JPS6238783A - Production of clad tube - Google Patents

Abstract

PURPOSE:To join the inner tube and outer tube metallurgically and to obtain the clad tube of high strength and high quality by closely fitting an inserting material with cold drawing via between two tube stocks, and by performing a diffusion joining with heating. CONSTITUTION:The composite tube inserting the inner tube 2 on which an inserting material 3 is wound on the whole face of the peripheral face into the outer tube 1 is fed to a die 4. A plug 5 is located in the drawing space of the die 4 and fitted closely to the inner side of the inner tube 2 and in n case of drawing prevents the pipe to be deformed. The outer tube 1 and inner tube 2 are drawn by the die 4 and plug 5 and fitted closely via the inserting material 3. Thereafter the closely fitted outer tube 1 and inner tube 2 are joined with diffusion joining by holding at the temp. higher than the melting point of the inserting material 3 by the heating furnace. A strong joining strength is obtd. because of the metallurgical joining.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing double pipes, and particularly to a high-strength and high-quality double pipe in which an inner pipe and an outer pipe are metallurgically joined. Relating to a method of manufacturing.

[Prior Art and its Problems] In the production of high-quality double-walled pipes, hot rolling has conventionally been widely used. This hot rolling method involves inserting the billet that will become the inner tube into the billet that will become the outer tube of the double tube at the billet stage where the outer tube and inner tube of the double tube are in the form of a vibrator, and then hot rolling. The inner tube and outer tube are metallurgically joined. The billet joined in this manner is made into a pipe using a rotary forge mill or the like.

However, in the case of this hot rolling method, the billet hot rolling process is an upper step in the tube manufacturing process, so the tube diameter of the product is determined by a tube manufacturing device such as a rotary forge mill. Pipe manufacturing equipment has the problem that it is difficult to change the pipe diameter of the product in a short time, so it is not suitable for low-volume, high-mix production, and the material yield is poor at the billet processing stage.

On the other hand, the technique of manufacturing double tubes using raw tubes close to the product shape is suitable for small-lot, high-mix production, and examples of this technique include shrink-fitting and lining-pulling. In the shrink fit method, the outer tube is held at a high temperature and expanded, the inner tube is inserted into the outer tube, and the outer tube is cooled to contract, and the outer tube and the inner tube are integrated. to produce double tubes. In the draw-together method, the inner tube is inserted into the outer tube and then cold drawn to integrate the outer tube and the inner tube to produce a double tube.

However, these methods have a problem in that the outer tube and the inner tube are joined mechanically, and therefore the bonding strength is low.

The manufacturing technology for double-walled pipes that is easy to produce in a wide variety of products and has high joint strength is to pressurize the joint surfaces of the outer pipe and inner pipe to be joined using an appropriate pressurizing means, and then pressurize the joint surfaces of the outer pipe and inner pipe under an inert gas atmosphere or vacuum. The outer tube and the inner tube are joined by heating, and the outer tube and the inner tube are joined by mutual diffusion of the atoms of the outer tube and the inner tube, or by the diffusion of the insert material inserted between the outer tube and the inner tube, thereby forming a double tube. There is a diffusion bonding method for manufacturing. In this method, an inner tube material having a higher coefficient of thermal expansion than foreign material is used, and after the inner tube is inserted into the outer tube, the outer tube and the inner tube are heated. Then, the inner tube, which has a higher coefficient of thermal expansion, expands more than the outer tube, so pressure is applied between the outer tube and the inner tube. By heating the outer tube and the inner tube in the presence of this pressure, the outer tube and the inner tube are diffusion bonded to produce a double tube.

However, in the case of this method, the joint surface between the outer tube and the inner tube needs to have a high surface smoothness, and the clearance between the outer tube and the inner tube before heating is Is it necessary to keep the amount of deformation due to thermal expansion less than or equal to the difference between the amount of deformation due to thermal expansion and the inner tube? Therefore, it is essential to perform extremely precise mechanical grinding between the outer tube and the inner tube. Further, in order to prevent oxidation of the joint surface between the outer tube and the inner tube, it is necessary to heat the joint surface using a large inert gas atmosphere furnace. As described above, this method has the problem that the manufacturing cost is extremely high because the process is complicated and an inert gas atmosphere furnace that requires a large amount of argon gas is required.

Other double pipe manufacturing techniques include the explosion bonding method, in which the outer tube and the inner tube are pressure piped by exploding explosives, and the overlay method, in which the material that will become the inner tube is welded to the inside of the outer tube. be.

However, the explosion bonding method has a problem in that when manufacturing a long tube, there are many parts that remain without being crimped, making it difficult to manufacture the long tube. Furthermore, the overlay method has problems in that welding defects are likely to occur and it is difficult to manufacture long double-walled pipes with small diameters.

[Means for solving the problem] This invention was made in view of the above circumstances, and
The bonding strength between the outer tube and the inner tube is excellent, the process is simple, no inert gas atmosphere furnace is required, the yield is high, multi-product production is easy, and long tubes can be produced. The purpose of the present invention is to provide a method for manufacturing a pipe.

The method for manufacturing a double pipe according to the present invention involves cooling two base pipes made of metal or alloy with an insert material made of a metal or alloy having a lower melting point than the base pipes interposed therebetween. The method is characterized in that the tubes are brought into close contact by thinning, then the entire tube is heated to a temperature higher than the melting point of the insert material, and the tubes are diffusion bonded using the insert material.

This invention will be specifically explained below.

In order to manufacture a double-walled tube according to the present invention, first, the outer tube and the inner tube are cold drawn to smooth the joint surfaces of the outer tube and the inner tube. In the cold drawing process, the inner and outer surfaces of the outer and inner tubes are cold-worked and smoothed by drawing the outer and inner tubes using a die and a plug. The method for smoothing the joining surface of the outer tube and inner tube is not limited to cold drawing, but may also be done by mechanical cutting, grinding, or polishing such as honing. It is preferable to use cold drawing because the processing speed is faster than mechanical grinding, etc., and the inner surface of a long tube with a small diameter, which is difficult to grind, can be easily smoothed.

Next, a foil insert material made of an alloy with a lower melting point than the material of the outer tube and the material of the inner tube is wrapped around the entire outer circumference of the inner tube, and this inner tube is inserted into the outer tube to form a composite tube. get. In this case, it goes without saying that the insert material may be attached to the inner circumferential surface of the outer tube instead of being wound around the outer circumferential surface of the inner tube.

Thereafter, this composite tube is subjected to a cold drawing process to firmly adhere the outer tube and the inner tube. FIG. 1 is a schematic diagram showing a process of bringing an outer tube and an inner tube into close contact with each other by cold drawing. The die 4 has a cylindrical space inside, and this space is formed with a tapered part 6 near the center of the die 4 whose diameter decreases in the direction in which the tube is drawn. The diameter of the space from which the tube is pulled out is smaller than the diameter of the space from which the tube to be processed is inserted. and,
A composite tube in which an insert material 3 or an inner tube 2 wrapped around the entire outer peripheral surface of the insert material 3 is inserted into an outer tube 1 is fed to the die 4. The plug 5 has a cylindrical shape, is located in the drawing space of the die 4, and is in close contact with the inside of the inner tube 2, thereby preventing the tube from being deformed when the tube is pulled out. The outer tube 1 and the inner tube 2 are pulled out using the die 4 and the plug 5, and the outer tube 1 and the inner tube 2 are brought into close contact with each other via the insert material 3. Thereby, the outer tube 1 and the inner tube 2 are firmly attached to each other through the insert material 3 over their entire length.

Thereafter, the outer tube and the inner tube are joined by diffusion bonding, and the outer tube and the inner tube, which are firmly attached to each other through the insert, are further firmly joined by cold drawing. In diffusion bonding, the pressure applied to the joint surface between the outer tube and the inner tube is created by using the residual stress generated during the cold drawing process described above to create a close bond between the outer tube and the inner tube through the insert material. The heated outer tube and inner tube are held at a temperature higher than the melting point of the insert material in a heating furnace, and the insert material is exposed to the liquid to diffuse the atoms of the insert material into the outer tube and inner tube. Join the outer tube and the inner tube. In this case, since the insert material is in a liquid phase, it is easily diffused, and even if the pressure applied to the surfaces to be joined is low, the outer tube and the inner tube can be firmly joined.

Note that if the inner tube is made of a material with a higher coefficient of thermal expansion than the outer tube, pressure will be applied to the joint surface due to the difference in thermal expansion during heating. Diffusion bonding can also be performed using this pressure.

In addition, by bringing the outer tube and inner tube into close contact through cold drawing, most of the air present at the joint surface is pushed out, leaving the joint surface in a state with extremely little air. is tightly packed through the insert material,
Since very little air enters this contact surface, the amount of oxidation of 1 g of the contact surface by air is extremely small. Therefore,
In the diffusion bonding of the present invention, the tubes to be bonded can be heated in an atmospheric heating furnace. In addition, after filling the space between the outer tube and the inner tube with dry inert gas, cold drawing can be performed to create a completely inert atmosphere at the joint surface to prevent the tube from being oxidized by heating as much as possible. can.

It is preferable that the double pipe joined as described above is used after improving its mechanical properties by subjecting it to cold working or heat treatment.

[Example] Examples of the present invention will be specifically described below.

The joint surface is made smooth by cold drawing, and the outer diameter is 601 mm.
5T with 11211φ, thickness 5mIR, length 6m
Prepare a B42 carbon steel pipe and a 5US304 stainless steel pipe with an outer diameter of 48.8 rumφ, a thickness of 3M, and a length of 6m with the joint surface smoothed by the same operation, and apply 10% to the entire outer surface of the stainless steel pipe. An amorphous foil (Ni-PIO%) of a Ni-based low melting point alloy containing P was evenly wrapped around the tube, and the stainless steel tube wrapped with this alloy foil was inserted into the inside of the carbon steel tube. The thus stacked carbon steel tube and stainless steel tube are cold drawn using a die whose diameter is 57 Mφ, which is the diameter of the space on the side where the tube is drawn, and the carbon steel tube and stainless steel tube are separated by Ni-based gold foil. I put it in close contact. Thereafter, the tubes that have been tightly joined by cold drawing are placed in a heating furnace and held at 1000°C for 1 hour to diffuse the Ni-based gold foil atoms into the carbon steel tubes and stainless steel tubes. A strongly bonded double tube could be obtained. Microstructural observation and shear strength tests were conducted on the joints of the double pipes thus manufactured. Assuming that the length of the tube is 1, the test piece is measured at 1/8, 1/412°, 1/2, 3/4, 7/8 from one end, and both ends in the length direction. Samples were collected from 7 locations. As a result, all the test pieces were metallurgically well bonded, with an average shear strength of 31 KS f /
It was possible to obtain a high value of 29.8/<gf/H2 at the minimum value, and the bonding surface had sufficient bonding strength.

[Effects of the Invention] According to the present invention, since the outer tube and the inner tube are metallurgically joined by diffusion bonding, strong joint strength can be obtained even in a long tube. In addition, before joining the outer and inner tubes through diffusion bonding via the insert material, the outer and inner tubes are brought into close contact by cold drawing. condition can be obtained, and the processing process of the raw pipe can be simplified. Furthermore, in the heating process, since the bonded surfaces are tightly bonded in advance by cold drawing, there is very little risk of the bonded surfaces being oxidized, so there is no need to use an inert atmosphere furnace, which is expensive to operate. Furthermore, since a raw tube close to the shape of the final product is used, by changing the diameter of the raw tube and the diameter of the die space, it is possible to easily produce a wide variety of products, and the product yield is high.

[Brief explanation of the drawing]

FIG. 1 shows a method for manufacturing a double pipe according to the present invention.
FIG. 3 is a schematic diagram showing a process of bringing an outer tube and an inner tube into close contact with each other by cold drawing. 1: Outer tube, 2; Inner tube, 3; Insert material, 4; Dice,
5; Plug; 6; Tapered portion.

Claims (1)

[Claims] Two base pipes made of metal or alloy are brought into close contact by cold drawing with an insert material made of metal or alloy having a lower melting point than the base pipe interposed therebetween, and then,
A method for manufacturing a double-layered pipe, characterized by heating the entire base pipe to a temperature higher than the melting point of an insert material, and diffusion-bonding the base pipe with the insert material.