Casting method and related equipment

Abstract

1. A method for casting a steel semi-finished product in which molten steel is poured from a ladle through a shroud into a tundish, the method comprising the steps of determining an intensity of light emitted from a surface of the molten steel in the tundish; detecting the presence of an open eye at the surface of the molten steel based on the determined intensity; and issuing an alarm to an operator when an open eye is detected.

Description

[Technical field]

[0001] The present invention relates to a method and associated apparatus for casting steel semi-finished products. [Background technology]

[0002] In the casting of steel semi-finished products, molten steel is poured into a mould through a submerged entry nozzle (SEN) and then slowly cooled until it solidifies into a semi-finished product such as a steel slab or billet. The molten steel is produced in a ladle to a given composition and temperature and then poured into a tundish through a ladle shroud. Inert gas is injected into the shroud to protect the molten steel from possible air ingress when the shroud is inserted into the ladle. The tundish is used to feed the molten steel into the ingot mould and acts as a reservoir and buffer for the molten steel to be fed to the caster to provide a smooth exit flow and regulate said flow.

[0003] The surface of the molten steel in the tundish is covered by a floating layer of tundish powder. The purpose of this powder is to prevent the molten steel from oxidizing due to contact with the outside air. For several reasons, such as fluctuations in the flow of the molten steel or the generation of bubbles by inert gas, the powder layer may not be continuous and multiple open areas may appear, which are called tundish open eyes (TOE) or tundish rolls.

[0004] The main consequence of the presence of an open eye is that the molten steel is exposed to air in this area. As a result, re-oxidation of the molten steel occurs and inclusions are formed. This is detrimental to the cleanliness of the steel and can cause defects in the solidified product. Furthermore, the inclusions can flow towards the SEN and agglomerate until they cause clogging of the SEN. When the SEN is clogged, the resulting steel semi-finished product has to be scrapped due to quality issues and the entire casting process is slowed down to replace the clogged SEN. This is therefore detrimental to both product quality and productivity.

[0005] The open eye phenomenon and its consequences are known, so in current practice, the operator is responsible for periodically inspecting the surface of the molten steel in the tundish and adding powder if necessary. However, as a human-based method, this has limitations. Because the operator does not continuously view the surface, there is always a delay between the formation of the open eye and the addition of powder, depending on the sensitivity of the steel grade, and even a small delay can have a negative impact on the quality of the steel produced. Furthermore, the accumulation of oxidation over a short period of time leads to inclusion buildup and clogging of the SEN. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for a method that allows accurate detection of the formation of an open eye on the surface of molten steel in a tundish. There is also a need for a method that allows improving the quality of the cast semi-finished product and improving the life of the submerged inlet nozzle. [Means for solving the problem]

[0007] This problem is solved by a method according to the present invention, which comprises the steps of determining the intensity of light emitted from the surface of the molten steel in a tundish, detecting the presence of an open eye at the surface of the molten steel based on the determined intensity, and issuing an alarm to an operator when an open eye is detected.

[0008] The method of the invention may also comprise the following optional features, considered separately or according to all possible technical combinations: Between the determining and detecting steps, the method includes a step of calculating a size of the open eye based on the determined intensity. The emission step is performed only if the calculated size of the open eye is greater than or equal to a predefined threshold size. After the step of issuing an alarm, the method comprises the step of pouring powder onto the surface of the molten steel in the tundish. -The calculation step is carried out using a regression model. The determination step is performed using a baseline of intensity representative of a steel surface with no open eyes.

[0009] The present invention also relates to a casting installation comprising a ladle, a tundish, a mold and an open eye alert device, the open eye alert device comprising: a measuring device capable of capturing data representative of light intensity, the measuring device being positioned to capture light emitted from a surface of the tundish; a processor capable of receiving the captured data representative of light intensity, the processor comprising a determining means capable of determining the intensity of light emitted from the surface of the molten steel in the tundish; a detecting means capable of detecting the presence of an open eye at the surface of the molten steel based on the determined intensity; and an alarm issuing means capable of issuing an alarm to an operator when an open eye is detected.

[0010] The measurement device may be an optical transmitter.

[0011] Other characteristics and advantages of the invention will become apparent from the non-limiting description of the invention given below by way of indication, in connection with the attached drawings, in which: [Brief description of the drawings]

[0012] [Figure 1] 1 shows a casting installation equipped with a device for carrying out the method according to the invention; [Figure 2A] 1 is an image of the layer of molten steel in a tundish. [Figure 2B] 1 is an image of the layer of molten steel in a tundish. [Diagram 3] 1 is a flow chart of a method according to the present invention. [Figure 4] 4 is a curve representing light intensity as a function of time during a casting operation. [Diagram 5] 1 is a curve showing the TOE size as a function of the measured light intensity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Elements in the figures are illustrative and may not be drawn to scale.

[0014] Figure 1 shows a casting installation 1 comprising a ladle 2, a tundish 3 and a mould 4. The molten steel 5 in the ladle 2 has the required temperature and composition according to the steel semi-finished product to be cast. The molten steel first flows from the ladle 2 through a ladle shroud 6 into the tundish 3 and then from the tundish 3 through a submerged entry nozzle (SEN) 7 into the mould 4. The molten steel then slowly flows out of the mould 4 and solidifies to form the semi-finished product.

[0015] Figures 2A and 2B are real images of the molten steel surface covered with tundish powder in a tundish 3. In Figure 2A, no open eyes are present, the powder layer is continuous and homogenous, and it can be inferred that the molten steel 5 is directly under the ladle shroud 6. In contrast, in Figure 2B, the formation of a large open eye 10 can be seen around the ladle shroud 6. The purpose of the illustration is to show that the size of the TOE (Tundish Open-Eye) can be increased and therefore a large amount of the steel surface can be reoxidized in contact with air. Therefore, it is important to detect the formation of such an open eye early in order to limit its consequences.

[0016] Figure 3 is a flow chart of the method according to the invention. In a first step 100, the intensity of light emitted from the surface of the molten steel in the tundish is determined. This step can be carried out by using any sensor capable of measuring the light intensity directly or indirectly. The sensor may be, for example, a light sensor measuring the light intensity, such as light sensor 8. This light sensor 8 may be any sensor capable of measuring the light intensity. It is preferable to use a light intensity transmitter, such as the BLUX510 manufactured by BASI Instruments. The advantage of using such a transmitter is that it is a simple device that can be easily protected to withstand the high temperature environment surrounding the tundish.

[0017] The sensor may measure the light intensity around the tundish, and the measured signal is then processed to remove all components that are not associated with the molten steel surface. For example, the ladle shroud, made of refractory, heats up and turns red when molten steel flows through it. The ladle shroud is therefore very bright, and it may be necessary to remove this light intensity component from the signal captured by the sensor in order to retain only the signal relative to the steel surface.

[0018] In a second step 110, the presence of an open eye at the surface of the molten steel is detected based on a predetermined intensity. This can be done, for example, by determining a baseline of intensity that represents a continuous power layer without an open eye. If the determined light intensity is above this baseline, it means that an open eye is present.

[0019] After this second step 110, an optional step 111 of calculating the size of the detected open eye may be performed. For that purpose, a regression model can be used. This regression model is constructed by correlating the open eye size measured by direct observation with the respective light intensity signals in a number of open eyes of various sizes. As a result, said model can be used to predict the future size of the open eye.

[0020] 5 is a curve showing the TOE size as a function of the measured light intensity. This King curve can be used in calculation step 111 to determine the size of the TOE.

[0021] After the second detection step 110 or the optional calculation step 111, a third step 120 is performed of issuing an alert to an operator when an open eye is detected. Optionally, this alert may be issued only if the calculated size of the open eye is above a predefined threshold. For a tundish with a length of 9 meters, the alert is issued, for example, only if the size is 90 centimeters or more.

[0022] The decision step 100, the detection step 110, the alarming step 120 and the calculation step 111 are preferentially carried out by at least one processor equipped with dedicated algorithms capable of carrying out all of said steps.

[0023] Once the alarm is generated in step 120, tundish powder is poured onto the surface of the steel to cover the open eye. This may be done by an operator, or via an automatic pourer receiving commands from an operator, or directly by a processor which performs the detection and / or calculation steps.

[0024] FIG. 4 is a curve representing the light intensity, expressed in Lux, versus time, measured during a casting operation using the casting method according to the invention. The sensor used to measure the light intensity is a BLUX510 light transmitter from BASI Instruments. Each encircled peak represents the beginning of a new heat, corresponding to the injection of steel into the tundish through the ladle shroud. At the beginning of each heat, the ladle and the ladle shroud are raised to replace the empty ladle with a full one. This increases the overall areal brightness, which corresponds to a peak of intensity. After the ladle is replaced, the ladle and the ladle shroud are lowered. It can then be seen that the light intensity is almost zero and increases more or less rapidly, depending on the heat considered. This corresponds to the appearance and growth of an open eye on the surface of the steel. This was visually confirmed during the tests. During the first heat, the size of the open eye exceeds a certain threshold and powder must be added, which is noted on the curve, with the sudden decrease highlighted in a bold rectangle.

[0025] The method according to the present invention can be envisaged to detect an open eye in the tundish and quickly alert the operator to reduce the impact on product quality and equipment uptime.

Claims

1. 1. A method of casting a steel semi-finished product, in which molten steel is poured from a ladle through a shroud into a tundish, comprising the steps of: A. determining the intensity of light emitted from a surface of molten steel in a tundish (100); B. detecting the presence of an open eye at the surface of the molten steel based on the determined intensity (110); C. issuing an alert to an operator when an open eye is detected (120); D. Pouring powder onto the surface of the molten steel in the tundish (130); A method for providing the above.

2. The method of claim 1 , further comprising between the determining step (100) and the detecting step (110) a step of calculating (111) a size of the open eye based on the determined intensity.

3. 3. The method of claim 2, wherein the issuing step (120) is performed only if the calculated size of the open eye is greater than or equal to a predetermined threshold size.

4. The method according to claim 2 or 3, wherein the calculating step (111) is performed using a regression model.

5. The method of any one of claims 1 to 4, wherein the determining step (100) is performed using a baseline of intensities representative of a steel surface with no open eyes.

6. A casting equipment for carrying out the method according to claim 1, comprising an automatic injection device and an open eye alert device capable of pouring tundish powder onto the surface of steel, a ladle (2), a tundish (3), and a mold (4), a measurement device (8) capable of capturing data representative of light intensity, the measurement device (8) being positioned so as to be able to capture light emitted from the tundish surface; a processor operable to receive the captured data representative of light intensity, i. a determining means capable of determining the intensity of light emitted from a surface of molten steel in a tundish; ii. A detection means capable of detecting the presence of an open eye at the surface of the molten steel based on the determined intensity; iii. an alarm means capable of issuing an alarm to an operator when an open eye is detected; A processor comprising: The casting equipment further includes:

7. 7. The casting installation of claim 6, wherein the measurement device is an optical transmitter.

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