JPH0527482B2 - - Google Patents

Description

[Detailed description of the invention]

"Objective of the Invention" (Industrial Application Field) The present invention provides a novel mandrel that can prevent the occurrence of flaws on the roll surface during biting and tailing of rolled material during rolling using a mandrel mill. This invention relates to a rolling control method for a mill. (Prior Art) A general outline of the pipe manufacturing method using a mandrel mill is as follows. First, a mandrel rubber is inserted into a rolled material that has undergone Mannesmann piercing rolling.
The rolled material is rolled by a two-roll set of a mandrel mill along the outer diameter of the mandrel bar, and then stretched. After rolling, the raw pipe is pulled out of the mandrel bar, and further stretched by a subsequent stretch reducer to become a product pipe. By the way, both end portions of the raw tube rolled by the mandrel mill are thicker than the steady portion excluding the two end portions, and the thick portion is thickened before being supplied to the reducer. will be truncated to Further, in the product tube rolled by the reducer, a phenomenon of thickening occurs at both ends of the tube, and the tube is similarly truncated as a crop. If the length of these cut-off portions is long, it is natural that the yield in the mandrel mill tube manufacturing method will decrease, which is not preferable. Conventionally, as shown in the time chart in Fig. 7, when the leading edge of the rolled material is biting in and the trailing edge of the material is being pulled out, the roll opening degree has been adjusted to increase the thickness of the rolled material during rolling by the mandrel mill and stretch reducer. The minimum roll opening position among the roll openings required for offset (the roll-down position at this time is referred to as the maximum roll-down position.Hereinafter,
same. ), thereby preventing the thickening phenomenon caused by the mandrel mill and also canceling out the thickening phenomenon caused by the reducer, thereby preventing the above-mentioned decrease in yield. (Problems to be Solved by the Invention) In conventional rolling control, the roll opening degree is controlled to the maximum rolling position before the rolled material is bitten, so it is difficult for the tip of the rolled material to get caught in the roll. As a result, there was a ``punching'' situation. Moreover, the surface of the roll was sometimes scratched by the above-mentioned poking. In addition, since the roll opening degree was controlled to the maximum reduction position even when the rolled material fell through, the rear end of the rolled material became abnormally thin and a "fishtail" was formed, and the fishtail The surface of the roll was crimped, and there were also scratches on the roll surface. The flaws on the roll surface are also printed on the outer surface of the raw tube after rolling, and the raw tube becomes a defective product. Therefore, the mandrel mill had to be shut down and each roll replaced with a defect-free roll. It should be noted that a mandrel mill usually has 7 to 9 stands arranged in series for holding rolls. In such a mandrel mill, if the maximum reduction control as described above is carried out between the stands that have a large cross-sectional reduction rate for the rolled material, the amount of roll reduction for both tube ends of the rolled material will be excessive, and the As shown in FIG. 8A, overfill 1a tends to occur on the flange portions 2a of the rolls 2, 2. As shown in FIG. 2B, the overfilm 1a impacted against the caliber groove bottom 2b of the rolls 2, 2 in the next stage stand, causing scratches on the rolls 2, 2. This phenomenon is particularly noticeable at the leading and trailing ends of the rolled material. The present invention has been made in view of the above-mentioned circumstances, and is a novel rolling control method for a mandrel mill that can prevent the occurrence of flaws on the roll surface during biting and tailing of the rolled material. (hereinafter referred to as the control method of the present invention). "Structure of the Invention" (Means for Solving the Problems) The gist of the control method of the present invention is that in the method of controlling the rolling of a blank pipe using a mandrel mill, After the fishtail generation area at the rear end of the rolled material, the roll opening is adjusted from the minimum roll opening position among the roll openings necessary to offset the thickness increase due to rolling by the mandrel mill and stretch reducer. It is also possible to control it in the open state. (Function) Before the biting area at the tip of the rolled material is bitten by the roll, the roll opening is kept open more than the maximum rolling position, and after the rolling material is bitten, the roll opening is changed to the steady rolling position. It is controlled so that it opens. In other words, the leading end of the rolled material is not rolled down excessively, and there is no risk of bumps occurring when the rolls are bitten. Therefore, the roll surface will not be scratched. In addition, at the rear end of the rolled material, the roll opening is first tightened as in the conventional method, but in the area where fish tails occur, the roll opening is controlled to be more open than the maximum rolling position. That is, the rear end of the rolled material is not rolled down excessively, and no fish tail is formed at the rear end. Therefore, the roll surface will not be scratched. (Example) The present invention will be described below based on drawings showing examples thereof. FIG. 1 is a time chart of the roll opening degree controlled by the control method of the present invention, where the vertical axis shows the roll opening degree and the horizontal axis shows time. As shown in FIG. 1, the most distinctive feature of the control method of the present invention is that in the roll control area A when the rolled material is biting and the roll control area B when the rolled material is pulled out, the Pa pattern and the Pb pattern are used, respectively. control. The Pa pattern performed in the roll control area A during biting is:
Before the rolled material is bitten, the roll opening degree is kept open to the steady rolling position, and from this state, at the same time as the rolled material is bitten, the axial center part obtained when rolling at the steady rolling position is This is a control pattern in which the material is tightened all at once to a thick-wall prevention reduction position (the same applies hereinafter), which is a reduction position at which a thickness that does not exceed the wall thickness is obtained. The thick-wall blocking reduction position where the rolls are most tightened is in a state that is open by h ₁ from the conventional maximum reduction position shown in FIG. That is, compared to the conventional rolling control method (see FIG. 7), the rolling reduction amount is reduced by _h1 . For this reason,
The tip of the rolled material is smoothly bitten and no bumps occur. Further, at time _t1 when the roll opening degree closes from the steady rolling position to the thick wall prevention rolling position, the rolled material has been rolled by a length corresponding to the rolling speed. That is, as shown in FIG. 2, the position of the rolled material 1 where the most force is applied in the biting area at the tip is l compared to the biting position (indicated by the two-dot chain line) at the conventional maximum rolling position. It will be shifted by ₁ length. Therefore, a relatively thick portion is left at the tip of the rolled material at the biting length _l1 portion, and overfilling is less likely to occur. In addition, the code|symbol 2 in the same figure is a roll, and the code|symbol 3 is a mandrel bar. After biting of the rolled material, the roll opening degree is controlled to immediately return to the steady rolling position. The Pb pattern performed in the roll control area B at the time of tail-off is a pattern in which the roll opening degree, which is open at the steady rolling position, is controlled to be tightened all at once to the thick-wall prevention rolling position before the rolled material comes off the bottom. It is. The thick-wall blocking reduction position, where the rolls are most tightened, is open by h ₂ from the conventional maximum reduction position. That is, compared to the conventional rolling control method (see FIG. 7), the rolling reduction amount is reduced by _h2 . Therefore, the rear end of the rolled material is not rolled down to an extreme degree, and no overfill occurs. After that, the roll opening degree is immediately returned to the steady rolling position and the rolling process is on standby. At this control point, at time _t2 when the roll opening degree is returned from the thick-wall prevention rolling position to the steady rolling position, the rolled material continues to be rolled by a length corresponding to the rolling speed. That is, as shown in FIG. 3, the position of the rolled material 1 at the rear end where it is most strongly rolled down is l ₂ length compared to the bottom drop position (indicated by the two-dot chain line) at the conventional maximum rolling position. It will shift by just that. Therefore, at the rear end of the rolled material, a relatively thick portion is left at the tail-off length _l2 , and no fishtail occurs. In this way, in the control method of the present invention, all of the bumps, fishtails, and overfills are prevented, so there is no occurrence of any flaws on the roll surface caused by these. Reduction amount h ₁ in roll control area A during biting
and biting length l ₁ and roll control range B at the time of tail slipping
The specific numerical values of the rolling reduction amount h ₂ and the bottom removal length l ₂ were determined as follows. First, for the raw pipe obtained without any roll control, the wall thickness distribution at both ends of the product pipe after reducer rolling is measured, and the basic pattern of the method of the present invention is determined based on the distribution results. . That is, the basic pattern is determined to be the same as the roll opening degree control pattern in the conventional rolling control method. Therefore, a known conventional control pattern may be used as is. Next, in the rolled material, the biting length of the tip part l ₁
and the tail end length l ₂ of the rear end are determined first. Regarding the raw pipe obtained by implementing the control method of the present invention,
Measure the crop length that inevitably occurs when a product pipe is produced by reducer rolling, and calculate the total length L ₁ of the tip of the raw pipe and the extra length L ₂ of the rear end of the raw pipe stretched to the crop length. Determine in advance. Then, the biting length l ₁ is made to be absorbed into the extra length L ₁ , and the tailing length l ₂ is made to be absorbed into the extra length L ₂ . The extra lengths L ₁ and L ₂ of the raw pipe are calculated using the following formula. L ₁ = (Length of tip crop) / (Stretching rate of reducer) × α L ₂ = (Length of rear end crop) / (Stretching rate of reducer) × α However, α: slip coefficient (0.75 was used) ) Now, let a be the length that the tip of the rolled material is rolled in the roll control area A during biting, then the extra length L ₁ is within the range of L ₁ ≒ (0.2 to 0.35) x a. If b is the length that the rear end of the rolled material is rolled in the roll control area B at the time of tail-off, then
It has been learned from many test rolling experiments that the extra length L ₂ is preferably determined within the range of L ₂ ≈(0.2 to 0.35)×b. Therefore, the above-mentioned biting length l ₁ and tailing length l ₂ were determined from these, excluding factors such as the deviation in the rolling down timing. That is, 0.2<l ₁ /a<0.3 0.2<l ₂ /b<0.3 If the biting length l ₁ and the tailing length l ₂ are found,
t ₁ and t ₂ in FIG. 1 can be calculated backwards from the relationship with the rolling speed of each stand determined by the material and wall thickness of the rolled material. Then, t ₁ and t ₂ are inserted into the horizontal axis of the basic pattern. Therefore, the intersection of the conventional basic rolling pattern and t ₁ is the rolling reduction amount h ₁ , and the intersection of the conventional basic rolling pattern and t ₂ is the rolling reduction amount h ₂ . Note that the control method of the present invention is not limited to the roll control pattern shown in FIG. Regarding the roll control range A during biting, a control pattern Pc shown in FIG. 4 can be considered. The control pattern
Pc is a pattern in which the roll opening degree is already tightened to the thick wall prevention rolling position before the rolled material is bitten. In this case, t ¹ and h ₁ are determined in the same manner as in the previous example. Furthermore, regarding the roll control range B at the time of trailing off, a control pattern Pd shown in FIG. 5 can be considered. The control pattern Pd is a pattern in which the roll opening degree is closed to the thick-wall prevention rolling position at the rear end of the rolled material, and the state is maintained to wait for the bottom of the rolled material to come off. In this case, t ₂ and h ₂ are determined in the same manner as in the previous example. Furthermore, the control patterns Pa and Pc in the roll control area A during biting or the control patterns Pb and Pd in the roll control area B during tailing can be combined as appropriate depending on the material and wall thickness of the rolled material. Is possible. For example, the control pattern Pc may be adopted in the roll control area A when the leading end of the rolled material is bitten, and the control pattern Pb may be adopted in the roll control area B when the trailing edge of the rolled material is pulled out. The case where rolling is carried out using this combination example is as follows. In this example, a mandrel mill consisting of eight stands was used. And actually,
Among the 8 stands, stands 1 to 5, which are in the rough rolling stage, are avoided, and stands 6 and 7, which are in the finish rolling stage, are
The control method of the present invention was implemented at stands No. 8 and No. 8. This is because the presence or absence of roll flaws is most noticeable on the product tube at the stand in the finish rolling stage, and this is most convenient for examining the effects of the present invention. Incidentally, the rolling reduction ratio of each stand in this case is as shown in FIG.
In addition, the roll opening degree is controlled by a hydraulic pressure reduction method with excellent quick response, and the timing is determined based on the engagement with the adjacent stand on the previous stage.

【table】

【table】

[Table] Note that stand No. 8 is a forming stage in preparation for pulling out the mandrel bar from the rolled material.
Therefore, feedforward control is performed by computer management based on the rolling situation at stand No. 6 or No. 7. Therefore, it is difficult to derive specific numerical values regarding the control method of the present invention, and they are omitted in this specification. In this example, even after continuous rolling for 16 hours, there was no need to replace the rolls due to scratches on the roll surface. On the other hand, in conventional rolling control methods, it is common to need to change the rolls two to three times during eight hours of continuous rolling. Note that the product tube obtained in this example has approximately
A crop with a length of 900 mm had occurred, and a crop with a length of approximately 650 mm had occurred at the rear end. but,
All of these crop lengths are within an unavoidable range in mandrel mill tube manufacturing. In addition, the position where the rolled material is rapidly reduced by the control method of the present invention is determined so that it is absorbed within the crop length after reducer rolling, so there is no problem with the quality of the product pipe. . (Study of Alternative Embodiments) In the method of the present invention, the mandrel mill is not limited to one consisting of eight stands, and the stands for implementation are not limited to stands No. 6 to No. 8. However, it goes without saying that it is most meaningful to implement the control method of the present invention in the finish rolling stage, since it is during the finish rolling stage that noticeable flaws remain in the raw pipe after rolling. In other words, even if a flaw occurs in the rolled material during the rough rolling stage, it will be smoothed as long as the subsequent rolls on the stand are free of flaws, so the calculation of l ₁ or l ₂ as described above is very important. isn't it. Furthermore, the roll opening degree control method is not limited to the hydraulic pressure reduction method, but may also be an electric pressure reduction method or the like. As described above, the detailed structure of the control method of the present invention can be changed as appropriate depending on the embodiment. "Effects of the Invention" As is clear from the above explanation, according to the method for controlling rolling of a mandrel mill according to the present invention, there is no need to replace the rolls due to scratches on the roll surface. Therefore, the production efficiency of the mandrel mill tube manufacturing method has been significantly improved. Of course, it has many advantages, such as having no effect on the quality of the raw pipe or finished pipe.

[Brief explanation of the drawing]

Fig. 1 is a time chart of the roll opening degree controlled by the control method of the present invention, Fig. 2 is a side sectional view of the upper half showing the thick wall prevention reduction position of the leading end of the rolled material;
Fig. 3 is a side cross-sectional view of the upper half showing the thick-wall blocking reduction position at the rear end of the rolled material, Fig. 4 is a time chart showing another control pattern when the rolled material is bitten, and Fig. 5 is the rolling A time chart showing another control pattern when the material bottoms out, Fig. 6 is a graph showing the rolling reduction rate of each stand, Fig. 7 is a time chart showing the conventional rolling control method, and Fig. 8 is a conventional defect phenomenon. It is a front sectional view of the mandrel mill showing. 1... Rolled material, 2... Roll, 3... Mandrel bar.

Claims (1)

[Claims] 1. In a method of controlling the rolling of a blank pipe using a mandrel mill, the opening degree of the rolls is controlled by the mandrel mill and the stretch reducer before the steady biting area at the leading end of the rolled material and after the fishtail generation area at the trailing end of the rolled material. A rolling control method for a mandrel mill, characterized in that control is performed in a state where the roll opening is more open than the minimum position among the roll openings necessary to offset the amount of wall thickness increase during rolling.