JPH06190408A - Device for manufacturing seamless steel tube and its manufacture - Google Patents

Abstract

PURPOSE:To prevent a perforation defect or the seizure of a rolled stock on a perforator guide shoe from occurring in a mandrel mill by arranging three roll minimizing type cross/oblique mill on the rear surface of the perforator as a mill having an inside tool and arranging a mandrel mill on its rear surface. CONSTITUTION:After a billet heated by a heating furnace is perforated by the perforator, it is drawn-rolled by the three roll compact type cross/oblique mill, then, finish-rolled by a mandrel mill. In this case, when the ratio of the external diameter to the outlet side wall thickness of the perforator is in >=15% and the rolling reduction of wall thickness in the mandrel mill is given by 0.5-6.0mm, high alloy steel such as 13% Cr steel can be rolled in a good quality. Besides, the perforation defect which was high in the frequency of occurrence cannot be found. Further, seizure on the guide shoe does not occur at all. Furthermore, the time necessary to change the guide shoe or a time necessary to treat a stock having a perforation defect is not required and the productivity is improved, as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arrangement of rolling mill groups for rolling a seamless steel pipe and reduction distribution in each rolling mill, and more particularly to a manufacturing facility and manufacturing method for a high alloy steel seamless steel pipe by mandrel mill rolling.

[0002]

2. Description of the Related Art Conventionally, a mandrel mill has been mainly used for manufacturing small-diameter pipes (outer diameter 170 mm or less), but in recent years, not only small-diameter pipes but medium-diameter pipes having an outer diameter of about 300 mm are manufactured. At that time, it is becoming mainstream to use a mandrel mill instead of the conventional plug mill. The reason is that the quality of the inner surface of the pipe is good because it is the final thickness rolling mill and a well-lubricated bar can be used as the inner surface tool. High productivity with continuous rolling. Can be summarized in two points.

With regard to seamless steel pipes, the demand for stainless seamless steel pipes has increased with the harsh environment of use, and the conventional hot extrusion method has low productivity and it is difficult to produce large-diameter long pipes. Therefore, stainless steel pipes have been manufactured in mandrel mills.

Table 1 shows an arrangement of seamless steel pipe manufacturing equipment using a conventional mandrel mill. The number 1 in which the mandrel mill is arranged immediately after the perforator is generally used, but as shown in the numbers 2 to 4, there are two rolls between the perforator and the mandrel mill, a Mannesmann Elongator, a disher mill or three rolls. In some cases, an assel mill is installed.
It should be noted that in FIG. 1 (a), an example of the equipment sequence corresponding to the number 1 is
The equipment row corresponding to the number 2 is shown in FIG.
Is the equipment sequence corresponding to the number 3, and the number 4 is shown in FIG.
The equipment columns corresponding to are shown respectively.

[0005]

[Table 1]

Table 2 shows an example of the wall thickness reduction amount of each rolling mill in the rolling mill train shown in Table 1. When a billet having an outer diameter of 310 mm is used as the punching material, the maximum thickness reduction amount in the punching machine is 133 mm, and the thickness / outer diameter ratio on the exit side of the punching machine corresponds to 7%. Further, the reduction amount in the mandrel mill is generally about 12 mm.

[Table 2]

[0007]

The first problem is to eliminate the defect called drilling which occurs in the mandrel mill. The rolled material in the mandrel mill is shown in Fig. 2.
As shown in FIG. 2, the part pressed down by the roll caliber and the bar (part a in FIG. 2) and the other unrestrained part (part b in FIG. 2) are similar in degree, and the deformation of the unrestrained part (in FIG. 2) Part b) is governed by the deformation of the part (part a in FIG. 2) that is rolled down by the other roll calibers and bars. The deformation of the material in the mandrel mill will be described in more detail by taking the deformation of the material in the first stand and the second stand as an example.

In FIG. 3, the thickness of the roll caliber of the first stand and the portion (a portion) pressed by the bar is naturally thinner than the other portions (b portion). In the second stand, the thick part (b part) in the first stand is rolled by the roll caliber and the bar, but the deformation of the b part in the second stand causes the b part to be bent in the first stand with respect to the b part. The elongation of the already thinned portion a is smaller than that of the portion b, but the portion a is subjected to a corresponding tensile force in a freely deformed state. If this tensile force exceeds the breaking limit of the material, the material after rolling may have a defect called perforation shown in FIG.

The occurrence of the above-mentioned defects is governed by the ability of the material to deal with elongation (hot workability) and the rolling conditions in the mandrel mill. If the wall thickness rolling amount in the mandrel mill is about 12 mm, the rolling is performed on ordinary steel. There is no occurrence of piercing defects, but the occurrence rate becomes higher in high alloy steel of 13% Cr steel or more, especially in the case of thin wall thickness of 5 mm or less after mandrel mill rolling. The rate of occurrence of clear defects exceeds 50%. That is, in mandrel mill rolling of high alloy steel, how to eliminate the perforation defects shown in FIG. 4 is an important issue.

The second problem is the seizure of the rolled material on the guide shoe in the Mannesmann inclined punching machine. Once this occurs, it cannot be prevented unless the guide shoe is replaced, and the quality of the outer surface of the product becomes poor. There are three types of guide shoes as shown in FIG. Among them, in the case of the fixed shoe 11 of (a), in the case of 13% Cr steel, it is necessary to replace after rolling about 10 bars. In the disc guide shoe 12 of (b), it may occur in high alloy steel (such as duplex stainless steel) of 13% Cr steel or more from the start of rolling. The drive roller shoe 13 of (c) does not cause seizure, but has the drawback that it cannot be used for thin materials.

In order to stably improve the quality of the outer surface of the product in the existing technology, it is necessary to use the drive roller shoe (c), but in this case, the original purpose of the guide shoe is to sufficiently suppress the material. If it is not so thin, the material easily enters between the roll and the shoe. Therefore, the perforation exit side dimension is limited to 15% or more in terms of wall thickness / outer diameter ratio. Also, in the press roll method that does not require a guide shoe, there is no problem of seizure flaws because a guide shoe is not required, but originally the perforation exit side dimension is as thick as the wall thickness / outer diameter ratio is about 25%. is there. Therefore, in order to manufacture a high quality alloy product with high quality, it is necessary to make the punching machine exit side dimension 15% or more in terms of wall thickness / outer diameter ratio.

As described above, thick-walled drilling is effective for economically drilling high-alloy steel, but since the maximum thickness reduction amount in a mandrel mill is about 15 mm, a thin-walled product equivalent to the conventional product. In the case of manufacturing a sheet, a stretching machine is required between the punching machine and the mandrel mill. For example, when manufacturing a pipe having an outer diameter of 280 mm and a wall thickness of 7 mm on the outlet side of a mandrel mill, conventionally, the outer diameter of the hole on the outlet side was 310 mm, and the wall thickness was 22 mm. In order to make the thickness / outer diameter ratio 15% or more, the punch-out side wall thickness is 47
It is necessary to make mm the thinnest. In that case, since the thickness reduction amount in the mandrel mill is 40 mm, it is necessary to arrange a stretching machine between the punching machine and the mandrel mill to reduce the wall thickness from 47 mm to 22 mm. That is, an outer diameter of 310 mm and a wall thickness of 22 mm are manufactured on the delivery side of this stretching machine. Therefore, it is possible to reduce the wall thickness by about 25 mm, and the wall thickness / outer diameter ratio is 15 which is the thin wall limit of the Mannesmann puncher.
It is necessary to manufacture a wall thickness / outer diameter ratio of 7%, which is a thin wall thickness exceeding 10%. Table 3 shows the characteristics of the intermediate drawing machine conventionally used in the seamless steel pipe rolling equipment using the mandrel mill.

[0013]

[Table 3]

In the case of the two-roll Mannesmann type in which the inner surface tool is a plug, the wall thickness reduction amount of 25 mm, which is the amount of compensation for thick wall perforation, is sufficiently possible, but a pipe with a wall thickness / outer diameter ratio of 7% is used. The fact that a drive roller shoe cannot be used as a guide shoe when rolling is the same as in the case of a punching machine, and when it is used as a stretching machine in rolling of high alloy steel, seizure of material on the guide shoe occurs and this does not solve the problem. Next, in the case of a disher mill, since the guide shoe is a disk type, the problem of seizure cannot be solved, and this is also unsuitable as a stretching machine in rolling high alloy steel. Furthermore, since the Assel mill has three rolls, no guide shoe is required. Therefore, there is no problem of product quality deterioration due to seizure on the guide shoe, but when the wall is thin, the rear end of the pipe protrudes into the gap of 3 rolls, making it difficult to slip out of the Assel mill. Is limited to about 12.5%. Therefore, this is also unsuitable as a stretching machine in high alloy steel rolling,
A drawing machine conventionally used for a seamless steel tube rolling equipment using a mandrel mill is not suitable for good rolling of high alloy steel. Therefore, the second problem is how to design the model of the stretching machine that can reduce the wall thickness of 25 mm or more between the punching machine and the mandrel mill and can roll the thin wall tube with the wall thickness / outer diameter ratio of 7% or less. It is converted into the problem.

[0015]

In order to solve the above two problems, the present inventor solves the problem of punching in a mandrel mill and eliminates the sticking of the rolling material to the guide shoe of the punch. In order to achieve this, it is necessary to achieve thick-walled drilling and to achieve a light reduction in the mandrel mill. To achieve this, a rolling equipment row was established in which a 3-roll reduction type cross-tilt rolling machine was placed between the drilling machine and the mandrel mill. Came to do.

To solve the first problem, the inventor has focused on the load in the mandrel mill. That is, it was judged that the perforation occurred because the material could not withstand the necessary stretching in the roll flange portion (b portion in FIG. 3) at the time of rolling, and fracture occurred, and the limit was clarified. FIG. 6 shows the rate of occurrence of perforation with respect to the reduction amount in the mandrel mill, which shows that the maximum reduction amount in the mandrel mill is 6.0 mm. Further, FIG. 7 shows the inner surface roughness of the material on the delivery side of the mandrel mill with respect to the reduction amount of the mandrel mill. One of the characteristics of the mandrel mill is that the inner surface quality is good. When this characteristic is secured, the inner surface roughness is 20 s at the mandrel mill exit side.
It shows that the roughness is required to be less than a certain degree, and for this purpose, a minimum rolling amount of 0.5 mm is required. Therefore, in order to roll the high alloy steel in a mandrel mill with good quality, it is necessary to set the wall thickness reduction amount to 0.5 mm or more and 6.0 mm or less.

Next, it is necessary to determine the type of the drawing machine, but in order to solve the first problem, the amount of wall thickness reduction in the mandrel mill should be made smaller than in the conventional case, so that the mandrel mill tube is smaller than in the conventional case. Need to be thin. In manufacturing a product having an outer diameter of 280 mm and a wall thickness of 7 mm on the exit side of the mandrel mill, the conventional mandrel mill tube had an outer diameter of 310 mm and a wall thickness of 22 mm, but the mandrel mill has a maximum wall thickness reduction amount of 6 mm. To do this, the wall thickness of the mandrel mill tube is required to be 13 mm or less, and the wall thickness / outer diameter ratio is required to be 4.2% or less. As described above, in selecting the type of the stretching machine that solves the first problem while solving the second problem, it is required that thinner rolling can be performed than ever before.

Therefore, the conditions to be provided as a stretching machine arranged in the middle of the mandrel mill are as follows. 1) A thickness reduction of 25 mm or more is possible. 2) The wall thickness / outer diameter ratio must be 4.2% or less. 3) Do not create new problems in achieving 1) and 2).

An intermediate stretching machine satisfying these conditions will be selected. When the rolling direction and the material advancing direction are the same as in a mandrel mill, the wall thickness reduction amount is 25 mm.
Therefore, the rolling method is inclined rolling. Also, if the inner surface tool is a plug, rolling with one plug 25
The life is about this. In the case of a punching machine, there is no choice but to use a plug as the inner surface tool, so with the current technology, a life of less than 10 rolling is required with one plug, but in the case of a drawing machine, a bar can be used and a bar can be used. By doing so, the life is dramatically increased. Therefore, the internal tool should be a bar. Therefore, the drawing machine becomes an inclined rolling machine using a bar. In addition, when the wall thickness / outer diameter ratio is 4.2% or less, it is not possible to select a guide shoe that does not cause seizure with the current technology as described above, so that the number of rolls is 3 or more and the guide shoe is unnecessary. To do.

When rolling a thin wall with a large amount of wall thickness reduction using an inclined rolling mill, it is important to secure a material flow in the pipe axis direction. FIG. 8 shows a 3-roll tilt rolling mill (see FIG.
It shows how the rolled material is deformed in the cross section in the (Assel mill) shown in (d), which is the case where the material easily flows in the pipe circumferential direction. In this case, the material is rolled by one roll and greatly bulges and is bitten by the next roll, which easily causes flaws on the outer surface of the material, and in the thin-walled pipe, the trailing end of the pipe is caught between the rolls, resulting in defective rolling. Cheap. Therefore, the feed angle of the material in the axial direction (α in Fig. 9
It is important to make the material easier to flow in the axial direction and to eliminate large bulges in the circumferential direction by increasing ().), Which enables to suppress the occurrence of external defects and enables the stable rolling of thin-walled materials. .

Next, the important point is to reduce the shear strain on the inner and outer surfaces of the tube cross section (indicated by γ in FIG. 10). The shear strain on this surface causes the entire length of the tube to rotate at the same number of revolutions against the force that the roll tries to twist the material when there is a difference between the rotational speed of the tube and the circumferential speed component of the roll surface. This occurs because only the outer surface layer of the tube tries to follow the roll speed. When a bar is used for the inner surface tool, in order to reduce the wall thickness, it is necessary to reduce the outer diameter of the pipe toward the pipe advancing direction as shown in FIG. 11 (D
in> Dout), the circumferential velocity of the roll surface can be reduced toward the rolling direction so that it can be the same as the velocity in the circumferential direction of the pipe at any point in the axial direction.
Therefore, the roll shape must be a reduction type in which the roll diameter decreases in the tube traveling direction.

Further, when the roll shape is a reduction type, in order to carry out the wall thickness reduction, the roll axis must be of a cross type so as to approach the pass line on the pipe outlet side. In this reduction type cross tilt rolling mill, if the cross angle formed by the roll axis and the pass line is selected to be about 30 degrees, the roll tilt angle is reduced to about 9 degrees while securing stable biting of the material into the roll. The material feed angle (α in FIG. 9) can be about 25 degrees. Therefore, the expansion of the pipe in the circumferential direction can be suppressed to a minimum, the occurrence of external surface defects can be eliminated, and the thin-walled pipe can be rolled. In the experiments conducted by the inventors, a wall thickness / outer diameter ratio of 3% was achieved on the outlet side of the stretching machine. The maximum wall thickness reduction of 25 mm has been achieved.

[0023]

The present invention is a seamless steel pipe rolling facility in which a three-roll reduction type cross-tilt rolling machine is arranged on the rear surface of the punching machine and a mandrel mill is arranged on the rear surface thereof, and the thickness ratio of the exit side of the punching machine and the outer diameter ratio are set. Is 15% or more, and the thickness reduction amount in the mandrel mill is 0.5 mm or more and 6.0 mm or less
Even high alloy steel such as% Cr steel can be rolled with good quality. It should be noted that between the punch and the 3-roll reduction cross-tilt rolling mill, or between the 3-roll reduction cross-tilt rolling mill and the mandrel mill, or between the punch and the 3-roll reduction cross-tilt rolling mill and the 3-roll reduction. Even if a rolling mill for expanding the pipe or a rolling mill for the contracted pipe is introduced between the die crossing inclined rolling mill and the mandrel mill, the above-mentioned action is not impaired.

[0024]

EXAMPLES Examples of the present invention will be described below. FIG. 12 is a row of seamless steel pipe rolling equipment according to the present invention. The billet heated in the heating furnace is perforated by a perforator, stretch-rolled by a 3-roll reduction type cross-tilt rolling mill, and then finish-rolled by a mandrel mill. After that, only the outer diameter is molded by a sizer mill and then sent to the refining process (not shown).

The punching machine used here is a well-known Mannesmann-type inclined rolling machine, and the guide shoe uses a drive roller guide. Further, the mandrel mill is a 4-stand mill, and the bar is returned to the mill entrance side after completion of rolling, and at the same time, the rolled material is sent to the rear surface of the mill by an extractor with 3 rolls and 2 stands. Furthermore, the 3-roll reduction type cross-tilt rolling mill is Japanese Patent Publication No. 57-13.
Although similar to the rolling apparatus shown in Japanese Patent No. 22, the three rolls are each driven by an electric motor via a drive shaft and a speed reducer. That is, the revolution mechanism as disclosed in Japanese Examined Patent Publication No. 57-1322 is not required.

Rolling was actually performed using the equipment train.
The material to be rolled is 13% Cr steel, and the outlet size of the mandrel mill is 280φ × 7.0 mmt. FIG. 13 shows the reduction distribution according to the conventional method and the present invention, and the dimensions on the delivery side of each rolling mill are also shown. The tube obtained there was free from the perforations that have been conventionally generated in the mandrel mill or the seizure that has been caused in the punching machine, and it is possible to obtain a high-quality tube. 22%
1 for Cr steel or austenitic stainless steel
Similar results are obtained with 3% Cr steel.

[0027]

FIG. 14 shows the difference in the occurrence rate of punching defects between the present invention and the conventional method in the production of 13% Cr steel. Conventionally,
There was no perforation that had a high incidence, and there was a remarkable effect. Further, seizure on the guide shoe was not generated at all, and high-alloy steel such as 22% Cr steel and austenitic stainless steel could be manufactured with good quality. In addition, the seizure of the guide shoe was completely eliminated, and the time required for its replacement or the time required for treating the material with hole defects in the mandrel mill was eliminated, thus improving the productivity.

[Brief description of drawings]

FIG. 1 Seamless steel pipe rolling equipment train having a mandrel mill.

[Fig. 2] Distribution of wall thickness reduction in a seamless steel pipe rolling facility having a mandrel mill.

FIG. 3 is a situation of wall thickness reduction in the first and second stands of the mandrel mill.

FIG. 4 is a diagram illustrating perforation.

FIG. 5 is a diagram illustrating a model of a guide shoe.

FIG. 6 is a ratio of occurrence of perforation to the reduction amount of the mandrel mill.

FIG. 7 shows the maximum inner surface roughness with respect to the reduction amount of the mandrel mill.

FIG. 8 is a diagram illustrating a cross-sectional shape during rolling in a 3-roll tilt rolling mill.

FIG. 9 is an explanatory diagram of a material feeding angle.

FIG. 10 is a diagram illustrating shear strain in a cross section.

FIG. 11 is a view showing a situation of axial thickness reduction when a bar is used as an inner surface tool.

FIG. 12 is a view for explaining a seamless steel pipe rolling equipment row of the present invention.

FIG. 13 is a view showing wall thickness reduction distribution in the conventional method and the present invention in the seamless steel pipe rolling equipment row.

FIG. 14 is a diagram showing a rate of occurrence of punching according to the present invention.

[Explanation of symbols]

 1 Perforator 2 Mandrel Mill 3 2 Roll Mannesmann Elongator 4 2 Roll Disher Mill 5 3 Roll Assel Mill 11 Fixed Guide Shoe 12 Disc Guide Shoe 13 Drive Roller Guide Shoe 15 Perforator Main Roll 21 Mandrel Mill Main Roll 22 Mandrel Bar ( Mandrel mill) 23 Mandrel mill rolling shell 51 Assel mill main roll 52 Mandrel bar (Assel mill) 53 Assel mill rolling shell

Claims (3)

[Claims] 1. A seamless steel pipe manufacturing facility for piercing and rolling a steel slab heated to a predetermined temperature in a heating furnace to obtain a predetermined outer diameter and wall thickness. A seamless steel pipe manufacturing facility characterized by a roll reduction type cross-tilt rolling mill and a mandrel mill on the rear surface. 2. The seamless steel pipe manufacturing method using the seamless steel pipe manufacturing facility according to claim 1, wherein the amount of wall thickness reduction in the mandrel mill is 0.5 mm to 6.0 mm. Production method. 3. The seamless steel pipe manufacturing method using the seamless steel pipe manufacturing facility according to claim 1, wherein the wall thickness / outer diameter ratio of the raw pipe on the exit side of the punching machine is 15% or more. None Steel pipe manufacturing method.