JPH0657846B2 - How to make a tungsten pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a tungsten pipe used as a vacuum furnace and atmosphere furnace part, a nuclear equipment part, and a thermocouple protector. is there.

(Prior Art) Since tungsten has a very high melting point, it has been widely used in the form of plates, rods, thin wires, etc., as a constituent material for electronic parts and the like that require heat resistance. Recently, there has been an increasing demand for tungsten pipes as parts of nuclear reactors and the like, but since tungsten has poor workability, it has been extremely difficult to produce an elongated pipe having a desired length.

As a method of producing a molybdenum pipe that is a similar refractory metal but has better workability than tungsten and has a much lower melting point, the metal powder is molded into a cylindrical body and then sintered, and the core portion is 6%. A method has been proposed in which a core made of a superplastic material such as a titanium alloy containing Al and 4% V is inserted, forged, and then the core is removed (JP-A-58-171505).
issue). Since the core after forging can be easily stretched by heating at 950 ° C, it is said that the core can be easily pulled out by pulling only the core on both sides.

(Problems to be Solved by the Invention) However, since tungsten must be heated to an extremely high temperature during plastic working, such a low melting point superplastic material can be used as the core (core). Therefore, there is a problem in that the above-described known method of subjecting a cylindrical sintered body to plastic working to form a pipe having a small diameter cannot be adopted for manufacturing a tungsten pipe.

(Means for Solving the Problems) In order to solve the above problems, the present invention uses a molybdenum round bar as a core material, and a cylindrical tungsten sintered body which is straightened in advance by a light forging process. After performing the forging process for reducing the diameter by inserting the core material into the hollow part, the core material was removed by using a mixed acid that selectively dissolves only molybdenum.

(Operation) As described above, since the molybdenum round bar, which is a refractory metal, is used as the core material, it can withstand the forging temperature of tungsten sufficiently, and can be straightened into a cylindrical tungsten sintered body in advance. The core material is easy to insert because it has undergone a slight forging process.

(Example) Hereinafter, the present invention will be described in detail based on examples.

First, as the starting material tungsten powder, the tungsten powder conventionally used for electronic materials and the like can be used. For example, an element such as potassium (K), aluminum (Al), or silicon (Si) is added as a doping agent to the tungsten powder when manufacturing a non-sag wire for a tungsten filament. It may or may not be included. Depending on the application, alloy components other than tungsten, such as rhenium (Re), tantalum (Ta), and thorium (Th), may be added in small amounts. Although the particle size of the powder is often about 3 microns, it is not limited to this.

This raw material powder is pressure-molded by a method such as a rubber press using a core material to obtain a molded body having a core hole.
Instead of using a rubber press, a mold 1 as shown in FIG. 1 is used and pressure molding is performed at an appropriate molding pressure, for example, a pressure of about 1.8 t / cm ² , and a molded body 2 as shown in FIG. After obtaining the above, the overhanging portion 2a may be scraped off to obtain a molded body having a circular cross section. In the figure, 1a is an upper mold, 1b is a lower mold, 3 is a molding core (core), and 4 is powder. In the case of pressure molding by any of the above methods, a tapered rod is used as the core material. This taper is a removal taper for removing the core material from the molded product after molding, and a taper of about 1/800 may be provided. For example, the outer diameter of the molded body is 26 mm, the inner diameter is about 10 mm, and the length is
In the case of 400 mm, the outer diameter of one end as the core material is 10 mm,
A core material with a gentle taper such that the other end has an outer diameter of 11 mm may be used. The core material may be a mild steel rod or other metal rod.

When the molding is completed, tap the end of the core material on the small diameter side to remove the core material. Since the core has a taper, it is extremely easy to remove. After removing the core material, pre-sinter in a hydrogen furnace. The pre-sintering temperature is a temperature at which strength that does not hinder the handling in the subsequent process is obtained, for example, 900
Hold at ~ 1000 ° C for 20 minutes.

The obtained pre-sintered body is subjected to drilling to expand the diameter of the core hole and straighten it. This processing is preferably repeated using a long drill in a plurality of stages. For example, if the final hole diameter is 18 mm, 10 to 10
First, make the 11mm hole diameter 13mm, then replace the drill every 1mm and repeat the expansion up to 18mm. Since the pre-sintered body is preliminarily formed with the core hole serving as the pilot hole, the powder removal is good and the drilling is easy. When the core hole has the specified inner diameter,
Next, the pre-sintered body is held by using a jig 5 as shown in FIG. The jig 5 is provided with a flange 5b at a position from one end of a core rod 5a that fits well in the core hole of the pre-sintered body 6 and a screw portion 5c at the other end. Insert the core rod 5a into the core hole until the flange 5b is in close contact with the end,
The jig 5 is firmly fixed to the pre-sintered body 6 by tightening the washer 8 with the nut 7 screwed to the screw portion. In this state, the grip 5d of the jig 5 may be chucked to grind the outer periphery of the pre-sintered body. In this way, for example, an inner diameter of 18 mm, an outer diameter of 24 mm, and a length of 400 mm with a uniform wall thickness (3 m
A pre-sintered body with m) is obtained.

Next, insert terminals 9, 9 are fitted to both ends of the core hole 6a of the pre-sintered body 6 as shown in FIG. Since the insertion terminal 9 serves as an electrode connection terminal during subsequent energization sintering, it must be excellent in conductivity and heat resistance, so it is preferable to manufacture it with a tungsten material. It is preferable that a pre-sintered body of tungsten that is pre-sintered at a temperature higher than the temperature, for example, about 1200 ° C., is machined to an outer diameter that tightly fits into the core hole 6a. The insertion terminal 9 is provided with an axial through hole 9a (for example, a hole diameter of 2 to 3 mm) in order to allow hydrogen gas to flow inside the core hole 6a during sintering.

The main sintering is performed in a hydrogen gas atmosphere using a commonly used bell jar sintering furnace. At this time, the pre-sintered body 6 is supported by holding the insertion terminals 9, 9 fitted to both ends thereof with clip type electrodes. The pre-sintered body supported in the bell jar is directly energized through the electrodes and the insertion terminals, and the heat generated by its resistance causes sintering. This sintering is performed, for example, in 1 cycle for 1 hour, and the maximum current is about 15% of the melting current.
A schedule that holds for minutes is adopted. The sintered body (ingot) that has been sintered is subjected to end cutting to remove the non-sintered portion at the end. The obtained cylindrical sintered body is an excellent one having a core hole with a small eccentricity and a uniform wall thickness, and it can be used as it is as a tungsten pipe depending on the application.

Next, in order to perform the forging process of the obtained sintered body, a processing core material is inserted into the core hole of the cylindrical sintered body, but prior to this, a slight forging is performed on the cylindrical sintered body. The light forging for straightening, which is performed by working and straightened, can be performed by using a swaging machine similar to that used for the forging for subsequent diameter reduction. That is, a cylindrical sintered body heated to a predetermined processing temperature (about 1600 ° C.) is rolled with a swaging machine, and the reduction ratio of the outer diameter in this case is about 2 to 3% or less. As a result, warpage and bending of the sintered body are removed, and the core material can be easily inserted. Tungsten is forged (swaging) for subsequent reduction in diameter
At this time, since the core material is heated to a high temperature of about 1600 ° C., it is necessary to use a material having high heat resistance and workability as the core material, and it is most preferable to use molybdenum as such a material. In this case, in order to prevent the deformation and cracking of the core hole, there must be no large gap between the core material and the core hole, but in the present invention, the cylindrical sintered body after sintering is hollow. As it is, it is lightly forged in advance and straightened, so that the core material can be easily inserted without eccentricity and brought into close contact with the core hole. The diameter of the core material may be such that it can be inserted into the core hole in a state of high adhesion, and it is usually preferable to use a core material having a diameter smaller than the inner diameter of the core hole by 0.2 to 1 mm. As shown in Fig. 5, after inserting the core material of the molybdenum rod into the core hole, swaging is performed while heating as in the case of processing the normal round rod, and if necessary, wire drawing is performed to reduce the diameter. Go on. At this time, the molybdenum core material in the core hole is also reduced in diameter along with the outer diameter of the cylindrical body.

When the desired diameter is obtained by plastic working such as swaging and wire drawing, the core material filled inside is removed. This removal method is carried out by drilling a prepared hole in the core material when the diameter is large and selectively dissolving only molybdenum, for example, a mixed acid solution of nitric acid 2, sulfuric acid 1 and water 1 in a weight ratio. It is dipped in to dissolve the molybdenum of the core material. The composition of the mixed acid is not limited to that described above, and may be any composition as long as it selectively dissolves molybdenum. When the diameter is small enough to prevent the drill from entering, the whole is immersed in the mixed acid solution to dissolve the end of the core material and form a recess in the end, and then as shown in FIG. 6 (a), With the injection tube 10 made of a material that is not affected by the mixed acid such as Teflon, the mixed acid is injected into the concave portion 11a at the end of the core material 11 and the core material 11 is gradually dissolved and removed. As the melting of the core material progresses, the tube 10 is inserted into the core hole as shown in FIG. 3B to completely dissolve and remove the core material inside. In the figure, reference numeral 15 is a mixed acid receiving container.

In this way, as shown in FIG. 7, a tungsten pipe 13 having a desired diameter having a core hole 12 having a straightness and a high roundness in the core portion can be obtained. The inner and outer diameters and the length of the tungsten pipe 13 can be freely selected over a wide range. As is clear from the above description, its manufacture is easy.

(Effects of the Invention) As described above, in the present invention, since molybdenum is used as the core material for plastic working, it is possible to perform good plastic working together with the tungsten cylinder. Since the cylindrical sintered body is straightened by forging in advance before inserting the molybdenum core material, the core material can be easily inserted. In addition, since the core material after plastic working is dissolved and removed by injecting mixed acid that selectively dissolves only molybdenum into the core material using a thin tube such as Teflon tube, in the case of a long pipe However, it has become possible to easily remove the core material without damaging the inner wall and the like, and it has become possible to easily manufacture an elongated tungsten pipe having a desired inner and outer diameters.

[Brief description of drawings]

FIG. 1 is a sectional view of a mold, FIG. 2 is a sectional view of a molded body, and FIG.
Figure is an illustration of jig, Figure 4 is an illustration of insert terminal, Figure 5
(a) and (b) are a front view and a vertical sectional view showing a state in which the core material is filled, FIG. 6 is an explanatory view of the core material removing method, and FIG. 7 (a),
(b) is a front view and a vertical sectional view of the tungsten pipe. DESCRIPTION OF SYMBOLS 1 ... Mold, 2 ... Molded body, 3 ... Core material for molding, 4 ... Powder, 5
... jig, 6 ... pre-sintered body, 9 ... insertion terminal, 10 ... Teflon tube, 11 ... core material, 13 ... tungsten pipe.

Claims (1)

[Claims] 1. A cylindrical sintered body of tungsten or a tungsten-based alloy is lightly forged for straightening, and a core material made of a molybdenum round bar is inserted into the hollow portion of the sintered body. A method of manufacturing a tungsten pipe, which comprises forging each of them, and then removing the molybdenum core material using a mixed acid that selectively dissolves only molybdenum.