JPH0569602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a seamless pipe by piercing and rolling a cylindrical metal material using an inclined boring machine.

[Prior art]

In the case of the Mannesmann method, seamless steel pipes are manufactured by piercing-rolling a solid round billet steel piece to form a seamless hollow shell pipe, and rolling the inner and outer diameters of this hollow shell pipe to desired dimensions. A Mannesmann type inclined perforation machine is used as a means for the above-mentioned perforation and rolling.

The perforation rolling by this inclined perforation machine is carried out by setting the respective axes of a pair of barrel-shaped rolls 1 and 1' parallel to each other in a plan view, as shown in FIG. 4 (plan view), and as shown in FIG. The solid round billet 4 is spirally fed between the rolls 1 and 1' in the axial direction (in the direction of the arrow) between the rolls 1 and 1'. A bullet-shaped plug 2 whose tip end faces in the opposite direction to the feeding direction is attached at its base end to a core metal 3 and is located between the rolls 1 and 1', and the round billet 4 to be fed is the plug. 2
A hole is made at the tip of the roll 1, 1' and plug 2.
The tube is rolled between the tubes and formed into a hollow tube 5. Thereafter, the hollow tube 5 is rolled using a Mannesmann type plug mill, mandrel mill, or the like to produce a seamless steel tube having desired inner and outer diameters.

Now, the outer diameter of round billet 4 is D, and round billet 4 is
Let d be the outer diameter of the round billet 4 at the position where it is perforated at the tip of the plug 2 (see Fig. 4), and let the tip draft rate α {=(D-d)/D} be, then the roll and round billet It is known that the frictional force generated between the two surfaces increases as α becomes larger and as the inclination angle β becomes smaller.

Since the rolls are inclined as the frictional force increases, the driving force for advancing the round billet also increases, which makes it easier to bite the round billet between the rolls.

[Problem that the invention seeks to solve]

By the way, in an inclined drilling machine, during rotary forging by the rolls while the round billet is bitten by the rolls and drilled into the plug, a crack occurs in the axial center of the round billet, and a so-called Mannesmann crack occurs, and this crack occurs after piercing and rolling. It may remain as a flaw on the inner surface of the hollow tube.

As before, the rate of occurrence of this flaw increases as the frictional force increases, that is, as α increases and β decreases. Therefore, there is a mutually contradictory relationship between improving the biting ability of the round billet between the rolls and improving the quality.

Figure 6 shows α, the biting defect rate (black circles), and the inner surface when a round billet made of 18%Cr-12%Ni-2.5%Mo steel is punch-rolled by changing the tip draft ratio α mentioned above. This is a graph showing the relationship with the flaw occurrence rate (white circle rate), with the tip draft rate (%) on the horizontal axis and the gouge failure rate (%) and internal flaw occurrence rate (%) on the vertical axis. It shows. Figure 7 is a graph showing the relationship between β when the same round billet as before was punch-rolled by changing the inclination angle β, the biting defect rate (black circles), and the internal flaw occurrence rate (white circles). , and the horizontal axis is the inclination angle β (deg),
The vertical axis shows the biting defect rate (%) and the internal flaw occurrence rate (%).

As can be understood from these two figures, the characteristics are opposite in the case of tip draft rate and in the case of inclination angle, but in both cases, quality decreases when priority is given to improving biting ability, and conversely, when priority is given to improving quality. There was a problem in that it was not possible to simultaneously improve the biting ability and quality, especially for round billets made of difficult-to-process stainless steel. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a seamless pipe that can both improve the biting property and improve the quality.

[Means for solving problems]

In the present invention, the frictional force is increased until the cylindrical metal material such as a round billet is bitten between the rolls and stable piercing rolling is performed, and after stable piercing rolling is performed, the frictional force is increased. Reduce force. That is,
The method for manufacturing a seamless pipe according to the present invention involves feeding a cylindrical metal material between the rolls of an inclined boring machine, and piercing and rolling the metal material using the rolls and a plug placed between the rolls to produce a seamless pipe. In the manufacturing method, the inclination angle of the rolls or the distance between the rolls is kept small until the position of the end in the feeding direction of the seamless pipe during piercing and rolling reaches the end in the feeding direction of the plug, and It is characterized by increasing the inclination angle of the rolls or the distance between the rolls beyond the end of the plug in the feeding direction.

[Effect]

In the present invention, during biting, the roll inclination angle or the distance between the rolls becomes small and the frictional force increases, and during piercing rolling after the biting is completed, the roll inclination angle or the distance between the rolls increases and the frictional force increases. becomes small.

〔Example〕

The present invention will be specifically explained below based on the drawings.
FIG. 1 is a schematic plan view showing a state in which the tip of a round billet 14 is pierced and rolled according to the present invention, and in the figure, reference numerals 1 and 1' indicate a pair of barrel-shaped rolls. The rolls 1 and 1' can be tilted in opposite directions by selecting an appropriate angle of inclination β with respect to the horizontal plane by means of a rotating means (not shown) while keeping their respective axes parallel in plan view. They are rotated in the same direction by a driving means.

A round billet 14 made of steel is placed between the rolls 1 and 1'.
is fed in the axial direction (direction of the arrow), and the cannonball-shaped plug 2 has its tip facing in the opposite direction to the feeding direction, and its base end has a diameter larger than the maximum diameter of the plug 2. It is provided horizontally with a rod-shaped core metal 3 having a small outer diameter attached thereto.

The distance between the rolls 1 and 1' can be adjusted by means not shown, and the plug 2 remains fixed during piercing rolling, but the position of its tip can be moved back and forth in the feeding direction when piercing rolling is not being performed. It's getting old.

The wall thickness of the hollow tube 15 is determined based on the distance between the rolls and the position of the tip of the plug 2, and the inner diameter is determined based on the maximum outer diameter of the plug.

A method for manufacturing a seamless pipe according to the present invention using the apparatus configured as described above will be explained.

As shown in FIG. 2, the inclination angle β and the distance between the rolls are set in two levels in advance: one in which emphasis is placed on biting, and the other in which emphasis is placed on quality. In other words, regarding the levels in each case, when emphasis is placed on biting, the inclination angle and distance between the rolls are set to low levels where the frictional force acting on the round billet 14 is large and biting can be done reliably and stably, and When quality is important, the angle of inclination and the distance between the rolls are set to a high level so that the frictional force acting on the round billet 14 is small and Mannesmann cracks do not occur.

When starting piercing rolling, first the inclination angle and the distance between rolls are each set to a low level. The round billet 14 is fed between the rolls 1 and 1' in this state,
Start piercing and rolling. Here, if the outer diameter of the round billet 14 is D ₁ and the outer diameter of the round billet 14 at the position where the round billet 14 is perforated by the tip of the plug 2 is d ₁ (see Fig. 1), then at the start of piercing rolling The tip draft rate α is large as (D ₁ − d ₁ )/D ₁ ,
Moreover, the inclination angle β is small. For this reason, round billet 1
The tip end of 4 is reliably and stably bitten between rolls and subjected to piercing rolling to form a seamless hollow tube 15.

After that, when the tip of the hollow gap 15 reaches the base end of the plug 2, that is, when the biting is completed and the piercing rolling is stabilized, the inclination angle and the distance between the rolls are set to high levels.

FIG. 3 is a schematic plan view showing the piercing and rolling state after the settings have been changed. In this state, the outer diameter of the round billet 14 at the position where it is perforated by the tip of the plug 2 is d ₂ (>d ₁ ), so the tip draft rate α is (D ₁ - _{d 2} )/ D becomes ₁ and becomes smaller,
Also, the angle of inclination becomes larger. Once the round billet 14 has been bitten in, it is easily bitten in after that, and since the part of the round billet 14 except the tip is pierced and rolled with a small frictional force, Mannesmann cracking does not occur and this The hollow tube 15 is formed into a high-quality hollow tube 15 with no inner surface flaws.

Thereafter, the hollow tube 15, which has different outer diameters between the tip and the other portions, is manufactured into a seamless steel tube with desired inner and outer diameters using a plug mill, a mandrel mill, or the like.

In addition, in the above embodiment, the inclination angle and the distance between the rolls are changed, but the present invention is not limited to this, and the friction force may be changed to an appropriate value by changing either the inclination angle or the distance between the rolls. Of course, it can be implemented.

Furthermore, in the above explanation, piercing and rolling is performed using a two-roll type inclined perforation machine, but the present invention is of course applicable to the case where piercing and rolling is performed using a type of inclined perforation machine having three or more rolls. It is.

Further, in the above description, the present invention is applied to the case of manufacturing seamless steel pipes, but it goes without saying that the present invention can also be applied to the case of manufacturing general seamless pipes made of different materials.

〔effect〕

As detailed above, in the present invention, the tip of a cylindrical metal material is pierced and rolled with high frictional force, so that biting can be performed reliably and stably, and after the biting is completed, the tip is pierced and rolled with a low frictional force. Therefore, there is no occurrence of internal flaws, and it is possible to achieve both improved biting performance and quality improvement, and in particular, even with difficult-to-process materials such as stainless steel, the occurrence of internal flaws can be suppressed and piercing rolling can be easily performed. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing the state in which the tip of a round billet is pierced and rolled according to the present invention;
Fig. 2 is an explanatory diagram of the manufacturing method of the present invention, Fig. 3 is a schematic plan view showing the state in which the part of the round billet excluding the tip is pierced and rolled according to the present invention, and Fig. 4 is a diagram of the conventional method. FIG. 5 is a front view of a conventional roll pair, and FIGS. 6 and 7 are explanatory diagrams of problems in the prior art. 1, 1'... Roll, 2... Plug, 3... Core bar, 14... Round billet, 15... Hollow tube.

Claims (1)

[Claims] 1. In a method of manufacturing a seamless pipe by feeding a cylindrical metal material between the rolls of an inclined perforation machine and perforating and rolling the metal material using the rolls and a plug placed between the rolls, there is no seamless pipe during the perforation and rolling. The inclination angle of the rolls or the distance between the rolls is made small until the position of the end of the pipe in the feeding direction reaches the end of the plug in the feeding direction,
A method for manufacturing a seamless pipe, characterized in that when the position exceeds the end of the plug in the feeding direction, the inclination angle of the rolls or the distance between the rolls is increased.