US1789177A - Furnace - Google Patents

Description

Jan. 13, 1931; c. L. IPSEN ET AL 1,789,177

FURNACE Filed Nov. 29. 1927 2 Sheets-Sheet I Q U Inverfisors: Carl L. lpsen, James L Mc Farlafid,

Their At-borneg Jan. 13, 1931.

FURNACE C. L. IPSEN ET AL Filed Nov. 29. 1927 2 Sheets-Sheet 2 Carl James L Mc Farlarwd LJ. Ipsen,

Their A-ttorneg.

- specifically to furnaces for brazing, anneal- Patented Jan. 13; 1931 v U T D- TA TES CARI. L. IPSEN AND JAMES L. McFABLAND, OF SCEENECTADY, NEW YORK, ASSIGNOBS TO GENERAL ELECTRIC COMPANY, A CORPORATION 01' YORK amines Applicationflled November 29,1927". Serial m. 236,530.

Our inventionrelates' to furnaces, more ing and the like, and has for its object the provision of a simple, reliable and eflicient furnace of this character.

In'one of its aspects our invention relates to furnaces for carrying out certain heating operations for metals, such as brazing and annealing, in an atmosphere of a selected gas, such as" hydrogen, which prevents oxidation of the metal during the heating operation. l

Our invention in'one form comprises a furnace structure providing an' elongated.

horizontal chamber which is-filled' with a which the articles selected gas and through A f portion 0 thisto be treated are passe chamber at the inlet end is heated to a: suitable temperature, while the remaining portion of the furnace constitutes a cooling chamber in which the temperature of the articles is reduced to such an extent that they may beremoved from the furnace and exposed to the air without detrimental .oxi-

dation. Suitable elevating -means is provided at the ends of the furnace for inserting and removing the charge, and mechanism for moving the charge through the chamber, together with interlocln'ngmechanism between the elevators and the mechanism for moving the charge for assuring a predetermined sequence of operation.

For a more complete understanding our invention reference should be had to the accompanying drawing inwhich' Fig. 1 isa side elevation view of an electric brazing furnace embodying our invention, the electrical interlocking mechanism being shown diagrammatically; Fig. 2 is an end elevation view partly in section to a lar er scale than Fig. 1; Fig. 3 is a sectional view along the line 3-3 of Fig. 1 looking in the direction of the arrows; Fig. 4 is a perspective view of the supporting means for the articles to be brazed; Fig. 5 is a fragmentary view in section. showing details of construction while Figs. 6, 7 and 8 are fragmentary views in section showing details of the actuating motors.

Referring to the drawing in carrying out our invention in one form, we provide a cylindrical gas-tight steel shell or casing 10 defining an elongated furnace chamber.- This shell is mounted on suitable supports, shown as steelcolumns 11,in a horizontal end of the-shell adjacent the heated portion.

This brickwork serves the purpose of heat insulation whereby loss of heat is'prevented.

The space between the shell and the brick is preferably'filled with a suitable powdered heat insulating material 14, such as a diatomaceous earth. Suitable heating means, such as electric heating resistors 15, (Fig.

2) isprovided in the heating chamber 13,

these resistors being hung on suitable heat refractory electrically insulating rojections or supports 16 built in the mace wall. Terminals for the heating units are brought out for connection to a suitable 'supply source through: openings 17, suitable electrical insulators being 'provided'for the -'terminals" and the opemngs being sealed around the terminals, as by means of asbestos packing. Inlet and outlet openings '18 and 19 respectively for the charge, are provided in the bottom of the shell at opposite ends thereof. Access may be had to the interior of the shell for'iepairs, if necessary, through bulkheads 20 provided with removable covers. I

The'heating portion or chamber 13 and the connecting passages 13 and13" occupy 'but a small portion of the total length of the furnace. For example, the totallength of the furnace, i. e., the total length of the cylindrical shell, may be about-sixtyfeet, of which the heating chamber 13 and passages 13 and 13 'may constitute approximately 15 feet. The remaining portion of the furnace constitutes a cooling chamber, no brick walls being provided in the interior of the shell in this portion. A substantial proportion of this cooling chamber, however, is provided with a water jacket. As shown, a second cylindrical shell 21 (Fig. 3) surrounds the shell 10 in spaced relation therewith throughout the cooling portion. This shell 21 is connected at its endswith the shell 10 so as to form tight joints and coolingof the articles through the furnace. For

example, the water may be admitted through an opening 23 at the bottom adjacent the outlet end of the furnace, and discharged through an opening 24 atthe 'top adjacent the heated portion 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 moved at a substantially uniform rate through the heating and cooling chambers to the opposite end where they are removed through the outlet opening '19. I For the purpose of facilitating movement of the articles through the furna'ce, two series 25 and 26 of rollers or wheels are provided. These wheels are secured to the bottom of the furnace chamber, the wheels in each series being in alignment so that in effect two' tracks of wheels are formed extending through the chamber. The metal articles 27 to be brazed, shown as an assembly of parts with brazing metal at the joints constituting a portion of an electric re.- frigerator, are carried on trays or supports 28 (see Fig: 4). These trays are filled with a, suitable powdered heat insulating material 29, such as a powdered diatomaceous earth, sometimes known as Silocel, whereby the wheels are protected by the supports from the high temperatures in the heating chamber. As shown the bottom of the heating' chamber is provided with a central,

longitudinal recess in which the wheels 25.

ming. This recess in the bottom of the heating chamber is the same width as the pas.- ages 13 and 13. v c

Suitable metallic supporting pins 30 extend upward from the trays and the articles 27 are placed'on these pins. By means of the pins, the article is held in spaced relation with the tray and also in spaced relation with bottom of the heating chamber so that the radiation of the heat to the article is not muflied. Furthermore, the increase in temperature of the article is not retarded by conduction of heat therefrom to the tray. It will be observed from Fig. 2 that the articles movesubstantially centrally through the heating and cooling chambers. This assures uniform heating of the article so that all parts of the article arrive at the desired brazing temperature at the same time. As shown four pins are provided for each tray and form supports for a single article 27. On the bottom of each tray are ridges or projections forming a groove 32 of sufficient width to receive a roller and a flat bearing ridge 31 which rides on the other set of rollers. The trays are moved through the heatin chamber on these rollers one .set of which %ears on the ridge 31 while the other set runs in the groove 32 whereby the trays are maintained in spaced relation with the walls of the chamber. Preferably, as shown in Fig. 4, the tray is made in two sections, a separate bottom section 28 being provided on which the ridge 31 and groove 32 are formed. This section 28? is secured to the tray proper in any suitable manner as by riveting. lVith this construction the section 28 is protected from the high temperature in the heating chamber by the heat insulating material in the tray and warping thereby prevented.

Suitable elevating means is provided just below each opening 18 and 19, comprising platforms or elevators 35 and 36, each of which is provided with counterweights. As shown,the platform 35 (Fig. 2) is supported at its ends by means of chains 37 and 38 which pass over sheaves 39 and 40 and are provided at the opposite ends with counterweights which are sufficiently heavy to raise the platform together with its load. The sheaves 39 and 40 are mounted on a shaft 41 to which is secured a sheave 42.

A flexible cable 43 j is wound up on this sheave 42 when the platform is raised by the counterweights. This cable it attached to the sheave 42 at one end and its opposite end is secured to a suitable motor, such as a piston moving in a cylinder 44. In order to lower the elevator, water or air, preferably air, is supplied under pressure to the cylinder 44 whereby the sheave42 is rotated against the counterweights so as to lower the platform. The elevator 36 is similarly arranged, and it is operated by means of a motor comprising a piston moving in a cylinder 45.

The elevators 35 and ,36' are each provided with sets of rollers 46 similar in size and spacing with the rollers 25 and 26 in the furnace chamber. As shown, two series of four rollers each are provided on each platform. These rollers are mounted in elevated positions on the latform on pins 35 which extend into the urnace openings and are of such height that when the elevators are raised the rollers 46 are on the same level as the rollers in the furnace, whereby a tray may be pushed from the elevator 35 into the heating chamber, and a tray received from, the cooling chamber onto the elevator 36. The trays are pushed through the furnace by means of a hydraulic motor 47 having a pusher piston 48 which extends through an opening in the inlet end of the furnace in a position to engage the trays.

The series of rollers on each elevator are inclined in each case toward the adjacent end of the furnace and stops are provided at these ends of the elevators against which a tray on the elevator comes to rest. This inclined arrangement of the rollers prevents the trays from rolling ofl" the elevators and furthermore assures that the trays will always occupy predetermined positions on the elevators.

The openings 18 and 19 of the furnace are only slightly larger than the trays, sufficient clearance being provided to avoid the possibility of jamming. This is also true of the passages 13 and 13 leading to the heating chamber, which passages are only slightly larger in a transverse direction than the trays and the articles carried thereby. Ordinarily, the elevators will remain in raised positions whereby the furnace openin are closed. A depending flange 49 (I i g. 5) is provided around each furnace openin and when the elevators are raised these anges fit into troughs 50 on the elevators which are filled with suitable powdered heat refractory sealing material, such as sand. This provides for tightly sealing the furnace chamber when the elevators are raised. Preferably also the openings 18 and 19 are each provided with a pair of doors 50 (Fi 5) which are hinged at opposite sides 0 the opening and when lowered come together inIthe middle so as to close the opening. -Each elevator is provided with a metal loop 51 which has its ends secured to the elevator and-extends upward embracing the tray and the articlescarried by it. As the elevator is raised the upper end of this loop engages the doors and pushes them upward, as indicated in Fig. 5, and when the elevator is lowered the doors are free to close as soon is lowered below the opening.

In order to still further conserve the heat a; metallic baflie plate 30 is secured on each tray so as to exten'd'across the tray in an upward direction. As shown in Fig. 4, this baflle plate is secured to the pins30 and its u per edge terminates just below the article 2?. This baffle plate is of substantially the same width as the tray, and it willbe observed that each tray with its article 27 and the baflle 30 substantially closes the passages 13 and 13 leadin to and from the heating chamber whereby t e escape'of heat from the heating'chamber is :prevented to a great extent. t I

Beneath the cylindrical casing 10 are two .a train of trays in end to end as the loop 51 parallel series of rollers 52 corresponding with the series of rollers 25 and 26 in the furnace chamber. These rollers are onthe same level as the rollerson the elevators 'when the elevators are in lowered positions,

rying the articles to be heated are pushed" through the furnace in end to end relation by means of the piston 48, the furnace chamber being filled throughout its length with relation, a tray resting on each of the elevators 35 and 36 and both elevators being in raised position, as shown in Fig. 1. Assuming these conditions, after a predetermined period has elapsed, to be determined by test, such as several minutes, the elex'ator 36 is lowered removing the tray and the article it. This tray is moved by the operator onto the rollers51 and 52 and the elevator immediately returned to closed position. The pusher 1notor-47--is then operated to advance the trays in the furnace for a distance equal to or slightly greater than the length of a tray. This pushes the tray at the opposite end of the heating chamber onto the carried by elevator 36 ready to be removed upon the repetition of the cycle of operations after the predetermined period previously referred to has elapsed. It should be noted that the tray is notpushed completely on the elevator 36, the final movement of the tray being completed by the force of gravity due to the inclination of the roller on the elevator. The elevator 35 is then lowered and a moved upon it and the elevator raised,

It will be understood that cooling water is moved from the elevator 36 are pushed "oh the rollers 51 and 52 to the opposite end of the furnace where they come to rest against a foot pedal operated stop 52, the

brazed articles being removed from the trays and replaced by treated.

It will be noted that the trays with the articles to be heated thereon are passed through the heating and cooling chambers at a substantially uniform rate, and the heating and cooling chambersare so arranged articles which are tobe tray containing an article to be brazed is are gradually cooled so that when each 7 reaches the opposite end of the furnace its temperature has been reduced to a predeterminedlow temperature at which no detrimental oxidation takes place when the article is removed and exposed to the outside air. Since the articles are upheldin spaced relation with the bottom, top and side walls of the heating and cooling chambers, the heating and cooling is effected at a substantially uniform rate throughout the article itself and with great efiiciency. With the particular furnace described, the charging mechanism is operated at approximately five minute intervals to remove an article and insert a cold one at the opposite end of the" furnace, and the period required in assing an article through the furnace from tiie inlet opening to the outlet opening is approximately two hours.

In order thatthe sequence of operations previously described may be assured, interlocking means is provided between the valves controlling the motor cylinders 44, and 47. Referring to Fig. 1, the valve for the pusher cylinder 47 is controlled by a'handle 55, the valve for the cylinder 44 is controlled by the handle 56, and the valve forthe cylinder 45 is controlled by the handle 57. It will be understood that these handles are secured to the stems of the respective valves: The upper ends of the handles are provided with notches 58, 59 and 60 respectively and latches 61, 62 and 63 are provided which drop into the notches when the handles are in their central positions, as shown in the drawing, -whereby the handles are locked. These latches may be lifted by means of operating coils 64, 65 and 66 respectively. Connected in parallel with the coils '64, 65 and 66 are operating coils 67, 68 and 69 which operate when energized toclose holding switches 70, 71 and 72; Cooperating with the handles are two-wa switches73, 74 and 75 which are normal y closed in one position, as indicated in the drawing, and when thehandles are moved toward the left, i. e., in a clockwise direction as shown in the drawing, these switches are moved to their opposite positions whereby one circuit is open and another circuit closed. Included in the connections are also push button switches 76 and 77, the switch 76 being normally open and the switch 77 being normally closed,

With the connections shown in the drawing, the operation of the system is initiated at the completion of a heatin cycle by closing the push button switch 76 whereby a circuit is "closed from the sup 'ly source 78 to the operating coil 66, thisclrcuit being from one side of. the supply source through the conductor 79, the coil, conductor 80,

conductor '81 and the switch 76 back to the other side of the source of supply. The operating coil 66'raises the latch 63. At the same time the coil 69 is energized and the switch 72 thereby closed. This establishes a holding circuit for the coil 66 after the push button 76 is released, this circuit being from the coil. 66through the switch 72, conductor 82, switch 75, conductor 83 and push button 77 back to the opposite side of the supply source. The handle 57 is now moved .first toward the right, i. e., in a counterclockwise direction, to lower the elevator 36 and when the tray on this elevator has been removed the handle 57 is moved to its extreme position to the left, i. e., in a clockwise direction, whereby air pressure is applied to the opposite end of the cylinder 45 and the elevator is raised. At the same time the switch 75 is temporarily moved to its other position whereby the holding circuit for the coil 66 is broken and the latch 63 thereby-released. Switch 75 in this position closes. the circuit for the operating coil 64 whereby the latch 61 is raised, this circuit being from one side of-the supply source through the coil 64, conductors 84 and 85, switch 86, conductor 87 ,switch 88, conductor 89, conductor 90, switch and thence through conductor 83 and push button switch 77 back to the opposite side of of the cylinder from the pusher rod 48 for the purpose of controlling this switch. Switches 86 and 88 are closed when the pistons of the cylinders 45 and 44 are forced IOU out and switch 91 is closed when the pusher rod 48 is retracted; Y

Continuing with the operation of the furnace, when the elevator 36 has been returned to its raised position the handle 57 is moved back to its mid-position whereby the supply of air is cut off from the cylinder .45 and the handle locked by the latch 63. When the coil 64 was energized to release the handle 55, as previously noted, the coil 67 was at the same time energized whereby the switch.70 was closed. This establishes a holding circuit for the coil 64 independent of switch 7 5, this circuit leading. from one side of the supply source through the coil, switch 70, conductor 92, switch 73 and push button 77 back to the other 'side of the supply source.

The handle 55 is now moved toward the right to operate the pusher mechanism and when this has been operated the handle is moved to its extreme left position to retract the pusher. At the same time switch 73 is moved from one position to the other whereby the coil 67 is deenergized and the holding circuit for the coil 64 thereby opened whereby the latch 61 is released. With the switch 73 temporarily held in its other position by the handle 55, a circuit is closed for the operating coil 65 by the closing of the switch 91 when the pusher has been retracted. This circuit leads from one side of. the supply source through the coil 65, conductor 93, switch 91, conductor 94, switch 73 and the push button switch 77 back to the other side of the sup y source. Atv the same time the coil 68 isenergized and the switch 71'thereby closed and a holding circuit thereby established for the coil 65, this circuit being independent of the switch 73. This circuit leads from one side of the supply source through the coils 65 and 68, switch 71, switch 74 to conductor 83 and thence back tothe opposite side of the supply source. As soon as the pusher mechanism has been retracted the operator moves the handle 55 back to its mid-position where it is locked by the latch In the next step the handle 56 is moved toward the right whereby the cylinder 44' is operated to lower the elevator and after the elevator has been lowered and a new tray and charge placed upon it, the handle 56 is moved toward the-left to its extreme position to raise the elevator. At the same time the switch 74 is thrown from one position to the other whereby the coils 65 and 68 are deenergized, and upon the closing of the switch 88 by the cylinder 44 when the elevator has been raised a circuit is establishedfor the coil 66. This circuit is from the supply source through the conductorz79, coil 66, conductors 80 and 85, switch 86, conductor 87, switch 88, conductor 89, switch 74 and conductor 83 back to the opposite side of the supply source. At the same time coil 69 is energized and switch 72 thereby closed whereby a holding circuit is established for the coil 66 independently of switch 74, as.

signal lamp 95 is provided. This lamp previously described. When the elevator 35 has been returned to its .raised position the handle 56 is returned to its mid-position in which it is locked by the latch 62. Aftera predetermined heating interval the cycle of operations is repeated as previously described. When it is desired to shut down the furnace the control relays may be deenergized by means of the push button 77.

In order that the operator may know when the pusher mebhanism has operated to advance the charge the desired distance, a red is connected in circuit-with a switch 96 which This is due to the fact is closed by the pusher mechanism when it has advanced the charge. A green signal lamp 98 is provided in circuit with a switch 97 which is closed when the pusherhas been retracted.

locking system has been put in operation by means of the push button 7 6, this push button will not be used, nor will the push button 77 be used except when the system is to be deenerfgized. It will be observed that by means o the interlocking arrangement, it is impossible to operate either elevator unless the other elevator is in raised position. that the operating coil 66 controlling the elevator. 36 can not be energized to release the handle 57 until the switch 88 is closed and this switch is closed only. when the elevator 35 is in raised position. It will be noted also that the coil controlling the latch' for the handle .56 can not be energized unless the switch 86 is closed and this switch is closed 0 y when the elevator 36 is in raised position, Furthermore, it will .be observed that the pusher can not be operated untilboth elevators are .in their raised positions for it willbe observed that the coil 64 can not be energized unless the switches 86 and 88 are both closed. Also a predetermined sequence of operation is established for it will be observed that the elevator 36 can be operated only after the pusher has been operated, while the pusher mechanism and. the elevator 35 can only be operated thereafter in the order mentioned. This interlocking system effectually prevents improper operation of the furnace which would result in delay and perhaps 7 damage to the furnace itself.

Suitable valve means for controlling the hydraulic and air motors is shown diagrammatically in Figs. 6,7 and 8. This arrangement is shown with reference to-the cylinder 45. although it will be understood that the slmilar valve means. its mid-position, as shown in Fig. 6, the ducts 99 and 100 leading to the ends of the cylinder 45, respectively, are closed as is also the duct 101 leadingto a suitable hydraulic or air-supply source, asthe case" may be. The exhaust duct 102 is also closed with the cylinders 44 and 47 will be provided with With the handle 57 in valvein this position. When the handle 57 is movedrtoithe right, as shown in, Fig. *7,

duct 99. is connected to the exhaust andlthe duct 100.- is connected .to the supply source whereby the piston is retracted to lower the elevator. With the handle 57 in its extreme position to, thenleft as indicated in F1g.- 8, the

duct-101 is connected to the exhaust duct and the duct 99 is connected to the supply duct 101, whereby the piston is. forced back to' the position shown in *Fig. 5 togralse the elevator. The pusher motor 47 is preferably 70 It as contemplated that after the mteroperated by water pressure in order to obtain more uniform operation of the pusher .rod. The elevator motors may be operated by compressed air. The counterweights for the elevators are made heavy enough to raise the elevators with their loads, .as previously noted, in order that the elevators may be raised or maintained in raised positions in the event of failure of the air supply for the operating motors.

In some cases it may be found desirable to use pure hydrogen gas or an explosive mixture thereof and under such conditions in the event that it is necessary to cool the furnace quickly as, for example, in case the operation of the furnace must be temporarily interrupted for repairs, the hydrogen gas may be first driven out by a-,non-explosive gas after which the furnace may be opened to the outside air and cooled rapidly by forcing acurrent of air through it. Nitrogen gas may be used to displace the hydrogen. The nitrogen gas being heavier than hydrogen, ma be admitted through a pipe '103 commumcating with the furnace chamber at the bottom thereof, while-the hydrogen gas may be allowed to escape at the top through the duct 53. It will be understood that the duct 53 will be disconnected from the source ing. 103. When either methodis used the skilled in the art without departing fromv two gases seem to mix to a considerable extent, and it has been found that the hydrogen can be driven out through the bottom opening 103 by admitting the heavier' nitrogen gas through the duct 53 at the top.

While weohave described our invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that we do not limit our invention thereto since various modifications thereof will suggest themselves to those the spirit of our invention, the scope of which is set forth in theannexed claims.

What we claim as new and desire to secure byLetters Patent of the United States, 1s' I an elongated chamber, said-.walls bein provided with inlet and outlet openings in the means for inserting 1. A furnace comprising walls forming ing said heating and cooling portions, said openings being substantially closed by said articles and supports in passin therethrough from the heating to the coo ing portion so as to prevent the escape of heat from said heating portion.

2. A furnace comprising Walls forming a horizontal elongated furnace chamber, said walls being provided with inelt and outlet openings in the bottom at opposite endsof saidchamber, means for maintaining a selectedgas in said chamber. means for heating aportion of said chamber adjacent said inlet opening, means for cooling another portion of said chamber, elevators adjacent said openings, trays for the articles to be heated, means for pushing atrain of trays through said chamber, and walls forming a restricted opening connecting said heating and cooling portions, said opening being substantially closed by said articles and trays inpassing therethrough from the heating to the cool- ,ing portion so as to prevent the escape of heat from said heating portion.

3. A furnace comprising walls forming a chamber provided with inlet and outlet openings in the bottom at opposite ends thereof, means for maintaining a selected gas in said chamber, heating means insaid chamber, separately movable supports on which the articles to be treated are held in spaced relation both with respect to said support and the bottom of said chamber whereby the heating and cooling of each article is effected at .a substantially uniform rate throughout the article, means for moving a train of supports through said chamber, and

and removing said supports. I

4. A furnace comprising walls forming elongated heating and cooling chambers communicating with each other at their ends, heating means in said heating chamber,

means for maintaining a selected gas in said chambers, supports on which the articles to be heated are held in spaced relation both with respect to said supports and with the bottom of said heating chamber whereby the heating and cooling of each article is effected at a substantially uniform rate throughout the article, means for moving a train of'supports through said heating and cooling chambers in succession, and means for. inserting and removing said supports.

5. A furnace comprising walls forming an elongated furnace chamber, said walls being provided with inlet and outlet openings in the bottom at opposite ends thereof, heatmunicating with the vators adjacent said openings, sealing means for said openings carried by said elevators,

trays for the articles to 'beheated, means on said trays for supporting the articles in spaced relation with the trays, and means If)? pushing said trays through said chamr. 6. A furnace comprisin walls formin a horizontal elongated chain er, said walls eing provided with inlet and outlet openings in the bottom at opposite ends of said chamber, heating means for said chamber, cooling means for another portion of said chamber, means for maintaining a selected gas in said chamber, elevators adjacent said openings for inserting and receiving the charge, means for pushing the charge successively through said heated and cooled portions, and interlocking means between said elevators and said pushing means, for establishing a predetermined sequence of operation betweeri them. i

.7. A furnace comprising walls forming an elongated chamber, said walls being provided with inlet and outlet. openings combottolii of said chamber at each end, heatin means in said chamber, elevators associate with said openingsfor. raising and lowering the articles to -be heated, a motor for actuating each of said A elevators, pusher mechanism for moving the articles through said chamber, a motor for actuating said pusher mechamsm, a manu-' ally operable control device for each of said motors, and interlockingmeans between said control devices for preventing the operation thereof except in a predetermined sequence so as to insure a predetermined sequence of 7 operation of said motors.

8. A furnace comprising a furnace structure including walls forming a horizontal,

' elongated furnace chamber, said walls being the bottom at opposite ends of in said chamber, heating means for a portion of said chamber at one end, cooling means for another porprovided with inlet and outlet openings tion of said chamber, means fbr maintaining v said articles through said a selected gas in said chamber, elevators below saidl openings for raising and lowering the artic es to e heated, a motor for actuating each of said elevators, means for pushing chamber, a motor for actuating said pusher mechanism, contrdl means for said motors, and interlocking means for said control means for establishing a predetermined sequence of operation of said motors.

9. A furnace comprising walls forming an elongated chamber,2said walls being. provided with inlet and outlet 0penings communicating with thebottom of said chamber at opposite ends thereof, heating means for said chamber, elevators below said openings her, and heat insulating means from preventing operation of either of said elevators except when the other one is in raised position, and means for preventing operation of said pusher mechanism except when said elevators are'inraised positions.

10. A furnace comprisi walls forming an elongated chamber, said walls being provided with inlet and outlet openings communicating with the'bottom of said chamber at opposite ends thereof, heating means for said chamber, elevators below saidopenings for raising, and lowering the articles to be heated, pusher mechanism for moving the articles through said chamber, and interlocking means between said elevators and said pusher mechanism whereby said outlet ele: vator can be operated only after said inlet elevator has been operated, said pusher mechanism can be operated outlet elevator has been operated, andsaid only after said pusher mechanism has been operated.

11. A furnace.v comprisihgwalls' forming a horizontal, elongated chamber, said walls.

being provided vwith inlet and outlet openngs at opposite ends of said chamber, heatmg means in said chamber, .twof series of wheels forming parallel rtracks extending through said chamber, supports for the articles to be heated arranged to be passed through said chamber said inlet opening to said outlet opening, and means provided on said supports operably associated with said wheels for guiding said supports through said chamber.

12. A f a horizontal, elpngated Jheating chamber, means for heating a portion of said chamber, two seriesof wheels tracks extending through said chamber, supports for the articles to be heated arranged to be passed through said chamber "on said wheels, said supports being provided with grooves for said wheels whereby the sup; ports are guided through the heating chamfor said S13)- ports, said supports being of substantia y the same width as the heated 'portion ofsaid chamber whereby said wheels are protected the" heat in the interior I ofsaid chamber. I

13. A'furna'ce comprising walls forming a horizontal, elongated chamber, said walls being provided with inlet and outlet openings at opposite' ends of said 'chamber,'heat.- ing means. for a portion of said chamber, cooling means for another P91131011 of sa d chamber, means for maintalmng an atmosphere of series of wheels forming "parallel tracks-extending through said chamber, tra s for-the articles to be brazed arranged to e passed.

on said .wheels fi o'in urnace comprising walls forming Q j forming parallel lio a selected gas in said chamber, two

, her is through said chamber 011 said wheels, heat insulating means in said trays, said trays being substantially thesame width as theheated portion of said chamber whereby the wheels in said heated portion are protected from the heat of the interior thereof.

14. A furnace comprising walls forming a horizontal, elongated heating chamber, said walls being provided with a longitudinal recess in the bottom of said chamber, means for heating said chamber, two series of wheels in said recess forming parallel tracks extending through said chamber, trays for the articles to be heated arranged to be passed through said chamber on said wheels, said trays being provided with grooves for said 'wheels, andheat insulating means for said trays, said" trays being of substantially the same width as said recess wherebysaid wheels are protected from the heat of said chamber.

15. A. furnace comprising walls forming .an elongated heating chamber having relatively small inlet and outlet passages connecting therewith, supports for the articles to beheated, means on said supports for supporting the articles to be heated in spaced relation with the supports, baflie members on said supports below said articles having substantially the samewidth as said supports, and means for moving a train of supports through said passages and heating chamber, said articles, bafile members and supports substantially closin said pas sages while passing therethroug whereby the escape of heat from said heating chamrevented.

16. an elongated'heating chamber having relatively small inlet and outlet passages connecting with said heating chamber at opposite ends thereof, supports for the articles to be heated, pins on said supports on which the articlesto be heated are held above said supports, bafl'le members on said supports below said articles having substantially the same width as said supports, and means for pushing said supports in end to end relation through said chamber, said inlet and outletpassages being substantially closed by said trays, articles and battles in passing therethrough whereby the escape of heat from said heating chamber is prevented.

. "17. A furnace comprising walls forming. a heating chamber having relatively :small inlet and outlet passages connecting with furnace comprising walls forming izo said heating chamber at opposite ends thereof, walls forming a cooling chamber con nected to one of said passages, supports for the articles to be heated, means on said supports for supporting the articles to be heated in spaced relation with said supports,

baflle members on said supports below said articles having substantially the same width as said supports, means for maintaining a-

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