JPH0857534A - Manufacture of tube multilayered with different kinds of metal having various thermal expansion coefficient - Google Patents

Abstract

PURPOSE: To eliminate residual stress in the radial direction of a multilayered tube composed of different kinds of metal by integrally hot-joining such tube whose cross section is different in most curvatures against a target tube shape and cold-deforming the cross section into the target tube shape. CONSTITUTION: In manufacturing a multilayered tube with different kinds of metal consisting of a carbon tube for the external tube 1 and a pure copper for the internal tube 2 for example, a duplex tube is first manufactured in a simple shape of a prescribed circumference, e.g. circular cross section, and the duplex tube is then formed into a special with a square or elliptical shape. Thus, the removal of residual stress in the radial direction is made possible by plastic deformation in the circumferential curvature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multi-metal tube of different metals having different coefficients of thermal expansion without residual stress in the radial direction.

[0002]

2. Description of the Related Art Two kinds of metals having different coefficients of thermal expansion are
When double pipes, which are metallurgically joined as an inner pipe and an outer pipe, are manufactured through a hot joining process such as hot isostatic pressing and brazing, compressive stress is applied to the part of the material with a small coefficient of thermal expansion. The tensile stress remains in the part of the material having a large coefficient of thermal expansion.

When a part of a double pipe having such a residual stress is cut and removed to manufacture a product, bending, diameter distortion, etc. occur due to the residual stress. It is relatively easy to correct the axial bend, but it is difficult to correct the radial distortion.
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 pipe in the cold.

[0004]

As described above, when cold pipe expansion or contraction is performed, residual stress is removed due to plastic working, but it is a deformed pipe and the inner pipe is pure copper. In such cases, it is difficult to expand or contract the tube, and the cost is high.

It is an object of the present invention to provide a method for manufacturing a dissimilar metal multi-tube, which is capable of eliminating the above-mentioned drawbacks, and which is capable of removing residual stress more simply and at low cost.

[0006]

The above object of the present invention can be achieved by adopting the following means. That is, a multi-metal tube having a cross-sectional shape different from most of the cross-sectional shape of the target tube in a curvature of the cross-section is hot-bonded and integrally formed, and the tube having the target shape is cold-formed. The residual stress in the radial direction is removed by deforming the cross section. More specifically, for example, in order to obtain a product having a quadrangular or elliptical cross section, a multiple pipe having a circular cross section may be deformed into a quadrangular or elliptical shape.

[0007]

EXAMPLES The present invention will be described below based on examples. When many outer tubes 1 are made of carbon steel and the inner tube 2 is made of pure copper and a number of short tubes having the shapes shown in FIGS. The tube is prepared in advance, and metallurgical joining is performed in a heated state by methods such as hot isostatic pressing, hot drawing, and brazing. In many cases, they are joined in a relatively long state and cut into short pieces, but sometimes joined in a short state. It is inevitable that carbon steel will be compressed and pure copper will be left with tensile stress by either method.

In both FIGS. 1 to 6, the occurrence of strain due to hot bonding is unavoidable and some correction is necessary. This is because even if a cutting allowance is left on the inner and outer surfaces, the respective thicknesses of carbon steel and pure copper deviate from the predetermined dimensions when strain is left. The products shown in FIGS. 1 and 2 are distorted when the outer periphery of carbon steel is cut and removed, and it is required to cut the inner and outer surfaces a small number of times. The products shown in FIGS. 5 and 6 are difficult to manufacture because the grooves 3 cause radial strain.

In the present invention, the residual stress in the radial direction can be obtained by preparing a simple tube having a predetermined circumference, for example, a double tube having a circular cross section, and using the modified tube having the shape shown in FIGS. Can be removed. Due to the change in the cross-sectional shape, a slight change in the circumferential length is unavoidable, which also contributes to the removal of the residual stress, but the gist of the present invention is to achieve most of the purpose by plastic deformation of the curvature of the circumference. It is a thing.

FIG. 7 shows a use state of the objects shown in FIGS. 1 and 2, and is used as a transition joint 6 for fixing a copper pipe 5 to a carbon steel plate 4 and performing seal welding. In the figure, both 7 and 8 are welded portions, but there is a possibility that the dissimilar material of the transition joint 6 may be peeled off by the welded portion 8 in particular, and removal of residual stress also helps prevent peeling.

The residual stress removing method described above is applicable not only to double pipes but also to multiple pipes of three or more pipes.

[0012]

As described above, according to the method of the present invention, first, a tube having a cross-sectional shape different from that of the final target tube is hot-worked, and then cold-worked so that the cross-sectional shape is changed. Therefore, plastic deformation occurs and residual stress in the radial direction can be removed.

[Brief description of 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 sectional view taken along the line AA of FIG.

FIG. 3 is a plan view of another double tube to be obtained in the embodiment of the present invention.

FIG. 4 is a sectional view taken along line BB in FIG.

FIG. 5 is a plan view of still another double tube to be obtained in the embodiment of the present invention.

6 is a partially cutaway front view of FIG.

7 is an explanatory diagram showing an example of a usage state of the double pipe shown in FIGS. 1 and 2. FIG.

[Explanation of symbols] 1 outer tube 2 inner tube

Claims (1)

[Claims] 1. When manufacturing a dissimilar metal multi-tube made of metals having different coefficients of thermal expansion, a multi-metal tube having a cross-sectional shape different from the cross-sectional shape of the target tube in most of the curvature of the circumference of the cross-section. Are joined together by heat and formed integrally, and the residual stress in the radial direction is removed by deforming the cross section into the pipe of the desired shape by cold deformation. Pipe manufacturing method.