Method for detecting liquid level of molten steel in tundish

Abstract

The invention discloses a method for detecting the liquid level of tundish molten steel. The method comprises the following steps that S1, the outlet molten steel flow of a crystallizer in the pouring process is calculated; s2, the inlet molten steel flow of the crystallizer in the pouring process is calculated; s3, the opening degree and the steel passing area of the stopper rod are calculated; and S4, according to the equal continuous equations in the step S1 and the step S2, a relational expression between the opening degree of the stopper rod and the height of the tundish is deduced and substituted into the relational expression in the step S3. According to the tundish molten steel liquid level detection technology, the tundish molten steel liquid level can be directly detected, the molten steel liquid level detection precision reaches the control precision, the tundish molten steel liquid level detection technology is low in installation and maintenance cost and can be repeatedly used, and in addition, the tundish molten steel liquid level can be accurately detected in the tundish covering agent crusting state.

Description

Technical Field

[0001] The invention relates to continuous casting technology, and more specifically to a method for detecting the level of molten steel in a tundish. Background Art

[0002] The tundish is the last process for molten steel to enter the crystallizer. The tundish has the following metallurgical functions: diversion, pressure stabilization, secondary oxidation prevention and inclusion removal. Among them, the pressure stabilization function of the tundish is to provide a stable molten steel level to stabilize the static pressure of the molten steel, so accurate detection and control of the molten steel level in the tundish is crucial.

[0003] At present, the main methods for molten steel level detection include weighing method, electromagnetic eddy current method and radar method.

[0004] Weighing method: The total weight of the container is measured by a sensor placed at the base of the molten steel container to calculate the liquid level of the molten steel. The main method for detecting the molten steel level in the tundish is the weighing method; for example, Chinese patent 201420005211.X discloses a high-temperature resistant continuous casting tundish weighing device, but this method detects the liquid level indirectly, and the accuracy of the liquid level detection is low, because the cost and maintenance cost of placing multiple sensors are relatively high.

[0005] Electromagnetic eddy current method: For example, Chinese patent 200510113914.X discloses a molten steel level detection device using an electromagnetic coil, which mainly uses the electromagnetic field generated by the electromagnetic coil to detect the molten steel level. The electromagnetic eddy current method has high accuracy in detecting the liquid level, but the range of this method is limited, generally only 200mm, so it is generally only used for liquid level detection of the crystallizer.

[0006] Radar method: For example, Chinese patent 200620096300.5 discloses a radar molten steel level detection system, which mainly uses radar waves to detect the molten steel level. The radar method has high detection accuracy, but the probe of this method is sensitive to shielding and on-site temperature.

[0007] According to the existing molten steel level detection technology, the technical difficulties of molten steel level detection in the tundish are:

[0008] (1) The space above the middle bag is relatively small, so the installation space for the testing equipment is limited;

[0009] (2) The tundish is covered with a tundish cover. The liquid level detection device can only detect the molten steel level in the tundish through the opening on the tundish cover. The temperature above the tundish cover hole is very high, up to 500 degrees or more, which is unbearable for the general liquid level gauge probe;

[0010] (3) The covering agent on the molten steel in the tundish may sometimes form a crust during the pouring process. Under the condition of crusting of the covering agent, the ordinary liquid level detection device cannot truly detect the height of the molten steel level. Summary of the invention

[0011] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for detecting the molten steel level in a tundish, which can not only directly detect the molten steel level in the tundish, but also achieve the controlled accuracy of the molten steel level detection. Moreover, the molten steel level detection technology for the tundish has low installation and maintenance costs and is reusable. In addition, the molten steel level in the tundish can also be accurately detected when the covering agent in the tundish is encrusted.

[0012] To achieve the above object, the present invention adopts the following technical solution:

[0013] A method for detecting the molten steel level in a tundish comprises the following steps:

[0014] S1. Calculate the outlet flow rate of the crystallizer during the casting process;

[0015] S2, calculate the inlet molten steel flow rate of the crystallizer during the casting process;

[0016] S3. Calculate the opening degree and steel passing area of ​​the stopper rod;

[0017] S4. Based on the equal simultaneous equations of step S1 and step S2, the relationship between the opening degree of the stopper rod and the height of the tundish is derived and substituted into the relationship of step S3.

[0018] Preferably, the outlet molten steel flow rate of the crystallizer in step S1 is calculated as follows:

[0019]

[0020] In the formula, Q m is the outlet flow rate of molten steel of the crystallizer, in kg / s; ρ s is the density of the steel billet, (7850*0.1+7200*0.9)kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c It is the pulling speed, in m / min.

[0021] Preferably, the inlet molten steel flow rate of the crystallizer in step S2 is calculated as follows:

[0022]

[0023] In the formula, Q k is the inlet molten steel flow rate of the crystallizer, unit: kg / s; ρ L is the density of molten steel, take 7200kg / m 3; h is the depth of molten steel in the tundish, in m; S(x) is the opening area under the flow control of the stopper rod, in m 2 ; C(x) is the correction coefficient; x is the stopper rod position. When the stopper rod and the immersed nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. The upward height based on this is the opening distance, in meters.

[0024] Preferably, the opening degree of the stopper rod in step S3 is calculated as follows:

[0025]

[0026] Wherein, L(x) is the opening line of the stopper rod, in m; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, in m; n is the distance in the numerical direction of the centers of the two arc surfaces when the stopper rod is closed, in m; r1 is the radius of the arc surface of the stopper rod, in m; r2 is the radius of the arc surface of the bowl mouth, in m; x is the position of the stopper rod. When the stopper rod and the immersion nozzle are completely fitted to block the outflow of molten steel, the x value is 0, and the height of walking upward based on this is the opening distance, in m;

[0027] The calculation of the steel area is as follows:

[0028]

[0029] Substituting formula (3) into formula (4) yields:

[0030]

[0031] Where S(x) is the steel area between the stopper and the bowl mouth, unit: m 2 ; L(x) is the minimum distance between the stopper rod and the bowl mouth, unit m; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, unit m; n is the numerical distance between the centers of the two arc surfaces when the stopper rod is closed, unit m; r1 is the radius of the arc surface of the stopper rod, unit m; r2 is the radius of the arc surface of the bowl mouth, unit m; x is the position of the stopper rod. When the stopper rod and the immersed nozzle are completely fitted to block the outflow of molten steel, the x value is 0. The height of walking upward based on this is the opening distance, unit m.

[0032] Preferably, the relationship equation substituted into step S3 in step S4 is as follows:

[0033] Q m =Q K (6)

[0034]

[0035]

[0036] Substituting formula (5) into formula (8) yields:

[0037]

[0038] Wherein, h is the depth of molten steel in the tundish, in m; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, in m; n is the distance in the numerical direction between the centers of the two arc surfaces when the stopper rod is closed, in m; r1 is the radius of the arc surface of the stopper rod, in m; r2 is the radius of the arc surface of the bowl mouth, in m; ρ s is the density of the steel billet, (7850*0.1+7200*0.9)kg / m 3 ρ L is the density of molten steel, take 7200kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c is the pulling speed, in m / min; C(x) is the correction coefficient, ranging from 0.6 to 0.9; x is the stopper rod position. When the stopper rod and the submerged nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. Based on this, the upward height is the opening distance, in m.

[0039] The method for detecting the molten steel level in the tundish provided by the present invention has the following beneficial effects:

[0040] 1) The relationship between the tundish liquid level and the stopper rod position is established, and the tundish liquid level is monitored in real time by detecting the stopper rod position value;

[0041] 2) The detection method of the present invention can directly detect the molten steel level in the tundish, and the molten steel level detection accuracy is high, achieving the accuracy of online control;

[0042] 3) The detection method of the present invention has low maintenance cost and can be reused;

[0043] 4) The detection method of the present invention can also accurately detect the liquid level of the molten steel in the tundish when the tundish covering agent is in the encrustation state. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of various parameters in the detection method of the present invention;

[0045] 1- stopper, 2- bowl mouth

[0046] Figure 2 It is a schematic diagram of the relationship between the stopper rod opening and the tundish liquid level height in the detection method embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0048] The present invention provides a method for detecting the molten steel level in a tundish, comprising the following steps:

[0049] S1. Calculate the outlet flow rate of the crystallizer during the casting process:

[0050]

[0051] In the formula, Q m is the outlet flow rate of molten steel of the crystallizer, in kg / s; ρ s is the density of the steel billet, (7850*0.1+7200*0.9)kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c It is the pulling speed, in m / min.

[0052] S2. Calculate the inlet molten steel flow rate of the crystallizer during the casting process:

[0053] In continuous casting, the stopper rod is used to control the opening of the tundish water inlet and adjust the flow rate of molten steel from the tundish to the crystallizer to maintain the stability of the molten steel level. According to formula (1), under the flow control of the stopper rod, the quality of molten steel flowing into the upper inlet of the crystallizer is mainly calculated by the tundish liquid level height and the stopper rod opening, and the flow rate Q k for:

[0054]

[0055] In the formula, Q k is the inlet molten steel flow rate of the crystallizer, unit: kg / s; ρ L is the density of molten steel, take 7200kg / m 3 ; h is the depth of molten steel in the tundish, in m; S(x) is the opening area under the flow control of the stopper rod, in m 2 ; C(x) is the correction coefficient; x is the stopper rod position. When the stopper rod and the immersed nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. The upward height based on this is the opening distance, in meters.

[0056] S3. Calculate the opening degree and steel area of ​​the stopper rod:

[0057] Opening line of stopper rod L(x): The geometric minimum distance between the stopper rod and the submerged nozzle when the stopper rod opening position is x (in mm), which is determined by Figure 1 The geometric relationships shown allow the expression of the opening line to be calculated.

[0058]

[0059] Wherein, L(x) is the opening line of the stopper rod 1, in m; m is the distance from the center line of the stopper rod 1 to the center point of the arc surface of the bowl mouth 2, in m; n is the distance in the numerical direction between the centers of the two arc surfaces when the stopper rod 1 is closed, in m; r1 is the radius of the arc surface of the stopper rod 1, in m; r2 is the radius of the arc surface of the bowl mouth 2, in m; x is the position of the stopper rod 1. When the stopper rod 1 and the immersion nozzle are completely fitted to block the outflow of the molten steel, the x value is 0, and the height of walking upward based on this is the opening distance, in m;

[0060] Through-steel area S(x): The area of ​​the surface formed by rotating the opening line along the center line of the stopper rod when the opening distance of the stopper rod 1 is x (unit: mm) 2 ), calculated as follows:

[0061]

[0062] Substituting formula (3) into formula (4) yields:

[0063]

[0064] Where S(x) is the steel area between the stopper rod 1 and the bowl mouth 2, unit: m 2 ; L(x) is the minimum distance between the stopper rod 1 and the bowl mouth 2, unit m; m is the distance from the center line of the stopper rod 1 to the center point of the arc surface of the bowl mouth 2, unit m; n is the numerical distance between the centers of the two arc surfaces when the stopper rod 1 is closed, unit m; r1 is the radius of the arc surface of the stopper rod 1, unit m; r2 is the radius of the arc surface of the bowl mouth 2, unit m; x is the position of the stopper rod. When the stopper rod 1 and the immersed nozzle are completely fitted to block the outflow of the molten steel, the x value is 0. The height of walking upward based on this is the opening distance, unit m.

[0065] S4. The mass of the molten steel flowing into the upper outlet of the crystallizer and the mass of the ingot flowing out of the lower outlet of the crystallizer are equal. The relationship between the stopper opening and the liquid level of the tundish is derived by establishing a continuous equation, and the relationship between the stopper opening and the steel passing area is substituted into the equation:

[0066] Q m =Q K (6)

[0067]

[0068]

[0069] Substituting formula (5) into formula (8) yields:

[0070]

[0071] Wherein, h is the depth of molten steel in the tundish, in m; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, in m; n is the distance in the numerical direction between the centers of the two arc surfaces when the stopper rod is closed, in m; r1 is the radius of the arc surface of the stopper rod, in m; r2 is the radius of the arc surface of the bowl mouth, in m; ρ s is the density of the steel billet, (7850*0.1+7200*0.9)kg / m 3 ρ L is the density of molten steel, take 7200kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c is the pulling speed, in m / min; C(x) is the correction coefficient; x is the stopper rod position. When the stopper rod and the submerged nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. Based on this, the upward height is the opening distance, in m.

[0072] During the pouring process, since other parameters remain unstable, only the tundish liquid level and the stopper rod position change with time, thereby establishing a relationship between the tundish liquid level h and the stopper rod position x.

[0073] The accurate value of the tundish liquid level h can be directly calculated through the stopper rod position x, and then the tundish liquid level h can be monitored in real time by detecting the stopper rod position value.

[0074] Example

[0075] In the pouring process of a casting machine, the pouring process parameters are shown in the following table:

[0076] Process parameters Numeric Crystallizer section thickness a 0.25m Crystallizer section width b 1.5m <![CDATA[Drawing speed V c > 1.5m / min <![CDATA[Radius r1 of the stopper arc surface]]> 0.054m <![CDATA[Radius r2 of the arc surface of the bowl mouth]]> 0.05m Distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth m 0.092m The vertical distance n between the centers of the two arc surfaces when the stopper is closed 0.0485m

[0077] During the pouring process, the height of the molten steel in the crystallizer remains stable, so the mass of the molten steel flowing into the upper mouth of the crystallizer and the mass of the ingot out of the lower mouth of the crystallizer are equal. The mass of the ingot out of the lower mouth of the crystallizer can be calculated by the casting speed and the cross-sectional dimensions, and the mass of the molten steel flowing into the upper mouth of the crystallizer is mainly calculated by the liquid level of the tundish and the stopper rod opening. Therefore, an equation relationship between the stopper rod opening and the liquid level of the tundish can be established, and the liquid level of the tundish can be calculated by the stopper rod opening. The specific calculation parameters and process are as follows:

[0078] (1) Flow rate of molten steel at the outlet of the crystallizer during casting:

[0079] a=0.25m,b=1.5m,V c =1.5m / min,ρ s =7265kg / m 3

[0080]

[0081] (2) Flow rate of molten steel at the inlet of the crystallizer during casting:

[0082] In continuous casting, the stopper rod is used to control the opening of the tundish water outlet and adjust the flow rate of molten steel from the tundish to the crystallizer to maintain the stability of the molten steel level. According to the above formula, under the flow control of the stopper rod, the quality of molten steel flowing into the upper inlet of the crystallizer is mainly calculated by the tundish liquid level height and the stopper rod opening, and the flow rate Q k for:

[0083]

[0084] (3) Calculation formula for stopper opening and steel passing area

[0085] According to the stopper rod and nozzle size on site, the following is calculated:

[0086] r1=0.054m, r2=0.050m, m=42.5mm+50mm=0.0925m, n=0.0485m

[0087] Substituting into formula (3) we can get:

[0088] Substituting into formula (4) we can get:

[0089] (4) The mass of the molten steel flowing into the upper outlet of the crystallizer and the mass of the ingot flowing out of the lower outlet of the crystallizer are equal. The relationship between the stopper opening and the liquid level of the tundish is derived by establishing a continuous equation, and the relationship between the stopper opening and the steel passing area is introduced:

[0090] Q m =Q K (14)

[0091]

[0092]

[0093] Q m =68.1kg / s,ρ L =7200kg / m 3 , C(x) = 0.82, g = 9.8, and substitute into formula (13)

[0094]

[0095] This embodiment can accurately detect the height of the tundish liquid level by detecting the stopper rod opening position and the amount of molten steel flowing through. The data of the tundish liquid level detected by this embodiment is as follows: Figure 2 shown.

[0096] In summary, the method for detecting the molten steel level of the tundish of the present invention establishes an equation relationship between the stopper rod opening and the tundish liquid level height, and calculates the tundish liquid level height through the stopper rod opening. The molten steel level of the tundish can be directly detected, and the molten steel level detection accuracy is high, achieving the accuracy of online control; the method for detecting the molten steel level of the tundish of the present invention can accurately detect the tundish liquid level and can be reused; the molten steel level detection device of the tundish can also accurately detect the molten steel level of the tundish when the tundish covering agent is in the crust state.

[0097] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for detecting the molten steel level in a tundish, characterized in that: The following steps are involved: S1. Calculate the outlet flow rate of the crystallizer during the casting process; S2, calculate the inlet molten steel flow rate of the crystallizer during the casting process; S3. Calculate the opening degree and steel passing area of ​​the stopper rod; S4. Based on the equal simultaneous equations of step S1 and step S2, the relationship between the opening degree of the stopper rod and the height of the tundish is derived and substituted into the relationship of step S3.

2. The method for detecting the molten steel level in the tundish according to claim 1, characterized in that: In step S1, the outlet flow rate of the crystallizer is calculated as follows: In the formula, Q m is the outlet steel liquid flow rate of the crystallizer, in kg / s; ρ s is the density of the steel billet, in kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c It is the pulling speed, in m / min.

3. The method for detecting the molten steel level in the tundish according to claim 2, characterized in that: In step S2, the inlet molten steel flow rate of the crystallizer is calculated as follows: In the formula, Q k is the inlet molten steel flow rate of the crystallizer, in kg / s; ρ L is the density of molten steel, unit: kg / m 3 ; h is the depth of molten steel in the tundish, in m; S(x) is the opening area under the flow control of the stopper rod, unit: m 2 ; C(x) is the correction coefficient; x is the stopper rod position. When the stopper rod and the immersed nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. The height moving upward based on this is the opening distance, in m.

4. The method for detecting the molten steel level in the tundish according to claim 3, characterized in that: In step S3, the opening degree of the stopper rod is calculated as follows: The calculation of the steel area is as follows: Substituting formula (3) into formula (4) yields: Where S(x) is the steel area between the stopper and the bowl mouth, unit: m 2 ; L(x) is the minimum distance between the stopper rod and the bowl mouth, in m; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, in m; n is the distance in the numerical direction between the centers of the two arc surfaces when the stopper rod is closed, in m; r1 is the radius of the arc surface of the stopper rod, in m; r2 is the radius of the bowl rim, in m; x is the stopper rod position. When the stopper rod and the immersed nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. The height moving upward based on this is the opening distance, in m.

5. The method for detecting the molten steel level in the tundish according to claim 4, characterized in that: In step S4, the equivalent equations of step S1 and step S2 are specifically as follows: Q m =Q K (6) Substituting formula (5) into formula (8) yields: Where, h is the depth of molten steel in the tundish, in meters; m is the distance from the center line of the stopper rod to the center point of the arc surface of the bowl mouth, in m; n is the distance in the numerical direction between the centers of the two arc surfaces when the stopper rod is closed, in m; r1 is the radius of the arc surface of the stopper rod, in m; r2 is the radius of the arc surface of the bowl mouth, unit is m; ρ s is the density of the steel billet, in kg / m 3 ; ρ L is the density of molten steel, unit: kg / m 3 ; a, b are the cross-sectional dimensions of the ingot, in m; V c is the pulling speed, in m / min; C(x) is the correction coefficient; x is the stopper rod position. When the stopper rod and the immersed nozzle are completely fitted together to block the outflow of molten steel, the x value is 0. The height moving upward based on this is the opening distance, in m.

6. The method for detecting the molten steel level in the tundish according to claim 2, 3 or 5, characterized in that: In formula (1), formula (2), and formula (9), ρ s Take (7850*0.1+7200*0.9)kg / m 3 , ρ L Take 7200kg / m 3 .

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