechanism to raise and lower said door. at will when said elevator is in its uppermost position, means forpreventing opening of said door and for maintaining it closed when said elevator is in its lowermost position in said quench tank, and means for preventing lowering of said elevator while said door is in its open position.

14. The combination set forth in claim 13 in which said means for actuating said elevator and for actuating said door respectively includes a door treadle and an elevator treadle each pivoted for movement between valveopening and valve-closing positions, and a pivoted lever having its ends movable respectively to positions within the path of each of said treadles for preventing operation of said door treadle for opening of the door when the elevator is in its lowermostposition and for preventing operation of said elevator treadle when said door is in its open position.

References Cited in the file of this patent UNITED STATES PATENTS 890,250 Thompson June 9, 1898 890,251 Thompson June 9, 1898 786,365 Kenworthy Apr. 4, 1905 1,713,136 Leek May 14, 1929 1,742,739 Urschel Jan. 7, 1930 1,808,241 Martin June 2, 1931 1,851,831 Hayes Mar. 29, 1932 1,940,948 Harsch Dec. 26, 1933 1,999,757 Harsch Apr. 30, 1935 2,064,532 Gilbert Dec. 15, 1936 2,223,603 Darrah Dec. 3, 1940 2,307,005 Ruben Dec. 29, 1942 2,307,522 Mahin Jan. 5, 1943 2,394,002 Ness Feb. 5, 1946 2,458,084 Lee Jan. 4, 1949 2,459,618- Cartier Ian. 18, 1949 2,465,864 Freeman et a1. Mar. 29, 1949 2,541,857 Besselman et a1 Feb. 13, 1951 2,493,135 Gruetjen Jan. 3, 1950 2,639,138 Dow May 19, 1953 FOREIGN PATENTS 222,575 Great Britain Oct. 6, 1924

Claims (1)

1. A HEAT-TREATING FURNACE HAVING A HEATING CHAMBER AND A VESTIBULE FOR RECEIVING WORK PREPARATORY TO DELIVERY INTO SAID HEATING CHAMBER, A FAN DISPOSED WITHIN SAID HEATING CHAMBER HAVING A HIGH-PRESSURE ZONE FOR FORCED CIRCULATION OF GASES WITHIN SAID HEATING CHAMBER, WALLS FORMING A FLOW PASSAGE EXTENDING BETWEEN SAID HEATING CHAMBER AND SAID VESTIBULE WITH AN ENTRANCE PORTION EXTENDING INTO SAID HEATING CHAMBER TO A POINT WITHIN SAID HIGH-PRESSURE ZONE AND ADJACENT SAID FAN PORTION EXTENDING INTO SAID HEATING CHAMBER TO A POINT FOR FORCED FLOW OF GASES FROM SAID HEATING CHAMBER INTO SAID VESTIBULE TO FORM THEREIN AN ATMOSPHERE HAVING SUBSTANTIALLY THE SAME CONSTITUENT QUALITY AS THAT WITHIN SAID HEATING CHAMBER, AND MEANS INCLUDING A CONSTITUENT-SENSITIVE DEVICE EXPOSED TO THE ATMOSPHERE OF SAID HEATING CHAMBER FOR CONTROLLING THE CONSTITUENT CONCENTRATION IN SAID HEATING CHAMBER AND OF THE ATMOSPHERE IN SAID VESTIBULE FORMED BY THE GASES TRANSFERRED THERETO FROM SAID CHAMBER.

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