JPS6326253A - Production of two-layered pipe - Google Patents

Abstract

PURPOSE:To improve the bonding strength of an inside layer and outside layer and to facilitate production by packing a powder material between a tapered pipe body and core material having ceramic surface layer and effecting melting and unidirectional solidification under a vacuum. CONSTITUTION:The tapered pipe body 1 having the wall thickness decreasing gradually from the lower toward the upper part is erected on a base plate 4 and the columnar core 3 having the ceramic surface layer in a hollow hole is disposed therein by aligning the centers. The powder material 2 for the inside layer is then packed between the pipe body 1 and the core material 3 and after the powder material 2 is heated to melt by a heater 5 in a vacuum chamber 6, the molten material is unidirectionally solidified. The core material 3 is removed and the outside surface of the outside layer material 1 and the inside surface of the inside layer material are machined, by which the two- layered pipe is obtd. The powder material 2 for the inside layer is unidirectionally solidified and the inside layer material is thereby formed; therefore, the denser structure thereof is formed and casting defects are decreased. The bonding strength between the inside and outside layers is thus improved and the production is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a double-layer tube useful as a cylinder, reaction tube, roll, etc.

[Conventional technology]

A double-layered pipe having a laminated structure in which different materials are joined as an outer layer material and an inner layer material is useful, for example, as a cylinder for an injection molding machine, a reaction tube for the petrochemical industry, or a roll for rolling and conveying steel materials.

A typical manufacturing method for double-layer pipes is to use the centrifugal force casting method, in which the outer layer is formed by first injecting molten metal as the outer layer material into the mold while centrifugally rotating the mold around its axis. A widely used method is to form an inner layer by injecting molten metal as an inner layer material into the inner surface of the outer layer.

[Problem that the invention seeks to solve]

The manufacturing method of double-layer pipes by centrifugal force casting has a relatively small number of steps and is suitable for mass production. Melting and refining must be carried out in parallel in a refining furnace, and in order to form a two-layer pipe in which the interface between the outer and inner layers is metallurgically integrated, the casting temperature and timing of each layer must be carefully controlled. Control of many factors is required. Furthermore, the selection and combination of materials for both layers is subject to many restrictions from the viewpoint of preventing defects such as casting cracks. There is also the problem that casting defects occur due to entrainment of gas and inclusions during casting.

The present invention has been made to solve the above problems.

[Means for solving problems]

The method for manufacturing a two-layer pipe of the present invention is to form a two-layer structure using a pipe made of a desired material as an outer layer material and a powder prepared to have a predetermined composition as an inner layer material. The feature is that the outer layer material is a tapered tube whose wall thickness gradually decreases from the bottom to the top, and a columnar core material with a surface layer made of ceramic is erected along the axis of the hollow hole. A space is defined between the core material and the columnar core material, the powder for forming the inner layer is filled in the space, the powder is heated and melted under vacuum, and then the molten material is cooled and the powder is poured upward from the bottom. The main feature is that the columnar core material is removed after the unidirectional solidification is completed.

In the present invention, a tapered tube with a thick bottom wall and a thin top wall is used as the tube body for the outer layer because the molten material is cooled during the cooling process of the molten powder material for the inner layer. This is to allow coagulation to proceed from the bottom upward. As the tube body, for example, one having a taper such that the wall thickness decreases by 1 to 2 degrees per 10 mm in the tube axis direction is used. It goes without saying that the shape of the tube body is not limited to a circular tube, but may be polygonal, for example, depending on the external shape of the intended two-layer tube.

In addition, the reason why the powder filled on the inner surface of the outer layer tube was heated and melted under vacuum was to deaerate the powder and prevent air bubbles from remaining in the melt. .

Furthermore, the reason why we decided to use a core material whose surface layer is made of ceramic as the columnar core material for forming the hollow pores is because the reaction and melting at the interface between the molten powder and the core material occurs during the heating and melting process of the powder. This is to prevent wear. As the core material, a metal column whose surface is coated with a sprayed layer of ceramic (for example, alumina), a fired ceramic column, or the like is used. In addition to being formed as a core material, for convenience of sampling work, a core material is used in which a plurality of divided bodies are separably joined and assembled into a predetermined columnar body. Further, the shape of the core material is not limited to a cylindrical shape, and a core material having a polygonal shape, for example, may be used depending on the inner shape of the intended two-layer pipe.

[Effect]

In the present invention, the powder that forms the inner layer is heated and melted under vacuum, and during the solidification process it is solidified unidirectionally from the bottom upward, thereby avoiding the occurrence of gas defects and creating a dense structure. An inner layer containing . Furthermore, by supplying a sufficient amount of heat during the heating and melting process of the powder, it is possible to strengthen the bond at the interface between the inner layer and the outer layer.

Furthermore, since the surface of the core material is ceramic and is extremely stable both thermally and chemically, reactions and diffusion (contamination of the inner layer and changes in component composition) at the contact interface with the formed inner layer will not occur. do not have. The presence of the ceramic layer also facilitates removal of the core material and prevents damage to the inner layer during removal.

〔Example〕

As shown in Fig. 1, a tapered outer layer tube (1) and a columnar core (3) located at the axis of the hollow hole are erected on a base (4) and attached to the tube. The powder (2) for the inner layer is filled, and in the vacuum chamber (6), the powder (2) is heated and melted by the heater (5), and then cooled and solidified.Then, the core material is removed, and the outer surface of the outer layer material is Then, the inner surface of the inner layer material was machined to obtain a two-layer tube of a predetermined size.

(1) Outer layer material: Carbon steel (345C) Pipe size: Inner diameter (d,) 70φ, lower outer diameter (d2) 20
0φ, top outer diameter (dz) 110φ, height H) 3004
(ms), (2) Powder for inner layer: Ni-based self-fusing alloy powder (melting point 94
(0°C), grain size 40 to 80 μm (3) Core material: common steel (SS41) The circumferential surface of a rectangular cylinder is coated with a sprayed layer of alumina powder. Outer diameter (d,) 60φ, height (H) 3001 (ms).

(4) Heating and melting of powder Heating temperature: 1100°C, holding time: 30 minutes.

The two-layer tube obtained above (outer layer: 545C1 inner layer: N
By cutting the i-based alloy in the radial and axial directions and observing the macrostructure and microstructure, we found that there were no gas defects such as pinholes or inclusions in the inner layer, and that the interface between the inner and outer layers was metallurgical. It was confirmed that the bonding was mechanically integrated, and that there was no reaction or contamination at the interface between the inner layer and the core material.

〔Effect of the invention〕

According to the present invention, the inner and outer layers are free from gas defects and inclusions due to the extremely simple process of filling the space between the outer layer material and the core material, heating and melting the powder, and cooling and solidifying the powder. , a healthy two-layer tube with a dense structure and a strong bond between the two layers can be obtained. The selection and combination of the outer layer material and the inner layer material is relatively free, and it is possible to easily manufacture a two-layer pipe having materials and characteristics that suit the application and conditions of use. Moreover, the shape can be formed into a circular tube, a polygonal shape, or any other arbitrary shape depending on the shape of the outer layer material and core material used.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view showing an embodiment of the method of the present invention. 1: Outer layer material, 2: Inner layer powder, 3: Core material, 4: Base,
5: Heater, 6: Vacuum chamber.

Claims (1)

[Claims] (1) A tapered tube whose wall thickness gradually decreases from the bottom to the top is used as the outer layer material, and a columnar core material with a surface layer made of ceramic is erected along the axis of the hollow hole to connect the outer layer material and the columnar core. Fill the space defined between the material and the powder for forming the inner layer, heat and melt the powder under vacuum, and then cool the melt to complete unidirectional solidification from the bottom upward. A method for manufacturing a double-layered pipe, which comprises removing the columnar core material.