JP2002011507A - Method for rolling seamless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain both uniformization of variation in the outside diameter in the axial direction of a hollow tube stock and improvement of the stripping property of a mandrel bar at the same time. SOLUTION: This method is a rolling method of a seamless steel tube with a mandrel mill 4 on the inlet side of which an outside diameter reducing stand 11 for reducing the outside diameter of the hollow tube stock 1b which is pierced by a piercer 3 is arranged proximately. The outside diameter of a rolled stock is measured on the outlet side of the mandrel mill 4. Based on this measured result, the roll gap of the outside diameter reducing stand 11 is adjusted within the range which is preliminarily determined by experiments and where defective stripping is not generated. Then, the variation of the outside diameter in the axial direction of the hollow tube stock is uniformized and the stripping property of the mandrel bar is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling a seamless steel pipe using a mandrel mill.

[0002]

2. Description of the Related Art One of the methods for producing a seamless steel pipe is to use a mandrel mill. In this method, as shown in FIG. 5, after the round steel slab 1a is heated by the heating furnace 2, it is pierced by the piercing machine 3 to form the hollow shell 1b. Elongation rolling by mandrel mill 4 to finish to predetermined thickness, or as it is or after reheating, diameter reduction rolling by stretch reducer 5 or sizer to finish outer diameter to predetermined dimensions, seamless steel pipe as product And that.

By the way, this mandrel mill 4 usually includes four to eight two-roll stands provided with a pair of perforated rolls, as shown in FIG. The roll-type rolls were successively arranged in the pass line direction by alternately shifting the phases of the rolls by 90 ° so that the rolling-down directions in the vertical plane were different, and making the roll-hole shape smaller in the later-stage roll stand. The rolling is performed by passing the hollow shell 1b in which the mandrel bar 4b is inserted into the roll hole mold of each roll stand 4a.

[0004] In the production of seamless steel pipes using such a mandrel mill, difficult-to-machine stainless steel containing high alloy components has been developed in accordance with the severe use of oil drilling oil fields and the need for weight reduction. The production range of steel pipes, ultra-thin steel pipes, thick-walled steel pipes, and the like has been expanded.

[0005] When a steel pipe using such a difficult-to-work material or an ultra-thin steel pipe or a thick steel pipe is rolled by a mandrel mill,
Since the coefficient of friction with rolling rolls and mandrel bars, and the rolling temperature, etc. are different from those of general materials, when rolling is performed with the same roll gap and roll speed as general materials, the outer diameter of the rolled material will be large or small. When the mandrel bar is pulled out of the rolled material after the completion of rolling, the rolled material is likely to stick to the mandrel bar or to be in a shrink-fit state.

Therefore, from the viewpoint of the stability of the rolling operation and the improvement of the yield, it is an important point in the mandrel mill rolling to improve the pulling property of the mandrel bar from the rolled material, ie, the stripping property. .

[0007] A hollow shell pierced and rolled by a piercing machine is
When the ratio of the thickness (t) to the outer diameter (D), that is, the thickness outer diameter ratio (t / D) is small, the phenomenon that the outer diameter at the rear end of the rolling becomes large at the time of piercing and rolling by a piercing machine. At the same time, the fluctuation of the outer diameter in the axial direction also increases.

In the case of such a hollow shell having a large variation in the outer diameter in the axial direction, or in the case where the number of roll stands of the subsequent mandrel mill is small, the axial length of the pipe is increased even after the elongation rolling by the mandrel mill. The thickness changes in the direction.

In view of the above, while preventing a change in the wall thickness in the axial direction at the outlet side of the mandrel mill due to a change in the outer diameter in the axial direction of the hollow shell drilled by the drilling machine, the post-rolling operation after the mandrel mill rolling is performed. There is a need for a rolling method that improves the stripping properties of mandrel bars.

However, conventionally, for example, Japanese Patent Application Laid-Open No. 8-71
As in No. 610, a 4-roll stand for reducing the outer diameter of the tube is arranged at the foremost stage of the stand row, followed by a 2-roll stand group for reducing the wall thickness, and a circle at the last stage. The first stage of a mandrel mill with a 4-roll stand for eliminating uneven thickness that reduces circumferential thickness variations
By setting the ratio (Di / Dm) of the pipe inner diameter Di and the mandrel bar outer diameter Dm at the roll stand exit side to 1.05 or less, the hole can be pierced by a piercing machine as disclosed in JP-A-10-94806. The outer diameter reduction stand for reducing the outer diameter of the hollow shell, which is arranged in the vicinity of the entrance side of the mandrel mill, is located outside the axial length of the hollow shell at the entrance side of the outer diameter reduction stand. It is only proposed to measure the diameter and adjust the roll gap of the outer diameter reducing stand based on the measurement result to prevent biting occurring due to outer diameter fluctuation in the axial direction. Met.

[0011]

SUMMARY OF THE INVENTION Among them, Japanese Patent Application Laid-Open No. 8-
No. 71610, that is, it is effective to set Di / Dm ≦ 1.05 on the exit side of the foremost stand as a countermeasure against roll biting of the four-roll stand for eliminating uneven thickness at the last stage. However, the material enters the final stage due to changes in the composition, dimensions, temperature and axial temperature of the rolling material, the surface properties of the rolling tool, ie, the rolling roll, the temperature and temperature changes of the mandrel bar, lubricity, etc. (chance characteristics). Because the outer diameter of the material fluctuates, roll roll-out does not occur, but the ratio between the inner diameter of the rolled material and the diameter of the mandrel bar at the exit of the final stage approaches 1.0, and the rolled material is shrink-fitted to the mandrel bar. May occur, and the stripping property may be degraded.

In the rolling method proposed in Japanese Patent Application Laid-Open No. Hei 10-94806, the outer diameter reduction stand is used to reduce the axial length at the exit side of the mandrel mill due to the outer diameter variation in the axial direction of the hollow shell. In order to prevent the pipe thickness fluctuation at the time, the outer diameter reduction degree of the outer diameter reducing stand (Ri = ｛(Di−D) /
Di｝ × 100), and no consideration is given to stripping properties after mandrel mill rolling.

As described above, none of the rolling methods proposed so far can achieve both the uniformity of the outer diameter fluctuation in the axial direction of the hollow shell and the improvement of the stripping property of the mandrel bar. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and achieves both uniform outer diameter fluctuation in the axial direction of a hollow shell and improvement in stripping properties of a mandrel bar. It is an object of the present invention to provide a method of rolling a seamless steel pipe that can be performed.

[0015]

In order to achieve the above-mentioned object, a method for rolling a seamless steel pipe according to the present invention measures an outer diameter of a rolled material at an outlet side of a mandrel mill, and based on the measurement result, Thus, the roll gap of the outer diameter reducing stand arranged close to the entry side of the mandrel mill is adjusted to a range in which stripping failures determined in advance by experiments do not occur. By doing so, it is possible to achieve both the uniformity of the outer diameter fluctuation in the axial direction of the hollow shell and the improvement of the stripping property of the mandrel bar.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A method of rolling a seamless steel pipe according to the present invention is directed to a mandrel mill in which an outer diameter reducing stand for reducing the outer diameter of a hollow shell drilled by a drilling machine is arranged close to an inlet side. In the method of rolling a seamless steel pipe according to the above, the outer diameter of the rolled material was measured on the outlet side of the mandrel mill, and based on the measurement result, the roll gap of the outer diameter reducing stand was determined in advance by an experiment. It is adjusted to a range that does not.

In the method for rolling a seamless steel pipe according to the present invention, an outer diameter of a rolled material is measured at an outlet side of a mandrel mill, and an outer diameter reduced diameter arranged close to an inlet side of the mandrel mill is determined based on the measurement result. Since the roll gap of the stand is adjusted in advance to a range that does not cause stripping failures obtained by experiments, both the uniformity of the outer diameter fluctuation in the axial direction of the hollow shell and the improvement of the stripping property of the mandrel bar are improved. Can be achieved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for rolling a seamless steel pipe according to the present invention will be described with reference to a control flow shown in FIG. FIG. 1 is a diagram showing a control flow for carrying out a rolling method of a seamless steel pipe according to the present invention.

In FIG. 1, reference numeral 11 denotes an outer diameter reducing stand, which is disposed close to the entry side of the mandrel mill 4 on the downstream side of the drilling machine 3 and outside the hollow shell (1b) drilled by the drilling machine 3. This is to reduce the diameter.

Reference numeral 12 denotes an outer diameter measuring device arranged on the exit side of the mandrel mill 4, which continuously measures the outer diameter Di at each position in the axial direction of the rolled material stretched and rolled by the mandrel mill 4, and measures the outer diameter Di. The measurement result is input to the calculator 13.

Computer 1 to which the measured outer diameter Di is input
Numeral 3 indicates the input outer diameter Di and the inner diameter clearance Kd (= 3.0 to 8.0 mm), which is determined by an experiment in advance and in which stripping failure does not occur, as shown in the following equation 1.
Are compared, and if they are not equal (Di ≠ Dr), the gap adjustment amount ΔR of the outer diameter reducing stand 11 is calculated by the following equation 2 so that both become equal.

[0022]

[Formula 1] Dr = Dm + 2WT + Kd where Dm: Outer diameter of mandrel bar WT: Finished wall thickness in mandrel mill (calculated value or measured value)

[0023]

ΔR = α × β × (Di−Dr) where α: material correction coefficient (= 1.0 to 3.0) β: dimensional correction coefficient (= 1.0 to 2.0)

The roll gap adjustment amount ΔR obtained by Expression 2 is output to a roll gap driving device 14a in the control device 14 of the outer diameter reducing stand 11, and is corrected for the reference roll gap Rg.

By the way, using a hollow shell (material: STKM13A) having an outer diameter of 320 mm and a thickness of 16.0 mm at the outlet of the outer diameter reducing stand, using a mandrel bar having an outer diameter Dm of 260 mm, and finishing wall thickness. WT is 6.0m
m, when the target outside diameter Dr is 276.0 mm (inner diameter clearance Kd = 4.0 mm) when the elongation rolling is performed by the mandrel mill, the mandrel mill exit side when the method of the present invention is applied and when it is not applied 2 and 3 show the results obtained by examining the outer diameter in the axial length direction.

If the method of the present invention was not applied and the gap was not adjusted in the outer diameter reducing stand, the outer diameter in the axial direction at the mandrel mill exit side was, as shown in FIG. However, when the method of the present invention was applied and the gap was adjusted in the outer diameter reduction stand, as shown in FIG. Thus, the amount of outer diameter variation in the axial direction on the mandrel mill exit side can be significantly suppressed, and the outer diameter variation in the axial direction can be made uniform.

Further, a hollow shell having an outer diameter of 315 mm and a thickness of 25 mm at the outlet of the outer diameter reducing stand (material: S
TKM13A) using a mandrel bar having an outer diameter Dm of 246.5 mm, a finished thickness WT of 15.0 mm, and a target outer diameter Dr of 280.0 mm (inner diameter clearance Kd =
FIG. 4 shows the results of examining the outer diameter distribution of the hollow shell after elongation rolling when the method of the present invention was applied and when the method of the invention was not applied, when elongation rolling was performed so as to be 3.5 mm). .

As is apparent from FIG. 4, when the method of the present invention was not applied and the gap was not adjusted in the outer diameter reduction stand (the □ portion in FIG. 4), the hollow shell after the elongation rolling was removed. In many cases, stripping defects with a diameter of 280 mm or less occurred, but when the method of the present invention was applied and the gap was adjusted with an outer diameter reducing stand (part ■ in FIG. 4), stretching was not performed. The outer diameter of the hollow shell after rolling is 2
There were few occurrences of stripping defects of 80 mm or less, and the stripping property of the mandrel bar was improved.

In this example, the results of an experiment conducted on ordinary steel (STKM13A) were shown. However, the method of rolling a seamless steel pipe according to the present invention is effective even when applied to hard-to-work stainless steel. Needless to say.

[0030]

As described above, the method for rolling a seamless steel pipe according to the present invention is arranged close to the entrance side of the mandrel mill based on the measurement result of the outer diameter of the rolled material at the exit side of the mandrel mill. The roll gap of the outer diameter reduction stand is adjusted to the range that does not cause stripping failure, which was determined in advance by experiments, so that the outer diameter fluctuation in the axial direction of the hollow shell becomes uniform and the stripping property of the mandrel bar is improved. Can be achieved together.

[Brief description of the drawings]

FIG. 1 is a diagram showing a control flow for implementing a method for rolling a seamless steel pipe according to the present invention.

FIG. 2 is a diagram showing an example of an outer diameter change in a shaft length direction on a mandrel mill exit side when a gap adjustment is not performed on an outer diameter reducing stand without applying the method of the present invention.

FIG. 3 is a diagram showing an example of an outer diameter change in an axial direction on a mandrel mill exit side when a gap is adjusted in an outer diameter reducing stand by applying the method of the present invention.

FIG. 4 is a diagram showing the results of examining the outer diameter distribution of a hollow shell after elongation rolling when the method of the present invention is applied (■) and not applied (□).

FIG. 5 is a view showing a process of manufacturing a seamless steel pipe by a Mannesmann mandrel mill method.

[Explanation of symbols]

 Reference Signs List 3 drilling machine 4 mandrel mill 11 outer diameter reducing stand 12 outer diameter measuring device 14 control device 14a roll gap driving device

Claims (1)

[Claims] 1. A method for rolling a seamless steel pipe by a mandrel mill in which an outer diameter reducing stand for reducing the outer diameter of a hollow shell drilled by a drilling machine is arranged close to an inlet side.
Measure the outside diameter of the rolled material on the exit side of the mandrel mill,
A method for rolling a seamless steel pipe, comprising: adjusting a roll gap of the outer diameter reducing stand to a range in which a stripping defect determined in advance by experiment is not generated based on the measurement result.