JPH0312962B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field] The present invention provides an automatic reduction control method for a reeling mill,
Specifically, the present invention relates to a method for automatically controlling the rolling reduction of rolling rolls in a reeling mill during the rolling process when seamless steel pipes are manufactured using the Mannesmann plug mill pipe manufacturing method.

[Background technology] A reeling mill (pipe polishing machine) is located between a plug mill and a sizer mill in the manufacturing process of seamless steel pipes. Reeling mills (polishing machines) are located between plug mills and sizer mills in the manufacturing process of seamless steel pipes. The purpose of this method is to correct the unbalanced wall thickness of the raw tube that has not been corrected up to now, to remove plug scratches that occur in the plug mill, and to ensure an appropriate amount of tube expansion for the sizer mill in the subsequent process. Polishing is performed by reducing the wall thickness of the raw pipe. A characteristic of reeling mills is that most of the wall thickness reduction, or wall thinning, changes into outer diameter expansion allowance, so if the amount of wall thinning for polished tubes varies, this will affect the longitudinal direction of the raw tube. The outer diameter after rolling with a reeling mill changes, causing the following inconveniences. In other words, if the amount of wall thinning during rolling is small, the outer diameter expansion rate during reeling mill rolling will be small and the outer diameter will be rolled small, and if the amount of wall thinning is large, the outer diameter expansion rate will be large and the outer diameter will be rolled large. Ru. In addition, if the outer diameter after reeling mill rolling is smaller than the specified value, an end-rolled portion will occur in the subsequent sizer mill, which will have a significant negative impact on the product outer diameter, and conversely, the outer diameter after reeling mill rolling will be smaller than the specified value. If it is too large, defects such as roll edge defects will occur during rolling in a sizer mill, which will also significantly deteriorate product quality. As described above, the rolling process using a reeling mill has a large effect on the dimensional accuracy of the final product and the yield of the product, so it is necessary to roll the outer diameter of the raw tube to a target in the reeling mill process.

Conventional control methods for reeling mills include (a) as shown in Japanese Patent Application Laid-open No. 53-37568. Method of controlling rolling power so that it is always constant throughout the entire length, (b) JP-A-1973-
As in No. 86663, in order to keep the wall thickness of the exit side constant, the outlet side is A method has been proposed in which a rolling power value pattern is set for each blank tube so that the cross-sectional area of the blank tube is constant, and the rolling power is controlled to be changed according to this pattern. Among these conventional methods, the former (a) control method ignores temperature changes for each rolled stock pipe and temperature changes in the longitudinal direction of the rolled stock pipe, so if constant rolling power control is performed, Since the deformation resistance is large in the low-temperature portion of the raw pipe, the amount of thinning is small, and therefore the outlet outer diameter cannot be expanded to a predetermined value, and the outlet outer diameter is not constant. Moreover, since the outer diameter of the raw tube at the entrance of the reeling mill changes in the longitudinal direction depending on the roll gap setting and rolling load during rolling of the plug mill, the reeling mill This will cause variations in the outer diameter of the exit side blank pipe. The latter method (b) controls the target power by changing it in a predetermined pattern in consideration of the temperature change in the longitudinal direction of the raw tube, but as in the former method (a), the The target power is simply set so that the cross-sectional area of the raw tube at the exit side of the reeling mill is constant, ignoring the change in the outer diameter of the raw tube in the longitudinal direction. The diameter varies both in the longitudinal direction of the tube and in the average outer diameter of each tube in the rod.

Furthermore, to add a drawback to method (b), in general, in plug mills, the temperature distribution in the longitudinal direction of the raw tube at the entrance of the plug mill tends to increase toward the rear end. As a shape,
The tube thickness tends to become thinner toward the rear end. In other words, the cross-sectional area pattern of the raw tube at the entrance of the reeling mill is generally
It has a pattern in which the cross-sectional area becomes smaller toward the rear end.

In order to make the cross-sectional area uniform in the longitudinal direction after rolling the entry-side blank pipe with such a cross-sectional area pattern using a reeling mill, it is necessary to The amount of meat must be reduced, resulting in a blank pipe having an outlet outer diameter that decreases toward the rear end, which has an undesirable effect on the outer diameter quality of the final product.

Furthermore, in methods (a) and (b), even if the rolling power is controlled, if the speed of the rolling motor changes during rolling, the rolling torque changes, making it impossible to obtain the specified outer diameter. There are drawbacks.

Furthermore, since the methods (a) and (b) are controlled by rolling current, the time delay cannot be ignored, which causes a delay in control and has the disadvantage of poor controllability.

In addition, as another conventional control method for a reeling mill, as shown in JP-A-57-17316, the actual amount of thinning during rolling is calculated from the rolling torque during rolling. There is a method of controlling the rolling position of the rolling roll so that it is equal to the target thickness reduction amount. However, with this method, it is necessary to detect rolling torque using a rolling current or a torque meter, and since acceleration/deceleration torque is not taken into consideration, control accuracy at the tip and rear end of the tube is poor, and When detecting rolling torque, there is a drawback that responsiveness is poor.

[Object of the Invention] An object of the present invention is to provide an automatic reduction control method for a reeling mill that maintains the outer diameter of the raw tube on the exit side of the reeling mill at a constant level with high precision.

[Structure of the Invention] The present invention calculates the following formula from the outer diameter D _P at each point in the longitudinal direction of the raw pipe on the entrance side of the reeling mill, the average wall thickness t _P , and the target outer diameter D _R on the exit side of the reeling mill. Find the target thickness reduction amount Δt ₀ in the longitudinal direction of the raw pipe (however, α is a value determined for each steel type of raw pipe size), Δt ₀ = t _P − (D _R /2) + √( _R 2) ² − ( _P −
_P )
t _P Calculate the actual thinning amount Δt _A in the longitudinal direction of the raw pipe during rolling from the temperature T of the raw pipe on the entry side of the reeling mill and the rolling loads P ₁ and P ₂ during rolling using the following formula (however, K _f is the deformation resistance determined from the raw tube temperature T, P ₁ ,
P ₂ is the rolling load of the pair of rolling rolls, D _R is the target outer diameter at the exit side of the reeling mill, β and γ are constants), Δt _A = 1/β・D _R + γ [P ₁ ² + P ₂ ² / K _f ² ] Change the setting of the roll interval E of the rolling rolls using the formula below so that the actual thickness reduction amount Δt _A is equal to the target thickness reduction amount Δt ₀ (however, E ₀ is the actual thickness reduction amount Δt _A calculated) (E is the roll spacing that should be newly changed), E=E ₀ −2 (Δt ₀ −Δt _A ) The rolling position of the rolling rolls is controlled. .

[Specific Description of the Invention] Next, the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic diagram showing a control system of the present invention in a reeling mill, and the reeling mill is viewed diagonally from above. Further, FIGS. 2 and 3 are diagrams schematically showing the rolling state of the reeling mill in a vertical section and a cross section, respectively. As shown in these figures, the rolled raw pipe 3 is made up of a pair of drum-shaped rolling rolls 6, 6 whose axes are inclined in opposite directions.
and the rolled plug 7 inserted into the raw pipe 3, the thickness is reduced by rolling while rotating in the direction of the arrow, and this causes uneven thickness of the raw pipe and the thickness of the rolled plug 7 that was generated in the plug mill in the previous process. The plugging flaws, etc. will disappear. 1 is a guide shoe that regulates the vertical position of the raw pipe 3; 8 is a plug bar of the rolled plug 7;
Reference numeral 9 denotes a reduction screw attached to the shafts of the rolling rolls 6, 6 to adjust the interval between the rolls, 10 a reduction motor for operating the reduction screw 9, and 12
is a rolling motor that rotationally drives the rolling rolls 6, 6;
13 is a thermometer for measuring the inlet tube temperature T;
14 is a load cell for measuring rolling load, 1
5 is a signal amplifier for the output signal of the load cell 14; Further, 16 is a hydraulic cylinder device that applies a preload to the load cell 14. In rolling with this reeling mill, most of the amount of thinning acts as an expansion of the outer diameter of the tube, so it is necessary to control the amount of thinning in order to control the exit outer diameter.

The inventors analyzed the relationship between the amount of wall thinning and the amount of pipe expansion based on a lot of data obtained from actual reeling mill rolling, and found that the target wall thinning amount Δt ₀ can be calculated using equation (1).
I found out that is required.

Δt ₀ : Target thickness reduction amount, D _R : Target outer diameter after reeling mill rolling D _P : Actual outer diameter after plug mill rolling (longitudinal pattern), t _P : Average wall thickness after plug mill rolling The value of α is for each base pipe. Dimensions This is a value determined for each type of steel. Using equation (1), we can calculate the optimal reduction amount in the reeling mill necessary to obtain the target outlet outer diameter D _R even when the inlet outer diameter D _P changes in the longitudinal direction of the raw pipe. You can decide.

Hereinafter, how to determine the outer diameter D _P of the raw pipe after plug mill rolling and the average wall thickness will be explained.

Outer diameter of the raw pipe after plug mill rolling D _P ; To calculate the outer diameter at each point in the longitudinal direction of the raw pipe after plug mill rolling, use the caliber shape of the plug mill rolling rolls and the roll gap of the upper and lower rolls 2 and 5 as shown in Fig. 4. G, rolling load during plug mill rolling
Calculate from _P according to equation (2). Equation (2) can be easily derived from FIG. 4 in the figure is a rolled plug of a plug mill.

D _P =2r ₁ θ ₁ +4r ₂ θ ₂ +2 (G-G ₀ +P _P /M)/π……(2
) Here, G ₀ is the standard roll gap, M is the mill rigidity of the plug mill, θ ₁ is the expected angle of the arc with radius r ₁ , θ ₂ is the expected angle of the arc with radius r ₂ , and r ₁ is the radius of the bottom of the caliber. , r ₂ is the radius of the caliber flange, the rolling load P _P and the roll gap G not only change from one raw pipe to another, but also in the longitudinal direction during rolling within the same raw pipe, so the Therefore, the outer diameter of the raw tube after plug mill rolling changes in the longitudinal direction. In particular, the rolling load at the tip and rear end of the raw tube where the temperature drops at the entrance of the plug mill is much larger than at the center, so the difference in the outer diameter near the tip and rear end and the outer diameter of the center portion of the raw tube changes to an extent that cannot be ignored. do.

Alternatively, to find the outer diameter after plug mill rolling, instead of using equation (2), directly measure the outer diameter of the blank tube at the exit side of the plug mill or the inlet side of the reeling mill in the longitudinal direction using an outer diameter measuring device. Well, you can ask for it.

Average value of the outer diameter of the raw pipe after plug mill rolling as described later
D _P is determined by averaging the outer diameters at each point in the longitudinal direction determined in this way.

This outer diameter D _P of the raw pipe after plug mill rolling is inputted to the AGC device 17 shown in FIG. 1 as reeling mill entry side outer diameter information.

Average wall thickness of the raw pipe after plug mill rolling _tP ; To determine the average wall thickness of the raw pipe after plug mill rolling _tP , weigh the material billet before charging it into the heating furnace to find its weight, and then After subtracting the scale loss amount and determining the weight W of the steel material in the plug mill, the actual length 1p of the raw pipe after the final pass rolling of the steel material in the plug mill is calculated, and the average outer diameter _P of the raw pipe after the plug mill as described above is calculated. _tP is determined from equation (3).

Here, ρp is the steel material density that depends on the steel material temperature of the plug mill rolled raw pipe.

This average wall thickness t _P is input to the AGC device 17 as raw pipe wall thickness information on the entry side of the reeling mill.

From the above equations (1), (2), and (3), in order to obtain the target outlet outer diameter D _r in the reeling mill, the optimal amount of thinning for each raw pipe and in the longitudinal direction of each raw pipe ( It becomes possible to determine the target thickness reduction amount) Δt ₀ .

Alternatively, the average wall thickness t _P may be directly determined using a wall thickness measuring device for the raw pipe in the same manner as the direct measurement of the outer diameter of the raw pipe described above.

On the other hand, from the rolling load in the reeling mill and the temperature of the inlet tube, the actual thickness reduction amount Δt _A during rolling is determined by taking deformation resistance into consideration. The inventors found equation (4) as a relational expression between rolling load and thickness reduction amount.

Δt _A = 1/β・DR+γ(P ₁ ² +P ₂ ² /Kf ² )…(4) P ₁ : Rolling load of rolling roll 6A P ₂ : Rolling load of rolling roll 6B Kf: Deformation resistance, DR: Reeling Mill target outer diameter, β, γ: constants, deformation resistance Kf are determined from the rolling temperature T of the raw pipe, other steel carbon content, etc.
Many calculation formulas have been proposed for calculating this value, so we will use an appropriate one among them. The rolling temperature T of the raw tube is obtained by directly measuring the temperature of the raw tube at the entrance of the reeling mill in the longitudinal direction with a thermometer 13.

Naturally, Kf will change during rolling if the temperature in the longitudinal direction of the raw pipe changes. This information is input to the AGC device 17 in Fig. 1, and according to equation (4), the actual value of the hollow shell tube being rolled is determined from the rolling loads P ₁ and P ₂ during rolling, the steel material temperature T during rolling, etc. The amount of thinning Δt _A can be determined. The deviation between the actual thickness reduction amount Δt _A determined in this way and the target thickness reduction amount Δt ₀ is determined, and the rolling position of the rolling roll is adjusted according to the magnitude of the deviation.

The roll distance E ₀ is set to E-2 (Δt ₀ .Δt _A ) by the reduction motor control device 18 (FIG. 1). however,
E ₀ is the roll interval actual value when the actual thickness reduction amount Δt _A is calculated, and E is the roll interval to be newly set and changed by the reduction motor control device 18. That is, when Δt _A <t ₀ , the roll interval is tightened so as to increase Δt _A , and when Δt _A >Δt ₀ , the roll interval is opened so as to decrease Δt _A.

As described above, according to the present invention, a method for quantitatively adjusting the roll interval is revealed. This is also one of the features of this method that is not found in conventional methods.

The present invention has the following advantages over the prior art.

(1) In the conventional technology, the reduction of the reeling mill was adjusted without taking into account the temperature change in the longitudinal direction of the raw pipe on the inlet side of the reeling mill, so the outer diameter of the outlet side could not be made uniform in the longitudinal direction. This is possible with the method of the present invention.

(2) In the conventional technology, the rolling reduction of the reeling mill was adjusted without considering the temperature change in the longitudinal direction of the raw pipe on the inlet side of the reeling mill, so that the outer diameter of the outlet side could not be made uniform in the longitudinal direction.

In particular, the outer diameter of the leading and trailing ends could not be controlled to the target value, but this method can.

(3) Some conventional techniques have the drawback that the outer diameter of the raw tube after rolling fluctuates in the longitudinal direction because it attempts to keep the wall thickness of the raw tube constant after rolling with a reeling mill. This method provides a uniform outer diameter in the longitudinal direction.

(4) In the conventional technology, the amount of reduction correction cannot be determined quantitatively when adjusting the reduction, so depending on the rolling size, controllability deteriorates and hunting phenomena and delays occur in control. Since the method uses a method of detecting the amount of thinning of the blank pipe at any given time from the rolling load during rolling, it is the only method that can be used to determine the necessary correction amount of the rolling roll spacing when the actual amount of thinning deviates from the target amount of thinning. , the control is very stable and no hunting or delay phenomena occur at all.

(5) In addition, since the rolling load is directly detected by a load cell, it has good responsiveness and completely ignores acceleration/deceleration torque, impact drop, etc. at the rear end of the pipe, resulting in high accuracy. It is possible to perform precise control.

[Effects of the Invention] As described above, according to the control method of the present invention, the outer diameter of seamless steel pipe products is always rolled according to the target, and no roll edge flaws occur at all in the sizer mill, and the product quality is significantly improved. A good effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the control system of the present invention in a reeling mill, Fig. 2 is a longitudinal sectional view schematically showing the rolling situation of the reeling mill, and Fig. 3 is a schematic diagram showing the rolling situation of the reeling mill. FIG. 4 is a cross-sectional view schematically showing a rolling situation in a plug mill in a pre-processing stage of a reeling mill. 3... Hollow tube, 6... Rolling roll, 7... Rolling plug, 9... Rolling down screw, 10... Rolling down motor, 1
2... Rolling motor, 13... Thermometer, 14... Load cell, 17... AGC device, 18... Rolling motor control device.

Claims (1)

[Claims] 1. From the outer diameter D _P at each point in the longitudinal direction of the raw tube on the entry side of the reeling mill, the average wall thickness t _P , and the target outer diameter D _R on the exit side of the reeling mill, the target is determined by the following formula. Determine the amount of thinning Δt ₀ in the longitudinal direction of the raw pipe (however, α is a value determined for each steel type of raw pipe size), Δt ₀ = t _P − (D _R /2) + √( _R 2) ² − ( _P −
t _P )t _P The actual thickness reduction amount Δt _A during rolling is calculated in the longitudinal direction of the material pipe from the temperature T of the material pipe on the entry side of the P reeling mill and the rolling loads P ₁ and P ₂ during rolling using the following formula ( However, K _f is the deformation resistance determined from the raw tube temperature T,
P ₁ and P ₂ are rolling loads of a pair of rolling rolls, D _R
is the target outside diameter at the exit side of the reeling mill, β and γ are constants), Δt _A = 1/β・D _R + γ [P ₁ ² + P ₂ ² /K _f ² ] Actual thickness reduction Δt _A is the target thickness reduction Change the setting of the roll spacing E of the rolling rolls using the following formula so that it is equal to the amount Δt ₀ (however, E ₀ is the actual roll spacing value when the actual thickness reduction amount Δt _A is calculated, and E is the new setting) roll spacing to be changed), E=E ₀ −2 (Δt ₀ −Δt _A ) A method for automatically controlling the rolling reduction of a reeling mill, characterized by controlling the rolling position of the rolling rolls.