JPH0452010A - Manufacture of seamless steel tube - Google Patents

Abstract

PURPOSE:To make the distribution of wall thickness uniform by rolling a tubing by opening roll gap stand by a specified distance more than the roll gap at the time of stable rolling when the specified ranges of the top end and rear end of tube are passed in a mandrel mill of full-float system. CONSTITUTION:Rolling is done by opening the roll gap of the rolling stand by 0.1-0.3 mm larger than the roll gap at the time of stable rolling when the parts of 1000-1500mm from the top end and rear end of tube are passed. Thus, the wall thickness of unstable part is thickness by 0.1-0.2mm and the distribution of wall thickness is made uniform. In this way, the distribution of wall thickness of shell in the longitudinal direction is made uniform in the mandrel mill of full-float system when the seamless steel tube is manufactured and percent defective of thin due to uneven distribution in wall thickness in the finish rolling with a succeeding stretch reducer is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for manufacturing seamless steel pipes with stable wall thickness and dimensional distribution in a full-float mandrel mill.

Conventional technology To manufacture seamless steel pipes using the mandrel mill method, a round steel piece is heated in a rotary hearth-type heating furnace, and then the hollow raw pipe obtained by piercing and rolling with a Mannesmann drilling machine is processed using a mandrel bar. The mandrel bar is inserted in the shape of a skewer and stretched and rolled to a predetermined size using a mandrel mill consisting of a plurality of sets of rolling roll stands, and then the mandrel bar is pulled out from the shell. The shell is heated in a reheating furnace and descaled, then finished with a stretch reducer to the required outer diameter and wall thickness, cooled, and then cut to the required length and sent to the finishing line.

As methods for manufacturing seamless steel pipes using the mandrel mill method, a full float method and a semi-float method are known. The difference between the two lies in whether or not the mandrel bar is restrained during rolling. In a full-float type mandrel mill, no external force acts on the mandrel bar during rolling other than the force originating from the rolling rolls. On the other hand, a semi-float type mandrel mill is equipped with a device that can drive the mandrel bar at a constant speed, and the bar and drive device are separated before the end of rolling.

The wall thickness distribution of the shell rolled by the above-mentioned full-float mandrel mill is such that the wall thickness at both tube ends (hereinafter referred to as "unsteady rolling section"), which is not affected by the tension between the stands, is compared to the steady rolling section. It becomes thinner by 0.2 to 0.3111m.

A shell with such a wall thickness distribution can be used when the outer diameter processing with the stretch reducer is less than 20% and the drawing processing is small.
The wall thickness distribution of the product remains the same as it was in the mandrel mill, resulting in thinner tube ends and sometimes falling outside the lower limit of the wall thickness dimension.

Therefore, conventionally, during the period of rolling in the unsteady rolling section where the wall thickness is expected to be thin, that is, during the period when the tube is bitten into each roll stand of the mill one after another and the period when it exits each roll stand, the roll A method has been proposed in which the rotational speed is appropriately increased and controlled to increase the thickness of the unsteady rolled portion to make the thickness distribution uniform.

Problems to be Solved by the Invention A method for increasing and controlling the rotational speed of the rolls during the rolling period of the unsteady rolling section to increase the thickness of the unsteady rolling section and making the thickness distribution uniform is as follows: Since the timing of the start of control and the amount of control have a large influence, the effect is small and it has been impossible to make the shell thickness uniform.

An object of the present invention is to provide a method for manufacturing a seamless steel pipe in which the thickness of the unsteady rolling section can be controlled in the same manner as the wall thickness of the steady rolling section in a full-float mandrel mill.

Means for Solving the Problems In order to achieve the above objectives, in the production of seamless steel pipes using a full-float mandrel mill, thinning of the unsteady rolled part during mandrel mill rolling is prevented, and a stable shell shape and wall thickness are achieved. As a result of testing and research to obtain the thickness distribution, the roll gap of each stand when passing through the unsteady rolling section was set to 01 to 0.3 mm from the roll gap during steady rolling.
The inventors have discovered that a stable shell shape and thickness distribution can be obtained by increasing the thickness by opening the shell, and have thus arrived at the present invention.

That is, the present invention provides a method for manufacturing a seamless steel pipe using a full-float type mandrel mill, in which the roll gap of the rolling stand when the pipe passes from 1000 to 1500 mm at the leading and trailing ends is 0.0 mm larger than the roll gap during steady rolling.
Rolling is performed with an opening of 1 to 0.3 mm.

Function In this invention, the tube tip and the rear end 1000 to 15
Since rolling is performed with the roll gap of the rolling stand 0.1 to 0.3 mm wider than the roll gap during steady rolling when passing 0.00 mm, the wall thickness of the unsteady rolling part is 0.1 to 0.0 mm.
The thickness is increased by 2mm, and the thickness distribution of the shell is made uniform.

The unsteady rolling part in this invention is 1000 to 1
The reason for setting it to 500 mm is that in conventional full-float type mandrel mills, the thinning of the shell R occurs concentrated at 1000 to 1500 mm from the tip and rear ends.

The roll gap of the rolling stand when passing through the unsteady rolling section should be 0.1 to 0.3 m larger than the roll gap during steady rolling.
If the m opening is less than 0.1 mm, the unsteady rolling part will not be thick enough, and if it exceeds 0.3 mm, the thickness of the unsteady rolling part will be greater than that of the steady rolling part. This is because the thickness of the shell becomes thick and the thickness distribution of the shell is not uniform.

Adjustment of the roll gap between the stands when passing through the unsteady rolling section in this invention is effective only at the final stand of the mandrel mill and the stand before it, but it can also be applied to all stands.

In order to adjust the roll gap of the rolling stand when passing through the unsteady rolling section in this invention, a shell edge detection device is installed in front of the rolling stand to detect passage of the front and rear ends of the shell, and the detection signal is used to control the roll interval. The roll gap may be controlled to be 0.1 to 0.3 mm wider than the roll gap during steady rolling for a predetermined period of time by inputting data into the device.

Example No. In a full-float mandrel mill consisting of stands 1 to 7, a round billet having the composition shown in Table 1 was pierced with a piercer, and a blank tube was obtained under the control conditions shown in Table 2. When the steady rolling section passed through stands No. 6, No. 7, and No. 7, rolling was performed with the roll gap opened from the roll gap during steady rolling.

Margin table below (unit: wt%) Obtained outer diameter 198 mm, wall thickness 11.0 mm, length 1
A 1300111 m glue full was finished using a stretch reducer to have an outer diameter of 177.8 mm, a wall thickness of 11.5 mm, and a length IJ of 950 mm.

In that case, the fluctuation of the rolling load in the mandrel mill No. 6 stand and the fluctuation of the roll gap using the roll gap during steady rolling as the reference cap are 1st rZ! (a
) Shown in J3 Yohi (b). In addition, Figure 2 (
. Shown in l).

Note that when the unsteady rolling section passed through stands No. 6, No. 6, and No. 7, rolling was performed under the same conditions as above, except that the roll gap was not adjusted and rolling was performed using the roll gap during steady rolling. The results of measuring the wall thickness of the rear end of the product finished with the stretch reducer in that case are shown in FIG. 2(b).

As shown in Fig. 1 (a) and (b), the unsteady rolling part is N
When passing through stands No. 6 and No. 7, the rolling load at No. 6 stand when the roll gap is controlled as shown in Table 2 is reduced by 10 to 20 tons or more compared to the rolling load at the steady rolling section. The roll gap when passing through the unsteady rolling section is 0.2 compared to the standard gap.
~0.3mm open.

As a result, as shown in Figure 2 (a), the wall thickness of the product after finishing with the stretch reducer was ±0.4 m at the rear end.
m or less. On the other hand, if the roll gap of the stand is not adjusted when passing through the unsteady rolling section, as shown in Figure 2 (
As shown in b), the wall thickness of the product after finishing with the stretch reducer varies greatly, with a thickness of 7 mm.

Effects of the Invention As described above, according to the method of the invention, the thickness distribution in the longitudinal direction of the shell in the full-float mandrel mill during seamless steel pipe production is made uniform, and the thickness distribution in the subsequent finish rolling with the stretch reducer is made uniform. It is possible to reduce the rate of defective thin walls due to non-uniform thickness distribution.

[Brief explanation of drawings]

Figure 1 (a) is a measurement chart of the rolling load in No. 6 stands of the full-float type mandrel mill in the example, Figure (b) is a measurement chart of the roll gap, and Figure 2 (a) is the example Figure (b) shows the wall thickness measurement chart near the rear end of the tube of the product after finish rolling when gap adjustment is performed, and (b) shows the wall thickness measurement chart near the rear end of the tube of the product after finish rolling when gap adjustment is not performed. This is a wall thickness measurement chart. Applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] 1. In a method for manufacturing a seamless pipe using a full-float mandrel mill, the pipe tip and rear end 1000 to 15
1. A method for manufacturing a seamless steel pipe, characterized in that rolling is performed with a roll gap of a rolling stand opened 0.1 to 0.3 mm from a roll gap during steady rolling when 00 mm is passed.