Method for preparing a charge ingot for production of products by casting

Abstract

The invention relates to metallurgical production, and more particularly to preparing a charge ingot which is used for producing bronze ingots by casting. As a starting charge material, a spent inert anode previously used in the electrolytic production of aluminium is utilised, that is covered with alumina, allowing same to react with a bath which flows out of the anode during a thermal treatment performed at a temperature within a range of 950-1200 C., followed by soaking in a furnace for at least 3 days. The invention makes it possible to obtain a charge ingot with a minimal electrolyte content.

Claims

1. A method for producing a charge ingot for production of castings containing copper, nickel and iron, the method comprising: covering a spent inert anode previously used in an electrolytic production of aluminium with alumina, wherein: the spent inert anode comprises copper, nickel, and iron, and dissolution of at least some of the iron during the electrolytic production of aluminum creates voids in the spent anode which are filled with a bath; executing a thermal treatment process that reacts the alumina on the covered spent inert anode with the bath to neutralize the bath during the thermal treatment process, wherein the bath flows out of the covered spent inert anode at a temperature within a range of 950-1200 C.; and in response to executing the thermal treatment process on the covered spent inert anode, soaking the covered spent inert anode in a furnace for at least 3 days.

2. The method according to claim 1, wherein the spent inert anode comprises 45-60 wt % copper and 10-25 wt % nickel with the remainder being iron.

3. The method according to claim 1, wherein covering the spent inert anode comprises fully immersing the spent inert anode in the alumina.

4. The method according to claim 3, wherein the volume ratio of the alumina is 3.4 times higher relative to the spent inert anode.

5. The method according to claim 1, wherein the charge ingot is used to produce castings based on one of: a centrifugal casting process, or a sand mold casting process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The essence of the invention is illustrated by the following drawings:

(2) FIG. 1 shows a graph for a distribution of chemical elements across the cross section of samples.

(3) FIG. 2 shows the location of the steel tank in the resistance furnace with the spiral heaters; said tank is filled with alumina and used for thermal treatment purposes.

(4) FIG. 3 shows both the area and direction of spectral scans of samples, at 11 different points, as per Embodiment 2.

(5) FIG. 4 shows a graph for the thermal treatment conditions as per Embodiment 3.

EMBODIMENT OF THE INVENTION

(6) During the electrolytic production of aluminium using inert anodes there is a reduction of iron content in them. Voids, formed upon iron dissolution during the electrolytic reduction, are filled with a bath that, during casting, makes it into the hearth of a melting furnace destructing the lining and contaminating liquid metal by non-metallic inclusions, and the air space above the furnace is filled with a large amount of fluorine-containing vapors.

(7) Samples of spent inert anodes were examined. The highest amount of fluorides is registered in the central porous part of a sample, moreover, the fluorine content varies within very wide limits (5% to 33%) which is explained by the presence of less porous areas in the structure of an oxide layer of an anode grid after an electrolytic test. Basic components of the bath are fluorine, sodium, and potassium. Results are given in Table 1.

(8) TABLE-US-00001 TABLE 1 Area No. O F Na Al Si Cl K Ca Cr Fe Ni Cu 1 26.01 1.12 72.88 2 23.99 0.83 75.18 3 23.81 0.84 75.36 4 24.95 2.01 0.13 72.91 5 21.97 8.2 2.73 3.74 0.36 0.19 59.24 1.22 2.34 6 4.39 24.78 9.96 8.38 0.96 0.64 10.36 12.73 27.8 7 1.89 7.28 2.73 0.2 0.35 5.66 26.34 55.56 8 1.53 5.1 2.01 0.17 0.34 4.95 27.08 58.81 9 1.75 6.33 2.38 0.2 0.48 4.86 26.96 57.05 10 2.28 27.77 12.3 9.72 1.17 0.77 4.9 12.99 28.13 11 3.02 32.28 13.02 10.69 1.46 0.82 5.2 10.68 22.84 12 1.94 32.61 13.16 11.27 1.55 0.84 4.78 10.69 23.16 13 1.89 24.29 10.59 8.89 1.09 0.73 4.86 15.08 32.58 14 1.47 6.05 2.31 0.17 0.39 4.87 26.96 57.8 15 1.53 4.84 1.85 0.14 0.37 5.17 27.19 58.91 16 0.01 8.01 3.96 3.03 0.2 0.14 0.34 0.45 5.98 24.89 53 17 3.48 14.92 6.81 5.13 0.48 0.5 0.17 6.71 20.63 41.17 18 5.11 21.55 8.54 7.34 0.79 0.44 11.26 14.09 30.88 19 13.3 16.52 5.64 5.39 0.5 0.29 31.3 8.77 18.28 20 22.63 5.5 1.68 2.47 0.15 67.13 0.44 21 24.47 1.82 0.14 73.58 22 24.28 4.72 1.25 3.33 66.42 23 24.51 0.9 74.59 24 25.07 0.77 74.16 All results are given in wt %

(9) To neutralize the bath obtained by melting, a spent inert anode is covered with alumina, allowing same to react with a bath which flows out of the anode during a thermal treatment. After a thermal treatment, alumina can be used upon the electrolytic production of aluminium.

(10) A spent inert anode is heat treated within a temperature range of 950 C.-1200 C. and is soaked in a furnace for about 3 days. These are optimal conditions for a thermal treatment of a spent inert anode, obtained experimentally, at which the technical result is achieved.

(11) Heating less than 950 C. will not allow to transform a bath into liquid state which is necessary to remove it from a spent inert anode, there is no need to maintain temperature over 1200 C. since by the time a furnace is heated to 1200 C. the entire bath is removed from a spent inert anode.

(12) Alumina is batched based on the condition of ensuring full immersion of a spent inert anode in it, experiments proved that this requires alumina ratio to be 3.4 times higher with regard to a spend inert anode. Such ratio provides a uniform alumina bed throughout the entire perimeter of a spent inert anode that does not allow a bath obtained by melting to interact with a tank where a thermal treatment is carried out, thereby destroying it.

(13) Upon pilot testing, an experiment was carried out to reduce the amount of alumina to 1-2 times higher with regard to a spent inert anode, as a result of which a tank was destroyed, a large emission of gaseous compounds was also observed upon a thermal treatment.

(14) The minimum baking time achieved was 72 hours or 3 days not including cooling down to a room temperature.

(15) Soaking in a furnace for less than 3 days is not expedient since a casting does not heat up as much as it is necessary to remove a bath, and more than 3 days will result in additional power costs.

(16) After pilot testing, samples of spent inert anodes were transferred to the Research Laboratory of the Casting Center of RUSAL ETC Ltd. for examination of their structure.

(17) Structure examination of samples submitted was carried out using OLYMPUS SZX16 optical stereo microscope (OM). To plot distribution graphs for contents of chemical elements across a cross section of submitted samples of spent inert anodes, an electron probe microanalysis was conducted using FEI Quanta FBG 650 scanning electron microscope (SEM) with X-MaxN SDD energy dispersive spectrometer (EDS).

(18) Upon a structural analysis, it was discovered that samples have a layered structure. A relatively dense oxide layer of various thickness is observed on the surface of samples, and the base is porous and non-uniform metal residues. The EDS analysis method was used to plot distribution graphs for contents of chemical elements across a cross section of spent anodes.

(19) The main composition of a charge obtained, wt %, is copper 45-60, nickel 10-25, ironthe remainder. This composition of a charge ingot allows to use it upon production of parts by casting with high copper and nickel contents. Distribution of chemical elements across a cross section of samples is shown in a distribution graph (FIG. 1).

Embodiments

(20) Embodiment 1. Laboratory tests.

(21) A 3 kA spent inert anode after 70 days of electrolytic reduction was selected as an initial material for developing a method for processing spent inert anodes with iron content over 70%.

(22) Using XMET3000EX+ X-ray analyzer (methodFP), concentration of the main alloying elements in a spent inert anode was determined, wt %: copper70, nickel19, iron11.

(23) A 2.6 kg spent inert anode was loaded into an alumina crucible, and was filled with alumina weighing 2 kg.

(24) Thermal treatment conditions: heating in Naberteherm H31\N furnace up to 1050 C., soaking for 3 hours, cooling down together with the furnace.

(25) About 20%-30% of alumina interacted with a bath.

(26) After a thermal treatment, a spent inert anode was clean, without dross, it does not require additional cleaning in a shot blasting unit.

(27) Weight of a spent inert anode after a thermal treatment was 2.2 kg, the weight difference was 0.4 kg.

(28) To determine the number of thermal treatment cycles, we load a spent inert anode into a crucible once again, and fill it with alumina weighing 2 kg. After carrying out a repeated thermal treatment, the weight of a spent inert anode was 2.2 kg. Therefore, a bath is completed removed upon these thermal treatment conditions.

(29) Embodiment 2. Pilot testing.

(30) A spent inert anode after 150 days of electrolytic reduction was selected as an initial material.

(31) A 20 kW resistance furnace with spiral heaters made of fechral was used for baking (FIG. 2). Heaters are located along the perimeter of the furnace and on the bottom, 3 chrome-aluminum thermocouples were placed into alumina protection tubes and were positioned throughout the furnace hearth to control the furnace response time in real time. Protection tubes with thermocouples inside a tank were filled with alumina together with a spent inert anode until its full immersion, alumina weight was about 1000 kg.

(32) One of the thermocouples measured temperature directly on heaters, the second onenext to the edge of the tank (external thermocouple), the third onein the middle of a spent inert anode (internal thermocouple).

(33) After placing a spent inert anode weighing 330 kg inside a furnace, it was heated up to a temperature of 950 C.

(34) After a thermal treatment, alumina that reacted with a bath separates from a spent inert anode rather easily in the amount of 10% of the weight of samples.

(35) Steel 20x23n18 was used as a material of a tank for thermal treatment.

(36) After a thermal treatment, minimal content of fluorine, sodium and potassium as bath components was detected in a sample which is indicative of almost complete purification of a spent inert anode. Results are given in Table 2. Data of a local chemical composition were collected from areas located along red lines (FIG. 3).

(37) TABLE-US-00002 TABLE 2 Area No. O F Na Al Si S Cl K Ca Cr Fe Ni Cu 1 18.01 0.18 1.39 0.17 0.45 38.32 11.24 30.24 2 15.96 0.01 0.14 2.32 0.14 0.17 0.16 36.45 12.13 27.2 3 11.2 0.12 1.55 0.22 0.14 0.2 16.99 22.05 47.53 4 7.47 0.08 1.09 0.23 0.19 0.19 0.21 8.5 25.78 56.26 5 8.3 0.33 1.12 0.14 0.12 0.22 0.15 10.82 23.08 55.72 6 6.99 0.16 0.05 1.21 0.16 0.18 12.88 22.2 54.17 7 6.11 0.93 0.19 0.11 0.2 10.33 24.86 57.28 8 8.01 1.17 0.11 0.18 13.78 23.34 53.4 9 8.91 1.08 0.23 0.17 14.71 22.65 52.25 10 13.44 0.15 1.83 0.15 0.2 22.45 18.09 43.69 11 14.97 0.17 1.86 0.21 0.18 26.6 15.7 40.29 All results are given in wt %

(38) Embodiment 3. Similar to embodiment 2, test were carried out at a heating temperature of 1050 C., all of the other data remained unchanged. After a thermal treatment, minimal content of fluorine, sodium and potassium as bath components was detected in a sample. Results are given in Table 3. A graph for the performed thermal treatment conditions is shown in FIG. 4.

(39) TABLE-US-00003 TABLE 3 Area No. O F Na Al Si S Cl K Ca Cr Fe Ni Cu 1 16.03 2.08 0.21 0.45 36.37 15.88 28.98 2 13.56 1.62 0.21 0.14 0.17 32.48 16.09 35.73 3 15.5 0.02 1.05 0.21 0.04 0.2 23.13 17.33 42.52 4 8.28 0.005 0.05 1.94 0.4 0.19 0.19 0.21 0.12 24.86 17.15 46.6 5 10.2 0.01 0.3 1.76 0.22 0.15 27.13 18.44 42.09 6 9.9 1.24 0.53 0.02 0.18 26.36 18.36 43.41 7 11.57 0.003 0.09 2.19 0.43 0.11 0.2 22.28 18.98 44.147 8 9.78 1.37 0.21 0.18 19.1 20.67 48.69 All results are given in wt %

(40) Embodiment 4. In the same manner, tests were carried out at a heating temperature of 1200 C., all of the other data remained unchanged. Obtained results were the same as for embodiments 2, 3.

(41) This method differs from all alternatives in that it refers to processing of bath-containing charge materials, particularly spent inert anodes that can be used for further remelting.

(42) This method allows to remove a bath from a spent inert anode to be re-used upon production of castings and ingots, without gas emissions into the environment.