JPH06285512A - Method for rolling by mandrel mill and device therefor - Google Patents

Abstract

PURPOSE:To obtain many kinds of seamless steel tubes small in thickness deviation in a peripheral direction through mandrel bars as few as possible. CONSTITUTION:A mandrel mill is a rolling device to thinning and drawing a shell which a mandrel bar 3 is inserted, composed of plural successive roll stands equipped with pairs of rolling rolls, 1i, 1i, 4t,1i+1, 1i+1' arranged in parallel with each other, each roll axis of a pair of rolling rolls is arranged and slanted in the opposite direction to each other to the running direction of a steel tube stock, at least one roll axis inclining stand whose inclination is adjustable and a rotatable stand which is arranged on the downstream side of a roll axis inclining stand and the roll axes for a pair of rolls can rotate around a pass line are equipped.

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 and apparatus for thinning and stretching a steel pipe material into which a mandrel bar is inserted in a manufacturing process of a seamless steel pipe by a mandrel mill.

[0002]

2. Description of the Related Art In a rolling line for producing a seamless steel pipe using a mandrel mill, a billet is pierced with a piercer, and then a mandrel mill is used to reduce the wall thickness to a predetermined wall thickness and then a stretch reducer. The outer diameter is reduced and finished to a predetermined outer diameter to obtain a seamless steel pipe.

In this case, in the mandrel mill, the shell (steel tube material) is pressed down in the gap between the hole-type roll and the mandrel bar to finish it to a predetermined wall thickness.
At that time, in order to reduce variations in wall thickness as much as possible, the roll die diameter and the mandrel bar diameter are uniquely determined. Therefore, when the finished wall thickness is different, it is necessary to use a mandrel bar having a different diameter each time, such as changing to a different mandrel bar. This is because it is easier to replace the mandrel bar than to replace the perforated rolls.

When the roll gap is changed, uneven thickness may occur in the circumferential direction. Since the wall thickness is determined geometrically by the pore diameter of the roll and the outer diameter of the mandrel bar used, the pore diameter (shape) defined by a pair of rolls except for a certain roll gap. ) Changes, and the interval also changes in the circumferential direction accordingly.

This is schematically shown in FIG. 3 by taking a perfect circular hole type as an example. In FIG. 3 (a), the interval defined by the roll pairs 1, 1'and the mandrel bar 3 is the circumference. If the thickness is uniform in the direction, that is, the wall thickness is uniform in the circumferential direction,
(b) shows the case where the wall thickness becomes non-uniform in the circumferential direction by changing the roll gap. Therefore, the mandrel bar needs to have a large number of sizes depending on the pitch of the finished wall thickness. Therefore, a large number of mandrel bars are required, which increases the manufacturing cost.

In order to solve such a problem, the present applicant has proposed a mandrel mill rolling apparatus equipped with a roll axis tilt stand and a rolling method thereof in Japanese Patent Application No. 4-039791. According to Japanese Patent Application No. 4-039791, for example, the roll arrangement of rolling roll pairs 1d and 1e in at least the last two stands, which are at least finishing roll stands in each of the rolling roll pairs 1a to 1e arranged in parallel with each other as shown in FIG. Are inclined in opposite directions to the traveling direction of the rolled material, and the state is as shown in FIG. 5, where FIG. 5 (a) is a plan view, FIG. 5 (b) is a side view, Figure (c) is a front view.

In FIG. 5, the roll pairs 1, 1'are arranged so that their roll axes are tilted by an angle θ in directions opposite to each other with respect to the traveling direction of the rolled material (shown by a white arrow). Therefore, for a bar having the same diameter, it is possible to roll steel pipes of various wall thicknesses while suppressing the occurrence of extreme circumferential thickness deviation by adjusting the roll gap adjustment amount and the inclination angle θ in an appropriate relationship. It is a thing. In addition, Japanese Patent Application No. 4-0397
In the conventional mandrel mills including No. 91, the adjacent roll stands are serially arranged around the rolling pass line with a 90 ° phase shift.

[0008]

In the technique of Japanese Patent Application No. 4-039791, a rolling material (shell) rolled by a roll axis tilt stand is used.
However, due to the effect of the inclination angle θ, the product is supplied to the next stand while being slightly twisted and rotated. However, the mandrel mill placed the adjacent stand at 90 °.
It has a hole shape that can suppress the circumferential thickness deviation by shifting the phases one by one. This is because the thickness reduction in the vicinity of the roll minimum diameter portion (roll groove bottom portion) of each stand is larger than in other portions. When the wall thickness is uniformly reduced in the circumferential direction at each stand, the shell bites on the flange side, so the wall thickness reduction becomes large on the groove bottom side and the wall thickness reduction becomes small on the flange side. As a result, the wall thickness of the shell located on the flange side in one stand reaches the groove bottom side in the next stand, and as a result, the wall thickness is evenly machined in the circumferential direction.

Therefore, when the shell is twisted by the rotation angle α between the roll axis tilt stand and the next stand,
Improper rotation with respect to the roll hole type of the next stand by the rotation angle α, and the shell is caught. As a result, uneven thickness occurs in the next stand, and the product dimensional accuracy is likely to deteriorate.

Needless to say, it suffices to provide a roll with a hole shape rotated by an angle α, but the above technique has the advantage of being able to perform tube rolling with different wall thicknesses by using a common roll hole shape, and this is the end of the roll. An object of the present invention is to obtain a wide variety of seamless steel pipes having a small thickness deviation in the circumferential direction and different wall thicknesses with the least possible number of mandrel bars.

[0011]

A rolling method by a mandrel mill according to the present invention is a method for thinning and stretching rolling of a steel pipe material having a mandrel bar inserted therein, which comprises a pair of rolling rolls arranged in parallel with each other. A roll axis in a roll axis tilt stand in which each roll axis is tilted in directions opposite to each other with respect to the traveling direction of the rolled material, and a roll axis of a pair of rolling rolls arranged subsequent to the roll axis tilt stand pass. It is characterized in that rolling is performed with an angle β formed by a roll axis of a rotatable stand rotatable around a line on a plane perpendicular to the pass line at β = (90 + α) °. Where α is the rotation angle of the rolled material between the roll axis tilt stand and the stand that can rotate around the pass line.

The mandrel mill rolling apparatus according to the present invention is
A device for continuously thinning and rolling a steel pipe having a mandrel bar inserted therein, comprising a plurality of roll stands provided with a pair of rolling rolls arranged in parallel with each other. At least one roll axis tilt stand whose tilts are opposite to each other with respect to the traveling direction of the rolled material, and the tilt of which is adjustable, and a pair of roll axis tilt stands disposed downstream of the roll axis tilt stand. It is characterized in that the roll shaft of the rolling roll is provided with a rotatable stand rotatable around the pass line.

[0013]

In the rolling method by the mandrel mill according to the present invention, the roll axis in the roll axis tilt stand and the roll axis in the rotatable stand arranged subsequent to the roll axis tilt stand are on a plane perpendicular to the pass line. Rolling is performed with an angle β formed between them of β = (90 + α) °.

Here, even if the steel pipe material is rotated by the rotation angle α due to the action of the tilt angle of the roll axis tilt stand, the angle β formed by the roll axis of the rotatable stand and the roll axis tilt stand is (90 + α) °. Therefore, the rotatable stand can be substantially 90 ° out of phase with the roll axis tilt stand, and uneven thickness in the circumferential direction can be suppressed. Further, since it can be rolled by the roll axis tilt stand, it is possible to obtain various kinds of seamless steel pipes having different wall thicknesses with the least mandrel bar.

In the mandrel mill rolling apparatus according to the present invention, the steel pipe material rolled by the roll axis tilt stand is rotated by the rotation angle α and reaches the rotatable stand for rolling. Here, by setting the angle formed by the roll axis of the rotatable stand and the roll axis of the roll axis tilt stand to be 90 + α, the rotatable stand is substantially 90 ° out of phase with the roll axis tilt stand. Can
Similarly, uneven thickness in the circumferential direction can be suppressed. Further, since it can be rolled by the roll axis tilt stand, it is possible to obtain various kinds of seamless steel pipes having different wall thicknesses with the least mandrel bar.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically below with reference to the drawings showing the embodiments. 1A and 1B are explanatory views of a mandrel mill used for carrying out a rolling method by a mandrel mill according to the present invention. FIG. 1A is a side view, FIG. 1B is a side view, and FIG. View from the arrow, Figure (c) is B- of Figure (a)
FIG. 6B is a view showing the relationship between FIG. 2B and FIG. 2C. Here, a case will be described as an example where the present invention is applied to at least the final two stands (i, i + 1 stands) that are at least finishing roll stands in each of the rolling roll pairs 1a to 1e shown in FIG.

The i-stand is composed of rolls 1 _i and 1 _i ′, and the roll axes of the rolls 1 _i and 1 _i ′ are tilted in opposite directions by a tilt angle θ _{i with} respect to a plane perpendicular to the pass line 4.
The (i + 1) stand is composed of rolls 1 _{i + 1} and 1 _{i + 1} ′, and the roll axes are opposite to each other by an inclination angle θ _{i + 1} (not shown) with respect to a plane perpendicular to the pass line 4. It is slanted in the direction. As can be seen from FIGS. 1 (b), 1 (c), and 1 (d), the (i + 1) stand has a phase shift of β = (90 + α) ° around the pass line 4 with respect to the i stand. Will be distributed. In the prior art, α = 0 °, and the phase is 9
It is 0 °.

[0018] i Since the roll 1 _i stand, 1 _i 'has a tilt angle theta _i, i inserting the mandrel bar 3
The shell 2 on the stand-out side reaches the (i + 1) stand while twisting at an angle ψ _i . That is, the point on the shell 2 that has passed the point C at the i stand passes the point D at the (i + 1) stand. The twist angle ψ _i is the tilt angle θ _i and i
It changes depending on the deformation of the shell 2 due to rolling on the stand.

Here, when the distance between the i to (i + 1) stands is L and the representative outer diameter of the shell 2 in the (i + 1) stand is d _{i + 1} , the rotation angle α is geometrically expressed by the following equation.

[0020]

[Equation 1]

[0021] Since the helix angle [psi _i changes by rolling conditions, as described above, the rotation angle α in accordance with a change in the helix angle [psi _i is a value to be changed. The outer diameter in Fig. 1 (c)
d _{i + 1} is the groove bottom spacing of rolls 1 _{i + 1} , 1 _{i + 1} ′, but the actual shell outer surface shape is not necessarily a perfect circle with a diameter d _{i + 1.} Is a value that should be selected as appropriate. Depending on the wall thickness of the steel pipe rolled in the mandrel mill, the inclination angles θ _i , θ
Both _{i + 1} may be 0, and in this case, the rotation angle α
= 0 is set.

On the leading end side and the trailing end side of the shell 2, rolling may become unsteady and the twist angle ψ _i may change. At this time, the rotation angle α may be changed during rolling. Of course, when the fluctuation range of the twist angle ψ _i is small, the rotation angle α during rolling may be fixed and kept fixed.

FIG. 2 shows an embodiment of a device (roll stand) capable of imparting a rotation angle α to the roll shaft. The roll stand 5 includes a substantially annular fixed housing 6 and a rotary housing 7 supported by the fixed housing 6 so as to be rotatable around the pass line. Roll 1 _{i + 1} , 1 _{i + 1} '
Is disposed in the rotary housing 7 so as to be capable of imparting a reduction amount and a tilt angle, and is rotationally driven by an external drive device (not shown). The rotary housing 7 is provided with a rotation angle α with respect to the fixed housing 6 via hydraulic cylinders 8, 8 ′.

In the embodiment shown in FIG. 2, the rotation angle α is realized by the rotary housing 7. However, a roll bearing portion is provided in the fixed housing without using the rotary housing, and this roll bearing portion rolls in the rolling direction. The rotation angle α can be imparted even if it is supported by a mechanism that is movable and adjustable in the axial direction. Further, in the above-described embodiment, the roll stand 5 is configured to be able to set the tilt angle, but the tilt angle may not be set.

[Experimental Example] Continuous rolling was performed by a five-stand mandrel mill shown in FIG. Inclination angles were given to the fourth and fifth stands 1d and 1e. The fifth stand 1e has the configuration shown in FIG. 2, and the rotation angle α can be set.・ Rolling material ..... φ60 × t5 × L 2000 (pure Al material) (mm) ・ Mandrel diameter ... φ48 (mm) ・ Table 1 shows the target representative dimensions and inclination angle of the shell on the stand outlet side. As shown in.

[0026]

[Table 1]

・ Stand spacing ..... 300 mm (common to all stands) First, for comparison, the rotation angle α of the fifth stand 1e is 0 °.
As a result, 10 steel pipe materials were rolled. The roll axes of all adjacent stands are 90 ° out of phase with each other. In addition, one of the ten rolling materials is rolled in the axial direction of the outer surface with a scoring needle to perform rolling, and the rolling mill is stopped in the steady rolling state, so that the rolling between the fourth and fifth stands is completed. The twist angle ψ of the shell was measured. When the circumferential thickness deviation rate of the nine strips that had been rolled over the entire length was measured, the average value was 9.5%. (Thickness deviation (%) = (Maximum value in the circumferential direction-Minimum value) / Average value x 100)
It was 1.5 °.

On the other hand, according to the method of the present invention, the fifth stand 1e
The angle of unevenness was measured by rolling the 10 materials with the rotation angle α given to. In the above formula 1, L = 300 mm, d _{i + 1} = 5
When 3.4 mm and ψ _i = 1.5 °, α = 16.9 °, so
A rotation angle α = 16.9 ° was given to the fifth stand 1e. As a result, the average value of the thickness deviation rate obtained was 4.2%, and the effect of reducing the thickness deviation according to the present invention was clearly recognized.

[0029]

As described above, according to the present invention,
The occurrence of uneven thickness in the circumferential direction due to the twist of the steel pipe material during rolling by a mandrel mill having a stand with an inclined roll axis is effectively suppressed. Therefore, a steel pipe material having a wide range of wall thickness can be rolled by a roll having the same hole shape and a mandrel bar having the same diameter, and at the same time, the thickness deviation of the obtained steel pipe material in the circumferential direction is extremely small.

[Brief description of drawings]

FIG. 1 is a schematic diagram of roll arrangement of roll pairs of a mandrel mill according to an embodiment of the present invention, in which FIG. 1 (a) is a side view and FIG. 1 (b) is A-A in FIG. 1 (a). 'A view, Figure (c) is the BB of Figure (a)', and Figure (d) is the same (b).
FIG. 6 is a diagram showing a relationship between FIG.

FIG. 2 is a front view of a roll stand in the mandrel mill rolling device according to one embodiment of the present invention.

FIG. 3 is a schematic diagram showing an example of a cause of circumferential wall thickness deviation.

FIG. 4 is a schematic diagram showing mandrel mill rolling.

FIG. 5 is a schematic view showing a roll stand in which a roll shaft is provided with an inclination angle.

[Explanation of Codes] 1 _i , 1 _i ′, 1 _{i + 1} , 1 _{i + 1} ′: Roll 2: Shell 3: Mandrel bar 6: Fixed housing 7: Rotating housing 8, 8 ′: Rotation angle setting hydraulic cylinder

Claims (2)

[Claims] 1. A rolling method by a mandrel mill for thinning and stretching rolling of a steel pipe material having a mandrel bar inserted therein, wherein each roll axis of a pair of rolling rolls arranged in parallel to each other is set in a traveling direction of the steel pipe material. On the other hand, in a roll shaft in a roll shaft tilt stand that is tilted in opposite directions to each other, and in a rotatable stand in which the roll shafts of a pair of rolling rolls that are arranged subsequent to the roll shaft tilt stand are rotatable around a pass line. A rolling method using a mandrel mill, wherein rolling is performed with an angle β formed between the roll axis and a plane perpendicular to the pass line at β = (90 + α) °. However, α is the rotation angle of the rolled material between the roll axis tilt stand and the stand that can rotate around the pass line. 2. A mandrel mill rolling apparatus comprising a plurality of roll stands, each of which is provided with a pair of rolling rolls arranged parallel to each other, for thinning and rolling a steel pipe material having a mandrel bar inserted therein, At least one roll shaft tilt stand in which the roll shafts of a pair of rolling rolls are tilted in mutually opposite directions with respect to the traveling direction of the steel pipe material, and the tilt can be adjusted; and the roll shaft tilt stand. A mandrel mill rolling mill, which is disposed on the downstream side of the rolling mill and has a rotatable stand on which a pair of rolling rolls can rotate around a pass line.