US2393306A - Melting furnace - Google Patents

Description

Jan. 22, 1946.

W. BONSACK MELTING FURNACE Filed May 22, 1943 3 Sheets-Sheet'l INVENTOR v Walter Bon-Sask ATTORNEYS l Parenteel. z2, 1946 i MELTING FURNACE Walter Bonsack, South Euclid, hio, assignor `to The National Smelting Company, Cleveland, Ohio, a corporation of Ohio Application May 22, 1943, Serial No. 488,035 .5 claims. (ci. 26o-33j This application is a continuation-impart of my prior application, Serial No. 401,770, led July 10, 1941, Patent No. 2,331,887, October 17, 1943. The invention relates to improvements in melting and holding furnaces for the melting of light alloys, such as aluminum alloys.

Aluminum valloys are generally melted in fur-v naces of the open-hearth typev where the flame comes in direct contact with the surface of the metal. It'has been recognized that such contact Furnaces have also been proposed for annealing and heat .treating metal castings and the like by circulating heating fluid or hot gases through tcrtuous passageways between a refractory lining and the insulated body portion of the furnace. Such -furnaces are entirely. unsuitable for the manufacture and melting of light alloys for the reason that unburned hot gases, or even A non-combustible gases, will pass right through with the surface of the metal is undesirable for the reason that contamination of the alloy with gaseous materials occurs and substantial loss of the alloying ingredients takes place. Furnaces vwherein the alloy is heated solely or substantially entirely by radiation and conduction to the upper faces of the metal, the alloys produced are also of varying characteristics because the alloying ingredients are more soluble at higher than-.at lower temperatures.

It has been proposed to overcome some of these dinlculties by retaining the heating fluid or.hot gases in a closed chamber above the surface of the metal so that heating is solely by radiation from the walls of the chamber. This prevents the hot gases from coming in contact with the surface of the metal, .but the differences in the temperatures of the upper and lower surfaces of the metal is,` not improved. Also, such furnaces using only radiant heat are not considered practical because it takes so long to heat the metal.

In the melting of metals such as lead or tin, or lead alloys, etc., which metals do not appreciably dissolve certain metallic material, ce. g. iron, copper and the like, it has also been pro posed to provide furnaces wherein the heating takes piace through the side vwalls-of a metallic -vessel holding the molten metal. Such a furnace or melting pot is illustrated in the Lundt Patent 2,137,693. Furnaces of this type, however, are entirely-unsuited for the melting of light metal alloys for the reason that aluminum alloys dissolve metallic constituents with which they come in contact, thereby causing contamination of the the porous refractory materials ofthe linings and contaminate the light alloys being melted to such an extent that they do not produce desirable castings. But such furnacesdo have the advantage in that the metal being melted has a more uniform temperature than that which is heated solely by contact between the heating fluid land the upper surface of the metal.

It is. an object of the present invention to provide a melting furnace of high efliciency, suitable for melting light alloys,r wherein the products of combustion do not contaminate the material being melted, so that a degasifying treatment is un-v necessary, and wherein melts of substantially7 uniform temperature throughout are produced? It" is another object of the present inventionto provide a furnace' of high efficiency wherein the .products of combustion are prevented from contacting the metal and wherein loss of the metal being melted is minimized.

It is another object of the present invention toprovide a melting and holding furnace which permits ready access to the molten metal for casting purposes and which utilizes -a larger proportion of the heat energy from the fuel than do furnaces heretofore proposed.

I t is still. another object of the present invention to provide a furnace which preventsI the products of combustion from contaminating the alloy being melted and which also has good life and has no metallic portions in contact with the metal.

lowing description of the invention, as illustrated by the drawings inwhich;

Figure 1 is a vertical sectional view of a furnace embodying the present invention;

Fig. 2 is a plan view, with parts broken away, of the furnace shown in Fig. 1;

Fig. 3 is an elevational view, partly in section, of a portion of atortuous, tubular conduit in a furnace embodying the present invention;

Fig. 4 is a sectional view on the line 4--4l of Fig. 5 is a sectional view. on the line .of Fig. 1; f v

Fig. 6 is a vertical, longitudinal sectional view of a modied form of furnace embodying the present invention;

Fig.` 7 is an elevational view of a portion of a tortuous conduit used in the furnace of Fig. 6;

Fig. 8 is a longitudinal, vertical sectional view of another modied form of furnace embodying the present invention;

Fig. 9 isv a` plan view, with parts broken away, of the furnace of Fig. 8; and

Fig. 10 is a vertical sectional view through a portion of the furnace shown in Fig. 8, taken on the line ill-I of Fig. 8.

The furnaces of the present invention have a suitable refractory material, such as silicon carbide. graphite, etc., in contact with the molten metal so that conduction of heat to the molten metal takes place substantially entirely through the refractory material.

Melting furnaces of the present invention have as conductive heating means tortuous tubular heating-ducts or passageways in the side` wallsV serves as a heat conductor but prevents contact between the-solubilizing aluminum or magnesium alloys and the materialof the tubes.

`The tubes are preferably composed of a refractory metal such as the high temperatureresistant alloys of steel containing nickel and/or chromium, or alloys of nickel. The vtubes prevent migration of gaseous material through the aseasoe suitable gas or oil conduit i2 and air connection I 3 to respectively supply fuel and air from suitable sources (not shown).

The tubes-8 and 9 and the molten metal in the hearth portion 1 of the melting chamber I are separated by a conductive-type refractory material II. The material I5 is preferably silicon carbide, graphite, mixtures of silicon carbide is preferably arranged over the entire bottom and side walls of the furnace, or at least over sumcient area in the bottom and walls of the furnace to overlie the tubular b urner tubes 9 and the connecting tubes 8, which formthe tortuous tubular heating passages. By forming the more conductive material in the sides or bottom with one or more tapered end portions so that the cross sec.- tional thickness of the material is gradually reduced from the vicinity of the tubes tothe edges,`

. the refractory Il in the. assembly of the furnace.

This may be accomplished byf'coating the tubes I and 9 with a combustible material, such for example as a thick starch paste,- so as to slightly increase their diameter, and thereafter embedding the coated tubes in the plastic mass of the refractory material Il. ,Upon use of the furnace, the starch is burned to provide the required room for expansion. v

Insulationsuch as a relatively non-conductive refractory material i8 is provided between the refractory. Even though .the tubular material has a substantially higher coefiicient of expansion, it is surprisingly found that it is possibleto utilize a refractory between the tubes and the metal without causing cracking of the refractory when the tubes are heated. The heat conducted from the tubular passageways may constitute the maior portion of the heat utilized in the melting of the metal, but in a preferred modification of the present invention, radiant heating means above the surface of the metal is also utilized.

Referring more particularly to the drawings. in which like parts are indicated by like numerals of reference throughout the several views, the furnaces of the presentinvention have a melting chamber I formedby a bottom wall 2, and walls I and 4, a top wall 5 and side walls l. vThe bottom wan z and portions of the side wens sl andV 4 form a hearth light alloy.

Conductive heating means, such as gas-impervious tubes 8, .are disposed in one or more walls of the melting chamber I. Thetubes l mayzbe of a refractory metal, suchV as steel alloys containingr a largeamount vof nickel, nickel alloys or the like. and they form a gas-impervious tortuous passageway for the passage of hot gases between the burner tube 0, which may be horizontally portion 'I to support the molten located beneath thev upper surface of the 'bottom wall 2, and a stack connection Il which may be open to .the atmosphere if4 desired. The burner tube i in the furnace of Figs. land 2 is in the bottom wall of the furnace 'and one end thereof is suitably connected to a burner II having a 1I inuse.

walls of the combustion chamber and the refractory material I5 therein and the outer surfaces of the furnace, which may be of sheet metal I9.

In the modification shown in Figs. 4 to 7, inclusive, the burner tube i which connects with the burner li and the tortuous passageway lformed by the tubes 8 is substantially vertical and is at least partly disposed within the conductive refractory material in the side walls of the hearth portion of the furnace. The stack connection III is connected to a horizontal exhaust portion 20 of the tubes I. Thus, in the modification of Figs. 4 to 7, the hot gases are tire passageway between the burner tube l and the stack connection Il substantially impervious to gas, the tendency for formation of gaseous metal is substantially eliminated. Also. by disposing the refractorymaterial Il between the bath of molten metal onthe hearth portion 1 and the tubes l and l, the destructive effects of the molten metal on the tubes I -and l are also eliminated. Since heat is applied through at leastthe side walls of the furnace. convection currents are set up which I have found maintain the' entire bath of metal at substantially uniform temperature. In addition, the emciency of the furnaces is much' higher than the eiliciency of the open-hearth The conductive material I5- fiunaces generally' In'the modifications of Figs. 8 10, one end of each of the burner tubesl 9 is connected yto a heat-supplying means, burner il, and the other end is connected througha suitable header or connector 2l to the tortuous passageway formed .bythe tubes 8 in the'side walls. Each offthe I burner tubes 9 serves as a radiant heating means in the radiant heating chamber 26 above the surface of the metal-retaining portion 1. The radiant heating means may comprise any number of burner tubes 9, substantially gas-impermeably connectedto the headers 25, which may be formed by sides 26 and 21 in conjunc- V tion with a portion ofthe walls of the furnace, as

illustrated. Usually one or two burner tubes 9 are suificient for most melting furnaces.

It is generally preferable to have portions of.

the side walls and the bottom of the furnace extend beyond the upper wall to provide a dipping chamber 29 in communication with the melting chamber. The dipping chamber may be used to charge the alloying ingredients into the furnace as well as, to` facilitate removal of the molten alloy.N The dipping chamber 29 may be substantially entirely separated from the radiant heating portion 28 above the surface of the metal -in the melting chamber by a .curtain wall 30,

which extends from the top of the furnace to almost the surface of the metal in the melting chamber.

Suitable openings, such as the clean-out opening 40 (see Fig. 6) which is controlled'by the counterbalanced closure M, may be provided connected to the' counterweight 42 by a conf nector I6 adapted to travel over the pulley 43.

While the heating tubes 8 and the burner tubes i are preferably of refractory metal, as abovedesignated, it is possible to utilize especially formed silicon carbide tubes which have low im- 4above the surface of the metal to serve as means connecting said burner to said bottom tubes and permeability to gases. The tubes 8 may be round or square, or of any desired cross sectional shape.

Although several embodiments of the invention have been herein shown and described, it

will be understood that numerous modifications of the construction shown may be resorted to without departing from the spirit of this invention as defined inthe appended claims.

What I claim is:

1. A melting furnace for meltinglight alloysl comprising end walls, side walls', bottom and top portions, which together form a melting chamber having a hearth portion substantially entirely of refractory material to receive and supsaid tortuous passageway whichl is not connected to said bottom tubes .and burners being .connected to a stack.

2. A melting furnace for melting light alloys comprising'end walls, side walls,'bottom and top portions, which togetherA form a, melting lchamber having a hearth portion substantially entirely of refractory material to receive and support the metal, conductive heating means in said bottom vand side walls of the furnace, said conductive heating means comprising a plurality of refractorymetal tubes connected together to form a tortuous, substantially gas-impervious passageway, silicon carbide surrounding said metal tubes and between them and the surfaces of said bottom and'side walls adapted to contact the metal in the melting chamber, the silicon carbide closely overlying said metal tubes, a burner for supplying heat to said furnace and a connecting tube connecting said burner to said bottom tubes and said tortuous passageway, the end of said passageway remote from the burner being connectedto a stack.

`3. A melting "furnace for melting light alloys comprising end walls, side walls, bottom and top portions, which together` form a melting chamber having a hearth portion substantially entirely of refractory material to receive and support the metal, conductive heating means in said bottom and sidewalls of the furnace, said conductive heating means comprising a plurality of `refractory metal tubes connected together to form a tortuous, substantially .gas-impervious roundingsaid metal tubes'and between them and the surfaces of said'bottom and side walls and adapted to contact the `metal in the melting chamben'said heatconductive refractory closely overlying said metal tubes, a burner for supplying heat to said furnace and a connecting tube tortuous. passageway for supplying heating fluid thereto, said connecting tube being substantially verticallydisposed in said heat conductive refractory in a side wall portion of the furnace, all portions of said walls in contact with the metal in the melting chamber being of a refractory material, whereby the solubilizing eiect of said metal on said tubes of the conductive heating means is eliminated, theend of said passagewayremote from the burner being connected to a stack.

4. A melting furnace for melting light alloys comprising end walls,side walls, bottom and top portions, which together form a melting chamber having a, hearth portion substantially entirely of refractory material to receive and support the metal, conductive heating' means in said bottom and side walls of the furnace, said conductive port the metal, conductive heating means inv said bottom and side walls of the furnace, said conductive heating means comprisinga plurality of refractory metal tubes connected together to form a tortuous, substantially gas-impervious passageway. heat conductive refractory surrounding said metal tubes and betweentheni and the surfaces of said bottom and side walls adapted to contact the metal in the melting chamber, said lconductive refractory *closely overlyingsaid metal tubes, burners having oneend thereof connected to said bottom tubes and Y to said connecting tortuous passageways for supheating means comprising a plurality oi refractory metal tubes connected together to form a tortuous, substantially gas-impervious passageway, heat conductive refractory surrounding safd metal tubes and between them and the surfacesof said bottom and side walls and adapted to contact the metal in the melting chamber, said heat conductive refractory closely overlying said metal tubes, a burner for supplying heat to said furnace and a connecting tube connecting said burner to said bottom tubes and tortuous passageway for supplying heating fluid thereto, said connecting tube being substantially horizontally disposed in said heat conductive refractory in the bottom portion 'of the furnace, all portions of said walls in contact withthe metal in the melting chaml 3 ,blying heating fluid therethrough, the end of` ber being of a refractory material.' whereby the solubilizing effect of said metal on said tubes of the conductive heating means is eliminated. the end of said passageway remote from the burner being connected to a stack.

v5. A melting furnace for melting light alloys comprising end walls, side walls, bottom and top portions, which together form a melting chamber j l having a hearth portion substantially entirely of refractory material to receive and support the metal, conductive heating means in said bottom and side walls of the furnace, said conductive heating means comprising a plurality of refractory metaltubes-connected together to form a jtortuous, substantially gas-impervious passagemay. heat conductive refractory' surrounding said metal tubes and between them the sura,aos,soo

I faces of said 'bottom and side walls and adapted 'surface ofthe metal in the melting chamber of said furnace. all portions of said walls inlcontact with the metal in the melting chamber being of a refractory material, whereby the solubilizing effect of said metal on said tubes ofthe conductive heating means is eliminated, the end of said passageway remote from the burner being connected to a stack.

WALTER BONSACK.

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