US2283982A - Bell type annealing furnace - Google Patents

Description

Patented. May 26,. 11942 Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania --Application October 7, 1939,.Serial No. 298,461

2 Claims.

Bell furnaces are known, and generally comprise a refractory-metal inner hood placed about a charge, the hood being encased by an outer insulating bell with sufficient clearance space between the hood and the interior of the bell to permit the disposition of heating means therein. My invention relates generally to bell furnaces which are to be direct-fired with combustible fluid fuel, but which lend themselves to accurate control and distribution of the temperature within their heating chambers, the degree of accuracy of control being comparable to bell furnaces heated by electrical heating means in the form of sinuously-shaped resistor ribbons.

Direct-firing by gas in the space between the bell and hood is known, but has heretofore been employed. only where relatively wide temperature discrepancies could be tolerated since it has been found extremely dimcult to obtain accurate temperature control of belltype furnaces employing direct gas-firing as a heating means. Accordingly, it is an object of my invention to provide a bell furnace construction adapted to be heated by direct 'gas-firing and which will have features enabling an accurate temperature control and distribution-in the furnace.

In accordance with my invention,\I provide av combustion space or chamber between the hood of the furnace and the encaslng bell in which its bottom provided with a frame-like member of large-capacity, or a multiplicity of burners individually supplying small amounts of heat, but in the aggregate enough to heat the furnace to the desired temperatures, As an example of a furnace employing my invention, and in which ac-- curate temperature control and distribution may be obtained with eflicient heating and long life,

reference may be made to the application of C.

Beck, Serial No. 298,456, filed concurrently herewith, and assigned tothe Westinghouse Electric 8! Manufacturing Company.

A further object of my invention is to provide a bell-type furnace, direct-fired by gas, which has a hood provided with a horizontal skirt restv ing on the base of the furnace, and a bell having of secondary air into the combustion space.

ther objects, features and innovations of my inv ntion will be apparent from the following description thereof, taken in conjunction with the drawing, in which Figure l is a vertical sectional view of the furnace-incl uding the features of my ihvention;

1 Fig. 2 is a plan view of a portion of the base frame-ring of the bell of the furnace;

Fig. 3 is a view, in section, of a detail v of the lower seal of another form of bell furnace; and

Fig. 4 is an enlarged view,'in section, of a burner mounted in the bell.

In many respects the bell-type furnace of my invention follows thegeneral customary design in providing a foundation 2 upon which rests the disturb the temperature'balance by interfering with the controlled combustible gas and air proportions admitted to the combustion space; V

An ancillary object of my invention is to provide a directly gas-fired bell-type furnace which is gas-tight at all places except the discharge flues for the products'of combustion.

base of the furnace, the base being indicated in its entirety by the reference numeral 4. The base, in general, comprises astructural steel framework, representedflby the reference numeral 6, supported by the foundation, and un-' derlying a base plate 8 which is, preferably, iron or steel'o'f heavy stock, and therefore, gas-tight.

' The importance of the features of my invention lies in the fact that, by controlling the amounts of the combustible fuel and airfor combustion that are admitted to the space between the hood and the bell, completetmp efature control of the heating process can beobtained,

Q whether the furnace has a few burners each of A refractory and insulating hearth Ill is suitably supported on the base plate 8 and comprises a horizontal portion l2 completely covering the base plate and a plurality of spaced vertical piers l4 disposed inwardly of the periphery of the base,

having embedded therein aheat-resistant skeleton framework l6 providing v I the charge-supporting part of the hearth.

A gas-tight O ,-1nd1catedin its entirety by the reference number ll. isdisposed on the base t with its lower portlonabout and slightly largerthan the piers l4. The hood- I! generally comprises an upstanding portion 20 having a top 20' so that any charge resting on the charge-supporting framework It is completel encased by the hood. In the illustrated embo ent of my invention, the lowermost part of the' hood is formed with an outwardly-directed, in this case,

er, so as to provide a combustion space or chamber 30 between the two. The bell comprises an outer, gas-tight metal casing 32 completely en casing it, and firebrick walls 34 having an inner refractory lining 38 defining part of the combustion chamber.

The construction of the furnace thus far described may be deemed to be somewhat conventional and in ordinary practice the bell isprovided with an apertured bar or some equivalent device 38 by which it may be raised and lowered from and to its operating position about the hood. Positioning devices for'mating the bell and base may also be employed.

of the bell through which the products of combustion may pass; There are, of course, a plurality of burnersin each horizontal row, and also a pluralityof flues, but in Fig.1 only one in each row has'lbeen shown, the others having been omitted for thesake of clearness; To keep the burning gas from directly impinging on the hood the burners may be provided with turnedup snouts 54, or such snouts may be turned upper portion of the hood but is somewhat large tangentially of the hood, or even omitted entirely with the bumers-directed tangentially of the hood if it be cylindrical.

One of the principal purposes of my invention is to gas-tightly seal the furnace at every place where secondary or extraneous air or gas that might disturb combustion may possibly seep into the combustion space between the hood and the bell to the end that I' may obtain in a directflred gas furnace a temperature distribution which is rigidly controllable. To this end the gas burners are secured gas-tight to the bell-cas .ing 32, and I prefer to use a construction by which Usually the charge inside the hood is heated have a composition to carry out certain desired reactions therewith. Such a protective atmosphere may be admitted through an inlet pipe 40 and suitably circulated b a fan 42. An outlet pipe 44 for the protectiv gas' may be provided extending through the base as an outlet for the atmosphere within-the hood so that the heattreatment chamber inside the hood may be purged when a heat treatment is started, and so that the atmosphere may be maintained clean and pure during the heat-treating process. The fan 42 for circulating the atmosphere within the hood maybe connected to any suitable mechanism including a motor 46 driving a shaft 48 to which the fan is secured.

The pipes 40 and 44 are gas-tightly sealed tov erick R. J. Davis, Serial No. 221,719, filed July- 28, 1938, and assigned to the Westinghouse Elec-' trio 8: Manufacturing Company; although any other seal may be employed which will assure a gas-tight joint between the shaft 38 and the base plate 8. In the same manner a thermocouple pipe 49 involved in the temperature control of the furnace passes through the base plate 8 and has a gas-tight joint with respect to it. Accordingly, the base plate 8 is gas-tight throughout its extent, and by providing a seal between the base plate and hood flange. the heat-treating chamber inside the hood is fully sealed.

For heating the furnace, a plurality of burners 50 may be arranged in vertically-spaced, horizontal rows, three such rows being shown in Fig. 1, and it may be observed that these burners are disposed in the lower part of the furnace. A plurality of flues 52 areprovided in the top each burner has an outer pipe 56 provided with an outside flange plate 51 whichcan be'secured gas-tight, as by welding, to the outer casing 32 of the bell. Each burner is further provided 'with a gas-tight end plate 50 provided with an inlet pipe 60 gas tightly secured to-the end plate 58 through which a-controlled mixture of gas and air may be supplied to a burner block 6|, it being understood that the entire structure is deliberately constructed so that no outside air can be inhaled by the burners. Consequently, the casing 32 can be considered air-tight except for the flues 52 which open into the atmosphere around the bell.

- While I have described the burners as a premix type, it is obvious that any other suitable types of burners may be employed so long as the openings in the bell in which the burners set are sealed gas-tight whereby only desired and controllable amounts of gas and air are admitted thereto, these being controlled in any suitable manner as, for example, by manipulation of valve-controlling mechanism 62, operable either manually or automatically in response to temperatures within the furnace, or by some other means, as is well known to the art.

It has been customary in the construction of directly gas-fired furnaces to terminate the outer metallic casing of the bell at approximately the horizontal skirt of the hood or some similar equivalent construction employed. This construction did not seal the combustion space of the furnace. While it might appear that in such a parent thata considerable amount of outside air can be drawn into the combustion space even through small crevices at the jointure 0f the botframe 63 for reenforcing the structiit' in the furnace.

periphery, and is further provided with addltional appurtenances comprising a plurality of vertical gusset plates 68 secured to the inside of the casing 32 and the upper side of the bottom M e, and also a frame ring 6.8 secured to the bottom side of the frame 63 and of relatively narrow width'compared thereto. The'weight of the bell is transmitted to the bell supporting means, in this case, the base 4, through the ring 68, the purpose of the ring 68 being to permit breathing of the lower part of the hood so that it will not have a I tendency to crystallize and crack through repeated expansions and contractions in the course of time.

An important feature of my invention is to I completely seal this abutting joint between the lower part of the bell and the upper part of. the

. hood or base, as the. case may be, so that the combustion space 30' is completely sealed against any seepage or infiltration of any gases which might disturb the controlled proportions of' the combustion mixture admitted through the burn ers 50. This leakage of secondary or unwanted air is very marked if the furnace is not sealed at the bottom 'due, primarily, to the chimneyv 3 other shapes offered in furnaces such as, for example, rectangular bell furnaces.

The operation of my furnace is, of course, obvious. The burners 50 supply regulatable amounts of gas and air to the combustion space 30 and since no other gases can seep into the combustion space, the heat produced is due only to the combustion of the desired amounts of gas and air flowing from the burners 50. Of course, it is obvious that if the admission of secondary air for :combustion is deliberately wanted,- its flow must'alsobe regulatable if accurate temperature control and distribution are to obtain, so that it would still be necessary to use a fur-i nacewith a; combustion space completely sealed except at its flues, the secondary airv in such case I being admitted through inlet means having appropriate flow-controlling means.

My invention enables me to construct a directfired gas furnace of the bell type for use where accurate temperature distribution or control is like action. caused by the difference in temperature between the gases inside the furnace and the air outside the furnace. To accomplish this, I gas-tightly secure to the casing 32 a downwardly extending flange 10 of metal completely encofnpassing the lower part of the bell, this flange 10 extending downwardly into the trough 28.

Accordingly, it may be observed that the combustion space is completely confined within a metallic structure comprisingthe upper part of the, hood I8 and the outer casing 82 of the bell, the only possible openings to the combustion space being at the fines 52 at the top of the bell, and the interspace between the flanges 24 and it at the bottom of (the furnace. Since no air can filter or seep into the combustion space through the .fiues because of the outgoing com-' bustion products, the space between the flanges 2d and 10 provides the onlypossible source of unwanted secondary air; this source, however, being suflicient to render ineflective attempts to control accurately the temperature distribution In accordance with my invention, the space between the hood and bell casing is sealed gastight, and in the particular embodiment this is accomplished by filling the trough 26 with aliquid sealing medium I2 which might be 011, water, or even molten metal. I prefer not to use a granular substance such as' sand or the like, since, as is well known, such materials are not impervious to the flow of gas therethrough.

My invention, therefore, provides a directlyfired bell furnace of the type described in which the combustion chamber or space is completely sealed against the admission of regulation-disturbing secondary air or gases which might affect the controlled combustion of the burning gases in the combustion space.

For extremely accurate temperature control,

desired, as distinguished from a similar furnace usable for heat-treating only with considerable. variations in temperature. In other words, I

have provided 'a directly gas-fired bell furnace whose temperature can be controlled within limits much narrower'than previously obtained.

By sealing the bottom of the furnace, the pressure conditions in the "combustion chamber are definitely controllable, and are not disturbedby infiltration of secondary orjextraneous air or gas which would not only disturb the pressure conditions, but also affect the combustion in the chamber, both in an upredictable manner.

leterious effects .are even greater in structures where the bell is supported upon a relatively narrow member such as the ring 68. In practice, such a ring may be about one inch to one and a half inchesin horizontal width, and about one inch'thlck for bells ranging from 8 to 14 feet in height with wallthicknesses ranging from 8 to 16 inches. It is quite apparent, therefore, that very shortseepage paths of only one'to one and a half inches in length are present all around the bottom of such a bell.

The provision of the sealing means suchas I have shown not only eliminates the factors which hinder the application of directly gas-fired bell furnaces, or have rendered them unsuitable, for

heat-treating processes requiringaccurate temperature distribution and control, especially hightemperature processes, but also results in a more efficient furnace since the seal, by enclosing the bottom joint'between the bell and hood, and providing a-de'ad air space "H as additional insulation, also decreases loss of heat by conduction and convection.

While I have shown my invention in'a form which I now believe to be the best practical application thereof, it is obvious that other forms of embodiments and many equivalents are possible. Thus, for one examp1e, the frames 83 might extend outward from the bell outer casing, a

gas-tight weld being provided between the two. Withsuch construction, the bell-sealing flange can be made integral with the frame 63 or gastightly secured thereto.

The structure of Fig. 3 differs from that of Fig. 1 in that thebell does not rest on the hood skirt but on a suitable understructure including 1- I beams 6'. The hood for this furnace has a skirt terminating in a flange 84 extending into the trough 80. To seal the space between the hood and the bell, a solid bottom frame 83' is gastightly secured to the bell casing 32, and is pro- These de- 4 vided with a sealing flange Ii. extending'into the trough 80. The sealing means for the combustion space in this embodiment therefore comprises the liquid in the trough 80, the flanges M and. 86,.and the bell bottom frame 63'. Ii it be desired to seal the heating chamber under the V hood. the base plate 8' may be provided; with a depending flange II also dipping into the sealing liquid containing in the trough 80.

I claim as my invention:

1. Adirectly gas-fired furnaceof the type described, comprising a base having a hearth.

adapted to support a charge to be heat-treated while enveloped by a )IOtCCtiVE atmosphere, said base comprising a metallic base plate; liquidcontaining gas-tight trough means in gas-tight relation to said base plate; a gas-tight metallicrefractory inner hood adapted to be placed about the charge supported by said base, said hood 00-.

- operating with said base to form an enclosure for said charge, said hood having an outwardlydirected skirt, said skirtterminating in a peripheral flange depending into the sealing liquid in said trough means; means for delivering protective atmosphere to, and removing it from said enclosure; a removable, insulating, walled bell about said hood. said bell having an inner wall spaced from said hood to providea combustion space, said bell having an outer air-tight metallic casing, said bell being providedwith a plurallty of distributed openings through its walls and casing, and with flue provisions in the upper portion thereof, said flue provisions being in communication with said combustion space for the discharge of gaseous products of combustion;

a plurality of gas burner means occupylns said openings, for admitting controllable amounts of combustion-supporting gas and combustible fluid to said combustion space; said casing being provided with a downwardly-extending flange which is gas-tight with respect thereto; said casing flange depending intoxthe sealing liquid in'said trough means,

2'. A directly gas-fired bell furnace of the type described. comprising a base adapted to support a charge to be heat-treated; a gas-tight metallicrefractory'inner hood adapted to be placed about said charge and cooperating with said base to enclose said charge, saidhood having a downwardly-directed peripheral hood flange: a removable, insulatin ,walled bell about said hood,

said bell having an inner wall spaced iromsaiti hood to provide a combustion space, said bell being provided with flue provisions in communication with said combustion space for the discharge of-g'aseous products ,of combustion; a plurality of gas .burner means for admitting controllable amounts or combustion-supporting gas combustion space gas-tight, said sealing means comprising liquid-containing trough means into which said hood flange and said casing flange depend.

JAMES H. GERMANY.

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