JPH05304A - Method for stretch reducing tube - Google Patents

Abstract

PURPOSE:To efficiently prevent the generation of thickened part where allowable dimension is added to both tube ends of a roll finished tube at the time of stretch reducing a tube. CONSTITUTION:A formula of wall thickness on the outlet side of stand with which the wall thickness is given and formula of forward slip with which forward slip is given in the case the tube is rolled under tensionless state are preliminarily set by respectively taking them as the function of rolling factors and the wall thickness on the outlet side of stand determined by substituting the values of prescribed rolling factors for the above-mentioned formula of wall thickness about each stand and the speed of material on the outlet side of stand is determined from the determined wall thickness and condition that mass flow is constant. The forward slip is determined by substituting the values of prescribed rolling factors for the above-mentioned formula of forward slip and the circumferential speed of roll at the stand is determined from the determined speed of material on the outlet side and the forward slip. Under the revolving speed of roll that is determined from that circumferential speed of roll, the tube is stretch reduced by driving a continuous multiple roll mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing and rolling a pipe, and more particularly, to a rolled finished pipe having an outer diameter and wall thickness of a target dimension by drawing and rolling a steel pipe produced in a drawing and rolling step which is a preceding step The present invention relates to a method for drawing and rolling a tube, which is suitable to be applied when manufacturing.

[0002]

2. Description of the Related Art A typical example of a method for producing a seamless steel pipe, which is one of the seamless pipes, will be briefly described with reference to the process diagram of FIG.

First, a raw material 10 (for example, round steel) is prepared. The material 10 is heated to a required temperature by a heating furnace 12, and then sent to a piercing and rolling machine 14 (for example, a Mannesmann piercer) to be piercing-rolled and processed into a hollow rod-shaped material 16.

Since the hollow rod-shaped material 16 thus formed by piercing and rolling is still thick, the mandrel bar 18 is inserted in order to reduce the wall thickness by the next drawing and rolling machine 20 (for example, mandrel mill). In this state, it is stretch-rolled and processed into the raw pipe 22 to be supplied to the following drawing-rolling machine 26.

The raw tube 22 formed by drawing and rolling
Is heated again to a required temperature by a heating furnace 24, and then sent to a drawing and rolling mill 26 (for example, a stretch reducer) and drawn and drawn to a required size to form a finished pipe 28.

As the reduction rolling machine applied to the above reduction rolling, the stretch reducer constituted by rolling rolls of 8 to 28 stands is most widely adopted.

In this stretch reducer, generally,
The outer diameter of the product (finished pipe 28) is fixed at the same time by applying the tension between the stands while applying an outer diameter reduction of 5 to 7% per one stand to squeeze and roll the raw pipe 22.
We are adjusting the wall thickness.

As described above, the finished pipe 28 obtained by drawing rolling with a stretch reducer generally exhibits a wall thickness distribution having a constant portion with a constant wall thickness in the central portion in the longitudinal direction as shown in FIG. 5, for example. .

In the above-mentioned conventional drawing rolling, rolling is carried out so that the target wall thickness can be obtained in the above-mentioned steady part. However, when drawing rolling is carried out by such a method, it is increased to an extent exceeding the allowable dimension. Both of the fleshed pipe ends are cut off as crops, which significantly reduces the product yield. The total amount of both ends of the head and tail pipes of one steel pipe generally reaches 5 to 10% in weight ratio, which is a large economical loss.

The following (1) and (2) are methods for suppressing the above-mentioned phenomenon of wall thickening at both ends of the pipe as much as possible.
The technologies shown in (1) to (4) are disclosed in the following publications.

(1) Detecting the moment when both pipe ends, which trigger the change in tension, pass through the stands, it is determined that the state is a transient state, and the front roll between the stands in the transitional time zone. By making the difference in the number of rotations of the rear roll and the rear roll larger than in the steady state (steel pipe is bitten by the front stand), a tension equal to that in the steady state is applied to the raw pipe (Japanese Patent Publication No. 49-37340, JP-B-50-13232, JP-B-54-20458
issue).

(2) The amount of increase in wall thickness is predicted in advance, and a base pipe with thin wall thickness at both pipe ends is prepared by rolling or other method according to the amount of increase in wall thickness, and the base pipe is drawn and rolled. A method of offsetting the wall thickness of the thickened portion by rolling in (Japanese Patent Publication No. 50-15232, Japanese Patent Publication No. 51-43825).

[0013]

However, in the method (1) described above, it is necessary to accurately detect that both ends of the head and tail of the steel pipe are approaching the stand, but the detection accuracy is limited. Yes, and when the head tube end reaches the stand and the material is caught in the roll,
Despite the complicated control method due to the temporary decrease in roll rotation speed and its recovery phenomenon, etc.,
On the other hand, the effect of reducing (shortening) the crop is not so great, and it is practically impossible to reduce the crop length to, for example, 4 to 5 m or less, and there is a limit in this respect.

The above method (2) is not practical because it not only complicates the process but is also disadvantageous in terms of cost.

Therefore, even with the techniques (1) and (2), it is not possible to effectively prevent the increase in the thickness of both ends of the rolled finished pipe in the reduction rolling process, so that the allowable dimension is exceeded. The thickened portion will be cut off as a crop, which inevitably causes a significant decrease in product yield, which remains a problem.

The present invention has been made to solve the above-mentioned conventional problems, and it is effective that a thickened portion exceeding the allowable dimension is generated at both pipe end portions of the rolled finished pipe when the pipe is drawn and rolled. It is an object of the present invention to provide a method for drawing and rolling a pipe which can be prevented.

[0017]

DISCLOSURE OF THE INVENTION The present invention is directed to a pipe drawing method for drawing a pipe by a continuous multi-stage rolling mill,
When rolling in a non-tensioned state, a stand-out side wall thickness formula that gives the stand-out side wall thickness and an advance rate formula that gives the advance rate are set in advance as functions of rolling factors. The value of the predetermined rolling factor is substituted into the side wall thickness formula to obtain the stand outlet side wall thickness, and the stand outlet side outlet material speed is determined from the obtained stand outlet side wall thickness and constant mass flow conditions, and , The advance rate was obtained by substituting the value of a predetermined rolling factor into the advance rate formula, and the roll peripheral speed of each stand was obtained from the obtained delivery side material speed and the advance rate, and was obtained from the roll peripheral speed. The above problems are achieved by driving a continuous multi-stage rolling mill under the roll rotation speed to reduce the rolling of the pipe.

Further, in the present invention, in the above-mentioned pipe drawing rolling method, the stand outlet-side wall thickness formula is a function having the pipe inlet-side wall thickness, inlet-side outer diameter and contracted pipe ratio as variables. The above-mentioned problem is certainly achieved by assuming that the formula is a function having the inlet outer diameter of the pipe and the contraction rate as variables.

[0019]

The present inventor has made various studies on the phenomenon of thickening that occurs at both ends of the head and tail of the finished rolled pipe when the raw pipe is drawn and rolled, and has obtained the following findings.

In the conventional pipe rolling method, the roll rotation speed is determined so that the tension between the stands is applied to match the finished tube with the target dimension, but the tension between the stands to be applied at that time is large. At times, it was found that there was a large tendency for thickening to occur. From this, it is considered that the cause of the wall thickness increase at both ends of the head and tail pipes of the finished rolled pipe is due to the inter-stand tension applied during rolling.

That is, in the conventional squeeze rolling method, the tension between the stands is positively applied, and the number of rotations of the roll is determined and rolled so that the wall thickness of the finished pipe reaches the target value in that state. However, in this method, as shown in FIG.
Although the target wall thickness can be obtained at the steady portion (the central portion in the longitudinal direction of the pipe), both the head and tail pipe ends of the pipe are held by a smaller number of stands than the steady portion, so that the tension is not applied sufficiently. Regardless of the fact that only the outer diameter of the pipe is reduced, it is considered that the phenomenon of thickening occurs.

The present invention has been made on the basis of the above findings, and provides a stand-out side wall thickness that gives a stand-out side wall thickness when rolled in a state where tension-free is achieved (a state in which tension is not applied between stands). The wall thickness formula and the advanced ratio formula that gives the advanced ratio are set in advance as functions of rolling conditions (factors), and the stand outlet wall thickness is calculated from the stand outlet wall thickness formula for each stand. And the outgoing material speed is obtained from the constant mass flow condition, and the advanced ratio is obtained from the advanced ratio formula, and the roll rotational speed is obtained from the roll peripheral speed obtained from the outgoing material speed and the advanced ratio. Therefore, by setting the roll rotation speed thus obtained for each stand, it becomes possible to perform the reduction rolling under the condition that no tension is generated between the respective stands during the reduction rolling. .

As a result, it is possible to suppress an increase in the thickness of both the head and tail pipe ends of the finished pipe caused by the tension, and to prevent the occurrence of crops.

An example of the result of carrying out the present invention is shown in FIG. In FIG. 3, the wall thickness distribution (average) in the longitudinal direction of many finished pipes obtained by carrying out the present invention is shown.

In FIG. 3A, the size of the raw pipe is 190.
0 mm, wall thickness 11.50 mm, finished pipe dimensions 12 OD
In the case of 7.0 mm and wall thickness 13.97 mm, the same figure (B)
Has an outer diameter of 190.0 mm and a wall thickness of 5.50 mm.
And, the dimensions of the finished pipe are 127.0 mm outer diameter and 6.72 inner diameter.
The thickness distribution is in the case of mm, and the thickness distribution in the longitudinal direction is shown when a reduction rolling mill consisting of 15 stands is used.

It can be seen from FIG. 3 that a finished pipe having a substantially uniform wall thickness over the entire length of the finished pipe and thus having less cropping is obtained.

As described above, according to the present invention, it is possible to suppress an increase in the thickness of both ends of the head and tail pipes of the rolled finished pipe, and since almost no cropping occurs, it is possible to greatly improve the product yield. Become.

[0028]

Embodiments of the present invention will now be described in detail with reference to the drawings.

In the present embodiment, the roll rotation speed of each stand is calculated according to the procedure of the flow chart shown in FIG. 1, the motor for driving the roll of each stand is controlled according to the calculated rotation speed, and each roll is adjusted to an appropriate roll. Rolling is performed under the condition that the rotation speed is set.

First, in step 1, the outlet side wall thickness of the I-th stand is determined from the stand outlet side wall thickness formula (1) described later.

Next, in step 2, from the outer diameter and wall thickness of the pipe on the stand-entry side (hereinafter, also referred to as the "entrance-side pipe, which is the raw pipe in the case of the first stand") and the inlet-side material velocity of the I-stand The mass flow is calculated, and the cross-sectional area Si is obtained by the equation (3) described later from the outlet wall thickness obtained in step 1 and the outlet outer diameter obtained from the product of the outer diameter of the inlet pipe and the contraction rate, The exit side material velocity Vi of the I-th stand is calculated by the equation (2) described later.

Next, in step 3, the advanced ratio of the I-th stand is obtained by using the advanced ratio formula (5) described later, and the process proceeds to step 4, and will be described later based on the advanced ratio calculated in step 3 (4). ) Calculate the roll peripheral speed of the No. 1 stand according to the formula).

In step 5, the roll rotation speed of the I-th stand is calculated based on the roll peripheral speed obtained in step 4.

Then, in step 6, it is judged whether or not the final stand is reached. If the determination result is negative and the setting of the rotation speeds for all the rolling rolls is not completed yet, the process returns to step 1 and a series of calculations are similarly performed for the next stand.

If the determination is positive, this procedure ends.

The processing according to each of the above-mentioned steps 1 to 5 is repeated to calculate the roll rotational speeds of all the stands of the continuous multi-high rolling mill, and the roll rotational speeds are set in the corresponding stands. The pipe is drawn and rolled.

By performing the squeeze-rolling of the raw pipe under the above conditions, it is possible to perform the rolling without substantially applying tension to the pipe, so that it is possible to suppress an increase in the thickness of both the head and tail ends of the finished pipe. Therefore, it is possible to reduce the crop and thus improve the yield.

For the above-mentioned drawing rolling, a drawing rolling machine whose basic constitution is substantially the same as that shown in FIG. 4 can be used.

This embodiment will be described in more detail. In addition,
In the following description, the notation of the I-th stand shown in the flowchart of FIG. 1 is referred to as the i-th stand for convenience.

First, a stand outlet-side wall thickness formula for obtaining a wall thickness t _i of a pipe on the outlet side of the i-th stand (hereinafter, also referred to as a outlet pipe) is set by the following model formula (1).

T _i = C1 + C2 · Ti + C3 · Di0 + C4 (ODR) (1)

This equation (1) is the size (control factor) of the inlet side pipe of the i-th stand, the inlet side wall thickness Ti and the inlet side outer diameter D.
This is a function with i0 and the reduced tube ratio ODR as variables, and has C1 to C
4 is a coefficient (constant).

The above-mentioned respective coefficients C1 to C4 are obtained by using a continuous multi-stage rolling mill and rolling the pipe within a range of predetermined rolling conditions and under a condition that tension-free is achieved (a condition in which tension is not applied between stands). By doing so, for example, the value of the outlet side wall thickness T1 of the first stand is actually obtained, and is determined by performing multiple regression.

Each coefficient C1 ~ determined by the multiple regression
Table 1 shows an example of the value of C4.

[0045]

[Table 1]

The coefficients C1 to C4 obtained by the multiple regression shown in Table 1 above have a correlation coefficient of around 0.99, so that they regress with extremely high accuracy and there is no problem in accuracy.

As described above, if the coefficients C1 to C4 are determined, the output side plate thickness t _i is determined by the equation (1) to be 3 of the inlet side wall thickness Ti, the inlet side outer diameter Di0 and the contraction rate ODR. It can be obtained by specifying two variables.

Under constant mass flow, the material velocity (average) on the outlet side of the i-th stand is calculated. That is, the mass flow is given by the product of the pipe cross-sectional area Si on the stand exit side and the exit-side material velocity Vi as shown in the following equation (2). The velocity Vi is determined. The mass flow can also be obtained as the product of the cross-sectional area of the tube on the stand-in side and the material velocity on the entrance side.

[0049]     Mass flow = Si x Vi (2)

The pipe cross-sectional area Si on the stand outlet side is given by the following equation (3) using the outlet side plate thickness t _i .

Si = t _i (D _i1 −t _i ) π (3)

Here, Di1 is the outlet side outer diameter (outer side tube outer diameter) in the i-th stand. This output side outer diameter Di1 is
It is given by the product of the entrance-side outer diameter Di0 and the reduced tube ratio ODR, and can also be obtained as the caliber diameter of the rolling roll.

By using the equations (1) to (3), the outlet material velocity Vi can be obtained from the equation (2) only from the control factors on the inlet side of the i-th stand.

On the other hand, the delivery side material velocity V of the i-th stand
i can be defined as shown in the following equation (4). Here, VRi is the roll groove bottom peripheral speed of the i-th stand (mm
/ Sec), and f _i is the advanced rate (%). Therefore, the advanced rate f
_{If i} is obtained, the roll groove bottom peripheral speed VRi can be obtained by using the delivery side material speed Vi obtained from the above equation (2), and the required roll rotation speed is obtained from this roll groove bottom peripheral speed. be able to.

Vi = VRi (1 + f _i ) ... (4)

Therefore, the advanced equation that gives the advanced rate f _i of the i-th stand is set by the model equation shown in the following equation (5).

F _i = x ₁ + x ₂ · ODR + x ₃ · Dio (5)

Then, as in the case of the delivery side wall thickness formula (1) described above, a continuous multi-stage rolling mill is used to roll the pipe under predetermined rolling conditions, and the above formula (4) is modified as follows. The advanced rate f _i of the i-th stand is obtained by the equation (6) and multiple regression is performed to determine the coefficients x _{1 to} x ₃ of the equation (5). Each coefficient x _{1 to} x determined by the multiple regression
Table 2 shows an example of the value of ₃ .

[0059]

[Table 2]

Coefficient x obtained by the multiple regression shown in Table 2 above
_{Since the} correlation coefficient of _{1 to} x ₃ is around 0.99, the regression is highly accurate and there is no problem in accuracy.

As described above, each coefficient x ₁ to equation (5) above
Once x ₃ is determined, the advanced rate f _i can be obtained by designating two variables of the contraction rate ODR and the entrance-side outer diameter Dio.

When the advanced ratio f _i is obtained in this way, the roll groove bottom peripheral velocity VR i of the i-th stand can be obtained from the equation (4).

Further, as shown in the equation (2), the mass flow is given by the product of the cross-sectional area of the pipe and the outlet material velocity Vi shown in the equation (4). Can also be expressed as. Therefore, the VRi can be calculated from the following equation (6).

[0064] _{f i = {(Vi -VRi)} / VRi} × 100 (%) ... (6)

The roll rotational speed of the i-th stand can be determined from the roll groove bottom peripheral velocity VRi obtained as described above.

By following the procedure detailed above, the first
It is possible to determine the roll rotation speed of all the stands from the stand to the final stand.

Next, the results obtained when the present embodiment was actually applied and the steel pipe was drawn and rolled will be shown. Specifically, it is intended to obtain a finished pipe having a target size from a raw pipe (steel pipe) having a size shown in Table 3 below.

[0068]

[Table 3]

That is, the outer diameter of the raw pipe before rolling is 190.0.
mm, wall thickness 5.56 mm, target dimension is 127.0 mm outer diameter,
When the wall thickness is 6.78 mm (invention example (1)), and when the raw pipe dimensions are 190.0 mm outside diameter, 7.00 mm thickness, and the target dimensions are 127.0 mm outside diameter and 8.62 mm thickness (Invention example (2)).

In each of the above cases, the number of used raw tubes was 200. In addition, the temperature of the raw tube on the 1st stand entrance side
20-930 degreeC, the 1st stand entrance side material (blank) speed was 1.24 m / sec. For comparison, the raw tubes shown in Table 3 were subjected to reduction rolling according to the conventional method under the conditions that the target wall thicknesses similar to those of the invention examples (1) and (2) were obtained (comparative example). (1), (2)).

FIG. 5 is a diagram showing the longitudinal wall thickness distributions of finished pipes according to Examples (1) and (2) of the present invention in comparison with Comparative Examples (1) and (2), respectively.

Further, the following Table 4 shows crop cut-off amounts in the case of the present invention example and the comparative example. Table 5 shows the shrinkage ratios used in this example and the comparative example.

[0073]

[Table 4]

[0074]

[Table 5]

As shown in Table 4, the crop cut-off amounts are 895 mm and 67 in the invention examples (1) and (2), respectively.
In contrast to 0 mm, Comparative Examples (1) and (2) have 2120 mm and 1960 mm, respectively. Therefore, it can be seen that the amount of crop cut-off can be significantly reduced and the yield can be significantly improved by adopting the present invention and performing reduction rolling.

Although the present invention has been specifically described above, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention.

[0077]

As described above, according to the present invention, it is possible to effectively prevent the phenomenon of thickening at both pipe end portions in the reduction rolling, so that the amount of crop cut-off is greatly reduced. Therefore, the yield can be significantly improved. Therefore, it has an excellent effect that the utility value is extremely high industrially.

[Brief description of drawings]

FIG. 1 is a flowchart showing a procedure of a main part of a reduction rolling method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a wall thickness distribution of a finished pipe obtained by this example.

FIG. 3 is a diagram for explaining the operation of the present invention.

FIG. 4 is an explanatory diagram showing an outline of a drawing rolling process.

FIG. 5 is a diagram showing a wall thickness distribution in a pipe longitudinal direction obtained by a conventional reduction rolling method.

[Explanation of symbols]

10 ... Material, 12, 24 ... Heating furnace, 14 ... piercing and rolling machine, 16 ... Hollow rod material, 18 ... Mandrel bar 20 ... Stretching rolling machine, 22 ... Tube, 26 ... Drawing rolling machine, 28 ... Finished tube.

Claims (2)

[Claims] Claim: What is claimed is: 1. A drawing method of a tube for drawing and rolling with a continuous multi-stage rolling mill, wherein a stand-out side wall thickness formula and an advanced rate are provided for giving a stand-out side wall thickness when rolling in a non-tension state. The advanced ratio formulas are preset as functions of rolling factors, and for each stand, the value of the predetermined rolling factor is substituted into the stand-out side wall thickness formula to obtain the stand-out side wall thickness, and the obtained stand-out face thickness is calculated. From the side wall thickness and constant mass flow conditions, find the outlet material speed on the stand outlet side,
Further, the value of a predetermined rolling factor is substituted into the above-mentioned advance rate formula to obtain the advance rate, the roll peripheral speed of each stand is obtained from the obtained delivery side material speed and the advance rate, and the roll peripheral speed is obtained. A method of drawing and rolling a pipe, characterized in that a continuous multi-stage rolling mill is driven under the roll rotation speed to draw and roll the pipe. 2. The stand outlet-side wall thickness formula is a function having the inlet-side wall thickness of the pipe, the inlet-side outer diameter, and the contraction ratio as variables, and the advanced ratio formula is the inlet-side pipe of the pipe. A method for drawing and rolling a pipe, which is a function having variables of an outer diameter and a reduced pipe ratio.