JPH0148499B2 - - Google Patents

Description

Detailed Description of the Invention The present invention involves applying 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 composition of the molten metal.
This is a direct emission spectrometry analysis of molten metal that aims to transport the molten metal using an inert gas flow to a plasma emission spectrometer set up at a remote location and analyze the content of various components in the molten metal in real time online. It is related to the 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 analysis that directly targets molten metals such as hot metal and molten steel has become necessary for faster manufacturing process control or operational management of new manufacturing processes such as multi-stage refining steelmaking methods. There is a strong need to develop a method. Until now, a method has been used to pulverize molten metal using a special atomizer using Ar gas and perform emission spectroscopic analysis (BISRA Annual Report: 78 (1966), 65, 78
(1967), 35 (1968)), research and development have been attempted using various methods. However, these methods have never been actually put into practical use at manufacturing sites.
All of these 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 location where the molten metal is present, and the molten metal should be pulverized by electrical discharge and transported. method is promising. The present invention provides a method for stably generating ultrafine particles of 0.1 μm or less and a narrow particle size distribution range from molten metal, and a method for efficiently transporting molten metal over long distances of several tens of meters by preventing the particles from adhering and remaining on the inner wall of the transport pipe. We have conducted research and development focusing on methods for introducing this into analytical equipment, etc., and have now provided a practical new analytical equipment that can perform analysis easily, quickly, and with high accuracy 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 apparatus of the present invention is broadly divided into a particle generation probe 1, a spark discharge device 18, a particle transport tube 22, a carrier gas distribution device 24, and an optical emission spectrometer 37 having a plasma excitation source. The particle generation probe 1 applies a high voltage between the molten metal 13 and the counter electrode 8 to generate a spark discharge, locally keeps the molten metal in a superheated state at a higher temperature, and generates particles representative of the composition of the metal in the form of smoke. This is the part that evaporates the water. 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.
The gap between the tip of the counter electrode 8 and the surface of the molten metal 13 is 5
When a spark discharge is emitted as mm, pulse discharge is repeated within a range of approximately 100 mmφ, and the discharge column 14
are formed stably, the amount of evaporation of fine particles is always stable, and good analytical results can be obtained. Discharge column 1 always flows from the tip of the counter electrode even if the hot water level changes slightly.
4 was formed, and fluctuations in the amount of evaporation of fine particles could be suppressed to a very small extent. When the gap between the electrodes was set to 5 mm, even if the hot water level varied by ±2 mm, the variation 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 moves and the reproducibility of the evaporation amount of fine particles becomes impossible.
Analysis accuracy was extremely reduced. 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 this fixing, but as shown in FIGS. 2 and 3, a cylindrical electrode holder 6 is connected to the lower end of the particle introduction tube 3 by welding or the like, and the central part of the electrode holder 6 is A suitable method is to insert the counter electrode 8 vertically into the electrode, open the particle introduction port 7, and fix it with screws 9 or the like.

The particulate introduction pipe 3 is made of steel or copper and has a small inner diameter of about 2 to 3 mmφ, 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 holes are drilled inside the cooling tube 2 so that a small gap 5 is formed concentrically around the outer circumference. , the upper part of this gap 5 is Ar
An inert gas supply pipe 15 such as the like is attached, and the lower part is connected to the 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 by radiant 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 immersed in the molten metal 13 to form a small space chamber 12 inside. An electrode holder 6 with a counter electrode 8 attached to the lower end of the particle introduction tube 3 is protruded from this small space chamber 12, and the tip of the counter electrode 8 is perpendicularly opposed to the molten metal surface 13, and is 5 to 10 mm The microparticle inlets 7 are set at regular intervals within the range of , and a particle inlet 7 opens downward slightly above the tip of the counter electrode. The gas outlet 10 is located at the top of the small space chamber 12, and its position above the particle introduction port 7 is more suitable for efficient introduction of evaporated particles.

A high voltage is applied between the tip of the counter electrode 8 and the surface of the molten metal 13 to cause a spark discharge, and the evaporated ultrafine particles of the molten metal are carried by the Ar gas flow discharged from the Ar gas outlet 10 to the counter electrode 8. The particles are quickly transported to the particle introduction port 7 located directly above the tip. The small space chamber 12 has a small volume with a diameter of 30 mmφ and a height of 30 mm or less, and the diffusion of evaporated particles is difficult to occur.
It is efficiently introduced into the introduction port 7 at the same time as it is 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-
Although H ₂ etc. are used, Ar gas is usually suitable. In order to prevent the generated fine particles from spreading, it is necessary to make the space chamber 12 in which the discharge occurs as small as possible,
For this purpose, it is usually blown at a rate of 10 to 20/min.
The molten metal surface is likely to be damaged by being cooled by the Ar gas. The temperature of the Ar gas passing through the introduction tube 3 accompanied by fine particles reaches several 100 degrees, but since the Ar gas of the present invention is supplied through the gap 5 made on the outer wall of the introduction tube 3, the heat is reduced. Since the molten metal is preheated by the exchange action before being blown in, cooling of the molten metal surface can be prevented. Further, the evaporated ultrafine particles have the 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 provided 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 efficiently contacts the outer wall of the introduction pipe 3. As such, it is necessary to have a concentric double pipe structure with a narrow gap outside the particle introduction pipe 3.

In addition, if the discharge continues for a long time, some of the evaporated particles will adhere to the tip of the counter electrode 8, so the polarity is intermittently reversed and the discharge is performed to evaporate the attached particles. Take measures such as removing it. However, in the case of long-term continuous analysis, it is necessary to replace the counter electrode. This replacement must be done quickly, but since the counter electrode 8 and the particulate introduction tube 3 are integrated in the present invention, it can be done quickly by simply removing the fixture on the top of the cooling tube 2 and pulling it upward. It has the advantage of being interchangeable.

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 cited document mentioned above, the fine particles generated are large, with a diameter of about 10 to 100 μm or more. Therefore, it is difficult to transport them over long distances, and since the width of the particle size distribution is wide, there are problems such as large fluctuations in emission intensity when excited and emitted, resulting in poor analysis 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 produce fine particles representative of the component composition of the molten metal. The method using laser irradiation has 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 amount is several 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 a particulate introduction tube is connected to a counter electrode 8 whose tip is placed on the surface of molten metal 13 with a slight gap. The terminal 16 attached to the upper end of the molten metal 13 serves as an anode and is connected to a spark discharge device 18, and a high voltage is applied to both poles to generate a spark discharge and evaporate the molten metal 13 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-induction 10μH, capacitance 3μF, resistance
Spark-like spark discharge set to 1Ω, voltage 1000V and each constant to 150μH, 8μF, 0Ω, 700V
Fine particles were generated on a steel sample under both arc-like spark discharge conditions (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 80 A and 400 μs). As a result of repeated analysis, it was found that Si containing 0.50%
The coefficient of variation of the analysis value is 2.5% for the former and 11.6 for the latter.
%, 1.04% Mn content is 3.8%, 12.6%, respectively.
The results for Cu containing 0.30% were 5.1% and 14.2%, respectively. 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,
The range from 50 to 800 Hz was investigated, and it was found that a frequency with a large number of discharges per unit time, such as 200 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 37 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 particles evaporated from the surface of the molten metal 13 and rising directly above the tip of the counter electrode 8 are prevented from spreading 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 particle introduction tube 3. A method was adopted in which the particles were carried away quickly by being carried by the Ar gas flow flowing into the opening 7. 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 to the opening 7 of the introduction tube 3 at a constant dilution factor. 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 needs to be located slightly above the opening 7 at the lower end of the particle introduction tube 3.

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 analyzing fine particles, it is important to prevent fine particles from adhering to and remaining on these inner walls. Since the particulate introduction pipe 3 is heated by the high heat of the molten metal, particulates are difficult to adhere to and there is no problem, but the longer the distance of the transport pipe 22, the lower the temperature and the more likely they are to remain attached. the result,
The concentration of particulates in the carrier gas fluctuates and contamination occurs, making it impossible to obtain accurate analysis values. Therefore, the diameter of the conveyor pipe 22 should be as small as possible to increase the flow rate of the carrier gas, or a heating device 23 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 24 diffuses the fine particles sent by the carrier gas from the carrier pipe 22 in a small space and further makes them uniform. part to the outside of the system to distribute the carrier gas,
Alternatively, particles that have become particularly coarse due to agglomeration progressing while being transported are removed from the system, and particle sizing is performed to 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, and the particulate transport tube 22 is inserted from the side wall to the tube end opening 25.
A particulate supply pipe 26 is attached from the top of the cylindrical pipe so as to face the transport pipe end opening 25 at a constant distance, and a discharge pipe 27 equipped with a flow rate regulator 28 is attached to the bottom of the cylindrical pipe. be. These three pipes are all thin pipes with a diameter of 10 mm or less, and coarse particles, excess fine particles, and carrier gas are removed from the bottom discharge pipe 2.
7 to the outside of the system, and the remaining particulates 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. Ar plasma section 3
3 and is excited to emit light. The excitation light is a spectrometer 34
The detector 3 consists of a photomultiplier tube, etc.
5. The component content calculation device 36 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 is most suitable as the analyzer 37 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 1 attached to the support frame 19 with the drive source 20 is heated to the molten metal 1 while blowing Ar gas into the Ar gas blowing pipe 15.
3. Lower toward the surface. 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. After adjusting the distance between the tip of the counter electrode 8 and the surface of the molten metal 13 to a predetermined distance, a high voltage is applied between the sample electrode 17 and the counter electrode 8 by operating the spark discharge device 18 to generate a spark discharge. The evaporated particles are fed into the plasma torch 29 via the particle introduction tube 3, the transport tube 22, and the gas distribution device 24, 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 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 particle generating probe 1 is pulled up from the molten metal 13, 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 large effect on quantitative accuracy, especially in the method of analyzing by excitation and emission in plasma, but the fine particles generated in molten steel with the device of the present invention are approximately 0.1μ
Extremely fine particles with an average particle size of less than m
In the case of 0.05 μm, the width of the particle size distribution was narrow, with approximately 70% or more falling within the range of 0.04 to 0.06 μm, making it ideal for plasma emission spectroscopy.

As explained above, according to the present invention, components contained in a molten metal sample can be directly analyzed quickly and accurately without performing operations such as sampling.
It is extremely effective for operational management of metal refining and steel manufacturing processes.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the entire apparatus according to the present invention;
The figure is an explanatory diagram of the tip of the particle generating probe, and FIG. 3 is a sectional view taken along line XX in FIG. DESCRIPTION OF SYMBOLS 1... Particulate generation probe, 18... Spark discharge device, 22... Particulate transport tube, 24... Carrier gas distribution device, 37... Plasma emission spectrometer, 13...
Molten metal, 8...Counter electrode, 2...Cooling tube, 3...Particle introduction tube, 5, 15...Ar gas blowing tube, 11...
Fireproof cylinder, 12... Small space chamber, 17... Sample electrode, 29
...Plasma torch, 34...Spectrometer.

Claims (1)

[Claims] 1 At the lower end, a round bar counter electrode with a conical tip is attached vertically so as to face the molten metal surface with a certain gap, and a particle inlet is provided just above the counter electrode.
The upper end is connected to the particle transport tube and is a small diameter, vertically shaped particle introduction tube that also serves as a conductor for the counter electrode, and the inert gas is provided concentrically around the outer circumference of the particle introduction tube and has a blowout port at the lower end. The introduction tube is enclosed and held through the blowing tube, and a cooling cylinder is provided with a cooling structure around it, and a small hermetically sealed tube is placed inside the lower end of the cooling cylinder, the lower end of which is immersed in molten metal during analysis. A particulate generation probe consisting of a refractory cylinder installed to form a space chamber; A spark discharge device comprising the upper end of the particulate introduction pipe connected to a sample electrode immersed in molten metal; A particulate transport connected to the particulate introduction pipe A carrier gas distribution device consisting of a small container attached to the end of the tube, a particle supply tube to the plasma light emitting device, and a discharge tube for excess carrier inert gas; connected to the end of the particle supply tube, and a high frequency inductively coupled 1. A direct analysis device for molten metal, comprising a light emitting device having a plasma excitation source such as plasma, and an emission spectrometer comprising a spectrometer, a detector, etc.