US1961766A - Furnace - Google Patents

Description

FURNACE Filed Feb. 28

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\QW Q ..n W w w r I m u w e T n o v A g M S m m w n m b C M; 2 2 3 H l A? t, 3 M 3 m m Patented June 5, 1934 UNITED STATES PATENT OFFICE FURNACE James H. Jennings, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York This invention relates to furnaces, more particularly to furnaces wherein a selected gas is used in the furnace chamber, such as furnaces for brazing and annealing, and it has for its object the provision of an improved furnace of this character.

Although it is not limited thereto, this invention has particular application to furnaces for effecting certain heating operations for metal,

such as brazing and annealing in an atmosphere of a selected gas which prevents oxidation of the metal during the heating operation.

One form of such a furnace is described and claimed in the United States patent to Carl L.

-Ipsen and James L. McFarland, No. 1,789,177 dated January 13, 1931, and assigned to the same assignee as this invention.

In the furnace there described, the furnace chamber through which the articles to be treated are passed is filled with a selected gas, such as hydrogen. The chamber is elongated, and a portion of it at the inlet end is heated so as to constitute a heating chamber in which the metal is heated; thus, this chamber may be' heated to a suitable high temperature to melt a brazing metal and form a brand joint. The remainder of the furnace chamber constitutes a cooling chamber arranged to reduce the temperature of the articles sufficiently to allow them to be removed from the furnace and exposed to the air without detrimental oxidation.

Suitable charging and discharging openings are arranged in the ends of the chamber, and elevators are provided for inserting and re- 5 moving the charge.

In furnaces of. this general type, it has been the custom to introduce the selected gas through the .top of the furnace at a point located substantially at the center of the furnace chamber.

From this inlet point the gas flowed in opposite directions throughthe heating and cooling portions to the ends of the chamber where usually burn-offs were provided through which the gas passed to the exterior of the furnace.

When using this arrangement and operating with reasonable assurance 'that no explosion of the hydrogen gas would occur, it was necessary to supply gas continuously. to the chamber at a rate substantially equal to the maximum rate 5 required when the elevators are opened to charge and discharge the furnace, and also during the draft period immediately following the closing of the elevators; it will be understood that when the elevators are opened, gas must be supplied in sufficiently large quantities to prevent the entrance of air at the elevator openings, and that during the draft period sufficient quantities must be added to compensate for the contraction of the gas from cooling when the cold charge is introduced and by the reduction in the gas volume resulting from the union of the hydrogen and any oxygen that might be trapped in the chamber by the elevatorsas they close.

Obviously, under these conditions of operation there is a considerable waste of gas because a considerably greater quantity of gas is required when the elevators are opened and during the draft period immediately following their closure than when the furnace is operating to treat the charge.

It is an object of this invention to provide a simple efficient and economical method and means forintroducing a selected gas to the furnace chamber.

In accordance with the invention, the selected gas is introduced to the furnace chamber continually in sufliciently large quantities to meet the normal requirements of the furnace, that is, the requirements when the furnace is heating -with the elevators closed, and an additional quantity of gas is supplied to meet the requirements of the loading and unloading period.

Preferably, the continuous flow of gas will be supplied at one end of the furnace-the cooling end in the above-named. specific application, while the additional quantity for the loading and unloading period will be supplied at a point intermediate the ends of the furnace.

In one form of the invention this additional gas requirement is controlled by means of a suitable valve which in turn is provided with suitable control means for operating it in accordance with the operation of the furnace chamber closure members-the elevators in the above-mentioned specific application, and to a time interval so that the valve is opened to admit additional gas to the furnace chamber when either one of the elevators is opened and to supply gas to the chamber continuously while the elevator is opened and for a predetermined interval of time after the elevator has been closed, i. e. during the draft period following the closure of the elevator.

For a more complete understanding of the invention, reference should be had to the accompanying drawing in which Fig. 1 is a vertical elevation of an electric brazing furnace embodying the invention; Fig. 2 is an end elevation partly in section of a portion of the furnace of Fig. 1, the elevation being to a larger scale than Fig. 1;

and Fig. 3 is section along the line 3-3 of Fig. 1

looking in the direction of the arrows, and taken on a larger scale than Fig. 1.

Referring to the drawing, the invention is shown in one form in connection with an electric 6 brazing furnace in which a hydrogen gas is selected for the working medium, and is shown as applied to the furnace described in the abovementioned United States patent to Carl L. Ipsen and James L. McFarland. As shown, the furnace comprises a cylindrical gas-tight steel shell or casing 10 defining an elongated furnace chamber, this shell being supported in a horizontal and elevated position by means of a pluralityof steel columns 11. Inside the shell at the inlet end are top, bottom and side walls 12 made of heat refractory bricks and defining a horizontal heating chamber 13 provided with relatively small inlet and outlet passages 13a and 13b.

Suitable heating means, such as electrical heat-.

ing resistors 15 (Fig. 2) is provided in the heating chamber 13, these resistors being hung on suitable heat refractory electrically insulating projections or supports 16 built into the furnace wall. It will be understood that suitable terminals for the heating units are brought out for connection to a suitable electrical source of supply through suitable openings (not shown). Inlet and outlet openings 18 and 19 respectively for the charge are provided in the bottom of the shell at the opposite ends thereof.

The heating chamber or portion 13 and the connecting passages 13a and 13b occupy but a small portion of the total length of the furnace. The remaining portion of the furnace chamber constitutes a cooling chamber, a substantial portion of which is provided with a water jacket (Fig. 3) through which cooling water 22 is circulated. Suitable inlet and outlet openings 23 and 24 respectively for the water are provided at the bottom and top portions of the furnace.

It will be understood that the articles to be heated are inserted into the heating. chamber through the inlet opening 18 and move at a substantially uniform rate through the heating and cooling chambers to the opposite end where they are removed through the outlet opening 19.

Two series 25 and 26 (Figs. 2 and 3) of tracks extending through the chamber are provided for the articles. The metal articles 27 to be brazed, shown as an assembly of parts with brazing material at the joints constituting a portion of an electric refrigerator, are provided with suitable supporting trays or supports 28 upon which they are supported in spaced relation. It will be understood that these trays 28 are moved through the heating chamber on the rollers 25 and 26.

Suitable elevating means is provided just below each opening 18 and 19, comprising counterweighted platforms or elevators 30 and 31. The elevators are operably connected with suitable operating motors 32 and 326. respectively which preferably will be of the fluid type. As shown, the elevator 30 is supported at its ends by means of chains 33 and 34 which pass over sheaves 35 and 36 and are provided at the opposite ends with counterweights (not shown) which are sumder pressure, is supplied to the motor 32 whereby the rod 40 is moved to the right, as viewed in Fig. 1, and the sheave 38 is rotated against the counterweights so as to lower the platform. The elevator 31 is similarly arranged, and is operated by means of its motor 32a in a similar manner.

It will be understood that when the elevators are raised, a tray will be pushed from the elevator 30 into the heating chamber and at the same time a tray will be received from the cooling chamber by the elevator 31. The trays are pushed through the furnace by means of a fluid motor (not shown) having a pusher piston 41 extended through an opening provided for it in the inlet end of the furnace in position to engage the trays.

The openings 18 and 19 will be suitably sealed during the operation of the furnace so as to conserve the selected gas and thus to conserve heat. Thus, these openings will be only slightly larger than the trays and moreover, will be normally closed by the elevators which ordinarily remain in their closed or raised positions. Preferably, also, the openings 18 and 19 are each provided with a pair of doors 41a which will be opened by the upward movement of the elevators and will be closed as the elevators are lowered. The heat will also be preserved to a great extent by means of the articles 2'7 and their supports (Fig. 2) which practically close the passages 13a and 13b leading to it from the heating chamber.

It will be understood that in the operation of the furnace, articles 27 will be inserted and removed from the furnace chamben'by means of the elevators 30 and 31. The articles will be 10 pushed through the heating and cooling chambers by the operation of push rod 41. The motor for operating this push rod and the motors 32 and 32a for operating the elevators will be suitably interlocked by means (not shown) to establish a 1 5 predetermined sequence of operation of the elevators and pusher mechanism, as described in detail and claimed in the above-mentioned Ipsen and McFarland patent.

As pointed out previously, it is an important object of this invention to provide improved means for introducing the selected gas to the furnace chamber so as to effect an efficient operation of the furnace and'economical use of the gas. Hydrogen gas is supplied from any suitable source of gas supply 42 and is conducted to the end of the cooling chamber remote from the heating chamber by means of a conduit 43 which, as shown in Fig. 1, communicates directly with the source of supply 42 and with the cooling chamber through its upper wall. The conduit 43 is controlled by means of a suitable valve 44, shown as a manually operable control valve.

It will be understood that in the operation of the furnace the valve 44 will be adjusted so as to provide a flow of gas from the source 42 into the cooling end of the furnace sufficient to meet the demands of the furnace when the elevators 30 and 31 are closed and the articles 27 are being heated.

The gas which flows from the source 42 to the cooling chamber passes through this chamber and thence through the heating chamber to a suitable burn-off 45 at the other end of the furnace chamber, that is, at the entrance end of the heating chamber 13, as clearly shown in Fig. 1. In other words, gas admitted from the conduit 43 passes through the entire length of the furnace chamber to the burn-off 45 at the heating end. It will be understood that the gas escaping from the burn-off 45 will be ignited and that the combustion taking place at the outlet end of the tube will constitute a signal thatthe gas is being supplied under suflicient pressure from the source 42 to prevent the leakage of air into the furnace chamber. If the flame disappears, the attendant will be warned that the furnace pressure is below the desired value.

' As previously pointed out, an additional quantity of gas is supplied to the furnace chamber when either one of the elevators or 31 is moved to open the associated furnace opening 18, 19. This gas is admitted at a point intermediate the ends of the furnace chamber, preferably at the end of the cooling section adjacent the passageway 131) leading from the heating chamber. This additional supply of gas is conducted to the heating chamber by means of conduits 46 and 46a which, as shown, are in communication with the gas supply source 42 and with the furnace chamber through its upper wall. The conduit 46 is provided with a manually operable control valve 47.

In addition to this control valve 47 the conduits 46 and 46a are provided with a second control valve 48. The control valve 48, as shown, is

mounted in a suitable valve housing 50 and is provided with a valve port or seat 51 arranged to establish communication between the gas supply source 42 and the furnace chamber. The valve 48 cooperates with the seat 51 so that the flow of gas from the supply source 42 to the furnace chamber can be cut off and established as the valve is moved to its closed and open positions.

The valve 48 is biased to its open position by means of a'suitable compression spring 52 which bears on an abutment 53 carried by the valve stem, as clearly shown in Fig. 1; the valve is operated to its closed position by means of a suitable electromagnetic device 54. The armature of this device, as shown, is connected directly with the valve 48 and is so arranged that when the operating coil of the device is energized the valve will be moved to its closed position against the bias of the spring 52.

The electromagnetic device 54 is controlled responsively to the operation of theelevators 30 and 31 and also to a time interval. When either elevator is moved to its open position, that is, when either elevator is lowered, the electromagnet 54 will be deenergized so that the valve can move to its open position under the influence of its spring 52 and the electromagnet will not be energized to close the valve until a predetermined interval of time after the elevator has moved to its closed position.

Thecontrol for the electromagnetic device 54 includes a pair of switches 55 and 56 which are normally biased to their open positions and are closed by the operation of the elevators 30 and 31 to their closed position. As shown, the switches 55 and 56 are biased to the open position by means of suitable springs 57 and 58, respectively, and are moved to their closed position by means of suitable abutments 60 and 61 provided on the piston rods 40 and 40a of the elevator operating motors 32 and 32a, respectively.

The control further comprises a second set of switches 62 and'63 which are also biased to their open positions-by means of suitable springs 64 to 65, respectively, and are operated to their closed positions by means of abutments 66 and 67, respectively, mounted on the piston rods 40 and 40a of the two motors 32 and 32a. These abutments 66 and 67 are pivotally mounted on the rods, as

shown in Fig. 1, so that when the rods are retracted, the abutments will merely rotate on their pivots when they engage the switches 62 and 63, thereby they will have no controlling action on the switches, but when either rod is moved outwardly to provide for the closure of its elevator, the associated switch 62, or 63 will be closed temporarily.

The control -further comprises a suitable timing device 70 which cooperates with the switches 55 and 56, and the switches,62 and 63 to effect the energization of the electromagnetic device 54 a predetermined interval of time after either of the elevators has been moved to its closed position.

While any suitable timing device 70 may be used, preferably a timing device will be used of -the type described and claimed in United States patent to H. M. Stephenson No. 1,699,125, dated January 15, 1929. This device is shown dia grammatically in Fig. 1 and, in brief, comprises electromagnets 71 and 72. Cooperating with the magnet '71 is an armature 73 biased to its unretracted position by gravity. This armature when attracted moves a resilient pivoted switch arm 74 to open its associated contacts 75. The arm '74 is moved to engage a latched switch arm 76 when the armature is attracted so as to be placed under a tension, whereby when the arm 76 is released it will be moved by the arm 74 to close its contacts 77. The arm '76 is latched by a latching member '78 which is released by the operation of the timing device motor. This motor comprises the electromagnet 72 and a disc 80 formed of non-magnetic electrically conducting material cooperating with it so as to provide a self-starting alternating current motor. This motor operates a worm 81 which is adapted to mesh with a worm wheel 82. The worm 81 is moved into mesh with the wheel 82 when the armature is attracted. After the motor has operated for a predetermined interval of time the wheel 82 will carry its abutment 83 to engage the latch 78 to release the arm 76. The armature carries a contact 84 cooperating with contacts 85 arranged to complete a holding circuit for the coils of the electromagnets 71 and 72, as will be pointed out in detail hereinafter.

The electromagnetic device 54 is provided with a suitable source of electrical supply 86 and is connected with the source by means of a suitable switch 87.

In operation: assuming that the various elements are in their respective operative positions shown in Fig. 1, and it is desired to operate the furnace, it will be understood that the gas will be introduced to the furnace from the source 42 so as to completely fill the furnace chamber in any suitable way, that is, it may be supplied to the furnace chamber when the furnace chamber is cold or it may be supplied to the furnace by the method described and claimed in the United States patent to J. -L. McFarland No. 1,789,187, dated January 13, 1931.

Then the switch 87 will be closed. This operation will complete an energizing circuit for the electromagnet 54 to close the valve 48, which circuit may be traced from the left-hand conductor of the supply source 86, through the switch 8'7, 'the contacts '75 of the timing device '70, a conductor 90, closed switch 55, conductor 91, closed switch 56, a conductor 92, a conductor 93 and thence through the operating coil of the electromagnet 54 to the right-hand conductor of the supply source 86. This operation of the electromagnet 54 to shut the valve 48' will cut off the iiow of gas from source 42 to the furnace chamber at the intermediate point.

The valve 44, however, will be adjusted so that gas can flow freely and continuously from the source 42 to the right-hand end of the furnace chamber in sumcient quantities to maintain sufficient pressure in the furnace chamber to prevent the leakage of air into the chamber. This gas, as previously pointed out, flows from the righthand end of the furnace chamber to its left-hand end where it escapes at the burn-off 45.

It will be understood, and as previously pointed out, the trays 28 carrying the articles 27 to be heated are pushed through the furnace in end-toend relation by means of the push-rod 41, the furnace chamber being filled throughout its length with a train of trays in end-to-end relation, a tray resting on each of the elevators 30 and 31. Let it be assumedthat after a predetermined period of time has elapsed, the elevator 31 is lowered so as to discharge the'article tray resting on the elevator. This operation is accomplished by the motor 3271 which attracts its piston rod 40a so as to lower the elevator. This operation of the motor 32a will allow the switch 56 to open. This, of course, will interrupt the energizing circuit for the electromagnet 54. As a result of this operation, the valve 48 will be moved immediately to its open position so as to allow an additional quantity of gas to flow into the furnace chamber through the conduits 48 and 46a. The valve 4'1 will be adjusted so as to provide the proper rate of flow of gas into the chamber so as to prevent the ingress of air while the elevator 31 is in its open position.

Now let it be assumed that the elevator 31 is moved to its closed position. While the elevator is being closed, the piston rod 400. will be extended to its position shown in Fig. 1. As the rod 40a moves-toward the right, the abutment 67 carried by the rod will temporarily close the switch 83. This switch 63 in moving to its closed position initiates the operation of the timing device '70. Thus, when the switch 63 is temporarily closed it will complete energizing circuits of the.

electromagnets '71 and '72 of the timing device; these energizing circuits may be traced from the left-hand supply conductor 86 through the switch 8'7, a conductor 95, a conductor 96, switch 63', a conductor 9'7, a conductor 9'71; and thence through the operating coils of the magnets 71 and '72 to the right-hand conductor of the supply source 86. The energization of the electromagnet '71 will attract its armature '73 whereby the worm 81 will be brought into engagement with the worm wheel 82. At the same time, the switch 84 operated by the armature '73 will be moved to close the contacts 85 associated with the switch; this operation will complete a holding circuit for the electromagnets '71 and '72 from the left-hand conductor of the supply source 86, through the closed contacts of a relay 98, the closed contacts 85 and thence through the operating coils of the electromagnets to the right-hand supply conductor 86. Thus, even though the switch 63 is but temporarily closed, the timing device '70 will rema n energized through the closed contacts 98 and 85. I v

4 Also when the armature '73 was operated to its closed position, the resilient switch arm '74 associated therewith will have been moved to open the switch contacts '75, so that the energizing circuit for the electromagnet 54 will be opened at this point even though the motor 32a acts to close the switch 56 when the elevator is raised;

by reason of this, it will be impossible to eifect an energization of the electromagnet 54 to close the valve 48 until the switch contacts '75 have been reclosed. The resilient switch arm '74 when it moves to open the contacts '75 will engage the switch arm '76 which is latched in its position shown in Fig. 1 by means of the arm '78.

The electromagnet '72 of the timing motor will operate the worm wheel 82 by means of the worm 81 so that eventually the pin 83 carried by the worm wheel will engage the catch '78 to release the switch '76. When the switch arm '76 is released, the resilient member '74 will move the switch arm to close the contacts '77. The closure of these contacts will complete an energizing circuit for the operating coil of the relay 98 through a circuit which may be traced from the left-hand supply conductor 86, through the operating coil of the relay 98, a conductor 99, closed contacts '77, a conductor 100, the conductor 93 and thence through the operating coil of the electromagnet- 54 to the right-hand conductor of the supply source 86. The movement of the relay 98 to its open position in response to the energization of its coil will deenergize the electromagnets '71 and D0 '72 of the timing device. As a result of this, the elements of this device comprising the armature '73, the resilient switch arm '74, the arm 76 and the latch 78 will return to their positions shown in Fig. 1 under the influence of the weight of the armature '73, as fully pointed out in the abovementioned Stephenson patent.

When the arm '76 moves to its open switch position, shown in Fig. 1, it will interrupt the above energizing circuit for the relay 9B which will move to its closed position. And the switch arm 74 when it moves to its closed position of Fig. 1 will maintain the energizing circuit for the electromagnet 54 which was completed when the switch arm 76 closed its contacts '77 to operate the relay 98 to its open position. This circuit for the magnet 54 will be identically the same as that previously described, namely, through the contacts '75, the switches 55 and 56, and thence through the operating coil of the electromagnet. 1%

It will be observed, therefore, that when the elevator 31 was moved to its closed position, the timing device 70 will have been energized and further, that the energizing circuit for the electromagnet 54 will not be completed until the timing device has operated to reclose the contacts 75 a predetermined interval of time after its operation was initiated- In a similar manner when the elevator 30 is lowered so as to receive a new charge the valve the other elevator is opened 'before the timing device '70 has had an opportunity to reclose the valve 48, the timing device will then function as previously described to reclose the contacts 75 which will have been opened when the elevator opened. The valve 48, however, will remain open 7 because the switches 55, 56 associated with the elevator that is open will be opened so as to prevent the completion of the energizing circuit for the valve; then when the elevator that is open is moved to its closed position the switches 62, 63 asobserved that as long as either of the elevators is open, the valve 48 will be open to allow an additional quantity of gas to flow to the heating chamber, and this additional flow of gas will be continued for a predetermined interval of time after the open elevator has been moved to its closed position.

In an actual test it has been found that this invention results in a saving of approximately 47% of the gas consumed before the invention was applied to the furnace.

While I have shown a particular embodiment of my nvention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. A furnace comprising walls forming a chamber provided with an opening therein, means for closing said opening, a timing device and means responsive to the operation of said means for closing said opening and to said timing device for supplying a selected fluid to said chamber continuously during the operation of said furnace and for admitting an additional quantity of said selected fluid to said chamber while said closure member is open and for a predetermined period of time after it has been closed.

2. A furnace comprising walls forming a chamber provided with an opening therein, a closure member for said opening, conduit means for supplying a selected gas to said chamber, valve means controlling said conduit means, a time element mechanism and means jointly responsive to the operation of said closure member and to said time element mechanism controlling said valve means to open said conduit means when said closure member is opened and to close said conduit means a predetermined interval of time after said closure member is closed.

3. A furnace comprising walls forming a chamber provided with an opening therein, a closure member for said opening, means for supplying a selected gas to said chamber, a timing device and means responsive to the operation of said closure member and that of said timing device controlling said gas supplying means so as to admit an additional quantity of gas while said closure member is open and for a predetermined period of time after said closure member is closed.

4. A furnace comprising walls forming a heating chamber provided with an opening therein, a closure member for said opening, a conduit for conveying a selected gas to said heating chamber, a valve for' said conduit, an electroresponsive device controlling said valve, a timing device and switching means controlled jointly by said closure member and said timing device controlling the energization of said electroresponsive device.

5. A furnace comprising walls forming a heating chamber provided with an opening therein, a closure member for said opening, a conduit for conveying a'selected gas to said heating chamber, a valve for said conduit, an electromagnetic operating device for said valve, an energizing circuit for said electromagnetic device, a timing device and switching means jointly responsive to the operation of said closure member and that of said timing device controlling said energizing circuit so that said valve is opened upon movement of said closure member to its open,positionand is reclosed a predeter mined interval of time after said closure member has been moved to its closed position.

6. A furnace comprising walls forming an elongated chamber having an opening inone end thereof, a closure member for said opening, a conduit for conveying a selected gas to the other end of said chamber, a second conduit for conveying selected gas to said chamber at a point between the ends thereof, a timing device and means jointly responsive to the operation of the closure member and to said timing device controlling said second conduit so that when said closure member is opened, gas is admitted to said chamber and also for a predetermined interval of time after said closure member has been closed.

'7. A furnace comprising walls forming an elongated chamber having openings in each end thereof, elevators adjacent said openings for inserting and receiving the furnace charge, said elevators sealing said openings when closed, means for operating said elevators, a conduit for conveying a selected gas to one end of said chamber, a second conduit for conveying selected gas to a point intermediate the ends of said chamber, a valve controlling said second conduit, an electromagnetic device controlling said valve, switching means controlling theenergization of said electromagnetic device in accordance with said elevator operating means so that said valve is operated to its open position when either one of said elevators is opened andla timing device controlling said electromagnetic device so that said valve is closed a predetermined interval of time after the elevator has been returned to its closed position.

8. A furnace comprising walls forming elongated heating and cooling chambers communicating with each other at their ends, heating means in said heating chamber, inlet' and outlet openings in the bottom at opposite ends of the furnace communicating with the heating and cooling chambers, elevators adjacent said openings for inserting and receiving said furnace charge, said elevators sealing said openings when closed, means for operating said elevators, a conduit for conveying a selected gas to the end of said cooling chamber remote from said heating chamber and a second conduit for conveying selected gas to a point intermediate the ends of said furnace substantially at the juncture of said heating and cooling chambers, a valve controlling said second conduit, an electromagnetic device controlling said valve, an energizing circuit for said electromagnetic device, switching means controlling said energizing circuit in accordance with the operation of said elevator operating means so that said device is deenergized to provide for the opening of said valve when either of said elevators is opened and a timing device controlling said energizing circuit so that said electromagnetic device is energized a predetermined interval of time after the elevator which is opened has been returned to its closed position so as to effect the closure of said valve.

9. The method of operating a-furnace wherein a selected fluid medium is used in the furnace chamber which comprises supplying a regulated quantity of said selected fluid to said chamber continuously while said furnace is in operation and supplying an additional regulated quantity of fluid when said chamber is opened to provide for the insertion or removal of a charge and for a predetermined interval of time after said chamber is closed.

10. The method of operating a furnace wherein a selected gas is used in the furnace chamber which comprises admitting gas to said chamber continuously while the furnace is in operation and admitting an additional quantity of said selected gas to said chamber while said chamber is opened to provide for the insertion and removal of a charge and for a predetermined interval of time after said chamber is closed.

11. The method of operating a furnace havingan elongated chamber which comprises admitting a selected gas continuously to one end of said chamber while the furnace is in operation and admitting an additional quantity of said selected gas to said chamber intermediate its ends while the chamber is opened to provide for the insertion and removal of a charge and for a predetermined interval of time after said chamber is closed.

12. A furnace comprising walls defining a heating chamber provided with an opening therein, means for closing said opening, means for supplying a selected gas continuously to a selected region of said chamber and means responsive to the operation of said means for closing said opening for supplying an additional quantityof said selected gas to another region of said chamber when said closure member is opened.

13. A furnace comprising walls defining an elongated heating chamber provided with openings in the ends thereof, closure members for said openings, means for supplying a selected gas continuously to one end of said furnace chamber and means responsive to. the operation of said closure members for supplying an additional quantity of said selected gas to said chamber at a point between its ends when either of said closure members is opened.

14. A furnace comprising walls defining an elongated heating chamber provided with openings in the ends thereof, closure members for said openings, heating means in said chamber adjacent one of said openings, means for continuously supplying a selected gas at the end of said furnace chamber remote from said heating means and means responsive to the operation of said closure members for supplying an additional quantity of said selected gas to said chamber at a point between its ends when either of said closure members is opened.

JAMES H. JENNINGS.

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