JP4402873B2 - How to use an electron gun - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a filament constituting an electron gun attached to a metal melting facility, and in particular, a product that effectively prevents filament breakage, improves the life of the filament, and thus enables stable thermal electron irradiation. It realizes excellent productivity.
[0002]
[Prior art]
Metal melting technology using thermoelectrons is widely used not only for melting iron and steel but also for melting refractory metals such as titanium. Such metal melting work is performed by evacuating the furnace after supplying the raw material into the metal melting furnace, and irradiating the raw material with thermoelectrons using an electron gun when the furnace pressure becomes sufficiently low. Start melting raw materials.
[0003]
A conventional electron gun includes a filament, a cathode, a grid, and an anode, and the electrons generated from the cathode are accelerated in the direction of the anode through the electron passage holes of the grid based on the impact of the electrons generated from the filament. A cover for shielding thermionic electrons from the filament going to the grid is arranged between the filament and the grid, and another cover for shielding thermionic electrons from the cover going to the grid is arranged between the cover and the grid. An arrangement is proposed (for example, see Patent Document 1). In the technique described in Patent Document 1, a second metal (for example, tantalum) cover 9 that shields thermal electrons from the cover 8 toward the grid 3 is provided between the metal cover 8 and the grid 3. By arranging and supporting the second metal cover on the support of the filament 1 so as to be at the same potential as the filament 1, the thermal electron irradiation is stabilized.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-6520 (pages 2, 3 and 2)
[0005]
[Problems to be solved by the invention]
However, when the metal is melted using the electron gun described in Patent Document 1, the irradiation of thermoelectrons may stop during the melting of the metal. In such a case, it is necessary to disassemble the metal melting furnace and inspect the inside. From the experience, this thermal electron irradiation stoppage is often caused by damage to parts constituting the electron gun, and in particular, the filament for heating the cathode constituting the electron gun is often broken.
[0006]
When the filament breaks in this way, the operation of the metal melting furnace can be resumed by replacing the broken filament with a new one. However, in such a case, it is not only necessary to disassemble the electron gun, but it is necessary to temporarily release the vacuum state in the metal melting furnace, so that it is impossible to realize excellent product productivity. There was a problem. Therefore, in recent years, there has been a demand for the development of a filament for an electron gun that is difficult to break during the operation of a metal melting furnace in order to realize stable thermionic irradiation and realize excellent product productivity.
[0007]
The present invention has been made in view of the above requirements, and in order to realize stable productivity of products by enabling stable thermal electron irradiation, an electron gun filament that is difficult to break during operation of a metal melting furnace is provided. It is intended to provide.
[0008]
[Means for Solving the Problems]
As a result of intensive research, the inventors have found that filament breakage may be caused by long-term use of the filament, but in many cases, the filament evaporates from the molten metal portion, regardless of the use time. It was found that the cause is that the metal ions released in this way fly to the filament side by the attractive force of the cathode and collide with the central portion of the filament in the radial direction.
[0009]
FIG. 1 is a diagram showing a general metal melting facility that has been widely used in the past. In the figure, reference numeral 10 denotes an electron gun attached to the equipment, and reference numeral 20 denotes a metal melting furnace. As shown in the figure, inside the electron gun 10, a filament 11, a cathode 12, an anode 13, a focusing lens 14, a guide tube 15, a focusing lens 16, and a deflection lens 17 are arranged in this order. On the other hand, in the metal melting furnace 20, a melting metal 22 is supplied to a hearth 21 installed at the bottom thereof. Under such a configuration, when the energization of the filament 11 is started, the filament 11 generates heat, and the cathode 12 positioned therebelow is heated. Thereby, thermoelectrons are emitted from the cathode 12, and the thermoelectrons fly to the anode 13 side located below the cathode 12 and are accelerated downward. The accelerated thermoelectrons are converted into an electron beam under the action of the focusing lens 14, the guide tube 15, the focusing lens 16, and the deflecting lens 17, and are used as a heating source for the metal 22 as indicated by an arrow on the left side of the drawing. Provided. The metal 22 irradiated with the electron beam is melted and guided to a crucible (not shown) to be solidified to form an ingot. When the electron beam is irradiated onto the metal 22 in this way, the metal ions evaporated and released from the molten metal portion fly upward as indicated by the arrow on the right side in the figure by the attractive force of the cathode 12. It is considered that the filament 11 passes through the cathode 12 and reaches the filament 11 to cause the breakage of the filament.
[0010]
FIGS. 2A and 2B show conventional electron gun filaments, respectively. For example, when each filament as shown in FIG. 2 (a) is used in an electron gun, the metal ions flying upward as described above are the radial direction of the filament, for example, the annular portion in FIG. 2 (a). It collides with the central part etc. (the central part in the width direction in the figure). Thus, the inventors have obtained the knowledge that if the hollow portion is formed at the radial central portion of the annular portion of the filament, the above-described collision can be avoided and the filament can be prevented from being broken.
[0011]
The present invention has been made on the basis of the above findings, and relates to a filament structure that is hard to break even when metal ions are evaporated and released from the molten metal portion. That is, the method of using the electron gun of the present invention is a method of using an electron gun composed of an electron gun filament comprising an annular portion and two lead wires connected at any different points of the annular portion. The electron gun has a filament and a cathode, the filament and the cathode are arranged in a straight line with respect to the metal to be melted, the filament is hollow at the center, and the annular part is approximately equidistant from the axis. And a filament having a ratio of the outer diameter to the inner diameter of the annular portion of 1.0 to 1.7 .
[0012]
In the present invention, the structure of the filament is as described above, that is, for example, the central portion in the radial direction of the filament, which is conventionally spiral as shown in FIG. It has a configuration that exists. Thereby, the collision of the metal ions evaporated and released from the molten metal portion with the filament can be avoided, and consequently, the filament can be prevented from being broken during the operation of the metal melting furnace. Therefore, according to the present invention, stable thermal electron irradiation is possible, and excellent product productivity can be realized.
[0013]
In the electron gun filament according to the present invention, in particular, the central portion is hollow, and the ratio of the outer diameter to the inner diameter of the annular portion is 1.0 to 3.0 , thereby maintaining the function as a heater. However, the effect that the collision of the metal ion which flew from the metal fusion | melting part can be avoided is acquired.
[0014]
In such an electron gun filament, the two lead wires may be linear or curved depending on the usage. Further, the annular portion may exist in the same plane such as a circular shape or may exist in a non-coplanar surface such as a spring shape. In addition, you may process a lead wire and a cyclic | annular part with one wire, and may comprise a filament.
[0015]
In such an electron gun filament, the outer diameter of the annular portion is preferably 10 to 30 mm. Although the electron gun filament depends on the output, when the outer diameter of the annular portion is less than 10 mm, the curvature of the coil increases, and the residual stress during processing may cause deformation or breakage of the coil. Further, if the outer diameter of the annular portion exceeds 30 mm, the outer diameter of the annular portion becomes larger than the outer diameter of the sword located below the filament in the electron gun, so that the cathode cannot be sufficiently heated. . In order to further obtain the above effect, the outer diameter of the annular portion is preferably 10 to 20 mm.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the filament for an electron gun of the present invention will be described in detail with reference to the drawings.
FIG. 3A shows an electron gun filament 30 of the present invention. The filament 30 includes an annular portion 31 and two lead wires 34 and 35 connected at arbitrary different points 32 and 33 of the annular portion 31, respectively. The annular portion 31 is spaced from the axis L at an approximately equal distance and extends one and a half times, and the ratio of the outer diameter to the inner diameter of the annular portion 31 is 1.7. The filament 30 shown in FIG. 2 has a configuration in which the central portion in the radial direction of the conventional spiral filament shown in FIG. 2 (a) has a hollow structure and the coil is concentratedly extended on the outer peripheral portion. With this configuration, collision of metal ions evaporated and released from the metal melting portion with the filament can be avoided, and consequently, breakage of the filament can be prevented during operation of the metal melting furnace. Therefore, when the filament 30 having the structure shown in FIG. 3A is used, stable thermal electron irradiation is possible, and excellent product productivity can be realized. Further, in the filament 30 shown in FIG. 3 (a), since it is particularly required to perform continuous operation for a long time by reducing the frequency of disconnection, the ratio of the outer diameter to the inner diameter of the annular portion 31 is 1. 7 and so on.
[0017]
Further, in the electron gun filament shown in FIG. 3A, setting the outer diameter of the annular portion 31 to 10 to 30 mm, and further to 10 to 20 mm prevents deformation and breakage of the coil. It is preferable in that the heating of the cathode is sufficiently realized.
[0018]
FIG. 3B is a view showing a filament 40 having a similar structure to the filament 30 shown in FIG. According to the figure, the filament 40 is composed of an annular portion 41 and two lead wires 44 and 45 connected at arbitrary different points 42 and 43 of the annular portion 41, respectively. It extends away from the axis L at approximately the same distance and extends one and a half, and the ratio of the outer diameter to the inner diameter of the annular portion 41 is 1.1. As described above, the filaments 30 and 40 can be circular or polygonal as described above by appropriately selecting the structure of the annular portions 31 and 41. 3B, the filament 40 having a polygonal shape as shown in FIG. 3B can provide stable thermal electron irradiation and has an excellent product as in the filament 30 having the structure shown in FIG. Productivity can be realized. In some cases, instead of concentrating the extending portion on the outer peripheral portion, a filament from which only the spiral central portion is removed may be used.
[0019]
The filaments 30 and 40 shown in FIGS. 3A and 3B constitute a kind of resistance heating element. For this reason, when not extending a coil to the radial direction center part of the annular parts 31 and 41 of the filament 30 and the filament 40, for example, compared with the conventional filament shown in FIG. Since it decreases, thermionic emission may not be sufficiently realized. However, the overall resistance can be maintained by reducing the wire diameter of the filaments 30 and 40.
[0020]
Furthermore, it is preferable to use a high melting point metal for the filaments 30 and 40, for example, Ta or W is suitable.
[0021]
The number of turns of the annular portions 31 and 41 of the filaments 30 and 40 is preferably 1 to 5 turns, more preferably 1 to 3 turns. The outer diameters of the filaments 30 and 40 are preferably limited to some extent as described above, and the central portion has a hollow structure. Therefore, if the number of turns of the coil is excessively increased, the temperature of the filaments 30 and 40 is increased. May rise too much and cause disconnection.
[0022]
【Example】
Next, examples of the present invention will be described in comparison with comparative examples.
[Example]
The filament of the present invention having the structure shown in FIG. 3 (a), the ratio of the outer diameter to the inner diameter of the annular portion being 1.7, and the outer diameter of the annular portion being 15 mm was employed. Using a metal melting facility equipped with an electron gun having an output of 600 kw having the filament, 300 kg of sponge titanium was melted and 20 titanium ingots were melted. As a result, there was no breakage of the filament and stable melting operation could be continued.
[0023]
[Comparative example]
On the other hand, it has the structure shown in FIG. 2A, the ratio of the outer diameter to the inner diameter of the annular portion corresponding to the annular portion 31 in FIG. 3A is 2.5, and the outer diameter of the annular portion is 15 mm. A conventional filament was adopted. Using a metal melting furnace equipped with an electron gun with an output of 400 kW and having this filament, 300 kg of sponge titanium was melted and a titanium ingot was melted. .
[0024]
【The invention's effect】
As described above, according to the present invention, the central portion in the radial direction of the annular portion of the filament is hollow, and the coil is intensively extended to the outer peripheral portion. The collision of the metal ions with the filament can be avoided, and the filament breakage can be prevented during the operation of the metal melting furnace. Therefore, the present invention is promising in that it can provide a gun filament that can realize stable productivity by enabling stable irradiation of thermoelectrons when performing the melting operation of metal using thermoelectrons. is there.
[Brief description of the drawings]
FIG. 1 is a front view showing a general metal melting facility.
FIGS. 2A and 2B are diagrams showing conventional filaments, respectively.
FIGS. 3A and 3B are diagrams showing filaments according to an embodiment of the present invention. FIG.
[Explanation of symbols]
30, 40 ... Filament, 31, 41 ... Annular part, 32, 33, 42, 43 ... Arbitrary different points of the annular part 31, 34, 35, 44, 45 ... Lead wire, L ... Axis.

Claims (2)

A method of using an electron gun comprising an electron gun filament comprising an annular part and two lead wires respectively connected at any different points of the annular part,
The electron gun has the filament and the cathode, and the filament and the cathode are arranged in a straight line with respect to the metal to be melted,
The filament has a hollow center part, the annular part is spaced at an equal distance from the axial line and extends at least once, and the ratio of the outer diameter to the inner diameter of the annular part is 1.0 to 1.7. A method of using an electron gun , characterized by being a filament . The method for using the electron gun according to claim 1, wherein an outer diameter of the annular portion is 10 to 30 mm.

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