JPS5950738B2 - Continuous production equipment for high-purity aluminum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for continuously producing high-purity aluminum using segregation solidification.

Fe that forms eutectic with aluminum in aluminum
, Si, Cu, Mg, etc. (hereinafter referred to as eutectic impurities), the impurity concentration in the initial solid phase of aluminum obtained when solidifying this molten aluminum after melting the aluminum. Cs is theoretically expressed by the following formula.

C5=koCo (1-fs) k0/1 In the above equation, ko is the equilibrium distribution coefficient, Co is the impurity concentration in the original aluminum, and fs is the solid phase fraction.

Since the equilibrium distribution coefficient ko of the eutectic impurity is smaller than 1,
As is clear from the above equation, the impurity concentration in the obtained solid phase is lower than the impurity concentration in the original aluminum.

Furthermore, as seen from the above equation, the higher the solid phase ratio fs, the higher the impurity concentration in the obtained solid phase.

An object of the present invention is to provide an apparatus that can efficiently and continuously obtain high-purity aluminum using the principle of the above formula.

The continuous production apparatus for high-purity aluminum according to this invention has the following features:
A melting furnace for melting aluminum, a plurality of interconnected molten metal holding tanks, and one molten metal holding tank placed in each molten metal holding tank that can be moved up and down to crystallize high-purity aluminum. The molten aluminum is fed from the melting furnace into one of the multiple molten metal holding tanks, and this molten metal passes through all the tanks in sequence and is discharged. This is what has been done.

A plurality of molten metal holding tanks are prepared, for example, by dividing one large tank into a plurality of sections using partition walls, and making each section a molten metal holding tank.

In this case, a communication port is provided in the partition wall to allow each molten metal holding tank to communicate with each other.

Alternatively, a plurality of molten metal holding tanks each consisting of a crucible may be arranged in front, and each crucible may be communicated with each other through a gutter.

When molten aluminum is supplied from the melting furnace to one of the multiple molten metal holding tanks, the molten metal should pass through each molten metal holding tank in turn and be discharged from the last molten metal holding tank. .

The rotary cooling body is used to crystallize high-purity aluminum on its circumferential surface.

That is, after the molten metal is put into each molten metal holding tank, the rotary cooling body is lowered and immersed in the molten metal, and when it is rotated, high-purity primary aluminum crystallizes on the circumferential surface of the rotary cooling body. Impurities are discharged into the liquid phase, and the ratio of the impurity concentration in the solid phase to the impurity concentration in the liquid phase at that time is represented by the equilibrium distribution coefficient Ko.

However, during the subsequent solidification process, the redistribution of impurities is not due to the equilibrium distribution coefficient Ko, but to the effective distribution coefficient K.
It will be dominated by E (KO≦KE≦1).

This is because impurities are discharged into the liquid phase during solidification, and a concentrated layer of impurities is generated near the solidification interface.

When the value of the effective distribution coefficient KH approaches the value of the equilibrium distribution coefficient KO, a solid phase of high purity aluminum can be obtained.

In order to bring the value of the effective distribution coefficient KE close to the value of the equilibrium distribution coefficient Ko, it is necessary to increase the rate of progress of the 4% solid surface (accompanying the solidification after crystallization) from high-purity primary aluminum to the solidification interface. The diffusion rate of the impurities discharged into the liquid phase from the liquid phase is very slow compared to the diffusion rate in the liquid phase, so that the impurities are diffused sufficiently far from the solidification interface, or the liquid phase is effectively stirred to diffuse the impurities near the solidification interface. It is effective to disperse and mix the impurities discharged into the entire liquid phase.

By the way, the effective distribution coefficient KE is expressed by the following formula: It is a well-known fact that

In the above equation, R is the solidification rate, δ is the thickness of the impurity concentrated layer formed near the solidification interface, and D is the diffusion coefficient of the impurity in the liquid phase.

From the above equation, in order to bring the value of the effective distribution coefficient KH close to the value of the equilibrium distribution coefficient KO, it is effective to decrease the solidification rate R and the thickness δ of the impurity concentrated layer, and to increase the diffusion coefficient R. It is true.

However, among the above variables, the diffusion coefficient is generally considered to be a constant determined by the type of impurity when the temperature of the liquid phase is constant, and therefore it is difficult to change the diffusion coefficient.

Furthermore, when considering industrial productivity, it is not appropriate to reduce the solidification rate R too much.

Therefore, reducing the thickness δ of the impurity-concentrated layer, in other words, reducing the thickness of the impurity-concentrated layer is effective for bringing the value of the effective distribution coefficient closer to the value of the equilibrium distribution coefficient Ko. be.

Furthermore, when impurities are discharged into the liquid phase at the solidification interface, dendrites are generated at the solidification interface, and as these dendrites grow, Fe, S discharged into the liquid phase near the solidification interface are
It is well known that impurities that form eutectics with aluminum, such as i, Mg, and Cu, can be trapped in the gaps between dendrites either as they are or by forming eutectics of several microns. This is an unfavorable phenomenon in terms of refining work.

In the above, dendrite growth occurs in a compositionally supercooled state such that the equilibrium liquidus temperature near the solidification interface is higher than the actual liquidus temperature.

Therefore, in order to prevent the growth of dendrites, it is necessary to make the temperature gradient in the impurity concentrated layer near the solidification interface larger than the temperature gradient of the equilibrium liquidus line.

When the cooling body is rotated, a relative movement occurs between the solid phase and the liquid phase, which effectively stirs and mixes the impurity concentrated layer formed near the solidification interface with most of the other liquid phase. The impurities in the impurity concentrated layer are dispersed throughout the liquid phase, and the thickness of the impurity concentrated layer becomes very thin as a result.

Naturally, the thickness of this impurity concentrated layer and the temperature gradient in the same layer are in an inversely proportional relationship, and as the thickness of the impurity concentration layer becomes thinner, the temperature gradient increases accordingly.

Therefore, the value of the effective partition coefficient KH can be expressed as the equilibrium partition coefficient KO
It is possible to proceed with solidification by approaching the value of , increasing purification efficiency and obtaining high-purity aluminum.

Further, during the solidification process, the generation of dendrites is suppressed as much as possible, and high purity aluminum having a very smooth solidified surface can be obtained.

In order to reduce the thickness of the impurity concentrated layer, it is better to increase the rotational speed of the cooling body, in other words, the relative speed between the cooling body and molten aluminum. However, if it becomes too large, centrifugal force increases. Otherwise, crystallized aluminum becomes difficult to adhere to the surface of the cooling body, resulting in a decrease in productivity.

Furthermore, the above effect can be further improved by reversing the direction of rotation of the cooling body at an appropriate frequency.

As this rotary cooling body, a cylindrical type or a tapered cylindrical type with a diameter gradually decreasing toward the bottom are used.

It is more preferable to use a tapered cylindrical cooling body as this makes it easier to recover high-purity aluminum crystallized on the circumferential surface of the cooling body.

The cooling body is cooled by feeding a cooling body such as air, argon gas, nitrogen gas, or a mixed liquid of air and water into the cooling body.

If the amount of heat supplied to the molten aluminum in the holding tank is increased by heating from an external heat source, and if more heat is removed by cooling the molten aluminum with the cooling body, the solidification rate will decrease and the cooling body and molten aluminum will be The heat flow between the solidification and solidification interfaces increases, and the temperature gradient in the liquid phase near the solidification interface increases.

Therefore, the effect of the rotation of the cooling body described above, that is, the effect of obtaining high-purity aluminum is further improved.

Furthermore, the portion of the circumferential surface of the cooling body in contact with the molten metal surface and its vicinity, as well as the bottom surface of the cooling body, are covered with a heat insulating material,
The cooling body is preferably immersed in the molten metal so that the upper edge of the upper insulating material is located above the surface of the molten metal and the lower edge is located in the molten metal at a position where it is not affected by the temperature of the outside air.

This is because if this is done, the efficiency of recovering high-purity aluminum by the cooling body will be improved.

In such high-purity aluminum production equipment, the cooling body is raised in advance, molten aluminum is supplied from the melting furnace to the molten metal holding tanks, and the cooling body is lowered only after the amount of molten metal in each holding tank is equal. immerse it in the molten metal and rotate it.

Then, the amount of molten metal supplied and discharged is adjusted so that the amount of molten metal in each molten metal holding tank remains unchanged during operation, and the amount of aluminum crystallized on the circumferential surface of each cooling body is adjusted to be equal. .

The amount of aluminum crystallized on the circumferential surface of the cooling body can be changed as appropriate depending on the temperature of the molten metal, the rotation speed of the cooling body, the cooling capacity, and the immersion time.

The concentration of impurities in the molten metal in each molten metal holding tank increases sequentially from the one closest to the melting furnace to the further away from the melting furnace.

of the total amount of aluminum recovered by each cooling body,
The average impurity concentration in all the aluminum obtained can be changed by changing the ratio of the supplied molten metal to the total amount (hereinafter referred to as the recovery rate), and the lower the recovery rate, the lower the above average impurity concentration. Become.

Therefore, by setting the recovery rate to a predetermined value, it is possible to obtain aluminum of higher purity than the original aluminum to be purified supplied from the melting furnace.

Furthermore, when the recovery rate is kept constant, the more molten metal holding tanks there are, the more pure aluminum can be obtained.

As described above, according to the apparatus for continuously producing high-purity aluminum of the present invention, by increasing the number of molten metal holding tanks, a large amount of high-purity aluminum can be efficiently obtained in one operation.

Further, if the effective distribution coefficient of impurities is known, it becomes possible to adjust the purity of aluminum obtained by changing the recovery rate, so aluminum of a predetermined purity can be easily obtained.

This invention will be explained below with reference to the drawings.

In FIGS. 1 and 2, a continuous manufacturing apparatus 1 for high-purity aluminum has a large tank 2 in the shape of an oblong rectangular parallelepiped placed on the right side of a melting furnace 7 for melting aluminum, and the tank 2 is divided into five sections by partition walls 3. Five molten metal holding tanks 4A to 4E are provided by dividing the molten metal holding tanks 4A to 4E, and the stirrer 5 is arranged in the leftmost molten metal holding tank 4A, and the other four molten metal holding tanks 4
One rotary cooling body 6 for crystallizing high-purity aluminum, which is movable up and down, is arranged in each of B to 4E.

The upper end of the partition wall 3 is cut out to provide a communication port 13, through which the molten metal holding tanks are communicated with each other.

The aluminum melted in the melting furnace 7 is fed into the molten metal holding tank 4A at the left end.

The molten metal sent into the holding tank 4A passes through the communication port 13, flows into the holding tanks 4B to 4E on the right side one after another, and is discharged to the outside from the holding tank 4E on the right end.

The rotary cooling body 6 has a hollow tapered cylindrical shape that gradually becomes thinner toward the bottom and is closed at both ends, and its upper and lower peripheral surfaces are covered with heat insulating materials 8 and 9, respectively.

The cooling body 6 has been raised in advance (
After a predetermined amount of molten metal is injected into the molten metal holding tanks 4A to 4E, the heat insulating material 8 comes into contact with the surface of the molten metal, and its lower edge is affected by the temperature of the outside air in the molten metal. It is immersed so that it is in a position where it will not receive any damage.

The upper end of the circumferential surface of the cooling body 6 is covered with a heat insulating material 8, and the heat insulating material 8 is in contact with the surface of the molten metal, and its lower edge is immersed in the molten metal at a position where it is not affected by the temperature of the outside air. This is due to three reasons.

One of them is that since the surface of the molten metal is in contact with the outside air, the temperature of the molten aluminum near the surface of the molten metal becomes lower than that of other parts due to the influence of the temperature of the outside air. Aluminum tends to crystallize near the surface, and as a result, the crystallization rate of aluminum in this part is faster than the crystallization rate of aluminum in other parts of the circumferential surface of the cooling body 6, so that the aluminum crystallized in this part The purity of aluminum is lower than that of aluminum crystallized on other parts, and when aluminum is recovered from the circumferential surface of the cooling body 6 after the refining work, the aluminum crystallized on other parts of the circumferential surface of the cooling body 6. This is because the purification efficiency as a whole decreases.

Another reason is that, as mentioned above, aluminum is more likely to crystallize near the molten metal surface on the circumferential surface of the cooling element 6 than in other parts, so this The cooling body 6 cannot be effectively rotated before a sufficient amount of high-purity aluminum crystallizes on other parts of the circumference of the cooling body 6. This is because the amount of high-purity aluminum recovered in the cooling body 6 decreases, resulting in poor work efficiency.

Furthermore, another reason is that when a large amount of aluminum crystallizes and aluminum lumps are formed near the molten metal surface on the circumferential surface of the cooling body 6, the aluminum lumps scatter the molten metal and scatter when the cooling body 6 is rotated. Low-purity molten metal adhered to and crystallized on the parts of the cooling body 6 that protruded from the molten metal, and when aluminum was recovered from the circumferential surface of the cooling body 6 after the production of high-purity aluminum was completed, crystallization occurred on the circumferential surface of the cooling body 6. This is because it mixes with aluminum and reduces the overall refining efficiency.

Moreover, covering the lower surface of the cooling body 6 with a heat insulating material 9 is as follows.
This is because the rotation of the cooling body 6 cannot be expected to have much of an effect on the lower surface of the cooling body 6, and the purity of the aluminum crystallized on the lower surface of the cooling body 6 is lower than the purity of the aluminum crystallized on the peripheral surface.

However, the heat insulating materials 8 and 9 are not necessarily required.

Furthermore, a tubular rotating shaft 10 extending upward and communicating with the inside of the cooling body 6 is provided at the upper end of the cooling body 6 .

A cooling fluid supply pipe 12 is disposed inside the rotating shaft 10 and has a lower end that extends into the cooling body 6 up to the lower end thereof and has a plurality of cooling fluid outlet ports 11 on the peripheral wall thereof.

The aluminum to be refined and melted in the melting furnace 7 is sent to each holding tank 4A to 4E.

This molten aluminum contains Fe, Si, Cu,
In addition to eutectic impurities such as Mg, impurities such as Ti, V, and Zr that form aluminum and peritectic el (hereinafter referred to as peritectic impurities) may be included.

If the molten aluminum contains peritectic impurities,
The concentration of peritectic impurities in the initial solid phase obtained when this molten aluminum is solidified is higher than the concentration in the original molten aluminum.

Therefore, in the leftmost molten metal holding tank 4A, when boron is added to the molten metal and stirred by the stirrer 5, the boron turns into Ti.

(2) TlB2. reacts with peritectic impurities such as Zr. VB2
Insoluble metal borides such as 5ZrB2 are formed.

This insoluble metal boride is kept away from the circumferential surface of the rotary cooling body 6 by centrifugal force when rotating the rotary cooling body 6 in the molten metal holding tanks 4B to 4E, so that it crystallizes on the circumferential surface of the cooling body 6. It will no longer be mixed into aluminum.

The amount of boron added is determined according to the amount of peritectic impurities in the aluminum to be purified, but it is preferable to add more than the minimum amount necessary to produce the metal boride.

Since boron forms a eutectic with aluminum, excess boron is removed as well as eutectic impurities such as Fe, Si, Cu, Mg, etc.

Further, boron may be added as an Al-B master alloy.

When the amount of molten metal in each of the molten metal holding tanks 4A to 4E reaches a predetermined amount, the cooling body 6 is lowered and immersed in the molten metal, and cooling fluid is blown into the inside from the outlet 11 of the cooling fluid supply pipe 12. Rotate this.

Then, aluminum crystallizes on the portions of the circumferential surface of the cooling body 6 that are present in the molten aluminum and are not covered with the heat insulating materials 8 and 9.

The temperature of the molten metal, the rotation speed of the cooling element 6, and the cooling capacity are controlled so that the amount of aluminum crystallized on the circumferential surface of the cooling element 6 in each type of 4B to 4E is equal, and the amount of molten metal in each type of 4B to 4E is controlled. The molten metal supply amount and discharge amount are controlled so that they are always equal, and the recovery rate is kept constant.

Here, if the impurity concentration in the molten metal supplied from the melting furnace 7 is expressed as C8, and the impurity concentration in the molten metal in each tank 4B to 4E is expressed as C1, C2, C3, and C4, then co<C1<C
2<C3<C4, and the ratio of impurity concentration C8 in the molten metal in each tank 4B to 4E (C1/Co), (C2/
Co), (C3/Co), (C4/Co) are the third
As shown in the figure, the amount of aluminum increases at the beginning of operation, but becomes constant when the amount of aluminum crystallized on the circumferential surface of the cooling body 6 reaches a predetermined amount.

At this time, the sum of the total amount of impurities Ms in the aluminum recovered by each cooling body 6 and the amount Mn of impurities in the molten metal discharged from the rightmost tank 4E is also the amount of impurities in the aluminum that should always be purified. It is equal to Mo.

Therefore, if the impurity concentration and the effective distribution coefficient of impurities in the molten metal in each tank 4B to 4E are known, high purity aluminum having a desired impurity concentration can be obtained by setting the recovery rate constant.

The smaller the recovery rate, the lower the concentration distribution of impurities in the molten metal in each of the holding tanks 4B to 4E, and therefore the higher the purity of the obtained ingot.

The aluminum purity obtained can then be determined by changing the recovery rate.

Furthermore, when the recovery rate is constant, as shown in FIG. 4, the greater the number of molten metal holding tanks, the higher the impurity concentration in the discharged molten metal. of aluminum can be obtained.

In the above, if the aluminum recovered by the cooling body 6 is used again in the same apparatus, aluminum of even higher purity can be obtained.

Furthermore, the purity of the molten metal discharged in the second operation was different from that in the first operation.
Since the purity is higher than that of the raw material used in the melting process, the yield for the raw material can be improved by returning it to the melting furnace 7.

Next, a specific example of producing high purity aluminum using the apparatus according to the present invention will be described.

Specific Example 1 This specific example was carried out using the apparatus shown in FIGS. 1 and 2.

First, while raising the cooling body 6, in the melting furnace 7, Fed, 10wt%, Sin, 05wt%, Tie
, 002wt% and Vo, 008wt% are melted, and the molten metal is transferred to the leftmost molten metal holding tank 4A.
supplied.

At this time, the boron concentration in the molten metal holding tank 4A is always o, 0.
Boron was added to the solution to give a concentration of 0.8 wt%, and the mixture was stirred using a stirrer 5.

When this molten metal flows into the other holding tanks 4B to 4E and each holding tank 4A to 4E is filled with the molten metal, the cooling body 6 whose diameter is 200 mm at the portion covered with the heat insulating material 8 is lowered. immersed in the molten metal, and while supplying cooling fluid from the cooling fluid supply pipe 12 to the inside of the cooling body 6, the rotation speed is 40 Orp.
The operation was started by rotating at m.

During operation, molten metal is continuously supplied from the melting furnace 7 so that the amount of molten metal in each molten metal holding tank 4A to 4E remains constant, and the boron concentration is always maintained at o, 008 in the leftmost tank 4A.
Boron was added continuously to maintain the wt%.

The eutectic impurity concentrations C1, C2, C3, and C4 in the molten metal in the four tanks 4B to 4E, excluding the leftmost tank 4A, have been increasing while maintaining the relationship of C1 < C2 < C3 < C4 since the beginning of operation. When the amount of aluminum recovered by the cooling body 6 reaches a predetermined amount, a steady state is reached.

The above eutectic impurity concentrations C1, C2, C when the effective distribution coefficient of eutectic impurities is 0.1 and the recovery rate is 0.7.
3. The ratio of C4 to the eutectic impurity concentration C6 in the aluminum supplied from the melting furnace 7 (C, /Co), (C2/
Co), (C3/Co) and (C4/Co) are each 1.3°1.6. 2 and 2.7, and the operation was continued under these conditions.

At this time, when the average impurity concentration in the obtained aluminum ingot was measured, it was found that Fed, 008wt%, Si
n, 008wt%, Tie, 0001wt%, VO
It was 0OO02wt%.

Specific Example 2 The recovery rate was set to 0.4, and other conditions were the same as those in Specific Example 1, and continuous operation was carried out in a steady state.

When the average impurity concentration in the obtained total aluminum ingot was measured, it was found that Fed, 005wt%, Sin,
006wt%, Tie, 0001wt%, VO,00
It was 0.02 wt%.

Specific Example 3 In this specific example, nine molten metal holding tanks were used instead of the five molten metal holding tanks in the above specific example 1, and the other conditions were the same as those of the above specific example 1.

However, the recovery rate was set to 0.7, which is the same as in Example 1, and continuous operation was carried out in a steady state.

When the average impurity concentration in the obtained aluminum ingot was measured, it was found that Fed, 0065 wt%, Sin, 0
07wt%, Tie, 0001wt%, VO,000
2 wt%, and higher purity aluminum was obtained at twice the production rate than in Example 1, which had five holding tanks.

[Brief explanation of drawings]

The drawings show an embodiment of the invention, and FIG.
Figure 2 is a partial enlarged view of Figure 1, and Figure 3 shows the ratio of the impurity concentration in the molten metal to the impurity concentration in the aluminum to be purified in each molten metal holding tank, and the ratio of the impurity concentration in the aluminum to be purified, and the A graph showing the relationship with the amount of aluminum crystallized,
FIG. 4 is a graph showing the relationship between the number of molten metal holding tanks and the ratio of the impurity concentration in the obtained aluminum to the impurity concentration of the aluminum to be purified. 4B, 4C, 4D, 4E... Molten metal holding tank, 6... Rotating cooling body, 7... Melting furnace.

Claims (1)

[Claims] 1. A melting furnace 7 for melting aluminum, a plurality of molten metal holding tanks 4B to 4E that are communicated with each other,
One is placed in each molten metal holding tank 4B to 4E,
It consists of a rotary cooling body 6 for crystallizing high-purity aluminum, which is movable up and down, and a plurality of molten metal holding tanks 4B.
-High purity aluminum in which molten aluminum is fed from the melting furnace 7 into one tank of 4E, and this molten metal is discharged through all the holding tanks 4B to 4E in sequence. continuous manufacturing equipment.