JPS6115761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a rolling control method for a reeling mill, in particular, when manufacturing a seamless steel pipe using the Mannesmann plug mill pipe manufacturing method, the reeling mill control method according to the actual length information of the raw pipe after plug mill rolling. The present invention relates to a rolling control method for controlling the outer diameter of the raw pipe on the exit side in the pipe longitudinal direction, thereby improving the length dimensional accuracy of the final product on the exit side of the sizing mill.

A block diagram of the rolling process using the Mannesmann plug mill tube manufacturing method is shown in Figure 1. The billet heated in the heating furnace 1 is pierced and rolled in a piercing mill 2, expanded and rolled in an elongator 3, and
It is rolled in a plug mill 4 to a length approximately equal to the product wall thickness, polished inside and outside by reeling mills (hereinafter referred to as reelers) 5 and 6, and expanded at the same time, and then expanded in a sizing mill (hereinafter referred to as sizer) 7. The final product is finished to a predetermined outer diameter. 8 is a cooling table. In this way, when rolling seamless steel pipes using the Mannesmann plug mill method, the wall thickness of the product is almost determined by the wall thickness of the raw pipe after plug mill rolling, so it is possible to reduce variations in product length or wall thickness and improve quality. In order to improve the rolling yield, it is considered most effective to control the length or wall thickness of the raw tube in a plug mill, and various measures have been taken to reduce the variation in the dimensions of the raw tube in conventional plug mills. has been undermined.

However, there are limits to wall thickness control with a plug mill, and as can be seen from Figure 1, the raw tube after plug mill rolling becomes the final product only after passing through two rolling processes: a reeler and a sizer. Even if the rolling control of only the plug mill is carried out while ignoring the two rolling mills, it will not be possible to obtain a great effect. Furthermore, in the past, constant rolling power control was carried out on the reeler with the aim of keeping the outer diameter of the raw pipe constant in the pipe length direction after reeler rolling in order to improve the outer diameter dimensional accuracy of the final product. There was no attempt to control the wall thickness or length of the final product after passing through the sizer, so its effectiveness was small.

The present invention has been made in view of this point, and an object of the present invention is to provide a rolling control method for a reeler that can further reduce variations in the length or thickness of the final product.

For this purpose, the present invention dynamically adjusts the reeler during rolling of the mother tube, makes the outer diameter of the mother tube uniform in the longitudinal direction of the tube after rolling with the reeler, and adjusts the target outer diameter of the mother tube after plug mill rolling. Corrections and changes are made during reeler rolling according to changes in the length of the raw pipe.

That is, the reeling mill rolling control method of the present invention is as follows:
After plug mill rolling, the amount of change from the target outer diameter of the reeling mill is calculated according to the actual length dimensional deviation of the blank pipe after plug mill rolling, and the amount of change from the target outer diameter of the reeling mill is calculated using equation (13) described later, and the sizing mill is used while correcting the amount of pipe expansion in the reeling mill. The amount of pipe expansion is controlled so that the length of the steel pipe after rolling matches a predetermined target value.

Next, a method of determining the correction amount of the target outer diameter of the raw pipe after reeler rolling will be explained.

The raw tube rolled in a plug mill is polished and rolled in a reeler, and the tube thickness is slightly reduced to increase the outer diameter. After being polished and rolled by a reeler, the raw tube is reduced to a predetermined outer diameter by a sizer. The wall thickness, outer diameter, and length of the final steel pipe after sizing are t.
_s , D _S , l _S The wall thickness, outer diameter, and length of the raw tube after being reeled are t _R , D _R , l _R , and the wall thickness, outer diameter, and length of the raw tube after plug milling are t _{P ,} respectively. , D _P , l _P
shall be. The rolling mechanism in a sizer is very similar to a reducing mill, which is widely used in small-diameter pipe manufacturing equipment, but the stretch factor in a sizer is almost zero.
In rolling when the stretch coefficient is zero, half of the strain generated by the contraction of the outer diameter during the tube shrinking process acts as a strain in the direction of increasing the tube thickness, and the other half acts in the longitudinal direction of the tube. It acts as a strain in the direction of length extension. That is, if logarithmic strain is adopted as the strain, l _o t _R /t _S = -1/2 l _o D _R /D _S ...(1) Equation (1) when the stretch coefficient is zero can be easily derived from rolling theory. be guided.

Furthermore, the inventors determined that the outer diameter D _P of the raw pipe after plug mill rolling, the wall thickness t _P and the outer diameter D of the raw pipe after reeler rolling.
As a result of investigating the relationship between _R and wall thickness _tR , it was found that the following relational expression holds true.

t _P /t _R = (D _R /D _P ) ^p ...(2) p=(t _P /D _P )...(3) The relationship of equation (3) can be illustrated as shown in Figure 2,
p increases as t _P /D _P increases.

Rewriting equation (2), l _o t _P /t _R = -pl _o D _P /D _R ...(4) From equations (1) and (4), l _o t _P /t _S = -pl _o D _P +1/2l _o D _S +(p-1/2)l _o D _R ...(5) In equation (5), t _S and D _S are the target wall thickness and outer diameter of the final product, even if t Even if _P , D _P , D _R , etc. change, t _S and D _S must be constant values that do not change. Differentiating both sides of equation (5) with respect to t _P and rearranging, dD _R /dt _P = (D _P ) ^P /D _S ^1/2・D _R
^(p-3/2)・1/p-1/2・1/t _S ...(6) If D _S D _R D _P , then equation (6) can be approximated as ΔD _R =-D _S /p- 1/2・1/t _S・Δt _P …
(7) Δt _P・_ΔDR is the amount of change from the reference value.

On the other hand, the target wall thickness t _R after reeler rolling, the target outer diameter D _R , and the target wall thickness t _P after plug mill rolling are determined in advance by the basic rolling schedule for each rolling size according to equations (1) and (2). It is built into the process computer as a. Equation (7) is an equation that gives the correction amount ΔD _R of the reeler target outer diameter when the actual wall thickness after plug milling changes by Δt _P with respect to the rolling schedule thus determined.
In other words, if the actual wall thickness after plug milling is fed forward after reeler rolling, the target outer diameter of the reeler tube is calculated using equation (7), and the reeler rolling mill is automatically controlled, the dimensional variations in the final product can be reduced. becomes smaller.

The reeler is controlled during rolling so that the reeler target outer diameter obtained as described above is obtained, and a predetermined outer diameter of the raw pipe after reeling is obtained in the longitudinal direction of the pipe. A specific method of controlling the reeler will be described below.

Let the obtained reeler target outer diameter be _DRO . Calculating the target thickness reduction amount Δt _O of the reeler to obtain the target outer diameter D _RO after reeler rolling, Here, t _P is the actual wall thickness after plug mill rolling, and D _P is the actual outer diameter after plug mill rolling.

For D _P , use the value obtained by measuring the outer diameter of the raw pipe by installing an outer diameter gauge after plug mill rolling. Further, t _P can be determined by measuring the length _P of the raw pipe after plug mill rolling. In other words, the billet material before being charged into the heating furnace is weighed to find its weight, and the weight W of the steel material in the plug mill is determined by subtracting the amount of scale loss in the heating furnace. It is determined by measuring the length l _P and calculating it using the following equation (9) from the outer diameter D _P of the raw pipe after plug milling, which is measured by an outer diameter meter.

Here, ρ _P is the steel material density depending on the steel material temperature at the time of length measurement. In addition, t _P is γ at the time of reeler entry.
Of course, it is also possible to set up a wall thickness measuring device using a wire method or the like and directly measure the thickness.

Furthermore, l _P /l _R in equation (8) can be calculated as (D _RO /D _P ) ^1-p . This is because there is no change in the total amount of strain before and after rolling. That is, _{l o} t _P /t _R + l _o DP /D _R + l _o l _P /l _R
=0...(10) From equations (2) and (10), l _o l _P /l _R = -(1-p) l _o D _P /D _R ...(1
1) That is, l _P /l _R = (D _RO /D _P ) ^1-p In this way, in order to achieve the target thickness reduction amount Δt _O determined by equation (8) throughout the rolling process, Control the reeler. The control method will be described below.

The inventors determined that the actual thickness reduction amount Δt _A in the reeler mill
is determined by the rolling torque during reeler _rolling and the _{deformation resistance} of the _steel material.
).

Here, T _rq : reeler rolling torque K _fn : deformation resistance of the steel material, a, b : fixed constants, and the deformation resistance K _fn is determined from the rolling temperature of the steel material, the carbon content of the steel material, etc. Many calculation formulas have been proposed in the past for calculating this, so it is best to use an appropriate one among them. The rolling temperature of the steel material is obtained by directly measuring the temperature of the material entering the reeler in the longitudinal direction. Naturally, K _fn changes during rolling depending on the temperature pattern in the longitudinal direction of the raw pipe.
The rolling torque T _rq is measured directly at the rolling roll using a torque meter. A strain gauge type torque meter may be used, but any torque meter may be used as long as torque can be measured. Incidentally, the torque T _rq may of course be calculated by detecting the armature voltage v _a , armature current I _a and rotational speed N _M of the rolling motor and using T _rq = V _a ·I _a /N _M. It is. In this way, the actual thickness reduction amount Δt _A determined by equation (12) and the target thickness reduction amount Δt _O determined by equation (8) are compared to control the rolling roll position of the reeler.

Next, the control system of an actual reeler will be explained. FIG. 3 is a diagram showing the control system of the present invention in the reeler, as seen from above. FIG. 4 is a cross-sectional view schematically showing the rolling state of the reeler. Rolled raw pipe 12
is thinned by rolling while rotating in the direction of the arrow by a pair of drum-shaped rolling rolls 10, 10' whose axes are inclined in opposite directions and a rolling plug 13 inserted into the blank pipe. As a result, uneven thickness of the raw pipe and plug scratches caused by the plug mill in the previous process are eliminated. 11,11'
14 is a guide shoe for regulating the vertical position of the raw pipe 12; 14 is a plug bar of the rolled plug 13; 17
a reduction screw 18 which is attached to the shaft portion of the rolling rolls 10, 10' and adjusts the interval between the rolls;
is a reduction motor that operates the reduction screw 17;
Reference numeral 15 denotes a rolling down motor that rotationally drives the rolling rolls 10, 10'. The control calculation device 21 stores the material temperature T measured by the thermometer 20, the rolling roll 10,
Information on the rolling torque T _rq from the torque meters 16, 16' attached to the spindles 22, 22' of the spindle 10', the wall thickness t _P of the raw pipe and the outer diameter D of the raw pipe measured after plug mill rolling and before reeler rolling. Based on this _information , the rolling control device 19 outputs a rolling control signal ΔE which executes rolling control to control the position of the rolling rolls 10, 10'. FIG. 5 is a diagram showing the control calculation flow. Target thinning amount Δ
The distance E between the rolling rolls 10 and 10' is controlled according to the difference (Δt _A −Δt _O ) between t _O and the actual thickness reduction amount Δt _A. That is, when Δt _A −Δt _O >0, the interval E
The rolling state is always maintained so that Δt _A =Δt _O by controlling the distance E to be large and decreasing the interval E when Δt _A −Δt _O <0.

The above is a control mode for reducing the variation in wall thickness of the final product. In the present invention, control is performed to reduce variation in the length of the final product.
In that case, the following equation (13) may be used instead of the above equation (7).

ΔD _R =-D _S /p-1/2・1/l _S・Δl _P …
(13) Here, Δl _F is the amount of change in the actually measured length from the standard length on the schedule in the plug mill.

The present invention controls the reeler so that the length variation of the raw tube after plug mill rolling is further reduced in the final product, so compared to the conventional technology, it greatly improves the quality and yield of the product. It is something that has an effect.

In other words, in the prior art, in order to control the wall thickness of the final product, attention was paid only to the plug mill and relied solely on the extension control of the plug mill. However, in this conventional method, the rolling characteristics of the reeler and sizer were not sufficiently researched and understood, so if wall thickness variations occur in the plug mill, it goes without saying that the wall thickness variations will remain in the final product. In other words, due to the disturbance effect at the reeler,
There was a tendency for variation to increase.

In this regard, the present invention is a method that actively reduces the variation in wall thickness and length of the final product, so it not only eliminates the disturbance effect at the reeler, but also
The wall thickness and length variations of the final product are significantly improved.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the rolling process of the Mannesmann plug mill pipe manufacturing method, and Figure 2 is a block diagram showing the rolling process of the Mannesmann _plug mill pipe manufacturing method.
3 is a diagram showing the rolling situation of the reeler when the present invention is applied, as _seen from above, and FIG. 4 is a diagram schematically showing the rolling situation of the reeler in a cross section. FIG. 5 is a diagram showing a control calculation flow according to the control method of the present invention. 10, 10'...Rolling roll, 12...Rolling tube, 13...Rolling plug, 15...Rolling motor,
16... Torque meter, 17... Reduction screw, 18... Reduction motor, 19... Reduction motor control device, 20... Thermometer, 21... Control calculation device.

Claims (1)

[Claims] 1. In a rolling control method in a reeling mill, the amount of change from the target outer diameter of the reeling mill is determined according to the actual length dimensional deviation of the blank pipe after plug mill rolling using the following formula (a). A rolling control method for a reeling mill, comprising controlling the amount of pipe expansion in the reeling mill so that the length of the steel pipe after sizing mill rolling matches a predetermined target value. . ΔD _R =-D _S /P-1/2・1/l _S・Δl _P …(A) However, D _S : Outer diameter of the steel pipe after rolling in a sizing mill, l _S : Length of the steel pipe after rolling in a sizing mill, P ; Function of (thickness)/(outer diameter) of the raw pipe after plug mill rolling, Δl _P : Actual length dimensional deviation of the raw pipe after plug mill rolling, ΔD _R : Amount of change from the target outer diameter of the reeling mill. 2. A rolling control method for a reeling mill as set forth in claim 1, characterized in that the rolling torque of the reeling mill is detected and the amount of tube expansion of the reeling mill is corrected during rolling.