NL8000567A - PROCESS FOR REDUCING THE CONTENT OF POLLUTANTS IN ALUMINUM MELTS AND MELTS OF ALUMINUM ALLOYS. - Google Patents

Description

F $ i :. 1 / '

A method for reducing the impurity content in aluminum smelting and aluminum alloy melting

The invention relates to a method for reducing the content of impurities in aluminum melts or in melting aluminum alloys, primarily for reducing the content of alkali metal, hydrogen gas and solid non-metallic impurities, with especially oxides.

Several methods of purifying metals are known. The most effective of this method uses an active gas: chlorine gas or salts that evolve chlorine-10 gas; halides. By flushing with chlorine gas (J.P.

Tomany: The control of aluminum chloride fumes. - Light Metal Age, 1968, 26_, No. 9-10, biz. 19-20), the gaseous hydrogen content of oxides and alkali metals in most alloys is reduced, but also the major part of the gas (which is introduced in the melt through graphite or steel tubes with a resistant coating) ) does not participate in the purification process and causes serious problems of neutralization and absorption. In the departments of factories where chlorine gas is used, the steel iron structures are exposed to corrosion and there is a continuous danger of poisoning in the handling, storage and neutralization of chlorine gas (P. Nölting: Betriebliche Erfahrungen mit der Chlorbehandlung von Aluminum-legierungen Giesserei 61, 1974, No. 1, pp. 7-10).

Solutions to this problem are known in which the gas introduced into the melt consists of a mixture of chlorine gas and nitrogen gas or one of the noble gases: argon, helium, neon, crypton, xenon alone or a mixture of these noble gases. gasses.

Nitrogen gas is also a gas that does not react with aluminum. 80 0 0 5 67 * * 2.

The generally accepted composition of the chlorine-nitrogen gas mixtures used is: 10 to 35% by volume of chlorine gas + 60 to 90% by volume of nitrogen gas.

5 The hydrogen gas-removing effect of these gas mixtures is smaller than that of pure chlorine gas, but greater than that of pure nitrogen gas (P. Presche and N. Wulmstrof: Treatment of Aluminum Schmelzen mit Gasgemischen, aluminum 48_, 1972, no. 10, p. 677 - 678). Of the gases inert to aluminum, argon provides a more effective reduction in hydrogen content than nitrogen (H. Ginsberg and AN Agrawal: Oberprüfung der Wirkungsweise gebrauchlicher Entgasungsmethoden für Metall-schmelzen aus Reinaluminium und Aluminum-Magnesium-Legierungen unter Anwendung der neuen Gasbestimmungsapparaties III Aluminum, 1541, 1965, No. 11, pp. 683 - 687. But argon and the other noble gases are also quite expensive and therefore they are not used in the aluminum industry.

By liquefying and fractionating air, large quantities of nitrogen gas can be obtained inexpensively. However, purging with nitrogen gas has the drawback that in the melting of an aluminum alloy, the degree of degassing is small, while at the same time a slag is formed on the surface of the metal melt, which contains a relatively large amount of metals and is difficult to treat, so that the metal losses are increased. Nitrogen-25 gas further does not decrease the alkali metal content of the melt and therefore nitrogen alone is not suitable for purifying melts contaminated with alkali metals and nitrogen gas should be used alone mixed with chlorine gas (AG Székely, AG: The Removal of Solid particles from Molten Aluminum in the 30 Spinning Nozzle Inert Flotation Process (Metallurgical Transactions, 7B, 1976, biz. 259 - 270). The sodium content is most effectively reduced by chlorine gas (B. Lagowski: Magnesium loss during chlorination of aluminum melts. Les Plaines III., Trans. Amer. Foundrymen's Soc. 77, 1969, 206 - 207).

35 Chlorine gas introduced into the melt forms AlCl ^ 80 0 0 5 67 * $ 3 whereby sodium is bonded according to the equations: A1Cl3 + 3 Na -> 3 NaCl + Al

NaCl + A1Cl3- ^ (AlCl3.NaCl) / S

The chlorides of the gas-developing salts, for example manganese chloride and zinc chloride, react with liquid aluminum to form aluminum chloride, which compound is gaseous at the treatment temperature (LM Marienbakh, LO Sokolovskii ,: Plavka slavov tsvetnykh metallov dlya fasonnogo litya, Moscow, 1967, pp. 184-189).

10 The reaction equation is: 3 MeCl2 + 2 Al -—> Aid 3 + 3 Me

Gaseous aluminum chloride also reduces contamination of the melt by sodium.

Hexachloroethane is also used for reducing the impurity content in aluminum smelting or melting aluminum alloys L.M. Marienbakh, L.O. Sokolovskii: Plavka slavov tsvetnykh metallov dlya fasonnogo litya. Mowcow, 1967, pp. 184-189).

The reactions of hexachloroethane in a melt of aluminum 20 are as follows: 3 C2C16 3 C2C14 + 3 Cl2 2 Al + 3 Cl2-τ '2 A1C13 3 C 1 Clr + 2 Al -> 3 CLC1L + 2 A1C1.

2 6 2 4 3 25 Due to the violent reactions taking place and the risk of explosion, the entire amount of treatment material required to achieve the desired effect cannot be added to the liquid metal at once. Some processes are known in which hexachloroethane is added to the melt in smaller amounts simultaneously. This means additional handling costs and the powder packed in films or capsules or the amounts of material compressed into tablets must be added by means of submersible clocks, a tedious manual method of addition which cannot be mechanized. seerd.

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In the case of furnace units with a large surface area of the melt, the addition will generally not be uniform and consequently the utilization rate of the hexa-chloroethane is low and a substantial amount of the treatment material is wasted with the waste gases.

Treatments under vacuum have also been used for purifying the said liquid metals (K. Alker: Aluminum grafting gases in the vacuum industry. Treatment treatment betriebssicher und umwelt-feeundlicher as Clorierungsverfahren. VDI-Nachrichten 2_7, 1973, 10 No. 22, p. 12 ). The drawback of this method is that only the upper part of the metal melt is degassed (Makarov, G.S .: Zakonomernosti udaleniya vodoroda pri vakuumnoi obrabotke rasplavlennogo alyuminiya. Techn. Legk. Splavov, 1970, No. 37 - 42). The method is expensive because the construction and operation of the vacuum furnaces require a high investment and high maintenance costs.

Ultrasonication treatments are also among the physical methods by which hydrogen content can be reduced (Livanov, V.A. et al .: Rafinirovaniye alyuminiya i 20 ego splavov ul trazvukovymi kelebaniyami, Tsvetnye Metally, 1968,

No. 6, pp. 82-84). That method has never been applied on a technical scale.

A general drawback of the physical processes is that they do not lower the alkali metal content of the aluminum melt or melt of an aluminum alloy.

In the last 15 years, the equipment for continuous metal treatment outside the furnace has undergone significant development. This equipment is described below.

The equipment of the brand FILD of the company Gautschi 30 combines a flushing treatment with nitrogen gas with filtration through spheres of activated aluminum oxide (Entgasung und Reinigung von Aluminumschmelzen, Gautsch folder, Aluminum 50, 1974,

No. 4, p. 297).

The firms BASF uses a continuous method and device 35 in which use is made of petroleum coke. With this 800 0 5 67? > 5 equipment is rinsed with a neutral gas combined with filtration through a mechanical filter bed with an active surface (Böhm, G .: Das Filtrieren und Entgasen von Aluminumschmelzen im Durchlaufverfahren, Aluminum, 1973, No. 11, pages 743 - 747).

5 In the equipment marketed by Carborundum, the main filter element is a melt-immersed filter consisting of porous tubes of the trademark Aloxit. These melt-dipped pipes are placed in a filter vessel equipped with an electric roof heating in such a way that the metal penetrates through the jacket of the pipes under the influence of the metallostatic pressure and enters a collecting space (Mahesh, C Mangalick: The Rigid Media Filter - Principles and Applications. Manuscript presented on the 102nd Annual Meeting of the ΑΙΜΕ, Chicago, 1972).

15 Union Carbide Corporation uses a flotation method instead of a filtration method to separate the solid impurity, using a SNIF equipment (Székely. AG: The Removal of Solid Particles from Molten Aluminum in the Spinning Nozzle Inert Flotation Process .

20 Metallurgical Transactions 7B, 1976, pp. 259-270).

The equipment developed by Alcoa includes two filter beds through which a mixture of chlorine and argon gas is allowed to flow (Blayden, LC - Brondyke, KJ: Alcoa 469. Low cost, non-polluting, continuous metal fluxing. Journal of Metals 1974, February 25, pp. 25-28).

The above-described processes are advantageous in continuously operating foundries where the casting time is long and the incessant treatment in the furnaces is not sufficient to maintain the hydrogen gas content of the melt at the desired lower level up to the end of the casting period.

A common drawback of this process, however, is that the gaseous reaction products are not completely dragged to the surface due to the relatively large flow rates (3-20 t / h) and the short residence times. To compensate for this drawback, multi-chamber reactors have been developed, 800 0 5 67 6 'but the dimensions and heating systems of these reactions are similar to those of the furnaces and therefore they are difficult or impossible to switch between the existing foundry and the ovens.

The object of the invention is now to eliminate the aforementioned drawbacks and to provide a continuous method for reducing the content of impurities in aluminum melting or melting of aluminum alloys, by means of which method the utilization of the treatment materials to a high degree is improved and the purification becomes easily controllable and can be controlled. According to the invention, an inert gas is introduced into the aluminum melt or melt of aluminum alloy which is sealed from the air at a temperature of 670 to 860 ° C under a pressure of less than 200 kPa, preferably nitrogen gas, which gas contains powder that produces gaseous chlorine.

Surprisingly, it has been found that upon introduction into the aluminum melt or melt of an air-sealed aluminum alloy, of a powder that develops chlorine gas, especially zinc chloride, magnesium chloride, hexachloroethane or manganese chloride, mixed with an inert gas, especially nitrogen dust, the amount of the chlorine gas developing powder required to remove a certain amount of impurities can be reduced by about 60% compared to the amount needed in the known methods.

The advantages of the method according to the invention are: 1. by using the method according to the invention the amount of chlorine gas-developing powder required for removing a certain amount of impurities is greatly reduced, ie the useful use of material is improved and the amount of treatment agent not consumed is reduced. This is immeasurably important from an economic point of view.

2. The method according to the invention can be carried out continuously and can be controlled very precisely automatically. Thus, the method according to the invention can be carried out with 800 0 5 67 * 7 less physical energy and with good control.

3. The purification takes place under the occlusion of air so that any oxide contamination can be eliminated. Namely, in the presence of atmospheric oxygen, further oxidic impurities could be formed.

4. Another advantage of the method according to the invention is that, when using this method, the aluminum content of the slag formed during the treatment is substantially lower than, for example, the aluminum content during treatment with all and nitrogen gas.

The method according to the invention can suitably be carried out with a device as schematically shown in figure 1.

The pressurized container indicated by (1) in Figure 1 and which can be filled after opening the lid (9) serves as a storage container for the treatment material. The conveyor (4) feeds the treatment material to the mixing space (5). The feeding speed can be varied very accurately and adjusted under certain values with the drive unit (3).

Replenishing the stock in the container with treatment material is controlled by a signal provided by the signal device (2).

The carrier gas enters the mixing space (5) via a pressure regulating and stabilizing device (7). The volume of the gas can be adjusted using the flow meter (6). The mixture of gas and treatment material prepared in the mixing space flows through the flexible tube or hose (8) to the treatment lance 10. The material of the treatment lance is resistant to the action of the liquid metal. Purification of metal using a mixture of gas and treatment material is used under factory conditions for treating aluminum smelting and aluminum alloy melting.

The treatment material is preferably hexachloroethane 35 and the carrier gas is preferably nitrogen.

800 0 5 67 8

The method according to the invention is now further elucidated by the following examples, which do not imply any limitation.

Example I

An aluminum magnetic silicon alloy melt was treated in a 15 ton tubular flame furnace using a device of the type shown in Figure 1. The volume flow of nitrogen carrier gas used for treatment 3 was 0.4-0.5 Nm / min. The treatment started at a temperature of 710-720 ° C. In half of the cases, no chlorine gas developing salt was added to the nitrogen gas. The amount of hexachloroethane used was 2 kg / t melt (0.2%). The gas content of the melt before and after the treatment is shown in Table h. The gas content was determined by the "first bubble" method. Nitrogen gas was able to remove 9 to 33% of the hydrogen gas from the melt. When hexachloroethane was added as a chlorine gas developing agent to the nitrogen gas, the hydrogen gas content was reduced by 48-77%. The slag formed was dry and powdery and had a low aluminum content, while when treated with nitrogen gas only the molded was slippery. With the addition of hexachloroethane, the temperature of the melt did not drop due to the reaction heat during the treatment. When treated with nitrogen gas alone, the temperature dropped by 15 ° C.

Example II

An aluminum-magnesium-silicon-alloy melt was treated in a 15-ton tubular flame or using the equipment shown in Figure 1, with the parameters set forth in Example 1. Powdered hexachloroethane 30 served as chlorine gas developing salt. For comparison, in another case, tablets of hexachloroethane were melt melted using an immersion clock. The amount of treatment material used in both cases was 2 kg / t melt. The hydrogen contents are shown in Table B. When supplied in a stream of nitrogen gas, due to the better reaction conditions, the gas content of the melt decreased by 58-70%, a value more than twice as high as the purification achieved with the hexachloroethane tablets.

The same effect occurred in the oxygen content of the melt. While the oxygen content of the melt after blowing in powdered hexachloroethane was 10 ppm, the oxygen content when treating the melt with tablets was 18 ppm. The variation in the oxygen content when treated with hexachloroethane tablets or powdered hexachloroethane plus nitrogen-10 gas is shown in Tables F and G.

Example III

The reduction of the hydrogen gas content in a melt of an aluminum-magnesium silicon alloy was examined as a function of the amount of powdered hexachloro-ethane introduced as chlorine gas developing agent using equipment of the type shown in Figure 1. Figures 2 and 3 show the efficiency of the purification comparing the effect of treatment with hexachloroethane tablets with the effect of treatment in a 15 ton tube furnace with powdered hexachloroethane blown in using nitrogen gas. Figure 2 shows the hydrogen gas content 3 of the melt (cm / 100 g) as a function of the specific hexachloroethane consumption (kg calculated per 1 t of the melt).

Figure 3 shows the initial hydrogen content (denoted as 3 25 S, and expressed in cm / 100 g) as a function of the specific hexachloroethane consumption (expressed in kg / t of the melt). Also the hydrogen gas content at the end of the treatment (indicated as shown). The solid lines refer to a treatment with powdered hexachloroethane plus nitrogen gas, while the dashed lines refer to a treatment with tablets of hexachloroethane. The efficiency of powdered hexachloroethane introduced using a stream of nitrogen gas exceeds that of the hexachloroethane tablet treatment. This is shown in Figure 3 for a starting hydrogen gas content of 0.3 cm / 100 g and for an initial 800 0 5 67 3 10 hydrogen gas content of 0.1 cm / 100 g. To achieve the same purifying effect, the reduction in hexachloroethane consumption can be as much as 60%. When blowing powdered hexachloroethane with the aid of a stream of nitrogen gas, the oxygen gas content in the case under investigation decreased to 5 ppm.

Example IV

With equipment of the type shown in Figure 1, an amount of 13 t of an aluminum-magnesium-silicon alloy melt was treated in a tubular furnace. The changes in the sodium content that arose as a result of the blowing in of 2 kg of powdered hexachloroethane as chlorine gas-supplying material per t melt were investigated. Table C compares the sodium levels before and after treatment. The reduction was 27 - 65%.

The purification efficiency that can be achieved by increasing the amount of hexachloroethane powder used is shown in Figure 4 which shows the sodium content (ppm Na) as a function of the specific hexachloroethane consumption (kg / t melt).

Example V

With equipment of the type shown in Figure 1, an aluminum-magnesium-silicon alloy melt was treated in a 15 t flame tube furnace. The stream of nitrogen gas used for the treatment was 0.4 - 0.5 N m / min. The temperature at which the treatment took place was 710-720 ° C.

Table D shows the oxygen content of the melt before and after the treatment with nitrogen gas. The oxygen content was determined using a neutron activation method. On average, no reduction in oxygen content was found. On the contrary, in most cases the oxygen content even increased.

Example VI

In a tubular furnace, 25 t of an aluminum-magnesium-silicon alloy melt was treated with hexachloroethane tablets. The changes in the sodium 35 content as a result of mixing the melt with two kg / t tablets of hexachloroethane as chlorine gas supplying material were noted. The treatment temperature was 710-720 ° C.

The sodium levels before and after treatment are shown in Table E. The sodium levels decreased by 14-57%.

5 Table A

Liquid content

Treatment with N ~ Treatment with N „+ C„ Clc _. .. _Z_Z Z o

For after

Treatment Reduced- Before After Reduced- 10 ml / 100 g ml / 100 g ring Treatment ring

Al_Al _% _ 0.23 0.21 9 0.20 0.09 55 0.11 0.08 27 0.26 0.10 62 0.21 0.14 33 0.21 0.06 71 15 0.27 0 , 24 11 0.23 0.12 48 0.24_0.17_29_0.22_0.05_77

Table B Hydrogen content

Treatment with C „Cl tablets Treatment with N„ + powder

Ζό Z

20 mig C0C1 ^ _______ ^ O_.

Before After Reduction Before After Reduction treatment_Treatment_

Ml / 100 g ml / 100 g% ml / 10Q g ml / 100 g Reduced Al Al Al ring _% _ 0.19 0.16 16 0.20 0.06 70 0.22 0.19 14 0 , 32 0.11 66 0.32 0.23 28 0.23 0.09 61 30 0.21 0.19 10 0.26 0.10 62 0.32_0_j_25_22_0.24 0.10_58

Table C Sodium content

Treatment with Nj + 2 kg / t powdered C ^ Cl ^ 35 Before treatment ppm After treatment ppm_Reduction% 15 11 27 80 0 0 5 67 12

continued Table C

Treatment with N „+ 2 kg / t powdered C„ Clr __Z_Z o

Before treatment dpm After treatment dpm_Reduction% 6 4 33 5 20 7 65 10 7 30 _7_4_43_

Table D

Oxygen content. Treatment with N 2 gas

Before treatment dpm_After treatment dpm_Change 30 40 + 10 30 65 + 35 25 38 + 13 15 25 43 + 18 38 30 - 8 40 35 - 5 38 40 +2 25 30 +5 20 40 35 - 5 30_30_0_

Table E Sodium content

Treatment with 2 kg / t tablets of C_C1 _Z o 25 Before treatment ppm After treatment ppm Reduction% 8 5 37.0 5 3 40.0 7 4 43.0 8 5 37.0 30 7 3 57.0 6 4 33, 0 9 6 33.0 7 6 14.0 10 _8_20.0 800 05 67 35 -ip 13

Table F Oxygen content

Treatment with C ^ Cl ^ tablets

Before treatment dpm After treatment dpm_Reduction% 5 30 25 17 55 45 18 35 30 14 40 35 13 45_35_22_

10 Table G

Oxygen content

Treatment with N „+ powdered C„ C1-_Z_ Z o

Before treatment ppm After treatment ppm Reduction% 35 20 43 15 30 20 33 25 15 40 25 20 20 30_25_17_ 80 0 0 5 67

Claims (5)

1. A method for reducing the impurity content of an aluminum melt or melt of an aluminum alloy, primarily for decreasing the alkali metal, hydrogen gas and / or solid non-metallic impurities content, in in particular oxide, characterized in that an inert gas is introduced into the aluminum melt or melt of aluminum alloy which is sealed from the air at a temperature of 670 to 860 ° C under a pressure of less than 200 kPa, preferably nitrogen gas, which gas contains a powder that develops chlorine gas. Process according to claim 1, characterized in that the chlorine gas-developing powder is zinc chloride, magnesium chloride, manganese chloride and / or hexachloroethane. Process according to Claim 1 or 2, characterized in that hexachloroethane is used as the chlorine gas-developing powder. 4. Process according to any one of the preceding claims, characterized in that the chlorine gas-developing powder is used in an amount of 0.05 - 10 kg / t aluminum melt or melt of an aluminum alloy. 5. Methods as described in the description and / or the examples. 80 0 0 5 67