JPS61206514A - Control method of rolling in mandrel mill - Google Patents

Abstract

PURPOSE:To make the wall thickness of pipe uniform by setting the wall thickness of pipe at the outlet side of each stand as well as estimating a rolling load based on the results, etc. and setting a draft position and the number of revolutions of roll for each pipe. CONSTITUTION:First, a prescribed rolling-down force is applied to upper and lower rolls in contact, to adjust a zero point of draft position as well as to set a reference gap. Next, the actual wall thickness of pipe stock at the outlet side of each stand is obtained to obtain further a distributing ratio of actually reduced wall-thickness. A rolling load of each stand is estimated from the measured temperatures, etc. of a mandrel bar and a pipe stock, to adjust the draft position based on the gauge-meter deviation of mandrel bar. Further, the number of revolutions of roll to be set is obtained based on the low of constancy of mass flow, to control the number of revolution of roll. By these methods, the rolling of mill is controlled in consideration of the deformation resistance and wall-thickness reduction rate of pipe stock, to make the wall thickness of pipe stock in its circumferential direction uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a rolling method using a mandrel mill, and particularly relates to a method for rolling with a mandrel mill. This invention relates to an improvement in a rolling control method for a mandrel mill that gradually reduces the outer diameter and wall thickness of a pipe using several stands and mandrel bars. [Prior Art] As a continuous rolling mill for a hot rolling line for seamless steel pipes The widely used mandrel mill uses a medium-thick wall blank tube (rolled material) 10, which is formed by drilling a round steel billet (billet) with a piercer after heating in a rotary heating furnace, as shown in Fig. 8. as,
Insert the mandrel bar 12 inside it, and ? ! The purpose is to roll the finished tube between 14 pairs of rolling rolls (caliber rolls) to form a finished tube with a uniform wall thickness and outer diameter over the entire length. , and is further sent to a stretch reducer or the like to be formed into a finished product. In such a mandrel mill, it is necessary to control the average wall thickness of the tube after rolling to a target value in order to make not only the average wall thickness uniform but also the wall thickness in the circumferential direction. This is because the roll hole shape of the final stands for finishing odd and even thicknesses is usually set so that when the average thickness matches the target value, the thickness in the circumferential direction becomes the most uniform. be. Also, the control I-! is made so that the wall thickness of the tube at the bottom of the roll groove of the final stands for odd and even wall finishing is equal. It is also necessary to make the wall thickness uniform in the circumferential direction. By the way, the main factors that influence the average wall thickness of the pipe after rolling are considered to be wear of the mandrel bar and rolls, and variations in the dimensions of the wood pipe and the rolling load. Therefore, in the past, for the wear of the mandrel bar, the diameter of the worn mandrel bar was calculated based on the average wall thickness of the pipe after rolling and the roll gap during the biting of the pipe. Therefore, a method has been proposed in which the reduced position is opened. According to this control method, a steel pipe with the same wall thickness can be obtained every time, despite repeated use of plugs and mandrel bars. In addition, for example, Japanese Patent Application Laid-Open No. 54-1
No. 21266 discloses a method of changing the roll circumferential speed ratio, in other words, the tension (including compression force) based on the length of the raw pipe. In addition, in order to eliminate variations in the rolled length or average wall thickness of the tube, in Japanese Patent Publication No. 59-16847, the circumferential speed of the roll was determined based on the coefficient of friction between the outer surface of the tube and the roll and the coefficient of friction between the inner surface of the tube and the mandrel bar. A method of changing the ratio has been proposed. [Problems to be Solved by the Invention] However, in the method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 54-102270, etc., in which the diameter of the worn mandrel bar is determined and the rolling position is determined by 1llllllll, the roll gap during tube biting cannot be corrected. It is important and necessary to obtain accurate results, but conventionally,
Since the zero adjustment of the reduction position of the mandrel mill was carried out without applying the reduction blade, variations in mill rigidity due to rattling of the rolling mechanical system (housing) and nonlinear parts of mill rigidity ( The problem is that sufficient accuracy cannot be obtained due to the influence of low load parts. Furthermore, in the control method of changing the roll circumferential speed ratio based on the length of the wood pipe, which was proposed in the above-mentioned Japanese Patent Application Laid-Open No. 54-121266, when rolling tension is applied, a predetermined tension is applied to the tip and rear ends of the pipe. Moreover, since the tension varies each time the tube gets caught in each stand or the tube exits from each stand, there is a problem that the wall thickness and outer diameter in the longitudinal direction of the tube after rolling fluctuate. . In addition, the rIi friction coefficient between the outer surface of the tube and the O-ru and the inner surface of the tube and the mandrel bar proposed in the above-mentioned Japanese Patent Publication No. 59-16847
In the control method of changing the roll circumferential speed ratio based on the friction coefficient between
There is a problem in that the longitudinal wall thickness and outer diameter of the tube after rolling fluctuate. Furthermore, the rolling load varies depending on the friction characteristics of the inner and outer surfaces of the tube as well as the deformation resistance and thinning rate of the tube, but so far no control method has been proposed that takes these into account properly.
No appropriate control method has been proposed to equalize the wall thickness of the tube at the bottom of the roll groove in each even-numbered finishing stand, and therefore, it is difficult to sufficiently suppress variations in the wall thickness and outer diameter of the tube after rolling. The problem was that it could not be done. OBJECTS OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional method. It is an object of the present invention to provide a rolling control method for a mandrel mill that can control the rolling position and roll rotation speed. (Means for Solving the Problems) The present invention provides a rolling control method for a mandrel mill that gradually reduces the outer diameter and wall thickness of a tube using a plurality of stands having slotted rolls and a mandrel bar, the method of which is shown in FIG. As shown in the summary, based on the actual wall thickness of the raw pipe and the rolled pipe, the set amount of thinning for each stand is determined so that the average wall thickness of the rolled pipe becomes the target value, and then the set amount of thinning for each stand is determined for each odd number and even number. Based on the actual wall thickness of the pipe in the final stand, the odd-even thickness reduction distribution ratio is determined so that the wall thickness of the pipe after rolling is uniform in the circumferential direction, and the set thickness reduction amount and setting are determined. Based on the odd-even thickness reduction distribution ratio and the actual thickness reduction distribution ratio of each stand, the set wall thickness of the pipe on the outlet side of each stand is determined, and the thickness of the woodwind and the mandrel bar is determined.
The pre-rolling load of each stand is determined based on the temperature, the set thickness reduction rate of each stand, the actual thickness reduction rate of each stand, and the actual rolling load, and the set wall thickness of the pipe on the exit side of each stand and the set wall thickness of each stand are determined. The above objective is achieved by setting the rolling position and O-ru rotation speed for each blank tube based on the predicted rolling load. Also, implementation of the present invention! i is the actual wall thickness of the pipe,
The accuracy of calculating the roll gap is improved by applying a predetermined rolling blade to the upper and lower rolls of each stand while making a zero adjustment of the rolling position. [Function] First, in order to obtain a good roll gap of 11 degrees during tube biting, it is necessary to remove the effects of mechanical system play and nonlinear parts of mill rigidity (low load parts). Therefore,
As shown in Figures 2 to 4, when assembling the rolls, the upper and lower rolls are kept in contact and a predetermined rolling blade (hereinafter referred to as preload load) is applied to the rolling position at zero adjustment wi (hereinafter referred to as preload load). , preload zero adjustment). That is,
Balance adjustment is performed in the state shown in FIG. 2, preload zero adjustment is performed in the state shown in FIG. 3, and reference gap is set in the state shown in FIG. 4. Therefore, the roll gap G at the time of tube biting can be determined with high accuracy using the following equation. G=Go+ <p-Ppr)/K...-(i> where GO is the roll gap before the tube bites, P is the rolling load, Ppr is the preload alliance, and K is the mill spring constant.Next The method of controlling the rolling position and roll rotation speed of each roll stand for each raw pipe will be explained with reference to Fig. 6. In the following explanation, the raw pipe will be described as a hollow pipe, and the rolled pipe as a shell. First, calculate the actual roll gap G of each stand (at the time of tube jamming) based on the above formula (1), and use that value and the mandrel bar diameter (whether measured in advance or directly set). good)
Find the actual wall thickness (at the bottom of the roll groove) on the exit side of each stand. In addition, the actual wall thickness tC13 (i is the stand number) of the finished R final stand for odd and even numbers and the actual shell wall thickness ts
The amount ΔG (hereinafter referred to as gauge meter deviation) corresponding to the wear of the roll and mandrel bar is determined by comparing the values, and this value is used when the mandrel bar is used next time. Also, calculate the corrected wall thickness jc(i) of each stand based on the gauge meter deviation ΔG and the actual wall thickness ((1). Next,
Based on this value and the actual hollow wall thickness th, the actual thinning distribution ratio Ror++, R for each stand for each odd number and even number.
Find 6t+t. Furthermore, based on the wall thickness finishing l of each odd number and even number and the corrected wall thickness tc (1) of the final stand, the odd number of the pipe to be rolled next,
Odd-even thinning distribution ratios Bo and Be are determined so that the corrected wall thicknesses of the final stands for finishing each even number of wall thicknesses are equal. Next, based on the actual shell wall thickness ts and the actual wall thickness th of the hollow to be rolled next, set the wall thickness reduction amount Δ of the total of each stand so that the shell wall thickness of the next rolled pipe becomes the target IfA value.
[Find α. Actual thinning distribution ratio RoC1 of each stand obtained from the above
], Ret++, set odd-even thinning distribution ratio BO1Be and set thinning amount Δ [Based on α, set wall thickness t of each stand
α(1) and set thinning rate 1-(tα+1)/lα(i-
zl). Next, the actual measured temperatures of the mandrel bar and hollow θ6, θ6
and the set thinning rate 1 (rα(+l/1(1(+-21
>, the predicted rolling load P (■) of each stand is calculated based on the actual thickness reduction rate and the actual rolling load P+1+.Furthermore, based on the predicted rolling load order t i + and the gauge meter deviation ΔG of the mandrel bar to be used. Set pressure lower @ss (+
) and adjust the rolling position Mj to this value. On the other hand, the roll rotation speed is controlled by setting the wall thickness t of each stand.
Using the cross-sectional area correction ratio Ca(i) determined based on αcl+, a set rotational speed N5ti] at which tensionless rolling is achieved based on the constant mass flow law is determined, and adjustment is made to this value. (It is possible to carry out rolling with a mandrel mill 11J II while taking into account the deformation resistance and thinning rate of the tube, and to make the wall thickness of the tube at the bottom of the roll groove of the final stand of odd and even wall thickness equal to each other.) [Example] Hereinafter, with reference to the drawings, an example of a rolling control device for a mandrel mill to which the present invention is adopted will be described in detail. As shown in FIG. 6, the mandrel includes a plurality of consecutively arranged sets of rolls 14 for sequentially rolling a tubular hollow 10 whose inner diameter is regulated by a mandrel bar 12 inserted therein. The present invention is applied to a mill, which includes various sensors including a load cell 2o for detecting the rolling load P(i), a pulse generator for detecting the rotation speed of the O-ru 14i of the i-th stand, etc.
Based on the sensor output, the set thickness reduction amount Δ(α) of the total of each stand is determined from the actual hollow wall thickness th and the actual shell wall thickness ts so that the average wall thickness of the pipe after rolling becomes the target value, and further, The actual wall thickness t of the pipe on the exit side of the finished final stands (in this example, the fifth and sixth stands) for each of the odd and even numbers
(5) Based on tc65, determine the set odd-even thickness thinning distribution ratio BO1Be so that the wall thickness of the tube after rolling is uniform in the circumferential direction, and calculate the set thinning amount Δ tα and the set odd-even thinning distribution ratio B
O1Be and actual thinning distribution ratio RoCi of each stand], R
Set wall thickness of outlet pipe of each stand based on ezl and [
α(11 is calculated, and the temperatures θh and θb of the hollow and said mandrel bars, and the set thinning rate 1-((α(l)
+/lα(1-2)) and the actual thinning rate of each stand 1-
(tc[t+/lc++-2+) and actual rolling load P(
+), calculate the predicted rolling load P(11) for each stand, and calculate the set wall thickness tα(1) of the pipe on the exit side of each stand.
and the predicted rolling load P(1) of each stand, the rolling position and roll rotation speed are set for each hollow, and the control lf1 of the roll rotation speed and rolling position is output to the control wJ device (not shown). The operation of the arithmetic unit 24 will be explained below with reference to the above-mentioned FIG. In this embodiment, the preload zero adjustment is performed in the roll shop as shown in FIGS. 2 to 4. That is, as shown in FIG. Insert the stopper gauge 16 into the roll bite, apply the reduction blade, and adjust the balance horizontally and vertically.Next, as shown in Fig. 4 Qton), perform the adjustment to the lowered position.Then, as shown in Fig. 4, set to the predetermined lowered position.In addition, the reference numeral 17 in Figs. 3 to 5 is a coupling; Reference numeral 18 indicates a motor, and reference numeral 19 indicates a cell thin. Therefore, the relationship between the roll gap and the rolling blade during temperature control in this embodiment is as shown in FIG. Measured values of weight, hollow length, hollow average outer diameter W1, Lh, Dh
From the scale loss rate μr in the rotary heating furnace and the density ρh of 〇-, the actual hollow thickness average value) th is calculated using the relationship of the following formula. ρhLhπ th (Dhr rh)−Wb (
1-μr) (2) Lh-(Dh/2) Next, the actual shell outer diameter Ds is calculated. Since the outer diameter shape of the shell is usually elliptical, it is calculated from the following ellipse director's approximation formula based on the actual measured values Dsβ and Dss of the shell outer diameter corresponding to the long side and short side. Ds-(2/π) x (0,9827D s fl + 0.311D
s s 0.2867 (Ds s ) 2/Ds I
t) - (4) Next, calculate the actual shell thickness ts. The actual shell wall thickness ts is calculated using the following equation, which is a modification of the equation (2), in the same way as the actual hollow wall thickness 1h. (s=(Ds/2)...(5) where ρS is the density of the shell. Next, calculate the actual wall thickness t(1) of each stand.The actual wall thickness of each stand [ (i) is calculated from the gap G (i) of the pipe-biting roll (at the bottom of the groove) and the diameter Db of the mandrel bar (actual measurement value or setting 1i1) using the relationship of the following formula: tri) - ( G(13-Db)/2...
...(6) In addition, the roll gap G (1
) is calculated using the following relationship. GC+) Dew S(Ico+2DK(1+ + (P+ + r - Pp r)/K・"<7) Here, Sc+) is placed under pressure!! Gap of roll flange part before biting), DK is Depth of roll hole shape, P(
() is the rolling load, Ppr is the preload Mli, and is the mill spring constant. Next, gauge meter deviation ΔG is calculated. This gauge meter deviation ΔG is the actual wall thickness [c
5], calculated from the following relationship based on t(6) and the actual shell thickness ts. ΔG-α g ×ΔG1-1 + (1-αg) × 2 x (tB-(t(st+tca+)/2)...
...... (8) Here, αg is a coefficient for smoothing, and ΔQt-1 is the mandrel bar 1 circulation, that is, the gauge meter 1 at the previous rolling.
Indicates m difference. The initial value of the gauge meter deviation ΔG is
Calculated using the following formula. ΔG= a1+ b+ IINr+ O+ -Nb...
・・・・・・・・・〈9) Here, Nr is the number of roll rolling, Nb is the mandrel bar
The number of rolling times, al, bl, and cl are coefficients obtained by analysis in advance. Next, the corrected wall thickness to (+) of each stand is calculated. This corrected wall thickness to (+) is the actual wall thickness 11
() and the gauge meter deviation ΔG, it is calculated from the relationship of the following equation. tC(i)-t(1)+ΔG/2 (10) Next, calculate the actual thickness reduction distribution ratio RocI) and Ret+t for each stand. Here, Roc+) indicates the actual thinning distribution ratio on the odd-numbered stand side, and RBtl] indicates the actual thinning distribution ratio on the even-numbered stand side. Actual thinning distribution ratio R of each of these stands
□tl], R@(i) are calculated based on the actual hollow thickness th and the corrected thickness tc(i) using the following relationship. RO(1)-(tC(i-2+-tC(it)/(t
l, -t(Hts+)...(11) ReClt-(tc
ti-2l-tcti))/(th-tccat)・
・(12) In the above formula, 1cc-, + and tc(0)
is assumed to be equal to the actual hollow thickness 1h. Next, the set odd-even thinning distribution ratio BO1Be is calculated. These set odd-even thickness reduction distribution ratios Bo and Be are determined by the corrected wall thickness [c(5], jc <
This is to ensure that s ) are equal. In addition, BO indicates the set thinning distribution ratio of the stands on the odd number side, and Be
indicates the set thinning distribution ratio for the even-numbered stands. The set odd-even thinning distribution ratio Bo, Be is the corrected wall thickness IC of each stand.
It is calculated from the relationship of the following formula based on t i + and the actual hollow thickness th. Bo-f th-(jc(s++ jc (s+)
/21. /(th tc (s))...
... (13) Be-(th-(tc Cs++
tc Ca+)/2J/ (th-tc (6))・
...=... (14) Next, calculate the rolling load learning coefficient Cpti) for each stand. This rolling load learning coefficient Cptx of each stand is a coefficient used when calculating the predicted rolling load pri+ of each stand, which will be described later. This rolling load learning coefficient Wlcp(+) is calculated from the following equation based on the smoothing coefficient αP, the mandrel bar temperature influence coefficient Cb, the hollow temperature influence coefficient Ch, etc. CP(11-αP-CPci)0″+(1-αP)X(
P(1+/[a2(i)+b2(lzx(1-(tc
＜+)/tc+i-z+))XCbXCh)
・・・・・・・・・(15) Here, a2(i),
1) 2cit is the coefficient obtained by analyzing each type of preformed steel, C
P(i)n''I indicates the rolling load learning coefficient for one main building of the pipe.The initial value is CP(1)-1.Next, exclude the shell thickness deviation Δ1. The shell thickness deviation Δ1. can be calculated from the relationship of the following formula: A t, -(ZiXΔtfn″I+ (1-(It)X
(tos −ts ) −······−(16) Here, αt is a coefficient for smoothing, and tos is the thickness of the shell. Note that the initial value is Δtf−O. Next, the set shell thickness tss is calculated. The set shell thickness tss is calculated from the following relationship. tss”tssn4+Δt, ・−・・−・・
- (1, 7) Note that the initial value is j138-j09s, that is, the target shell thickness. Using the actual values calculated as described above, various setting amounts for the hollow to be rolled are calculated as follows. First, the set thickness reduction amount Δta is obtained by subtracting the set shell thickness tss from the actual hollow wall thickness th. That is, the set thickness reduction amount Δ1. Calculate. Δ ta −th −ts s ---(18
) Next, the set thickness reduction amount Δ teLt + ) of each stand
Calculate. Set thickness reduction amount Δ tat() for odd-numbered stands
is calculated using the following relationship. Δt,,IC1+-(th-tss)XRoti)X
Bo ・・・・・・・・・(19) On the other hand, the set thinning amount Δ ta (i) of even-numbered stands is calculated by the relationship of the following formula: Δ ta (+) −(th − tss)XRe t
l)XBe・・・・・・・・・(20)
Here, the initial value of the actual thickness reduction distribution ratio RO (ir, Ret 1) is the value obtained in advance, the set odd-even thickness reduction distribution ratio Bo, Be
The initial value of is 1. Next, calculate the set wall thickness [α(11) of each stand. This set wall thickness tcLC1+ is the set wall thickness (αc1− It is obtained by subtracting the set thickness reduction amount Δt of each stand from (1) from 2).In other words, the set wall thickness 1cL((
) is calculated. [α (1) Sir ta (1-23-Δ [α C
i)・・・・・・・・・(21) Note that tcL(-+ 3- IcL(0) -th) ◎Next, the predicted rolling load P(1) of each stand is calculated using the following formula. Calculate according to the relationship: pc i )-[a2 c l )+ b2
c l ]x(1-(tc(i)/tc
*cl-2)))]XCp (+)XCb
XCh ・+・to−・−(22>However, Cb=
kb・(θob/θb), Chsol(h・(θoh/
θh). Here, kbq kh is an experimentally determined coefficient, θob
is the standard mandrel bar temperature, θb is the measured mandrel bar temperature, θoh is the reference hollow density, and θh is the measured hollow temperature. Although the thermal expansion of the mandrel bar diameter due to the mandrel bar temperature can be ignored, the state of lubricant application on the mandrel bar surface varies depending on the mandrel bar temperature, which changes the I]iWA characteristics of the tube inner surface and the mandrel bar. Rolling load fluctuates. Therefore, the above-mentioned mandrel bar temperature influence coefficient Cb takes into consideration the effect of this mandrel bar temperature, and by using this mandrel bar temperature influence coefficient Cb, the IIItli characteristics of the tube inner surface and the mandrel bar change. This is to correct fluctuations in rolling load. Also, even if the steel type is the same, the deformation resistance will differ if the temperature of the hollow differs, so this is taken into account by the aforementioned hollow temperature influence coefficient Ch. This corrects fluctuations in deformation resistance. In addition, other factors that are difficult to estimate, such as the influence of the friction characteristics between the tube outer surface and the rolls, are corrected using the learning coefficient CP (1) described above.Next, the set reduction position Ss (1) of each stand is , the setting interval F11tαc1), the mandrel bar diameter Db, the Gehage meter deviation ΔG, the predicted pressure cylinder IP (1), and the roll hole shape depth DK (1). Sst ()-2taCH3+Db-ΔG8-(P(1)-Ppr)/to 2DK(i)... (23)
Next, the cross-sectional area correction ratio CQ+++ of each stand is calculated based on the set wall thickness tα(1) according to the relationship of the following formula: CCL(+3−kc(++X(ja(11/to) (1+) ・・・・・・・・・(24) Here, kα is a coefficient calculated in advance by analysis, and 0 indicates the reference wall thickness.Next, the set rotation speed Ns t i ) of each stand is calculated based on the cross-sectional area correction ratio C(L(1)) using the following relationship: Nst+]-<No++)/Cc(++)...
...(25) Here, NO indicates the set rotation speed at the time of the standard wall thickness. The set reduction position 5sri) and set rotation speed Ns (i+) obtained in this way are output to the control device of the mandrel mill to control the drive motor that drives the rolls of each stand. Activate the pressure reduction device. △ Therefore, in this embodiment, the predicted pressure cylinder flP(i)
The calculation of
Calculation takes into account the variation in deformation resistance due to temperature changes in the tube, as well as the influence of the friction characteristics between the tube outer surface and the rolls, so that the wall thickness of the tube in the circumferential direction after rolling becomes uniform. The rolling position can be controlled. Thereby, it is possible to control the average wall thickness of the tube after rolling to a target value. In addition, the set wall thickness [α(i)] of each stand is changed to the corrected wall thickness tc
The set odd-even thinning distribution ratio Bo, Be calculated based on the actual hollow wall thickness 1h and the actual thinning distribution ratio Ro(
i+, Rst+) and the set wall thickness reduction amount Δt, the set wall thickness reduction rate is calculated based on this set wall thickness t(1t(), and the predicted pressure wind cylinder l1IPcI) is calculated. It is possible to control the wall thickness of the tubes at the bottom of the roll groove of the finishing stands of odd and even numbers to be equal. Therefore, the wall thickness of the rolled tube in the circumferential direction can be made uniform. In addition, the cross-sectional area correction ratio CαtB+ is calculated from the set wall thickness tαC1+ and the actual hollow wall thickness th, and by calculating the set rotation speed N5 (11) from this cross-sectional area correction ratio Cc(i), tensionless rolling is performed. This makes it possible to prevent variations in the wall thickness and outer diameter in the longitudinal direction of the tube after rolling.In particular, in this example, by performing preload zero adjustment, the roll gap during tube biting can be adjusted accurately. Therefore, the rolling position can be controlled with high accuracy.In other words, the zero adjustment of the rolling position of a mandrel mill was conventionally carried out without applying the rolling blade.
Due to variations in mill rigidity due to backlash of the housing, etc., the gap during rolling has an error within a certain width, as shown in FIG. On the other hand, in this embodiment, as shown in FIG. 7, zero preload adjustment eliminates the influence of variations in mill rigidity and allows the roll gap during rolling to be determined with high accuracy. This is because by applying the preload load PPr, the origin of the roll gap can be moved to the right in FIG. 7, and the influence of the nonlinear part of the mill rigidity can be eliminated. [Effects of the Invention] As explained above, according to the present invention, it is possible to control the wall thickness of the tubes at the bottom of the roll groove of the final stands of odd and even thickness to be equal. It is possible to make the wall thickness of the tube uniform in the circumferential direction, and
It has the excellent effect of being able to control the average wall thickness of the tube after rolling to a target value.

[Brief explanation of drawings]

Fig. 1 is a flow factor showing the gist of the rolling control method of a mandrel mill according to the present invention, Fig. 2 is a front view showing a state in which the balance of the rolling rolls is being adjusted, and Fig. 3 is a preload of the rolling rolls. 1 is a front view showing a state in which the rolling roll is adjusted to zero, FIG. 4 is a front view showing a state in which the rolling roll is set to the standard gap, and FIG. Control [1] A block diagram showing the configuration of the arithmetic unit used in the embodiment of the device, Fig. 6 shows the configuration of the embodiment of the rolling control m+ device of the mandrel mill in which the present invention is adopted, and the deformation situation of the pipe. FIG. 7 is a scale diagram showing the relationship between the roll gap and rolling load or rolling blade according to the method of the present invention, and FIG. 8 is an enlarged longitudinal cross-sectional view including a block diagram and a side view. A schematic side view, FIG. 9, is a diagram illustrating the relationship between the roll gap and rolling load or rolling blade according to the conventional method. 1o...Hollow, 12...Mandrel bar-1 14...Roll, 24...Drawing device.

Claims (2)

[Claims] (1) In a rolling control method for a mandrel mill that gradually reduces the outer diameter and wall thickness of a pipe using multiple stands with slotted rolls and a mandrel bar, the method is based on the actual wall thickness of the raw pipe and the rolled pipe. Calculate the set amount of wall thinning for each stand so that the average wall thickness of the pipe after rolling reaches the target value, and then calculate the wall thickness after rolling based on the actual wall thickness of the pipe at the exit side of the final stand for finishing each odd and even wall thickness. Calculate the set odd-even thickness reduction distribution ratio so that the wall thickness of the pipe in the circumferential direction is uniform, and calculate the thickness reduction distribution ratio for each stand based on the set thickness reduction amount, the set odd-even thickness reduction distribution ratio, and the actual thickness reduction distribution ratio of each stand. Determine the set wall thickness of the outlet pipe, and determine the predicted rolling load for each stand based on the temperature of the raw pipe and the mandrel bar, the set thinning rate for each stand, the actual thinning rate for each stand, and the actual rolling load. . A rolling control method for a mandrel mill, characterized in that the rolling position and roll rotation speed are set for each blank pipe based on the set wall thickness of the pipe on the outlet side of each stand and the predicted rolling load of each stand. (2) The actual wall thickness of the pipe is determined by applying a predetermined rolling blade to zero adjustment of the rolling position while keeping the upper and lower rolls of each stand in contact with each other. rolling control method for mandrel mill.