CN1231615C - Continuous electrolytic pickling and descaling of carbon steel and stainless steel - Google Patents

Abstract

Continuous electrolytic process in neutral solution for pickling and descaling of carbon and stainless steels in the presence of electrolytic current indirect effects, said current being AC or DC current with a frequency lower than 3Hz, characterized in that the anodic treatment time and the cell current are selected according to the formula [ It ═ c + kI ], where I is the cross-cell current density; t is the anodic treatment time; c is the charge density constant fraction output for the direct oxide transition anodic reaction; k is the time constant for the calculation of the fraction of charge density proportional to the current density I, which is output for the indirect anodic reaction linked to the development of oxygen and the consequent acidification that takes place at the steel/electrolyte solution interface (carbon steel) or at the scale/electrolyte solution interface (stainless steel).

Description

Continuous electrolytic pickling and descaling of carbon and stainless steel

Description of the invention

The invention relates to continuous pickling of hot-rolled carbon steel strips by means of electrolysis in a neutral solution (pH range from 6.0 to 8.0). The invention further relates to the field of continuous descaling of stainless steel strips. The descaling is to remove surface oxides formed due to the influence of heat treatment, including hot rolling and annealing.

Compared with the traditional method carried out in the acid tank, the method of neutral electrolytic pickling and descaling basically has the following advantages: the pickling tank with no danger, no harm and no pollution is used; the residue is easy to handle and recycle; the material High surface quality after pickling.

As known, the main anodic reactions that can theoretically occur on the oxidized surface of hot-rolled carbon steel in solution can be systematically expressed by the following formula:

(0)

(1)

(2)

(3)

The first reaction (0) occurs only at low electrode potentials and is insignificant as a pickling reaction; when the current density value (I) exceeds a predetermined threshold (I ₀ ), the reaction is in fact can be ignore.

Therefore, when I>I ₀ , the second reaction (1) and the third reaction (2) occur on the steel surface covered by oxides. Reaction (1) acidifies the metal-scale interface, followed by reaction (2) which converts the scale into soluble compounds due to the presence of the acidic interface. Therefore, these two reactions (1) and (2) constitute the basic mechanism of electrolytic pickling in neutral solution.

When the surface oxide scale is almost completely dissolved, the anodic oxidation of the underlying metal according to the fourth reaction (3) begins to grow until the equilibrium in the passivation state is reached when the oxide scale is completely removed from the surface (pickling treatment ends) rate. Therefore, under the electrolytic pickling mechanism defined by the second reaction (1) and the third reaction (2), the fourth reaction (3) is insignificant.

Of course, in order to form the circuit, a suitable auxiliary electrode (also called a counter electrode) is used, the cathodic reaction on which can electrically neutralize the stock solution.

In this neutral solution electrolytic pickling method, the above-mentioned anodic reaction takes place under diffusion control. This means that the reaction rate depends on the diffusion of reactants and reaction products through the interface layer (flow), which in turn depends on the hydrodynamics on the steel surface. Apparently, an increase in solution vortex at the interface has the opposite effect on the rate of scale erosion, since it also increases the flow of hydrogen ions (H ⁺ ) leading to interface acidification [reaction (1)].

Furthermore, from electrolytic Faraday's law, which applies to both anodic dissolution and cathodic deposition methods, the amount of (changed) species obtained at the electrodes is directly proportional to the amount of charge passing through the electrolytic circuit. More specifically, the amount of charge required to acquire (change) a given amount of a substance is a constant: for example, for one equivalent of either substance, 1 farad, or 96500 coulombs, of charge is required. The above can be expressed as the following equation:

Q=I _tot *t=constant

Here, Q is the amount of charge (in coulombs, C), I _tot is the current used (in amperes, A), and t is the electrolysis time (in seconds, the potential, s).

This equation holds for any choice of I _tot or t, so that the same effect can be obtained by applying several different current values I _tot for corresponding electrolysis times.

As is known, due to the high sensitivity of chromium to oxidation, the surface scale of heat-treated stainless steel is significantly rich in chromium oxide, which is difficult to remove in the subsequent pickling treatment in acidic solution.

Usually, for ecological reasons, a mixture of strong mineral acids is used in the pickling of stainless steel, namely HNO ₃ /HF solution or more recently H ₂ SO ₄ /HF/H ₂ O ₂ solution.

However, prior to chemical pickling, descaling pretreatment is used in stainless steel manufacturing in order to speed up the entire process of removing scale from the surface. The purpose of this descaling step is to modify the oxide scale to facilitate its subsequent removal. The scale treatment method of hot-rolled stainless steel strip is mainly to use molten salt washing tank (thermochemical descaling) or electrolytic treatment.

One thermochemical method currently used for descaling is immersion in an oxidizing molten salt bath, which converts chromium oxide (or chromium/iron mixed oxides) into soluble hexavalent chromium compounds.

Electrolytic descaling is a common industrial process and can be carried out in acidic or neutral electrolytes, the anions are usually sulfate ions. Particularly attractive is the electrolytic descaling method performed in a neutral solution. In fact, this type of descaling effectively dissolves the scale and enables the removal of the scale to be separated directly from solution by precipitation without the need for treatment of the residue (eg by neutralization). In addition, the construction of such devices does not require particularly corrosion-resistant materials.

In a neutral solution, the main anodic reactions leading to the scale transformation of electrolytic descaling can be systematically expressed as follows:

(4)

(5)

To form the electrolytic circuit, an auxiliary electrode (or counter electrode) is used, on which the cathodic reaction enables electrical neutralization of the stock solution.

The above two anodic reactions produce acidification at the scale/solution interface. The acidification determines the further dissolution of the scale according to the following reaction:

(6)

( ) (7)

Of course, reaction (7) occurs only on austenitic stainless steels, since nickel as an alloy metal is not present in suitable amounts in ferritic stainless steels.

_A side effect of the dissolution of iron and nickel oxides is that a large amount of _Cr2O3 can undergo anodic transformation.

Therefore, the final neutral solution electrolytic descaling mechanism involves anodic oxidation of chromium and interfacial acidification, which determines the dissolution of iron oxide and, if present, nickel oxide.

When the surface oxide scale is nearly completely dissolved, the anodic oxidation of the underlying metal begins to increase until an equilibrium rate in the passivated state is reached according to the reaction shown below:

(8)

Here, Me denotes the Fe-Cr-Ni alloy; then, only reactions (1) and (5) take place, however, the latter at a much slower rate than the former.

In the neutral solution pickling descaling method, all the above reactions take place under diffusion control. This means that the reaction rate depends on the diffusion of reactants and reaction products through the interface layer, which in turn depends on the hydrodynamics on the steel surface. Apparently, an increase in solution vortex at the interface has an opposite effect on the rate of scale erosion, since it can also increase the flow of hydrogen ions (H ⁺ ) leading to interface acidification [reaction (1)].

Furthermore, from electrolytic Faraday's law, which applies to anodic dissolution and also to cathodic deposition methods, the amount of (changed) species obtained at the electrodes is proportional to the amount of charge passing through the electrolytic circuit. More specifically, the amount of charge required to obtain (change) a given quantity of a substance is a constant (eg, 1 farad, or 96500 coulombs, is required for one equivalent of any substance). Therefore, for the electrolytic transformation of a quantitative species, the corresponding current density is constant.

Q=I _tot *t=constant

Here, Q is the amount of charge (in coulombs, C), I _tot is the current used (in amperes, A), and t is the electrolysis time (in seconds, the potential, s). This equation holds for any choice of I _tot or t, so that the same effect can be obtained by applying several different current values I _tot for corresponding electrolysis times.

It has been found that, for neutral solution electrolytic pickling or descaling methods, the above classical electrolytic equation may lead to erroneous results. In fact, for a quantitative surface scale (assuming a constant scale composition and structure) and a defined process setting, it can be seen that in order to obtain a satisfactory pickling or descaling, i.e. complete transformation of the scale, For 1 ^dm2 of oxidized steel surface, an anodization of at least 15 A for 40 s (carbon steel) and 10 A (stainless steel) for 10 s is applied. Now, if one wishes to treat (pickling/descaling) this same material with another value of current density I (e.g. 60A/ ^dm2 to speed up the process), the new treatment time cannot be calculated using the classical electrolysis formula, because Operating at too high a current density, the resulting values will prove to be too short to ensure that the method is effective.

Therefore, the information derived from the classical electrolytic equations is not suitable for calculating the amount of charge applied to the electrolytic cell in the neutral electrolytic method.

Therefore, in this particular field, methods are required that provide the correct choice of anodization time and cell current in the presence of current indirect effects, and also allow the calculation of the corresponding descaling lines and equipment dimensions.

The present invention fulfills this need and further provides other advantages which will be apparent hereinafter.

In fact, the object of the present invention is a continuous electrolytic process for pickling and descaling of carbon and stainless steel in neutral solutions in the presence of electrolytic current indirect effects. The current is a DC current or an AC current with a frequency lower than 3 Hz, and is characterized in that the anodic treatment time and the electrolytic cell current are selected according to the following formula:

It=c+kI

here:

-I is the current density across the cell;

-t is the anodizing time;

-c is the charge density constant part of the output for the direct oxide conversion anodic reaction; and

-k is the time constant used to calculate the portion of the charge density output proportional to the current density I (kI) for the indirect anodic reaction associated with oxygen development and consequently in carbon steel's steel/ Electrolyte solution interface, associated with acidification that occurs at the scale/solution interface of stainless steel.

A preferred neutral saline solution consists of sodium sulfate at a concentration of 0.5 to 2.5M and a temperature in the range of 30 to 100°C.

In particular, it was found in DC electrolysis that when the minimum amount of charge c is in the range of 200 to 1250C/dm ² (carbon steel) and 40 to 200C/dm ² (stainless steel) and the time constant k is in the range of 2s to 25s Ranges, preferably 2 to 11 s for carbon steel and 2 to 25 s for stainless steel, gave satisfactory results.

For carbon steel, the processing time is in the range of 7 to 50 s, and for stainless steel, the processing time is in the range of 2 to 45 s. Current densities range from 10 to 80A/dm ² (carbon steel) and 5 to 150A/dm ² (stainless steel).

According to theoretical considerations not published here, the unpredictable results according to the present invention can be explained by considering the mechanism of electrolytic pickling and its heterogeneity, and the different effects of current on the individual electrolytic pickling reactions. Thus, the increase in the rate of the electrochemical conversion reaction was found to be less than the increase proportional to the total cell current.

A practical consequence of this fact, as mentioned so far, is that the electrolytic process in neutral solutions cannot be controlled in terms of the constancy of the amount of charge delivered, which is usually the case in electrolytic processes that do not contain current indirect effect (acidification of the surface as a result). The choice of anodization time and cell current should take into account that the amount of charge increases as the applied current increases.

The conditions governing the neutral electrolysis method should also be observed in design-related pickling lines, which should ensure the efficacy of the method at different flow rates of the strip being processed.

The anodizing time depends on the line speed (v) and the total length of the electrodes (L) for anodizing the strip being treated. Therefore, the previously described equation for the amount of charge output by the neutral solution electrolysis method can be rewritten as follows:

I=c/(L/v-k)

Another object of the present invention is therefore the use of the above-mentioned electrolytic process, characterized in that by setting the width and flow rate of the strip, the total anode electrode length, and thus the associated continuous neutral electrolytic treatment line Length, to determine the output current selected according to the above method.

The electrolytic treatment of steel strip is usually carried out in electrolytic cells consisting of a series of electrodes connected to opposite poles of the power supply, optionally determining the sequence of anodic or cathodic polarization on the strip to be descaled. Although the descaling process requires only anodic polarization, the addition of the cathodic part brings the advantage that the electrochemical reaction takes place directly on the strip without the strip having to be directly connected to a power source; thus, the use of expensive conductive rollers can be avoided. Therefore, the total length (L) of the electrodes applying anodic polarization on the strip is given by the sum of the individual lengths (L _a ) of the individual electrode elements.

The slots can be deployed vertically or horizontally, depending on the convenience criteria of the equipment.

In addition, the neutral electrolysis process equation disclosed in the present invention shows that there is an electrolysis time (k) that is inactive to the process. This means that in the design of equipment for neutral solution electrolytic treatment of steel strip, it should be taken into account that the total anodic treatment time (t) is greater than k

t=L/v>k

In practice, the electrolytic descaling process is carried out in sequential sections with anodic and cathodic current pulses:

L=n*L _a

(where L _a is the length of each anodic current pulse and n is the number of current pulses), the frequency (f) of each anodic current pulse should be

f=v/L _a <*n/k

Here, the coefficient  is introduced to account for the total processing time (thus assuming a symmetrical cathodic current pulse)

For k _min =2s and n _max =12,

Available f _max <3hz

This frequency limit for neutral solution electrolytic pickling is compatible with the advanced reaction mechanism of the treatment method, implying electrochemical interfacial acidification to facilitate oxide dissolution. For hot-rolled carbon steel strip such as under predetermined industrial conditions (using a constant post-rolling cooling pattern), the resulting scale has a nearly constant composition and morphology, and the minimum charge c required for electrolytic pickling depends on The mechanical treatment of crushing the scale before pickling.

The electrolysis process in neutral solution according to the invention can also be carried out with an AC current with a frequency lower than 3 Hz, for suitable values of c' and k' the total treatment time and the current used are determined according to the following formula:

It=c'+k'Xt

Heretofore, the present invention has only been briefly described, and hereafter, to make its objects, features, advantages and application modes apparent, embodiments of the present invention are disclosed by means of the following examples and accompanying drawings.

Fig. 1 is a descaling schematic diagram of scale fraction P(t)/ _PT as a function of time, the initial scale is _PT1 and _PT2 , and _PT2 > _PT1 . The figure is combined with a descaling equation derived from experimental observations of mass loss during descaling.

Figure 2 refers to the situation where c=70C/dm ² , and shows four hyperbolic branches, from bottom to top, k is equal to 1, 2, 3 and 4s in turn, and has an asymptote I=0A/ dm ² and t=ks.

Example 1

A conventional low carbon steel, with hot rolled scale, mechanically pretreated with rolling induced crushing (approximately 2.5% elongation), was subjected to continuous electrolytic pickling in neutral solution according to the method of the present invention. For this type of scale, c = 490C/dm ² and k = 3.7s were found. Moreover, in order to enable the scale transformation reaction to occur, the current density I used should satisfy I>I ₀ , and I ₀ =10A/dm ² should be used.

To the used continuous neutral electrolytic pickling operation line of 1.5m wide strip, work under the stable state at 90m/min, when the roll starts and stops at 20m/min, according to the neutral electrolytic pickling equation according to the present invention The total anode electrode length (L) and thus the length of the pickling equipment are set according to the specified electrolytic cell current.

According to the equation considered, the current density (I) applied to the electrolytic pickling cell listed in column 3 of Table 1 is a function of the length of the anode electrode (L) and the variable operating line speed (V). function; column 4 is the charge density (Q) and column 5 is the total current output (I _tot ), which is calculated as the current density multiplied by the surface of the anode electrode. Clearly, at a steady state speed of 90 m/min, the charge density (Q) output for electrolytic pickling increases as the length of the anode electrode decreases. Likewise, the total current used (I _tot ) increases.

Table 1 v, (m/min) operating line speed L, (m) anode length I, (A/dm ² )I=490/(L/v-3.7) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 90 32 28 593 267 221 90 28 33 611 275 221 90 twenty four 40 637 287 221 90 20 51 678 305 221 90 16 70 750 338 221 20 16 11 531 53 49 20 8 twenty four 579 58 49

The current I _tot ° in column 6 is calculated according to the classical electrolytic law (I _tot °=I°*S=490*v/L*S). Obviously, regardless of the method of the present invention, when the operating line speed is the same, as the length of the equipment decreases, the size of the power supply current will be obviously insufficient to ensure complete pickling.

Furthermore, it can be deduced from Table 1 that operation at low speed (20 m/min) means that the total anode electrode length used cannot exceed 16 m, lest the condition I>I ₀ is not satisfied. This can be achieved by segmenting the electrodes and part of the power supply regardless of the total length of the anodes contained in the cell.

Example 2

A silicon steel (3% Si) for magnetic applications, with hot-rolled scale, mechanically pretreated by in-line shot peening, subjected to continuous neutral electrolytic pickling according to the method of the invention. Since the shot blasting machine removes a part of the scale, the complete removal of the scale is inversely proportional to the operating line speed, so it is found that for this material, when v=20m/min, c ₁ =525C/dm ² , when v=40m /min, c ₂ =680 C/dm ² , k=3.1 s in both cases, and, to enable the scale transformation reaction to take place, a current density of I > 15 A/dm ² is used.

To the used continuous neutral electrolytic pickling operation line of 1.2m wide strip, work at 40 and 60m/min, set the total The length of the anode electrode (L), and thus the length of the pickling equipment is set.

According to the equation considered, the current density (I) applied to the electrolytic pickling cell listed in Table 2 is a function of the length of the anode electrode (L) and the variable line speed (v), all other relevant The amounts are also listed in the table.

Table 2 v, (m/min) operating line speed L, (m) anode length I, (A/dm ² )I=c/(L/v-3.1) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 20 12 16 574 46 42 20 10 20 586 47 42 20 8 25 603 48 42 20 6 35 634 51 42 20 4 59 708 57 42 40 twenty four twenty one 744 119 109 40 20 25 758 121 109 40 16 33 781 125 109 40 14 38 798 128 109 40 12 46 821 131 109 40 10 57 857 137 109 40 8 76 917 147 109

Thus, it was confirmed that, at equal speeds, the charge density (Q) output for electrolytic pickling increases as the length of the anode electrode decreases. Likewise, the total current used (I _tot ) increases. When the speed is 20m/min, the actual anode length should not exceed 12m, so as to avoid the current density being too low (I<I ₀ ). From this it can be deduced that the pickling equipment considered for this material is conveniently dimensioned to have an anodic electrode length between 10-14 m.

However, also in this case, designing an electrolytic pickling plant according to classical electrolytic laws would lead to an underestimation of the power supply.

Example 3

Application of the method according to the invention to the descaling of ordinary hot-rolled steel pretreated by mechanical descaling in Example 1 (c=490C/dm ² , k=3.7s and I ₀ =10A/dm ² ) .

Operable speeds for pickling lines containing a total anode electrode length L = 24 m (strip width = 1.5 m) range from 60 to 120 m/min.

The current density (I) applied to the electrolytic pickling cell listed in Table 3 is a function of the length of the anode electrode (L) and the operating line speed (v). All other relevant quantities are also listed in Table 3.

table 3 v, (m/min) operating line speed L, (m) anode length I, (A/dm ² )I=490/(L/v-2.1) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 60 twenty four twenty four 579 174 147 70 twenty four 29 597 209 172 80 twenty four 34 617 247 196 90 twenty four 40 637 287 221 100 twenty four 46 659 330 245 110 twenty four 52 683 376 270 120 twenty four 59 706 425 294

Obviously, regardless of the disclosed invention, as the line speed increases, the magnitude of the supply current will be significantly insufficient to ensure complete pickling.

Example 4

The method according to the invention was applied to conventional hot-rolled steel pretreated for mechanical descaling in Example 1 (c=490C/dm ² , k=3.7s and I ₀ =10A/dm ² ).

The descaling equipment consists of 12 slots, each with a single anode length L _a = 2m, so that the total length L = 24m (strip width = 1.5m); the equipment should be able to operate in the speed range of 40 to 120m/min , according to two different process control logics: in one case (see Table 4a) the logic maximizes the power usage of the single power supply used (ie, the number of slots used is proportional to the line speed), and in the other In the case (see Table 4b), all slots used are constant (ie use a current density proportional to the operating line speed). The results obtained are listed in Table 4a and Table 4b below.

Table 4a v, (m/min) operating line speed Slot number n I, (A/dm ² )[I=490/(L/v-3)] Q, (C/dm ² )[Q=I*t] I _tot (kA)[I _tot ＝I*S] I _tot °(kA) 40 4 59 708 142 98 60 6 59 708 213 147 80 8 59 708 283 196 100 10 59 708 354 245 120 12 59 708 425 294

Table 4b v, (m/min) operating line speed Slot number n I, (A/dm ² )[I=490/(L/v-3)] Q, (C/dm ² )[Q=I*t] I _tot (kA)[I _tot ＝I*S] I _tot °(kA) 40 12 15 546 109 98 60 12 twenty four 579 174 147 80 12 34 617 247 196 100 12 46 659 330 245 120 12 59 708 425 294

The equations for continuous neutral electrolytic pickling in accordance with the present invention show that the two process control logics are not equivalent, since operating at the maximum number of cells used generally reduces the total pickling current required .

The difference between these two control logics cannot be understood from the classical electrolytic formula and would underestimate the need for pickling current.

Example 5

For cold-rolled stainless steel strip, a neutral electrolytic descaling equipment is inserted into a pickling-annealing combined operation line, the total anode electrode length L=4m and the strip width=1.25m used for operation, in order to meet the different thickness of stainless steel Depending on the need for consistent thermal cycling of the strip, processing speeds that can be used vary from 20 to 70 m/min.

Shown according to the descaling equation, the direct current density (I) of the electrolytic pickling tank is listed in the second column of table 5 under different operating line speeds (v); is the charge density (Q), and in column 4 is the total current to be output (I _tot ), which is calculated by multiplying the current density by the electrode surface:

table 5 Working line speed v, (m/min) I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 20 8 93 8 6 30 14 112 14 8 40 twenty three 140 twenty four 12 50 39 187 38 14 60 70 280 70 18 70 163 560 164 20

In column 5, the current I _tot ° is given by the classical laws of electrolysis (I _tot °=I°*S=70*v/L*S). Obviously, regardless of the findings according to the present invention, as the line speed increases, the magnitude of the supply current will already be significantly insufficient to ensure complete pickling.

Example 6

A neutral electrolytic descaling plant, operated in the same speed range (20-70m/min) as in Example 5, using a larger total electrode length, L = 5.12m (strip width = 1.25m). The operating parameters of the plant calculated according to the descaling equation of the present invention are listed in Table 6.

Compared with the situation in Example 5, according to the law of electrolysis, when the working line speed increases, the total current I _tot ° will remain the same as the situation in Example 5. In fact, at equal speeds, the current required for the descaling equation according to the invention is reduced relative to the previous example.

Table 6 Working line speed v, (m/min) I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 20 6 88 8 6 30 10 99 12 8 40 15 115 20 12 50 twenty two 137 28 14 60 33 169 42 18 70 50 221 64 20

However, also in this case, designing according to the known laws of electrolysis will lead to an underestimation of the power supply.

Example 7

For a neutral electrolytic descaling device, the total anode electrode length is equal to L=8m (strip width=1.25m) during operation, and the available processing speed is in the range of 60 to 120m/min. The operating parameters of the equipment calculated according to the descaling equation of the present invention are listed in Table 7.

Table 7 Working line speed v, (m/min) I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 60 14 112 28 18 70 18 124 36 20 80 twenty three 140 46 twenty four 90 30 160 60 26 100 39 187 78 30 110 51 224 102 32 120 70 280 140 36

This example also demonstrates that, for other operating line speeds, the magnitude of the supply current according to the classical laws of electrolysis will be clearly wrong.

Example 8

The neutral electrolytic descaling equipment consists of 4 tanks, the anode electrode length of each tank is L _a =2m, the total length L=8m (strip width=1.25m).

In Example 7 it has been observed that the current profile is a function of line speed. Now, assuming that the plant is capable of operating even with only 3 tanks (eg due to operational reasons, malfunctions, etc.), whereby L=6m, the descaling currents used are listed in Table 8.

Table 8 Working line speed v, (m/min) I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 50 17 120 26 14 60 twenty three 140 36 18 70 33 168 50 20 80 47 210 70 twenty four 90 70 280 106 26 100 117 420 176 30

The fact that operation with 3 cells, as the speed increases, causes an additional demand on the total current cannot be predicted by the classical laws of electrolysis.

Example 9

The neutral electrolytic descaling equipment consists of n=6 tanks, the length of a single anode is L _a =1m, and the total length L=6m (strip width=1.25m); in one case (see Table 9a), the process control The logic is that the power usage of each power supply is maximized (i.e., use the number of slots proportional to the line speed), or alternatively (see Table 9b) all slots are used constant (i.e., use the number of slots proportional to the line speed). proportional to the current density).

Table 9a Working line speed v, (m/min) Slot number n I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 10 1 23.0 13.8 5.7 2.9 20 2 23.0 13.8 11.5 5.9 30 3 23.0 13.8 17.2 8.7 40 4 23.0 13.8 23.0 11.7 50 5 23.0 13.8 28.7 14.7 60 6 23.0 13.8 34.5 17.5

Table 9b Working line speed v, (m/min) Slot number n I, (A/dm ² )I=70/(L/v-3) Q, (C/dm ² ) Q=I*t I _tot (kA)I _tot =I*S I _tot °(kA) 10 6 2.1 76 3.1 2.9 20 6 4.7 85 7.0 5.9 30 6 7.7 92 11.5 8.7 40 6 11.7 105 17.2 11.7 50 6 17.0 123 25.5 14.7 60 6 23.0 138 34.5 17.5

These two process control logics are not equivalent because the total descaling current required is generally reduced when operating at the maximum number of cells. Also in this example, the descaling current would still be underestimated according to the classical electrolysis laws.

In order to meet further possible needs, those skilled in the art can further improve and change the method described above, but all of these fall within the protection scope of the present invention defined in the appended claims.

Claims (8)

1. continuous electrolysis method in neutral solution, this method is used for carbon steel and stainless pickling and de-scaling, and there is a Faradaic current indirect effect, described electric current is AC or DC electric current, its frequency is lower than 3Hz, and anodizing time when wherein using required electrolytic cell currents and the electrolytic cell currents when adopting required treatment time are selected according to following formula:

It＝c+kI

Here:

-I strides electrolytic cell currents density;

-t is the anodizing time;

-c changes the electric density constant component that anodic reaction is exported for the direct oxidation thing;

-k is that the part (kI) of the electric density that is directly proportional with current density I is calculated and used the time constant, this electric density be for produce oxygen and on the steel/electrolyte solution interface of carbon steel or stainless oxide skin/solution interface, produce the indirect anodic reaction of acidifying thereupon and export

To each steel and each oxide skin, constant c and k are known,

For carbon steel, be the 7 anodizing times and 10 that arrive 50sec to arrive 80A/dm at scope ²Current density, the value of quantity of electric charge c from 200 to 1250C/dm ²Scope, and time constant k is from 2 to 11sec scope;

For stainless steel, be the 2 anodizing times and 5 that arrive 45sec to arrive 150A/dm at scope ²Current density, the value of quantity of electric charge c from 40 to 200C/dm ²Scope, and time constant k is from 2 to 25sec scope.

2. the continuous electrolysis method in neutral solution in the claim 1, this method is used for carbon steel and stainless pickling and de-scaling, and there is a Faradaic current indirect effect, described electric current is AC or DC electric current, its frequency is lower than 3Hz, wherein neutral solution is made up of sodium sulfate, and concentration is from 0.5 to 2.5M scope, and temperature is from 30 to 100 ℃ scope.

3. the application of one of any continuous electrolysis method in neutral solution of claim 1 to 2, this method is used for carbon steel pickling, and there is a Faradaic current indirect effect, described electric current is AC or DC electric current, frequency is lower than 3Hz, it is characterized in that, by setting width and the speed v and the electrolytic cell currents I of pickling band, according to following formula determine total anode electrode length and and then determine the length L of the continuous neutral electrolytic pickling service line of being correlated with:

I＝c/(L/v-k)

This formula is by replacing time t with ratio L/v, the rewriting of the formula in the claim 1 being obtained.

4. the application in the claim 3, wherein the technology controlling and process logic of Cai Yonging is, uses the number of the electrolyzer that is directly proportional with service line speed, and uses maximum available output.

5. the application in the claim 3, wherein the technology controlling and process logic of Cai Yonging is, the current density that constant use of all electrolyzers and use are directly proportional with service line speed.

6. the application of claim 1 or 2 the continuous electrolysis method in neutral solution, this method is used for stainless de-scaling, and there is a Faradaic current indirect effect, described electric current is AC or DC electric current, frequency is lower than 3Hz, it is characterized in that, treat the width of de-scaling band and speed v ' and electrolytic cell currents I ', determine total anode electrode length and and then determine the length L of relevant continuous electrolysis neutrality de-scaling service line according to following formula by setting ':

I’＝c’/(L’/v’-k’)

This formula is to obtain by using ratio L '/v ' to replace time t ', the formula in the claim 1 being rewritten.

7. the application in the claim 6, wherein the technology controlling and process logic of Cai Yonging is, uses the number of the electrolyzer that is directly proportional with service line speed, and uses maximum available output.

8. the application in the claim 7, wherein the technology controlling and process logic of Cai Yonging is, the current density that constant use of all electrolyzers and use are directly proportional with service line speed.