JPH0221884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a mandrel mill for rolling raw tubes, and in particular, the present invention relates to a mandrel mill for rolling raw tubes, and in particular, to a mandrel bar whose advancing speed is controlled by a drive device. The present invention relates to a mandrel bar tension control device that maintains the tension (hereinafter abbreviated as inter-stand mandrel bar tension) constant.

[Technical background of the invention]

Generally, seamless steel pipes are manufactured by PIERCER.
A mandrel bar is inserted into a blank pipe (hereinafter referred to as a shell) that has been perforated with a hole, etc., and a plurality of stands each having a grooved roll are used to obtain a predetermined wall thickness, length, and roundness. Continuously rolled.

A mandrel mill, which consists of a mandrel bar and a rolling stand with grooved rolls, is a type of continuous rolling mill using grooved rolls. It's different.

Such mandrel mills can be roughly divided into two types depending on the method of operating the mandrel bar. That is, the first method is the so-called full float method, in which a mandrel bar is inserted into the shell on the entrance table of the mandrel mill, and rolling is completed without operating the mandrel bar during rolling. ,
The second method is to insert the mandrel bar into the shell on the entrance table of the mandrel mill, but then fix the proximal end of the mandrel bar to the mandrel propulsion block before inserting it into the rolling mill, and the progress of this mandrel propulsion block is For example, this method is called the MPM method, in which rolling is performed while controlling the speed.

The present invention relates to the latter rolling method of the above two methods, which restricts the movement of the mandrel bar, and its outline will be explained below.

First, FIG. 1 is a diagram for explaining a basic model for rolling with a mandrel mill, in which a shell 3 is rolled between a pair of grooved rolls 1 and a mandrel bar 2. Here, if the grooved roll 1 is provided at the first stand of the plurality of stands, the rear tension T _Bi acts on the mandrel bar 2, but the front tension T _Bi+1 is zero. Also, for shell 3, the rear tension T _ni is also the front tension
T _ni+1 also has no effect, and both are zero. Although compressive force may act on the mandrel bar and shell, this can be treated as negative tension, so this compressive force is also referred to as tension hereinafter.

In FIG. 1, when the rolling load is P _ip and the rolling torque is G _ip , the rolling torque G _ip is expressed by the following equation.

G _ip = T _Bi・+2ai・P _ip ...(1) However, Ri is the average roll determined by the shape and dimensions of the grooved roll 1, the dimensions and shape of the shell before and after rolling, and the diameter of the mandrel bar 2. The radius, ai, is generally used for rolling plate materials or long steel products, etc.
It is a coefficient expressed as 2ai=G _ip /P _ip .

Here, since the mandrel bar 2 and the shell 3 move relatively, if the coefficient of kinetic friction between them is μi, the rear tension T _Bi is T _Bi =2 μi・Pio (2), and the above From equations (1) and (2), rolling torque Gio can be expressed as follows:

Gio=(2μi・+2ai)Pio...(3) That is, this equation (3) shows the relationship between rolling load and rolling torque when there is no tension when rolling a pipe material using a mandrel bar.

The above is a case of a single stand, but mandrel mills usually have multiple stands and continuous rolling is performed using these stands, so front and rear tensions act on the mandrel bar and shell, respectively, so rolling The relationship between load and rolling torque becomes more complex.

FIG. 2 is a diagram for explaining this relationship, and for convenience, shows a state in which the shell 2 is rolled by three stands i-1, i, and i+1.

Note that the roll axes of adjacent stands are
Although they differ by 90 degrees, they are all expressed the same here to simplify the drawing.

In Figure 2, if we pay attention to the i-stand, we can see that there is a rear tension T _Bi and a front tension with respect to the mandrel bar 2.
T _B (i+1) is the rear tension T _ni for shell 3,
The forward tension T _n (i+1) acts, and this i
The rolling torque Gi of the stand is expressed by the following formula.

Gi=T _Bi・Ri−T _B (i+1)・Ri+2ai・Pi+△
Gib−△Gif…(4) However, △Gib is Ciel 3 when viewed from the i stand.
Similarly, _ΔGif represents the torque change due to the generation of the forward tension Tm(i+1) in the shell 3 when viewed from the i stand.

On the other hand, due to the balance of forces in the rolling direction, the rear tension T _Bi and front tension T _B (i+1) of the mandrel bar are expressed by the following equations.

T _Bi =2μi・Pi T _B (i+1)=2μ(i+1)・P(i+1) ...(5) Therefore, the above equations (1) to (5) are one of the basic model equations for shell rolling using a mandrel mill. However, as understood from these equations, the inter-stand tensions T _Bi and T _B (i+1) acting on the mandrel bar greatly influence the rolling state.

[Problems with the Background Art] By the way, in the rolling method that restricts the movement of the mandrel bar, the proximal end of the mandrel bar is fixed by a mandrel propulsion block, and the mandrel propulsion block is moved at a predetermined speed. However, if there is a torque fluctuation in the device that drives the mandrel block, that is, the mandrel bar driving device, the tension of the mandrel lever will also vary greatly due to this torque fluctuation.

As is clear from the above model formula, if the tension of the mandrel bar fluctuates, the tension acting on the shell also fluctuates, which hinders stable rolling. In the past, no measures were taken against variations in the mandrel bar tension between stands, resulting in a disadvantage in that the yield and quality of seamless steel pipes deteriorated.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks, and even when there is a torque fluctuation in the mandrel bar drive device, the rolling state is stabilized by keeping the mandrel bar tension between the stands constant. The purpose of this invention is to provide a mandrel bar tension control device for a mandrel mill that can produce seamless steel pipes with high precision.

[Summary of the invention]

In order to achieve this object, the present invention provides a mandrel mill in which a mandrel bar whose advancing speed is controlled by a drive device is inserted into a blank pipe and is engaged with a plurality of stands each having a grooved roll. A tension detection device detects the tension at the proximal end of the mandrel bar, and outputs a reference signal between the rolls of each stand depending on the setting,
The mandrel bar tension between the stands is calculated based on the tension signal of the tension detection device, and the mandrel bar tension is calculated based on the tension fluctuation at the proximal end of the mandrel bar due to the torque fluctuation of the drive device. Between the rolls so as to absorb fluctuations in tension〓 Between the rolls that correct the reference signal〓 Between the setter and this roll〓 Between the rolls of the setter〓
The present invention is characterized by comprising a roll-to-roll control device that controls the roll-down device in accordance with a reference signal.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 3 is a block diagram showing the configuration of the mandrel bar tension control device of the present invention, in which grooved rolls 11, 12, 1 are provided on the first and second stands, respectively.
3...1n shows an example in which the shell 3 is rolled to a predetermined thickness.

Here, a tension detection device 10 for detecting the tension of the mandrel bar 2 is provided at the base end of the mandrel bar 2. This tension detection device 10 may be one that calculates based on the driving torque of the mandrel bar drive device, or may be one that directly detects it using a load detector, in short, the tension at the base end of the mandrel bar. It suffices as long as it can detect.

In addition, each stand has grooved rollers.
In addition to outputting a reference signal, the tension detection device 10
roll gap setting devices 21 to 2n that calculate the tension located between the stands of the mandrel bar 2 based on the tension signal and correct the roll gap reference signal;
and roll gap detectors 41 to 4n that detect the roll gap according to the positions of the roll lowering devices 51 to 5n.
By inputting the roll gap reference signals of the roll gap setters 21 to 2n and the roll gap signals of the roll gap detectors 41 to 4n, the rolling down devices 51 to 5n are controlled so that the difference between the two becomes zero, As a result, roll gap control devices 31 to 3n are provided which cause the roll gap to conform to the roll gap standard.

The operation of the mandrel bar tension control device configured as described above will be explained below together with a model equation that is well known in the field of rolling theory.

First, the roll gap between the grooved rolls 11 to 1n of each stand is set to be narrower in the downstream direction in the rolling direction, so that the wall thickness of the shell 3 gradually becomes thinner and at the same time becomes longer in the axial direction. It is then rolled. Note that the roll gaps are manually set by roll gap setting devices 21 to 2n, respectively.

By the way, if the roll gap of the i-th stand among the first to n-th stands is hoi, the shell thickness on the exit side of the rolls is h1i, and the rolling load is Pi, the following equation holds true.

h1i=hoi+Pi/M...(6) However, M is Mill's constant.

On the other hand, the rolling load Pi and the tension T _Bi of the portion of the mandrel bar 2 located between the stands can be obtained by substituting the above equation (5) into the following equation.

h1i=hoi+KiT _Bi ...(7) However, Ki=1/2μi・M.

Therefore, if the roll gap hoi and the mandrel bar tension T _Bi between the stands are detected, the wall thickness h1i on the exit side of the rolls can be controlled to a predetermined dimension.

However, it is difficult to individually detect the mandrel bar tension T _Bi between the stands between each roll, and here, the roll gap setters 21 to 2n determine this based on the tension signal of the tension detection device 10. .

Here, if the tension signal of the tension detection device 10 (hereinafter referred to as a detection signal) is T _B , then T _B = _o 〓 ⁱ⁼¹ T _Bi = _o 〓 ⁱ⁼¹ 2μi·Pi (8).

Now, if the detection signal T _B when the mandrel bar is caught only in the first stand is T _B1 , then
From the detection signal T _B when the mandrel bar is caught in the first and second stands, the mandrel bar tension T _B2 between the first and second stands is T _B2 = T _B − T _B1 ...( 9).

Also, from the detection signal T _B when the mandrel bar is caught in the first to third stands, the mandrel bar tension T _B3 between the second and third stands is T _B3 = T _B - (T _B1 + T _B2 )... can be obtained by (10).

Based on the same idea, the (n-1)th and nth
The tension T _Bo of the mandrel bar between the stands can be obtained from T _Bo = T _B − _o-1 〓 ⁱ⁼¹ T _Bi ……(11).

In this way, if the mandrel bar tensions T _B1 , T _{B2 ,} . Become. Therefore, torque fluctuation occurs in the drive device that drives the mandrel bar 2, and it is difficult to determine which stand and with what weight should be used to correct the tension fluctuation of the tension detector due to this torque fluctuation. can.

Therefore, each time the mandrel bar 2 is bitten by each stand, the roll gap setting devices 21 to 2n store the detection signal of the tension detection device 10 and calculate the mandrel bar tension according to the above equations (9) to (11). Further, when a tension fluctuation signal from the tension detection device 10 due to torque fluctuation of the drive device is added, the roll gap reference signal is corrected according to the magnitude of the mandrel bar tension between the stands. However, the above equation (7) is used for this correction. In other words, the roll exit side wall thickness h1i is determined by the roll gap h0i and the mandrel bar tension _TBi , as shown in equation (7), but the roll exit side shell thickness due to variations in the mandrel bar tension TBi is determined by the roll gap h0i and the mandrel bar tension TBi. By correcting the variation in the roll gap h0i, rolling with a uniform exit wall thickness can be obtained. In this case, the relationship between the mandrel bar tension variation and the outlet shell thickness variation can be clarified by experiment or formulating the experimental results using the concept of influence coefficient.

Note that, in order to simplify the control, these controls may be omitted for stands where the mandrel bar tension is low.

On the other hand, the roll gap control devices 31 to 3n compare the roll gap reference signals of the roll gap setters 21 to 2n and the roll gap detection signals of the roll gap detectors 41 to 4n to control the roll gap of each stand to the set gap. are doing.

Next, FIG. 4 shows the mandrel bar tension detection device 1.
0, the driving system of the mandrel bar is shown, and the traveling device 4 is connected to the mandrel bar 2.
Travel while holding the proximal end of shell 3.
The mandrel bar 2 is inserted into the stand, and then the grooved roll 1 of the stand is engaged with the mandrel bar 2. Further, the traveling device 4 is driven by an electric motor 6 having a speed control device (not shown).

Here, in order to detect the tension at the base end of the mandrel bar 2, a current detector 8 detects the current of the electric motor 6, a voltage detector 9 detects this voltage,
A tachometer 7 for detecting the angular velocity of the motor shaft is provided, and signals from these detectors are sent to the tension detection device 1.
Added to 0. The tension detection device 10 first determines the mandrel bar operating torque G _B based on the detected current signal Ia, voltage signal Va, and angular velocity signal ωB using the following equation.

G _B =β·(Va−laRa)Ia/ω _B (12) However, β is a constant determined by the specifications of the traveling device 4, and IaRa is the voltage drop of the armature.

Next, the tension detection device 10 calculates the mandrel bar tension T _B using the following equation.

G _B 〓 _B = T _B V _B + α _B ... (13) However, V _B is the motion speed of the mandrel bar α _B is a constant determined by the specifications of the traveling device 4.

The motion speed V _B of this mandrel bar is a rigid body that does not undergo plastic deformation, and can be easily determined from the angular velocity ω _B and the reduction ratio of the traveling device 4.

Further, the method for detecting the tension at the base end of the mandrel bar is not limited to this, and for example, direct detection using a load detector is also possible. Figure 5 shows this, and Figures a and b are examples in which a load detector 61 is installed on the mandrel bar propulsion block 5.
Figure c shows the tension applied to the mandrel bar 2 by connecting the mandrel bar operation control beam 62 and the operating rod 63 via the load detector 61.
This is an example of detecting T _B.

On the other hand, if a hydraulic mechanism is employed as a device for operating the mandrel bar, the tension at the base end of the mandrel bar can be detected by detecting the operating hydraulic pressure.

〔Effect of the invention〕

As is clear from the above description, according to the mandrel bar tension control device of the present invention, torque fluctuations are caused in the drive device that drives the mandrel bar during continuous rolling with stepped rolls using mandrel bars or other mandrels. Even if the mandrel bar is heated, the tension between the stands of the mandrel bar is detected and the roll gap is corrected according to this tension between the stands, so the tension between the stands of the mandrel bar is always kept constant, and as a result, the thickness of the shell is Thickness and roundness can be maintained substantially constant, and high-quality seamless steel pipes can be manufactured.

[Brief explanation of drawings]

1 and 2 are rolling state diagrams showing a basic model when rolling a blank pipe by a mandrel mill, and FIG. 3 shows the configuration of an embodiment of the mandrel bar tension control device according to the present invention. FIG. 4 is a block diagram shown together with the rolling system, FIG. 4 is a block diagram shown together with the mandrel bar drive device, and FIG. FIG. 7 is a diagram showing the state in which main elements are attached in order to explain the configuration of another embodiment of the mandrel bar drive device according to the invention. 1, 11-1n... Grooved roll, 2... Mandrel bar, 3... Base tube, 4... Travel device, 5... Mandrel bar propulsion block, 6... Electric motor, 7... Angular velocity detector, 8... Current detector, 9... Voltage detector, 10... Tension detection device, 21-2n... Roll gap setting device, 3
1 to 3n... Roll gap control device, 41 to 4n... Roll gap detector, 51 to 5n... Rolling down device, 61...
Load detector, 62... Mandrel bar operation control beam, 63... Operating rod.

Claims (1)

[Scope of Claims] 1. In a mandrel mill in which a mandrel bar whose advancing speed is controlled by a drive device is inserted into a blank pipe and is engaged with a plurality of stands each having a grooved roll, the proximal end of the mandrel bar is a tension detection device for detecting tension between the stands; and a tension detection device configured to output a reference signal between the rolls of each stand according to settings, and calculate the mandrel bar tension between the stands based on the tension signal of the tension detection device; an inter-roll setting device that corrects the inter-roll reference signal so as to absorb a variation in the calculated mandrel bar tension with respect to tension variation at the proximal end of the mandle bar due to torque variation of the drive device; A mandrel bar tension control device for a mandrel mill, comprising: a control device for controlling a roll lowering device according to a reference signal; 2. Claim 1, wherein the tension detection device detects the tension at the proximal end of the mandrel bar based on the drive torque of the drive device.
A mandrel bar tension control device for a mandrel mill as described in . 3. The mandrel bar tension control device for a mandrel mill according to claim 1, wherein a load detector is used as the tension detection device.