JPH0149891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention applies a high voltage between the molten metal surface and a counter electrode to cause electrical discharge such as a spark to evaporate ultrafine particles representative of the component composition in the molten metal. Direct emission spectroscopy of molten metal is carried out using an inert gas flow to analyze the content of various components in the molten metal in real time online by transporting the molten metal to a plasma emission spectrometer set up at a remote location. This relates to an analytical device.

Spark emission spectroscopic analysis of sampled and solidified block samples is often used for manufacturing process control in the metal manufacturing industry. However, in recent years, especially in the steel industry, online real-time technology that directly targets molten metals such as hot pig iron and molten steel has become available for faster manufacturing process control or operational management of new manufacturing processes such as multi-stage refining steelmaking. There is a strong need to develop analytical methods for this.

Until now, the method of pulverizing molten metal using a special atomizer using Ar gas and performing emission spectroscopic analysis (BISRA, Annual Report: 78 (1966), 65,
Research and development has been attempted using various methods such as 78 (1967) and 35 (1968)). However, these methods have never been actually put into practical use at a manufacturing site and have only been attempted on a laboratory scale.

In order to create a direct analysis device for molten metal that can be put to practical use at actual manufacturing sites, it must first be taken into account that the manufacturing site has a very poor measurement environment, including high temperatures, vibrations, and dust. Precision measuring instruments such as spectrometers and detectors, which can cause problems in such poor measurement environments, should be installed away from the molten metal, and the molten metal should be pulverized by electrical discharge before being transported. The following methods are promising.

The present inventors have developed a method to stably generate ultrafine particles with a narrow particle size distribution range of 0.1 μm or less from molten metal, and to efficiently cover long distances of several tens of meters by preventing fine particles from adhering to the inner wall of the conveying pipe. We have conducted research and development focusing on transportation methods and methods of introduction into analytical equipment, and have now provided a practical new analytical equipment that can be analyzed simply, quickly, and with high precision and sensitivity.

The details of the present invention will be explained using an embodiment of the present invention shown in FIGS. 1 and 2.

The device of the present invention can be roughly divided into a particulate generation probe 1, a vertical position adjustment device 20 for the probe that works in conjunction with a hot water level gauge 38, a refractory cylinder 39 that takes molten metal from deep into the lower part of the probe, a spark discharge device 18, It is composed of a particle transport pipe 22, a carrier gas distribution device 24, and an emission spectrometer 37 having a plasma excitation source. Fine particle generation probe 1
The function is to apply a high voltage between the molten metal 13 and the counter electrode 8 to cause a spark discharge, keep the molten metal locally in a superheated state at a higher temperature, and evaporate fine particles representing the composition of the metal in the form of smoke. This is the part that does this.
The counter electrode 8 is suitably a round bar with a small diameter of about 2 to 5 mm with a pointed tip, and the suitable material is tungsten, which is a high melting point metal with little evaporation consumption. The conical shape of the tip is important for evaporating fine particles at a constant rate.

When the gap between the tip of the counter electrode 8 and the surface of the molten metal 13 is set to 5 mm, and a spark discharge is caused, the pulse discharge is repeated within a range of about 10 mmφ, and the discharge column 1
4 is also stably formed, the amount of evaporation of fine particles is always stable, and good analytical results can be obtained. Even if the hot water level fluctuated a little, a discharge column 14 was always formed from the tip of the counter electrode, and fluctuations in the amount of evaporation of fine particles could be suppressed to a very small amount. 5mm gap between electrodes
When set to , even if the hot water level fluctuates by ±2 mm,
Fluctuations in the amount of fine particles produced could be suppressed to within 5%.

However, if the tip of the counter electrode is a cross section of a round bar or the cross section of the pipe of the particle introduction tube 3 is directly used as the tip of the electrode, a stable discharge column will not be formed, and especially if the melt level fluctuates, the discharge The column moved, and the reproducibility of the amount of evaporated particles could no longer be obtained, resulting in an extremely low analytical accuracy.

For these reasons, the particle introduction tube 3 is used as a conductor for the counter electrode 8, but the counter electrode for spark discharge is fixed at the tip of the introduction tube 3. There are several methods for fixing this, but as shown in Figure 2, a cylindrical electrode holder 6 is connected to the lower end of the particle introduction tube 3 by welding or the like, and a counter electrode is attached to the center of the electrode holder 6. Insert 8 vertically,
A suitable method is to open the particle inlet 7 and fix it with screws 9 or the like.

The particle introduction pipe 3 is made of steel or copper and has an inner diameter of 2 to 3 mmφ.
A pipe with a relatively small diameter is used, and the upper part is fixedly held at the top of the cooling cylinder 2 via a heat-resistant insulating material. The outside of the particulate introduction tube 3 is coated with a heat-resistant insulating tube 4 made of alumina, magnesia, etc., and the cooling tube 2 is coated with a small gap 5 concentrically around the outer circumference.
A hole is made inside, and an inert gas supply pipe 15 such as Ar is attached to the upper part of this gap 5, and the lower part is connected to a gas outlet 10.

The cooling cylinder 2 itself is equipped with a mechanism capable of being cooled by air cooling or water cooling in order to prevent heating of the molten metal due to side radiation heat. Further, a cylinder 11 made of an insulating refractory material such as boron nitride is attached around the lower part of the cooling cylinder 2, and the lower end is connected to the molten metal 1.
3 to form a small space chamber 12 inside.

The electrode holder part 6 with the counter electrode 8 attached to the lower end of the particle introduction tube 3 is connected to the small space chamber 12.
The tip of the counter electrode 8 is exposed to the molten metal 1.
The microparticle inlets 7 are perpendicularly opposed to the surfaces of the electrodes 3 and are set at regular intervals in the range of 5 to 10 mm, and slightly above the tip of the counter electrode, a particle inlet 7 is opened downward. The gas outlet 10 is located at the top of the small space chamber 12, and if it is located above the particle inlet 7,
Suitable for efficient introduction of evaporated fine particles.

A high voltage is applied between the tip of the counter electrode 8 and the surface of the molten metal 13 to cause spark discharge, and the ultrafine particles of the evaporated molten metal are collected at the Ar gas outlet 10.
The particles are quickly carried into the particle introduction port 7 located directly above the tip of the counter electrode 8 by riding on the Ar gas flow discharged from the counter electrode 8 . The small space chamber 12 has a small volume with a diameter of 30 mmφ and a height of 30 mm or less, so that diffusion of evaporated particles is difficult to occur, and as soon as they are generated, they are efficiently introduced into the introduction port 7. The inert gas blown into the small space chamber 12
This is necessary to expel the atmosphere inside the tank to create an atmosphere conducive to spark discharge, and to transport the generated particulates to the analyzer.

The type of gas affects the particle size and amount of fine particles generated, and Ar, He, Ar-H2, _etc. are used.
Ar gas is usually suitable. In order to prevent the dispersion of the generated fine particles, it is necessary to make the space chamber 12 in which the discharge occurs as small as possible.
The molten metal surface is likely to be cooled by the Ar gas blown in at a rate of /min. The temperature of the Ar gas passing through the introduction pipe 3 with fine particles is several
Although the temperature reaches 100 degrees, Ar gas according to the present invention is supplied through the gap 5 made on the outer wall of the introduction pipe 3, so it is preheated by heat exchange before being blown into the molten metal. Cooling of the surface can be prevented.

Further, the ultrafine particles produced by evaporation have a property of immediately adhering to the inner wall of the tube when the temperature of the inner wall is low, making it difficult to quantitatively transport the fine particles. Alternatively, it is necessary to intermittently apply high pressure and blow Ar gas at high speed in order to clean the particulates that adhere and remain inside the pipe, which tends to occur when the particulate transport pipe 22 is made long, such as several tens of meters. . For these purposes, the particulate introduction pipe 3 installed in the cooling cylinder 2 is not cooled by directly contacting the cooling cylinder 2, and the Ar gas injection gap 5 is made as narrow as possible, so that the gas can efficiently contact the outer wall of the introduction pipe 3. In order to do this, it is necessary to form a concentric double pipe structure with a narrow gap on the outside of the particle introduction pipe 3.

Also, if the discharge continues for a long time,
Since some of the evaporated particles adhere to the tip of the counter electrode 8, a method is used in which the polarity is intermittently reversed and discharge is performed to evaporate and remove the attached particles. However, in the case of long-term continuous analysis,
The counter electrode will need to be replaced. This replacement must be done quickly, but since the counter electrode 8 and the particle introduction tube 3 are integrated in the present invention, the cooling cylinder 2
It has the advantage that it can be replaced quickly by simply removing the upper fixture and pulling it upwards.

A problem with directly analyzing molten metal is that the level of the molten metal fluctuates dramatically, and it is rare for the level to remain static. That is, since the purpose of analysis to know the component content is process control of metal manufacturing, direct analysis during the manufacturing process is necessary, and the molten metal level during the manufacturing process is usually not stable. Taking steel manufacturing as an example, the amount of hot metal that flows from the blast furnace into the gutter changes from moment to moment, and during subsequent processes such as dephosphorization, desulfurization, and decarburization in the ladle, changes in the level of the hot metal occur. is in a state of intense boiling. Even if the analysis is carried out by mechanical means or by selecting a relatively stable period, the gap between the tip of the counter electrode 8 and the surface of the molten metal 13 when fine particles are evaporated and generated by spark discharge is Since it usually needs to be 10mm or less, it is essential to take measures against fluctuations in the level of the hot water.

Therefore, in the present invention, as shown in FIG. 1, a hot water level detector 38 is installed facing the surface of the molten metal 13 to constantly detect the hot water level and use this detection signal to hold the counter electrode 8. A method was adopted in which a vertical position adjustment device 20 for vertically driving the cooling cylinder 2 of the fine particle generation probe 1 was operated to maintain the interelectrode gap between the counter electrode and the molten metal at a constant interval.

The hot water level detector, which is suitably of a capacitance type, is fixedly held on the particulate generation probe 1 or the supporting frame 19 of the probe. A driving source 20 for vertical movement of the probe 1 is attached to the top of the probe using an electric motor, screw jack, etc. Small level fluctuations on the hot water surface can be largely eliminated by immersing the refractory tube 11 in the molten metal to form the small space chamber 12;
The level detection accuracy by the hot water level meter 38 is ±0.5
mm or more, the speed at which the detection signal is converted into vertical motion is fast, and according to this method, the gap between the electrodes is always 5 mm ±
It has become possible to adjust the diameter to 1 mm, stably generate fine particles, and conduct analysis with good accuracy.

Another major problem in direct analysis of molten metal is the elimination of slag that floats to the surface of the molten metal and the incorporation of deep weld metal into the particulate-generating probe. Usually, slag floats on the surface of the molten metal, and an oxide film is formed, and for analysis, it is necessary to remove these and expose the surface of the molten metal. Furthermore, the composition of the molten metal directly under the slag layer is often different from that of the molten metal in the deeper layer due to the influence of the slag-metal reaction, so it is necessary to eliminate the slag and also analyze the molten metal in the deeper layer. There is.

In the present invention, as shown in FIG. 1, a slag containing a particulate generation probe 1 and a molten metal level gauge 38, and a cap 41 made of a material having a melting point equal to or lower than that of the target molten metal is covered at the lower end. A method was adopted in which a shielding refractory cylinder 39 was infiltrated into the molten metal 13. Cylinder 39 made of refractory materials such as magnesia, alumina, and boron nitride.
A lifting device 40 is attached to the top of the slag shielding cylinder 39. Before starting analysis, the refractory cylinder 39 is lifted above the molten metal in the same way as the particle generation probe 1. lowering and passing through the slag layer 42 to remove the slag,
Infiltrate into the molten metal 13.

The cap 41 attached to the bottom holds the molten metal 1.
3, and the molten metal in the deep layer is taken into the refractory cylinder 39. After this, the particle generation probe 1 is lowered to start analysis. After the analysis is completed, the refractory cylinder 39 is pulled up together with the particle generation probe 1, and a new cap 41 is attached to the lower end of the refractory cylinder 39, waiting for the next analysis.

That is, since the cap 41 is used as a consumable item, it needs to be easy to replace, but it can be attached by fitting it lightly into the lower end of the cylinder 39. This cap 41 is melted by the molten metal 13 and becomes the subject of analysis, but since the amount of the cap 41 is small compared to the total amount of molten metal taken into the refractory cylinder 39, it is hardly a problem. If possible, use materials that do not contain the component to be analyzed.

In order to reduce the amount of cap that dissolves into the molten metal and to increase the mechanical strength of the cap, it is possible to cover the bottom of the refractory cylinder 39 with a refractory material, make a small hole in the center, and cover the outside with the cap. The method was effective. According to the method of the present invention described above, slag could be sufficiently removed and deep molten metal could be collected satisfactorily.

There are various methods of converting molten metal 13 into fine particles, but in the method of atomizing by a spray action using a high-speed Ar gas flow, as in the above-mentioned cited document, the fine particles generated are approximately 10 to 100 μm or more in diameter. Because of their large size, it is difficult to transport them over long distances, and because their particle size distribution is wide, the emission intensity fluctuates greatly when excited and emitted, leading to problems such as poor analysis accuracy. In the method of superheating evaporation by direct current arc or arc column irradiation with plasma arc converged by the pinch effect of water cooling, the interelectrode gap between the counter electrode and the molten metal surface must be kept at an extremely short distance of about 1 to 2 mm. For example, so-called selective evaporation is likely to occur, in which the evaporation of fine particles exceeding a certain amount does not occur and the evaporation of components with low vapor pressure takes priority, and it is difficult to stably generate fine particles that are representative of the component composition of the molten metal. It's difficult.

Methods using laser irradiation have the advantage of being applicable to non-conductive materials, but continuous lasers such as CO ₂ lasers have a small amount of evaporation, so a giant pulse laser has to be used, but the evaporation rate is several tens of tens of times per second. This is also not very suitable for accurate on-line analysis since it is not possible to irradiate at high power for more than one time.

The present inventors continued detailed research into the suitability of an energy source for vaporizing and generating molten metal as fine particles, and as a result, they selected spark discharge as the optimal method. That is, a rod-shaped electrode 17 made of carbon or high-melting point metal immersed in molten metal 13 is used as a sample electrode and a cathode, and fine particles are introduced whose tip is electrically connected to a counter electrode 8 installed on the surface of molten metal 13 with a slight gap. The terminal 16 attached to the upper end of the tube 3 is used as an anode, connected to a spark discharge device 18, and a high voltage is applied to both poles to generate a spark discharge, and the molten metal 1
3 is evaporated as fine particles.

In order to evaporate and transport molten metal as fine particles and analyze the amount of various components contained in the molten metal, it is especially important to stably generate fine particles that represent the contained components. How it is set also has an impact. self-guided
Spark-like spark discharge and each constant set to 10μH, capacitance 3μF, resistance 1Ω, and voltage 1000V.
A steel sample was examined under both arc-like spark discharge conditions set at 150 μH, 8 μF, 0 Ω, and 700 V (as seen from the discharge current waveform, the former had a peak current of 200 A and a holding time of 30 μS, and the latter had a peak current of 200 A and a holding time of 30 μS, respectively). As a result of generating fine particles in the target and repeatedly analyzing each component, the coefficient of variation of the analysis value for Si containing 0.50% was 2.5% for the former, 11.6% for the latter, and 3.8% and 12.6% for Mn containing 1.04%, respectively. , 0.30% Cu content was obtained as 5.1% and 14.2%, respectively.

That is, as described above, spark-like spark discharge is more suitable for stably vaporizing each component of molten metal as fine particles than arc-like spark discharge. Regarding the discharge frequency, we investigated the range from 50 to 800 Hz, and it was found that a frequency of 200 Hz or higher, in which the number of discharges per unit time is large, is advantageous in terms of analysis accuracy.

In the present invention, which aims at component analysis in molten metal, unlike the case where fine particles are simply generated, the evaporated fine particles must be constantly and stably fed to the analyzer 37 together with the carrier gas at a constant flow rate, resulting in a more efficient method. Good particle transport technology is required. In the present invention, the fine particles evaporated from the surface of the molten metal 13 and rising directly above the tip of the counter electrode 8 are prevented from diffusing to the surroundings, and are blown out from the lower end 10 of the Ar gas blowing tube 5 to the lower end of the fine particle introduction tube 3. A method was adopted in which the Ar gas flowing into the opening 7 of the Ar gas flow was carried away quickly.

Since the small space chamber 12 in which the particles are generated has no outlet other than the opening 7 of the particle introduction tube 3, the particles are drawn into the Ar gas flow and sent into the opening 7 of the introduction tube 3 at a constant dilution ratio. It will be done. In order to form an Ar gas flow to stably send fine particles to the opening 7 without disturbing the discharge of the discharge column 14 formed by the tip of the counter electrode 8 and the surface of the molten metal, it is necessary to The outlet 10 at the lower end of the tube 5 is larger than the opening 7 at the lower end of the particle introduction tube 3.
It should be located slightly at the top.

The particles introduced into the particle introduction pipe 3 are carried by the Ar gas flow and are transported to the carrier gas distribution device 24 through the particle transport pipe 22 connected by the insulating connector 21. When performing analysis on fine particles such as these, it is important to prevent the fine particles from remaining on the inner walls. Since the particulate introduction pipe 3 is heated by the high heat of the molten metal, it is difficult for the particulates to adhere to it and there is no problem, but as the distance of the transport pipe 22 becomes longer, the temperature decreases and it becomes easier for the particulates to remain attached. . As a result, the concentration of particulates in the carrier gas fluctuates,
Contamination occurs and accurate analysis values cannot be obtained.

Therefore, the diameter of the transport pipe 22 is made as small as possible to increase the flow rate of the transport gas. As shown in the drawing, a heating device 23 is installed to heat the surface constantly, or fine particles once attached can be easily peeled off within a short period of time, so a method such as cleaning by blowing carrier gas at a higher speed is adopted. did.

The carrier gas distribution device 24 once diffuses the fine particles sent by the carrier gas from the carrier pipe 22 in a small space to further make the particles uniform. plasma torch 29
In order to obtain the optimum flow rate of the carrier gas introduced into the system, the carrier gas is distributed by discharging a certain portion out of the system. Or, agglomeration progresses while being transported,
In particular, it is used to perform particle sizing, etc., in order to exclude coarse particles from the system and send only fine particles to the plasma torch 29.

The distribution device 24 is a small-diameter cylindrical tube with a heating device 23 attached to its outer periphery.The particle conveying tube 22 is inserted through the side wall, the tube end opening 25 is directed upward, and the particle supply tube 26 is conveyed from the top of the cylindrical tube. A discharge pipe 27 is attached to the bottom of the cylindrical tube so as to be opposite to the tube end opening 25 at a constant distance. These three tubes are
Both are thin tubes with a diameter of 10 mm or less, and coarse particles, excess fine particles, and carrier gas are discharged from the system through a bottom discharge pipe 27, and the remaining fine particles are introduced into the supply pipe 26 together with a constant flow rate of carrier gas.

The particle supply pipe 26 is connected to a plasma excitation emission spectrometer 37 . As shown in the figure, the introduced particles are carried into a triple-tube plasma torch 29 consisting of a particle supply pipe 26, a plasma gas supply pipe 30, and a cooling gas supply pipe 31, and are heated to a high temperature generated by a high frequency generator 32. The light reaches the Ar plasma section 33 and is excited to emit light. The excitation light is separated into spectra by a spectrometer 34, and the intensity of each spectral line is measured by a detector 35 consisting of a photomultiplier tube or the like and a component content calculation device 36, which quickly calculates the content of each component in the molten metal. is required. Although a high-frequency inductively coupled emission spectrometer is most suitable as the analyzer 37 that excites the particles to emit light, other types of plasma-excited emission spectrometers such as arc discharge or atomic absorption spectrometers can be used.

The analysis operation of the apparatus of the present invention will be briefly described.

First, the slag shielding refractory cylinder 39 is lowered into the molten metal 13 through the slag layer 42 by the lifting device 40 . The cap 41 at the tip is melted and the molten metal 13 in the deep layer is taken into the cylinder 39. Next, the particle generation probe 1 attached to the support frame 19 with the drive source 20 is
While blowing Ar gas into the gas blowing pipe 15,
It is lowered toward the surface of the molten metal 13. While blowing out Ar gas from the Ar gas outlet 10 and expelling the atmosphere inside the refractory tube 11, the lower end of the refractory tube 11 is immersed in the molten metal 13 to seal the small space chamber 12. Between the tip of the counter electrode 8 and the surface of the molten metal 13, there is a level gauge 38 and a vertical position adjustment device 20.
By operating the spark discharge device 18, a high voltage is applied between the sample electrode 17 and the counter electrode 8 to generate a spark discharge.

The evaporated particles are transferred to the plasma torch 2 via the particle introduction pipe 3, the transport pipe 22, and the gas distribution device 24.
9 to emit excited light, and the content of each component is measured from the integrated emission intensity value for about 10 seconds. After the analysis is completed, Ar gas is intermittently blown at high pressure from the Ar gas blowing pipe 15 of the particulate generation probe 1 to wash off the particulates adhering to the inner wall of the particulate transport pipe 22, etc.

Next, the refractory cylinder 39 and the particulate generation probe 1 are pulled up from the molten metal 13, and when it becomes necessary to analyze again, the refractory cylinder 39 with a new cap attached to the tip is then lowered, and the probe 1 is lowered, and the probe 1 is lowered. Repeat the operation and perform the analysis. The particle size and particle size distribution of the generated fine particles are important because they have a large effect on the quantitative accuracy, especially in the method of analyzing by excitation and emission in plasma. teeth,
They are extremely fine particles of approximately 0.1 μm or less, and when the average particle size is 0.05 μm, there are approximately 70 particles in the range of 0.04-0.06 μm.
The width of the particle size distribution was narrow, so that the particle size distribution was more than %, making it ideal for plasma emission spectroscopic analysis.

As explained above, according to the present invention, the components contained in a molten metal sample can be directly analyzed quickly and accurately without sampling or other operations, making it extremely useful for operational management of metal refining and steelmaking processes. Great effect.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the entire apparatus according to the present invention;
The figure is an explanatory view of the tip of the particle-generating probe. 1: Particulate generation probe, 2: Cooling cylinder, 3: Particulate introduction pipe, 5, 15: Ar gas blowing pipe, 8:
Counter electrode, 11: Fireproof cylinder, 12: Small space chamber, 13:
Sample electrode, 17: Sample electrode, 18: Spark discharge device, 20: Probe vertical position adjustment device, 22:
Particulate transport pipe, 24: Carrier gas distribution device, 29:
Plasma torch, 37: Plasma emission spectrometer, 38: Hot water level meter, 39: Fireproof cylinder for slag shielding, 41: Cap, 42: Slag.

Claims (1)

[Claims] 1 At the lower end, a round rod counter electrode with a conical tip is attached vertically facing the molten metal surface, and an opening for introducing particles is provided directly above the counter electrode, and the upper end is connected to the particle transport pipe. It is connected to a small-diameter, vertically-shaped particulate introduction tube that also serves as a conductor for the counter electrode, and a concentric circle around the outer circumference of the same particulate introduction tube, with a supply port at the top and a discharge port at the bottom end. The introduction tube is enclosed and held through an inert gas blowing tube, and a cooling cylinder with a cooling structure is placed around the cooling cylinder, and the lower end of the cooling cylinder is immersed in the molten metal during analysis. , a particle generation probe consisting of a refractory cylinder installed to form a small sealed space inside; a spark discharge device in which the upper part of the particle introduction pipe and a sample electrode immersed in molten metal are respectively connected; A function that controls the electrode gap between the tip of the counter electrode and the molten metal surface to a desired dimension in conjunction with the detection signal of the hot water level meter that faces the metal surface and is fixed to the fine particle generation probe or the support frame of the probe. It has a vertical position adjustment device attached to the top of the probe; it contains the above-mentioned particle generation probe and liquid level gauge, and a cap made of a material with a melting point equal to or lower than that of the target molten metal is attached to the bottom. , a refractory cylinder for slag shielding, which has a length that allows it to penetrate deep into the molten metal during analysis, and is equipped with a vertical movement drive; the end of the particle transport pipe connected to the upper end of the particle introduction pipe; , a carrier gas distribution device consisting of a small container to which the lower end of a particulate supply pipe and a discharge pipe for excess carrier gas are attached; a plasma excitation source such as high-frequency inductively coupled plasma connected to the end of the particulate supply pipe; 1. A direct analysis device for molten metal, comprising: a light emitting device having a light emitting device; an emission spectrometer having a spectrometer; and a detector.