JP2973851B2 - Tube continuous rolling method and three-roll mandrel mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous rolling method for a tube in which a mandrel bar is inserted by using three rolls in a process of manufacturing a seamless steel tube and a mandrel mill.

[0002]

2. Description of the Related Art As a method for manufacturing a seamless steel pipe, a method using mandrel mill rolling is frequently used. In this tube making method, a heated solid billet is pierced by a piercing mill to form a hollow tube, a mandrel bar is inserted into the tube, and a stand composed of opposed rolls is connected. The raw tube is passed through a mandrel mill and rolled to a predetermined size. After this rolling, the inserted mandrel bar is pulled out of the seamless steel pipe and recycled for circulation.

FIG. 2 is a perspective view showing the entire structure of a conventional basic mandrel mill. The mandrel mill is a method of rolling mainly by reducing the wall thickness of a raw tube. As shown in the figure, a stand incorporating two opposing grooved rolls 1 and 2 is rolled to a roll of a roll of an adjacent stand. 90 ° axis alternately
Five to eight units are arranged in tandem so that the phases are shifted. The continuous elongation rolling of the seamless steel pipe is performed through the raw pipe 5 having the mandrel bar 4 inserted into the mandrel mill.

[0004] In contrast to such a mandrel mill, as a continuous elongation rolling suitable for rolling a high alloy seamless steel pipe which is difficult to form, each stand is formed by three hole-shaped rolls whose rotation axes cross each other at 60 °. Mandrel mill rolling has been proposed in which a stand row is formed by changing the roll arrangement between adjacent stands by 60 ° at the same time (see Japanese Patent Publication No. 63-25844).

[0005] In a mandrel mill in which a stand is formed by two hole-shaped rolls and rolled (hereinafter, simply referred to as a "two-roll mandrel mill"), a pipe portion corresponding to about 45 ° from the bottom of the roll groove overlaps. Due to the reduction, the temperature during rolling is significantly reduced as compared with other portions. This decrease in temperature does not become a hindrance to rolling in ordinary steel or low-alloy steel, but in high-alloy steel, the deformability decreases, and fine cracks occur on the surface of the raw tube. However, a mandrel mill (hereinafter, referred to as a mandrel mill) that forms a stand with three grooved rolls and rolls the stand.
When a pipe is formed by simply using a "3 roll mandrel mill", the temperature unevenness in the circumferential direction of the raw pipe is reduced, and it is possible to prevent fine cracks due to a temperature difference and to perform rolling at the same efficiency as ordinary steel. I have.

[0006] In the mandrel mill rolling, stripping of the mandrel bar after rolling is an important factor in order to recycle the mandrel bar as described above.
The hole type roll used for the three-roll mandrel mill has two rolls.
In comparison with the roll type roll of the roll mandrel mill, the roll hole type perimeter cannot be increased due to its geometrical restrictions.

FIG. 1 is a view showing an example of a roll shape of a stand-shaped roll of a stand in a three-roll mandrel mill described later, and FIG. 3 is a view schematically showing a shape of a hole-shaped roll of a stand in a two-roll mandrel mill. .

In FIG. 3, T indicates a gap between the groove bottom of the roll hole type and the mandrel bar, and Rm indicates a radius of the mandrel bar. These dimensions are determined by rolling conditions.

In order to increase the perimeter of the roll hole in a three-roll or two-roll mandrel mill, it is necessary to increase the radius of curvature R1 at the bottom of the groove of the roll hole. In the three-roll mandrel mill, the circumference of the roll die becomes maximum when R1 is made infinite, that is, as shown in FIG. 4, the roll die is formed into an equilateral triangle at the bottom of three linear grooves. This is the case when forming. The roll hole type perimeter (total perimeter) at this time is calculated to be 6 · (3) ^1/2 · (T + Rm), and (T + Rm)
Rm). On the other hand, in the case of a two-roll mandrel mill, the roll hole circumference can be appropriately increased by increasing R1, and (T +
Rm) is not subject to any restrictions.

[0010] From the above restrictions, the circumference of the tube at the end of rolling at the final stand in the three-roll mandrel mill is 2
It becomes smaller than the circumference of the pipe in the roll mandrel mill, and the inner circumferential surface of the rolled steel pipe comes into close contact with the mandrel bar, making stripping difficult. In particular, when the base tube is made of a high alloy steel, even in a two-roll mandrel mill, the rolled steel tube and the mandrel bar often adhere to each other and stripping becomes impossible. Ripping is the most important issue.

In recent years, in order to improve the productivity and quality of a seamless steel pipe, a rolling method called a wrist-less mandrel mill in which a mandrel mill and a sizer are arranged in series has been adopted. The method of pulling out the mandrel bar in this wrist-laid mandrel mill is such that the rolled steel pipe is bitten into the sizer before the mandrel mill rolling is completed over the entire length, while the mandrel bar inserted into the steel pipe is completed with the mandrel mill rolling. At the same time, the mandrel bar is pulled out of the steel pipe by a pulling force generated by the sizer rolling by fixing or retracting in the direction opposite to the rolling direction on the entry side of the mandrel mill.
Since the pulling force generated here is based on the frictional force between the sizer roll and the surface of the steel pipe, there is naturally a limit to the pulling force that can be used for stripping the mandrel bar. In an actual operation, a stripping mistake immediately leads to a stoppage of the mandrel mill, and therefore, as described above, stripping of the mandrel bar is the most important problem, especially when rolling high-alloy steel.

[0012]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned problems of the mandrel mill and provides a three-roll mandrel mill for rolling a high alloy steel seamless steel pipe. Also in adopting the present invention, an object of the present invention is to provide a continuous rolling method and a mandrel mill in which stripping errors of a mandrel bar do not occur.

[0013]

SUMMARY OF THE INVENTION The gist of the present invention is the following (1) continuous rolling method for pipes and (2) a three-roll mandrel mill.

(1) Two or more stands are constituted by three hole-shaped rolls whose rotation axes cross each other at an angle of 60 degrees, and the pipe arrangement is changed by changing the roll arrangement between adjacent stands by 60 degrees. A continuous rolling method for pipes, wherein a continuous working degree S of pipes in a final stand represented by the following formula (1) is set to a negative value in continuous rolling.

[0015] _{S = {1- (L n /} L n-1)} × 100 (%) ··· (1) _{However, L n = R1 n · α} n + R2 n · β n + R3 n · γ n L _n-1 = R1 _n-1 · αn _-1 + R2 _n-1 · βn _-1 + R3 _n-1 · γn _-1 R1, α: radius of curvature of the bottom of the roll-type groove and its forming angle R2, β: The radius of curvature of the roll hole flange relief and its forming angle R3, γ: The virtual radius of curvature of the roll gap and its forming angle _n indicate the dimensions of the roll hole die of the final stand, and _n-1 The attached figures show the dimensions of the roll hole type of the immediately preceding stand.

(2) It is composed of two or more stands composed of three hole-shaped rolls whose rotation axes cross each other at an angle of 60 degrees, and the roll arrangement between adjacent stands changes by 60 degrees. A three-roll mandrel mill, characterized in that the roll die circumference of the die roll of the last stand is larger than the roll die circumference of the die roll of the immediately preceding stand.

[0017]

The present inventor has studied in detail the force required for stripping the mandrel bar in mandrel mill rolling (hereinafter simply referred to as "stripping force"). As a result, the stripping force is the residual stress generated in the final stand. The inventors have found that the present invention is greatly affected by the present invention, and have completed the present invention.

Normally, when a plurality of stands are arranged to perform continuous elongation rolling of a tube, the final stand must have a finishing dimension as a finishing stand, so that the working degree can be suppressed lower than other stands. Therefore, recrystallization is unlikely to occur in the tube after the finish rolling, and the residual stress generated by the reduction in the final stand remains as it is, and the surface pressure due to the residual stress is applied to the mandrel bar.

The stripping of the mandrel bar requires a stripping force equal to or higher than the value obtained by multiplying the surface pressure applied to the mandrel bar by the coefficient of friction between the outer surface of the mandrel bar and the inner surface of the pipe. Therefore, when the surface pressure increases due to the residual stress generated in the final stand as described above,
The stripping force required after rolling increases accordingly.

According to the inventor's knowledge, the surface pressure applied to the mandrel bar by the residual stress can be reduced by improving the roll shape of the hole-shaped rolls of the final stand and the immediately preceding stand. . In other words, if the roll hole circumference of the hole roll of the last stand is made larger than the roll hole circumference of the hole roll of the immediately preceding stand, the surface pressure is reduced and stripping of the mandrel bar becomes easy. Become.

Since the circumference of the tube to be rolled is determined by the roll hole circumference of the hole roll, in other words, the circumference of the tube at the last stand is larger than the circumference of the tube at the immediately preceding stand. By rolling, the stripping force can be reduced.

FIG. 1 is a diagram (upper half) showing an example of a roll shape of a hole-type roll of a stand in a three-roll mandrel mill. All three hole-type rolls 1, 2, and 3 constituting the stand are shown. Since they have the same shape, only the hole-shaped roll 1 is shown by a solid line, and the other hole-shaped rolls and the mandrel bar are shown by two-dot chain lines. In the drawing, R1 indicates the radius of curvature of the groove bottom portion of the roll hole type, R2 indicates the radius of curvature of the flange escape portion of the roll hole type, and R3 indicates the virtual radius of curvature of the roll gap portion. C1 is the center of the three rolls 1, 2 and 3 and the center of curvature of R1, and C2 is the center of R2.
, C3 indicates the center of curvature of R3, α indicates the forming angle of R1, β indicates the forming angle of R2, and γ indicates the forming angle of R3.

As shown in FIG. 1, the circumference of the roll-hole type is expressed as the sum of the groove bottom portion, the flange relief portion, and the roll gap portion of the roll-hole type. Here, the reason why the roll hole circumference of the hole roll of the final stand is made larger than the roll hole circumference of the hole roll of the immediately preceding stand is as follows.

The tube rolling process is classified into a process of reducing the outer diameter of the tube and reducing its circumference (diameter reduction) and a process of reducing the wall thickness of the tube (wall processing). You. Usually, a mandrel mill combines these processes. When diameter reduction processing is performed by a mandrel mill, the wall thickness of the raw tube moves toward the inner surface side as the circumference decreases, so that the surface pressure applied to the mandrel bar increases and the residual surface pressure after rolling also increases. On the other hand, when only the thickness processing is performed, the residual surface pressure after rolling becomes small. Therefore, in the present invention, the roll hole perimeter of the perforated roll of the last stand is made larger than the perforated length of the perforated roll of the immediately preceding stand, so that the tube is not subjected to the diameter reduction processing, and the wall thickness processing is performed. It was decided to do.

When comparing the perforated length of the perforated roll of the last stand with that of the immediately preceding stand, the determination is made by using the perimeter working degree S of the pipe in the last stand calculated by the following equation (1). Is simplified. That is, if a roll having a perforated length S of a pipe designed to have a negative value (%) is used for the final stand and the immediately preceding stand, the stripping force of the mandrel bar is significantly reduced. be able to. In the formula (1), the reference numeral (n) indicates the size of the roll hole type of the last stand, and the reference numeral (n-1) indicates the size of the roll hole type of the immediately preceding stand.

[0026] _{S = {1- (L n /} L n-1)} × 100 (%) ··· (1) _{However, L n = R1 n · α} n + R2 n · β n + R3 n · γ n L _n-1 = R1 _n-1 · αn _-1 + R2 _n-1 · βn _-1 + R3 _n-1 · γn _{-1 The} above effect is obtained when the pipe material is made of ordinary steel, low alloy steel, and high alloy steel. Even in the case of, the same can be obtained. For this reason, even if the rolling method of the rest-reinforced mandrel mill is adopted, it is possible to eliminate stripping errors of the mandrel bar.

[0027]

Example 1 In order to confirm the effect of the present invention, a rolling test was carried out under the following conditions using a five-roll, three-roll mandrel mill.

1. Mandrel bar diameter: 44mm 3. Perforated roll The perforated length of the 4th stand roll perforated (per roll):
27.06mm constant 5th stand roll hole circumference (per roll):
26.91 to 27.36 mm After the finish rolling, the stripping force was measured, and the results are shown in Table 1.

[0029]

[Table 1]

As is evident from Table 1, when the circumferential length S of the pipe in the final stand is negative, that is, the roll hole circumference of the fifth stand is made larger than the roll hole circumference of the fourth stand. In this case, the stripping force in a three-roll mandrel mill can be significantly reduced.

[0031]

According to the present invention, in a three-roll mandrel mill for rolling a seamless steel pipe of a high alloy steel, even when a rolling method of a wrist-rein mandrel mill is employed, the occurrence of stripping mistakes of a mandrel bar is prevented. can do.

[Brief description of the drawings]

FIG. 1 is a view showing an example of a roll shape of a hole type roll of a stand in a three-roll mandrel mill of the present invention.

FIG. 2 is a perspective view showing the entire structure of a conventional basic mandrel mill.

FIG. 3 is a view showing a schematic shape of a hole type roll of a stand in a two-roll mandrel mill.

FIG. 4 is a diagram showing a roll shape in which a roll hole type perimeter in a three-roll mandrel mill is maximized.

[Explanation of symbols]

1, 2, 3 ... hole type roll, 4 ... mandrel bar, 5
… Base pipe R1, R2, R3… Radius of curvature, C1, C2, C3… Center of roll and roll center of curvature α, β, γ… Forming angle

Claims (2)

(57) [Claims] 1. The rotation axes intersect at an angle of 60 degrees with each other.
Two or more stands are constituted by two hole-shaped rolls,
When continuously rolling the pipe by changing the roll arrangement between adjacent stands by 60 degrees, the peripheral processing degree S of the pipe in the final stand represented by the following equation (1) is set to a negative value. Continuous rolling method for pipes. _{S = {1- (L n /} L n-1)} × 100 (%) ··· (1) _{However, L n = R1 n · α} n + R2 n · β n + R3 n · γ n L n-1 = R1 _n-1 · α _n-1 + R2 _n-1 · β _n-1 + R3 _n-1 · γ _n-1 R1, α: radius of curvature of the bottom of the roll-type groove and its forming angle R2, β: roll The radius of curvature of the flange relief part and its forming angle R3, γ: The virtual radius of curvature of the roll gap part and its forming angle _n indicate the dimensions of the roll mold of the final stand, and those with _n-1 The dimension of the roll hole type of the immediately preceding stand is shown. 2. A stand comprising at least two stands each comprising three hole-shaped rolls whose rotation axes cross each other at an angle of 60 degrees,
In a three-roll mandrel mill in which the roll arrangement between adjacent stands changes by 60 degrees, the roll die circumference of the die roll of the final stand is greater than the roll die circumference of the die roll of the immediately preceding stand. A 3-roll mandrel mill characterized by being large.