JP2005193247A - Method for manufacturing seamless steel tube and mandrel mill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent local decrease in the thickness of a tube stock which is rolled with a mandrel mill. <P>SOLUTION: In the mandrel mill provided with a plurality of roll stands having a pair of grooved rolls opposing each other, the thickness of the tube stock in the direction of the final screw-down in the position of the outlet side of the final roll stand and/or the 90° direction to the direction of the final screw-down are measured with thickness measuring instruments and, when the measured value is smaller than a calculated value by comparing the measured value with the calculated thickness value with a comparing means, rolling reduction of a roll stand at which the reduction is performed in the same direction of screw-down as the measuring direction in the upstream before at least two stages of the final roll stand is decreased through a control section. By this invention, the local decrease in the thickness of the tube stock which is rolled with the mandrel mill is surely prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a seamless steel pipe and a mandrel mill.

  An example of the manufacturing process of the seamless steel pipe in the mandrel mill is shown in FIG. In FIG. 6, a round steel piece 1 which is a material of a seamless steel pipe is heated in a rotary hearth type heating furnace 2, extracted from the rotary hearth type heating furnace 2, and drilled by a punching machine 3. Become. The raw tube 4 is a mandrel mill 6 and a mandrel bar 5 is inserted from the rear end side thereof, and a 5 to 9-stage roll stand (hereinafter simply referred to as a stand) having a pair of perforated rolls is used in one pass. It is rolled to a predetermined dimension.

  When the raw tube 4 is rolled by the mandrel mill 6, the mandrel bar 5 inside is pulled out, and the outer shape is adjusted by the outer shape adjusting machine 7 such as a sizer or a stretch reducer to have a predetermined outer diameter. Thereafter, the seamless steel pipe having a predetermined outer diameter is cooled in a cooling bed and cut into a predetermined length, or is subjected to bending correction, test inspection, marking, and the like to become a steel pipe of a product.

  The external shape adjuster 7 mainly increases the roundness and outer diameter accuracy of the seamless steel pipe, and the wall thickness of the seamless steel pipe is mainly determined by the mandrel mill 6. That is, the inner diameter of the seamless steel pipe is determined by the outer diameter of the mandrel bar 5 inserted into the raw pipe 4 during rolling by the mandrel mill 6, and the amount of reduction that is reduced by each stand, particularly the final two stages including the final stand. The thickness of the stand is determined by the amount of reduction of the stand.

  In the mandrel mill 6, each stand is alternately displaced by 90 degrees in a direction perpendicular to the axis of the mill, so that the thickness in the groove direction of the hole roll of the final stand and the hole roll of the stand upstream of the first stage The gap between the mandrel bar 5 and the hole-type roll is adjusted so that the thickness in the groove direction is a predetermined thickness. This adjustment method is based on the premise that the thickness in the groove portion direction of the perforated roll in the latter two-stage stand changes following the distance between the mandrel bar 5 and the perforated roll.

In the retract type mandrel mill in which the extractors are arranged in series with the mandrel mill, a hot wall thickness measuring device is arranged in the pressure reduction direction of the subsequent three-stage stand in the mandrel mill, and the hot wall thickness measuring device is used for measurement. Some of them are provided with a gap control unit that adjusts the roll gap of the subsequent three-stage stand in the mandrel mill based on the measured thickness measurement result. The final stand of the mandrel mill is a stand made up of four hole rolls, and is different from a stand made up of two pairs of hole rolls.
JP-A-8-71616

  However, depending on the rolling condition of the mandrel mill, the wall thickness at the position corresponding to the groove bottom position of the perforated roll may already be a predetermined value or less in the stand upstream of the subsequent two-stage or three-stage stand. In this case, in the technique proposed in Patent Document 1 or the like, even if the interval between the hole rolls with respect to the mandrel bar is adjusted to a predetermined value in the subsequent two-stage or three-stage stand, it is already less than the predetermined value. In this state, the thin portion of the steel pipe does not change following the interval between the hole-type rolls, and there is a problem that the thickness cannot be adjusted.

Here, the wall thickness of the tube at the exit of the final stand of the mandrel mill is not uniform in the circumferential direction, and the portion corresponding to the groove bottom of the perforated roll is the thinnest, and the shaft from the groove bottom to the shaft The position shifted 45 degrees with respect to the heart is thickest. Although the difference between the thin part and the thick part is a slight value, the production standard thickness value in the mandrel mill is an intermediate value between them. The position of the hole-shaped roll is adjusted so that the position of the groove bottom of the hole-shaped roll becomes a predetermined position on the basis of the production standard thickness value which is an intermediate value.
The “predetermined value” of the gap between the hole rolls with respect to the mandrel bar in the above problem is a value at a position corresponding to the groove bottom portion having a wall thickness thinner than the production standard wall thickness value. It is obtained by calculation from the groove bottom interval (Lr) of the perforated rolls opposed to each other, the displacement rate (k) of the stand, the rolling load (L), etc. (hereinafter referred to as a calculated thickness value).

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a method of manufacturing a seamless steel pipe and a mandrel mill capable of obtaining a seamless steel pipe having a stable wall thickness.

In order to achieve the above-described object, the present invention provides a wall thickness measuring device that is provided on the exit side of the final stand and measures the wall thickness of the raw tube in the direction of 90 degrees with respect to the final rolling direction and / or the final rolling direction. When,
A comparison means for comparing the measured value based on the output from the wall thickness measuring instrument with the calculated wall thickness obtained by the calculation;
When the measured value is smaller than the calculated thickness value, the amount of reduction of the target stand is reduced so as to reduce the amount of reduction of the stand that receives the output from the comparison means and lowers at least two stages upstream from the final stand in the same direction as the measurement direction. Use a mandrel mill with a control unit to control
When the thickness of the raw tube in the direction of 90 degrees with respect to the final reduction direction and / or the final reduction direction is measured on the exit side of the final stand, and the measured value is smaller than the calculated thickness value obtained by calculation The amount of reduction of the stand that is reduced in the same direction as the direction in which the measurement is performed at least two stages upstream from the final stand is reduced.

In the present invention, the thickness of the raw tube in the direction of 90 degrees with respect to the final reduction direction and / or the final reduction direction is measured with a thickness measuring device provided at the exit position of the final stand, and the measured value is a calculated thickness value. When it is smaller than the final stand, it is decided to reduce the reduction amount of the hole-type roll of the stand at least two stages upstream from the final stand.
1) Since the position where the thickness reduction is most likely to occur immediately after the rolling of the tube is measured, the thickness reduction is reliably detected.
2) The position where feedback control is performed in response to the thickness reduction is not the final stand, but a stand more than two stages upstream from the final stand, so that the thickness reduction is surely eliminated.
3) Because the distance between the wall thickness measurement position and its feedback position is short, even if wall thickness reduction is measured, the amount of wall thickness reduction generated is small.
4) The rolling balance between the stands is maintained, the amount of raw pipe wall flowing into the flange portion of each stand is reduced, the rolling down is increased at the part where the hole roll diameter is small, and the tension between the stands of the blank tube is increased. It is not disturbed, so the diameter of the tube is prevented from increasing due to the increased tension, and the adhesion to the mandrel bar is reduced, reducing the mandrel bar pulling trouble.
5) In addition, the present invention can be carried out only by rearranging the conventional thickness measuring instrument and changing the control software, without requiring new equipment and its installation location.
There is an effect.

The present invention will be described in detail below.
The present inventor has always worked on the development of a stable product with little uneven thickness when manufacturing seamless steel pipes by a mandrel mill. Although the rolling of the mandrel mill is automated, sometimes a thin thickness portion or uneven thickness less than the reference value may occur. In such a case, the distance between the perforated roll and the mandrel bar was adjusted to reduce the amount of reduction at the final stand of the mandrel mill and restore the wall thickness, but still a thin wall or uneven thickness occurred. Was. The present inventor has found that these thin portions and uneven thickness do not necessarily occur due to the distance between the hole roll of the final stand of the mandrel mill and the mandrel bar.

FIG. 1 exaggeratedly shows the positional relationship between the thin-walled position 41 of the base tube 4 and the perforated roll 61 when the base tube 4 is cut and examined at the exit position of the final stand of the mandrel mill 6. It is. Reference numeral 61 a denotes a groove portion of the hole-type roll 61, 61 b denotes a flange portion of the hole-type roll 61, and 61 aa denotes a groove bottom of the hole-type roll 61.
From FIG. 1, the thin wall position 41 of the raw tube 4 coincides with the groove bottom 61 aa of the perforated roll 61, and the shape of the thin wall position 41 is the outer periphery of the mandrel bar 5 inserted into the raw tube 4. It turns out that it is different from the shape. That is, the thin thickness position 41 was not rolled on the final stand.

Therefore, the inventor investigated the rolling form in the mandrel mill 6. The rolling form is shown in FIG.
2A is a view showing a state where the mandrel bar 5 is inserted into the raw tube 4. FIG. The inner diameter of the raw tube 4 is slightly larger than the outer diameter of the mandrel bar 5, and there is a gap between the inner diameter of the raw tube 4 and the outer diameter of the mandrel bar 5.
X is the axis of the mandrel mill 6, and each stand is set in a straight line around the axis X and is concentric with the center of the mandrel bar 5.

  (B) is the figure which showed the state which is rolling the raw tube 4 in which the mandrel bar 5 was inserted in the stand of the uppermost stream | stage. The stand-type rolls 61 of the stand are provided to face each other with the reduction direction inclined 45 degrees to the left with respect to the perpendicular. When the tube 4 is crushed by the perforated roll 61, the thickness of the unrolled tube 4 is reduced as shown in the figure, while the thickness of the flange portion 61b is not rolled and extruded in the direction of the flange portion 61b. The base tube 4 itself is elliptical. Moreover, the gap between the inner diameter of the raw tube 4 and the mandrel bar 5 flows in the direction of the flange portion 61b and changes into a large space.

  (C) is the figure which showed the state which rolls the raw | natural pipe | tube 4 with the stand of the 2nd step | line following the most upstream step | paragraph. In this second stage stand, the position of the perforated roll 61 is displaced by 90 degrees in the direction orthogonal to the axis X with respect to the position of the perforated roll 61 of the most upstream stage stand. The thickness in the flange portion 61b direction that has not been performed is rolled. Also in this case, as in the case of rolling at the uppermost stream stand, the thickness of the flange portion 61b portion of the second-stage stand is not rolled, and the raw tube 4 is extruded in the direction of the flange portion 61b portion. It has become. Then, the area of the inner surface of the raw tube 4 in the direction of the flange portion 61b is smaller than that of rolling at the most upstream stand between the mandrel bar 5 but remains as a protruding gap. ing.

  Such rolling is sequentially repeated, and in the subsequent stage including the final stand, the shape of the groove 61a of the perforated roll 61 is rolled so as to approximate the outer diameter of the finished tube 4 in the mandrel mill 6, and the mandrel mill in the final stand. 6 is finished to the outer diameter and thickness of the manufacturing standard dimensions as 6. Note that the amount of reduction at each stand is determined from the stage of perforation by the perforator 3 according to the product dimensions.

  FIG. 3 is a view showing a state in which the raw tube 4 is being rolled down at the front stage stand of the mandrel mill 6. The mandrel bar 5 located at the center determines the inner diameter of the seamless steel pipe that is the product, so that the outer diameter dimension is sufficiently controlled, and there is no surface flaw, and the cross-sectional shape is close to a perfect circle. It has become. On the other hand, the outer surface portion of the raw tube 4 is restrained by the groove portion 61 a of the hole-type roll 61. As shown in the figure, the arc of the groove bottom 61aa of the hole-shaped roll 61 is not concentric with the mandrel bar 5, but is larger than the diameter of the mandrel bar 5, and the groove bottom 61aa of the hole-shaped roll 61 is the most. The amount of reduction is large, and the amount of reduction is reduced as it goes to the flange portion of the perforated roll 61. In FIG. 3, the hatched portion of the cross section of the raw tube 4 indicates the range where the rolling force is applied.

  The groove 61a of the perforated roll 61 is shaped as described above, so that it is impossible to simultaneously reduce the same amount over the entire circumference of the element tube 4, and the thickness of the element tube 4 is reduced. Since it is difficult to absorb all of the accompanying portions in the longitudinal direction (axial direction) of the raw tube 4, the portion that is not absorbed in the longitudinal direction is projected on the flange portion of the perforated roll 61. . Then, the arc of the groove 61a is enlarged as a means to escape without a step so that the overhanging portion does not cause wrinkles on the surface of the raw tube 4.

By adopting the shape of the groove portion 61a shown in FIG. 3, the portion that could not be absorbed in the longitudinal direction (axial direction) accompanying the thickness reduction of the raw tube 4 can be released in the flange portion direction of the perforated roll 61. , And so on.
Of course, in the mandrel mill 6, it goes without saying that the rotational speed of the hole-type roll 61 of each stand is optimally controlled so that the base tube 4 does not adhere to the mandrel bar 5 and extends in the longitudinal direction as much as possible.

  On the other hand, by forming such a shape, a recess 42 corresponding to the gap with the mandrel bar 5 is generated on the inner surface of the raw tube 4 in the flange portion. Although this dent 42 disappears at the final stand of the mandrel mill 6, it has been found that the dent 42 sometimes becomes large and the trace of the dent 42 may not disappear at the final stand.

  The cause of the increase in the size of the recess 42 is influenced by the material, the heating temperature, and the like. For example, as can be seen from FIG. 3, when the amount of reduction is increased, the amount of thickness overhang in the flange direction is increased, and the depression 42 is increased accordingly. That is, when the amount of reduction is too large, the amount of the depression 42 in the 90-degree direction increases as the thickness in the reduction direction becomes excessively thin. Further, when the direction of the depression 42 is reduced by the next stand, the enlarged depression 42 portion moves in the thickness direction which is excessively thinned by the previous stand, and the deformation resistance is further reduced due to the thin thickness at that time. As a result, a larger recess 42 is likely to occur in the thin-walled portion.

  In this way, a large dent 42 tends to be generated in the large reduction direction, and when the dent 42 remains in a state where it does not completely disappear even in the final stand, the dent 42 portion is thinner than the calculated thickness value. Thick. Therefore, in order to prevent the occurrence of a thin wall in such a case, adjustment of the reduction amount of the rear stand of the mandrel mill 6 cannot be eliminated, and the same reduction direction as the upstream measurement direction that caused the generation of the recess 42 is generated. The amount of reduction on the stand must be reduced.

  Therefore, the method for producing a seamless steel pipe according to the present invention uses a mandrel mill having a plurality of stands each having a pair of hole-type rolls facing each other, and the final reduction direction and / or the final reduction direction on the exit side of the final stand. When the measured thickness is smaller than the calculated thickness value obtained by calculation, the same direction as the direction in which the measurement was performed at least two stages upstream from the final stand. This reduces the amount of rolling of the stand that is rolled down.

  Further, the method of the present invention described above is provided on the exit side of the final stand in a mandrel mill having a plurality of stands each having a pair of hole-type rolls facing each other, and is 90% with respect to the final reduction direction and / or the final reduction direction. A thickness measuring device for measuring the thickness of the raw pipe in the direction of orientation, a comparison means for comparing the measured value based on the output from the thickness measuring device and the calculated thickness value obtained by the calculation, and the measured value When the value is smaller than the calculated wall thickness value, the reduction amount of the target stand is controlled so as to reduce the reduction amount of the stand that receives the output from the comparison means and is lowered in the same direction as the measurement direction at least two stages upstream from the final stand. It can be carried out by a mandrel mill equipped with a control unit.

In the present invention, on the exit side of the final stand, the thickness of the raw tube in the direction of 90 degrees with respect to the final reduction direction and / or the final reduction direction is measured. This is because the thickness dimension of the raw tube can be measured earliest, so that when the thin wall thickness is detected, the amount of generation can be minimized.
Further, as described above, the position of the raw pipe where the thickness of the raw pipe is equal to or less than the calculated thickness value is a position corresponding to the groove bottom position of the perforated roll. Since it is a position in two directions displaced by 90 degrees from the position in the reduction direction, at least the thickness dimension in either of these two directions is measured. Of course, the thickness dimension in these two directions may be measured.

  Further, in the present invention, the amount of reduction of the hole-type roll of the stand at least two stages upstream from the final stand is reduced because the mandrel mill alternately displaces each stand by 90 degrees in the direction orthogonal to the axis. A pair of final stands and a stand upstream of the pair are provided as a finishing stand in the mandrel mill, and the thickness and outer diameter are adjusted with a relatively small amount of reduction. The final stand as a stand is removed from the control target.

  In other words, the thin wall thickness in the rolling direction at the final stand is an effect due to the large amount of rolling at the second stage upstream from the final stand, and the thin wall thickness in the 90 degree direction with respect to the rolling direction at the final stand. This is because the thickness corresponds to a thin wall thickness in the rolling direction at the first stage upstream stand, and is affected by the fact that the amount of rolling down at the third stage upstream from the final stand is large.

The amount of reduction to reduce the reduction amount must be maintained at the calculated thickness value at least at the last stand and the stand upstream of that one stage, so the difference between the calculated thickness value and the thickness of the thin thickness portion The reduction amount is reduced within a range obtained by multiplying the gain margin, for example, 1.2.
When the reduction amount of the roll-type roll subject to reduction in the reduction amount becomes extremely small as the reduction amount decreases, the reduction amount of the further-stage hole-type roll in the same reduction direction is reduced to reduce the reduction amount. It is desirable to balance the amount of reduction.

  In addition, the value to be compared with the measured value is not the production standard wall thickness value, but is the calculated wall thickness value because a different mandrel bar is used for each rolling of the blank tube, and the rolling load etc. This is because it is difficult to prevent thin wall thickness stably if the contrast value is set to a constant value.

This calculated thickness value is calculated by the following calculation formula using, for example, the distance between the groove bottoms of the perforated rolls in the final stand.
T = (Lr−ODbar) / 2 (1) Equation T: Calculated thickness value (mm)
Lr: Distance between groove bottoms of opposing hole rolls during reduction (mm)
ODbar: Outer diameter of mandrel bar (mm)
Lr = Lr0 + Gr + δ
Lr0: Distance between groove bottoms (mm) when the flange portions of the opposed hole rolls are brought into contact Gr: Opening interval (mm) of the opposed hole rolls (flange portion)
δ: Displacement of stand due to rolling load (mm)
δ = k × L
k: Displacement rate of the stand (mm / N)
L: Reduction load (N)

Hereinafter, the manufacturing method and mandrel mill of the seamless steel pipe in this invention are demonstrated based on drawing.
FIG. 4 is a diagram showing a mandrel mill according to the present invention.
In this embodiment, the raw tube 4 is rolled by five stands, ie, stands st1 to st5 from the upstream side in the arrow direction. Note that st1 is the most upstream stand and st5 is the final stand.

Each of the stands st1 to st5 includes a pair of hole-type rolls opposed to each other, and each hole-type roll is rotatably attached to an attachment frame body positioned outside the flange portion via a chock. The rotation of the hole-type roll is performed by a motor provided outside the chock and connected to the rotation axis (center axis) of the hole-type roll.
In addition, a load meter is provided in the chock to measure a load (rolling load L) applied to the hole-type roll. When the opening of the pair of hole-type rolls is closed to the maximum, the flange portion comes into contact with each other to form a minimum elliptical shape, and the center of the elliptical shape is the same as the axis X of the mandrel mill 6 (the axis center of the mandrel bar 5). ). When the flange portion is in contact, that is, by moving the chock of each hole roll symmetrically by the same amount on the basis of the distance Lr0 between the groove bottoms at this time, the hole roll moves forward and backward (reduction) Amount adjustment). The amount of movement of the chock becomes the open gap Gr between the flange portions of the opposed hole rolls.

  Each of the above-mentioned stands is provided by alternately shifting the rolling direction by 90 degrees, and among the stands st1 to st5, the three stands st1, st3, and st5 are in the same rolling direction and in the circumferential direction of the raw tube 4. Rolling the same position. Further, st2 and st4 are both displaced 90 degrees in the rolling direction with respect to the previous stand, and the part that has not been rolled by the previous stand is rolled. That is, the raw tubes 4 are alternately rolled every 90 degrees in the circumferential direction by the stands st1 to st5. In this case, the raw tube 4 is finished to a predetermined thickness in the circumferential direction in two stages st4 and st5 in the subsequent stage.

  For example, the control units 111 to 115 are provided for each of the stands st1 to st5, and in accordance with instructions from the control units 111 to 115, the rotational speed of the hole roll and the forward / backward movement with respect to the axis X of the mandrel mill 6, that is, the hole type The amount of roll reduction can be controlled.

  On the exit side of the stand st5 that is the final stand, for example, a thickness measuring device 81 that measures the thickness of the stand st5 in the rolling direction, and the thickness of the stand st4 and the rolling direction of the stand st4 that is displaced by 90 degrees in the rolling down direction. A thickness measuring device 82 for measuring the thickness is provided, and the thickness in each direction is measured. The data measured by the wall thickness measuring devices 81 and 82 are transmitted to the calculation / comparator 9 one by one.

  The setting device 10 not only sets the manufacturing standard wall thickness value, but also switches between automatic operation and manual operation of the mandrel mill 6, changes the automatic setting value, emergency stop, and other instructions for displaying operation data on the CRT and the printer. A print instruction or the like is possible. For example, those signals are transmitted from the setting unit 10 to the arithmetic / comparator 9 and processed through the arithmetic / comparator 9.

The calculation / comparator 9 1) receives signals from each external device, 2) calculates and compares those received signals according to a program stored in advance, and 3) relates the calculation / comparison results. It has a function to send to each external device.
The received signals of the arithmetic / comparator 9 are measured values from the thickness measuring devices 81 and 82, set values set from the setting device 10 each time, and control units 111 to 115 provided in each stand. Measured values such as the rotational speed of each perforated roll, the opening interval Gr of the perforated roll, the rolling load L, product information from the manufacturing process computer, manufacturing information of the mandrel mill 6, manufacturing information of each process, etc. It is.

The arithmetic / comparator 9 performs various arithmetic / comparison processes according to various received signals such as a preset arithmetic program, the relationship between the ratio of the rolling load L of each stand and the displacement of the stand at that time, that is, the displacement rate k, etc. I do.
For example, the outer diameter ODbar is obtained from the rolling load L from each of the control units 111 to 115, the opening gap Gr of the hole roll, and the mandrel bar outer diameter list stored separately and the used mandrel bar name transmitted. The calculated wall thickness value T is calculated according to the above equation (1).

  Further, the arithmetic / comparator 9 calculates the calculated thickness value T derived from the equation (1), the set thickness value set in the setting device 10, and the measured values from the thickness measuring devices 81 and 82. Are compared to calculate the magnitude. As a result of the calculation, when the measured thickness value is smaller than the calculated thickness value T, a value obtained by multiplying the difference by, for example, 1.2 as a gain margin is set as a reduction amount of the target stand.

  Moreover, the arithmetic / comparator 9 compares the received values from the control units 111 to 115 of the hole roll speed and the indicated values, and calculates the magnitude. These series of calculations also follow a preset calculation program. These calculations and comparisons are performed continuously.

  When the predetermined condition is satisfied as a result of the above processing, the arithmetic / comparator 9 continues to issue a control signal to the control units 111 to 115 to continue the production under the current conditions as it is. When the measured values from 81 and 82 are smaller than the calculated thickness value T, the amount of reduction with respect to the target stand among the control units 111 to 115 provided in each stand so as to restore the measured thickness value to a predetermined value. Send a control signal to change.

  For example, when the measured thickness value at the thickness measuring device 81 is smaller than the calculated thickness value T, the thickness measuring direction at the thickness measuring device 81 is the reduction direction at the stand st5, the stand st3, or st1. Therefore, the amount of reduction in the roll of the stand st3 corresponding to two stages upstream from the final stand st5 is reduced, and the thickness at the outlet of the final stand st5 is restored. In this case, the reduction amount to be decreased is the calculated decrease value described above. It should be noted that the reduction amount of the hole-type roll of the stand st1 that is two stages upstream from the stand st3 may be reduced by a small amount in accordance with the reduction amount of the reduction amount of the stand st3.

  Similarly, when the measured thickness value at the thickness measuring device 82 is smaller than the calculated thickness value T, the thickness measuring direction at the thickness measuring device 82 is the reduction direction at the stand st4 or the stand st2. Then, the amount of reduction at the hole type roll of the stand st2 that is three stages upstream from the final stand st5 is reduced, and the thickness at the outlet of the final stand st5 is restored.

  The processing for reducing the amount of reduction by the hole-type roll is performed by transmitting a signal from the arithmetic / comparator 9 to the control unit 113 for the stand st3 and to the control unit 112 for the stand st2, Controls the amount of reduction of the hole roll. On the contrary, when the measured thickness value at the thickness measuring device 82 is particularly larger than the calculated thickness value T, the calculation / comparator 9 causes the control unit 115 or 114 attached to the finishing stand to reduce the hole roll. Signal to increase quantity.

In addition, regarding the rotation speed control of the hole-type roll, a control signal is transmitted from the arithmetic / comparator 9 to the control unit corresponding to the hole-type roll.
The control unit of each stand receives a control signal from the arithmetic / comparator 9, and based on the received signal, the number of revolutions of the motor and the like corresponding to the control signal is controlled, and the amount of reduction and the number of revolutions of the hole roll are adjusted. . The adjusted value is fed back to the arithmetic / comparator 9 again.

An example of using the above-described apparatus of the present invention and controlling the amount of reduction of the perforated roll according to the calculated thickness value of the present invention using the conventional measured thickness value is shown below.
Number of mandrel mill stands: 5 Stand mill inlet tube size: outer diameter 250mm, wall thickness 20-30mm
Mill outlet tube size: 210mm outer diameter, 10-20mm wall thickness
Thickness measurement position: At the exit position of the final stand st5, the two types of thickness measurement equipment: the downward direction corresponding to the groove bottom of the same-hole roll, and 90 degrees relative to that direction: Transmission type Reduced amount of reduction when the γ-ray thickness gauge is insufficient: 1.14 times the amount of insufficient thickness

The implementation results of the present invention are shown in FIG. 5 together with the results of a comparative example in which the amount of rolling reduction is not controlled by the measured thickness value of the thickness measuring instrument.
In FIG. 5, the white bar graph is the example of the present invention, and the black bar graph is the comparative example, and the measured thickness value and the production at the groove bottom position of the perforated roll at both ends of the seamless steel pipe cut to a predetermined length. The difference from the standard wall thickness value is shown.

  From FIG. 5, the average value of the example of the present invention is +0.04 mm with respect to the production standard thickness value, the deviation σn-1 is 0.11, and the ratio of the number with a small thickness with respect to the production standard thickness value is 32.6%. On the other hand, the average value of the comparative example is -0.58 mm with respect to the production standard thickness value, the deviation σn-1 is 0.12, and the number with a small thickness with respect to the production standard thickness value is almost the total amount. It was. As described above, in the present invention, the production of a steel pipe with a small wall thickness is greatly reduced, the measured wall thickness approaches the production standard wall thickness value, and the thickness variation (uneven wall thickness) is also greatly reduced and improved. I know that. Further, as the thickness measuring device, not only a transmission type γ-ray thickness meter but also a laser ultrasonic interferometer, an electromagnetic ultrasonic thickness meter, or the like can be used.

  When the measured value of the wall thickness in the direction of 90 degrees with respect to the final rolling direction and / or the final rolling direction is smaller than the calculated wall thickness value on the exit side of the final stand, the same direction as the measurement direction at least two stages upstream from the final stand Therefore, the present invention can be applied regardless of the number of stands of the mandrel mill and the size of the seamless steel pipe.

It is the figure which exaggerated and showed the positional relationship of the thin thickness position of a raw tube, and a hole-type roll. It is the figure which showed the rolling form in a mandrel mill, (a) is a figure which shows the state which inserted the mandrel bar in the base pipe. (B) is the figure which showed the state which is rolling the raw pipe | tube with the stand of the uppermost stream | stage of a mandrel mill. (C) is the figure which showed the state which is rolling the raw pipe | tube with the 2nd stand of a mandrel mill. It is the figure which showed the rolling-down state of the raw pipe | tube in the front stage stand of a mandrel mill. It is the figure which showed the mandrel mill in this invention. It is the figure which showed the difference of the measured thickness value in the groove bottom part position of the hole-type roll in the example of this invention, and a manufacture reference | standard thickness value. It is a figure which shows an example of the manufacturing process of the seamless steel pipe in a mandrel mill.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Round steel piece 2 Rotary hearth type heating furnace 3 Punching machine 4 Base pipe 41 Thin wall thickness position 42 Indentation 5 Mandrel bar 6 Mandrel mill 61 Hole type roll 61a Slot part of hole type roll 61aa Hole bottom of hole type roll 61b Hole type roll Flange part 7 External shape adjustment machine 81, 82 Thickness measuring instrument 9 Calculation / comparator 10 Setting instrument 111, 112, 113, 114, 115 Control unit X axis

Claims (2)

In the method of manufacturing a seamless steel pipe using a mandrel mill provided with a plurality of roll stands having a pair of hole-type rolls facing each other,
Measure the wall thickness of the raw tube in the direction of 90 degrees with respect to the final reduction direction and / or the final reduction direction on the exit side of the final roll stand,
When the measured value is smaller than the calculated wall thickness value, the rolling amount of the roll stand that is rolled down in the same direction as the measurement direction at least two stages upstream from the final roll stand is reduced. Steel pipe manufacturing method. In a mandrel mill having a plurality of roll stands having a pair of hole-type rolls facing each other,
A wall thickness measuring device that is provided on the exit side of the final roll stand and measures the wall thickness of the raw tube in the direction of 90 degrees with respect to the final rolling direction and / or the final rolling direction;
Comparison means for comparing the measured value based on the output from the wall thickness measuring instrument with the calculated wall thickness value;
When the measured value is smaller than the calculated thickness value, the target roll receives the output from the comparing means and reduces the amount of roll reduction of the roll stand that is rolled in the same direction as the measurement direction at least two stages upstream from the final roll stand. A mandrel mill comprising a control unit for controlling a reduction amount of a stand.

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