JPH03128107A - Rolling method for inclined drawing of pipe - Google Patents

Abstract

PURPOSE:To obtain a high internal face quality as far as possible by using a mandrel bar equipped with a tapered part connected to a regular part and the rear side thereof, bringing the whole length of the effective part of the mandrel bar into contact with a pipe and moving it according to the roll interval change in the vicinity of the pipe end. CONSTITUTION:The mandrel bar 2 having a regular part 2a and tapered part 2b is used and it is displaced to the upper stream side than the terminal of a roll bite part at the front end of the regular part 2a thereof, in the case of the rolling start. When the front end of the above mentioned regular part 2a reaches the above terminal with the movement being started together with the engagement of the pipe with the roll bite part, it is positioned so that the front end of the pipe reaches the same point simultaneously with it. Simultaneously the movement of the mandrel bar from the initial position is made at the speed decided so that its arrival and that of the pipe rear end to the roll bite part start point may be carried out simultaneously, while until the rear end of the regular part 2a reaches the roll bite part terminal. The no contribution part in the rolling of the pipe does not priority is caused in the thermal load and lubricity and a high internal face quality can be obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention uses a mandrel bar as an inclined roll and an inner surface regulating tool in a Mannesmann pipe manufacturing line, for example, in order to reduce the thickness J7 of the raw pipe obtained with a piercer. The present invention relates to a method for inclined rolling of pipes performed using -.

[Prior art]

A method for inclined stretching and rolling of a pipe, which is carried out to reduce the wall thickness between inclined rolls arranged around the pass line of the pipe and an inner surface regulating tool penetrated into the inside of the pipe, includes The plug method and the mandrel bar method
However, for boat fishing, the latter method is superior in terms of inner surface quality and wall thickness accuracy of the rolled tube. This is due to the fact that the plug has a bullet shape and is not moved during rolling, whereas the mandrel bar is columnar and is moved during rolling. This is because the latter, which has a longer contact length, has an advantage in terms of load and lubricity.

That is, when elongation rolling is performed while moving the mandrel bar in the same direction as the tube, different parts of the mandrel bar sequentially contact the tube being rolled, which provides superiority in the heat load and lubricity. Therefore, when product pipes are required to have high inner surface quality and wall thickness accuracy, an inclined stretch rolling method is used in which a mandrel bar is moved at a predetermined speed.

In this inclined stretch rolling method, by increasing the moving speed of the mandrel bar and increasing the length of the mandrel bar that contacts the tube per unit rolling length, it is possible to further improve the inner surface quality and wall thickness accuracy.

Figure 9 shows various changes in the moving speed of the mandrel bar,
This is a graph showing the results of measuring the inner surface roughness of the obtained tube. The horizontal axis of the figure is the ratio of the moving speed of the mandrel bar to the entrance speed of the tube (bar speed ratio), and the vertical axis is the inner surface roughness of the tube. The 10-point average roughness is shown respectively. It is clear from this figure that the inner surface quality improves with increasing bar speed ratio, i.e. increasing the speed of movement of the mandrel bar.

However, when a high moving speed is applied to the mandrel bar, a long mandrel bar is required to be positioned inside the tube at the location where the rolling rolls are arranged until the entire length of the tube is rolled. is necessary and is not realistic. In reality, the length of the mandrel bar is limited due to bearing problems and tool costs, so it is necessary to use the mandrel bar of limited length as effectively as possible to meet the above requirements. This has become an important issue for responding to these demands.

FIGS. 10(a) to (C1) are schematic diagrams showing the implementation state of the conventional inclined stretch rolling method aimed at effectively using the entire length of the mandrel bar. Between the mandrel bar 20, which advances on X-X in the direction shown by the white arrow in the figure and penetrates into the interior thereof, and the rolling rolls 1.1 arranged around the bus line X-X. The inlet side of the rolling rolls 1, 1 is a thick-thickness rolling part 1a composed of an inclined surface that approaches the pass line x-X as it approaches the exit side. Lower part 1a
The part connected to the outlet side is a ring part 1b formed of a surface substantially parallel to the pass line The pipe P is then held between the reeling part 1b and the mandrel bar 20, and the wall thickness is reduced by stretching at + and H, respectively, and the pipe P having the desired wall thickness is sent out. . That is, the part (roll bite part) of the rolling roll 1 involved in stretching the raw pipe H extends from the position where the biting occurs between the thick rolling part 1a and the mandrel bar 20 to the rear end position of the reeling part 1b. It is between.

Figure 10fa) shows the state at the start of rolling, and Figure 10fa) shows the state at the start of rolling.
C1 is the state immediately before the end of rolling. Mandrel bar-20
has an effective part processed to have an equal diameter, and when starting rolling, the front end of the effective part in the advancing direction is aligned with the end point of the roll bite part, that is, the rear end of the reeling part 1b. , the front end of the raw pipe H in the advancing direction reaches the starting point of the roll hide part, and the end part is caught between the thick-walled part 1a and the mandrel bar 20. There is no way to start moving. The moving speed of the mandrel bar 20 is determined so that the rear end of the effective portion and the rear end of the blank pipe F (rear end) simultaneously reach the starting point of the roll hide portion, as shown in FIG. 10(C). As a result, as is clear from FIGS. 10(a) to (C1), the mandrel bar 2 is
The pipe P can contribute to substantially the entire length of the effective part of 0, and a pipe P having high inner surface quality can be obtained.

[Problem to be solved by the invention]

However, in this case, the mandrel bar 20 is still moving even after the start of rolling until the front end of the raw tube I4 reaches the end point of the roll bite section, that is, the rear end of the reeling section 1b. ), as shown in the figure, the mandrel bar 20
The length corresponding to the moving distance from the front end of the effective part to this distance,
The part does not contact the raw pipe H and cannot contribute to rolling, and the existence of this non-contributing part with a length of L8 puts a limit on the improvement of the inner surface quality of the obtained pipe P. There was a problem.

In addition, it is known that in the part rolled after the time shown in Figure 1O (ci), the wall of the rolled pipe P becomes thinner as it reaches the rear end, and this thinning is caused by the next rolling mill. In finishing rolling mills where relaxation cannot be expected, the cropping amount increases and the yield decreases. This is a graph showing the wall thickness distribution in the longitudinal direction of the pipe in correspondence.From this figure, it is clear that the wall thickness decreases over a considerable length range from the front and rear ends, and that It can be seen that the rolling load decreases in accordance with the range.
This occurs because the contact length between the roll hide part of the rolling rolls 1 and the raw pipe H gradually decreases as the raw pipe H progresses.On the other hand, there is a difference between the rolling load and the roll opening degree. There is a relationship as shown in Fig. 12, and the roll opening degree decreases as the rolling load decreases.This is because the rolling roll 1.1 is not a completely rigid body but an elastic body with a predetermined amount of mill spring. This is because the gap between both rolls 1, 1, that is, the roll opening degree changes according to the saturation rigidity tth line in FIG. 12 in accordance with changes in rolling load.

The present invention was made in view of the above circumstances, and it is possible to make the entire length of the effective part of the mandrel bar contribute to rolling, to obtain the highest possible inner surface quality with a mandrel bar of a limited length of five, and to improve the quality of the inner surface after rolling. An object of the present invention is to provide a method for inclined stretching and rolling of a pipe, which can alleviate the thinning that occurs at the front and rear ends of the pipe and achieve high wall thickness accuracy over the entire length.

[Means to solve the problem]

The method for inclined stretch rolling of a pipe according to the present invention comprises a mandrel bar that is penetrated inside the pipe and moves in the same direction, and a roll of inclined rolls arranged around the base line of the pipe, which moves at a predetermined speed. In the method of stretching and rolling between the roll bit part and the roll bit part, there is provided a tapered part that is longer than the roll bite part and whose diameter decreases toward the rear end in the moving direction, and a tapered part of an appropriate length that is connected to the front side of the tapered part. the initial position of the mandrel bar at the start of rolling and the moving speed until the rear end of the equal diameter part in the moving direction reaches the end point of the roll bite part; under the condition that the rear end and the rear end of the tube in the traveling direction simultaneously reach the start point of the roll bite section, and the front end of the equal diameter section and the front end of the tube simultaneously reach the end point of the roll bite section, An end point is determined based on the advancing speed of the tube and based on the actual results of thinning that occurs at the rear end of the tube after rolling, and the end point is determined in the middle of the tapered part, and the end point and the rear end of the tube are determined. The present invention is characterized in that the moving speed of the mandrel bar after reaching the end point of the roll bite portion is continuously changed so that the end point of the roll bite portion is reached at the same time.

[Effect]

In the present invention, a mandrel bar having an equal diameter part and a tapered part is used, and when rolling starts, the mandrel bar
The front end of the equal diameter part is located upstream of the end point of the roll bite part, and when the pipe is bit into the roll bite part, it starts moving, and the front end of the equal diameter part is located upstream of the end point of the roll bite part. When the end point is reached, the front end of the tube is positioned so that it reaches the same point at the same time, and the mandrel bar is moved from this initial position until the rear end of the equal diameter section reaches the end point of the rolled hide section. During this period, the speed is determined so that this arrival and the start point of the roll bite part of the front and rear ends occur simultaneously, and from this point on, the rear end of the pipe and the taper are The speed is continuously changed so that the end point set in the middle of the part reaches the end point of the roll bite part at the same time.

〔Example〕

The present invention will be described in detail below with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram of an apparatus used to carry out the method of inclined stretching and rolling of pipes according to the present invention (hereinafter referred to as the method of the present invention).

The raw pipe H before rolling advances on the pass line XX in the direction shown by the white arrow in the figure, and there is a mandrel bar 2 placed inside it and a mandrel bar 2 disposed around the bus line XX. The tube P is stretched between a pair of rolled rolls 1.1 and sent out as a tube P having a desired wall thickness. The rolling roll 1.1 is
They are arranged at a predetermined intersecting angle T and a predetermined inclination angle β (not shown) with respect to the pass line The advancing force of the raw pipe H is mainly caused by the rolling roll 1.
．． It is given by one rotation. Further, on both sides of the raw pipe I at the location where the rolling rolls 1, 1 are arranged, day scrolls, plates, roller guide shoes, etc. (not shown) are arranged to restrict the movement of the raw pipe I in the radial direction during rolling. ing.

The mandrel bar 2 is fixed to the tip of a retainer 3 extending from the exit side of the rolling rolls 1, 1 on the pass line XX, and the base end of the retainer 3 is connected to the motor M, for example. It is connected to a bar drive section 4 comprising a chain R driven by the chain R. And mandrel bar-2
is moved in the same direction as the raw tube H along the pass line XX in accordance with the operation of the bar drive unit 4 transmitted via the retainer 3. FIG. 2 is an enlarged view of the mandrel bar 2. As shown in the figure, the mandrel bar 2 is provided with an equal diameter portion 2a having a constant outer diameter Dbs and a length Lbs on the side fixed to the retainer 3, that is, on the front side in the moving direction.
On the rear side, the diameter decreases as it reaches the end, and the length is Ll + L.
When rolling the raw pipe H, all of the equal diameter part 2a and part or all of the tapered part 2b are used as effective parts contributing to rolling, as will be described later.

The driving source of the bar driving section 4, in other words, the mandrel bar
The motor M, which is the drive source of the motor 2, is driven according to a speed control signal given from the calculation side 1ff11 section 5, and the rotational speed of the motor M obtained by this driving is the same as the rotational speed of the motor attached to it. It is detected by the detector 10, and the detection result is given to the arithmetic control section 5 as a feed bank signal. As a result, the mandrel bar 2
can move at a speed determined by the arithmetic control section 5 as described later. The calculation control unit 5 includes
Roll roll 1. Load detector IL 11 attached to 1
Therefore, the detection result of the rolling load on the roll 1.1 is
Further, a power detector 12 (not shown) attached to these drive sources provides a detection result of the rolling power, and a roll gap detector 13 interposed between both rolls 1.1 provides a detection result of the roll opening. It is being Further, the arithmetic control section 5 is given the detection result of the wall thickness of the tube P from a thickness detector 14 arranged facing the outside of the tube P on the exit side of the rolling roll 1. For example, a position detector 14 disposed facing a part of the retainer 3 provides a detection result of the moving position of the mandrel bar 2. Furthermore, the arithmetic control unit 5 includes
Dimensions of the raw pipe H and its advancing speed (inlet speed V,), dimensions of the pipe P after rolling and its advancing speed (outlet speed ■)
, the dimensions of each part of the rolling roll 1.1, the set value of the roll opening degree, the dimensions of each part of the mandrel bar 2, and past performance data regarding the thinning that occurs at the rear end of the pipe P, etc., as will be described later. Various related rolling data are given in advance from an external input device (not shown).

FIGS. 3(a) to 3(dl) are schematic diagrams showing the implementation state of the method of the present invention. As shown in this figure and FIG. 1, the inlet side of the rolling roll 1. Line X
The thickness reduction part 1a is formed of an inclined surface approaching -x, and the part that continues to the exit side of the thickness reduction part 1a is formed of a surface parallel to the pass line XX. Tari-
This is a ring portion 1b. The raw tube H traveling on the pass line It is held in between and stretched from the position where the biting occurs to the rear end of the reeling part 1b (roll bite part).

FIG. 3(a) shows the state in which the front end of the raw pipe H has reached the starting point of the roll bite part and is bitten between the thick-walled rolling part 1a and the mandrel bar 2, that is, the state at the start of rolling. FIG. 3(b) shows the state when the raw pipe H has further advanced and its front end has reached the end point of the roll bite section, that is, the rear end of the reeling section 1b. Figure 3 (C) shows the state in which the rear end of the raw pipe I (the rear end has reached the starting point of the roll bite part), and Figure 3 (fd) shows the state in which the rear end of the raw pipe H has reached the end point of the roll bite part. The figure shows the state reached, that is, the state at the end of rolling.

In the method of the present invention, at the start of rolling, that is, as shown in FIG.
The initial position of the mandrel bar 2 in the state shown in FIG. It is set so that it reaches the end point of the roll bite part with
In addition, when the rear end of the raw pipe (■) reaches the starting point of the roll hide part, that is, when the state shown in FIG. The moving speed of the mandrel bar 2 up to this point is determined so that the rear end of the equal diameter section 2a reaches the end point of the roll bite section.

The initial position and moving speed of the two are determined as follows.

The initial position of the mandrel bar 2 is determined by the protrusion length Lt of the front end of the equal diameter portion 2a from the starting point of the roll hide portion in the moving direction.
(Refer to Fig. 3) As a representative example, when the moving speed is Vbs, the 4; 1 end of the equal diameter portion 2a and the front end of the blank pipe 11 reach the end point of the roll bite portion at the same time, that is, the Figure 3 (b
) If the following formula (1) is established from the condition that the state shown in ) is realized, then Lr Lt −Vbs・T + −(1)
The condition is that when the rear end of the raw pipe I (reaches the point of the roll hide part, the rear end of the equal diameter part 2a coincides with the end point of the roll hide part, that is, the state shown in FIG. 3 (C1) is realized. Therefore, the following (2) 2 holds true.

Lr Lt + Lbs-Vbs ・TZ ・(2
) In these formulas (fl), (2), Ll is the length of the roll hide portion, and Lbs is the length of the equal diameter portion 2a as described above.

Also, T is the time required for the tip of the raw pipe H to pass through the roll hide part, and T2 is the time required for the tip/end of the raw pipe H to be bitten by the roll bite part until the rear end is bitten. time,
That is, it is the time from when the front end of the raw pipe 11 reaches the starting point of the rolled hide section until the rear end reaches the same point.

Among these values, Lbs is a value specific to the mandrel bar 2, and T2 can be easily determined from the length of the blank tube 11 and its advancing speed (inlet side speed V,).

Further, Lr is the sum of the length of the part that contributes to rolling in the thick rolling part 1a and the length of the reeling part 1b, and the unknown former is the roll spacing distribution in the axial direction in the thick rolling part 1a, the mandrel bar It can be calculated from the outer diameter of the equal diameter portion 2a at -2, and the dimensions of the raw pipe I, and furthermore, T is the calculated roll bite length, the entry speed V, and the exit speed ■. It can be found from

Therefore, the above equations (1) and (2) can be expressed as follows:
The moving speed V and the protrusion length LL are two-dimensional simultaneous equation 2, for example.

The movement speed Vbs is determined by the following (3) 2 obtained by erasing
is obtained, and by substituting this into (1)2, the protrusion length representative of the initial position of the mandrel bar 2 is obtained.

Now, by executing vbs and LL determined in this way, when the state shown in FIG. Therefore, in order to perform subsequent rolling without any trouble, the length bL of the tapered part 2b must be equal to the length 8 of the roll bite part.
It is necessary that the value is 1 or more, and it is required that the following (4) 2 is satisfied.

Lbt≧L, ...(4) In order to shorten the mandrel bar 2, it is desirable to make Lbt equal to or greater than 2, but it is necessary to take into account that an error will occur in the subsequent speed adjustment as described below. However, in order to ensure the presence of the tapered part 2b inside the raw pipe H during rolling, the length Lbt of the tapered part 2b is preferably slightly longer than the length of the roll bite part.

This calculation is performed in the calculation control section 5 using rolling data manually inputted in advance, prior to the start of rolling.The calculation control section 5 issues a drive command to the bar drive section 4, Using the detection results of 14 as a feed bank signal,
Calculated overhang length.

In order to realize this, the mandrel bar 2 is moved and its initial position is set. After this, when the raw pipe H is bitten into the roll bit part and becomes the state shown in FIG. The mandrel bar 2 should be recognized and issued a speed control signal to the par drive unit 4, and the mandrel bar 2 should be moved at the calculated moving speed Vbi using the detection result of the rotational speed detector IO as a feedback signal (operating. As a result of the operation, the mandrel bar 2 is moved at a constant speed, i.e., the moving speed 1, from the time when the front end of the blank pipe H reaches the starting point of the roll bite section until the rear end reaches the same point.

Next, the determination of the moving speed of the mandrel bar 2 during the period from the state shown in FIG. 3(C) to the state shown in FIG. do.

During this time, the moving speed of the mandrel bar 2 is V b t ,
This is determined in order to prevent thinning of the rear end of the pipe P after rolling. For this reason, the results of wall thickness measurements in rolling performed using a conventional mandrel bar (mandrel bar 20 in FIG. 10) whose effective section length is the same diameter are used. FIG. 4 is an enlarged graph showing the vicinity of the tube end of the wall thickness measurement results.

As described above, the thinning of the tube P is caused by the contact length between the raw tube H and the roll bite portion decreasing as the raw tube H advances after the state shown in FIG. 3 (C1), and the rolling roll 1. As a result, as shown in Fig. 4, the pipe P has a portion spaced apart from the rear end by a predetermined length (Fig. Thinning occurs from the pipe end (part of the pipe), and the maximum thickness reduction occurs at the rear end due to the approximately linear thickness reduction.In the method of the present invention, as shown in Fig. 4, the maximum thickness reduction occurs at the pipe end. The amount Δt, the distance Zp from the starting point of thinning to the tube end, and the inclination angle α when the distance is approximated by a straight line are used.

The following relationship (5) holds between these multi-values.

Δt=Z, ・tan α, ・(5) On the other hand, the second
As shown in the figure, if the taper surface angle of the tapered portion 2b is α, the outer diameter I)bt at a portion where the distance from the starting point of the tapered portion 2b is ZL is determined by the following equation (6). .

Dbt”Dbs 2 ・Zt ・tan α,
...-(ct+However, Dbs is equal diameter part 2a as mentioned above)
is the outer diameter of

Now, the wall thickness of the pipe P is controlled by the rolling state at the end of the roll bite part of the rolling rolls 1, 1, that is, at the rear end of the reeling part 1b, and at the rear end of the reeling part 1b and the matching part thereof. It is known that the gap is approximately equal to the gap between the mandrel bar 2 and the outer periphery thereof. Therefore, when the roll gap at the rear end of the reeling part 1b is 04 and the outer diameter of the mandrel bar 2 is D5, the wall thickness t of the part extracted from the roll bite part is expressed by the following equation (7). Ru.

t = (Gro-Db) /2 (7) As mentioned above, the thinning of the pipe P occurs due to the decrease in G□ in the above formula (7) during rolling near the front and rear ends. , this reduced state of Go appears as a thinned state of the pipe P obtained by using a mandrel bar whose effective part has the same diameter over the entire length. Further, the starting point of the thinning of the pipe P and the starting point of the tapered portion 2b of the mandrel bar 2 coincide in the state shown in FIG. 3(C). Therefore, the moving speed V of the mandrel bar 2 from the state shown in FIG. 3(C) to the state shown in FIG. 3(d)
61 is determined so that the decrease in the roll spacing G ra is offset by the decrease in the outer diameter 1) bt at the tapered portion 2b, thereby maintaining the wall thickness of the resulting pipe P approximately constant;
It becomes possible to significantly reduce the occurrence of wall thinning.

This means that an end point 2c (see Fig. 2) is set in the middle of the tapered portion 2b at which the outer diameter decreases from the outer diameter I)bs of the equal diameter portion 2a by twice the maximum thickness reduction Δt. However, this end point 2c is achieved by determining the moving speed V0 under the condition that the end point 2c coincides with the end point of the roll bite portion at the end of rolling (the state shown in FIG. 3(d)). Tapered part 2
If the distance from the start point of b to the end point 2c is 21, the outside jl D b t at the end point 2c is the (
Since it is given by Equation 6), the above-mentioned condition is satisfied by this and Equation (5) when the following (8) 2 is satisfied.

Z, ・tan cx, =Z1 ・tan α,
...(s) In equation (8), Z, and Zt are all functions of time T starting from the time point in FIG. speed of progress,
That is, it is expressed by the following equation (9) using the outlet speed V0.

Z, -V.・T...(9) On the other hand, zt is obtained using the moving speed VbL of the mandrel bar 2, but until this speed VbL is achieved, the constant speed ■ before the state of C1 in FIG. It is necessary to increase or decrease the speed of the mandrel bar during this speed change.
If the moving distance of the mandrel bar 2 is l6 and the moving distance of the pipe P is 7!2, then the mandrel bar 2 will require the elapsed time T from the state shown in Fig. 3(C) and the distance 1p required for the pipe P to move. time 7
! p/■. Since it moves at the speed Vbt between this difference,
The following 00)2 holds true.

By substituting this formula into (8)2 and transforming it into a formula for determining VbL, the following 002 is obtained.

...OD In other words, in (C) to (dl in Fig. 3), when the mandrel bar 2 is given a moving speed ■ that changes as shown by the 0υ formula with respect to time T, the rolling roll 1 changes during tube end rolling. .1
The change in the roll gap G9 that occurs between the tubes is offset by the diameter reduction of the tapered portion 2b, and thinning at the tube end can be eliminated.

The calculation of the moving speed VbL as described above is performed in the calculation control section 5 using rolling data manually inputted in advance, prior to the start of rolling. In order to make this possible, the arithmetic control unit 5
The data for measuring the known wall thickness shown in FIG. 4, which was obtained by rolling using a mandrel bar having the same diameter over the entire length, is input in advance. As for the input values, only the maximum thickness reduction amount Δt, the distance Zp from the start point of thinning to the pipe end, and the inclination angle α2 are sufficient. It is desirable to perform these calculations. Further, ll and l in the formula 00 can be determined in the arithmetic control section 5 from the required shift amount from Vbs to Vbt and the characteristics of the bar drive section 4, and α9. Both α and Vo are given to the calculation control section 5 as rolling data. The arithmetic control unit 5
Between figures (a) to (C), after issuing a speed control signal to maintain a constant movement speed Vbi, the movement speed corresponds to ■1,
A speed control signal that changes according to time T is generated, and the detection result of the rotational speed detector 10 is used as a feedback signal to operate to move the mandrel bar 2 at the moving speed VIAL. As a result, when rolling near the pipe end where thinning occurs, stretching is performed between the rolling rolls 1, 1 and the tapered portion 2b whose diameter is successively reduced, thereby preventing the thinning from occurring. . During the rolling of the tube end, the detection results of the roll gap detector 13 and wall thickness detector 15 are sequentially taken in, and correspond to the detection results of the position detector 14 that detects the moving position of the mandrel bar 2. It will be remembered. This stored result is used to change the timing of switching from ① to ② and to correct the calculation result of VbL in the next step of rolling.

By implementing the method of the present invention as described above, FIGS.
As shown in d), all of the effective parts of the mandrel bar 2, that is, the equal diameter part 2a and the tapered part 2b, come into contact with the raw pipe H at some point during rolling, and the rolling of the raw pipe H Since no non-contributing parts are generated, it is clear that the heat load and lubricity during rolling are excellent, and a pipe P having high inner surface quality can be obtained.

FIG. 5 is a graph showing the measurement results of the inner surface roughness of the tube P obtained by implementing the method of the present invention, and FIG. 6 is a similar graph of the tube P obtained by the conventional method.

Note that both of these rolls have a diameter of 350 mm, an IIPI length of 200 mm, and an effective length (=L bs + L
bt) In an inclined stretch rolling mill equipped with a 215 mm mandrel bar, the outer diameter is 60 mm and the wall thickness is 8 mm.
The length is 300mm.

10 each of 500mm and 600mm raw tubes H (total 3
0), the human speed V was 50 mm/s, and the stretching ratio was 2.
This is the result of stretching and rolling under conditions of 0. When comparing FIG. 5 and FIG. 6, there is clearly a significant difference between the two, and it can be seen that the internal quality of the product tube is improved by implementing the method of the present invention.

Moreover, FIG. 7 is a graph showing the 1(ll) constant result of the wall thickness distribution in pipe P4 obtained by implementing the method of the present invention, and FIG. 8 is a graph showing the same result in pipe I) obtained by the conventional method. It is a graph.

Both of these have a diameter of 350n+m and a body length of 200m.
In an inclined stretch rolling mill equipped with m+n rolling rolls and a mandrel bar 2 with an effective length of 215 mm, the outer diameter is 6 On.
on.

Wall thickness is 8mm1. A raw tube I4 with a length of 300 mm,
This is the result of stretching and rolling under the conditions that the entrance speed (1) was 50 mm/s and the stretching ratio was 2.0. Note that when implementing the method of the present invention, the length L bt of the tapered portion 2b is 100 m.
A mandrel bar 2 with a taper angle α of 0.76 was used. When comparing FIG. 7 and FIG. 8, there is a clear significant difference between the two. In the conventional method, thinning occurs from a position approximately 100 mm away from the tube end, whereas in the method of the present invention, It is clear that the thinning occurs only in the very vicinity of the tube end, and that the thinning can be solved by implementing the method of the present invention.

In this example, the case where the mandrel bar 2 is supported on the exit side of the rolling roll 1.1 has been described, but it goes without saying that the method of the present invention can also be applied to the case where the mandrel bar 2 is supported on the entry side. stomach.

〔effect〕

As detailed above, in the method of the present invention, a mandrel bar having an equal diameter part and a tapered part continuous to the rear side of the mandrel bar is used, and the entire length of the effective part of the mandrel bar is in contact with the pipe, and the part near the end of the mandrel bar is in contact with the pipe. During rolling, the taper part is used and the mandrel bar moves to change the outer diameter in accordance with the change in the roll interval, so there is no part that does not contribute to the rolling of the tube, compared to the conventional method where there is a non-contributing part. Further advantages in heat load and lubricity during rolling are achieved, resulting in the highest possible internal surface quality for a mandrel bar of limited length, and the same internal surface quality can be achieved in a shorter length than before. The present invention exhibits excellent effects, such as being able to guarantee this with a mandrel bar of the same size, and also being able to almost completely eliminate the thinning that conventionally occurs at the tube end, thereby achieving an improvement in product yield.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus used to carry out the method of the present invention, and FIG. 2 is a block diagram of a mandrel bar used to carry out the method of the present invention.
, FIG. 3 is a schematic diagram showing the implementation state of the method of the present invention, FIG. 4 is an explanatory diagram of quantification of thin-walled parts, and FIG. 5 is a measurement of the inner surface roughness of the tube obtained by the method of the present invention. A graph showing the results, FIG. 6 is a graph showing the measurement results of the inner surface roughness of the tube obtained by the conventional method, and FIG. 7 is a graph showing the measurement results of the wall thickness distribution of the tube obtained by the method of the present invention. Figure 8 is a graph showing the measurement results of the wall thickness distribution of the pipe obtained by the conventional method.
Figure 9 is a graph showing the correlation between the moving speed of the mandrel bar and the inner surface roughness of the product tube, Figure 1O is a schematic diagram showing the state of implementation of the conventional method, and Figure 11 is the rolling load when implementing the conventional method. Graph showing temporal changes in average wall thickness and average wall thickness, 12th
The figure shows the mill stiffness curve.

Claims (1)

[Scope of Claims] 1. A mandrel bar that penetrates inside a pipe that moves at a predetermined speed and moves in the same direction; and a roll bite section of inclined rolls arranged around the pass line of the pipe. In the method of elongation rolling, the tapered part is longer than the roll bite part and is reduced in diameter as it reaches the rear end in the moving direction, and the equal diameter part of an appropriate length is connected to the front side of the tapered part. The initial position of the mandrel bar at the start of rolling and the moving speed until the rear end of the equal diameter part in the moving direction reaches the end point of the roll bite part are determined as described above. of the tube under the conditions that the rear end and the rear end in the traveling direction of the tube simultaneously reach the start point of the roll bite section, and the front end of the equal diameter section and the front end of the tube simultaneously reach the end point of the roll bite section. An end point is determined in the middle of the tapered part based on the progress speed and the actual result of thinning that occurs at the rear end of the tube after rolling, and the end point and the rear end of the tube are connected to the roll bite. 1. A method for inclined stretching and rolling of a pipe, characterized in that the moving speed of the mandrel bar is continuously changed after reaching the end points of the sections at the same time.