JPH06106238A - Method for drawing mandrel bar in manufacture of seamless steel tube - Google Patents

Abstract

PURPOSE:To prevent the temperature of a tube stock when a mandrel bar is drawn from being lowered and restrain the shape of the end part of the tube stock from deteriorating when the mandrel bar comes in contact with a stopper. CONSTITUTION:When a seamless steel tube is manufactured by the Mannesmann mandrel mill method, in a method that the end part of the tube stock after it is rolled by the mandrel mill is brought into contact with a die or the stopper to draw a mandrel bar from the tube stock, the drawing speed is decelerated to the low speed before the end part of the tube stock comes in contact with the die or the stopper and when drawing is started the drawing speed of the mandrel bar is accelerated to a high speed. In this way, reduction of yield by cutting off the tube end bad in shape can be refrained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of seamless steel pipe by the Mannesmann mandrel mill method, which suppresses deterioration of the shape of the end of the raw pipe at the time of drawing the mandrel bar from the raw pipe after stretch rolling. The method of pulling out the mandrel bar at the time.

[0002]

2. Description of the Related Art Normally, a seamless steel pipe is pierced at the center of a heated round steel piece by using a piercing and rolling machine such as a Mannesmann piercer, and a cored bar is inserted into the obtained hollow shell to make a mandrel mill or the like. It is a general manufacturing method that a product having a predetermined outer diameter and a predetermined wall thickness is finished by being stretch-rolled by the above-mentioned stretch-rolling machine and further drawn by a reduction-rolling machine such as a stretch reducer. The stretch reducer most widely used as a rolling mill is usually composed of 8 to 24 stands,
The main purpose is to reduce the outer diameter of the raw tube stretch-rolled by a stretch-rolling machine such as a mandrel mill to reduce the outer diameter to a product size.

The mandrel mill of the drawing and rolling mill in the production of the seamless steel pipe by the above-mentioned Mannesmann mandrel mill system has a roll stand consisting of a pair of hole type rolls.
It is composed of a multi-stand continuous rolling mill in which 9 units are alternately arranged at an inclination of 90 °, and a mandrel bar is inserted into the hollow shell pipe perforated by the piercing and rolling mill, and the outer diameter and the thickness between the hole-type roll and the mandrel bar are increased. Stretch rolling is performed by a method of reducing the thickness. The mandrel bar stretched and rolled by the mandrel mill is a method of pulling the mandrel bar from the mandrel bar by an extractor in the rolling line, and the mandrel bar is conveyed to another line. There is a method to pull out from the tube.

The method of transporting the drawn and rolled element pipe and the mandrel bar to another line and pulling out the mandrel bar from the element pipe is generally performed by applying the end of the element pipe to a stopper. In this case, the drawing of the mandrel bar is carried out by pulling out the mandrel bar from the stretch-rolled raw tube with a constant drawing speed.

[0005]

When the mandrel bar is pulled out from the raw tube which has been stretch-rolled while keeping the pulling speed constant, when the mandrel bar is pulled out at a high speed, the raw tube is impacted by the contact with the stopper. In order to prevent the end shape from deteriorating and to prevent rolling trouble in the stretch reducer which is the subsequent drawing and rolling machine, it is necessary to cut off the portion with the poor pipe end shape, resulting in a decrease in yield. If the mandrel bar is pulled out at a low speed, it is possible to suppress the deterioration of the end pipe shape due to the impact when it comes into contact with the stopper, but the processing time becomes longer and workability deteriorates, and the temperature of the raw pipe drops. Then, there is a problem in that the mandrel bar pulling operation becomes impossible due to the contraction.

The object of the present invention is to prevent the temperature of the stretch-rolled raw pipe from being lowered when the mandrel bar is pulled out from the stretch-rolled raw pipe, and to suppress the deterioration of the shape of the raw pipe end contacting the stopper. It is to provide a method of pulling out a mandrel bar that can be used.

[0007]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object. As a result, when pulling out the mandrel bar from the stretch-rolled blank pipe, it is slowed down to a low speed before the end of the blank pipe contacts the stopper, and when the pulling is started, the pulling speed of the mandrel bar is accelerated to a high speed. By pulling out, it was clarified that it is possible to suppress the deterioration of the shape of the end portion of the raw pipe due to the impact at the time of contact with the stopper,
This invention was reached.

That is, the present invention is a method of pulling a mandrel bar from a raw pipe by abutting the end of the raw pipe after stretching and rolling in the mandrel mill against a die or a stopper when manufacturing a seamless steel pipe by the Mannesmann mandrel mill system. In the above method, the end of the raw tube is decelerated to a low speed before it comes into contact with the die or the stopper, and when the drawing is started, the drawing speed of the mandrel bar is accelerated to a high speed.

[0009]

In the present invention, when the mandrel bar is pulled out from the raw pipe after being stretch-rolled by the mandrel mill using the die or the stopper, the speed is reduced to a low speed before the end of the raw pipe contacts the die or the stopper. When the drawing of the mandrel bar is started from the tube, the drawing speed of the mandrel bar is accelerated so that the drawing speed of the mandrel bar is accelerated.Therefore, the drawing speed of the mandrel bar becomes low at the start of drawing when the end of the tube touches the die or stopper. Therefore, the deterioration of the shape of the end portion of the raw pipe due to the impact at the time of contact with the die or the stopper is suppressed. In addition, when the drawing is started, the drawing speed of the mandrel bar is accelerated to a high speed, so that the temperature of the raw tube is prevented from dropping, and the mandrel bar drawing work is not disabled, and the mandrel bar can be drawn stably. You can

The acceleration / deceleration pattern of the drawing speed of the mandrel bar is such that the end of the raw pipe is decelerated to a low speed before coming into contact with the die or the stopper, and is accelerated to a high speed when the drawing is started. The roller chain speed is switched from high speed to low speed two seconds before the contact with the die or the stopper, and the roller chain speed is switched from low speed to high speed one second after the end of the raw pipe contacts the die or stopper. This mandrel bar withdrawal speed acceleration / deceleration pattern varies depending on the mandrel bar withdrawal characteristics that depend on the outer diameter of the raw pipe, wall thickness, chemical composition of the raw pipe, mandrel bar temperature, mandrel bar lubrication, etc. , It may be determined based on experiments and the like.

[0011]

【Example】

Example 1 Outer diameter 151.0 mm, wall thickness 4.0 mm, length 25,000 mm stretch-rolled by a 7-stand mandrel mill.
The mandrel bar with an outer diameter of 139.0 mm, which is inserted into the blank tube, is drawn out by changing the drawing speed to 1 to 5.5 m / sec using a stripper with a stopper, and the drawing speed of the mandrel bar and the tube end The relationship with the length of defective shape was measured. The result is shown in FIG. As shown in FIG. 2, the lower the mandrel bar drawing speed is, the shorter the defective shape length of the raw pipe end is. In particular, when the mandrel bar drawing speed is 3 m / sec or less, the defective shape length of the raw pipe end is 100 mm. It is a degree. From this, it is judged that the drawing speed can be reduced to a low speed before the mandrel bar drawing is started, and the drawing speed can be accelerated when the drawing is started, so that the length of the defective shape of the tube end can be suppressed.

Example 2 An outer diameter of 151.0 mm, a wall thickness of 6.0 mm, and a length of 27,000 mm stretched and rolled by a seven-stand mandrel mill.
The mandrel bar having an outer diameter of 135.0 mm inserted in the raw pipe of No. 1 was drawn out in the pulling speed pattern shown in FIG. 1 using a stripper having a stopper under the condition of the raw pipe temperature after stretch rolling of 980 ° C. And withdrawal speed 4
The length of the defective shape of the end of the raw pipe was measured for each of the comparative examples drawn at a constant speed of m / sec. As a result, in the case of the present invention in which the drawing speed pattern shown in FIG. 1 was used, the defective shape length of the raw pipe end was 100 mm, whereas the drawing speed of the comparative example was 4 m / sec. In the case, the length of the defective shape of the tube end is 150 mm
Met.

[0013]

As described above, according to the method of the present invention, the deterioration of the shape of the end portion of the raw pipe can be suppressed, the temperature of the raw pipe can be prevented from lowering, and the mandrel bar can be stably pulled out. The length of the defective shape of the pipe end can be reduced, and the reduction in yield due to the cut-off of the defective shape of the pipe end can be suppressed.

[Brief description of drawings]

FIG. 1 is a graph showing a drawing acceleration / deceleration pattern of a mandrel bar according to the present invention.

FIG. 2 is a graph showing the relationship between the drawing speed of the mandrel bar and the defective length of the tube end.

Claims (1)

[Claims] 1. A method for pulling a mandrel bar from a raw pipe by abutting a die or stopper against the end of the raw pipe after stretch rolling in the mandrel mill during the production of a seamless steel pipe by the Mannesmann mandrel mill system. Decelerate to a low speed before the pipe end abuts the die or stopper,
When the drawing is started, the drawing speed of the mandrel bar is accelerated to a high speed, and the mandrel bar drawing method at the time of manufacturing a seamless steel pipe.