US2331887A - Melting furnace - Google Patents

Description

Oct. 19, 1943. w. BoNsAcK mamma FURNACE Filed July 10, 1941 3 SheetsSheet 1 Z 6 AINVENTR Walter Bonsack f- 67 ATTORNEYS Oct. 19, 1943. w, BONsAK ,MELTING FunNAoE Filed .July 1o, 1941 5 Sheets-Sheet `v2 lll INVENTOR uralter Bansck Y ATTORNEYS Patented Oct. 19, 1943 UNIT T @F FlcE Walter Bonsack, Smith, Euclid, V0h12), assig'norv to I The National Smeltin'ggCompany, Qleveland,

Ohio, a corporation of Qhio' l Application July 1o, 1941, semina-01,770 s claims. ici. zee-33) This invention relates to improvements in melting and holding furnaces for use in connection with the melting of light alloys, such as aluminum and magnesium alloys.

Even though it is recognized that it is undesirable to permit the products of combustion and the ame to come into direct contact with the surface of the metal, it has been considered necessary in the furnaces heretofore proposed to allow the products of combustion or the flame to pass into the melting chamber in order to obtain the requisite heat and efficiency.

It is an object of the present invention to provide a furnace having high eiiiciency wherein the products of combustion are completely isolated from the melting chamber.

It is another objectof the present invention to provide a furnace whereinthe products of combustion are prevented from contacting the metal, and the molten metal is substantially gas-free, whereby degasifying treatment is unnecessary and the metal may be used directly to make nonporous castings.

It is a further object of the present invention to provide a melting and holding furnace which permits ready access to the molten metal for casting purposes, which utilizes a larger proportion of the heat energy from the fuel than'do furnaces heretofore proposed, and 'which is adapted to rapidly melt aluminum alloys and maintain them at the'correct temperature.

It is another object of the present invention to provide a furnace having eilicient operation` wherein the flame and the products of combustion are kentirely excluded from the melting chamber and wherein heat from the fuel is rapidly transmitted to the metal, and which maybe operated in a continuous manner.

Other objects will be apparent from the following description of the invention as illustrated by the drawings, in which: v

Figure 1 is a side elevational view of a furnace embodying the present invention, with parts broken away and partly in section;

Fig. 2 is a plan viewof the furnace'shown in Fig. 1, with parts broken away to show the arrangement of the passageways for the products of combustion;

Fig. 3 is a vertical sectional View, taken on the line 3--3 of Fig. 1;

Fig. 4 is a vertical sectional view, taken on the line 4-4 of Fig. 1;

' L/ Fig. 5 is an elevational sectional view of a modified form of furnace especially designed for relatively continuous operation;

Fig. 6 is a plan view, with portions broken away,

of the furnace illustrated in Fig. 5; 'and Fig. 7 is a sectional View.V taken on the line 'l-'I of Fig. 5.

The melting furnaces of the present invention have a lmelting chamber entirely separated from' the combustion gases'by a plurality ofheat conducting ducts of ceramic material and, preferably, of silicon carbide which has superior heat conductivity. The metal is heated both by heat radiated from suitable means, suchas highly heated combustion tubes or ducts, over the metal and by conduction from dujcts or flues arranged about the side walls and preferably about the bottom of the melting furnaces to providea tor'- tuus or circuitous passageway for the hot gases.

Referring more particularly to the drawings, in

ing chamber has a heat reflecting dome 6, a g hearth la, which is adapted to receive and support lthe metal 5, and a radiant'heating portion lb above the metal supporting portion or hearth and above the normal level of the metal 5. Radiant shape, but which are preferably tubular, extend longitudinally within the melting chamber and are substantially above the normal liquid level 8. Burners 9 are suitably carried at one end of each of the combustion ducts. The other end of the combustion ducts terminates in suitable headers l0, which are in substantially gas-tight connection with said combustion ducts and are adapted to receive the gases from the combustion ducts l and divert them, without loss of gas, into suitable conductive heating means, such a's vertical ducts l2. The vertical ducts l2 are arranged in the walls of the melting chamber, preferably substantially adjacent each other, and extend throughout-a substantial proportion of the walls of the-melting chamber. Conducting liners I3 separate the vertical ducts from the melting chamber.

Adjacent vertical ducts may be connectedjtogether alternately at their upper and lower portions, as shown, to provide a tortuous, heat conducting passageway. terminating gn the one end in substantially gas-tight connection with the header I or the combustion chamber in (the radiant heating tubes or ducts 1. At the other end, one of the passageways in the conduction Vheating means connects with a stack. A heat exchanger I is preferably disposed between the `asl-beams or channelsrI', one or more casing -ends 22, and a top portion" 23, which may, if

desired, alsox house-the heat exchanger I5 Lwhich isv adapted to Withdraw a large proportion of the sensible heat' from the'uegas'es. l

Insulation 251s disposed between the melting chamber I or the conductive heating means and the 'outergsurface of ythe furnace..V

and the melting chamber, from the outer casing and prevents a large proportion of theheat lost to the outside of the furnace.'v

Preferably,l and especially `when the funaces are to be moved fequentlyforitransported, ,a

frame comprising vertical supports 26 on each side of t e furnace, upper connecting tie bars 21 which xtendhorizontally.overthe top pf the furnace, and a lower clamping memberi which extends horizontally through and substantially perpendicular to the stlffening members 2I, is provided for reinforcing the furnace walls. LWith such a frame holding the casing together, disassembly of the furnace is facilitated.

IThe heat exchanger I5 has a hot gas chamber 3l which is connected with a stack 32 and the passageway in the conductive heating means. A plurality f metal pipes 34 extend through the hot gas passageway 3|, one end of the pipes terminating in a header 33 and the other end terminating at the atmosphere. Air for com- The insula' tion serves to insulatejboth the heating meansV Chamber.

melting chamber I. The burning or substantially burnt gases from the tubes- 1 first pass into the header Ill and are then deflected into the heat conducting, vertical duct I2'in communication therewith, and then successively in a tortuous manner through the remainingl vertical ducts I2 and the heat exchanger, out of the stack 32. In the vertical ducts I2 a large proportion of the heat is withdrawn from the gases and transmitted into the body of the metal by conduction.

In the modification illustrated in Figs. 5 to 7, inclusive, the radiant heating means, such as the heat radiating combustion tubes 1, extend transversely of the melting chamber and the burners in alternate tubes are arranged on opposite sides of the furnace. Each of the combusl tion tubes terminates on the one end in the burner 9 and on the other side in the vertical ducts I2 contained in the side walls 3 of the furnace. These ducts .I2 are separated from the melting chamber by the lining I3. Each of the vertical ducts l2 may communicate with one or more of the horizontal ducts 40, which may extend horizontally and preferably in a longitudinal direction underneath substantially the entire melting The ducts are in substantially gastight connection tothe combustion chamber in the' radiant heating means and communicatev with the stack or a suitable heat exchanger connected at their exits 4I. Since the combustion gases have cooled substantially and occupy bustion,v sucked .through the pipes, by suitable I, means, such as a blower 35, withdraws a substantial amount of heat from the flue gases passing through the hot passageway 3| with theresult that the heat output of the burners 3, which are supplied with'fuel from the pipe'36, is substantially increased.

It is usually preferable to have at least portions of the side walls and the bottom -of the,-

furnace extend beyond the upper portion to provide a dipping chamber 33 in communication with the melting chamber to facilitate withdrawal of metal from the melting chamber. The dipping chamber 3B is substantially entirely separated from the radiant heating chamber 5 by the skimmer wall 39, which extends from the top of the furnace to almost the surface of the metal in the melting chamber.

` In the operation of the furnace illustrated in Figs. 1 to 4, inclusive, the air for combustion is drawn through the pipes 34 of the heat exchanger I5, where it is heated in substantial amount and forced by the blower 35 into the burners 9. supplied from a fuel source (not shown) through the pipe 36. The flame from the burners 9 isproiected by the burners into the chambers 1a of the radiant heating tubes 1, which serve as a combustion chamber, causing the tubes to radiate heat against the surface of the metal in the but a fraction of their original volume, two or more of the vertical ducts l2 may be connected into a single horizontal duct 40 without unduly restricting the passageway.

In the operation of the furnaces shown in Figs. 5 to 7, inclusive, the unmelted metal mai1 be added at the metal charging end 42 and withdrawn from the dipping end or the dipping chamber 33 through a lever-operated discharge plug 44. The gas and air supplied through the burners 9 from a suitable source (not shown) are projected into the radiant heating tubes 1; causing them to glow. It then successively passes through the vertical ducts I2 and the horizontal ducts 40, arranged about the sides of the melting chamber, and into the stack. Heat 'is radiated against the-surface of the metal from the silicon carbide radiant heating tubes 1 and `conducted into the metal from the tubular vertical ducts I2 and the tubular horizontal ducts 40, also preferably of silicon carbide. The ducts comprising the conductive heating means are also preferably of 'silicon carbide, but are preferably of rectangular cross section toA provide .l greater surface for conductive heat transfer.

It will be seen from the above that by providing a plurality of substantially parallel conducting ducts of relatively small cross section, that the surface for absorbing heat from the fuel is greatly increased by the furnaces of the present invention and it is unnecessary to have the name or products of combustion come in contact with the metal.4 The impurities incident to products What I claim is:

whereingthe products of combustion do not contact the ,surfaceof the metal, comprising side walls, end walls, a bottom anda" top portion, together forming aimelting chamber having a hearth to receive and support the metal, and a radiant heating portion abovethe normal level of the metal on said hearth, portions of said hearth for contact with the metal being of re: fractory material, radiant heating means in'said radiant heating portion, said radiant heating means having a combustion chamber separate f from said melting chamber for the combustion of fuel, heating means for conductively heating the metal through said refractory in contact .with the metal and being disposed in the side walls of said-melting chamber, said heating means having a passageway connected to said combustion chamber, and insulation between said melting chamber and the outer surfaces ofthe furnace.

2. A melting furnace for melting light alloys wherein the products of combustion do not contact the surface of the metal, comprising side walls, end walls, a bottom and a top portion, together forming a melting chamber having a hearth to receive and support the metal, and a radiant heating portion above the normal level,

of the metal on said hearth, portions of said hearth for contact with the metal being of refractory material, a plurality of combustion tubes in said radiant heating portion, said combustion tubes each having a combustion chamber forl combustion of fuel, heating means having a plurality of chambers in substantially gas-tight connection kwith the combustion chamber in said combustion tubes, said heating means being in the sides of said melting chamber for conductively heatingthe metal through said refractory material in contact with the metal and having a tortuous passageway in gas-tight communication with a. combustion chamber of at least one of said combustion tubes, and insulation between said ,melting chamber and the outer surfaces of the ing means in said radiant heating portion, said radiant heating means having a plurality of combustion chambers for the combustion of fuel, heating means in the sides and bottom of said melting chamber and having a passageway in substantially gas-tight communication, with a combustion chamber in said radiant heating means, said heating means conductively heating the metal through said refractory material in contact therewith and insulation between said melting chamber and the outer surfaces of the furnace.

portion t0 provide a metal dipping portion in communication with`said melting chamber, said melting chamber having a hearth to receive and support'the metal, and a radiant heating portion above the normal level offthe metal onf-said hearth, radiant heating means in s'aid radiant heating portion, portions of said hearth for contact withsaid metal being of a refractory material, said radiant heating means having a plurality `of, combustion chambers for the combustion of.A

fuel, Vheating means in the 4sqids andybottom of said melting chamber to4 conductively heat the. metal through said refractory material in contact with the metal and having a passageway in substantially gas-tight communication with a combustion chamber in said radiant heating means, and insulation between said melting chamber and the outer surfaces of the furnace.

5. A melting furnace for melting light alloys wherein the products of combustion do not contact the surface of the metal, comprising side walls, end walls, a bottom and a top portion, together forming a melting chamber having a hearth to receive and support the metal, and a radiant heating portion above the normal level of the metal on said hearth, portions of said hearth for contact with the metal being of refractory material, al combustion tube in said radiant heating portion and ,extending -longitudinally thereof, said combustion tube having a combustion chamberfor the combustion of fuel therein, heating means in the sides of said melting chamber tov heat the metal through said refractory material in contact with the metal and having a tortuous passageway, one end of which terminates at and is in substantially vgas-tight relation with said combustion chamber, the other end .being connected to a stack, a burner at one end 0f said combustion tube/ means for supplying fuel yto said burners and means for supplying air for combustion to `said burners, and a heat exchanger between said tortuous passage- Iway and said stack to withdraw heat from the flue gases to preheat the air supply. for said burners. J

6. A metal melting furnace wherein the products of combustion do not contact the surface o'f the metal, comprising side walls, end walls, a bottom and a top portion, together forming a melting chamber having a hearth to receive and support the metal, and a radiant heating portion above the normal level of-the metal on said hearth,

portions of said hearth for contact with the metal being of refractory material, a plurality of combustion tubes in said radiant heating portion, said combustion tubes running substantially transversely of said melting chamber, heating means in the sides and bottom of said melting chamber-having a passageway for receivingthe products of com` bustion from said combustion tubes, one end of the passageway in said heating means being con- 4. A metal melting furnace wherein the prod- L.

ucts of combustion do not contact the surface'of the metal, comprising side walls, end walls, a bottom and a/top portion vsubstantially enclosed within a Vmetal housing, a melting chamber substantiallyenclosed by said sidewal1s, end walls, bottom "and top portions, said ottom and pornected in substantially gas-tight relation to said A combustion tubes and the other end of said passageway being connected to a stack, a-refractory lining between-said melting chamber and said heating means, and insulation between said heatf wherein the products of combustion-fdo not contact Lthe surface ofltheme'tal, comprising side walls, end walls,a"bott'om and a top portion, together formingfjar melting chamber having a hearth to receive and support the metal, and a tions of said sidewalls extending-"beyond said top i radiant heating portion above the normal level hearth for contact with the metal being of refractory material, radiant heating means in said radiant heating portion, said radiant heating means having a combustion chamber for the combustion of fuel, heating means in the side walls of said meltingv chamber for conducting heat through said refractory material in contact with` the metal, said heating means having a passageway connected to said combustion charnber, the top of said melting chamber being curved to reflect heat from said radiant heating means to the surface of the metal, and insulation -between said melting chamber and the outer surfaces of the furnace.

8. A melting furnace for melting light alloys comprising refractory side walls, end walls, bottom and top portions, together forming a, melting chamber and having a hearth to receive and support; the metal, and a radiant heating portion above the normal level of the metal on the hearth, a plurality of radiant heatingtubes of refractory material in said radiant heating portion, a burner at one end of each of said tubes, tortuous passageways for combustion gases connected to the opposite ends of said tubes and disposed in the furnace side walls below the heating chamber so that refractory material which is in contact with the metal is between said tortuous passageways and the metal, and a stack into which combustion gases are delivered from such passageways,- said top portion of said furnace being shorter than said bottom portion and having a depending skimmer wall spaced from an end of the bottom portion to provide an open dipping chamber free from radiant heating tubes.

WALTER'BONSACK.

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