US2351489A - Metallurgical furnace - Google Patents

Description

June 13, 1944. H, s, COOPER METALLURGICAL FURNACE Filed March 21, 19412 l l! /H /1 ,f l

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ATTORNEY June 13, 1944. H. s, cooPx-:R

METALLURGICAL FURNACE Filed March 2l, 1942 3 Sheets-Sheet 2 INVEN TOR.

Hug/i Cooper June 13, 1944.

H. s. COOPER 2,351,489

METALLURGICAL FURNACE Filed March21, 1942 3 Sheets-Sheet 3 lllllllll lllllllllll lll lay/1 5. faapr Patented June 13, 1944 UNITED STATES PATENT OFFICE METAILURGICAL FURNACE Hugh S. Cooper, Cleveland, Ohio, assgnor of onehalf to Frank H. Wilson, Cleveland, 01110 Application March 21, 1942, Serial No. 435,673

6 Claims.

f distillation methodof producing magnesium described and claimed in my co-pending application Serial No. 434,078 led Marchy 10, 1942.

Other objects 'and advantages will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects I have devised the metallurgical furnace illustrated in the accompanying drawings, wherein- Fig. 1 is a sectiona.1 side elevational view of the metallurigical furnace of the present invention;

Fig. 2 is a sectional'view of the same along plane 2-2 of Fig. 1 illustrating one feature of the present invention;

Fig. 3 is a sectional view along plane 3-3 of Fig'. 1 illustrating a second feature of the present invention;

Fig.l 4 is a sectional'view along plane 4--4 of Fig. 1 illustrating a third feature of the present invention;

Fig. 5 is a view illustrating a modification of one feature of the present invention;

Fig. 6 is a view along plane 6-6 of Fig. 1;

Fig. 7 is a side elevational view of a complete furnace assembly including an auxiliary fur-v nace (shown in section) utilizable with the furnace of the present invention when adapted to the productionof magnesium; and n Fig. 8 is a sectional view of the auxiliary furnace of Fig. 7 shown in a second position.

Referring to the drawings, the furnace design illustrated is particularly adapted to the production of magnesium by the method described and generally as briquettes, of any desired and convenient size, and the briquettes, are heated to elevated temperatures above the vaporization temperature or boiling joint of magnesium and up to about 1600o C. in a container closed to the atmosphere and in an inert atmosphere at a Dressui/e within the range 0.0 to 766 millimeters of mercury.

-At temperatures above the vaporization temperature or boiling .point of magnesium at the gas pressure employed, the aluminum-silicon alloy reduces the 'magnesium oxide according to the equation:

The magnesium produced in this reduction reaction Volatilizes or vaporizes from the heated briquettes and may be collected in a suitable conclaimed in co-pending Iapplication Serial No. A.

434,078 led March 10, 1942, above identified.

In accordance with this said method, magnesium oxide is intimately mixed with a non-vaporizable reducing agent, such as 'an aluminumsilicon alloy ycontaining from about 20- to not over about silicon, each in nely divided condition and the lmixture is compacted under pressure to porous 'agglomerates, known in the art denser chamber having a temperature below the boiling point of magnesium and preferably substantially below the melting point of the magnesium.

I have found that the rate of reduction of magnesium oxide by the aluminum-silicon alloy at any temperature above the boiling point of magnesium at the .pressure employed, is markedly effected by the rapidity with which the magnesium vapor phase is removed from the reduction reaction zone and that by locating the condenser surface relatively close to the reaction zone thereby providing a relatively short path of travel for the vapor, the reaction temperature may be markedly lowered and the reaction time interval at the lower temperature is materially shortened.

This condition is provided in the furnace arrangement illustrated in the drawings. As may be seen from the drawings (Fig. 1)' the furnace consists oi two separable parts or sections, consistingof a base B and a vaulted cover C with means S to hermetically sealthe two parts B and C together.

-Base B is provided with a shallow hearth I -I consisting of refractory material, Ysuch as aluminum oxide, high melting fire clay, and the like, preferably surface interlorly with aluminum silicate (Ahoi-25102).

In the bottom of hearth H is located a plurality of electrical lresistors R which, for Vpurposes of the present invention, may be comprised of any suitable high resistance electrical conductor, such as one o f the heretofore well known Cr-containing alloys of Fe, Co, Ni, or of molydenum rod, or may be comprised of'carbon.

Vaulted cover section C is provided with an interiorly located depending condenser A which may 'be cooled interiorly by liquid or gaseous media, and which is substantially centrally located therein in concentric spaced relation to t e inner side walls of the cover C which may or m y not be lined with refractory material I0,'for example, aluminum-silicate (Al'zOs-ZSiOz) The condenser A provides a condensing surface II in relatively close spaced relation to briquettes I2 disposed on hearth H upon which the magnesium I3 is to be collected by condensation during operation of the furnace.

The particular size, shape and configuration of condenser A may be varied widely without essential departure from the present invention as may also the size, shape and configuration of surface II. Thedesign illustrated, however, when employed with substantially round or annularly shaped sections B and C appears to produce the best results, particularly for use in combination withthe auxiliary means illustrated in Fig. '7, as will be more fully hereinafter described. The location` of condenser A centrally within thefurnace cover C in the manner shown affords a means for directionally condensing the magnesium upon surface II. to shape condenser surface I I as a portion of a sphere so that radiated heat energy from hearth H will be reflected outwardly therefrom and in major part onto the side walls of the cover Cto help maintain the said side walls at a relatively higher temperature than condenser surface II.

The cooling of condenser A may be effected in a plurality of different ways without essential departure from the present invention. It isV desired to maintain the deposit of metal I3 collected on surface II at a temperature below the melting point butin a range of temperaturesfavorable for the formation of relatively large sized metal f crystals from th'e condensing vapor phase, particularly where magnesium is the metal pro- Y should be adapted to maintain themagnesium deposit I3 at a temperature in the range 350 C. to 450 C. The temperature of the magnesium in the vapor phase is at least 1100D C. and, depending on the temperature of the briquettes on hearth H, may be as high as 1600 C. The cooling means provided must be such as 4to carry away rapidly the thermal units evolved by the magnesium on condensation on surface II of the condenser. The latent heat of fusion of magnesium is about '72 Cal/gram and the latent heat of vaporization at 9654 C. approximates 2020 CaL/gram according to the most'reliable data available.

This has been found to be effectively accomplished by feeding a liquid, such as water, maintained at a temperature of 35-40 C., at a con- -trolled pressure through pipe I4 directly onto the inner face of the spherical shaped condenser surface I I at the point of closest approach of the surface to the heat zone on hearth H and .dispersing or distributing the same along the curved inner face of surface II in the space gap between said inner face and spherical shaped perforated plate I5, the perforations in plate I5 being designed to effect distribution of the liquid at the pressure employed within the said space gap, such as, for example, by grading the size of the perforation openings 40 and the total number thereof from the center outwardly, the larger diameter openings being located the farthest distance For this reason, I prefer from the pipe I4 and adjacent the outer edges of plate I5.

To attain this result the discharge end o f inlet pipe I4 is substantially centrally located in plate 5 I5 and means (not shown, but common in the art) is provided to feed liquid at a substantially constant temperature of about 40 o to pipe I4 under a regulated and contrlle pressure, and means such as dual outlet or discharge pipes Iii-I6' is provided to carry off the liquid from the interior of the condenser.

Condenser A is preferably comprised of metal, such as low carbon, iron or steel, to facilitate the rapid transfer of heat energy from thesurface II to the water flowing interiorly the condenser. The manner of sustaining condenser A interiorly the cover C may be varied widely without essential departure from the present invention. The arrangement shown seems to be the most convenient and practical. In this arrangement, the top of condenser A is provided with an annular collar I1 having an annular shoulder I8 adapted to engage an annular recess along the inner periphery of a centered opening in cover C which is closed by cover plate I9 having a plurality of bolts passing therethrough, the threaded ends thereof engaging in complementary threaded recesses in thetop of collar I1 with an annular gasket 2I disposed in sealing relation therebetween.

Cover C.is also provided with a two-way valved port opening 22 for connecting the interior of thevfurnace to an exhausting means, such as a standard type vacuum pump V (Fig. 7) and an inert gas ushing means, such as a tank T (Fig.

7) ofy inert gas, such as hydrogen or helium, under pressure'.

In the present invention, one of the most desirable features is the means S provided to hermetically seal cover C onto base B. This is effected by means of an annular resilient sealing member, such as a rubber gasket 23 sustained in fixed position on the outside of base B in channel extension 24 formed integrally with the outer wall of base B and coacting with annular rib extension 25 on the bottom of cover C. To prevent excessive heating of gasket 23 the rib extension 25 is provided with a cooling means, such as annular water cooling chamber 26. Alternatively, cooling chamber 26 may be disposed around gasvket 23 and channel 24 without essential de-' parture from the present invention.

The sealing means S provided, namely, coacting parts 23 and 25, are automatically operative to effect sealing of the furnace interior to the atmosphere as cover C is located in position on base B and to become a vacuum tight seal immediately following a reduction of pressure of the furnace interior by operation of the exhaust means V and' to maintain the. seal as long as the pressure interiorly the furnace is less than atmospheric pressure. Upon the return of the pressure ,interiorly the furnace to atmospheric pressure (or above), the normal weight of the cover C is sufficient to maintain a gas tight joint between these annular parts 23 and 25, but the parts are readily separable by movement of cover C vertically upward from base B.

- In such a furnace it is usually diiilcult to maintain a vacuum tight seal around the leading-in conductors or electrodes passing through the furnace walls to resistors R in base B. I have provided a vacuum seal for this purpose which is shown in section o'n the left of Fig. 1 and in more detail in Fig. 4. In this arrangement, electric l current for energizing resistors R is delivered from any convenient source by conductors 38-30' to water cooled metal electrodes 3I--3I which extend to the interior of base B through openings in the wall 32 thereof and are connected electrically by a sliding contact to connector 33. The opening in the furnace wall through which water cooled electrodes 3i-3l 4extend are each provided with an annular extension 34-34 in the outer face of which is disposed an annular gasket 35 comprised of resilient material such as rubber and on each electrode 3l-3I' is located a collar 36-36 on which is provided an -annular rib extension 31--31 in a position to engage gasket 35. A plurality of threaded bolts 38 are provided passing tlirough unthreaded openings in collars 38-36' to engage in correspondingly threaded recesses in extension Si to an extent at least sufficient to draw collars :i6-38' and electrodes 3l-3l' in the direction towards the furnace interior a sufficient distance to bring rib extension 3l into sealing engagement with gashet 35.

With this arrangement electrodes .3i-3l' each are free to move inwardly .a further distance as the pressure of the furnace interior is lowered, but are restrained vby bolts 3B from moving outwardly beyond sealingl position of rib 31 with gasket 35. Accordingly, as the furnace pressure is reduced the seal engagement between rib 3l and gasket 35 becomes greater. This movement of electrodes 3I-3i' inwardly must be compensated for by providing a sliding contact between electrodes 3l-3l and connectors 33-33.

In the practice of the method invention of said co-pending application, it is desirable to heat the briquettes in hearth H to the reduction reaction temperature by direct contact of the briquettes with the incandesced electric resistors R. This is desirable primarily because not only is the magnesium oxide content of the briquettes a high refractory material With a relatively low thermal conductivity but the reaction product aluminum-silicate is of similar refractoriness and low thermal conductivity.

Accordingly, I prefer to provide a plurality of resistor elements R located in spaced relation in the bottom of hearth H and on which the briquettes I2 may be deposited for heating by direct contact therewith to the reaction temperature. These resistor elements R may be electrically connected in parallel between electrodes 3i--3I' as shown in Fig. 1 or in series, as indicated in Fig. 5. The current when Aconnected in series is less than when connected in parallel but the parallel connection may be used with low' voltages.

Referring now to Figs. 7 and 8, a complete assembly for the production of magnesium in the furnace of the present invention is shown. In the manufacture of magnesium by distillation as contemplated by the practice of the method described and claimed in my said co-pending application, the condensed magnesium metal is highly pyrophoric due to the fact that the surface of the metal is not coated with a protective oxide film.

In accordance with my invention, the maintaining of a relatively high temperature within the range E50-450 C. during the condensation of the magnesium vapors onto surface i i of condenser A provides for the formation of relatively large sized crystals or aggregates of crystals of magnesium metal. Following the complete reduction of the magnesium oxide in briquettes i2,

as may be determined by observation through window W and by experiment ascertained to occur within a determined time interval of heating for any given mass of briquettes l2 of determined MgO and Al-Si content, the furnace interior is allowed to cool to a low temperature before releasing the vacuum or low pressure formed therein.

I then gradually raise the pressure within the furnace by bleeding slowly therein an inert gas, such as hydrogen or helium, which contains a. relatively low percentage of an oxidizing gas, such as water vapor (up to 5%). By thus slowly oxidizing the surface of the magnesium deposit on condenser A, the heating up of any of the crystals or particles of metal to a temperature at which rapid oxidation will occur is substantially inhibited. As the pressure approximates atmospheric pressure or above, cover C may be vertically raised from base B by motor hoist means K and transferred horizontally to a position over auxiliary melting furnace M (Fig. '7) and lowered vertically to a position immersing condenser A in a molten salt bath D contained in crucible E of the furnace M. By r proper design of furnace M and crucible E cover C may be adapted to form a cover over Crucible E as shown in Fig. 8, so that the magnesium will be protected from contact with the oxidizing gases discharging through flue F in furnace M during melting from condenser A. Furnace M may be heated by gas burner means G as shown (Fig. 7) or alternatively by an electrical resistance heating means, if desired or deemed advisable, without essential departure from the present invention.

Molten salt bath D preferably consists of a mixture of potassium and sodium chlorides, melting at about 650 C., but many other fusion mixtures are available in the art for the purpose and the bath composition, per se, forms no particular part of the present invention.

It is believed apparent from the above description of the metallurgical furnace of the present invention and from the drawings illustrating the same that the invention maybe widely modified without essential departure from the present invention and all such modifications and adaptations thereof are contemplated as may fall within the scope of the following claims.

What I claim is:

1. In a vacuum furnace consisting of base and cover sections each exteriorly provided with a Vacuum tight shell and adapted to seat one upon theother to provide an enclosed area to be evacuated by means extending through the shell of one of the said sections, means providing a vacnum tight joint therebetween while the said sections are seated one upon the other rwhilethe interior ypressure is below atmospheric pressure, but providing for ready separation of the parts at interior pressures approximating atmospheric pressures and above, said means comprising an annular gasket consisting of resilient material mounted upon the outer periphery of the shell of said base section adjacent the open end thereof and facing substantially upward and an annular rib member mounted upon the outer periphery of the shell of said cover section adjacent the open end thereof and extending beyond the said open end of said cover section a distance adapted to bring the said rib member into engagement with the said annular gasket when the cover section is seated upon the said hase section with the open end of the cover section held in spaced relation to the open end ci the said base section with the cover section free to move towards the base section against the resiliency of said gasket as the pressure of the area enclosed by said baseand cover sections is low -said gasket is detrimentally effected.

2. A vacuum furnace for the distillation production of readily vaporizable metals, said furnace comprising in combination an open-ended base section enclosed-by a hermeticshell and provided with a relatively'shallow hearth in the bottom of which hearth is located an electrical resistance heating means for heating material disposed in. the hearth and an open-ended vaulted section enclosed by a hermetic shell and provided with an interiorly depending water cooled condenser chamber and with means connecting the cover interior to an evacuating means, and means disposed about the periphery of each said section adjacent the open endsJ thereof to hermetically seal the two said sections together when the said cover section is seated in covering position over the open end of said base section at all pressures below atmospheric pressure, said means comprising an annular gasket consisting of resilient material sustained facing substantially upward about the outer periphery of said base section adjacent the open end thereof and an annular ri-b extension depending from the outer periphery of said cover section and extending beyond the open end of said cover section a distance adapted to bring the forward edge 'of the said rib extension into hermetic seal engagement with the upwardly facing surface of said gasket when the said cover section is seated upon the said base member with the open end of the said cover section spaced away from the open end of the said base section a distance providing for the free movement of the cover Isection towards the said base section against the resiliency of said gasket as the pressure of the area enclosed by the two said sections is lowered l below atmospheric pressure to as low as a high vacuum.

3. The furnace of claim 2, wherein the said dependent water cooled condenser in said cover section is adapted to provide a relatively short path of travel for the metal vapors-driven oil from .said hearth by locating the major condensing surface of said condenser in close spaced relation to the open end of said base section with the said cover in seated position thereon.

4. A metallurgical furnace for the distillation production of vaporizable metals, said furnace consisting of a base section and a cover section, the base section Ibeing provided with a relatively lshallow horizontally located hearth having an electrical resistance heating means disposed in the bottom thereofin substantially direct contact with material disposed in the said hearth and the said cover section being vaulted and provided with a depending water cooled condenser chamber disposed in covering position over said hearth in the basemember and in relatively close spaced relation thereto providing a short distance of travel for metal vapors arising from the said hearth,v each said section being provided with an outer shell consisting of material impermeable to gases at all pressures, and means to hermetically seal the said cover section in covering position on said base section, said means consisting of an annular gasket comprised of resilient material located in the periphery of said base section adjacent the open end thereof and an annular rib extension of the peripheral surface of said cover section adjacent the open end thereof and extending beyond the said open end a distance adapted to provide for the gravity weighted engagement of the forward edge of the said rib with the face of said gasket when the cover section is seated on said 'base section with the cover section free to move against the resiliency of the said gasket as the pressure of the area enclosed by the two sections is lowered below atmospheric pressure and to return to iirst position as the pressure of the said area returns to atmospheric pressure, and means passing through one said section' to evacuate the said enclosed area.

5. A vacuum metallurgical furnace for the distillation production of magnesium, said furnace consisting of a substantially cylindrical base section provided with an annular horizontally located channel member facing upwardly about its outer periphery adjacent the top thereof with anannular gasket of resilient material located therein and with a substantially dish-shaped hearth having an electrical resistance heating means located in the bottom thereof, and a vaulted cover section provided with a refractory' lining and with an annular depending rib exten-Y sion about its outer periphery adjacent the open end thereof having a diameter and location adapting the same 'for seating engagementen the said annular gasket when the said cover is disposed in covering position on said ybase section, an interiorly depending hollow condenser chamber in the top of said cover, said chamber including cooling means to maintain the ex-Y terior surface of at least the bottom surface thereof at a desired temperature, means to exhaust gases from the furnace interior and means to introduce a desired gas atmosphere `at a deatmospheric pressure within the said furnace interior.

6. In combination, the furnace of claim 5, and a melting furnace provided with a crucible having an outside diameter less than the inner diameter of the said vaulted cover and an inside diameter greater than the outside diameter of said condenser chamber and transfer means for transferring the cover said -base section to covering position on said crucible with the condenser chamber thereof immersed in a molten salt bath contained in said Crucible.

HUGH S. COOPER.

from covering position on

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