US2686665A - Heat-treating furnace - Google Patents

Description

1954 G. M. TAUBER ETAL HEAT-TREATING FURNACE 3 Sheets-Sheet 2 Filed Oct. 14. 1950 INVENTORS. GUSTAVE M. TAUBER JOHN J. SCHULTZ ATTORNEYS g 17, 1954 G. M. TAUBER ETAL HEAT-TREATING FURNACE 3 Sheets-Sheet 3 Filed ON. 14. 1950 4 00 sec 000 I IOIOOI lz oo m oo leoo Temperature Degrees Fahrenheit I000 I200 I400 I600 300 Temperature Degrees Fahrenheit INVENTORS. GUSTAVE M. TAUBER BY JOHN J. SCHULTZ ATTORNEYS Patented Aug. 17, 1954 HEAT- TREATING FURNACE Gustave M. Tauber, Philadelphia, and John J. Schultz, Drexel Hill, Pa., assignors to Leeds and Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania 1 Application October 14, 1950, Serial No. 190,152

This invention relates to heat-treating furnaces of the forced convection type used for tempering, annealing, carburizing, nitriding and similar heat-treating processes.

In many furnaces of this type, a fan, disposed in the bottom of the furnace below an open- 3 Claims. (Cl 266-) ended basket which contains the work to be 1 treated, forcibly circulates the furnace atmosphere repeatedly through the work container and a heating space between the work container and the internal wall of the furnace.

In accordance with the present invention, en-

closure of the fan and support of the work container is provided by a casing structure essentially comprising. an apertured plate forming the upper wall of a fan housing and from which downwardly extend a plurality of vanes whose lower edges rest upon the furnace base, thus to form fan discharge outlets or ducts opening into the heating space of the furnace. Further and more specifically in accordance with the invention, a peripherally continuous sealing skirt extends upwardly fromthe apertured plate with its upper portionforming a supporting ring or flange for the bottom of the work basket or tray. More particularly, a removable screen passed by the sealing skirt overlies the fan inlet opening or openings in the apertured plate and is preferably positioned by bracing ribs of the sealing skirt.

Further in accordance with theinvention, the fan outlet vanes extend beyond the sealing skirt with the upper edges of the vane extensions respectively joined to projecting areas of the apertured plate.

Further in accordance with the invention, the fan housing is provided with members extending upwardly from it to center the work container supported thereon with respect to the sealing skirt and fan inlet; more. specifically, the lower and vertical portions of the center members respectively merge with the apertured plate and with the sealing skirt to impart additional strength and rigidity to the entire unit.

The invention further resides in novel and useful features of construction, combination and arrangement. 1

For a more detailed understanding of the invention and for illustration of the embodiments thereof, reference is madeto the accompanying drawings, in which:

Fig. 1 is a side elevational view, in section, of one type of furnace utilizing thenew fan housing andwork support unit; 1

Fig. 2 is a bottom view of the fan housing unit of Fig. 1;

Fig. 3 is a top plan view, on enlarged scale, of the fan housing structure of Fig. 2; 1

Fig. 4 is an elevational view, partly in section, of the housing shown in Fig. 3;

Fig. '5 is a perspective view of the fan housing of Figs. 2- 1;

Figs. 6A and 6B are explanatory figures referred to in discussion of a furnace embodying the new fan housing; and

Fig. 7 is a perspective view, partly broken away, of another type of furnace utilizing the housing structure of Figs. 1-5.

In Fig. 1 there is shown a heat-treating furnace l 0 of type generally shown in United States Letters Patent including 2,176,473; 2,168,028; 2,161,162; 2,032,209; 1,999,757; 1,926,234; 1,949,- 716; 1,940,948; and 1,721,840. In brief, the work to be treated is disposed in a work continer H whose upper and lower ends are open and whose sidewalls are imperforate. The grid l2 in the bottom of the work basket, tray or equivalent container ll provides support for the work pieces and yet permits free passage of the furnace atmosphere. As later more fully discussed, the work container rests upon and is supported by a fan housing structure l3 disposed in the bottom of the heat-treating chamber I 4 defined by the base member I5, the retort 16, or equivalent internal wall structure of the furnace, and the removable cover member I! which serves: as a removable closure for the top of the heat-treating chamber 14.

The cover I! is provided with a downwardly directed flange which is received by the channel It at the upper end of retort l6 and filled with sand or other sealing material to prevent escape from chamber [4 of the furnace atmosphere.

The furnace may be gas-fired or electrically heated as shown by aforesaid patents; in the particular furnace shown in Fig. 1, the furnace atmosphere and work are raised to treating temperature by the electrical heater elements l9 suitably supported by the wall structure 20 of the furnace which like base member I5 is of heat-insulating brick and refractory. To minimize heat losses, the cover of the furnace is similarly provided with an outer layer 2| of heatinsulting brick or equivalent.

In the preferred arrangement shown in Fig. 1, the furnace retort I 6 has a closed bottom and is supported by the ring or flange provided by the extension of the bottom plate 22 of the furnace beyond the side wall structure 2! In this respect the construction differs from that of aforesaid patents in which the retort has an open bottom with the lower edge received by a sand seal.

For forcible circulation of the furnace atmos phere within the treating chamber i l so defined, there is provided a fan 23 supported below the open bottom of the work container l l by attachment to the upper end of a motor shaft 2 which extends through the base it. Escape of furnace gas along shaft 24 is precluded by a suitable sealing gland. The shaft M is driven by motor 25 suitably suspended as by bolts 25 from the underface of the furnace base member it which in the embodiment of Fig. 1 is within the retort so that the base It, motor 25, fan 23 and the combined fan-housing and container support it are insertable into and removable from the furnace as a unit with the retort.

As shown more clearly in Figs. 2-5, the housing [3 for the fan 23 comprises a plate ill which forms the upper wall of the fan housing. This plate is provided with a central opening it of diameter suitably less than the diameter of the fan 23 or otherwise suitably apertured to provide a fan inlet. From the underface of plate 2? there downwardly extends a plurality of vanes 29, whose lower edges are free to engage and rest upon the upper face of the base member is of the furnace, as shown in Fig. 1. The inner edges 8| of the vanes 25 define a circle of diameter slightly greater than the fan circle, and the outer edges 32 of the vanes define a circle approximately circumscribed by the retort l5. Thus, when the housing It is in place, the vanes 29 in coaction with plate El or the housing and base lb of the furnace form fan outlets discharging into the gas-heating space between the retort it and the work container ll. Preferably and as shown, the fan 23 is of the centrifugal type and the vanes 29 extending substantially tangent to the fan circle are of spiral or volute form.

As shown most clearly in Figs. 2-5, the vanes 29 project beyond the main circular area of the plate 2? but are respectively joined to that area by minor areas 33 of approximately triangular shape. These minor areas 33 serve as upper walls of the fan outlet ducts and also as barriers which prevent dislodged work objects from entering the fan housing. Objects which fall in the gaps between these areas fall on the flat up per surface of the base l5 below the fan and externally of the housing and so do not damage the fan.

Preferably and as shown, from the main annular area of the plate 2? there upwardly extends a sealing skirt of outline substantially corresponding with that of the work container and having a flange 35, preferably inwardly directed, peripherally to engage the lower edge of the work container for support of the container and its load. Thus, the opening till provided by the flange 35 closely approximates the area of the opening in the bottom of the work container for free flow of the furnace atmosphere.

The sealing skirt 3G is stiffened to resist de formation by the weight of the work basket and its contents at the high temperatures involved in heat-treatment by series of bracing ribs 36 which extend inwardly from the inner periphery of the sealing skirt 3 3. The inner ends oi the sealing ribs serve as steps or centering lugs for positioning a protective screen above the 4 fan inlet opening 28 in the upper wall plate 21 of the fan housing. The opening 39 defined by the flange 35 of the sealing skirt is of larger diameter than the screen 38 to permit easy removal of the screen.

For centering of the work basket II] as it is lowered into the furnace retort for engagement with the fan housing E3, the housing is provided with a plurality of basket-centering members 59 having upper portions which extend upwardly and outwardly from the upper portion of the housing l3. Specifically, the lower portion of each of the centering members 48 merges with a projecting area 33 of the plate 27, and the inner vertical edge of the lower portion of each of the centering members merges with the periphery of the sealing skirt 35: the centering members therefore also serve to strengthen and stiffen the fan housing structure. As most clearly appears in Fig. 3, the centering members 40 and the ribs 33 are angularly spaced about the periphery of the sealing skirt to afford distribution of the stiffening eifects.

The fan housing and basket support I 3 is preferably cast as a unitary structure although it may be fabricated from components welded together to form a unitary structure. For long life, the housing it should be of metal resistant to the furnace gases and temperatures.

The fan housing and work basket support l3 not only is of advantage in construction and maintenance of the furnace, but also is of operational advantage in that temperature uniformity of a fresh work charge within the container II is more rapidly attained. Referring to Fig. 6A, the curve A represents the temperature of work at zone #6 of the work basket, the coolest zone during initialheating, and curve B represents the temperature of work in zone #1, the hottest zone during the initial heating. As apparent from Fig. 6A, hich is based upon measurements in a furnace not using the present invention, a substantial difference of temperature exists between these two zones for the initial heating interval T preceding arrival of these zones at the control point or desired heat-treating temperature which in the particular case illustrated is 155i)". With the same furnace construction using, however, the improved fan housing, the temperature difference between the hottest and coolest zones of the furnace during the initial heating significantly is less as shown by the narrowed gap between curves A and B of Fig. 63. For example, with fan housing E3, the work in furnace zone #6 attained a temperature of about 500 when the temperature in zone #1 was about 250 higher (Fig. 63), whereas with the prior arrangement, by the time the work in zone #6 had attained a temperature of 500 the work in zone was 350 higher (Fig. 6A). Moreover, with the prior arrangement, when the hot zone temperature reached the control point, the temperature spread in the work basket was about (Fig. 6A), whereas with the new arrangement the emperature difference upon arrival at the control point is only about .6". This feature of the new fan housing is particularly of advantage for short runs, as in tempering, because affording increased furnace output without sacrifice of uniformity of product.

For some heat-treating operations, the furnace atmosphere forcibly circulated by the fan is essentially air; for other heat-treating processes, the furnace atmosphere may comprise or consist of a gas, or gases, inert or active. For use of treating atmospheres other than air, there is provided, as more fully shown in certain of the aforesaid patents above identified, an inlet 42 (Fig. 1) for admission of the treating gas or source thereof. A sight gauge 43 may be provided when liquid is fed in drops into the fur nace for vaporization and liberation of active gaseous agents. An exhaust pipe 44 is provided for escape of the partially depleted furnace atmosphere, a hinged cap 45 being provided to permit insertion and removal of test samples, if desired, during a heat-treating cycle.

Use of the fan housing and work support [3 is not restricted to the top-loading cylindrical type shown in Fig. 1 and may be to advantage used in box furnaces which are side or frontloaded. In Fig. 7, illustrative of one type of box furnace, the fan housing I3 is disposed within the furnace with the lower edges of its vanes 29 resting upon the upper face of the furnace base [5A. The base, as in Fig. 1, thus forms the lower wall of the fan housing and coacts with the vanes of the housing to define fan discharge ducts which open into the heating space of the furnace between the furnace side walls and the work container resting upon the flanged upper edge of the sealing skirt 34. In both Figs. 1 and 7 the fan housing is held against the furnace base by bolts or equivalent securing means which engage hold-down lugs 4| extending from at least some of the vanes. In Fig. 7, the upper edge of the sealing skirt 34 is approximately in the same plane as the lower edge of the opening 46 in the front wall of the furnace. Thus, a work basket. or container may be slid through the opening onto the fan housing. If desired, rails or guides may be provided to facilitate this loading operation. When used ina box furnace, some of the members 40 may be omitted to avoid obstruction to the work basket as: it is slid onto the sealing skirt though at least one of the members 40 may be retained to serve as a rear stop 40A for the work basket.

It will be understood by those skilled in the art that the invention is not limited to the specific embodiment shown and that changes and modifications may be made within the scope of the appended claims.

What is claimed is:

1. For use in a heat-treating furnace having adjacent its base a fan for forcibly circulating the furnace atmosphere repeatedly through a removable work-container having an open bottom of area substantially coextensive with the crosssectional area of the container, a unitary structure forming a fan housing and a work-container support comprising a sealing skirt member having an upper edge for peripherally engaging the bottom edge of the work-container and defining an opening substantially coextensive with said open-bottom area of the work-container, a plate member joined to the lower edge of said skirt member to form the upper wall of the fan housing and apertured within the fan diameter, and a plurality of vanes attached to and extending downwardly from said plate member for engagement with the furnace base which thereupon forms the lower wall of the fan housing and supports said unitary structure, said vanes extending tangentially of the fan diameter to project beyond the periphery of said sealing skirt and the work-container, said plate member having substantially triangular extensions respectively closing the gaps between the upper projecting edges of the vanes and the sealing skirt member.

2. An arrangement as in claim 1 in which the outer vertical edges of the vanes of said unitary structure define a circle closely circumscribed by the periphery of the inner wall structure of the furnace for free discharge from said outer vertical edges of the fan into the heating space between said wall structure and the work-container.

3. An arrangement as in claim 1 in which spaced bracing ribs extend inwardly of the sealing skirt and upwardly of the plate member, the inner ends of said ribs terminating short of the aperture through said plate member, and in which a screen passed by the opening in the sealing skirt member is positioned by said ends of the bracing ribs to overlie the aperture through the plate member.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 126,639 Leffel May 14 1872 1,870,551 Brown Aug. 9, 1932 1,976,557 Haskell Oct. 9, 1934 2,168,028 Harsch Aug. 1, 1939 2,245,647 Burby June 17, 1941 2,249,411 Woodson July 15, 1941 2,463,222 Vaughan Mar. 1, 1949 FOREIGN PATENTS Number Country Date 673,878 Germany Mar. 3!), 1939

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