JPS6012294A - Production of composite pipe - Google Patents

Abstract

PURPOSE:To make mass production of a water flow pipe such as a piping for a water heater by solar heat or the like with which a substantial rust-preventive effect is obtainable by fitting a metallic pipe having high corrosion resistance and the larger coefft. of thermal expansion than a steel pipe into said steel pipe, reducing or expanding one of the pipes and heating the pipes to unite the same into one body. CONSTITUTION:A copper inside pipe 2 having about 0.1-0.3mm. wall thickness and the diameter smaller than the diameter of a steel outside pipe 1 having about 0.5-0.8mm. wall thickness is loosely fitted into said outside pipe. The position G in the figure is gripped and both pipes 1, 2 are passed through a die 3 and are drawn toward the arrow. Then the pipe 1 is reduced by the mandrel drawing and the boundaries between the pipes 1, 2 contact tightly with each other. When such pipes 1, 2 are heated to about 900 deg.C in a nonoxidative or reducing atmosphere, the boundaries between the pipes 1 and 2 are metallurgically fixed and the intended composite pipe is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a composite pipe whose inner circumferential surface has been subjected to anti-corrosion treatment, and particularly relates to a method of manufacturing a composite pipe that allows water to pass through piping of a solar water heater or the like.

Conventionally, this type of composite pipe with an anti-rust coating on the inner surface has been made by electroplating or chemical plating of copper, zinc, tin, etc. on the inner surface of the steel pipe, or by hot-dip plating of tin, zinc, etc. on the inner surface of the steel pipe, and It is generally known that the inner surface of a steel pipe is coated or lined with a synthetic resin.

However, in this type of composite pipe, operations such as plating or coating for forming an inner surface anti-rust coating are difficult and costly, and this tendency becomes more pronounced as the inner diameter of the steel pipe becomes smaller. For this reason, costs increase significantly for relatively small-diameter composite pipes such as those for solar water heaters.

In addition, in order to minimize the cost increase of the above-mentioned anti-rust coating,
It is customary to limit the film thickness to about several microns to several tens of microns, and therefore there is also the problem that a sufficient antirust effect cannot always be obtained.

'The present invention was made in view of the current situation, and an object of the present invention is to provide a method for manufacturing a composite pipe that is easy to manufacture, can reduce costs through mass production, and can provide a sufficient rust prevention effect. .

As a means for achieving the above object, the present invention has an inner tube made of a metal having excellent corrosion resistance and a higher coefficient of linear expansion than the outer tube, and in which at least one of the tubes is completely fitted into an outer tube made of steel. It is characterized in that both tubes are brought into close contact by diameter reduction or diameter expansion processing, and then heated in a non-oxidizing or reducing atmosphere to integrate them.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows an example of a composite tube according to the present invention. This composite tube consists of an outer tube 1 made of steel and an inner tube 2 made of copper which is excellent in corrosion resistance and has a higher coefficient of linear expansion than the outer tube 1. The two tubes 1.2 are metallurgically fixed, that is, the interfaces of both tubes 1.2 are integrated by alloying.

Next, a method for manufacturing this composite pipe will be explained with reference to FIG.

During manufacturing, first, a steel outer tube 1 with a wall thickness of 0.5 to 0.8 mm and a wall thickness of 0.1 to 0.311111
An inner tube 2 made of copper and having a smaller diameter than the outer tube 1 is prepared, and the inner tube 2 is loosely fitted into the outer tube 1. Then, the symbol G shown in FIG.
While holding the position, pass the die 3 all the way through and pull out both tubes 1 and 2 in the direction of the arrow. Then, the diameter of the outer tube 1 is reduced by the die 3 using this core metal, and the interface between the outer tube 1 and the inner tube 2 is brought into close contact with each other.

Next, the outer tube 1 and the inner tube 2, which are in close contact with each other, are heated to about 900° C. in a non-oxidizing or reducing atmosphere.

Then, the interface between the outer tube 1 and the inner tube 2 is metallurgically fixed. That is, the metal near the interface between the tubes 1 and 2 is alloyed by heating, thereby fixing the tubes 1.2 together.

Here, the coefficient of linear expansion of copper as the material for the outer tube 1 is 6 12X10 , and the coefficient of linear expansion of copper as the material for the inner tube 2 is 3
1 x 1(+ -', and the inner tube 2 has a larger value than the outer tube 1. Therefore, when both tubes 1.2 are heated, the inner tube 2 expands more than the outer tube 1. Expand the diameter and make both tubes 1.
Pressure will be applied to the interface between the two.

As a result, the adhesion between both tubes 1 and 2 is improved, and reliable and uniform alloying can be expected.

Therefore, it is possible to obtain a composite tube with excellent corrosion resistance by using the inner tube 2 made of copper, and since it is easy to manufacture and has high mass productivity, it can be manufactured at low cost.

In addition, by adjusting the pressure during diameter reduction processing, the outer tube 1 and the inner tube 2 can be
Since the wall thickness of the tube can be adjusted as desired, a desired composite tube can be easily obtained.

FIG. 3 shows another embodiment of the present invention, in which the outer peripheral surface of the inner tube 2 is pre-plated with tin 4, and the inner tube 2 is fitted loosely into the outer tube 1 to reduce its diameter. It is then heated together to form a composite tube.

Next, a method for manufacturing this composite pipe will be explained.

During manufacturing, first the wall thickness is 0.5 to 0, J3n
Prepare an outer tube 1 made of steel with a thickness of about A and an inner tube 2 made of copper with a wall thickness of 0.1 to 0.3. Inner tube 2 is loosely fitted into tube 1. Then, the diameters of both tubes 1.2 are reduced by the same method as in the embodiment described above, and the interfaces of both tubes 1, 2 are brought into close contact with each other through the layer of tin plating 4.

This is then heated in a non-oxidizing or reducing atmosphere. Then, the tin plating 4 at the interface melts and becomes a bronze layer, and both tubes 1.2 are welded and integrated via this bronze layer. That is, the tin plating 4 at the interface functions as a brazing material.

Even in this case, the same effects as those of the embodiment described above can be obtained.

In both of the embodiments described above, both pipes 1.2 are brought into close contact with each other by diameter reduction processing.
Conversely, the inner tube 2 may be mainly expanded in diameter so that the two tubes 1.2 are brought into close contact with each other.

Further, in both of the embodiments described above, a steel pipe is used as the inner pipe 1, but an aluminum pipe may be used instead of the steel pipe.Aluminum has a coefficient of linear expansion of 24 Since it has a sufficiently large coefficient of linear expansion compared to the outer tube 1 made of copper, it can be expected to have the same effect as in the case of copper.

As explained above, the present invention includes fitting an inner tube made of a metal with excellent corrosion resistance and a coefficient of linear expansion larger than that of the outer tube into an outer tube made of steel, and shrinking at least one of the tubes. The two tubes are brought into close contact by processing the diameter or diameter expansion, and then heated in a non-oxidizing or reducing atmosphere to integrate them, making it easy to mass produce regardless of the size of the tube diameter. It is possible to reduce manufacturing costs.

In addition, the two tubes are not only brought into close contact with each other through diameter reduction or diameter expansion processing, but also heated and metallurgically integrated, so that performance can be made uniform and a highly reliable composite tube can be obtained.

Furthermore, since the wall thickness of both tubes can be adjusted during diameter reduction or diameter expansion, a composite tube suitable for the purpose can be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view showing an example of the composite tube obtained by the present invention, FIG. 2 is an explanatory diagram showing an example of the method for manufacturing the same, and FIG. 3 is a diagram showing another example of the composite tube obtained by the present invention. FIG. 1...Outer tube, 2...Inner tube, 3...Die, 4...
Tin plated. Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] 1. An inner tube made of a metal with excellent corrosion resistance and a higher coefficient of linear expansion than the outer tube is inserted into an outer tube made of steel, and at least one of the tubes is compressed. A method for producing a composite pipe, which is characterized in that the two pipes are brought into close contact with each other by diameter or enlargement processing, and then heated in a non-oxidizing or reducing atmosphere to integrate them. 2. The inner pipe is a steel pipe. 3. The method for manufacturing a composite pipe according to claim 1, characterized in that the inner pipe is a steel pipe having a tin layer on the outer circumferential surface. A method for manufacturing a composite tube. 4. A method for manufacturing a composite tube according to claim 1, characterized in that the inner tube is an aluminum tube. 5. Wall thickness of the inner tube i0.1 to 0.3fi, 5. The method of manufacturing a composite tube according to claim 1, wherein the outer tube has a wall thickness of ?0.5 to 0.811II.