JPS63186090A - Metallic pipe having excellent bending property - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal tube with excellent bendability used in heat exchangers and the like.

[Prior art and its problems]

Conventionally, soft phosphorus-deoxidized copper tubes with uniform wall thickness have been used as metal tubes for heat exchangers and the like that are bent and used.

Evaporators and condensers for air conditioners usually use plate-fin type heat exchangers made of copper tubes and aluminum plates, and the copper tubes are bent into a hairpin shape.

In recent years, copper tubes have become thinner and smaller in order to reduce costs and downsize equipment. When the wall thickness of a metal tube becomes thinner, the inside of the bend will be compressed and buckled, wrinkles will occur, and the flow resistance of refrigerant will increase, and the outside of the bend will be under tension and the wall thickness will become extremely thin, leading to corrosion or , there is a risk of damage due to the internal pressure of the refrigerant, etc.

[Means for solving the problems and their effects] In view of the above-mentioned circumstances, the present invention has been developed as a result of extensive research into metal pipes for bending, and has been developed by appropriately distributing the wall thickness and hardness of metal pipes. It was discovered that the above-mentioned bending problem could be solved. That is, the present invention provides a metal tube with excellent bending workability, characterized in that a rod-shaped or band-shaped hardened region is provided in the thin-walled portion of the metal tube with uneven thickness in the cross section in the tube axis direction.

In the present invention, the volume ratio of the hardened region in the metal tube is preferably 5 to 35%, and the width of the hardened region is preferably one-half or less of the outer circumference of the metal tube. The metal tube of the present invention is bent so that the thick, softened region is on the outside and the thin, hardened region is on the inside, and as a result, the required thickness is ensured on the outside of the bend even after the bending process, Moreover, since the wall thickness is thin and hardened on the inside of the bend, wrinkles do not occur.

The reason why it is desirable to set the volume ratio of the hardened area to 5 to 35% is that if it is less than 5%, it is insufficient to suppress the occurrence of wrinkles, and if it exceeds 35%, cracks are likely to occur. .

Further, the reason why it is desirable that the width of the hardened region be one-half or less of the outer circumference of the metal tube is that if the width exceeds one-half, bending becomes difficult.

Examples of methods for making metal tubes uneven in thickness include (a) making the heating temperature of the billet for hot extrusion uneven; (b) drilling eccentric holes in the billet for extrusion; and (c) drawing during the drawing process. Tilt the die in the direction (2) Design the die and plug for drawing to produce uneven thickness (
e) Welded pipes can be made from strips with varying wall thickness.

Commercially available metal pipes can also be used as long as they have uneven thickness.

The wall thickness deviation ratio (the percentage of the value obtained by dividing the difference between the maximum wall thickness and the minimum wall thickness by the maximum wall thickness) varies depending on the conditions, but if it is 8% or more, it can be used.

As a method for obtaining a metal tube in which hardened regions are provided in a predetermined distribution state in a softened region, for example, in the case of work hardening type alloys, work hardening of the entire body is performed by drawing, forming, rolling, etc., or precipitation hardening. For alloys, the method is to harden the entire body by rapidly cooling it from a high temperature, and then locally heated with a laser beam, electron beam, plasma arc, etc. to form a locally softened region, and for quench hardening type alloys, There is a method in which the entire material is softened by annealing, then locally heated by a laser beam, electron beam, plasma arc, etc., and then cooled to form a locally hardened region.

In a welded pipe, a hardened region can be formed in a softened region by performing the same treatment as described above in the raw material or in any step after pipe manufacturing. The material of the metal tube applied to the present invention is copper, copper alloy, aluminum, iron, stainless steel,
The material is not particularly limited to titanium or the like, and the present invention can also be applied to composite pipes in which the above metals are clad with different types of metals or synthetic resins.

Further, the cross-sectional shape of the metal tube applied to the present invention is circular, elliptical,
The present invention is not particularly limited to other irregular shapes, and can also be applied to tubes with fins on the outer and/or inner surfaces.

Of course, the present invention also includes a tube in which the portion to be bent is the metal tube of the present invention and the other portion is a conventional metal tube.

The metal tube of the present invention is applicable not only to heat exchangers but also to a wide range of fields where the metal tube is bent and used.

〔Example〕

Next, the present invention will be explained in detail with reference to examples.

Example (1) Outer diameter: 9.52 mm, maximum wall thickness: 0.37 mm, minimum wall thickness: 0.3 mm.
25 hard phosphorus deoxidized steel pipe with large uneven thickness (J■5H33
00C1220T), while the tube is moving straight, an electron beam is applied to the outer surface of the tube to heat it.
Go back A and cut the minimum thickness part (groove part) as shown in Figure 1.
The metal of the present invention has a hardened region 1 with a width of about 3 mm on the outer circumferential surface of the tube in the vicinity, and a softened region 2 with a width of about 25+n+n on the outer circumferential surface of the tube in other parts including the maximum wall thickness part. Got the tube.

In addition, in order to compare with the metal tube of the present invention, a conventional product with an outer diameter of 9.52 mm, a maximum wall thickness of 0.32 m, and a minimum wall thickness of 0.30 mm was used.
Light soft phosphorus deoxidized copper tube with small uneven thickness (JIS H33
00C1220? ) was prepared.

Hairpin bending was performed on the two types of metal tubes thus obtained. That is, the bending conditions were as follows: the bending radius was 12.7 mm, the difference between the outer diameter and the inner diameter of the pipe was 0.2 mm using a mandrel, and the minimum thickness part was on the side undergoing compression processing. We investigated the occurrence of wrinkles, maximum wall thickness, and minimum wall thickness at the bent portion. The results are shown in Table 1.

Table 1 As is clear from Table 1, the steel pipe according to the present invention does not cause wrinkles compared to conventional copper pipes, and the thinning of the wall due to bending concentrates on the thick parts, making it difficult for extreme wall thinning to occur. Therefore, it was confirmed that it had excellent bending workability.

Example (2) Regarding a hard aluminum brass tube (equivalent to JISH3300C6870T) with a large thickness deviation with an outer diameter of 15.9+n[++, a maximum wall thickness of 1.12 mm, and a minimum wall thickness of 0.90 mm+, the outer surface of the tube was As shown in FIG. 1, similar to the metal tube of the present invention, a hardened region with a width of about ioam on the outer circumferential surface of the tube is formed near the minimum wall thickness (thin wall) by repeating the heating process by applying a laser beam. 1, and the width at the outer peripheral surface of the tube is approximately 4 in other parts including the maximum wall thickness part.
Metal tubes of the present invention each having a softened region 2 of 0 mm were obtained.

In addition, in order to compare with the metal tube of the present invention, the outer diameter of the conventional product is 1.
5.9mm, maximum wall thickness 1.03mm, minimum wall thickness 0.98
+nm soft aluminum brass tube with small thickness deviation (JAS
83300 C6870T) was prepared.

The two types of metal tubes thus obtained were subjected to U-shaped bending. In other words, the bending radius is 35 mm,
A mandrel (core metal) was used, the difference between the outer diameter and the inner diameter of the tube was set to 0.3+nm, and the minimum thickness part was placed on the side receiving compression processing. The occurrence of wrinkles, maximum wall thickness, and minimum wall thickness at the bent portion were investigated.

The results are shown in Table 2.

Table 2 As is clear from Table 2, the aluminum brass tube according to the present invention has no wrinkles compared to the conventional aluminum brass tube, and the thinning caused by bending concentrates on the thick parts, so the aluminum brass tube according to the present invention is extremely thin. It was confirmed that the material had excellent bending workability because it was difficult to form flesh.

(Effects of the present invention) According to the present invention, since the thickness 1'1 of the bent part after bending is uniform, it has excellent pressure resistance, and since wrinkles do not occur on the inner surface, the flow resistance of refrigerant etc. is small, which is remarkable in industry. It is effective.

[Brief explanation of the drawing] FIG. 1 is a perspective view of a metal tube according to the present invention. 1... Hardened area in thin wall part 2...Softening area in thick wall part

Claims (3)

[Claims] (1) A metal tube with excellent bending workability, characterized in that a rod-shaped or band-shaped hardened region is provided in the thin-walled portion of the metal tube with uneven thickness in the cross section in the tube axis direction. (2) The volume ratio of the hardened area in the metal tube is 5 to 35%
A metal tube with excellent bending workability according to claim 1. (3) A metal tube with excellent bending workability according to claim 1, wherein the width of the hardened region is one-half or less of the outer peripheral length of the metal tube.