JP3007259B2 - Manufacturing method of seamless metal pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a seamless metal pipe or its intermediate material from a billet having a square cross section with high accuracy in one pass.

[0002]

2. Description of the Related Art Regarding a method of obtaining a seamless metal pipe by a press-piercing method without using an inclined drilling machine, a circular hole shape is provided in a 2Hi rolling mill, and a parallel portion of a plug is provided immediately below a roll axis on a pass line. The method of holding the plug with a mandrel bar and pushing it through from the entry side to pierce is described in
9260. In this method, a draw ratio of at most about 1.2 can be obtained due to the problem of biting.

[0003] As a method of preventing biting and obtaining high stretching,
Japanese Patent Publication No. 58-56664 discloses a horizontal (H) roll-vertical (V) roll tandem structure in which the distance between the horizontal (H) roll and the vertical (V) roll is less than twice the plug diameter.
The plug position is such that the tip protrudes forward in the rolling direction upstream from the axial center plane (hereinafter referred to as immediately below the roll) orthogonal to the horizontal (H) roll pass line, and the plug diameter is immediately below the subsequent vertical (V) roll. The diameter of the parallel portion is set to 0.9 or more, and the hole shape of the horizontal (H) roll is made elliptical, and the cross-sectional shape of the material to be rolled on the horizontal (H) roll exit side is deliberately made oval. Thereafter, a method for manufacturing a seamless metal pipe in which a vertical (V) roll having a circular hole shape is stretched while also performing shape correction is shown. Although this method enables high stretching, the plug is long and expensive, and the mill structure is complicated.

Japanese Patent Application Laid-Open No. 55-112107 discloses that an elliptical hollow shell is formed by a 2Hi indentation punch having an elliptical hole shape, a circular hole is formed at the rear, and a plug is formed immediately below the roll. A continuous piercing and rolling method for producing a circular hollow shell in a vertical 2Hi rolling mill (or a group of subsequent rolling mills arranged in a plurality of VHV-...) Is shown. These Japanese Patent Publication No. 58-56664 and Japanese Patent Application Laid-Open No. Sho 55-11
No. 2107 discloses a method in which a hollow pipe having an elliptical shape is first formed with an elliptical hole shape, and a high-stretching is realized by a method in which the hollow element is continuously modified into a circular shape by a subsequent mill. Use one plug (Japanese Patent Publication No. 58-566)
No. 46) or two or more of them are connected in tandem (JP-A-55-112107).

Regarding the position of the plug, Japanese Patent Publication No. 58-566
No. 46 describes that high stretching can be achieved by positioning the parallel portion behind immediately below the roll (column 3, lines 7 to 19 of the same publication). However, the plug tip position in FIG. 3 for explaining this is located forward of immediately below the roll. In Japanese Patent Publication No. 55-36402, regarding a plug position in a 2Hi press drilling machine, a plug lead (a distance from immediately below a roll to a tip of a plug: forward from a position immediately below a roll to a forward side in a rolling direction) is defined by a roll and a material to be rolled. The positive value is defined as the maximum contact length of 0.4 to 0.85. FIG. 6 of JP-A-55-112107 exemplifies the position of a plug used for the leading punch, but the technical operation and effect regarding the installation position are not clear.

JP-B-59-27642 and JP-A-58-58
Japanese Patent Publication No. 176008 discloses a plurality of (2 to 4) roll-type press-punching methods in which the axis is considered to be arranged in the same plane perpendicular to the pass line. It does not specify the position of the plug or the plug in the pass line direction, but relates to the shape of the plug or the material and the positional relationship with the hole-shaped opening. Further, regarding the drive of the rolls in the press-in punching method using four rolls, there is no technology for driving only one of two opposing sets.

[0007]

SUMMARY OF THE INVENTION According to the present invention, in the indentation punching method, by preventing biting, high stretching can be realized in one pass regardless of tandem, and uneven thickness and oval shape are prevented. A drilling method that makes it possible to manufacture seamless metal pipes and, when a hole is formed by a total of four rolling rolls, suppresses the complexity of the drive system and the rise in equipment costs due to the use of all rolls. It is intended to provide.

[0008]

According to the present invention, (1) a hole is formed by a plurality of rolling rolls whose axes are arranged in the same plane perpendicular to the pass line, and a center portion of the hole on the pass line is formed. In a device for manufacturing a hollow circular tube by pressing a raw material into a hole-shaped gap by a pressing device installed on the entry side, a tip of the perforation plug is positioned rearward on the rolling exit side from the center of the rolling roll axis. A method for producing a seamless metal pipe, wherein the hole shape of each roll satisfies the formula (1) so that the shape after perforation is circular, and more preferably (2) the method described above. In (1), the hole shape is constituted by four rolling rolls, and every other rolling roll is a non-driven driven roll, and the hole width of the driven roll / the hole width of the driving roll = 1. 0.0 to 0.2
In the range.

(Equation 2) Here, θ is the angle between the perpendicular from the center of the hole to the axis of the rolling roll and the line connecting the center of the hole and any point of the hole. R is the hole radius l _{P at the} angle θ. The distance r _O from immediately below the roll axis to the plug parallel part start position is the hole radius when rolling at l _P = 0.

[0009]

In order to realize a high pressure in the piercing and rolling, it is necessary to prevent entanglement. As shown in FIG. 2, when the tip of the plug is pierced by positioning the tip of the plug forward (inward side) from immediately below the roll, the push-expanding (expanding from inside) area of action by the plug (area B in FIG. 2) and the outer diameter reduction by the roll ( There will be an area where the working area (area A in FIG. 2) overlaps. At this time, if all the volume removed by both actions can be extended in the length direction, no biting will occur. However, as a matter of course, at the roll flange portion, the gap is reduced to just below the roll, and is expanded after being just below the roll. Therefore, in the vicinity immediately below the roll where the material restraint by this roll is maximal, since the expanded tube from the inside and the contracted region from the outside overlap, the volume to be removed rapidly increases, so that the flow cannot be completely discharged in the length direction. A small volume results in a material flow in the direction of the roll flange gap, resulting in large biting.

Therefore, in order to prevent biting, FIG.
As shown in the figure, the expansion area B and the contraction area A from inside and outside should not be wrapped, or if the exclusion volume suddenly increases due to wrapping and it escapes in the direction of the roll flange gap, it will not bite. It is sufficient to use an oval hole shape having a sufficient margin as described above. Conventional technology of Japanese Patent Publication No. 58-56
It is considered that JP-A-646 or JP-A-55-112107 is directed to the latter, but as a result, in these methods, the shape of the material to be rolled on the outlet side is also oblong, so that the shape must be corrected. In addition, a drawing path for correcting the shape is added.

According to the present invention, the tip of the piercing plug is positioned rearward of the rolling-out side from the axial center of the rolling roll to separate the inner and outer expanding and contracting regions to prevent biting even under high stretching. It is. Further, as a further effect of the present invention,
The material to be rolled is pressed against the roll hole surface by the expanding action of the plug from just below the roll to the outlet side, and the roll also rotates in the direction of the tube expansion, so that the material to be rolled in the vicinity of the hole flange is rubbed up. An effect of making biting less likely can be expected.

However, when the plug is positioned at the tip of the plug and the pipe is expanded rearward from immediately below the roll using a circular hole as described above, the hole at the position where the material to be rolled is separated from the roll is different from the hole immediately below the roll. In contrast, the material to be rolled becomes a vertically long oval, and as a result, the material to be rolled also becomes a vertically long oval. This is referred to below as 2
The case of the Hi roll will be described as an example. When the distance from immediately below the roll to the plug parallel part start position is l _P , the pitch diameter is D _P, and the roll is rolled in a circular hole shape with a radius r _{O in} order to obtain a hollow tube having an outer diameter of 2r _O , Due to the pipe expansion action by the above and the above-mentioned rolled-up material rubbing action by the roll, the pipe expansion completion position is almost shifted rearward by l _P toward the rolling exit side. Therefore, the gap between the upper and lower rolling rolls at that position, that is, the hole shape is different from the circular shape immediately below the roll,
As shown in FIG. 3, at the position of the angle θ from the center of the hole diameter,
It deviates from the original circular hole shape by the amount Δr approximated by the equation (2).

(Equation 3)

Here, the plug parallel portion start position is defined by a boundary point between the conical portion and the cylindrical portion having a rounded tip when the plug is formed of the conical portion.
In the case where the outer diameter increases continuously from the tip, it is defined as a position where the outer diameter is 95% of the maximum outer diameter. The pitch diameter D _P is twice the distance between the Anagata center and the roll axis.

Therefore, as shown in FIG. 1 (b), if the hole shape is made small in advance, that is, shallow when viewed from the depth of the groove bottom in consideration of the above-mentioned shift, the rolled material restraint by the roll is completed. The substantially hole-shaped shape at the time of performing can be kept substantially circular. Specifically, Equation (3) is satisfied so that the radius of the hole after deviating from the original hole for any θ is equal to the hole radius r _O when rolling at l _P = 0. What is necessary is just to manufacture a hole shape with the hole shape radius r.

(Equation 4)

According to the present invention, the shape of the hole is devised as described above so that the shape of the material to be rolled does not deviate from the circular shape when the material to be rolled comes out of the constraint of the hole. .

In the indentation punching method having the above-mentioned action, the number of rolling rolls constituting the hole shape can be any number of 2 or more. However, when a billet having a square cross section is used as the material, the corner of the billet has a hole shape. It is preferable that the rolling roll is formed of four rolling rolls so as to come to the bottom of the groove. However, if it is composed of four rolling rolls, the driving mechanism becomes complicated. Therefore, in the present invention, one pair of rolling rolls opposing each other in a point symmetry is skipped, that is, every other roll is driven. In this case, in order to secure the gripping force of the roll, it is necessary to reduce the driven resistance by making the width of the hole of the non-driven rolling roll smaller than that of the driving roll, and balance the gripping force with the driving roll.
In the case of four rolls, for example, a horizontal roll pair can be driven and a vertical roll pair can be deactivated. At that time, FIG.
As shown in (c), the width of the hole of the vertical roll that is not driven is made smaller than that of the horizontal roll. The degree is appropriately selected depending on the rolling size and the material size. The inventors have empirically found through experiments that rolling can be carried out without any problems if the width of the non-driving roll / the width of the driving roll is between 0.2 and 1.0.

[0017]

EXAMPLES According to the inventors' plasticine experiment, 72 mm
The square billet is composed of four rolling rolls driven only by horizontal rolls, roll diameter 400mm, hole average diameter 85mm, hole groove bottom shall be shallow by 1.5mm at the center of roll, and plug tip position just below the roll Perforation with a wall thickness of 8.6 mm was made 5 mm behind. As a result, in the range of vertical roll hole width / horizontal roll hole width = 1.0 to 0.2, good perforation was possible without problems such as poor biting and biting.

[0018]

According to the present invention, it is possible to form a seamless metal pipe having a good shape, which does not bite even if the stretching is increased, from a square billet. In addition, a universal mill type for H-section steel having a hole shape composed of four rolling rolls and having a driven horizontal roll pair and a non-driven vertical roll pair becomes possible.
The equipment structure is simple and the equipment can be installed at low cost.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating the present invention, wherein FIG. 1A is an explanatory view of a mechanism for preventing biting by placing a plug position immediately below and behind a roll, and FIG. FIG. 4C is a view for explaining a hole shape for preventing a hole shape from deviating from a circular shape and preventing a material to be rolled from becoming an oval, and FIG. It is explanatory drawing in the case of making some rolls (vertical rolls) of a shape non-drive.

FIG. 2 is a view for explaining a cause of occurrence of biting in the related art.

FIG. 3 is a diagram for explaining a deviation between a hole shape immediately below a roll and a substantial hole shape at a position where a material to be rolled is separated from restraint by a roll.

Continuation of the front page (56) References JP-A-55-88906 (JP, A) JP-A-5-123707 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 17 / 00 B21B 27/02

Claims (2)

(57) [Claims] 1. A hole is formed by a plurality of rolling rolls whose axes are arranged in the same plane perpendicular to the pass line, a perforation plug is arranged at the center of the hole on the pass line, and installed on the entrance side. In a device for manufacturing a hollow circular tube by pressing a material into a hole-shaped gap by a pressing device, a tip of a piercing plug is positioned rearward of a rolling exit side from a center of a rolling roll, and a shape after piercing is circular. A method for manufacturing a seamless metal pipe, wherein the hole-shaped shape of each roll satisfies the expression (1). (Equation 1) Here, θ is the angle between the perpendicular from the center of the hole to the axis of the rolling roll and the line connecting the center of the hole and any point of the hole. R is the hole radius l _{P at the} angle θ. The distance r _O from immediately below the roll axis to the plug parallel part start position is the hole radius when rolling at l _P = 0. 2. The method according to claim 1, wherein the hole is formed by four rolling rolls, and every other rolling roll is a non-driven driven roll, and the other rolling rolls are driving rolls. A method for producing a seamless metal pipe, wherein the width of the driven roll / the width of the drive roll is 1.0 to 0.2.