JPH1029005A - Production of eliptic inner surface tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly efficiently produce an eliptic inner surface tube by displacing the center position in either one side caliver between adjacent roll stands in the extending direction of the roll gap from a pass center. SOLUTION: In the case of displacing the center of caliver in a second stand upward from the pass center PL, large load on a groove bottom part 2a positioned at the lower part of the second stand is acted on the other hand, the load acted on the flange part 2b positioned at the upper part of this stand becomes small. By this method, since the reducing ratio of thickness at the groove bottom part 2a positioned at the lower part of the stand becomes large, the rolled tube thickness is further thinned by the rate which the reducing ratio of thickness is increased. Further, since the increasing ratio of thickness at the flange part 2b positioned at the upper part of the stand becomes small, the rolled tube thickness is further thinned by the rate which the increasing ratio of thickness is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tube whose circumferential wall thickness is asymmetrical with respect to the tube axis, specifically, a so-called inner elliptic tube whose outer diameter is a perfect circle and whose inner diameter is elliptical. And a method for producing the same.

[0002]

2. Description of the Related Art For example, in a header pipe for a boiler or the like, there is a deformed pipe in which the wall thickness of this portion is increased in order to secure the strength of a portion where a nozzle hole for mounting a heat exchange tube is formed. .

FIG. 6 is a view showing an example of such a modified pipe. This modified pipe has an elliptical outer diameter and a perfect circular inner diameter, and has a thicker pipe wall on the major axis side of the outer diameter. A hole is drilled.

[0004] Such a deformed tube has been conventionally manufactured by the following method. A first method is a hot extrusion pipe making method using a die having a die hole having the same shape as the outer shape of the desired deformed tube or / and a mandrel having a cross-sectional shape similar to the inner shape of the desired deformed tube. A method for directly producing deformed tubes by In the second method, a pipe having a wall thickness equal to the circumferential direction is formed by using an appropriate pipe manufacturing method, and a die having a die hole having a shape similar to the outer shape of a desired deformed pipe is formed in the pipe. And / or cold drawing using a mandrel having the same cross-sectional shape as the inner shape of the desired deformed pipe to form a deformed pipe.

[0005] However, in the case of the hot extrusion tube forming method or the cold drawing method, it is necessary to use dies or mandrels (plugs) of a special shape, so that the tool cost increases and the manufacturing cost increases. There were drawbacks.

For this reason, the development of a method for efficiently manufacturing a deformed pipe, particularly a deformed pipe whose wall thickness is not symmetrical with respect to the pipe axis as shown in FIG. 6 described above, without using a special tool. Was desired.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a manufacturing method using only a hot extrusion pipe making method or a cold drawing method. SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly efficient manufacturing method of an inner elliptic tube, which cannot be performed.

[0008]

The gist of the present invention resides in the following method for manufacturing an inner elliptic tube.

[0009] A plurality of three-roll stands, each of which has three hole-type rolls arranged around a path center and forming a triangular round hole shape as a whole, are incorporated. By a tube rolling mill installed in such a way that the direction is 60 ° around the path center,
When squeezing and rolling the outer diameter of a hollow shell having a uniform wall thickness in the circumferential direction without using an inner surface regulating tool, the hole center of one of the adjacent roll stands is formed into a hole. A method for manufacturing an inner elliptic tube, comprising displacing from a path center in any one of three roll gaps facing a center of a groove bottom of each grooved roll.

The inventor of the present invention has developed a sizer, a stretch reducer, and a mandrel mill in which a plurality of three-roll stands having three hole-type rolls, which are well known as a high-efficiency hot finishing rolling mill for tubes, are arranged in series. Paying attention to the extractor sizer that is arranged on the side and separates the stretched rolled tube and the mandrel bar inserted therein, as a result of various experimental studies, as a result of The position is set to one of the three roll gaps facing the center of the groove bottom of each grooved roll constituting the grooved mold.
The present invention has been found that, in the case where rolling is performed by displacing from the path center in the roll gap extending direction, an inner elliptic tube having an outer diameter of a perfect circle having an arbitrary ellipticity according to the amount of displacement is obtained. I came to

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings.

The above hot finish rolling mills such as the sizer and the stretch reducer and the extractor sizer are all rolling mills configured as follows. Hereinafter, a three-roll sizer will be described as an example.

FIG. 1 is a schematic side view showing a three-roll sizer, and FIG. 2 is a front view showing the roll arrangement. As shown in FIG. 1, the three-roll sizer is configured by arranging a plurality of roll stands 1, 1,... In the direction of the pass center PL. In addition, three roll-type rolls 2, 2, and 2 are incorporated in each roll stand 1. And
Each of the perforated rolls 2, 2, 2 incorporated in the adjacent roll stands 1, 1, is arranged in the A configuration and the B configuration shown in FIG.
It is arranged alternately with the arrangement.

As shown in FIG. 3, each of the roll-type rolls ₂ , ₂ , ₂ of each of the roll stands 1, 1 has an arc shape having a radius of curvature R having a center O ₂ at a position displaced from a path center PL. And the center O ₁ coincides with the path center PL, and the relationship between the radius B at the center of the groove bottom and the radius A of the flange portion is “A> B”, so that a triangular round hole is formed as a whole. Form 3 is constituted. Furthermore, the above-mentioned radius of curvature R generally decreases from the front roll stand to the rear roll stand.

The sizer constructed as described above is usually
It is used in the final step of the seamless pipe manufacturing process, and the outer diameter of the finish rolling tube drawn and stretched by a draw rolling machine such as a plug mill is changed from `` regular triangular shape '' to `` reverse Finish-rolling is performed by alternately repeating "triangular" drawing rolling to obtain a perfect circular product pipe having a predetermined dimension.

Here, attention is paid to rolling by a single roll stand in the sizer configured as described above. As shown in FIG. 3, since the shape of the die 3 is triangular as a whole, The subsequent wall thickness is characterized in that the portion rolled at the groove bottom 2a becomes thin, and the portion rolled at the flange 2b becomes thick.

The above-mentioned characteristic is obtained by changing the working ratio (outer diameter drawing ratio) defined by the following equation (1), in other words, when the load by the roll is variously changed, for example, as shown in Table 1. .

Degree of work = {(D _i −D _O ) / D _i } × 100 (%) (1) where D _{i is the} average outside diameter of the entrance side (mm) D _{O is the} average outside diameter of the exit side ( = A + B) (mm)

[0019]

[Table 1]

Table 1 shows that a lead pipe having an outer diameter of 50 mm and a wall thickness of 10 mm has dimensions A and B of 24.85 mm and 24.56 at the reference roll gap G (see FIG. 3), respectively.
Rolling by a roll stand having a hole die 3 having a hole diameter of 3 mm and a working ratio at this time of 2.8% is regarded as normal rolling, and the working ratio is changed by changing the A dimension and the B size by changing the roll gap G. The pipe wall thickness at two locations, that is, the groove bottom 2a and the flange 2b in the case where the thickness is changed in two ways, 1.5% and 3.9%, is obtained by using a three-dimensional rigid-plastic finite element method. The behavior is shown by a wall thickness increase rate with respect to the wall thickness of the raw pipe defined by the following equation (2).

Thickening rate = {(T _i −T _O ) / T _i } × 100 (%) (2) where T _i : thickness of inlet pipe (mm) T _O : thickness of outlet pipe (Mm) As is clear from Table 1, in the tube rolling by the three-roll stand in which the shape of the die 3 is triangular as a whole,
When the working ratio is reduced, in other words, when the load due to the roll is reduced, the wall thickness of the groove bottom 2a is reduced, and the pipe wall thickness of the portion becomes larger than that in the normal rolling.
In the case of b, the amount of wall thickness increase is small, and the wall thickness of this portion becomes thinner than that in normal rolling. Conversely, when the working ratio is increased, in other words, when the load due to the roll is increased, the wall thickness of the groove bottom 2a increases and the pipe wall thickness of the portion becomes thinner than that during normal rolling. It can be seen that the wall thickness increases and the wall thickness of the tube becomes thicker than during normal rolling.
This is for the following reason.

That is, at the groove bottom portion 2a, the wall thickness of the tube gradually increases in the pre-deformation region until the material (base tube) bites into the hole type roll 2, and the wall thickness is reduced by biting into the hole type roll 2. The behavior of wall thickness change is taken. On the other hand, in the flange portion 2b, the material takes a behavior of a change in thickness such that the material is increased by receiving a compressive force in the circumferential direction of the hole. The degree of increase in the wall thickness of the tube in the pre-deformation region differs depending on the timing of the start of the contact of the material with the porous roll 2, and is large when the contact start time is late and small when the contact start time is early.

For this reason, when the working degree is increased, the contact between the material and the grooved roll 2 is accelerated, so that the wall thickness increase in the pre-deformation region is suppressed, and in this state, the thickness is reduced by biting into the holed roll. As a result, when the working ratio is increased, the wall thinning rate is increased at the groove bottom 2a, and the groove becomes thinner than that during normal rolling. Conversely, when the working degree is reduced, the contact between the material and the roll 2 becomes slow, so that the wall thickness in the pre-deformation region becomes remarkable. As a result, when the working ratio is increased, the wall thinning rate is reduced at the groove bottom 2a, and the groove is thicker than that during normal rolling.

On the other hand, in the flange portion 2b, when the working ratio is increased, the compressive force in the circumferential direction of the hole is increased, so that the flange portion 2b becomes thicker than that in the normal rolling. Since the compression force in the circumferential direction of the groove decreases, the wall becomes thinner than that in the normal rolling.

When such a single three-roll stand has a change in working ratio, in other words, a change in wall thickness when a load is changed by a roll, the thickness change behavior of a plurality of units, specifically, an even-numbered unit among three or more odd-numbered units. When the hole-type center position of the roll stand is displaced from the path center, the load by the roll changes, which is the same, and the inner elliptic tube can be manufactured with high efficiency. This is apparent from the following description.

FIG. 4 shows that the arrangement of the grooved rolls is as shown in FIG.
The first stand and the third stand in the arrangement, and the arrangement of the hole type rolls include the second stand in the B arrangement shown in FIG.
The case where the hole-type center of the second stand is displaced upward from the path center PL (condition 1) and the case where it is displaced downward (condition 2) are shown.

FIG. 5 shows the vertical relationship of each stand in a front view under the conditions 1 and 2, and the relationship between the degree of processing and the increase or decrease in the thickness of each part of the groove.

When the center of the hole shape of the second stand is displaced above the path center PL as in the condition 1,
While a large load acts on the groove bottom 2a located at the lower part of the stand of the second stand, the load acting on the flange part 2b located at the upper part of the stand is reduced. In other words, while the processing degree at the groove bottom 2a located at the lower part of the stand is increased, the flange part 2 located at the upper part of the stand is increased.
The degree of processing at b becomes small. As a result, the wall thinning rate at the groove bottom 2a located at the lower part of the stand becomes large, and the wall thickness of the tube rolled at this portion becomes thinner by the increase in the wall thinning rate. Further, since the wall thickness increase rate at the flange portion 2b located at the upper portion of the stand is reduced, the wall thickness of the tube rolled at this portion becomes thinner by the decrease in the wall thickness increase rate.

On the other hand, the front and rear first and third stands have a flange portion 2b having a small working degree at the lower portion of the stand, a groove bottom portion 2a having a large working amount at the upper portion of the stand, and a flange at the lower portion of the stand. The wall thickness is suppressed in the portion 2b, and the wall thickness is promoted in the groove bottom 2a on the upper part of the stand. For this reason, the wall thickness of the portion corresponding to the upper and lower portions of the stand becomes thinner than that of the other portion due to the heavy thickness of the above-mentioned thickness change behavior in the second stand and the first and third stands before and after the second stand. . As a result, an inner elliptic tube having an outer diameter of a perfect circle having an elliptical inner surface whose major axis is the vertical direction is formed.

On the other hand, in the case of the condition 2, detailed description thereof is omitted, but since the thickness change behavior is opposite to that described above, the condition 2 has an elliptical inner surface whose major axis is in the left-right direction. An inner elliptical tube having a perfect outer diameter is formed.

This is clear from the experimental results shown in Table 2.

[0032]

[Table 2]

[0033]

[Table 3]

Table 2 shows that the arrangement of the grooved rolls is shown in FIG.
The first and third stands of the arrangement and the arrangement of the grooved rolls consist of the second stand of the B arrangement shown in FIG. 2, and the dimensions A and B shown in FIG. The results of rolling using a model rolling mill on a lead pipe having an outer diameter of 50 mm and a wall thickness of 10 mm are shown.

Rolling is performed when the center of the groove shape of the three stands coincides with the path center (normal rolling).
Only the hole-shaped center of the stand is 1 m above the path center.
The test was carried out in three cases: a displacement of m (Condition 1) and a displacement of only the center of the hole of the second stand 1 mm downward from the pass center (Condition 2). The hole-shaped roll of each stand used had a separation distance of 60 mm from the pass center to the roll axis. Further, in Table 2, the second
The absolute value of the pipe wall thickness of the portion rolled at the lower part of the stand (groove bottom 2a) and the upper part of the stand (flange part 2b), the ellipticity of the inner surface of the pipe after passing through all stands, and the inner diameter in the vertical direction When a is the inner diameter in the left-right direction and b is the inner surface ellipticity determined by the following equation (3).

Inner ellipticity = {(ab) / a} × 100 (%) (3) As is clear from the results shown in Table 2, under the condition 1, the second condition
The wall thickness of the tube rolled at the groove bottom 2a at the lower part of the stand and the flange part 2b at the upper part of the second stand is thinner than that at the time of normal rolling. On the other hand, in condition 2, the groove bottom 2a at the lower part of the second stand and the flange part 2 at the upper part of the second stand
The wall thickness of the tube rolled in b is thicker than that in the normal rolling. Also, the pipe inner surface ellipticity after passing through all stands is
In normal rolling, 0 (zero) is a perfect circle, but in condition 1, +
An inner elliptic tube having a major axis in the vertical direction at 1.1% is a condition 2
Thus, an inner elliptic tube having a major axis in the left-right direction at -1.4% is obtained.

In the above description, the case where the center of the hole shape of the second stand is vertically displaced from the path center has been described. Also, for the same reason as described above, the inner elliptical tube is formed. Accordingly, the center of the groove shape of the second stand is in the roll gap extending direction of any one of the three roll gaps G (see FIG. 3) facing the center of the groove bottom of each grooved roll constituting the groove shape. At the center of the path.

As is apparent from the above description, when the drawing rolling is performed in accordance with the method of the present invention, the center position of the groove of the existing rolling mill is merely displaced without using a special tool, and the inner loss surface is reduced. The elliptic tube can be manufactured with high efficiency.

The ellipticity of the inner surface is determined by the shape of the holes A and B.
It depends on the ratio of the dimensions, the degree of processing to be added, and the displacement of the center of the hole shape of each even-numbered stand with respect to the path center. Therefore, these relationships are obtained in advance by experiments and the like, and the inner elliptic tube having the desired ellipticity is obtained by changing the displacement of the hole-shaped center of each even-numbered stand with respect to the path center based on the results. You should get it.

[0040]

EXAMPLE A three-roll sizer consisting of 21 stands having a groove having dimensions A and B shown in Table 4 (see FIG. 3) was prepared. At this time, a hole-type roll having a separation distance of 203 mm from the pass center to the roll axis was incorporated in all stands.

[0041]

[Table 4]

Using the above three roll sizer, the outer diameter 110
The outer diameter of a carbon steel tube having a thickness of 8.5 mm and a wall thickness of 8.5 mm is 31.
At the time of rolling to 8 mm, the center of the hole shape of all stands is made to coincide with the path center, and the center of the hole shape of all even-numbered stands is uniformly moved upward (+) or downward (-) from the path center. A total of seven types of rolling were performed when the displacement was set by 3 mm and 5 mm.

The outer diameter and inner diameter of each of the obtained product tubes in the circumferential direction were measured, and the inner surface ellipticity was examined based on the above equation (3). Table 5 shows the results.

The outer diameter was almost a perfect circle in each case.

[0045]

[Table 5]

As is evident from the results shown in Table 5, the product pipe obtained by rolling the center of the hole shape of all stands to the path center has an inner surface ellipticity of 0 (zero), and No elliptic tube was obtained.

On the other hand, when the product pipe obtained by rolling the center of the hole shape of all the even-numbered stands uniformly from the path center is in the upward (+) direction, 2. An inner vertical elliptic tube having an inner ellipticity of 2 to 16.2% was obtained. Further, when the displacement direction of the hole-shaped center with respect to the path center is downward (-), 2.4 to 1
An inner horizontal elliptic tube having an inner ellipticity of 5.2% was obtained.

As can be seen from the above results, the inner surface ellipticity varies depending on the displacement amount and the direction of the hole center from the path center. Therefore, it is apparent that a desired inner surface ellipticity can be obtained by variously changing the displacement amount and the direction of the hole center from the path center.

[0049]

According to the method of the present invention, it is possible to manufacture an inner elliptical mold with high efficiency by using an existing multi-stand constant-diameter rolling mill such as a three-roll sizer or a three-roll stretch reducer. As a result, the manufacturing cost of the product can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of a three-roll sizer.

FIG. 2 is a schematic front view showing an arrangement example of a hole-type roll of a three-roll sizer.

FIG. 3 is a schematic front view showing a hole type example of a three-roll sizer.

FIG. 4 is a diagram showing a rolling mode of the present invention.

FIG. 5 is a diagram for explaining a wall thickness change mechanism in the present invention.

FIG. 6 is a cross-sectional view showing an example of a conventional deformed pipe.

[Explanation of symbols]

 1: roll stand, 2: roll-type roll, 2a: groove bottom, 2b: flange, 3: hole-type,

Claims (1)

[Claims] The present invention comprises a plurality of three-roll stands in which three hole-type rolls arranged around a path center and forming a triangular round hole shape as a whole are incorporated, and each hole-type roll of an adjacent roll stand. By a tube rolling mill continuously installed so that the rolling direction of
When squeezing and rolling the outer diameter of a hollow shell having a uniform wall thickness in the circumferential direction without using an inner surface regulating tool, the hole center of one of the adjacent roll stands is formed into a hole. A method for manufacturing an inner elliptic tube, comprising displacing from a path center in any one of three roll gaps facing a center of a groove bottom of each grooved roll.