JP2007167857A - Method for treating molten metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such problems that the remains after recovering metallic aluminum become an industrial waste and not only the circumferential environment is deteriorated but also a squeezing work is accompanied with a large danger because salinity remains in the floated slag, in the conventional method with which flux mainly containing chloride or fluoride is added into the wet-state floated slag and separated and further, molten aluminum is squeezed. <P>SOLUTION: The floated slag 9 generated at near the surface of molten aluminum M is one kind of form for enclosing the air 13 with the molten aluminum 11. Therefore, eddy current 7 is generated by rotating the molten aluminum M and the floated slag 9 is finally broken to bubble with the centrifugal force and the air 13 is separated and the separated air is taken off to the outside of the molten aluminum from the upper part and removed. This method can be utilized in treatment of molten metal having the problem of the floated slag of not only the aluminum but also zinc or the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molten metal treatment method, and more particularly to a molten metal treatment method suitable for solving the problem of buoyancy that has inevitably occurred when aluminum or zinc is dissolved.

Since aluminum is active on the surface of the molten aluminum, there is a slight difference in the amount depending on the type of the aluminum raw material, but wet buoyancy occurs immediately after the molten metal is generated. In particular, when the aluminum raw material is aluminum scrap such as chips, pellets, and small pieces, a lot of buoyancy occurs. Further, when casting, molten aluminum is transferred in a sequential manner such as a melting furnace or a heat-retaining furnace, but buoyancy occurs at each transfer stage.
If this remains in the molten aluminum as it is, it will be mixed into the finally solidified aluminum product, leading to deterioration of the quality of the aluminum product.
For this reason, it has been separated and removed from the molten aluminum before finally casting, and from the viewpoint of economic efficiency and environmental consideration, metal aluminum has been recovered from the recovered float as much as possible. The main methods being used are as follows.

First, a flux mainly composed of chloride or fluoride is added to a wet float to make it dry to improve fluidity and wettability, and then separated from the molten aluminum and taken out. Then, the taken-out dry buoy is put into an apparatus usually called a squeezer, and further flux is added to generate oxygen and to oxidize (exothermic reaction) finely to promote reaction with oxygen. Cause it to heat up. Next, mechanical agitation force is applied to separate the molten aluminum confined in the oxide film from the oxide (oxide film), and the molten aluminum particles are enlarged using the mechanical agitation action to descend below the container. To recover the molten aluminum.
The dry buoy, whose metal content is recovered by the squeezing machine and reduced in the pure aluminum content, is transported to another factory and classified after dry pulverization, and the metal portion having a diameter of 1 mm or more is recovered as a raw material for metal aluminum.

  However, when flux is added, salt remains in the buoyancy, which causes inconvenience when the remaining metal aluminum is used as a steel material or cement material. Therefore, most of it becomes industrial waste. Moreover, since a flux mainly composed of chloride or fluoride is added, the surrounding environment is deteriorated. Furthermore, the work of taking out molten aluminum from the dry buoy with a squeezer involves great danger.

  In addition, as a method for improving the above, there has also been proposed a method in which a dry buoy taken out from an aluminum melting furnace is subjected to pressure or impact to take out aluminum, and the remaining buoy is solidified to form a steel deoxidizer. However, since flux is used in any method, the inconvenience remains and the recovery rate of the metal aluminum content is at most about 60% by weight.

Moreover, when performing hot dip galvanizing on a steel strip, high pressure gas is sprayed on the steel strip pulled up from the hot dip galvanizing bath to adjust the amount of plating on the steel strip. At that time, the molten zinc is oxidized to form a float containing zinc oxide in the molten zinc on the plating bath. Float is a viscous fluid that hinders the flow of the plating bath and impairs the plating quality. Therefore, the float is drawn out of the plating tank using a ladle or the like and separated.
When recovering metallic zinc from the float, it has been proposed to heat the float to a temperature equal to or higher than the melting point of zinc and drop the deposited zinc to separate it from the float. However, in this method, the recovery rate of metallic zinc is at most about 80%.
A method has been proposed in which the float is heated to the boiling point of zinc and vaporized and recovered, but a large-scale and expensive heating device called a heated distiller that heats the float to the boiling point of zinc is proposed. I need.

Japanese Patent Laid-Open No. 6-49550 JP-A-6-192755 JP 7-26335 A JP-A-4-32544 Japanese Patent No. 7-292451

  Therefore, the conventional problems that the recovery rate of the metal is high, the waste is not generated as much as possible, the safe operation can be performed using the relatively inexpensive equipment, and the surrounding environment is not deteriorated at the same time. In addition, it is an object of the present invention to provide a novel molten metal processing method that can be solved with a high balance.

The present inventor, in the trial and error stage, while staring at the buoyancy of the aluminum over and over, this buoyancy is not included in the state that the aluminum is mainly oxidized as conventionally said. Most of it is contained in the form of metallic aluminum, and it floats on the molten aluminum as a float in the melting furnace because molten aluminum has taken in air and created a foam (bubble) with a low specific gravity. As a result, when the components of the float were actually analyzed, it was found that the metal aluminum content was 95% by weight. That is, it was confirmed that the idea of the present inventor was correct.
Based on this knowledge, the present inventor has been able to separate the massless air by rotating the molten aluminum containing wet floats and applying centrifugal force as a result of earnest research. I found out that I can do it.
And since the generation source of dross is not limited to aluminum, it can be applied as a treatment method for all molten metal in which dross is generated, and based on the above knowledge, the molten metal treatment method of the present invention is proposed. It was.

A major company representing Japan, which is the applicant of Patent Document 3, also describes that dross is mainly composed of aluminum oxide in Patent Document 3, and is a hard and heavy specific oxide. It was common knowledge not only at that time but also at present to think that aluminum was mainly contained. Therefore, mechanical processes such as drawing and grinding were included in the conventional methods.
However, according to the discovery of the present inventor, in the method of using a conventional flux and taking out metallic aluminum from a dry soot with a squeezer, a large amount of metallic aluminum becomes a compound by oxidation, nitridation, and chlorination. It means losing value, in other words, committing suicide.
Therefore, the above knowledge of the present inventor is clearly deviated from technical common sense.

The invention specifically proposed is as follows.
According to a first aspect of the present invention, there is provided a molten metal treatment method, wherein a centrifugal force is applied to a floating foam to cause bubbles to break on a molten metal surface, thereby separating the molten metal from air. It is.

  According to a second aspect of the present invention, there is provided the molten metal processing method according to the first aspect, wherein a centrifugal force is generated by rotating the molten metal at a high speed.

  According to a third aspect of the present invention, there is provided a molten metal melting treatment method according to the second aspect, wherein an eddy current is generated in the molten metal in a low frequency induction furnace to rotate the molten metal at a high speed. It is a processing method.

  According to a fourth aspect of the present invention, in the molten metal processing method according to any one of the first to third aspects, the molten metal that is an object to be processed is an aluminum-based material composed of metallic aluminum or an aluminum alloy, or metallic zinc or a zinc alloy. A method for treating a molten metal, which is a zinc-based material comprising:

  According to a fifth aspect of the present invention, in the molten metal processing method according to any one of the first to fourth aspects, the molten metal that is the object to be processed is obtained by re-dissolving the solidified buoy. It is a processing method of molten metal.

  According to a sixth aspect of the present invention, in the method for treating a molten metal according to any one of the first to fifth aspects, the molten metal that is an object to be treated includes floats generated in a melting furnace, a heat-retaining furnace, or a crucible. It is the processing method of the molten metal characterized.

  According to the molten metal processing method of the present invention, by using a commercially available low frequency induction furnace, melting can be easily and safely eliminated without affecting the surrounding environment.

(Processing object)
Typical metals are aluminum raw material and zinc raw material.
The aluminum material is metallic aluminum or aluminum alloy, but the main assumption is to crush aluminum scrap itself, such as aluminum chips, aluminum cans, aluminum foil, aluminum caps, etc. A series of various aluminum raw materials including those obtained by incineration removal of resin, granulated, so-called aluminum pellets separated from aluminum and oxides, and a variety of aluminum raw materials including the above materials and high-grade casting aluminum and aluminum alloys It is a wet-shaped buoy produced during the casting process. The buoy may be immediately after taken out from a melting furnace or the like, or may be solidified once.

However, other than those described above, for example, high-grade aluminum or aluminum alloy itself for normal casting production may be used. Even when casting using such high-grade aluminum raw materials, if a melting furnace is used as in the past, a significant amount of flotation is inevitable on the molten aluminum. If the molten aluminum is treated using an apparatus capable of performing the melting treatment method of the present invention instead of a furnace, even if buoyancy occurs, it can disappear on the spot, and at least the occurrence of buoyancy can be prevented in the apparatus. .
If only aluminum scraps or floats are used as the aluminum raw material, the initial solubility is poor, and therefore it is preferable to use it together with the starting aluminum raw material.

  The zinc raw material is metallic zinc or a zinc alloy, but what is mainly assumed is a molten zinc plating bath in which flotation is likely to occur.

(Dissolution treatment method)
<First embodiment>
A low-frequency induction furnace 1 shown in FIG. 1 is mainly composed of a crucible refractory 3 and an induction coil 5 disposed outside the crucible refractory 3. When an alternating current is supplied to the induction coil 5 from a power source 6, a conductive load, in this case In this case, an eddy current (inductive current) is induced in the aluminum material and melts to form a molten aluminum M.
Further, an electromagnetic stirring force is generated by the eddy current, and the molten aluminum M is given a high-speed rotational force by the electromagnetic stirring force. As a result, as shown by the solid line arrow in FIG.

In this vortex system, centrifugal force is applied to the moving mass.
As shown in the enlarged cross-sectional view of the buoy in FIG. 2 (1), the buoy 9 is a kind of bubbles (foam) formed by encapsulating air 13 with molten aluminum 11. Therefore, when centrifugal force is applied to the vortex 7 as indicated by the white arrow in FIG. 2, the buoy 9 formed by encapsulating air 13 having no mass is formed as shown in the order of (1) and (2). They gather toward the central axis of rotation, and in the process, the adjacent buoys 9 collide with each other and coalesce and become coarse. Then, as shown in (3) and (4), the enlarged buoyancy floats to the molten metal surface of the molten aluminum M due to its own buoyancy, and finally the molten aluminum 11 contains a large amount of air 13 therein. Without encapsulating, bubbles break on the molten aluminum M. When the float 9 breaks, the air 13 contained therein escapes out of the molten aluminum M. Thus, even if the buoy 9 is generated, it will disappear at any time.
In this induction furnace 1, a plurality of vortex flows 7 are generated, and the air 13 escapes from each vortex system.
Conventionally, buoys were not broken and floated on the molten aluminum, but in the present invention, they are actively broken and disappeared.

<Second Embodiment>
In FIG. 2, the rotation axis of the molten aluminum M is substantially horizontal, but this is because the molten aluminum M is rotated using the induction furnace 1 of the type shown in FIG. If the low frequency induction furnace 15 of the type as shown in FIG. 3 is used as the form, the rotational axis of the molten aluminum M becomes substantially vertical.
This induction furnace 15 is a partial modification of the structure of the induction furnace 1 and is provided with an electromagnetic stirring means comprising an iron core 17 and an induction coil 18 separately from the induction coil 7 for melting means. When an alternating current is supplied from the power source 19 to the induction coil 18, a rotational force around the crucible axis is applied. As a result, a spiral flow is generated as shown by the arrows in FIG.

In the induction furnace 15, the molten aluminum M generates a vortex 20 having a rotating shaft in the vertical direction, so that the centrifugal force is no longer applied to the buoy 9 that has gathered at the center and becomes relatively large. Since it can reach the molten metal surface of the molten metal M, the air 13 becomes easier to escape.
That is, when the induction furnace 1 is used, the float 9 can float on the surface of the molten aluminum when it becomes coarse enough to have a buoyancy that exceeds the centrifugal force, but smaller when the induction furnace 15 is used. It will be possible to float on the molten aluminum surface with buoyancy.

<Third embodiment>
The difference from the second embodiment is that the induction furnace 21 used in this embodiment has an iron core 17 and an induction coil 18 as electromagnetic stirring means disposed below the induction furnace 15. .
When this induction furnace 21 is used, the float 9 may remain near the molten metal surface of the molten aluminum M. For example, when an aluminum can containing a pigment such as titanium oxide (TiO ₂ ) is used as an aluminum raw material, the molten aluminum contains titanium oxide and the like. When it is used, titanium oxide or the like is taken into the float that is generated near the molten metal surface.
Therefore, when solidified except for the float, high-quality aluminum products can be cast from aluminum scraps such as aluminum cans.

<Fourth embodiment>
In any of the first to third embodiments, an induction furnace is used. However, a melting means for aluminum material and a stirring means for molten aluminum may be provided separately.
For example, after the aluminum raw material is melted in the melting furnace to produce the molten aluminum M, the molten aluminum M is supplied to the stirring device 23. As shown in FIG. 5, the vortex 7 of the molten aluminum M is connected to a circulation path 25, for example, in a cylindrical stirring vessel 23, and a pump 27 is provided in the circulation path 25, and the molten aluminum M is placed in the stirring vessel 23. It is generated by a configuration that always ejects in the tangential direction.
Needless to say, the stirring vessel 23 is provided with a temperature holding means (not shown), and the molten aluminum M in the vessel 23 is held in a hot (liquid) state.

Although the embodiment of the present invention has been described above, the specific configuration of the present invention is not limited to the above-described embodiment, and even if there is a design change within a range not departing from the gist of the present invention. Included in the invention.
For example, in the above embodiment, the induction furnace has a structure described in Japanese Patent Application Laid-Open No. 2004-108666, but is not limited thereto. Incidentally, Japanese Patent Application Laid-Open No. 2004-108666 does not describe how to use centrifugal force as in the present invention.
In principle, the higher the rotational speed of the eddy current, the greater the centrifugal force. Therefore, annihilation due to bubble breakage is promoted, but there are limiting factors such as the capacity of the furnace. Those skilled in the art may set as appropriate. Since the buoyancy breakage can be visually observed, the optimum range should be easily determined by a preliminary test according to the furnace used by those skilled in the art.
Moreover, although it is related with aluminum in the said embodiment, it cannot be overemphasized that it can process similarly about the molten metal which generate | occur | produces a float, such as zinc.

Example 1 (normal dissolution)
(Aluminum raw material)
Aluminum pellets, that is, aluminum cans, aluminum foils, and aluminum caps were crushed as aluminum raw materials, the resin content was removed by incineration, granulated, and aluminum and oxide separated.
A starting block was also used in order to improve solubility.

(melting furnace)
A low frequency induction furnace 1 having the structure shown in FIG. 1 was used. Specific specifications of the induction furnace 1 are as follows.
Official Name: Crucible Low Frequency Induction Melting Furnace Model: For Aluminum Alloy Dissolution: Max 3ton
Applied power: 800 kW
Frequency: 50Hz
Manufacturing company: Taichiku Co., Ltd.

  In the induction furnace 1 described above, it has been confirmed that a vortex can be generated in the molten metal of about 2.3 tons from the bottom of the furnace.

(Process 1)
After 1,000 kg of starting aluminum block was put into the induction furnace 1, it was melted with the tap 5 (560A 1020V 550W).
(Process 2)
After the starting aluminum block was melted, aluminum pellets were gradually added and melted with tap 6 (580A 1060V 620W).

(Process 3)
The charging was stopped when the induction furnace 1 was full, that is, when 2000 kg of aluminum pellets was charged.
(Process 4)
When the temperature of the molten aluminum reached 760 ° C., the supply of alternating current was stopped.
(Process 5)
As soon as it stopped, buoyancy occurred on the molten aluminum and was removed with a tool. At that time, the amount of buoys removed was about 100 kg.
(Step 6)
About 1 ton of molten aluminum was poured out into two ingot cases.
(Step 7)
Since there was about 100 kg of float on the molten aluminum melted in the ingot case, it was made into a mass of 200 kg together with the float generated in step 5.
(Process 8)
200 kg of starting blocks and 200 kg of aluminum pellets were put into 800 kg of molten aluminum remaining in the induction furnace 1.

Steps 3 to 8 were repeated 10 times, and the total amount of the collected buoy (lumps) was about 2,000 kg.
Thereafter, the following step 9 and subsequent steps were performed.

(Step 9)
Finally, all the remaining molten aluminum (about 750 kg) was poured out into one ingot case.
(Process 10)
The float (about 30 kg) on the molten aluminum discharged from the ingot case in step 9 was taken and hardened.
(Step 11)
About 20 kg of metal aluminum and oxide finally remained at the bottom of the induction furnace 1.

In the above steps 1 to 11, the yield of aluminum pellets was calculated as 90% as follows.
(Aluminum raw material)
Starting block 1,000kg + (9 × 200kg) = 2,800kg
Pellet 2,000kg × 10 = 20,000kg
(Product)
Ingot 2,000kg × 10 + 750kg = 20,750kg
Float (Lump) 200kg × 10 = 2,000kg
Bottom 20kg
Disappearance 30kg
(Pellet primary yield)
20,800kg-2,800kg = 18,000kg
18,000kg ÷ 20,000kg = 90%

In the induction furnace 1, buoyancy has occurred in the process 5. This is probably because no vortex is formed in the upper aluminum melt of about 0.7 ton.
However, the yield was still very high at 90%.

Example 2 (dissolution of buoyancy)
(Process 1)
After 1,000 kg of starting aluminum block was put into the induction furnace 1, it was melted with the tap 5 (560A 1020V 550W).
(Process 2)
After the starting aluminum block was melted, a solid float (about 1,000 kg) was added and melted with tap 8 (650A 1160V 750W).
(Process 3)
When the temperature of the molten aluminum reached 760 ° C., the supply of alternating current was stopped. In addition, no buoyancy occurred even when stopped.
(Process 4)
About 1 ton of molten aluminum was poured into one ingot case.
(Process 5)
Since there was about 50 kg of float on the molten aluminum discharged from the ingot case, it was returned to the induction furnace 1.

(Step 6)
About 1,000 kg of the solidified buoyancy generated from the normal melting described above was charged into the 1,000 kg molten aluminum remaining in the induction furnace 1 and melted with the tap 8 (650A 1160V 750W).
(Step 7)
When the molten metal temperature reached 760 ° C., the supply of alternating current was stopped. Normally, buoyancy occurred on the molten metal, but there was none in this test.
(Process 8)
About 1,850 kg of molten aluminum was divided into two ingot cases.
(Step 9)
The float (about 100 kg) on the molten aluminum discharged from the ingot case in step 8 was taken and hardened.
(Process 10)
About 20 kg of metal aluminum and oxide remained at the bottom of the induction furnace 1.

In the above steps 1 to 10, the yield of floating was calculated as 92% as follows.
(Aluminum raw material)
Starting block 1,000kg
Float (lump) 2,000kg
(Product)
Ingot 2,850kg
Float (lump) 100kg
Bottom 20kg
Disappearance 30kg
(Floating yield)
2,850kg-1,000kg = 1,850kg
1,850kg ÷ 2,000kg = 92%

Furthermore, if the last remaining buoyant mass is dissolved, it becomes an ingot.

1,950kg ÷ 2,000kg = 97%.

  In any of the above-described embodiments, since one induction furnace 1 having a small capacity was used, the buoy was solidified and remelted. Needless to say, however, if there is another furnace, it can be melted without being solidified.

Comparative example Since buoy (lump) may be dried and melted in a heavy oil 5 ton rotary furnace, the buoy (lump) made by the same method as this test was commissioned for comparison. As a result, the following results were obtained.

(Aluminum raw material)
Starting block 1,000kg
Float (lump) 2,000kg
(Product)
Ingot 2,200kg
600 kg of dry powder
Dust collection / disappearance 200kg
(Floating yield)
2,200kg-1,000kg = 1,200kg
1,200kg ÷ 2,000kg = 60%

According to the molten metal processing method of the present invention, not only the recovery rate of the metal content can be increased, but also a tedious and dangerous process is unnecessary, and no final waste is generated.
Further, the molten metal treatment method of the present invention is economical because it can be operated in practice by using a commercially available low-frequency induction furnace so as to generate eddy currents.

It is a cross-sectional structure figure of the induction furnace used for the melting treatment method which concerns on the 1st Embodiment of this invention. It is explanatory drawing of the melt | dissolution processing method using the induction furnace of FIG. It is a cross-sectional structure figure of the induction furnace used for the melt | dissolution treatment method which concerns on the 2nd Embodiment of this invention. It is a cross-sectional structure figure of the induction furnace used for the melt treatment method which concerns on the 3rd Embodiment of this invention. It is a longitudinal cross-sectional structure figure of the stirring apparatus used for the melt | dissolution treatment method which concerns on the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Low frequency induction furnace 3 ... Crucible refractory 5 ... Induction coil 6 ... Power supply 7 ... Eddy current 9 ... Float 11 ... Molten aluminum 13 ... Air 15 ... Low frequency induction furnace 17 ... Iron core 18 ... Induction coil 19 ... Power supply 20 ... Vortex 21 ... Low frequency induction furnace 23 ... Agitator 25 ... Circuit path 27 ... Pump
M ... molten aluminum

Claims (6)

  In the molten metal processing method, a centrifugal force is applied to the floated foam to cause bubbles on the molten metal surface to separate the molten metal from the air.   The molten metal processing method according to claim 1, wherein a centrifugal force is generated by rotating the molten metal at a high speed.   The molten metal melting method according to claim 2, wherein an eddy current is generated in the molten metal in a low frequency induction furnace to rotate the molten metal at a high speed.   The molten metal processing method according to any one of claims 1 to 3, wherein the molten metal that is an object to be processed is an aluminum-based material composed of metallic aluminum or an aluminum alloy, or a zinc-based material composed of metallic zinc or a zinc alloy. A method for treating a molten metal.   5. The method for treating a molten metal according to claim 1, wherein the molten metal as the object to be treated is obtained by re-dissolving once solidified buoyancy. The molten metal processing method according to any one of claims 1 to 5, wherein the molten metal that is an object to be processed includes floats generated in a melting furnace, a heat-retaining furnace, or a crucible furnace. Processing method.

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