JPH0148498B2 - - 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 generate an electrical discharge such as a spark, evaporates fine particles representative of the composition of the molten metal, and separates them. Direct emission spectroscopy of molten metal is carried by an inert gas flow to an emission spectrometer with a plasma excitation source installed at a location, and the content of various components in the molten metal is analyzed online in real time. This relates to an analytical device.

Spark emission spectrometry using sampled and solidified solid block samples is often used to control the manufacturing process of metals and alloys in the metal manufacturing industry. However, in recent years, there has been an increase in the demand for online real-time processing for metal samples in a molten state, such as hot metal or molten steel, for faster manufacturing process control, especially in the steel industry, or for operational management of new manufacturing processes, such as multi-stage refining and steelmaking processes. There is a strong need to develop analytical methods for this. Up 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, 78 (1967), 35 (1968))
Research and development is being attempted using various methods such as However, these methods have never been put to practical use in an actual 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 into practical use at actual manufacturing sites, we must first take into consideration the fact that the manufacturing site has an extremely poor measurement environment, including high temperatures, vibrations, and dust. Therefore, precision measuring instruments such as spectroscopic detectors are prone to trouble and do not function properly in the above-mentioned measurement environment, and should be installed away from areas where molten metal exists, and molten metal should not be exposed to electrical discharge. The most promising method is to pulverize the material and transport it. The present invention allows molten metal to
A method to generate ultrafine particles with a narrow particle size distribution range of 0.1 μm or less, preventing them from sticking to the inner wall of the conveyor pipe and reducing the number of particles.
We have conducted research and development focusing on methods for efficiently transporting products over long distances of 10 meters and methods for introducing them into analysis equipment, and have now provided a practical new analysis equipment that can perform analysis easily, quickly, and with high accuracy and sensitivity. It is something.

According to FIGS. 1 and 2 showing embodiments of the present invention,
The details of the device of the present invention will be explained. The device of the present invention can be roughly divided into a particle generation probe 1, a spark discharge device 2, a particle transport pipe 3, and a carrier gas distribution device 4.
and an emission spectrometer 5 having a plasma excitation source
It consists of The particle generation probe 1 applies a high voltage between the molten metal 6 and the counter electrode 7 to generate a spark discharge, locally heats the molten metal to an even higher temperature, and turns the particles representative of the composition of the metal into smoke. This is the part that works to evaporate. The counter electrode 7 is usually a tungsten round rod with a small diameter of about 2 to 5 mmφ and a pointed tip. The counter electrode 7 is made of steel and is attached to the lower end of the vertically cylindrical cooling tube 8 so that its tip faces the surface of the molten metal 6, and there is usually a constant gap of 5 to 10 mm between the tip of the counter electrode 7 and the surface of the molten metal. Set it up like this. The cooling tube 8 is heated by the radiant heat of the molten metal and is cooled by air or water cooling, but also serves as a conductor for the counter electrode 7. A small-diameter hole is drilled through the center of the cooling cylinder 8 in the longitudinal direction, and a particle introduction tube 9 made of a small-diameter tube with an inner diameter of about 2 to 3 mmφ is inserted into this hole.
It is fixedly held at the upper part of the cooling cylinder 8. The gap between this particulate introduction pipe 9 and the hole penetrating the cooling cylinder 8 is 1 to
A concentric double pipe with a narrow width of 2 mm is formed, and this gap serves as a passage for an inert gas such as Ar that is blown from the top of the cooling cylinder 8, that is, an inert gas injection pipe 10, and the lower end of the cooling cylinder Gas is blown out from the section 27 at high speed. Further, a cylinder 11 made of an insulating refractory material is attached around the lower end of the cooling cylinder 8, and the lower end is immersed in the molten metal 6 to form a small space chamber 12 inside. The above particulate introduction tube 9
The lower end 28 of the electrode protrudes from the small space chamber 12, but it is close to about 10 mm directly above the tip of the counter electrode 7, and opens facing the surface of the molten metal. The gas blowing pipe 10 has a blowing port 27 at the top of the small space chamber 12, and is located above the opening 28 of the particulate introducing pipe 9 with a gap of about 10 mm.

A high voltage is applied between the tip of the counter electrode 7 and the surface of the molten metal 6 to cause a spark discharge, and the ultrafine particles of the evaporated molten metal are transferred to the Ar gas stream blown out from the outlet 27 at the lower end of the Ar gas blowing tube 10. The particles are then quickly carried into the opening 28 of the particle introducing tube 9 located directly above the tip of the counter electrode 7. 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 the evaporated ultrafine particles hardly diffuse within the chamber, and are efficiently introduced into the introduction tube 9 at the same time as they are generated. The inert gas blown into the small space chamber 12 is necessary to expel the atmosphere in the small space chamber 12 to create an atmosphere where spark discharge is likely to occur, 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, but Ar gas is usually suitable. In order to prevent the generated fine particles from dispersing, it is necessary to make the space chamber in which the discharge occurs as small as possible, but for this reason, the molten metal surface is cooled by the Ar gas that is normally blown in at a rate of 10 to 20 minutes, causing damage. .

The temperature of the Ar gas passing through the introduction pipe 9 accompanied by fine particles is particularly high, reaching several hundred degrees when the target is 1600°C molten steel, but the Ar gas is blown along the outer wall of the introduction pipe 9. Therefore, the molten metal surface is preheated by the heat exchange action, and cooling of the molten metal surface can be prevented. In addition, when the particulate transport pipe 3 is several tens of meters long, 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. For these purposes, the Ar gas blowing tube 10 provided in the cooling cylinder 8 needs to have a double tube structure concentrically outside the particle introduction tube 9, with the gap therebetween being as narrow as possible. 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. From this point of view, the particle introduction pipe 9 is
Do not touch the cooling tube 8 directly to avoid being cooled.
A structure using the Ar gas blowing pipe 10 is essential.

The particulate introduction tube 9 is made of a material that has excellent heat resistance and does not easily attract particulates, and stainless steel pipes or alumina pipes are suitable. Heat-resistant synthetic resins are not suitable because they cause fine particles to remain attached due to static electricity. The refractory tube 11 is made of materials with excellent insulation and heat resistance, such as magnesia and alumina, but boron nitride, which has these properties and is resistant to heat shock caused by loading and unloading the molten metal 6, was optimal.

There are various methods of converting molten metal 6 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 large, with a diameter of about 10 to 100 μm or more. Therefore, it is difficult to transport over long distances, and since the particle size distribution range is large, there are problems such as large fluctuations in emission intensity when excited and emitted, resulting in poor analytical accuracy. In the method of superheated evaporation by irradiating a DC arc or an arc column with a plasma arc converged by the pinch effect of water cooling, it is necessary to maintain an extremely short gap between the counter electrode and the molten metal surface of about 1 to 2 mm. So-called selective evaporation tends to occur, in which more than a certain amount of fine particles do not evaporate and the evaporation of components with low vapor pressure takes priority, making it difficult to stably generate fine particles representative of the component composition of the molten metal. The method using laser irradiation has the advantage that it can be applied to non-conductive materials, but continuous lasers such as CO ₂ laser have a small amount of evaporation, so a giant pulse laser has to be used.
This is also not very suitable for accurate on-line analysis since it is not possible to irradiate at high power over a few tens of times per second.

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 13 made of carbon or high-melting point metal immersed in molten metal 6 is used as a sample electrode and a cathode, and a cooling tube 8 is connected to a counter electrode 7 whose tip is placed on the surface of molten metal 6 with a slight gap.
is connected to the spark discharge device 2 as an anode, and high voltage is applied to both poles to generate spark discharge and melt the molten metal 6.
evaporates 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 particularly important to stably generate fine particles that represent the contained components.
The method of setting each discharge constant in spark discharge also has an influence. Self-induction 10μH, capacitance 3μF,
Spark-like spark discharge with resistance 1Ω and voltage 1000V, and each constant 150μH, 8μF, 0Ω,
Arc-like spark discharge set to 700V (from the discharge current waveform, the former is the peak current value)
200A, holding time 30μs, latter 80A each,
As a result of repeatedly analyzing each component by generating fine particles in a steel sample under both discharge conditions (400μs),
The coefficient of variation of the analysis value of Si containing 0.50% is 2.5 for the former.
%, the latter contains 11.6% and 1.04% of Mn, respectively, is 3.8%.
%, 12.6%, and 0.30% Cu content is 5.1% and 14.2%, respectively.
Results such as % were obtained. That is, as mentioned above, spark-like spark discharge is more stable than arc-like and suitable for evaporating each component in the molten metal as fine particles. Regarding the discharge frequency, we investigated the range from 50 to 800Hz, but the
A larger number of discharges per unit time, such as Hz or more, was 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 5 together with the carrier gas at a constant flow rate, resulting in a more efficient method. Fine particle transport technology will be required. In the present invention, the fine particles evaporated from the surface of the molten metal 6 and rising directly above the tip of the counter electrode 7 are prevented from diffusing to the surroundings, and are blown out from the lower end 27 of the Ar gas blowing tube 10 to the lower end of the fine particle introduction tube 9. A method was adopted in which the particles were quickly carried away by the Ar gas flow flowing into the opening 28. Since the small space chamber 12 where the particles are generated has no outlet other than the opening 28 of the particle introduction pipe 9,
It is drawn into the Ar gas flow and sent into the opening 28 of the introduction tube 9 at a constant dilution ratio. In order to form an Ar gas flow to stably send fine particles to the opening 28 without disturbing the discharge of the discharge column formed by the tip of the counter electrode 7 and the surface of the molten metal, an Ar gas blowing tube is required. The outlet 27 at the lower end of the particle introducing tube 9 needs to be located slightly above the opening at the lower end of the particle introduction tube 9 .

The particles introduced into the particle introduction tube 9 are carried by the Ar gas flow and are conveyed to the carrier gas distribution device 4 through the particle transfer tube 3. However, when analyzing particles as in the present invention, In this case, it is important to prevent fine particles from adhering to and remaining on these inner walls. Since the particulate introduction pipe 9 is heated by the high heat of the molten metal, the particulates do not easily adhere to it and there is no problem, but the transport pipe 3 has a long distance and the temperature decreases, making it easy for the particulates to remain attached. As a result, the concentration of particulates in the carrier gas fluctuates and contamination occurs, making it impossible to obtain accurate analytical values. Therefore, the diameter of the conveyor pipe 3 should be as small as possible to increase the flow rate of the carrier gas, or a heating device 14 should be attached as shown in the drawing to keep it constantly heated, or fine particles once attached can be easily peeled off within a short time after adhesion. Therefore, we adopted a method of cleaning by blowing carrier gas at a higher speed.

The carrier gas distribution device 4 diffuses the fine particles sent by the carrier gas from the carrier pipe 3 once in a small space and further makes them uniform. This is used to distribute the carrier gas by discharging the particles out of the system, or to eliminate particles that have become particularly coarse due to agglomeration while they are being transported out of the system, and to send only fine particles to the plasma torch 15. It is for making grains etc. The distribution device 4 is a small diameter cylindrical tube with a heating device 14 attached to the outer periphery of the particle conveying tube 3.
is inserted from the side wall so that the pipe end opening 17 faces upward, and the particle supply pipe 16 is attached from the top of the cylindrical pipe so as to face the transport pipe end opening 17 at a constant distance. A discharge pipe 19 with a vessel 18 is attached. These three pipes are all thin tubes with a diameter of 10 mm or less, and coarse particles, excess particles, and carrier gas are discharged from the system through the bottom discharge pipe 19, and the remaining particles are introduced into the supply pipe 16 along with a constant flow rate of carrier gas. be done.

The particle supply pipe 16 is connected to the plasma excitation emission spectrometer 5 . As shown in the figure, the introduced fine particles are carried into a triple tube plasma torch 15 consisting of a fine particle supply pipe 16, a plasma gas supply pipe 20, and a cooling gas supply pipe 21, and are then transferred to a high frequency generator 2.
2. High temperature Ar plasma part 23 formed by
When it reaches this point, it is excited and emits light. The excitation light is separated into spectra by a spectroscope 24, and a detector 25 consisting of a photomultiplier tube, etc.
The component content calculation device 26 measures the intensity of each spectral line, and the content of each component in the molten metal can be quickly determined. Although a high-frequency inductively coupled emission spectrometer has been most suitable as the analyzer 5 for exciting 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 particle generation probe attached to the support frame 29 with the drive source 30 is lowered toward the surface of the molten metal 6 while blowing Ar gas into the Ar gas blowing tube 10. Ar gas outlet 27
While blowing out Ar gas from the refractory tube 11 and expelling the atmosphere inside the refractory tube 11, the lower end of the refractory tube 11 is exposed to the molten metal 6.
The small space chamber 12 is sealed. After adjusting the distance between the tip of the counter electrode 7 and the surface of the molten metal 6 to a predetermined distance, a high voltage is applied between the sample electrode 13 and the counter electrode 7 by operating the spark discharge device 2 to cause a spark discharge. The evaporated particles are fed into the plasma torch 15 via the particle introduction tube 9, the transport tube 3, and the gas distribution device 4, and are excited to emit light. The content of each component is measured from the integrated emission intensity value for about 10 seconds. After the analysis, the Ar of the particle generation probe 1
Ar gas is intermittently blown in at high pressure from the gas blowing pipe 10 to wash away particles attached to the inner wall of the particle transport pipe 3, etc. Next, the particle generating probe 1 is pulled up from the molten metal 6, and when it becomes necessary to analyze again, the probe 1 is lowered and the above operation is repeated to perform the analysis. The particle size and particle size distribution of the generated fine particles are important because they have a great influence on the quantitative accuracy, especially in the method of analyzing by excitation and emission in plasma. Extremely fine particles of approximately 0.1 μm or less, with an average particle size of 0.04 to 0.05 μm
The width of the particle size distribution was narrow, with approximately 70% or more falling within the 0.06 μm range, making it ideal for plasma emission spectroscopy.

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. DESCRIPTION OF SYMBOLS 1... Particulate generation probe, 2... Spark discharge device, 3... Particulate transport pipe, 4... Carrier gas distribution device,
5... Plasma emission spectrometer, 6... Molten metal,
7...Counter electrode, 8...Cooling tube, 9...Particle introduction tube, 1
0... Ar gas blowing pipe, 11... Fireproof tube, 12
... Small space chamber, 13... Sample electrode, 15... Plasma torch, 24... Spectrometer.

Claims (1)

[Claims] 1 A rod-shaped counter electrode is fixedly installed at the bottom so that the tip faces the molten metal surface with a certain gap, a vertically long cylindrical cooling tube that also serves as a conductor for the counter electrode, and a lower end is installed around the bottom of the cooling tube. An insulated refractory tube is installed so as to be immersed in the molten metal to form a small space inside the tube.It penetrates the center of the cooling tube and its lower end opens to the surface of the molten metal just above the tip of the counter electrode. , the upper end has a vertically long and narrow particle introduction tube that is attached so that it can pass through the top of the cooling cylinder, and the outlet is slightly above the lower end opening of the particle introduction tube, and the introduction tube is arranged concentrically with a small gap. A particulate generation probe consisting of an inert gas blowing tube provided inside; a spark discharge device connected to the cooling cylinder and a sample electrode immersed in the molten metal; an end portion of the particulate transport pipe connected to the particulate introduction pipe; , a carrier gas distribution device consisting of a small container equipped with a particle supply pipe to the plasma light emitting device and a discharge pipe for excess carrier inert gas; connected to the end of the particle supply pipe to generate plasma such as high-frequency inductively coupled plasma. 1. A direct analysis device for molten metal, comprising: a light emitting device having an excitation source; and an emission spectrometer comprising a spectrometer, a detector, etc.