JP2001038407A - Piercing rolling method of seamless metallic pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control diameter reduction of the rear end portion of a hollow material pipe by moving a plug in the direction opposite to the piercing rolling direction when a predetermined portion on the rear end side in the rolling direction is rolled. SOLUTION: When a predetermined portion of a billet reaches a gorge portion 9, a plug 5 is moved in the direction opposite to the advancing direction of the billet 2, thus making thinner the wall thickness of the rear end portion of a hollow material pipe 8 in comparison with the center portion. The plug can be moved continuously till the completion of piercing rolling with a drive unit 10 provided at the rear end of a mandrel, but may be stopped after the wall thickness is reduced to prescribed thickness. When the plug 5 moves, the wall thickness of the rear end portion is made thinner and the outside diameter and the inside diameter are increased, thus preventing diameter reduction of the rear end portion. If the thin portion in wall thickness of the rear end portion is too long, a trouble tends to occur during rolling in the following process, and therefore, the timing for starting to move the plug 5 should be within the range where the distance from the rear end face 2b of the billet 2 to the gorge portion 9 is 0.5 times or more but 5 times or less of the billet diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for piercing and rolling a seamless metal pipe using an inclined rolling mill.

[0002]

2. Description of the Related Art As is well known, in a so-called Mannesmann pipe manufacturing method widely used as a method for manufacturing a seamless metal pipe, a round billet (hereinafter also referred to as a billet) heated to a predetermined temperature is used as a material. A hole is drilled in the axial core portion of the inclined rolling mill having a main roll and a plug (hereinafter, also referred to as a piercer) to obtain a hollow shell. Next, after the hollow shell is expanded or reduced in diameter by an elongator or sizer having the same configuration as the piercer as it is or as necessary, a subsequent drawing mill such as a plug mill or a mandrel mill is used. It is stretched and rolled. afterwards,
A product pipe is manufactured through a refinement process of performing polishing pipe, shape correction and sizing by a rolling mill such as a stretch reducer, a reeler, and a sizer.

In the rolling of the piercer, the rear end of the hollow shell tends to have a smaller outer diameter and inner diameter than the center in the longitudinal direction. For example, the inner diameter of the rear end face is several percent smaller than the inner diameter of the central portion.

If the rear end of the hollow shell is reduced in diameter, the contact area between the rolling roll and the hollow shell, which is the material, is reduced in the subsequent rolling by an elongator or plug mill. The driving force of the hollow shell may be reduced, causing an operation trouble in which the hollow shell stops between the rolls.

[0005] In the rolling by the mandrel mill, if a hollow shell having a reduced diameter is used, the mandrel mill bar may be damaged or a product surface flaw may occur. That is, in the rolling of the mandrel mill, a mandrel bar coated with a lubricant is inserted from the rear end of the hollow shell, and the thickness of the hollow shell is reduced by the grooved roll and the mandrel bar. At this time, the gap between the mandrel bar and the inner surface of the hollow shell is usually set to several mm to about several tens mm in order to prevent the material (hollow shell) from being entangled from the roll. The tube is bent in the longitudinal direction, and it is difficult to match the center of the rear end of the hollow shell with the center axis of the mandrel bar. Therefore, if the rear end surface of the hollow shell is reduced in diameter, the mandrel bar comes into contact with the rear end of the hollow shell when the mandrel bar is inserted into the hollow shell, and the lubricant on the surface of the mandrel bar is peeled off. As a result, seizure occurs between the mandrel bar and the inner surface of the hollow shell, resulting in a decrease in product surface quality and a shortened life of the mandrel bar.

When the mandrel bar is inserted into the hollow shell, the mandrel bar and the hollow shell collide with each other, not only causing the hollow shell to buckle, but also causing serious damage to the mandrel mill entrance equipment. .

In order to prevent the diameter reduction at the rear end of the hollow shell, Japanese Patent Application Laid-Open No. Hei 4-143004 discloses a method in which a plug is moved in the same direction as the billet travels. A method for increasing the thickness has been proposed.

[0008]

The present inventors carried out piercing and rolling based on the method disclosed in the above-mentioned publication, but could not confirm any effect of suppressing the diameter reduction at the rear end of the hollow shell. . The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of piercing and rolling a seamless metal pipe capable of suppressing a diameter reduction of a rear end portion of a hollow shell.

[0009]

Means for Solving the Problems The present inventors conducted various experiments to solve the above-mentioned problems, and when the predetermined portion at the rear end side in the rolling direction of the material was rolled, the plug was billeted. In the direction opposite to the direction of travel,
Preferably, together with this, it has been found that the diameter of the rear end of the hollow shell can be suppressed by tightening the opening degree of the main roll.

The present invention has been completed based on the above findings, and the gist is as follows. (1) Perforation and rolling of a seamless metal pipe to obtain a hollow shell by piercing a raw material with an inclined rolling mill in which a plug is arranged along a pass line between a pair of main rolls arranged obliquely around a pass line A method for piercing and rolling a seamless metal pipe, characterized in that the plug is moved in a direction opposite to the piercing and rolling direction when a predetermined portion on the rear end side in the rolling direction of the material is rolled.

(2) The piercing and rolling of the seamless metal pipe according to the above (1), wherein the opening of the main roll is tightened when the plug is moved in the direction opposite to the piercing and rolling direction. Method.

[0012]

FIG. 1 is a perspective view showing an example of a basic configuration of a piercer according to the present invention. Symbol 1 is piercer, 2
Indicates a billet, 3 indicates a main roll, 4 indicates a disc roll, 5 indicates a plug, 6 indicates a cored bar, and 9 indicates a gorge portion.

As shown in FIG. 1, a piercer 1 has a pair of main rolls 3 which are inclined in opposite directions to each other with a pass line XX serving as a feed line of a billet 2 as a raw material, and are opposed to each other.
3 and a pair of disc rolls 4 and 4 which are arranged so as to be 90 ° out of phase with the main roll with the pass line interposed therebetween, and a plug 5 as a piercing tool is provided on the pass line XX. It is supported by gold 6.

In the piercer configured as described above,
The main rolls 3, 3 are provided at an inclination angle β with respect to the pass line XX, and are rotated in the same direction by a driving device (not shown). For this reason, the billet 2 fed in the direction of the arrow along the pass line XX is bitten between the main rolls 3, and then spirally rotates and moves, and its axis is moved by the shell type plug 5. A hole is made in the core and the wall thickness is gradually reduced to form a hollow shell. At this time, the distance between the main rolls 3 and 3 (hereinafter referred to as the roll opening) and the pass line XX of the plug 5
By adjusting the upper position, a predetermined thickness can be obtained. The disc roll 4 serves to guide the billet 2 between the main rolls, and also suppresses the hollow shell being rolled from expanding in a direction perpendicular to the direction in which the main rolls 3 and 3 face each other, thereby reducing the outer diameter shape. The billet 2 is used to prevent seizure caused by sliding with the perforated hollow shell.
Is driven to rotate in the same direction as the feeding direction. In some cases, a fixed type guide shoe may be used instead of the rotary disk roll 4.

[0015] The fixed type guide shoe is advantageous for adjusting the outer diameter of the hollow shell since the shape of the guide shoe can be changed according to the deformation of the material during rolling. There is a disadvantage that is easily generated.

FIG. 2 is a schematic view for explaining an example of the method of the present invention, schematically showing a state in which an inclination angle is not given to a main roll. Reference numeral 2b denotes a billet rear end surface, 7 denotes a sensor, 8 denotes a hollow shell, 10 denotes a driving device, 11 denotes a pressure-lowering device, Rg denotes a main roll opening, and the same elements as those in FIG.

As shown in FIG. 2, on the entrance side of the main roll 3,
A billet detection sensor 7 is provided. The type of the sensor is not particularly limited. For example, a non-contact sensor such as an infrared detector can be used.

Billet rear end face 2 passing on the pass line
b is sensed by the sensor 7, and the distance from the predetermined speed of the billet, for example, the distance from the rear end face of the billet, is 0.5 times the billet diameter based on the traveling speed of the billet 2 and the distance between the sensor 7 and the gorge portion 9. The time required for any part within the range of 6 times or more to reach the gorge part is obtained. The traveling speed of the billet can be measured with a speedometer. Alternatively, two sensors may be arranged on the main roll entry side, and the traveling speed of the billet during rolling may be obtained from the time when the billet passes between the sensors.

Next, the plug 5 is moved in the direction opposite to the billet advancing direction in accordance with the time at which the predetermined portion of the billet reaches the gorge portion, and the thickness of the rear end of the hollow shell 8 is reduced to the central portion. Thinner than The movement of the plug can be continuously performed until the completion of the piercing and rolling by the driving device 10 such as an electric motor provided at the rear end of the cored bar. However, the movement is stopped after the thickness is reduced to a predetermined thickness. You may. The thickness of the rear end portion is reduced by the movement of the plug, the outer diameter and the inner diameter are enlarged, and the diameter reduction of the rear end portion can be prevented. If the thickness of the thin portion at the rear end is too long, troubles are likely to occur at the time of rolling in the next process. It is desirable to carry out within a range of 0.5 times or more and 5 times or less.

A preferred embodiment of the present invention is characterized in that the plug is moved and the opening of the main roll is tightened. The thickness of the rear end portion can be reduced by moving the plug, but by further reducing the opening of the main roll (Rg in FIG. 2), the thickness reduction becomes more effective and the diameter can be prevented from being reduced. More effective. Adjustment of the opening degree of the main roll is performed by a draft elevating device 11 such as an electric motor provided on the main roll. If the gap between the disc roll and the main roll is large, a phenomenon occurs in which the material being rolled starts to bite out of the gap between the main roll and the disc roll. Therefore, it is necessary to set the gap to be narrow from the viewpoint of preventing biting, so that the reduction amount (tightening amount) of the opening degree of the main roll is preferably about several mm at the maximum.

[0021]

EXAMPLE A piercer having the basic configuration shown in FIG. 2 was used. Table 1 shows the main specifications and rolling conditions of the piercer.

[0022]

[Table 1]

An infrared detector (hereinafter, referred to as a sensor) for detecting the trailing end face of the billet is placed 1210 from the gorge portion to the rolling entry side.
mm, the time from when the sensor detects the rear end face to when the plug starts moving in the direction opposite to the rolling direction (hereinafter referred to as delay time) is variously changed, and the amount of movement of the plug is changed. The piercing and rolling were carried out with changes. In other words, the plug movement start time is one hour from the billet rear end face.
22mm (0.65 times billet diameter)-634mm
(3.4 times the billet diameter) reached the gorge portion. Billet travel speed is 640 ± 20mm
/ Sec, the sensor detects the trailing edge of the billet and
After 5 seconds, the trailing end of the billet started to contact the main roll.
In addition, rolling was performed by tightening the opening of the main roll at the same time as the start of the movement of the plug. On the other hand, as a conventional example, rolling was performed under the condition that neither the movement of the plug nor the tightening of the roll opening was performed. In addition, the gap between the main roll and the disc roll is 3 mm in order to prevent the material from biting out.
Therefore, the amount of reduction (tightening amount) of the main roll opening was set to 2.2 mm at the maximum.

The outer diameter and wall thickness of the rear end face of the hollow shell obtained by the above rolling and the outer diameter of the central portion in the longitudinal direction were measured.
The thickness reduction of the rear end face was determined, and the rear end face diameter reduction rate defined by the following equation was calculated. The thickness reduction of the rear end face is the thickness (T1) of the rear end face of the hollow shell obtained in the conventional example.
And the difference (T1-T) between the wall thickness (T) of the rear end face of the hollow shell obtained under each condition.

Rear end face diameter reduction rate = (average outer diameter of central portion of hollow shell−outer diameter of rear end face of hollow shell) / average outer diameter of central portion of hollow shell ×
100 (%) Next, the hollow shell obtained by the above-mentioned rolling was supplied to a mandrel mill and stretch-rolled. In rolling the mandrel mill, a new mandrel bar was used under any of the test conditions, and when it was visually determined that the mandrel bar had to be replaced, the test under each condition was terminated. Mandrel bar life. In addition, the presence or absence of occurrence of internal flaws in the obtained product was investigated, and the internal flaw generation rate ((number of internal flaws generated / total rolling number) ×
100%). Table 2 shows the conditions of the plug movement and the roll opening, the rear end face wall thickness reduction, the rear end face diameter reduction rate, the mandrel bar life, and the inner surface flaw generation rate.

[0026]

[Table 2]

As shown in Table 2, the test No. Test No. 2, in which the main roll opening was tightened together with the movement of the plug and the plug. Examples of the present invention of Test Nos. 4 to 6 are Test Nos. As compared with Comparative Example 1, the diameter reduction ratio of the rear end face was reduced, the life of the mandrel was improved, and the effect of reducing the occurrence rate of inner surface flaws was obtained.

In the test No. in which the plug was moved and the main roll opening was tightened. Example 5 of the present invention
Test No. in which the main roll opening was not tightened with the same plug travel distance. It was found that the above effect was further enhanced as compared with No. 3.

[0029]

According to the present invention, the diameter of the rear end of the hollow shell can be suppressed by a simple method. Therefore, when the hollow shell is rolled by a subsequent rolling mill such as a mandrel mill, the occurrence of internal surface flaws of the product is suppressed, and a product tube with excellent internal surface quality can be obtained. Further, the life of the mandrel bar is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a basic configuration of a piercer according to the present invention.

FIG. 2 is a schematic diagram illustrating the method of the present invention.

[Explanation of symbols]

1: piercer, 2: billet, 2b: rear end face of billet,
3: Main roll, 4: Disc roll, 5: Plug, 6:
Core metal, 7: sensor, 8: hollow shell, 9: gorge part, 1
0: drive device, 11: pressure-lowering device, Rg: main roll opening.

Claims (2)

[Claims] 1. A seamless metal pipe for obtaining a hollow shell by piercing a raw material with an inclined rolling mill having a plug arranged along a pass line between a pair of main rolls arranged obliquely around a pass line. In the piercing and rolling method, the plug is moved in a direction opposite to the piercing and rolling direction when a predetermined portion on the rear end side of the material in the rolling direction is rolled. 2. The method for piercing and rolling a seamless metal pipe according to claim 1, wherein when the plug is moved in the direction opposite to the piercing and rolling direction, the roll opening of the main roll is tightened.