JPH03281006A - Manufacture of metallic tube with special shaped inner surface - Google Patents

Abstract

PURPOSE:To prevent the breakage of mandrel and to obtain a high-quality tube of product without flaws and chipping-off by forming projecting parts and recessed parts alternately and continuously from the vicinity of rolling starting point to the vicinity of rolling ending point in the circumferential direction of the outer surface of a mandrel through the side wall. CONSTITUTION:The end part F on the side of the rolling starting point A of the mandrel is made into a complete roundness with an outside diameter somewhat smaller than the inside diameter of a tube stock with a uniform wall thickness in the circumferential direction. The outside diameter of the mandrel is proportionally and gradually reduced from the end part F toward the other end part E. The projecting parts corresponding to the groove parts 11 of a tube 10 with grooved inner surface is formed in the direction of the axial line of the mandrel on eight places in the circumferential direction of the outer surface of the mandrel from the vicinity of rolling starting point A to the end part E. The recessed parts corresponding to the higher parts 12 of the tube 10 with the groove inner surface are formed between adjacent projecting parts.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for manufacturing a metal tube with a deformed inner surface, in which grooves and peaks extending in the axial direction and having an arcuate cross section are alternately and continuously formed in the inner circumferential direction. In particular, it relates to a manufacturing method using a cold pilger mill.

[Prior Art] This type of metal tube with a deformed inner surface, which is often used as a heat exchange tube such as a pyrolysis tube in an ethylene plant, has conventionally been manufactured by hot extrusion. However, hot extrusion pipe manufacturing has low dimensional accuracy, and in the case of difficult-to-process materials such as high Nt and high Cr steel, there is also the limitation that small diameter and thin walled pipes cannot be manufactured. Therefore, recently, a cold rolling method using a cold pilger mill has also been used.

In the method for manufacturing metal tubes with irregular inner surfaces using a cold pilger mill, the outer surface shape of the mandrel, which determines the inner surface shape, is important. Mandrels with improved external shapes are disclosed, for example, in JP-A-60-166108 and JP-A-6
It is disclosed in Japanese Patent No. 2-212006.

One of the features of the mandrel disclosed in JP-A-60-166108 is that, as shown in FIG. This is because it is designed.

Therefore, the arc-shaped convex portions and concave portions of the mandrel are already formed alternately and continuously in the circumferential direction of the outer surface via the side wall constituted by the contact point common to both at the rolling start point.

Then, from the rolling start point to the rolling end point, the mandrel outer diameter gradually decreases, and the tip arc radii of the convex portions and concave portions gradually decrease. However, the angle formed by the adjacent side walls does not change, so the depth of the recess is deep at the rolling start point, gradually becomes shallower toward the rolling end point, and finally reaches the peak height of the product pipe. Match.

As shown in FIG. 7, the mandrel disclosed in JP-A-62-212006 has a recess that gradually becomes deeper as the outer diameter gradually decreases from the rolling start point to the rolling end point. The shape of the crest of the tube is characterized in that the locus of the tube is moved in the axial direction of the mandrel with the tip of the ridge aligned with the bottom of the recess, resulting in a four-part shape. Therefore, although the depth of the recess increases from the rolling start point to the rolling end point,
The tip arc radius of the recess and the angle formed by the adjacent side walls are constant in the axial direction of the mandrel.

[Invention to be Solved by the Invention] In the method of manufacturing a tube with a deformed inner surface using such a mandrel, the following problems are unavoidable.

In the case of the mandrel shown in FIG. 6, since the concave part of the mandrel is deep near the rolling start point, in the early stage of rolling, when the tube does not protrude into the concave part, as shown in FIG.
The tube 1 does not come into close contact with the bottom of the recess of the mandrel 2, and the roll 3,
3 acts intensively only on the convex portion of the mandrel 2, there is a high risk that the mandrel 2 will break.

Further, in the mandrel shown in FIG. 7, a smooth portion is formed between the concave portions on the outer surface and continuous at the same radius in the circumferential direction. The circumferential length of this smooth portion increases as it approaches the rolling start point. Therefore, in the early stage of rolling, as shown in FIG.
is thinned by the roll 3.3 and the smooth part of the mandrel 2 and extends mainly in the axial direction, with almost no overhang into the recess.

As a result, tensile stress acts on the inner surface of the tube that slightly protrudes into the recess, and cracks as shown in FIG. 10 are likely to occur at the peaks of the product tube. In addition, since the concavities of the mandrel are insufficiently filled with material in the early stage of rolling, there is a risk that unfilled areas may appear in the peaks of the resulting tube with a deformed inner surface, and this tendency is especially true for difficult-to-process materials. big.

An object of the present invention is to provide a method for manufacturing a metal tube with a deformed inner surface using a cold pilger mill, which can prevent breakage of the mandrel and produce a high-quality product tube without defects or defects.

[Means for Solving the Problems] The manufacturing method of the present invention is to reduce the diameter and thickness of a blank pipe having a uniform wall thickness in the circumferential direction using a cold pilger mill, thereby forming grooves and peaks having an arcuate cross section extending in the axial direction. is a method for manufacturing an internally deformed metal tube, in which the internally deformed metal tube is formed alternately and continuously in the inner circumferential direction via side walls formed by a common tangent to both,
As a mandrel, the outer diameter gradually decreases from near the rolling start point to near the rolling end point, and the side wall has protrusions and recesses that form grooves and peaks on the inner surface of the tube, each of which has a common tangent line. The angle between adjacent side walls near the rolling start point is larger than the angle near the rolling end point, and gradually decreases toward the end of rolling. Accordingly, the method is characterized by using a mandrel with a deformed outer surface in which the depth of the recess gradually increases from near the rolling start point to near the rolling end point.

[For production]

FIG. 1 is a schematic diagram showing changes in the axial direction of the cross-sectional shape of a mandrel used in the manufacturing method of the present invention, corresponding to FIGS. 6 and 7.

In the mandrel used in the manufacturing method of the present invention, convex portions and concave portions are alternately and continuously formed in the circumferential direction of the outer surface via the side wall from the vicinity of the rolling start point to the vicinity of the rolling end point, so that the concave portions near the rolling start point The protrusion of the tube into the recess is also promoted near the rolling start point, where there is a continuous flat portion with the same radius in the circumferential direction. Moreover, the angle formed by the adjacent side walls is larger near the rolling start point than near the rolling end point.
The recess is shallow near the rolling start point, so even at the beginning of rolling,
As shown in FIG.
are pressed together with sufficient margin to prevent material from being underfilled, and at the same time, the tensile load acting on the inner surface of the tube is reduced and cracks are prevented. Furthermore, since the rolling load acting on the mandrel 20 is dispersed, breakage of the mandrel 20 is also prevented.

〔Example〕

The manufacturing method of the present invention will be described below with reference to Examples.

FIGS. 3(a) and 3(b) are cross-sectional views showing the cross-sectional shape of the tube with a deformed inner surface manufactured in this example.

On the inner surface of the inner surface deformed pipe lO, a plurality of grooves ll formed by a part of an arc with a radius R1 and a plurality of peaks 12 formed by a part of a circular arc with a radius R2 are arranged alternately in the circumferential direction (in the illustrated example, 8 each
Both tubes are straight in the tube axis direction. The adjacent groove portion 11 and peak portion 12 are connected to the straight side wall 1.
They are connected by 3.

The groove portion 11 has an angle θ (22.5 in this example) around the tube center O.
It is composed of a range of angle r' out of a circular arc of a required radius drawn on the opposite side of the tube center O centering on a point P on a straight line divided by '). In addition, the peak portion 12 is configured within an angle δ′ of an arc of a required radius drawn toward the tube center O side with the center at point E on a line at a position θ from a line passing through the center of the groove portion 1m. . Hereinafter, γ' of the groove it will be referred to as the groove arc angle, and δ' of the peak 12 will be referred to as the peak arc angle.

The side wall 13 has a groove 11. It is a straight line composed of common tangents at each end point of the mountain part 12, and the extension line of this side wall 13, -Lx, is the extension line M of the line connecting the center P of the groove part 11 and the pipe center 0. The extended line LITL! which intersects at point F outward from the bottom of the groove. The intersection angle 2a is the groove arc angle γ′ of the groove portion 11, the peak arc angle δ′ of the peak portion 12, the groove bottom inner diameter d5 which is the distance between the corrugations of the opposing groove portions 11, and the distance between the peaks of the opposing peak portions 12. It is determined by the peak inner diameter d and the groove depth (mountain height).

FIG. 4 is a side view of the mandrel used for manufacturing the tube with a deformed inner surface, and FIG. 5 is a longitudinal sectional front view showing changes in the cross-sectional shape of the mandrel in the axial direction at points A--D in FIG. 4.

The end portion F of the mandrel on the side of the rolling start point A is a perfect circle having an outer diameter slightly smaller than the inner diameter of the blank pipe having the same thickness in the circumferential direction. The outer diameter of the mandrel gradually decreases proportionally from the end F to the other end E. Reference numerals 25 and 26 are mounting threads provided at both ends of the mandrel 20.

There are rolling start points A at eight locations in the circumferential direction of the outer surface of the mandrel 20.
From the vicinity of the groove 11 of the inner grooved tube 10 to the end E
Convex portions 21 corresponding to the convex portions 21 are formed in the mandrel axial direction, and concave portions 22 corresponding to the peak portions 12 of the internally grooved tube IO are formed between adjacent convex portions 21. Adjacent convex portions 21 and concave portions 22 are connected by a side wall 23 formed by a common tangent to both. Note that at the rolling start point A, the four portions 22 do not exist, and the mandrel 20 has a hexagonal shape.

In Fig. 5, H is the outer diameter of the convex portion and is the outer diameter of the mandrel, which corresponds to the groove bottom inner diameter d1 of the internally grooved tube lO, and G is the outer diameter of the concave portion, which corresponds to the top inner diameter d2 of the internally grooved tube lO. This is the mandrel outer diameter. In addition, Ra is the convex arc radius corresponding to the groove arc radius R1, Rb is the concave arc radius corresponding to the peak arc radius R2, γ is the convex arc angle corresponding to the groove arc angle T', and δ is the peak arc Each represents the concave arc angle corresponding to the angle δ'. 2α is the inclination angle of the side wall at the convex part,
2β is the inclination angle of the side wall in the recess, 11 oblique angle 2α
is the extension line of the internally grooved pipe lO, L.

This corresponds to the intersection angle 2a of .

These are designed as follows between the rolling start point A and the rolling end point. However, as described above, the recess 22 does not exist at the rolling start point A.

From the rolling start point A to the rolling end point, the outer diameter of the convex portion H-
And the outer diameter G of the recess gradually decreases. However, as will be described later, the degree of reduction in the outer diameter is greater for the outer diameter G of the concave portion than for the outer diameter H of the convex portion.

The convex arc radius Ra and the concave arc radius Rb are constant.

The convex arc angle γ and the concave arc angle δ gradually increase from the rolling start point A to the rolling end point, and accordingly, the side wall inclination angles 2α and 2β both increase from the rolling start point A to the rolling end point. It is gradually increasing.

Therefore, the degree of decrease in the outer diameter toward the rolling end point is that the outer diameter G of the recess is larger than the outer diameter H of the convex part, and the depth of the recess (H-G
) gradually increases from the rolling start point A, which is substantially 0, to the rolling end point.

Each dimension at the rolling end point is a part of each corresponding dimension in the internally deformed tube IO.

The region from the rolling end point O to the end B is a relief portion, and although the outer diameter H of the convex portion gradually decreases, the outer diameter of the recessed portion, the shape of the recessed portion, etc. are constant.

Note that the convex arc radius Ra and the concave arc radius Rb can also be gradually decreased from the rolling start point A to the rolling end point.

When such a mandrel is used for rolling with a cold pilger mill, there is no continuous flat surface with the same radius in the circumferential direction near the rolling start point A of the mandrel 20.
Moreover, since the recess 22 is shallow, even in the early stage of rolling when it is relatively difficult for the tube to overhang within the recess 22, the overhang of the tube into the recess 22 is promoted, and the recess 22 is filled with tube material (
(See Figure 2). Therefore, a situation in which the rolling load is concentrated on the convex portion 21 of the mandrel 20 (see FIG. 8) is avoided, and breakage of the mandrel 20 is prevented. Furthermore, since no unfilled portions occur and a situation in which tensile load is applied to the inner surface of the tube protruding into the recess 22 (Fig. 9) can be avoided, there is no risk of defects or cracks shown in Fig. 1θ occurring in the product pipe. It also disappears.

A raw pipe made of 25Cr-25N] (0.2C) with an outer diameter of 75 mm and an inner diameter of 44 mm was rolled with a cold pilger mill using a mandrel (A-D open circuit $1720 m) with dimensions shown in Table 1. Even after rolling for 3,000 m, no breakage occurred in the mandrel, and the produced tubes (ethylene plant pyrolysis tubes) had no cracks on the inner surface, and no defects were observed in the peaks. .

On the other hand, when the conventional mandrel shown in Fig. 6 is used, the mandrel breaks after rolling 20 m, and when the conventional mandrel shown in Fig. 7 is used, it is possible to roll over 100 m, but it is possible to A crack occurred in the part.

〔Effect of the invention〕

The method of manufacturing a tube with a deformed inner surface according to the present invention eliminates the risk of breaking the mandrel, and reduces tool costs. In addition, since the peaks of the product tube are sufficiently filled with material and there is no risk of cracks occurring on the inner surface, the quality of the product tube can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing changes in the axial shape of the mandrel used in the method of the present invention, Fig. 2 is a schematic diagram showing rolling conditions using the mandrel at the initial stage of rolling, and Fig. 3 is an example of the method of the present invention. A cross-sectional view of the tube with a deformed inner surface to be manufactured, and FIG. 4 is a side view of the mandrel used to manufacture the tube with a deformed inner surface.
Fig. 5 is a longitudinal sectional front view of Fig. 4, Figs. 6 and 7 are schematic diagrams of a conventional mandrel, Figs. 8 and 9 are schematic diagrams showing rolling conditions using the mandrel, and Fig. 1O shows cracks. It is a perspective view for explaining a flaw. lO: inner surface deformed tube, 11: groove, 12: peak, 20: mandrel, 21: protrusion, 22: recess, 23: side wall. Figure ■ Figure Figure (b) Figure 6 Figure Figure Figure Figure (b)

Claims (1)

[Claims] (1) A side wall made by rolling a blank pipe with equal wall thickness in the circumferential direction to reduce its diameter using a cold pilger mill, and having grooves and peaks with an arcuate cross section extending in the axial direction formed by a common tangent to both. A method for manufacturing an internally deformed metal tube in which the internally deformed metal tube is formed alternately and continuously in the inner circumferential direction via a mandrel, the outer diameter gradually decreasing from near the rolling start point to near the rolling end point, Convex portions and concave portions for forming grooves and peaks on the inner surface of the tube are alternately and continuously formed in the circumferential direction of the outer surface via a side wall formed by a common tangent to both, and adjacent portions are formed in the vicinity of the rolling start point. The angle formed by the side wall is larger than the angle near the end of rolling and gradually decreases toward the end of rolling, and along with this, the depth of the recess increases from near the start of rolling to near the end of rolling. A method for producing a metal tube with a deformed inner surface, characterized in that a mandrel with a deformed outer surface is gradually increased in size.