US20080196550A1

US20080196550A1 - Method of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold

Info

Publication number: US20080196550A1
Application number: US12/025,560
Authority: US
Inventors: Toshio Abe; Masayuki ANDOU
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 2005-08-02
Filing date: 2008-02-04
Publication date: 2008-08-21
Also published as: JP2007038252A; JP4593397B2; WO2007015491A1

Abstract

A method of producing an oxygen-free copper wire material, containing: continuously guiding a molten copper obtained by melting electric copper, into a tundish through a conduit; injecting the molten copper in the tundish, into a rotational movable mold; cooling and solidifying the molten copper, to form an ingot; and continuously drawing the ingot out of the mold, followed by continuous rolling; the method further containing: allowing the molten copper in the conduit to react with a solid reducing agent, under blowing an inert gas thereinto; allowing the molten copper in the tundish to react with a solid reducing agent, under blowing an inert gas thereinto; and adding a phosphorus compound to the molten copper, so that the phosphorus content in the ingot would be from 1 to 10 ppm; and controlling the temperature of the molten copper in the tundish from 1,085 to 1,100° C.

Description

TECHNICAL FIELD

The present invention relates to a method of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold.

BACKGROUND ART

Oxygen-free copper wire materials have been usually produced by a dip forming method and a continuous cast-rolling method or the like, using a rotational movable mold, typical examples thereof include a belt and wheel method. The dip forming method is a method of: continuously solidifying an oxygen-free molten copper on an outer circumference of an oxygen-free copper core rod, to obtain a copper bar material; and rolling the copper bar material. This method, however, has such a drawback that the production facilities are small with low productivity, thereby to render the production cost high. On the other hand, the continuous cast-rolling method using a rotational movable mold is a method of: injecting a molten copper which has been melted in a large melting furnace, such as a shaft furnace, into a rotational movable mold casting machine, which is constituted of an endless belt that performs a circulating transfer motion and a casting wheel that rotates with a part of the circumference of the casting wheel in contact with the endless belt; solidifying the molten copper by cooling, to form an ingot; and continuously drawing and rolling the ingot. By this method, it is possible to conduct mass production using large-scale facilities with a low production cost. Further, in the conventional continuous cast-rolling method using a rotational movable mold, an oxygen-free copper is obtained, by conducting a reducing treatment with a reducing gas and/or an inert gas in mid course of conveying the molten copper from the melting furnace to the casting machine.
However, in producing oxygen-free copper wire materials by the aforementioned continuous cast-rolling method using a rotational movable mold, when an ingot is formed by cooling and solidifying the molten copper, holes and cracks occur in the resultant ingot, and when rolling, streaks or scratches (flaws) occur on the surface of the oxygen-free copper wire material, each of which cause the problem of surface quality deterioration.
With respect to the problem, by taking note of hydrogen in the molten copper as a cause of the aforementioned holes and cracks to occur in the ingot, known techniques include: dehydrogenating the molten copper, by stirring the molten copper, or by providing weirs for allowing the flow passage of the molten copper to meander, in mid course of conveying the molten copper; or improving the surface quality of oxygen-free copper wire material, by reducing the concentration of hydrogen in the oxygen-free copper wire material to 1 ppm or less. However, even by using these techniques, incidence of holes and cracks in the ingot is not so decreased, and streaks or scratches on the surface of the oxygen-free copper wire material upon rolling is not so suppressed from being occurred. Consequently, the surface quality of the oxygen-free copper wire material remained insufficient yet.
Furthermore, although it is not described to be used in the continuous cast-rolling method using a rotational movable mold, with respect to the technique in mid course of conveying molten copper, it is known to adjust the content of phosphorus to the range from 10 to 140 ppm, in a conduit for conveying the molten copper from the melting furnace to the casting machine, and to reduce the molten copper with a solid reducing agent, followed by blowing an inert gas into the molten copper under stirring, thereby to deoxidize the molten copper. When this technique is combined with the continuous cast-rolling method using a rotational movable mold, incidence of holes and cracks in the ingot which is obtained by cooling and solidifying the molten copper can be reduced, and streaks or scratches on the surface of the resultant oxygen-free copper wire material can be hardly formed upon rolling, to thereby make it possible to give an oxygen-free copper wire material having a good surface quality. Herein, ‘oxygen-free copper’ means copper whose oxygen content is 10 ppm or less.
However, the oxygen-free copper wire material produced by combining the aforementioned known deoxidization of molten copper and continuous cast-rolling method using a rotational movable mold, contains as high as from 10 to 140 ppm of phosphorus that serves as an impurity, although the material is referred to an oxygen-free copper. Consequently, the electric conductivity of the drawn oxygen-free copper wire obtained by further applying cold-working to the oxygen-free copper wire material is as low as less than 98%, and it has such a problem that the resultant wire cannot be used for applications in which a high electric conductivity of 98% or more prescribed in JIS C1011 temper (quality rank) H is required.

DISCLOSURE OF INVENTION

One aspect of the present invention contemplates for providing a method of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold, at a low production cost, with a good surface quality, and by which method a drawn oxygen-free copper wire having an electric conductivity as high as 98% or more can be obtained by further applying the oxygen-free copper wire material to cold-rolling.
According to the present invention, there is provided the following means:
(1) A method of producing an oxygen-free copper wire material, comprising the steps of:
continuously guiding a molten copper obtained by melting electric copper, into a tundish through a conduit;
injecting the molten copper in the tundish, into a rotational movable mold;
cooling and solidifying the molten copper, to form an ingot; and
continuously drawing the ingot out of the mold, followed by subjecting the drawn ingot to continuous rolling,
the method further comprising the steps of:
allowing the molten copper in the conduit to react with a solid reducing agent;
blowing an inert gas into the molten copper;
allowing the molten copper in the tundish to react with a solid reducing agent; and
blowing an inert gas into the molten copper; and
adding a phosphorus compound to the molten copper, so that the phosphorus content in the ingot would be from 1 to 10 ppm; and
controlling the temperature of the molten copper in the tundish in the range from 1,085 to 1,100° C.;
(2) The method of producing an oxygen-free copper wire material according to Item (1), wherein the phosphorus compound is added to the molten copper, so that the phosphorus content in the ingot would be from 2 to 8 ppm; and
(3) The method of producing an oxygen-free copper wire material according to Item (1) or (2), wherein the temperature of the molten copper is controlled in the range from 1,085 to 1,095° C.
Other and further features and advantages of the invention will appear more fully from the following description, appropriately referring to the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING [FIG. 1]

FIG. 1 is an explanatory diagram showing an example of the method of the present invention of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold.

DESCRIPTION OF NUMERICAL REFERENCES

1 Shaft furnace
2 Conduit
3 Tundish
4 Nozzle for injecting a molten copper
5 Molten copper
6 Belt
7 Wheel
8 Turn roll(s)
9 Ingot
10 Rolling machine
11 Wire material
12 Coiler
13 Pallet

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the method according to the present invention of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold will be described in detail, with reference to the drawing. FIG. 1 is an explanatory diagram showing an example of the production method according to the present invention.
As shown, for example, in FIG. 1, the method according to the present embodiment of producing an oxygen-free copper wire material comprises the steps of: obtaining a molten copper (not shown) by melting virgin ingot of electric copper or the like using a shaft furnace 1 under a reducing atmosphere; continuously guiding the molten copper into a tundish 3 through a conduit 2; injecting the molten copper in the tundish 3 into a rotational movable mold (not shown) composed of a belt 6 and a wheel 7 both rotating with turn rolls 8; cooling and solidifying the molten copper, to form an ingot 9 thereof; continuously drawing the ingot 9 out of the mold; and continuously rolling the drawn ingot as it is directly with a rolling machine 10. The rotational movable mold is not limited to a so-called belt-and-wheel-type rotational movable mold, which is composed of the belt 6 and the wheel 7, as shown in FIG. 1, and in addition to that, use may be made, for example, of a so-called twin belt-type rotational movable mold, which is composed of two belts.
In this method, the molten copper is allowed to react with a solid reducing agent (not shown) in the conduit 2, and an inert gas (not shown) is blown into the molten copper, and further the molten copper is also allowed to react with the solid reducing agent in the tundish 3, and the inert gas is blown into the molten copper; in addition to the above, a phosphorus compound, for example, copper phosphide (abbreviated to as CuP, hereinafter), is added to the molten copper so that the phosphorus content in the ingot would be from 1 to 10 ppm, preferably from 2 to 8 ppm, and the temperature of the molten copper in the tundish 3 is controlled in the range from 1,085 to 1,100° C., preferably from 1,085 to 1,095° C.
There is no particular limitation on the method of allowing the molten copper to react with the solid reducing agent in the conduit 2, under blowing the inert gas into the molten copper, including the conditions thereof, such as the amount, kind, size, void ratio or the like of the solid reducing agent to be used, and the kind, amount or the like of the inert gas to be used. Examples of the method include a method of: allowing charcoal to float on the surface of the molten copper to an extent enough for covering most of the surface; and forcibly blowing nitrogen gas or argon gas from the bottom of the molten copper. Furthermore, the molten copper is allowed to react with the solid reducing agent in the conduit 2, under blowing the inert gas into the molten copper, this is to conduct, for example, deoxidization and dehydrogenation of the molten copper.
The method of allowing the molten copper to react with the solid reducing agent in the tundish 3, under blowing the inert gas into the molten copper is not particularly limited in the same manner as in the above-mentioned method in the conduit 2. Further, the method of adding the phosphorus compound into the molten copper so that the phosphorus content in the ingot would be in the range from 1 to 10 ppm is also not particularly limited, and examples of the method include a method of adding a suitable amount of CuP to the molten copper. For example, in the same manner as in the method in the conduit 2, charcoal is allowed to float on the surface of the molten copper so that the surface is almost covered with the charcoal, nitrogen gas or argon gas is forcibly blown from the bottom of the molten copper, and CuP is added to the molten copper in an amount that gives a phosphorus content of from 1 to 10 ppm in the ingot. In this method, the CuP to be added preferably has a particulate shape of a particle diameter of about 2 mmφ so that dissolution and dispersion of CuP can be conducted easy in the molten copper.
Further, the temperature of the molten copper in the tundish 3 is controlled in the range from 1,085 to 1,100° C., preferably from 1,085 to 1,095° C., and the method and apparatus for controlling the temperature are not particularly limited. The temperature of the liquid metal in the tundish 3 is preferably controlled, by providing a temperature controlling tank at a vicinity of the tundish in the conduit 2.
Furthermore, the molten copper is allowed to react with the solid reducing agent in the tundish 3 and the inert gas is blown into the molten copper, this is to conduct, for example, deoxidization and dehydrogenation of the molten copper in the same reason as mentioned in the above. The phosphorus compound is added to the molten copper in the tundish 3, for the purpose of conducting deoxidization of the molten copper as well as conducting dehydrogenation, thereby decreasing the number of holes in the ingot, and further for the purpose that the residual phosphorus compound in the ingot allows the strength at crystal grain boundaries to be enhanced and incidence of cracking in the ingot to be reduced. Furthermore, the temperature of the molten copper in the tundish 3 is adjusted in the range from 1,085 to 1,100° C., for the purpose of remarkably exhibiting dehydrogenation of the molten copper with the phosphorus compound and enhancement of the strength at the crystal grain boundaries of the ingot, so that incidence of holes and cracks in the ingot is reduced, and that scratches and streaks on the surface of the oxygen-free copper wire material are hardly occurred upon rolling, even when the phosphorus content in the ingot is as small as 10 ppm or less.
Further, the phosphorus compound is added to the molten copper in the tundish 3, for the purpose of improving the addition yield and of facilitating the controlling of the phosphorus content in the oxygen-free copper wire as a final product.
The phosphorus content in the ingot is set to the range from 1 to 10 ppm, and this is because, when the phosphorus content is less than 1 ppm, incidence of holes and cracks in the ingot obtained by cooling and solidifying the molten copper cannot be decreased, and scratches and streaks on the surface of the oxygen-free copper wire material are liable to appear upon rolling, to thereby deteriorate the surface quality. On the other hand, when the phosphorus content exceeds 10 ppm, the electric conductivity of the drawn oxygen-free copper wire obtained by further subjecting the oxygen-free copper wire material to cold-working becomes as low as less than 98%.
The temperature of the molten copper in the tundish 3 is set to the range from 1,085 to 1,100° C. This is because the molten copper may be solidified at a temperature of less than 1,085° C. On the other hand, when the temperature exceeds 1,100° C., dehydrogenation of the molten copper with the phosphorus compound and enhancement of the strength at the crystal grain boundaries of the ingot cannot be sufficiently exhibited, and consequently, incidence of holes and cracks in the ingot obtained by cooling and solidifying of the molten copper increases, and scratches and streaks on the surface of the oxygen-free copper wire material upon rolling tend to occur.
Furthermore, a holding furnace may be provided between the shaft furnace 1 and the conduit 2, or at the midway of the conduit 2, although it is not shown in FIG. 1.
According to the continuous cast-rolling method of the present embodiment using a rotational movable mold, an oxygen-free copper wire material having a good surface quality can be produced with a low production cost. Further, a drawn oxygen-free copper wire, which is obtained by further subjecting the oxygen-free copper wire material to cold-working, has an electric conductivity as high as 98% or more.

EXAMPLES

The present embodiment will be described in more detail based on examples given below, but the invention is not meant to be limited by these.
In the continuous cast-rolling method using a rotational movable mold as shown in FIG. 1, a molten copper was obtained by melting an electric copper ingot in the shaft furnace 1 under a CO atmosphere; the molten copper was continuously guided into the tundish 3 through the conduit 2; the resultant molten copper 5 in the tundish 3 was injected into the rotational movable mold composed of the belt 6 and wheel 7, from the injection nozzle 4 attached to the tundish 3, to obtain the ingot 9 by cooling and solidifying of the molten copper; the ingot 9 was continuously drawn out of the mold; and the drawn ingot was directly subjected to continuous rolling with the rolling machine 10, to form an oxygen-free copper wire rod with a diameter of 8 mmφ, and then the thus-obtained wire material 11 was wound onto a pallet 13 by means of a coiler 12.
At that time, charcoal in an amount enough for covering almost the surface of the molten copper was made to float on the surface of the molten copper in the conduit 2, and nitrogen gas was forcibly blown at a flow rate of 200 liter/min from the bottom of the molten copper. Further, charcoal in an amount enough for covering almost the surface of the molten copper was also made to float on the surface of the molten copper in the tundish 3, and nitrogen gas was forcibly blown at a flow rate of 200 liter/min from the bottom of the molten copper. Granular CuP with diameter 2 mmφ was added to the molten copper in the tundish 3 so that the phosphorus content in the ingot would be in the range from 0 to 20 ppm (CuP was not added, when the phosphorus content was 0 (zero)), and the temperature of the molten copper in the tundish was controlled in the range from 1,085 to 1,150° C. Specifically, the oxygen-free copper wire rods with diameter 8 mmφ were produced by the production methods in Examples 1 to 7 and Comparative Examples 1 to 4, respectively, with the respective temperature of the molten copper in the tundish and the respective phosphorus content of the wire rod, as shown in Table 1 below, (CuP was added to the molten copper in the tundish 3, so that the phosphorus content in the wire rod would be met). Further, the oxygen-free copper wire rod was further applied to cold-working, to produce a drawn oxygen-free copper wire with diameter 2.6 mm+.
Then, the surface quality of the thus-obtained oxygen-free copper wire rod was evaluated, and electric conductivity was measured with respect to the drawn oxygen-free copper wire obtained by further subjecting the oxygen-free copper wire rod to cold working. Further, with respect to the oxygen-free copper wire rod, the phosphorus content thereof was measured, and the contents of oxygen and hydrogen were also measured by well-known measures. The results are summarized in Table 1.
Furthermore, the surface quality was qualitatively evaluated with respect to the number and size of stretches and streaks, using an eddy current stretch/streak tester (an eddy current tester, manufactured by Foerster Japan, Ltd.). The meanings of marks representing the level of surface quality in Table 1 are as follows: i.e. “∘∘” represents quite excellent with substantially no stretches and streaks on the surface; “∘” represents no problem of practical use, although some small stretches and streaks were seen on the surface; “x” represents not usable with a substantially large number of small stretches and streaks or some large stretches and streaks on the surface; and “xx” represents no commercial value with many large stretches and streaks on the surface.

	TABLE 1

	Example	Comparative example

	1	2	3	4	5	6	7	1	2	3	4

Temperature (° C.) of	1,090	1,085	1,085	1,095	1,100	1,095	1,090	1,090	1,095	1,150	1,090
molten copper in
tundish
Phosphorus content
	1	2	3	3	3	8	10	0	0.5	3	20
(ppm) in wire rod
Surface quality of wire	∘	∘∘	∘∘	∘∘	∘	∘∘	∘∘	xx	x	x	∘∘
rod
Electric conductivity	99.5	99.4	99.1	99.1	99.1	98.5	98.1	99.6	99.5	99.1	96.8
(%) of drawn
oxygen-free copper
wire
Oxygen content (ppm)	6	6	5	5	5	5	4	7	6	5	3
in wire rod
Hydrogen content	0.5	04	0.4	0.4	0.4	0.4	0.4	0.6	0.5	0.4	0.4
(ppm) in wire rod

As is apparent from Table 1, the oxygen-free wire rods in Examples 1 to 7, which were produced by adding CuP to the molten copper in the tundish so that the phosphorus content in the ingot would be in the range from 1 to 10 ppm and the temperature of the molten copper in the tundish was set to the range from 1,085 to 1,100° C., had good surface quality, and the electric conductivity of the drawn oxygen-free copper wires obtained by cold-working the oxygen-free copper wire rods was as high as 98% or more. Further, the oxygen-free copper wire materials were sufficient for use, with the oxygen content in the range from 4 to 6 ppm and the hydrogen content in the range from 0.4 to 0.5 ppm.
Further, it is also apparent that the oxygen-free wire rods in Examples 2, 3, 4 and 6, which were produced by adding CuP to the molten copper in the tundish so that the phosphorus content in the ingot would be in the range from 2 to 8 ppm and the temperature of the molten copper in the tundish was set to the range from 1,085 to 1,095° C., were quite excellent in the surface quality, and the electric conductivity of the drawn oxygen-free copper wires obtained by cold-working of the oxygen-free copper wire rods was as quite high as 98.5% or more. Of course, the oxygen-free copper wire materials were sufficient for use, with the oxygen content in the range from 5 to 6 ppm and the hydrogen content of 0.4 ppm.
Contrary to the above, Comparative Examples 1 and 2 were examples for comparison, in which CuP was added to the molten copper in the tundish so that the phosphorus content in the ingot was less than 1 ppm; although the electric conductivity of the drawn oxygen-free copper wire obtained by cold-working of the oxygen-free copper wire rod was as quite high as 99.5% or more, the surface quality was poor. In particular, the surface quality in Comparative Example 1 in which no CuP was added was quite poor. Since the amount of addition of phosphorus was less than 1 ppm, dehydrogenation of the molten copper was insufficient and the strength at crystal grain boundaries in the ingot was insufficiently enhanced, and it was impossible to suppress holes and cracks from being occurred in the ingot.
In Comparative Example 3, CuP was added to the molten copper in the tundish so that the phosphorus content in the ingot was 3 ppm, which satisfies the range according to the present embodiment from 1 to 10 ppm. However, at that condition, the temperature of the molten copper in the tundish was 1,150° C., which is outside of the temperature range according to the present embodiment from 1,085 to 1,100° C. In other words, Comparative Example 3 only differs from Examples 3, 4 and 5 in the temperature of molten copper. Consequently, the surface quality was poor in Comparative Example 3, as in Comparative Examples 1 and 2. This is because, due to the temperature that exceeded 1,100° C., it was impossible to sufficiently exhibit dehydrogenation of the molten copper by the added phosphorus compound and enhancement of the strength at the crystal grain boundaries of the ingot, and it was impossible to suppress holes and cracks from being occurred in the ingot obtained by cooling and solidifying the molten copper.
As described in the above, in the method of the present embodiment of producing an oxygen-free copper wire material by a continuous cast-rolling method using a rotational movable mold, the molten copper was allowed to react with a solid reducing agent in a conduit, an inert gas was blown into the molten copper, the molten copper was allowed to react with a solid reducing agent in the tundish, and an inert gas was blown into the molten copper, and in addition to those, a phosphorus compound was added in the molten copper so that the phosphorus content in the ingot would be in the range from 1 to 10 ppm, and the temperature of the molten copper in the tundish was controlled to the range from 1,085 to 1,100° C. Consequently, the oxygen-free copper wire material good in the surface quality can be produced with a low cost, and the drawn oxygen-free copper wire obtained by further subjecting the oxygen-free copper wire material to cold-working has an electric conductivity as high as 98% or more.

INDUSTRIAL APPLICABILITY

The method of the present embodiment of producing an oxygen-free copper wire material can produce an oxygen-free copper wire material good in surface quality with a low production cost, and the drawn copper wire obtained by cold-working the oxygen-free copper wire material has a high electric conductivity. Thus, the thus-obtained oxygen-free copper wire material can be favorably used, for example, for conductors, codes, and cables, which are used for interior or exterior wiring of electric and electronic instruments.
Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

Claims

1-5. (canceled)

5. A method of producing an oxygen-free copper wire material, comprising the steps of:

continuously guiding a molten copper obtained by melting copper material;

allowing the molten copper to react with a solid reducing agent, and blowing an inert gas into the molten copper;

adding a phosphorus compound to the molten copper;

controlling the temperature of the molten copper in the range from 1,085 to 1,100° C.;

injecting the molten copper into a rotational movable mold;

cooling and solidifying the molten copper to form an ingot whose phosphorus content is in the range from 1 to 10 ppm; and

continuously drawing the ingot out of the mold, followed by subjecting the drawn ingot to continuous rolling, to form a rod.

6. The method of producing an oxygen-free copper wire material according to claim 5, wherein the molten copper is guided into a tundish through a conduit by the step continuously guiding the molten copper obtained by melting copper material.

7. The method of producing an oxygen-free copper wire material according to claim 6, wherein the step of allowing the molten copper to react with a solid reducing agent, and blowing an inert gas into the molten copper, is done in the tundish and/or conduit.

8. The method of producing an oxygen-free copper wire material according to claim 5, wherein the phosphorus compound is added in the step of adding a phosphorus compound to the molten copper, so as to form the ingot whose phosphorus content is in the range from 1 to 10 ppm.

9. The method of producing an oxygen-free copper wire material according to claim 5, wherein the phosphorus compound is added in the step of adding a phosphorus compound to the molten copper, so as to form the ingot whose phosphorus content is in the range from 2 to 8 ppm.

10. The method of producing an oxygen-free copper wire material according to claim 5, wherein the temperature of the molten copper is controlled in the range from 1,085 to 1,095° C.

11. The method of producing an oxygen-free copper wire material according to claim 5, wherein said rotational movable mold is belt and wheel type.

12. The method of producing an oxygen-free copper wire material according to claim 5, wherein said rotational movable mold is twin belts type.

13. The method of producing an oxygen-free copper wire material according to claim 5, wherein the step of allowing the molten copper to react with a solid reducing agent, is the step that charcoal is allowed to float on the surface of the molten copper.

14. The method of producing an oxygen-free copper wire material according to claim 5, wherein the step of blowing an inert gas into the molten copper is a step that nitrogen gas or argon gas is forcibly blown from the bottom of the molten copper.

15. The method of producing an oxygen-free copper wire material according to claim 5, further comprising

the step of applying the rod to cold-working.

16. An oxygen-free copper wire material produced by the method comprising the steps of:

continuously guiding a molten copper obtained by melting copper material;

adding a phosphorus compound to the molten copper;

injecting the molten copper into a rotational movable mold;

17. The oxygen-free copper wire material according to claim 16, whose oxygen content is in the range 6 ppm or less.

18. The oxygen-free copper wire material according to claim 16, whose hydrogen content is in the range 0.5 ppm or less.

19. An oxygen-free copper wire material produced by the method comprising the steps of:

continuously guiding a molten copper obtained by melting copper material;

adding a phosphorus compound to the molten copper;

injecting the molten copper into a rotational movable mold;

cooling and solidifying the molten copper to form an ingot whose phosphorus content is in the range from 1 to 10 ppm;

continuously drawing the ingot out of the mold, followed by subjecting the drawn ingot to continuous rolling, to form a rod; and

the step of applying the rod to cold-working.

20. The oxygen-free copper wire material according to claim 19, whose electric conductivity is 98% or more.