JPS5853683B2 - Method for manufacturing molybdenum pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a molybdenum pipe, and more particularly, to a method for manufacturing a molybdenum pipe that can mass-produce thin-walled and long molybdenum pipes. .

Due to its poor high-temperature workability, molybdenum pipes have traditionally been made by first making a sintered ingot using powder metallurgy technology, then producing a solid material (round bar or square bar) by forging, etc., and then machining. It is manufactured by hollowing out, extrusion using a hot extruder, or electrolytic processing.

In the case of thin-walled pipes, the pipe is manufactured by bending a sintered plate and seaming it using an electron beam or the like.

However, all of these conventional methods have complicated manufacturing processes, cannot be said to be suitable for mass production, and have many technical and economical problems.

In particular, for large and long tubes, conventional methods have not been able to provide satisfactory results.

Furthermore, in the case of seamless thin-walled pipes, it is extremely difficult to manufacture them.

The present inventors have solved these drawbacks of the prior art,
In particular, as a result of intensive research to develop a method suitable for manufacturing thin-walled long molybdenum pipes, we found that by forming a cylinder from molybdenum powder before sintering and sintering this, molybdenum pipes can be manufactured. The present invention was completed by succeeding in manufacturing relatively easily.

That is, the object of the present invention is to have excellent mass productivity, and particularly to produce thin-walled long pieces (inner diameter of 8wφ or less, wall thickness of ammJJ or less, length of 500m).
The purpose of the present invention is to provide a manufacturing method suitable for molybdenum pipes (m or more).

The present invention is characterized in that, before sintering, a cylindrical body is formed from molybdenum powder, and then the cylindrical body is sintered on a V-shaped boat-shaped sintering jig.

As a method for forming the cylinder, a method is used in which a mandrel (type 6) is used to form the cylinder using the mandrel as a core, and then the mandrel is pulled out.

This method is particularly suitable for manufacturing thin-walled long molybdenum pipes used for protection tubes and the like.

As shown in FIGS. 1 and 2, the method using a mandrel is to put a hard rubber bag 2 into a liner 1, place a mandrel 3 in the center, and then fill it with molybdenum powder 4.
This is a method of forming by hydrostatic pressing and then pulling out the mandrel.

The mandrel may be made of any material as long as it does not shrink during hydrostatic pressing and has a suitable bending property, but molybdenum and iron are preferred, particularly soft iron. mandrels are preferred.

After molding molybdenum powder using the mandrel as a core, the mandrel is punched out, and the ease with which it can be pulled out is determined by the mandrel's diameter, length, and degree of curvature.

Generally, if the mandrel is thin, long, or curved, it is difficult to pull it out.

When the diameter of the mandrel becomes less than a certain value relative to the wall thickness of the molded body, the mandrel becomes difficult to pull out rapidly, but this is thought to be because the so-called spring or back phenomenon of the molded body becomes smaller.

To facilitate drawing, it is preferred that the mandrel be slightly tapered.

The material of the liner is usually iron or plastic, and its diameter is selected taking into account material yield due to post-processing of the molded product (for example, lathe processing to produce a finished surface) and shrinkage due to sintering of the molded product. There is a need to.

Usually, it is designed by considering shrinkage due to sintering of 15 to 20% and material yield due to processing of 80 to 90%.

The length is selected depending on the length of the molded body or finished product.

The molybdenum powder used as a raw material has a particle size of 2 to 5 μm, preferably 3 to 4 μm.

After filling with molybdenum powder, molding is performed by isostatic pressing, and the molding pressure at this time is usually 1 to 3 tons/crA.
and preferably about 2 tons/cd.

The cylindrical body thus obtained is preferably lathe-processed to obtain a finished surface and then sintered. At this time, the cylindrical body is sintered using a ■-shaped boat-shaped sintering jig (hereinafter simply " ■
A molded body 6 is placed on the molded body 6, and the molded body 6 is sintered in a furnace.

The material of the V-shaped boat is preferably molybdenum, and the opening angle of the bottom is preferably 90±10°.

Further, during sintering, it is convenient to attach sliding powder (for example, alumina powder) to the surface of the molded body in order to improve the sliding between the V-shaped boat and the molded body as the molded body shrinks.

In addition, in order to prevent the tube from warping or bending due to sintering and to obtain a straight long tube, a weight 7 preferably made of molybdenum is placed on the molded body. It is preferable to place it densely.

The sintering temperature is usually 1700 to 1900°C, and the sintering time is usually 5 to 7 hours, although it varies depending on the sintering temperature.

The sintered molybdenum cylinder thus obtained can be made into a finished molybdenum pipe by performing processing such as sealing on one side, if necessary.

In addition, according to the method of the present invention, there is no need to perform sealing on one side after sintering, and it is also possible to form the molded body itself into a molded body with a plug at one end.

Further, the thick-walled sintered body can be further processed into a thin-walled long tube by a drawing method (plug-draw method).

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, and the characteristics of the molybdenum pipe obtained by the present invention will be clarified, but the present invention is not limited thereby.

PVC liner (650mmX20mmφ
(inner diameter)], place a hard rubber bag in the center, and place 7.
A soft iron mandrel with a diameter of 1 mm was installed, and the grain size was 4.2.
Filled with μm molybdenum powder.

This was processed using the hydrostatic press method at a molding pressure of 2.0 tons/cr.
After forming, the mandrel was pulled out to form a cylinder.

After applying alumina powder (sliding powder) to this cylinder, it was placed on a V-shaped boat with a length of 600 mm and an opening angle of 900 mm at the bottom, and a molybdenum wire of 2.5 mrnφ x 25 mm was placed on top of this cylinder at both ends. 4 to 5 rods were placed at 30-degree intervals in the center, and weights were placed at 50-degree intervals in the center.

Next, the cylindrical body placed on the V-shaped boat was placed in a sintering furnace.
Sintering was carried out at ℃ for 7 hours.

Table 1 shows the dimensions of the compacts after isostatic pressing and the finished products after sintering, as well as the specific gravity of the finished products for Samples/161 to 4.

Regarding the finished product samples //61 and 2 thus obtained,
A bending test was conducted using the three-point support method.

As a comparative example, a sintered forged molybdenum rod of 101rL1rtφ was cut* to produce a pipe of the same shape and subjected to a bending test.

The test conditions and results are shown in Table 2. As is clear from Table 2, the sintered bodies obtained by the method of the present invention exhibit properties equivalent to those of the conventional ones in terms of transverse rupture strength.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing the method of forming a cylinder according to the method of the present invention using a mandrel, FIG. 2 is a cross-sectional view at the same AA, and FIG. FIG. 2 is a perspective view showing a sintering method using a boat. 1 Niliner, 2: Rubber bag, 3: Mandrel, 4: Molybdenum powder, 5: V-shaped boat, 6: Molded body, 7: Weight.

Claims (1)

[Claims] 1. A cylindrical body is formed by rubber pressing molybdenum powder with hydrostatic pressure using a mandrel, and then the cylindrical body is sintered on a V-shaped boat-shaped sintering jig. A method for manufacturing molybdenum pipes. 2. The manufacturing method according to claim 1, wherein sliding powder is attached to the surface of the cylindrical body during sintering. 3. The manufacturing method according to claim 1, wherein a weight made of molybdenum is loaded onto the cylinder in the diametrical direction of the cylinder during sintering. 4 The opening angle of the bottom of the V-shaped boat-shaped sintering jig is 90±10
0. The manufacturing method according to claim 1, wherein