Device for assessing the internal state of moulded baked carbon blocks

Abstract

The invention relates to the field of the electrolytic production of aluminium, and more particularly to assessing the quality of moulded baked carbon blocks for the detection of internal flaws. The invention makes it possible to provide better quality inspection of the internal structure of a moulded baked carbon block and thereby detect internal flaws having the maximum permissible dimensions, using direct current and an additional group of probes on one plane of a moulded baked carbon block which are electrically connected to an opposite second plane of the moulded baked carbon block.

Description

[0001] DEVICE FOR ASSESSING THE INTERNAL CONDITION OF MOLDED BURNT CARBON BLOCKS

[0002] Field of technology

[0003] This technical solution relates to the field of electrolytic production of aluminum, namely, to the assessment of the internal state of molded fired carbon blocks in terms of finding internal defects and quality control.

[0004] The invention relates to the field of flaw detection (non-destructive testing) of a molded baked carbon block (anode block) and can be used in non-ferrous metallurgy, where electrically conductive electrodes are used.

[0005] State of the art

[0006] The assessment of the quality of the molded fired carbon block is understood as the presence of detected internal defects in the body of the molded fired carbon block, not obvious to an external observer, i.e., flaw detection of the molded fired carbon block. Defects occur during the manufacture of molded carbon blocks during pressing and processing in firing furnaces. In the operating mode, defects lead to a redistribution of current in the body of the molded fired carbon block, which reduces the productivity of the electrolysis process, as well as to an uneven consumption of the body of the molded fired carbon block, up to the need to replace the spent molded fired carbon block. Defects are mainly extended internal cracks or cavities with different geometric parameters. In addition, defects should include formations with a more or less high density relative to the body of the fired block with a uniform density.The molded fired carbon blocks are examined for internal defects at the testing stage, as a result of which a decision is made on the admissibility of installing the block in the electrolyzer. The use of molded fired carbon blocks of low quality, i.e. with internal defects, in the production process of electrolysis is not allowed, since it reduces the productivity of the electrolyzer and reduces the durability of the process equipment.

[0007] In the process of electrolytic production of liquid aluminum, the use of a large number of blocks formed on the basis of graphite material that has undergone special molding and firing stages is widespread. As a result of these operations, internal defects may appear, which generally reduce the efficiency of aluminum production.

[0008] There are known methods of assessing internal defects on direct or alternating current, acoustic, infrared 3D-tomography, etc. The most common in industrial application is the method and its variations of defectoscopy on direct current. Below is a short list of the most effective theoretical and experimental works in this direction with a critical analysis of the results achieved.

[0009] A device for measuring the electrical resistance of a baked anode is known, described in the article “NEW METHOD FOR REPRESENTATIVE MEASUREMENT OF ANODE”

[0010] ELECTRICALRESISTANCE) / / Light Metals 2012, p. 1299-1302. It is proposed to use a group of probes electrically connected to the body of the anode block and to monitor internal currents. In this proposal, the probes are placed only on one side of the anode block, which is the main drawback, since only part of the anode block body is monitored, so the proposal is of little use in a continuous production process. According to the non-destructive flaw detection method according to patent RU 2686570, published on 04 / 29 / 2019, at least a pair of electrically conductive contacts are placed on the outer surfaces of the anode being flaw detected, passing a given value of direct electric current through the anode, at least one sensor is placed near the outer surface of the anode being flaw detected, and the amplitude and direction of the magnetic field strength or induction vectors are measured. A significant drawback is the incomplete flaw detection of the anode block body.Therefore, the use of this solution in industrial production conditions is unlikely.

[0011] From the patent US 3735253, published 22.05.1973, a method and device for measuring the electrical resistance of a carbon electrode - anode block are known. The device includes a plurality of sensors for measuring current and voltage by electrical contact with the surface of the electrode over a wide area. The current flows through the electrode along a plurality of paths between the conductive means and a plurality of sensors, which are placed in a place of the anode block remote from the surface. A source of direct current voltage is connected to the anode block. The method ensures measuring the ohmic resistance in each of the plurality of paths of current flow through the body of the anode block. But the assessment of possible defects is not provided.

[0012] The closest to the proposed technical solution (prototype) is a non-destructive testing device for assessing internal defects based on electromagnetic technology according to patent US 7123004, published on 17.10.2006, also described in the article "Assessment of the quality of the baked anode of an aluminum electrolyzer and methods for its diagnostics", "Non-ferrous Metals" No. 1, 2017, pp. 33-38. The prototype installation contains an excitation current generator, which enters the body of the baked anode block using current leads, several current leads and current and voltage measuring sensors, a group of conductive probes located at a distance from each other in electrical contact with the surface of the anode block. Increased sensitivity of detection of internal defects is ensured by local heating of the front surface of the anode block.Local heating / cooling of a part of the anode block is a rather labor-intensive process and therefore this method has no prospects for industrial use; in addition, the accuracy of flaw detection is not high enough and only very large structural discrepancies are detected.

[0013] Disclosure of invention

[0014] The objective of the proposed invention and the technical result is to improve the quality of monitoring the internal state of a molded fired carbon block (anode block) based on the use of an exciting direct current in order to detect possible internal defects over the maximum volume of the body of the molded fired carbon block.

[0015] The problem is solved and the result is achieved due to the fact that the device for assessing the internal state of molded fired carbon blocks (1) contains an excitation current generator (2) electrically connected to the molded fired carbon block (1) subjected to flaw detection, a first group of probes (3) adjacent to the body of the molded fired carbon block on one side (first plane), and a first switch (4), the information inputs of which are connected to the outputs of the first group of probes.According to the proposed invention, in order to increase the accuracy of flaw detection, the device is provided with a second group of probes (3') electrically connected to the second long vertical plane of the molded baked carbon block (1), a second switch (4'), the information inputs of which are connected to the outputs of the second group of probes (3'), two analog-to-digital converters (5, 5'), the information input of the first of which is connected to the output of the first switch (4), and the information input of the second analog-to-digital converter is connected to the output of the second switch (4'), a computing and indicator unit (6), the information inputs of which are connected to the corresponding outputs of the first (5) and second (5') analog-to-digital converters, a control unit (7), the control outputs of which are connected to the corresponding control inputs of the first and second switches and the control inputs of the first and second analog-to-digital converters.The first plane is defined according to the length, i.e. the longest plane or side is selected. The second plane or side is opposite to the first plane or side.

[0016] The combination of the listed differences allows to improve the quality of control of the internal structure of the molded fired carbon block, thus determining internal defects with maximum permissible dimensions, using direct current and an additional group of probes of one plane of the molded fired carbon block, electrically connected to the second opposite plane.

[0017] Brief description of the drawings

[0018] Fig. 1 shows a structural diagram of the device according to the proposed technical solution.

[0019] Fig. 2 shows an example of the placement of receiving probes on the left (according to the drawing in Fig. 1) plane - the face of the molded fired carbon block.

[0020] Fig. 3 shows a conventional graph of currents in the body of a molded baked carbon block (anode block).

[0021] Implementation of the invention

[0022] The molded fired carbon block (1) is usually made in the form of a parallelogram with two long vertical side faces - planes - and two narrow vertical (end) planes - faces. The long vertical side planes are used in the proposed technical solution for placing probes. Excitation current generator (2) 1 в03b generates a direct current of a significant magnitude (up to 200 or more Amperes) at a sufficiently low voltage (units of Volts). The working current enters the center of the narrow side face of the molded baked carbon block (1) from the positive pole of the excitation current generator. The working current passes the body of the molded baked carbon block, and the electric circuit is closed at the negative pole of the excitation current generator (2). In addition, due to the theoretically assumed homogeneity of the material of the Molded baked carbon block, the current in it spreads along multiple paths from the "current input" point to points on the faces of the molded baked carbon block, in which conductive probes (3, 3') are installed in advance. The probe (3, 3') is a converter of the value of a part of the excitation current flowing along one of the possible routes, into a direct voltage, which is hereinafter called informative.

[0023] The probes on the left side of the molded baked carbon block (Fig. 1 and Fig. 2) are designated Ki, on the opposite side - Nj, where i£ (i0 ... imax) and j£ (j0 ...jmax). The physical distance between the location of the probes Ni and Kj determines the accuracy of the defect coordinates. In Fig. 1, the probes from Kg to Kshchax and from N2 to Nmax, as well as the corresponding inputs of switches 1 and 2, are shown by a dotted line-ellipsis.

[0024] Fig. 2 shows a conventional left (according to the drawing in Fig. 1) vertical long side face of the molded baked carbon block with an arbitrary arrangement of probes. The current lead "current input" in Fig. 2 connects the molded baked carbon block to the positive pole of the excitation current generator. The current lead "current output" in Fig. 2 connects the molded baked carbon block to the negative pole of the excitation current generator in Fig. 1. Fig. 2 shows the arrangement of eight probes on a long side plane. The distance between the probes, including between the probe layers, and the number of probes determine the size of the examined volume of the molded baked carbon block. The minimum distance between the probes determines the resolution by the size of the defect being detected. If the probes are placed close together, this will ensure the maximum volume under study and, accordingly, the detection of defects in the body of the molded baked carbon block (anode block) and the determination of their coordinates.

[0025] Each probe (3, 3') on both sides of the molded fired carbon block has a constant and stable electrical contact with the body of the block (1), for example, due to mechanical pressure.

[0026] The informative voltages taken from the probes (the left side of the block (1) in Fig. 1) are converted to digital form in the analog-to-digital converter (5) ADC1. The sequence of connecting the informative voltages from the probes of the left side of the molded baked carbon block to the ADC1 in Fig. 1 is provided by the switch (4). Similarly, the informative voltages of the Probes of the right side of the block (1) are processed by the analog-to-digital converter (5') ADC2 using the switch (4').

[0027] The ADC1 and ADC2 blocks are triggered by pulses from the corresponding outputs of the control block (7). The control pulses may coincide in time of appearance or follow an individual period. In any case, the implementation of the control program located in the computing and indicator block, which receives digital readings of the informative voltages from the outputs of the ADC and ADC2, provides hardware functions.

[0028] The first function of the computing-indicating unit is software processing of accumulated measurement results with output of flaw detection results to the indicator panel, which is part of the computing-indicating unit. The second function of the computing-indicating unit is generation of commands for the control unit, which converts commands into sequences of electrical signals for controlling the functions of the switches (4, 4'), as well as the ACS and ADC2. It is possible to control the launch of the ACS and ADC2 units in automatic mode or under the control of an operator, whose workplace is located in front of the indicator panel of the computing-indicating unit.

[0029] The arrangement of the probes on both sides of the molded baked carbon block allows for various combinations of readings (samples of informative voltages) from the Kj and Ni probes. One of the options may be the following.

[0030] Collection of samples of informative voltages, i.e. measurements are performed in the order of enumeration of probes Kj with a fixed value of the location of the probe opposite the plane of the block Ni (or vice versa):

[0031] 10 e (jo ...jmax)

[0032] 11 G jo ...jmax) etc.

[0033] In the first cycle io = jo =1 •

[0034] The probes are selected during the measurement process until the measurement procedures are completed upon reaching the value i niax .

[0035] In each measurement, the values ​​of the informative voltages Ui and Uj, generated by the corresponding probes Ki and Nj, are estimated based on Ohm's law using the formulas:

[0036] Ui = Ri li + AUi

[0037] Uj = Rj Ij + AUj, where Ri (Rj) is the ohmic resistance of the material of the molded baked carbon block (anode block) under normal conditions, i.e. in the absence of a defect, in the section from the input of the exciting current into the molded baked carbon block to the probe with number i, respectively j. AUi (AUj) is the interference component caused by the internal electromagnetic environment of the shop.

[0038] It is obvious that in the absence of interference, absence of defects and homogeneity of the material of the molded fired carbon block, which at i = j ensures Ri = Rj, the equality Ui = Uj will be fulfilled.

[0039] Therefore, the sign of the absence of a defect is the proximity of the difference to zero.

[0040] Ui - Uj = O

[0041] If this condition is not met, it means that there is a defect on one of the paths of the exciting current. Fig. 3 schematically shows the paths of the currents from the input point 1 ВОЗb to the corresponding probes Ki, K2 and N1, N2. The defect in Fig. 3 is designated by the letter D. The condition of approximate equality of Ui and Uj in the absence of a defect is valid only for i=j, since the path of the current is the same. As can be seen, the one-sided placement of the probes according to the prototype (Fig. 3) allows, in the simplest case, to detect a defect only in one half of the molded baked carbon block relative to the conditional line of symmetry from input 1 ВОЗ b into the body of the molded fired carbon block before exiting. This is the main drawback of the prototype. According to the proposed technical solution, the defect is detected at i=j, but with inequality of Ui and Uj. If it is necessary to specify in which of the above-mentioned halves the defect is, then it is possible to use the known path length (since the probes are located in pre-known positions) and the specific ohmic resistance of the material of the molded fired carbon block body.

[0042] In the proposed technical solution, the voltage value is measured in two stages. In the first of them, the exciting current 1 ВОЗ b = 0- This operating mode allows to record the internal electromagnetic interference environment of the shop, which distorts the result of the assessment of the internal state of the molded fired carbon block. The interference components AUi, AUj are measured by pairs of probes Ki and Nj with enumeration in the order specified above. The measured interference components are stored in the memory of the computing and indicator unit in the form of a matrix Ml.

[0043] In the second stage, work is carried out at the nominal excitation current 1 ВО zb- After the formation of the matrix M2 with a nominal 1 ВО zb the working matrix M3(i, j) = M2(i, j) - Ml(i, j) is formed (with identical indices i, j). This reduces the influence of interference components on the diagnostic result of the molded fired carbon block.

[0044] Thus, by eliminating the inevitable intra-shop electromagnetic interference and using the second group of probes placed on the opposite side of the vertical plane of the molded fired carbon block relative to the placement of the first group of probes, an increase in the accuracy of flaw detection of molded fired carbon blocks is achieved.

[0045] The current in the FOUB body (formed baked carbon block) is distributed along multiple paths, since the probes are located on the FOUB surface, the probe registers only part of the flowing current. When registering the current, the voltage is measured, which is considered informative for further quality assessment.

[0046] The scope of legal protection is claimed in relation to a device for assessing the internal state of shaped fired carbon blocks (1), comprising an excitation current generator (2), electrically connected to the shaped fired carbon block (1) subjected to flaw detection, a first group of probes (3), adjacent to the selected first long vertical plane of the shaped fired carbon block on one side, and a first switch (4), the information inputs of which are connected to the outputs of the first group of probes (3).In this case, the device is additionally provided with a second group of probes (3') electrically connected to the selected second long vertical plane of the molded baked carbon block (1), a second switch (4'), the information inputs of which are connected to the outputs of the second group of probes (3'), two analog-to-digital converters (5, 5'), the information input of the first of which is connected to the output of the first switch (4), and the information input of the second analog-to-digital converter (5') is connected to the output of the second switch (4'), a computing and indicator unit (6), the information inputs of which are connected to the corresponding outputs of the first (5) and second (5') analog-to-digital converters, a control unit (7), the control outputs of which are connected to the corresponding control inputs of the first (4) and second (4') switches and the control inputs of the first and second analog-to-digital converters (5, 5').The excitation current generator (2) forms a direct current of a significant magnitude of about 200 A and higher at a low voltage of up to units of V, the working current enters the center of the narrow side face of the molded baked carbon block (1) from the positive pole of the excitation current generator, passes the body of the molded baked carbon block (1), and the electric circuit closes on the negative pole of the excitation current generator (2), wherein the current is distributed along a plurality of paths from the "current input" point to the points on the faces of the molded baked carbon block (1), in which conductive probes (3, 3') are installed in advance. Each probe (3, 3') is a converter of the value of a part of the excitation current flowing along one of the possible routes, into a direct voltage, which is taken as informative.The current lead "current input" connects the molded baked carbon block (1) to the positive pole of the excitation current generator (2), the current lead "current output" connects the molded baked carbon block (1) to the negative pole of the excitation current generator (2). The distance between the probes (3, 3') and the number of probes (3, 3') are determined based on the size of the investigated volume of the molded baked carbon block (1), wherein each probe (3, 3') has a constant and stable electrical contact with the body of the block (1). The informative voltages taken from the probes (3, 3') are converted to digital form in the analog-to-digital converters (5, 5') ADC1, ADC2, respectively, while the sequence of connecting the informative voltages from the probes is ensured by the switches (4, 4'), the ADC1 and ADC2 blocks are triggered by pulses from the corresponding outputs of the control unit (7), the control pulses can coincide in time of appearance or follow an individual period.The shaped fired carbon block (1) is preferably made in the form of a parallelogram with two lateral long vertical planes, which are used to accommodate the probes (3, 3').

Claims

CLAUSE OF INVENTION 1. A device for assessing the internal state of molded fired carbon blocks (1) comprising an excitation current generator (2) electrically connected to the molded fired carbon block (1) subjected to flaw detection, a first group of probes (3) adjacent to a selected first long vertical plane of the molded fired carbon block on one side, and a first switch (4) whose information inputs are connected to the outputs of the first group of probes (3), characterized in that the device is additionally provided with a second group of probes (3') electrically connected to the selected second long vertical plane of the molded fired carbon block (1), a second switch (4') whose information inputs are connected to the outputs of the second group of probes (3'), two analog-to-digital converters (5, 5'), the information input of the first of which is connected to the output of the first switch (4),and the information input of the second analog-to-digital converter (5') is connected to the output of the second switch (4'), the computing and indicator unit (6), the information inputs of which are connected to the corresponding outputs of the first (5) and second (5') analog-to-digital converters, the control unit (7), the control outputs of which are connected to the corresponding control inputs of the first (4) and second (4') switches and the control inputs of the first and second analog-to-digital converters (5, 5')., 2. The device according to item 1, in which the excitation current generator (2) generates a direct current of significant magnitude of the order of 200 A and higher at a low voltage of up to units of V, the working current enters the center of the narrow side face of the molded baked carbon block (1) from the positive pole of the excitation current generator, passes through the body of the molded baked carbon block (1), and the electrical circuit is closed on the negative pole of the excitation current generator (2), and the current is distributed along multiple paths from the “current input” point to points on the edges of the molded fired carbon block (1), in which conductive probes (3, 3') are installed in advance.

3. The device according to item 1, in which each probe (3, 3') is a converter of the value of a portion of the excitation current flowing along one of the possible paths into a constant voltage, which is taken as informative.

4. The device according to claim 1, wherein the current lead “current input” connects the molded baked carbon block (1) to the positive pole of the excitation current generator (2), the current lead “current output” connects the molded baked carbon block (1) to the negative pole of the excitation current generator (2).

5. The device according to item 1, in which the distance between the probes (3, 3') and the number of probes (3, 3') are determined based on the size of the investigated volume of the molded fired carbon block (1), wherein each probe (3, 3') has constant and stable electrical contact with the body of the block (1).

6. The device according to item 3, in which the informative voltages taken from the probes (3, 3') are converted to digital form in the analog-to-digital converters (5, 5') ADC, ADC2, respectively, wherein the sequence of connecting the informative voltages from the probes is ensured by the switches (4, 4'), the ADC and ADC2 blocks are triggered by pulses from the corresponding outputs of the control unit (7), the control pulses can coincide in time of appearance or follow an individual period.

7. The device according to I. 1, in which the molded fired carbon block (1) is preferably made in the form of a parallelogram with two long vertical side planes, which are used to accommodate the probes (3, 3') -

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