JPH07102369B2 - Mandrel mill - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a mandrel mill.

[0002]

2. Description of the Related Art As a method for rolling a seamless steel pipe, 5 to 8 hole-shaped roll stands consisting of a pair of upper and lower rolling rolls are continuously arranged, and the roll axes of adjacent hole-shaped roll stands are perpendicular to the rolling axis. 2. Description of the Related Art There is a method in which a mandrel mill in which a mandrel bar is inserted is rolled by a mandrel mill which is displaced in a plane and crossed with each other.

In this mandrel mill, the pipe material may have holes during rolling. This is called a "drilling defect". "Perforated defects" are serious quality defects. If the same steel type and the same outside diameter of the pipe material are used, the thinner the finished wall thickness of the rolled pipe material is, the more easily the “perforated defect” is generated.
If the finish dimensions of the pipe material are the same, "perforated defects" are more likely to occur in high alloy steel, which is inferior in deformability to ordinary steel.

Therefore, various methods have heretofore been proposed in order to prevent the "drilling defect". As a general method, there is a method of improving the hot deformability of the rolled pipe material, as disclosed in JP-A-58-224155.

As another method, as shown in Japanese Patent Laid-Open No. 63-84720, the mandrel mill is used to reduce the rolling reduction of the stand where "perforated defects" occur, and the load is reduced to the other ones. Methods have been devised to disperse in the stands or reduce the wall thickness of the inlet side tube to reduce the rolling reduction in each stand of the mandrel mill.

[0006]

[Problems to be Solved by the Invention] (1) JP-A-58-224155
Only by the method disclosed in the publication, it is not possible to obtain sufficient hot deformability at a temperature of 950 degrees to 1050 degrees during mandrel mill rolling, which may cause "perforated defects". The method proposed in JP-A-63-84720 was devised.

(2) The method proposed in Japanese Patent Application Laid-Open No. 63-84720 can prevent "drilling defect", but has the following problems. That is, if there is a stand where the rolling load exceeds the reference value even if the reduction load is distributed to each stand,
The wall thickness of the inlet tube is reduced to reduce the rolling reduction of the entire mandrel mill. However, there is a limit to the reduction rate of the punching machine for manufacturing the raw pipe, and the wall thickness of the raw pipe cannot be made smaller than the lower limit value. Therefore, there is a case where a thin pipe material cannot be rolled.

An object of the present invention is to solve the above-mentioned problems in the mandrel mill and prevent "drilling defects".

[0009]

According to the present invention, by appropriately designing a roll hole die of a stand row in which a mandrel mill is continuously arranged, a "drilling defect" occurring in mandrel mill rolling is prevented. is there.

As a result of investigating the cause of the occurrence of the "drilling defect" in the mandrel mill rolling, the present invention was discovered by discovering a novel mechanism of the drilling which was not known in the past.

It has been conventionally considered that the cause of the "drilling defect" in the mandrel mill rolling is that when the material is pulled in the longitudinal direction at the flange portion which is not subjected to reduction during rolling, it breaks due to insufficient deformability. There is.

However, the present inventors have discovered another new mechanism of perforation. If the rolling reduction is larger on both sides of the roll groove bottom than in the groove bottom center, the necking phenomenon may occur due to lack of material in the groove bottom center part in the process of extending the rolling part in the longitudinal direction. This is a phenomenon in which the wall becomes thinner and in extreme cases, holes are made.

FIG. 2 shows a specific example in which the rolling reduction is larger on both sides than in the center. For example, since the roll hole shape of the first stand is usually elliptical, the wall thickness in the circumferential direction of the pipe material on the outlet side of the first stand is the smallest at the center part of the roll groove bottom, and becomes thicker as it goes away from it. This portion rolled at the bottom of the roll groove of the first stand is not subjected to reduction in rolling of the second stand, so that the wall thickness distribution is substantially preserved even after passing through the second stand. In the third stand, the roll hole shape is designed to be a more perfect circle in order to make the thickness distribution in the circumferential direction uniform. Since the thickness distribution on the outlet side of the first stand is thin at the groove bottom and thicker on both sides, the reduction ratio in the third stand is larger at both sides than in the center of the groove bottom.

The same phenomenon as in the third stand also occurs in the fourth stand. Since the roll hole shape of the second stand is also usually elliptical, the circumferential wall thickness of the tube material groove bottom on the outlet side of the second stand is thinnest at the center part of the roll groove bottom, and becomes thicker as it goes away from it. This portion rolled at the roll groove bottom of the second stand is not subjected to reduction in the rolling of the third stand, so that the wall thickness distribution of this portion is substantially preserved even after passing through the third stand. In the fourth stand, the roll hole shape is designed to be a more perfect circle in order to make the circumferential wall thickness distribution uniform. Since the thickness distribution on the outlet side of the second stand is thin at the groove bottom and thicker on both sides thereof, in the fourth stand, the rolling reduction is larger at both side portions than at the center of the groove bottom.

In order to make the thickness of the finished pipe material uniform in the circumferential direction, the roll hole shape of the finishing stand of the mandrel mill is designed so that the groove bottom portion is a perfect circle. Generally, in the mandrel mill, the wall thickness is finished from the 4th stand to the 6th stand. If the roll hole shape of any one of the stands upstream of the thick finish stand is elliptical, in order to make the circumferential wall thickness distribution uniform in any of the following stands, both sides of the groove bottom center rather than the groove center Inevitably, the reduction rate increases.

In order to make the rolling reduction distribution in the circumferential direction of the roll groove bottom rolling portion uniform, the radius of curvature of the roll groove bottom central portion of the upstream stand of the mandrel mill should be set as much as possible.
It should be close to 0.5 times.

That is, as shown in the representative example of FIG. 1, (1) the roll hole shape of the first stand has a groove bottom curvature radius R1 of 0.54 times or less than a roll groove bottom interval B. Shape, (2) Roll hole shape of the second stand, groove radius of curvature R1
Is a roll groove bottom interval B of 0.52 times or less, and a mandrel mill having a roll hole shape is proposed.

[0018]

According to the present invention, in the roll hole shape in the mandrel mill, by providing an upper limit value for the hole shape groove bottom curvature radius of the upstream stand, the "hole drilling" caused by the unevenness of the groove bottom reduction which has been overlooked in the past is achieved. "Defects" can be prevented.

That is, in the mandrel mill which tends to cause "hole defects" in the third stand, by designing the roll-hole-shaped groove bottom curvature waveform of the first stand to be 0.54 times or less the roll groove bottom interval. , The circumferential distribution of the rolling reduction at the bottom of the third stand groove can be made uniform, and it is a "perforated defect" in practical use.
Can be prevented. Similarly, the mandrel mill, which tends to cause "drilling defects" in the 4th stand,
By designing the roll-hole-shaped groove bottom radius of curvature of the stand to be 0.52 times or less than the roll groove bottom interval, the circumferential distribution of the rolling reduction at the fourth stand groove bottom can be made uniform, and in practice, "hole-defects" Can be prevented.

In the mandrel mill, whether or not the "drilling defect" occurs in one of the third stand and the fourth stand, or in both of them depends on the individuality of the mill or the reduction distribution to each stand. Etc.

[0021]

EXAMPLES Table 1 shows the rolling conditions of the mandrel mill for ordinary steel pipe material according to the present invention, and Table 2 shows the rolling results. In the rolling conditions according to the present invention, the roll-hole-shaped groove bottom curvature radius of the first stand is 0.54 times the roll groove-bottom spacing, and the roll hole-shaped groove bottom curvature radius of the second stand is 0.52 times the roll-groove bottom spacing,
Under the conventional rolling conditions, the radius of curvature of the groove groove bottom of the first stand is 0.6 times the gap of the groove groove width of the roll, and the radius of curvature of the groove groove of the roll roll of the second stand is 0.
55 times.

[0022]

[Table 1]

[0023]

[Table 2]

Table 3 shows the rolling conditions of the mandrel mill for pipe materials of 13% Cr steel according to the present invention, and Table 4 shows the rolling results. In the rolling conditions according to the present invention, the roll-hole-shaped groove bottom curvature radius of the first stand is 0.54 times the roll groove-bottom spacing, and the roll hole-shaped groove bottom curvature radius of the second stand is 0.52 times the roll-groove bottom spacing, Under the conventional rolling conditions, the radius of curvature of the roll hole of the first stand is 0.6 times the gap of the roll groove bottom, and the radius of curvature of the roll hole of the second stand is the radius of curvature of the groove bottom. 0.55 times.

[0025]

[Table 3]

[0026]

[Table 4]

According to the present invention, it is recognized that a pipe material of ordinary steel having an outer diameter of 180 mm and a wall thickness of 4 mm with a mandrel mill can be manufactured without "perforating defects".

The mandrel mill outlet side has an outer diameter of 180 m.
It is recognized that it is possible to manufacture a tube material of 13% Cr steel having a wall thickness of 5 mm and a wall thickness of 5 mm without "perforation defects".

[0029]

In carrying out the present invention, it is not necessary to add a new device to the existing mandrel mill.

According to the present invention, by designing the roll-hole-shaped groove bottom curvature radii of the first stand and the second stand in the mandrel mill to be equal to or less than a set value, the "hole" which has conventionally been generated in the central portion of the groove bottom. It is possible to prevent "bright defects". In particular, the effect of preventing "drilling defects" in the mandrel mill rolling of thin tube materials and high alloy steels with poor deformability is remarkable.

[Brief description of drawings]

FIG. 1 is a view showing a roll hole shape of the present invention.

FIG. 2 is a schematic diagram for explaining that in the third stand of the mandrel mill, the rolling reduction is small at the center of the groove bottom and large on both sides thereof.

[Explanation of symbols]

 11, 12, 13 Hole type roll 4 Mandrel bar 5 Tubing

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B21B 37/78

Claims (3)

[Claims] 1. A mandrel mill for rolling a pipe, comprising a plurality of hole-shaped roll stands, arranging a mandrel bar in a roll hole-shaped array formed by the hole-shaped roll stands, and rolling hole shapes of the first stand. The mandrel mill is characterized in that the radius of curvature of the groove bottom is less than 0.54 times the gap between the roll groove bottoms. 2. A mandrel mill for rolling a pipe, comprising a plurality of hole-shaped roll stands, arranging a mandrel bar in a roll hole-shaped array formed by the hole-shaped roll stands, and rolling a tube of the second stand. The mandrel mill is characterized in that the radius of curvature of the groove bottom is less than 0.52 times the gap between the roll groove bottoms. 3. A mandrel mill for rolling a pipe, comprising a plurality of hole-shaped roll stands, arranging a mandrel bar in a roll hole-shaped array formed by the hole-shaped roll stands, and rolling a tube of the first stand. The mandrel mill is characterized in that the groove bottom radius of curvature is 0.54 times or less than the roll groove bottom interval, and the roll hole type groove bottom curvature radius of the second stand is 0.52 times or less than the roll groove bottom interval.