US3188068A - Apparatus for heat-treating metals - Google Patents

Description

June 8, 1965 r. scHMlDT APPARATUS FOR HEAT-TREATING METALS 3 Sheets-Sheet l Filed Nov. 5, 1962 Theodor Schmidt INVENTOR FIG. 2

AGENT.

June 8, 1965 T. SCHMIDT APPARATUS FOR HEAT-TREATING METALS Filed Nov. 5, 1962 3 Sheets-Sheet 2 Theodor schmidt INVENTOR June 8, 1965 T. SCHMIDT APPARATUS vFOR HEAT-TREATING METALS 3 Sheets-Sheet 3 Filed NOV. 5, 1962 Theodor Schmldt INVENTOR,

AGENT.

nrrnnarns retrasar-annimmt; Marais r :Theodor Schmidt, Essen,- G-erma'ny, assigner to lndugas,

Gesellsehaftffiir ndustrieile Gasverwendnng in bJ-i.,

Essen, Germany, a eorporationof Germany Y liiiied Nov.5, 1962, SerxNo. 235,191 Ciaims priority, application Germany, Nov. 9,1961,

4 Claims. (Cl. 266.-5)

vMy present invention relates to a method of and an apparatus vfor heat-treating metals and,V moreparticularly, to annealing apparatus of the dome or hoodrtype.

Hood-type ovens for the annealing and heat treatment of round metal-lic bodies, such as sheet-metal coils and the like, have been provided heretofore with a furnace housing adapted to be disposed upon -a base supporting the material to be treated with annular lclearance wheref by heating means (eg. burners) may be disposed in this clearance. Usually a protective gas containing at most minimal quantities of oxidizing constituents is circulated around and/ or throughthe coils for bringing them to the proper temperature. Since this protective gas was only limitedly heated by its contact with the furnace walls, it had been proposed to provide additional heat-exchange surfaces which project radially inwardly from the housing to effect a more rapid heating of the gas. This was particularly important in open-coil arrangements wherein the gas passed between individual turns of the coil and was, `in eifect, a heating fluid. These heat-exchange surfaces have been found to be only Elimiltedly effective. Another disadvantage of known annealing furnaces of the character described was that the heating means radiated temperature was thus raised 'inordinately higher than the desired treatment temperature whileother portions of the body remained at temperatures below that usually required for the heat treatment. heating cannot, forthe most part, be avoided in hitherto l ,existing heat-treatment apparatus.

It is an object of the present inventionto' provide a method of heating metal bodies whereby the aforementioned disadvantages may be obviated. i

it is another ,object 'of this invention to provide an improved hood-type annealing oven whereby metal bodies can be heated substantially uniformly to the appropriate heat-treatment temperatures.

According to one aspect' of rthis invention a body to be heated is disposed with. clearance within a heated furnace chamber and a protective gas is circulated around the body and through the clearance while an apertured conductive layer is .interposed between the heating means andthe body for preventing excessive heating vof those portions of the latter-upon whichthe radiant energy of the heater would otherwise impinge directly. The protective gas vcan thus pass through the interstices of the conductive layer and is, consequently, heated by contact fcreases considerably the thermal efliciency of an anneal` ing furnace, without requiring unusually high gas velocities, as a consequence of the large heat-transfer area presented by the apertured layer., Moreover, this layer functions as a Davy heat shield inasmuch as it conducts radiant energy away from hot-spots to equalize the temperature within the furnace.` l d *According to another aspect of the invention, an ap- This nonuniformity of lence promoters capable of effecting a substantial increase masses i d `Patented `Furie 8, i965 l l E" I Y i i .2 I

v Y l the heat-treatment of cylindrical or round objects com#` 3,133,068 prises a housing surrounding these objects with peripheral clearance and heating means at, at least, one wall of the v housing confronting a surface of the objects to be heated;

circulating means is provided for continuously passing a protective gas (`e.g. an Vinert or reducing gas) through this clearance and around the bodies to be heated. A heat-conductive perforate shieldis'disposed around the body intermediate the latter and the heating means which may-comprise exposed gas burners or the .like `and/or a radiant-heating body suchas a mantle or partition. Theshield is provided with portions extending generally transversely to the direction of propagation of the gas and may be formed from wire mesh, bars or the like which span substantially the entire clearance in the transverse direction. The heat shields also constitute turbuin the heat-transfer characteristics of the furnace; While,

in general, it is desirable to interpose the heat shield` `directly between the furnace wall and thebody to be` heated, in which case the body itself may form with the housing anv annularl compartment for the passage of the heating fluid, it .is also possible to form this compartment by means of a partition interposed between the body and the furnace wall. layer is disposed between this partition and the wall.

Advantageously the apertured layer can be a woven wire cloth` or avwire netting wliichis corrugated transversely `to the direction 'of ow of the gas and which heat directly onto a juxtaposed surface of the body whose thus spans the entire width of the compartment. It should be noted, however, that perforated corrugated sheet metal can alsoV be employed in this connection while Wire dust filters are also suitable. The corrugated material preferably contacts both the Wall of the furnace and the confronting surface forming the compartment therewith. When a partition -is dispensed with, the corrugations abut the body directly. The lapertured layer f may also be so constructed that direct radiation between Vthe furnace wall and the body is prevented. The mesh of the wire screen and the thickness of the wires constituting it are so selected as to effect an optimum heat trans-k FIG. 3 is a cross-sectional view taken along the `line i ttt-m: of FIG. 1; l

Y paratus for treating metal bodies and, particularly,for

FlG. 4 is a similar cross-sectional view, with parts broken away, showing another oven; i

FIGS. 5 and 6 are fragmentary perspective views illustrating other embodiments of the invention;

FIG. 7 is an elevational view of a further apertured layer; and ,i Y

IFIG. 8 is a perspective view illustrating still another layer.

are'mounted. Blower 7 isof the axial-intake and radialoutiiow type and supplies a protective gas lto a plurality ofradial heat channels 14 which carry this gas into an annular clearance 8 between the furnacewall 2 and the In the latter case the apertured 'v This` concrete base 1 carriesa pedestal 12 .compos-ed of ceramic `bloc-ks upon which a motor 13 and its blower 7V coils B. The furnace housing formed by this wall 2 and a cover 3 is generally cylindrical and can be lifted from the base 1 yby means of lugs ll'S. The `furnace housing Zandmantlel alsocarry a conical plate 16 from which axially -extending flanges 17 depend. These flanges project into the liquid contained in respective channels l1 and lprevent the escape ofgases from the furnace.

The mantle or-liner 1S is of r-efractorymaterial and is spaced from the lhousingZ, forming therewith an annular compartment 4 for gas burners 6 or anyl other suitable heating means.v The partition 18 constitutes a so-cal-led radiating hood for emitting thermal energy in the direction of the bodies B. The latter form with this hood the annular compartment 8 through which the protective gas passes upwardly toward the domed roof 19 of cover Y3. A Davy-like mesh 9 of corrugated wire screening forms a heattransfer layer .and heat shield intermediate the radiating partition 18 and the bodies B vwith the high-ts of the corrugations in contact with the confronting surfaces 5 and Y20 of the partition and the bodies. The corrugations extend transversely to the direction of gas dow as indicated by the arrows. Stakes 21 serve to hold the blocks of pedestal l2 in place.

In operation, the cover 3, via its lugs 2Z, or the housing 2 is lifted lfrom kthe base l to permit the coils B, whose turns are open to allow passage of "gas therebetween, to be place-d upon the vanes 23 (see also vanes Z3 of FIG. 4). The cover 3 and/or the housing 2 are then replaced and a pr-otective gas introduced via a pipe 25. Burners 6 are then ignited and serve to heat the mantle I8 while the gases .areV circulated upwardly by blower -7 through the channels 1 4 and compartment 8, are deflected downwardly by the roof 1-9 and descend between the turns of .coils B and back to the blo-Wer 7 past the vanes 23. The corrugated mesh 9 serves to heat the gas by. contact and is in tu-rn heated by both radiation and yconductionfrom the mantle 18. The conductive mesh, however, serves'to prevent direct irradiation vof the bodies B bythe mantle 1S and also acts'to equalize the furnace temperature in a manner of a Davy screen by conducting heat rapidly away from overheated regions of the furnace. The high surface area of th-e screen renders i-t quite capable of maintaining the gas at a 'suitable temperature. In fact, it has been found that when the temperature in chamber 4 between the partition 18 and the furnace wall 2- is approximately 1000 C. a well-defined gas temperature between 600 and 700 C. results with a consequent uniform heating of the coils 4B -to a temperature between 600 and 700 C. without'overheating even at their surfaces proximal to the partition 18. FIGS. 2 and 3 show the corr-ugated wire screen B in further detail. In the open-coil method the aligned axial passages of the coils are blocked by ya plate k44 from Athroughiiow of the gas which is, consequently, forced to flow around each individual turn.

In FIG. 4 4I show a furnace, ygenerally similar to that,

of FIG. V1, for a heat treatment of coils by the closedcoil method. In this case the coil B is again disposed upon radial vanes 23 but the plate '44'is dispensed with so that the gas passes over the coils into the axial intake of blower 7 whose radial outow again proceeds through channels 14' `as previously described.' The mantle 1S is also dispensed with in the embodiment of FIG. 4 so that the transversely corrugated screen 9 is interposed directly between the burners A6 andthe coil B. In FIG. 5 I show an arrangement whereby a gratelike `metal shield 25 is'disposed between a radiant-heat ing mantle 18' and the body 'B to be heated. The grate 25 is provided with apertured portions'26 extending transversely to the direction ofgas Yilow and lin contact with tion 27 between mantle 1% and body B which forms with thevmantle an annular chamber 2S for the transversely corrugated screen 9" which contacts both the mantle and the partition 27. The gas passes, as indicated by the arrows, .through compartment 28 into contact with the bodies B. The 'apertured shield 30 of FIG. 7 has its perforations 31 inclined to the plate so that direct radiation through these apertures is prevented. An expended-metal shield may also be provided to achieve an identical result. vA. shield of this type can be used with the structure shown in FIG. 4 wherein the radiating mantle 18 or 18 is dispensed with. Again transversely extending flanges 32, suitably apertured to permit `the passage of gas, are provided. The shield 33 of FIG. Sis corrugated in a manner similar to that described withreference to the `screens 9, 9' and is likewise of a thermallyV conductive metal. Perforations 34 to permit the passage of gas are, of course, provided. It shouldbe noted that none of the heat shields described herein functions to provide a substantial hindrance to the ow of the gas therethrough or resul-ts in' abnormally high pressure drops within the furnace.

The invention as described and illustrated is believed to admit of many modications and variations within the ability of persons skilled in the art, all suchmodiications and variations being deemed to be inc-luded within the spirit and scope of the appended claims. i

What is claimed is:

ll. An annealing oven for sheet-metal coils and `the like, comprising a hood-like housing forming a generally cylindrical furnace chamber for a coil to be annealed and surrounding the latter within said chamber with peripheral clearance; partition means in said chamber forming an annular compartment with said housing and confronting said coil within said chamber; burner means within said compartment for heating said partition means; circulating means for passing a protective gas through said clearance and around said coil in said chamber in heat-exchanging relationship with said wall; and a corrugated mesh of thermally conductive wire disposed within said clearance with the corrugations thereof extending transversely to the direction of flow of said gas whereby the openings in said mesh promote turbulence in saidgas,

said mesh being interposed between said annular partition means and said coil for preventing excessive irradiation of the latter by said partition means.

2. An annealing oven for sheet-metal coils and the like, comprising a hood-like housing forming a generallycylindrical furnace chamber for a coil to be annealed and surrounding the latter within said chamber with peripheral clearance; partition means in said chamber forming .an annular compartment with said housing and confronting said coil within said chamber; a plurality of angularly equispaced burners within said compartment for heating said partition means; circulating means for passing a-protective gas through said clearance and around said coil in said chamber in heat-exchanging relationship with said wall; and a corrugated mesh of thermally conductive wire disposed within said clearance with the corrugations thereof extending transversely to the direction of how of said gas wherebyl the openingsin said mesh promote turbulence in said gas, said mesh Vbeing interposed between said annular partition means and said coil for preventing excessive irradiation vof the latter by said partition means.

3. An annealing oven for sheet-metal coils and the like, comprising a base, a hood-like housing removably positioned on said base, said housing forming a generally cy` lindrical furnace chamber for a coil to be annealed and surrounding the latter Within said chamber with peripheral clearance; a'heating mantle in said chamber forming anl annular compartment with said housing and confronting a coil Within said chamber; a plurality of angularly equispacedburners within said compartment for heating said mantle; a blower centrally disposed within said chamber for passing a protective gas through said clearance and around said coil in said chamber in heat-exchanging relationship with said wall; a corrugated Woven mesh of thermally conductive wire disposed within said clearance with the corrugations thereof extending transversely to the direction of flow of said gas whereby the openings in said mesh promote turbulence in said gas, said mesh being interposed between said annular mantle and said coil for preventing excessive irradiation of the latter by said mantle while contacting both said mantle and said coil; and sealing means between said yhousing and said base for preventing the escape of gas from said chamber. p

4. An annealing oven for sheet-metal coils, comprising a base, a hood-like housing removably positioned on said base, said housing forming a generally cylindrical furnace chamber with vertical axis for a coil to be annealed and surrounding lthe latter within said chamber with peripheral clearance; a heating mantle in said chamber forming an annular compartment with said housing and confronting a coil within said chamber; burner means positioned within said compartment for heating said mantle;

circulating means disposed at the bottom of said cham! ber for passing a protective gas upwardly through said the liow of said gas whereby the openings in said mesh promote turbulence in said gas, said mesh screening said coil from said mantle and minimizing irradiation of the coil by said mantle; and sealing means between said housing and said base for preventing the escape of gas from said chamber.

References Cited by the Examiner UNTED STATES PATENTS 2,1125743 3/38 R. Poole.

FOREIGN PATENTS 632,406 11/ 49 Great Britain.

MORRIS O. WOLK, Primary Examiner. JAMES H. TAYMAN, JR., Examiner.

Claims (1)

1. AN ANNEALING OVEN FOR SHEET-METAL COILS AND THE LIKE, COMPRISING A HOOD-LIKE HOUSING FORMING A GENERALLY CYLINDRICAL FURNACE CHAMBER FOR A COIL TO BE ANNEALED AND SURROUNDING THE LATTER WITHIN SAID CHAMBER WITH PERIPHERAL CLEARANCE; PARTITION MEANS IN SAID CHAMBER FORMING AN ANNULAR COMPARTMENT WITH SAID HOUSING AND CONFRONTING SAID COIL WITHIN SAID CHAMBER; BURNER MEANS WITHIN SAID COMPARTMENT FOR HEATING SAID PARTITION MEANS; CIRCULATING MEANS FOR PASSING A PROTECTIVE GAS THROUGH SAID CLEARANCE AND AROUND SAID COIL IN SAID CHAMBER IN HEAT-EXCHANGING RELATIONSHIP WITH SAID WALL; AND A CORRUGATED MESH OF THERMALLY CONDUCTIVE WIRE DISPOSED WITHIN SAID CLEARANCE WITH THE CORRUGATIONS THEREOF EXTENDING TRANSVERSELY TO THE DIRECTION OF FLOW OF SAID GAS WHEREBY THE OPENINGS IN SAID MESH PROMOTE TURBULENCE IN SAID GAS, SAID MESH BEING INTERPOSED BETWEEN SAID ANNULAR PARTITION MEANS AND SAID COIL FOR PREVENTING EXCESSIVE IRRADIATION OF THE LATTER BY SAID PARTITION MEANS.

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