SU1696598A1 - Method of quality control of cathode section of aluminium electrolyzer - Google Patents

Abstract

The invention can be used to control the durability of cathode sections in aluminum electrolysis cells and to assess the influence of the quality of casting blooms with cast iron in the cathode sections. The purpose of the invention is to increase the reliability of detection of defects in the block. In the method of quality control of manufacturing the cathode sections of an aluminum electrolysis cell, by passing an electric current and measuring the contact electrical resistance at the interface of the coal block with the metal part of the section, the change of the contact electrical resistance between the coal block and the metal part of the cathode section is recorded during heating in the temperature range of 180-390 ° C and the occurrence of defects of cracks in the coal block is judged by the moment of transition from a decrease in electrical resistance to its increase. 2 Il. 2 tab.

Description

The invention relates to non-ferrous metallurgy and can be used to control the durability of cathode sections in aluminum electrolyzers and to assess the influence of the quality of casting blooms with iron in the cathode sections.

The purpose of the invention is to increase the reliability of detection of defects in the block.

FIG. 1 shows a scheme for controlling the cracking of cathode sections; in fig. 2 is a graph of the dependence of the electrical resistance (R) of the cathode section on the temperature (T) of its heating, represented by three curves: —A curve A shows the dependence of R-T at the contact block — iron casting; - curve B - R-T dependence in the block –blue contact (both curves show that block cracking was not observed during heating), - curve C gives the R – T dependence in contact with the block-blues in the event of cracks in the coal block.

This control scheme includes a registering device 1 connected by a current lead 2 to a coal block 3, a current lead 4 to a cast iron fill 5, a current lead 6 to a metal rod 7 (Blum) and a thermocouple 8 to a cast iron fill 5.

About- About Os

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When the cathode section is heated, consisting of coal block 3, bloom 7 and cast iron fill 5, bloom 7 increases in volume and, through cast iron fill 5, exerts pressure on the groove walls in the coal block 3. The thermal expansion coefficient of the coal block is significantly less than that of the steel block. Blum, therefore in case of violation of the technological regime, in the process of casting iron (for example, the composition of the iron is not maintained), thermal expansion of the blum can have a destructive effect on the coal block. In this case, most often at the corners of the groove of the coal block in which bloom is poured, cracks 9, the so-called whiskers, are formed.

To simplify the control circuit and the convenience of connecting the conductors, the potential can be removed not from the cast iron fill, but directly from the bloom, i.e. measure the contact resistance in the area of the coal block - bloom (Fig. 2, curve B). A change in the electrical resistivity of steel and cast iron during the heating process does not significantly affect the values of the contact electrical resistivity, so curves A and B are almost parallel to each other.

Example 1. In the process of testing the bottom section is placed in a heating furnace. A thermocouple 8 is installed in the cast iron core. Potential conductors (conductors 2.4 and b) are led out of the section from the furnace to the outside. The thermocouple and potential conductors were connected to the recording device 1. A direct current of 50 A was passed through the cathode section. The device records the heating temperature and the voltage drop in the contacting surfaces of the cathode section. Since the current in the circuit does not change, the change in the contact electrical resistance is judged by the change in voltage drop.

At the initial moment of crack formation, when the contact electrical resistivity begins to increase, no cracks were visually detected, and only later on during heating, when the material expands more strongly, is it possible to visually see the cracks.

The reliability of this method is confirmed by measurements on several sections when heated in a furnace.

 In tab. 1 shows the results of measurements on three sections. From tab. Figure 1 shows that, for each section, the temperature at which the cracks start to form is different, in general, the process of formation of cracks with the existing technology of casting the section with cast iron occurs in the temperature range 180-340 ° C, i.e. From the temperature at the end of the compensation of shrinkage dimensions of the metal to the temperature at which the elasticity of the metal decreases markedly, it becomes more plastic.

Consequently, up to a temperature of 180 ° C, cracks in the block do not occur, since in this gap the process of expansion

0 bloom, compensating for the shrinkage of cast iron fill. At temperatures above 340 ° C, no cracks in the block are also observed, as the metal begins to lose its elastic properties.

5 In table. Figure 1 indicates the temperature at which cracking begins in the coal block when the cathode section is heated. From the table it can be seen that the lowest temperature of cracking is 184 ° C, the highest 385 ° C.

When installing section 3, before casting with iron, the blums are preheated to 597 ° C. The table shows that the contact electrical resistance for this section decreases over the entire temperature range and no cracks were found in the coal block both during the heating process and during the cooling of the section.

Example 2. The method for controlling cracking was tested on industrial electrolyzers.

In the process of pouring a metal case for thermocouple poured into cast iron. In the coal block, cast iron fill and bloom, sockets were drilled in which the potential ends were fastened. The conductors were insulated with ceramic beads, protected by a metal tube.

Potential ends and thermocouple removed from the cathode casing on the gun and connected to the recording device. During the test period, the current in the cathode sections is determined by measuring the current distribution over the bloom. By the difference in the voltage 5 in the contacting surfaces and in the magnitude of the current, changes in the contact electrical resistivity are calculated. The data are summarized in table. 2. 4 cathode sections were measured on two experimental electrolyzers. Of

tab. 2 it can be seen that the temperature range of the beginning of destruction is approximately the same as when the sections are heated in the furnace, however, during firing on the metal, the destruction starts at higher temperatures than at

0 roasting on the electrolyte, since the speed on

heating sections on the metal is much lower

than when roasting on electrolyte.

In the examples, the characteristic

are the temperatures at which the contact electrical resistance is minimal. So when firing in a furnace at section 1 285 ° С, at section 2 196 ° С (Table 1) when firing on metal section 1 331 ° С, section- 2 337 ° when firing on electrolyte section 3 184 ° С, section 4 305 ° С (tab. 2).

The application of the method for monitoring the cathode section cracking allows one to make selective control of the quality of the filled sections, which makes it possible to choose the optimal mode of filling, which prevents the thermal destruction of the sections. This method makes it possible to monitor the integrity of the bottom of the start-up electrolysis cells, accurately determine the destroyed sections and take measures to prevent disconnection. The method makes it possible to assess the effects of firing and start-up conditions, the use of various carbon materials for installation, and

wash the features of the technological mode of operation of electrolyzers.

Claims (1)

Claims The method of controlling the quality of manufacturing a cathode section of an aluminum electrolysis cell by passing an electric current and measuring the contact electrical resistance at the interface of the coal block with the metal part of the section is characterized in that, in order to increase the reliability of detection of defects in the block, the change in contact electrical resistance between the carbon block and the metal part of the cathode section when heated in the temperature range of 180-390 ° С and the occurrence of cracks in the coal block is fixed according to the moment of transition from a decrease in electrical resistance to its increase. + 16 35 72 84 98 115 128 140 159 170 196 240 275 320 300 245 232 225 196 171 191 96 81 L7 L7 70 i§ 29 49 63 85 97 112. 13S 147 163 184 221 261 221 201 191 - 72 164 151 138 118 102 94 72 64 64 The temperature at which the occurrence of alarms occurs in blocks. 1 When mounting the cathode section, the blues are preheated before casting with iron. metal 1 electrolyte + 21 208 + 21,196 + 19,250 + 19,208 29 197 33 181 38 209 38,187 35,182 40 176 61 176 72 159 41 170 52 153 58, 152 61 T49 13910b 112 131 138 99 The temperature at which cracks appear in Spokes. When mounting the cathode section, the blums are preheated before the pig iron. Table 1 301, 342 369 400 "O 73 76 80 76 83 §§ 525 557 590 619 635 85 85 87 87 88 28 289 335 362 385 440 44 38 35 32 28 459 488 507 537 554 597 2Г 16 12 75 T 5 Table 3 6 7 four . 85 131 92 118 239 69 246 61 115 112 W 96 173 “5 J68 76 293 361 7481 with 305 45 370 58 225 82 231 54 440 99 445 64 273 31 280 31 F 112 512 75 331 24 W® 585 79 335 33 390 21 629 165 6C 80 Sh 42 441 29 712 5OT T t i ° c