JPH0569606B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for continuous rolling of seamless pipes, and particularly to a rolling control method for a mandrel mill in which a mandrel bar is inserted into a hollow pipe and the pipe is continuously stretched and rolled by mandrel mills arranged in tandem. [Prior Art] In the process of manufacturing seamless pipes, a raw pipe supplied from a piercer or an elongator is rolled by a mandrel mill. This mandrel mill can be roughly divided into two types. In other words, there are two types: one in which the speed of the mandrel bar is restricted and the other in which the mandrel bar is freed for rolling. When rolling is performed with the mandrel bar free, the mandrel bar speed changes at the stage where the tube tip part engages with each stand and at the stage where the tube rear end part exits each stand, so the rolling conditions also change. As a result, variations in wall thickness occur at the tip and rear ends of the tube, resulting in
Cross-sectional area accuracy decreases. On the other hand, when the mandrel bar speed is restricted, the wall thickness and cross-sectional area variations that occur due to changes in the mandrel bar speed as described above do not occur. but,
If there is a change in the wall thickness or outside diameter of the raw pipe, or if the bar diameter changes due to temperature changes, the problem remains that these effects will affect the product wall thickness and cross-sectional area, worsening dimensional accuracy. . [Object of the Invention] The present invention simultaneously controls the number of rotations of the rolls excluding the key stand and the amount of reduction at each stand, thereby controlling the wall thickness, outer diameter, and deformation resistance of the raw pipe, and the product wall thickness and bar diameter variation. The present invention provides a rolling control method for a mandrel mill that eliminates the influence on the cross-sectional area and improves the dimensional accuracy of the product. [Summary of the Invention] The present invention is a mandrel mill in which the mandrel bar speed is restricted (restricted mandrel mill), and even when changes occur in the raw tube wall thickness, outer diameter, deformation resistance, and bar diameter, The roll rotation speed and rolling reduction amount are controlled to keep the product wall thickness or product wall thickness/sectional area constant, and the purpose is achieved by the following method. The first control method according to the present invention is to rotate the rolls so that the tension between each stand in the previous stage becomes zero in response to changes in pressure conditions due to changes in the raw pipe size, mandrel bar radius variation in the previous stand, etc. In addition, the number of roll rotations is controlled so that the tension between each stand is zero in response to variations in mandrel bar deformation in subsequent stands, and thickness variations due to variations in mandrel bar radius are corrected. The feature is that the wall thickness is made constant by adjusting the amount of reduction in the subsequent stand. In addition, the second control method according to the present invention is such that the tension between each stand in the previous stage becomes zero in response to changes in pressure conditions due to changes in the raw pipe size, mandrel bar radius variation in the stand in the previous stage, etc. While controlling the roll rotation speed, and controlling the roll rotation speed so that the tension between each stand in the front stage becomes zero in response to variations in the mandrel bar radius in the stands in the latter stage,
In addition to correcting wall thickness fluctuations due to variations in the mandrel bar radius, the amount of reduction in the subsequent stands was adjusted to control the outer diameter of the free deformation portion of the raw tube, and tension was generated between each subsequent stand. A feature is that the wall thickness and cross-sectional area are kept constant by controlling the rotation speed of the rolls. [Embodiments of the Invention] Next, the thought process of the present invention will be explained, and then embodiments will be explained. First of all, in rolling mills such as mandrel mills, in which a mandrel bar is inserted into a hollow tube supplied by a piercer or elongator and continuously rolled with grooved rolls, the following factors worsen the product dimensional accuracy: Items such as: <Factor 1>: Change in mandrel bar speed during rolling <Factor 2>: Change in wall thickness/outer diameter of the raw tube and change in temperature (deformation resistance) <Factor 3>: Temperature of the tube during rolling (deformation resistance) Change in <Factor 4>: Change in mandrel bar temperature (mandrel bar diameter) during rolling Change in mandrel bar diameter due to wear If the mandrel bar speed is restricted, <Factor 1> can be removed, but other dimensions There is no effect on accuracy deterioration factors. The present invention is <Factor 2>~
This also excludes the influence of <Factor 4>, and in order to consider these influences, the following items, namely:
() Continuous rolling characteristics without control, and () Effects obtained by controlling the inter-stand tension to a constant level will be discussed. [] Characteristics of continuous rolling without control When the roll rotation speed and rolling reduction amount are not controlled at all (normal re-slaind mandrel mill),
We will evaluate how much each variable factor affects product dimensional accuracy and consider quantifying the product accuracy of conventional restrained mandrel mills. When rolling is carried out using continuous stands such as in a mandrel mill, variations in the shape of the base tube or bar diameter generate large tensions between each stand, and the wall thickness and outer diameter at the bottom of the caliber as well as the mandrel bar are affected. It also has a large effect on the wall thickness and outer diameter of the freely deformed part that does not come into contact with the rolls. In addition, in the next stand, this free deformation part is rolled at the bottom of the caliber, which causes a complicated phenomenon in which new tension fluctuations occur. As a result of these phenomena, variations occur in the product wall thickness and cross-sectional area, causing deterioration in dimensional accuracy. Next, we will discuss the effects of raw tube wall thickness and outer radius, deformation resistance at each stand, and bar diameter variations on product dimensions. (i) Effect of change in wall thickness of the stock pipe In Figure 1, when the wall thickness of the stock pipe ΔHo changes by ΔHo/Ho = 1, that is, the wall thickness of the stock pipe is 100%.
If it changes, caliber bottom wall thickness variation on the exit side of each stand Δh ⁱ _c / h ⁱ _c flange side wall thickness variation Δh ⁱ _f / h ⁱ _f caliber bottom outer radius variation Δr ⁱ _c / r ⁱ _c flange side outer radius variation It shows how Δr ⁱ _f /r ⁱ _f changes. From this figure, the following characteristics regarding changes in the wall thickness of the raw pipe can be obtained. (b) After passing through No. 1 and No. 2 stands, the wall thickness changes on the flange side and bottom side of the caliber decrease rapidly. This is because the roll is rolled once on the caliber bottom in both directions. (b) After No. 3 stand, there is no sharp decrease in wall thickness fluctuation in both directions, and some influence appears on the exit side of No. stand (product wall thickness). (c) The outer radius of the flange on the exit side of each stand will change to the same extent as the wall thickness. From the above results, when there is a change in the wall thickness of the raw pipe, the tension between all stands changes, so No.
It also affects the dimensions of the exit side of the stand. It can also be seen that this dimensional change is larger in the flange than in the bottom of the caliber. (ii) Changes in the outer radius of the raw tube Figure 2 shows the changes in the shape of the exit side of each stand when the outer radius of the raw tube ΔRo changes by ΔRo/Ro=1. From this result, the following characteristics regarding changes in the outer radius of the raw tube can be obtained. (a) Changes in the outer radius of the raw pipe cause dimensional changes in the radius and wall thickness of the flange on the exit side of each stand. (b) No.7 stand exit side (product wall thickness/outer radius)
There is also an impact on In other words, it can be seen that in the restrained mandrel mill, when there is dimensional variation in the outer radius of the raw tube, the dimensional accuracy of the product wall thickness and outer radius deteriorates. (iii) Effect of change in deformation resistance at each stand on the product Figure 3 shows the product wall thickness, outer radius, and section when the change in deformation resistance at each stand becomes Δk ⁱ / _f / k ⁱ / _f = 1. The effect on area is shown. From FIG. 3, the following characteristics became clear. That is, the influence of the change in deformation resistance at each stand on the product shape is not so large. The above results are as follows: - When the mill rigidity is high even when the rolling load changes due to changes in deformation resistance,
The effect is not very large (it is large when the mill stiffness is low). ●Since the change in deformation resistance has little effect on the advance rate, there is little tension variation between each stand. This is thought to be due to the following reasons. (iv) Effect of bar diameter change at each stand on the product Figure 4 shows the effect on the product wall thickness, outer radius, and cross-sectional area when the bar diameter change at each stand is ΔS _Bi /S _Bi = 1. It shows. From FIG. 4, the following characteristics were clarified. (b) The influence of the rear stand has a very large effect on the flange side wall thickness/outside diameter and the caliber bottom wall thickness. (b) The influence of the previous paragraph cannot be ignored. As is clear from the discussion in (), if the rotation speed and reduction amount are not controlled, even if the mandrel bar speed is constrained, variations in the bar diameter, raw pipe wall thickness, and outer radius will affect the product dimensions. It can be seen that it has an impact. That is, even in a restrained mandrel mill, product dimensional changes are unavoidable due to rolling disturbances such as changes in the wall thickness and outer radius of the raw tube, changes in material temperature during rolling, and changes in the mandrel bar diameter. () Effects obtained by controlling the tension between the stands at a constant level. In order to improve dimensional accuracy, when tensionless rolling is performed by controlling the rotation speed, the thickness of the raw tube, outer radius, and bar diameter Consider how variations in this affect product dimensions. (i) Effect of changes in the wall thickness of the raw pipe In Figure 5, the wall thickness at the bottom of the caliber on the outlet side of each stand changes when the wall thickness ΔHo of the raw pipe changes by ΔHo/Ho=1 Δh ⁱ _c / h ⁱ _c flange side wall thickness Fluctuation Δh ⁱ _f / h ⁱ _f Caliber bottom outer radius variation Δr ⁱ _c / r ⁱ _c flange side outer radius variation Δr ⁱ _f /r ⁱ _f shows how it changes. From FIG. 5, the following results were obtained. That is, No.1, No.2
After passing through the stand, almost no impact remains. (ii) Effect of change in the outer radius of the raw tube Figure 6 shows the shape of each stand exit when the outer radius ΔRo of the raw tube changes by ΔRo/Ro=1. From the results shown in FIG. 6, the following characteristics are obtained. In other words, as in the case where there is variation in the thickness of the raw pipe, after passing through the No. 1 and No. 2 stands,
Almost no effect remains. (iii) Effect of bar diameter change at each stand on the product Figure 7 shows the effect of bar diameter change at each stand on the product wall thickness, outer radius, and cross-sectional area when ΔS _Bi /S _Bi = 1 shows. From this FIG. 7, the following results can be obtained. (a) Changes in the bar diameter in the subsequent stands (No. 1 to No. 5 stands) have almost no effect on product dimensional accuracy. (b) The influence of changes in bar diameter at the later stages (stands No. 6 and No. 7) remains extremely large on changes in product wall thickness. As is clear from the discussion in this section (), tensionless rolling control by controlling the rotation speed has the following control characteristics regarding changes in the raw pipe wall thickness, outer radius, and bar diameter, which are factors that deteriorate product dimensional accuracy. be. (a) By performing tension-free control by controlling the rotation speed, the effects of changes in the wall thickness and outer diameter of the raw tube and changes in the bar diameter at the front stand on the product dimensional accuracy are eliminated. (b) Changes in product dimensions due to changes in bar diameter at the rear stand cannot be eliminated by controlling the tension between the stands alone. As is clear from the above study, tensionless rolling control by controlling the rotation speed can eliminate the effects of changes in the material tube wall thickness, outer radius, and bar diameter at the front stage stand on product dimensional accuracy; It was made clear in the section () above that it is impossible to eliminate the influence of bar diameter changes. From these results, in order to eliminate the effects on the product of changes in the wall thickness and outer radius of the raw pipe, deformation resistance in all stands, and changes in bar diameter, we found that the next step is to actively control the rolling reduction amount at the same time as controlling the roll rotation speed. Two control methods were invented. <First control method> Method of controlling product wall thickness <Second control method> Method of controlling product wall thickness and cross-sectional area The characteristics of these control methods will be described below, and then the specific implementation method will be explained. do. The above-described first and second control methods according to the present invention are performed by the following methods (A) and (B). (A) Tensionless rolling is performed on the front stand by controlling the roll rotation speed. This eliminates the influence of the wall thickness and outer radius of the raw pipe, as well as bar diameter variations in the front stand, on product dimensional accuracy. (B) Simultaneously control the roll rotation speed and reduction amount on the rear stand. This operation prevents deterioration of product dimensional accuracy due to changes in bar diameter on the subsequent stand. In this case, the first control method is to control the reduction amount so as to offset bar diameter fluctuations while controlling the roll rotation speed so that there is no tension between the subsequent stands. In this first control method, when the reduction amount is manipulated in response to changes in the bar diameter, the wall thickness at the bottom of the caliber becomes constant, but the outer radius of the bottom of the caliber changes, causing fluctuations in the cross-sectional area. The second control method is a control method that also prevents this cross-sectional area variation. In this control method, the reduction amount and rotation speed are simultaneously controlled in the rear stage stand, but rather than no tension, an appropriate tension is actively generated and the cross-sectional area is kept constant by controlling the outer radius of the flange. Next, a specific method for implementing the control method according to the present invention described above and a method for determining the manipulated variables of the rotation speed and the amount of reduction will be described. As an example, the control device is the rotation speed ΔN ₂ , ΔN ₃ , ΔN ₄ , ΔN ₅ , ΔN ₆ , except for No. 1 stand, which is the Γ key stand.
ΔN ₇ Γ No. 6 and 7 stand reduction amounts ΔS _r6 and ΔS _r7 will be explained. These control devices are controlled by the following items that cause deterioration in product dimensional accuracy: Γ Variations in the wall thickness and outer radius of the original tube ΔHo, ΔRo Γ Variations in deformation resistance at each stand Δk ^{1,2,3,4,5,6,7} _f Γ Obtain the bar diameter variation ΔS ^{1,2,3,4,5,6,7} _B at each stand by measurement or estimation. The number of rotations and the amount of reduction are controlled in accordance with each of these factors. The operating amount of rotation speed and reduction can be determined by the following method for each variable factor. (a) Rate of change in wall thickness of base tube (ΔHo/Ho), rate of change in outer radius of base tube (ΔRo/Ro) These changes can be handled by reducing the product wall thickness and cross-sectional area by reducing the tension between each stand to zero. fluctuations can be removed. If we now use the No. 1 stand as a key stand,
When a blank pipe with variations in wall thickness and outer radius is rolled, the No. 1 stand exit speed varies in response to changes in the advance rate. In order to avoid generating tension between the stands at this time, the rotational speeds of all stands No. 2 to No. 7 may be operated so as to offset this change in the advance rate. (b) Deformation resistance change rate for each stand (Δk _f /
k _f ) _i=1, … _,7 When the mil stiffness is sufficiently high, the effect of changes in the material's deformation resistance on the product dimensions is very small. Therefore, changes in deformation resistance are dealt with by increasing the mill rigidity. (c) Change in bar diameter at the front stage stand (ΔS _B /h _c ) _i=1,2,
Regarding bar diameter changes in _{the 3rd, 4th,} and 5th front stands (Nos. 1, 2, 3, 4, and 5), product dimensional variations can be eliminated by controlling the tension between each stand to zero. Regarding the bar diameter variation at No. 1 stand, which is the key stand, as well as the variation in the material tube wall thickness and outer radius, it is also true for all stand No. 1 downstream from the key stand.
Adjust the rotation speed of stands 2 to No. 7. Regarding bar diameter changes in other stands, it is possible to make the inter-stand tension zero by adjusting the rotational speed of the relevant stand and the next downstream stand. (d) Change in bar diameter at rear stand (ΔS _B /h _c ) _i=6,7
In order to eliminate the influence of changes in bar diameter on the product dimensions at the rear stage stand, it is necessary to control not only the number of rotations of the rolls but also the amount of rolling reduction to offset the change in bar diameter. In this case, the two control methods described above can be implemented depending on the method of manipulating the roll rotation speed. The first control method is to control the tension to be constant by correcting the advance rate change caused by the bar diameter variation by manipulating the roll rotation speed, and to manipulate the reduction amount so as to offset the bar diameter change. The second control method is a control method in which not only the product wall thickness but also the cross-sectional area is made constant. In the first control method, the thickness of the product remains constant, but the cross-sectional area varies. For example, if we consider the case where the bar diameter in stand No. 7 becomes thicker due to thermal expansion, the roll gap should be opened in order to keep the product wall thickness unchanged. At this time, the wall thickness of the product remains constant, but the outer diameter toward the bottom of the caliber is enlarged, so the cross-sectional area also increases. In this case, this second control method is used in No. 6.
~ No. 7 The roll rotation speed is manipulated to generate a tensile force between the stands, and this tensile force reduces the outer diameter on the flange side to keep the cross-sectional area constant. By superimposing the above-described manipulations of the reduction amount and rotation speed in response to various disturbances, it becomes possible to control product dimensions for all disturbances. This concept can be expressed in equation (1) for the first control method. (See page 22) The meaning of this formula will be explained below. In this equation (1), the No. 1 stand is a key stand, and in the matrix of 8 rows and 9 columns, the first column is the ΔN ₂ /
N ₂ , ΔN ₃ /N ₃ , ΔN ₄ /N ₄ , ΔN ₅ /N ₅ , ΔN ₆ /
Each control amount of N ₆ , ΔN ₇ /N ₇ , ΔS _r6 /h ⁶ _c , and ΔS _r7 /h ⁷ _c is shown. The second column shows the variation in the outside diameter of the raw pipe ΔRo/R
The above-mentioned control amounts when =1 are shown. The third column is No. 1 stand bar radius variation ΔS _B1 /h ¹ _c = 1,
The fourth column is No. 2 stand bar radius variation ΔS ² _B /h ² _c =
1. 5th row is No. 3 stand bar radius variation ΔS ³ _B /
h ³ _c = 1, 6th row is No. 4 stand bar radius variation ΔS ⁴ _B / h ⁴ _c = 1, 7th row is No. 5 stand bar radius variation ΔS ⁵ _B / h ⁵ _c = 1, The 8th column shows No. 6 stand bar radius variation ΔS ⁶ _B /h ⁶ _c = 1, and the 9th column shows No. 6 stand bar radius variation ΔS ⁷ _B /h ⁷ _c = 1. Indicates the control amount.

【table】

de bar half


Diameter variation


......(1)
First, a method of controlling bar diameter fluctuations in the rear stage stand, which is a feature of the present invention, will be described. (1) When there is a change in the bar radius at the rear stands (No. 6, No. 7); Bar radius at No. 7 stand △S ⁷ _B is the bottom wall thickness of the caliber of No. stand h ⁷ _C 's 10 % increase. ΔS ⁷ / _B / h ⁷ / _c = 0.1 At this time, from (1), the operation amount of each stand control device is given as follows. (△N ₂ /N ₂ )=0.0 (△N ₃ /N ₃ )=0.0 (△N ₄ /N ₄ )=0.0 (△N 5 /N ₅ )=0.0 (△N ₆ / _{N 6 )} =0.0 (△N ₇ /N ₇ )=0.0091 (=0.09×0.1) (△S ⁶ _r /h ⁶ _c )=0.0 (△S ⁷ _r /h ⁷ _c )=0.0997 (=0.0997×0.1) In other words, No. By controlling not only the number of roll rotations but also the amount of roll reduction on stand No. 7, we prevent deterioration of product wall thickness accuracy due to changes in the bar radius on stand No. 7. If the flat diameter of the bar at No. 7 stand changes by △S ⁷ / _B / h ⁷ / _c = 0.10 (10%), the wall thickness at the bottom of the caliber will naturally change by about ¹⁰ _% unless control is performed. Decrease. Therefore, adjust the reduction amount △S ⁷ _r of No. 7 stand by ∆S ⁷ / _r / h ⁷ / _c = 0.0997 to keep the bottom wall thickness of No. 7 caliber constant. However, the reason why it is not 0.10 in the above formula is because the variation in wall thickness due to changes in rolling load was taken into account. Also, if the above operation is performed, the entry speed of No. 7 stand will be reduced by 0.91%. At this time No. 6~
Tension is generated between No. 7 stands. Yotsute No.7
Increase the roll rotation speed △N ₇ of the stand by 0.91% to prevent the generation of tension. In other words, the rotation speed operation amount of No. 7 stand is (ΔN ₇ /N ₇ )=0.0091. As shown above, by controlling not only the number of rotations of the No. 7 stand but also the amount of reduction at the same time, it is possible to completely control the influence of the bar diameter fluctuation on the No. 7 stand. . Similarly, the rotation speed reduction amount at No. 6 stand is manipulated in response to the bar radius variation at No. 6 stand.
And the No. 7 stand assists in its operation. (2) When there is a variation in the bar radius at the front stand (No. 2 to No. 5); For example, if the bar radius at No. 3 stand ΔS ³ _B is
Assume that the caliber bottom wall thickness h ³ _c of No. 3 stand increases by 10%. ΔS ³ / _B / h ³ / _c = 0.1 At this time, from equation (1), (△N ₂ /N ₂ ) = 0.0 (△N ₃ /N ₃ ) = 0.0495 (=0.495×0.1) (△N ₄ /N ₄ )=0.0180 (=0.180×0.1) (△N ₅ /N ₅ )=0.0 (△N ₆ /N ₆ )=0.0 (△N ₇ /N ₇ )=0.0 (△S ⁶ _r /h ⁶ _c ) =0.0 (ΔS ⁷ _r /h ⁷ _c ) = 0.0 In other words, if there is a variation in the bar radius at No. i stand, it is only necessary to manipulate the rotation speed of No. i and No. i+1 stands. This means that when the bar radius of No. 3 stand increases by 10%, the entry speed of No. 3 stand becomes slower. Therefore, in order to prevent the generation of tension between the No. 2 and No. 3 stands, the roll rotation speed is increased enough to cancel out the tension. Similarly, the number of rotations of the No. 4 stand is increased so as not to generate tension between the No. 3 and No. 4 stands. From No. 5 stands onwards, almost no tension can be ensured without adjusting the rotation speed, and No.
During rolling on stands No. 5, No. 6, and No. 7, the influence of bar diameter variation on product wall thickness is completely eliminated. Therefore, there is no need to operate the reduction amount at No. 6 and No. 7 stands. (3) The rate of variation in the wall thickness of the raw pipe (△Ho/Ho), the rate of variation in the outer radius of the raw pipe (△Ro/Ro), and the rate of variation in the bar radius at No. 1 stand (△S′ _B /h′ _c ) In some cases: These fluctuations are disturbances in the No. 1 stand, which is the key stand, and in order to maintain tension-free tension between each stand, it is necessary to manipulate the rotational speed of all the stands. As an example, consider a case where the material pipe wall thickness variation ΔHo is 10% larger than the reference material pipe wall thickness. △Ho/Ho=0.1 At this time, from equation (1), the control device operation amount for each stand is (△N ₂ /N ₂ )=0.0119 (=0.019×0.1) (△N ₃ /N ₃ )=0.0127 (=0.127) ×0.1) (△N ₄ /N ₄ )=0.0116 (=0.116×0.1) (△N ₅ /N ₅ )=0.0116 (=0.116×0.1) (△N ₆ /N ₆ )=0.0116 (=0.116×0.1 ) (△N ₇ /N ₇ )=0.0116 (=0.116×0.1) (△S _r6 /h ⁶ _c )=0.0 (△S _r7 /h ⁷ _c )=0.0. This is the No. 1 stand and is 10% higher than the standard pipe wall thickness.
When rolling thick raw tubes, the material speed on the exit side of No. 1 stand increases by 1.19%. At this time, unless the rotational speed of the No. 2 stand and subsequent stands is controlled, compressive force will be generated between each stand and the product dimensional accuracy will deteriorate. To prevent this, increase the number of rotations of No. 2 stand.
Increase speed by 1.19% to prevent tension between No. 1 and No. 2 stands. Similarly, by correcting the change in material speed at No. 2 stand at the next stand No. 3,
Tension between No. 2 and No. 3 stands can also be prevented. In other words, since tensionless rolling is performed between stands No. 1, No. 2, and No. 3, the influence of variations in the wall thickness of the raw pipe can be almost eliminated. Naturally, the number of rotations of stand No. 3 is increased, so if the number of rotations from stand No. 4 to No. 3 is increased by the same amount as that of stand No. 3, tensionless rolling is possible from stand No. 4 to No. 7. .6, No.7
There is no need to manipulate the amount of reduction of the stand. The first control method described above is summarized as follows. Variation in wall thickness of raw tube △Ho／Ho Variation in outer diameter of raw tube △Ro／Ro Variation in radius of No.1 stand and bar △S ¹ _B /h ¹ _c Variation in radius of No.2 stand and bar △S ² _B /h ² _c No.3 stand bar radius variation △S ³ _B /h ³ _c No.4 stand bar radius variation △S ⁴ _B /h ⁴ _c No.5 stand bar radius variation △S ⁵ _B /h ⁵ _c Control is possible only by manipulating the rotation speed of the rolls. No. 6 stand bar radius variation △S ⁶ _B /h ⁶ _c No. 7 stand bar radius variation △S ^{7 B /h 7 c For No. 6 stand bar radius variation △S 7} _{B / h 7 c ,} ^the reduction amount and rotation speed of No. 6 and No. 7 stands are simultaneously adjusted. It needs to be manipulated and controlled. The above embodiment is the first control method, but the second
The control method is basically the same, with the following points being applied: an appropriate tension is applied between the No. 6 stand and No. 7 stand, and the wall thickness is controlled to be constant, and the The difference is that the area is controlled to be constant.
This second control method can be expressed as equation (2). (See page 31) In relation to equation (1), the values marked with * are different, and the specific operating method is the same as the first control method.

〔Effect of the invention〕

As is clear from the above explanation, according to the method according to the present invention, the tension can be kept constant against disturbances such as the wall thickness of the raw pipe, the outer diameter, the deformation resistance of each stand, and the bar diameter fluctuation in the previous stand. The wall thickness is kept constant by controlling the rotation speed so that the tension between each stand in the front stage is zero, and the tension between each stand is zero even when the mandrel bar diameter changes in the rear stage stand. While controlling the rotation speed, the amount of reduction in the subsequent stand is controlled to compensate for variations in wall thickness due to variations in bar diameter, making it possible to obtain products with highly accurate wall thickness. Furthermore, according to the present invention, the outer diameter at the free deformation part is controlled by applying appropriate tension between each stand in the latter stage, so that not only the wall thickness but also the cross-sectional area can be kept constant. be able to.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the influence of the outlet shape of each stand on changes in the wall thickness of the raw pipe (△Ho/Ho=1), and Figure 2 is a characteristic diagram for each stand on the change in the outer radius of the raw pipe (△Ro/R=1). Characteristic diagram showing the influence on the exit side shape. Figure 3 is a characteristic diagram showing the influence of each stand deformation resistance change (△K _fi /K _fi = 0) on the product shape. Figure 4 is the characteristic diagram showing the influence of each stand bar diameter change. (△S _Bi /h ^ci = 1) is a characteristic diagram showing the influence on the product shape.
Characteristic diagram showing the influence of =1) on the exit side shape of each stand, Figure 6 shows the change in the outer radius of the raw pipe (△Ro/R0=1)
A characteristic diagram showing the influence of the change on the shape of each stand exit side, Figure 7 shows the change in the diameter of each stand bar (△S _Bi /h ^ci = 1)
FIG. 3 is a characteristic diagram showing the influence of FIG. 8 is a block diagram of a control system for carrying out the method according to the invention, and FIGS. 9 and 10 are characteristic diagrams showing the effects of the method according to the invention.

Claims (1)

[Scope of Claims] 1. A step of measuring the raw pipe dimensions on the entry side of the front stage stand and measuring the radius fluctuation of the mandrel bar in the front stage stand, and the measured raw pipe dimensions and the radius fluctuation of the mandrel bar. a step of detecting a change in the pressure condition in the front stage stand based on the change in the pressure condition in the front stage stand, and a step of controlling the rotation speed of the roll so that the tension between each front stage stand becomes zero when a change in the pressure condition is detected in the front stage stand. and a process of measuring the radius variation of the mandrel bar in the rear stage stand. When the mandrel bar radius variation is detected in the rear stage stand, while controlling the roll rotation speed so that the tension between each of the rear stage stands becomes zero, A rolling control method for a mandrel mill characterized by controlling the wall thickness of a blank pipe to a constant value, comprising the step of adjusting the rolling reduction amount of a subsequent stand in order to correct wall thickness fluctuations due to radius fluctuations of a mandrel bar. . 2. A step of measuring the raw pipe dimensions on the entry side of the front stand and measuring the radius fluctuation of the mandrel bar in the front stand, and measuring the pressure in the front stage based on the measured raw pipe dimensions and the radius fluctuation of the mandrel bar. A process of detecting a change in conditions; a process of controlling the rotation speed of the rolls so that the tension between each stand of the front stage becomes zero when a change of pressure conditions is detected in the front stage stand; and a process of controlling the rotation speed of the rolls in the rear stage stand. (a) When the radius variation of the mandrel bar is detected in the rear stage stand, (a) the roll rotation speed of the front stage stand is controlled so that the tension between each stand of the front stage becomes zero, and (b) Adjust the reduction amount of the rear stage stand in order to compensate for wall thickness fluctuations due to radius fluctuations of the mandrel bar, (c) In order to control the outer diameter of the free deformation part of the raw pipe,
A mandrel mill rolling process comprising the step of controlling the number of rotations of the rolls of the rear stand so that tension is generated between each stand of the rear stage, and the wall thickness and cross-sectional area of the raw pipe are controlled to be constant. Control method.