JP2009285692A - Hydraulic flattening method of metallic pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that in the conventional flattening technique, in order to prevent the deterioration of flatness and a break in edge parts in a flattening part, the use of a core is needed and the deterioration of working efficiency is caused. <P>SOLUTION: Liquid is poured into the inside of the inner periphery of a metallic tube 10 and, under the state where internal pressure is loaded by the pressure of that liquid, flattening work is applied until the height h of flatness becomes a prescribed height H of the flatness of a product of ≤0.5 times the outside diameter D of the metal tube before the flattening work. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydraulic flattening method for metal pipes.

For example, a heat exchanger fin tube or the like is manufactured by flattening a metal pipe such as a steel pipe. In flattening, the specified product flatness height ratio H / D (H: product height, D: raw tube outer diameter) is obtained by sandwiching the outer peripheral surface of the base tube, which is a metal tube before flattening, with a pair of molds. However, if the product flat height ratio is relatively large, the ear part, which is the tube peripheral part that projects freely in the direction perpendicular to both the crushing direction and the tube axis direction, may be bent or gold Molding defects such as a flatness defect occurring in a flat portion which is a pipe peripheral portion to be pushed and flattened by the mold head plane (see FIG. 2 (a)). Therefore, in order to prevent these molding defects, it is often performed to use a core (or a core metal) and insert it into the inner peripheral side of the pipe and flatten it while restraining the inner surface of the pipe to some extent. In addition, as a literature about the press work technique using a metal core, there exists patent document 1 (manufacturing method of a branch pipe) etc., for example.
Japanese Patent Laid-Open No. 5-164281

  However, when flattening is performed using a core, it is necessary to remove the core from the product after the flattening, and the removal operation is not easy. That is, in the conventional flat processing technique, in order to prevent the flatness deterioration of the flat portion and the back of the ear from breaking, there is a problem that the use of a core is required and the processing efficiency is deteriorated.

As a result of intensive studies to solve the above problems, the inventors have made the present invention having the following gist configuration.
(Claim 1)
A liquid is injected into the inner peripheral side of the metal tube, and the flat height h is reduced to a predetermined product flat height H of 0.5 times or less of the outer diameter D of the metal tube before crushing under an internal pressure load state due to the pressure of the liquid A method for hydraulic flattening of a metal tube, wherein the metal tube is crushed until it reaches the end.
(Claim 2)
The internal pressure p1 until the flat height h reaches 0.5 × D from D so that the following equation (1) holds, and the internal pressure p2 until the flat height h reaches the predetermined product flat height H from 0.5 × D The method for hydraulic flattening of a metal pipe according to claim 1, wherein the crushing is performed while adjusting so that the following formula (2) is satisfied.

Record
0 <p1 <(2 × t × YS) / (D-2 × t)… (1)
(t × TS) / (3 × (h-2 × t)) <p2 <(t × TS) / (h-2 × t)… (2)
t: Metal tube wall thickness before crushing [mm], D: Metal tube outer diameter before crushing [mm], YS: Yield strength [MPa] obtained by tensile test of metal tube before crushing, TS: Tensile strength [MPa] obtained by the tensile test of the metal tube before crushing, h: Flat height [mm] during flattening processing, p1: Internal pressure [MPa] until h reaches 0.5 x D from D, p2: Internal pressure [MPa] until h reaches the specified product flat height H from 0.5 x D
(Claim 3)
The seam welded pipe is used as the metal pipe, and the seam welded pipe is positioned so that the welded seam part is on the flat part side, and the crushing process is performed. Hydraulic flattening method for steel pipes.
(Claim 4)
A hydraulic flattened metal tube manufactured using the hydraulic flattening method according to claim 1.

  ADVANTAGE OF THE INVENTION According to this invention, the flat processed metal tube which has sufficient flatness in a flat part, and does not have a waist | hip_fold in an ear | edge part can be manufactured efficiently without using a core.

  In the hydraulic flattening method of the present invention, first, as shown in FIG. 1A, one end of the metal tube 10 in the longitudinal direction is a seal head (for forming water introduction and sealing) 5 and the other end is a seal head ( (For molding water sealing) 6, each of which is sealed, and a liquid such as molding water is injected into the inner peripheral side of the metal tube 10. Then, as shown in FIG. 1 (b), an internal pressure p is applied to the metal pipe 10 by the forming water, and the upper mold 1 having a flat head portion of the pipe longitudinal direction portion in the internal pressure load state. In each mold head plane of the lower mold 2, pressing is performed from both ends in the tube diameter direction to perform crushing (flattening). An apparatus that can be preferably used for this crushing process is that the upper mold 1 is the upper mold holder 3, the lower mold 2 is the lower mold holder 4, and the mold head plane is kept parallel to the longitudinal direction of the pipe. However, it is preferable to support it so that it can move in the vertical direction, and to urge the vertical movement by an actuator (not shown) composed of a hydraulic cylinder or the like. Thereby, a hydraulic flattened product (hydraulic flattened metal tube) as shown in FIG. 1C is obtained. In such a hydraulic flattened product, a pressing portion by the mold head plane is referred to as a flattened portion. FIG. 1 (d) is a cross-sectional view taken along the line AA of FIG. 1 (b). As shown in FIG. The mold head plane interval h between the mold 1 and the lower mold 2 is referred to as a flat height. Crushing is performed until the flat height h reaches a final flat height that is equal to the product flat height H. As shown in the figure, the ear portion is located between the upper and lower mold head planes, and is a pipe circumferential direction portion that is not restrained by the mold head plane and can be deformed freely. A flat part is the remainder except an ear | edge part from the whole pipe circumferential direction located between upper and lower mold head planes.

  As a result, it is possible to manufacture a flat-worked metal tube having sufficient flatness in the flat portion and having no hip break in the ear portion without using a core. However, in the case of flat machining where the product flat height H is less than 0.5 times the outer diameter D of the raw pipe (meaning the metal pipe before crushing), the core is not used and there is no internal pressure load. The shape of the flattened product is good, and the product shape improvement effect due to flattening under the internal pressure load condition due to hydraulic pressure does not appear remarkably. Therefore, in the present invention, from the viewpoint of effect manifestation, the present invention is limited to flat processing where H ≦ 0.5 × D.

  The inventors have also found that there is an appropriate range for the internal pressure applied during flattening where H ≦ 0.5 × D. When an internal pressure that falls outside the appropriate range is applied, as shown in FIG. 2 (a), the flatness of the flat part deteriorates and the tendency of the ears to break is increased. On the other hand, when an internal pressure outside the appropriate range is applied, as shown in FIG. 2 (c), the increase in the peripheral length of the flat part (peripheral length increase rate: see FIG. 4) becomes large. Local thinning and breakage are likely to occur at these points. This appropriate internal pressure range varies depending on the h / D value range during flattening. That is, the appropriate range of the internal pressure p1 in the range of h / D: 1 to 0.5 is given by the above formula (1): 0 <p1 <(2 × t × YS) / (D−2 × t). In addition, the appropriate range of the internal pressure p2 in the range of h / D: 0.5 to H / D is the above formula (2): (t × TS) / (3 × (h−2 × t)) <p2 <(t × TS) / (h-2 × t). Where, t: thickness of metal tube before crushing [mm], D: outer diameter of metal tube before crushing [mm], YS: yield strength obtained by tensile test of metal tube before crushing [MPa] , TS: Tensile strength [MPa] obtained by tensile test of metal tube before crushing, h: Flat height [mm] during flattening, p1: Internal pressure until h reaches 0.5 x D from D [ MPa], p2: internal pressure [MPa] until h reaches a predetermined product flat height H from 0.5 × D.

FIG. 3 is a graph showing an example of the appropriate internal pressure range in the case where the steel pipe shown in Table A in the figure is subjected to hydraulic flattening according to the processing specifications shown in the same table.
In addition, when the base pipe is a seam welded pipe (for example, an electric resistance welded steel pipe), if the weld seam is located on the ear side, there is a high possibility that cracks will occur starting from the weld seam during crushing. It is preferable that the seam welded pipe is arranged and crushed so that the weld seam portion is on the flat portion side.

As an example, seamless steel pipe (SL) shown in Table 1 and ERW steel pipe (ERW), which is one of seam welded pipes, are used as the raw pipes, respectively. Experiments were performed to evaluate the processing characteristics. The contents of the evaluation items for processing characteristics are shown in FIG. 4 as an explanatory diagram. In this experiment, a hydraulic flattening apparatus similar to that shown in FIG. 1A was used, and the hydraulic flattening was performed according to the following procedure.
1) Insert the steel pipe 10 between the upper and lower molds 1 and 2 as shown in FIG.
2) As shown in FIG. 5A, the upper mold holder 3 is clamped and the seal heads 5 and 6 are advanced to the seal position.
3) As shown in FIG. 5B, molding water is poured into the inner peripheral side of the steel pipe 10, and the upper and lower molds 1 and 2 are advanced while adjusting to a predetermined internal pressure, and crushing is performed until a predetermined product flat height is reached. Do.
4) As shown in FIG. 5C, the upper and lower molds 1 and 2 are retracted to be opened.
5) As shown in FIG. 5D, the upper mold holder 3 is opened, and the seal heads 5 and 6 are opened. Thereafter, the steel pipe 10 is taken out.

  Table 1 shows the evaluation results of the processing characteristics. From Table 1, it can be seen that in the example of the present invention, the dent ratio of the flat surface (the outer peripheral surface of the flat part) is much smaller than in the comparative example, and the flatness of the flat part is excellent. In all of the comparative examples, cracks occurred at the sites indicated in the same table. In Table 1, the R stop portion is a portion near the boundary with the flat portion in the ear portion, and the ear vertex is the portion farthest from the tube center axis in the ear portion. On the other hand, in the example of the present invention, no crack was generated except that the crack was generated at the position of the weld seam portion in No. 11 in which the weld seam portion was arranged on the ear portion side.

  As described above, according to the present invention, it is possible to manufacture a flat processed metal tube that has sufficient flatness in the flat portion and does not fold back in the ear portion without using a core. This manufacturing process is highly efficient because it does not involve troublesome core removal operations.

It is a schematic diagram which shows the outline | summary of the hydraulic flatness processing method. It is a schematic diagram which shows the internal pressure dependence tendency of the form of a hydraulic flattened product. It is a graph which shows an example of a proper internal pressure range. It is explanatory drawing which shows the evaluation item of the process characteristic in an Example. It is a schematic diagram which shows the hydraulic flatness processing procedure in an Example. It is a schematic diagram which shows the hydraulic flatness processing procedure in an Example. It is a schematic diagram which shows the hydraulic flatness processing procedure in an Example. It is a schematic diagram which shows the hydraulic flatness processing procedure in an Example. It is a schematic diagram which shows the hydraulic flatness processing procedure in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper die 2 Lower die 3 Upper die holder 4 Lower die holder 5 Seal head (for forming water introduction and pipe end sealing)
6 Seal head (for pipe end sealing)
10 Metal pipe (eg steel pipe)

Claims (4)

  A liquid is injected into the inner peripheral side of the metal tube, and the flat height h is reduced to a predetermined product flat height H of 0.5 times or less of the outer diameter D of the metal tube before crushing under an internal pressure load state due to the pressure of the liquid. A method for hydraulic flattening of a metal tube, wherein the metal tube is crushed until it reaches the end. The internal pressure p1 until the flat height h reaches 0.5 × D from D so that the following equation (1) holds, and the internal pressure p2 until the flat height h reaches the predetermined product flat height H from 0.5 × D The method for hydraulic flattening of a metal pipe according to claim 1, wherein the crushing is performed while adjusting so that the following formula (2) is satisfied.
Record
0 <p1 <(2 × t × YS) / (D-2 × t)… (1)
(t × TS) / (3 × (h-2 × t)) <p2 <(t × TS) / (h-2 × t)… (2)
t: Metal tube wall thickness before crushing [mm], D: Metal tube outer diameter before crushing [mm], YS: Yield strength [MPa] obtained by tensile test of metal tube before crushing, TS: Tensile strength [MPa] obtained by the tensile test of the metal tube before crushing, h: Flat height [mm] during flattening processing, p1: Internal pressure [MPa] until h reaches 0.5 x D from D, p2: Internal pressure [MPa] until h reaches the specified product flat height H from 0.5 x D   The seam welded pipe is used as the metal pipe, and the seam welded pipe is positioned so that the welded seam part is on the flat part side, and the crushing process is performed. Hydraulic flattening method for steel pipes.   A hydraulic flattened metal tube manufactured using the hydraulic flattening method according to claim 1.

Images