JPH09248605A - Method for pierce-rolling seamless metallic tube and pierce-rolling apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the defective ratio of a hollow stock tube and to improve the yield by predicting the fusing damage of the tip part of a plug based on the measured result of a measuring means of a billet progressing velocity and a measuring means of a piercing time and judging whether the plug can successively be used or not. SOLUTION: The billet progressing velosity (v) measured with the billet progressing velocity measuring means 6 and the piercing time (t) measured with the piercing time measuring means 9 are inputted into a calculating means 8. In the calculating means 8, the temp. at the tip part of the plug just after applying the pierce-rolling is obtd. by using a formula and calculating with a finite element method. In the case, the obtd. surface temp. at the tip part of the plug is higher than the m.p. of a surface scale of the plug as a calculation object, the tip part of the plug is fusing-damaged, and the plug is considered to be reached to the service life and a command to exchange into the new one is transferred. In the case the surface temp. at the tip part of the plug is lower than the m.p. of the surface scale of the plug, the temp. at the tip part of the plug is predicted by using the temp. thereof and calculating with the finite element method. Then, the calculating means judges whether the plug can successively be used or not.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a piercing and rolling method and a piercing and rolling apparatus for seamless metal pipes.

[0002]

2. Description of the Related Art As is well known, the so-called Mannesmann tube-making method, which is widely used as a method for producing a seamless metal tube, uses a solid round billet heated to a predetermined temperature as a raw material and punches this round billet. It is fed to a rolling mill (hereinafter referred to as a piercer) and a hole is bored in its shaft core to obtain a hollow shell. Then, the obtained hollow shell is used as it is, or if necessary, passed through an elongator having the same structure as the piercer to expand the diameter and reduce the thickness, and then fed to a subsequent drawing and rolling machine such as a plug mill or a mandrel mill. Stretch and roll.

[0003] After that, the finishing raw tube obtained by drawing and rolling is passed through a finishing rolling machine such as a reeler, sizer or stretch reducer to finish the finished product tube through a finishing step of polishing the tube, correcting the shape and sizing. Is.

FIG. 5 is a perspective view showing an example of a piercer used for carrying out the Mannesmann pipe manufacturing method as described above. The illustrated piercer includes a pair of main rolls 1 and 1 which are arranged to face each other with a pass line X-X serving as a feed line of a solid round billet 4 which is a material to be punched sandwiched in opposite directions. , The main roll is 90 ° out of phase with the pass line X
A pair of disk rolls 2 and 2 which are material guide members opposite to each other across -X are provided, and a plug 3 as a drilling tool is supported by a core metal 5 on the pass line XX. ing.

In the piercer constructed as described above, the main rolls 1 and 1 are rotated in the same direction while being provided with an inclination angle β with respect to the pass line XX. Therefore, the round billet 4 fed in the direction of the white arrow on the pass line X-X is screwed and moved after being caught between the main rolls 1 and 1, and the plug 3 makes a hole in its axial center portion. The hollow shell is opened. During this time, the disk rolls 2 and 2 are
It serves as a guide member for the round billet 4 during rolling, and at the same time, the main roll 1 of the hollow shell pierced by the plug 3.
1 has a role of controlling the bulge in the direction 90 ° in phase with the facing direction and adjusting the outer diameter shape. Further, the disc rolls 2 and 2 are rotationally driven in the same direction as the feeding direction of the round billet 4 so as to reduce sliding with the perforated hollow shell and prevent seizure.

Further, the plug 3 is usually heat-treated in an oxidizing atmosphere before being used in order to impart seizure resistance and heat insulation, and a scale containing iron oxide as a main component is formed on the surface thereof. . Further, the temperature of the plug 3 used for piercing and rolling reaches a high temperature, and if it is continuously used as it is, the life is extremely shortened. Therefore, a plurality of plugs are repeatedly circulated and repeatedly used while being cooled.

[0007]

By the way, in the above piercing and rolling method, the plug is heavily worn and its life is a major problem in operation. That is, the tip of the plug often melts due to the heat load received from the round billet as the material to be rolled during piercing and rolling. If the plug whose melted tip is damaged is used as it is, there is a problem that the inner surface of the obtained hollow shell is flawed and the quality of the product is deteriorated. In order to eliminate this problem, conventionally, an operator visually checks the melting end of the plug to determine whether or not continuous use is possible. However, visual judgment by workers is one of the most important causes of not only large fluctuations and uncertainties, but also inefficiency and reduced efficiency, increased labor costs, and increased manufacturing costs. ing.

Further, as oil well pipes and line pipes that account for most of the demand for seamless metal pipes in recent years, with the increasing development of oil wells and gas wells in a poor environment, high corrosion resistance materials such as stainless steel have been developed. A product consisting of is required. However, since these materials have a larger deformation resistance than carbon steel, they are heated to a higher temperature than carbon steel and supplied to piercing and rolling. Therefore, a larger pressure and heat load act on the plug. As a result, the life of the plug is shortened to about several times, and it is necessary to more surely determine the occurrence of melting damage at the tip portion of each end of piercing and rolling, and the development of a method therefor is desired. Is the reality.

The object of the present invention has been made in view of the above situation, and it is possible to predict the temperature of the plug tip immediately after use and determine whether or not the tip is melted by piercing and rolling a seamless metal tube. A method and its piercing and rolling apparatus are provided.

[0010]

[Means for Solving the Problems] If the temperature of the plug tip immediately after the completion of piercing and rolling can be accurately predicted, the occurrence of melting damage of the plug can be grasped and whether or not the plug can be continuously used can be easily determined. become.

By the way, factors that affect the temperature rise of the plug during piercing and rolling are heat transfer from the material to be rolled, friction heat generation and processing heat generation.

Therefore, as a result of various experimental studies, the inventors of the present invention accurately determine the temperature rise of the plug tip based on the time required for piercing and rolling, in other words, the piercing time and the traveling speed of the round billet. It was found that it is possible to determine whether or not continuous use is possible by this.

That is, as the piercing time increases, the temperature of the plug increases as the heat transfer from the material to be rolled increases because the contact time of the plug with the material to be rolled heated to a high temperature becomes longer. Further, the billet advancing speed at the tip of the plug is equal to the advancing speed of the material, but if the billet advancing speed becomes faster, frictional heat generation at the tip of the plug increases and the temperature of the plug rises. Further, the frictional heat generation is also caused by a difference in rotational speed between the plug and the material being rolled in the rotational direction. When the rotational speed difference becomes large, the temperature of the plug rises.

FIG. 1 shows a case where piercing and rolling were carried out under the condition of a piercing ratio (the length of the hollow shell after piercing / rolling / the billet length before piercing / rolling) 2.6, which was calculated based on the billet advancing speed at this time. It is a figure which shows an example of the material advancing velocity distribution of each position of the axial direction of a plug.

As can be seen from FIG. 1, the material advancing speed at the plug tip portion is equal to the billet advancing speed as described above. However, the material advancing speed sharply rises in the rolling part which is the first half part of the plug, and if the speed difference between the raw tube advancing speed that has been separated from the plug after the completion of piercing and rolling is 100%, The billet traveling speed in the rolling part of the plug is 90% of the traveling speed of the raw pipe.
However, the speed increase in the reeling portion, which is the latter half of the plug, is extremely small.

The material advancing speed Mvi at each position in the plug axial direction based on the billet advancing speed VB is yi at the coordinate position in the axial direction of the plug with the tip of the plug as the origin, L1 is the rolling portion length of the plug, and If the reeling length is L2 and the perforation ratio is EL, the following formula (1) or (2)
It can be calculated by a formula.

[0017]

[Equation 1]

The material advancing speed Mvi at each position in the longitudinal direction of the plug and the advancing speed difference VLi between the material and the plug.
Between the and, the plug is supported on the pass line by the core bar immovably in the axial direction, and the plug advancing speed in the material advancing direction is 0 (zero), so the relationship of the following equation (3) is established. To do.

VLi = Mvi (3) FIG. 2 shows the results of piercing and rolling under the same conditions as above, showing the rotational speed distribution of the plug and the material at each position in the axial direction of the plug. It is a figure which shows an example.

As can be seen from FIG. 2, the rotating speeds of the material and the plug during rolling are equal at the plug tip portion, and the rotating speed difference is 0 (zero). However, the rotation speed is similar to that of the above-mentioned material advancing speed, and the rotation speed of the plug sharply rises in the rolling section and gradually increases in the reeling section to reach 100% at the end section.
Has been reached. On the other hand, regarding the material rotation speed,
At the end of the rolling part of the plug, it reached 110% of the rotation speed of the plug in the reeling part, and thereafter remained constant. The difference in rotational speed between the two gradually increases toward the terminal end of the rolling part of the plug, and gradually decreases toward the terminal end of the reeling part. large.

As for the billet rotation speed RB, the diameter of the billet is DB and the diameter of the gorge portion (maximum diameter portion) of the main roll is D.
Let R be the rotation speed of the main roll, R R be the inclination angle of the main roll, and β be the formula (4) below. The billet rotation speed RB is equal to the plug rotation speed.

RB = [(DR × RR) / DB] × cos β (4) Further, the plug rotation speed R at each position in the plug axis length direction
Pi and the material rotation speed RMi are the coordinate position in the axial direction of the plug with the origin at the tip of the plug as yi, the plug radius at yi as Pri, the plug radius at the starting point of the reeling portion as PrL, and the maximum radius of the plug (reeling). When the part end point radius) is Prmax, it can be calculated by the following equation (5) and equation (6) or (7) using the billet rotation number RB.

RPi = 2 × π × Pri × RB (5) RMi = RPi × (1.1 × Prmax / PrL) (6) where 0 ≦ When yi ≤ L1, RMi = 2.2 x π x Prmax x RB (7) However, when L1 <yi ≤ (L1 + L2) Therefore, the rotational speed difference VRi between the material and the plug is It is represented by (8) below.

VRi = RMi-RPi (8) On the other hand, as a factor that raises the temperature of the plug, there is a processing heat generated by material deformation during piercing and rolling.

However, this material deformation hardly occurs at the plug tip portion, and mainly occurs after the plug tip portion. Therefore, the processing heat is hardly generated at the plug tip portion and is generated at the plug tip portion and thereafter.

The amount of processing heat generated after the tip of the plug is generated in accordance with the processing strain ε of the material being rolled,
It increases when the processing strain ε increases, and decreases when the processing strain ε decreases. This processing strain ε is given by
It is expressed by equation (9).

Ε = ln (AM / AP) (9) Further, the moving speed Mvi of the material at the yi position can be obtained based on the moving speed VB of the billet as described above. . Since the material advancing speed Mvi is equal to the advancing speed difference VLi between the material and the billet, the following equation (10) is established between the advancing speed and the cross-sectional area.

AP × VB = AM × Mvi (10) Therefore, the processing strain ε can be expressed by the following equation (11) by substituting the equation (10) into the equation (9).

Ε = ln (Mvi / VB) (11) Therefore, the processing heat qi generated by the deformation of the material during piercing and rolling is the work equivalent of heat J, where σ is the deformation resistance of the material. (4.19 J / cal), gravitational acceleration gn (9.8 ×
10 ³ mm / s ² ) and the above processing strain ε,
It can be obtained by the equation (12). However, this processing calorific value qi is extremely smaller than the calorific value generated by the progress and rotation of the material.

Qi = [0.9 × σ × ln (Mvi / VB) × gn] / J (12) As is apparent from the above description, the perforation time and the billet advancing speed on the piercer entry side are When using two,
It is possible to accurately predict the temperature rise of the plug immediately after being subjected to piercing and rolling, and particularly it is possible to accurately predict the temperature rise of the tip of the plug.

The temperature of the tip of the plug immediately after being subjected to piercing and rolling is determined using the analytical model formula (13) shown below, which enables three-dimensional simulation in consideration of piercing time and billet progressing speed. You can

[0032]

[Equation 2]

Here, the heat transfer from the material to the plug is treated as heat transfer, and the third term on the right side of the equation (14) for obtaining Q in the equation (13) [h. (TM-T) .S]. ]].

The plug that has been subjected to piercing and rolling is air-cooled and / or water-cooled and then repeatedly used. At this time, the first term [μ · σ · (VLi
² + VRi ² ) ^1/2 · gn / J] and the second term [qi] are both given the plug temperature as 0 (zero) and the third term [h · (TM −T) · S]. The inside environmental temperature of the plug is given to TM and the total surface area of the plug is given to S.

FIG. 3 is a diagram showing an example of the temperature distribution of the plug obtained by solving by the finite element method using the above analytical model formula. As can be seen from FIG. 3, the temperature distribution is very high only at the tip of the plug having a small volume. Therefore, melting loss occurs at the plug tip portion.

The temperature distribution of the plug shown in FIG. 3 is 2 when the piercing and rolling conditions of the case shown in Table 1 and the chilling and cooling conditions of the case shown in Table 2 are performed.
The temperature distribution of the plug immediately after being subjected to the first piercing and rolling is shown.

[0037]

[Table 1]

[0038]

[Table 2]

By the way, as described above, the scale layer containing iron oxide as a main component having a heat insulating effect is formed on the surface of the plug. In this case, the scale layer is melted and disappears when the surface temperature of the plug exceeds the melting temperature of the scale, and the heat insulating effect is lost, so that the temperature of the plug base material rapidly rises. As a result, the deformation resistance of the plug base material decreases, and is smaller than the deformation resistance of the material to be rolled.
The tip of the plug will melt.

Therefore, immediately after being subjected to rolling, if the temperature of the plug tip portion obtained by using the above analytical model formula exceeds the melting temperature of the scale, when the plug is subjected to the next rolling, the plug tip portion is Will melt. Therefore, the plug in this case must be discarded without being subjected to the next rolling and replaced with a new plug.

The melting temperature (melting point) of the scale formed on the surface of the plug differs depending on the material of the base material of the plug and the conditions for the scale generation treatment. One example is shown in Table 3.

[0042]

[Table 3]

The melting points of the scales shown in Table 3 are all obtained by heat treatment using a butane gas furnace and holding at 1050 ° C. for 6 hours in an atmosphere having a steam partial pressure of 10% or more. Is.

The present invention has been made based on the above findings, and its gist is the following (1) and (2) piercing and rolling method for a seamless metal tube and piercing and rolling apparatus for a seamless metal tube. is there.

(1) A solid round billet is used by using a piercer in which a plug is arranged along a pass line between a pair of main rolls and a pair of material-to-be-rolled material which are arranged to face each other around the pass line. In the method for producing a seamless metal tube in which a hollow shell is obtained by making a hole in the center by screwing and moving, the traveling speed of the round billet is measured, and the billet traveling speed and the piercing time required for piercing and rolling. The temperature of the plug tip immediately after use is calculated based on the above, and based on this result, the melting loss of the plug tip is predicted to judge whether or not the plug can be used continuously, and it is used for rolling. Drilling and rolling method.

(2) A solid round billet is used by using a piercer in which a plug is arranged along the pass line between a pair of main rolls and a pair of rolling material guide members which are arranged to face each other around the pass line. Is a piercing and rolling apparatus for a seamless metal tube, in which a hollow shell is obtained by screwing and moving a hollow core tube, and a billet advancing speed measuring means for measuring an advancing speed of a round billet at an entrance side of the piercer. And, a piercing time measuring means for measuring the piercing time required for piercing and rolling, and predicting the melting loss of the plug tip by obtaining the tip temperature of the plug repeatedly used based on the measurement results of the both measuring means, A piercing and rolling apparatus for a seamless metal tube, comprising a calculating means for determining whether or not the plug can be continuously used.

In the piercing and rolling method (1), it is preferable to consider the melting temperature of the scale formed on the surface of the plug when determining whether or not the plug can be continuously used.

[0048]

DETAILED DESCRIPTION OF THE INVENTION The method and apparatus of the present invention will be described in detail below with reference to FIG.

In FIG. 4, reference numeral 1 is a main roll constituting a piercer which is an inclined rolling mill, 3 is a plug supported by a core metal 5, 4 is a solid round billet, H is a hollow shell, and 6 is a piercer. The billet advancing speed measuring means, 7 is a piercing time measuring means, and 8 is a calculating means arranged on the inlet side of the.

The billet advancing speed measuring means 6 comprises two optical sensors 6a, 6a arranged at a predetermined interval.
The billet advancing speed v is obtained from the time when the rear end of the round billet 4 passes between the two optical sensors 6a, 6a.

The traveling speed v of the round billet 4 is determined by the outer diameter thereof, the dimensions of the main rolls 1 and 1 and the inclination angle β (and the crossing angle γ) of the traveling speed of the hollow shell H. It can also be obtained indirectly by dividing by. However, the above-mentioned perforation ratio usually varies even under the same perforation conditions and the length of the round billet 4 also varies, and thus it cannot be obtained very accurately. Therefore,
In the present invention, the billet advancing speed v is measured by the measuring means 6.

The piercing time measuring means 7 uses a load detector (load cell) attached to the main roll 1 and obtains the output time of the rolling load detected by the load detector to obtain the piercing time t. Is designed to measure.

This piercing time t is, instead of the above, as shown by the broken line in FIG. 4, at the rear end of the core metal 5 supporting the plug 3, a load detector (for detecting the thrust load acting during rolling). The drilling time t may be measured by providing a load cell 9 and determining the output time of the thrust load detected by the load detector 9.

In the piercing and rolling apparatus of the present invention constructed as described above, the billet advancing speed v measured by the billet advancing speed measuring means 6 and the piercing time measuring means 7 are measured.
The perforation time t measured by is input to the calculating means 8.

In the calculating means 8 to which the billet advancing speed v and the piercing time t have been inputted, the temperature T of the plug tip immediately after being subjected to an arbitrary number of piercing and rolling of each plug which is repeatedly circulated is analyzed as described above. It is calculated by the finite element method using the model formula (step 1).

When the calculated surface temperature T of the plug tip is equal to or higher than the melting temperature of the plug surface scale to be calculated, it is considered that the plug tip has melted and has reached the end of its life. A command to replace the plug with a new plug is issued (step 2).

On the other hand, when the obtained surface temperature T of the plug tip portion is lower than the melting temperature of the plug surface scale, the current value is calculated based on the billet advancing speed v and the piercing time t measured at the time of piercing and rolling this time. The temperature of the plug tip when the plug to be calculated is subjected to the next piercing and rolling is calculated and predicted by the finite element method using the analytical model formula as in the above (step 3).

As a result of the above, when the predicted surface temperature of the plug tip is equal to or higher than the melting temperature of the plug surface scale, it is predicted that the plug tip will be melted and damaged when the plug is subjected to the next piercing and rolling. Therefore, a command to replace the plug with a new plug is issued (step 4).

On the other hand, when the expected temperature of the tip of the plug is lower than the melting point of the scale, a command is issued to use this plug for the next piercing and rolling (step 5) and prior to reuse. The surface temperature of the plug after being cooled is determined by, for example, the method described above (step 6).

That is, the calculating means 8 uses the above step 1
By repeating the operation from Step 6 to Step 6, it is determined whether or not each plug that is repeatedly used repeatedly can be used for the next rolling.

In this way, when the temperature of the tip of each plug that is repeatedly used in circulation is obtained based on the billet advancing speed and the piercing time, and whether or not the plug can be used is determined from the results, the plug is pierced and rolled. Since the tip portion does not melt, it is possible to stably obtain a hollow shell having excellent inner surface properties.

[0062]

【Example】

(Example 1) Using the five No. D plugs shown in Table 3 above, the conditions of the case shown in Table 1 above are as follows:
When performing piercing and rolling under the conditions of the case shown in Table 2 above as the plug cooling conditions, any one of the above five plugs when the method of the present invention is carried out is targeted,
Table 4 shows the results calculated by using the analytical model formula in consideration of the measured values (billet advancing speed, drilling time) and the determination result of the necessity of plug replacement based on the calculation results.

[0063]

[Table 4]

As shown in Table 4, both the present temperature and the next predicted temperature up to No. 6, the surface temperature of the plug tip portion calculated and obtained is lower than the melting temperature of 1070 ° C. of the plug surface scale. Low. However, the current calculated value was 1070 ° C or higher at the 7th use of No. 7. Therefore, the plug was replaced without predicting the next temperature. Therefore, from No. 8 onward, a new plug was used and piercing and rolling were continued, but at No. 12's fifth use,
Immediately after the completion of the next piercing and rolling, the expected surface temperature of the plug tip portion became 1070 ° C. or higher, so the plug was replaced with a new plug again. Further, when piercing and rolling was performed using the new plug that was replaced again, the surface temperature of the current plug tip portion of No. 18 became 1070 ° C. or higher, so the plug was replaced with a new plug.

When the same plug as described above was used without applying the present invention, the number of times each plug can be used until melting damage occurs at the tip of the plug is the same as when the present invention is applied. there were. Then, the presence or absence of melting loss of the plug tip immediately after its use was able to be visually determined to some extent by the operator, but it was not possible to accurately determine whether or not melting loss occurs at the plug tip portion at the next rolling. I could not judge.

(Embodiment 2) Five plugs made of No. D shown in Table 3 are repeatedly used repeatedly, and the conditions are the same as the case shown in Table 1 above. When performing the piercing and rolling under the conditions shown in Table 2 above as the plug cooling conditions, the occurrence status of defective products in the obtained hollow shells when the method of the present invention was carried out and when it was not carried out investigated.

The defective product was a defective product in which the inner surface of the hollow shell after piercing and rolling was visually observed and a flaw due to melting damage at the plug tip portion was required on the inner surface.

The results are shown in Table 5.

[0069]

[Table 5]

As is clear from the results shown in Table 5, when the method of the present invention was applied, in any case, no problems occurred after the rolling this time. Since the plug that is predicted to be melted is replaced with a new plug, the defective product rate of the hollow shell is as low as about 0.5%.

On the other hand, when the method of the present invention was not applied, in any of the cases, no problems occurred after the rolling this time, but it is predicted that the melting tip of the plug tip will occur in the next rolling. Since the formed plug is used as it is, the defective product generation rate is 2% or more, and it is understood that defective products are generated about four times or more as compared with the case where the present invention is applied.

[0072]

According to the present invention, by determining the temperature of the tip of the plug on the basis of the advancing speed of the billet and the piercing time, it is possible to accurately predict the presence or absence of melting damage at the tip and to determine the timing. It was possible to continue piercing and rolling while replacing the plug with a new plug without loss. As a result, the defect occurrence rate of the hollow shell after piercing and rolling can be significantly reduced, and the yield is improved. Further, since labor is not required to continuously use the plug, labor costs can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a material advancing speed distribution at each position in the axial direction of a plug, which is obtained based on a billet advancing speed.

FIG. 2 is a diagram showing an example of rotational speed distributions of a plug and a material at respective positions in the axial direction of the plug.

FIG. 3 is a diagram showing an example of the temperature distribution of the plug obtained by the method of the present invention.

FIG. 4 is a diagram showing a configuration of a piercing and rolling apparatus of the present invention.

FIG. 5 is a diagram showing a configuration example of a piercer.

[Explanation of symbols]

 1: main roll, 2: disc roll, 3: plug, 4: round billet, 5: core metal, 6: billet advancing speed measuring means, 6a: optical sensor, 7: piercing time measuring means, 8: computing means, 9 : Load detector.

Claims (3)

[Claims] 1. A solid round billet is formed by using a piercer in which a plug is arranged along a pass line between a pair of main rolls and a pair of rolling material guide members which are arranged to face each other around a pass line. In a method for producing a seamless metal tube in which a hollow shell is obtained by making a screw movement to form a hole in the center thereof, the traveling speed of the round billet is measured, and the billet proceeding speed and the piercing time required for piercing and rolling. Based on this, the temperature of the plug tip immediately after use is determined, and based on this result, the melting loss of the plug tip is predicted to determine whether or not the plug can be used continuously, and is used for rolling. Rolling method. 2. The method of piercing and rolling a seamless metal tube according to claim 1, wherein the melting temperature of the scale formed on the surface of the plug is taken into consideration when determining whether or not the plug can be continuously used. 3. A solid round billet is formed by using a piercer in which a plug is arranged along a pass line between a pair of main rolls and a pair of rolled material guide members which are arranged to face each other around a pass line. A seamless metal tube piercing and rolling device for screwing and moving to form a hole in the center thereof to obtain a hollow shell, and a billet advancing speed measuring means for measuring an advancing speed of a round billet at an entrance side of the piercer. The piercing time measuring means for measuring the piercing time required for piercing and rolling, and predicting the melting loss of the plug tip by obtaining the tip temperature of the plug repeatedly used based on the measurement results of both the measuring means, A piercing and rolling apparatus for a seamless metal pipe, comprising a calculating means for determining whether or not the plug can be continuously used.