CN111618266B - Method for controlling pulling speed of small square billet - Google Patents
Method for controlling pulling speed of small square billet Download PDFInfo
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- CN111618266B CN111618266B CN202010452475.XA CN202010452475A CN111618266B CN 111618266 B CN111618266 B CN 111618266B CN 202010452475 A CN202010452475 A CN 202010452475A CN 111618266 B CN111618266 B CN 111618266B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/053—Means for oscillating the moulds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
Abstract
The invention discloses a method for controlling the pulling speed of a small square billet, which comprises the following specific steps and parameters: A. controlling the superheat degree of the molten steel of the tundish at 25 +/-5 ℃; B. the thickness of a liquid slag layer of the crystallizer casting powder is controlled to be between 10 and 20mm, the temperature of a hemispherical point of the crystallizer casting powder is less than 1100 ℃, and the viscosity of the crystallizer casting powder at 1300 ℃ is less than 0.3 Pa.s; C. the width of a water gap of the crystallizer is 3.5mm, the flow rate and the water pressure of cooling water at the water gap are respectively more than 12m/min and more than 1.2MPa, the taper form of the crystallizer is a continuous parabola, and the total taper is less than or equal to 1.25 percent; D. the crystallizer vibration device adopts non-sinusoidal vibration, the amplitude of the vibration is 0-12mm, and the vibration frequency is 30-350 times per minute; E. the zero section and the first section of the secondary cooling area adopt high-pressure (more than or equal to 1.0Mpa) water cooling, and the second section and the third section adopt medium-pressure (more than or equal to 0.8Mpa) water cooling or gas spray cooling; F. the fluctuation of the liquid level of the crystallizer is controlled to be +/-5 mm. The invention provides a method for controlling the pulling speed of a small square billet, which is used for improving the pulling speed of the small square billet, thereby improving the yield of a single-strand continuous casting machine, saving energy, reducing consumption and lowering cost.
Description
Technical Field
The invention relates to the technical field of continuous casting. More particularly, the invention relates to a method for controlling the billet drawing speed.
Background
Since the invention of continuous casting technology, the continuous casting of steel has undergone a complex process of circuitous development and diversified continuous casting production organization patterns. Currently, the production model of conventional continuous casting → reheating/hot charging soaking → rolling has already matured. In view of the characteristics of different steel varieties and specifications and large difference of yield, the continuous casting in the future is a pattern with a plurality of continuous casting modes coexisting. The construction type long steel has high yield and single specification, so that the development of small square billet high-drawing-speed continuous casting and the realization of high-temperature knockout direct rolling have very important technical and economic values.
The high-casting-speed continuous casting is characterized in that higher casting speed is realized on the premise of ensuring stable and good casting blank quality, however, in the actual production process, along with the improvement of the casting speed, the fluctuation of the liquid level of the crystallizer is aggravated under the unstable working condition, the energy consumption of the crystallizer casting powder is reduced, and the stability and the uniformity of a casting powder film between a copper pipe of the crystallizer and a billet shell are possibly reduced, so that the heat transfer of the billet shell in the crystallizer is uneven, the friction resistance is increased, the billet shell is caused to be bonded and cracked, and the risk of process steel leakage is increased. In addition, another core problem affecting the high drawing speed of billets is that as the drawing speed increases, the liquid core of the cast billet becomes longer, feeding becomes more difficult, and the internal quality deteriorates rapidly. Therefore, not only does an increase in the pulling rate bring about a risk of aggravating surface quality defects of the cast slab, but also an increase in the risk of internal quality defects due to an increase in the length of the liquid core. Thus, the high pull rate control method is a systematic project that is virtually an all-around upgrade from continuous casting process to continuous casting equipment and automatic control.
Disclosure of Invention
The invention aims to solve the problems and provides a method for controlling the drawing speed of a small square billet so as to improve the drawing speed of the small square billet, thereby improving the yield of a single-strand continuous casting machine, saving energy, reducing consumption and lowering cost.
To achieve these objects and other advantages in accordance with the purpose of the present invention, a billet drawing speed control method is provided, the specific steps and parameters are as follows:
A. controlling the superheat degree of the molten steel of the tundish at 25 +/-5 ℃;
B. the thickness of a liquid slag layer of the crystallizer casting powder is controlled to be between 10 and 20mm, the temperature of a hemispherical point of the crystallizer casting powder is less than 1100 ℃, and the viscosity of the crystallizer casting powder at 1300 ℃ is less than 0.3 Pa.s;
C. the width of a water gap of the crystallizer is 3.5mm, the flow rate and the water pressure of cooling water at the water gap are respectively more than 12m/min and more than 1.2MPa, the taper form of the crystallizer is a continuous parabola, and the total taper is less than or equal to 1.25 percent;
D. the crystallizer vibration device adopts non-sinusoidal vibration, the amplitude of the vibration is 0-12mm, and the vibration frequency is 30-350 times per minute;
E. the zero section and one section of the secondary cooling area are cooled by high-pressure full water, and the water pressure of the high-pressure water is more than or equal to 1.0 Mpa; the two sections and the three sections of the secondary cooling area are both cooled by medium-pressure full water or gas fog, and the water pressure of the medium-pressure water is more than or equal to 0.8 Mpa;
F. the fluctuation of the liquid level of the crystallizer is controlled to be +/-5 mm.
Preferably, in the method for controlling the billet pulling speed, the length of the copper pipe of the crystallizer is between 900 and 1000mm, and the copper pipe is made of phosphor copper.
Preferably, in the method for controlling the billet drawing speed, a plurality of air gap grooves are uniformly distributed at 1/3 on the upper end of the inner wall of the copper pipe of the crystallizer.
Preferably, in the method for controlling the billet drawing speed, the specific water amount of the secondary cooling zone is 1.5-2.5L/kg.
Preferably, in the method for controlling the billet drawing speed, the water pressure of the cooling water in the secondary cooling area is more than 1.0 MPa.
Preferably, in the method for controlling the billet drawing speed, the cooling water spray coverage length of the secondary cooling area is 5-6 m.
The invention provides a systematic control method of the small square billet casting speed by optimizing the crystallizer, improving the crystallizer vibration device, resetting the secondary cooling system, optimizing the crystallizer casting slag and re-establishing related auxiliary process parameters, and can obviously improve the casting speed of the uniflow continuous casting machine, thereby improving the yield, and achieving the purposes of saving energy, reducing consumption and reducing cost.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Detailed Description
The present invention is further described in detail below with reference to examples so that those skilled in the art can practice the invention with reference to the description.
< example 1>
The embodiment of the invention provides a method for controlling the pulling speed of a small square billet, which comprises the following specific steps and parameters:
A. controlling the superheat degree of the molten steel of the tundish at 25 +/-5 ℃;
B. the thickness of a liquid slag layer of the crystallizer casting powder is controlled to be between 10 and 20mm, the temperature of a hemispherical point of the crystallizer casting powder is less than 1100 ℃, and the viscosity of the crystallizer casting powder at 1300 ℃ is less than 0.3 Pa.s;
C. the width of a water gap of the crystallizer is 3.5mm, the flow rate and the water pressure of cooling water at the water gap are respectively more than 12m/min and more than 1.2MPa, the taper form of the crystallizer is a continuous parabola, and the total taper is less than or equal to 1.25 percent;
D. the crystallizer vibration device adopts non-sinusoidal vibration, the amplitude of the vibration is 0-12mm, and the vibration frequency is 30-350 times per minute;
E. the zero section and one section of the secondary cooling area are cooled by high-pressure full water, and the water pressure of the high-pressure water is more than or equal to 1.0 Mpa; the two sections and the three sections of the secondary cooling area are both cooled by medium-pressure full water or gas fog, and the water pressure of the medium-pressure water is more than or equal to 0.8 Mpa;
F. the fluctuation of the liquid level of the crystallizer is controlled to be +/-5 mm.
Wherein the length of the crystallizer copper tube is between 900 and 1000mm, and the crystallizer copper tube is made of phosphor copper.
Wherein, 1/3 position of the copper pipe inner wall upper end of crystallizer is equipped with a plurality of air gap grooves.
Wherein the specific water amount of the secondary cooling area is 1.5-2.5L/kg.
Wherein the water pressure of the cooling water in the secondary cooling area is more than 1.0 MPa.
Wherein the cooling water spray coverage length of the secondary cooling area is 5-6 m.
< example 2>
Example 2 a more systematic approach to increasing billet pull rate was proposed by optimization of the crystallizer, improvement of the crystallizer vibration device, resetting of the secondary cooling regime, optimization of the crystallizer mold flux and reformulation of the relevant auxiliary process parameters.
1. Optimizing the crystallizer: the crystallizer is a key link of initial solidification and formation of molten steel and is commonly called as a casting machine heart. The design reasonability and the manufacturing quality of the casting blank casting device play a vital role in the smooth production of the continuous casting machine and the quality of the casting blank. The crystallizer is redesigned through numerical simulation analysis of solidification shrinkage, flow field, heat transfer and frictional resistance of molten steel in the crystallizer. In order to strengthen the heat transfer of the crystallizer, the following steps are adopted: 1) a regular air gap groove is arranged at 1/3 on the upper end of the inner wall of the copper pipe of the crystallizer, so that molten protective slag is fully filled at a meniscus, the heat flow at the meniscus is reduced to be too concentrated, and the heat flow is more uniformly distributed along the casting flow direction; 2) the inverse taper of the copper pipe of the crystallizer is designed into a continuous parabolic taper, so that the air gap between the primary blank shell and the wall of the copper pipe is more uniform; 3) the corner of the crystallizer is designed into a large round angle, so that the cooling of the corner of a casting blank is slowed down, the cooling uniformity of the casting blank is improved, and the risks of corner cracks and steel leakage are reduced; 4) reducing the water gap of the crystallizer to 3.5mm from 4mm, improving the water flow velocity of the water gap and increasing the heat exchange speed of the crystallizer; 5) the water flow and the water pressure of the crystallizer are increased so as to improve the cooling capacity of the crystallizer; 6) the number of nozzles at the zero section is increased, the original single-row nozzles are changed into two rows of nozzles, and 4 nozzles in each row are changed into 8 nozzles.
2. Optimizing the vibration of the crystallizer: the non-sinusoidal vibration technology is a new technology for realizing the vibration of the crystallizer by utilizing the reciprocating motion of a hydraulic cylinder or an electric servo cylinder. Compared with the traditional sinusoidal mechanical vibration, the non-sinusoidal vibration technology has the following advantages:
the method can realize online adjustment of the vibration waveform, frequency and amplitude of the crystallizer, and select the optimal vibration characteristic parameters aiming at the pulling speeds of different steel grades so as to obtain the optimal surface quality of the casting blank.
Non-sinusoidal vibration technical parameters:
| vibration curve: | sinusoidal or non-sinusoidal, the non-sinusoidal rate being 10% -40% (sinusoidal when the coefficient is 0) |
| Amplitude: | 0-12mm total amplitude, and can be automatically adjusted |
| Frequency: | 30-350 times/min |
3. And (3) optimizing a secondary cooling system: the secondary cooling of continuous casting is to cool the surface of the casting blank uniformly and forcibly, so that the casting blank is cooled and solidified fully in a short time. The second cooling zone must follow the principle of strong and weak uniform cooling from top to bottom, generally requires a cooling speed of less than 200 ℃/m, a surface temperature return of the billet shell of less than 100 ℃/m, and controls the temperature of the billet straightening zone to avoid a brittle temperature zone of 700 ℃ and 900 ℃.
The high pulling speed control scheme has the following characteristics: 1) the secondary cooling water has higher cooling strength, and the specific water amount is close to 2.0L/kg; 2) the secondary cooling water supply pressure is larger: 0.8-1.2 Mpa; 3) the secondary cold water spraying coverage length is long: 5-6 m; 4) a mixed cooling mode: the zero section and the first section are forcibly cooled by high-pressure water, and the second section and the third section are cooled by medium-pressure water or gas fog, so that the casting blank can be rapidly cooled, and the casting blank can be prevented from being rapidly cooled.
4. Crystallizer mold flux: if the continuous casting is carried out at high drawing speed, the general casting powder is still used, and when the drawing speed is greatly increased, the thickness of a liquid slag layer on the molten steel surface becomes thinner along with the increase of the drawing speed, the slag forming speed cannot be kept up with the liquid slag, and the liquid slag cannot be supplemented to the specified thickness, so that a slag film between a blank shell and a copper wall is very thin or does not adhere to the blank shell to cause a drawing leakage accident. And the probability of surface defects such as longitudinal cracks and the like of the casting blank is increased. Therefore, in order to adapt to high drawing speed, the slag mixing principle is as follows: 1) the higher melting speed is used for controlling the thickness of the liquid slag layer to be between 10 and 20mm so as to ensure that the amount of slag flowing into the crystallizer and the copper wall is stable; 2) the melting point is low, and the semisphere point temperature of the slag is less than 1100 ℃; 3) lower viscosity, viscosity at 1300 ℃ less than 0.3 pas.
5. The probability of midway cracking inside the cast slab is increased at a high drawing speed, but midway cracking can be avoided when the superheat degree is below 30-25 ℃. Of course, the cracks in the middle of the casting blank are related to other process factors, particularly the secondary cooling strength, the distribution of secondary cooling water and the distribution of cooling strength on the surface of the blank shell have direct influence, and the influence of the superheat degree of molten steel on the internal quality of the casting blank is only explained here.
< example 3>
Example 3 a more systematic approach to increasing billet pull rate was proposed by optimization of the crystallizer, improvement of the crystallizer vibration device, resetting of the secondary cooling regime, optimization of the crystallizer mold flux and reformulation of the relevant auxiliary process parameters.
The quality of cooling water in the crystallizer is softened water, the water pressure is not lower than 1.2MPa, and in secondary cooling water, oil removal, secondary filtration and the like are carried out, and the water pressure is not lower than 0.8 MPa; the superheat degree of the molten steel of the tundish is 25 +/-5 ℃; ensuring the sufficient coverage length of the secondary cooling area, and controlling the negative influence of the casting blank temperature return at the tail end of the secondary cooling area on the quality of the casting blank; the knockout system needs detailed calculation to ensure smooth and timely knockout.
The crystallizer copper tube with high drawing speed is characterized in that a plurality of air gap grooves are regularly formed in an inner cavity (or the outer side) of a certain interval with the length of about 1/3 from the upper opening of the crystallizer copper tube, so that the heat dissipation problem of a crystallizer in the blank drawing process is solved. The grooved copper pipe can form an artificial air gap at the meniscus, so that the large heat flow at the meniscus is inhibited and transferred to the middle part and the lower part, the heat flow in the crystallizer is relatively balanced along the axial distribution of the crystallizer, and the heat flow in the meniscus area is reduced.
Aiming at the optimized arrangement of the nozzles of the secondary cooling section, the heat transfer mode in the secondary cooling area is mainly spray water of the nozzles and heat transfer on the surface of the casting blank, and the controllability is realized. The secondary cooling area has a wider flow regulation range, smaller influence of flow change on water distribution, higher injection speed, easy evaporation, large coverage and the like. The contact surface of the nozzle cooling water and the casting blank is generally 3-5 times of the nozzle area, the surface of the casting blank is cooled very uniformly, the surface temperature amplitude is 50-80 ℃, and the width direction of a secondary cooling area of continuous casting has certain influence on the internal quality. The cooling solidification is uneven, cracks are more and more, serious segregation can occur in a high-temperature area, the setting is carried out according to the water distribution characteristics of the nozzles, the water distribution of the nozzle assembly is controlled to be even, and the influence on the quality of the casting blank can be avoided.
The secondary cooling water system adopts a composite cooling technology. And the zero section or the zero section is added with a section of high-pressure full water cooling, and the two section or the three section is cooled by gas fog or medium-pressure water. And cooling the casting blank out of the crystallizer to stably increase the thickness of the blank shell, and reducing the cooling strength after the blank shell is increased to a certain thickness to avoid the casting blank from cracking, namely, the casting blank follows the principle that the cooling strength is from high to low from top to bottom.
The process parameters for example 3 are shown in the following table:
while embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the embodiments shown and described without departing from the generic concept as defined by the claims and their equivalents.
Claims (6)
1. A method for controlling the drawing speed of a small square billet is characterized by comprising the following specific steps and parameters:
A. controlling the superheat degree of the molten steel of the tundish at 25 +/-5 ℃;
B. the thickness of a liquid slag layer of the crystallizer casting powder is controlled to be between 10 and 20mm, the temperature of a hemispherical point of the crystallizer casting powder is less than 1100 ℃, and the viscosity of the crystallizer casting powder at 1300 ℃ is less than 0.3 Pa.s;
C. the width of a water gap of the crystallizer is 3.5mm, the flow rate and the water pressure of cooling water at the water gap are respectively more than 12m/min and more than 1.2MPa, the taper form of the crystallizer is a continuous parabola, and the total taper is less than or equal to 1.25 percent;
D. the crystallizer vibration device adopts non-sinusoidal vibration, the amplitude of the vibration is 0-12mm, and the vibration frequency is 30-350 times per minute;
E. the zero section and one section of the secondary cooling area are cooled by high-pressure full water, and the water pressure of the high-pressure water is more than or equal to 1.0 Mpa; the two sections and the three sections of the secondary cooling area are both cooled by medium-pressure full water or gas fog, and the water pressure of the medium-pressure water is more than or equal to 0.8 Mpa;
F. the fluctuation of the liquid level of the crystallizer is controlled to be +/-5 mm.
2. The method as claimed in claim 1, wherein the length of the copper tube of the crystallizer is between 900 and 1000mm, and the copper tube is made of phosphor copper.
3. The method of claim 1, wherein a plurality of air gap grooves are uniformly formed at 1/3 on the upper end of the inner wall of the copper tube of the mold.
4. The method of controlling a billet drawing speed according to claim 1, wherein the specific water amount in the secondary cooling zone is 1.5 to 2.5L/kg.
5. The method of controlling a billet drawing speed according to claim 4, wherein the water pressure of the cooling water in the secondary cooling zone is more than 1.0 MPa.
6. A billet drawing speed control method according to claim 5, wherein the secondary cooling zone is sprayed with cooling water over a length of 5 to 6 m.
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| CN113927007A (en) * | 2021-10-14 | 2022-01-14 | 四川德胜集团钒钛有限公司 | Continuous casting square billet production process of vanadium-containing anti-seismic steel |
| CN114632918A (en) * | 2022-03-25 | 2022-06-17 | 福建三钢闽光股份有限公司 | Continuous casting high-drawing-speed production method of small square billets |
| CN115106497A (en) * | 2022-06-14 | 2022-09-27 | 河钢乐亭钢铁有限公司 | Method for controlling vibration mark defect of continuous casting slab |
| CN115323257A (en) * | 2022-08-26 | 2022-11-11 | 宝武集团鄂城钢铁有限公司 | Method for improving production efficiency of carbon structural steel Q235 square billet continuous casting |
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| CN102441648A (en) * | 2010-10-08 | 2012-05-09 | 攀钢集团钢铁钒钛股份有限公司 | Method for continuously casting steel plate billets for automotive frames |
| CN102303108B (en) * | 2011-09-22 | 2016-06-01 | 首钢贵阳特殊钢有限责任公司 | A kind of continuous casting manufacturing technique improving automatic steel slab quality |
| CN106216624B (en) * | 2016-08-25 | 2018-07-06 | 江苏省沙钢钢铁研究院有限公司 | A kind of low-carbon high-chromium ferrite corrosion-resisting steel continuous small-billet casting manufacturing method |
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