JPH0833282B2 - Method for closing and opening tap hole of refining furnace or molten metal container - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for closing or opening a tap hole of a container such as a furnace or a ladle for smelting or refining highly clean metal. (Prior art) In the field of metal refining, refining and post-refining treatment (out-of-furnace refining, degassing, casting, etc.) avoiding contact with the atmosphere in order to improve the cleanliness of the final products, metals and alloys. I have something to do. Vacuum refining is a typical example, but in addition to that, ladle and tundish (these are simply referred to as "containers" below) are used to transfer molten metal to another container while cutting the molten metal from the atmosphere and casting. There are many things to do. The products requiring high cleanliness as described above are diverse, from high-grade steels and high-alloy steels for special applications to non-ferrous metal alloys such as Ni-based alloys and Ti and Zr alloys. Then, there is a common problem in the treatment of any of these metals. That is, for example, even if clean molten metal is smelted in a vacuum refining furnace, it does not make sense to mix a substance that contaminates the molten metal when it is transferred to another container (for example, when it is poured into a mold). The isolation from the atmosphere can be achieved by casting in a vacuum container, or by sealing the tapping passage and replacing it with an inert gas. However, it is inevitable that contaminants such as refractories are mixed in the molten metal when the tap hole that is blocked during refining is opened. Now, the conventional technology and its problems will be described in detail by taking vacuum refining of high-grade steel as an example. The presence of air during the melting and refining of metals causes the oxidation of metals and the formation of non-metallic inclusions. The vacuum treatment also serves to remove gas components in the molten metal. A vacuum melting furnace that is generally used is often a furnace that uses high-frequency or low-frequency induced current. FIG. 1 is a cross-sectional view showing an example of a high-frequency induction heating type vacuum refining apparatus (details will be described in the section of Examples). In this apparatus, there is a vacuum melting tank 1 in the upper part and a vacuum casting tank 2 in the lower part, and the space between them is airtightly connected. The refined steel is discharged from the tap hole 3 and injected into the mold 4. Since the processes from refining to casting are all performed in a vacuum, it is the most suitable method for producing a metal for which inclusion of oxides and other inclusions must be strictly suppressed. FIG. 2 is an enlarged sectional view showing a portion of the tap hole in FIG. As shown in the drawing, the tap hole 3 (here, the upper nozzle) is blocked with a filler during refining. A commonly used nozzle plug is a non-metal oxide such as silica sand (or a mixture of carbon powder). While these fillers are melting or refining the metal, they are in a granular or sintered state to prevent molten metal from entering the nozzle interior. At the stage of tapping, a method is adopted in which the filling material drops to open holes and the molten metal is tapped. As shown in the figure, when the nozzle is a sliding gate, a filling material typified by silica sand is loaded into the upper nozzle portion housed in the tuyere brick. While melting or refining the metal, the upper part (upper part) of the silica sand sinters while the lower part remains granular. At the time of tapping, when the slider is set to the "open" position (state shown in the figure), the lower nozzle attached to the slider becomes coaxial with the upper nozzle, and granular silica sand drops and opens. By the way, in fact, the success rate of silica sand falling and molten metal coming out is about 60-80% just by setting the slider to the "open" position. 20-40% cannot be tapped because silica sand sinters and blocks holes. When tapping is not possible in this way, oxygen is supplied from the bottom of the lower nozzle from the pipe filled with iron wire, the iron wire is oxidized and burned at the tip of the pipe, and the sintered silica sand is melted by the heat generated. Make a hole. When producing a metal that requires high cleanliness, melting, refining and casting of that metal do not involve atmospheric oxidation or nitrogen absorption,
As described above, it is ideal to carry out in a vacuum. However, when the sliding nozzle cannot be used to open the holes, the silica sand opening by supplying oxygen gas is under atmospheric pressure, so it is difficult to maintain this high cleanliness for 20 to 40% of the molten metal discharge times. . Another problem is contamination of the molten metal by filler such as silica sand, that is, deterioration of cleanliness. In the conventional method, filler such as silica sand is always in contact with the molten metal during melting and refining of the metal. Silica sand sinters at about 950 ° C and melts at about 1700 ° C, but it contaminates the molten metal by being mixed into the molten metal or by reacting with components in the molten metal (eg, Al, Mg, etc.). It will be. Also,
As mentioned above, at the same time when the sliding gate is opened, the filling sand falls prior to tapping, but it is difficult to prevent the falling matter from entering the next container or mold. After all, as long as the conventional filling material is used, the high-cleanliness metal obtained by the vacuum vacuum refining is also contaminated by the non-metallic substance of the filling material, and contains undesirable inclusions. When the filling cannot be opened and the filling is dissolved by oxygen gas etc. as described above, in addition to the above-mentioned direct contamination such as the mixing of the filling, the atmosphere forms the casting atmosphere and the secondary pollution is forced. . In this case, it is extremely difficult to keep the cleanliness of the molten metal high. (Problems to be Solved by the Invention) The present invention is directed to the handling of molten metal in the process from holding to discharging (injection) of molten metal, particularly in the state of being cut off from the atmosphere, that is, under vacuum or in an inert gas atmosphere. The problem is to prevent pollution caused by A direct object of the present invention is to provide a new method of closing and opening the discharge holes of a furnace or various molten metal containers. (Means for Solving the Problems) The gist of the present invention is a method of closing and opening a tap hole of a metal refining or molten metal container in which the tap hole is formed by an upper nozzle of a sliding nozzle, Is a metal filler that does not contaminate the molten metal and closes the tap hole.
The method for closing and opening a tap hole by irradiating a metal filling with a laser beam or an electron beam to open the tap hole. A typical example of the metal refining furnace in the present invention is a high-frequency or low-frequency induction heating type vacuum refining furnace as shown in FIG. In addition to this, AOD, VOD, VAD, etc., regardless of the type of heating means and its presence, and whether melting or refining operation is performed in an air-shielded state or under atmospheric pressure,
All types of furnaces for melting and refining higher metals (alloys) are covered by the present invention. The molten metal storage container means a ladle, a tundish, etc., which are not only used for temporary storage and transportation of molten metal, but recently, in which refining agents are added and gas is blown. In many cases, refining reaction is performed. Hot water is often discharged from such a container to another container or mold in a state where the atmosphere is shut off. In that case, the method of the present invention can be effectively utilized. The term "melting water" generally means the operation of discharging molten metal from the furnace or container as described above. In the above-mentioned furnace or container, the tap hole is usually provided at the bottom of the furnace or container, but in some cases, a tundish or the like has a tap hole on the side surface. In any case, the method of the present invention can be applied to all tap holes that need to be closed and opened. One of the features of the present invention is that the tap hole is closed by "a metal filling that does not contaminate the molten metal". The metal having the same composition as the molten metal is most preferable as the metal constituting the filling material. However, even if the metals do not have completely the same components, any metal that does not cause actual damage by being mixed with the molten metal may be used. For example, when the molten metal is alloy steel, pure iron, carbon steel, or another metal that is a constituent of alloy steel can be used. However, when the temperature of the molten metal is kept high, it is necessary to consider the composition of the metallic filling to have a slightly high melting point so that the metallic filling does not melt during this period. In the case of a high frequency furnace,
Since the position of the tap hole is not in the position where the induced current is directly applied,
Even if the upper part of the metal filling melts, the lower part can maintain a solid state. There is no particular restriction on the form of the filling. Cylindrical forging material, casting material, sintered material, etc. that match the shape of the tap hole can be used,
In some cases, metal particles or powder may be packed. The shape of the filling is basically determined by the shape of the tap hole.
However, the height (length) of the filling is 2 of the minimum diameter of the tap hole.
It is preferable to design the tap hole so that the tap hole is doubled or more, preferably about three times or more. The upper part of the filling metal comes into contact with the molten metal, and a part thereof is melted, but it is preferable that the filling metal has a height (length) of twice the minimum diameter or more so that the filling metal remains until the tapping. Further, if this height (length) becomes 5 times or more the minimum diameter of the tap hole, the time for melting the filling metal by the energy beam becomes too long. Although there are restrictions on equipment, the height (length) of the filling is 2 to 4 times the minimum diameter, which is practically easy to use. A second feature of the present invention is that the metal filling is melted by irradiation with an energy beam to open a tap hole when tapping. As shown in FIGS. 1 and 2, the tap hole is located at the bottom of the furnace, and there is a filling in the narrow part of the auxiliary equipment such as a sliding gate. Therefore, in order to melt this filling, heat must be centrally supplied from the bottom of the furnace to the correct location. For that purpose, an energy beam having a high energy density and capable of giving directionality must be used. Such energy beams include plasma (mainly argon gas plasma), laser beams, and electron beams. Since these energy beams can be used in an inert gas in vacuum, they do not have any adverse effects such as the above-mentioned opening by the oxygen gas. The electron beam can be easily used in a small container and high vacuum conditions, and the laser beam can be used even in a relatively low vacuum condition, and since it can be guided by an optical fiber, it is easy to maintain a vacuum inside the container. The type of beam and the energy supply conditions can be selected according to the equipment scale of the refining furnace and the container, conditions such as refining, and the distance to the metal filling to be melted and the material of the filling metal. In operation, as shown in FIG. 3, the upper nozzle is filled with metal filling prior to charging the furnace with metal.
When tapping, the slider is set to the "open" position and the energy beam is irradiated from below the lower nozzle (in this figure, plasma). Since the plasma under high vacuum can preferentially dissolve the metal filling, it will open up after some time. According to the method of the present invention, metal contamination due to clogging can be eliminated and the success rate of opening and tapping can be 100%, so that a metal with high cleanliness can be manufactured. Example 1 The method of the present invention was carried out in the vacuum melting-casting apparatus shown in FIG. The apparatus shown in FIG. 1 comprises a tiltable melting tank 1 having an upper lid 6 which is detachably attached to the upper side and which is connected to a vacuum duct 5, and a casting vessel 2 which has a mold 4 below, and is provided in the processing vessel. This is a method of manufacturing an ingot by flowing molten metal into a casting tank. In addition, 7 is a lance for temperature measurement and sampling, 8 is a lance for supplying refining oxygen and a refining agent, 9 is a hopper of added alloy iron, 10 is a high frequency coil, 11 is an inert gas or the like blown into the molten metal. 16 is an intermediate trough, and 17 is a turntable for moving the mold. A gate valve 13 and other vacuum valves separated and independent from each of the tanks, a sliding nozzle 14 in a passage for allowing the molten metal in the melting tank to flow down into the casting tank, and a leakage mechanism for the molten metal A partition wall 12 having a and is provided, and the partition wall can be moved laterally from an intermediate portion of both tanks. Below the sliding nozzle, there is an energy beam irradiation device (here, a plasma torch) 15. FIG. 3 is an enlarged cross-sectional view of the sliding nozzle portion (the main structure thereof is the same as that of FIG. 2 described above). A 1% C steel ingot having the shape shown in FIG. 4 was inserted into the upper nozzle as a metal filling, and a plasma torch was installed below the lower nozzle portion. When tapping the molten metal (1% C steel) in the melting tank, after opening the gate valve, the melting tank and the casting tank were evacuated to a vacuum of 1 mmHg or less. After the sliding nozzle was set to the "open" position, the plasma torch was moved below the lower nozzle to irradiate the filling metal with the argon gas plasma. The plasma torch used was a type in which irradiation was performed with the torch side as the cathode and the filling metal (molten metal and molten catalyst) as the anode. The degree of vacuum during plasma irradiation is 1 mmHg or less (usually 0.5 mmHg),
An argon gas amount of 0.8 / min and a plasma power source of 40 kW were used. About 13 to 17 minutes after the start of plasma torch irradiation, the filling metal was eluted and the molten metal could be discharged at the same time. (Example 2) Using the vacuum melting furnace described in Example 1, the shape of the metal filling was changed and tested. As the shape, five types of height of the filling metal were used, which were 1.5 times, 2 times, 3 times, 4 times and 5 times the minimum diameter of the upper nozzle. (FIG. 4 shows a three-fold increase.) Table 1 summarizes the test results. When the value of (height of filling metal / minimum diameter) is 1.5, about 40% of the metal is discharged at the same time when the sliding nozzle is opened and the porosity is good, but the cassette of the sliding nozzle (Fig. 2, Fig. 2) The entire temperature (slider, slide plate, etc. in FIG. 3) became high, and it was observed that the molten metal was inserted into these gaps after tapping. Therefore, it has been found that the value of (filling metal height / minimum diameter) is preferably 2 or more in order to stably discharge hot water. On the other hand, when this value is 5 or more, the plasma irradiation time (melting time of the filling metal) is required to be 20 minutes or more, which is too long for actual operation. Example 3 As shown in FIG. 5, the plasma beam used in tapping the vacuum melting furnace in Example 1 was replaced with an electron beam. The lower nozzle has a plate nozzle -1 for opening operation and a main hot water discharge nozzle -2, unlike the one shown in FIG. In this case, the provisional nozzle is irradiated with an electron beam to open a hole, and then the main tapping nozzle is moved to the position of the upper nozzle to start tapping in full scale. When performing electron beam irradiation, the beam irradiation angle should be a few degrees below the lower nozzle for the purpose of protecting the beam generation hole from the elution droplets of the filling metal (preventing the elution droplets from blocking the beam). To do. The electron beam irradiation conditions were such that the degree of vacuum was 10 ⁻³ to 10 ⁻⁴ mmHg or more, and 1 to 2 A and 25 KV. Tungsten was used for the filament. About 3 to 5 minutes after the irradiation with the electron beam, the filling metal could be eluted and the molten steel could be discharged at the same time. The difference between the plasma beam and the electron beam used in Example 1 is as follows. The electron beam is an energy beam of high voltage and low current, has good directivity, and is easy to use because it does not use gas. Operability is good because the elution time of the filling metal is about half that of plasma. On the other hand, when an electron beam is generated, a high vacuum of 10 ^-3 to 10 ^-4 mmHg or higher is required, and therefore it is suitable for a vacuum melting furnace of a relatively small scale. The effect on the quality and properties of the molten metal is not directly related to the type of energy beam used for the opening, and the effect of improving the cleanliness of steel described below is the same whether it is an electron beam or a laser beam. (Comparative Example) Using the same apparatus as in the example, the operations of melting and tapping using conventional silica sand as a filler were performed. That is, about 1 to 2 kg of silica sand (0.5 to 1.0 mmφ particles) was inserted into the upper nozzle hole portion to close it.
When the molten metal (1% C steel) in the melting tank was discharged, the gate valve was opened, and then the melting tank and the casting tank were evacuated or the sliding nozzle was set to the “open” position under atmospheric pressure argon atmosphere. The nozzle plug (silica) that flows out at the same time as the nozzle "opens" usually falls into the mold together with the molten metal that flows out. However, we also tried to remove the silica that flows out in the initial stage from the passage of the molten metal by using a silica sand removal plate as shown in FIG. That is, a thin iron plate is placed on the trough of the vacuum casting tank to eliminate silica sand that falls in the initial stage. When the molten steel begins to fall, the thin iron plate melts and holes are formed, and thereafter the molten steel is poured into the mold. After the silica sand that flows out at the same time as the nozzle "opens", the molten metal in the melting tank continues to flow out (melting), but when the amount of molten metal in the melting tank is small, the static pressure due to the molten metal is small and the upper nozzle The silica sand (filling material) that was sintered in step 2 may not be broken and the hot water may not come out. At this time, both melting and casting tanks were set to atmospheric pressure (air atmosphere), oxygen gas was blown into the iron wire from below the lower nozzle to oxidize and burn the iron wire, and sintering was performed by the heat. The filling was melted and tapped. The effects of the conventional method and the method of Example 1 on the cleanliness of steel were compared and examined. The 1% C steel of Example 1 has a high cleanliness, that is, T.

The target is to reduce the [0] (total oxygen concentration) to 9 ppm or less and to reduce inclusions as much as possible. The commonly used ASTM method was used to evaluate inclusions. (A) T.

[0] (Total Oxygen Concentration) Distribution Figure 7 shows the T. of a total of 130 samples taken from each of the 18 ingots tested.

The distribution of [0] is shown. In the figure, (a) is a result of Example 1, (b) is a result of Conventional Method 1 (using a silica sand removing plate), and (c) is a result of Conventional Method 2 (using no silica sand removing plate). In Example 1, T.

[0] ... Average 6.4 ppm In conventional method 1, T.

[0] ... Average 12.9 ppm In conventional method 2, T.

[0] ... The average was 17.3 ppm. (B) Evaluation of inclusions by ASTM AS of 68 mmφ steel piece cast and rolled from cast ingot
Table 2 shows the results of investigations on B-type and C-type inclusions in the TM method. In the conventional method, there are many B-type and C-type inclusions, but in Example 1, a slab with extremely high cleanliness was obtained although there was some thin (narrow width). The success rate of hot water discharge also influences the results shown in FIG. 7 and Table 2. The porosity of tapping holes by the method of the present invention is almost 100%. On the other hand, in the conventional method, the success rate of tapping (opening) was at most 30%. That is, about 70% of the conventional method has a high T.S.

It appears as a [0] value and variation, and results in many inclusions as shown in Table 2. Improving the success rate of hot springs
It is an indispensable factor for suppressing quality variations and ensuring stable operation and quality. (Example 4) Using the same apparatus as in Example 1, the Ti alloy and the Ni-based alloy were refined, and the conventional method and the method of the present invention were compared. A plasma beam was used for the opening of the method of the present invention. Table 3 shows the T. of refining alloys, tap hole fillings, and cast alloys.

[0] value, defect detected by ultrasonic test (UST) or inclusion evaluation by ASTM method, and success rate of tapping molten metal are shown together. From this table, it is clear that the method of the present invention can be applied to the treatment of all kinds of metals and alloys requiring high cleanliness, and exerts a great effect. (Effect of the Invention) The present invention achieves the above-mentioned remarkable effects by a combination of closing the tap hole with a metal filling and opening the hole with an energy beam. The method of the present invention greatly contributes to the development and production of high-performance metal materials, which have been actively carried out recently.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a vacuum refining apparatus to which the method of the present invention is applied, and FIG. 2 illustrates a conventional method for closing and opening a tap hole of a furnace as shown in FIG. FIG. 3 is a schematic sectional view, FIG. 3 is a diagram for explaining the method of the present invention, FIG. 4 is a diagram illustrating a metal filling used in the method of the present invention, and FIG. 5 is the same as the method of the present invention in FIG. FIG. 6 is a diagram showing one improvement example in the test of the conventional method, and FIG. 7 is a measurement result of the total oxygen content in steel obtained by the method of the present invention and the conventional method. FIG.

Claims (1)

[Claims] 1. A method for closing and opening a tap hole of a metal refining or molten metal storage container in which the tap hole is formed by an upper nozzle of a sliding nozzle, the metal filling being free from the possibility of contaminating the molten metal during use. A method for closing and opening a tap hole by closing the tap hole with a metal, and at the time of tapping, the metal plug is irradiated with a plasma beam, a laser beam or an electron beam to melt the plug. .