JPS6357509B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a filling joint material used when joining a metal conductive rod to prebaked carbon in a prebaked carbon anode used in an aluminum electrolytic furnace or the like. For example, in a pre-baked aluminum electrolytic furnace, 20 to 30 pre-baked carbon anodes (hereinafter simply referred to as anodes) are usually installed per electrolytic furnace, and as the electrolysis progresses, the anodes that are consumed are replaced one after another. It's getting old. The anode is made by bonding a metal conductive rod to pre-fired carbon. One of the bonding methods is to inject coal tar pitch and carbonaceous aggregate (hereinafter referred to as the joint) into the bonding gap between the two. A so-called joint filling method is known in which a joint material consisting of aggregate (hereinafter simply referred to as aggregate) is filled using an appropriate press cutting edge. However, the conventional joint filling method has two major drawbacks: the electrical resistance of the joint is large at low temperatures, and the suspension strength is reduced in a medium temperature range. In other words, since the coal tar pitch used as a binder is itself an electrical insulator, it is difficult for current to flow through the anode immediately after replacement due to the high electrical resistance at the joints, causing the temperature of the anode to rise and the pitch to be fired. , for 1 to 2 days until the electrical resistance of the same part decreases and the standard current flows, the current shared by the other anodes increases, and this is one of the causes of deterioration in the power consumption rate. In addition, as the temperature of the anode rises after replacement, the pitch softens and the suspension strength (the strength with which the metal conductive rod suspends its own weight of carbon) gradually decreases, especially when the
In the range of 300℃, the strength may be less than half of the strength at room temperature. In the operation of an aluminum electrolytic furnace, the anode is sometimes moved up and down to eliminate the anode effect or adjust the distance between the electrodes, but if such work was performed when the suspension strength was weak, there was a risk that the anode would fall off. The inventors of the present application believe that the above-mentioned drawbacks are due to the use of highly viscous coal tar pitch, and as a result of various studies on the type of binder, the viscosity of the aggregate, the combination of the two, etc., the present invention was completed. That is, the present invention provides a filled joint material with excellent properties for use in pre-baked anodes, in which a thermosetting resin liquid with a viscosity of 5 to 300 poise at room temperature is used as a binder liquid, and a joint width It is characterized by blending an aggregate containing 10 to 45% by weight (hereinafter simply referred to as %) of particles having a size of 1/3 or more. Joint using conventional coal tar pitch (usually used in combination with anthracene oil, etc.; the viscosity at room temperature is about 10 ⁴ to ^{10 6} poise when the ratio of pitch: anthracene oil is 7:4) is used as a binder. In order to prevent the formation of crosslinks between aggregate particles and improve filling properties, it is common for the maximum particle size of aggregate to be approximately 1/4 of the joint width or less. The small particle size was also a cause of high electrical resistance at the joints. In the present invention, the viscosity at room temperature is 5 to 5.
By using a thermosetting resin liquid with a low viscosity of 300 poise, the filling properties of the aggregate are improved, making it possible to use aggregate with a much larger particle size than before, and at the same time covering the surfaces of individual particles. As a result, the binder film in the joint becomes more easily destroyed, thereby reducing the electrical resistance of the joint at low temperatures. In addition, since the binder is mainly a thermosetting resin, the suspension strength increases as the temperature of the anode increases (approximately in the range of 100 to 300 degrees Celsius). The phenomenon of falling off almost completely disappears. In addition, if the suspension strength at room temperature is insufficient, the strength may be increased by using a known curing accelerator or by performing a preliminary heat treatment. The thermosetting resin used as a binder carbonizes at high temperatures, but it acts in the same way as in pitch, and the anode according to the present invention has a lower electrical resistance as the temperature increases. The viscosity of the binder liquid is 5 to 300 as mentioned above.
If it is less than 5 poise, the residual stress within the joint will be easily released after filling the joint material and the joint may become loose, resulting in an increase in electrical resistance or a decrease in suspension strength. happens. Moreover, if it is more than 300 poise, there is a high risk of crosslinking of aggregate particles, and on the other hand, the probability of breakage of the binder film is also low, making it impossible to obtain the desired effect. The particle size of the aggregate used in the present invention needs to be in the range of 10 to 45% of the joint width; if it is less than 10%, the electrical resistance of the joint will not be sufficiently reduced. If it exceeds 45%, the filling property becomes poor, resulting in an increase in electrical resistance and a decrease in suspension strength, which is not preferable. In addition, as aggregates, artificial graphite,
Natural graphite, petroleum coke, pitch coke, etc. can be used. The thermosetting resin used has an effect on the suspension strength at low to medium temperatures, and carbonizes at high temperatures and has an effect on the electrical resistance and suspension strength, similar to that in pitch, so the carbonization value of the binder liquid It is preferable that it is 25% or more. Furthermore, as the thermosetting resin, phenolic resins and furan resins, which themselves have a high carbonization value, can be advantageously used. Phenol resins are broadly classified into resol type and novolak type, but in the present invention, either type can be used, and alcohol, alcohol,
Examples include ethylene glycol. In the case of novolac type, it is desirable to use a curing agent such as hexamethylenetetramine. It is also possible to use a mixture of the above two types, but the combination may be determined by taking storage stability, heat curing speed, etc. into consideration. On the other hand, in the case of furan resin, a suitable binder liquid can be obtained by condensing furfuryl alcohol in the presence of maleic anhydride or phosphoric acid and adjusting the condensation reaction appropriately. The blending ratio of the binder liquid and the aggregate is preferably 6 to 15% for the binder liquid and 94 to 85% for the aggregate. If the binder liquid is less than 6%, the fluidity of the joint material will be poor, while if it is more than 15%, the fluidity will be too high, resulting in poor filling properties, lowering the suspension strength, and increasing electrical resistance. As explained above in detail, by using the filled joint material according to the present invention, it is possible to obtain a pre-baked carbon anode that has significantly improved conductivity at low temperatures and suspension strength at medium temperatures, which were problems in the past. can. Examples of the present invention are shown below. Example 1 A round groove with a diameter of 50 mm and a depth of 50 mm was provided in prebaked carbon, a mica plate was laid on the bottom, and a 70 mm long groove was placed in the center of the groove.
A conductive rod made of mild steel with a diameter of 30 mm was placed, and various joint fillers were filled into a 10 mm wide joint. For filling, use a press cutting edge with a thickness of 6 mm, divide it into 5 layers, and fill with 100
After filling at a pressure of Kg/cm ² , the electrical resistance of the joint at room temperature was measured. The composition and electrical resistance value of the joint material are shown in Table 1 along with those of the comparative example. The phenolic resins used were of novolac type 3 and resol type 1, and no curing agent was used. Further, the furan resin was synthesized using furfuryl alcohol as a raw material to obtain a desired viscosity by a conventional method, and only the carbonization value was measured. Although Comparative Example No. 6 in Table 1 is outside the scope of the present invention, its electrical resistivity value is equivalent to that of the Example, but when a joint material with this composition is used. If a shock is applied after filling, the electrical resistivity value will change.
There were cases where the number increased by 1.5 to 2 times.

[Table] Example 2 A round groove with a diameter of 58 mm and a depth of 50 mm is provided in prebaked carbon, a mica plate is laid on the bottom, and a 70 mm long groove is placed in the center of the groove.
A conductive rod made of mild steel with a diameter of 30 mm was placed, and a joint material having a composition shown in Table 2 was filled into a joint part with a width of 14 mm. Filling was carried out under the same conditions as in Example 1, except that a press cutting edge with a thickness of 7 mm was used, and the suspension strength and electrical resistance were measured at various temperatures. The results are summarized in Table 2 together with those of comparative examples. The type of phenolic resin used was the same as in Example 1, and no curing agent was used.

[Table] Example 3 Press one side of a square iron conductive rod into the square groove of pre-baked carbon in a 120KA aluminum electrolytic furnace, and use No. 1 joint filler from Example 2 at the joint between the other side and the square groove. Then, the mixture was divided into nine layers and filled under pressure at a pressure of 250 kg/cm ² at the press cutting edge. In the case of the joint material according to the present invention, the electrical resistance of the joint immediately after anode replacement is reduced by about half, and the time required to reach the standard current is 1/2 to 1/2 compared to the conventional pitch joint material. 3, and as a result, we were able to reduce the electricity consumption rate by 250kWh/t・Al. Moreover, no falling off of the anode occurred.

Claims (1)

[Claims] 1. Carbonaceous aggregate containing 10 to 45% by weight of particles with a particle size of 1/3 or more of the joint width is added to a thermosetting resin-containing binder liquid having a viscosity of 5 to 300 poise at room temperature. A filling joint material for pre-baked carbon anodes, which is characterized by being made of a pre-baked carbon anode. 2. The filling joint material for a prebaked carbon anode according to claim 1, wherein the binder liquid has a carbonization value of 25% or more. 3 6 to 15% by weight of binder liquid and carbonaceous aggregate
The filling joint material for a prebaked carbon anode according to claim 1 or 2, characterized in that the content is 94 to 85% by weight.