JPH07106368B2 - Manufacturing method of seamless pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a perforator widely used in a method for producing a seamless pipe, in particular, a Mannesmann pipe manufacturing method which is a typical production method for a seamless pipe. The present invention relates to a piercing / rolling method using a rolling machine using so-called inclined rolls such as a (piercer) and a stretching rolling machine (elongator).

(Prior Art) Generally, in a seamless pipe manufactured by the Mannesmann pipe manufacturing method, a heated round steel piece is first passed through a piercer, a plug is pressed into the center of the piercer, and the hollow shell is pierced to obtain a hollow shell. Directly or, if necessary, further passed through an elongator for diameter expansion and stretching rolling, then further stretching rolling with, for example, a plug mill, polishing with a reeler and sizer, shape correction, sizing, and through a refining process. Being manufactured.

By the way, in the above-mentioned piercer and elongator, there is a so-called inclined rolling machine that combines, for example, a round billet or a barrel-shaped rolling roll (hereinafter referred to as an inclined roll) having a tilted axis with respect to the path center of the hollow shell and a plug. Used.

For example, referring to the piercer, as shown in FIG. 1, this is the gorge portion 21, which has the maximum diameter in the middle of the axial direction,
And on both sides of this gorge portion 21, the entrance surface 22 in the form of a truncated cone whose diameter is gradually reduced toward each terminal side,
Inclined roll 1 which is a pair of work rolls with an exit face 23
, 1r, which is a warhead shape as a whole and which has a substantially conical shape from the tip side, a rolling section 25 which has a substantially truncated cone shape following the rolling section 24, and a relief section 26 whose diameter is reduced toward the base end. And a plug 2 having Both inclined rolls 1 and 1r are round steel slabs 30 pass center X-
On both sides of Y, the axial center line is parallel to the path center in plan view, and the one inclined roll 1 has the tip of the inlet face 22 facing upward in side view, and the other inclined roll 1r has the inlet face.
The tip of 22 is arranged so as to be inclined downward with respect to the path center by an inclination angle β (not shown).
Is arranged with its axis aligned with the path center XY.

Then, when the heated round steel piece 30 is transferred in the axial direction as indicated by the hollow arrow, the inlet surfaces 22 of the both inclined rolls 1 and 1r,
The round steel slab 30 is bitten between the two, and the round steel piece 30 is rotated around the axis by the inclined rolls 1 and 1r, and the plug 2 is inserted into the center thereof, and the inclined rolls 1 and 1r and the plug 2 pierce and roll. It is supposed to be done.

Even in the conventional case, in such a piercer, each range of the rollable condition and the suitable rolling condition that does not cause a flaw or the like on the pipe is set in advance, and the roll interval is within the range.
Data of the advanced plug amount (plug lead) and the guide shroud is calculated for each rolling of one round billet to predict the rolling result, and in the successive rolling, the calculated result is compared with the actual rolling result. A rolling control method (Japanese Patent Application Laid-Open No. 57-115907) has been developed in which feedback control is performed.

From the correlation diagram of each range of the above rollability aptitude rolling conditions, it is found that there is a limit condition that biting failure, bottom slipping out failure occurs, but this biting, bottoming out limit condition depends on the inclined roll friction coefficient. Since it changes, the suitability conditions prepared in advance may not be applicable depending on the magnitude of the friction coefficient of the roll.

In addition, the rolling material biting, bottom slipping limit conditions are the friction coefficient of the above-mentioned inclined roll, plug lead, roll interval, guide shoe interval, roll diameter, material diameter, perforation ratio, plug shape, roll shape, guide shoe shape, Since it changes depending on the material of the roll, the material of the guide shoe, etc., it is very difficult to accurately predict the limit conditions for biting and the trailing edge.

(Problems to be solved by the invention) When manufacturing a hollow shell from a billet using a piercer that uses an inclined roll, set the roll inclination angle to a small value, or adjust the draft ratio of the plug tip (plug to billet radius r ₀₎ . When the reduction ratio of the shortest distance r ₁ from the path center to the roll peripheral surface at the tip and the reduction ratio (defined by equation (1)) is increased, Mannesmann fracture in front of the plug causes the material being perforated as shown in FIG. Holes (fractures) may occur at the center, and the fracturing may cause flaws on the inner surface of the hollow shell.

Draft rate of plug tip = (r ₀ −r ₁ ) / r ₀ × 100 (%) (1) As described above, the influence of roll inclination angle β and draft rate of plug tip on the cracking caused by Mannesmann fracture is Shown in Figure 2. However, free-cutting steel (AISI standard 12L14) was used as the test material, and other conditions were heating temperature = 1150 ° C, drilling ratio 2.8, pipe expansion ratio 3%, plug diameter 48m.
m, diameter of perforated material is 60 mm, diameter of roll gorge is 350 mm.

Further, the inner surface flaw of the hollow shell tends to occur frequently when the circumferential shear strain generated during piercing and rolling increases. FIG. 3 shows the relationship between the rate of occurrence of internal defects (the number of defects generated / the number of piercing and rolling) and the circumferential shear strain. The circumferential shear strain is determined by the formula (2) by inserting the pin in the billet radial direction as shown in Fig. 4 (a) and measuring the twist angle of the pin after piercing and rolling as shown in Fig. 4 (b). It was

However, r ₂ : Outer radius of the hollow shell after drilling θ: Twist angle in the circumferential direction of the hollow shell after drilling t: Wall thickness of the hollow shell after drilling Further, if the roll inclination angle is large, it is a circle The circumferential shear strain is small. FIG. 5 shows the relationship between the roll inclination angle and the circumferential shear strain.

As is clear from FIG. 5, the roll inclination angle may be increased in order to suppress the occurrence of inner surface defects.

Therefore, as a conclusion of the above explanation, in order to prevent the inner surface flaw of the rolled material, the roll inclination angle should be as large as possible and the plug tip draft ratio should be as small as possible.

By the way, as the inclination angle β increases, the thrust force in the rolling direction acting on the plug increases. In other words, the force impeding the advancement of the perforated material is large, and it is necessary to provide the perforated material with sufficient propulsive force from the roll to rotate and advance the perforated material.

In addition, when the unsteady rolling is carried out and when slipping out, the thrust for advancing the material is insufficient due to the reduction of the contact area between the roll and the material, resulting in poor biting into the material top.
Defects in the bottom of the material (braking) occur,
Rolling may be stopped.

Furthermore, when the thrust as described above is insufficient, the inclination angle β
If the value is too large, the amount of reduction of the perforated material per half rotation increases, the slip between the roll and the material increases, and piercing and rolling stop.

Further, if the draft ratio of the plug tip is too small, the contact area of the pierced rolled material contacting the inclined roll and reaching the tip of the plug in the unsteady rolling state is reduced, and the propulsive force is further reduced, resulting in poor biting. Rolling stops.

Therefore, it is an object of the present invention to provide a method for producing a seamless pipe which eliminates the above-mentioned bite defect and bottom defect, and which can be pierced and rolled without generating inner surface defects.

Further, it is an object of the present invention to provide a seamless pipe inclined roll rolling direction in which the rolling efficiency and rolling yield are improved and the occurrence of inner surface defects is suppressed to improve the tube quality.

(Means for Solving Problems) The present invention has been made in view of such circumstances, and its gist is to include the biting time and the tail of a material to be rolled during piercing and rolling by an inclined roll mill. The slip-out time was measured, and based on each of the obtained measured values, the slip ratio at the time of biting and the slip ratio of the rolled material at the slip-out were obtained, and both slip ratios and the reference slip ratio obtained in advance were calculated. If both slip ratios are below the reference value, the difference between the slip ratio at the time of biting and the reference slip ratio should be as zero as possible, and both or one of the slip ratios should be above the reference value. Adjust one or more of the plug lead, roll inclination angle, roll crossing angle, and roll opening before the start of the next rolling so that the difference between the higher slip ratio and the reference value is as zero as possible. Seams characterized by rolling by rolling It is a pipeless manufacturing method.

In a specific embodiment thereof, the present invention uses a slant roll to cause a plug to penetrate along the axial direction while screwing the rolled material in the axial direction, and piercing-rolls the rolled material. When rolling the inclined rolls, the rolling load or rolling torque acting on the inclined rolls is measured, and the biting time and the trailing edge removal time are calculated based on the measured values. Calculate each slip ratio of the rolled material at the time of pulling out, compare it with the reference slip ratio, and in order to reduce the difference as much as possible, plug after the rolling of the rolled material and before the rolling of the next material. Lead, roll tilt angle,
A method for producing a seamless pipe is characterized in that at least one of a roll crossing angle and a roll opening is adjusted to perform rolling with a high inclination angle and a low draft rate as much as possible.

Here, the reference slip ratio is a slip ratio within the range of the slip ratio or more that can be piercing-rolled, and refers to a value preset in consideration of the biting property, the slip-out property, etc. in the operation, in a preferred embodiment, It is preferable to set the reference slip as the limit slip rate at which piercing and rolling can be performed. Therefore, the present invention is characterized by making the inclination angle as large as possible with a slip ratio close to the slip ratio of the limit condition for perforation, and making the draft ratio as low as possible (in other words, making the plug lead large). To do. In piercing and rolling, even if the material to be rolled has the same size and the same material, the slip ratio changes depending on the chance of rolling. This is because, for example, the temperature of the roll is different at the time of starting the rolling operation and at the time of rolling after several hours, and the knurling (surface roughness) of the roll is also different.

The slip ratio is calculated using the learning values of the rolling load and rolling torque actual value of the previous material.

Note that FIG. 6 is a schematic diagram for explaining the part names of the arrangement structure of the inclined rolls.

(Operation) Hereinafter, the present invention will be described with reference to the drawings showing an embodiment thereof.

FIG. 7 is a schematic block diagram of an inclined rolling mill used for carrying out the method of the present invention. FIG. 7 (a) is a schematic view of the side surface of the rolling mill, and 1 and 1r are inclined rolls whose axis lines are inclined in different directions with respect to the pass line, and each inclined roll is inclined by the automatic positioning device 40. The angle β is changed.

FIG. 7 (b) is a schematic view of the rolling mill as seen from the top, and the inclined rolls 1 and 1r can be made to intersect with the pass line in the direction of the dotted arrow in the figure by the automatic positioning device 41. There is. Further, the automatic positioning devices 40 and 41 move the inclined rolls 1 and 1r to change the roll opening.

The plug lead is changed by the automatic positioning device 42.

Incidentally, the load cell 4 for detecting the rolling load acting on the inclined roll 1r is provided on the inlet side and the outlet side of the one inclined roll 1r.
The thrust block 45 behind the mandrel bar 44 is provided with a load cell 46 for detecting the thrust force acting on the plug.

A drive motor 47 that drives the tilt roll 1 is provided with a current detector 48 that detects a load current.

Note that the slip ratio reference setting unit 50 is given the slip ratio at the time of unsteady rolling that allows piercing and rolling and when slippage occurs.

Tilt roll 1r or load cell 43, 4 of tilt roll 1 required to measure biting time and slip-out time
3, the output values of the load cell 46 and the current detector 48, the output of the rolling load level setter 51, the output of the plug load level setter 52, and the output of the motor current level setter 53 are given to the arithmetic storage unit 54, respectively. To be Further, the calculation value of the calculation storage device 54 is given to the calculation control device 55,
The calculation result is given to the automatic positioning devices 40, 41, 42.

The present invention is the above load cell 43, 43 or load cell 4
6, or the output of the current detector 48 is used to measure the biting time and trailing edge time, calculate the slip ratio based on the measured values, and change the roll set value for the next material according to the calculated values. Is.

Next, a method of controlling using the rolling load value acting on the inclined roll will be specifically described with reference to FIGS. 7 to 9.

First, the roll set value set by the standard setter 58 before the round billet 30 is rolled by the inclined rolls 1r, 1 is the arithmetic and control unit.
It is input to the automatic positioning devices 40, 41, 42 via 55, and the inclined rolls 1r, 1 are set to standard values. Piercing and rolling is started under these roll conditions. At that time, the output sum of the load cells 43, 43 is sampled at each time in the arithmetic storage device 54 during the perforation (during steady rolling), and the average value Pm is stored in the same device. The load chart when there is no problem with the biting failure and the slip-out failure at the time of piercing and rolling becomes as shown in FIG. 8 (a), and as the slip increases, it becomes as shown in FIG. 8 (b). Rolling time during steady rolling becomes longer. The phenomenon that the slip ratio becomes large appears when the inclination angle β is increased or the draft ratio of the plug tip is decreased, that is, the roll opening is increased and the plug lead is increased.

An object of the present invention is to pay attention to the slip ratio during the unsteady rolling for each rolled material and to constantly increase the inclination angle β or the draft ratio of the plug tip as small as possible while monitoring it.

Next, the measurement of the biting time t ₁ and the trailing edge time t ₂ shown in FIG. 9 is carried out by the arithmetic storage device 54, and the contents of the calculation will be described with reference to FIG.

First, the biting time t ₁ is measured by activating the timer built in the arithmetic storage device 54 at the same time when the signals of the load cells 43, 43 rise, and set the rolling load level to the load value at the time of biting set by the setter 51. When it reaches, the arithmetic storage unit 54 is made to stop the timer, the operating time of this timer is stored in the unit 54 as the biting time t ₁ , and the timer is reset.

The load value set by the rolling load level setter 51 may be rewritten based on the average value Pm of the rolling load during steady rolling of the previous material which is already stored in the calculation storage device 54. If there is no front material, the conventional actual value may be used. However, in that case, it is better to set the load value to 90% or less of the actual value to prevent malfunction of the timer. Next time t ₂
In the measurement of, the rolling load is reduced when the tail is slipping out, so the load of the calculation storage device 54 is reached when the load cell output reaches the load value when the tail is slipping, which is set by the rolling load level setting device 51, contrary to the time of biting. The timer is activated, and when the rolled material leaves the roll, the timer is stopped. The operating time of this timer is stored in the device 54 as the trailing edge time t ₂ , and the timer is reset.

As described above, the biting time t ₁ and the tail slip-out time t ₂ stored in the arithmetic storage device 54 are given to the arithmetic and control unit 55, and the slip ratio at the time of biting and slip-out is calculated by the device 55. To be done. The details of the calculation will be described below.

The slip rates S ₁ and S ₂ are calculated based on the equations (3) to (7) using the times t ₁ and t ₂ .

The material velocity V ₁ during biting is The material speed V ₂ when slipping out is However, Δt ₁ and Δt ₂ are correction amounts and are used when there is a difference between the timer value and the actual unsteady rolling time.

l ₁ is the distance from the point where the rolled material contacts the inclined roll to the point where it leaves the roll.

Here, assuming that the velocity component V _f in the forward direction of the inclined roll is determined by the equation (5), the slip rate S ₁ at the time of biting and the slip rate S ₂ at the time of slipping out of the tail are equations (6) and (7). Becomes

V _f = π ・ D ・ N ・ Sinβ (5) N: Roll rotation speed (rps) D: Roll gorge diameter (mm) β: Inclination angle (deg) The values of S ₁ and S _{2 in} equations (6) and (7) increase in the positive direction. The problem is that it is easy for jamming defects and slip-out defects to occur.

The slip ratios S ₁ and S ₂ obtained as described above are compared with the slip ratios S ₀₁ and S ₀₂ which are set by the slip ratio reference setter 50 for each steel type and perforation ratio, and the difference Δ in the slip ratios.
Find S ₁ and ΔS ₂ .

ΔS ₁ = S ₀₁ −S ₁ (8) ΔS ₂ = S ₀₂ −S ₂ (9) If both of the values of S ₁ and S ₂ above or only one of them is larger than the reference value, If both S ₁ and S ₂ are smaller than the reference slip ratio based on the larger ΔS ₁ or ΔS ₂ , the roll set value for the next material is changed based on ΔS ₁ .

First, if you want to change the tilt angle, the correction amount Δβ is (10),
Equation (11) is obtained.

If the values of S ₁ and S ₂ are both greater than or equal to the reference value (10), then Eq. (11) is established, and if both S ₁ and S ₂ are less than the reference value, Eq. (12) is established.

When ΔS ₁ <ΔS ₂ Δβ = ΔS ₁ × K ₁ … (10) ΔS ₁ > ΔS ₂ Δβ = ΔS ₂ × K ₁ … (11) Δβ = ΔS ₁ × K ₁ … (12) However, K ₁ is the coefficient of influence of the inclination angle β on the slip ratio, and this value is determined based on the actual value.

The calculation controller 55 calculates the tilt angle of the next material based on the tilt angle correction amount Δβ, and the calculated value is input to the automatic positioning device 41 to set the tilt angle. When Δβ is positive, the roll inclination angle is increased.

If S ₁ is smaller than S ₀₁ and there is no problem with slip-out, calculate the correction amount of the plug lead and roll opening necessary to reduce the draft ratio of the plug tip based on ΔS ₁ as follows. .

The correction amount ΔD _f of the draft ratio of the plug tip is given by equation (12).

ΔD _f = K ₂ × ΔS ₁ (13) K ₂ is a coefficient determined by the relationship between the biteability and the draft rate of the plug tip.

The draft ratio of the plug tip is expressed by the equation (1) as already explained, and the billet radius r ₀ cannot be changed by the equation (1), but as shown in FIG. 9, r ₁ is the roll opening and the plug lead. , The crossing angle (adjusting the figure of the roll) can be changed individually or in combination.

Here, a case where the plug tip draft ratio is corrected by combining the roll opening and the plug lead will be described.

The plug lead correction amount ΔL _d and the roll opening correction amount ΔR _g are calculated as shown in formulas (14) and (15) from ΔD _f obtained by the formula (13).

Plug ΔL _d = K ₃ × ΔD _f … (14) Opening ΔR _g = K ₄ × ΔD _f … (15) K ₃ and K ₄ are geometrically determined coefficients and the material thickness after piercing and rolling does not change. To decide.

The controller 55 calculates the roll opening of the next material and the set value of the plug lead by the plug lead correction amount ΔL _d and the roll opening correction amount ΔR _g , and the calculated values are input to the automatic positioning devices 40, 42. Settings are made.

The set values for the next material are determined by the correction amounts obtained in (10), (11), (12) and (14), (15). In this case, (10), (11), (12) ), (14) and (15) are too large to be corrected and there is a risk of defective biting or slipping out of the next material, set the respective coefficients K ₁ , K ₃ and K ₄ to small values. The target value may be gradually increased while confirming the slip condition for each rolled material. Further, the change of the inclination angle and the change of the draft ratio of the plug tip may be carried out separately or simultaneously.

In this example, the operation is performed based on the signals of the load cells 43, 43 arranged on the inclined roll, but the signal of the load cell 46 for detecting the thrust force applied to the plug may be used instead of the signal of the load cell. If the load cell is not provided, the output of the current detector 48 of the drive motor 47 may be used. In each case, the load value and the current value may be set in the plug load level setter and the motor current level setter, respectively. Other operations are similar to those already described. The signal of the load cell 46 and the output of the current detector 45 have the same pattern as the output of the load cells 43, 43.

The present invention can be applied to a case where the number of rolls is 3 or more, and the roll shape may be either a cone type or a barrel type, and the guide roll may be either a plate or a disc in the 2-roll type.

Although the first piercer, in which the occurrence of chaffing due to Mannesmann fracture and the shear strain in the circumferential direction are problems in the above-described embodiment, is described in detail, but in the second piercer (elongator) in which only the occurrence of shear strain in the circumferential direction is a problem. The present invention is also applicable.

(Effects of the Invention) If carried out as described above, it is possible to determine the state of biting and the trailing edge slippage for each rolled material under the roll conditions that are currently undergoing piercing and rolling. Since the inclination angle can be made as high as possible and the draft ratio of the plug tip can be made as small as possible without causing misrolling due to defective pulling out, it is possible to suppress cracks and inner surface defects as much as possible as shown in FIGS. 2 to 4. Therefore, high quality rolling and reduction of miss rolls enable high efficiency and high yield piercing and rolling.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state of piercing and rolling with an inclined roll; FIG. 2, FIG. 3 and FIG. 5 are graphs showing the relationship between flaws or defects occurring during piercing and rolling and rolling conditions; (A) and (b) are explanatory views of circumferential shear strain; FIG. 6 is a block diagram showing a control system of the method according to the present invention; FIG. 7 is an arrangement of inclined rolls and respective departments. FIG. 8 and FIG. 9 are explanatory views of respective rolling load charts found in the present invention. 30: Round billet, 1r, 1: Inclined roll, 40, 41, 42: Automatic positioning device, 43, 46: Load cell, 48: Current detector, 44:
Mandrel bar

Claims (1)

[Claims] 1. When piercing and rolling with an inclined roll mill,
Measure the biting time and slip-out time of the material to be rolled, and based on each measurement value obtained, determine the slip ratio at the time of biting and the slip ratio of the material to be rolled at the time of slipping out, and both slip rates and the slip ratio in advance. Compare the calculated reference slip ratio, if both slip ratios are less than the reference value, so that the difference between the slip ratio at the time of biting and the reference slip ratio becomes zero as much as possible,
If both or one of the slip ratios exceeds the reference value, the plug lead, roll inclination angle, and roll should be adjusted before starting the next rolling so that the difference between the higher slip ratio and the reference value becomes zero as much as possible. A method for producing a seamless pipe, which comprises rolling by adjusting at least one of a crossing angle and a roll opening.