JP2897700B2 - 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 mandrel mill rolling method capable of equalizing the temperature at the time of rolling a mandrel bar inserted into a hollow shell when manufacturing a seamless steel pipe by a mandrel mill method.

[0002]

2. Description of the Related Art A seamless steel pipe is manufactured by mandrel mill rolling. A round billet of a material is heated in a rotary hearth heating furnace, and then drilled with a drilling machine to form a hollow shell. After inserting the mandrel bar coated in a skewer shape and elongating and rolling to a predetermined size with a mandrel mill, pulling out the mandrel bar from the tube, reheating in a reheating furnace, descaling with high-pressure water, and using a multi-stand It can be finished to predetermined product dimensions with a stretch reducer.

In mandrel mill rolling, a hollow shell having a mandrel bar inserted on a bar inserter conveyor is conveyed to a mandrel mill together with the mandrel bar. The tube drawn and rolled by the mandrel mill is kicked out of the run-out conveyor together with the mandrel bar and sent to a stripper table, where the mandrel bar is pulled out. This pulled out mandrel bar
After being cooled with water in a cooling tank, the lubricant is applied to the surface, and then returned to the bar inserter conveyor for reuse.

[0004] The lubricant applied to the mandrel bar is 11
It acts as a protective coating for preventing seizure of the mandrel bar inserted into the hollow shell at 00 to 1200 ° C, reduces friction between the mandrel bar and the hollow shell during elongation rolling, and reduces the shell shape and thickness. It is intended to stabilize the distribution and to facilitate pulling out the mandrel bar from the rolled material after elongation rolling.In order to secure these functions, controlling the lubricant film thickness is an important management item. Has become.

[0005] The thickness of the lubricant applied to the mandrel bar can be controlled by the moving speed of the mandrel bar at the time of application, even if the supply amount and viscosity of the lubricant are set to predetermined values in accordance with the dimensional specifications of the mandrel bar. It is inevitable that the temperature changes depending on the temperature. That is, the thickness of the lubricant becomes thinner as the temperature of the mandrel bar increases, and the amount of adhesion decreases even when the temperature becomes too low, and becomes thinner. It gets thicker as it gets higher.

As a countermeasure, a method of controlling the flow rate and concentration of the lubricant applied to the mandrel bar in accordance with the longitudinal temperature distribution of the mandrel bar (Japanese Patent Laid-Open No. 58-10 / 1983).
No. 7203), a transfer table for conveying a mandrel bar while rotating the mandrel bar in a direction perpendicular to the axial direction thereof,
Heating means provided in the substantially used base end passage area of the mandrel bar above and below the transfer table, and a plurality of divisions in the axial direction of the substantially used area of the mandrel bar other than the heating area above and below the transfer table, In addition, a uniform cooling device for a mandrel bar comprising a plurality of cooling medium injection nozzles arranged in the transfer direction (Japanese Patent Laid-Open No.
No. 1-42405), a lubricant is applied to the surface of the mandrel bar while moving the bar, the thickness of the applied lubricant is measured, and a deviation between the measured film thickness and a predetermined target film thickness is obtained. A lubricant supply amount for solving this problem is obtained, and if the supply amount is within a predetermined controllable range, the supply amount is adjusted.If the supply amount exceeds the controllable range, the supply amount is adjusted. There has been proposed a method including a step of controlling the mandrel bar speed while maintaining the mandrel bar speed within the controllable range (Japanese Patent Laid-Open No. 3-210905).

[0007]

SUMMARY OF THE INVENTION The above-mentioned JP-A-58-10
The method disclosed in Japanese Patent No. 7203 controls the flow rate and concentration of the lubricant by focusing only on the temperature distribution in the longitudinal direction of the mandrel bar, and it is difficult to delicately adjust the flow rate and concentration of the highly viscous lubricant. There is a problem that it is not possible to control the film thickness in an appropriate manner. Further, the method disclosed in JP-A-61-42405 is to cool the mandrel bar uniformly, but it is difficult to delicately control the temperature of the mandrel bar whose temperature changes in the longitudinal direction, and it There is a problem that control is not possible. Further, the method disclosed in Japanese Patent Application Laid-Open No. 3-210905 calculates a deviation between a measured film thickness and a predetermined target film thickness, and controls a lubricant supply amount and a mandrel bar speed in order to eliminate the deviation. However, the temperature of the mandrel bar is not constant in the longitudinal direction, and even if the supply amount of the lubricant is controlled correspondingly, not all of the supply amount is applied and applied, and the mandrel bar speed is controlled. It is difficult to control the thickness, and there is a problem that the film thickness cannot be sufficiently controlled.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mandrel mill rolling method which can solve the above-mentioned disadvantages of the prior art, can maintain the temperature of the entire length of the used area of the mandrel bar almost constant, and can control the lubricant film thickness to the target film thickness. To provide.

[0009]

Means for Solving the Problems The present inventor has conducted various tests and studies to achieve the above object. As a result, the temperature distribution of the mandrel bar was found to be high or low at the same longitudinal position due to the mill characteristics, and the amount of protrusion of the mandrel bar from the hollow shell was determined for each pass. The present inventors have found that it is most effective to control the temperature of the mandrel bar by moving the mandrel bar at a high temperature without fixing the portion where the temperature is high, and arrived at the present invention.

That is, the present invention provides a method of elongating and rolling a hollow shell into which a mandrel bar coated with a lubricant is inserted by a mandrel mill, wherein the amount of protrusion of the mandrel bar from the hollow shell is varied for each pass. A mandrel mill rolling method characterized by moving a high-temperature portion of the mandrel bar to make the heat history of the mandrel bar uniform.

Further, the present invention provides a method for elongating and rolling a hollow shell into which a mandrel bar coated with a lubricant is inserted by a mandrel mill, wherein the amount of protrusion of the mandrel bar from the hollow shell is varied for each pass. In addition, by moving the high temperature part of the mandrel bar to make the heat history of the mandrel bar uniform and changing the lubricant application area of the mandrel bar according to the amount of protrusion of the mandrel bar from the hollow shell And a mandrel mill rolling method.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 5, a temperature distribution of a used portion of a mandrel bar in a mandrel mill usually fluctuates in a range of 50 to 200 ° C. Therefore, a lubricant is applied at a target film thickness of 50 μm. However, as shown in FIG.
In a low-temperature portion of 100 ° C. or lower and a high-temperature portion of 150 ° C. or higher, the amount of the attached lubricant is small, and the thickness of the lubricant becomes thin. For this reason, in the elongation rolling of the mandrel mill,
The wall thickness distribution over the entire length of the pipe becomes non-uniform. In particular, in a full float mandrel mill, not only a thickening phenomenon called a stomak occurs, but also the surface roughness of the mandrel bar tends to occur, and the burst ripping property deteriorates.

In the present invention, for example, as shown in FIG. 4, when the set amount of the normal mandrel bar projecting from the hollow shell is X (m), the mandrel bar is moved by 1 m every rolling pass number of times. By moving the high temperature part of the mandrel bar for each rolling pass to equalize the heat history of the mandrel bar, it is possible to easily control the cooling of the mandrel bar and easily uniform the lubricant film thickness can do.

Further, in the present invention, the set amount of protrusion of the mandrel bar from the hollow shell is varied for each rolling pass, and the portion of the mandrel bar where the temperature becomes high is moved to uniform the heat history of the mandrel bar. At the same time, by changing the application area of the lubricant on the mandrel bar according to the amount of protrusion of the mandrel bar from the hollow shell, the cooling of the mandrel bar can be easily controlled, and the control of the lubricant film thickness is easy. Not only can be performed, but also can prevent the surface roughness of the mandrel bar,
In addition, since lubricant can be applied to the minimum required area,
This leads to an improvement in the basic unit of lubricant.

The length by which the set amount of the ordinary mandrel bar protruding from the hollow shell is moved for each rolling pass is not particularly limited, and the length, outer diameter, and diameter of the mandrel bar are not particularly limited. What is necessary is just to determine suitably according to a material, the extending | stretching amount, the site | part which becomes high temperature of a mandrel bar, etc. In addition,
As a particularly desirable range, 1-2 m is desirable, and 1 m
In the following, the temperature distribution is not eliminated, and when it is 2 m or more, the temperature change is rather promoted. Furthermore, the lubricant application range must be applied to the range that contributes to the rolling of the hollow shell, and the rolling portion of the bar changes according to the change in the amount of protrusion of the mandrel bar. Change the application range.

[0016]

EXAMPLE In a mandrel mill consisting of eight stands, a tip of a mandrel bar protruded from 8000 mm to 1000 m in a hollow shell 8 m long pierced by a piercer.
By repeating the three steps up to 6000 mm by shortening each rolling pass by mm, the outer diameter is 198 mm and the wall thickness is 6.5.
mm, the case of the present invention stretched 150 times to a length of 28000 mm, and a mandrel bar tip protrusion amount of 8000 mm
Constant outer diameter 198mm, wall thickness 6.5mm, length 2800
The relationship between the distance from the tip of the mandrel bar after 150 passes and the temperature of the mandrel bar, the change in the surface roughness of the mandrel bar, the increase in ΔRz, and the mandrel burst ripping property were measured for each of the conventional examples stretched 150 times to 0 mm. . The results are shown in FIGS. In addition, the change in the surface roughness of the mandrel bar is obtained by measuring the surface roughness before and after use by the stylus method, and calculating the surface roughness increase ΔRz from the ten-point average roughness Rz before and after use, Mandrel burst ripping was evaluated by the load current during burst ripping. The lubricant film thickness on the mandrel bar was set to 50 μm in both the present invention example and the conventional example.

As shown in FIG. 1, in the embodiment of the present invention, the temperature of the mandrel bar is kept constant at about 100 ° C. over the entire length, whereas in the conventional example, the tip of the mandrel bar is about 50 ° C. From 13 to 20m at 200 ° C
It is rising. As a result, as shown in FIG. 2, in the example of the present invention, there is almost no increase ΔRz in the surface roughness of the mandrel bar, whereas in the conventional example, the increase ΔRz in the surface roughness exceeds 5 μm. Further, as shown in FIG. 3, in the example of the present invention, the burst ripping current is 1500 A, whereas the value of the conventional example is close to 3000 A.

[0018]

As described above, according to the method of the present invention, the temperature of the mandrel bar can be kept almost constant over the entire length, and the elongation rolling can be stably performed in the longitudinal direction, and the stomak phenomenon can be suppressed. Also, the surface roughness of the mandrel bar main body can be reduced, and the stripping property can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the distance from the tip of the mandrel bar and the temperature of the mandrel bar of the example of the present invention and the comparative example in the example.

FIG. 2 is a graph showing mandrel bar surface roughness increase ΔRz of an example of the present invention and a comparative example in an example.

FIG. 3 is a graph showing bar strip currents of an example of the present invention and a comparative example in an example.

FIG. 4 is a graph showing an example of a pattern when the amount of protrusion of the mandrel bar of the present invention into the hollow shell is changed, and is a graph showing the relationship between the number of rolling passes of the mandrel bar and the amount of protrusion.

FIG. 5 is a graph showing an example of a temperature distribution from a tip of a portion where a mandrel bar is used before a lubricant is applied in a conventional mandrel mill.

6 is a graph showing a lubricant film thickness distribution from the tip of a mandrel bar using portion under the conditions of FIG. 5;

Claims (2)

(57) [Claims] In a method of elongating and rolling a hollow shell into which a mandrel bar coated with a lubricant has been inserted by a mandrel mill, the amount of protrusion of the mandrel bar from the hollow shell is changed for each pass, and A method for rolling a mandrel mill, comprising: moving a hot portion to make the heat history of the mandrel bar uniform. 2. A method for elongating and rolling a hollow shell into which a mandrel bar coated with a lubricant has been inserted by means of a mandrel mill, wherein the amount of protrusion of the mandrel bar from the hollow shell is varied for each number of passes. It is characterized by moving the high temperature part to make the heat history of the mandrel bar uniform and changing the lubricant application area of the mandrel bar according to the amount of protrusion of the mandrel bar from the hollow shell. Mandrel mill rolling method.