US2020101A - Melting and holding furnace - Google Patents

Description

NOV- 5, 1935', J. w. BROWN MELTING AND HOLDING FURNACE Filed Nov. 25, 1931 2 Sheets-Sheet 2 f /f a l A frane/vers.

Patented Nov. 5, 1935` UNITED STATES PATENT GFFICE MELTING AND HOLDING FURNACE John W. Brown, Cleveland, Ohio Application November 25, 1931, Serial No. 577,182

13 Claims.

This invention relates to improvements in melting and holding furnaces for use particularly in connection with the making of non-ferrous castings.

It has long been realized that the methods commonly employed in the manufacture of die castings and permanent mold castings are faulty in that the molten metal being cast attacks the container and the apparatus for transferring the molten metal from the container to the die or mold. these parts being constructed usually of ferrous metal, with the result that the apparatus deteriorates rapidly and has to be replaced, and with the further result that the molten metal is contaminated by the iron absorbed from the walls of the apparatus. This is especially true in the case of the aluminum alloys, which require a higher melting heat than the zinc, tin, or lead base alloys. In some cases, the iron content of aluminum allow die casings rises on this account to three or more per cent. 'Ihe contamination of the metal in this manner changes the physical characteristics of the castings, with results that are quite serious in some instances. The corrosion of the iron pot in which the metal is melted, by the absorption of metal into the molten contents of the pot, not only reduces-the life of the pot, but also necessitates the shut-down of the whole machine whenever it becomesnecessary to replace a pot, and therefore interferes with production and increases production costs.

Attempts have been made to overcome these diillculties by applying coatings of various kinds to the interior surfaces of the pots. In such cases, however. the coating is necessarily a relatively poor conductor of heat and necessitates the heating of the pot to a higher temperature in order to meltand hold the metal molten. This high temperature tends to accelerate the burning out of the pot from the outside, such condition being the most serious, of course, when metal of a relatively high melting point, like aluminum, is being worked, and this effect is accentuated when the molten metal is being withdrawn q'uite rapidly and cold metal introduced to take its place. In such cases, when the coating cracks, blisters, or fails in any manner, and exposes a small portion of the iron surface to the Vcontents of the pot, corrosion takes place at that spot at a rate considerably higher than would be the rate if the pot were not so coated and consequently not so highly heated. Then too, the coating increases the fuel consumption and the costs incident thereto.

'I'he method of the present invention departs from the established practice of heating the metal by the application of heat exteriorly to an iron pot, and substitutes therefor apparatus for applying heat to the metal directly while held in a closed container, thereby reducing the degree (Cl. 26S-39) of heat required over that necessary ln the old method, even where the pot was not coated with inert material, and permitting the successful and long continued use of refractory inert material for the inner surface of the container, thus eliminating entirely the contamination of the molten metal in the manner above described.

One of the objects of the invention, therefore, is the provision of a method and means for melting metal preparatory to its use in a permanent mold or in a die casting machine, which shall eliminate contaminationof the molten metal by absorption from the container surfaces and which results in a longer life for the metal heating apparatus.

Another object of the invention is the provision of a method and means for melting and holding molten metal which shall lend itself to the superheating of the molten metal in order that the viscosity of the metal may be lowered, permitting it to ,ll a complicated mold or die more readily, and permitting the making of -thinner walled castings, as well as enabling the making of castings from a given alloy having different .characteristics depending upon the temperature of the metal when cast.

Another object is the provision of a melting method and apparatus which shall result in practical uniformity of temperature in that part of the metal from which the charge is taken by the metal transferring means, that is to say, the means by which metal is transferred from the container to the die. l

Another object is the provision in such metal transfer means of surfaces that are inert to the metal being cast, whereby contamination of the metal from this source is likewise eliminated, this feature of the invention when applied to the gooseneck form of transfer means involving the building of the gooseneck in three layers, the middle layer being the strength member, and the inner and outer layers being refractory and nonmetallic, and hence inert.

Still another object of the invention is the provision of special heating means of different forms for the melting of the metal in the metal container.

Other objects and features of novelty will appear as I proceed with the description of thoseA embodiments of the invention, which for the purposes of the present application, I have illustrated in the accompany-lng drawings, in which Figure 1 is a side elevational view of a die casting machine for carrying out my new method, and embodying certain novel structural features, the open compartment of the metal container being shown in vertical section,

Figure 2 is an end elevation of the same machine with portions of the metal container broken -ing means.

In the drawings. the frame of a casting machine is shown at I0. It contains an intake passage I I for the molten metal, with which the gate I2 of the ixed part Il of the die is caused to register. The movable part I4 of the die is shown attached to a die plate I5, that is slidably sup- 1 ported upon guide rods IB and is connected -by links I1 with a head I8 which may be moved back and forth by connecting rod I! attached to a piston (not shown) within an air pressure cylinder 20. These portions of the machine are standard, and in so far as their detailed construction is concerned, have nothing to do with the present invention.

2l is a compressed air line including a valve 22 which may be turned on and olii by along handle 22 employed for the convenience of .the operator. The iixed part of the air line terminates at 24 in a socket adapted to receive a tapered connection 2,5 on one end of an angular pipe 28- which is supported in a bracket or web 2l, forming a portion of the gooseneck metal transferring means 28. The other end of the pipe 2S is rigidly mounted in the vertical portion ofy the gooseneck 2l. The laterally extending portion of the gooseneck terminates in a beveled end which is adapted to make a detachable duid-tight connection with the exposed end of intake passage I I. Hence, when the gooseneck is lled with molten metal and raised to the position illustrated in Flg. l, the valve 22 maybe opened, admitting compressed air to the surface of metal in the vertical portion of the gooseneck, whereby the metal is delivered under pressure from the lateral portion of the gooseneck through passages II and I2 into the die.

As illustrated in Fig. l, the gooseneck is mounted for movement from the position shown in 'that figure to a lowered position suchl that its' delivery end enters the molten metal and thereby takes up a charge lof metal, the pipe 26 at that time serving as an -air vent. For this purpose, the web 21 maybe pivotally connected at 29 to links 80, which are pivotally connected with a second pair of links Il. Mounted in a pair of brackets 32, attached to the frame of the machine, there is a rock shaft 33, to which the links 3I are rigidly secured. An operating handle 34 is also secured to this rock shaft.-When the handle 34 is swungupwadlfyjy theoperator, the

gooseneck 28 and-the pipe 26 are drawn away from their connections II and 24, and are depressed suiliciently to enable the gooseneckto receive a charge of molten metal, and the reverse movement directly following will return the parts' to the position illustrated, ready for the next casting operation. 'I'he general construction and mounting of the gooseneck just described are well known in the art, and form no part of the present invention.

The preferred form of my new container for melting and holding molten metal will now be described. It comprise'sa suitable base 25 upon therethrough of a height preferably below the normal level of the molten metal in the container. Over that portion, of the container to the left of the transverse wall 38, as viewed in Fig. 2,

= there is a cover comprising an outer metal casing 40, insulating material 4I and an inner refractory material 42, whereby there is formed a"cov'eed compartment 43. The remainder of the container is left open at the top to form an open compartment 44 to the right of wall $8 and in alignment with the gooseneck 28. An opening 45 is formed in the cover member of the closed 2() compartment, and a channel-shaped metalfdeector 4B is preferably attached to the container in alignment with this opening, in order that flames leaving the compartment 43 may cause no damage.

Where the fuel employed for melting the metal is gas, a forced draft is more or leas essential, and in such case, I may mount a blower 4l upon a shelf 48 supported by braces 49 for forcing air mixed with gas delivered by a service pipe 50, into 3Q a burner located within the compartment 43.

While the use of a gooseneck as the means for transferring molten metal from the container to the dieis not essential to the invention, and might be supplanted, for instance, by a plunger pump, particularly one in which the. surfaces exposed to molten metal were made of non-metallic refractory material, nevertheless the gooseneck transfer means is preferred and is illustrated in detail in Figs. 3 and 4.

Fig. 3 illustrates a movable gooseneck of the form employed in the machine herein illustrated and having a three-layer wall. The middle layer 5I is metallic, preferably cas* iron, and has a fluid-tight connection with the pipe 26. The inner and outer walls 52 and 52 respectively, are formed of a hard refractory material inert to the action of the molten metal.

' Fig. 4 is similar to Fig. 3, with the same threelayer construction but thelgooseneck is of the xedtype, the metal being admitted through a valve opening I4 in the bottom, the valve being controlled by a rotatable shaft 55 with a handle 55 on its exposed upper end.

The cover of the metal surface of the gooseneck as herein disclosed, has the advantages, before mentioned, of reducing the coutaminationvof the molten metal, but in addition has other important advantages; that is to say, it decreases the iiow and loss of heat up through the gooseneck to the air, it decreases the chilling effect upon the metal adjacent to its walls when it is plunged into the metal bath, and it decreases the chilling eii'ect on thek metal which it takes up from the bath, so that the temperature of the vmetal in the gooseneck closely approximates that of the bath (which is the temperature that is measured, and by which the die casting process is controlled).

In Figs. 5 to 8 inclusive, I have illustrated various ways of heating the compartment 43, and 70 thereby appLving heat directly to the metal within the compartment rather than indirectly f through the walls of the container, as has been the practice heretofore. In Fig. 5, a gas burner l1 of elongated formis mounted withinthe con- 75 lil combustion. as of solid fuel. takes place to some extent at least, outsideV of the container, but wherein the products of combustion and such gases as remain unbumed, are caused to pass through a conduit 38 which is provided with openings arranged at intervals along its length by` means of'which the heated air and other gases are discharged into the compartment 43, where the final combustion takes piace. Fig. 7 illustrates a container ofthe same form, wherein the heat is obtained from an electric arc embodying terminals 39 and 63. In Fig. 8. an electric resistance heater embodying a heating coil 6I is employed.

Fig. 9 shows a somewhat different type of furnace or metal container, comprising an open compartment 62 for the reception of the gooseneck Il, and no closed compartment. In this figure. 33 indicates a refractory container wall, C4 a layer of heat insulating material, and 65 an outer metal casing. The molten metal is indicated at 36. Communicating with the bottom of the compartment 62 there is a U-shaped passage 3l formed in the refractory material of the container. There is also embedded, or partially embedded, inv this material, an electric coil 68, which surrounds one leg of the passage 61 and thereby heats the metal in the passage by electrical induction.

'I'he operation of the machine herein illustrated will be obvious to those skilled in the art. The compartment 43 of the metal container is, in effect, a reverbatory furnace, lined with hard refractory material inert to the molten metal to be heated therein. Because of the opening 39 in the transverse wall 38, free circulation of metal takes place between the closed compartment 43 and the open compartment 44, the hot metal flowing from compartment 43 to compartment- 44 through the upper portion of opening 39, and the cooler metal in compartment 44 flowing through the lower part of opening 39 back to compartment 43 and upward therein, principally near the center of the latter compartment. There is also some circulation of metal in the compartment 43 itself, the hotter metal flowing from the upper center outwardly toward the walls oi' the compartment. Then, as it cools somewhat, it flows downwardly along the side walls and radially inward along the bottom and up again at the center of the container'. This is in contradistinction to what happens in the present iron heating pots, where the circulation of the hottest metal is upward along the walls of the pot, the cooler metal flowing downwardly at the center. This direction of movement of metal in the iron pot, that is, the hot metal flowing upwardly along the sides of the pot, accounts partially for the tendency of the metal to pick up impurities from the walls of the pot. Furthermore, with my method, the pumping action resulting from the raising and lowering of the gooseneck in the open compartment of the container causes the metal to switch back and forth between the two compartments, tending strongly towards-the rapid transference of heat from the closed compartment to the open compartment, and towards maintaining uniform temperature which is so important in securing uniformity of metal in the castings.

In the foregoing description, I have necessarily gone somewhat into detail in order to explain fullythe particular' embodiments of the invention herein illustrated, but I desire it to be understood that such detailed disclosures are not to .be construed as amounting tu limitations, except as they may be included in the appended claims.

Having thus described my invention, I claim:

l. In a furnace, a two-compartment container, l

one compartment thereof being substantially closed and the other being open at the top, the inner surfaces of both of said compartments comprising refractory non-metallic material, means for applying heat internally to said closed cornpartment, said two-compartments being disposed side by side and connected by an opening below the intended level of molten metal and of sumcient magnitude and height to permit free circulationof molten metal from one compartment to the other. whereby the metal in the open compartment is maintained at a practically uniform temperature, substantially equivalent to the average temperature within the closed compartment.

2. A metal melting and holding furnace compl'ising a substantially closed chamber and an outside open container placed in juxtaposition with a refractory wall between them, said wall having an opening therethrough extending upwardly from the bottom thereof and terminating below the intended level of molten metal, and heating means applied internally to said chamber exclusively, whereby free circulation of molten metal between said chamber and said container is permitted and whereby the metal in said container is heated exclusively by said circulation and by conduction of heat in the metal itself.

3. A metal melting and heating furnace comprising a metallic casing, a refractory lining therefor, a. transverse wall dividing the furnace into two compartments, said wall having refractory surfaces on both sides thereof, means for applying heatrinternally to one of said compartments above the metal therein, said Wall having an opening therethrough extending downwardly from a point slightly below the liquid level and being of such area. that the metal in the unheated compartment is maintained at substantially the same level and temperature as that in the melting and heating compartment by a flow of heat through the metal into the unheated compartment and by the circulation of metal through said opening.

4. A furnace for melting and holding non-ferrous metals in which a low iron content is desired, comprising bottom and side Walls formed of refractory material, a cover formed of refractory material extending over a portion of said furnace, a refractory wall interposed between two of said side walls and depending from said cover to a point below the normal line of molten metal in said furnace but above the bottom of said furnace, thereby dividing the furnace into a substantially closed melting chamber and an -open holding chamber, said refractory wall being spaced from the bottom of the furnace to permit molten metal to flow freely from the melting chamber into the holding chamber but depending below the surface of the molten meta-l to prevent slag formed in the melting chamber from entering the holding chamber.

5. A furnace for melting and holding non-ferrous metals in which a low iron content is desired, comprising the combination of a melting chamber and a holding chamber, the melting chamber being a substantially enclosed chamber formed of refractory material and the holding 'having a sufficient uncovered surface to permit metal to be withdrawn therefrom by means of a ladle, the walls of said chambers being substantially continuous with each other, means for supplying heat to said enclosed melting chamber, and a passageway leading therefrom into the holding chamber, said passageway being located in such a position that the molten metal may now freely into said holding chamber but being situated below the operating level of molten metal in the melting chamber, thereby preventing slag and the products of combustion formed in the melting chamber from entering said holding chamber.

6. A furnace for melting and holding non-ferrous metals in which a low iron content is desired, comprising a refractory bottom and refractory end Aand side walls, a cover of refractory material extending over one end portion of the furnace well above the liquid level, and a. wall formed of refractory material extending downwardly from the inner end of said cover to a point in the region of the operating level of the molten metal in said furnace, thereby dividing the furnace into a heating portion and an open holding portion, means for supplying heat to said enclosed heating portion, and means for permitting the escape of products of combustion therefrom, said refractory wall being so located with respect to the two portions as to permit the free now of metal into said open holding portion and to retain the heat within said enclosed heating portion. 7. A furnace for melting and holding non-ferrous metals in which a low iron content is desired, comprising a refractory bottom and refractory end and side walls, a cover formed of refractory material extending over one end portion of the furnace well above the liquid level, the' inner end of said cover having a refractory wall depending downwardly a short distance below the walls of the uncovered portion of the furnace, thereby dividing the furnace into a substantially enclosed heating chamber and an open holding portion, and means for supplying heat to said heating chamber, said refractory wall permitting metal to flow into and substantially fill said open holding portion so that molten metal may be removed therefrom by means of a ladle but preventing the slag and products of combustion formed in the heating chamber from entering the open holding portion.

8. A furnace for melting and holding non-,ferrous metals in which a low iron content is desired, comprising a refractory bottom and refractory end and side walls, a cover ofrefractory ma.-

terial extending over one end portion of the fur-` nace well above the liquid level, and a refractory wall extending downwardly from the inner end of said cover to the region of the operating level of the molten metal in said furnace, thereby dividing the furnace into a heating chamber and an open holding portion, means for supplying heat to said heating chamber, and means for the escape of products of combustion' therefrom, said refractory wall being so located as to permit the Vfree flow oi.' metal into said open holding portion and to retain heat within said heating chamber.

9.- A melting pot for metal, comprising, a casing providing a covered melting chamber and an ,open dipping pool, said chamber and vpool being in communication with each other at a level below the normal level of the molten metal, whereby molten metal passes to said dipping chamber while slag is retained in said melting chamber,

said melting chamber having an opening in its rear wall, and means for projecting a ame jet through said opening into said chamber so as to heat the walls and ceiling of said chamber.

10. A melting pot for metal, comprising a casing providing a. covered melting chamber adapted to contain a pool of molten metal having an extensive surface, means providing a dipping pool in communication with said rst pool, said communication being below the normal level of the molten metal in the chamber and pool, and means for projecting a flame into saidl chamber adapted to heat the interior of said chamber and the metal therein.

1l. A furnace for melting and holding non-I ferrous metals in which a low iron content is desired, comprising the combination of a melting chamber and a holding chamber, the melting chamber being formed of refractory material and the holding chamber being formed of refractory material and having a sufiicien. uncovered surface to permit metal to be Withdrawn therefrom by means of a ladle in the usual nie casting operation, means for melting non-ferrous metals in said melting chamber, and a passageway leading from the melting vchamber into the holding chamber, said passageway being located in such position that the Vmolten metal may flow freely into said holding chamber but being situated below the normal level of molten metal, thereby preventing slag and the products of combustica formed in the melting chamber from entering the holding chamber.

12. A furnace for melting and holding a nonferrous metal in which a, low iron content is de- 5 sired, comprising bottom and side walls formed of refractory material, a cover formed of refractory material extending over a portion of said furnace, leaving a portion of the furnace uncovered to permit the withdrawal of molten metal4 therefrom by means of a ladle in the usual die casting operation, a refractory wall interposed between two of the s'ide walls and extending downwardly from the free end of said cover'portion to a point below the normal level of molten metal in the furnace, thereby dividing the furnace into a substantially closed melting chamber and an open holding chamber, said refractory wall permitting the molten metal formed in said melting chamber to flow into said holding cham- 5 Iber but preventing slag and gaseous products of combustion formed in the melting chamber from entering the holding chamber.

1\3. A furnace for melting and holding nonferrous metals in which a low iron content is de- 5 sired, comprising a refractory bottom and refractoryllend and side walls, a cover of refractory material extending over one end portion of the furnace, and a wall formed of refractory material extending downwardly from the inner end of said e cover to a point substantially below the normal level lof the molten metal in said furnace, thereby dividing the furnace into a melting chamber and a `holding chamber, means for melting metal in said melti chamber, and means for permitting 6 the escape products of combustion therefrom, said last m tioned refractory wall being so located With pect to the two chambers that it permits the e flow of metal into said holding chamber but, revents slag or the products of 7 combustion for A`ed in said meltingchamber from entering said holding chamber.

JOHN W. BROWN.

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