JP4284657B2 - Perforated rolling roll group, mandrel mill rolling method using the perforated rolling roll group, and mandrel mill - Google Patents

Description

  The present invention is used in a mandrel mill, which is a seamless pipe-making facility, and prevents rolling defects that may occur at an even stand (an even-numbered stand counted from the entrance side of the mandrel mill) located at the subsequent stage of the mandrel mill. , A mandrel mill rolling method and a mandrel mill using the hole rolling roll group, and in particular, a biting failure in the fourth stand (fourth stand counted from the entrance side of the mandrel mill) The present invention relates to a perforated rolling roll group capable of effectively preventing roll slip and a mandrel mill rolling method and a mandrel mill using the perforated rolling roll group.

  In the manufacture of seamless pipes by the Mannesmann-Mandrel mill method, first, a round billet or square billet of a material is heated to 1200 to 1260 ° C. in a rotary hearth heating furnace, and then pierced and rolled with a plug and a rolling roll with a piercing machine. To manufacture hollow shells. Next, a mandrel bar is inserted into the inner surface of the hollow shell in a skewer shape, and the outer surface is normally constrained by a perforated rolling roll with a mandrel mill consisting of 5 to 8 stands, thereby extending to a predetermined thickness. Reduce meat. Then, after extracting the mandrel bar, the thinned tube is shaped and rolled to a predetermined outer diameter with a drawing mill to obtain a product.

  Conventionally, as a mandrel mill, there are many two-roll mandrel mills in which a pair of perforated rolling rolls opposed to each stand are arranged, and the rolling rolls are alternately arranged by shifting the rolling direction by 90 ° between adjacent stands. It is used. In addition, a four-roll type mandrel mill in which four roll-type rolling rolls having an angle of 90 ° in the rolling direction are disposed on each stand is applied in part, and the angle formed in the rolling direction in each stand A three-roll mandrel mill is also proposed in which three perforated rolling rolls with a 120 ° are disposed and are alternately arranged with the rolling rolls being shifted by 60 ° between adjacent stands.

  Here, out of the stands constituting the mandrel mill, the thickness of the raw tube on the entrance side of the odd numbered stand (odd numbered stand from the mandrel mill entry side) is relatively uniform, but the entrance side of the even number stand. As for the thickness of the raw tube in the hole rolling roll, the thickness at the position corresponding to the groove bottom of the perforated rolling roll becomes larger than the thickness at the position corresponding to the flange, resulting in an excessive reduction in the groove bottom, so-called It is known that rolling defects such as biting failure and roll slip are likely to occur.

  Conventionally, although many countermeasures for preventing rolling defects have been proposed for the second stand (second stand counted from the entrance side of the mandrel mill) located in the front stage of the mandrel mill, the fourth stand (installed in the mandrel mill) has been proposed. Little measures have been studied to prevent rolling failure for the fourth stand from the side.

  For example, Patent Document 1 discloses that a blank tube at a position corresponding to a flange portion is obtained by setting the perimeter processing degree of a hole type in an even-numbered roll stand (even-numbered stand) from a mandrel mill entry side to a predetermined value or more. An invention that suppresses perforation is disclosed (paragraph 0050 of Patent Document 1).

  Further, Patent Document 2 discloses that a flange portion is formed by setting the perimeter processing degree of a hole mold to a predetermined value or more in a stand having a large stretch ratio after the third stand (the third stand counted from the mandrel mill entry side). The invention which suppresses the perforation of the raw tube in the position corresponding to is disclosed (Claim 2 etc. of Patent Document 2).

  In the inventions described in both Patent Documents 1 and 2, it is possible to suppress perforation of the raw tube at a position corresponding to the flange portion. However, according to the experiment by the inventors of the present invention, it is possible to prevent a biting failure, a roll slip, and the like due to an excessive amount of reduction at the groove bottom of the perforated rolling roll in the even stand (particularly the fourth stand). I found it impossible.

  Further, Patent Document 3 discloses that a perforated rolling roll disposed on the third stand is closed (a flange of a perforated profile) in order to prevent perforation due to a biting failure or roll slip in the fourth stand. (Patent Document 3 paragraphs 0011 and 0023 to 0026).

According to the invention described in Patent Document 3, it is possible to substantially prevent perforation due to biting failure, roll slip, and the like. However, according to experiments by the inventors of the present invention, rolling failure such as biting failure and roll slip cannot be completely prevented, and wrinkles occur on the surface of the raw tube. It turns out that there is a problem that it is necessary to scrape the outer surface flaws.
JP-A-8-57506 JP-A-8-276208 JP 2000-351006 A

  The present invention has been made to solve such problems of the prior art, and a group of perforated rolling rolls capable of effectively preventing biting failure and roll slip in the fourth stand and the perforated mold. It is an object to provide a mandrel mill rolling method and a mandrel mill using a rolling roll group.

  As a result of intensive investigations by the inventors of the present invention to solve the above problems, as will be described later, the distance between the center of curvature of the groove bottom profile of the perforated rolling roll disposed in the fourth stand and the perforated center. If S4 is set to about half of the distance S2 between the center of curvature of the groove bottom profile of the perforated rolling roll disposed on the second stand and the perforated center, the perforated rolling roll disposed on the fourth stand Can reduce the amount of rolling at the part of the raw pipe that is rolled down at the part located between the groove bottom part and the flange part (hereinafter, referred to as “QP part” as appropriate), and thereby the biting failure in the fourth stand and the roll It has been found that slip can be effectively prevented. In other words, as disclosed in Patent Document 3, in the fourth stand, the amount of reduction tends to be larger on both sides (near the QP portion) than the center of the groove bottom portion. Focusing on the fact that if the reduction amount can be reduced, it can be expected to effectively prevent biting failure and roll slip in the fourth stand, and as a result of intensive studies, the groove of the perforated rolling roll disposed in the fourth stand The distance S4 between the center of curvature of the bottom profile and the center of the hole mold may be set to about half of the distance S2 between the center of curvature of the groove bottom profile of the hole-type rolling roll disposed on the second stand and the center of the hole mold. I found out. The present invention has been completed based on the knowledge of the inventors.

That is, the present invention is a group of perforated rolling rolls used in a mandrel mill in which a plurality of perforated rolling rolls are arranged in each stand,
The distance S2 between the center of curvature of the groove bottom profile of the perforated rolling roll disposed in the second stand and the center of the perforated center, and the center of curvature of the groove bottom profile of the perforated rolling roll disposed in the fourth stand and the hole The distance between the center of the mold and the distance S4 is set so as to satisfy the following formula (1).
S2 × 0.40 <S4 <S2 × 0.60 (1)

  The present invention is also provided as a mandrel mill rolling method using the perforated rolling roll group, or a mandrel mill characterized in that the perforated rolling roll group is provided. .

  According to the present invention, it is possible to effectively prevent biting failure and roll slip in the fourth stand.

  Hereinafter, an embodiment of a group of perforated rolling rolls according to the present invention will be described by taking as an example a case where it is applied to a two-roll mandrel mill, with appropriate reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view schematically showing a configuration of each stand constituting a mandrel mill to which a perforated rolling roll group according to the present embodiment is applied. As shown in FIG. 1, the center of curvature of the groove bottom profile (hole profile in the vicinity of the groove bottom B) of the hole rolling roll R (the center of the arc of radius r constituting the groove bottom profile) O ′ and the hole center ( If the distance from the center (O of the pass line PL) O is Si (i is a stand number), the distance S2 in the second stand and the distance S4 in the fourth stand are set so as to satisfy the following formula (1). ing.
S2 × 0.40 <S4 <S2 × 0.60 (1)

  Hereinafter, the reason why the above equation (1) is set to be satisfied will be described.

  As described in Patent Document 3, generally, the fourth stand of the mandrel mill is a finishing stand, and it is necessary to form the base tube P in a perfect circle. It is set to a small value in the vicinity. More specifically, the distance S4 is generally set to a small value of about 0.0 to 0.2 times the distance S2.

  However, the inventors of the present invention, as long as the distance S4 for the perforated rolling roll disposed in the fourth stand is set large, as long as the dimensions of the resulting product fall within the dimensional tolerance, It has been found that the amount of reduction at the QP portion can be reduced, thereby effectively preventing biting failure and roll slip in the fourth stand. In particular, in the case of a mandrel mill having a sixth stand, it can be set larger.

  More specifically, when the distance Si between the center of curvature O ′ of the groove bottom profile of the hole rolling roll R and the hole center O is increased, the thickness of the QP portion of the raw tube P corresponds to the groove bottom B. It becomes larger than the wall thickness of the position to be. Generally, in the second and third stands, the distance Si (S2, S3) is a positive value (that is, the center of curvature O ′ is outward from the hole center O (from the groove bottom B of the hole roll R). Since the perforated rolling roll set to be located) is disposed, the thickness of the raw pipe P on the entry side of the fourth stand also corresponds to the thickness of the groove bottom B. It is larger than the wall thickness at the position to be.

  On the other hand, in the conventional general roll-type rolling roll disposed on the fourth stand of the mandrel mill, the distance S4 is set to a small value as described above. Therefore, there is a tendency that biting failure and roll slip are likely to occur.

  Therefore, while setting the distance S4 for the perforated rolling roll disposed in the fourth stand to be large, if the thickness of the QP portion to be reduced by the fourth stand is distributed to the fifth stand and the subsequent, the fourth stand Focusing on the fact that the amount of reduction at the QP portion is reduced and it is likely that biting failure and roll slip can be prevented, a rolling test described below was performed.

<Rolling test 1>
A group of perforated rolling rolls in which the distance Si between the center of curvature of the groove bottom profile and the center of the perforated roll of each perforated roll disposed in each stand is set to each value shown in Table 1 is applied to a two-roll mandrel mill. And a rolling test was carried out. In this test, a mandrel bar with an outer diameter of 367.6 mm was used, and 100 elementary pipes made of ordinary steel were used for each condition, with an outer diameter of 380 mm, a wall thickness of 6 mm, and a length of 23 m on the mandrel mill outlet side. It rolled so that it might become. Then, by evaluating the occurrence rate of surface flaws generated in the seamless pipe after rolling, it was decided to evaluate the occurrence of rolling defects such as biting failure and roll slip.

  As shown in Table 1, if the value of S4 / S2 is too small as in the prior art (conditions 1-7, etc.), many surface defects occur, but conversely, the value of S4 / S2 is too large ( Condition 1-1, etc.) As a result of the reduction of the QP portion at the fourth stand being reduced, the reduction amount of the QP portion at the sixth stand was excessive and a large number of surface defects were generated, and S4 / S2 It was found that no surface defects were generated at all when the value was set in the vicinity of 0.50 (Condition 1-4). From the results shown in Table 1, in order to effectively prevent rolling defects, it is sufficient to set 0.40 <S4 / S2 <0.60, which satisfies the above formula (1). means.

<Rolling test 2>
A group of perforated rolling rolls in which the distance Si between the center of curvature of the groove bottom profile and the center of the perforated roll of each perforated roll disposed in each stand is set to each value shown in Table 1 is applied to a 2-roll mandrel mill. And a rolling test was carried out. In this test, a mandrel bar having an outer diameter of 359.3 mm was used, 50 pipes made of stainless steel under each condition, an outer diameter of 377 mm, a wall thickness of 9 mm, and a length of 12 m on the mandrel mill exit side. It rolled so that it might become. Then, by evaluating the occurrence rate of surface flaws generated in the seamless pipe after rolling, it was decided to evaluate the occurrence of rolling defects such as biting failure and roll slip.

  As shown in Table 2, if the value of S4 / S2 is too small as in the prior art (Condition 2-2), many surface defects occur, while S4 / S2 is set to 0.50 (Condition 2-2). As a result, it was found that no surface defects occurred. Therefore, also for stainless steel, as in the case of the rolling test 1 described above, if set to 0.40 <S4 / S2 <0.60 (if set to satisfy the above formula (1)), It is expected that rolling defects can be effectively prevented.

  Based on the reason described above, the group of perforated rolling rolls according to the present embodiment includes a distance S2 between the center of curvature of the groove bottom profile of the perforated rolling roll disposed on the second stand and the center of the perforated, The distance S4 between the center of curvature of the groove bottom profile of the perforated rolling roll disposed on the four stands and the perforated center is set so as to satisfy the above formula (1). It is possible to prevent biting failure and roll slip effectively.

  In addition, although this embodiment demonstrated the case where it applied to a 2 roll type mandrel mill, this invention is not limited to this, It can apply similarly to a 3 roll type or 4 roll type mandrel mill.

FIG. 1 is a longitudinal sectional view showing a schematic configuration of each stand constituting a mandrel mill to which a perforated rolling roll group according to an embodiment of the present invention is applied.

Explanation of symbols

B ... groove bottom O ... hole center O '... center of curvature of groove bottom profile P ... raw pipe R ... hole rolling roll PL ... pass line

Claims (3)

A group of perforated rolling rolls used in a mandrel mill in which a plurality of perforated rolling rolls are arranged in each stand,
The distance S2 between the center of curvature of the groove bottom profile of the perforated rolling roll disposed in the second stand and the center of the perforated center, and the center of curvature of the groove bottom profile of the perforated rolling roll disposed in the fourth stand and the hole A group of roll-type rolling rolls, characterized in that the distance S4 from the mold center is set to satisfy the following formula (1).
S2 × 0.40 <S4 <S2 × 0.60 (1)   A mandrel mill rolling method using the perforated rolling roll group according to claim 1.   A mandrel mill, wherein the group of perforated rolling rolls according to claim 1 is disposed.

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