JPS59150660A - Method for forming porous layer on surface of hollow metallic material - Google Patents

Abstract

PURPOSE:To form a porous material having high performance on the outside surface of a metallic pipe, etc. by packing the powder of a metal and a brazing material between the outside or inside surface of the pipe and a non-solderable spacing material and heating the pipe in a specific atmosphere thereby brazing the pipe. CONSTITUTION:An aluminum pipe 1 or the like is mounted to a non-solderable stainless steel pipe 2 or the like and a bottom cap 4. A powder mixture 5 composed of aluminum and a brazing material or the like is packed in the space 3 therebetween. These materials are heated at about 600 deg.CX10min in a vacuum, non-oxidative atmosphere or reducing atmosphere and after cooling in a furnace, the pipe 2 and bottom cap 4 are drawn and the pipe having the porous inside surface is formed. If the relation between the pipe 1 and the pipe 2 is reversed, the pipe having the porous outside surface is obtd. The porous boiling heat transfer surface having high performance is formed on the surface of the hollow material by the above-mentioned method. Since no flux is used in this method, the need for a succeeding washing stage is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for forming a metallic porous layer on the inner or outer surface of a hollow metal material, particularly in a heat pipe, water-fluorocarbon heat exchanger, etc. The present invention relates to a method of forming a porous layer by brazing metal powder on the inner or outer surface of a material, etc., for the purpose of forming a high-performance porous boiling heat transfer surface on the surface.

Conventionally, sintering methods, machining methods, powder plating methods, etc. are known as methods for forming a metal porous layer on the surface of a metal body, but all of these methods require troublesome process control and are expensive. There were problems such as difficulty in forming a thick, high-performance boiling heat transfer layer.

In view of the above problems, the present invention provides a method for easily forming a uniform porous metal layer with an arbitrary thickness on the inner or outer surface of a hollow metal material using extremely simple working steps. This is what we are trying to provide.

Therefore, the present invention provides the following features:
A gap forming member of a non-soldered column made from a mandrel or a pipe is arranged with the outer or inner surface facing the wall surface of the hollow member with a predetermined gap therebetween, and a metal powder is placed in the gap between the two. After filling the mixture with brazing filler metal powder, the metal powder is brazed to the metal hollow material by heating in a vacuum, a non-oxidizing atmosphere, or a reducing atmosphere, and then the gap forming member is removed. The present invention relates to a method for forming a porous layer on the surface of a hollow metal material, which is characterized by removing the porous layer from the surface.

1. The metal hollow material and the metal powder may be metals that can be brazed together, and the combination thereof can be selected arbitrarily. The most commonly used metal hollow materials are pipes made of aluminum, copper, etc., and the metal powders include aluminum cylinders and alloys thereof.

The spun brazing material is selected appropriately in relation to the hollow metal material and the metal powder to be brazed to it.
Generally, a brazing material made of an Al-5 to 20% 5i-Q and 5 to 3% Mg alloy is preferably used.

The particle size of both the metal powder and the brazing material powder is 20 to 1
000 μm should be used. In particular, the particle size of the metal powder should be selected appropriately in relation to the intended use of the product. It is difficult to form a heat transfer surface. Furthermore, if the particle size of the brazing filler metal powder is smaller than 20 μm, it is difficult to obtain it industrially, and if the particle size is larger than 1000 μm, it is difficult to obtain uniform distribution when mixed with metal powder. .

The gap forming member forms a required powder-filled gap between the hollow metal material and the inner or outer surface on which the porous layer is to be formed. Therefore, when forming a porous layer on the inner surface of a hollow material, a pipe or rod having an outer diameter smaller than the inner diameter is used as a mandrel for loading, and a porous layer is formed on the outer surface of the hollow material. In this case, a hollow member such as a pipe having an inner diameter larger than its outer diameter is used as the outer circumferential covering material. Of course, this gap forming member must not be joined to the brazing material, so it is made of a non-brazing material, such as stainless steel, iron, sintered ceramics, etc. Especially, when forming a porous layer on the outer surface of a hollow metal material, it is necessary to select and use a material with a coefficient of thermal expansion smaller than that of the hollow metal material as the gap forming member. That is, by using such a gap-forming member, the metal hollow material and metal powder, which thermally expanded during heating during brazing, contract relatively more than the gap-forming member after brazing is completed.
It is possible to easily take out the metal hollow material on which the porous layer is formed from the gap forming member.

By the way, when the metal hollow material is made of copper and when trying to braze aluminum powder to it to form a porous layer, heat brazing sometimes causes the copper hollow material to form due to the diffusion of aluminum and copper. may be eroded. In particular, the Al-CuO eutectic point temperature (548℃
) If heated too quickly, the above-mentioned diffusion will proceed further, making it difficult to braze the aluminum powder to the surface of the hollow material. Therefore, in such cases, it is effective to form a diffusion prevention layer made of a metal that is difficult to diffuse with copper, especially nickel or iron, on the surface of the copper hollow material by plating, ion-blating, etc. . The formation of this diffusion prevention layer prevents the aluminum powder from diffusing into the copper hollow member, and the aluminum powder can be firmly brazed onto the diffusion prevention layer. The thickness of the diffusion prevention layer is desirably 2 μm or more, particularly about 10 to 20 μm.

Brazing in this invention is performed without using flux. Although it is possible to obtain a porous layer by brazing using flux, brazing is not preferable because flux remains even after cleaning.

According to this invention, a gap forming member is disposed inside or outside of a hollow metal material to form a gap between the two, and a mixture of metal powder and brazing metal powder is filled into the gap to perform heat brazing. Since the gap forming member is then removed, it is possible to easily add a metal porous layer to the inner or outer surface of the gold hollow material, which has been considered difficult in the past. Of course, the work process is simple and does not require special skill, and it is advantageous in terms of workability and cost.

Moreover, the thickness of the porous layer can be freely controlled by setting the above-mentioned gap, and together with the formation of a uniform porous layer and scales, it is possible to create a porous boiling heat transfer surface with excellent performance. Obtainable.

Next, examples of this invention will be shown.

Example 1 As shown in Fig. 1, outer diameter is 20+++m, wall thickness is 2rrr
A stainless steel pipe (2) (gap forming member) with an outer diameter of 12+nm and a wall thickness of 1° Own is placed concentrically inside an aluminum pipe (1) (metallic hollow material), and a uniform gap is formed between the two over the entire circumference. A gap (3) of two widths was formed, and the lower end of this gap was closed with a bottom cap (4) provided integrally with the stainless steel pipe (2). on the other hand,
Aluminum powder with an average particle size of 840 μm and an average particle size of 84
A dry mixture (5) is prepared by mixing 0 μm AI-7,5%Si-1,o%Mg alloy brazing filler metal powder at a weight ratio of 3:1, and the mixture is poured into the above-mentioned gap. (
3) Filled inside. Then, this filled product is heated in a vacuum furnace at 605°C for 10 minutes to perform vacuum brazing, and after cooling in the furnace, the stainless steel pipe (2) is attached to the bottom cap (
It was removed along with 4).

As a result, as shown in Fig. 2, a uniform porous layer (6 mm) with a thickness of approximately 2 +
), it was possible to obtain a composite hollow material suitable for use as a heat pipe, for example.

Example 2 As shown in Fig. 3, the diameter is 25.4 mm, and the thickness is 10 mm.
A nickel plating layer (lla) with a thickness of 20 μm is formed on the outer surface of a copper pipe (11) with a length of 100 mm by electroplating, and on the outside of the copper pipe with the plating layer, Diameter 30 mm, thickness 08 mm, length 150 mm
A bleached stainless steel pipe (12+ (lJj formation member) was fitted between the two so that a uniform gap (13) was formed over the entire circumference, and the bottom was closed with a bottom camp (14). 125μm 99.7% aluminum powder and AI-7,5%5i-10%Mg
Prepare a mixture 4 in which a total Mg brazing filler metal powder is uniformly mixed at a weight ratio of 3:1, and mix it in the gap t131.
After filling the inside, 4. Brazing was performed by heating at 605° C. for 15 minutes in a vacuum furnace under the pressure of X i Q tart. After the furnace was cooled, the copper pipe (11) was taken out of the furnace and extracted from the stainless steel pipe (12). ],,1.a
) It was possible to obtain a composite hollow material having a porous layer on the outer surface to which the aluminum powder was completely brazed without eroding the pipe base material in any way.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the first embodiment, FIG. 2 is a sectional view of a composite hollow material obtained by the first embodiment, and FIG. 3 is a sectional view of the second embodiment.

Claims (1)

[Claims] A non-soldered column gap forming member is placed inside or outside of the hollow metal material to form a predetermined gap between the two, and after filling the gap with a mixture of metal powder and brazing metal powder, A porous layer is formed on the surface of the hollow metal material, characterized in that metal powder is brazed to the hollow metal material by heating in an oxidizing atmosphere or a reducing atmosphere, and then the gap forming member is removed. How to form.