US2032209A - Heat treating apparatus - Google Patents

Description

Feb. 25, 1936. J. w. HARSCH HEAT TREATING APPARATUS 2 Sheets-Sheet 1 Original Filed Jan. 50, 1929 llllll I .1

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Feb. 25, 1936. J. w. HARSCH HEAT TREATING APPARATUS Original Filed Jan. 30, 1929 2 Sheets-Sheei 2 Q shell I by insulating material III of suitable char- Patented Feb. 25, 1936 UNITED STATES 2,032,209 PATENT OFFICE HEAT TREATING APPARATUS John W. Harsch, Gwynedd, Pa... assignor to Leeds & Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Original application January 30, 1929, Serial No.

Divided and this application January 28, 1931, Serial No. 511,694. Renewed May 9,

Claims. (Cl. 266-5) my application Serial No. 336,065, flled January 30, 1929, of which this application is a division.

In accordance with my invention, structure is provided for sealing the'gaseous atmosphere, for example one consisting of or containing a chemically active gaseous medium for effecting reaction with the work for production of a diifusion-alloy case, within the furnace during the entire process of treatment; for this purpose there are provided one or more of the structures as follows: sealing means associated with the 'exteriorly driven driving means for the mechanism within the furnace which forcibly stirs the treating atmosphere, to prevent ingress into the furnace atmosphere of air or extraneous gas or gases; sealing means between the furnace and a removable wall or cover thereof, comprising coacting structures in one of which is held displaceable sealingmaterial in which the other is insertedor immersed upon closure of the fur- For an understanding of my invention and for I illustration of my apparatus, reference is to be had to the accompanying drawings in which:

Fig. l is an elevational view, partly in section, of a furnace.

Fig. .2 is a plan sectional view of the apparatus illustrated in Fig. 1 taken along the line 2-2.

Fig. 3 is a detailed view of apparatus associated with the furnace.

Referring to Fig. 1, there is illustrated a furnace orv heating structure comprising an outer cylindrical shell I having its lowerportion closed by a bottom plate 2 suitably secured to the lower edge of shell I, as by bolts 3 to flange 4. To the bottom plate-2 is secured the furnace-supporting structure 5. The upper edge of shell I is united to a siniilarshell Shaving. an inwardly turned flange I whose inner edge is secured andsealed, as-by weld 8, to=the upper edge of a shell 9, disposed concentrically within, and spaced from acteristics. Shell 9, which comprises the inner lining of the furnace, is open at its upper end, and is closed at its lower end by members II and I2, members 9, II and I2 being secured to each other by the sealed welded joints I3. Member I2, comprising the bottom portion of the furnace chamber, is secured and spaced with respect to plate 2 by members II which are also welded to member I2 for purposes of sealing. Upright supports I5, comprising angular members, are

mounted upon the bottom of the furnace chamher by means of studs Ma, and support a plurality of heating elements, as electrical resistors I6, by means of annular supporting bands IGa and insulators I6 b. Mounted also upon supports I5 is a cylindrical shell-like member I'I, open at 'its top and bottom,'and within which a work container I8 is concentrically disposed. The work container I8 comprises a cylindrical shelllike wall having an open grille work or spider I9 secured to the lower edge thereof, and an annular supporting flange 20 secured to the upper edge thereof adapted to seat upon the upper edge of cylinder I I, and thereby closing the in- V tervening space from circulation of gases. Supporting flange 20 is provided with eyes or handles 2| for facilitating withdrawal of the work container from furnace.

Suspended beneath the furnace by means of structure 22 and through-bolts 22a is a motor M having the axis of its rotor shaft disposed in a vertical plane. Rotor shaft 23 extends through the bottom plates 2 and I2, and is substantially sealed with respect to the furnace walls by means of a packing gland 24 and a sleeve or collar 25 forming a part of said gland and welded to the bottom member I2 at I26. It is quite necessary that the opening afforded by the motor shaft be sealed by gland 24, or equivalent, as otherwise, fan 28 draws in cold atmospheric air and forces it directly' against the furnace load to produce a more or less localized cool spot. The chemical and heat treatment of metal located in such a spot'undesirably. differs from the remainder of the load. Air so entering causes presence of oxygen, which, in carburizing produces carbon dioxide, a; decarburizing agent, and in nitriding causes a blue surface on the work. Shaft 23 terminates beyond a conical flow-deflecting member 2! I, and has secured to the end'thereof a fan or impeller 28.

Resistors I6 are connected to an external source of electro-motive force by means of lead memat its lower end and supporting a sleeve-like member 32 for supporting the iead conductor 21.

The conducting members 28 and 21 are suitably spaced and insulated with respect to their supporting members, as by an electrical insulating.

bushing 33, asbestos packing as and an insulating cement 35 which also serves to insure sealing of the conduits from the exterior against gas leakage. An electrical insulating bushing 35 and a lead terminal 31 are disposed at the end of sleeve 32. Although but one outlet supply conduit has been described and illustrated, it will be noted, referring to Fig. 2, that a proper number of them are supported by and extend through the furnace wall, for supplying current to the resistors, depending upon the power characteristics desired.

Cover structure for the furnace comprises a cylindrical shell-like member 38 of somewhat larger diameter than member 6, having the dished plate-iike members 39 and 40 suitably secured thereto, member 39 being welded at its outer periphery to member 38 for purposes of sealing the junction of these members. Members 39 and 40 are spaced from each other forming an enflexible tube or conduit 43 having interposed therein a measuring device, as a flow meter 44 and a flow controlling device, as a needle valve 45 for contro ling the flow from a supply conduit 46. a

The lower portion of shell 38 comprises a sleeve-like structure surrounding the outer wall of the furnace and co-acting with a liquid seal, as an oil seal 61 for sealing the furnace chamber with respect to the atmosphere. The seal 4'! comprises an annular wall structure 48 having its lower portion sealed at 48a, as by welding, to the outer side of member 5, and forming therewith-an annular receptacle for containing a sealing liquid such as oil, for example. As illustrated in Fig. 1, the lower portion of shell 38 extends into the oil to a suitable depth, thereby effectively sealing the interior of the furnace from theatmosphere. The oil should have high flash and boiling points to avoid destruction of the seal by flame or huh-- I bling and be substantially inert to the nitriding gas; for example, medium to heavy motor oil is suitable. Molten metal, as solder or other metal or alloy whose melting point is below the temperature to which it is subjected, may be used as a seal, particularly when more isclated from atmosphere and subjected more to the furnace temperaturethan in the particular apparatus shown, in which the heat insulating material In, asbestos packing 49, etc., greatly reduce transfer of heat to the seal. In any event, the molten metal seal is preferably disposed within the furnace, as adjacent wall 8 for example, in order that the furnace heat may keep it in a liquid state.

Suitable heat resisting and resilient material,

such as asbestos rope 49, is disposed along the upper. edge of the furnace wall to provide a seat for the cover structure which, including the thermo-responsive device 4| and the conduit 42, may

be lifted as a unit from the furnace by hoisting means connected to the lifting hook or eye 53.

The furnace is provided with an outlet or exhaust conduit 5|, welded at 5|a to the furnace lining, having seated at its outer end a gasketed closure member or plug 52 adapted to be unseated to open the outer end of the conduit by a member 53, pivoted at 54, and connected to the closure member through a pivoted connection 55. The closure member 52 may be maintained in snug and sealing engagement'with the end of conduit 5| by means of the screw clamp 55 pivotaliy mounted at 51.

Referring more particularly to Fig. 3, conduit.

5| communicates with a conduit 58 terminating within a trap providing a liquid seal and comprising a container 53, a sealing liquid 50 and an outlet or exhaust conduit 6|. During closure of member 52, exhaust from the furnace chamber may take place through conduit 5|, conduit 58 and the liquid seal above described, provided of course that sufiicient pressure exists in the furnace chamber. Y

The material of the exposed parts of the interior furnace structure, such as the lining 3 and shell H, which serves to shield the work within container l8 from direct radiant heat from the resistors, and other structure subject to contact by the particular gaseous medium utilized in the furnace chamber, comprises a metal or alloy thereof resistant to corrosive action of the nitriding gas, as dissociated ammonia, such as for example, nickel-chrome, or chromium-nickel iron alloys. The electrical resistors l5 which are also exposed to the action of the furnace gas or gases are also composed of a corrosive-resisting material, as nickel-chrome alloy.

The operation of the system is as follows:- Assuming the furnace to be in condition for recharging, the cover structure is removed by suitable lifting or hoisting mechanism secured to member 50, after which work container I2 is lifted from the furnace by means. of eyes 2|. A work container filled with material to be treated is subsequently lowered into the furnace to the position shown in Fig. 1, after which the cover structure is lowered into its sealing position. In order that the furnace chamber may be entirely free from any gas other than that used in the treating process, the furnace is flushed for an appreciable length of time by the treating fan, between the inner work containing chamber and the outer annular heating chamber containing resistors l6. this manner, the treating gas is caused to circulate throughout all parts of the furnace interior to effectively flush out all gases such as air or other oxygen-containing gases, and te effect discharge of the same through exhaust conduit 5| and the liquid seal 50. The flushing can be eifected without running the fan though circulation is preferable; During the flushing process, resistors I6 ar deenergized and generate no ,heat', so that the new batch of material to be treated remains comparatively cold and is not. acted upon to any appreciable extent by the flushing treating gas.

pressure, the pressure therein during normal operation will be somewhat above atmospheric, so that there is a continuous new of gas through the exhaust conduit and seal, thereby insuring a continuous supply of fresh treating gas.

After the flushing process has been completed, resistors l6 are energized from a source of power (not shown) and the furnace interior accordingly increases in temperature. Assuming now that fan 28 rotates in suchdirection that the furnace gas is caused to flow upwardly through the open grille or spider IQ of the work container l8, through the batch of work therein, the gas will return to fan 28 by way of the annular heating chamber, and flow around and contact with the highly heated resistors during the downward return path to fan 28, where it is guided by the conical deflecting member 2'" towards the fan blades which again impel the gas through the same cycle. By reversing the motor M, and consequently the direction and rotation of fan 28, the gas or gases flowing directly from the heating chamber first come into contact with the work at the top of the container "3, instead of that at the bottom, as in the previous instance.

The above described method of periodically reversing the direction of circulation of gas within a furnace efiects uniformity of heating of the work therein, and is fully described and claimed in my Patent 1,578,027, March 23, 1926.

After the furnace interior has been brought up to the desired temperature, it may be maintained substantially constant by any known control means associated with the'thermoresponsive device ti, for example, such as disclosed in my aforesaid patent. During the treatment, the hitriding gas is caused to flow continuously through conduit 12 to replenish the gases which are exhausted during the treatment and to force out of the furnace through the exhaust seal such exhausted gases. in general, the temperature of the work itself is a determining factor in governing the rate and/or extent-of reaction of the treating gas with the work. By utilizing the gas itself as the principal heat vehicle between the source and the work, the cylindrical shield H to-- gether with container 58, both of which are unperforated, effectively preventing appreciable transmission of radiant heat to the work, it is possible to effect gradual and uniform heating of the work while at the same time subjecting it to the even and uniform flow of the treating gas or gases, whereby the gas and the metal or material to be treated are concurrently in heattransfer and chemically-reacting relations;

Although no definite rate of circulation of the combined heat, vehicle and treating gas is contemplated, the fan or impeller 28 should rotate at such speed that the circulating medium effectively removes or wipes off stagnant films on the surfaces of the work under treatment, in order that the rate of treatment may be materially increased, instead of being reduced by the existence of stagnant films which tend to prevent or .retard the desired reaction between the treating gas and the work.

When the work within the furnace has been subjected to a predetermined duration and extent of treatment, the electrical resistors are deenergized and the fan motor shut ofi.

Before removal of the furnace cover. however, the exhaust conduit is opened to atmosphere so that removal of the cover structure, which in effect increases the furnace volume until seal 41 is broken, will not create a vacuum or reduce the pressure within the furnace interior below that of the external atmosphere and so cause the liquid within seals 41 and 60 to be drawn into the furnace. To this end, sealing plug 52 is released by unloosening clamping nut 56, after which lever 53 is rotated in a counter-clockwise direction to move plug 52 out .of sealing engagement with the end of conduit 5|. Accordingly, the interior of the furnace is now directly in communication with atmosphere and hoisting of the cover structure cannot therefore create a vacuum within the furnace to break and disrupt the aforesaid liquid seals. It is essential that the sealing plug 52 be open only while the cover structure is being lifted from the furnace to permit removal of the work, since replacement of the cover would only tend to force excess air through the exhaust seal. Ammonia, part of which is dissociated into nitrogen and hydrogen for the nitriding of steel, is utilized to effect concurrent heat and chemical treatment. As is well known in the art, a nitrided steel or suitable aly thereof has valuable wear-resisting. characteristics, the nitrided material having a very hard outer surface or shell highly resistant to wear, corrosion, abrasion, etc. An example of a practical use to which a nitrided steel may be put, lies in its application to shafts or equivalent members incorporated in high speed machinery. such as in automotive engines, and parts of valves, particularly those which must be resistant to corrosive action of hot gases or liquids.

Before the nitriding treatment is actually started the ammonia gas or vapor is introduced into the furnace, and preferably, is caused to circulate, in the manner previously described, by the fan for an appreciable length of time, generally about an hour, through the treating chamber and other parts of the furnace to the exterior through the exhaust seal, in order that air or any other undesirable gas, as an oxygen-containing gas for example, shall be substantially completely forced out of the furnace. During this gas flushing period, the batch of metal to be treated is not acted upon by the ammonia, since the electrical resistors are tie-energized. After the flushing period has been completed, the circuit through the resistors is closed, and the furnace interior accordingly increases in temperature. As the fresh ammonia gas is introduced under pressure into the upper portion of the furnace, it is caused to flow downwardly either through the treating chamber or the heating chamber, depending on the direction of rotation of the fan, and to circulate between the source of heat and metal.

As an individual charge of ammonia would become exhausted within a comparatively short period of treatment, a continuous supply, controllable by the furnace operator, is admitted to the furnace as the weakened or exhausted gas is discharged from the furnace through the yielding exhaust seal to atmosphere, or to gas recovery apparatus.

A carbonaceous gas may also be used in the above described manner as the principal medium of heat transfer for the purpose of gas carburizing the metal to give also a greater degree of hardness thereto. The carbonaceous gas may obviously vary somewhat in composition, depending upon the degree of hardening required.

It will be understood that the heat may be developed by any suitable method, as by gas firing, electrical resistors or other means. In general, it is characteristic of my apparatus that the reaction chamber be sealed with respect to the atmosphere in order that the nitriding gas, which wall and cover member for sealing the said heating chamber, and means for eifecting communication between said chamber and the external atmosphere independently of movement of the cover to prevent formation of a vacuum within said chamber during movement of the cover to open position.

2. A heat-treating furnace comprising an inner or heating chamber, an outer wall spaced from and surrounding said chamber, a removable cover member for said chamber, heat-resistant material interposed between the cover. member and the top of the furnace, and a fluid seal coacting with said outer wall and cover member for completely sealing the heating chamber with re spect to atmosphere.

3. A furnace structure comprising a wall enclosing a heating chamber, a cover member for closing said chamber, a liquid seal co-acting with said wall and cover member for sealing the said heating chamber, and means for preventing the liquid of said seal from being drawn into the furnace, comprising means for efiecting communication between said chamber and the external atmosphere independently of movement of the cover to prevent reduction of pressure within said chamber below the pressure of the external atmosphere during movement of the cover to open position.

4. A furnace structure comprising a wall enclosing a heating chamber, a cover member for closing said chamber, a liquid seal co-acting with said wall and cover member for sealing the said heating chamber, means for forcibly circulating said treating gas in contact with the material under treatment, and means for preventing the liquid of said seal from being drawn into the furnace, comprising means for opening said chamber to the external atmosphere during movement of the cover to open position.

5. A furnace structure comprising a wall en- .closing a heating chamber, a removable cover member for closing said chamber, a liquid seal coacting with said wall and cover member, the cover member'having a portion extending into the liquid of the seal, withdrawal of the cover increasing the furnacevolume while its said portion continues in said liquid, and means for preventing said liquid from entering the furnace due to consequent reduction in pressure within the furnace as the cover is removed, comprising means for opening the heating chamber to the external atmosphere during movement of the cover to open position. Y

6. A difiusion alloy case-forming furnace comprising stationary wall structure and removable structure coacting therewith to form a chamber, a seal for said chamber comprising displaceable sealing material held by one of said structures and in which the other of said structures is inserted to isolate said chamber from the extemal atmosphere, mechanism for forcibly stirring the diffusion alloy case-forming atmosphere in contact with the work in said chamber, means external to said chamber for driving said stir-,1

ring mechanism, and a seal for said means preventing entry of extraneous gas into said case-forming atmosphere.

7. A difiusion alloy case-forming furnace com prising a chamber in which is disposed in a gaseous atmosphere the metal upon which the case is to be formed, means for generation of heat, a source of diffusion alloy case-forming reagentindependent of said generation of heat, means for replenishing said atmosphere with reagent from said source thereof, means for ensuring uniformity of the case comprising mechanism for forcibly stirring said atmosphere, means external to said chamber for driving said stirring mechanism, and means for isolating said chamber to prevent ingross of extraneous gas including sealing means agspciated with said driving means of said stirring mechanism.

8. A carburizing furnace comprising a chamber in which is disposed in a gaseous atmosphere the metal upon which the carbide case is to be formed, means for generation of heat, a source of carburizing reagent independent of said generation of heat, means for replenishing said atmosphere with reagent from said source thereof, means for insuring uniformity of the carbide case formed on the metal comprising mechanism for forcibly stirring said atmosphere in contact with the metal, means external to said chamber for driving said stirring mechanism, and means for isolating said chamber to prevent ingress of air including sealing means associated with said driving means of said stirring mechanism.

9. A diffusion alloy case-forming furnace comprising a chamber in which is disposed in a gaseous atmosphere the metal upon which the case is to be formed, means for generation of heat, a source of diffusion alloy case-forming reagent independent of said generation of heat, means for replenishing said atmosphere with reagent from said source thereof, means for insuring uniformity of the case comprising reversible mechanism for causing flow of said atmosphere in either direction with respect to the metal and for forcibly stirring said atmosphere in contact with the metal, means external to said chamber for dri ng said mechanism, and means for isolating said chamber to prevent ingress of extraneous gas including sealing means associated with said driving means of said reversible mechanism.

10. A nitriding furnace comprising a chamber in which is disposed in a gaseous atmosphere the metal upon which a nitride case is to be formed,

JOHN w. HARSCH. c

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