US1825841A - Method of melting metals - Google Patents

Description

.l melted and brought Patented Oct. 6, 1931 PATENT FFlCE LOTHAR R. ZIFFERER, 0F COLUMBIA, PENNSYLVANIA; MABEL C. ZIFFERER, HARRY E. CHAMPION, AND H. NELSON ALBRIGHT, EXECUTORS OF SAID LOTHAB, R. ZIF- FERER, DECEASED, ASSIGNORS TO COLUMBIA MALLEABLE CASTINGS CORPORATION,

0F COLUMBIA, PENNSYLVANIA, A CORPORATION 0F NEW YORK METHOD OF MELTING METALS` Application led April 17,

While the invention is particularly suitable for employment in connection with the melting of cast iron and will be described in connection therewith, it must be understood that it is not intended to limit the invention thereto since other ferrous and non-ferrous metals and alloys may 'also be melted in accordancewith the invention.

According to the invention the metal is to a desired temperature by the injection, first of a fluid fuel and then a finely divided solid fuel. Amongthe fluid fuels'which may be employed, may mention oil and gas. Ordinarily the former is preferred for economical reasons. rlhe solid fuel is preferably pulverized coal, although other solid fuels, such as coke, c harcoal and the like, may be employed, if desired.

The invention is particularly suitable for use in connection withv reverberatory furnaces although it may be practic'ednn any type of furnace in which the fuel is injected into the space occupied by the metal.

As will hereinafter appear, the particular order of the fuels has far reaching effects upon the quality of the metal, and the ca stings or the like formed therefrom. The invention is particularly applicable to the roduction of high grade iron castings, suc as malleable castings. The invention will readily be understood fiom the following description of its application to the melting of iron for this purpose, taken in conjunction with the accompanying drawings which illustrate a furnace suitable therefor. In the drawings- Figure 1 is a plan view of a reverberatory furnace embodying the invention; e

Fig. 2 is aA longitudinal section on the line 2 2 of Fig. 1, and

Fig. 3 is aperspective detail showing the front end of the furnace and the fuel supply means.

Referring to the drawings, the numeral 10, designates a reverberatory furnace. The furnace comprises a hearth 11 of refractory material, a front wall 12, a bridge 13, side walls 14 and a roof 15 which is formed of removable sections to permit charging of the metal to be melted.

i930. serial No. 444,996.

In operation the metal is placed upon the hearth 11, and fuel, together with air for its combustion, is injected through` the front wall in the manner hereinafter described. The products of combustion impinge upon the metal and eventually pass over the bridge into the flue 16, from whence they escape into the stack 17. The furnace is adapted to be fired by pulverized coal. The coal is placed in the hopperAlS, from which it is fed by a suitable mechanism to a pulverizer 19 driven as by an electric motor 20. The pulverizer is connected by a pipe 2l to the suction side of a blower 25, the outlet of which is connected to the nozzles 26 which extend through the front wall of the furnace. The blower lis operated by the motor 27. Regulable openings 28 permit a controlled amount of volumetric air to enter the furnace with the pulverized fuel to insure combustion of same. In addition to the nozzles 26, the front wall is provided with a nozzle 29 for the injection of fluid fuel. @il is supplied to the nozzle 29 by the valved pipe 30. For the purpose of atoinizing liquid fuel, such as oil, the nozzle 29 is provided with a valved comi pressed air pipe 31 in a known manner. An opening 32 may be provided in the front wall to permit inspection of conditions within the furnace. The motors 20 and 27 are controlled by the switches 33 and 31 respectively.

Serious difficulties have been encountered when furnaces of the type mentioned are fired with pulverized coal. Combustion is frequently incomplete, particularly in the beginning of the melt, owing to the size of some of the fuel particles. Combustion is retarded by the impingeineiit of the coal and air against the cold metal and furnace walls. The unburiit particles of coal, together with slate, pieces of pyrites, ash and the like, are deposited on the hearth and throughout the charge before the latter'is melted. rEhe result is that the melt is very dirty, and also the sulphur content is increased so as to make the production of high grade castings uncertain or impossible. One important factor in the increase ofthe sulphur content is that the iron pyrtes which normally occurs with coal is more difficult to pulverize than is coal, so that the pyrites particles are of substantial size and readily find their way to the hearth through the pieces of metal placed thereon. Excessive sulphur is harmful in any cast iron, but it is particularly so in malleable cast iron, as it seriously affects complete graphitization in the annealing process with the result that ductility is decreased, machining is rendered diflicult and the reliability of the casting is impaired.

Fluid fuels are much more expensive than coal. Oil is the cheapest fluid fuel and is sometimes used, notwithstanding its higher cost. In addition to its relatively high cost, oil possesses serious technical disadvantages. It causes high oxidation losses and excessive carbon losses from the metal, particularly when the latter is in the molten state. These disadvantages are substantially absent where heating temperatures below the melting point of castiron are produced by means of a reducing fiame. For heating cast iron to a pouring temperature, oil requires an excess of air which results in the oxidation of the metal and the high carbon losses referred to. One outstanding virtue of oil, as a heating medium, is that it has no appreciable tendency to increase the sul hur content.

I In accordance with tie present invention, the initial part of the heating is effected b means of oil, while the latter heating is e fected by means of coal. The change over` from oil to coal may suitably be made at or about the time when the metal is melted wholly or in part. By this manner of operating I avoid substantially all the difficulties and disadvantages inherent in the use of either heating medium alone. The oil 1s used in the initial part of the heatmgso as to provide a reducing atmosphere within the furnace, which in turn reduces the tendency for oxidation of iron and the subsequent loss of silicon, manganese and carbon to a minimum. The oxidation of iron is much more sensitive to furnace atmospheres while the metal is in a solid state or partially melted state, as the density of mass while iron is solid or partially so revents the migration of carbon to the sur ace, allowing any free Oxygen present to attack the iron directly to form iron oxide, which later in the melt reacts to reduce the carbon, silicon and manganese, and the last traces of such oxides remain in the melted metal to cause casting difficulties. In addition to keeping the oxidation of iron and other elements to a minimum, as indicated above, my invention also prevents increase of sulphur content and by its use there is no appreciable ash or solid residue as in the case of pulverized coal.

When the change over to powdered coal is made, it is possible to completely consume the coal owing to the high temperature of the furnace. Ash and non-combustible portions of fuel fall upon the slag on the surface of the molten metal and do not contaminate the same. At this stage of the melting cycle, by the use of pulverized coal, it is also possible to maintain a reducing or neutral atmosphere together with high temperatures, which is not possible While using oil as a fuel. This preventsrhigh carbon loss and makes possible a more economical melting mixture.

In order to more completely illustrate the invention, I give below a more minute description of a specific example in which twenty tons of iron are melted in a furnace of suitable size for that quantity. The sprue and/or scrap iron, together with pig iron to form a desired charge, is placed upon the hearth ll and the furnace roof replaced. It may be noted that owing to the fact that the present method does not add to the sulphur content of the melt, somewhat increased quantities of high sulphur iron may be employed in the charge. llhe blower 25 is started so as to supply the volumetric air for the combustion of the oil which is introduced by the nozzle 29 together with atomizing air supplied by the pipe 3l. The volumetric air is controlled by partially opening or closing a shutter type damper, 28, on the intake side of the blower, which runs at constant speed. During the first hour or fifty minutes or so, a slightly lesser amount of oil is consumed than during the next two hours or so, since the higher temperature of the furnace facilitates the combustion of a greater amount of oil. At the end of three hours or so, the

charge is largely or completely molten and a slag .is formed upon the surface. The supply of o1l and atomizing air, by the nozzle 29 and pipe 3.1, may then be discontinued, ollowing which the motor 20 is started to feed a supply of pulverized coal to the nozzles 26 together with the air from the blower 25. Owing to the high temperature of the furnace the coal consumption is highly efficient. This heating is continued for perhaps another three hours, or through such time as is sufficient to raise the temperature of the molten metal to a degree suitable for pouring.

Although the invention has been disclosed in connection with the details of a specific embodiment thereof, it must be understood that such details are not intended to be limitative of the invention except in so far as set forth in the accompanying claims.

I claim:

l. The method of melting metals in a fured solid fuel into the furnace and supplying air thereto while the metal is liquid.

3. The method of melting metals in a reverberatory furnace which comprises injecting fluid fuel into the furnace and supplyin air thereto to effect combustion of the fue above the hearth to heat the metal substantially to melting, and thereafterinjecting finely divided solid fuel and air to raise the temperature of the liquid metal to pouring oint.

4. The method of melting metals in a reverberatory furnace which comprises injecting fluid fuel into the furnace and supplyin air thereto to effect combustion of the fue above the hearth While the metal is solid, and injecting finely divided solid fuel and air while the metal is liquid.

5. The method of melting iron in a reverberatory furnace which comprises injecting oil into the furnace and supplyin airv thereto to effect combustion of the oil a ove the hearth to heat the metal substantially to melting, and thereafter injecting finely divided solid carbonaceous fuel and air to raise.

limited amount to effect combustion of the oil above the hearth While maintaining reducing conditions While the metal is solid,fand Y injecting finely divided solid carbonaceousv fuel and air While the metal is liquid. r l

In testimon whereof, I have hereunto set my hand this ilth day of April, 1930.

LOTHAR R. ZIFFERER.

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