CN101698224B - Method for dynamically controlling cooling water quantity for secondary cooling of continuous casting billets and electromagnetic stirrer - Google Patents

Abstract

The invention relates to the field of metal casting, in particular to a method for controlling the cooling water quantity for the secondary cooling of continuous casting billets and an electromagnetic stirrer in the continuous casting production process. The method has the main inventive concepts that a model for computing the ratio of the thickness of a solidified shell at the position of the electromagnetic stirrer to an un-solidified liquid phase is established so that in the continuous casting production process, when technological parameters are changed, the electromagnetic stirring parameters can be controlled dynamically by adjusting the cooling water quantity for the secondary cooling to obtain higher-quality continuous casting billets.

Description

The kinetic controlling equation method of the continuous casting billet two cold but water yields and magnetic stirrer

Technical field

The present invention relates to field of metal casting technology, particularly in the continuous casting production process to the kinetic controlling equation method of the continuous casting billet two cold but water yields and electromagnetic agitation, make that the effect of continuous casting two cold and electromagnetic agitation combination control is even more ideal, obtain the strand and the solidified structure of better internal soundness.

Background technology

For the internal soundness of improving continuous casting billet and the solidification structure that improves strand, as alleviate the center segregation of strand, increase the equiaxed zone ratio of strand etc.Therefore in continuous casting production process, different parts at conticaster is provided with electromagnetic mixing apparatus (magnetic stirrer), crystallizer electromagnetic mixing apparatus (MEMS) is comparatively typically arranged, two cold electromagnetic mixing apparatus (SEMS), solidification end electromagnetic agitation (FEMS), sometimes be that two or more electromagnetic mixing apparatus exists simultaneously, be used that its mixing effect is more obvious like this.Electromagnetic agitation is by the agitator coil is set different electric current and power frequency, thereby the molten steel that does not flow is produced to flow, quicken the solidification and heat transfer of molten steel, smash " front end " of the column crystal that has formed, in not solidifying liquid molten steel, form a large amount of solid particles, form the heterogeneous body forming core easily, increase the equiaxed zone ratio in the casting blank solidification tissue, reduce microcosmic and gross segregation.

The present electromagnetic agitation that continuous casting billet is implemented, its technology is electric current, the fixed-frequency of agitator coil, although continuous casting is produced its technological parameter of casting process and can be changed, variation as pulling rate, molten steel overheat, secondary cooling water amount, but the electric current and the frequency of agitator coil do not change, still adopt fixing mixing parametric that strand is implemented electromagnetic agitation, this will have influence on the mixing effect of strand.The producer of nearly all application electromagnetic agitation, (middle smelting continuous casting project technology Co., Ltd of domestic big designing institute, middle smelting capital engineering Co., Ltd, Zhongye Saidi Engineering Technology Co., Ltd, Xi'an Heavy Machinary Research Institute etc.) or offshore company's (VAI, C-MARK, Da Nieli etc.) designed its electromagnetic agitation mode of conticaster as mentioned above, do not change stirring parameter according to the variation of technological parameter, simultaneously not to the thickness of solidified slab shell in secondary of magnetic stirrer position and not the solidification liquid phase volume fraction control, exist the mixing effect instability, the in-and-out defective of slab quality.Its reason is because the variation of technological parameter, the volume that causes the thickness of solidified slab shell in secondary of (the agitator fixed-site that conticaster has been provided with) strand in the agitator position and do not solidify liquid phase changes, so the mixing parametric of magnetic stirrer also should be regulated accordingly; Even the technological parameter of continuous casting (pulling rate, molten steel overheat, secondary cooling water amount etc.) changes little in the production process in addition, also should guarantee the thickness of solidified slab shell in secondary of magnetic stirrer position and the solidification liquid phase ratio is constant or change seldom as far as possible, adopt fixing stirring parameter (stirring coil electric current, frequency) just can make strand obtain mixing effect preferably like this, mixing effect is also comparatively stable, satisfy each steel grade segregation requirement, solidified structure obtains satisfied equiaxed zone ratio.

Summary of the invention

Purpose of the present invention, be by collection technological parameter in the continuous casting production process, when changes in process parameters, by connecting the parameter of adjusting the two cold but water yields and magnetic stirrer, make that the effect of continuous casting two cold and electromagnetic agitation combination control is even more ideal, obtain the strand and the solidified structure of better internal soundness.

The method of the invention is as follows:

(1) gather technological parameter in the continuous casting production process, the parameter of collection comprises: pulling rate, and two cold-zone cooling water inflows, the crystallizer cooling water inflow is imported and exported water temperature difference, steel grade, molten steel overheat;

(2) monitor and calculate magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase in real time;

(3) during changes in process parameters, adjust the two cold but water yields, make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the setting value that the ratio of liquid phase approaches this position;

(4) when adjusting ratio that the two cold-zone water yields make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify liquid phase and equate with the setting value of this position, the electric current of magnetic stirrer and frequency need not adjustment;

(5) when adjusting ratio that the two cold-zone water yields can not make magnetic stirrer position thickness of solidified slab shell in secondary and not solidify liquid phase and equate with the setting value of this position, according to the agitator position thickness of solidified slab shell in secondary that calculates in real time and do not solidify the ratio of liquid phase, determine electric current and frequency that magnetic stirrer adopts.

In the technique scheme, step (1) is calculated magnetic stirrer position thickness of solidified slab shell in secondary and is not solidified the method for ratio of liquid phase as follows in real time:

(21) model of the solid rate of inner every of strand is calculated in foundation: $f_s(i,j)=\frac{T_l-T(i,j)}{T_l-T_s},$ Wherein T (i, j): be the temperature of strand inside mesh point, unit ℃; Tl: be liquidus temperature, ℃; Ts: be solidus temperature, ℃

(22) determine the node that solidifies of all solid rates of strand＞0.7;

(23) calculate thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase according to solidifying node.

In the above-mentioned steps, also adopted base trace model in age when calculating the solid rate of inner every of strand, that is: a section just is set and has followed the tracks of every certain-length on the continuous casting billet, each section has been write down rise time, elapsed-time standards and apart from information such as meniscus distances.When pulling rate was stablized, the rise time of each section was all identical, and is steady state value apart from the meniscus distance divided by elapsed-time standards in any position; When pulling rate changed, the rise time of section changed, and promptly when pulling rate changed, the temperature computation speed of moving down of each section was different.Therefore, described base trace model in age has reacted the variation of pulling rate.During promptly the model of every solid rate calculates in strand inside, considered the temperature T (i of inner certain mesh point of strand, j) the pulling rate factor in, magnetic stirrer position thickness of solidified slab shell in secondary reaches the actual value of the ratio that does not solidify liquid phase when making the result accurately reflect changes in process parameters.

In above-mentioned steps (3), (4), (5), the setting value that described magnetic stirrer position thickness of solidified slab shell in secondary reaches the ratio that does not solidify liquid phase is to determine by a large amount of field experiment.

In the technique scheme, the electric current that step (5) magnetic stirrer adopts and the adjustment of frequency are to establish by a large amount of field experiment.

The cooling water inflow that technique scheme is adjusted two cold-zones is that the PLC by the scene controls two cold-zone water valve apertures and realizes.

This method is by the control to the two cold but water yields, in casting process, can be in real time come the thickness of solidified slab shell in secondary at magnetic stirrer place and the ratio that do not solidify liquid phase are controlled according to changes in process parameters, the parameter of perhaps in good time change magnetic stirrer, make that the effect of continuous casting two cold and electromagnetic agitation combination control is even more ideal, obtain the strand and the solidified structure of better internal soundness.

Description of drawings

Fig. 1 is the schematic diagram of casting blank of continuous casting machine process of setting and magnetic stirrer.

Figure 2 shows that thickness of solidified slab shell in secondary reaches the computation model of the ratio that does not solidify liquid phase.

The specific embodiment

The continuous casting billet two cold but water yields of the present invention and electromagnetic agitation specifically comprise following implementation method:

(1) collection of technological parameter, the parameter of collection comprises: pulling rate, two cold-zone cooling water inflows, the crystallizer cooling water inflow is imported and exported water temperature difference, steel grade, molten steel overheat.Technological parameter is gathered by PLC, passes to 2 grades of computers after the collection and calculates and handle and show monitoring.

(2) monitor and calculate magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase in real time.Specifically be with the basic solution of solidification and heat transfer:

The solidification and heat transfer equation of setting up continuous casting billet according to the strand characteristics of heat transfer is as follows:

$\mathrm{\ρc}\frac{\∂T}{\∂t}=\frac{\∂}{\∂x}\left(\mathrm{\λ}\frac{\∂T}{\∂x}\right)+\frac{\∂}{\∂y}\left(\mathrm{\λ}\frac{\∂T}{\∂y}\right)---\left(1\right)$

Wherein:

λ: thermal conductivity factor, J/ (m ℃);

C: specific heat, J/ (kg ℃)

J·kg ^-1·℃ ^-1；

In solid-liquid two-phase region, there is following formula to set up

$C_{\mathrm{sl}}=\frac{(C_s+C_l)}{2}+\frac{L_f}{T_l-T_s}---\left(2\right)$

Lf: crystallization latent heat, J/kg;

T1, Ts: be respectively the solid-liquid phase line temperature, ℃;

Provide corresponding primary condition and boundary condition, as follows:

1) initial temperature: T=T _c(pouring temperature).

2) strand center: strand center line both sides are that symmetry is conducted heat $\frac{\∂T}{\∂x}=0---\left(3\right)$

3) casting billet surface:

Crystallizer: $q=A-B\sqrt{\mathrm{\τ}},---\left(4\right)$

Two cold-zones: q=h (T _S-T _W) (5)

Radiation area: $q=\mathrm{\ϵ\σ}(T_S^4-T_O^4)---\left(6\right)$

In the formula: q---heat flow density, kWm ^-2

H---heat transfer coefficient, kWm ^-2℃ ^-1

T _S, T _W, T _O---casting billet surface, cooling water and environment temperature, ℃;

σ---Boltzmann's constant, 5.67 * 10 ^-8KWm ^-2℃ ^-4

ε---radiation coefficient (blackness), this model gets 0.8.

The zone of finding the solution according to strand marks off computing grid, according to grid node above-mentioned equation (1) is carried out discretization to (6), can obtain strand temperature inside field, can calculate the solid rate of inner every of strand then by following formula,

$f_s(i,j)=\frac{T_l-T(i,j)}{T_l-T_s}---\left(7\right)$

Wherein, and T (i, j): be the temperature of strand inside mesh point, unit ℃.Ts, Tl: be respectively the solid-liquid phase line temperature, ℃;

Determine the node that solidifies of all solid rates of strand＞0.7 then; Calculate thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase according to solidifying node again.As shown in Figure 2, calculate the solid rate of inner every of strand after, such as 14 nodes are arranged on thickness or width, wherein 4 nodes (I, j, k on the thickness direction, l) solid rate is all greater than 0.7, then shell thickness is S (distance+k between S=j and i between distance+i and k and the distance between l), and the ratio that does not solidify part is (L-S)/L, also can be according to area ratio, area/the gross area that does not solidify part is then arranged, if square billet, symmetry promptly has: (L-S) ²/ L ²

The calculating of the solid rate that above-mentioned strand is inner every is if obtain more accurate numerical value, the also necessary influence of considering the pulling rate variation to this model.Because in computational process, equation (1) $\mathrm{\ρc}\frac{\∂T}{\∂t}=\frac{\∂}{\∂x}\left(\mathrm{\λ}\frac{\∂T}{\∂x}\right)+\frac{\∂}{\∂y}\left(\mathrm{\λ}\frac{\∂T}{\∂t}\right)$ Be subjected to influence that pulling rate changes very greatly, and then (i is the calculating of the solid rate model of inner every of the temperature of inner certain mesh point of strand and strand j), therefore must consider T (i, j) the pulling rate factor in to have influence on T.Therefore also adopted base trace model in age, promptly just tracked by a section every certain-length (as 100mm) on the continuous casting billet, each section has been write down rise time, elapsed-time standards and apart from information such as meniscus distances.When pulling rate was stablized, the rise time of each section was all identical, and is steady state value apart from the meniscus distance divided by elapsed-time standards in any position.When pulling rate changed, the rise time of section changed, and during the temperature computation of each section, the speed of moving down is different.Thereby the actual conditions when adopting this base trace model in age result of calculation accurately to reflect changes in process parameters.

(3) technological parameter of gathering according to step (1) is when it changes, and the PLC by the scene controls that two cold-zone water valve apertures realize.Adjust the two cold but water yields, make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the setting value that the ratio of liquid phase approaches this position; When adjusting ratio that the two cold-zone water yields make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify liquid phase and equate with the setting value of this position, the cooling water inflow of two cold-zones is rational cooling water inflow, stop to adjust, fixing electric current, the frequency of magnetic stirrer employing this moment stirs and need not to adjust; When adjusting the two cold-zone water yields and can not make that agitator position thickness of solidified slab shell in secondary and the ratio that does not solidify liquid phase equate with the setting value of this position, according to the agitator position thickness of solidified slab shell in secondary that calculates in real time and do not solidify the ratio of liquid phase, adjust electric current and frequency that magnetic stirrer adopts.

Magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the setting value of ratio of liquid phase in the above-mentioned steps, and changes in process parameters is when excessive, the determining of electric current that magnetic stirrer adopts and frequency are established by a large amount of field experiment.And above-mentioned experimental technique is a known technology.Shown in the following table be the position of the terminal electromagnetic agitation of billet caster of domestic certain 200 * 200mm of factory at distance meniscus 7.5m, by what a large amount of experiment drew, when changes in process parameters is excessive, electric current and frequency that magnetic stirrer adopts.

Sequence number	Solidification liquid phase ratio % not	Stirring parameter (electric current A, frequency Hz)
			1	80	200，3
2	70	200，5
			3	60	250，6
4	50	300，8
			5	40	350，10
6	30	400，12
			7	20	450，15
8	10	500，15
			9	0	0，0

Conticaster production process as Fig. 1 prior art, wherein, 1 is the above molten steel of liquidus temperature, and 2 is the two-phase section between liquidus curve and the solidus temperature, and 3 is the following solid phase area of solidus temperature, 4 is carrying roller, 5 is magnetic stirrer, and 6 are the straightening roller, and 7 is the secondary cooling water nozzle, 8 is crystallizer, and 9 is two cold-zones.

After molten steel enters into Fig. 2 crystallizer 8, cooling water inflow by Fig. 1 crystallizer and secondary cooling zone 9 is taken away the heat of molten steel, the temperature of molten steel reduces, liquid molten steel becomes solid-state steel, when technological parameter is stablized, comprise steel grade, the composition of steel, pulling rate, molten steel overheat, the crystallizer water yield, parameters such as secondary cooling water amount, above-mentioned parameter all can be recorded and be monitored, the ratio of magnetic stirrer 5 position thickness of solidified slab shell in secondary and liquid phase is certain, and apply fixing electric current and a frequency by giving agitator 5 this moment, just can carry out electromagnetic agitation to not solidified molten steel in the agitator.When changes in process parameters, change as pulling rate, the casting blank shell thickness of magnetic stirrer position reaches not, and the solidification liquid phase ratio can change, therefore needing the water yield of adjustment secondary cooling water nozzle 7 is the cooling water inflow of secondary cooling zone 9, and monitoring in real time, make the ratio of magnetic stirrer 5 position thickness of solidified slab shell in secondary and liquid phase near the setting value at this place, this setting value is to determine according to prior a large amount of experiments as mentioned above, when equaling this setting value, the parameter of magnetic stirrer 5 need not to adjust.

When changes in process parameters is very big, change greatly as pulling rate, adjusting the continuous casting two cold cooling water inflow can not make thickness of solidified slab shell in secondary and liquid phase ratio that magnetic stirrer 5 positions have been installed equate with setting value, thickness of solidified slab shell in secondary that calculates according to model and the ratio that does not solidify liquid phase are determined the adjustment of agitator parameter again.Thereby guarantee the internal soundness of strand and solidified structure.

This method can realize the kinetic controlling equation method of the continuous casting billet two cold but water yields and electromagnetic agitation in the continuous casting production process, make that the effect of continuous casting two cold and electromagnetic agitation combination control is even more ideal, again through carrying roller 4 and straightening roller 6, finish continuous casting production process, obtain the strand and the solidified structure of better internal soundness.

Calculated examples:

1, the round base electromagnetic agitation control of domestic certain factory.

Calculating parameter

Steel grade

Liquidus temperature

Solidus temperature

Pouring temperature

The cast diameter

Crystallizer discharge

The crystallizer Inlet and outlet water temperature difference

45

1494℃

1410℃

1515℃

Φ270 mm

2500L/min

5.1℃

Result of calculation

2, the square billet electromagnetic agitation of domestic certain factory control.

Calculating parameter

Steel grade

Liquidus temperature

Solidus temperature

Pouring temperature

The cast section

Crystallizer discharge

The crystallizer Inlet and outlet water temperature difference

82B

1478℃

1378℃

1505℃

150× 150mm 2

2000l/min

7.2℃

Result of calculation

Though described the present invention by embodiment, those of ordinary skills know, without departing from the spirit and substance in the present invention, just can make the present invention that many distortion and variation are arranged, and scope of the present invention is limited to the appended claims.

Claims (6)

1. the kinetic controlling equation method of the continuous casting billet two cold but water yields and magnetic stirrer is characterized in that described method is as follows:

(1) gathers technological parameter in the continuous casting production process;

(2) monitor and calculate magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase in real time;

(3) during changes in process parameters, adjust the two cold but water yields, make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify the setting value that the ratio of liquid phase approaches this position;

(4) when adjusting ratio that the two cold-zone water yields make magnetic stirrer position thickness of solidified slab shell in secondary and do not solidify liquid phase and equate with the setting value of this position, the electric current of magnetic stirrer and frequency need not adjustment;

(5) when adjusting the two cold-zone water yields and can not make that agitator position thickness of solidified slab shell in secondary and the ratio that does not solidify liquid phase equate with the setting value of this position, according to the agitator position thickness of solidified slab shell in secondary that calculates in real time and do not solidify the ratio of liquid phase, adjust the electric current and the frequency of magnetic stirrer.

2. the kinetic controlling equation method of continuous casting billet two cold-zone cooling water inflows according to claim 1 and electromagnetic agitation, it is characterized in that: in described step (2), calculate magnetic stirrer position thickness of solidified slab shell in secondary in real time and do not solidify the method for ratio of liquid phase as follows:

(2.1) model of the solid rate of inner every of strand is calculated in foundation:

Wherein T (i, j): be the temperature of strand inside mesh point, unit ℃; T1: be liquidus temperature, ℃; Ts: be solidus temperature, ℃

(2.2) determine the node that solidifies of all solid rates of strand＞0.7;

(2.3) calculate thickness of solidified slab shell in secondary and do not solidify the ratio of liquid phase according to solidifying node.

3. the kinetic controlling equation method of continuous casting billet two cold-zone cooling water inflows according to claim 2 and electromagnetic agitation, it is characterized in that: the model of the solid rate that described calculating strand is inner every, also adopted base trace model in age, accurately reflection is when changes in process parameters to make result of calculation, and magnetic stirrer position thickness of solidified slab shell in secondary reaches the not actual value of solidification liquid phase ratio; Described base trace model in age is: a section is set and follows the tracks of every certain-length on continuous casting billet, each section its rise time of record, elapsed-time standards and apart from the meniscus distance.

4. the kinetic controlling equation method of continuous casting billet two cold-zone cooling water inflows according to claim 1 and electromagnetic agitation, it is characterized in that: in described step (3), (4), (5), it is to determine by field experiment that described magnetic stirrer position thickness of solidified slab shell in secondary reaches the ratio set of not solidifying liquid phase.

5. the kinetic controlling equation method of continuous casting billet two cold-zone cooling water inflows according to claim 1 and electromagnetic agitation is characterized in that: in the described step (5), the electric current that magnetic stirrer adopts and the adjustment of frequency are to determine by field experiment.

6. the kinetic controlling equation method of continuous casting billet two cold-zone cooling water inflows according to claim 1 and electromagnetic agitation is characterized in that: the cooling water inflow of described adjustment two cold-zones is that the PLC by the scene controls two cold-zone water valve apertures and realizes.

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