US3462538A - Method and apparatus for the continuous charging of sponge iron granules into an electric furnace - Google Patents

Description

Filed April 8, 1968 4 Sheets-Sheet 1 Aug. 19, 1969 5 PELLEGRlNl ET AL 3,462,538

METHOD AND APPARATUS FOR THE CONTINUOUS CHARGING 0F SPONGE IRON GRANULES INTO AN ELECTRIC FURNACE Aug. 19, 1969 R. E. PELLEGRIN! ET AL 7 3,462,538

METHOD AND APPARATUS FOR THE CONTINUOUS CHARGING 0F SPONGE IRON GRANULES INTO AN ELECTRIC FURNACE 4 Sheets-Sheet 2 Filed April 8, 1968 N at Aug. 19, 1969 Filed April 8, 1968 R. E. PELLEGRINI ET AL 3,46 ,538

METHOD AND APPARATUS FCR THE CONTINUOUS CHARGING OF SPONGE IRON GRANULES INTO AN ELECTRIC FURNACE 4 Sheets-Sheet I 3 Aug. 19, 1969 v PELLEGRW] ET AL 7 3,462,538

- METHOD AND APPARATUS FOR THE 'com nuous CHARGING 0F SPONGE IRON GRANULES INTO- AN ELECTRIC FURNACE Filed April 8, 1968 4 Sheets-Sheet 4 7 v i A FIG. 4

United States Patent O Italy Filed Apr. 8, 1968, Ser. No. 719,582 Claims priority, applicgtogn g Iexico, May 19, 1967,

Int. Cl. 1105i) 7/18, 11/00 U.S. Cl. 13-9 6 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for continuously charging sponge iron granules into an electric arc furnace wherein said sponge iron granules are injected into the furnace through the wall thereof and substantially midway between the ends into the vicinity of the furnace electrodes.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the manufacture of steel utilizing an electric arc furnace, and more particularly, to such an arrangement wherein sponge iron granules are injected into the molten bath contained in the furnace.

Prior art In the manufacture of steel, the electric arc furnace is generally known which contains electrodes to supply, by means of electric arcs, the heat needed to fuse the metal. These electrodes may be in the form of coal bars, or the like, and normally extend through the entire length of the furnace and in substantially the central portion thereof. The charge or principal raw material used in these known furnaces may take several forms, such as a relatively low quality steel obtained from a Bessemer converter, or the like, which is further refined, or iron scrap and fuse cast iron, or molten liquid iron, etc.

It is also generally known to utilize sponge iron granules in connection with the above operation to obtain a superior product due to the greater density, compactness, and higher degree of homogeneity of the granules. However, in these known arrangements, the granules are introduced into the "molten bath from the top of the vat which creates problems.

For example, in introducing the granules from the top of the vat, great amounts of acid slag are produced which cannot be timely eliminated. This creates a strong erosion on the refractory lining of the furnace, along with increasing electrode wear and electric energy consumption, largely due to the longer duration of the fusion re fining phases. The ultimate result of this is great dephosphorization difficulties that preclude spontaneous slagging when the bath temperature is relatively low.

A further disadvantage that results from the introduction of the sponge iron granules from the top of the furnace is that the electrodes are not always capable of perforating the charge, so that fusion takes place from the bottom up. This, of course, results in less efficiency which again causes excessive deterioration of the refractory lining, in addition to a slow and difficult diffusion of the sponge iron deposited on the bottom. Furthermore, the fusion takes place when the steel temperature almost reaches its maximum value which provokes a violent liquid reaction with subsequent ejection of steel out the working door of the furnace. Also, undesirable elements contained in the sponge iron return and again contaminate the bath provoking a cooling that is ditficult to control.

Also, in addition to undergoing a synthesis tendency, the sponge iron undergoes a greater re-oxidation when introduced from the top of the furnace, due to the extended sponge iron fusion period under oxidating atmosphere at high temperature.

Even further disadvantages arise in the form of operating inconveniences, which, for example, include delay in fusion and initiation of the refining periods, excessive wear of the furnace refractory involved due to the high acid slag content, increased electrode wear and electric energy consumption, larger decrease of metallic productivity, and insutficient dephosphorization.

It should be noted that all of the above disadvantages are aggravated as the iron content decreases in the mineral from which the sponge iron is obtained.

SUMMARY OF THE INVENTION Briefly summarized, the present invention relates to a method and apparatus for manufacturing steel wherein an electric arc furnace is provided having a plurality of electrodes extending from one end of the furnace to the other, with a metered amount of sponge iron granules being injected into the furnace through the wall and substantially between the two ends thereof and in the vicinity of the electrodes.

The present invention also relates to a device adapted to inject sponge iron granules into an electric arc furnace and an automatic metering device adapted to continuously feed a metered amount of sponge iron granules into the ejecting device.

The present invention further relates to an apparatus for the manufacture of steel including a hopper adapted to supply sponge granules to a pair of vibrating conveyors which, in turn, supply the granules to metering devices for injection of the granules into electric arc furnaces.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying drawings for a better understanding of the nature and objects of the present invention, which drawings illustrate the best mode presently contemplated for carrying out the objects of the invention and its principles, and are not to be cons rued as restrictions or limitations on its scope. In the drawings:

FIG. 1 is a perspective view, partially cut away, which shows an electric arc furnace and associated apparatus of the present invention,

FIG. 2 is a plan view of the apparatus of the present invention showing a pair of electric arc furnaces with their respective associated apparatus,

3 FIG. 3 is a cross-sectional view taken along line 33 of FIG. 2, and

FIGS. 4 and 5 are a plan view and a side elevational view, respectively, of the ejecting device of the present invention, with FIG. 5 being shown partially in section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring in general to the drawings, and specifically to FIG. 1, thereof, the reference numeral 6 depicts an electric arc furnace which is shown partially cut away in the interest of clarity, and which has three electrodes extending through the ends, and approximately in the central portion thereof. 1

An ejecting device 7 is provided which is adapted to inject sponge iron granules 8 into the furnace, and is provided with a charge tube 9 which extends through the lateral wall of the furnace 6 to direct sponge iron granules into the central zone thereof, that is, a zone substantially midway between the two ends of the furnace, and in the vicinity of the electrodes 10, as shown in FIG. 1. An automatic metering device 11 is also provided which continuously feeds the sponge iron granules to the ejecting device in order that a controlled amount of particles may be injected into the furnace.

The ejection device 7 mechanically imparts to the granules the energy needed for ejecting them through the charge tube 9 and into the furance, and is shown in greater detail in FIGS. 4 and 5. As shown, a thin rotor 12 is provided which rotates within a fixed housing 13 provided with an inlet opening registering with the feeding hopper 15 under the metering device 11, and with a tangential discharge opening 14 registering with the charge tube 9.

A cover 16 is provided on housing 13 which extends perpendicular to the axis of rotor 12, and which is resiliently mounted on the housing by means of a spring means 17 adapted to yield in case of agglomeration of the material, to avoid ruptures and deformation of the associated apparatus.

Rotor 12 is connected to an electric motor by means of a transmission shown generally at 24, and a friction coupling 19 which protects the motor in the event the rotor 12 may become jammed.

FIGS. 2 and 3 depict an arrangement in which two electric arc ovens are utilized, it being understood that a larger number may be provided as necessary. In particular, a hopper 20 is provided which generally extends between the furnaces and into which is fed the sponge iron deposits by means of a conveyor and a fiuting elevator, or the like, not shown. Hopper 20 has two discharge openings 21 which, by means of vibratory feeders 22, feed the sponge iron to their respective metering devices 11.

In operation, the furnace or furnaces are started after being partially filled with an initial iron scrap charge, this initial charge being approximately from to by weight of the expected total charge. When this initial charge is totally fused by means of the heat supplied by the electrodes, the ejecting devices 7 are actuated in order to inject sponge iron granules into each furnace through the wall and substantially midway between the ends thereof, and in the vicinity of the electrodes 10. The amount of granules injected is controlled by the metering devices 11 in order that a predetermined amount enter the furhaving high phosphorous content, this being largely due to the fact that the slagging takes place at the initial fusion phase when the bath temperature is relatively low, thus obtaining a good metal dephosphorization. The nature of the slag is continuously controlled without difliculty by adding fusers and additives in predetermined amounts and intervals. Also, the slag formation may be obtained during the pre-refining phase by means of lime addition.

Further, in the above arrangement, the low electrical conductivity characteristic of sponge iron is substantially diminished and since the sponge iron charge is initiated only after the initial partial charge of steel scrap or the like is inserted into the furnace and is practically fused, the overall fusion is carried outwith theelectrodes always submerged in the slag, ,thus producing a constant charge system in a continuous bath movement. This, of course, facilitates physical and chemical interchanges between-the slag and the steel, which in 'turn allows a decrease of the time for refining. Since the latter is achieved, a decrease in electrode wear,electric energy, and furnace refractory is, of course, alsodiminished.

An even further advantage of the present invention is the elimination of the danger of violent reactions created by a retarded fusion, due to the fact that the sponge iron substantially never adheres to the bottom of the furnace. Of course, this results in an improvement of the operation of the furnace and in an improved metallic productivity.

Since the sponge iron granules are ejected through the side wall of the furnace, no unnecessary openings are required in the top, as in previous arrangements, and this again results in a saving of time and electric energy.

Of course, other variations of the specific construction and arrangement of the method and apparatus herein disclosed can be made by those skilled in the art without departing from the invention as defined in the appended claims.

We claim:

1. A method for continuously charging sponge iron granules into an electric arc furnace having electrodes contained therein, comprising the steps of fusing an initial partial charge of substantially scrap iron in said furnace, metering the amount of granules to be injected into said furnace, imparting sufiicient energy to said injecting sponge iron granules to eject them into said furnace through the wall thereof and substantially midway'between the two ends thereof in the vicinity of the electrodes, and tilting said furnace simultaneously with said step of injecting to cause the slag formed in said furnace to fall out of the furnace as soon as it is formed to thereby obtain a uniformly fused material.

2. An apparatus for continuously charging sponge iron into an electric arc furnace comprising at least one electric arc furnace having at least one electrode contained therein for fusing an initial partial charge of scrap iron in said furnace, injecting means to continuously inject sponge iron granules into said furnace through the wall thereof substantially midway between the two ends of said furnace in the vicinity of said electrode, said injecting means comprising a housing having an inlet opening, a tangential out let opening, a charge tube connected with said outlet opening and extending through the wall of said furnace, metering means to meter the amount of granules fed into said inlet opening, a rotor rotatably mounted within said housing, a drive motor connected to drive said rotor to thus impart sufficient energy to said granules to eject them through said charge tube, and means to tilt said furnace simultaneously with the injection of said granules into said furnace to cause the slag formed in the furnace to fall out therefrom as soon as the slag is formed.

3. The apparatus of claim 2, wherein two electric arc furnaces are provided, injection means and a metering means being provided for each ofsaid furnaces, and further comprising a hopper adapted to supply the granules to both of said metering means.

5 4. The apparatus of claim 3 further comprising a pair of vibratory feeders adapted to feed the granules from said hopper to both of said metering means.

5. The apparatus of claim 2, wherein said injecting means further comprises a cover for said housing and 5 6 References Cited UNITED STATES PATENTS 2,236,329 3/1941 Bryan 1310 2,528,571 11/ 1950 Babcock 1310 3,167,420 1/1965 Robiette 139 X 7 2,868,860 1/1959 Foyn et a1 139 X BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner U.S. Cl. X.R. 13-10

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