JPH0818051B2 - Mandrel for cold rolling of inner grooved pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mandrel used when cold-rolling an inner grooved tube having a plurality of straight grooves formed in the tube axial direction in the inner circumferential direction. .

[Conventional technology]

Conventionally, in heat exchange pipe materials such as pyrolysis pipes of ethylene plants, in order to improve heat exchange efficiency, a plurality of straight grooves or inclined grooves are formed in the pipe axial direction in the inner surface circumferential direction to increase the pipe inner peripheral length. A long inner grooved tube is used. This inner grooved pipe is required to be long, and the machining length is limited by machining such as cutting.Therefore, conventionally, an inner grooved pipe having straight grooves is manufactured by hot extrusion. The inner grooved tube having the inclined groove was manufactured by twisting the inner grooved tube. However, those manufactured by hot extrusion have poor dimensional accuracy, and in the case of difficult-to-machine materials such as high Ni-high Cr steel, there is a restriction that small-diameter and thin-walled products cannot be manufactured in terms of extrusion press capability.

As is well known, there is a cold working method as a pipe manufacturing method with better dimensional accuracy than the hot extrusion method, and cold rolling method using a cold pilger mill is also applied to the tube with inner groove. There is. And, the mandrel used in the case of manufacturing the inner grooved tube having the straight groove as described above by this cold rolling method is disclosed in JP-A-60-166108 and JP-A-62-166108.
-212006.

The mandrel disclosed in JP-A-60-166108 is
As shown in FIG. 4 (a), the outer diameter H of the convex portion is the rolling start point A.
From the rolling end point B to the shaping area B
The outer diameter is the same between .about.B '. Further, the outer diameter G of the concave portion corresponding to the inner diameter of the crest of the inner grooved pipe is reduced from the rolling start point A to a point A'in the middle at a rate higher than the outer diameter reduction ratio,
It is reduced to the same extent as the outer diameter reduction ratio from the point A'to the rolling end point B, and the cross-sectional shape of the pipe is similar to the cross-sectional shape of the finished pipe in the initial stage of rolling the pipe. .

The mandrel disclosed in JP-A-62-212006 is
As shown in FIG. 4B, the outer diameter H of the convex portion and the outer diameter G of the concave portion
Is gradually reduced from the rolling start point to the rolling end point according to a predetermined formula (the formula recommended by Mannesmann), and the crest shape of the inner surface grooved pipe is made so that the tip of the crest always matches the groove bottom. The locus moved to is a mandrel concave shape.

[Problems to be Solved by the Invention]

Among these conventional mandrels, the former mandrel has a cross-sectional shape of the pipe similar to that of the finished pipe, and therefore the cross-sectional shape of the mandrel at each position in the axial direction is different. Such a mandrel cannot be manufactured only by machining such as a milling cutter, and since it requires manual work, the number of mandrel manufacturing steps is extremely large.

On the other hand, in the latter mandrel, for example, if a cutter having a full-scale blade from the center of the convex portion of the mandrel to the center of the adjacent convex portion is used, the amount of pushing the cutter from the outer diameter of the mandrel from the rolling start point to the rolling end point It can be processed by enlarging it toward the point. Therefore, unlike the former mandrel, there is no problem in manufacturing the mandrel. However, with this mandrel, for example, when an inner grooved tube having eight grooves on the inner surface used for a pyrolysis tube of an ethylene plant is manufactured,
There is a problem that it is difficult for the material to fill the concave portion of the mandrel. This problem will be described in detail with reference to FIG.

This figure shows the cross-sectional shape of the mandrel at three positions in the axial direction, and a is a cross section at a position 1/3 from the rolling start point when the length between rolling start point and rolling end point is roughly divided into three, Similarly, b is the cross section at 2/3, and c is the cross section at the rolling end point.

As can be seen in the figure, this mandrel has an outer diameter on the rolling start point side that is larger than the outer diameter on the rolling end point side.
The circumference on the rolling start point side is longer than the rolling end point. Also,
The recess depth on the rolling start point side is shallower than the rolling end point. Therefore, smooth portions 1a, 1b are formed in the circumferential direction on the convex portion of the mandrel on the rolling start point side from the rolling end point. The circumferential lengths of the smooth portions 1a and 1b become longer as they approach the rolling start point.

Then, in rolling, a pair of grooved rolls provided facing the mandrel are rolled, but in the vicinity of the rolling start point, the pipe is thin-walled by the roll and the smooth portion of the mandrel and mainly in the axial direction. It extends and almost does not project into the recess. As described above, the smooth portion has a circumferential length that becomes shorter as it approaches the rolling end point side, so that the region of the pipe subjected to the thinning rolling becomes smaller and the pipe projects to the concave portion of the mandrel. However, since the material in the recesses of the mandrel is insufficiently filled at the initial stage of rolling, an unfilled portion occurs in the crests of the obtained inner grooved tube, and this tendency is particularly large in the case of difficult-to-machine materials.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of the prior art, to provide a mandrel which is easy to manufacture and which can surely fill the concave portion of the mandrel with material by the end of rolling.

[Means for solving the problem]

In the mandrel of the present invention, straight groove portions and mountain portions are alternately formed in the pipe axial direction in the inner surface circumferential direction, and the extension line of the line connecting the groove bottom center of the groove portion and the pipe center has an extension line of the side wall. This mandrel is used when cold rolling an inner grooved pipe that intersects outward from the groove bottom, and gradually decreases from the rolling start point to the rolling end point at least from the rolling start point to the rolling end point. With the outer diameter, the convex portions and the concave portions alternately formed in the outer circumferential direction have substantially the same shape as the groove portion and the mountain portion of the inner groove tube at least over the entire length from the rolling start point to the rolling end point. Yes, the outer diameter H of the convex portion gradually decreases from the rolling start point to the rolling end point in accordance with the gradual decrease of the outer diameter, and the inclination angle of the hypotenuse connecting the convex portion and the concave portion is at least from the rolling start point to the rolling end. Over the entire length up to the point The recess outer diameter G decreases more gradually than the convex outer diameter H from the rolling start point to the rolling end point so that it becomes substantially the same as the slant angle, and the difference between the convex outer diameter H and the concave outer diameter G decreases. In order to absorb, the length of the hypotenuse decreases from the rolling start point to the rolling end point, and at the rolling end point, the convex outer diameter H, the concave outer diameter G, and the hypotenuse length are the inner diameter of the groove bottom of the inner groove tube. It is characterized in that it is substantially the same as d ₁ , the peak inner diameter d _3, and the side wall length.

[Action]

In the mandrel of the present invention, the convex portions and the concave portions that are alternately formed in the outer circumferential direction thereof have substantially the same shape as the groove portion and the mountain portion of the inner grooved pipe which is the product, and the entire rolling effective portion. The change in the distance between the convex portion and the concave portion and the change in the depth of the concave portion relative to the convex portion due to the change in the outer diameter in the axial direction are adjusted by the length of the hypotenuse connecting the convex portion and the concave portion. Therefore, if a blade having a shape corresponding to each of the convex portion and the concave portion is prepared, the mandrel can be manufactured only by adjusting the cutting depth. During rolling, not only the recesses are sequentially filled with material, but also there is no circumferential smooth portion in the protrusions, so there is almost no thinning rolling in the axial direction of the pipe, and the recesses are closer to the rolling start point. The material is positively filled into the inner grooved pipe, and no unfilled portion is generated in the crest portion of the obtained inner grooved pipe.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIGS. 1 (a) and (b) show an example of the cross-sectional shape of the inner grooved tube which is the subject of the present invention. On the inner surface of the inner grooved tube 10, a plurality of groove portions 11 and mountain portions 12 formed by a part of an arc are alternately formed in the circumferential direction (eight in the illustrated example), and the groove portions 11 and mountain portions 12 are Straight in the tube axis direction. Adjacent groove portion 11 and mountain portion 12 are connected by a straight side wall 13.

When the groove portion 11, the peak portion 12 and the side wall 13 are described in detail with reference to FIG. 1B, the groove portion 11 has an angle θ (2 in this example) about the pipe center O.
Of the circular arc of the required radius drawn on the opposite side of the pipe center O centering on the point D on the straight line divided by 2.5 °), it is constructed within the range of the angle 2β. Further, the ridge portion 12 is formed within a range of an angle 2γ of an arc having a required radius drawn on the pipe center O side with a point E on a line at a position θ from the line passing through the center of the groove portion 11 as the center. Hereinafter, β of the groove 11 is referred to as a groove half angle, and γ of the mountain 12 is referred to as a mountain half angle.

The side wall 13 is a straight line formed by a common tangent line at each end point of the groove portion 11 and the mountain portion 12, and is an extension line l ₁ , l of the side wall 13.
₂ is an extension line m of the line connecting the center D of the groove 11 and the center O of the pipe.
At the point F outside the groove bottom of the groove 11. The intersection angle 2α of the two extension lines l ₁ and l ₂ is the half-angle β of the groove 11 and the peak 1
2 is determined by the half-angle γ of the crest portion, the groove bottom inner diameter d ₁ that is the distance between the bottoms of the opposing groove portions 11, the crest inner diameter d ₃ that is the distance between the tops of the opposing crest portions 12, and the groove depth (height). Note that α is hereinafter referred to as a sidewall inclination angle.

FIG. 2 shows an example of the mandrel of the present invention used when the inner grooved pipe of FIG. 1 is manufactured by cold rolling.

The same figure (a) is a side view and (b) is a sectional view at the rolling end point. The outer diameter of the mandrel corresponding to the inner diameter d ₁ of the groove bottom of the inner grooved tube 10 is referred to as the outer diameter of the convex portion and is represented by H. The outer diameter of the mandrel corresponding to the inner diameter d ₃ of the crest is referred to as the outer diameter of the recess and is represented by G.

The inner surface grooved pipe 10 is provided at eight locations in the outer circumferential direction of the mandrel 20.
A convex portion 21 corresponding to the groove portion 11 is formed in the mandrel axial direction, and a concave portion 22 corresponding to the mountain portion 12 of the inner grooved tube 10 is formed between the adjacent convex portions 21. Then, between the rolling start point A and the rolling end point B, the convex portion outer diameter H gradually decreases toward the rolling finish point B side at the same angle in a tapered shape. H is a tube with internal groove 10
The inner diameter of the groove bottom is required to be d ₁ .

FIG. 2 (c) is an enlarged cross-sectional view of the mandrel, (d) is an enlarged view showing the cross-sectional change stepwise in the axial direction, e in FIG. 2 (d) is the rolling start point A, and f is the intermediate point. , G are cross sections at the rolling end point B, respectively. As can be seen in both figures, the convex portion 21 is the groove portion 11 of the inner grooved pipe 10 over the entire length.
Is a part of an arc (radius Rb, half-angle β) that is substantially the same as, and the recess 22 also extends over the entire length, and is a part of an arc (radius Rt, half-angle γ) that is substantially the same as the ridge 12 of the inner groove tube 10. is there.

The oblique side 23 connecting the concave portions 22 of the adjacent convex portions 21 extends over the entire length from the rolling start point A to the rolling end point B and the inner grooved pipe 10
The side wall 13 has the same inclination angle α as the inclination angle α. That is, the angle formed by the line n connecting the axis OM of the mandrel 20 and the center of the convex portion and the extension of the hypotenuse 13 is α over the entire length.
In order to realize this, the outer diameter G of the concave portion is gradually reduced from the outer diameter H of the convex portion from the rolling start point A to the rolling end point B. As a result, the length of the oblique side 23 decreases from the rolling start point A toward the rolling end point B, and at the rolling end point B, it is the same length as the side wall 13 of the inner grooved tube 10. Therefore, in the outer surface shape of the mandrel 20, only the length of the hypotenuse 23 becomes shorter with the reduction from the rolling start point A to the rolling end point B,
At the rolling end point B, the shape is completely the same as the inner surface shape of the inner grooved tube 10.

In addition, as shown in FIG. 2 (a), the same taper outer diameter portion 20 continuous to the rolling start point A is provided on the base end side from the rolling start point A.
A and an outer diameter portion 20b having the same diameter subsequent thereto are formed, and the concave portion is escaped by an appropriate radius on the base end side from the rolling start point A. Further, from the rolling end point B to the tip side,
Shaped part having the same cross-sectional shape as the rolling end point B
20c is formed.

The mandrel 20 having the above shape is manufactured as follows. First, as shown in FIG. 3, a full-shaped mountain cutter 31 corresponding to the convex portion 21 and the oblique side 23 and a full-shaped valley cutter 32 corresponding to the concave portion 22 and the oblique side 23 are prepared. Next, in a mandrel material in which the round material or both ends have the same diameter and the middle portion is roughly processed into a taper shape, the blade bottom of the mountain cutter 31 is directed from the base end side toward the tip end side along the taper outer diameter. Cutting with the mountain cutter 31 while increasing the pushing amount. Then the mountain cutter 31
A valley cutter 32 is provided between the opposing side walls cut by the step, and the oblique side of the valley cutter 32 is cut so as to match the oblique side cut by the mountain cutter 31. This allows the mandrel 20 to be easily manufactured.

When cold rolling is performed using such a mandrel 20,
At the rolling start point A, the mandrel 20 has an inner grooved tube 10
Since the arc-shaped convex portion 21 having a shape corresponding to the groove portion 11 is formed, the thin portion rolling by the roll and the mandrel smooth portion is not substantially performed, the convex portion 21 bites into the inner surface of the pipe, and the excess thickness is the concave portion 22. To the side of. Around the rolling start point A
Since there is little overhanging on the 22 and the recess 22 is deep,
22 is not completely filled, but as rolling further progresses, the overhang of the surplus increases and the recess 22 becomes shallower,
The concave portion 22 is filled up, and in the vicinity of the rolling end point B, the convex portion 21 and the concave portion
By rolling the entire 22 and the hypotenuse 23, the inner grooved pipe 10 having the shape of the rolling end point of the mandrel 20 can be obtained.

 The results of using the mandrel of the present invention will be described below.

The target pipe is a pyrolysis pipe of the ethylene plant shown in FIG. 1, and has eight straight grooves in the circumferential direction on the inner surface in the pipe axial direction. The mandrel used to manufacture this tube by cold rolling is that shown in FIG.
To the rolling end point B is 720 mm.

To be more specific, cold rolling using a two-mandrel shown in Table 1 for a blank tube made of 25Cr-25Ni (0.2C) with an outer diameter of 75 mm, an inner diameter of 44 mm, and a wall thickness of 15.5 mm. went. The dimensions between the two types produced are shown in Table 2. No.1
The No. 2 pipe is manufactured using the No. 1 mandrel, and the No. 2 pipe is
It was manufactured using the No. 2 mandrel. The peaks of all the tubes had a perfect shape over their entire length.

In the above embodiment, the outer diameter H of the convex portion of the mandrel 20 is tapered between the rolling start point A and the rolling end point B. However, the present invention is not limited to this and, for example, the formula recommended by Mannesmann. Alternatively, it may be calculated by improving this formula.

Further, as the inner grooved tube 10, the groove portion 11 and the mountain portion 12 are connected by the straight side wall 13 has been described, but there is no straight portion and the arc of the groove portion 11 and the arc of the mountain portion 12 are directly connected. But it's okay. However, even in this case, it is necessary that the common tangent line of both arcs intersects with a straight line passing through the groove center and the pipe center outside the groove bottom.

Further, the groove portion 11 and the mountain portion 12 are not limited to circular arcs, but may be so-called trapezoidal shapes, triangular shapes, or the like.

〔The invention's effect〕

The mandrel of the present invention is easy to manufacture and therefore low in cost, and moreover, the mandrel of the inner groove is sufficiently filled with the material, and the mandrel has a great effect on the quality improvement.

[Brief description of drawings]

FIG. 1 is an explanatory view of a target pipe material of the mandrel of the present invention, FIG. 2 is an explanatory view of the mandrel of the present invention applied to the pipe material, FIG. 3 is an explanatory view of its manufacturing method, and FIG. 4 is a conventional mandrel. FIG. In the figure, 10: inner grooved tube, 11: groove part, 12: mountain part, 20: mandrel, 21: convex part, 22: concave part, 23: hypotenuse.

Claims (1)

[Claims] 1. A straight groove portion and a mountain portion which are straight in the pipe axis direction are alternately formed in the inner peripheral surface direction, and an extension line of a side wall of an extension line of a line connecting the groove bottom center of the groove portion and the pipe center is a groove. A mandrel used when manufacturing an inner grooved pipe that intersects outward from the bottom by cold rolling, and gradually decreases from the rolling start point to the rolling end point at least from the rolling start point to the rolling end point. The convex portion and the concave portion, which have an outer diameter and are alternately formed in the outer circumferential direction, have substantially the same shape as the groove portion and the ridge portion of the inner groove tube at least over the entire length from the rolling start point to the rolling end point. The outer diameter H of the convex portion gradually decreases from the rolling start point to the rolling end point in correspondence with the gradual decrease of the outer diameter,
The outer diameter G of the recess is set so that the inclination angle of the hypotenuse connecting the protrusion and the recess is substantially the same as the inclination angle of the sidewall of the inner grooved pipe over at least the entire length from the rolling start point to the rolling end point. From the rolling start point to the rolling end point, the length of the oblique side decreases from the rolling start point to the rolling end point so as to absorb the difference between the convex portion outer diameter H and the concave portion outer diameter G. At the end of rolling, the outer diameter H of the convex portion, the outer diameter G of the concave portion, and the length of the hypotenuse are the inner diameter d ₁ of the groove bottom and the inner diameter crest of the inner grooved pipe.
A mandrel for cold rolling of an internally grooved tube, which is substantially the same in length as d ₃ and side wall.