JP4319387B2 - Treatment method for molten aluminum - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating molten aluminum that removes impurities such as hydrogen, oxides, and non-metallic inclusions in a molten aluminum or aluminum alloy, and collects and reuses aluminum dross.
[0002]
[Prior art]
When the molten aluminum is exposed to the atmosphere, it is easily oxidized to form a large amount of oxide and inclusions (hereinafter referred to as dross) attached to the oxide. In addition to oxides such as Al ₂ O ₃ , MgO, Al ₂ MgO ₄ , SiO ₂ , silicate, Al · Si · O, FeO, Fe ₂ O ₃ , carbides (Al ₄ C ₃ , Al ₄ O ₄ C, graphite carbon), boride (AlB ₂ , AlB ₁₂ , TiB ₂ , VB ₂ ), Al ₃ Ti, Al ₃ Zr, CaSO ₄ , AlN, and various halides. When dross is mixed in molten aluminum due to suspension, it eventually becomes non-metallic inclusions, which leads to deterioration in quality of products such as wrought materials, forged products, and die-cast products. For this reason, it is necessary to separate and remove dross from the molten metal in each stage such as a melting furnace, a holding furnace, and a ladle.
[0003]
Patent Document 1 discloses a technique for separating and discharging dross from molten metal by changing the rotational gradient of the melting furnace and efficiently recovering the dross. Thus, dross can be efficiently recovered in the melting step. However, since the Al molten metal contains an impurity gas component such as hydrogen, it is necessary to degas the remelting process.
[0004]
Patent Documents 2 to 5 each disclose a degassing treatment method in which a treatment gas such as argon, nitrogen, or chlorine is blown into a molten metal in a treatment tank and gas bubbling is performed. That is, conventional methods include blowing the flux into the molten metal during gas bubbling (Patent Document 2) or stirring the molten metal during gas bubbling with rotating blades (Patent Documents 3, 4, and 5).
[0005]
[Patent Document 1]
JP-A-10-227567 (pages 4 to 5)
[0006]
[Patent Document 2]
JP 63-183136 A (pages 1 to 4, FIGS. 1 and 2)
[0007]
[Patent Document 3]
JP-A-10-306330 (pages 3 to 4, FIGS. 5 and 6)
[0008]
[Patent Document 4]
Japanese Patent Laid-Open No. 62-297422 (1 page, FIG. 1)
[0009]
[Patent Document 5]
Japanese Patent Publication No. 7-68591 (1 page, Fig. 1)
[0010]
[Problems to be solved by the invention]
However, in the conventional degassing treatment, dross with a high aluminum content is generated because the impurities float on the molten metal surface. The dross generated by this degassing process has its aluminum content removed in the next ash-squeezing process, but the degassing process has a negative effect on recycling because it is different from the dissolving process. That is, dross containing a large amount of aluminum generated in the degassing process must be periodically removed and reprocessed in the ash squeezing process, resulting in high processing costs and utility costs, and poor recyclability.
[0011]
In addition, since the dross with a lot of aluminum generated in the degassing process is processed by an exothermic reaction in the ash drawing process, it is difficult to maintain a constant quality such as an increase in oxide and mixing of iron, deoxidizer for steel, There was a problem in recycling as a cement raw material.
[0012]
Furthermore, although the heated dross is cooled through the cooling kiln, the equipment cost and the light heat cost have increased due to repeated overheating cooling.
[0013]
The present invention has been made to solve the above-described problems, and minimizes the removal of aluminum-rich oxides and inclusions (dross) without degrading the quality of the molten metal, thereby reducing the quality of dross. It aims at providing the processing method of the molten aluminum which can be collect | recovered stably.
[0014]
[Means for Solving the Problems]
The molten aluminum treatment method of the present invention is a molten aluminum treatment method for degassing a molten aluminum made of Al or an Al alloy. The molten aluminum is moved from the melting furnace to the treatment tank together with oxides and inclusions attached to the oxide. And the sodium chloride (NaCl), potassium chloride (KCl), aluminum fluoride (AlF ₃ ), sodium fluoride (NaF), calcium fluoride (CaF), PAF (K ₃ AlF ) to the molten metal in the treatment tank. ₆ ), sodium silicofluoride (Na ₂ SiF ₆ ), potassium silicofluoride (K ₂ SiF ₆ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), potassium nitrate (KNO ₃ ), nitric acid Sodium (NaNO ₃ ), potassium sulfate (K ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ) , A flux composed of one or more compounds selected from the group consisting of magnesium chloride (MgCl ₂ ) and carnarit (MgKCl) is charged , and the agitator equipped with a rotary blade and a gas outlet is lowered, and the rotary blade Is immersed directly under the molten metal surface in the treatment tank, the rotating blades are rotated to stir the molten metal and the flux directly under the molten metal surface, and the reaction between the molten metal and the flux is promoted to be mixed in the molten metal. A step of reforming the oxide, separating the reformed oxide and inclusions adhering to the oxide from the molten metal, and further lowering the stirrer so that the gas blowing portion and the rotary blade are at the bottom of the treatment tank; The non-oxidizing gas is diffused into the molten metal by rotating the rotary blade while blowing non-oxidizing gas from the gas blowing part into the molten metal, and mixed in the molten metal. A step of degassing the molten metal with floating the oxides and inclusions attached to the oxide melt-surface, the oxide was the modified emerged in molten steel surface by using a heat-resistant dross scraper member and oxidation to A step of collecting inclusions adhering to an object at a specific location in the processing tank, and discharging and recovering the modified oxide and the oxide adhering to the oxide from the processing tank by a suction discharge device. It is characterized by doing.
[0016]
Since aluminum is active after melting, oxides are generated on the surface of the molten metal, but if left untreated, they react with oxygen and nitrogen and are entrained in the molten metal, generating dross. This dross not only deteriorates the quality of the molten metal but also floats on the surface of the molten metal to deteriorate the thermal conductivity, and when kept at a high temperature, the aluminum surface is oxidized to form γ-Al ₂ O ₃ . To do. If this state is maintained for a certain period of time, the dry γ-Al ₂ O ₃ transforms into wet aluminum oxide (α-Al ₂ O ₃ ) and settles and floats in the molten metal, so that removal is extremely difficult. It becomes difficult. In addition, wet aluminum oxide (α-Al ₂ O ₃ ) easily adheres to surrounding members and is difficult to separate and discharge outside the treatment tank. Take the trouble.
[0017]
Therefore, in the present invention, before starting the degassing process, the flux is introduced into the molten metal, and the rotating blades of the stirrer are immersed directly under the molten metal surface to stir the molten metal and the flux to wet the dross in the molten metal. The α-Al ₂ O _{3 was then changed} to dry γ-Al ₂ O ₃ , and then the gas blowing part of the stirrer was lowered to the vicinity of the bottom of the treatment tank to perform gas bubbling, and the reformed dross was brought to the molten metal surface. Make it rise.
[0019]
In this case, in order to promote the reaction of the flux, the vertical blade reciprocating motion and the rotational motion and the reaction are promoted using a rotating blade type stirrer. A rotating blade and a gas blowing part are attached close to the lower part of the stirrer, the gas blowing part has a porous material with a porosity of 15 to 75% and an average pore diameter of 100 μm or less, and inside the gas blowing part A gas reservoir is formed, and the shape of the gas blowing portion forming the outer periphery of the gas reservoir is cylindrical. Such a rotating blade type stirrer discharges bubbles of non-oxidizing gas from the outer periphery, and the rotating blade contacts the upper part of the gas blowing part to suppress the stirring of the molten metal, and only for the dispersion of the non-oxidizing gas It is possible to impart a weak stirring force to the molten metal.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0021]
As shown in FIG. 1, the degassing apparatus 10 as a molten metal processing apparatus includes a processing tank 4, a gas supply / rotation drive mechanism 30, and a stirrer 40. The treatment tank 4 has a refractory attached to the inside, an outer periphery covered with an iron skin, and is installed on the gantry 2 via a frame 3 attached to the iron skin. The treatment tank 4 has a treatment capacity capable of degassing a molten aluminum of up to 1500 kg per batch.
[0022]
A melting furnace (not shown) is installed adjacent to the processing tank 4, and molten aluminum is poured from the melting furnace into the processing tank 4 in a non-oxidizing atmosphere. The melting furnace has a dross separation / removal function. In the melting furnace, a lot of dross is separated and removed from the molten metal. Nevertheless, a considerable amount of dross 6 together with the molten metal 5 is melted. Enters the treatment tank 4. The dross 6 entering from the melting furnace is in a wet state, and this wet dross is likely to adhere to surrounding members and difficult to remove by the conventional method.
[0023]
Further, the degassing apparatus 10 includes a flux charging device (not shown) for charging the flux 7 into the molten aluminum 5 in the processing tank 4. The flux feeding device has a plurality of hoppers and shooters that contain an aluminum scavenger as a flux, mixes a predetermined component of the aluminum scavenger in a predetermined mixing ratio, and inputs a predetermined amount into the treatment tank 4. It has a function.
[0024]
As shown in FIG. 1, the agitator 40 is rotatably supported by the gas supply / rotation drive mechanism 30, and the gas supply / rotation drive mechanism 30 is cantilevered by the arm 20. Further, as shown in FIG. 3, the arm 20 is supported by a support shaft 22 in the post 12 so as to be able to turn and ascend and descend.
[0025]
A motor unit 13 is provided on the top of the post 12. In the motor unit 13, a belt 16 is stretched between a driving pulley and a driven pulley 15 of the rotating shaft of the motor 14. Further, a driven pulley 17 is provided below the post 12, and an elevating belt 18 is stretched between the pulley 17 and the pulley 15 in the motor unit 13. A plurality of pairs of nuts 19 are fixed to the elevating belt 18, and an arm 20 is connected to the elevating belt 18 via these nuts 19.
[0026]
Limit switches 21a and 21b are attached to the upper and lower proper positions of the post 12, respectively, at positions where the upper and lower stoppers 23a and 23b attached to the ends of the arm 20 can come into contact with each other. When the upper stopper 23a comes into contact with the upper limit switch 21a, the raising of the arm 20 is stopped, and when the lower stopper 23b comes into contact with the lower limit switch 21b, the lowering of the arm 20 is stopped. Incidentally, the lifting stroke of the arm 20 (stirrer 40) is about 1.5 m. As shown in FIG. 3, a plurality of lift stoppers 50 are arranged at appropriate positions in the vicinity of the processing tank 4 as safety devices.
[0027]
The post 12 is mounted on the power supply unit 11. A turning drive mechanism for turning the arm 20 around the support shaft 22 is built in the power supply unit 11. Further, the circuit of the power supply unit 11 is connected to the power switches of the elevating motor 13 and the rotary drive motor 34 via the flexible cable 24. Incidentally, the turning radius of the arm 20 (stirrer 40) is about 2 m.
[0028]
The stirrer 40 includes a hollow rotary shaft 32 and a rotary blade 41. The hollow rotary shaft 32 is made of sintered carbon or ceramics below the flange joint 32b, and is made of stainless steel or heat-resistant steel above the flange joint 32a. As shown in FIG. 2, the upper portion of the hollow rotary shaft 32 is rotatably supported by the motor unit 31 by two bearings 39 of the gas supply / rotation drive mechanism 30. A driven pulley 33 is fitted into the upper part of the hollow rotating shaft 32, and a belt 36 is stretched between the driven pulley 33 and the driving pulley 35 of the motor 34, and the rotational driving force of the motor 34 is applied to the hollow rotating shaft 32. It is to be transmitted.
[0029]
A gas supply pipe 38 is attached to the uppermost end of the hollow rotary shaft 32 via a loose fitting joint 37, and passes through a hollow portion of the hollow rotary shaft 32 from a gas supply source (not shown) to the lowermost gas blowing portion 42 of the stirrer 40. A processing gas is supplied to the gas tank. Incidentally, the outer diameter of the hollow rotating shaft 32 is 25 mm to 50 mm, and the inner diameter is 5 to 45 mm.
[0030]
The gas blowing part 42 includes a gas reservoir (header) and a porous member attached immediately below the rotary blade 41. The porous member is attached to the outer periphery of the gas reservoir so as to surround the gas reservoir, and has a porosity of 15 to 75% and an average pore diameter of 100 μm or less.
[0031]
It is desirable to taper the processing gas outflow portion of the porous member. In this case, it is preferable that the shape of the processing gas outflow portion is cylindrical and bubbles of the processing gas are discharged from the outer peripheral portion.
[0032]
Further, the rotary blade 41 preferably adopts the shape described in, for example, Patent Document 3 and Patent Document 4, and has a weak stirring force only for the diffusion of the processing gas while suppressing stirring of the molten metal. It is desirable. In this case, it is preferable that the side surface of the rotary blade 41 be tapered or reversely rounded so that the processing gas can be diffused to the lower portion of the processing tank 4.
[0033]
Although not shown in FIGS. 1 to 3, as shown in FIG. 4, a scraping jig 61 and a suction / discharge device 62 are respectively provided at appropriate positions above the processing tank 4. The scraping jig 61 is made of plate-like carbon, a refractory material, and a ceramic member, and its surface is specially processed so that dross does not adhere. The suction / discharge device 62 has a trumpet-shaped suction port made of a heat-resistant material, and communicates with a recovery pot (not shown) via a suction pump (not shown). The scraping jig 61 and the suction / discharge device 62 are both supported by a lifting mechanism (not shown) so as to be lifted and lowered.
[0034]
Next, the processing method of the present invention will be described with reference to FIG.
[0035]
After melting aluminum in the melting furnace, the molten aluminum 5 is transferred together with the dross 6 from the melting furnace to the treatment tank 4 (step S1). The dross 6 from the melting furnace is wet and wet, and is easily attached to surrounding members.
[0036]
Next, the flux 7 having a predetermined component is charged into the treatment tank 4, the stirrer 40 is lowered, and the rotary blade 41 is immersed immediately below the molten metal surface of the molten metal 5 in the treatment tank. And the rotating blade 41 is rotated and the molten metal 5, the dross 6, and the flux 7 are stirred for several minutes. As a result, the dross 6 in the wet state (easy to adhere) is reformed to the dross 6A in the dry state (difficult to adhere), and the dross 6A is separated from the molten metal 5 (step S2). This stirring is preferably performed for at least 1 minute.
[0037]
Next, the stirrer 40 is further lowered, and the gas blowing part 42 and the rotary blade 41 are positioned in the vicinity of the bottom of the processing tank 4. Then, argon or nitrogen gas is blown into the molten metal 5 from the gas blowing portion 42 as a non-oxidizing gas, the rotating blade 41 is rotated while gas bubbling is performed, the molten metal 5 is stirred, and the dross 6 mixed in the molten metal 5 Impurity gas components such as hydrogen are floated on the hot water surface (step S3). The stirring force at this time is weak enough not to inhibit the gas bubbling reaction. After the gas bubbling is continued for several minutes, the gas blowing is stopped and the degassing process is terminated.
[0038]
Next, the stirrer 40 is further lowered, the rotary blade 41 is positioned at the deepest place in the treatment tank 4, and the molten metal 5 is stirred. The heat-resistant dross scraping member 61 is lowered, the lower part thereof is immersed in the hot water surface, and the dross 6A is gathered at a specific location in the processing tank 4 (step S4). The collected dross 6A is sucked and discharged from the processing tank 4 by the suction / discharge device 62 and collected in the recovery pot (step S5).
[0039]
In addition, when the rotation speed of a rotary degassing apparatus is 500 rpm or more, there exists a danger of aluminum scattering, and since it is dangerous, 300-400 rpm is preferable. Since the rotary degassing device rotates and reciprocates up and down, no baffle plate (baffle plate) is required to prevent entrainment, and the mixer processing gas discharge part of the rotary degassing device is porous with porous gas dispersion effect at low speed rotation A structure having
[0040]
(Example)
Next, examples will be described.
[0041]
Alloy type: AC4CH
Processing temperature: 700 ° C
The ladle treatment was performed under the above conditions.
[0042]
1 kg of flux is added to 500 kg of molten aluminum which is discharged from the melting furnace into a ladle and 7 kg dross is generated on the surface, and a rotating body having a degassing mechanism is immersed in about half of the molten metal depth. 5 kg of dross discharged from a melting furnace or the like was added at the stage where rotation started and dross on the surface was caught.
[0043]
After 1 minute, the dross and the flux sufficiently reacted and the aluminum content in the dross was completely separated. Next, the rotating body was immersed to the vicinity of the furnace bottom, and the degassing process was dispersed at a low speed for 2 minutes to remove the hydrogen gas.
[0044]
The dross generated in the normal process is 7 kg in the ladle + 5 kg in the melting furnace dross, a total of 12 kg, whereas the present invention can reduce the dross to 1 kg.
[0045]
When this treatment was repeated 10 times, the average remaining amount of aluminum in the dross was 30%. Moreover, when the amount of H ₂ gas in the ladle was measured, it was reduced from the conventional 0.62 cc / 100 g Al to 0.11 cc / 100 g Al, and it was confirmed that there was no problem in use in the casting process.
[0046]
The sample melt was filtered for a predetermined time with IA500b, the sample melt after filtration was solidified, cut and polished, and the cross section was observed with a microscope.
[0047]
The filtration time was measured using a molten metal filtration method (Olin frit method).
[0048]
The conditions of the molten metal filtration method are shown below.
[0049]
Inclusion determination machine: 1A-500b
Molten metal temperature: 720 ° C ± 10 ° C
Molten metal weight: 2.50 to 3.00 kg
Filter pore diameter: 70-80 μm
Filter diameter: 14mm
Pressure; 0.068-0.070 MPa
FIG. 5A is a photograph showing a cross section of a comparative example sample taken from the molten aluminum before the treatment, and FIG. 5B is a photograph showing a cross section of the embodiment sample taken from the molten aluminum treated by the method of the present invention. .
[0050]
6A is a photomicrograph showing the metal structure of a comparative sample processed using the conventional method, and FIG. 6B is a photomicrograph showing the metal structure of an example sample processed using the method of the present invention. is there.
[0051]
As is apparent from these photographs, it was confirmed that nonmetallic inclusions were greatly reduced by using the method of the present invention.
[0052]
(Comparative example)
Chip treatment alloy type: ADC12
Conventional method: Holding chamber The molten metal 5000 k was held in a 200 kg aluminum chip melting and holding furnace of a 5000 kg chip treatment tank, and the molten metal was charged at a rate of 200 kg / hr for melting. After 1 hour, the dross on the surface of the melting furnace was removed and the measurement was 700 kg. Further, when the dross was ash-squeezed, 600 kg of aluminum was recovered and 100 kg of dross was generated. It was confirmed that the molten metal in the holding chamber oxidizes the molten metal in the holding chamber and a large amount of dross was produced, resulting in poor yield.
[0053]
Although 5200 kg was melted, 4500 kg of molten metal was recovered in the holding furnace, and 600 kg was recovered by ash drawing in a separate process. However, since it was in a solid state, a utility cost was required for remelting.
[0054]
(Example)
Next, after the dross was moved from the holding chamber to the front furnace by the method of the present invention and shielded by the partition plate, the molten metal was processed by the above-described rotary degassing apparatus and the flux by reciprocating and rotating. At this time, the molten metal after the treatment of the treated ladle was returned to the holding chamber. According to the method of the present invention, dross generated in the front furnace was 10 kg, and 5190 kg of molten metal could be obtained. For comparison, when a pressure filtration test was performed with a filter having an average pore size distribution of 70 μm and a nitrogen gas of 0.1 MPa, a difference in the amount of inclusions was confirmed as shown in FIGS.
[0055]
FIG. 7 is a bar graph showing a comparison between the method of the present invention and the conventional method in order to explain the effects of the present invention. In the figure, Comparative Example 1 is before degassing treatment, Comparative Example 2 is a processed product of another company, Comparative Example 3 is a combination of stirring with a rotary blade and degassing treatment, and Example 1 uses the method of the present invention. Each was shown. The filtration time by the molten metal filtration method was 150 seconds for Comparative Example 1, 180 seconds for Comparative Example 2, 125 seconds for Comparative Example 3, and 90 seconds for Example 1. Thus, it was confirmed that the molten metal processed using the method of the present invention significantly shortens the filtration time by the molten metal filtration method.
[0056]
【The invention's effect】
According to the present invention, dross removal can be minimized and stable quality dross can be recovered stably without deteriorating the quality of the molten metal.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a part of a molten metal treatment apparatus used in a method of the present invention.
FIG. 2 is a schematic cross-sectional view showing a treatment tank and a stirrer.
FIG. 3 is a plan view showing a molten metal treatment apparatus used in the method of the present invention as viewed from above.
FIG. 4 is a process diagram showing a method for treating molten aluminum according to an embodiment of the present invention.
5A is a photograph showing a cross section of a comparative example sample taken from a molten aluminum before the treatment, and FIG. 5B is a photograph showing a cross section of an example sample taken from the molten aluminum treated by the method of the present invention.
6A is a photomicrograph showing the metal structure of a comparative sample processed using a conventional method, and FIG. 6B is a photomicrograph showing the metal structure of an example sample processed using the method of the present invention. .
FIG. 7 is a bar graph showing a comparison between the method of the present invention and the conventional method in order to explain the effects of the present invention.
[Explanation of symbols]
2 ... the frame,
3 ... Frame,
4 ... treatment tank,
5 ... Molten aluminum,
6, 6A ... Dross,
7 ... Flux,
10 ... Molten metal treatment device (degassing treatment device),
11 ... power supply unit,
12 ... Post,
13 ... Motor unit,
14 ... motor,
15, 17 ... pulley,
16, 18 ... belt,
19 ... nuts,
20 ... arm,
21a, 21b ... limit switches,
22 ... support shaft,
23a, 23b ... stopper,
24 ... Flexible cable,
30: Gas supply / rotation drive mechanism,
31 ... motor unit, 32 ... hollow rotary shaft, 32a, 32b ... flange joint,
33, 35 ... pulley, 34 ... motor, 36 ... belt,
37 ... loose fitting joint, 38 ... gas supply pipe, 39 ... bearing,
40. Stirrer,
41 ... Rotating blades, 42 ... Gas blowing part,
50 ... Lift stopper,
61 ... scraping jig, 62 ... suction / discharge device.

Claims (1)

In the processing method of the molten aluminum for degassing the molten aluminum made of Al or Al alloy,
Transferring the molten aluminum from the melting furnace to the treatment tank together with the oxide and inclusions attached to the oxide ;
Sodium chloride (NaCl), potassium chloride (KCl), aluminum fluoride (AlF ₃ ), sodium fluoride (NaF), calcium fluoride (CaF), PAF (K ₃ AlF ₆ ), silicon Sodium fluoride (Na ₂ SiF ₆ ), potassium silicofluoride (K ₂ SiF ₆ ), potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), potassium nitrate (KNO ₃ ), sodium nitrate (NaNO ₃₎ ), Potassium sulfate (K ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ), magnesium chloride (MgCl ₂ ), and a flux composed of two or more compounds selected from the group consisting of carnarit (MgKCl). And lowering the stirrer provided with the rotary blade and the gas blowing section, and the rotary blade of the molten metal in the treatment tank Immersed just under the surface, said rotary blade is rotated to stir the molten metal and the flux immediately below molten metal surface, modify the oxide reaction to promote mixed with the molten metal of the molten metal and said flux, reforming Separating the oxides and inclusions adhering to the oxides from the melt;
Further, the stirrer is lowered so that the gas blowing part and the rotary blade are positioned in the vicinity of the bottom of the treatment tank, and the rotary blade is rotated while blowing non-oxidizing gas from the gas blowing part into the molten metal. A step of diffusing a non-oxidizing gas into the molten metal, causing oxides mixed in the molten metal and inclusions attached to the oxide to float on the molten metal surface, and degassing the molten metal;
The modified oxide that floated on the molten metal surface using a heat-resistant dross scraping member and the inclusions attached to the oxide were collected at specific locations in the treatment tank, and the modified oxide and oxide A step of discharging and collecting the inclusions adhering to the processing tank by a suction discharge device;
A method for treating molten aluminum, comprising:

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