JPH07227613A - Stretch length control method for seamless tube - Google Patents

Abstract

PURPOSE:To minimize difference with the target length of stretch length of a seamless tube. CONSTITUTION:Speed integral type length measuring instruments 14, 16, and 18 and temperature detectors 15, 17, and 19 are installed at the exit of a mandrel mil 1 and that of a sizer or stretch reducer 6. Temperature correction is performed by finding the stretch ratios of a base tube 5 and a tube 7 from speed difference between an entry and the exit, and difference between the stretch ratio to which the temperature correction is applied and a target stretch ratio set in advance is found, and the roll gap of the mandrel 1 or the roll rotating speed of the sizer or stretch reducer 6 are controlled based on the difference with the target stretch ratio. In this way, defective crop length can be reduced by improving product dimension accuracy, and product yield can be improved by that share.

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 a stretch length of a seamless pipe in a mill in which a mandrel mill, a sizer and a stretch reducer are arranged in tandem in the production of the seamless pipe.

[0002]

2. Description of the Related Art A manufacturing process for a seamless pipe is performed by heating a round or square billet and then piercing it, a thinning process of stretching and rolling the pierced hollow shell, and a predetermined finishing of the stretched mother pipe. It consists of a constant diameter rolling process of drawing and rolling to size.
Known rolling mills in the thickness reduction process include a plug mill, a mandrel mill, an assel mill, and a pilga mill. Among the seamless pipe manufacturing methods, the Mannesmann-mandrel mill method, which is excellent in productivity, is as shown in FIG.
Rotate the round billet 51 of the material in the rotary hearth type heating furnace 52 to 120
After heating to 0 to 1260 ° C, plug 5 with the punch 53.
A hollow shell 56 is obtained by piercing and rolling with 4 and a roll 55. The hollow shell 56 at this stage has an outer diameter of several sizes,
The wall thickness is also very thick compared to the product.

The mandrel mill 57 for the next wall thinning process has a hollow stand in which 4 to 8 roll stands in which a pair of hole type rolls 58 are incorporated are continuously arranged by changing the roll arrangement by 90 °. Between the mandrel bar 59 inserted in 56 and the hole-type roll 58, thickness reduction and stretch rolling are continuously performed to a predetermined thickness. Generally, the amount of thinning in the mandrel mill 57 is generally reduced by about 7 to 15 mm in order to reduce the roughness of the inner surface. Thinned and stretch-rolled mother tube 60
The mandrel bar 59 is pulled out by a stripper (not shown). If the temperature of the raw pipe is too low compared to the workability before the thickness reduction and the stretch rolling, the mother pipe 60 is reheated in the reheating furnace 61.
Is heated to 900 to 1100 ° C., but if the temperature does not decrease, it is finished to a predetermined finish dimension by directly reducing the outer diameter and slightly adjusting the wall thickness with a reduction rolling machine 62 such as a sizer or a stretch reducer. Generally an outside diameter of 17
A large-diameter mill that manufactures seamless pipes with a diameter of 7.8 mm or more does not have a reheating furnace, and a small-diameter mill that specially rolls seamless pipes with an outer diameter of 177.8 mm or less requires a reheating furnace. Target.

Conventionally, in a large-diameter mill for producing a seamless pipe having an outer diameter of 177.8 mm or more, it is common to arrange a 2-roll mandrel mill and a 2-roll sizer or a 3-roll sizer in tandem on the same axis. It was in this case,
When removing the mandrel bar, a stripper cannot be installed, so the extractor or sizer grips the mother pipe and sends it to the exit side of the pass line while reducing the outer diameter, and when the mother pipe slips out of the final stand of the mandrel mill, it is removed by the retrainer. This is performed by pulling back the mandrel bar to the entrance side of the pass line (JP-A-3-11).
4605).

In the Mannesmann-mandrel mill system, the management of the outer diameter and wall thickness of the product seamless pipe is generally performed by controlling the product elongation length in the stretch reducer. In other words, it is necessary to control the outer diameter and wall thickness of the product seamless pipe so that the stretched length corresponds to the material weight.Therefore, the material weight at the heating furnace inlet and the mother pipe length at the mandrel mill exit side are controlled. , And the tube length on the exit side of the stretch reducer, feedforward and intermaterial feedback control are performed, and tracking processing is performed for each material in order to transmit information necessary for this control. For example, in a mandrel mill, based on the hollow shell length after piercing and rolling, the rolling gap of each stand of the mandrel mill is adjusted, and the roll speed of each stand is set to match the target elongation length, The roll gap is changed to calculate the predicted length by extending the billet weight and the cross-sectional area of the mandrel mill outlet mother tube and to correct the difference between the target length and the cross-sectional area of the mother tube.

In the stretch reducer, the rotation speed of each stand is set for each mother tube so as to match the target length after the final outer diameter drawing, based on the mother tube length measured after the mandrel mill rolling. To improve accuracy. That is, as shown in FIG. 4, when the length of the mother tube after stretching and rolling in the mandrel mill is short, the rotation speed ratio Rn is increased to make a well-expanded setup, and conversely, the length of the mother tube after stretching and rolling in the mandrel mill is increased. When is long, the setup is used to suppress the elongation by lowering the rotation speed ratio Rn. The rotation speed ratio R
n is a value obtained by dividing the roll rotation speed of the final rolling stand by the roll rotation speed of the first stand. The relationship between the elongation rate and the roll rotation speed ratio Rn in the stretch reducer is as shown in FIG. The elongation percentage in FIG. 5 is the ratio of the length of the mother pipe at the outlet of the mandrel mill and the length of the pipe at the outlet of the stretch reducer after temperature correction. Figure 5
As shown in, it is possible to control the stretch length by changing the roll rotation speed ratio Rn. FIG. 6 shows the result of the accuracy of stretch length being improved by the control.

As a method for controlling the tube extension length in the mandrel mill, the frictional characteristic values of the mandrel bar, which have been obtained in advance by experiments, and the weight and temperature information of the raw tube measured or predicted online, A method of matching the length of the finished mother pipe after rolling with the target value by changing the roll peripheral speed ratio for each raw pipe (Japanese Patent Publication No. 59-16847).
Issue). Further, as a method for controlling the elongation length of the pipe in the drawing and rolling process of the mother pipe after the drawing and rolling with the mandrel mill, the actual length and the planned length of the mother pipe obtained by the process immediately before the final rolling process of the drawing and rolling are performed. In comparison, when the actual length is longer than the planned length, a final rolling is performed under a predetermined wall thickness tolerance and weight tolerance to obtain a rolled product having a length equal to or longer than the planned length (Japanese Patent Laid-Open No. 4-371307). In the length control that controls the rotation speed with either the input side or the output side stand of the drawing mill as a fixed reference point, the variable side rotation speed set value obtained by the length control model is the equipment limit value or the operation. When the reference speed defined by the conditions is exceeded, a method for maintaining the inclination of each stand rotation speed from the entrance side to the exit side stand by increasing or decreasing the excess setting rotation speed to the fixed side setting rotation speed 5-5 117
No. publication) is proposed.

[0008]

In recent years, there has been proposed a rolling method using a tandem mill in which a sizer or a stretch reducer is arranged in tandem at a fixed distance from the mandrel mill outlet and a reheating furnace is omitted. In this tandem mill, the pipe is simultaneously subjected to outer diameter drawing by a sizer or a stretch reducer during mandrel mill rolling, so the total length of the mother pipe cannot be measured at the mandrel mill outlet. Therefore, the above Japanese Patent Publication No. 59-16
The methods disclosed in Japanese Patent No. 847, Japanese Patent Application Laid-Open No. 4-371307, and Japanese Patent Application Laid-Open No. 5-50117 disclose control using the hollow shell measured at the mandrel mill inlet and the mother tube length measured at the outlet, and the mandrel mill outlet. Since the control uses the mother pipe length measured in and the pipe length measured at the sizer or stretch reducer outlet, the sizer or stretch reducer cannot be used as it is for a tandem mill in which a sizer or stretch reducer is arranged in a tandem with a certain distance at the mandrel mill outlet. .

An object of the present invention is a tandem mill in which sizers or stretch reducers are arranged in tandem at a fixed distance from the mandrel mill outlet, and there is no seam that can minimize the difference between the pipe extension length and the target length. It is to provide a method for controlling the stretched length of a tube.

[0010]

[Means for Solving the Problems] The inventors of the present invention have conducted earnest research to achieve the above object. As a result, a speed integration type elongation length measuring device and a temperature detector were installed on the mandrel mill outlet side and the sizer or stretch reducer outlet side, and the pipe elongation rate was calculated from the speed difference to correct the temperature. By obtaining the difference between the corrected elongation and the target elongation and controlling the roll gap of the mandrel mill or the roll speed of the sizer or stretch reducer, the difference between the stretched length of the pipe and the target length can be minimized. In addition, a fixed length measuring device was installed on the exit side of the sizer or stretch reducer to measure the total length of the final rolled product, and the error in the length of the pipe stretched by the speed integral type length measuring device was measured. It was clarified that the difference between the stretched length of the pipe and the target length can be further reduced by the correction, and the present invention has been reached.

That is, according to the present invention, the extension length of a seamless pipe in a mill in which a mandrel mill and a sizer or stretch reducer are arranged in tandem at a distance shorter than the length of a mother pipe stretch-rolled on a rolling pass line having the same axis. In the control method, a velocity measuring type length measuring device and a temperature detector are installed at the mandrel mill outlet and the sizer or stretch reducer outlet, and the elongation rate of the mother pipe and pipe is calculated from the speed difference between the inlet and outlet to correct the temperature. The difference between the temperature-corrected elongation and the preset target elongation is determined, and the roll gap of the mandrel mill or the roll speed of the sizer or stretch reducer is controlled based on the difference between the target elongation. This is a method for controlling the stretch length of a seamless pipe.

Further, according to the present invention, in the above-mentioned method for controlling the elongation length of a seamless pipe, a hollow element pipe velocity at the inlet of a mandrel mill is predicted or a velocity integral type length measuring device provided at the inlet of the mandrel mill is used. The measured tube speed is used. Furthermore, in the present invention, in the method for controlling the extension length of the seamless pipe, a fixed length measuring device is installed on the exit side of the sizer or the stretch reducer to measure the total length of the pipe, and the length of the velocity integration type is measured. The measurement error of the measuring device is corrected based on the actual measurement value of the fixed length measuring device.

[0013]

In controlling the tube extension length in the tandem mill, the hollow shell tube velocity and cross-sectional area at the mandrel mill inlet are set to V ₀ and A _0, and the pipe velocity and cross-sectional area of each stand of the mandrel mill are Vi. , Ai (i indicates the stand number). Assuming that volume change due to heat shrinkage, scale-off, etc. can be ignored, the passing volume is constant, so V ₀ A ₀ = ViAi,

[0014]

[Equation 1]

Therefore, the pipe velocity is increased at the reduction ratio of the cross-sectional area. The above holds when the pipe velocity and the cross-sectional area do not change, but in reality, the pipe velocity and the cross-sectional area also change with time. Assuming that the tube length at each stand is Li, AiLi = constant (2) from the condition of constant volume, and the cross-sectional area ratio and the stretched length ratio are in inverse proportion.
From equation (1) and equation (2)

[0016]

[Equation 2]

Therefore, it is possible to predict the elongation rate by measuring the speed. Further, the length measuring device of the velocity integration type measures the length with L = ∫vdt. Above (3)
The equation becomes the following equation when the velocity changes with time.

[0018]

[Equation 3]

Tp is the rolling time of the tube. Regarding the cross-section of the pipe before rolling, there is no problem in practice even if it is considered that the same cross-section is secured after rolling, and the above equation is generalized to equation (4).

[0020]

[Equation 4]

Here, t is the rolling time after the tube is bitten at each stand, and li is the rolling length of the tube until t time elapses.
l ₀ is the length of the hollow shell rolled by one stand at the inlet of the mandrel mill. Differentiating the above equation (4) gives:

[0022]

[Equation 5]

It becomes If the velocity at the exit of the last stand is used as v _i now, vi = vf.

[0024]

[Equation 6]

However, L _f is measured by measuring the target lengths v ₀ and v _f of the mother pipe at the outlet of the mandrel mill, and controlling the roll gap so as to match the ratio with L _f / L _0. Can be accurately matched with the target length L _f of the mother tube. If v ₀ fluctuates, measure v ₀ during rolling,
The ratio of the velocity vf after t hours from the start of the final stand rolling to v ₀ after t hours from the start of one stand rolling is

[0026]

[Equation 7]

Next, the control of the sizer or stretch reducer is performed by the following control by the velocity integration type stretch length measuring device installed at the inlet of the sizer or stretch reducer and the velocity integration type stretch length measuring device provided at the outlet. I do.

[0028]

[Equation 8]

Where Lso is the length of the mother pipe at the outlet of the mandrel mill, vso is the inlet velocity of the sizer or stretch reducer, Lsf is the length of the outlet of the sizer or stretch reducer, and vsf is the velocity of the sizer or stretch reducer outlet. . If there is no heat shrinkage or cross-sectional area variation between the mandrel mill and sizer or stretch reducer, and no scale-off, L _so =
L _f , v _so = v _f . Differentiating the equation (7)

[0030]

[Equation 9]

It becomes If the roll rotation number is controlled _so that the ratio of v _so / v _sf = L _so / L _sf , the stretched length can be accurately matched with the target stretched length. Therefore,
If temperature is measured at the same time and temperature correction is added,

[0032]

[Equation 10]

Here, α is the coefficient of linear expansion, θ _so and θ _sf are the respective tube measured temperatures, and θ ₀ is the standard temperature.

Further, a fixed length measuring device OP-1 is installed at the exit of the sizer or stretch reducer from the center of the final stand roll by L _M1, and the fixed length measuring device OP-1 is installed from the center of the final stand roll by L _M. Correct the value measured by the length measuring device. That is, when the tip of the pipe reaches the fixed length measuring device OP-1 at the outlet, the integrated length measuring device measures (L _M1 −L _M ). There is no error in the above, and the above-mentioned control may be performed. However, the extension length measured by the integral type extension length measuring device is L _I , and Li− (L _M1 −L _M ) = Δl> 0 or <0 In that case, correction is necessary. When Δl> 0, it is necessary to change the target setting for a longer control target ΔL. For example,
The length when rolled without correction is

[0035]

[Equation 11]

It is predicted that Considering the ratio between this predicted value and the target length, and the remaining length ratio of the rolling section, the exit speed is adjusted.

[0037]

[Equation 12]

The target is changed as follows. Also, Δl <0
In case of

[0039]

[Equation 13]

It is assumed that By installing several fixed length measuring devices at the exit of the sizer or stretch reducer, the extension length accuracy can be further improved.

In the present invention, a velocity measuring type length measuring device and a temperature detector are installed at the mandrel mill outlet and the sizer or stretch reducer outlet, and the elongation rate of the mother pipe and the pipe is determined from the difference in velocity between the inlet and the outlet. The temperature is calculated and corrected, and the difference between the temperature-corrected elongation and the preset target elongation is calculated, and the roll gap of the mandrel mill or the roll speed of the sizer or stretch reducer is controlled based on the difference between the target elongation. By doing so, it is possible to control the extension length of the pipe in the mandrel mill and sizer or stretch reducer to the target extension length with high accuracy, and it is possible to greatly reduce the deviation in the variation of the extension length of the pipe. .

Further, in the present invention, the pipe speed at the inlet of the mandrel mill is the predicted speed when the hollow shell is conveyed by a chain or a conveyor, and when the transport speed of the hollow shell accurately matches the predicted value. , Or a velocity integrating type length measuring device is installed at the inlet of the mandrel mill, and the velocity measured by the velocity integrating type length measuring device is used to control the stretched length in the mandrel mill to obtain a pipe in the mandrel mill. The stretched length can be controlled to the target stretched length with high accuracy, and the deviation of the variation in the stretched length of the pipe can be significantly reduced. Furthermore, a fixed length measuring device was installed on the exit side of the sizer or stretch reducer to measure the entire length of the pipe, and the measurement error of the velocity integration type length measuring device was measured based on the measured value of the fixed length measuring device. By making corrections, the measurement error of the velocity integration type length measuring device can be corrected, and the tube extension length of the sizer or stretch reducer can be controlled to the target extension length with higher accuracy. It is possible to further greatly reduce the deviation of the variation in the stretched length.

As the velocity integration type length measuring device in the present invention, a laser Doppler length meter and a measuring roll system can be used alone or in combination of both. Further, a radiation thermometer, a multicolor thermometer, or the like is used as the temperature detector in the present invention, but it is advisable to use it together with the material temperature prediction model. Further, as the fixed length measuring device installed on the exit side of the sizer or the stretch reducer, a photo switch system, an optical pinch scale, or the like can be used. For controlling the roll gap of the mandrel mill based on the difference from the target elongation rate, for example, a preliminary experiment was performed to find the relationship between the roll gap narrowing amount of the final two stands and the elongation amount of the mother pipe, and the result was used as the result. It is a good idea to control the roll gap of the mandrel mill based on this. Furthermore, control of the roll rotation speed of the sizer or stretch reducer is performed, for example, based on the target dimensions of the hollow shell, the mother pipe, and the product seamless pipe, and preliminary experiments are performed to perform the rotation speed ratio Rn and the elongation rate of the sizer or stretch reducer. It is a good idea to find the relational expression with and to control the roll speed of the sizer or stretch reducer based on the result.

[0044]

【Example】

Embodiment 1 Details of the method of the present invention will be described below with reference to FIGS. FIG. 1 is a control system diagram of an apparatus for carrying out the method of the present invention, and FIG. 2 is an arrangement diagram of a measuring apparatus for correcting a measurement value of a velocity integration type length measuring apparatus. In FIG. 1, 1 is a mandrel mill for thinning and stretching the hollow shell 2, 3 is a mandrel bar inserted in the hollow shell 2,
4 supports the rear end of the mandrel bar 3 and advances the mandrel bar 3 at a predetermined speed, and at the same time, reduces the wall thickness of the hollow shell 2.
A retrainer that retracts the mandrel bar 3 and pulls it out of the mother tube 5 when the mother tube 5 slips out after the stretching and rolling ends.
Numeral 6 is a sizer arranged in tandem on the same axis at a distance shorter than the length of the mandrel mill 1 and the stretch-rolled mother pipe 5, and the thickness-reduced and stretch-rolled mother pipe 5 is drawn to a predetermined outer diameter. The product seamless pipe 7 is formed by thick-walled shaping.

Reference numeral 11 is a laser Doppler length meter installed at the entrance of the mandrel mill 1, and reference numeral 12 is also the mandrel mill 1.
The radiation thermometer installed at the entrance of the mandrel mill 1
The velocity and surface temperature of the hollow hollow tube 2 at the inlet are measured and output to the tube length control unit 13. 14 is a laser Doppler length meter installed at the outlet of the mandrel mill 1, 15 is a radiation thermometer also installed at the outlet of the mandrel mill 1, both of which measure the velocity and surface temperature of the mother pipe 5 at the outlet of the mandrel mill 1. Output to the pipe length control unit 13. Reference numeral 16 is a laser Doppler length meter installed at the entrance of the sizer 6, and 17 is a radiation thermometer also installed at the entrance of the sizer 6, both of which measure the speed and surface temperature of the mother pipe 5 at the entrance of the sizer 6 to control the pipe length. It is output to the unit 13. 18 is a laser Doppler length meter installed at the exit of the sizer 6, 19 is a radiation thermometer also installed at the exit of the sizer 6, both measuring the speed and surface temperature of the product seamless pipe 7 at the exit of the sizer 6 Output to the control unit 13.

The length and cross-sectional area of the hollow shell 2, the target elongation rate of the mandrel mill 1 and the target elongation rate and wall thickness of the sizer 6 are preset and input to the tube length control unit 13 from a host computer (not shown). Has been done. Pipe length control unit 13
Are laser Doppler length meters 11 and 14 and radiation thermometers 12 and 1 installed at the entrance and exit of the mandrel mill 1.
Based on the velocity and the surface temperature of the hollow shell 2 and the mother pipe 5 input from 5, the elongation rate is calculated from the speed difference between the inlet and the outlet of the mandrel mill 1, the temperature is corrected, and the temperature-corrected mandrel mill 1 is used. The elongation rate of the mandrel mill 1 is compared with the target elongation rate, and based on the difference, the mandrel mill controller 20 is instructed so that the elongation rate of the mandrel mill 1 becomes the target elongation rate, and the roll gap of the mandrel mill 1 is controlled. Has been done.

Further, the pipe length control unit 13 includes a laser Doppler length meter 16 installed at the inlet and the outlet of the sizer 6,
18 and radiation thermometers 17, 19
And based on the speed and surface temperature of the product seamless pipe 7, the elongation rate is calculated from the inlet and outlet speed difference of the sizer 6 to correct the temperature, and the elongation rate of the temperature-corrected sizer 6 is compared with the target elongation rate. Based on the difference, command the sizer control unit 21 so that the growth rate of the sizer 6 becomes the target growth rate,
It is configured to control the roll speed of the sizer 6.

With the above configuration, when the hollow shell 2 is thinned and stretch-rolled by the mandrel mill 1, the pipe length control unit 13 causes the laser Doppler length meter installed at the inlet and the outlet of the mandrel mill 1. Based on the speeds and surface temperatures of the hollow shell 2 and the mother pipe 5 that are input to the pipe length control unit 13 from the radiation thermometers 11, 14 and the radiation thermometers 12, 15, the pipe length control unit 13 determines the inlet and outlet of the mandrel mill 1. The elongation rate is calculated from the speed difference and the temperature is compensated. The elongation rate in the temperature-compensated mandrel mill 1 is compared with the preset target elongation rate, and the elongation rate in the mandrel mill 1 is calculated based on the difference. Mandrel mill control unit 2
Since the roll gap of the mandrel mill 1 is controlled by commanding 0, the stretched length of the pipe in the mandrel mill 1 can be controlled with high accuracy.

When the mother tube 5 is squeezed and rolled by the sizer 6, the tube length control unit 13 inputs from the laser Doppler length meters 16 and 18 and the radiation thermometers 17 and 19 installed at the inlet and the outlet of the sizer 6. Based on the speed and surface temperature of the mother pipe 5 and the product seamless pipe 7, the elongation rate is calculated from the inlet and outlet speed difference of the sizer 6 and the temperature is corrected, and the elongation rate and the target elongation of the temperature-corrected sizer 6 are calculated. Compare rates,
Based on the difference, the sizer control unit 21 is instructed so that the elongation rate in the sizer 6 becomes the target elongation rate, and the roll rotation speed of the sizer 6 is changed. Therefore, the extension length of the pipe in the sizer 6 can be accurately adjusted. It can be controlled, and the deviation from the target elongation value of the final product seamless pipe 7 can be minimized.

As shown in FIG. 2, on the exit side of the sizer 6, for example, a fixed length measuring instrument 31 composed of a photoswitch is provided at a position separated from the center of the final stand of the sizer 6 by a predetermined distance L _M1 , and the sizer is also provided. A fixed length measuring instrument 32 composed of a photo switch is arranged at a position separated by a predetermined distance L _M2 from the center of the final stand of 6, and the fixed length measuring instruments 31, 32 are arranged.
Detects the tip of the product seamless pipe 7, outputs the tip detection signal to the pipe length control unit 13, and the laser Doppler length meter installed at a position separated by a predetermined distance L _M from the center of the final stand of the sizer 6. Correct the stretched length by 18. That is, the pipe length control unit 13 determines that when the product seamless pipe 7 tip detection signal is input from the fixed length measuring device 31, the extension length input from the laser Doppler length meter 18 is (L _M1 − When L _M ) is measured, there is no error in measuring the stretched length of the laser Doppler length meter 18, and the above control may be performed. However, when the product seamless pipe 7 tip detection signal is input from the fixed length measuring instrument 31, the extension length input from the laser Doppler length meter 18 is L _I , and L _I −
If (L _M1 −L _M ) = ΔL and ΔL> 0 or ΔL <0, correction is necessary. Similarly, the pipe length control unit 13
When the extended length input from the laser Doppler length meter 18 is (L _M2 −L _M ) when the product seamless pipe 7 tip detection signal is input from the fixed length measuring device 32, There is no error in measuring the stretched length of the laser Doppler length meter 18,
The above control may be performed. However, the fixed length measuring instrument 32
When the product seamless pipe 7 tip detection signal is input from
The extension length input from the laser Doppler length meter 18 is L
_J , L _J − (L _M2 −L _M ) = ΔLa, and ΔLa> 0.
Alternatively, if ΔLa <0, correction is required.

If ΔL> 0, it is necessary to change the target setting for a longer control target ΔL. For example, the length when rolled without correction is predicted to be L _sf −ΔL × L _sf / (L _M1 −L _M ). Considering the ratio between this predicted value and the target length, and the remaining length ratio of the rolling section, the exit speed is adjusted.

[0052]

[Equation 14]

The target is changed as follows. Also, ΔL <0
In case of

[0054]

[Equation 15]

It is assumed that When ΔLa> 0, it is necessary to change the target setting for a longer control target ΔLa. For example, the length when rolled without correction is predicted to be L _sf −ΔLa × L _sf / (L _M2 −L _M ). Considering the ratio between this predicted value and the target length, and the remaining length ratio of the rolling section, the exit speed is adjusted.

[0056]

[Equation 16]

The target is changed as shown in FIG. Also, ΔLa <
If it is 0, the reverse of the above

[0058]

[Equation 17]

It is assumed that

Example 2 No. No. 2 roll mandrel mill consisting of 1 to 8 stands. In a seamless pipe manufacturing line in which a sizer consisting of 1 to 7 stands is arranged in tandem on the same axis at a distance shorter than the length of the mother pipe, the hollow shell having the dimensions shown in Table 1 is
Table 1 shows the case where the elongation length control of the pipe of the present invention was performed so as to be rolled into the mother pipe and the seamless pipe having the target dimensions shown in Table 1, and the case where it was not performed (measurement of the length of the seamless pipe after the reduction rolling). Based on the values, learning calculation was performed, and when the material was fed back to the next material), the variation in the elongation length with respect to the target dimension in the mandrel mill and sizer was calculated. The results are shown in Table 2. For the control of the roll gap in the two-roll mandrel mill, an experimental value was used in which a preliminary experiment was performed and the roll gap of the final two stands was narrowed by 0.1 mm to extend by 0.5%. For the relationship between the roll rotation speed ratio Rn of the sizer and the elongation rate, the following relational expression obtained by conducting a preliminary experiment was used. Lsf / Lso = 0.930 × Rn + 0.185 (CASE1) Lsf / Lso = 0.920 × Rn + 0.206 (CASE2)

[0061]

[Table 1]

[0062]

[Table 2]

As shown in Table 2, when the control of the present invention is performed, it is reduced to about half as compared with the conventional example in which the control of the present invention is not performed, and the effect is clear. In addition, when the expansion length of the laser Doppler length meter is corrected by the fixed length meter consisting of the photo switch installed on the exit side of the sizer, the deviation deviation of the elongation length from the target size on the sizer is 0 in CASE1. .18%, CA
SE2 was further reduced to 0.21%.

[0064]

As described above, according to the method of the present invention, the elongation percentage is obtained based on the speed difference of the pipe and the predetermined target elongation length of the final product is controlled to achieve the target elongation with high accuracy. The length can be controlled, the product dimensional accuracy is improved, the defective crop length is reduced, and the product yield is improved accordingly.

[Brief description of drawings]

FIG. 1 is a schematic control system diagram of an apparatus for carrying out the method of the present invention.

FIG. 2 is an arrangement diagram of a measuring device that corrects a measurement value of the velocity integration type length measuring device of the present invention.

FIG. 3 is a schematic system diagram of a Mannesmann-mandrel mill pipe manufacturing method.

FIG. 4 is an explanatory diagram of the number of stands used and the roll rotation speed ratio Rn in the stretch reducer.

FIG. 5 is a graph showing a relationship between a roll rotational speed ratio Rn and an elongation rate in a stretch reducer.

FIG. 6 is a graph showing a relationship between a deviation of a mother pipe length and a finishing length from a target length and a frequency.

[Explanation of symbols]

 1,57 Mandrel mill 2,56 Hollow shell 3,59 Mandrel bar 4 Retrainer 5,60 Mother pipe 6 Sizer 7 Product seamless pipe 11, 14, 16, 18 Laser Doppler length meter 12, 15, 17, 19 Radiation thermometer 13 Pipe length control unit 20 Mandrel mill control unit 21 Sizer control unit 51 Round billet 52 Rotary hearth type heating furnace 53 Drilling machine 54 Plug 55 roll 58 Hole type roll 61 Reheating furnace 62 Drawing rolling machine

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B21B 37/00 BBS

Claims (3)

[Claims] 1. A method for controlling a stretch length of a seamless pipe in a mill in which a mandrel mill and a sizer or a stretch reducer are arranged in tandem at a distance shorter than the length of a mother pipe stretch-rolled on a rolling pass line having the same axis. , A velocity integration type length measuring device and a temperature detector are installed at the mandrel mill outlet and the sizer or stretch reducer outlet, and the elongation rate of the mother pipe and pipe is calculated from the speed difference between the inlet and outlet, and the temperature is corrected to correct the temperature. The difference between the above-mentioned elongation rate and a preset target elongation rate is obtained, and the roll gap of the mandrel mill or the roll rotational speed of the sizer or stretch reducer is controlled based on the difference between the target elongation rate. How to control the length of pipe. 2. The seamless pipe according to claim 1, wherein the velocity of the hollow shell at the inlet of the mandrel mill is a predicted velocity, or the pipe velocity measured by a velocity integration type length measuring device provided at the inlet of the mandrel mill is used. How to control the length of pipe. 3. A fixed length measuring device is installed on the exit side of the sizer or stretch reducer to measure the entire length of the pipe, and the measurement error of the velocity integration type length measuring device is measured by the fixed length measuring device. The method for controlling the stretch length of a seamless pipe according to claim 1 or 2, wherein the stretch length is controlled based on the value.