JP2976831B2 - Tube rolling method - 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 of rolling a seamless pipe, mainly a pipe used for manufacturing a seamless steel pipe, and more particularly to a method of rolling a pipe using a drawing rolling machine such as a mandrel mill.

[0002]

2. Description of the Related Art As one method of manufacturing a seamless steel pipe, there is a method using an elongation rolling mill. In this method, after heating a round billet, which is a material, in a heating furnace, it is pierced with a piercing machine to form a hollow shell, and subsequently, the shell is subjected to a wall-thinning process with a stretching rolling mill, and the outer diameter is finished to a predetermined size. . Mandrel mills with high productivity are often used as elongation mills. FIG. 1 shows tube rolling using a mandrel mill.

[0003] A mandrel mill is usually composed of six to eight two-roll stands 10 having a pair of slotted rolls. The rolling direction in each roll stand 10 is shifted in order by 90 °. The base tube 20 is passed through each stand 10 with the core bar 30 inserted therein, and is sequentially reduced in thickness between the pair of hole-shaped rolls 11 provided on each stand 10 and the core bar 30.

Here, when the thickness of the rolled material is changed, that is, when a rolled material having the same outer diameter and a different thickness is manufactured, usually, the roll is not replaced or the roll position is adjusted, and the roll is not formed. Changing the outer diameter of the core bar to be inserted changes the interval (groove bottom thickness) between the hole-shaped roll and the core bar. This is shown in FIGS.

In FIGS. 2 and 3, the same grooved roll is used, and the groove radius R ₀ at the groove bottom is the same. In addition, the center of the hole radius R ₀ coincides with the center of the cored bar, which is the basis of tube rolling using a mandrel mill. By fixing the roll gap to S ₀ and reducing the outer diameter of the cored bar from D ₁ to D ₂ , the hole-shaped roll and the cored bar can be maintained while the center of the hole radius R ₀ remains the same as the center of the cored bar. (Groove bottom thickness) increases from t _G1 to t _G2 .

[0006] By the way, when changing the thickness of the rolled material,
In addition to changing the outer diameter of the core bar, a method of changing the hole size by changing the roll while keeping the outer diameter of the core bar constant can be considered. However, this method is not usually adopted because it has a disadvantage that the operation is stopped due to the roll change, and furthermore, the man-hour for changing the rolls and the number of rolls to be held are enormous.

[0007] A rolling stand provided with a pair of grooved rolls is usually equipped with a roll position adjusting mechanism, and by using this adjusting mechanism, it is possible to adjust the distance between the grooved roll and the cored bar. is there. However, if the roll position is changed without changing the outer diameter of the cored bar and the interval between the hole-shaped roll and the cored bar is changed, the interval becomes uneven in the circumferential direction.

FIG. 4 shows a state in which the roll gap is tightened from the state shown in FIG. By reducing the roll gap from S ₀ to S, the center of the hole radius R ₀ deviates from the center of the cored bar, and the groove bottom thickness decreases from t _G2 to t _G1 as in FIG. The spacing between the metal rod and the metal bar becomes uneven in the circumferential direction.
4 position) causes uneven thickness which becomes a thickness peak. This uneven thickness becomes more remarkable as the tightening amount of the gap is increased as shown in FIG. Conversely, when the interval is increased, unevenness occurs in which four portions in the circumferential direction become thin portions.

[0009] The tolerance in the standard in which uneven wall thickness is allowable differs depending on the pipe type. However, considering that uneven wall thickness occurs in each process of the pipe production line and that dimensional accuracy is a part of product quality, it is considered. The permissible value of the thickness deviation amount generated by adjusting the roll position (changing the rolling position) is at most about 2%. For this reason, the change range of the rolling position is narrow, and even if the sharing of the cored bar is attempted by changing the rolling position, the effect is small.

In view of the above, at present, by changing the outer diameter of the cored roll inserted into the die roll without changing the die roll or its position, the distance between the die roll and the cored bar is changed to perform rolling. Corresponds to changes in material thickness.

However, in this method, it is necessary to have an enormous number of cored bars corresponding to the types of wall thickness to be rolled. Usually, in rolling by a mandrel mill, the rolling schedule is determined at a thickness pitch of 0.5 mm, and the outer diameter of the core bar changes at a pitch of 1.0 mm. In order to further roll one kind of thickness, there is a process in which the cored bar is pulled out from the rolled material, then cooled, and a lubricant is applied for the next rolling. Is required. Therefore, an enormous number of metal rods are required.

A technique developed to solve such a problem is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-28011. It is. With this technology,
As shown in FIG. 6, a four-roll stand in which four hole-shaped rolls are combined is arranged on the output side of a two-roll stand row for thinning a raw tube. The four-roll stand has a rolling direction of 45 degrees with respect to the rolling direction of the immediately preceding two-roll stand.
°, which eliminates uneven thickness caused by the two-roll stand row. FIG. 7 shows the effect.

When the roll gap is tightened from the reference value in the two-roll stand row, the wall thickness increase at four locations in the circumferential direction is eliminated by passing through the four-roll stand. Thereby, in the two-roll stand row, the adjustment range of the roll gap is widened. As a result, a wide range of wall thickness can be rolled with the same core bar, and the number of types of core bars can be reduced. A similar technique is disclosed in JP-A-60-87907 and JP-A-6-87008.

[0014]

In the roll-sharing system in which a four-roll stand is combined with the exit side of a two-roll stand row, the roll gap is tightened from a reference value in the two-roll stand row, and the center of the hole radius is formed. Is rolled out of the center of the core bar to obtain a finished tube having a wall thickness smaller than that obtained by normal rolling, in which the center of the hole radius matches the center of the core bar. Thereafter, the wall thickness fluctuation caused by tightening the roll gap in the two-roll stand row and having four peaks at 45 ° from the groove bottom coincided with the wall thickness peak and the groove bottom position of the porous roll. The problem is solved by rolling with one 4-roll stand. The four-roll stand has a roll-down adjustment mechanism for each roll-type roll, and is used to obtain finished pipes having different wall thicknesses with core rods having the same outer diameter.
If you change the roll reduction position in the roll stand row,
The rolling reduction is also performed on the four-roll stand to reduce the thickness variation generated in the two-roll stand row.

By the way, in a general mandrel mill, when a normal gap is rolled with the roll gap at each stand set to a reference value, the design of the hole type roll is designed so that the workability of the mandrel mill becomes a constant pattern. Has been done.
This is to prevent rolling troubles such as biting, drilling, poor biting, etc. in any of the stands.In the first half of the stand, strong rolling is performed, and in the finishing stand, light rolling is performed to secure dimensional accuracy. It is common to do. The roll gap reference value at each stand when performing normal rolling is usually the same at each stand due to roll cutting.

In the case where the above-mentioned common core rod rolling is performed without changing the wall thickness of the raw tube using such a mandrel mill, the roll at each roll stand is changed according to the wall thickness change amount of the finished tube. Although the gap is tightened from the reference value, if the tightening amount is the same for each stand, No. 1, 2
If only the degree of processing on the stand increases and the tightening amount increases, poor biting occurs at the No. 1 stand. Therefore, in the two-roll stand row, the tightening amount of the roll gap is made smaller in the front stage, and the increase in the working degree due to the change in the wall thickness of the finished pipe is evenly distributed to each stand.

However, even with such considerations, 2
It is inevitable that the degree of processing increases at each stand in the roll stand row. For this reason, before the unevenness correction effect of the four-roll stand is saturated, the two-roll stand row starts to bite due to an increase in the working degree and form a hole. This rolling trouble is caused by difficult-to-roll thin-walled tubes (thickness / outer diameter: small)
Also, it is remarkable in a material having a lower hot workability than ordinary steel. And, this rolling trouble results in a limited amount of tightening at each stand. Therefore, in the conventional core bar sharing rolling, the range of sharing is not as wide as expected.

An object of the present invention is to reduce the occurrence of rolling troubles in a two-roll stand array in a shared roll of a core rod in which finished pipes having different wall thicknesses are rolled using core rods having the same outer diameter. An object of the present invention is to provide a tube rolling method for expanding the range of common use of a metal rod.

[0019]

SUMMARY OF THE INVENTION According to the present invention, two sets of two-roll rolls having a pair of roll-type rolls whose pressing directions are orthogonal to each other are provided on the output side of a plurality of two-roll stands having one set of roll-type rolls. A four-roll stand with a 45 ° depressed direction shifted from the stand is placed, and the base tube is passed through these stand rows with the core bar inserted, and the wall thickness is reduced by the two-roll stand rows. It is intended for tube rolling that reduces circumferential wall thickness fluctuations.

In this type of conventional tube rolling, when a finished tube having a different thickness is rolled using a cored bar having the same outer diameter, a raw tube having the same size is supplied to a two-roll stand row. Therefore, as the thickness change amount of the finished tube increases, the degree of processing in the two-roll stand array increases, and the thickness change amount of the finished tube is limited due to the rolling trouble that occurs. Therefore, the present inventor changed the idea, and did not change the wall thickness of the finished pipe in the two-roll stand row, but instead performed it in the raw pipe, so that the wall thickness change in the two-roll stand row was substantially the same as that of normal rolling. The present inventors have conceived a rolling method that can be used in common with a metal core rod, and have reached the present invention.

According to the tube rolling method of the present invention, two sets of two-roll rolls whose rolling directions are orthogonal to each other are provided on the output side of a plurality of two-roll stands having one set of rolls. On the other hand, a four-roll stand whose rolling direction is shifted by 45 ° is arranged, and the base tube is passed through these stand rows with the cored bar inserted, and the wall thickness is reduced by the two-roll stand row.
In tube rolling, in which the thickness variation in the circumferential direction is reduced by a roll stand, using a core bar having the same outer diameter, the roll gap is tightened in a two-roll stand row and a finished pipe having a different thickness is rolled as compared with the normal rolling. In case, two roll stun
The amount of tightening of the roll gap in the row
A two-roll stand that is qualitatively the same and that has a thickness change amount substantially the same as the thickness change amount of the finished tube is made on the side of the raw tube supplied to the two-roll stand row. This avoids an increase in the degree of processing in the row.

According to a second aspect of the present invention, there is provided a method for rolling a tube.
The thickness is changed by changing the inner diameter of the pipe .

[0023]

[0024]

In the pipe rolling method of the present invention, when finishing pipes having different thicknesses are rolled by using core rods having the same outer diameter, the thickness of the finished pipe is changed by changing the thickness of the raw pipe. Although the roll gap in the row of roll stands is tightened more than in normal rolling, an increase in the working degree is avoided in the row of two roll stands, and the rolling burden is substantially the same as in normal rolling.

[0025] 2 tightening the amount of roll gap of a roll stand column, are virtually identical in each stand. By doing so, in each stand of the two-roll stand row, the distribution of the working degree at the time of designing the die is almost reproduced, and even if the wall thickness of the finished tube is largely changed, rolling free of rolling trouble is realized.

In the normal rolling and the common-metal-rolling rolling, it is preferable that the tightening amount of the roll gap is the same for all the stands in order to realize the reduction in the roll shape design.
In actual rolling, it is rare that rolling is performed in a state where the roll gaps of all stands are completely uniform. That is, in the rolling of the pipe, control is performed to keep the length of the rolled material on the exit side of the mandrel mill constant, and the variation in the elongation length due to the variation in the weight of the round billet as the material, the variation in the average outer diameter of the cored bar used, etc. Is made uniform by changing the target thickness. Therefore, the roll gaps of the finishing stands are different for each rolled material, and the roll gaps of all the stands are not completely uniform. Further, in the rolling of the mandrel mill, the roll gap of each stand may be adjusted in order to be affected by the friction state between the core bar inserted into the rolled material and the rolled material, the friction state between the rolled material outer surface and the roll, and the like. From this point of view, the roll gap of all stands is not completely uniform.

In the case of normal rolling, the roll gap adjustment amount of each stand is at most ± 0.5 mm or less.
It is relatively small compared to the amount of tightening of the roll gap in the roll sharing of the core bar, and can be regarded as substantially the same roll gap. As described above, making the roll gap tightening amount of the cored bar shared rolling constant for all stands and making a relatively small roll gap correction can be achieved by almost completely reproducing the working ratio distribution of the groove design in the shared cored bar rolling. It has no effect on the technical idea of the present invention to prevent the occurrence of defects.

The wall thickness of the raw tube is preferably changed by changing the inner diameter without changing the outer diameter because of easy setting of the drilling machine. When such a tube is rolled by tightening the roll gap with a two-roll stand array, that is, a mandrel mill, the outer diameter reduction amount in the mandrel mill becomes larger than that in the normal rolling. However, the No. 1 stand of the mandrel mill has a vertical elliptical relationship between the vertical diameter and the horizontal diameter of the hole shape so that even if the outer diameter of the base tube fluctuates slightly, poor biting does not occur. Even if the amount of reduction is increased, poor biting is unlikely to occur. Furthermore, for the No. 2 stand and subsequent stands, the ratio of the vertical diameter to the horizontal diameter of the hole type is close to 1, and it is a hole type that tends to cause biting failure, but it is inevitable by tightening the roll gap The relationship between the vertical diameter and the horizontal diameter of the hole shape during rolling is in the shape of a horizontal ellipse, and the outer diameter is reduced by rolling the No. 1 stand. .
Since there is no effect on the second and subsequent stands, poor start-up due to an increase in the outer diameter reduction amount does not occur.

[0029]

EXAMPLES Examples of the present invention will be shown below, and the effects of the present invention will be clarified by comparison with comparative examples.

In six six-roll stands, an outer diameter of 173 mm × thickness of 3 was measured using a core bar having an outer diameter of 107 mm.
A case where a 1-mm tube was rolled into a finished tube having an outer diameter of 151 mm and a wall thickness of 20 mm was defined as normal rolling, and a common-core rolling was performed. In the rolling with a common core rod, one 4-roll stand was arranged on the exit side of six 2-roll stands, and rolling was performed by tightening the roll gap at each stand.

[0031]

[Table 1]

Table 1 shows the rolling conditions at that time. Of the six stands, the latter two stands are finishing stands.
The groove radius R ₂ at the bottom of the groove in the two stands is 73.50 mm,
The hole-shaped radius angle θ was 50 °. The hole radius R ₄ at the bottom of the groove in the 4-roll stand is 68.36 mm, and the hole radius angle θ
Was 25 °.

In the normal rolling, as shown in FIG. 3, a hole radius R ₀ is set so as to obtain a uniform finished pipe thickness in the circumferential direction.
Rolling was performed with a cored bar having an outer diameter D ₂ = 107 mm determined from = 7.35 mm. The roll gap S _{0 at} this time
Is a setting of 25 mm, which is a gap when a mold is designed. The wall thickness distribution of the finished tube as shown in FIG. 5 as normal rolling was obtained.

For reference, as shown in FIG. 4, rolling was performed by tightening the roll gap from the design gap S ₀ = 25 mm to S = 19 mm using a two-roll stand without changing the outer diameter D ₂ of the cored bar. Here is an example. The gap tightening amount is 6 mm. Although the groove bottom thickness t _G1 is 17 mm, the thickness t ₁ ′ at the flange portion is larger than t _G1 . As a result, the thickness distribution of the finished pipe is shown in FIG. As shown in FIG.

In the roll-sharing operation using a four-roll stand in combination with a core rod, rolling is performed by tightening a roll gap with a two-roll stand in the same manner as the above-mentioned reference rolling. Then, rolling is performed on a four-roll stand in which the rolling direction is shifted by 45 ° with respect to the two-roll final stand. As a result, uneven wall thickness generated at the four positions of 45 ° from the groove bottom generated by the two-roll rolling is eliminated, and a finished pipe having good dimensional accuracy as shown after the four-roll rolling in FIG. 7 is obtained.

At this time, in the four-roll stand, the rolling position was set according to the thickness change amount of the finished tube so that the distance between the bottom of the roll groove and the bar during rolling was the target thickness. On the other hand, in the two-roll stand row, the following two roll positions were set.

In the prior art, as shown in Table 2, the base tubes having the same wall thickness are used, and the roll gap in the two-roll stand row is tightened more gradually than in the normal rolling to reduce the wall thickness of the finished tube. It was performed with a decrease. Finishing stand (No. 5,
The roll gap at (6 stands) is set to a value corresponding to the thickness of the finished pipe in order to secure the target thickness. If the roll gap of the stand other than the finishing stand is the same as that of the finishing stand, the degree of processing increases only in the No. 1 and 2 stands, and a rolling trouble occurs here. The roll gap was increased as the front stage stand was distributed. As a result, the increase in the working degree due to the change in the wall thickness of the finished pipe does not concentrate on a specific stand. However, when the wall thickness change amount reaches 6 mm, a rolling trouble occurs, and further wall thickness change cannot be performed. Was. Even at this stage, uneven wall thickness of the finished tube was within an acceptable range.

On the other hand, in the present invention, as shown in Table 3, an amount of thickness change corresponding to the change in the thickness of the finished pipe is performed by changing the inner diameter of the raw pipe, and in the two-roll stand row, the thickness of the finished pipe is changed. Each stand was tightened with the same roll gap as the finishing stand. As a result, at each stand, the increase in workability due to the change in wall thickness of the finished pipe was avoided, and the workability distribution at the time of designing the die was almost realized. Did not occur. However, at this stage, since the uneven thickness of the finished pipe exceeds the allowable value, the actual possible wall thickness change is 8.4.
mm.

Table 4 shows the range of wall thickness obtained by sharing the cored bar in each rolling. Note that the amount of correction of the roll gap of each stand performed after the uniform roll gap was tightened by all the stands by the shared roll of the core bar in the present invention was ± 0.5 mm or less, and the roll gap was tightened by the shared roll of the core bar. It shows a relatively small value as compared with the embedding amount, and the roll gaps of all the stands could be regarded as substantially constant.

[0040]

[Table 2]

[0041]

[Table 3]

In the prior art, when the thickness change amount becomes 6 mm or more, rolling failure occurs in the two-roll stand row.
Although there is room for the uneven thickness ratio, the thickness change range by sharing the bar is limited to 5 mm. On the other hand, in the present invention, since the occurrence of rolling failure in the two-roll stand row is prevented, the thickness deviation rate after the four-roll rolling gradually increases with the increase in the wall thickness change due to the shared use of the bars, 8.4 mm, which exceeds the target value of the wall ratio of 2%, is the limit of the wall thickness change amount. That is, in the present invention, the effect of correcting uneven thickness by four-roll rolling can be completely used.

As a result, under the rolling conditions shown in the examples,
By applying the technique of the present invention, the thickness change range is expanded 1.6 times by sharing the bar. Therefore, in this embodiment, it is possible to use 8 mm in common without greatly deteriorating the wall thickness unevenness of the finished pipe, and the number of bars and the man-hour for bar replacement performed every time the wall thickness of the finished pipe is changed. , Compared with the prior art, and reduced to 1/8 with respect to normal rolling.

[0044]

[Table 4]

[0045]

As described above, according to the tube rolling method of the present invention, rolling in which the roll gap is tightened by a two-roll stand row is performed, and a circumferential thickness variation caused by the rolling is reduced by a four-roll stand. In the case of tube rolling, in which the thickness of the finished tube is reduced by rolling, and the thickness change of the finished tube is borne by the raw tube side, the degree of work accompanying the thickness change in the two-roll stand row is increased. Can be avoided, and the thickness change range can be greatly expanded. As a result, not only does the bar replacement work performed each time the wall thickness of the finished tube changes at a constant pitch significantly decrease, but also the bar storage space and the cost of owning the bar greatly decrease.

Further, by making the tightening amount of the roll gap in the two-roll stand row substantially the same in each stand, the rolling trouble in the two-roll stand row can be more effectively prevented, and the thickness change range can be further reduced. Can be expanded.

In the tube rolling method according to the second aspect , the thickness of the raw tube is changed by changing the inner diameter of the tube, so that the operation of changing the thickness is easy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing rolling by a mandrel mill.

FIG. 2 is a schematic diagram showing a rolling state in a two-roll finishing stand.

FIG. 3 is a schematic diagram showing a state in which the outer diameter of a cored bar is changed to change its thickness.

FIG. 4 is a schematic view showing a state in which a roll gap is tightened to change a wall thickness.

FIG. 5 is a table showing a relationship between a roll gap tightening amount and uneven thickness.

FIG. 6 is a schematic diagram showing rolling with a cored bar shared with a four-roll stand.

FIG. 7 is a chart showing the effect of rolling with a common core rod.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Roll stand 11 Hole type roll 20 Element tube 30 Core rod

Claims (2)

(57) [Claims] 1. An outlet side of a plurality of two-roll stands provided with one set of roll-type rolls, two sets of roll-type rolls whose pressing-down directions are orthogonal to each other, and the roll-down direction of which is 45 degrees with respect to the immediately preceding stand. A four-roll stand that is shifted is placed, and the pipe is passed through these stand rows with the core bar inserted. The wall thickness is reduced by the two-roll stand row, and the wall thickness fluctuation in the circumferential direction is reduced by the four-roll stand. In the reduction of tube rolling, when the roll gap is tightened in a two-roll stand row using core rods of the same outer diameter and the roll gap is tightened as compared with the normal rolling, and the finished pipes with different wall thicknesses are rolled, a row in a two-roll stand row is used.
The amount of tightening of the gap is virtually the same for each stand
In addition, the thickness change of substantially the same amount as the thickness change amount of the finished pipe is performed on the side of the raw pipe supplied to the two-roll stand row, and processing in the two-roll stand row accompanying the thickness change is performed. A tube rolling method characterized by avoiding an increase in degree. 2. The pipe thickness is changed by changing the pipe inner diameter.
Pipe rolling method according to claim 1, wherein the cormorants.