JPH0261849B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for controlling the elongation length of a mandrel mill, and in particular, it is suitable for use in a hot rolling line for seamless steel pipes. Relating to an improvement in the elongation length control method of a mandrel mill, in which the target length of the rolled pipe material is determined from the target values of the outer diameter and wall thickness, and the roll gap and roll rotation speed are set so as to obtain the target length. .

[Conventional technology]

A mandrel mill, which is widely used as a continuous rolling mill for hot rolling lines for seamless steel pipes, is a medium-thick-wall raw pipe made by drilling a round billet (billet) after heating it in a rotary heating furnace with a piercer. A mandrel bar is inserted inside the tube, and the tube is rolled between multiple pairs of rolling rolls (caliber rolls) to form a finished tube with a target uniform wall thickness and outer diameter over the entire length. This finished tube is further sent to a stretch reducer or the like to be formed into a finished product. In this mandrel mill, even if the volume of the raw tube is constant, if its cross-sectional area changes, the rolling mill has a finite spring constant, so the roll gap of each stand changes, and the cross-section of the tube after rolling changes. The area (in other words, the length) will no longer meet the target value. Therefore, for each raw pipe, the target length of the rolled pipe material is determined from the volume of the raw pipe and the target values of the outside diameter and wall thickness of the rolled pipe material, and steps are taken to obtain the target length. So-called extension length control is performed to set the roll gap and/or roll rotation speed. In other words, conventional extension length control first determines the standard roll gap of each stand for the cross-sectional area of the standard raw pipe for each size and steel type, and then determines the standard roll gap for each stand based on this and the roll caliber shape. Then, the cross-sectional area of the pipe material at the exit side of each stand is determined, and the roll rotation speed of each stand is determined based on this and the law of constant volume velocity. Next, for the roll gap and roll rotation speed set as above, the roll gap and roll rotation speed are determined according to the cross-sectional area of the raw pipe, for example, according to the ratio with the standard pipe material cross-sectional area on the exit side of each stand. The roll rotation speed setting has been changed.

[Problems to be solved by the invention]

However, the actual cross-sectional area of the pipe material at the exit side of each stand changes depending on rolling conditions such as the temperature of the raw pipe and the mandrel bar, and generally differs from the standard cross-sectional area described above. Therefore, with the conventional elongation length control method, there is a problem that the tube material of the rolling mill may not reach the target length.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and after determining the actual cross-sectional area of the pipe material at the exit side of each stand with high precision, the roll gap and roll rotation speed of the pipe material to be rolled next are determined with high precision. It is an object of the present invention to provide a method for controlling the elongation length of a mandrel mill, which can be set and therefore has improved control accuracy.

[Means to solve the problem]

The present invention calculates the target length of the rolled pipe material for each raw pipe from the volume of the raw pipe and the target values of the outer diameter and wall thickness of the rolled pipe material, and makes sure that the target length is obtained. In a mandrel mill elongation length control method in which the roll gap and/or roll rotation speed are set at The speed of the pipe material at the exit side of each stand is calculated based on the speed, the length of the preceding pipe material at the exit side of each stand is determined, and from these, the length of the pipe material after rolling, and the volume of the raw pipe, the pipe material is Each time a piece of pipe is rolled, the actual average cross-sectional area of the preceding pipe material at the exit side of each stand is calculated, and for the pipe material to be rolled next, the cross-sectional area of the raw pipe material and the target cross-sectional area after rolling are calculated for each stand. The target cross-sectional area at the exit side is determined, and the target cross-sectional area at each stand when rolling the next pipe material is calculated based on the actual average cross-sectional area of the preceding pipe material and the target cross-sectional area at the exit side of each stand for the pipe material to be rolled next. The above objective is achieved by setting the roll gap and roll rotation speed.

[Effect]

In a mandrel mill, in order to find the actual cross-sectional area of the tube material on the outlet side of each stand, as mentioned above, the speed (or length) of the tube material on the outlet side of each stand and the speed (or length) of the raw tube material on the input side of the mandrel mill. There is a method of determining the volume velocity (or volume) based on the law of constant volume velocity (or volume). The issue here is the speed (or length) of the pipe material on the outlet side of each stand.
It is conceivable to directly measure the speed using a Tatsuchiro-type or laser-type speedometer as a measuring device, but this has not been put to practical use due to problems with the installation space and atmosphere. Therefore, in the present invention, the advancement rate f _i of the tube material at each stand is determined, for example, by a method of correcting the standard advancement rate determined from the transit time between each stand of the tube material by the change in rolling torque ΔGi. That is, an example of the rolling torque of the first stand of a so-called full-float type mandrel mill in which the mandrel bar is not restrained in any way is as shown in FIG. 2, and the rolling torque is large when the mandrel bar is biting, and then decreases. This is because immediately after biting, the speed of the mandrel bar is slower than the speed of the material, and the material receives frictional force from the mandrel bar in the opposite direction to the rolling direction (at this time, the advance rate is generally small). In the process of material being bitten after the stand, the speed of the mandrel bar becomes faster than the speed of the material.
This is because the material receives frictional force from the mandrel bar in the rolling direction (at this time, the advance rate is generally large). Therefore, it can be seen that the advance rate f _i is inversely proportional to the rolling torque Gi to some extent. Therefore, the advanced rate f _i can be determined using the following equation. f _i = f _0i {1-(ΔGi/G _0i )} ...(1) ΔGi=Gi-G _0i ...(2) Here, f _0i is the distance from the i-th stand engagement to the i-th +
Advancement rate until 1 stand bite (standard advance rate),
G _0i is also from the i-th stand biting to the i+1-th
The average rolling torque until the stand bites, i is the stand number. Next, the velocity v _i of the pipe material on the outlet side of the i-th stand is determined using the following equation based on the determined advance rate f _i of each stand and roll circumferential speed v _ri . v _i =v _ri (1+f _i )...(3) Also, the length Li of the pipe material on the exit side of the i-th stand is determined by the following formula. Li=L _0i +∫ ^t2 _t1 v _ri (1+f _i ) dt ...(4) Here, L _0i is the distance between the i-th stand and the i+1-th stand, and t ₁ is the distance between the i-th stand and the i+1-th stand. The time _t2 is the time when the pipe material comes off from the i-th stand. Therefore, the time when the pipe fell out from the i-th stand
The average cross-sectional area of the pipe material at _t2 , that is, the average cross-sectional area Ai of the i-th stand exit side, is determined by the following formula. Ai=A _i-1 L _i-1 /Li...(5) i=1, 2,...,n Here, _A0 is the cross-sectional area of the raw pipe, _L0 is the length of the raw pipe, and Ln is The length of the tube material after rolling, n, is the final stand number of the mandrel mill. If you do the above, each time you roll one tube,
Actual average cross-sectional area of the preceding blank pipe A ₀ , A ₁ ...
An can be calculated. In addition, the cross-sectional area A ₀ of the raw pipe can be calculated using the formula (22) shown below, for example, by calculating the volume V ₀ and length of the raw pipe.
It can be calculated from L ₀ . Therefore, from this, the stretching ratio Ei at each stand is determined using the following formula. Ei = (A ₀ - Ai) / A ₀ ... (6) Then, using the following formula, using the cross-sectional area A ₀ ' of the next rolled pipe material and the target cross-sectional area As of the pipe material after rolling,
Determine the target elongation ratio E _ai at each stand when rolling the next pipe material. E _ai = (E _ao / En) Ei ... (7) E _ao = (A ₀ ′−As) / A ₀ ′ ... (8) Furthermore, the target cross-sectional area A _ai at the exit side of each stand is:
It is determined by the following formula. A _ai = A _ai-1 (1-E _ai ) ……(9) A _a0 = A ₀ ′ ……(10) Therefore, the roll gap setting value Si′ and roll rotation speed when rolling the next blank pipe The set value Ni' is determined by the following formula according to the ratio of the target cross-sectional area A _ai at the exit side of each stand and the actual cross-sectional area Ai of the preceding pipe material. Si′=Si{1−k _s (A _ai −Ai)/Ai} ……(11) Ni′=Ni{1+k _o (A _ai −Ai)/Ai} ……(12) Here, k _s , Both k _o can be simply constants, or, for example, the control result e{=
(An-As)/As} using the moving average or exponential average value e〓 and the roll gap and roll rotation speed distribution coefficient β, the following equation can be determined. k _s =k _s0 βe〓 ……(13) _ko = _ko0 (1−β)e〓 ……(14) Here, both _ks0 and _ko0 are constants. In this way, by using the advance rate of each stand, the length of the tube at each stand, and therefore the actual average cross-sectional area, can be determined with precision for the preceding tube, and then the length of the tube at each stand can be determined with accuracy. By accurately setting the roll gap and/or roll rotation speed of each stand for the tube material, it is possible to improve the accuracy of stretching length control.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an elongation length control device for a mandrel mill to which the present invention is applied will be described in detail with reference to the drawings. In this embodiment, as shown in FIG. 3, a plurality of sets of rolls 14i, 14i+ are continuously arranged to sequentially roll a tube material 10 whose inner diameter is regulated by a mandrel bar 12 inserted _therein. The present invention is applied to a mandrel mill containing _{No. 1} .
A pulse generator 20 for detecting the rotation speed of the roll 14i of the stand, a load cell 22i for detecting that the tube material 10 is caught in the roll 14i of the i-th stand, and a roll 14 of the i+1-th stand in the next stage. Counting is started by the load cell 22 _i+1 for detecting that the tube material 10 is caught in the _i +1 and the load cell 22 i of the i-th stand, and the load cell 22 _i of the i-th stand A pulse counter 24 that stops counting upon detection of biting by ₊₁ and outputs the cumulative number of pulses C during that time, and a reference advance rate f _0i calculated from the cumulative number of pulses C output by the pulse counter 24.
is corrected by the change in rolling torque ΔGi to obtain the advance rate f _i at the time of preceding pipe material rolling, and the advance rate
The actual average cross-sectional area Ai of the preceding pipe material calculated based on f _i , the cross-sectional area A ₀ ' of the pipe material to be rolled next, and the target cross-sectional area As of the pipe material after rolling.
According to the target cross-sectional area A _ai of each stand obtained from It is composed of an arithmetic unit 26 that outputs to a device (not shown). Hereinafter, with reference to FIG. 4, the arithmetic unit 26
Explain the effect of The calculation device 26 first calculates the cumulative number of pulses C output from the pulse counter 24 and the distance between the stands.
From L _0i , roll radius R, and pulse generation rate α (pulses/rotation) of the pulse generator 20,
Using the relationship of the following formula, the standard advanced rate f _0i of each stand
Calculate. f _0i =L _0i /(2πRC/α)−1 (15) Next, the rolling torque Gi from the i-th stand engagement to the i+1-th stand engagement is calculated.
That is, in general, the rolling torque Gi is obtained by subtracting the acceleration/deceleration torque G _ai from the motor output torque G _ni to correct losses such as mechanical loss. Here, the motor output torque G _ni (J) at the i-th stand is the motor terminal voltage V (V), armature current Ii (A), rotation speed Ni
(rpm) can be actually measured and obtained from the relationship of the following equation. G _ni = (V-Ii・r _i −Vb)Ii/Ni×2π/60)
...(16) Here, r _i is armature resistance (Ω), and Vb is brush voltage drop (V). Also, the acceleration/deceleration torque G _ai (J) at the i-th stand is
It is determined by the following formula from the moment of inertia and the actually measured acceleration/deceleration rate dNi/dt. G _ai = (GD ² )i/4・dNi/dt・2π/60
...(17) (dNi/dt) _o-1 = (Ni-N _{i o-2} )/2τ ...(18) Here, GD ² is the moment of inertia converted to the motor shaft (Kgm ² ), and τ is , is the sampling period (seconds). Here, motor terminal voltage V, armature current Ii,
The reason why the sampled value of the rotational speed Ni is shifted each time is to match the phase of the acceleration/deceleration torque and the motor output torque, since what is determined by the current sampling is the acceleration/deceleration rate. Next, the rolling torque Gi' is calculated from the motor output torque G _ni and the acceleration/deceleration torque G _ai using the relationship of the following equation. Gi′=(R _gi /2×9.8)(G _ni −G _ai )……(19) Here, R _gi is the gear ratio. The rolling torque Gi′ obtained in this way is
Since it includes the acceleration/deceleration rate, which is a differential value of the rotation speed, a small change in the rotation speed will cause a considerable fluctuation, resulting in unnecessary fluctuations. Therefore, using a machine that suppresses this using a digital filter, for example, the loss torque is corrected using a regression equation as shown in the following equation, which was determined by experimentally measuring the rolling torque, and the final rolling Find the torque Gi. Gi=aGi'+b...(20) Here, a and b are regression coefficients. Next, the rolling torque obtained in this way
Calculate the average value G _0i of Gi. In the end, the advancement rate f _i of the leading pipe material after the i+1st stand is bitten can be determined from the following relationship. f _i =f _0i {1+k _g (Gi−G _0i )/G _0i } (21) Here, k _g is a constant. Next, using the above equation (3) from the roll circumferential speed v _ri and the advance rate f _i . Calculate the velocity v _i of the pipe material on the exit side, integrate this from the i-th stand engagement to the i-th stand end dropout, and further add the inter-stand distance L _0i ,
From the relationship of equation (4) above, calculate the length Li of the pipe material on the exit side of the i-th stand of the preceding pipe material. On the other hand, the length of the raw pipe L ₀ and the length of the pipe material after rolling Ln
can be measured using a conventional length meter, and the volume of the raw pipe V ₀ is
Since it can be calculated from the weight, specific gravity, and scale loss rate of the billet, the cross-sectional area A ₀ of the raw pipe can be found using the following formula. A ₀ =V ₀ /L ₀ (22) Therefore, the actual cross-sectional area Ai of the leading pipe material at the exit side of each stand can be determined by the above equation (5). Afterwards,
Thereafter, by calculating according to equations (6) to (12) or equations (6) to (14) above, the set values Si′, Ni of the roll gap and roll rotation speed when rolling the next blank pipe are obtained. ' can be calculated, and these values are output to each control device.

【Effect of the invention】

As explained above, according to the present invention, the cross-sectional area (in other words, the stretched length) of the pipe material after rolling is calculated for the next blank pipe based on the actual cross-sectional area of the pipe material at the exit side of each stand. It is possible to accurately determine how the roll gap and/or roll rotation speed of each stand should be adjusted to reach the target value. Therefore, it has the excellent effect of improving the control accuracy of the extension length.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing the outline of the elongation length control method of a mandrel mill according to the present invention, and Fig. 2 is a flow chart showing the gist of the elongation length control method of a mandrel mill according to the present invention. FIG. 3 is a diagram showing an example of changes in rolling torque for explaining the principle of the method of determining the advance rate by . FIG. 4 is a block diagram showing the structure of the arithmetic unit used in the embodiment. f _i ...Advance rate, v _i ...Speed of pipe material, Li...Length of pipe material, Ai...Average cross-sectional area of pipe material, Si'...Roll gap setting value, Ni'...Roll rotation speed setting value,
10...Pipe material, 12...Mandrel bar, 14
i, 14 _i+1 ...Roll, 26...Arithmetic device.

Claims (1)

[Claims] 1. For each raw pipe, the target length of the rolled pipe material is determined from the volume of the raw pipe and the target values of the outer diameter and wall thickness of the rolled pipe material, and the target length is determined. In the mandrel mill elongation length control method, which sets the roll gap and roll rotation speed so as to obtain The length of the preceding pipe material at the exit side of each stand is determined by calculating the speed of the pipe material, and from these, the length of the pipe material after rolling, and the volume of the raw pipe, each stand Calculate the actual average cross-sectional area of the preceding pipe material at the exit side, and then calculate the target cross-sectional area of the pipe material to be rolled at the exit side of each stand from the cross-sectional area of the raw pipe and the target cross-sectional area after rolling. Setting the roll gap and roll rotation speed of each stand when rolling the next pipe material according to the actual average cross-sectional area of the preceding pipe material and the target cross-sectional area at the exit side of each stand of the pipe material to be rolled next. A method for controlling the elongation length of a mandrel mill, which is characterized by: