DE812211C - Process for the production of the lower part of the crucible of cells for molten electrolysis and cells for molten electrolysis produced by this process - Google Patents

Description

(WiGBL p. 175)

ISSUED AUGUST 27, 1951

p 22925 VIa / 40c D

Jean Grolee, Paris

has been named as the inventor

Froges et Camargue, Paris

The cells for molten electrolysis work with a voltage of around 4 to 6 volts. So one is interested in to reduce the voltage drops that are not necessary for the electrolysis as far as possible. This is true for the voltage drop in the bottom of the crucible, the z. B. the cathodic part of the cell in the Case of the electrolysis of aluminum oxide dissolved in molten cryolite for the production of aluminum or, on the contrary, the anodic part of those intended for refining aluminum Cell forms. It is also desirable that this voltage drop have a low value during throughout the life of the lining of the cell and that this lining lasts for as long as much as possible so that the cell can be kept in operation with as few interruptions as possible can. The lining of the crucible containing the electrolysis bath is made of carbon, with the The base, which is the cathode part of the electrolysis cell, is often made from previously fired carbon blocks is established, and the voltage drop caused by the passage of current through the ground depends largely on the electrical connection between these blocks and the metallic ones Current outlet or current inlet rails, which are mostly made of steel or copper are.

This connection is made by making a groove in the pressed carbon block.

cuts whose cross-section is larger than that of the power outlet or power inlet rail. On that this rail is inserted into the groove and the one between the metal and the pressed one is filled Carbon remaining space with a warm paste made from a mixture consists of carbon dust and hard pitch or any other carbonaceous substance, such as molasses (sugar pulp). When the electrolysis cell is put into operation, this paste is burned thus ensuring the electrical connection between the pressed carbon block and the metallic power outlet or power inlet rail.

> 5 The voltage drops in the lower part of the crucible of the electrolytic cells produced in this way when the cell is new they usually reach values of 0.45 to 0.50 volts and increase with it the time down to 0.80 volts.

ϊο For the purpose of improving this voltage drop it has been proposed that the bond between the pressed carbon and the Manufacture metal rail by means of cast iron. Indeed, you got a better one Voltage drop in the lower part of the cell's crucible when it was new, but a certain amount A number of carbon blocks burst when the cast iron was poured and had to be replaced which increased spending. Furthermore, a large number of blocks showed without bursting completely, slight cracks that opened further during operation of the electrolytic or refining cell.

These cracks caused an increase in the voltage drop in the lower part of the crucible of the cell, since the split carbon block against the continued passage of current corresponds to an abnormal resistance]. In addition, these cracks limited the life of this lower part of the crucible of the cells, as detailed below will be. · I

These serious drawbacks have hindered the development of the molten cast pouring method.

The invention enables to avoid these inconveniences by using for casting the Stromausk ^r angs- or current input bus bars in the pressed carbon blocks, a molten metal which has a melting temperature in excess of 1000 ⁰ C and after solidification is substantially free of components having a could suffer conversion associated with an increase in volume if they are kept ^{at a temperature of 900 0 C for a longer period of time.}

In the electrclyc cells produced in this way namely, the voltage drop in the lower part of the crucible is of the order of magnitude 0.25 volts, which is not enough to generate enough Joule heat to reach the bottom of the crucible to keep it at the desired temperature. It is imperative to have this floor with a Provide thermal protection to ensure a mushy and solid deposit on the upper part of the Avoid carbon blocks; because this one

Precipitation would increase the voltage drop, so that the gain in total voltage of the cell would be lost again. Thanks to this thermal protection, the lower part of the pressed carbon blocks, where the current outlet or current inlet rails are cast, is kept at a temperature of about 900 ^° C. during normal operation. But it has now been found that under these conditions any casting used for pouring showed an increase in volume which was much greater than the normal expansion with increases in temperature. This swelling of the cast expanded the cracks in the blocks and caused the serious accidents described below. In some cases the swelling of the casting was so significant that it itself caused cracks to form in blocks which had remained perfectly intact when the lower part of the crucible of the electrolysis cell was made. These inconveniences are completely avoided if a metal, such as z. B. copper is used. Bronze with less than io ° / o tin is also suitable, as well as cast iron, which is virtually free of sulfur and fixed carbon, but you can also use any other metal or alloy which has a melting temperature in excess of 1000 ⁰ C and having no part of , which could suffer a conversion associated with increase in volume upon solidification, when it is maintained at a temperature of 900 ⁰ C a long time.

A cast iron melt with the following composition gives good results:

Carbon. . . about 3%

Silicon 2.5 to 3%

Phosphorus .... 1 to 1.5 ° / ₀

Manganese less than 0,5%

Sulfur less than 0,05%

Iron rest

Fig. Ι is a vertical longitudinal section of the electrolytic cell;

Fig. 2 is a cross section of this cell;

Figs. 3 and 4 show, on a larger scale, one of the cathodic parts of the cell Carbon blocks with the current output rails with encapsulations of a known type;

Figures 5, 6 and 7 are views corresponding to Figures 3 and 4 illustrating potting according to the invention; "'.' .: '.':

Fig. 8 shows a diagrammatic representation of three carbon blocks, which can be potted with the same power outlet rail are prepared;

Fig. 9 shows in plan the casting of a rail in a long block;

Fig. 10 depicts a three-phase process for casting the melt in order to carry out the pouring process Fig. 6.

In Figures 1 and 2 of the drawings, 1 is the Metal box in which the crucible of the electrolytic cell is built; the carbon lining 3, 4 of this crucible is from the metal box ι and the rails 5 with the help of ieuer- 1 * 5 solid stones 2 isolated. The the cathodic part

of the cell-forming plastic blocks 4 are with the metallic current outlet rails 5 are connected with the aid of the cast melt 6.

In the known devices shown in Fig. 3 and 4, the power outlet rail is in a Xut 7 cut into the carbon block 4 is inserted, with the molten metal 6 in the space is poured; however, when the block is inserted into the bottom of the crucible, the solidified one protrudes Do not melt beyond the horizontal lower surface of the block.

As indicated above, this gave a lower voltage drop than without the melt poured between the metal rail and the carbon blocks, but a certain number of carbon blocks split at the moment the melt was poured and had to be replaced. Furthermore, a large number of blocks showed slight cracks without completely splitting, which opened further when the electrolytic or refining cell was operated. These cracks caused an increase in the voltage drop in the lower part of the crucible of the cell because the cracked carbon block offered an abnormal resistance to the passage of current. In addition, these cracks limited the life of this lower part of the crucible of the cells. If a crack appeared on each side of the pouring by means of the melt 6, as shown at 4 ¹ in Fig. 3, this crack, enlarged by the abnormal swelling of the melt, gradually reached the edges of the carbon block 4, and the upper part of this block loosened finally j. The liquid metal located at the bottom of the crucible, e.g. B. aluminum, has been contaminated from contact with the pouring melt 6 and metal rail 5, forcing the cell to be taken out of service to repair the bottom of the crucible. The same disturbance, albeit less severe, occurred when a single crack formed in the carbon block 4 from the pouring melto upwards, as shown at 4 ¹ in Fig the ; Melt was poured out. The crack 4 ¹ gradually elongated upwards and the liquid aluminum seeped through the crack until it came into contact with the pouring melt.

In the arrangement shown in Fig. 5, the over the edges of the pouring groove 7 forms Melt 6 a cap 6 ° from ι to 2 cm thick, which against the lower horizontal surface of the; Carbon block 4 rests. j

Fs is clear that exerts at the pouring out of the shrinkage of the melt in the Xut 7 to the cap 6 "a] force which seeks strongly to press against the block, which is electrically low. One can so a voltage drop in the order of magnitude ■ intimately of 0.20 volts.

This gain is further increased if one uses a form of potting of the type shown in Figs. 6 and 7, in which the pouring spout 6 not only fills the Xut 7 and covers the lower horizontal surface of the block at 6 ", but also this on the four vertical surfaces at 6 ^b at a height that can reach 10 cm. The voltage drop can thus be reduced to 0.14 to 0.15 volts.

The power outlet or power entry rails 5 are generally made of soft, malleable Martin steel with a breaking strength of 45 kg / mm ² and an elongation of 30%.

You will be targeted on the press. If the billets are square, they are allowed show no warping, otherwise their asymmetrical expansion when pouring the melt would be detrimental to the good quality of the connection and the formation of cracks in the carbon blocks could cause.

For the further good production of the bottom of the crucible, it is desirable that the permissible Deflection on one of the sides does not exceed 1.5 mm per meter, but this condition is for the good execution of the pouring itself is not indispensable.

The portion of the bus bar of iron or copper, which comes into contact with the casting metal must sanded with dry sand and dry air, or to be free of any Oxydspuren preferably ground w ^r grounded. It must not be moist or greasy at the time of use. On the other hand, it is not disadvantageous if it is rough or has tool marks if it has been machined, which is not absolutely necessary. It has been found to be advantageous to heat the carbon blocks prior to pouring. It is best to put them in a stove so that they are heated evenly on all sides; in the absence of such, one can be content with heating only the grooved side.

For cubic blocks with a side length of about 50 cm, a temperature of 80 ° C is required in the surface layers considered sufficient.

Preheating the blocks is not essential and trained personnel can do a lot the cold blocks can be poured out well, provided that they are free of moisture are; however, preheating is advantageous.

The melting point of the above-mentioned halbphosphorigen melt is at about 1150 ⁰ C.

It is convenient, however, to bring this melt to a temperature such that, after emptying into the casting ladles and after the transport of these pans, the temperature of the beam at the moment of pouring of the rails 1200-1300 ⁰ C to the casting station. This ensures the thin liquid required for perfect execution of the potting.

After all, it would be superfluous and dangerous to heat to a much higher temperature, which means the already very violent thermal shock suffered by the carbon block in exaggerated Way would be increased. ,

It is clear that the liquid melt must be carefully deslagged several times before pouring. You can be satisfied with the power

to dry step or power entry rails in heating ovens at a temperature of a few tens of degrees, however, it is not recommended to exaggerate the heating, otherwise the danger is easy there is an oxidation of the surfaces, which, as already mentioned, must be perfectly clean.

Fig. 8 shows, as an example, an advantageous arrangement for potting a metal rail in three blocks with a side length of 500 or 600 mm.

The carbon blocks 4 are placed on the floor with the pouring groove 7 facing upwards and, if necessary aligned for the introduction of the rail 5. The ends of the rail are placed on two trestles 8 placed, which they hold at a suitable height so that it penetrates all the grooves 7 of the blocks. It it is very important that the non-potted ends of the rail 5 can expand freely. It is consequently it is better not to fix them with bolts, wedges or the like.

ao If it is about horizontal rails which enter the grooves 7 of several blocks 4, so you can see the necessary supports and connecting pieces 9 between these, so the melt fills the groove 7 of each block,

but does not cross over from one groove to the other. It is, so to speak, a matter of providing expansion joints in the melt. You connect everyone Blocks through a casting frame 10.

It is poured in compliance with the temperatures and purification indicated Precautions. If there are three blocks on the same rail 5, the three Blocks 4 poured out at the same time by letting three groups of foundries work. One avoids that the pouring stream hits the rail directly or remains at the same pouring point, but on the contrary moves it in the space between Blocks and rail back and forth to avoid dangerous local overheating. As soon as the Surface of the casting has started to solidify, you hurry, everything a quick cooling could hinder removal; one removes the intermediate pieces 9 made of asbestos and sand, the casting * - frame 10 must be removed immediately, etc. It is namely necessary to turn on the heat as quickly as possible discharge into the environment in order to reduce their uptake by the block to a certain extent, thereby reducing the risk of cracking.

In addition, it is to avoid any stress that causes internal stresses could, advantageous, to give free play to all expansions, not only for the rail, but also for the blocks themselves, which may be, for. B. only straight in a solid casting frame the time required for casting may be used.

As a last precaution, avoid that

to move arrangement formed by the rails and the cast blocks before they are sufficient has cooled, d. H. you wait several hours after pouring and possibly until next days.

To produce the encapsulation according to Fig. 6, it has proven to be more advantageous in three phases proceed as shown in Fig. 10.

To form the first part 11 of the potting the groove 7 is filled up to the level of the horizontal surface of the block, namely in the reference suitable arrangement shown in Fig. 8. The second part 12 of the potting is made in place in the cell, using the refractory lining of the sole as the mold serves. The third part 13 is of course carried out on the spot. Fig. 10 shows an assembly scheme of a cathode part for aluminum furnaces with a potting of the type shown in Fig. 6. Weld the melt sections 11, 12, 13 of the blocks at the joints in a sufficient manner.

It should be noted that the successive pouring operations from each other by a sufficient Period of time are separated so that the arrangement blocks-rails at a temperature in remains close to the ambient temperature. However, at the same time at the construction site we succeeded Casting parts 11 and 12, with part 12 a shape is used.

The method described above is for potting the power outlet or power entry rails suitable in carbon blocks, the dimensions of which do not exceed 600 mm.

For a long time it was avoided, with the help of cast iron or bronze, the conductor rails in the bottom of the crucible of cells for molten electrolysis or of electrometallurgical Pour the furnace-forming carbon blocks as soon as the length of the encapsulation is an order of magnitude exceeded by 500 to 600 mm.

The first attempts had led to many failures as the blocks split apart or broken and become unusable and, on the other hand, very expensive due to their dimensions was.

The above operation has allowed horizontal rails to be poured with certainty long blocks and bases of crucibles with the same properties in terms of service life and voltage drop, like those obtained with shorter blocks.

Indeed, it has been found that previous failures resulted from underestimating the precautionary measures originated, which one has to take, to avoid the harmful influence of thermal shock on the blocks and the expansions or contractions of the rail or melt to reduce.

It has been shown to reduce the stresses thus created in the blocks It is advisable to: pour the pouring in sections iao; a free space the size of Provide a width of 2 to 3 cm between the sections; these sections at certain time intervals and pour in a certain order; to regulate the heat dissipation; the side walls of the Recesses for the power outlet or power

Entrance rails have a regular profile and pretty to give smooth walls.

In the following, the pouring of a block of 1500 X soo X 500 mm is given as an example (Fig. 9).

All preparatory work for pouring is the same as for the one mentioned at the beginning Procedure: preheating the block, cleaning the rail and using a melt with certain Properties.

The block 4 is turned over so that the groove 7 is on top, and after the centering of the rail 5, the space in which the melt is to be poured is divided into three sections by suitable means. This division into three sections with expansion joints 14 allows the heat transfer from one casting to the other to be delayed and gives the melt the opportunity to expand when it is brought to a temperature of the order of magnitude of 900 ^° C. during operation.

Each of the pouring sections is poured separately with a time difference of several hours, so that the heat is supplied by the liquid melt itself three times, which is good for the behavior of the carbon block and the expansion of the rail is beneficial.

The order in which it is poured is not indifferent; it has been shown to be more beneficial is to be seen, first of all, the pouring of the middle part 15 is carried out. Because it is It is clear that the heat exchange and the expansion stresses are so carefully balanced will.

As soon as the metal has solidified, one destroys the intermediate parts that separate the cast parts from one another to facilitate the cooling, which can be accelerated by going through allows a gentle stream of air to flow through the space thus exposed.

Allow about an hour to pass, then it is advantageous to cover the To protect not yet poured sections, so that they slowly heat up in the mass.

Some time later you complete the protection of the carbon block against too rapid cooling, by covering the part that is still open. These precautions are only available by desire determined, at the moment when you proceed to pour the second section, a warm block, d. H. to have a block with a temperature between 40 and 80 ° C. So you are sure that none moisture from condensation is present, and one comes to the thermal Shock and the internal tension that arise from the next work step a little earlier.

If the length of the block has the presence

of four sections, it is advisable to always put the middle section first Pour sections so that never a significant section of the rail, e.g. B. 40 to '' 50 cm, between two castings that have already been carried out or between two individual castings, one of which is just made remains free. For the sake of expansion, this is to avoid the latter way of working.

In terms of time, it is advantageous to have at least 12 hours and possibly 24 hours between to allow the execution of the individual casting sections to elapse.

It is therefore advantageous not to cast the two ends at the same time.

In general it can be said that a too hasty casting of the individual elements, even if it is exceptionally can give a good result, offers no guarantee and becomes a significant one Rejects, which should normally be zero.

One last, less important, precaution can be mentioned: It is beneficial that the profile of the side surfaces of the groove 7 in the block is regular and that the surfaces are fairly smooth are so that they can easily displace the masses of the solidified or solidified Do not offer any harmful resistance to metal.

If the above rules are observed, the pressed carbon blocks are after the Potting of the power outlet or power entry rails with the help of cast metal and intact without any crack. In this way, a voltage drop is obtained in the lower part of the crucible which, if the The crucible is new, on the order of 0.25 volts for a current density of about 0.5 amps per square centimeter in the carbon blocks. The service life of this lower part of the crucible has been reached 4 years and even 5 years, whereby the voltage drop is then on the order of 0.35 volts and at most 0.40 volts.

The certainty that the blocks will be completely intact after the rails have been cast is a given nor, the voltage drop at the junction of the current inlet or outlet rails with to improve the carbon blocks by taking advantage of the contraction of the metal that causes the Block clasped as it cools, which reduces the voltage drop to 0.15 volts, as it continues indicated above (Fig. 5, 6, 7).

The passage of current through the lower part of the crucible of electrolytic cells, which are based on the in the in the manner described in the preceding paragraphs, causes a voltage drop of 0.15 to 0.25 volts. The Joule heat developed is insufficient to contribute to the bottom of the crucible In the absence of thermal protection, to keep it at its operating temperature. It is therefore absolutely necessary under the bottom and on the sides of the crucible of the electrolytic cell layers of refractory Provide heat protection bricks, the thickness of which depends on the value of the voltage drop in the lower iao Part of the crucible depends. As an example it should be stated that with a voltage drop of 0.15 volts Good results are obtained by placing a 50 cm layer of refractory material under the bottom of the crucible Arranges stones, under which there are 40 cm insulating stones. On the sides of the crucible sways

the thickness of the refractory layer from top to bottom between 15 and 40 cm.

With a voltage drop of 0.25 to 0.30 volts

one can be content with placing a 20 cm layer of refractory under the bottom of the crucible To arrange stones, over which 13 cm insulating stones are provided.

Claims (12)

PATENT CLAIMS: i. Process for the manufacture of the lower part of the crucible of cells for molten liquid Electrolysis, at. which this lower part by previously fired carbon blocks is formed, the electrical connection of which with the metallic current outlet or current inlet rails is achieved by means of a cast metal, characterized in that there is electrical contact between the the lining of the bottom of the cell forming blocks _ao (4) made of pressed carbon and the metal rails for supplying power to these blocks by means of a molten metal which has a melting temperature of over 100 ° C and, after solidification, is practically free of components which could undergo a conversion associated with an increase in volume; if they are kept at a temperature of 900 ^{° C. for a longer period of time.} 2. Cell for smelting electrolysis, manufactured according to claim 1, characterized in that the molten metal is made of copper, bronze or consists of cast iron practically free of sulfur and bound carbon. 3. Cell for the smelting electrolysis, manufactured according to claim 1, characterized in that the cast iron melt has the following composition: Carbon ... about 3% Silicon 2.5 to 3% Phosphorus .... 1 to 1.5% / ₀
Manganese ..... less than 0,5 ° / o
Sulfur ..... less than 0,05 ° / o
Iron rest 4. The method according to claim 1, characterized in that that the metallic current outlet or current inlet rails and the carbon blocks (4) are heated before pouring be so. that they are free from moisture. 5. Cell for melting electrolysis, manufactured. . according to claim 1 or 4, characterized in that that the metal rails are as straight as possible (alignment) and free from twisting around its axis (warping). 6. The method according to claim 1, characterized in that the temperature of the melt is kept during the casting of the rails in the carbon blocks between 1200 and 1300 ⁰ C, wherein the jet of the liquid metal must not hit the rail directly, but during the casting is moved along the space between the carbon blocks and the metal rail. 7. The method according to claim 1, characterized in that that during the casting of the molten metal, and in any case immediately afterwards, the metal rails and the carbon blocks are freed from anything that their expansion can hinder and delay their cooling. 8. The method according to claim 1, characterized in that that when pouring the same rail in several carbon blocks, the length of which does not exceed 500 to 600 mm, that Casting metal is poured onto the different blocks at the same time, avoiding that the melt can penetrate into the spaces between the blocks. 9. The method according to claim 1, characterized in that that when potting a rail in a single long carbon block the pouring length into several separate sections which are separated from each other by a free space of 2 to 3 cm, wherein a single section at a time is poured by standing at one of the mid-length of the block begins, for which one waits several hours before one the casting metal poured into the following section, so as to continue to the end, whereby one it avoids that at any point in time a not yet poured section between two already poured sections is located. 10. Cell for smelting electrolysis, produced according to one of claims 1, 4 or 6 to 9, characterized in that the casting metal is attached to the carbon blocks via a Groove of any shape protrudes, so that it forms an approximately ι to 2 cm thick cap, which against the lower horizontal surface of the block (Fig. 5). 11. Cell for smelting electrolysis, produced according to one of claims 1, 4 or 6 to 9, characterized in that the casting metal has a groove made in the carbon block any shape, covers the lower horizontal surface of the block and places it on the comprises four perpendicular surfaces at a height of the order of magnitude of 5 to 10 cm (Fig. 6 and 7). 12. The method according to any one of claims 1,4 or 6 to 9, characterized in that the bottom and the sides of the crucible of the cell are one Heat protection obtained from superimposed layers of refractory bricks and consists of insulating bricks, the thickness of the layers depending on the value of the voltage drop depends in the ground. 1 sheet of drawings Q 1334 8.