DE1521349A1 - Aluminum spray process - Google Patents

Description

Oakland, California, U «8.A. concerning

Aluminum injection molding priority: March 22, 1965 - Y.St.A »

around

The invention relates to a spraying process for aluminum in the molten state and in particular relates to the application of sprayed aluminum coatings to pre-baked hollow anodes for use in electro-optical cells for the production of aluminum in order to burn the anode during operation in the electric cell air to protect.

When aluminum is produced by means of conventional electrochemical processes, the electrolyte- perforated cell generally comprises a steel casing with a bottom lining made of carbon, the lining being provided with a layer of electrolytically produced molten aluminum, which collects on it and serves as a cathode. Olson, one or more carbon electrodes are arranged on the cell and their lower end is immersed in a layer of molten electrolyte that is in the cell. During operation, the electrolyte becomes a mixture in the Torah

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besides aluminum oxide and cryolite introduced into the cell and a electrolytic «}! * Current from the anode to the cathode via the layer of the molten electrolyte is sent through the cell, whereby aioh oxygen accumulates at the anode · on the surface of the A solid base of the electrolyte and the bath forms Aluminum oxide, and this layer is usually also with one additional layer of aluminum oxide covered.

The usual electrochemical process has hitherto used airei Types of electrolytic cells used, namely the so-called "Torgebackene" cell and the Soderberg »Ue. With both cells the reduction takes place according to exactly the same chemical reactions. The main difference lies in the structure · In the prebaked cell, the sole anodes are prebaked before they are used in the cell while at the Sodabergaelle The anode is baked in situ, i.e., during operation of the electrolytic cell, with part of the excess produced by the reduction being used. The invention relates in particular to prebaked cells.

The oxygen deposited on the anode reacts with the hot carbon and forms carbon dioxide, which then reduces to a certain extent carbon monoxide by the hot carbon will. Theoretically * carbon consumption with a power efficiency of 100 £ and with the production of pure carbon oxides is 0.333 kg Carbon per kg aluminum. The carbon consumption leaves sioh consider ala electrochemical reaction at 100 # current effects

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degree, while dio cathodic reaction © etattfindet 70 to $ 90> StromwirkungBgrad. Therefore, in order to deposit the Xohlenstoffverbrauch kathodisohen from the reaction, the Kohlenetoffverbrauch should be corrected for the cathode efficiency · Br should also be corrected for the coal quality, which is about 98 to £ prebaked with common anodes. The compensation of this carbon loss gesohieht by using larger or higher anode at the beginning of operation than is actually required, and therefore, only a cable of the anode is initially immersed in the electrolyte. Hit increasing consumption of carbon anode is this lowered into dae bathroom, all in common by meohanisohe or automatic means to the desired anode-cathode separation in the bath upright eu receive. Obviously, the larger the anodes used, the fewer the number of used anodes to be replaced and the number of anodes used in the cell.

The lying above the bath rope of the electrode is exposed to the atmosphere and is combusted by air, if it is not * gesohtttzt in any way. A tell-white cover is given by aluminum oxide or the coating on the electrolyte crust , but since higher anodes are more and more used in industry, it is a good practice to heat the anodes to prevent air burns; necessary.

Various solutions to this problem have become known. In Europe a cap made of GtLÖaluminium is often used around the

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exposed toil flex anode to protect it against an air attack. A method used in part in Europe consists of molten aluminum in a coarse, heavy form Beam on the surface of the anode exposed to the atmosphere to apply. This process is described, inter alia, in US Pat. No. 3,053,748 by F. Mure11 and AeI. According to In one American solution, an aluminum bleoh is adhesively bonded to the exposed part of the anode. This The method is described in US Pat. No. 5,060,115.

When prebaked cells for a high load and a high. Current density are used, the limited range between the anodes and their high operating temperature excludes the use of cast aluminum caps or even of coarse, heavy spray coatings made of molten aluminum, such as are used in Europe. In order to maintain the working distance and to form caps which do not melt and do not converge, a thin, non-porous coating must be applied which is resistant to pouting during the life of the anodes and which protects the anodes against attack by air. For this purpose, the method of wrapping with an aluminum sheet described in US Pat. No. 3,060,115 is useful. Sa must be the aluminum sheet but first produced and then applied with an adhesive> is the Wirtechaftliohkeit this muddled nioht seh2 satisfactory. In fact, the induction system's own molten metal would have to be used to protect the anode from air.

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The invention is based on the object of an economical and safe method for protecting carbon anodes for To create aluminum electrolysis.

The solution to the problem is essentially to be seen in the fact that a protective coating on the anode for aluminum reduction cells is made by introducing molten aluminum into a stream of air at a temperature and under conditions » so that an atomized liquid aluminum jet is created that the duration of action on the direct air stream is adjusted so that an oxide content within a certain critieohen Area in which the molten aluminum is produced and that the atomized aluminum beam is then transferred to the Anode is precipitated.

It has been found that the proportion of aluminum oxide contained in the aluminum oversug is critical with respect to the protective properties of the coating, if not sufficient There is aluminum oxide in the aluminum coating on the Torhanden anode, it melts under the action of the heat of the bath and therefore gives little or no protection at all. if sin au large proportion of aluminum oxide in the aluminum coating Anode is Yorhanden, it ruptures, so that the carbon anode is exposed to the atmosphere and rerbrennt by exposure to air. By correct dimensioning of the aluminum oxide content in the Aluaini coating of the anode does not crack or burn » so that the anode is then protected against oxygen. Bs was

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found that the minimum content of aluminum oxide, which must be present in the highly, about 1 1 ° is · If donne coatings of aluminum used, "ie coatings to s O ₉₀₄₁ om thickness of Aluniniumoxydantell la the üb eräug to ta Be 10 ^. If thicker coatings are applied to the anode, i.e. excess sweetness in thicknesses between 0.041 and 0.318 om bead, the aluminum oversug can contain a maximum of about 3 # aluminum oxide . Although the exact mechanism of increasing the base of the anode due to the presence of oxide in the coating cannot be fully understood, it is possible that the oxide particles hold the aluminum together during melting by the heat of the electrolytic cell and therefore prevent the aluminum from being oohmolated from the anode expires and the carbon anode rod then comes into contact with the atmosphere.

The apparatus for carrying out the method according to the invention is essentially a spray device that has a direct Gives off airflow. Suitable fuel packs are commercially available for this purpose.

The invention is illustrated below with reference to schematic drawings additionally described using an exemplary embodiment.

Figure 1 is a view of a device according to the invention.

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FIG. 2 shows a graph of the ratio of the fuel sack and the proportion of aluminum oxide in the coating for a low-speed fuel jet and FIG

FIG. 3 shows a similar graph for a high speed atomized jet

The device shown in FIG. 1 has a spout tube 11 which is filled from an oven 12 via a pouring channel 13. The molten aluminum flows in a stream from the feed funnel 11 through the guide channel H and is intercepted by a uniformly flowing air stream that emerges from a nozzle that is connected to the compressed air source 17 via a line 16. The air flow from the nozzle 15 breaks the aluminum steel and blows the molten aluminum against the anode 18. This is arranged on a turntable 19 which sits on a spindle 20 and rotates so that the surface of the anode 16 can be coated evenly .

Her in the deposited on the anode aluminum content contained in alumina depends on the metal temperature, the StröDiiingoatärkü doe molten metal, the air pressure and the type is carried in the dae £ oechmolaene aluminum in the emerging from the nozzle air flow until the Meets anode and is deposited here. Therefore influencing the composition is done by influencing the type of low-skiing agent of

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Aluminum on the anode. This kind of arrangement creates a fairly coarse, slow jet of oxide with splashes on the anode surface. It is also possible to use a spit system for a higher speed , if only care is taken that it also emits a direct jet of air . A special commercial spray device for this Zweok Boll produce a beam at any parking · "wipe a fairly broad beam low Oxydgehaltes and an extremely fine" hoohozydierten beam is · Dasu is

P necessary to wrap the beam of geeohmolssnen metal in a redu ornamental Gaeflamme prevent zn to excessive oxidation and the aluminum melted au keep · With a dorartigen Flammenspritzvorrlohtung is prepared, the protective coating on the anode in such a manner, the molten aluminum Dafi into an air stream is introduced at a temperature and under conditions such that a disrupted, atomized liquid aluminum jet is produced, that this jet is passed through a reducing flame, that the length of time during which the jet

. is the air flow niohtturbulenten exposed to produce the GE wünsohten oxide content in the molten aluminum is set properly, and that the liquid jet is then sprayed on the anode, and forms a protective coating thereon.

For example, carbon anodes were 39.4 cm wide, 52 cm! · Caught and used 52.4 cm in height and according to the invention via chi ohtet. Figure 2 shows the relationship between spray dioke and proportion

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Alumina in the coating using a low speed spray and Figure 3 shows the same situation using an atomized jet at high speed.

In the first case, the anode was provided with a metal coating τοη 0.305o »Dioke. According to Figure 2, the coating contained 3 1/3 i> alumina at this thickness. The anode was operated with a current of 60,000 amperes in the aluminum reduction cell , which had essentially no aluminum oxide deodorant or any other means of protection against the ingress of air . laohde «the

Cell a short time had been in operation, Giant ™ originated in the coating and burns the carbon anode dmroh air access · In the next experiment, the proportion was the Aluainiunoxyds la the Abdeokmetall 3 £ reduced and brought dl · anode as described above into the cell and During operation of the cell with the relevant anode , small cracking occurred and the spray coating remained impermeable.

In a further experiment was also using a low speed SprltzBtrahles a coating Bit 11 * | Aluminum oxide used The results were comparable to those when using a coating with a content of 3% aluminum oxide.

In a further test with a low-speed spray jet, a coating was applied to the anode with an amount of 0.8% aluminum oxide and 60,000 amperes

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Aluminum reduction operations. In a short time came in Remove the coating and leave bare spots the carbon anode. After further operation of the cell, one was set Excessive burning of the anode occurs.

In a next series of attempts, a stunned ray was found used high speed, the geeohaoliene metal was enveloped by a reducing flame, the oxidation la monitor. In this system, a 3 1/3 Jf Aluminum oxide applied to the same anode as in the previous experiments. Oversuf was liable for the operation of the Zeil satisfactory at the anode and remained unrelenting during the process. There was no burning of the anode throughout the loft.

In a further experiment with an atomized jet of high speed, a coating of O ₁ 04 om Sloke was applied with an aluminum oxide content of 10 ^. When the anode prepared in this way was operated with 60,000 amperes, there was a slight RIA formation in the upper eye. When the proportion of oxide was increased to 11% in a further attempt, a more extensive riffling of the coating occurred during operation of the anode and, accordingly, greater combustion by air.

In another Vernuoh an aluminum coating of 0.011 om Dioke applied to the anode with an atomized jet high Speed. The oxide content was determined by means of the reducing

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Gas flame set to $ 5> aluminum oxide in the coating. The anode prepared in this way was operated as in the previous experiments with 60,000 amperes in an aluminum reduction unit. There was no melting and no cracking of the upper draft and no disruptive combustion of the anode by air.

Table 1 shows comparative results of standard anodes measuring 39.4 52 χ 32.4 cm, which were only provided with a Sonirdetni as a protection against combustion by air »wob ·! an anode coated according to the invention with a fuel as tr iah 1 low Oe * ™ speed was used, the coating containing 3 # aluminum oxide. Table I also leigt comparisons of the standard anode with higher anode, ie old anodes of 38.7 cm and of 45 "75 cn height been genäfi the invention old coated Spriteetrahl a low speed, wherein the top pull 3 contained i> alumina. In this table, carbon efficiency is defined as the corrected theoretical carbon consumption, as stated above, divided by the actual consumption, expressed in terms of frost. Dl «| The results compiled in tabular form clearly show that AsJ, as a result of the coating of the anode according to the invention, the carbon efficiency increases considerably and i η is in all cases 13 to 14 $> higher. It can also be seen from the table that the aluminum products are significantly increased. In addition, the number of pot shifts per anode is also significantly higher. These advantages bring considerable savings, as are the production costs. we cents are reduced, and not just because of

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dee reduced coal consumption, but also because of the lower personnel costs for erosion of the anodes, since their. The service life when the invention is applied is noticeably increased .

Table I.

Beeohiohtet coated Standard beeohicht "t Anodenmeseungen 39.4 χ 52 39.4 52 39.4 ζ χ 52 39" 4 x 52 cm χ 32.4 χ approximately 32.4 χ 38.7 χ 45.75

Amperage 59,000 60,000 62,000 62,000 Current effects - ν
grad ™ 81.5 82.0 83.0 83.0 Net kg Al per
Crucible and day 387 399 414 414 Crucible change / anode 20th 23 30th 38 kg coal / kg Al 0.590 0.490 0.485 0.490 corrected theor.
Coal consumption 0.413 0.411 0.406 0.406 Coal efficiency f ί 70.0 83.8
t 83.6 82.8

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Claims (7)

Claims 1 · A process for the production of a protective cover on hollow anodes for aluminum reduction ropes, characterized in that molten aluminum is introduced into a directed air flow at a temperature and under conditions such that a jet of aluminum liquid flows into the other, so that the duration of the action of the air flow is set in such a way that that an oxide content in the molten aluminum 1 to 10 1 * results, and that the liquid Aluminiumetrahl aodann al "coating is applied to the carbon anode. 2. The method according to claim 1, characterized in that AaJ the aluminum jet is passed through a reducing urine 3. The method according to claim 1, characterized in that the air flow is a directed air flow of low QeBdMindlgigkeit and that a liquid aluminum spray is generated. 4. The method according to claim .3, characterized in that the liquid aluminum spray will strike down as a coating on the anode. 5. The method according to claim 1 to 4, characterized in that a coating up to 0.041 on thickness is used » 6. The method according to claim 1 to 4, characterized in that a dafl Extremely organic to 0.318 ca thickness is used. 909821/0941 -H- 7. The method according to claim 6, characterized in that the oxide content is adjusted to 3 1/3 *. 909821/0841 ^{BAD 0R1G} ' ^NAL