DE3413589A1 - Method for measuring the composition and the temperature of liquid steel and liquid slag in a smelting crucible - Google Patents

Abstract

The invention relates to a method for determining the temperature and chemical composition of a melt, in which method high-intensity pulsed light is focused through a duct onto a part of the melt surface and there generates a plasma consisting of ions, atoms and electrons, which emits radiation specific for the elements contained in the plasma, which radiation is returned through the duct onto a spectrograph and is dispersed there, and in which the signal spectrum obtained is used to recognise the elements excited in the melt to emit radiation and/or to measure the temperature pyrometrically. The method according to the invention makes it possible to continuously obtain information, as a metallurgical process proceeds, on the composition and temperature of the melt, so that measures for setting the desired final composition can be controlled according to the current composition and temperature or the required alloying materials can be adjusted specifically.

Description

Method of measuring composition and temperature

of liquid steel and liquid slag in a melting vessel Die The invention relates to a method for measuring the composition and the temperature of liquid steel and liquid slag in a melting pot.

In the smelting metallurgical processes in which metals are melted, be refined or alloyed, it has so far only been possible to select the respective Determine composition of metal or slag by taking a sample which has been processed by chemical or physical processes is. In the case of the physical processes, e.g. emission spectral analysis or X-ray fluorescence analysis examines the prepared sample and its composition certainly.

In emission spectral analysis, the elements are e.g. electric arc excited to blast at the point of impact, whereby from the Radiation spectrum closed on the proportion of the individual elements in the sample can be. Since sampling from the melt is only carried out discontinuously can and for the preparation, transport and treatment of the sample in the most favorable case a time of at least about 5 minutes is required with this process concept not only used expensive production time and energy. It is also disadvantageous that Changes occurring during sampling can only be detected approximately. In many cases, the desired final composition can be sufficiently accurate to be achieved; however, the melt often has to be devalued the, because this cannot be achieved.

In the case of discontinuous sampling, it was also often necessary for the precise adjustment of the desired composition metallurgically complex Carry out rework. Furthermore, the most favorable litigation could be achieved a metallurgical objective cannot always be clearly identified.

You have already tried at least at a certain point in time With the help of a sublance, get an insight into the course of the metallurgical process to be able to. With the help of such a sublance, the temperature of the melt can be determined will. At the same time, a sample can be taken and over the stopping point while cooling whose carbon content can be determined.

With the help of such a device, however, the temperature and the Composition of the metal bath not continuously during the entire process to be determined. The sample must also be analyzed later in the laboratory, so that a considerable time elapses between taking the sample and knowing the composition.

A continuous temperature measurement has also been proposed of liquid metal in a crucible in such a way that carry through a quartz rod passed through the wall of the melting vessel the melt has been discharged to the outside and measured. Such measurements were possible for a short time. But after a short period of operation, it was turned towards the melt The surface of the quartz bushing becomes blind, so that no more radiation could be collected, which allowed conclusions to be drawn about the temperature of the metal bath.

The aim of the present invention is to carry out a continuous Process that provides constant information during the ongoing metallurgical process provides information on the current composition of the melt and its temperature, so that the measures for setting the desired final composition according to the respective Composition and temperature controlled or the required alloys can be set in a targeted manner.

This object is achieved by the method steps specified in claim 1 solved. The light from a pulsed laser is preferably used as the light of high intensity focused through a channel on a surface element of the melt that passes through a gas which is inert in the melt flows through it and is kept free of the melt by this will. In any case, the channel must be designed in such a way that there is either no optical elements are located or that in it an optical waveguide or an optical Window is arranged so that the laser light can be directed to the melt. This high-intensity light increases the temperature there to several 10,000 "C, whereby a plasma consisting of electrons, ions and neutral atoms is formed. Part of the light emitted by this plasma passes through the one already mentioned Channel or another angled to this channel arranged second channel, the can be carried out in the same way as the first channel, back outside. After the light emerges from the channel, it is in the first case after beam splitting, in the second case, it is directed directly to the input optics of a spectrograph. In the The image plane of the spectrograph is a line of diodes with an electro-optical shutter arranged so that the light broken down by the spectrograph over a certain wavelength range Time-resolved or, with the shutter open, detected in a time-integrated manner in parallel can. The signal spectrum obtained in this way is provided by a downstream Electronics processed and fed to a computer. A through beam division Second signal obtained which is proportional to the frequency-integrated intensity of the plasma is used to normalize the signal spectrum obtained. In the calculator the signal spectrum compared with a sample pool and a classification of the Elements made in the melt.

The radiation spectrum emitted by the melt between the plasma excitations is used for pyrometric temperature measurement.

To the practical application of the invention the functionality to ensure the channel necessary for the passage of light in the manner described, can be done, for example, as follows: A tube, preferably made of copper, is inserted into the metal bath so that one end of the tube is below the surface of the metal bath, the other end of the tube is outside of the melting vessel or pan is located. The tube can e.g. lead through an opening in the delivery be or protected from above by the slag layer by a refractory ceramic immerse in the metal bath. With a well-known, largely opposite the melt inert gas, e.g. argon, flowing through the tube becomes the opening of the tube kept free. In many cases another gas, e.g. nitrogen, can also be used will. The tube has an inside diameter of about 2 to 10 mm, preferably 2 to 4 mm.

The gas throughput depends on the free cross-section. The gas velocity should be about 10 to 150 m / sec., preferably 20 to 60 m / sec. Speeds up to the speed of sound of the gas are possible, for economic reasons but not wanted. The tube is cooled by the gas flow at the same time, so that it can withstand the thermal conditions.

The aim is to achieve a gas throughput that is just sufficient for the tube to obtain. In the case of a passage of the tube through the notch will in the course of the wear and tear of the lining, the tube is also degraded, so that it is generally does not protrude into the liquid metal, but only just penetrates the lining.

It must be avoided in any case that by an excessive Gas throughput and an associated excessive cooling are in front of the tube a solid approach of metal and / or slag forms, which then allows a clear view sealed by the tube to melt. The gas throughput should be set in this way that the mouth of the tube does not freeze over in any case. Should accordingly, the opening in the case of overcooling due to excessive gas throughput through the tube are closed to the melt by solid approaches, the same is always closed Part hit by the laser beam, excited to radiation and from this the composition certainly. In this case the analysis result will remain constant. As long as the opening is free, the composition of the flowing metal will have certain fluctuations exhibit. This is in addition to the mentioned temperature measurements on the tube is another way of recognizing whether this is due to an excessive gas throughput the nozzle has overcooled, so that buildup has occurred.

Another control option is pyrometric temperature measurement even in connection with the ongoing determination of the composition of the laser affected volume element. If, for example, from spectral analysis and temperature measurement it can be concluded that the temperature of the metallic volume element struck is below that of the melting point, a metallic solid has formed in front of the tube Approach formed.

If the build-up has occurred, this can be caused by brief Switching from inert gas to oxygen will be burned off again, in turn the spectral analytical or pyrometric results show when the Burning free of the tube closed by attachments has taken place. After that, will switched back to inert gas, e.g. argon or nitrogen, and the throughput slightly lowered to avoid further freezing.

On the other hand, the punctiform heating of the metal acts at the nozzle mouth by the laser beam itself against an obstructive build-up.

In a further embodiment of the method according to the invention is used to improve the dissipation of the laser beam at the point of impact generated radiation in the tube centrally a fiber optic, e.g. made of quartz, inserted so that between the tube and the optical waveguide opposite the melt inert gas can flow to the mouth according to the previous discussion to keep clear and the pipe lead-through and the fiber optic cable against excessive To protect against the effects of temperature. The optical fiber is designed so that the Laser beam can be guided past him through the tube to the point of impact. The optical waveguide can be made rigid or flexible.

In another embodiment of the invention, the laser beam is also used guided through the optical fiber, a window or a focusing lens. The implementation through an optical waveguide is required when due to thermal stress the straightforwardness of the implementation can be called into question. In this case, the laser beam is guided through a flexible optical waveguide a solution, although it must be taken into account that a part the energy of the laser beam is lost when passing through the optical fiber.

The end face of the fiber optic cable or the window must not Get in contact with liquid metal or liquid slag because of their transmittance is severely impaired and the remaining intensity of the radiation for a measurement is no longer sufficient. As already mentioned, this can be achieved through the gas throughputs can be achieved, which enforced through the remaining opening through the tube if the optical fiber inserted into the tube does not melt is carried out directly, but from the liquid melt or the liquid Slag is given a safety margin of at least 10 to 30 mm, and the gas flow rate sufficient to keep the space in front of the optical components free of slag and metal.

As the lining wall thickness decreases, the pipe penetration is shortened, and the distance between the optical fiber end face and the melt is shortened, so that the return radiation is prevented from entering the optical waveguide will.

For this reason, the fiber optic cable is designed as a fiber bundle, the fibers of which protrude at different depths into the tube. This is with decreasing lining wall thickness the number of functional fiber optic fibers less, but the remaining number is sufficient to direct the light with ensure sufficient intensity.

Another embodiment of the safeguarding of the functionality of the light-optical Transmission consists in the fact that if the safety distance mentioned above is not reached the end face of the optical waveguide is withdrawn mechanically. According to the invention is in the area in front of the nozzle orifice that is excited by the laser beam, depending on the process-related movement of the melt, metal and slag stochastically alternately stream. But since metal and slag are clearly different constellations different components in certain limit areas, depending on the given melting process, it is possible due to the given basic compositions of metal and slag to detect whether the volume element just excited to radiation is out Slag or metal.

It is thus possible, quasi simultaneously, the respective composition of slag and metal. In addition, there is the above-mentioned pyrometric Temperature determination in the pauses between two laser beam excitations.

In a broader sense, it can take a melt consisting of metal and slag there is any other liquid for the method according to the invention be understood or a mixture of different liquids and solid components, whereby the respective liquids and / or liquid mixtures and / or solids containing liquids can have different temperatures. The procedure can be used in this case under simplified physical boundary conditions.

In the same way, gaseous or heterogeneous mixtures can also be used which consist of solid, liquid and gaseous particles can. The influence of the thermal radiation in front of the nozzle mouth The gas flow rate can be taken into account empirically with a constant gas flow rate through the tube will.

The invention provides a simple method to the Composition of liquid slag and metal, continuous or discontinuous to analyze and determine their temperature at the same time.

A particular advantage of the method according to the invention is that the analysis can be carried out without contact.

The parallel reading of the spectrum of the is also advantageous Plasmas. This enables the classification of the spectrum to be carried out quickly and reduces the analysis time. By immediately recognizing the Composition of slag and metal as well as the associated temperatures result Improvements in the metallurgical process management that were not previously possible.

The method according to the invention is based on one in the Drawing illustrated embodiment explained.

1 shows the schematic representation of a device for measuring the composition and temperature of liquid steel on a melting pot and FIGS. 2a and 2b show the course of the composition of slag and metal as well the temperature of a melt in graphical representation.

In a melting vessel 1 for refining steel with the infeed 2 is a melt consisting of slag 4 and metal 5. Through the Lance 6, an oxygen jet 7 is directed onto the bath surface and the metal 5 refurbished in the converter. Depending on the oxygen activity, the basic slag and metal, distribution ratios of phosphorus, silicon, Manganese and sulfur between slag and metal. The metal contains predominantly Iron and only small amounts of oxygen and calcium, while the slag contains high levels of calcium and high levels of oxygen. The temperature of the melt changes from 12500C to 16300C during freshening.

Through the infeed 2 a copper tube 8 with a clear Inside diameter of 3 mm out with a gas feed 9. In the tube is Argon blown at a flow rate of about 30 m / sec. On the tube Thermocouples 10 and 11 are attached to control the temperature of the tube. The gas flow rate is adjusted so that, controlled by the thermocouples 10 and 11, no temperatures> 7000C arise on the tube. When exceeded the gas throughput is increased accordingly to this temperature limit. Through the tube 8, a pulsed laser beam 13 is sent through a focusing lens 17. He meets on the melt at the mouth of the tube at point 14. Here is created at At the point of impact a plasma in which the elements are excited to produce specific radiation will. The radiation is sent back through the tube 8 and by the optical fiber 15 via a beam splitter and a focusing lens 18 onto the entrance slit of a Spectrograph 16 in focus. From the beam splitter 19, some of the light is on a photodiode 20 is guided. A reference signal is generated here and sent to the signal processor 21 headed.

In the spectrograph 16, the decomposed light is transmitted via an electro-optical Shutter 22 led to diode array 24. The electronic signal generated here arrives into the signal processor 21 and from here into the classification and control computer 16.

The electro-optical shutter 22 is controlled by the pulse shaper 23, the is again controlled by the master pulser via a delay line 24. The master pulser 25 in turn receives its control commands from the classification and control computer 16. On the other hand, the master pulser 25 controls via a Q-switch trigger 26 and a flash lamp trigger 27 the laser 28.

The laser pulses 13 run at a distance of 1 to 10 ???.

The decay time of the radiation excitation in the plasma 14 lasts several times psec. In the meantime between two of these excitation cycles, the thermal radiation of the area in front of the mouth of the tube 8 in the spectrograph 16 or on the Diode 20 passed. The gas throughput through the tube is adjusted after a Maximum temperature of 700 "C set constant. At the gas throughput, the temperature is at the thermally radiant blown point of impact about 1300C lower than that of the bathroom. This deviation was previously determined by thermocouple measurements carried out in parallel determined and taken into account in the evaluation of the pyrometric radiation values. As a result of the intense movement of the bath during the inflation process, slag and metal became mixed so that stochastically alternating slag and metal particles in the plasma were excited to the specific elementary radiation. There have also been cases in where borderline situations arose, in which slag and metal particles together were stimulated to radiation.

The radiation pulses are captured and broken down by spectral analysis and recorded by the computer after the intensity test.

The analysis collectives of an impulse determined in this way were arranged according to guiding elements. Calcium is used as the guiding element for the slag and oxygen is used, i.e.

Calcium must be> 7% and oxygen 10%.

Iron and oxygen are used as guiding elements for the metal phase. The iron content must be 95% and the oxygen 40.2% around the illuminated area to be identified as a metal surface.

All analysis collectives whose guiding element does not fall into the specified Limits dropping cannot be used, since then slag and metal particles will fall were stimulated to radiation at the same time.

The collectives determined and sorted according to slag and metal analysis Each radiation pulse is preceded by collectives of the same type Radiation pulses combined and their average composition of metal and slag issued separately. Also with the pyrometric temperature measurement several Individual measurements combined to form a mean temperature.

According to the course of the composition of slag shown in FIG and metal and the temperature of a melt, the process can be controlled. It is known that the phosphorus content of the metal is a function of the ratio from Ca0 to Si02 and iron oxide content of the slag. According to current knowledge of the respective composition if the dephosphorization process is inadequate and excessive decarburization speed in the time range of 10 min blowing time Increase the distance between the lance after a blowing time of 11 minutes, the decarburization rate and the drop in the iron oxide content of the slag is significantly reduced.

In Fig. 2 it can also be seen that later the phosphorus content of the metal reached the desired final value of 0.015% phosphorus with a carbon content of 0.07% achieved. On the other hand, it can be seen from the temperature profile that 2-3 minutes before the end of the blowing an addition of 0.6% of the raw weight of ore was necessary to set the desired final temperature at 1640 "C.

Claims (10)

Claims (5 l method for determining temperature and chemical composition of a melt, characterized in that pulsed High intensity light through a channel onto a surface part of the melt is focused and there a plasma consisting of ions, atoms and electrons generates radiation that is specific for the elements in the plasma emitted, which is fed back through the channel to a spectrograph and decomposed there is, and that the signal spectrum obtained for the detection of the melt in the melt Radiation-excited elements used and / or for pyrometric temperature measurement is used. 2. The method according to claim 1, characterized in that the pulsed High intensity light is a pulsed laser beam. 3. The method according to claim 1 or 2, characterized in that the channel consists of a tube made of refractory material, which is from a gas that is inert to the melt flows through it and through this flows from the melt is kept free. 4. The method according to any one of the preceding claims, characterized in that that the signal spectrum obtained is processed by downstream electronics and fed to a computer. 5. The method according to any one of the preceding claims, characterized in, that a second signal obtained by beam division, that of the frequency intensity of the plasma is proportional for standardization of the signal obtained at L: t w 6th Method according to one of the preceding claims, characterized in that in the image plane of the spectrograph is a diode array with an electronic shutter is arranged. 7. The method according to any one of the preceding claims, characterized in, that an optical waveguide is arranged in the channel for returning the radiation. 8. The method according to any one of the preceding claims, characterized in, that the optical fiber is made of quartz. 9. The method according to any one of the preceding claims, characterized in, that the optical waveguide consists of flexible individual quartz fibers. 10. The method according to any one of the preceding claims, characterized in, that the optical waveguide is designed as a fiber bundle, the fibers of which are different protrude deep into the canal.