JP3400564B2 - Method for manufacturing dissimilar metal multi-tubes with different coefficients of thermal expansion - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a dissimilar metal multi-tube having different coefficients of thermal expansion in which residual stress in the radial direction does not remain. [0002] Two kinds of metals having different coefficients of thermal expansion are
When metallurgically bonded double pipes are manufactured as an inner pipe and an outer pipe, respectively, through a heat bonding process such as hot isostatic pressure bonding or brazing, compressive stress is applied to the parts of the material with low coefficient of thermal expansion. However, tensile stress remains in the portion of the material having a large coefficient of thermal expansion. When a product is manufactured by cutting and removing a part of a double tube having such residual stress, bending or diameter distortion occurs due to the residual stress. Correction of axial bending is relatively easy, but diameter distortion is difficult to correct.
Therefore, it is particularly desirable to remove the residual stress in the radial direction, and it is conceivable to remove the residual stress by expanding or contracting the tube in a cold state. [0004] If the expansion or contraction of the tube is carried out in the cold state as described above, the residual stress is removed because of the plastic working, but the deformed tube and the inner tube are not used. In the case of soft pure copper, expansion and contraction are difficult and costly. An object of the present invention is to provide a method of manufacturing a dissimilar metal multi-tube which can eliminate the above-mentioned drawbacks and is simpler and can remove residual stress at low cost. The above object of the present invention can be achieved by employing the following means. That is, a multiple metal tube whose cross-sectional shape is different from the cross-sectional shape of the target tube in the shape of the curvature of the cross section of which is largely different, is hot-bonded, integrally formed, and cold-formed to the target-shaped tube. By deforming the cross section, the residual stress in the radial direction is removed. More specifically, for example, in order to obtain a product having a square or elliptical cross section, the multiple tube having a circular cross section may be deformed to have a square or elliptical shape. Hereinafter, the present invention will be described with reference to examples. When the outer tube 1 is made of carbon steel and the inner tube 2 is made of pure copper, and a large number of short tubes having the shapes shown in FIGS. Is prepared, and metallurgical joining is performed in a heated state by hot isostatic pressing, hot drawing, brazing, or the like. In many cases, bonding is performed in a relatively long state and cut into short lengths. In some cases, bonding is performed in a short state. In any case, compression stress on carbon steel and tensile stress on pure copper remain inevitable. In all of FIGS. 1 to 6, the occurrence of distortion due to hot bonding is inevitable, and some correction is required. This is because, even if a cutting allowance is left on the inner and outer surfaces, the thickness of each of the carbon steel and pure copper deviates from a predetermined dimension in a state where the strain is left. When the outer periphery of the carbon steel is cut and removed, distortion occurs in the object shown in FIGS. 1 and 2, and a small number of times of cutting the inner and outer surfaces are required. The thing shown in FIG. 5 and FIG. 6 causes distortion in the radial direction due to the cutting of the groove 3 and is difficult to manufacture. In the present invention, the residual stress in the radial direction is obtained by preparing a simple pipe having a predetermined peripheral length, for example, a double pipe having a circular cross section, and forming it into a modified pipe having a shape as shown in FIGS. Can be removed. Due to the change in the cross-sectional shape, a slight change in the circumferential length is inevitable, which also contributes to the removal of residual stress, but the gist of the present invention is to achieve most of its purpose by plastic deformation of the circumferential curvature. Things. FIG. 7 shows a use state of the object shown in FIGS. 1 and 2. The copper tube 5 is fixed to a carbon steel plate 4 and is used as a transition joint 6 for seal welding. In the figure, reference numerals 7 and 8 are both welded portions. In particular, there is a possibility that the dissimilar material of the transition joint 6 may be peeled off by the welded portion 8, and the removal of residual stress also helps to prevent peeling. The above-described method of removing the residual stress is applicable not only to a double pipe but also to a triple or more multiple pipe. As described above, according to the method of the present invention, first, a pipe having a different cross-sectional shape from that of the final target pipe is made hot, and the cross-sectional shape is changed cold. Since the processing is performed, plastic deformation occurs and residual stress in the radial direction can be removed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a double pipe to be obtained in an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA of FIG. FIG. 3 is a plan view of another double pipe to be obtained in the embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line BB of FIG. 3; FIG. 5 is a plan view of still another double pipe to be obtained in the embodiment of the present invention. FIG. 6 is a partially cutaway front view of FIG. 5; FIG. 7 is an explanatory view showing an example of a use state of the double pipe shown in FIGS. 1 and 2; [Explanation of symbols] 1 outer tube 2 inner tube

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B21C 37/06 B21C 37/15 B23K 31/00

Claims (1)

(57) [Claims 1] When manufacturing a dissimilar metal multi-tube made of metals having different coefficients of thermal expansion, the cross-sectional shape is different from the cross-sectional shape of the target tube in the circumferential curvature of the cross-section. It is characterized by removing the residual stress in the radial direction by joining multiple metal tubes of mostly different shapes hot, forming them integrally, and deforming the cross-section of the tube into the desired shape cold. A method for producing dissimilar metal multi-tubes having different coefficients of thermal expansion.