JP3458712B2 - Perforated plug - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a technique for producing a seamless steel pipe, and more particularly to a piercing plug provided with cooling means for the outer surface of the plug for a piercer or an elongator,
The present invention relates to a method for cooling the perforated plug.

[0002]

2. Description of the Related Art The manufacture of a seamless steel pipe by the Mannesmann mill system is usually carried out by the following procedure. (1) A round billet (hereinafter referred to as "billet") is heated to about 1100 to 1300 ° C in a heating furnace. (2) A hollow shell (hereinafter referred to as "hollow shell") is formed by punching with a plug by a first perforator (hereinafter referred to as "piercer"). (3) The hollow shell is expanded and stretched with the plug of the second punching machine (hereinafter referred to as "elongator"). Due to the piercing of the billet by the piercer and the expansion / stretching of the hollow shell by the elongator, the plug is exposed to heat due to contact with the billet and hollow shell and frictional heat, and the plug surface is subject to melting damage, engraving, etc. Cannot be used. Above all, when manufacturing seamless pipes of high alloy steel such as high chromium steel, the durability is extremely lower than that of ordinary steel, and the durability has been improved by cooling the outer surface of the plug and cooling water by sending cooling water to the inner surface of the plug. Improvements have been made.

As the prior art of these, Japanese Patent Laid-Open No. 58-58-
No. 168405 and JP-A No. 61-219404, a method of passing cooling water through a mandrel bar to inject the cooling water onto the outer surface of the plug and ejecting the cooling water from the tip of the plug (prior art 1), A method of covering a thin coating material centered on SS material on the tip of the plug of Japanese Patent Laid-Open No. 3-124305 (Prior Art 2), cooling water is fed into the plug of Japanese Patent Laid-Open No. 3-291106, and irregularities are formed inside the plug. By providing a method for increasing the heat transfer area to promote inner surface cooling (Prior Art 3), several plugs and mandrel bars of Japanese Patent Laid-Open No. 8-117817 are provided, and the mandrel bar is replaced for each perforation, and the entire mandrel bar is provided. Cooling method (Prior Art 4), and cooling holes are provided at predetermined intervals in the circumferential direction of the plug in the cross-section of the plug wall thickness of JP-A-10-43804. Method of cooling by feeding the liquid (prior art 5) had respectively.

[0004]

However, in the prior art 1, since the injection hole is closed during drilling, the cooling water is not constantly supplied, and there is almost no effect of cooling the inner surface of the plug. Further, this method has a problem that the billet itself is unnecessarily cooled. In Prior Art 2, although the plug tip was coated with SS material to improve lubrication between the plug and the billet during drilling, the plug was not cooled, so the temperature of the plug increased each time drilling and the plug was deformed or deformed. The wear could not escape and did not lead to a significant improvement in durability. In Prior Art 3, the heat transfer area increased due to the unevenness of the inner surface of the plug, but there was no effect of lowering the surface temperature of the plug, which affects the life of the plug. In addition, even if unevenness was provided, the heat transfer area was limited to about 1.5 times, and the cooling promotion effect was limited.

In the prior art 4, although the plug can be surely cooled, there is a problem that the equipment cost is high and the maintenance cost is too high. Further, the mandrel bar was replaced, which hindered the rolling efficiency. In the prior art 5, the temperature of the plug can be lowered by providing the cooling hole in the cross section of the plug, but in order to lower the temperature of the plug surface, the cooling hole is required near the plug surface, and the tip portion having a strong curved portion is required. It is difficult to provide cooling holes near the surface. Further, there is a problem that it is difficult to form the cooling hole and the manufacturing cost of the plug is three times or more that of the conventional plug.

As described above, there has been no technique capable of reliably cooling the plug by an inexpensive method for improving the durability of the plug. At present, when performing piercing with a piercer and an elongator, the total amount of heat flowing into the plug from a new plug several times after the start of piercing the billet is larger than the total amount of heat removed from the outer surface cooling of the plug performed after the piercing of the billet. Therefore, the average plug temperature gradually rises,
Eventually, the temperature gradually approaches the temperature at which the amount of heat flowing in and the amount of heat removed by cooling are balanced. Therefore, unless the cooling time for cooling the outer surface of the plug is significantly lengthened, it is impossible to lower the asymptotic temperature of the plug, which is one of the causes of deteriorating the durability of the plug. It has been impossible to significantly increase the cooling time of the outer surface of the plug in terms of production efficiency. In addition, in order to cool the plug at all times, a cooling medium such as cooling water is sent to the inner surface of the plug through a mandrel bar to cool the inner surface of the plug.In cooling the inner surface of the plug, the space between the outer surface of the plug that contacts the billet during drilling and the inner surface of the plug that contacts the cooling liquid. Therefore, it was difficult to lower the temperature of the outer surface of the plug, and the effect of cooling the inner surface was not fully exerted. In view of the above problems, an object of the present invention is to provide a perforated plug that is inexpensive and can reliably cool the outer surface of the plug in order to improve the durability of the plug.

[0007]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The plug of the present invention comprises a plug base, a plug hole, and a mandrel bar, and the plug base is made of plastic.
A plug having a reinforcing material for reinforcing a hole for drilling, and a means for supplying and discharging a cooling liquid through a mandrel bar between the plug base and the hole for plugging.

(2) A plug base portion, a plug perforation portion, and a mandrel bar, wherein the plug base portion has a reinforcing material for reinforcing the plug perforation portion, and the mandrel bar is provided between the plug base portion and the plug perforation portion. A perforated plug, characterized in that a means for supplying and discharging a cooling liquid is provided at the tip of the perforated portion. (3) It consists of a plug foundation , a plug bore, and a mandrel bar. The plug foundation reinforces the plug bore.
A means for supplying and discharging the cooling liquid is provided at the tip of the plug drilling portion through a mandrel bar between the plug foundation and the plug drilling portion. A perforated plug formed by the plug perforation portion along an inner surface of the plug perforation portion. (4) The perforated plug according to any one of (1) to (3), wherein the plug outermost surface is used at a maximum temperature reached on the outer surface of the plug of 800 ° C. or less. (5) Regarding the plug piercing portion, the wall thickness of the plug piercing portion: t is set based on the following equation (1) so that the maximum temperature reached on the outer surface of the plug is 800 ° C. or less according to the piercing time: Ts.
h is set, The perforated plug in any one of (1) thru | or (4) characterized by the above-mentioned. th = 147 (Ts) ^-0.776 (1) where th: thickness of plug perforated portion (mm), Ts: perforation time (second).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have obtained the following findings. 1 to 4 show the outline of a perforation process using a general piercer (for example, Mannesmann type). The state of FIG. 1 is a punching process. As shown in FIG. 1, a cast steel roll 14 having a special shape is placed on two parallel vertical planes, and the horizontal direction is about 5 degrees.
The rolls 14 are tilted in the opposite directions by 15 ° to 15 °.
Rotate in the same direction. When the heated billet 15 is inserted between the two rolls 14, the billet 15 first has a smaller outer diameter, and the surface thereof is pulled obliquely forward by the spiral motion. When the shell-shaped plug 1 is pressed from there through the mandrel bar 8 from the front, the billet 15 is perforated, and the hollow shell 16 (hollow shell) is obtained.

The state shown in FIG. 2 is a drawing process. Plug 1 from hollow shell (hollow shell) 16 obtained by drilling
Is pulled out through the mandrel bar 8. The state of FIG. 3 is a cooling process. The mandrel bar is arranged so that the plug 1 which has been heated to a high temperature by the contact with the billet 15 and the hollow shell 16 and the frictional heat in the punching step (FIG. 1) and the drawing step (FIG. 2) described above enters the outer surface water cooling device 13. 8 to move the outer surface of the plug 1 to the outer surface water cooling device 13
Cool with. The state of FIG. 4 is a standby process. After cooling the outer surface of the plug 1 with the billet 15 inserted between the two rolls 14, the plug 1 is extruded from inside the outer surface water cooling device 13 via the mandrel bar 8 to roll the plug 1 before piercing the roll 14. Wait near the entrance. One billet 15 is punched in the steps of FIGS. 1 to 4 (each pass is called one pass). Replace the plug in Fig. 1
The temperature history of the plug outer surface temperature and the plug inner temperature from the third pass to the third pass is shown. When piercing starts, the temperature of the outer surface of the plug rises rapidly until the end of piercing.
The plug is pulled out from the billet that has become a hollow shell, and then it is cooled and the outer surface temperature drops. On the other hand, the temperature inside the plug gradually rises and rises with each drilling.

FIG. 6 shows the temperature history of the plug when continuously drilling from the 1st pass to the 20th pass. In this case, the internal temperature of the plug asymptotically approaches a certain temperature when the number of passes exceeds 10 and is about 450 ° C. Leading to. In addition, the maximum temperature of the outer surface of the plug also approaches each pass as the internal temperature approaches a certain temperature. In the case of Fig. 6, the maximum temperature on the outer surface of the plug is about 8
It is asymptotic at 00 ° C., and the maximum temperature from the 10th pass to the 20th pass is almost 800 ° C., and this asymptotic temperature is taken as the maximum reached temperature. The asymptotic temperature inside the plug and the maximum reached temperature on the outer surface of the plug are determined by the heat input from the outer surface of the plug in one pass and the amount of heat removed by subsequent cooling and heat radiation.
In recent years, in the operation pattern that emphasizes efficiency, it is not possible to take a long cooling time after drilling, especially when manufacturing high-alloy steel pipes, it takes a long time to drill and frictional heat during drilling is large, so the maximum temperature reached is high. The service life of was deteriorated.

Therefore, the present inventors have made detailed studies on the factors that govern the plug durability, and as a result, have revealed the following. Even if the outer surface of the plug 1 is strongly cooled in the cooling step of FIG.
Further, it has been found that when the outer surface temperature of the plug 1 exceeds 800 ° C., the plug 1 is significantly worn and the hot strength is lowered, and the plug 1 is engraved and deformed even during the perforation.

Therefore, a method of lowering the maximum temperature reached on the outer surface of the plug 1 will be considered next. In order to reduce the maximum temperature to 800 ° C or less, (1) shortening of the drilling time and (2) extension of the water cooling time after drilling can be considered, but it is impossible to shorten the drilling time under normal operating conditions. And again
Prolonging the water cooling time after perforation could not be performed because it deteriorates the efficiency. On the other hand, the method of constantly cooling the inner surface of the plug is also effective in lowering the temperature of the inner surface of the plug, but the outer surface of the plug during drilling could not be kept at 800 ° C or lower. FIG. 7 shows the outer surface of the plug and the inner surface (cooling surface) of the plug when continuous perforation is performed in the perforation step 13 seconds, the withdrawal step 5 seconds, the cooling step 7 seconds, and the standby step 5 seconds while always cooling the inner surface. It is the figure which showed the relationship between the wall thickness and the highest temperature reached on the outer surface of the plug. As shown in FIG.
When the wall thickness of the plug punched portion is thicker than 20 mm, the maximum temperature reached exceeds 800 ° C. The wall thickness of the plug hole is 20m
The maximum temperature reached on the outer surface of the plug exceeding m is no matter how strong the water cooling of the outer surface of the plug after drilling is, no matter how strong the cooling is, the unevenness is provided on the inner surface of the plug to accelerate the cooling of the inner surface, and the heat transfer area is 1.5. Even if it was increased about twice, the maximum temperature reached did not fall below 800 ° C. This is considered to be because the temperature of the plug surface is dominated by heat conduction in the vicinity of the outer surface layer of the plug, so that no matter how strongly the inner surface of the plug is strongly cooled, the outer surface is not significantly affected. Therefore, it was found that the maximum temperature reached on the outer surface of the plug can be lowered by reducing the temperature gradient between the outer surface of the plug and the inner surface of the plug by reducing the wall thickness of the plug perforated portion. Based on the above findings, the inventors of the present invention have a means for supplying and discharging a cooling liquid through a mandrel bar between the plug base portion and the plug perforation portion, and the maximum temperature on the outer surface of the plug decreases the hot strength 800 In order to improve the durability of the plug by setting the wall thickness of the plug perforation part so that the temperature does not exceed ℃ Completed the invention.

Embodiments of the present invention will be described below. The piercing plug of the present invention is, for example, as shown in FIG.
The plug base portion 3 and the plug perforation portion 2 and the mandrel bar 8 are provided, and a means (circulation pump or the like) for supplying and discharging the cooling liquid 9 through the mandrel bar 8 is provided between the plug base portion 3 and the plug perforation portion 2. It is characterized by that. That is, at the time of cooling the inner surface of the plug 1, the cooling liquid 9 is fed from one pipe of the double-pipe mandrel bar 8 (the mandrel bar inner pipe 5), and the plug piercing portion 2 and the plug foundation 2 are passed through the center of the plug foundation portion 3. The cooling liquid 9 which has been sent between the parts 3 and which has been cooled is again sent back through the other pipe (mandrel bar outer pipe 4) of the mandrel bar 8. Therefore, the cooling water 9 does not flow out into the billet being punched.

As described above, the reason for providing the means for supplying and discharging the cooling liquid 9 through the mandrel bar 8 is to prevent the leakage of the cooling water to the billet during the drilling of the plug and the overcooling of the inner surface of the hollow shell after the drilling of the billet. This is because

Further, in the present invention, in order to facilitate the attachment / detachment,
The plug is divided into a plug piercing portion 2 and a plug base portion 3 in order to reduce the weight of the plug. As a method for attaching / detaching the plug piercing portion 2 and the plug base portion 3, a method of attaching by screwing in a direction in which the plug piercing portion 2 and the plug base portion 3 are not displaced by the rotation at the time of piercing the billet was used, but the attaching / detaching method is not limited to this.

Incidentally, as shown in FIG. 10, in order to give strength to the plug perforation portion 2, it is desirable to insert a reinforcing material 6 in conformity with the plug shape of the plug base portion 3. Also,
The plug perforation portion 2 is used, for example, at a maximum plug outer surface temperature of 800 ° C. or less at a portion in contact with the billet. If the maximum temperature on the outer surface of the plug exceeds 800 ° C,
This is because, as described above, the plug 1 is significantly worn out and the hot strength is lowered, and the plug 1 is engraved and deformed even during the perforation.

Further, regarding the plug piercing portion 2, the maximum temperature of the outer surface of the plug is 800 ° C. according to the piercing time: Ts.
The thickness: th of the plug punching portion 2 is set so as to be as follows. th = 147 (Ts) ^-0.776 (1) where th: thickness of plug perforated portion (mm), Ts: perforation time (second).

This has been clarified by the following experiments conducted by the present inventors. That is, the inventors have found that the perforation time (T
As a result of obtaining the plug wall thickness (th) so that the outer surface of the plug does not exceed 800 ° C even when s) is changed (see Fig. 8), the relationship between the drilling time and the wall thickness of the plug drilling portion is as described above. It is expressed by equation (1).

According to this formula, the wall thickness of the plug can be set under other drilling conditions. In addition, since a large force is applied to the vicinity of the surface of the plug when the plug is punched, it is necessary to have appropriate strength. Therefore, the plug wall thickness cannot be made too thin. Usually, the thickness is 10 mm or more even if it is thin. Examples of the present invention will be given below to prove the effects of the present invention.

[0021]

EXAMPLE 1 Example 1 of the present invention is shown in FIG. A high alloy steel 13Cr steel billet was perforated with a piercer and a perforation plug to manufacture a hollow shell. For drilling, a set of drilling plugs with a maximum diameter of 140 mm shown in FIG. 9 is used, and a cooling water as a cooling liquid 9 is a double pipe mandrel bar between the plug base portion 3 and the plug drilling portion 2 having a wall thickness of 20 mm. 8 central pipe (inner pipe) 5 to about 100 l /
Water was distributed to cool the plug hole portion 2, and the cooling water after cooling was discharged through the pipe 4 outside the mandrel bar 8.
It should be noted that the plug hole 2 has JIS standard SK for hot work tool steel.
T4 is used, and the plug base 3 is JIS for general structure.
Standard S45C was used.

The perforation conditions were as follows. (1) The billet is made of 13Cr steel and the total length is about 2.5m.
Met. (2) The billet was heated to about 1270 ° C in a heating furnace.

(3) The total process for one pass is about 30 seconds, and the time for each process is about 12 seconds for the punching step, about 5 seconds for the step of withdrawing from the billet, and about 7 seconds for the step of cooling the outer surface of the plug.
Second, the waiting process before the billet was about 6 seconds. (4) The wall thickness of the plug was set to 20.0 mm because the wall thickness was calculated to be 21.3 mm from the equation (1). As a result of carrying out under the above conditions, continuous drilling was possible up to an average of 31.3 passes using the plug of the present invention. The temperature of the outer surface of the plug immediately after drilling was measured with a radiation thermometer. As a result, the plug temperature was kept at 800 ° C or lower at about 770 ° C. When the service life of the plug was exhausted, continuous drilling was still possible, but the lubricity of part of the plug was lost. This is probably due to wear and deterioration of the plug. (Example 2) As in Example 1, a 13Cr steel billet was perforated with a piercer and a perforation plug to manufacture a hollow shell. When piercing, a set of piercing plugs having a maximum diameter of 140 mm shown in FIG. 10 is used, and the thickness of the plug piercing portion 2 is 18
8 mm of the reinforcing material 6 of the plug piercing portion 2 are laid radially in the plug base portion 3 at equal intervals in the longitudinal direction of the plug 1. A central pipe 5 of the mandrel bar 8 having a double pipe of cooling water as a cooling liquid 9 between the plug base portion 3 and the plug drilling portion 2.
About 100 l / min to cool the plug perforation portion 2, and the cooled cooling water was discharged through the pipe 4 outside the mandrel bar 8. In addition, JIS standard SKT4 for hot tool steel was used for the plug piercing part 2, and JIS standard S45C for general structure was used for the plug base part 3.

The perforation conditions were as follows. (1) The billet is made of 13Cr steel and the total length is about 2.5m.
Met. (2) The billet was heated to about 1270 ° C in a heating furnace.

(3) The total number of steps per pass is about 30 seconds, the time for each step is about 13 seconds for punching, about 5 seconds for drawing from the billet, and about 7 for cooling the outer surface of the plug.
Second, the waiting process before the billet was about 5 seconds.

(4) When the wall thickness is calculated from the equation (1), it is 2
Since the thickness is 0.0 mm, the thickness of the plug is 18.0 mm
And As a result of carrying out under the above-mentioned conditions, continuous drilling was possible up to an average of 35.3 passes using the plug of the present invention. The temperature of the outer surface of the plug immediately after drilling was measured with a radiation thermometer. As a result, the plug temperature was 800 ° C at about 720 ° C.
I kept it below. When the durability of the plug is lost, it is considered that the plug is worn or deteriorated. (Example 3) As in Example 1, a 13Cr steel billet was perforated with a piercer perforation plug to manufacture a hollow shell. When piercing, a set of piercing plugs with a maximum diameter of 140 mm shown in FIG. 11 is used, and the thickness of the plug piercing portion 2 is 1
With a thickness of 5.0 mm, the plug base portion 3 is made of a cannonball-shaped body having substantially the same size as the inner inner surface of the plug perforation portion 2, and
The outer surface of the plug base 3 has a depth of 10 mm and a width of 10 m.
There are 10 or more cooling grooves through which the m cooling liquid 9 passes.

The cooling water, which is the cooling liquid 9, is fed from the central pipe 5 of the mandrel bar 8 which is a double pipe at a flow rate of about 100 l / min, and passes through the cooling groove of the plug base 3 while the plug perforation 2 is formed. The cooling water after cooling was discharged through the pipe 4 outside the mandrel bar 8. In addition, JIS standard SKT4 for hot tool steel was used for the plug piercing part 2, and JIS standard S45C for general structure was used for the plug base part 3. The perforation conditions were as follows. (1) The billet is made of 13Cr steel and the total length is about 2.5m.
Met.

(2) The billet was heated to about 1270 ° C. in a heating furnace. (3) The total process per pass is about 30 seconds. The time of each process is about 13 seconds for the punching step, about 5 seconds for the drawing step from the billet, about 7 seconds for the plug outer surface cooling step, and before the billet. The waiting step was about 5 seconds.

(4) When the wall thickness is calculated from the equation (1), it is 2
Since the thickness is 0.0 mm, the plug thickness is 15.0 mm.
And As a result of carrying out under the above-mentioned conditions, continuous drilling was possible up to an average of 35.3 passes using the plug of the present invention. The temperature of the outer surface of the plug immediately after drilling was measured with a radiation thermometer. As a result, the plug temperature was 800 ° C at about 720 ° C.
I kept it below. When the durability of the plug is lost, it is considered that the plug is worn or deteriorated. (Comparative Example 1) Comparative Example 1 is the same as Example 1 except that it is made of high alloy steel 1
A hollow shell was punched from a 3Cr steel billet by a piercer. When drilling, maximum diameter 140 mm shown in Fig. 9
Using a set of plugs, the plug base 3 and wall thickness 40 mm
Between the central pipe 5 of the mandrel bar 8 which is a double pipe of cooling water as the cooling liquid 9 between the plug perforation parts 2 of
The plug perforation portion 2 was cooled by sending 0 l / min of water, and the cooled cooling water was discharged through the pipe 4 outside the mandrel bar 8. The perforation conditions were as follows. (1) The billet is made of 13Cr steel and the total length is about 2.5m.
It was m.

(2) The billet was heated to about 1270 ° C. in a heating furnace. (3) The total process per pass is about 30 seconds. The time of each process is about 12 seconds for the punching step, about 5 seconds for the step of drawing from the billet, about 7 seconds for the step of cooling the outer surface of the plug, and before the billet. The waiting step was about 6 seconds.

(4) When the wall thickness is calculated from the equation (1), it is 2
It was 1.0 mm. As a result of carrying out under the above conditions, the wall thickness of Comparative Example 1 is 40
With a mm plug, only 6.8 passes could be continuously drilled on average. Further, as a result of measuring the temperature of the outer surface of the plug immediately after drilling with a radiation thermometer, it is considered that the maximum attainable temperature exceeded 800 ° C because it was about 870 ° C and the thickness of the plug was thick.

[0032]

As described above, according to the present invention, by specifying the wall thickness of the plug perforation portion and the internal cooling means, particularly useful effects can be brought about in the production of the high alloy steel seamless pipe.

(1) By setting the wall thickness of the plug perforation portion according to the perforation time, the maximum temperature reached on the outer surface of the plug can be maintained at 800 ° C. or less, which leads to a great improvement in durability.

(2) The improved durability of the plug leads to improved productivity and cost reduction. (3) Since the cooling water in the plug is sent and drained through the mandrel bar, the cooling water does not leak to the billet during the drilling of the plug, and the inner surface of the hollow shell after drilling the billet is not overcooled. (4) By dividing the plug into the plug piercing portion and the plug base portion, the attachment and detachment of the plug is facilitated, and the weight of the portion where the plug is replaced is reduced, and the labor for replacement is reduced. (5) The present technology can be introduced without making major changes to existing equipment, and cost performance is good.

[Brief description of drawings]

FIG. 1 is a schematic view showing a drilling process with a piercer.

FIG. 2 is a schematic diagram showing a drawing process with a piercer.

FIG. 3 is a schematic diagram showing a cooling process with a piercer.

FIG. 4 is a schematic diagram showing a waiting process in a piercer.

FIG. 5 is a graph illustrating the temperature history of plugs 1 to 3rd pass.

FIG. 6 is a graph illustrating a temperature history of plugs 1 to 20.

FIG. 7 is a graph illustrating the relationship between the wall thickness of the plug hole and the ultimate temperature.

FIG. 8 is a graph illustrating the punching time and the ideal wall thickness of the plug.

FIG. 9 is a sectional view of the plug according to the first embodiment of the present invention.

FIG. 10 is a sectional view of a plug according to a second embodiment of the present invention.

FIG. 11 is a sectional view of a plug according to a third embodiment of the present invention.

[Explanation of symbols]

1 ... Plug, 2 ... Plug piercing part, 3 ... Plug base part, 4
… Mandrel bar outer tube, 5… Mandrel bar inner tube, 6…
Reinforcement plate, 7 ... Plug wall thickness, 8 ... Mandrel bar, 9 ... Coolant flow direction, 13 ... External water cooling device, 14 ... Roll,
15 ... Billet (round steel slab), 16 ... Hollow shell (hollow shell).

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Fujibayashi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Shogo Tomita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Within the corporation (56) Reference JP-A-10-118703 (JP, A) Actual development Sho-53-43023 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B21B 25/00 -25/04

Claims (5)

(57) [Claims] 1. A plug base portion, a plug perforation portion, and a mandrel bar, wherein the plug base portion has a reinforcing material for reinforcing the plug perforation portion, and a cooling liquid is passed through the mandrel bar between the plug base portion and the plug perforation portion. A perforated plug, characterized in that it is provided with means for supplying and discharging. 2. A plug base portion, a plug perforation portion, and a mandrel bar, wherein the plug base portion has a reinforcing material for reinforcing the plug perforation portion, and the plug perforation is performed through the mandrel bar between the plug base portion and the plug perforation portion. A perforated plug, characterized in that it comprises means for supplying and discharging a cooling liquid at the tip of the portion. 3. A plug foundation portion, a plug perforation portion, and a mandrel bar, wherein the plug foundation portion complements the plug perforation portion.
A means for supplying and discharging the cooling liquid is provided at the tip of the plug piercing portion through a mandrel bar between the plug foundation and the plug piercing portion. A piercing plug, characterized in that it is formed by the portion and the plug piercing portion along the inner surface of the plug piercing portion. About wherein said plug perforation was characterized by its plug outer surface maximum temperature is used at 800 ° C. or less, drilling plug according to claim 1. 5. A perforation time: T for the plug perforation part.
The maximum thickness of the outer surface of the plug to be 800 ° C. or less according to s, the thickness of the plug perforated part: th is set based on the following formula (1) .
A perforated plug according to any of the above. th = 147 (Ts) ^-0.776 (1) where th: thickness of plug perforated portion (mm), Ts: perforation time (second).