JPS6188913A - Rolling control method of reeling mill - Google Patents

Abstract

PURPOSE:To improve the dimensional accuracy in thickness by finding the quantity varied from the target outer diameter with specified equation according to the actual thickness deviation of the tube stock after a plug mill rolling and by correcting the tube expansion quantity of the reeling mill based thereon. CONSTITUTION:The tube stock after a plug mill rolling is reduced by rolling with the rolling rolls 10, 10' including its axial line in reverse direction each other and a rolling plug 13. The informations of a material temp. T, rolling torque Trq and the informations of the tube stock thickness tp before reeler rolling, outer diameter Dp are inputted into a control arithmetic unit 21. The actual thickness size deviation DELTAtp of after the plug mill is then found for the predetermined rolling schedule. Further a correction signal is inputted into a rolling reduction control device 19 with finding the correction value of the expansion by the reeler according to the equation I together with the outer diameter Ds of after sizing and thickness ts. With said method the size accuracy in thickness is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION When manufacturing a seamless steel pipe using the rolling control method of the beam mill of the present invention, particularly the Mannesmann plug mill pipe manufacturing method, the reeling mill is controlled according to the actual wall thickness information of the raw pipe after plug mill rolling. A rolling control method is proposed in which the outer diameter of the blank tube on the exit side is controlled in the pipe longitudinal direction, thereby improving the accuracy of the wall thickness 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, and expanded and drawn in an elongator 3.

The plug mill 4Vc is used to roll the product to approximately the same length, and then the product is rolled to a length that is approximately equal to the thickness of the product.
At the same time as the inner and outer surfaces 7 (5) are formed into tubes, the tubes are expanded and finished to a predetermined outer diameter in a sizing mill (hereinafter referred to as a sizer) 7 to become the final product.

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 tube after plug mill rolling, so it is possible to reduce variations in product wall thickness, improve quality, and improve rolling yield. In order to improve performance, controlling the length or wall thickness of the raw pipe in a plug mill is considered to be the most effective method, and various measures have been taken to reduce the variation in the dimensions of the raw pipe in plug mills. .

However, there are limits to wall thickness control using plug mills.

Also, as can be seen from Figure 1, the raw pipe after plug mill rolling becomes the final product only after passing through two rolling processes: a reeler and a sizer, so these two rolling mills can be ignored and rolling control performed only by the plug mill. Even if you implement it, you won't get a big effect. In addition, in the past, in order to improve the outside diameter dimensional accuracy of the final product, constant control of the rolling ring force has been implemented with the reeler (rolling ring) for the purpose of keeping the outside diameter of the raw pipe constant in the pipe length direction after reeling. However, sizer 1
- The effect was small because no attempt was made to control the wall thickness or length of the finished product.

The present invention has been made in view of this point.

It is an object of the present invention to provide a rolling control method for a reeler that can further reduce variations in wall thickness of a final product.

For this purpose, the present invention dynamically adjusts the IJ + roller during rolling of the raw pipe, makes the outer diameter of the raw pipe uniform in the longitudinal direction of the raw pipe after rolling, and achieves the target outer diameter of the raw pipe. The VcG is positively changed during reeler rolling according to changes in the wall thickness of the raw tube after plug mill rolling.

Next, a method of determining the correction amount of the target outer diameter of the raw pipe after reel 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 and the outer diameter is increased. 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 111°D and 1. The wall thickness, outer diameter, and length S and S of the raw tube after reeling are respectively t and l I) RI IB + The wall thickness, outer diameter, and length of the raw tube after plug milling are tp ''P, respectively.
” Let it be P.

The rolling mechanism in a sizer is very similar to a reducing mill that is widely used in small-diameter steel pipe production equipment, but in a sizer, the stretch coefficient is almost zero. In rolling when the stretch coefficient is zero, half of the strain generated by shrinking 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 as a strain in the direction of increasing the tube thickness. acts as a strain in the direction of elongation.

That is, if logarithmic strain is adopted as strain, equation (1) when the stretch coefficient is zero can be easily derived from rolling theory.

Furthermore, the inventors found that the outer diameter and wall thickness of the raw pipe after plug mill rolling were 1. As a result of investigating the relationship between the outer diameter DR2 and the wall thickness tR of the raw pipe after reel-rolling, it was found that the following linear relational expression holds true.

P=fCt,/D, )...(3) The relationship of equation (3) is illustrated in FIG. 2, and P increases as tP/DP increases.

Rewriting equation (2), from equations (1) and (4), we get that in equation (5), t, and D are the target wall thickness and outer diameter of the final product, even if tP, Dl, Dl, etc. tll and D8 must be constant values that do not change even if they change. Differentiating both sides of equation (5) with tP and rearranging it, we get D
2, then equation (6) is approximately D ΔD・=2−”1/2°π°″′・°゛°(″)Δt1
．． ΔD3 is the amount of change from the reference value.

On the other hand, target wall thickness after reel rolling tR1 target outer diameter D target wall thickness after plug mill rolling 1. A basic rolling schedule for each rolling size is built into the process computer according to formulas (1) and (2). (The force formula is a formula that gives the correction amount ΔDR of the reeler target outer diameter when the actual wall thickness after plug milling changes by Δ1. with respect to the rolling schedule determined in this way.

Feed forward the actual wall thickness after plug milling to the reeler and calculate the target outer diameter of the reeler raw tube using equation (7).
If the reeler rolling mill is automatically controlled, the dimensional variation of the final product will be reduced.

The reeler is controlled during rolling so that the reeler has the target outer diameter determined as described above, 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 D8o. Reeler
Calculate the target thickness reduction amount ΔtO of the reeler to obtain the target outer diameter Dnot- after rolling.

Here, t: Actual wall thickness after plug mill rolling.

DP: Actual outer diameter after plug mill rolling.

D: After plug mill rolling, do you install an outside diameter gauge? Use the value obtained by measuring the outside diameter of the tube. Further, 1. can be determined by measuring the length l of the raw pipe after plug mill rolling. In other words, the material billet before being charged into the heating furnace is weighed to determine its weight, the scale loss in the heating furnace etc. is subtracted to determine the weight W of the steel material in the plug mill, and then the length of this steel material after plug mill rolling is determined. The outer diameter DP of the raw pipe after plug milling is measured by the outer diameter meter.
It is calculated from the following equation (9).

Here, ρ is the steel material density depending on the steel material temperature at the time of length measurement. Note that tP can be directly measured by installing a thickness measuring device using a gamma ray method or the like on the inlet side of the reeler. This is because there is no change in the total amount of strain before and after rolling. That is, from the equation (2) and the equation (8), the target thickness reduction floating amount Δ
1of: Control the reeler so that it can be achieved throughout rolling. The control method will be described below.

The inventors believe that the actual thickness reduction ΔtA in the reeler mill is determined by the rolling torque during reeler rolling and the deformation resistance of the steel material.

I found that it can be found as

Here, T: Reeler rolling torque.

q Kfm; deformation resistance of steel material; a, b; Fixed constants.

The deformation resistance K is determined from the rolling temperature of the steel material, the carbon content f weight 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 formula 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, Kfm changes during rolling depending on the temperature pattern in the longitudinal direction of the raw pipe.

The rolling torque Trq is directly measured on 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. Note that the torque Tr may of course be obtained by detecting the armature voltage Va, m armature control, and rotational speed NMt of the rolling motor and calculating qNM using T=μniha. In this way 02
The actual thickness reduction amount ΔtA determined by the formula and the target thickness reduction amount Δto determined by the formula (8) are compared and the reeler rolling 9-
control the position of the file.

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. Also the fourth
The figure is a cross-sectional view schematically showing the rolling state of the reeler. The 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 and 10' whose axes are inclined in opposite directions, and a rolling plug 13 inserted into the raw pipe. As a result, uneven wall thickness of the raw pipe and plug scratches caused by the plug mill in the previous process are eliminated. Reference numerals 11 and 11' refer to guide shoes for regulating the vertical position of the raw tube 12, reference numeral 14 indicates plug bars of the rolling plug 13, and reference numeral 17 indicates rolling rolls 10 and 10'.
18 is a rolling motor that operates the rolling screw 17, and 15 is a rolling motor that rotationally drives the rolling rolls 10 and 10'. The control arithmetic unit 21Vc controls the material temperature T measured by the thermometer 20 and the rolling rolls 10, 10.
information on the rolling torques T and q from the torque meters 16 and 16' attached to the spindles 22 and 22';
After plug mill rolling, the reeler--information on the raw tube wall thickness tp and raw tube outside diameter measured before rolling is input manually, and based on this information, a reduction control is executed to control the position of the rolling rolls 10 and 10'. A reduction control signal ΔE is output to the reduction control device fffil9. FIG. 5 is a diagram showing the control calculation 70-. Difference between target thickness reduction amount Δto and actual thickness reduction amount Δ1 person (
The distance E between the rolling rolls 10 and 10' is controlled in accordance with Δt^−Δto)IC. That is, when ΔL^-Δ1゜〉0, the interval E is controlled to be large.

By controlling the interval E to be small when Δt mu Δ1o<0, the rolling state is always maintained so that Δt^=Δto.

The present invention controls the reeler so that the variation in wall thickness of the raw pipe after plug mill rolling is further reduced in the final product, compared to the prior art. E.A.
This has a great effect on product quality and yield.

In other words, in the conventional technology, in order to control the wall thickness of the final product, attention was focused only on the plug mill and relying only on the rolling control of the plug mill. However, in this conventional method,
Since the rolling characteristics of reelers and sizers had not been sufficiently researched and understood, it goes without saying that when wall thickness variations occur in plug mills, those thickness variations remain in the final product. due to the disturbance effect.

There was a tendency for variation to increase.

Point 1: Since the present invention is a method of actively reducing the wall thickness variation of the final product, it not only eliminates the disturbance effect at the reeler, but also significantly improves the wall thickness variation of the final product.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the rolling process of the Mannesmann plug mill pipe manufacturing method, Figure 2 is a diagram showing the relationship of P = f (''/D,), and Figure 3 is a diagram showing the rolling process when the present invention is applied. FIG. 4 is a diagram schematically showing the rolling state of the reeler in a cross section, and FIG. 5 is a diagram showing the control calculation flow according to the control method of the present invention. DESCRIPTION OF SYMBOLS 10, 10'... Rolling roll 5 12... Rolling raw pipe, 13... Rolling plug, 15... Rolling motor, 16... Torque meter, 17... Rolling screw. 18... Reduction motor, 19... Reduction motor control device. 20... Thermometer, 21... Control calculation device.

Claims (2)

[Claims] (1) In the rolling control method in a reeling mill, the amount of change from the target outer diameter of the reeling mill is determined by the following formula (A) according to the actual wall thickness dimensional deviation of the raw pipe after plug mill rolling, and the reeling A rolling control method for a reeling mill, comprising controlling the amount of pipe expansion in the mill so that the wall thickness of the steel pipe after sizing mill rolling matches a predetermined target value. ΔD_R=D_S/(P-1/2)・1/t_S・Δt
_P...(A) However, D_S: Outer diameter of the steel pipe after rolling with a sizing mill, t_S: Wall thickness of the steel pipe after rolling with a sizing mill, P: Function of (thickness)/(outer diameter) of the raw pipe after rolling with a plug mill , Δt_P; actual wall thickness dimensional deviation of raw pipe after plug mill rolling, Δ
D_E: 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 pipe expansion of the reeling mill is corrected during rolling.