US2297798A - Industrial heat treating furnace - Google Patents

Description

Oct 6, 1942- c. E. PEcK 2,297,798

I INDUSTRIAL HEAT TREATING FURNACE .Filed Maron ie, 1940 2 sheets-sheet 1,

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ATroRNEY omu e, 1942. C. E. PECK 2,297,798

INDUSTRIAL HEAT TREATING FURNACE Filed March 1e, 1940 2 Sheets-sheet 2 wlTNEssEs; S r

Paieoied Oei. 6, 1942 i INDUSTRIAL HEAT rnEaTiNGrFUaNAcE Clarence E. Peck; Wilkinsburg, Pa., 'asslgnor to Westinghouse Electrica Manufacturing Company, East Pittsburgh, l?a a corporation of Pennsylvania l Application Maren 1s, 1940, serai No. 324,409v

' s claims. `(ci. zes- 5) 'I'his invention relates to charge-supporting hearths for heat-treating furnaces, preferably of the bell and hood typewhich are to be operated at' fairly high temperatures. and in which the charges are to be heat-treated while enveloped by a protective or controlled gaseous atmosphere.

It is an object of my invention to provide'a relatively long hearth capable of withstanding high temperatures in the neighborhood of 1600 to l800 F., and above," which will have provisions for permitting all the necessary differential expansions between its hot parts inside the furnace, and the cooler'outer parts without damage. In this respect it is a further purpose of my invention to so construct and divide the metallic parts `of the hearth so that their displacements, due to expansion and contraction,

wi1l.be reduced, keeping the maximum displacement of any part to relatively small proportions: Additionally, in accordance with this aspect .of my invention, the spaces between the divided parts are provided with suitable sealing or closure i means.

It is a further object of my invention to provide a hearth comprising a non-metallic refractory base portion which will not chemically react, especially in a hydrogen atmosphere, with a metallic charge-supporting means which it supports.

It has beenfound by experience that if the metallic charge supporting means was made of an inexpensive ferrous metal, such as mild steel, the metal would react chemically with the nonmetallic refractory directly supporting it, particularly during the purging of air and moisture from the furnace by a continuous flow of a controlled hydrogen atmosphere; the melting point and strength of the refractory being adversely affected. It is my opinion that as the temperature of the furnace increased, any small layer of iron oxide on the surface of the metal was reduced by the hydrogen, and if such reaction occurred where the metal was in contact with the refractory. the refractory material would fuse and melt, forming a material of a much lower melting point than the original refractory.

Accordingly; it is an object of my invention to provide a hearth of the type described which utilizes relatively inexpensive materials for the charge plate and the non-metallic supporting refractory, but which will include means for limiting the deterioration of the non-metallic supporting refractory. v

It is 'a further object of my invention to provide means to convey thev controlled atmosphere through the hearth to the inside of the furnace, preferably inside the hood enclosing the hearth. To this end I provide suitable gas-sealing means which will enable all of the required inlet and discharge pipes to expand independently of each other, and thus I overcome a difficult expansion between parts having considerably different temperatures. All welded joints and metallic type expansion joints which may crack and fail are eliminated in my construction.

In accordance with my invention, the hearth comprises a non-metallic refractory base upon which rests a base plate made of a plurality of sections having spaced edges so that the sections may expand and contract toward and away from each other. However, a suitable means is provided covering and sealing the spaces between these edges, thisv means being substantially gastight, but not interfering with the displacement of the sections. Additionally, theouter -periphery of the base plate preferably is provided with depending lips or flanges which extend into a suitable gas-sealing channel around the base portion of the refractory base, the flanges and channel being also provided with means, substantially gas-tight, which will permit these parts to expand and contract without extensive displacement. vention, the anges are provided with guiding means for positioning the lowerv edges of the furnace hood suitably in the same gas-sealing channel into which the flanges extend.

In the preferred form of my invention, the base plate takes the form ofga container for holding a nnely divided refractory sand, such as alumina vor magnesia, which provides a sand bed that can be easily levelled. A charge-supporting plate, smaller than the container, rests on this bed, with its edges inward of the'inner periphery of the container to allow for maximum changes in the dimensions ofthe plate with variations in temperature. A hearth, embodying a refractory sand bed confined .in a container, with a charge plate resting on the bed, is described and .claimed in Patent No. 2,189,624 of J. H. Bramble, issued February 6, 1940, and assigned to the Westinghouse Electric 8L Manufacturing Company. 1

Many other objects and features of my invention, and details thereof, in addition. to those aforesaid, will lbe apparent from the following description thereof which is to be taken in con- Junction with the drawings, in which:

Figure 1 is a verticali. longitudinal, sectional, 7

view of a hearth employing my invention, and

As a further novel feature of my inhood omitted for clarity of illustration;

schematically showing a. hood for enclosing a charge to be placed. on the hearth;

Fig. 2 is a plan view of the hearth, with the Fig. 3 is an enlarged fragmentary, vertical, sectional view, on the line III-III of Fig. 2, more fully showing the constructional details by which the controlled atmosphere is directed into the charge heat-treating space under the hood, `a preheating conduit system being within the hearth;

Fig. 4 is an enlarged side view of a detail;

Fig. 5 is a fragmentary, vertical, sectional view, somewhat enlarged, of a modified form of hearth construction, and

Fig. 6 is a schematic, vertical, sectional view, on a much reduced scale, of a furnace incorporating my invention. v i

My invention is primarily applicable to a belltype furnace such as shown very schematically in Fig. 6, although my invention is not necessarily limited to this type of furnace.

The bell-type furnace comprises a support or base 2 of a non-metallic refractory material provided with an upwardly protruding base wall portion 4 forming part of a hearth which also includes' a container, indicated in its entirety by the reference numeral 6, supported on the base portion,v and comprising a multi-section base plate 8 and multi-section sides I0. The container is,iilled with a non-metallic refractory sand' I2 which can be levelled, and wl :h supports a fiat charge plate I4 on its surface, the charge plate being a single piece of suitable metal having a periphery Within the inside periphery of the sides l0 and being suitably spaced therefrom at all points so that the plate may expand and contract without contacting the sides. A hearth of this general character is shown in the aforementioned patent.

A removable heating bell I6 having side wall heating elements I8 can be removably set on the base 2 which has an outside sealing channel 20 around it. This channel is lled with any suitable sealing substance for receiving a depending lip 22 of an outer metallic shell or casing 24, provided for the bell. A similar outer metallic casing 26 is provided for the outside of the base 2, so that the bell and base are rendered, as far as possible, gas-tight, as is customary in the art. The base portion 4 has a sealing means 30 around it for receiving the lower edges of a removable metallic hood or shield 32 so that any charge placed upon the hearth willbe suitably enclosed within a heat-treatment space 34 defined by the hood and hearth. l

In the preferred form of bell-type furnace to which my invention is applied, the heating units I8 extend below the charge plate I4 so that all parts of any charge within the heat-treatment chamber 34 will be adequately heated.

The sealing means 20 and 38 may include any suitable sealing medium, such as finely divided non-metallic refractory sand for the inner sealing means 30, and a similar sand or a suitable liquid for the outer sealing means 20.

The base portion 4 has a suitable gas inlet means schematically indicated in Fig. 6 at 36, and in greater detail in Figs. 1, 3 and 5, for a protective gas to be discharged after being preheated,

n along the inside surfaces of the hood.

Referring more particularly to the embodiment l of my invention shown in Fig. 1, the base portion 4 is shown as comprising a continuous refractory wall which may be made of any suitable highportion 4 is the container 6 with its base plate 8 comprising a plurality of separate sections, shown in this instance as two sections 40 and 42, the facing vertical edges44 and 46 of which are spaced from each other to provide an intervening space 48. A platel 50 has one edge welded, or otherwise secured, to the section 40 and its other edge slidable on top of the other section 42. This plate 50 covers the space 48 so that the container can be filled with sand to provide the sand bed I2. Secured to and coextensive with the other vertical edges of the sections 48 and 42 are upstanding lips or flanges 52 and 54, respectively, comprising upper portions forming the sides I0 of the container 6, and lower portions extending into the sealing means 38. y

In order to render these vertical flanges substantially continuous along the space 48, suitable closing members 56 and 58 are provided on each side of the hearth, each having an end portion welded or otherwise secured to the part of the flange 52 in proximity to the space 48, with the other end portion slidably contacting the flange 54. The members 56 and 58 have outer sides which are of substantially the same height and abut the outer surfaces of the flanges 52 and 54, and have inner sides which abut the inner surfaces of theanges 52 and 54. The inner sides of the members 56 and 58 are of a height substantially equal to the distance from the top surface of the plate 50 to the top of the ilanges 52 and 54. The two si'des of each of the members 56 and 58 are bridged by a cross piece so that each member is, in eifect, of inverted U-shape with an inner leg shorter than the outer leg which .extends into the sealing means 30.

The sealing means 36 comprises a generally U-shaped channel 6I) for conmng the refractory sealing sand 62 into which the flanges 52 and 54, including the outer sides of the members 56 and 58, extend, and in order to provide suitable expansion means for the channel 60 it is also split into a pair of spaced sections which are edgewise separated in the region when the container 6 is split. Insert troughs 64 and 66 bridge the space formed by the separated edges of the channel 60, these troughs closely tting the interior surfaces of the channel 60, so as to render the latter, in effect,l continuous. One end portion of each of these troughs may, if desired, be secured to one section of the channel 1 60, the other end portion of each trough being in slidable contacting relation with the corresponding side of the other section of the channel.

Each section of the container 6 has a freedom of movement for expansion and contraction in space 48 and the end portions of the sand seals 30, the small closure means comprising the plate 50 and the inverted U-shaped members 56 and 58 keeping the variable space 48 covered during such displacement. Additionally, the sections of the channel 60 can also expand and contract, the closure troughs 64 and 66 keeping the channel complete at all times. Consequently, the container 6 is full-floating with provisions for expanding and contracting at a plurality of points distributed along its length so that each displacement is relatively small as compared to what would have been the displacement if the container had been made solid. In other words, the movement of any part of the cons therewith to form a sand tainer due to great variations in temperature is kept small in my novel construction. v

In order to convey. preheated protective at -mosphere into the heat-treatment chamber I4,

I prefer to provide the base portion 4 and the base oi' the containervwith suitable apertures v in which may be disposed 4the gas inlet system Il which has means for allowing all of the necessary differential expansions and contractions between the hotinner parts of the furnace .and cooler outer parts of the pipe system. To this end the outer casing 24 oi the base is provided withan aperture to asrbyiwelding, gas 'inlet pipes 10. In this particular embodiment. two similar inlet systems are provided, one at each end of the container.

Each inlet pipe 'I0 extends through a sand sealing means comprisingl a cylindrical outer member 12 about the pipe 10 and cooperating sealing meansfor conilning the sealing sand 14.- Each` of the sections 40 and 42 is also provided with apertures defined by stepped surfaces 'l0 for receiving a cover plateplll which has a plurality of holes into which are fitted L-shaped pipes 00 which are embedded in the sand bed |2. A conduit 02 is directly `below the cover plate 10, having one edge in the sealing sand 14 and projecting upwardly in proximity to the cover plate 18. Gastightly secured to the upper outside edge of the conduit 82 is an annular plate 04, and depending downwardly therefrom and also gas-tightly secured thereto is a cylindrical sealing member 00 extending downwardly into aI sealing sand bed l0 confined in an annular sealing channel 90 about the pipe 02, the sealing channel 00 being gas-tightly secured to a` section of the base 8 about the aperture for the cover plate 10. A

g handle bar` 02 is secured acrossthe top of the pipe section 82 so that it may be readily removed, or inserted in position.

The L-shaped pipes 80 have thei longerv legs substantially horizontal, the legs passing through suitable holes 4in the flanges 52 and 54, and terminating somewhat above and slightly outward from they inner side of the channel 00, where the protective atmosphere is discharged. A guard 96, closed at the bottom and sides, and open at the top, protects the outlets of the horizontal legs of the discharge pipes 80 and also diverts discharging gases upward. The vertical legs of the pipes 00 provide duct means for conveying the gases to the horizontal legs of the pipes from` the distributing chamber below the cover plate 18 and formed therewith in conjunction with the channel 90, the sealing member 00, and the annular plate 04.

The sand bed I2 covers the pipes 80 and may be levelled to support the flat charge plate I4 in accordance with the teachings of the aforesaid Bramble patent.

- In order to prevent damage to the guard elements 96 during lowering of the hood, and also toguide the hood into vide guides |00 spaced along the anges 52 and 54, and secured thereto, the guides having inclined upper 'surfaces for directing the hood evenly into the sealing channel 30.

I have found that in furnaces for heat-treating a charge in the presence of a large amount of a reducing gas such as hydrogen, a ferrous metal plate directly in contact with the supproper position, I pro- Aporting refractory tile caused chemical reaction between the refractory tile and the plate if the plate were made of a relatively inexpensive which is sealed,

ferrous metal such as mild steel. In order to prevent this reaction and to reduce the use of a'la'rge amount of expensive non-reacting heat- 4 resistant metal, I have found that by interpos- 5 ing a thin sheet of non-reacting metal between the base plate 0 and the base portion 4, contamination and destruction of the refractory are avoided, or at least considerably reduced. Such sheets are indicated at |02 in Figs. l and 3. The sheets are, of course, suitably formed to fit the construction and configuration of the hearth, ,being suitably apertured for the gas inlet system and split in the middle, as shown, for expension and contraction. f

The modification of the hearth shown in Fig. 5 is similar in substantially all respects to that XshoWn in Fig. l, except that the base portion il constructed with piers for supporting the container, the piers having alloy caps |22 for 2o preventing reaction between' the refractory and ythe mild steel base of the container. l

I have Vfound that a chromium nickel alloy containing 25% chromium, 12% nickel, balance iron, will suitably reduce the chemical reaction 25' between the refractorytile and mild steel base plate l of the container in a bell furnace opcrating in the neighborhood from-1600 to 1800 F., and utilizing `a substantially pure and fairly .dry protective atmosphere of hydrogen which. is maintained at a slight positive pressure higher than the pressure in the heating zone'betwrcn the hood and the bell so that the gas leaks slowly through the sand seals, although it may be withdrawn in greater amounts through outlet pipes |24 when a large flow of the protective atmosphere is desired in the heat-treatment chamber 34.

While I have shown my inventionin forms which I now prefer, it is obvious that many 40 changes may be made in the details thereof and equivalents employed. I

I claim as my invention: 1.`A furnace for'heat-treating a charge in a gaseous atmosphere, comprising a base portion, a container having a bottom and sides, said container comprising a plurality of sections supported by said base portion, relatively movable covering means for covering the spaces between said sections, a nely divided refractory bed in said container, a charge-supporting plate means on said bed, and gas conveying means comprising a plurality of pipe means embedded insaid bed, each of ,said pipe means being associated with a diierent one of said sections. 2. In a furnace, the combination 'with a charge-supporting hearth means, of a raisable and 'lowerable hood cooperating therewith for providing a heat-treatment chamber in which charges are heat-treated in a controlled .atmosphere; said charge-supporting hearth means comprising an elongated non-metallic refractory base portion; a container supported by said base portion, said container containing a divided material; anges means. depending from said container along its edges; a gas-sealing means comprising generally U-shaped channel means around said base portion, said channel means having gas-sealing medium therein, the bottoms of said hood and said flanges being disposed in said gas-sealing medium; said containeigilange means, and channel means being formed of spaced sections for permitting expansion and contraction, and limiting the -displacement thereof whereby any single displacement of said flange means in said channel means is less than said channel means spaced slightly from said` 3. In a furnace, the combination with a charge-supporting hearth means, of a raisable and lowerable hood cooperating therewith for providing a heat-treatment chamber in which charges are heat-treated in a controlled atmosphere; said charge-supporting hearth means comprising an elongated non-metallic refractory base portion, a heat-resistant metal on, and

in contact with, said refractory base portion, said metal being of a type substantially chemically inert with respect to said refractory base portion in the presence of hydrogen at high temperatures; a container on, and in direct contact with, said heat-resistant'metal, said container containing a divided material; iiange means depending from said container along its edges; a gas-sealing means comprising generally U-shaped channel means around said base portion, said channel means having gas-sealing medium therein, the bottoms of said hood and said flanges being disposed in said sealing medium; said container, flange means, and channei means being formed of spaced sections for permitting expansion and contraction,l and limiting the displacement thereof whereby any single displacement of said flange means in said channel means is less than the# total displacement; covering means for keeping the spaces between saidsections covered at all times; conduit means for directing controlled atmosphere l from outside of said heat-treatment chamber to the inside of said heat-treatment chamber, said conduit means comprising substantially horizontally arranged preheatingpipe means disposed in said divided material, and duct means connected to said preheating pipe means, said duct means opening below said container, said heat-resistant metal having an opening around said duct means, said preheating pipe means having gas outlets at said channel means near the lower edge of said hood and above sraid gas-sealing medium; and guide means for guiding said hood during lowering for positioning said hood in said channel means slightly spaced from said "gas outlets.

4. In a furnace, the combination with a raisable and lowerable hood, of a charge-supporting hearth means cooperating therewith for providing a heat-treatment chamber in which charges are heat-treated in a controlled atmosphere, said charge-supporting hearth means comprising an elongated non-metallic refractory base portion, a container supported Iby said -loase Iportion. said container comprising spaced sections and relatively movable covering means for covering the spaces between said sections, said container containing a finely divided material and comprising a base plate, conduit means for directing controlled atmosphere through said hearth means to said heat-treatment chamber, said conduit means comprising substantially horizontally arranged pipemeans disposed in said finely divided material, said conduit means having gas-outlet duct means extending through said base plate to said pipe means, a gas-distributing chamber -below said base plate into which said duct means opens, and gas inlet means for conveying controlled, atmosphere to said gas-distributing chamber.

5. In a furnace, the combination with a raisable 'and lowerable hood, of a charge-supporting hearth means cooperating therewith for providing a heat-treatment chamber in which charges are heat-treated in a controlled atmosphere, 'said charge-supporting hearth means comprising an elongated non-metallic refractory base portion, a container supported by said base portion, said container containing a finely divided material and comprising a base plate, conduit means for directing controlled atmosphere through said hearth means to said heat-treatment chamber, said conduit means comprising substantially horizontally arranged pipe means disposed in said finely divided material, said conduit means having gasoutlet duct means extending through said base plate to said pipe means, a gas-distributing cham- -ber below-said base plate into which said duct' means opens, andfgas inlet means for conveying controlled atmosphere to said gas-distributing chamber, said gas inlet means comprising a gasV inlet pipe having a discharge end in said gasdistributing chamber, andgas-sealing means for said discharge end permitting said inlet pipe to expand and contract.

6. A heat-treating furnace for heat-treating a charge at relatively high temperatures while the charge is enveloped yby a controlled reducing at-

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