JP2636689B2 - Mandrel mill rolling method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled material capable of obtaining a rolled material having a stable wall thickness and dimensional distribution even when the friction coefficient of a mandrel bar fluctuates in the manufacture of a seamless tube by a mandrel mill method. About the method.

[0002]

2. Description of the Related Art A seamless pipe manufactured by a mandrel mill system is manufactured by heating a round steel slab of a material in a rotary hearth type heating furnace, and then piercing and rolling it with a Mannesmann piercing machine to form a hollow shell.
Next, the mandrel bar is inserted into the hollow shell, stretched and rolled to a predetermined size by a mandrel mill, and then the mandrel bar is pulled out of the tube. The tube is heated in a reheating furnace, descaled, finished to a required outer diameter and thickness by a stretch reducer, cooled, cut to a required length, and sent to a finishing line.

[0003] In the manufacture of a seamless tube by the mandrel mill method, in the mandrel mill, a lubricant is applied to the surface of the mandrel bar for the purpose of protecting the surface of the mandrel bar, stabilizing the shell shape, and mandrel burst ripping. Shell shape and wall thickness in the above mandrel mill rolling, along with the number of roll rotation, roll hole,
Affected by friction between mandrel bar and material. Therefore, in order to make the friction coefficient between the mandrel bar and the material in the circumferential and longitudinal directions uniform (hereinafter referred to as the bar friction coefficient) and to obtain a stable shell shape and thickness distribution, a lubricant film applied to the surface of the mandrel bar A method for managing thickness has been proposed.

For example, Japanese Patent Application Laid-Open No. 58-107203 discloses a method of controlling the flow rate and concentration of a lubricant when a lubricant is applied to the surface of a mandrel bar. Japanese Patent Application Laid-Open No. Sho 61-42405 discloses a method for controlling the cooling of a mandrel bar. Further, as another method, there has been proposed a shape control method for adjusting the number of rolls of each stand of a mandrel mill and the roll gap in order to make the dimension distribution uniform from the viewpoint of rolling control.

[0005]

SUMMARY OF THE INVENTION The above-mentioned JP-A-58-10
The method described in JP-A-7203 and JP-A-61-42405 manages the thickness of the lubricant applied to the mandrel bar uniformly, eliminates the fluctuation of the bar friction coefficient, and makes the thickness distribution uniform. Things. Therefore, it is not possible to cope with the fluctuation of the bar friction coefficient, and it is impossible to obtain a stable shell shape and wall thickness distribution.

An object of the present invention is to provide a mandrel mill rolling method capable of obtaining a stable shell shape and thickness distribution even when the bar friction coefficient changes.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies and studies to achieve the above object. As a result, in the manufacture of seamless pipes by the mandrel mill method, as a result of testing and research on obtaining a stable shell shape and wall thickness distribution in response to the fluctuation of the bar friction coefficient during mandrel mill rolling, it was applied to the mandrel bar. It has been found that there is a certain relationship between the lubricant film thickness and the bar friction coefficient. Therefore, if the thickness of the lubricant applied to the mandrel bar is measured at regular intervals and the bar friction coefficient is determined, and the roll speed and roll gap during rolling are controlled for each roll according to the variation, a stable shell can be obtained. The inventors have determined that a shape and thickness distribution can be obtained, and have reached the present invention.

That is, the present invention relates to a method of manufacturing a seamless pipe by a mandrel mill method, wherein the thickness of a lubricant applied to a mandrel bar is measured at regular intervals, and the thickness of the lubricant and the friction determined in advance by an experiment are determined. A mandrel mill rolling method is characterized in that a bar friction coefficient is determined from a relationship with a coefficient and a roll rotation speed of each stand is corrected for each stand.

The bar average friction coefficient in the longitudinal direction of the mandrel bar is determined as the bar friction coefficient.
Further, as a bar friction coefficient, a bar friction coefficient distribution in a longitudinal direction of the mandrel bar is obtained, and during each rolling, for each stand,
This is performed based on the bar friction coefficient determined by predicting the position of the mandrel bar.

[0010]

According to the present invention, during the production of a seamless tube, the thickness of the lubricant applied to the mandrel bar is measured at regular intervals, and the relationship between the thickness of the lubricant and the coefficient of friction obtained in advance through experiments is determined. Since the bar friction coefficient is determined and the rolling speed of each stand is corrected for each stand and rolling is performed, even if the amount of lubricant applied to the mandrel bar changes and the bar friction coefficient fluctuates, the mandrel is also changed. The bar friction coefficient is predicted from the amount of the lubricant adhering to the bar, and the roll rotation speed is changed for each roll in accordance with the bar friction coefficient. For this reason, even if the friction coefficient of the bar fluctuates due to the fluctuation of the film thickness of the lubricant applied to the mandrel bar, the circumferential and longitudinal wall thickness distribution of the shell is made uniform, and the mandrel mill rolling is stabilized. You can do it.

In the present invention, the measurement of the lubricant film thickness is performed by
Use an electromagnetic coating measuring device. In the electromagnetic coating measuring device, the magnetic resistance changes depending on the thickness of the nonmagnetic coating,
The change in the magnetic resistance is converted into a voltage to measure the thickness of the coating. Then, based on the measured lubricant film thickness, a bar friction coefficient is determined from a diagram showing the relationship between the lubricant film thickness obtained by an experiment in advance and the bar friction coefficient. The roll rotation speed is corrected based on the relationship between the obtained bar friction coefficient and the roll rotation speed pattern of each stand. in this case,
The relationship between the bar friction coefficient and the roll rotational speed pattern of each stand is determined for each shell size, and the roll rotational speed is corrected by selecting and using the shell size according to the shell size.

There are two methods of correcting the roll rotation speed based on the bar friction coefficient in the present invention. One of them is to calculate the bar average friction coefficient from the lubricant film thickness measured at regular intervals in the longitudinal direction of the mandrel bar, and to determine the bar average friction coefficient from the relationship between the bar friction coefficient and the roll rotation speed pattern of each stand. A method of correcting the roll rotation speed. The other is to determine the bar friction coefficient distribution in the longitudinal direction of the mandrel bar from the lubricant film thickness measured at regular intervals in the longitudinal direction of the mandrel bar, and to predict the position of the mandrel bar for each stand and determine the bar position. This is a method for correcting the number of rotations of the roll according to the friction coefficient.

[0013]

Embodiment 1 The details of the method of the present invention will be described below with reference to FIGS. 1 to 3 showing an embodiment. FIG. 1 is a schematic layout diagram of a mandrel mill factory, FIG. 2 is a graph showing an example of a relationship between a material of a hollow shell, a film thickness of a lubricant, and a bar friction coefficient, and FIG. 4 is a graph illustrating an example of a relationship between rotation speed ratios. In FIG. 1, 1 is a mandrel bar cooling floor, 2 is a mandrel bar cooled by the mandrel bar cooling floor 1, and 3 is a lubricant coating device, which is conveyed while controlling the conveying speed by a conveyor or a vertical feed chain (not shown). The lubricant is sprayed from the nozzle onto the surface of the mandrel bar 2 when passing through the mandrel bar 2. Reference numeral 4 denotes a lubricant film thickness measurement device provided immediately after the lubricant application device, and the lubricant film thickness of the mandrel bar 2 coated with the lubricant is measured at regular intervals.

Reference numeral 5 denotes an inserter table, 6 denotes a hollow shell, 7 denotes a mandrel mill rolling machine, and the inserter table 5 rolls the hollow shell 6 into which the mandrel bar 2 coated with a lubricant is inserted. Reference numeral 8 denotes a stripper line, which is a hollow shell 6 rolled by a mandrel mill 7
The mandrel bar 2 is pulled out from the container and is conveyed to the mandrel bar cooling floor 1. In addition, 9 is a reheating furnace, and 10 and 11 are thermometers of the mandrel bar 2. The lubricant film thickness of the mandrel bar 2 measured by the film thickness measuring device 4 is input to a rolling schedule control device of a mandrel mill rolling mill 7 (not shown). In the rolling schedule control device, for example, as shown in FIG. 2, the relationship between the material of the hollow shell, the thickness of the lubricant, and the bar friction coefficient is input in advance. The bar friction coefficient is determined based on the lubricant film thickness, and the roll rotation speed is corrected based on the relationship between the rotation speed ratios of the respective stands due to the fluctuation of the bar friction coefficient as separately stored, for example, as shown in FIG. It is configured.

There are two methods for controlling the number of roll rotations. One of them is to calculate the average bar friction coefficient from the input lubricant film thickness measurements at regular intervals, and to determine the relationship between the material of the hollow shell, the lubricant film thickness and the bar friction coefficient as shown in FIG. This is a method of correcting the roll rotation speed in accordance with the fluctuation of the average bar friction coefficient. The other is to obtain a bar friction coefficient distribution in the longitudinal direction of the mandrel bar 2 from the input lubricant film thickness measurement values at regular intervals, and during rolling, for each rolling stand,
This is a method in which the rotational speed is corrected according to the bar friction coefficient determined by predicting the position of the mandrel bar 2. The rotation speed correction method in this case is as follows.

[0016]

## EQU1 ## Corrected rotation speed Ni (t) of i-stand at time t
Is Ns: number of stands ni: reference rotation number of i stand μi (t): bar friction coefficient immediately below i stand at time t fi: rotation number correction corresponding to fluctuation of friction coefficient immediately below i stand gij: j stand (j ≠) i) i-stand rotation speed correction due to friction coefficient fluctuation

In this way, by performing rolling while changing the roll rotation speed of each stand in accordance with the rolling position of the mandrel bar, ie, the bar friction coefficient calculated from the bar friction coefficient distribution, the length of the rolled material can be increased. The thickness distribution in the direction is made uniform, and stabilization of mandrel mill rolling can be achieved.

Example 2 C: 0.20%, Si: 0.18%, Mn: 0.72
%, P: 0.010%, S: 0.012%, a round billet consisting of the balance Fe and unavoidable impurities was formed into a hollow shell by perforating with a Mannesmann perforator, and when this was rolled by a mandrel mill, When the thickness of the lubricant applied to the mandrel bar was measured at intervals of 50 cm using an electromagnetic coating measuring device, the average thickness was 55 μm and the average bar friction coefficient was 0.12. Using the average bar friction coefficient, the rotation speed of the roll was corrected according to the average bar friction coefficient fluctuation from the relationship between the bar friction coefficient and the rotation speed pattern for each size, and the hollow shell into which the mandrel bar was inserted was rolled. The thickness distribution in the longitudinal direction of the obtained shell was measured. Table 1 shows the results. For comparison, Table 1 shows the results of a conventional method in which rolling was performed under the same conditions except that the film thickness of the lubricant was not measured and the roll rotation speed was set to the reference rotation speed.

[0019]

[Table 1]

As shown in Table 1, when constant diameter rolling was carried out by the conventional method, the thickness variation width in the longitudinal direction of the shell ± 0.5.
mm, but the thickness of the lubricant applied to the mandrel bar is measured to obtain a bar average friction coefficient, and in the case of this invention method in which the roll rotation speed of each stand is corrected based on the bar average friction coefficient, , The thickness variation width in the longitudinal direction of the shell ±
0.3 mm.

Example 3 C: 0.51%, Si: 0.31%, Mn: 0.75
%, P: 0.018%, S: 0.010%, a round billet consisting of the balance Fe and unavoidable impurities was formed into a hollow shell by punching with a Mannesmann drilling machine, and when this was rolled with a mandrel mill, The thickness of the lubricant applied to the mandrel bar was measured at intervals of 50 cm using an electromagnetic coating measuring device. The thickness distribution in the longitudinal direction of the mandrel bar was 40 to 80 μm. Bar friction coefficient distribution is calculated based on the film thickness distribution in the longitudinal direction of the mandrel bar. The rolling was performed after correcting the number of rotations according to. The thickness distribution in the longitudinal direction of the obtained shell was measured. Table 2 shows the results.

[0022]

[Table 2]

As shown in Table 2, a bar friction coefficient distribution was obtained from the lubricant film thickness distribution in the longitudinal direction of the mandrel bar.
During rolling, the position of the mandrel bar is predicted for each stand, and when the rolling is performed with the rotation speed corrected according to the bar friction coefficient based on the relationship between the bar friction coefficient and the rotation speed pattern for each size, the bar shown in Table 1 is used. The thickness variation width in the longitudinal direction of the shell is smaller than in the case where the rotation speed is corrected according to the average friction coefficient.

[0024]

As described above, according to the method of the present invention, the wall thickness distribution in the longitudinal direction of the shell in the mandrel mill during seamless pipe manufacturing can be made uniform.

[Brief description of the drawings]

FIG. 1 is a schematic layout view of a mandrel mill factory.

FIG. 2 is a graph showing an example of a relationship among a material of a hollow shell, a film thickness of a lubricant, and a bar friction coefficient.

FIG. 3 is a graph showing an example of a relationship between rotation speed ratios of each stand due to a change in a bar friction coefficient.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling floor 2 Mandrel bar 3 Lubricant coating device 4 Film thickness measuring device 5 Inserter 6 Hollow shell 7 Mandrel mill 8 Stripper line 9 Reheating furnace 10, 11 Thermometer

Claims (3)

(57) [Claims] In a method for manufacturing a seamless pipe by a mandrel mill method, the thickness of a lubricant applied to a mandrel bar is measured at regular intervals, and the thickness of the lubricant and the friction coefficient obtained in advance by experiment are determined. A mandrel mill rolling method, wherein a friction coefficient of a mandrel bar is obtained from the relationship, and the roll rotation speed of each stand is corrected for each stand. 2. The mandrel mill rolling method according to claim 1, wherein the average friction coefficient in the longitudinal direction of the mandrel bar is obtained as the friction coefficient of the mandrel bar. 3. The method according to claim 1, wherein a friction coefficient distribution in a longitudinal direction of the mandrel bar is obtained as a friction coefficient of the mandrel bar, and the rolling is performed according to a friction coefficient determined by predicting the position of the mandrel bar for each stand during rolling. Item 4. The mandrel mill rolling method according to Item 1.