JPH08215713A - Rolling method for seamless steel tube and rolling equipment - Google Patents

Abstract

PURPOSE: To ensure quality equal to that of products by mandrel rolling and to improve rolling efficiency by constituting a rolling mill train of a 2-roll type and 4-roll type rolling mills as an alternative rolling method of an existing plug mill. CONSTITUTION: A mandrel bar 4 whose axial center is made to coincide with the center of the pass line is provided on the inlet side of a rolling line and a 1st and 2nd rolling stands 14, 15 are arranged at the rear of it. The 1st stand 14 is taken as the 2-roll type rolling mill consisting of two opposite rolls 1 having an elliptic groove to improve the biting property of a material 3 to be rolled at the 2nd stand 15 and the 2nd stand 15 is taken as the 4-roll type rolling mill having two set of circularily grooved roll pairs 5, 6 to ensure rolling- reduction of a degree equal to that of the plug mill and prevent fin flaws from the opening of roll. During rolling, the mandrel bar 4 which is inserted through the material 3 to be rolled is moved inversely to the rolling direction with a retainer 10 and detached from the material 4 at the time of completing rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an inner surface quality equivalent to the inner surface quality of a pipe rolled by a mandrel mill by a simple modification of a plug mill used in a drawing and rolling process of a seamless steel pipe, and a polishing machine. TECHNICAL FIELD The present invention relates to a rolling method and a rolling facility for a seamless steel pipe that does not require heat.

[0002]

2. Description of the Related Art The rolling process of a seamless steel pipe is roughly classified into a plug mill process shown in FIG. 4 (a) and a mandrel mill process shown in FIG. 4 (b). The scope of application of these two rolling processes varies slightly depending on the manufacturer,
Currently, the outer diameter of the final product is around 180 mm,
Those with a larger outer diameter are manufactured by the plug mill process, and those with a smaller outer diameter are manufactured by the mandrel mill process. A big difference when comparing the respective processes is that in the former case, a plug mill is used in the drawing and rolling process, and in the latter case, a mandrel mill is used in the drawing and rolling process.

When a mandrel mill and a plug mill are compared with each other, it is generally known that the mandrel mill is a rolling mill which greatly improves the quality of the inner surface of the pipe as compared with the plug mill. The basis for this is, as described in Japanese Patent Laid-Open No. 63-33107, generally in plug mill rolling, a plug, which is a tool inserted into the pipe during rolling, is fixed and moves during rolling. Therefore, the thermal / stress load cannot be withstood, and the plug is worn, so that the inner surface of the material is flawed.

On the other hand, in the mandrel mill rolling, the mandrel bar inserted inside the pipe is not fixed. Since it moves along with rolling, the thermal and stress loads are reduced, the mandrel bar is less likely to wear, and the inner surface quality of the rolled tube is superior to that of plug mill rolling. In addition, in plug mill rolling, generally, a polisher is installed to finish the inner surface of the pipe after plug mill rolling smoothly, but in the case of mandrel mill rolling, a polisher is necessary because of the excellent inner surface quality for the reasons described above. Not.

In order to utilize the above-mentioned characteristics of the mandrel mill, in particular, the characteristics of greatly improving the quality of the inner surface of the pipe as compared with the plug mill, the outside diameter of 180 mm or more which is conventionally produced by using the plug mill rolling. Even in a seamless steel pipe manufacturing facility generally called a medium-diameter size, it is often manufactured by using the mandrel mill rolling.

[0006] Generally, in plug mill rolling,
Since it is one-stand rolling composed of two hole type rolls, in order to make the outer shape of the rolled material after rolling into a circular cross section, as shown in the outline in FIG. By rolling the rolled material backward to a predetermined position on the rolling mill entrance side and rotating it 90 ° about the tube axis, the portion of the rolled material located at the roll opening in the first pass is rolled at the bottom of the roll groove in the second pass. It is a two-pass rolling in which a predetermined reduction is applied. On the other hand, since mandrel mill rolling is a multi-stand rolling, the rolling direction of the roll can be changed for each stand, and the material to be rolled is unidirectional from the mill entrance side to the mill exit side. Rolling is completed only by moving one-pass rolling. Therefore, the plug mill rolling is an inefficient rolling method as compared with the mandrel mill rolling.

As described above, in the conventional plug mill rolling method, the one-pass rolling requires the two-pass rolling without the outer shape of the rolled material having a circular cross section.
As described in Japanese Patent Laid-Open No. 04-04, the hole type of the plug mill is such that the center part of the groove bottom is a perfect circle, and both sides, so-called flanges, have a large radius of curvature of the hole type, and the plug and hole which are the inner surface tool. This is because the gap between the die of the die roll and the die is enlarged to prevent seizure flaws between the roll and the material to be rolled, which is called edge flaws, which are caused by the difference in roll peripheral speed depending on the location of the die.

As a result, after the first pass rolling, the material to be rolled has a circular cross section at the position corresponding to the true circular hole-shaped portion in the groove bottom center portion of the hole-shaped roll, but in other words, on both sides thereof. Then, the cross-sectional shape near the opening of the hole-type roll does not become circular, and the shape of the material to be rolled at the opening of the hole-type roll becomes a projection-like cross-sectional shape called so-called protrusion. In the second pass following this part, it is necessary to carry out a two-pass rolling in which the outer shape of the material to be rolled has a circular cross section by applying a reduction at the perfect circular hole-shaped portion at the center of the groove bottom of the hole-type roll. Become. Therefore, by using the mandrel mill rolling as an alternative rolling method of the conventional plug mill rolling, it is possible to improve the rolling efficiency.

However, while the plug mill is a rolling mill consisting of one stand, the mandrel mill is generally 7-8.
Since it has a stand and is larger in scale than the plug mill, it is difficult to replace the existing plug mill because of the huge investment amount and the problem of the equipment installation area. In many cases.

As a method for solving such a problem of the existing plug mill, Japanese Patent Laid-Open No. 58-125304 discloses a drawing and rolling machine for a seamless steel pipe, which comprises two stands each having three hole-type rolls. Although shown, when considering the existing plug mill replacement, in the method described in the publication, stripping of the mandrel bar after rolling is performed outside the pass line after completion of rolling. Since a new apparatus is required and the roll driving becomes complicated in the three-roll method, the equipment must be remodeled on a large scale when used as a substitute for the existing plug mill.

[0011]

As a substitute for the existing plug mill rolling, the present invention provides a rolling method which has a low equipment cost, a higher productivity than the existing plug mill, and an inner surface quality equivalent to that of a mandrel mill rolling product. It aims to provide rolling equipment.

[0012]

That is, the present invention is as follows.
(1) In the seamless steel pipe rolling method in which a steel slab heated to a predetermined temperature in a heating furnace is perforated and rolled to obtain a product having a predetermined outer diameter and wall thickness, after inserting a mandrel bar into the inner surface of a hollow pipe. , A two-roll type rolling mill having a pair of elliptical hole type rolls as a first rolling mill and a four roll type rolling mill having two sets of circular hole type rolls as a second rolling mill (2) In the above rolling method, the mandrel bar is moved in the direction opposite to the rolling direction during drawing and rolling, and the mandrel bar after rolling is pulled out from the pipe. This is an unnecessary rolling method. Furthermore, (3) a mandrel bar on the rolling mill entrance side in a rolling facility for seamless steel pipes that punches and rolls a steel slab heated to a predetermined temperature in a heating furnace to obtain a product with a predetermined outer diameter and wall thickness. A retainer device that holds the rear end of the rolling mill and controls the speed of the mandrel bar, and the number of stands of the rolling mill is two, and the first stand is a two-roll mill having a pair of elliptical hole-type rolls. , The second stand has two pairs of circular hole type rolls, only one of which is a driving roll, and the driven groove pair central part of the pair of rolls is driven. Is arranged so as to correspond to the long diameter part of the elliptical hole type of the first rolling mill, and the other pair of rolls is a rolling mill consisting of four rolls which are driven rolls. Rolling equipment. In addition,
The roll pair of the present invention refers to a combination of two rolls arranged to face each other.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is an overall layout of rolling equipment used in the present invention. A retainer 10, an electric motor 11 for driving the retainer, and a speed reducer 12 are provided on the rolling mill entrance side, and control the speed of the mandrel bar 4 during rolling. The mandrel bar 4 is installed so that its axis coincides with the center of the pass line, and is operated so as to maintain the relationship even during movement. Further, preferably, a lubricant applying device 13 is also installed on the inlet side of the rolling mill to enable in-line application of the lubricant to the mandrel bar 4. The rolling mill consists of two stands 14 and 15, the first of which is
The stand 14 is a two-roll type rolling mill having two opposing elliptical hole types, and the second stand 15 has two
It is a 4-roll type rolling mill having a pair of circular hole type rolls. The drive of the roll of each stand is driven by the electric motors 16 and 1.
7, speed reducers 18 and 19 and distributors 20 and 21.

First, the inventors of the present invention examined the hole-shaped shape of the roll, an example of which is shown in FIG. 7, on the premise of one-pass rolling using a mandrel bar as an inner surface tool. In this case, the problems are the improvement of the shape of the material to be rolled in the portion of the center 27 of the groove of the roll-hole type groove that does not correspond to the round-hole-shaped portion 29, and the seizure due to the reduction of the roll peripheral speed difference depending on the position of the roll-shaped die. It is to prevent flaws and to make the rolled material cross-sectional shape after rolling into a perfect circular shape.

As a remedy for this problem, the present inventors have studied by focusing on the number of rolls. The reason for focusing on the number of rolls is as follows. As the number of rolls increases, the difference in roll diameter between the center portion 27 of the groove and the end portions 28 of the roll hole type becomes smaller, that is, the difference in roll peripheral speed depending on the position of the roll hole type becomes smaller. Edge defects due to occurrence of bite are reduced. As a result, it becomes possible to use a hole-shaped roll having a shape close to a perfect circle, and it becomes possible to make the cross-sectional shape of the material to be rolled into a substantially perfect circle by rolling in one pass. Therefore, first, the possibility of one-pass rolling by applying multiple rolls was examined.

FIG. 6 shows a case where two rolls, three rolls, and four rolls are used, and the same groove bottom reduction amount is applied to a pipe having a true circular cross-section by using a true circular hole type roll. The ratio of the protruding height is shown. From the figure, it can be seen that the protruding height decreases as the number of rolls increases. Furthermore, as a result of the investigations by the present inventors, in the case of 4 rolls,
It has been found that when a substantially circular hole type is used in which the circular arc radius of the flange portion of the hole type roll is slightly larger than the circular arc radius of the perfect circular portion at the center of the groove bottom, almost no bulging occurs.

As described above, the number of hole type rolls having a perfect circular shape is 4 rolls, that is, 2 roll pairs of two rolls arranged facing each other are used as the hole type rolls. It has been clarified that it is optimal to construct and use.

In the experiment in which the results of FIG. 6 were obtained, all the rolls were driven regardless of the number of rolls of 2, 3, and 4, but it is not always necessary to drive all the four rolls. Further, in the case of four rolls, the roll axes may be arranged on the same plane, but the driving system of the rolls becomes complicated, and therefore, the hole type roll pair having the vertical roll axis and the hole type having the horizontal roll axis are provided. It is preferable to have a structure in which the roll pairs are arranged close to each other in the traveling direction of the material to be rolled.

Generally, in the case of assuming an alternative modification from a plug mill that rolls using a rolling mill having two horizontal rolls, the rolling arrangement of the rolling mill having four rolls is a horizontal roll. It is preferable to use a combination of a pair of No. and a pair of vertical rolls. Further, in this case, it is preferable from the viewpoint of modification from the existing plug mill that one roll pair is driven and the remaining one roll pair is driven.

From such a point of view, the inventors of the present invention drive one horizontal roll pair, use the other vertical roll pair as a driven roll, and use four rolls of a true circular cross-section tube. That is, the rolling was performed using a rolling mill (hereinafter, referred to as a four-roll rolling mill) having a hole shape composed of two pairs of rolls. As a result, in four-roll rolling in which one pair of driving rolls and one pair of driven rolls were combined, the tip of the material to be rolled did not bite into the rolls, so-called defective biting occurred, and rolling was impossible.

In the biting, the drive roll pair applies a driving force to the material to be rolled in order to move the material to be rolled forward while the biting to the material to be rolled is caused. This is because the pair of driven rolls that are not included resist the forward movement of the material to be rolled and prevent the forward movement of the material to be rolled. Therefore, it is necessary to apply a sufficient driving force to the material to be rolled by the material being bitten into the pair of driving rolls.

Therefore, in front of the 4-roll rolling mill, a rolling mill having an elliptical hole type consisting of two rolls and a pair of rolls is arranged as the first rolling mill, and the long diameter of the elliptic hole type is arranged. The side is arranged so as to correspond to the central portion of the groove bottom of the second rolling mill, that is, one pair of driving rolls of the four-roll rolling mill.

As a result, the shape of the material to be rolled before entering the second rolling mill, that is, the 4-roll rolling mill, is the second rolling mill, that is, the 4-roll rolling mill. It is possible to make an elliptical shape whose major axis is a line connecting the two. When the material to be rolled having this elliptical cross section is rolled by the above-mentioned first rolling mill having a perfect circular hole shape composed of four rolls, the major axis side first starts contact with the driving roll. The rolled material is sufficiently gripped by
After a sufficient driving force is applied, contact with the driven roll of the material to be rolled is started, so that it is possible to prevent defective biting.

As described above, the rolls of the first rolling mill and the second rolling mill are arranged such that the major axis of the elliptical hole type of the first rolling mill corresponds to the center of the groove bottom of the second rolling mill. It is necessary to set the positional relationship of the hole type of the roll pair of each stand.
Further, when the above-described 4-roll rolling mill which is the second rolling mill has a structure in which the horizontal roll pair and the vertical roll pair illustrated above are closely arranged in front and back, the first rolling side of the second rolling mill Must be a drive roll pair. The first rolling mill does not necessarily have to be a horizontal roll pair, but may be a vertical roll arrangement (vertical roll pair).

FIG. 2 is a view showing an example of a roll hole shape applied to the present invention. FIG. 2 (a) shows a pair of elliptical hole type applied to the first stand, which is composed of a pair of left and right hole type vertical rolls 1, and the roll 1 is composed of left and right roll chocks 2 incorporating roller bearings. It is supported and can rotate freely. In this figure, the rolls of the first stand are in the vertical roll arrangement,
As described above, if the relationship with the drive roll of the second stand is satisfied, the horizontal roll arrangement may be possible.

FIG. 2B shows a 4-roll circular hole type applied to the second stand of the present invention. It consists of a pair of upper and lower hole-type horizontal rolls 5 and a pair of left and right hole-type vertical rolls 6, and each roll has a chock 7 for upper and lower rolls and a chock 8 for left and right rolls in which roller bearings are incorporated.
It is supported by and can rotate freely. As the mill type of the second stand, for example, the same type as a universal mill used in the field of strip rolling can be applied. At this time, the rolls of the two stands are arranged so as to have a point-symmetrical positional relationship with respect to the pass line center 9 for both stands.

Regarding the point that the number of stands is increased by one, in the conventional plug mill, it is necessary to retract the material to be rolled after the first pass rolling for the second pass rolling as described in the prior art. Therefore, it has a stand composed of two horizontal rolls, which are generally called return rolls, in the rolling-out side direction. Therefore, although the conventional plug mill has one stand rolling for rolling, it has a two-stand rolling mill as a facility, and even if the number of stands is increased by one, the existing plug mill can be replaced. There is no problem of equipment installation area.

From the above, the rolling mill in the case of replacing the existing plug mill with a highly efficient rolling mill that does not require two-pass rolling without greatly expanding the equipment installation area is:
The roll arrangement is such that the first stand has an elliptical hole shape 2
It is clear that the rolling mill consists of two rolls, the second stand is a two-stand rolling mill consisting of two opposing drive rolls having a circular hole shape and two opposing driven rolls having a circular hole shape. It was

Next, there is a problem when a mandrel bar is used as an inner surface tool in order to improve the inner surface quality.
The drawing of the mandrel bar from the material to be rolled after the completion of rolling will be described.

Conventionally, the pulling out of the mandrel bar from the material to be rolled after the completion of rolling is generally done in JP-A-63-3310.
As described in Japanese Patent Publication No. 7, a method of carrying out a material to be rolled with a mandrel bar inserted after rolling from the line and restraining and pulling out the mandrel bar and the material to be rolled off-line, Alternatively, a method of pulling out a device called an extractor on a line behind the mandrel mill is used. In both of these two methods, it is necessary to provide a device for pulling out the mandrel bar as an accessory device of the rolling mill.

In the present invention, the mandrel bar is pulled out from the material to be rolled after the rolling is completed by providing the retainer device without providing such auxiliary equipment. That is, in general, in the mandrel mill rolling, the mandrel bar during rolling proceeds in the same direction as the material to be rolled although there is a difference in the absolute value of the speed, whereas in the present invention, the mandrel bar is started at the same time as the start of rolling. By controlling the moving speed of the
Upon completion of rolling, the mandrel bar and the material to be rolled are separated.

As a means for controlling the moving speed of the mandrel bar during rolling, as described in Japanese Patent Laid-Open No. 63-33107, the moving speed of a mandrel bar generally used in a mandrel mill rolling mill is regulated. A semi-floating (or retained) method can be used. That is, the mandrel bar is pulled out from the pipe during rolling by moving the mandrel bar in the direction opposite to that of the material to be rolled by controlling its moving speed.

A device generally called a retainer is used for controlling the moving speed of the mandrel bar. This device
The mandrel bar is moved by converting the rotational movement of the electric motor, which is the drive source of the retainer, into a linear movement by the retainer consisting of a combination of a rack and a pinion gear.The movement speed is controlled by controlling the rotational speed of the electric motor. It is something to do.

FIG. 3 shows a method of operating the mandrel bar according to the present invention. In the present invention, the mandrel bar 4 during rolling is operated in the direction opposite to the rolling direction. That is, FIG. 3A shows the end point of the previous rolling operation, and after the rolling, the mandrel bar 4 continues to retreat to a predetermined retreat end position, and the next rolled material 3
It stands by at this retreat end position until is conveyed from the rolled material supply floor 23 to the pass line. FIG. 3B shows the state immediately before the start of rolling, and the mandrel bar 4 penetrates through the hollow pipe of the material 3 to be rolled from the backward end position after the end of the previous rolling by the start of rolling. The mandrel bar is advanced to the predetermined position on the exit side of the second stand 15, and then stopped. Then, at the same time when the rolling roll starts rotating, it moves forward and then starts retreating toward the rolling-in side at a predetermined speed, and at the end of rolling, pulling out of the mandrel bar is completed.

The material 3 to be rolled is, as shown in FIG.
When the mandrel bar 4 is at the backward end position, it is conveyed on the pass line. Next, the mandrel bar 4 is shown in FIG.
In the process of advancing to the position of, the mandrel bar 4 is inserted into the material to be rolled 3, and after the insertion, the mandrel bar 4 is advanced with the mandrel bar 4, and then the tip comes into contact with the stopper 22 installed on the entrance side of the first stand 14. As a result, it stops at the standby position before rolling. Then, at the same time when the rolling roll starts rotating, the stopper 22 is released, and the material to be rolled 3 advances together with the advancing mandrel bar 4 and is caught in the roll of the first stand 14.

At the same time when the material to be rolled 3 is caught in the roll of the first stand 14, the mandrel bar 4 starts to retreat. After being rolled by the first stand 14, the tip of the material 3 to be rolled continues to move forward as the subsequent portions are rolled sequentially by the first stand 14, and is pushed between the rolls of the second stand 15. Rolling at the second stand 15 is started. The rolled material 3 that has been rolled by the second stand 15 has its internal mandrel bar 4 pulled out almost at the same time as the rolling is finished, and is transported to the next step by the transport device on the exit side of the existing plug mill.

As described above, in the method of the present invention,
Insert the mandrel bar into the hollow pipe, which is the material to be rolled, until the tip of the mandrel bar projects from the tip of the material to be rolled. At the same time, it is pulled out from the material to be rolled and separated.

[0038]

In the present invention, the number of rolls on the second stand is 4
As a result, it is possible to prevent the rolled material from sticking out at the roll opening while ensuring the same amount of reduction as the plug mill. Further, by disposing the rolling machine of the two-roll system having the elliptical hole type rolls on the first stand, it is possible to prevent the defective rolling of the material to be rolled in the second stand rolling. By moving the mandrel bar during rolling in the direction opposite to the rolling direction, the mandrel bar can be separated from the material to be rolled at the end of rolling, and the mandrel bar after rolling becomes unnecessary.

Further, in the present invention, the mandrel is provided after disposing the two-roll type rolling mill having the elliptical hole type rolls on the first stand and the four roll rolling mill having the circular hole type rolls on the second stand. By providing the retainer device capable of controlling the speed of the bar, the one-pass rolling can be performed, and the mandrel bar can be moved in the direction opposite to the rolling direction during rolling.

Further, by rolling the material to be rolled into an elliptical shape on the first stand to improve the biting property of the material to be rolled on the second stand, all four rolls of the second stand are driven. It is not necessary to drive only a pair of rolls corresponding to the long axis of the elliptical hole type of the first rolling mill, and the remaining two rolls can be driven rolls.
A simple modification from the existing plug mill is also possible.

[0041]

EXAMPLES In the examples of the present invention, the raw tube to be stretch-rolled was inclined-rolled, the outer diameter was 126 mm, and the wall thickness was 3.
It is a carbon steel hollow tube with a length of 4 mm and a length of 1200 mm, and the dimensions after drawing and rolling are an outer diameter of 122 mm, a wall thickness of 2.3 mm, and a length of 184.
It was 0 mm. The outer diameter of the used mandrel bar is 117.4 mm.

By the start of rolling, the mandrel bar 4 was moved forward from the backward end position after the end of rolling to the end of the mandrel bar until the tip of the mandrel bar was 700 mm on the exit side of the second stand 15, and then stopped. Then, the rolling roll started to rotate at the same time as it started to move forward, and after 0.3 seconds, started to move backward toward the rolling entrance side at a speed of 0.1 mm / sec.

On the other hand, at this time, the first stand 1 of the rolled material
The rotation speed of the roll was set so that the 4-entry speed was 0.3 m / sec. The reason why the mandrel bar 4 starts to move backward after advancing for 0.3 seconds is in consideration of the distance between the tip of the material 3 to be rolled and the roll of the first stand 14 at the standby position before rolling.

In this embodiment, the relationship between the speed at which the rolled material 3 enters the first stand and the speed at which the mandrel bar 4 retreats is as follows:
It is selected from the viewpoint of securing the inner surface quality of the material 3 to be rolled, and the distance from the tip of the mandrel bar 4 positioned on the exit side of the second stand 15 by the start of rolling to the second stand 15 is determined by the mandrel bar 4 at the end of rolling. The tip is set so as to be located substantially at the center of the second stand 15 as viewed in the pass line direction. Actually, since it is necessary to roll the entire length of the material 3 to be rolled by using the mandrel bar 4, the tip of the mandrel bar 4 is located at the exit side of the second stand 15 by about 60 mm at the end of rolling.

At the end of rolling, the mandrel bar 4 is set to 1
Even if it is still inserted in the tube for about 50 mm,
The mandrel bar 4 is separated from the material 3 to be rolled by the inertial force of the progress of the material 3 to be rolled after the rolling. As described above, as a result of the rolling in the present example, the inner surface of the rolled material was about the same as that obtained by the mandrel mill rolling, and the rolling time was about the same as that obtained by the conventional plug mill method. It became possible to shorten it to 1/3.

[0046]

According to the present invention, by simply modifying the plug mill, it becomes possible to secure the product inner surface quality equivalent to the product obtained by the mandrel mill rolling, and the rolling time is reduced to about 1/3, so that the rolling efficiency is improved. It has become possible to improve.

[Brief description of drawings]

FIG. 1 is a diagram showing a planar arrangement of a two-stand mandrel mill according to the present invention.

FIG. 2 is a cross-sectional view perpendicular to a pass line of a roll-related portion of the rolling equipment of the present invention, (a) showing two rolls of the first stand and (b) showing four rolls of the second stand. .

3 (a), (b) and (c) are views showing an operating method of the mandrel bar of the present invention.

FIG. 4 is a diagram showing a rolling manufacturing process of a seamless steel pipe,
(A) is a plug mill process, (b) is a figure which shows a mandrel mill process.

FIG. 5 is a diagram showing the deformation of the material to be rolled in the conventional plug mill rolling, where (a) shows the shape after the first pass rolling, and (b) shows the rolled material in the pipe circumferential direction before the second pass rolling. The state rotated by 90 degrees, (c) is a diagram showing the shape of the material to be rolled after the second pass rolling.

FIG. 6 is a diagram showing the relationship between the number of rolls and the protruding height, with a case of two rolls as a reference value.

FIG. 7 is an explanatory view of a roll and its hole shape, (a)
Shows an example in the case of 2-roll rolling, and (b) shows an example in the case of 4-roll rolling.

[Explanation of symbols]

 1: 1st stand left / right roll 2: 1st stand left / right roll chock 3: Rolled material 4: Mandrel bar 5: 2nd stand up / down roll 6: 2nd stand left / right roll 7: 2nd stand up / down roll chock 8: 2nd stand Left and right roll chock 9: Center of pass line 10: Retainer 11: Retainer drive electric motor 12: Reduction gear 13: Lubricant applying device 14: 1st stand 15: 2nd stand 16: 1st stand electric motor 17: Second stand motor 18: First stand reducer 19: Second stand reducer 20: First stand distributor 21: Second stand distributor 22: Stopper 23: Rolled material supply floor 24: Plug mill Roll rolling direction: 25: 2 Roll for rolling 26: 4 Roll for rolling 27: Roll hole type groove bottom center part 2 : Roll grooved at both ends 29: circularity grooved portion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Yamamoto 1-1 Tobahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside Nippon Steel Co., Ltd. Yawata Works (72) Koji Narasaki, Inaba, Kitakyushu, Kitakyushu-shi, Fukuoka No. 1 town No. 1 Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. A seamless steel pipe rolling method for piercing and rolling a steel slab heated to a predetermined temperature in a heating furnace to obtain a product having a predetermined outer diameter and wall thickness, in which a mandrel bar is inserted into the inner surface of a hollow pipe. After that, a two-roll type rolling mill having an elliptical hole type roll pair and two sets of circular hole type rolls are provided,
One of the pair of hole type rolls was arranged so that the center part of the groove bottom of the hole type corresponds to the long diameter part of the elliptical hole type of the rolling mill having the elliptical hole type roll to form a circular hole type 4 A method for rolling a seamless steel pipe, which comprises sequentially stretching and rolling by a rolling mill train of two stands including a rolling mill of rolling type. 2. The method for rolling a seamless steel pipe according to claim 1, wherein the mandrel bar is moved in the direction opposite to the rolling direction during drawing and rolling to pull out the mandrel bar from the pipe. 3. In a rolling facility for a seamless steel pipe, in which a steel slab heated to a predetermined temperature in a heating furnace is perforated / rolled to obtain a product having a predetermined outer diameter / thickness, after a mandrel bar on the inlet side of the rolling mill. A retainer device that holds the end and controls the speed of the mandrel bar, a two-roll type first rolling machine that has one pair of rolls that form an elliptical hole type, and two pairs of rolls that form a circular hole type. And only one set of roll pairs therein is a drive roll, and the groove-shaped groove bottom central portion of the set of driven roll pairs is an elliptical hole-type long diameter part of the first rolling mill. The second rolling mill of the four-roll system, which is a driven roll, is sequentially arranged as the other pair of rolls, and the rolling mill of the seamless steel pipe is characterized in that.