JPS6152930A - Production of metallic pipe of polygon section having larger diameter pipe part with step - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy of a large diameter pipe part by leaving a residual wall thickness pipe part with performing the external cutting by the prescribed thickness of the end of the thicker thickness part having less draft then by performing the pipe drawing of the residual wall thickness part. CONSTITUTION:A round pipe having a thicker wall thickness part on the outer diameter side is formed in advance and a pipe drawing is performed with moving the thick wall thickness part to the inside by the die of the necessary sectional shape. A small diameter pipe part B1 is then formed with drawing the one part of the thinner wall thickness part pinching the thicker wall thickness part (a) from the one end side to the end (e1) of the thicker wall thickness part (a) by a die 1 and plug 2. A residual wall thickness pipe part (a') is left with the external cutting by the prescribed thickness of the end of the thicker wall thickness part having less draft and the residual wall thickness pipe part (a') is subjected to a pipe drawing. The thinner wall thickness part at the bottom side is in succession worked similarily and the polygon sectional pipe having smaller pipe parts B1, B2 at both sides together with the larger diameter pipe part in the medium part is obtd. With said method the dimensional accuracy of the large diameter pipe part is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a metal tube with a polygonal cross section having a stepped large diameter tube section in the middle.

[Prior art and its problems]

In recent years, so-called breeder reactors have been developed and are approaching the stage of practical use. The core of this type of nuclear reactor includes fuel assemblies, control rods disposed between the fuel assemblies,
It consists of a radial bracket fuel assembly, a neutron shield, etc. surrounding these, and these
It has a structure in which the fuel assemblies are housed in sheath tubes with a hexagonal cross section that touch each other. A gap is provided between the sheath tubes housing the fuel assemblies, etc., and the refrigerant is allowed to flow through this gap to generate Therefore, a spacer pad is provided on the outer surface of the intermediate portion of the sheath tube to ensure the above-mentioned space.

By the way, since the paulownia material that constitutes the reactor core is used to handle fast neutrons generated by nuclear fission, its material limitations are particularly severe.For this reason, the sheath tube with the spacer pads described above can also be constructed without welding. Preferably, it is integrally molded. As shown in Figure 2, such a sheath tube has a polygonal cross section and a large diameter tube section (A) (pad section) with a step in the middle that also has a polygonal cross section. It is required to have a special shape and to have a constant cold working amount (reduction) over the entire length.

As a manufacturing method for such a tube body, Japanese Patent Application Laid-Open No. 58-1282
In No. 19, the tube was externally machined to form a large-diameter portion in the center, and after heat treatment, both sides of the tube body bordering on the center of the large-diameter portion were formed into plugs and stepped dies. A method of cold diameter reduction has been proposed, but machining with a stepped die is difficult to achieve accuracy, especially in the enlarged diameter section, and the stepped die has no choice but to be a half-cut die. This also causes problems with accuracy, and considering the use of this type of tube, it is difficult to say that this is a preferable manufacturing method.

Means for Solving Problem C] In view of the above circumstances, the present invention aims to efficiently and precisely manufacture the above-mentioned vertical special-shaped pipe integrally with uniform hardness over its entire length. The aim is to provide a method that allows for

Therefore, the basic feature of the present invention is that cold working is performed in the following procedure.

(1) Externally milling the entire raw material tube to create a round tube with a thicker wall in the middle that increases toward the outside diameter.

(2) This tube is elongated using a die corresponding to the cross-sectional shape to be formed, while moving the thick portion toward the inner diameter side.

(3) Using a small-diameter pipe die and a plug, one thin-walled part of the pipe sandwiching the thick-walled part is expanded from one end of the pipe to the end of the thick-walled part to form one small-diameter pipe part. Form.

(4) The end of the thick wall part that has been formed in a tapered shape on the outside diameter side of the pipe by this process is externally machined in a tapered shape within a certain range of D1, and this part has a diameter larger than that of the small diameter pipe part that has been machined. A remaining flesh tube portion is formed.

(5) Using a small-diameter pipe die and a plug, carry out a pipe-drawing process in which the remaining wall pipe is at least stretched to /J's diameter on the end side of the small-diameter pipe. Start from

(Pass the plug into the 6-inch small-diameter tube to expand its diameter, and process the entire length of the small-diameter tube to the same inner diameter.)

(7) Place the other thin walled portion of the tube between the thick walled portions in the
Process according to steps 3) to (6)t.

In the present invention, the degree of cold working is lower in the tapered portion at the end of the thick wall portion that has gone through the tube drawing processes (2) and (3) than in other parts. (4) (5)
By going through external machining and pipe drawing of that part in the process, the degree of cold working increases, and the uniformity of hardness in the lengthwise direction of the pipe cannot be achieved. Further, by externally machining the ends of the thick-walled portions, the length dimensions of the dog-diameter tube portion and the small-diameter tube portion can be determined accurately, and the precision of the product can be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In the present invention, first, as shown in FIG. 1(A), a material tube is externally machined to produce a tube (round tube) having a thick inner part (a) in the middle part with increased wall thickness on the outer diameter side. The end of part (a) is formed into a tapered shape.Then, this pipe is cold drawn using a die and plug corresponding to the cross-sectional shape to be formed, and the thick part (a) is formed into a tapered shape.
a) Shift to the inner diameter side. In this stretched pipe, the thick part (a)
is subjected to outer diameter and wall thickness processing using dies and plugs, resulting in what is called a core drawing process. a) is given the desired cold force Loe degree n
Ru.

As described above, the tube is formed into a cross-sectional shape (for example, hexagonal shape) having the same outer diameter over its entire length by a series of tube expansions.

Next, as shown in Fig. 1 0 →, using a small diameter pipe die (1) and a plug (2), make 10,000 thin-walled parts (bl) () on the tubular side that sandwich the thick-walled part (a). The thin-walled part) is expanded from one end side to the end (et) of the thick-walled part (a) to form a small diameter pipe part (Bθ) of -10,000.The hole shape of the die (1) is is the straight part (101), and the entrance part is the tapered part (
102), and this tapered portion (102) forms a tapered portion on the outer diameter side of the end of the thick walled portion (a).

In this state, the pipe is partially drawn out, removed from the government gold die (1), and the plug (2) is pulled out.

Here, if the outer diameter of the plug (2) is not smaller than the inner diameter of the thick wall part (a), it will pass through the thick wall part (a)' and the mouth constriction part (
C) Since it cannot be set in the hessor, the outer diameter is made smaller than that of the thick part (a). Therefore, in the stopped state, a step (d) due to the diameter difference between the two remains formed near the end of the thick portion (b).

The end (el) of the thick wall part formed in a tapered shape on the outer diameter side of the tube by the above tube drawing process is externally milled within a predetermined range t (length) as shown in Fig. 1). , This part has a machined small diameter pipe section (
A remaining wall tube portion (a) having a larger diameter and thicker wall than B1) is left. Next, as shown in FIG. 1(E), using a small diameter pipe die (1) and a plug (2), the main purpose is to process the remaining wall part (a), in other words, to process the remaining wall part (a). Meat tube part (a)
When the tube is expanded to the diameter of the small-diameter tube, the process is performed from the end side of the small-diameter tube. In this processing step, the small diameter tube section (Bl) other than the residual wall tube section is usually also processed, and the small diameter tube section is substantially subjected to the second tube elongation process.

The purpose of the present invention is to obtain a pipe body with a uniform degree of cold working in the longitudinal direction of the pipe. As for the thick part (a), the initial figure 1 (b))
In the process shown in FIG. In other words, the degree of cold working of the tapered portion at the end of the thick wall portion is not so large compared to other portions, and large variations in the degree of cold working occur in this portion. That is, in the pipe drawing process of the thick wall part shown in Fig. 1 (b) K, the taper part has a lower degree of processing than the thick part, and the subsequent thin wall part is drawn to 6 diameters ( In Figure 1), if you try to process the tapered part to the extent that the required degree of cold working is obtained, you will have to process the thick wall part to a certain extent, and conversely, the degree of working in that part will be reduced to a certain extent. This will cause variations in the

In the present invention, this problem can be solved by externally cutting the end of the thick wall part with a small degree of machining by a predetermined thickness to leave a residual wall tube part (a') corresponding to the required degree of machining, and removing this residual thickness. The solution was to increase the degree of cold work in that part by drawing the tube part (a'). This adoption made it possible to adopt a basic and efficient machining (external cutting-pipe drawing) method in the previous process.

Next, as shown in FIG. 1(f), a plug (3) is passed through the small diameter pipe section (Bθ) to enlarge the diameter.

In the process up to Fig. 1 (E), due to the diameter difference between the inner diameter of the thick wall part (a) and the outer diameter of the plug (2) during elongation of the thin wall part, the inner diameter of the pipe (the end of the tapered thick wall part) There is a step (d) near the inner surface of the
9 is formed, and this step part (d) is formed by the above-mentioned diameter expansion process.
is resolved. Through this process, the processing of 10,000 thin-walled portions (bθ (top side thin-walled portions)) sandwiching the thick-walled portion (a) is completed.

Subsequently, the other thin wall part (b2) (bottom side thin wall part) is processed in the same manner, that is, by the procedure shown in FIG. As shown, it has a large diameter pipe part (A) in the middle part, and small diameter pipe parts (Bl) on both sides.
) (B2) is completed.

In such a series of manufacturing steps of the present invention, as described above, by partially increasing the degree of cold working at the end of the thick wall part, the degree of cold working is made uniform in the longitudinal direction of the pipe. By externally machining both ends of the thick-walled part for this purpose, the length of the thick-walled part (a) that will eventually become the large-diameter pipe part can be determined with high precision. A tube body with good dimensional accuracy of the large diameter tube portion can be obtained. In general, sheath tubes used in nuclear reactor cores are made of materials such that the hardness of the various surface parts of the tube body is Hv230-340, and the length tolerance of the large diameter tube section (pad section) is 4o-, (m). Although strict dimensional requirements are imposed on the above, according to the method of the present invention as described above, the variation in hardness in each part of the pipe body can be reduced.
It becomes possible to suppress the length of the large-diameter pipe portion to less than vl O and to strictly control the length dimension of the large-diameter pipe portion. Further, since an integral die can be used as the die, dimensional accuracy can be appropriately ensured in this aspect as well.

EXAMPLE A metal tube having a hexagonal cross section and having a large-diameter tube portion in the center was manufactured according to the present invention from an NFC light tube that had been previously subjected to tube drawing, heat treatment, and honing over its entire length. The manufacturing procedure is described below, along with the dimensions of each part of the tube body in each step. [Effects of the Invention] As described above, according to the present invention, a metal tube having a polygonal cross section having a stepped large diameter tube portion in the middle portion is provided. An excellent effect can be obtained in that it can be efficiently manufactured while ensuring uniform hardness over the entire length of the tube and good dimensional accuracy of the tube diameter section, especially the large diameter tube section.

[Brief explanation of the drawing]

FIGS. 1(A) to 1(G) are explanatory diagrams showing step by step a part of the manufacturing process according to the present invention. FIG. 2 is a perspective view f1 showing an example of a polygonal cross-sectional metal tube having a stepped large-diameter tube portion, which is a manufacturing target of the present invention. In the figure, (11(1) is a die, (21(21(3)
) is the plug, (a) is the thick wall part, (a) is the remaining wall pipe part, (b
θ(b2) is the thin part, (d) is the stepped part, (e+)(ez)
(A) shows the large-diameter pipe part, and (B1) and (B2) show the small-diameter pipe part. Patent applicant: Nippon Nabekan Co., Ltd. No. 1

Claims (1)

[Scope of Claims] A method for manufacturing a metal tube with a polygonal cross section having a large diameter tube section in the middle section whose diameter expands toward the outer diameter side by cold drawing, characterized in that the tube processing is performed according to the following procedure. A method for manufacturing a metal tube with a polygonal cross section having a stepped large diameter tube portion. (1) Externally milling the material tube to create a round tube with a thicker wall in the middle that increases toward the outside diameter. (2) This tube is expanded using a die corresponding to the cross-sectional shape to be formed, while moving the thick portion toward the inner diameter side. (3) Using a small-diameter pipe die and a plug, one thin-walled part of the pipe that holds the thick-walled part is stretched from one end of the pipe to the end of the thick-walled part to form one small-diameter pipe. to form. (4) The end of the thick-walled part, which is tapered on the outside diameter side of the tube through this process, is externally machined in a tapered shape within a predetermined range, and this part has a residual wall with a diameter larger than that of the small-diameter pipe that has already been machined. The tube portion is left to form. (5) Using a small-diameter pipe die and a plug, perform a tube-expanding process in which the residual wall tube is at least expanded to the diameter of the small-diameter tube from the end side of the small-diameter tube. (6) Insert a plug into the small-diameter tube to enlarge the diameter, and process the entire length of the small-diameter tube to the same inner diameter. (7) Place the other thin walled portion of the tube between the thick walled portions in the
Process according to steps 3) to (6).