JP2001239311A - Method for controlling roll rotating number in pipe rolling machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling roll rotating number to realize a high accurate finishing measurements in rolling a pipe. SOLUTION: When rolling a seamless steel pipe by using a pipe rolling machine having plural stands, thickness in an outlet side of each stand is calculated, based on a condition formula of stress and distortion and the roll rotating number at each stand is calculated, regarding the thickness as the desired thickness. A frictional coefficient between a roll and a pipe at each stand in rolling each pipe is corrected and the roll rotating number at each foregoing stand is calculated, based on the corrected frictional coefficient. These calculations are characterized in this method for controlling the roll rotating number.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the number of revolutions of a roll of a tandem rolling mill, and more particularly to a method of finishing a steel pipe to a target size with high accuracy, which is used in a pipe rolling mill in a seamless steel pipe manufacturing process. The present invention relates to a roll rotation speed control method suitable for improving the yield.

[0002]

2. Description of the Related Art A typical manufacturing process of a seamless steel pipe is to perform piercing and rolling of a round steel slab (a billet) heated to a predetermined temperature with a piercing mill (piercer) to form a hollow shell, followed by rolling. This is a process in which, after the thickness is reduced mainly by a mill, heating is performed again if necessary, and the outer diameter and the thickness are finished to desired dimensions by a finishing rolling mill.

[0003] As the above rolling mill, there is a tandem rolling mill in which tension is generated between a plurality of stands to elongate and roll a raw tube. For example, a stretch reducer used as a finishing rolling mill is composed of a plurality of stands (usually 8 to 26 stands) arranged side by side along a pass line of the tube, and the tube is rolled by a hole-type roll of each stand. In addition to rolling to the outer diameter of the product, the wall thickness is processed by generating tension between stands.

Here, the qualitative relationship between the gradient of the number of roll rotations between the stands and the wall thickness of the tube will be described with reference to the drawings.

FIG. 2 is a diagram showing an example of setting the number of roll rotations at each stand of the stretch reducer. In addition,
The horizontal axis in the figure indicates the stand number counted from the entrance side of the stretch reducer, and the vertical axis indicates the number of roll rotations at each stand. A, B, and C in the figure represent A as a steep gradient of the set value of the number of roll rotations at each stand, C as a gentle gradient, and a gradient intermediate between A and C. B is shown.

As shown in FIG. 2, when the gradient of the set value of the number of roll rotations between the stands from the first stand to the final stand is increased as indicated by A, the tension between the stands increases, and after rolling, When the tube thickness is reduced as in C, the tension between the stands decreases, and the tube thickness after rolling increases. However, at the time of rolling of the stretch reducer, in order to obtain a finished steel pipe having an intended target size, regardless of a change in rolling conditions such as a raw pipe size, a raw pipe surface temperature, a roll shape, or a roll surface property,
It is necessary to appropriately correct the gradient of the number of roll rotations between the stands.

As means for solving the above-mentioned problems, Japanese Patent Application Laid-Open No. Hei 4-238608 discloses a method based on the outer diameter and thickness of a raw tube, the outer diameter and thickness of a finished tube, and the contraction ratio of each stand. Find the maximum tensile coefficient for each stand,
A method is disclosed in which a reference tensile coefficient is set for each stand within the maximum tensile coefficient, and a tensile coefficient for the next rolling is reset to control the number of roll rotations.

In Japanese Patent Application Laid-Open No. 6-106219, the maximum tensile coefficient and the set tensile coefficient at each stand obtained from the lengths of the pipes measured by the length measuring instruments on the entrance and exit sides of the stretch reducer are used. A method is disclosed in which a roll rotation speed pattern is set by using the above-mentioned method, and the roll rotation speed pattern is automatically controlled.

[0009]

In controlling the number of roll rotations at each stand such as a tandem rolling mill, a change in the roll shape or a change in the rolling temperature of the raw tube due to the difference in the number of rolls actually occurs. Further, the coefficient of friction between the roll and the pipe in each stand changes every moment due to the effect of the change of the roll itself which changes every time during operation such as the change of the roll surface shape due to the type of steel to be rolled. However, according to the control method disclosed in the above publication, the constantly changing friction coefficient cannot be reflected on the control of the number of roll rotations.
There was a problem that the dimensional accuracy of the finished steel pipe was deteriorated.

The present invention has been made in view of the above-mentioned problems. First, the ever-changing operating conditions change the friction coefficient between the roll and the pipe of each stand, and the finished steel pipe in a pipe rolling mill is manufactured. Focusing on reducing the dimensional accuracy of
A pipe that calculates the coefficient of friction that changes with changes in operating conditions each time rolling is performed, enables changes in operating conditions to be reflected in control, and enables finishing from the first rolled steel pipe to the last rolled steel pipe to target dimensions accurately. An object of the present invention is to provide a method for controlling the number of rotations of a rolling mill.

[0011]

The present invention provides the following (1):
The gist is a method of controlling the number of rolls of a tube rolling mill shown in (2). (1) When rolling a seamless steel pipe using a pipe rolling mill having a plurality of stands, calculate the outlet wall thickness of each stand from the conditional expressions of stress and strain, and use this as the target wall thickness for each stand. A roll rotation control method for calculating a roll rotation speed, comprising correcting a coefficient of friction between a roll of a stand and a tube for each tube rolling to calculate a roll rotation speed of each of the stands. This is a method of controlling the number of roll rotations of the machine.

In the above control method, it is desirable to use the friction coefficient used for the previous roll rotation speed control as correction data for the next friction coefficient. (2) A method of controlling the number of rolls of a tube rolling mill for rolling a seamless steel pipe, comprising: a pipe making information storage section for storing a rolling condition in advance; and friction between a roll and a pipe in each stand used for rolling. A friction coefficient storage unit that stores a coefficient,
Further, a roll information management unit that outputs data necessary for correcting the friction coefficient between the roll and the pipe in each stand based on the data obtained from them, and a roll information management unit based on the data input from the roll information management unit. A friction coefficient correction unit for correcting the friction coefficient between the roll and the pipe in the stand,
A roll rotation speed calculation unit that calculates a roll rotation speed in each stand based on the corrected friction coefficient corrected by the friction coefficient correction unit and the set target thickness; The roll rotation number control method for a tube rolling mill according to the above (1), further comprising a roll rotation number setting unit that adjusts the roll rotation number in each stand to realize the roll rotation number.

In the above control method, in the friction coefficient storage unit, data obtained by correcting the friction coefficient between the roll and the pipe each time rolling is performed is stored in a table, and the number of roll rotations of each stand is stored. It is desirable to be able to calculate.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The content of the method for controlling the number of rotations of a roll according to the present invention will be described using a tube rolling mill assuming a stretch reducer.

As described above, in the conventional control method,
The variation in the coefficient of friction between the roll and the tube is not considered, and a fixed value has been used for the coefficient of friction regardless of the position of the stand or the number of times the roll is used. However, in actuality, due to the structure of the tube rolling mill, the rolls in the first half (5 to 20 stands counted from the entrance side of the tube rolling mill) are used for rolling raw tubes of various sizes, Rolls of 3 to 5 stands counted from the exit side of the machine) are used to finish to the target product size, so the rolling history of the rolls of each stand is not uniform, and the properties and shape of the rolls of each stand are different. different.

Further, since the degree of outside diameter processing and the degree of wall thickness processing of the pipe differ for each stand, and the degree of wear of the rolls of each stand also changes accordingly, the friction of each stand in the operation of the tube rolling mill is increased. It is necessary to change the coefficient. Hereinafter, a method of correcting a friction coefficient, a method of setting a target thickness, and a method of setting a target rotation speed in the roll rotation speed control method of the present invention will be described.

FIG. 1 is a block diagram showing an embodiment of a tube rolling mill using the roll rotation speed control method of the present invention.

However, although not shown, the friction coefficient storage unit 16 in FIG. 1 stores the initial value of the friction coefficient for each roll identification number (hereinafter referred to as "initial value storage unit"). ) And a part for storing the friction coefficient currently used in each stand (hereinafter, referred to as an “updated value storage unit”).

The pipe making information storage section 17 stores data inputted regarding the material of the raw pipe currently used and the type of roll steel, and when the lot is changed, any of the above data is changed. Is input.

<First Stage> The friction coefficient storage unit 16 responds when the roll of the i-th stand (hereinafter referred to as “i-th stand”) counted from the entrance side of the tube rolling mill 11 is replaced. When the roll identification number k is input, the friction coefficient stored in the update value storage unit is automatically updated to the friction coefficient μk obtained from the initial value storage unit.

<Second Stage> In the roll information management unit 15, the updated value storage unit of the friction coefficient storage unit 16 and the pipe production information storage unit 17
From this, data such as the coefficient of friction at each stand, the material of the raw tube, the type of roll steel, and the like are taken in, and the data such as the current rolling temperature are taken in from a thermometer installed in the tube rolling mill 11. According to the data, the roll information management unit 15 outputs data necessary for correcting the friction coefficient to the friction coefficient correction unit 14.

[0022] In <Third step> friction coefficient correction unit 14, and outputs a friction coefficient μk of the new i-th stand inputted from the role information management unit 15 to the roll rotation speed calculation unit 13 as the friction coefficient mu _i. Further, in the friction coefficient correction unit 14, each time rolling is performed, the friction coefficient μ _i is corrected using the following equation (1).
_i 'is calculated.

Μ _i ′ = f (μ _i , T, d _i , d _i−1 , k ₀ , k ₁ , k ₂ , k ₃ , k ₄ ) (1) where T is the rolling temperature, d _i is the average outer diameter of the pipe at the outlet side of the i-th stand, and is obtained as the sum of the major and minor radii of the roll hole type at the i-th stand. Further, k0 is a constant indicating a friction coefficient variation that changes every rolling,
k ₁ is the correction factor to hold each material of the blank tube, k ₂ is the correction factor to hold each roll steel species, k ₃ is the correction coefficient of the rolling temperature, k ₄ is the outer diameter working ratio [(d _i-1 -d _i ) / d _i-1 ].

Further, the friction coefficient correction unit 14
The corrected friction coefficient μ _i ′ at the i-th stand obtained by the equation (1) is output to the friction coefficient storage unit 16.

<Fourth Step> The friction coefficient storage unit 16 changes the current friction coefficient of the i-th stand stored in the updated value storage unit to the corrected friction coefficient μ _i ′.

<Fifth Step> The work procedure from <Second Step> to <Fourth Step> is repeated, and the role information management unit
In 15, when the corrected friction coefficient corrected by the friction coefficient correction unit 14 exceeds a preset allowable limit value of the friction coefficient between the roll and the pipe, a roll change notification is output. The role is exchanged based on this notification, and the identification number of the new role is input.

<Sixth Step> In the roll rotation speed calculating section 13,
The target roll rotation speed is set using the new friction coefficient μ _i ′ input from the friction coefficient correction unit 14 in the above <Third Step>. First, a method of calculating the target wall thickness in the pipe rolling mill 11 will be described. It is shown below.

The tube axially occurring mother tube during rolling in the i-th stand of the rolling mill 11, each of the mean log distortion in the circumferential direction and the radial direction, φl _i, φθ _i and [phi] r _i are constant volume law Thus, it can be obtained from the following equations (2), (3) and (4).

Φl _i = ln [{t _i−1 (d _i−1 −t _i−1 )} / {t _i (d _i −t _i )}] (2) φθ _i = ln {(d _i −t _i ) / (d _i−1 −t _i−1 )} (3) φ r _i = ln (t _i / t _i−1 ) (4) where the above equations (2) to (4) t _i in shows the wall thickness of the tube in the i stand delivery side and, d _i is a mean outside diameter of the tube in the i stand delivery side, the long radius of the roll caliber in the i stand And the short radius.

Further, the axial direction occurring mother tube during rolling in the i stand, Shigumaeru respective stress in the circumferential and radial directions _i, when the Shigumashita _i and .sigma.r _i, from the relationship between the stress and strain of the following ( 5) is, (6) below the breakdown condition Von M _i ses is satisfied, respectively. _{(σl i -σθ i) / (} φl i -φθ i) = (σθ i -σr i) / (φθ i -φr i) = (σr i -σl i) / (φr i -φl i) ... (5 ^{_{) (σl i -σθ i) 2}} + (σθ i -σr i) 2 + (σr i -σl i) 2 = 2kf i 2 ... (6) where, kf _i above (6) wherein is the i 3 shows the deformation resistance in the stand. Further, the shape change coefficient v _i , the outer diameter thickness ratio ξ _i , and the stretch coefficient Z _i in the i-th stand are derived from the following equations (7) to (9), respectively.

[0031] _{ν i = 0.5 + φθ i /} φl i ... (7) ξ i = t i / d i ... (8) Z i = σl i / kf i ... (9) above (2) to (9) Then, the following equations (10) and (11) are derived. d _i (1-ξ _i ) {d _i ² ξ _i (1- _i )} ^{ν i-0.5} = d _i-1 (1-ξ _i-1 ) {d _i-1 ² _{-1 i-1} (1 ^{_{-ξ i-1)} ν i}} -0.5 ... (10) ν i 2 [3Z i 2 - {ln (1 / (1-2ξ i))} 2 -2ln (1 / (1-2ξ i)) - by _{1] -3ν i {1 + ln} (1 / (1-2ξ i)} + 2.25 (Z i 2 -1) = 0 ... (11) solving the simultaneous equations of the above (10) and (11) , it can be determined exit side thickness t _i of the i stand. Thus, the control method of the present invention, the tube mill the exit side thickness t _i at each stand is determined in this way as the target thickness May be set.

Here, taking into account the balance of the axial force in the tube being rolled, the roll speed of the i-th stand is derived by the following method.

In general, the rolling state of a pipe differs before and after a position (hereinafter, referred to as a “neutral line”) at which the axial moving speed of the pipe coincides with the circumferential speed of the roll. More specifically, in an area where the roll and the pipe are in contact with each other before (outward side) the neutral line (hereinafter referred to as “forward sliding area”), the peripheral speed of the roll is lower than the moving speed of the pipe, and In a region (hereinafter, referred to as a “backward sliding region”) where the roll and the tube are in contact later (on the entry side), the peripheral speed of the roll is faster than the moving speed of the tube. That is, the balance equation of the axial force of the pipe in the i-th stand is expressed by the following equation (12).

Fb _i + G _i = μ _i │σrb _i │ · 3 (Sb _i −Sf _i ) + Ff _i (12) where Fb _i in the above equation (12) is the tension behind the neutral line, F
f _i is the tension in front of the neutral line. Further, Sb _i is the area of the rear sliding region, the Sf _i is the area of the front sliding area and the total contact area between the rolls and pipe and _{St i, St i = Sb i} + Sf i
Has the relationship Further, μ _i in the equation (12) is the friction coefficient between the roll and the pipe in the i-th stand, and
In step>, it is input from the friction coefficient correction unit 14.

Furthermore, G _i is the radial stress axial rolling pressure tube in the i stands, the Shigumarb _i acting outside the tube surface, the following are (13), represented by equation (14) .

[0036] _{G i = │σrb i │π {(} d i-1/2) 2 - (d i / 2) 2} ... (13) σrb i = 2σr i = ν i / (3ν i 2 +2.25 ) 1/2 · kf _i · ln {1 / (2-ξ _i )} (14) Next, at the slip-free point where the moving speed of the pipe at the exit side of the i-th stand and the peripheral speed of the roll coincide with each other. roll radius (effective radius) Rw _i is represented by the following equation (15).

Rw _i = RO _i + d _i {1-cos (ψ _i )} / 2 (15) In the above equation (15), RO _i is the groove bottom radius of the i-th stand, and ψ _i is Using the distance x _i between the non-slip point and the central axis in the circumferential section on the exit side of the i-th stand, sinψ _i = x _i /
(d _i / 2).

Further, the number n of roll rotations of the i-th stand
_i from roll radius Rw _i above, the formula (16) below.

[0039] _{n i = 60V i / (2πRw} i) ... (16) where, V _i is the speed of movement of the tube at the exit side of the i-th stand, the speed of movement of the tube in the inlet side of the i-th stand V0
_{When i} is given, it is represented by V _i = V 0 _i · exp (Σφl _i ).

By solving the above equations (12) to (16),
It can be obtained roll rotation speed n _i of each stand to meet the target thickness t _i, and outputs the roll rotation speed n _i of each stand as the target rotational speed on the roll rotational speed setting unit 12 of each stand.

<Seventh Step> The roll rotation speed setting unit 12 calculates the current roll rotation speed of each stand of the tube mill 11 from the roll rotation speed calculation unit 13 and sets the target value of the roll rotation speed at each stand. In order to achieve this, the drive of the roll drive motor of each stand is controlled so as to obtain a roll rotation pattern having a predetermined gradient between the stands.

<Eighth Step> The tube rolling mill 11 controlled by the roll rotation number setting unit 12 outputs data such as the rolling temperature to the roll information management unit 15 every time the rolling is performed.

In the method of controlling the number of rotations of the roll according to the present invention, by repeating the above-described work procedure from the first stage to the eighth stage, the optimum number of rotations can always be ensured. From the time immediately before the next roll change, the target wall thickness and length of the pipe can be achieved. In addition, since the coefficient of friction between the roll and the pipe is calculated each time the rolling is performed, the roll can be replaced before the roll slip occurs due to the decrease in the coefficient of friction between the roll and the pipe, and the rolling accuracy of the pipe rolling machine is reduced. Can be prevented beforehand.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described below in which a stretch reducer is used as a tube rolling mill.
In this embodiment, the rolling temperature is set using a roll of chilled steel.
At 800 ° C., carbon steel was produced under the following dimensional conditions.

Condition (1): A raw tube having an outer diameter of 110 mm, a wall thickness of 4.0 mm, and a length of 27420 mm was rolled by a stretch reducer.
Manufactures finished steel pipes with an outer diameter of 34 mm, a wall thickness of 3.4 mm, and a length of 108639 mm.

Condition (2): A raw tube having an outer diameter of 151 mm, a wall thickness of 5.75 mm, and a length of 28410 mm is rolled by a stretch reducer.
Manufactures finished steel pipes with an outer diameter of 63.5 mm, a wall thickness of 5.2 mm, and a length of 76647 mm.

In the example of the present invention, when rolling under the above conditions (1) and (2), the following formula (17) is used instead of the above formula (1) for calculating the corrected friction coefficient. Modified friction coefficient μ
_i ′ was calculated, and the roll drive motor was controlled and rolled at the roll rotation speed obtained using this value.

Μ _i ′ = μ _i + k ₀ · k ₁ · k ₂ · k ₃ · k ₄ · T · (d _i−1 −d _i ) / d _i−1 (17) As described above, here , T is the rolling temperature, k ₀ is a constant that indicates the friction coefficient fluctuation to vary the rolling, the correction coefficient k ₁ is held in each material of the blank tube, k ₂ is the correction factor to hold each roll steel species, k ₃ Is the correction factor for the rolling temperature, and k ₄ is the degree of outer diameter reduction [(d _i-1
−d _i ) / d _i-1 ].

On the other hand, in the comparative example, the above conditions (1) and
Upon rolling (2), the friction coefficient between the rolls and the tube as remains of the initial fixed value mu _i, controlled rolling roll speed. Table 1 shows the rolling results.

[0050]

[Table 1] The extension length deviation in Table 1 is a percentage obtained by dividing the difference between the actual length of the finished pipe and the target extension length by the target extension length. From these results, the elongation length deviation is 0.83% and 0.65% in the comparative example, whereas it is 0.26% and 0.30%, which is less than half in the example of the present invention, and the rolling is performed by the control method of the present invention. This shows that the target dimensions can be secured with high accuracy.

[0051]

According to the method for controlling the number of rolls of a tube rolling mill of the present invention, a target finished size can be realized with high accuracy in rolling a tube, and the quality and yield of a product can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a roll speed control method of the present invention in a tube rolling mill.

FIG. 2 is a diagram qualitatively illustrating a relationship between a gradient of a roll rotation speed between stands in a stretch reducer and a thickness of a finished pipe.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B21B 37/18 BBS B21B 37/12 115A

Claims (4)

[Claims] When a seamless steel pipe is rolled using a pipe rolling mill having a plurality of stands, an outlet wall thickness of each stand is calculated from a conditional expression of stress and strain, and this is set as a target wall thickness. A roll rotation speed control method for calculating a roll rotation speed of a stand, wherein the roll rotation speed of each stand is calculated by correcting a coefficient of friction between a roll of a stand and a pipe for each tube rolling. A method for controlling the number of rolls of a tube rolling mill. 2. The method according to claim 1, wherein the coefficient of friction used in the previous control of the number of rolls is used as correction data for the next coefficient of friction. 3. A method for controlling the number of rolls of a tube rolling mill for rolling a seamless steel pipe, comprising: a pipe making information storage section for storing rolling conditions in advance; and a friction between a roll and a pipe in each stand used for rolling. A friction coefficient storage unit for storing a coefficient, and a roll information management unit for outputting data necessary for correcting a friction coefficient between a roll and a pipe in each stand based on data obtained from the roll information management unit; A friction coefficient correction unit for correcting the friction coefficient between the roll and the pipe in each stand based on the data input from the information management unit, and a correction coefficient of friction corrected by the friction coefficient correction unit and a set target wall thickness. A roll rotation speed calculation unit that calculates the roll rotation speed in each stand by using the roll rotation speed calculation unit that calculates the roll rotation speed in each stand. Roll speed control method of a tube mill according to claim 1 or 2, characterized in that a roll rotational speed setting unit for adjusting the roll speed for each stand order. 4. The friction coefficient storage unit stores data obtained by correcting the friction coefficient between a roll and a pipe each time rolling is performed in a table and stores the data, and calculates the roll rotation speed of each stand. The method for controlling the number of rolls of a tube mill according to claim 3.