JP3682192B2 - Transition type plasma heating anode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a transition type plasma anode, and more particularly to a transition type plasma heating anode that is suitable for heating in molten steel in a tundish.
[0002]
[Prior art]
The outline of the direct current twin torch type plasma heating apparatus for heating the molten steel in the tundish is as shown in FIG. The tundish cover 2 is inserted with two plasma torches, which are an anode 3 and a cathode 4, respectively, and generates a plasma arc 6 between the torches 3, 4 and the molten steel 5 to heat the molten steel. It is. At this time, the electron flow 7 travels from the cathode 4 to the anode 3 through the molten steel 5.
[0003]
An example of the anode plasma torch is shown in FIG. The figure shows a cross section of the tip of the anode torch. For example, oxygen-free copper is used as the material of the anode 3. The anode torch comprises a stainless steel or copper outer cylinder nozzle 8 that covers the outside, and an inner copper anode body 3. The tip of the anode 3 has a flat disk shape, and both the anode 3 and the nozzle 8 have a cooling structure. The cooling water inlet side and the outlet side water channel are partitioned by cylindrical partition plates 9 and 11, respectively. (10 and 12 in the figure indicate the flow of cooling water). Further, there is a gap 13 between the nozzle 8 and the anode 3, and the plasma gas is blown out from the gap 13.
[0004]
[Problems to be solved by the present invention]
One problem with the DC current anode plasma torch is that the anode tip is damaged and its life is short. Since the anode serves as an electron receiver during the plasma heating operation, the electrons collide with the outer surface of the tip of the anode, and the heat load applied to the outer surface of the tip is large. Also, heat tends to concentrate on the center of the outer surface of the anode tip, and most of the case where the anode reaches the end of its life is due to perforation in the center of the tip. Further, once a current concentration point (anode spot) is formed on the anode surface, there is a property that current is further concentrated on the anode spot. In other words, when the damage starts on the outer surface of the anode tip due to melting, the damage is further promoted, and finally the melt reaches the cooling water side and reaches the lifetime.
[0005]
FIG. 3 explains the pinch effect on the plasma. The plasma 15 has a property (thermal pinch effect) that tends to concentrate in the center direction due to the gas flow 14 having a sufficiently low temperature compared to the plasma blown out from the gap 13 between the nozzle and the anode. Since the current density in the plasma is generally an increasing function with respect to temperature, and the current density in the plasma center portion 16 can be said to be larger than the overall average, the current density incident on the anode tip outer surface center portion 17 is increased. Therefore, the anode tip outer surface center portion 17 is more damaged than the tip outer surface outer peripheral portion 18. Further, the electrons 21 moving toward the anode in the plasma by the interaction with the rotating magnetic field 20 generated by the current 19 flowing in the plasma receive a force 22 toward the center (magnetic pinch effect).
[0006]
Also, as shown in FIG. 4, the tip of the anode is deformed outwardly by the cooling water pressure, thermal stress and creep flowing inside. This convex deformation forms a projection 23 at the center 17 of the outer surface of the anode tip, and the electric field 32 concentrates on the projection 23. Since the electrons 21 moving in the plasma are accelerated in the direction of the electric field 32, the current 19 is likely to concentrate on the protrusion 23, which further causes current concentration to the central portion of the outer surface of the anode tip. That is, the anode tip outer surface center portion 17 is more easily damaged. When damage to the anode tip outer surface center portion 17 progresses, the cooling water passage 25 is eventually broken at the anode tip outer surface center portion 17 and becomes inoperable. In this way, the service life of the anode is significantly shortened due to the current concentration at the center of the outer surface of the anode tip.
[0007]
FIGS. 5a to 5d illustrate current concentration on the anode spot. In an initial state where the cleanliness of the outer surface of the anode tip is good (FIG. 5a), the electrons 21 are incident substantially perpendicularly to the outer surface 26 of the anode tip. However, as described above, the current tends to concentrate on the anode tip outer surface center portion 17 shown in FIG. 4, and the copper melts and evaporates due to the anode tip outer surface becoming high temperature, so that the copper vapor near the center of the outer surface. Cloud 27 is formed (FIG. 5b).
The electrons in the evaporated copper atoms 28 are excited and ionized by the collision of the electrons 21. At this time, since the electrons 29 ionized from the copper atoms have a small mass and a high mobility, they immediately enter the outer surface of the anode tip. However, since the copper ions 30 have a low mobility and stay in the vapor cloud 27, the vapor cloud is positively charged (FIG. 5c).
Due to the positive charge potential of the vapor cloud 27, the electrons 21 in the plasma arc are subjected to acceleration toward the vapor cloud 27 (FIG. 5d).
As a result, when the anode spot 31 is generated, electrons in the plasma arc are concentrated at the central portion of the outer surface of the anode tip in the vicinity of the outer surface of the anode tip. By such a mechanism, the damage of the anode tip proceeds at an accelerated rate.
The present invention relates to the anode tip shape and material for delaying the damage rate of the anode tip as described above in the plasma heating anode and extending the life.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the gist of the present invention is as follows:
(1) A transitional plasma torch for heating a molten metal while supplying a direct current to the molten metal in the container and generating Ar plasma, and comprising an anode made of a conductive metal having an internal water cooling structure, A metal protector having an internal water cooling structure with a constant interval on the outside, and a gas supply means for supplying a gas containing Ar to the gap between the anode and the protector, and a central portion of the anode tip outer surface A negative electrode for transition type plasma heating characterized by being recessed inside.
(2) A transitional plasma torch for heating a molten metal while passing a direct current through the molten metal in the container and generating an Ar plasma, comprising an anode made of a conductive metal having an internal water cooling structure, A metal protector having an internal water cooling structure with a constant interval on the outside, and a gas supply means for supplying a gas containing Ar to the gap between the anode and the protector, and the entire outer surface of the anode tip is A transition type plasma heating anode characterized in that it is recessed inside.
(3) A transitional plasma torch for heating a molten metal while supplying a direct current to the molten metal in the container and generating Ar plasma, and an anode made of a conductive metal having an internal water cooling structure; A metal protector having an internal water cooling structure with a constant interval on the outside, and a gas supply means for supplying a gas containing Ar to the gap between the anode and the protector, and a rib on the anode tip cooling surface A positive electrode for transfer type plasma heating characterized by comprising.
(4) A transition type plasma torch for supplying a direct current to a molten metal in a container and heating the molten metal while generating Ar plasma, comprising an anode made of a conductive metal having an internal water cooling structure, A metal protector having an internal water cooling structure with a constant interval on the outside, and a first gas supply means for supplying a gas containing Ar to the gap between the anode and the protector, 2. A transition type plasma heating anode, comprising: 2 gas supply means, wherein the second gas supply means has a function of blowing gas from the outer surface of the anode tip.
(5) The transition type plasma heating anode as described in (1), wherein the central portion and the whole of the outer surface of the anode tip are recessed inward.
(6) The transition type plasma heating anode according to any one of (1), (2), and (5), wherein the anode tip cooling surface has a rib.
(7) A second gas supply means is provided inside the anode, and the second gas supply means has a function of blowing gas from the outer surface of the anode tip. (1), (2), (3 ), (5) or (6) The transition type plasma heating anode described in any one of (6).
(8) The entire outer surface and / or central portion of the anode tip outer surface is recessed, and one or more permanent magnets that are rotatable in the circumferential direction are provided inside the anode tip (1). ) To (7), the transition type plasma heating anode.
(9) The anode for transitional plasma heating according to any one of (1) to (8), wherein the anode tip material is a copper alloy containing Cr or Zr.
It is.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As described above, what causes damage to the center of the anode tip is current concentration due to the pinch effect applied to the plasma, convex deformation of the anode tip that accelerates current concentration, and formation of an anode spot. In the present invention, in order to prevent such current concentration, convex deformation and anode spot formation, the anode tip shape is changed, a high strength alloy is applied to the anode tip, and a disturbance generating device for preventing anode spot formation Is installed.
In order to prevent current concentration at the center of the outer surface of the anode tip from the plasma pinch effect, it is conceivable to increase the effective area of the anode. However, there are cases where the effective area of the anode cannot be made sufficiently large, such as a problem in connection with equipment and a problem of the limit of the torch holding equipment because the mass of the torch increases by increasing the anode. Therefore, it is necessary to prevent current concentration at the center of the outer surface of the anode tip by making the anode part into an appropriate shape. An example of the present invention according to (1) having such a shape is shown in FIG. In FIG. 6, the anode tip outer surface central portion 17 is recessed. In FIG. 7, since the electric field 32 is perpendicularly incident on the conductor surface, the electric flux density at the central part of the outer surface of the anode tip is lowered by denting the central part of the outer surface of the anode tip as compared with the comparative example shown in FIG. Current concentration can be prevented.
[0010]
The area of the recess is preferably a circle having a radius of 1/5 to 3/4 of the anode tip radius Ra from the center of the anode tip to secure a current concentration prevention region. The center height Hd of the recess is preferably 1/3 to 2/1 of the recess region radius Rd in order to secure the current spreading effect. In the present invention, the gas supplied from the gas supply means may be Ar 100%, or Ar 75% or more, containing 0.1 to 25% N ₂ for increasing the voltage, and the remainder may be inevitable impurities.
[0011]
FIG. 8 shows an example of the outer shape of the outer surface of the anode tip for preventing convex deformation of the anode tip in the present invention according to (2). In FIG. 8, in order to cancel the convex deformation due to the water pressure and thermal stress applied to the anode tip, a recess (crown) is formed on the entire outer surface 33 of the anode tip. The height Hc of the crown is preferably 100 to 500 μm because the outer surface of the anode tip is kept horizontal by deformation during plasma heating.
[0012]
In the present invention according to (5), current concentration can be further prevented by combining the present invention according to (1) and (2).
[0013]
In order to prevent convex deformation of the anode tip, it is necessary to keep the rigidity of the anode tip high even at a high temperature at the anode tip. As one aspect of the present invention according to the above (3) or (6), a rib is provided on the anode tip cooling surface side as one of the techniques for maintaining high rigidity. FIG. 9 is a cross-sectional view of an anode in which ribs 34 are provided on the outer peripheral portion on the anode tip cooling surface side. One or more ribs are installed in the circumferential direction, preferably four or more ribs at equal intervals.
The rib height Hr, radial length Lr, and width Dr are respectively 1/5 to 2/3 of the anode tip radius Ra in order to maintain high rigidity and prevent the flow of cooling water, and the anode tip. It is preferable that the radius Ra is 1/5 to 2/3 and the anode tip cooling water channel width Dc is 1/4 to 1/1. However, when installing a rib in the cooling surface, it is necessary to change the shape of the cooling water channel and the partition plate, so in order to maintain high rigidity, such as Cr-Cu, Zr-Cu or Cr-Zr-Cu It is desirable to apply a high strength material.
[0014]
From the above, current concentration at the center of the outer surface of the anode tip can be prevented. However, as described above, when the anode spot is formed, further current concentration occurs at the anode spot. Even if an anode spot is formed, current concentration may still occur in the anode spot. An example of a disturbance generator for preventing anode spot formation is shown in FIGS.
[0015]
In FIG. 10 showing the example of the present invention according to (4) above, the second gas supply means 43 for blowing out the plasma working gas from the anode tip outer surface 26 and causing disturbance or swirl in the gas flow in the vicinity of the anode tip outer surface. By providing, the anode spot 31 can be moved. The second gas supply means 43 is preferably a cylindrical tube penetrating the outer surface of the anode tip, and the outer diameter of the cylindrical tube is set to 1 mm to 5 mm so that gas can be reliably supplied without obstructing the flow of cooling water. The material is preferably stainless steel, copper or copper plated with corrosion prevention to prevent corrosion. Further, even one effect can be obtained. Preferably, as shown in FIG. 10, one is provided at the center of the anode and 4 inside the cooling water channel partition plate 9 installed inside the anode at equal intervals in the circumferential direction. It is preferable to install 10 to 10.
[0016]
In FIG. 11 showing the example of the present invention according to (8) above, a permanent magnet 36 is embedded in the anode, and the permanent magnet is rotated to form an external magnetic field 38 (FIG. 19) that varies with time, thereby forming an anode spot. Can be moved. As shown in FIG. 13, the wings connected to the permanent magnets are provided in the cooling water passage, and the permanent magnets can be rotated by the flow of the cooling water.
[0017]
As one means for maintaining high rigidity, in the present invention according to (9), a copper alloy capable of maintaining high strength is applied to the tip of the anode. However, in order to keep the anode tip outer surface temperature low, the thermal conductivity of the copper alloy needs to be about the same as or higher than that of oxygen-free copper which is a conventional material. Examples of copper alloys that satisfy such conditions include Cr—Cu, Zr—Cu, and Cr—Zr—Cu. For example, in Cr—Zr—Cu, there are commercially available Cr of 0.5 to 1.5%, Zr of 0.08 to 0.30%, and the remaining copper.
[0018]
【Example】
Examples of the present invention will be described below.
12, 13, 17 and 18 are cross-sectional views showing an embodiment of the present invention.
The features of the anode shown in FIGS. 12 and 17 are as follows (1) to (5). FIG. 12 is a vertical sectional view of the present invention, and FIG. 17 is a horizontal sectional view of the present invention.
(1) The anode tip radius Ra = 25 mm and the anode tip thickness Da = 3 mm.
(2) The dent (crown) on the entire outer surface of the anode tip is a spherical surface with a curvature Rc = 1041 mm, and the height at the tip center is Hc = 300 μm. With this crown, the outer surface of the anode tip during plasma heating operation becomes substantially flat due to thermal stress deformation.
[0019]
(3) A spherical concave portion 40 having a radius of curvature Rd = 15 mm in a range of radius rd = 10 mm formed in the anode tip outer surface central portion 17 is installed. The height of the recess 40 at the center of the tip is Hd = 4 mm. As shown in FIG. 16, the electric field 32 incident on the central portion 17 of the outer surface of the anode tip is dispersed and the current density is reduced as compared with the conventional type having no recess 40. However, the boundary 41 between the concave portion on the outer surface of the anode tip and the outside thereof needs to be smoothly connected so as not to form a large convex portion. The curvature of the boundary 41 is desirably Rb = 30 mm or more. In this embodiment, Rb = 50 mm.
[0020]
(4) Since the outer surface of the tip of the anode is exposed to a high temperature of 500 ° C. or more, the conventional anode using oxygen-free copper may be deformed by creep. In particular, when damage to the outer surface of the anode tip progresses and the tip thickness decreases, the creep deformation increases and the anode tip deforms into a convex shape. Therefore, a copper alloy containing 0.08% Cr and 0.15% Zr was applied to the anode material. FIG. 14 shows the creep deformation amount (hc [mm] shown in FIG. 15) at the center with respect to the plate thickness of a copper (or copper alloy) disk having a radius of 25 mm. In contrast to the oxygen-free copper indicated by the straight line 49 in the figure, the Cr-Zr-Cu indicated by the straight line 50 in the figure has a small creep deformation, and is especially three orders of magnitude smaller at the anode tip thickness of 1.5 mm. That is, Cr—Zr—Cu is less susceptible to creep deformation than oxygen-free copper and can suppress convex deformation at the tip of the anode.
[0021]
(5a) Eight outlets 42a to 42h for blowing out working gas to the outer surface of the anode tip are arranged on the circumference of the outer surface of the anode tip, and one outlet 42i (not shown) is the center of the outer surface of the anode tip. The inner pipes 43a to 43h for passing the working gas connected to the outlets 42a to 42h are installed inside the partition plate 9, and the inner pipe connected to the outlet 42i (not shown) is arranged on the central axis of the anode. Have. Moreover, in order to cause the swirling of the working gas, the inner pipes 42a to 42h are inclined below the anode. The anode spot can be moved by swirling the flow of the working gas in the vicinity of the outer surface of the anode tip by the working gas blown out from the blowing ports 42a to 42i.
Compared to the conventional transfer plasma heating anode shown in FIG. 2, the lifetime of the transfer plasma heating anode according to the present invention is increased by 1.5 to 2 times.
13 and 18 have the same features as (1) to (4) of the anode shown in FIGS. 12 and 17, and the fifth feature has the following features, and the fifth feature has the following features. FIG. 13 is a vertical sectional view of the present invention, and FIG. 18 is a horizontal sectional view of the present invention.
[0022]
(5b) Two permanent magnets 36 are provided in the partition plate 9 inside the anode. The two permanent magnets 36a and 36b are installed at positions symmetric with respect to the axis of symmetry of the anode and are connected by a connecting rod 44. The connecting rod 44 is a rotary shaft installed 5 mm vertically above the center of the anode tip cooling side. 45, and the permanent magnets 36a and 36b are rotatable in the circumferential direction around the rotation axis. Further, by installing the wings 46 fixed to the connecting rod 44 in the cooling water channel 47, the permanent magnets 36a and 36b are rotated in the circumferential direction by the flow 48 of the cooling water. In the vicinity of the outer surface of the anode tip, the magnetic field 38 (see FIG. 19) formed by the permanent magnets 36a and 36b periodically varies with time as the permanent magnets 36a and 36b rotate. Since the charged particles moving with the magnetic field interact, the movement of ions and electrons in the plasma is also affected by the fluctuation by the magnetic field 38 that fluctuates over time. Therefore, even if an anode spot is formed on the outer surface of the anode tip, the charged particles can be moved by the disturbance due to the magnetic field that varies with time.
Compared with the conventional transfer plasma heating anode shown in FIG. 2, the lifetime of the transfer plasma heating anode according to the present invention is increased by 1.5 to 2 times.
[0023]
【The invention's effect】
According to the present invention, the damage speed of the anode tip of the direct current twin torch type plasma heating apparatus can be delayed and the life can be extended.
[Brief description of the drawings]
FIG. 1 is a schematic view of a tundish and a plasma torch.
FIG. 2 is a schematic view of a transitional plasma anode for heating molten steel in a tundish according to the prior art.
FIG. 3 is an explanatory diagram of a pinch effect of plasma.
FIG. 4 is an explanatory diagram of current concentration due to a convex deformation of the anode tip.
FIG. 5 is an explanatory diagram of current concentration due to anode spot formation.
FIG. 6 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
7 is a schematic diagram of an electric field that emerges from the tip of one example of the transition type plasma heating anode shown in FIG. 6;
FIG. 8 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
FIG. 9 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
FIG. 10 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
FIG. 11 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
FIG. 12 is a vertical sectional view of an example of a transfer plasma heating anode according to the present invention.
FIG. 13 is a vertical sectional view of an example of a transfer type plasma heating anode according to the present invention.
FIG. 14 shows material comparison of creep deformation amount.
15 is an explanatory diagram of the graph shown in FIG.
16 is a schematic diagram of an electric field that emerges from the tip of the transfer plasma heating anode according to the prior art shown in FIG.
17 is a horizontal cross-sectional view of the transition type plasma heating anode shown in FIG.
18 is a horizontal sectional view of the transition type plasma heating anode shown in FIG.
19 is a schematic diagram of a magnetic field in the present invention shown in FIG.
20 is a horizontal sectional view of the transition type plasma heating anode shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tundish 3 Anode 5 Molten steel 6 Plasma arc 7 Electron flow 9 Partition plate 17 Anode tip outer surface central part 19 Current 21 Electron in plasma 23 Anode tip convex deformation part 26 Anode tip outer surface 31 Anode spot 29 Anode tip outer surface Crown 32 Electric field 34 Ribs 36, 36a, 36b Permanent magnet 38 Magnetic field 40 Anode tip recess 42 Working gas blowing port 43 Second gas supply means (small tube for working gas blowing)

Claims (9)

A transfer type plasma torch for heating a molten metal while supplying a direct current to the molten metal in a vessel and generating Ar plasma, and an anode made of a conductive metal having an internal water cooling structure, and a constant outside the anode And a gas supply means for supplying a gas containing Ar to the gap between the anode and the protective body, and the central portion of the outer surface of the anode tip is on the inner side. Transition type plasma heating anode characterized by being recessed. A transfer type plasma torch for heating a molten metal while supplying a direct current to the molten metal in a vessel and generating Ar plasma, and an anode made of a conductive metal having an internal water cooling structure, and a constant outside the anode A metal protective body having an internal water cooling structure and a gas supply means for supplying a gas containing Ar to the gap between the anode and the protective body, and the entire outer surface of the anode tip is recessed inward. A transition type plasma heating anode characterized by the above. A transfer type plasma torch for heating a molten metal while supplying a direct current to the molten metal in a vessel and generating Ar plasma, and an anode made of a conductive metal having an internal water cooling structure, and a constant outside the anode A metal protector having an internal water cooling structure, a gas supply means for supplying a gas containing Ar to the gap between the anode and the protector, and a rib on the anode tip cooling surface. A transition type plasma heating anode. A transfer type plasma torch for heating a molten metal while supplying a direct current to the molten metal in a container and generating Ar plasma, and an anode made of a conductive metal having an internal water cooling structure, and a constant outside the anode And a first gas supply means for supplying a gas containing Ar into the gap between the anode and the protective body, and a second gas inside the anode. A transition type plasma heating anode comprising a supply means, wherein the second gas supply means has a function of blowing gas from the outer surface of the anode tip. 2. The transition type plasma heating anode according to claim 1, wherein the central part and the whole of the outer surface of the anode tip are recessed inward. 6. The transition type plasma heating anode according to claim 1, wherein the anode tip cooling surface has a rib. The second gas supply means is provided inside the anode, and the second gas supply means has a function of blowing out gas from the outer surface of the anode tip. 2. The transition type plasma heating anode according to claim 1. 8. The outer surface of the anode tip and / or the central portion is recessed, and one or more permanent magnets that are rotatable in the circumferential direction are provided inside the anode tip. The anode for transfer type plasma heating of any one of these. The transition type plasma heating anode according to claim 1, wherein at least the anode tip material is a copper alloy containing Cr or Zr.

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