JPS60152315A - Speed control method of mandrel mill - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy in the longitudinal direction of a material by controlling automatically the speeds each stand and a mandrel and keeping a tension and a compressive force burdened on a material between roll stands at the prescribed values by adjusting said speeds in the next material. CONSTITUTION:Rolling by each stand and a mandrel is started by lowering the speeds of each stand and mandrel at the fixed rates with respect to the previously set speeds of them. Under said low speed running, the change of an electric current of a stand located at the front stage of an optional stand of mills, formed into a continuous mill line, which is in a state before or after biting a material, is detected. According to the detected results, the roll speed of at least one of the optional stand and the front stange stand is instantly changed, or the results are stored in an arithmetic unit so that the speed setting at the rolling of the next material is corrected. Successively, the speeds of each stand and the mandrel are simultaneously accelerated and are returned to the speeds set in the beginning. In this way, a tensionless or fixed tension and a compressive force can be set easily.

Description

Detailed Description of the Invention (Industrial Field of Application) Seamless steel pipes can be manufactured using, for example, a punching machine that presses a square piece of steel into a roll having circular holes to form a hollow blank pipe;
An inclined roll rolling machine that further reduces the wall thickness of this hollow tube,
Furthermore, this is carried out by a mandrel mill, which inserts a mandrel into the tube to continuously reduce the wall thickness, or by a stretch resouser, which reduces the outer diameter after heating the tube again.

The present invention provides a method for rolling a metal tube using a so-called mandrel mill, that is, a continuous rolling mill having a plurality of individually driven rolling stands arranged in series and a mandrel in the manufacturing process 9 of such a seamless steel tube. Regarding f.

(Problems with the prior art) In general, what is important in continuous rolling mills in all fields is the balance of material speed between the valley stands that make up the rolling mill row, and between any two stands. In this case, it is a good practice to match or maintain a desired relationship between the material output speed of the first stand and the material inlet speed of the second stand.If this is not satisfied, Excessive tension or compression forces act on the material, resulting in changes in cross-sectional dimensions in the longitudinal direction.

In order to solve this problem, the following method is known, as disclosed in Japanese Unexamined Patent Publication No. 49-449625, in which speed control is applied to a continuous rolling mill.

In other words, the first part of a continuous IJE rolling mill consisting of 11 stands
Record the current value immediately after the tip of the material is bit into the stand, and use this value as a reference to determine whether the current value changes after the tip of the material bites into the (〃+1)th stud. The rotation speed of the (#+l) stand is immediately changed to the epicenter before the rolling of the L(''+2) stand starts. In this method, the steps are performed sequentially without returning to the standard 1 stream and 1 shift.

This is the 7.J elephant of the present invention. The above-mentioned so-called mandrel mill can be roughly divided into three methods depending on the state of restraint of the mandrel during rolling. The first is the full floating mandrel mill method, which rolls freely without restraining the mandrel, and the 28th! The third method is the semi-floating mandrel mill method in which the mandrel is rolled at a constant speed. There is a method of rolling.

In the first method, since the mandrel speed changes every moment during rolling, the reference current value changes, so that the two-way speed control method cannot be practically applied. However, the methods described in the second and third methods do not change the reference current value, and in principle it is possible to apply the speed control method 1 described above. When rubbed, the following problems arise.

(1) When the distance between the stands is large and the current change during biting (so-called inopactodoronop) is large (1
A stable reference current value cannot be obtained for the primary stand engagement M.

(2) The time it takes to reach the next stand is short, and the current value may not return to the reference value and the previous stand may be stuck.

Therefore, using a mandrel mill and a G machine, it is possible to control the cutting between consecutive stands to a stable tension-free state or a constant tension state or a compressive force state using the method described above. l
! Ill L < , the monthly accuracy in the longitudinal direction is defined as the side ζ
I'm dying to be turned into a single button.

(Objective of the Invention) The present invention (U) is basically based on the principle of the speed control method using an electric current described above, but the levers have been improved by considering the problems in actual application. By automatically controlling the speed, or by detecting the tension state and adjusting the speed at the primary material, the tension and compressive force applied to the splinter between the stands can be maintained at 0 or a constant value, and the monthly longitudinal The purpose is to improve dimensional accuracy in the direction.

(Structure 9 of the Invention) Figure 1 and (-) of the speed adjustment method in a continuous rolling mill also do not show the principle of the well-known current memory system.

Memorize the current '+o' of the flat 1 rolling mill during single star rolling.

2-stand continuous IT: By comparing with the current value 11□ immediately after the start of spreading, if 5 (■, .-■12) < O, it is determined that compressive force is acting between the studs.

1. = 1. ．． 2 + In the trench, increase the number of rotations of the second stand, and conversely, when (■ o, -" + 2) > 0 (Y, it is judged that tension is acting between the stands. If the rotation speed of the second stand is increased by F, a tension-free state can be obtained.

However, if the distance between the first stand and the second stand is small or the rolling speed is relatively high, a stable current value as shown in Fig. 1 cannot be obtained, and the In addition to shortening the rolling time for one stand alone, there is also a change in current when the first stand is engaged (so-called in-cut dronop), and the current value changes irregularly as shown in Figure 2.

Reference current value ・1-11 cannot be obtained. Similar irregular changes occur when controlling the rotation speed after the first hill, and when there is a third stand, the control time itself is short, and the control is completely When 11 did not finish, he entered the third stand and took shelter. There are cases where such a phenomenon (well, not only does it deteriorate control accuracy, but also actually makes it possible to suppress the sound).

This invention was made to solve problems in rolling steel pipes and the like using a mandrel mill.
arranged in series. A method for rolling metal tubes by a continuous rolling mill train having a plurality of stands each driven individually is predetermined. Rolling was started at each stand and mandrel speed with a constant ratio of low F to each stand and mandrel speed, and under this low speed condition.

Before and after the material is bitten into any one of the stands that make up the continuous rolling mill row. A change in current in the stand preceding the arbitrary stand is detected, and based on the detection result, immediately determines whether to change the J-ru speed of at least one of the arbitrary stand and the stand preceding it.
In order to correct the rolling speed setting of the primary material, the detection result is stored in the calculation device, and then the speed of each stand and mandrel is added all at once to return to the predetermined speed. The present invention relates to a speed control method for a mandrel mill, which is characterized by making the speed of the mandrel mill tighten.

According to this method, for example, by rolling at a rolling speed of 3AI, the leading edge of the material reaches the (nth
+ 1) The time it takes to reach the stand (doubles), and the time for the transient change in current due to the drop in rotation speed and recovery due to the impact remains the same, so the current value The stable state continues for a long time, and the current value during this period can be detected accurately.

On the other hand, a low rolling speed increases the rolling time of one piece of material and leads to a decrease in the mill temperature. Therefore, as soon as the speed control and the detection of the tension state by electric current etc. are completed, the rolling speed is quickly accelerated. Terminate it. This (Ma.

This becomes possible without issuing an acceleration command to the motor based on the load cell signal or the like when the leading edge of the material passes through each stand.

Note that there are many known speed control methods, such as a method using only a current value and a method using a combination of current and load, but the present invention does not apply equal constraints to any of these methods. 1.

FIG. 3 shows a three-stand mandrel mill with stand spacing I 111 and a first stand speed l u
A comparison was made between the current change (, a) of each stand during rolling for 7 seconds and the current change (1)) when the rolling process was carried out. (a) In lc, the time after the first stand engages, the time at the second stand engages 1M, the time after the second stand engages, and the time at the third stand engages 1 is about 1 second, respectively. At this time, a stable state of current change before and after the biting is not obtained.

(1)) When the tip of the material passes through all the stands, the speed of each stand is f(a)%.

Therefore, the time between the first stand being engaged and the second stand being almost engaged, and the time between being engaged with the second stand and the third stand being engaged are each about 2 seconds.

As a result, stable current change before and after biting (15), 0
'3 is obtained.

In this case, speed control +tp+ is not applied, and at this time, the tension state is determined from the direct current change (to), and the speed (rotation speed) is calculated and corrected from the primary material. By setting the rotation speed to the specified speed, tension will not be applied.
Pi Nobu became 04 Noh. Of course, from the current changes (1) and (2), it is also possible to control the rotation speed so that the amount of change immediately becomes O.

Incidentally, it is already known in other fields9 to perform speed control simultaneously with acceleration and deceleration;

In order to prevent troubles during rolling, rolling is performed at low speed and then accelerated.In the present invention, the speed is controlled while the speed is constant, or one current is detected, and then,
I would like to add that each stand accelerates at the same time, and that they are essentially different.

(Thus, the difficulty of adjusting the speed of so-called mandrel mills has been overcome, and it has become possible to easily set no tension, constant tension, or compression force, and it has become possible to control dimensional changes in the longitudinal direction.) .

[Brief explanation of the drawing]

Figure 1 shows the principle of the current memory method as a speed control method for continuous rolling mills, and Figure 2 shows an example of two-stand flow changes when the stand distance is short and the speed drops. FIG. 3(a) shows an example of current change in a three-stand mandrel mill, and FIG. 3(1)) shows an example of the present invention. Patent Applicant Representative Patent Attorney Tomoyuki Yafuki (and 1 other person 9)

Claims (1)

[Claims] A method is predetermined in which a metal tube is rolled by a continuous rolling mill row having a plurality of stands arranged in series with a mandrel fitted into the hollow part, each of which is individually driven. Rolling is started at a valley stud and mandrel speed that is reduced by a certain ratio to the speed of each stand and mandrel, and under this low speed condition, the material is bitten into any stand that makes up the continuous rolling mill row. Before and after. Detecting the current change in the stand preceding the stand in question, and based on this detection result, immediately changing the roll speed of any one of the stand and the stand preceding it; or The detection result is stored in the calculation device in order to correct the speed setting for rolling the next material, and then the speed of each stand and mandrel is accelerated all at once to return to the speed specified in 1) 1■. A speed control method for a mandrel mill characterized by: