US3528803A

US3528803A - Method for manufacturing oxygen-free copper by casting

Info

Publication number: US3528803A
Application number: US683285A
Authority: US
Inventors: Hiroshi Ichikawa; Rokuro Kawanishi
Original assignee: Hitachi Cable Ltd
Current assignee: Hitachi Cable Ltd
Priority date: 1966-12-28
Filing date: 1967-11-15
Publication date: 1970-09-15
Anticipated expiration: 1987-09-15
Also published as: JPS5223969B1; BE707763A

Description

Sept. 15, 1970 HIROSHI c w ET AL 3,528,803

METHOD FOR MANUFACTURING OXYGEN-FREE COPPER BY CASTING Filed NOV. 15, 1967 GRAPH SHOW/N6 THEOXYGE/V-HWROGE/V EOU/L/BR/UM. RELATION 0F MOL TE/V COPPER HYDROGEN 0 0.'/ ofz 0:3

OXYGHV 9;)

. INVENTOR S l/llFOS/V/ ICWM'A W Pal/mo MUM/5M ATTORNEYS United States 3,528,803 METHOD FOR MANUFACTURING OXYGEN-FREE COPPER BY CASTING Hiroshi Ichikawa and Rokuro Kawanishi, Tsuchiura-shi,

Japan, assignors to Hitachi Cable, Ltd, Tokyo, Japan,

a corporation of Japan Filed Nov. 15, 1967, Ser. No. 683,285 Claims priority, application7Japan, Dec. 28, 1966, 42/ 44 Int. Cl. C22b /14 U.S. Cl. 75--76 15 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing oxygen-free copper, which method comprises the steps of adding a very small amount of dehydrogenating agent to a molten electrolytic copper to react said dehydrogenating agent with hydrogen contained in said copper and then subjecting said dehydrogenating agent to a reaction with the oxy gen contained in the resultant molten copper and thereafter contacting dehydrogenating agent With a reducing as to effect deoxydation of the molten copper.

BACKGROUND OF THE INVENTION The present invention pertains to the industries for manufacturing copper articles such as wires, rod, bars and other electric articles.

It is known to subject tough-pitch copper obtained by refining copper ore in a reverberatory furnace to horizontal casting to produce copper in the form, principally, of wirebar, and also cake which is small in amount. This horizontal casting system has shortcomings, for example, that the cast products have an oxygen-rich layer on their surfaces and that the density of the castings is low.

Oxygen-free copper, in general, refers to deoxidized copper having no residual deoxidizing agent and is characterized by not becoming brittle when it absorbs hydrogen, and by the superior electric conductivity which is at least 100%, and further by the absence of exfoliation of the oxide film.

ASTMB 170-59 describes a method for testing the increased brittleness of copper due to contact with hydrogen. The relationship between the oxygen content of the copper and the increased brittleness due to the absorption of hydrogen by the copper, the permissible oxygen content of oxygen-free copper should be 0.0015% (15 ppm.) or less. It has been elucidated that in case the oxygen content is in the range between 0.0016% and 0.0019% (16-19 p.p.m.), the copper may or may not become brittle, and also that when the oxygen content is in the level of 0.02% (200 ppm), all of the test pieces invariably become brittle. While the aforesaid toughpitch copper is relatively superior in both electric conductivity and resistance to developing exfoliation of oxide film, it has a disadvantage that it easily becomes brittle when brought into contact with hydrogen. This poor resistance to brittleness when exposed to hydrogen is attributed to the fact that this tough-pitch copper contains a large amount of oxygen, for example, as much as 0.032% (320 p.p.m.). In spite of the recent progress in the techniques of manufacturing tough-pitch copper ingots in association with the techniques of dry refining process, and despite the fact that the electrolytic refining process has been put into practice resulting in an improvement in the purity of copper to the order of 99.997%, the re-casting method has not yet undergone any drastic progress. Under such situation, tough-pitch copper is still used in the re-casting without incorporating 3,528,803 Patented Sept. 15, 1970 any improved re-casting techniques. Thus, the purity of the cast products of copper still remains in the range of from 99.96% to 99.97%. In order to compensate for the shortcoming of the tough-pitch copper in becoming brittle when it absorbs hydrogen, a proposal to deoxidize copper with phosphorous has been made. This attempt, however, requires the use of a large amount of phosphorus to reduce the oxygen content of the copper and according to this proposed method, it has been impossible to decrease the oxygen content to a level of 0.005% (50 ppm.) or lower. Moreover, the introduction of a large amount of phophorus serves to markedly reduce the electric conductivity of copper which is the most outstanding property of the copper and at the same time results in affecting the desirable condition of not exfoliating the oxide film. Furthermore, the use of phosphorus gives rise to the problem in casting that such substances as Cu O and P 0 are present in the interface between the mold and the ingot.

Other attempts of obtaining oxygen-free copper include the techniques of melting copper in vacuum. This method, however, is limited to use in laboratories because of the equipment requirements and since the yield is limited to the order of 500 kg. a day. Thus, this vacuum-melting technique is not suitable for adoption in the production of oxygen-free copper on an industrial basis Where quantity production is required.

Other technological problems encountered in the casting of molten copper into oxygen-free copper ingots and cast products include the effect of the oxygen-hydrogen equilibrium of the molten copper on the productivity of oxygen-free copper ingots and cast products. The oxygen-hydrogen equilibrium relationship in the molten copper in general is shown in the accompanying drawing.

The velocity of the following reaction:

(dissolved in molten copper) till an equilibrium is reached is great and this fact has already been experienced in actual operation or in the manufacutre of tough-pitch copper in reverberatory furnaces.

In the ingots, such as wirebar, cakes and billet, which have absorbed hydrogen as the result of the aforesaid reaction, pin-hole and blow-holes which result in a reduction in the specific gravity of the cast products obtained and also the creation of unsound properties of the ingots produced are formed. These products present various problems when in use. Therefore, the greatest technological problem in the manufacture of oxygenfree copper ingots and cast products remains the control of the hydrogen which is easily dissolved in molten copper.

SUMMARY OF THE INVENTION It is an object of the present invention to provide deoxidized copper containing no residual deoxidizing agent, namely, to provide oxygen-free copper.

Another object of the present invention is to provide oxygen-free copper which is superior in the property of not becoming brittle when in contact with hydrogen, which is superior in electric conductivity and which does not develop exfoliation of oxide film.

Still another object of the present invention is to provide a novel method for manufacturing oxygen-free copper, said method being such that it is capable of extremely minimizing the oxygen and hydrogen contents of the molten copper.

Yet another object of the present invention is to provide a novel method for manufacturing oxygen-free copper, which is easy and which can be put into practice on an industrial basis and which is suitable for quantity production.

A further object of the present invention is to provide a novel method for manufacturing oxygen-free copper, said method being such that is suitable for the re-casting of copper ingots such as electrolytic copper.

A still further object of the present invention is to provide a novel method for manufacturing oxygen-free copper, said method being such that is suitable for being applied to the semi-continuous casting system and also to the fully-continuous casting system of copper.

A yet further object of the present invention is to provide a novel method for manufacturing oxygen-free copper, said method being such that can be applied to the production of either one of the products such as wirebars, ingots, cakes, billets and moldings, irrespective of their size.

Another object of the present invention is to provide a novel method for manufacturing oxygen-free copper, said method being such that is extremely economical in the aspect of cost of re-casting relative to the quantity of molten metal.

Still another object of the present-invention is to provide a method for manufacturing oxygen-free copper whose oxygen content is 0.0015% ppm.) or less and whose electric conductivity is 100% or more, by the use of a reducing gas.

BRIEF DESCRIPTION OF THE DRAWING Figure is an equilibrium diagram showing the rela tions between the amounts of oxygen and hydrogen concontained in a molten copper.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the description of the present invention, the terms molten copper points to such copper as electrolytic copper or other mass of copper which requires re-casting and which is in the state of being molten by being melted in a melting furnace or in an electric furnace.

The term casting herein used implies the casting processes which are generally used in the semi-continuous casting system, as well as in the fully-continuous casting system and also in other types of casting process of copper. The term mold used in such casting is understood to mean such mold as is used in any one of these proc esses. The'terms cast product of copper not only include Wirebars, ingots, cakes, billets and mold-castings, but also other cast masses obtained from casting and further includes all kinds of copper products obtained by further processing these cast masses into rods, wires, pipes or the like, regardless of their shape and size.

The dehydrogenating agent which is used in a very small amount in the present invention includes P, Li, Na, Pd and V. Besides these, Cr and Mn are also usable. The amount of such a dehydrogenating agent which is used is very small. In case the dehydrogenating agent consists of, for example, Li, Pd or V, the amount is 0.003% or less by weight. In case it is P, the amount is in the range between 0.003% and 0.001% or less by weight. In case the dehydrogenating agent consists of other substances, the amount may be 0.0003%0.0004% by weight, or in some other cases, it may be 0.0006 %-0.0008% by weight. With some other kind of dehydrogenating agent, it is uniformly introduced into 16-18 tons of molten copper contained in a melting furnace in an amount of 0.0003 0.0004% by weight so that the dehydrogenating agent is uniformly contained in the cast product in an amount 0.0003% or less by weight. These dehydrogenating agents may be introduced into the molten copper either independently or in appropriate combination or in the form of an appropriate alloy of copper, and in appropriate shape such as ingot, plate, rod, chip, grain and powder. Such a dehydrogenating agent may be charged into the melting furnace simultaneously with the copper stock which is to be re-cast. Alternatively, the dehydrogenating agent may be added to the molten copper at a desired arbitrary site or sites such as in the molten metal transport vessel, the casting holding furnace and the casting vessel.

As some of the examples of the techniques of charging dehydrogenating agents, grains of Cu-base alloy consisting of 15% by weight of P, and Cu for the remaining part, are introduced into the melting furnace continuously. Or alternatively, 0.01% by weight of P and 500 to 1000 kg. of copper billet after being deoxidized with phosphorus are charged jointly at predetermined intervals of time. Or alternatively, copper tubes having a diameter of 15 mm. and having, therein enclosed, powder of Cubase alloy containing 15% by weight of P are charged into a melting furnace at predetermined intervals of time. Or alternatively, a 30 kg. of a Cu-base alloy containing 0.15% by weight of P is charged into the melting furnace at each calculated casting time.

In charging the dehydrogenating agent, it is advantageous to arrange that the agent is contained in the copper in the stage where the latter is melted in the melting furnace, because by doing so, the dehydrogenating agent is uniformly blended in the molten copper and also because the dehydrogenating agent can be made to conveniently contact a reducing atmosphere, in the later stage, which is produced by the use of a reducing agent.

The dehydrogenating functions of the aforesaid dehydrogenating agents which are displayed by their reaction with hydrogen, are shown, as an example, as follows:

The significance of the use of a dehydrogenating agent in the present invention is described below.

FIG. 1 shows the oxygenhydrogen equilibrium of the molten copper. An additional explanatory statement will be hereunder made regarding this figure. In the case, for example, where electrolytic copper is melted in a melting furnace while being covered by a layer of charcoal and then the molten copper is reduced with CO in the molten copper transport vessel, the molten copper is rendered to a condition that the latter quite easily absorbs hydrogen (H and as a result, the molten copper is allowed to absorb a large amount of H till an equilibrium value is attained in accordance with the amount of the water vapor (moisture) or the partial pressure of H in the atmosphere to which tre molten copper is exposed.

From FIG. 1 or as is clear from the reasons which will be stated later, the oxygen content of the molten copper may be arranged so as to assume an ideal value such as 0.001%0.0004% (1.0-4 p.p.m.). However, if the inside of the preserving vessel through which the molten metal is passed is kept under a reducing atmosphere by having the surface of the molten metal covered with a thick layer of charcoal, the molten metal will be cast, with H being retained in the metal. In the fully-continuous casting system, there is provided gas-exhausting means 1n the equipment. However, such gas-exhausting means does not evenly exhaust gas from the molten metal. If the gas-exhausting function is such that is effective, for example, up to the depth of mm. from the surface of the molten metal, it will remove the gas satisfactorily if the molten metal has a depth of 150 mm. or less. In the event, however, that the molten copper is as deep as 250 mm. or 400 mm., the gas expulsion function of such means is not carried out with a suflicient eifectiveness, with the result that the retention of H in the molten metal will not be avoided. If the hydrogen content of the molten meal exceeds a certain level, pinholes will develop in the ingot, and further, will result in the occurrence of a secondary crack formation in the ingot, leading to a reduction in the specific gravity of the ingot. The technological problems in the present invention is focused on how to effectively control the presence of hydrogen which is easily absorbed into the molten metal during the manufacture of oxygen-free copper ingot. In other words, the aim of the present invention lies in how to deviate the oxygen-hydrogen equilibrium from its relation diagram shown in FIG. 1 and eliminate oxygen and hydrogen from the molten copper.

Various studies have been conducted to find an effective deoxidizing agent for use in molten copper. However, no systematic research has been conducted with regard to dehydrogenating agents. As a result of extensive experiments it has now been found that substances such as P, Li, Pd and V are effective and powerful dehydrogenating agents.

The experiments consisted of daily draining 2 tons of molten copper which was stabilized in an induction furnace after setting the melting furnace and the preserving vessel into operation, and the corresponding quantity of copper was supplemented accordingly.

When the resulting molten copper was cast in a mold, there occurred a marked rising of the surface of the metal when the copper became solidified. Intensive absorption of H by the copper from the moisture which was retained in the material which constituted the furnace was thus confirmed. The ingot thus produced was remelted in a crude-oil furnace, and the molten copper was transferred toanother preservation furnace where phosphorus was introduced into the molten copper to produce a copper ingot which had been already dioxidized 'by the phosphorus. Alternatively, the molten copper drained from the first-mentioned induction furnace was transferred to still another preservation furnace and an ingot was produced in the same manner. In the case where a phosphorus containing Cu-base alloy was introduced into the molten copper with a normal proportion of blending, no trace of phosphorus in the cast product was detected.

Furthermore, blending of phosphorus of 3 to 5 times in amount that of the normal proportion was attempted. However, the cast product contained only a trace of phosphorus. It has been found that the phosphorus introduced first reacts with hydrogen and then with oxygen. From this knowledge, it has been confirmed that phosphorus serves as a powerful dehydrogenating agent. Experiments were also conducted on other agents, namely, Li, Pd and V. It was confirmed that they also had a dehydrogenating function.

In the present invention, P, Li, Pd and V are used as the dehydrogenating agents for the expulsion of hydrogen from the molten copper and also for the prevention of intrusion of hydrogen into the molten copper. The amount of the dehydrogenating agent used in the present invention is quite small, and in case the dehydrogenating agent consists of P, the amount used is 0.001% or less by weight,

while in case Pd or V is used, the amount is 0.003% or less by weight. As soon as a dehydrogenating agent, for example, P, is introduced into a melting furnace which contains H the charged P begins to react with this H (in accordance with the reaction formula already described), and the reacted P and H is discharged outside the molten copper in the form of gas which is insoluble in the molten copper.

After there is no more H remaining in the molten copper, the P which is located in the interface between the molten copper and the space thereabove then reacts with the H contained in the atmosphere located in the space above the face of the molten copper so that the P prevents the intrusion of hydrogen into the molten copper. Thus, so long as P is present, even in a very small amount, in the molten copper, the intrusion of hydrogen into the molten copper contained in the furnaces of the casting equipment is inhibited. As a result, the oxygen-hydrogen equilibrium in the molten copper, shown in FIG. 1, is broken. This is a very important element of the present invention. After the hydrogen has been removed from molten copper, the hydrogen-free molten copper can then be easily deoxidized by a reducing agent, for example, CO, which will be described later, without being restrained by the oxygen-hydrogen equilibrium of the molten copper. As a result, substantially pure copper containing hardly any hydrogen or oxygen can Ibe manufactured. The amount of the dehydrogenating agent which is used in the present invention can be determined, within a range of a trifle amount, appropriately, in accordance with the hydrogen content of the molten copper.

The terms reducing agent used in the present invention point to carbon monoxide (CO), carbonic acid gas (CO carbon (C), and hydrocarbons (both saturated and unsaturated hydrocarbons), which may be used either independently or in appropriate combination. Carbon includes charcoal.

The principal object of bringing molten copper into contact with a reducing agent in the present invention resides in the expulsion of oxygen contained in the molten copper. Therefore, the means of doing so as well as the sites where such contact is effected can vary. In general, a melting furnace is provided with an opening through which the materials are charged. For this reason, a reducing agent such as CO is not suitable for use in a melt ing furnace, but charcoal will satisfy the purpose. Since the molten copper transport vessels are connected to a melting furnace sideways or verticalwise in case the molten copper is drained from the melting furnace into the trans port vessels, this means that the atmosphere in the melting furnace will be completely dissociated from the transport vessels and also from the subsequent stages. Both the preserving furnace and the transport vessel are, on the other hand, generally substantially closed and, therefore, they share the same atmosphere.

It is convenient as well as economical to cover, with charcoal, the face of the molten copper contained in both the melting furnace and the preserving furnace. In case where a special arrangement is provided so as to feed a reducing agent of the following composition, i.e. 70% of N 28% of CO, 1% of CO and 2% of H from a protective gas generating furnace, the contact between the molten copper and the reducing gas which serves as the reducing agent can be easily and positively carried out by feeding the gas at three sites, i.e. an upper portion of the holding furnace, a side portion and the central portion of the transport vessel and the preserving furnace, respectively. Alternatively, a thick layer of charcoal is laid on the surface of the molten copper contained in the preserving furnace so that the gas which is produced from imperfect combustion of the charcoal in said preserving furnace and which is allowed to ascend in the transport vessel may be utilized.

Where the aforesaid protective gas is used, the oxygen content of the copper ingot and molded product can be reduced to 0.0008%0.0004% (84 p.p.m.). The gas produced from imperfect combustion of charcoal is composed roughly of 6% of CO, 12.5% of CO and 3% of H The oxygen content of the copper ingot and cast product obtained from the use of said gas can be reduced to 0.001% (10 ppm.) or less. As a result of various experiments, it has been found that, 'by the use of 4% or more by volume of CO, the oxygen content can be decreased to 0.0006% (6 ppm). In case CO is used, the dioxidizing action of CO will decrease where the amount of CO decreases to 4% or less. Therefore, it is desirous that additional charcoal be supplied to the preserving furnace to increase the amount of CO which is generated. In case the CO is not controlled properly, the oxygen content may increase to a level of 0.0015% (15 ppm.) or more, resulting in the occurrence of brittle ingots and cast products due to the presence of hydrogen, and therefore, attention must be paid to he control of CO.

Description will hereunder be directed to the manufacture of an oxygen-free copper ingot and cast product by casting molten copper, using a fully-continuous casting equipment comprising a melting furnace having a charging inlet of 1300 mm. x 300 mm. in size (and made of a low frequency channel type induction furnace with four 3- phase inductors of 1250 kva., the molten metal accommodation capacity being 16 to 18 tons, and the maximum melting capacity being 3.5 tons per hour, with the normal melting capacity being 3.0 tons per hour), a molten metal transport vessel (Sillit 3-phase heat generator having a capacity of 77 kw.), a preserving furnace (low frequency channel type induction furnace having a single-phase inductor of 120 kva., with the molten metal accommodation capacity being 2 tons), a casting vessel, a mold, and a protective gas generator (modified propane-charcoal, the reducing component being 70% of N and 30% of CO, with the capacity being 40 Nm. /hr. 100 mm. water column).

Electrolytic copper plates were continuously charged into the melting furnace through the inlet, while copperbase alloy ingots containing 0.15% by weight of phosphorus were introduced at each calculated casting time to insure that blending be made so that the 16 to 18 tons of molten copper in the melting furnace uniformly contained 0.0003% to 0.0004% by weight of phosphorus. A thick layer of charcoal was laid on the surface of molten copper contained in both the melting furnace and the preserving furnace so as to cover the surface of the molten copper.

From the separately installed protective gas generator, a gas having the composition of 30% of CO and 70% of N and serving as the reducing agent was fed to three sites, namely, a central portion of the molten copper transport vessel, a side portion of the preserving furnace and an upper portion of the preserving furnace, through pipes, respectively.

The molten copper contained in the melting furnace was passed from the outlet thereof into the molten copper transport vessel, and therefrom to the preserving furnace, and therefrom into the casting vessel, successively, and then finally into the mold, and thus a desired cast product was obtained.

In the melting furnace, among the foregoing operation steps, the dehydrogenating agent reacted with the hydrogen which was present in the molten copper as well as in the space above the face of the molten copper, in the following manner, namely,

Kcal.

The hydrogen contained in the molten copper reacted with phosphorus and was discharged outside the molten copper in the form of a gas insoluble in the molten copper. Thus, the hydrogen contained in the molten copper was expelled therefrom, while the hydrogen located in the space above the molten copper also selectively reacted with the phosphorus which was located in the interface between the molten copper and the space so as to prevent the hydrogen from intruding into the molten copper.

The resulting hydrogen-free molten copper was then brought into contact, in both the molten copper transport vessel and the preserving furnace, with the CO which was fed from the protective gas generator and was positively deoxidized thereby, and thus, it was possible to obtain a cast product of pure copper which hardly contains any oxygen or hydrogen.

The phosphorus content of the cast product thus obtained was 0.0005 (5' p.p.m.) or less by weight, while the oxygen content was in the range between 0.0008% and 0.0004% (between 8 and 4 ppm.) by weight.

The composition of the oxygen-free copper which was produced by casting the molten copper according to the present invention was compared with the compositions of the already reported cast copper products, and the result is shown in the following Table 1.

TABLE 1.OOMPARISON BETWEEN THE COMPOSITIONS OF THE COPPER OF THE PRESENT INVENTION AND THE COPPER MADE BY OTHER METHODS Oxygen-free Oxygen- Oxygen-free copper of free Toughcopper of Element the present copper of pitch Co. 8 of invention 00. A of copper Yugoslavia U.S.A.

Percent Cu.- 99. 992-99. 996 99. 94-99. 97 99. 96-99. 99

P.p.m.:

O 4-10 320 7-10 Ag.... 9-12 10 10 9-15 Ni 1-2 (3 1 2-25 Sb 1-2 5 1 2-5 As. 1-2 3 3 4-10 Fe 4-15 5 5 10-15 Sn.. 1 2 1 Tr. 1 Pb. 3-5 6 15 2-3 Bi.... 1 1 1 Tr. 2 P..." 2-5 Tr. 1 Si.. l-3 3 Zn 1-8 S.. 6-10 25 2-30 Se. 2 2-4 Te 1 Tr. 1

1 Not reported yet.

The cast products obtained according to the present invention are of an extremely high purity and are perfectly homogeneous in contrast to the tough-pitch copper which is heterogeneous and contains a eutectic of CD20. For this reason, the oxygen-free copper of the present invention completely eliminates the shortcomings of both the tough-pitch copper and the copper deoxidized by phosphorus of the prior art, but bears all the strong points of these copper products of the prior art.

For example, the ingot or the cast product of the present invention is sound in itself and does not tend to develop flaws during the subsequent processing steps. Moreover, it has a high electric conductivity, does not discharge any gas, can be easily processed, and can be easily drawn deeply and has a superior arc-resisting property.

Above all, the ingot and the cast product of the present invention is manufactured in such manner that its hydrogen and oxygen contents are minimized to an extreme degree by a novel manufacturing method designed so as to break the oxygen-hydrogen equilibrium of the molten copper. As a result, the product is given a superior property not to develop exfoliation of oxide film and not to develop pinholes or blowholes in the cast mass, and thus, the cast product of the present invention is characterized by its being sound in quality as a cast mass and also by high density of the cast mass.

The density of the cast mass of the product of the present invention is compared with that of the toughpitch copper in the following Table 2. The superior quality of the cast product of the present invention will be appreciated by reviewing this table.

TABLE 2 Processed Product Ingot article Oxygen-free copper of the present invention (gin/cm. 8. 8. 945 Tough-pitch copper (gin/emf) 8. 55 8. 89

Comparison of mechanical properties including resistance to bending, twisting and winding between the copper of the present invention and tough-pitch copper is shown in the following Table 3.

TABLE 3.-COMPARIS2 OF RESISTANCE TO TWISTING Since the cast product of the present invention has an oxygen content of 0.0015% or less as has been described, it will be obviously understood that its property of not getting brittle by contact with hydrogen is such that even when hydrogen should intrude into the copper, the following reaction would not occur:

and thus, no brittleness from the contact with such hydrogen would result. The presence of phosphorus in the cast product of copper is effected in such pattern that the phosphorus is present in the form of solid solution, and this phosphorus reduces the electric conductivity of the product. Therefore, phosphorus is used in the present invention only in a very minute amount and strictly as a dehydrogenating agent. The content of such phosphorus in the copper is in the order of from 0.0002% to 0.0005 (2 to 5 p.p.m.). As such, the cast product of the present invention is of an excellent electric conductivity.

The manufacturing method of the present invention is suitable for use in the re-casting of, for example, electrolytic copper into a cast product. In case this method is employed in the semi-continuous casting system and fullycontinuous casting system, it will provide a good efficiency of the operation, and therefore, the method of the present invention is suitable for quantity production and satisfies the industrial requirements.

Other advantages of the manufacturing method of the present invention include that it can be applied not only to the manufacture of wirebars, ingots, cakes, billets, mold-castings of both large and small size and ingots of other desired shapes, but also to the manufacture of goods such as rods, pipes and wires which are obtained by processing the ingots thus obtained continuously after the ingots are produced.

One advantage of the manufacturing method of the present invention in the aspect of operation is that the performance and control of this method can be quite easily effected.

According to the present invention, where electrolytic copper is re-casted, for example, there are detected not only the elements which constitute the electrolytic copper, i.e. 99.997% by weight of Cu, 6.1 gr./ton of Ag, 0.068 gr./ton of Au, 0.0001% by weight of Ni, 0.0001% by weight each of Sb, As, Fe and Zn and further 0.0006% by weight of S and 0.0003% by weight of Pb, but also P, Li, Na or Pd which is used as a dehydrogenating agent. It is, therefore, easily inferred when these substances are detected by the analysis of the product, that the manufacturing method of the present invention is employed in the manufacture of such product.

What we claim is:

1. A method of manufacturing oxygen-free copper comprising:

adding an effective amount up to about 0.003% by weight of a dehydrogenating agent to molten copper to react with the hydrogen in said molten copper and thereby remove substantially all of the hydrogen contained in said copper;

contacting the dehydrogenated molten copper with a reducing agent to deoxidize the molten copper.

2. A method as defined in claim 1, wherein the eifective amount is from about 0.0003% to 0.003% by weight.

3. A method as defined in claim 1, wherein the dehydrogenating agent is selected from the group consisting of P, Li, Pd, Na, Cr, Mn and V.

4. A method as defined in claim 1, further comprising casting said molten copper into a mold to form an ingot.

5. A method of manufacturing cast oxygen-free copper ingots comprising the steps of:

adding an effective amount up to about 0.003% by weight of a dehydrogenating agent to molten copper to cause a reaction between the dehydrogenating agent and hydrogen contained in said molten copper thereby effecting the removal of said hydrogen;

contacting said dehydrogenated molten copper with a reducing agent to deoxidize the molten copper; casting said molten copper into a mold to form ingots. 6. A method as defined in claim 5, wherein the effective amount is from about 0.0003 to 0.003% by weight.

7. A method as defined in claim 5, wherein the dehydrogenating agent is selected from the group consisting of P, Li, Pd, Na, Cr, Mn, and V.

8. A method of manufacturing cast oxygen-free copper ingots comprising:

admixing molten copper with an effective amount up to about 0.003% by weight of a dehydrogenating agent so as to cause reactions between the dehydrogenating agent and hydrogen contained in the molten copper and between the dehydrogenating agent at the top surface of the said molten copper and the hydrogen present in the atmosphere in the space above the surface while the copper is still in the molten state, thereby effecting dehydrogenation of the molten cop P contacting said dehydrogenaetd molten copper with a reducing agent to deoxidize: the molten copper;

casting said molten copper into a mold to form ingots.

9. A method as defined in claim 8, wherein the effective amount is from about 0.0003 to 0.003% by weight.

10. A method as defined in claim 8, wherein the dehydrogenating agent is selected from the group consisting of P, Li, Pd, Na, Cr, Mn and V.

I11. A method of manufacturing cast oxygen-free copper ingots comprising the steps of:

adding an effective amount of up to about 0.003%

by weight of phosphorus to molten copper to cause a reaction between the phosphorus and the hydrogen contained in said molten copper thereby effecting the removal of said contained hydrogen;

contacting said dehydrogenated molten copper with a reducing agent to deoxidize the molten copper; casting said molten copper into a mold to form ingots.

12. A method as defined in claim 11, wherein the effective amount is from about 0.0003 to 0.003% by weight.

13. A method of manufacturing cast oxygen-free copper ingots as claimed in claim 5, wherein the reducing agent is a reducing gas such as carbon monoxide (CO).

14. A method of manufacturing cast oxygen-free copper ingots as claimed in claim 8, wherein the dehydrogenating agent consists of 0.0003 to 0.003% by weight of phosphorus and the reducing agent is a reducing gas such as carbon monoxide (CO) or carbon dioxide (CO 15. A method of manufacturing oxygen-free copper which comprises:

adding 0.0003 to 0.003% by weight of phosphorus to molten copper, wherein said phosphorus reacts with the hydrogen contained in said molten copper thereby removing substantially all of the hydrogen from said pp contacting the dehydrogenated molten copper with a reducing agent selected from the group consisting of carbon monoxide and carbon dioxide, to deoxidize the molten copper.

References Cited UNITED STATES PATENTS 1,869,498 8/1932 Osborg -76 2,031,518 2/1936 Von Forster et al. 75---7-6 2,102,742 12/ 1937 Poland 75-7 6 2,452,996 1 1/ 1948 Corson 7576 2,479,311 8/ 1949 Christensen 7 5-76 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner U.S. Cl. X.R. 164-56, 57