JPH0754065A - Refining method and recycling method for aluminum scrap - Google Patents

Abstract

PURPOSE:To rapidly refine Al scrap having a high Si concn. in a large amt. by stirring molten metal and specifying a cooling rate and the pressure of a press stamp in a method for press-solidifying Al crystallized substance deposited by a crystal fractionating method. CONSTITUTION:The molten metal 2 which is housed in a container 1 and consists of, for example, the brazing sheet scrap for Al radiators having the high Si concn. is rotationally stirred by energizing an electromagnetic coil 4 until the rotation stops of itself spontaneously. The molten metal is kept controlled at <=20 deg.C/min cooling rate by a hater 3 and is cooled in this state down to a temp. below the liquidus line temp. and above the solidus line temp. of the molten metal 2. The molten metal is held at this temp. to allow primary crystal paricles to grow uniformly over the entire area of the molten metal. The molten metal crystallized with the primary crystals are thereafter pressurized under 1 to 15MPa by lowering a the stamp 5 to separate the liquid phase part contg. concentrated impurities above the stamp 5 and to solidify the primary crystal particles below the stamp 5. The latter compressed part of the primary crystals in then recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining and reusing aluminum scrap, and more particularly to a brazing sheet for aluminum radiators and a product which can be reused as a wrought material after removing Si which is an impurity in the product scrap. Is.

[0002]

2. Description of the Related Art A brazing sheet, which is a material for an aluminum radiator, has an Al--Mn alloy (3003, etc.) as a core material and an Al--Si alloy (4043, etc.) as a skin material. ) Is clad on one side or both sides, and a large amount of scrap is generated as both ends of the rolled material and slitter scraps in the manufacturing process.

In order to reuse these scraps,
A method has been proposed in which only the skin material of scrap is heated to a temperature at which it melts, and only the skin material is melted and separated.However, since this method is a thin material, the core material also easily melts when heated rapidly, In addition, since it is necessary to lengthen the heating time in order to perform precise temperature control, it is not economical because a large amount of processing takes a long time.

On the other hand, in order to process a large amount of brazing sheet scrap, if the scrap is melted as it is, it becomes an Al-Si-Mn-based component, and the material of this component is inferior in malleability, so that it can be reused. It is necessary to remove Si or Mn. In particular, the Si concentration at this time varies depending on the composition of the material to be clad and the clad ratio, but since it becomes a high concentration of 2 to 3%, an economical Si reduction / removal method is required for reuse. there were.

Currently, as one of the methods for treating impurities from molten metal, there is a crystal fractionation method. This is to obtain a high-purity metal by recovering a high-purity primary crystal at the time of solidifying a molten metal. Specific examples thereof are shown in Table 1.

[0006]

[Table 1]

In general, when the impurity concentration becomes high, the primary crystal that crystallizes during solidification becomes more dendrite-like, and the liquid phase in which the impurity is concentrated tends to be trapped between the dendrite gaps and the crystal grains. Therefore, even if the method shown in the above table is applied to the brazing sheet scrap having a high Si concentration, there is an inherent problem that the impurity removal rate is not high. Further, in the above-mentioned Pecine method and Alcoa method, since it is a method of recovering the primary crystal formed immediately below the surface of the internal cooling body immersed or the molten metal, it takes a long time to recover a large amount of the primary crystal. It wasn't economically practical.

On the other hand, as a method for purifying a Pb-Sn alloy,
The technologies shown in Table 2 below have been proposed.

[0009]

[Table 2]

In this method, as shown in FIGS. 7 (a) and 7 (b), a filter (12) is provided on the bottom surface of a metal (11) which has been reheated to a predetermined temperature below the liquidus temperature and above the solidus temperature. The metal (11) is housed in a provided container, and the metal (11) is pressurized from above by a piston (13) to concentrate impurities in a liquid phase (14) that has passed through a filter (12).

However, in this method, if a large-diameter ingot is used for a large amount of processing, a separate line for producing the large-diameter ingot is necessary, and it takes time to raise the temperature when reheating the large-diameter ingot. However, there is a problem that it is difficult to make the temperature of the ingot uniform. Furthermore, the larger the ingot, the larger the pressure applied to the ingot and the filter, and the more likely the filter is damaged. In terms of equipment, when there is a large clearance between the piston and the container, there is a problem that the liquid phase part easily flows out above the piston from the clearance part.
It wasn't practical.

[0012]

As enumerated above, it has been recognized that the problems of the prior art are the primary crystal formation method and the pressure applied. Therefore, the present invention was obtained by studying a method of producing a large amount of primary crystals in a short time and sufficiently separating a concentrated liquid phase between primary crystal grains.
That is, the present invention has been made as a result of earnest studies on a method of refining a large amount of brazing sheet scrap at low cost and reusing it.

That is, according to the refining method of the present invention, while stirring a molten aluminum scrap made of an aluminum alloy, the temperature is below the liquidus temperature of the alloy and above the solidus temperature or the eutectic temperature of 20 ° C./min. By cooling at the following cooling rate and holding at that temperature, primary crystal grains are uniformly generated in the entire area of the molten metal, and then the molten metal is pressed with a pressure stamp at a pressure of 1 to 15 MPa, After separating the liquid phase above the stamp, the liquid phase part and the primary crystal compression part below the stamp are solidified, and then the solidified primary crystal compression part is recovered. At this time, as the aluminum scrap, an aluminum alloy containing 0.5 wt% or more and 10 wt% or less of Si is effective.

The method for reusing aluminum scrap of the present invention is characterized in that the solidified primary crystal compression part obtained by the above method is mixed with another raw material aluminum scrap melt.

That is, the present invention is a method for reducing and removing Si in a melted brazing sheet by a crystal fractionation method to produce a low-Si material, and has the following features. In order to generate a large amount of primary crystals in a short time, the molten metal in the processing container is uniformly cooled at a cooling rate of 20 ° C / min. Further, stirring is applied to the molten metal in order to generate a primary crystal having a granular shape and a small grain size throughout the molten metal. In order to separate the primary crystal particles and the concentrated liquid phase, mechanically 1
By applying a pressure of ~ 15 MPa, Si can be economically refined.

[0016]

Here, the smaller the cooling rate of the molten metal, the more preferable, but if it is too slow, it takes a long time for cooling, which is not economical. Also, when the heat extraction from the side surface or the top surface of the container is too large and the cooling rate exceeds 20 ° C / min., The crystallization of the primary crystal occurs from the container wall or the top surface of the molten metal, and the primary crystal is uniformly distributed in the container. Cannot be distributed.

As means for stirring the molten metal, electromagnetic and mechanical methods can be considered, but an electromagnetic method which does not contact the molten metal is preferable. When the electromagnetic method is used, the magnetic flux density of the electromagnetic coil must be 100 Gauss or more in order to generate granular fine primary crystals. Further, the higher the rotational speed (flow velocity) of the molten metal, that is, the higher the magnetic flux density of the electromagnetic coil is, the more preferable, but it is economically difficult. Therefore, as a means for stirring molten metal, 100-500 Gau
It is desirable to use an electromagnetic coil having a magnetic flux density of ss. By stirring the molten metal in this manner, granular fine primary crystals can be generated throughout the molten metal, and the liquid phase in which the impurities are concentrated can be easily removed.

A pressure stamp is used to separate the primary phase particles from the liquid phase part. The reason why the molten metal containing the liquid phase and the primary crystal particles is concentrated by the pressure stamp is to concentrate impurities. This is because the liquid phase can be excluded above the stamp to collect primary crystal particles having a low impurity content below the stamp. At this time, by using the stamp having a through hole in the vertical direction, the liquid phase may be removed through the through hole and above the stamp, or by using the stamp having no through hole in the vertical direction, The liquid phase may be discharged above the stamp through the clearance between the side surface of the stamp and the inner surface of the container. At this time, in order to prevent the primary crystal grains from flowing out above the stamp, the size of the through hole or clearance is preferably 10 mm or less. When the pressure applied to the molten metal by the pressure stamp is less than 1 MPa, the concentrated liquid phase coexisting with the grain boundaries is sufficiently formed at a temperature below the liquidus temperature of the molten metal, above the solidus temperature or above the eutectic line temperature. Since it cannot be eliminated, the impurity concentration of the recovered primary crystal compressed portion remains high. That is, if the pressure is 1 MPa or more, it is almost completely eliminated, and as the pressure increases, the impurity removal effect increases, but on the other hand, if it exceeds 15 MPa, the impurity removal effect does not improve so much, and the impurity removal effect and the primary crystal compression part There is no significant difference in the recovery rate as compared with the case where stirring is not added.

[0019]

The present invention will be described in detail below with reference to the drawings.

Example 1 As shown in FIG. 1, 50 kg of brazing sheet scrap molten metal (Al-3% Si-0.9% Mn) melted in a melting furnace (not shown) was placed in a refractory container (1) (inner diameter 300 mm). , Height 500 mm). Energize the electromagnetic coil (4) installed around the container (1),
Stirring was applied until the molten metal (2) stopped spontaneously (magnetic flux density 220 Gauss). Thus, in this embodiment, the electromagnetic method was used as the molten metal stirring means. In this electromagnetic stirring method, a force is applied in the circumferential direction to the molten metal (2) by winding the electromagnetic coil (4) in the vertical direction in FIG.
Is rotated and stirred.

Further, the molten metal is kept at a liquidus temperature (641 ° C.) or lower at a eutectic line temperature (577) while being controlled at a cooling rate of 5 ° C./min. By a heater (3) arranged around the container (1). (° C.) or higher to a predetermined temperature. Next, when the molten metal reached 629 ° C., the pressure stamp (5) was lowered into the molten metal (2) from above the molten metal (2), and the molten metal (2) was applied at each pressure as shown in Table 3. The pressure was maintained (Fig. 2). As shown in FIG. 4, this pressurizing stamp (5) is provided with 24 through holes (6) having a diameter of 6 mm in the vertical direction, and the molten metal in which the primary crystal is crystallized is pressed by the stamp (5). As shown in FIG. 2, the liquid phase portion (7) with concentrated impurities is collected above the stamp (5) through the through hole (6), while the primary crystal grains are the primary crystals below the stamp (5). It was concentrated in the compression section (8).

Then, after completely solidifying the liquid phase portion and the primary crystal compression portion, as shown in FIG. 3, a pressure stamp (5).
By pulling up, the coagulation liquid phase part (9) and the solidification primary crystal compression part (10) are taken out from the container (1) and the primary crystal part is cut.
Separated and collected, while the coagulated liquid phase part was reheated and collected. Component analysis and weight measurement of the obtained primary crystal compressed part were performed, and Si removal rate of the primary crystal compressed part and recovery rate of the primary crystal compressed part (=
(Primary crystal compression part weight / molten metal weight) × 100) was determined and the results are shown in Table 3. As a comparative example, Table 3 also shows the results when the above method was carried out without stirring the molten metal.
Also described in.

[0023]

[Table 3]

Recovery rate of primary crystal compression part and Si of primary crystal compression part in Table 3
The results of the removal rate are shown in FIGS. From these results, it can be seen that the effect of stirring the molten metal is more remarkable when the pressure applied to the pressure stamp is smaller, and particularly when the pressure applied to the pressure stamp is 1 to 5 MPa. Although the scrap having a high Si concentration was refined in this example, other impurities such as Fe having an equilibrium distribution coefficient of 1 or less can be removed by the same method. In this example, the liquid phase part and the primary crystal compression part were completely solidified while the pressure stamp was held in the container.However, after the pressure stamp was taken out of the container, the liquid phase part and the primary crystal were removed. The compression part may be completely solidified.

(Embodiment 2) Next, an embodiment of the present invention relating to a method for recycling aluminum scrap will be described. The Al-3% Si-0.9% Mn brazing sheet scrap was refined under the same conditions as in Example No. 6 above. The components of the scrap after removing impurities are Al-
It became 0.6% Si-0.63% Mn. After the scrap was melted, Fe, Cu, Mn, Zn, etc. were added and reused as a 3003 alloy.

Example 3 Al having the same composition as in Example 1
The scrap was refined under the same conditions as in Example 2 above. The components of the scrap after removing impurities are Al-
It became 0.9% Si-0.75% Mn. After the scrap is melted, the scrap and 1000 series Al scrap molten metal are blended, and Fe, Cu, Mn, Zn, etc. are further added,
It was reused as 03 alloy.

[0027]

EFFECTS OF THE INVENTION According to the present invention, impurities can be easily removed from scraps made of Al alloy with a simple facility, so that the recycling of aluminum scraps can be efficiently realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a procedure of an example of the present invention.

FIG. 2 is an explanatory diagram of the same.

FIG. 3 is likewise an explanatory diagram.

FIG. 4 is an explanatory plan view showing an example of a pressure stamp used in the present invention.

FIG. 5 is a graph showing the relationship between the primary crystal recovery rate and the applied pressure in the example.

FIG. 6 is a graph showing the relationship between the Si removal rate and the pressure applied in the example.

FIG. 7 (a) and (b) are explanatory views showing a conventional example of metal refining by pressing.

[Explanation of symbols]

 1 Refractory Container 2 Molten Metal 3 Heater 4 Electromagnetic Coil 5 Press Stamp 6 Through Hole 7 Liquid Phase Part 8 Primary Crystal Compressed Section 9 Solidified Liquid Phase Section 10 Solidified Primary Crystal Compressed Section 11 Reheat Metal 12 Filter 13 Piston 14 Impurity Concentration Liquid phase

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihito Omata 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Koichi Ohara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. A molten aluminum scrap made of an aluminum alloy is stirred to a temperature below the liquidus temperature of the alloy and above the solidus temperature or the eutectic line temperature.
By cooling at a cooling rate of 20 ° C / min. Or less and maintaining the temperature, primary crystal grains are uniformly generated in the entire area of the molten metal, and then the molten metal is applied with a pressure stamp at a pressure of 1 to 15 MPa. By pressing, after separating the liquid phase above the stamp, the liquid phase part and the primary crystal compression part below the stamp are solidified,
Then, a method for refining aluminum scrap, which comprises recovering the solidified primary crystal compression portion. 2. Aluminum scrap contains 0.5 wt% Si
% Or more and 10 wt% or less of aluminum alloy.
A method for refining aluminum scrap as described. 3. A method for reusing aluminum scrap, which comprises adding another element to the solidified primary crystal compression part obtained by the method of claim 1 and mixing it with another raw material aluminum scrap melt.