Casting method and related device

Abstract

A method of casting a steel semi-finished product, in which liquid steel is poured from a ladle to a tundish by means of a shroud, the method comprising the steps of determining the intensity of the light emitted from the surface of the liquid steel in the tundish, detecting the presence of a slag eye at the surface of the liquid steel on the basis of the determined intensity, and issuing an alert to an operator when a slag eye is detected.

Description

[0001] The present invention relates to a method of casting of steel semi-products and to a related device.

[0002] In the casting of steel semi-products, the liquid steel is poured into a mould through a submerged entry nozzle (SEN) and then slowly cooled until it solidifies and becomes a semi-product, such as a steel slab or a billet. The liquid steel is produced in a ladle to a given composition and temperature, then poured through a ladle shroud into a tundish. Inert gas is injected into the shroud to protect the liquid steel from possible air entry when the shroud is inserted into the ladle. The tundish is used to feed the liquid steel into ingot moulds, acting as a reservoir and buffer for the liquid steel to feed to the casting machine, providing a smooth outflow and regulating said flow.

[0003] The surface of the liquid steel in the tundish is covered by a floating layer of tundish powder. The purpose of this powder is to avoid the liquid steel from coming into contact with the external air and oxidizing. For several reasons, such as fluctuations in the liquid steel flow or gas bubbles generated by the inert gas, the powder layer can not be continuous and some open areas can appear, which are called tundish open eyes (TOE) or tundish rolls.

[0004] The main consequence of the presence of open eyes is the exposure of the liquid steel to air in this area. As a result, the liquid steel re-oxidizes and inclusions are formed. This is detrimental to the cleanliness of the steel and can lead to defects in the solidified product. In addition, inclusions can flow towards the SEN and accumulate until causing the SEN to clog. When the SEN is clogged, the resulting steel semi-product has to be discarded for quality issues and the whole casting process is slowed down to replace the clogged SEN. This is therefore detrimental to both the product quality and the productivity.

[0005] The open eye phenomenon and its consequences are known, which is why in current practice the operator is responsible for checking the surface of the liquid steel in the tundish periodically and adding powder when necessary. However, this method, like any human-based method, has its limitations. Since the operator does not observe the surface continuously, there is always a delay between the formation of an open eye and the addition of powder, depending on the sensitivity of the steel grade, even a small delay can have a detrimental effect on the quality of the produced steel. In addition, the accumulation of hour-by-hour oxidations will lead to the accumulation of inclusions and clogging of the SEN.

[0006] Therefore, there is a need for a method that enables precise detection of the formation of open eyes on the surface of the liquid steel in the tundish. There is also a need for a method that enables improving the quality of the cast semi-product and increasing the lifetime of the submerged entry nozzle.

[0007] This problem is solved by a method according to the invention, comprising the steps of: determining the intensity of the light emitted from the surface of the liquid steel in the tundish; detecting, on the basis of the determined intensity, the presence of a slag eye at the surface of the liquid steel; and, upon detection of a slag eye, alerting an operator.

[0008] The method of the invention can also comprise the following optional features, taken separately or in all possible technical combinations:

[0009] - the method comprises, between the determining step and the detecting step, a step of calculating the size of the slag eye on the basis of the determined intensity;

[0010] - the alerting step is performed only if the calculated size of the slag eye is greater than or equal to a predetermined threshold;

[0011] - the method comprises, after the alerting step, a step of injecting a powder to the surface of the liquid steel in the tundish;

[0012] - the calculating step is performed using a regression model;

[0013] - the determining step is performed using a reference representative of the intensity of a steel surface free of slag eye.

[0014] The invention also relates to a casting installation comprising a ladle, a tundish, a mould and a slag eye alerting device, the casting installation comprising: a measuring device capable of capturing data representative of the intensity of the light and positioned so as to be able to capture the light emitted from the surface of the tundish; a processor capable of receiving the captured data representative of the intensity of the light and the processor comprising: a determining device capable of determining the intensity of the light emitted from the surface of the liquid steel in the tundish; a detecting device capable of detecting, on the basis of the determined intensity, the presence of a slag eye at the surface of the liquid steel; an alerting device capable of alerting an operator upon detection of a slag eye.

[0015] The measuring device can be a light emitter.

[0016] Other features and advantages of the invention will appear clearly from the following description, given by way of indication and in no way limiting, with reference to the appended drawings in which:

[0017] - Figure 1 a casting installation provided with a device for performing a method according to the invention is shown,

[0018] - Figure 2A and Figure 2B is an image of a layer of liquid steel in a tundish,

[0019] - Figure 3 is a flowchart of a method according to the invention,

[0020] - Figure 4is a curve representative of the light intensity as a function of time during the casting activity,

[0021] - Figure 5 is a curve representative of the TOE size as a function of the measured light intensity.

[0022] The elements in the drawings are illustrative and can not be drawn to scale.

[0023] Figure 1 A casting installation 1 comprising a ladle 2, a tundish 3 and a mould 4 is shown. The liquid steel 5 in the ladle 2 has the temperature and composition required according to the steel semi-product to be cast. The liquid steel 5 in the ladle 2 flows first from the ladle 2 to the tundish 3 through a ladle shroud 6 and then from the tundish 3 to the mould 4 through a submerged entry nozzle (SEN) 7. The liquid steel then flows slowly from the mould 4 and solidifies to form the semi-product.

[0024] Figure 2A and Figure 2B is a real image of the liquid steel surface in the tundish 3 covered by the tundish powder. In Figure 2A , there is no scum eye, the powder layer is continuous and uniform and it can be guessed that the liquid steel 5 is just below the ladle shroud 6. On the contrary, in Figure 2B , a large scum eye 10 can be seen formed around the ladle shroud 6. The purpose of the figures is to illustrate that the size of the TOE (tundish scum eye) can be large, so a large amount of steel surface is in contact with the air and can be re-oxidized. That is why it is important to detect the formation of such a scum eye at an early stage to limit its consequences.

[0025] Figure 3 is a flow chart of the method according to the invention. In a first step 100, the light intensity emitted from the surface of the liquid steel in the tundish is determined. This step can be performed by using any sensor able to measure the light intensity directly or indirectly. The sensor can for example be a light sensor measuring the light intensity, like the light sensor 8. This light sensor 8 can be any kind of sensor allowing to measure the light intensity. It is preferred to use a light intensity transmitter such as the BLUX 510 from BASI Instruments. The advantage of using such a transmitter is that it is a simple device that can easily be protected to withstand the high temperature environment around the tundish.

[0026] The sensor can measure the light intensity around the tundish and then process the measured signal to remove all components that are not related to the steel surface. For example, the ladle shroud made of refractory material heats up when the liquid steel flows through and becomes red. It is therefore very bright and it can be necessary to remove this light intensity component from the signal captured by the sensor to keep only the signal relative to the steel surface.

[0027] In a second step 110, the presence of a slag eye at the surface of the steel liquid is detected on the basis of the previously determined intensities. This can be performed for example by determining a reference of the intensity of the power layer representative of a continuity without slag eye. If the determined light intensity is higher than this reference, it means that there is a slag eye.

[0028] After this second step 110, an optional step 111 can be performed, which comprises calculating the size of the detected slag eye. For this, a regression model can be used. This regression model is established by correlating the size of slag eyes measured by direct observation with the corresponding light intensity signals of a plurality of slag eyes of various sizes. Thus, it is possible to use said model to predict the size of future slag eyes.

[0029] Figure 5 is a curve representative of the size of the TOE as a function of the measured light intensity. This curve can be used in the calculation step 111 to determine the size of the TOE.

[0030] After the second detection step 110 or the optional calculation step 111, a third step 120 is performed, which comprises issuing an alert to the operator when a slag eye is detected. Optionally, this alert is only issued when the calculated size of the slag eye is higher than a predetermined threshold. For a tundish of nine meters in length, the alert is for example only issued when the size is greater than or equal to 90 centimeters.

[0031] The determination 100, the detection 110, the alert issuance 120, the calculation 111 steps are preferentially performed by at least one processor provided with a dedicated algorithm capable of performing all said steps.

[0032] When the alert is issued in step 120, the tundish powder is injected on the surface of the steel to cover the slag eye. This can be done by the operator or by an automatic pouring device receiving instructions from the operator or directly by the processor performing the detection and / or calculation steps.

[0033] Figure 4is a curve representing the light intensity in lux as a function of time as measured during a casting campaign using the casting method according to the application. The sensor used to measure the light intensity is a BLUX 510 light transmitter from the company BASI instruments. Each circled peak represents the start of a new heat, corresponding to the pouring of steel into the tundish through the ladle shroud. At the start of each heat, the ladle and the ladle shroud are raised to replace the empty ladle with a full one. This in turn increases the overall area brightness corresponding to the peaks 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 a slag eye on the surface of the steel. During the trial, a visual check was made of this. During the first heat, the size of the slag eye exceeded the predetermined threshold and powder had to be added, which can be noted on the curve with a sudden decrease highlighted in bold rectangle.

[0034] With the method according to the application, the tundish slag eye can be detected and a rapid alert sent to the operator to reduce the impact on the quality of the product and the duration of the equipment.

Claims

1. A method of casting a steel semi-finished product, wherein, A method of pouring liquid steel from a ladle to a tundish by means of a shroud, said method comprising the steps of: A. determining the intensity of light emitted from the surface of the liquid steel in the tundish; B. detecting the presence of a slag eye at the surface of the liquid steel based on the determined intensity; C. alerting an operator upon detection of a slag eye; Further comprising, between the determining step and the detecting step, a step of calculating the size of the slag eye based on the determined intensity.

2. The method of claim 1, wherein, The alerting step is performed only if the calculated size of the slag eye is greater than or equal to a predetermined threshold size.

3. The method of any one of claims 1 and 2, further comprising: A step of injecting a powder to the surface of the liquid steel in the tundish, after the alerting step.

4. The method of any one of claims 1 and 2, wherein, The calculating step is performed using a regression model.

5. The method of any one of claims 1 and 2, wherein, The determining step is performed using a reference representative of the intensity of a steel surface free of slag eye.

6. A casting installation comprising a ladle (2), a tundish (3), a mould (4) and a slag eye alerting device to perform the method of claim 1, said installation further comprising: - a measuring device (8) capable of capturing data representative of light intensity, said measuring device being positioned so as to be able to capture light emitted from the surface of the tundish; - a processor capable of receiving the captured data representative of light intensity, and said processor comprising: i. a determining device capable of determining the intensity of light emitted from the surface of the liquid steel in the tundish; ii. a detecting device capable of detecting the presence of a slag eye at the surface of the liquid steel based on the determined intensity; iii. an alerting device capable of alerting an operator upon detection of a slag eye.

7. The casting apparatus of claim 6, wherein, The measuring device is a light transmitter.

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