JPH0741475B2 - Double tube manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a double pipe in which a stainless pipe is adhered inside a steel pipe.

<Prior Art> In a steel pipe in which a high-pressure fluid flows, such as a fuel injection pipe of an automobile, the inner wall of the steel pipe causes cavitation erosion due to the flow of the high-pressure fluid. In order to prevent this, a double pipe in which an inner pipe made of a corrosion resistant material is formed in a steel pipe is desirable. Japanese Unexamined Patent Publication No. 59-222691 discloses a double tube of this type in which a ceramic tube is used as an inner tube and the ceramic tube is shrink-fitted and joined to a steel tube.

<Problems to be Solved by the Invention> A double tube having the above-mentioned ceramic tube as an inner tube is not preferable because of increased weight and increased cost. Also, in order to improve the adhesion between the ceramic pipe and the inner wall of the steel pipe,
A complicated process is required in which the outer peripheral surface of the ceramic tube is a rough surface having irregularities, and a metal sprayed layer is formed on the rough surface to shrink-fit the steel tube.

<Means for Solving the Problems> The present invention provides a method for manufacturing a double pipe that solves the above-mentioned problems. The gist of the present invention is that the diameter of the steel pipe is smaller than the inner diameter of the steel pipe to be the outer pipe. Pass a cored bar through a stainless steel tube to be an inner tube, and insert it into the steel tube to expand it so that the inner diameter of the steel tube approaches the outer diameter of the stainless steel tube. It is heated above ℃, taken out of the furnace, rapidly cooled, finished and expanded to a predetermined size, and the cored bar is removed.

<Operation> By the above method, a lightweight double-pipe steel pipe having a stainless steel pipe having high cavitation erosion resistance and high strength as an inner pipe can be easily manufactured.

<Examples> Examples of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a steel pipe that serves as an outer pipe, and 2 is a stainless steel pipe that serves as an inner pipe. The stainless steel pipe 2 is preliminarily stretched so that the outer diameter dimension D2 is smaller than the inner diameter dimension D1 of the steel pipe 1. Pass the core metal 3 through this stainless steel tube 2,
This is inserted into the steel pipe 1 and expanded as shown in FIG. 2 so that the inner diameter dimension D1 of the steel tube 1 approaches the outer diameter dimension D2 of the stainless steel tube 2. This expanded double tube is heated at 1000 ° C or higher in a furnace (not shown), taken out of the furnace and rapidly cooled. Further, the pipe is finished and drawn to a predetermined size, and the cored bar 3 is removed. As shown in FIGS. 3 and 4, a stainless steel pipe 2 is used as an inner pipe, and a steel pipe 1 is used as an outer pipe. To do.

SUS304 is suitable for the stainless steel tube 2. This SUS304
Contains Cr and Ni, Cr has corrosion resistance and erosion resistance, and Ni forms a solid solution in the Fe crystal to strengthen the matrix.

By heating the steel pipe 1 having the stainless steel pipe 2 having such characteristics as an inner pipe to 1000 ° C. or more in the furnace, the steel pipe 1 and the stainless steel pipe 2 are brought into close contact with each other by thermal expansion, and taken out of the furnace to rapidly By cooling, the precipitation of chromium carbide from the stainless steel pipe 2 is prevented, and the double pipe is manufactured without cracking the stainless steel pipe 2. Incidentally, when the material is gradually cooled in the furnace after the heating, chromium carbides are precipitated at the grain boundaries of SUS304, causing grain boundary corrosion and cracking.

<Effects of the Invention> As described above, according to the present invention, since the inner pipe of the stainless pipe is provided in the steel pipe, the double pipe has cavitation erosion resistance due to the stainless pipe, and is lightweight.
Especially suitable for high pressure fuel injection tubes.

Further, in the method of the present invention, the stainless tube is inserted into the steel tube, and the tube is expanded so that the inner diameter of the steel tube approaches the outer diameter of the stainless tube and heated to 1000 ° C. or higher, which is rapidly cooled. Prevents the deposition of chromium carbide on the tube,
Heat treatment can be obtained without cracking the stainless steel pipe,
Hardening of stainless steel tube It has an advantage that a double tube with rigidity of Hv350 or more can be manufactured by a simple process.

[Brief description of drawings]

Drawing shows an embodiment of the present invention, Fig. 1 is a cross-sectional view of a state in which a stainless steel pipe is inserted into a steel pipe, and Fig. 2 is a cross-sectional view of a state in which the steel pipe is expanded and the outer diameter of the stainless steel pipe is used. , Third
Figure is a cross-sectional view of the finished product after heat treatment, and Figure 4 is IV-IV in Figure 3.
It is a line sectional view. 1 ... Steel pipe, 2 ... Stainless steel pipe, 3 ... Core metal.

Claims (1)

[Claims] 1. A core metal is passed through a stainless steel pipe which is an inner pipe having a diameter smaller than the inner diameter of a steel pipe which is an outer pipe, and is inserted into the steel pipe so that the inner diameter of the steel pipe approaches the outer diameter of the stainless pipe. Characterized by expanding the tube, heating the expanded double tube to 1000 ° C or higher in the furnace, taking it out of the furnace, rapidly cooling it, finishing it to a specified size and expanding it to remove the core metal. And a method for manufacturing a double pipe.