KR100662900B1 - Multi layer metal rod and method for manufacturing the same - Google Patents

Abstract

A power transmission multiple metal rod with good high-temperature strength and a manufacturing method for the same are provided to improve power transmission characteristic in various frequency bands by inserting conductive copper rods into inner and outer pipes and using the inner pipe made of low-carbon steel. The power transmission multiple metal rod(1) with good high-temperature strength is composed of a conductive metal rod(10) for easily applying power; an inner metal pipe(30) fitted by the conductive metal rod and integrally welded with the conductive metal rod with covering the outside of the conductive metal rod, to keep the transmission characteristic of power in various frequency bands; and an outer metal pipe(50) inserted by the inner metal pipe fitted by the conductive metal rod and integrally welded with the inner metal pipe, to protect the metal rod and the inner pipe under high temperature and high pressure conditions.

Description

Multi-layered metal rod and method for manufacturing the same for power transmission with high temperature strength

1 is a perspective view showing a multi-metal rod for power transmission excellent in high temperature strength according to the present invention

Figure 2 is a partial cutaway perspective view of the present inventors multiple metal rods

Figure 3 is a schematic diagram showing the manufacturing step of the inventors multiple metal rods

Figure 4 (a) and (b) is a photograph showing a multiple metal rod of the present invention

Explanation of symbols on the main parts of the drawings

1 .... multiple metal rods

10 .... conductive metal rods (copper rods)

30 .... Endothelial Metal Pipe (Low Carbon Steel Pipe)

50 .... Sheath metal pipe (stainless steel pipe)

The present invention relates to a multi-metal rod for electric power transmission having excellent high temperature strength, which is used for electric power transmission or self-heating under high temperature, such as ground heating or oil drilling, and high temperature environment, and more specifically, It is durable and can be used as a safety well for power transmission or its own heating element even in harsh environments such as high temperature, high pressure ground heating or oil drilling operation, and especially in low and high frequency bands. The present invention relates to a multi-metal rod for power transmission having excellent high temperature strength and improved manufacturing method.

BACKGROUND ART A power (electrical) transmission medium known so far uses a conductive metal, for example, copper wire, which is easy to apply electricity, and wraps and uses various types of envelope materials in order to protect the copper wire.

However, such a conventional power transmission medium cannot be used in an environment of high temperature or high pressure due to the characteristics of the shell material, and especially when the length of the medium is long, it is difficult to use it under high tensile stress by its own weight. This was because, of course, the strength of the copper wire itself was weak.

On the other hand, especially high temperature and high pressure environment, which is used for power supply for heating rods for ground heating or for oil drilling equipment for drilling solid petroleum, or for supplying power to rock drilling equipment. It is impossible to use a power transmission medium in the form of a copper sheath with a simple shell such as when used.

Therefore, in order to enable the power transmission medium to be used at high temperature and high pressure, the high temperature strength of the medium must be increased. For example, a shell covering a copper medium (copper rod, copper wire), which is a conductive metal, has a high heat resistance, durability, and corrosion resistance. For example, stainless steel or the like is used.

For example, a high-temperature-powered power transmission medium (metal body) and a method of manufacturing the same that can be used in a high-temperature and high-pressure harsh environment such as ground heating or oil drilling operation have been filed by a Korean applicant. A patent application 2004-0063853 has been presented.

That is, in the patent application, the copper rod, which is a conductive metal body, and the stainless pipe, which is a shell metal body, which protects it, are integrally joined together without a seam, so that it can be used for power transmission or heating element even in a harsh environment such as high temperature, high pressure ground heating, or oil drilling. Disclosed is a multiple metal rod and a method of manufacturing the same.

Such a multi-metal body is particularly excellent in high temperature strength, and in particular, the problem of the conventional copper rods and stainless steel joining technology to improve the problem is characterized in that the copper rods and stainless pipes integrally bonded together.

However, the multi-metallic body proposed in the patent application is suitable for transferring power (voltage / current) due to the copper rod, which is a conductor, and can be used for heating elements, but there is a problem in terms of power transmission characteristics according to frequency bands. there was.

For example, from 50Hz to hundreds of Hz from low frequency to high frequency, the current tends to flow intensively on the surface of the multi-metal body, and in this case, the electrical resistance generated from the stainless steel, which is the shell of the multi-metal body, This rapidly increases, thereby causing a problem that the power transfer characteristics are degraded, and in particular, the power transferability is lowered toward higher frequencies.

Therefore, the applicant of the present invention can be used for power transmission or heating elements stably in a harsh environment of high temperature and high pressure, as well as high temperature strength with improved power transmission characteristics in various frequency bands regardless of low-high frequencies. Proposed multiple metal rods for transmission.

Such a multi-metal bar of the present invention, at a high temperature of about 735 ℃, at a depth of more than 1km underground, stably delivers power in a variety of frequency bands, as well as providing a high temperature strength, creep strength, and power transmission characteristics that can be used stably. something to do.

The present invention has been made in order to improve the conventional problems as described above, the object of the present invention is to provide heat resistance and durability stably for power transmission or its own heating element even in a harsh environment such as high temperature, high pressure ground heating or oil drilling operation. The present invention provides a multi-metal rod for power transmission having excellent high temperature strength and a method of manufacturing the same.

In addition, another object of the present invention is to provide a high-temperature strength multi-metal rod for excellent power transmission, and a method of manufacturing the same, in particular, including a low-carbon steel to the outer skin side to further improve the power transmission characteristics, regardless of the low-high frequency To provide.

As one technical aspect to achieve the above object, the present invention, a conductive metal rod easy to apply power;

An endothelial metal pipe which is inserted into the conductive metal rod to surround the outside thereof and is integrally bonded and maintains a power transmission characteristic at various frequencies; And,

An outer shell metal pipe which is inserted into the endothelial metal pipe into which the metal rod is inserted and integrally joined to protect the metal rod and the endothelial pipe under high temperature and high pressure;

It provides a multi-metal rod for power transmission excellent in high temperature strength configured to include.

In another aspect, the present invention, the pre-treatment step of providing an outer shell metal pipe with high durability and heat resistance, an inner shell metal pipe for stabilizing power transmission characteristics irrespective of the frequency band and a conductive metal rod having excellent power applicability;

A pipe insertion step of inserting a conductive metal rod into the endothelial metal pipe and inserting the conductive metal rod into the outer shell metal pipe;

A drawing step of integrally pointing the multiple inserted rods and pipes, and then performing a drawing process for preliminary joining to remove the space between the pipes while passing the die to reduce the cross-sectional area;

Heat-treating the pre-bonded metal rods and pipes to fully bond the pipes; And,

Post-processing multiple metal rods of fully bonded rods and pipes;

Provides a multi-metal bar manufacturing method for power transmission excellent in high temperature strength configured to include.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, as shown in Figures 1 and 2, the multi-metal rod 1 for power transmission excellent in high temperature strength according to the present invention is a conductive metal material capable of transferring electrical power, such as voltage / current, for example, a poor environment with only copper rods Since high temperature strength and creep strength cannot be secured at, the inner and outer metal pipes, which are relatively thick, for example, are inserted into the inner and outer pipes of low carbon steel and stainless steel pipes with low strength but excellent power applicability. And pipes are integrally joined to manufacture multiple metal rods.

In addition, the present invention is known so far, but is not a joining method between copper and stainless steel plate accompanying a number of problems, and after pre-bonding the inner and outer pipes surrounding the copper rod through the drawing process, which is a kind of cold plastic working. Since the pipes are integrally and completely joined together by heat treatment, they are made of multiple metal rods longer than a certain length, but there is no need for joint work between the copper rods and inner and outer pipes. In particular, it is possible to use stably even in a harsh environment of high temperature and high pressure.

On the other hand, as shown in Figures 1 and 2, the high-temperature, high-pressure multi-metal bar (1) of the present invention is largely easy to apply the power to the conductive metal rod 10 and, while surrounding the outside of the conductive metal rod 10 It is configured to include the inner and outer metal pipes 30 and 50 that are integrally bonded together seamlessly and configured to protect the conductive metal rods under high temperature and high pressure.

At this time, the conductive metal rod 10 is responsible for the transmission of electrical power, the endothelial metal pipe 30 maintains the characteristics of power transmission regardless of various frequencies, that is, low-high frequency, the outer pipe is a stainless pipe ( 50) provides the property of maintaining the high temperature strength of the metal rod.

That is, as shown in Figures 1 and 2, the multiple metal rod 1 of the present invention, the conductive metal rod 10 is easy to apply power, the double inner, outer shell metal pipe 30, 50 is completely Since it is a structure that is integrally joined together seamlessly while being wrapped in sequence, the conductive metal rod 10 having low strength even in an environment of high temperature and high pressure, for example, solid petroleum drilling or ground heating, has an inner and outer metal pipe 30. While being protected as (50), it is possible to stably maintain the power transmission (heating) or the heat-generating characteristics, and in particular, even when the length of use is long, bending phenomenon due to its own load is not easily generated.

At this time, preferably, the conductive metal rod 10 uses a copper rod having the highest conductivity, and the endothelial metal pipe 30 which covers and protects the conductive metal rod 10 uses a low carbon steel pipe having a carbon (C) content of 0.2% or less. , The outermost outer shell metal pipe 50 is used for high temperature strength stainless steel pipe excellent in durability and heat resistance.

However, the low carbon steel pipe, which is a low carbon steel pipe, which improves power transmission characteristics in various frequency bands, should have a carbon (C) content of 0.2% or less. When the difference in resistance is small, but the carbon content is lower than 0.2%, the electric resistance decreases significantly and at least maintains (improves) the power transmission characteristics in various frequency bands. The content is preferably 0.2% or less.

That is, in the multi-metal rod 1 of the present invention, the low carbon steel, which is the endothelial pipe 30, is weaker in terms of strength than stainless steel, but maintains a certain strength while maintaining the power transmission characteristic regardless of the frequency band. The copper rod 10 and the stainless shell pipe 50 are bonded to each other to solve the problem of power transmission instability in the high frequency band when the conventional stainless shell is used only.

On the other hand, since the outer shell metal pipe 50 must be equipped with heat resistance and durability, it is most preferable to use 347H-based stainless steel of stainless steel.

At this time, the bonding state between the conductive metal rod 10, which is the copper rod as described above, and the inner and outer shell metal pipes 30 and 50 surrounding it, is very important. For this purpose, in the present invention, the conductive metal rod 10 is first referred to as the endothelial metal pipe ( 30) and the inner skin metal pipe 50 into which the conductive metal rod 10 is inserted into the inner skin metal pipe 30 by inserting the copper rod and the inner and outer metal pipes 10, 30 and 50 into one. By drawing and heat-treating, when the copper rod and the inner and outer pipes 10, 30, 50 are connected, the gap is not generated at all without a seam, which will be described in more detail in the following manufacturing method.

Accordingly, the multi-metal rod 1 of the present invention is substantially poor in high temperature and high pressure, while the electric transmission medium copper rod 10 and the inner and outer metal pipes 30 and 50 that are wrapped on the outside thereof are integrally bonded together. It can be used very stably for power transmission or heating element even in the use environment.

And, as shown in Figure 1, the final diameter (D) of the multi-metal rod 1 of the present invention is 29-32 mm, most preferably 30.7 mm, which is each pipe 10, 30, 50 However, if the thickness is smaller than 29mm, the high temperature strength of the multiple metal rods is weak and cannot be used in the desired high temperature environment. As the cost increases due to drawing and heat treatment, the requirements of copper rods and inner and outer pipe materials are increased, and the handling, movement and storage of the produced multiple metal rods is not easy, the multiple metal rods of the above diameter range are most desirable.

And, in Figure 1, the low carbon steel endothelial pipe 30 is preferably composed of an outer diameter of 16-23 mm and a thickness of 2.5-4.5 mm, if the outer diameter is larger than the above range, the thickness of the outer pipe becomes thin (metal rod total diameter) Since the overall strength becomes weak and the outer diameter is smaller than the above range, the diameter of the central copper rod becomes smaller, resulting in a problem in that the resistance increases and the power loss increases during power transfer.

In addition, the shell pipe 50 made of 347H stainless steel in Figure 1 is preferably composed of an outer diameter of 29-32mm and a thickness of 4-6mm, since the outer diameter is equal to the overall product diameter (D) of this range Beyond this, the problem described earlier will occur.

On the other hand, the maximum allowable thickness of the endothelial pipe 30 is 4.5 mm and the maximum allowable thickness of the outer sheath pipe is 6 mm, which is substantially thicker than the endothelial pipe, since the outermost outer pipe is affected by temperature and pressure. This is because it is preferable.

Next, the manufacturing steps of the present invention the multi-metal bar 1 based on Figure 3 as follows.

First, as shown in Figure 3, the pre-treatment step (S1) is carried out, in this pre-treatment step (S1), the copper rod, the conductive metal rod 10, and the inner and outer shell metal pipes 30, 50 low carbon steel And prepare stainless pipes of appropriate diameter and thickness.

At this time, in the pre-treatment step of the shell stainless pipe 50, the heat treatment (S12) of the produced (S11), and then the film process (S14) for forming a lubricating film layer on the surface of the stainless pipe through the pickling process (S13) Perform.

Then, the endothelial low carbon steel pipe 30 (S15) is heat-treated (S16) to have a strength at high temperature, and then subjected to pickling, calibration (S17) to facilitate the insertion of the copper rod 10 and the outer diameter of In order to increase the dimensional accuracy, the tireless polishing (S18) is performed.

At this time, the outer diameter of the copper rod 10, which is the material of phosphorous power produced in the pretreatment step (S1) is 18-22mm, and the copper rod and inner and outer pipes 30 and 50 are 26-30mm and 38-42, respectively. It has an outer diameter of mm, the outer diameter of each of the pipes in consideration of the diameter of the final multi-metal bar (1) described above, taking into account the rate of cross-sectional reduction generated during drawing.

Next, the step of inserting the copper rods and pipes for joining the copper rod 10 and the inner and outer metal pipes 30 and 50 prepared as described above (S2) is performed, first, the surface of the endless low carbon steel pipe The copper rod 10 prepared in the inside of the 30 is inserted (S21), and the endothelial low carbon steel pipe 30 into which the copper rod is inserted is inserted into the inside of the shell stainless pipe 50 (S22).

At this time, the outer surface of the endothelial low carbon steel pipe 30 to increase the precision through the tireless grinding in the pretreatment step, to facilitate the insertion into the stainless pipe (50).

Next, a drawing step (S3) for integrally pre-bonding the copper rod 10 and the inner and outer shell metal pipes 30 and 50 integrally inserted through the insertion step (S2) as described above is performed.

That is, this drawing step (S3), first, the pointing work so as not to slip each other during the drawing process of each copper rod and the inner and outer pipes, that is, the copper rod and one end of the pipes about 250-300mm integrated point (pointing machine Using a) to reduce the outer diameter to perform the pointing operation (S31) to prevent the pipes from slipping each other during the drawing operation.

And, the pipes of the pointing work is completed through the drawing (S32) through each pipe 10, 30, 50 as the cross-sectional area is reduced, the preliminary bonding state in which the space (gap) between each pipe is eliminated and in close contact with each other To be.

At this time, such drawing (S32) is pulled to the opposite side through the die (die) to the copper rod 10 and the pipe 30, 50 of a predetermined diameter in the form of a hole formed in the die By processing into a cross-sectional product according to the present invention, since a die of a cemented carbide is used in recent years, the degree of drawing processing can be performed very precisely.

In the drawing process (S32) of the present invention, when the overall diameter of the multi-metal bar 1 described above is 29-32mm, preferably 30.7mm, the machining is performed under the condition of 19.0-42.0% cross-sectional reduction rate.

At this time, if the cross-sectional reduction rate of the drawing process is less than 19.0%, a drawing work process and a subsequent process are added to cause problems such as work efficiency and yield reduction. On the contrary, if the cross-sectional reduction rate is higher than 42.0%, the processing rate is high instead of the material. The problem that the consumption becomes excessively necessary, and most preferably, when the diameter of the multi-metal bar produced through the final step of the present invention is 30.7 mm, the cross-sectional reduction rate is 34%.

Next, as shown in Figure 3, after the drawing step (S3) is performed, the heat treatment step (S4) is performed, in this heat treatment step processing of the copper rod 10 and the stainless steel 50 generated in the drawing step While eliminating the hardening, the bonding force between the copper rods 10 pre-bonded in the drawing step and the respective low carbon steel and stainless pipes 30 and 50 is increased to completely bond the bonded state.

At this time, the pre-bonded copper rod 10 and the inner and outer pipes (30, 50) in an atmosphere heat treatment furnace for heat-treating through the atmosphere gas, the temperature of approximately 400-600 ℃, preferably 500 ℃ 1 to 2 hours Preferably it is heated for 1.5 hours to heat-treat the joined multiple metal rods 1 and then cool by air cooling.

At this time, if the heat treatment temperature is lower than 400 ℃ 구리 the effect of removing the internal stress of the copper bar is insufficient, on the contrary, if higher than 600 ℃ the thermal expansion difference between the copper rod and the outer pipe is generated and the phenomenon of the separation between the pipes due to the slip phenomenon. In the case of heat treatment, a suitable temperature range during the heat treatment is 400-600 ° C., for example, 500 ° C. is most suitable when the diameter of a multi-metal rod is 30.7 mm.

Therefore, the copper rods pre-bonded in the drawing step and the inner and outer pipes can be seamlessly joined together seamlessly during the heat treatment step.

Next, the multi-metal rod 1 of the present invention completely bonded without passing through the heat treatment step (S4) undergoes a post-treatment step (S5), in this post-treatment step, the upper and lower rolls of the multi-metal bar bent during the heat treatment Using a type of straightening machine (straightening machine) to correct to maintain a constant straightness (S51), and cut the corrected power carrier to a certain length (S52), the scale of oxidation that can be generated on the surface of the stainless pipe during heat treatment Surface treatment to remove the (S53) is performed.

In this case, when the final production of the dimensional precision of the multi-metal bar (1) is required to be subjected to tireless polishing work on the outer surface during the surface treatment, if the dimensional accuracy is not required to perform a shot blast to remove the scale of oxidation of the surface Finally, the multi-rod bar product is finally produced through the inspection and packaging steps.

Hereinafter, a description will be given of an embodiment of a multi-metal bar 1 for power transmission excellent in high temperature strength according to the present invention, the multi-metal bar 1 produced in this embodiment has a total diameter of 30.7 mm.

In this case, the material specifications of the copper rod and the inner and outer shell metal pipes 30 and 50, which are the conductive metal rods 10 prepared in the pretreatment step S1 of phosphorescence, are shown in Table 1 below.

Specifications of copper rods and pipes before drawing, prepared in the pretreatment stage. division Outer diameter (mm) Thickness (mm) Inner diameter (mm) Jacketed Pipes (50) 39.5 5.2 29.1 Endothelial Pipe (30) 28.2 3.4 21.4 Copper Rod (10) 20.0 - -

At this time, the copper rod 3.5m, pipes 30, 50 after providing a length of 4m, heat treatment (S12) (S16), pickling (S13) (S16), lubricating film (S14) or non-abrasive (S18) Through the pretreatment step (S1) was performed.

At this time, in the case of the outer shell stainless pipe 50, the particle size should be maintained in the 4.5 to 6.5 to secure high temperature strength, for this purpose was carried out heat treatment (S12) for heating for 10 minutes or more at 1170 ℃ or more.

In addition, the straightness of the endothelial low carbon steel pipe 30 into which the copper rod 10 is inserted is calibrated to be 3/1000 or less, which is to enable insertion of the copper rod into the endothelial pipe within a 1 mm tolerance.

Next, the copper rod 10 is inserted into the endothelial pipe 30 (S21), and then the endothelial pipe 30 is inserted into the outer shell pipe 50 integrally with the copper rod (S22), and the diameter is 250 mm long. After pointing the end under the condition of 28 mm, the copper rod and the inner and outer pipes were drawn (S3) while passing through a die with a diameter of 30.7 mm, and the cross-sectional reduction rate was 34%.

Next, the copper rod 10 and the inner and outer pipes 30 and 50 in the preliminary bonded state in which the space (gap) between the metal bodies is lost through the drawing process are heat-treated at 500 ° C. for 1.5 hours in an atmosphere heat treatment furnace ( S4), the copper rod and the inner and outer pipe were completely integrally bonded.

Next, the copper rod, which is a conductive metal body, and the shell metal pipes surrounding the conductive metal body are straightly connected to each other by a straightener through a straightener (S51), and cut to a length of about 6 m (S52), and then formed on the surface. The surface treatment was performed to remove the scale using the shot blast (S53).

Therefore, the multi-metal rod 1 of the present invention, which is used in high temperature and high pressure harsh environments, for example, ground heating or solid petroleum drilling, is connected to copper bars, which are conductive metals, and inner and outer metal pipes, which are shields. By integrally bonding together, not only facilitates the manufacture of the multi-metal bar itself, but also can greatly reduce the cost, and in particular, it is possible to stably use even in a harsh environment of high temperature and high pressure.

In particular, the low carbon steel endothelial pipe 30 having a low carbon (C) content of 0.2% or less is bonded to the copper rod 10 even in a high frequency band, thereby improving power transmission characteristics regardless of low-high frequencies. It can be used stably regardless of low-high frequency.

Next, Figure 4 shows a photograph of the multi-metal bar 1 of the present invention manufactured by the manufacturing step as described above.

That is, as shown in Figure 4, the multi-metal rod 1 of the present invention can be seen that the copper rod 10, which is a conductive metal and the inner, outer shell pipe 30, 50 that is a protective body is integrally completely joined. . Overall, the multiple metal rods 1 of the present invention may be stably used even in a harsh environment of high temperature and high pressure for power transmission (supply) or its own heating element.

In the case of a long elongation, the clamping strength will be maintained.

According to such a multi-metal rod for electric power transmission excellent in high temperature strength and a method of manufacturing the same according to the present invention, a power transmission body such as a power supply line or a heating element, which requires high temperature strength and high temperature creep strength, has heat resistance, durability, and corrosion resistance. It provides the effect of stable use even in harsh environments such as ground heating and oil drilling.

In addition, since the double metal pipe is wrapped in the copper rod, which is a conductive metal body, there is another effect of further enhancing the heat resistance, durability, and corrosion resistance of the multiple metal rod.

In particular, it is possible to insert conductive copper rods into inner and outer pipes, and to draw them integrally and heat-treat them, while using low carbon steel endothelial pipes to improve power transfer characteristics at various frequencies regardless of low-high frequencies. To provide.

While the invention has been shown and described in connection with specific embodiments so far, it will be appreciated that the invention can be varied and modified without departing from the spirit or scope of the invention as set forth in the claims below. It will be appreciated that those skilled in the art can easily know.

Claims (11)

Conductive metal rods easy to apply power; An endothelial metal pipe which is inserted into the conductive metal rod to surround the outside thereof and is integrally bonded and maintains power transmission characteristics at various frequencies; And, An outer shell metal pipe which is inserted into the endothelial metal pipe into which the metal rod is inserted and integrally joined to protect the metal rod and the endothelial pipe under high temperature and high pressure; Multi-metal rods for excellent power transfer, including high temperature strength configured. The multi-metal rod of claim 1, wherein the conductive metal rod is made of a copper rod, the shell metal pipe is made of a low carbon steel pipe, and the shell metal pipe is made of a stainless pipe having excellent durability and heat resistance. The method according to claim 2, wherein the endothelial metal pipe is made of low carbon steel having a carbon (C) content of 0.2% or less, and composed of an outer diameter of 16-23 mm and a thickness of 2.5-4.5 mm, The outer shell metal pipe is made of 347H stainless steel, a multi-metal rod, characterized in that the outer diameter of 29-32mm and made of 4-6mm thick. The method of claim 1, wherein the conductive metal rods are inserted into the endothelial metal pipes, and after they are inserted into the outer shell metal pipes, the copper rods and the respective pipes are integrally joined together seamlessly after being drawn and heat treated. Multiple metal rods, characterized in that composed of a diameter of 32 mm. A pretreatment step of providing a shell metal pipe having high durability and heat resistance and an inner shell metal pipe for stabilizing power transmission characteristics regardless of frequency bands, and a conductive metal rod having excellent power applicability; A pipe insertion step of inserting a conductive metal rod into the endothelial metal pipe and inserting the conductive metal rod into the outer shell metal pipe; A drawing step of integrally pointing the multiple inserted rods and pipes, and then performing a drawing process for preliminary joining to remove the space between the pipes while passing the die to reduce the cross-sectional area; Heat-treating the pre-bonded metal rods and pipes to fully bond the pipes; And, Post-processing multiple metal rods of fully bonded rods and pipes; Multi-metal bar manufacturing method for power transmission excellent in high temperature strength configured to include. The method of claim 5, wherein the pre-treatment step, a conductive metal rod of a predetermined length, and inner and outer metal pipes are provided, and the inner and outer metal pipes are heat-treated and pickled, and the outer metal pipes are subjected to a coating process. Forming a lubricating film on the surface, the surface of the endothelial metal pipe is a multi-metal rod manufacturing method, characterized in that the non-grinding treatment. The method of claim 5 or 6, wherein the conductive metal rod is provided with a copper rod, the endothelial metal pipe is composed of a low carbon steel pipe having a carbon (C) content of 0.2% or less, the outer metal pipe is excellent in durability and heat resistance 347H-based stainless steel pipe manufacturing method characterized in that consisting of. The phosphorus outer diameter of the conductive metal rod is 18-22 mm, the phosphorus outer diameter of the inner and outer pipes is composed of 26-30 mm and 38-42 mm, respectively, The cross-sectional reduction rate, which is the drawing condition of the drawing step, is 19.0-42.0%, characterized in that the multiple metal rod manufacturing method. The method of claim 5, wherein the metal rods and pipes pre-bonded in the heat treatment step after the drawing step are heat treated at a temperature of 400-600 ° C. 6. The method of claim 5, wherein the post-treatment step comprises a surface treatment step of correcting the bent pipe during the heat treatment, cutting it to a certain length, and removing the surface scale of the shell metal pipe. 6. The method of claim 5, wherein the multi-rod metal rod has a final diameter of 29-32 mm.

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