Patent Application
20070256807
1. Field of the Invention
The invention relates to a continuous casting apparatus, more particularly to a continuous casting apparatus that can simultaneously perform melting and refining processes of a base metal and that can permit addition of a trace element to the base metal.
2. Description of the Related Art
The forming mold 13 is disposed within the receiving hole 121, and is formed with a horizontal forming passage 131 that is in fluid communication with the inner portion of the holding furnace 12. The molten metal in the holding furnace 12 is passed through the passage 131 of the forming mold 13 to thereby form a cast metal element.
The cooling unit 14 is provided for cooling the cast metal element.
The drawing unit 15 includes two rollers 151 that rotate in opposite directions for drawing continuously and horizontally the cast metal element.
From the aforementioned description, the melting furnace 11 and the holding furnace 12 of the conventional horizontal continuous casting apparatus 10 are directly exposed to the atmosphere, and only the layers of the graphite or carbon flakes are used to cover the liquid surfaces of the molten metal in the respective furnaces 11, 12 to prevent the molten metal from being oxidized. However, it is still possible for the liquid surface of the molten metal to be in contact with the atmospheric air through a gap between the graphite or carbon layer and a surrounding wall of the corresponding furnace 11, 12. In addition, the molten metal may be contaminated by the material from which the melting furnace 11 and the holding furnace 12 are made. In either case, the composition of the molten metal in each furnace 11, 12 may be altered. Further, if it is necessary to perform a refining operation after the smelting of the metal, the metal must be transferred to a refining device, for example, a vacuumed heating furnace. Hence, not only are the production time and the costs for purchasing additional devices increased, but further contamination of the metal is also likely to occur. When it is desired to manufacture a metal with a high degree of purity, high production costs will surely be incurred. Moreover, the apparatus 10 does not permit addition of a trace element to a base metal, and hence, the mechanical properties of the metal cannot be enhanced, nor can other special requirements of the metal be satisfied.
In operation, a solid metal is heated in the melting furnace 21 to form molten metal. The molten metal flows from the hole 211 into the passage 231 of the forming mold 23, and is heated at the same time by the heating device 24 so as to maintain the temperature of the molten metal. Since the molten metal starts to solidify prior to drawing by the drawing unit 26, the temperature thereof has to be controlled strictly. Through simultaneous operations of the drawing unit 26 and the cooling unit 25, the molten metal can be drawn and solidified in a horizontal manner. By reducing the speed of the drawing unit 26 to a low setting, and by using a highly pure 4N˜6N copper (=99.99%˜99.99%), a single crystal high-end audio wire material can be produced.
Although the conventional OCC apparatus 20 may not experience the problems of oxidation of the molten metal by contact with the atmospheric air, or contamination by the material of the apparatus 20 itself, it is not provided with any refining means to remove impurities so that if refining is necessary, transfer to a refining device is still required. Further, the OCC apparatus 20 does not permit addition of a trace element for alloying.
Since the conventional upcast continuous casting apparatus 30 upwardly draws the resulting cast solid metal, the drawing unit 35 has to be designed carefully by taking into consideration the weight of the cast solid metal. Further, some of the molten metal may remain on a bottom portion of the casting mold 33. This results in high replacement rate of the mold 33 because the mold 33 is immersed constantly in the high-temperature molten metal. Moreover, the apparatus 30 also does not permit addition of a trace element for alloying.
Recently, the requirements for super fine gold and copper wires used as bonding wires in electronic packages for application in dentology and in wafer-testing microprobes are becoming increasingly stringent. The materials for the aforementioned special uses must be transferred to a vacuum heating furnace to undergo a re-melting process. This increases the manufacturing time, increases the chance of oxidation and contamination, and makes necessary the use of additional equipment and space.
Therefore, the object of the present invention is to provide a continuous casting apparatus that can perform simultaneous operations of smelting and refining of material, that can remove low-temperature impurities to obtain a high degree of purity of material, and that can reduce the chance of oxidation and contamination of the material, so that the production time and costs can be minimized.
According to this invention, a continuous casting apparatus comprises a housing, a vacuum unit connected to the housing, a furnace unit, an agitating gas supply unit, a casting mold, a protective gas supply unit, a cooling unit, and a drawing unit. The furnace unit is disposed in the housing, and is adapted to receive and heat a solid metal into a molten metal. The agitating gas supply unit is connected to a bottom end of the furnace unit, and is adapted to supply an inert gas to the furnace unit to agitate the molten metal. The casting mold is connected to the bottom end, extends outwardly from the housing, and has a downward passage in fluid communication with the furnace unit and adapted to permit flow of the molten metal therethrough. The protective gas supply unit is connected to an inner space of the housing which surrounds the furnace unit. The cooling unit surrounds the casting mold, and is adapted to cool the molten metal that flows through the downward passage. The drawing unit is disposed below the casting mold, and is adapted to draw continuously a solid metal cast by the casting mold.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which:
Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure.
Referring to
The housing 50 includes a first window 501, a temperature-measuring device 500 provided in the first window 501 to measure the temperature inside the housing 50 and the temperature of the molten copper, a second window 502 adapted to permit viewing of the melting condition of the copper inside the housing 50 by an operator, and a bottom opening 503. The first and second windows 501, 502 are spaced apart from each other, and are located on a top portion of the housing 50. The temperature-measuring device 500 can sense the temperature of the molten copper using infrared temperature measurement technique or through direct contact with the molten copper.
The vacuum unit 52 is connected to the housing 50, and is adapted to draw air out of the housing 50 to create a near vacuum environment in the housing 50. In this embodiment, the vacuum unit 52 creates a vacuum in the housing 50 ranging from 2.2×10−1 to 1.0×10−4 torr (or lower). The vacuum unit 52 may be a single vacuum pump, or a combination of a mechanical pump, a roots pump, and a diffusion pump.
The furnace unit 54 is disposed in the housing 50, and includes a first furnace 56 adapted to receive and heat a solid copper into a molten copper and maintain the same at an appropriate temperature, i.e., a preset heating temperature. The first furnace 56 has a graphite crucible 561, and a high frequency heater 562 surrounding and heating an outer periphery of the graphite crucible 561. The graphite crucible 561 has a first hole 563 that is formed at a bottom end thereof and that is aligned with the bottom opening 503 of the housing 50. Preferably, the first hole 563 is located at the center of the bottom end of the graphite crucible 561. Since the graphite crucible 561 is made of graphite, it will not contaminate the copper material held and heated by the first furnace 56.
The high frequency heater 562 uses a high frequency current signal to quickly heat and maintain the temperature of the electrolytic copper in the graphite crucible 561, and to provide vibration and agitation effects to the molten copper simultaneously. In this embodiment, the preset heating temperature of the electrolytic copper is about 1150° C.˜1300° C., and the temperature is maintained for about 15˜30 minutes. When a different metal is melted, the preset heating temperature and the time of maintaining this temperature can be adjusted as needed.
The agitating gas supply unit 62 is connected to the bottom end of the graphite crucible 561 of the first furnace 56, and is adapted to supply to the same an inert gas, such as nitrogen, helium, argon, neon, krypton, or xenon. The inert gas forms bubbles to agitate the molten copper in the graphite crucible 561. Simultaneously, by adjusting the speed of the agitating gas supply unit 62, impurities or residues accumulated at the bottom end of the graphite crucible 561 can either be vaporized or float to the surface of the molten copper so as to prevent the impurities from entering the casting mold 68 and causing defects in the final product. The agitating gas supply unit 62 includes a storage tank 621 to store the inert gas, and a connecting tube 623 connected to a control valve 622 and inserted upwardly into the bottom end of the graphite crucible 561. Inert gas is used for agitation since it tends not to react with molten copper. In preferred embodiment, nitrogen gas or argon gas is used to minimize costs. It should be noted that the connecting tube 623 shown in
The first protective gas supply unit 64 is connected to an inner space of the housing 50 which surrounds the furnace unit 54, and fills the housing 50 with a protective gas, such as an inert gas, so as to restore the housing 50 to a normal pressure condition, and to prevent oxidation of the high-temperature molten copper. The first protective gas supply unit 64 includes a storage tank 641 to store the protective gas, a connecting tube 643 connected to the storage tank 641 and to supply the protective gas into the housing 50, and a control valve 642 connected to the connecting tube 643. In this embodiment, the storage tank 641 of the first protective gas supply unit 64 and the storage tank 621 of the agitating gas supply unit 62 are independent elements, but they may be replaced with a single storage tank.
The material input device 66 extends partially into the housing 50 proximate to the graphite crucible 561, and is adapted to permit addition of one or more trace elements into the graphite crucible 561. Preferably, the trace element(s) is added into the graphite crucible 561 when the housing 50 is filled with the protective gas. Through operation of the agitating gas supply unit 62, the trace element and the molten copper can be thoroughly mixed. The trace elements may be selected from platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), calcium (Ca), etc., and a combination or one or more of the aforementioned metals. The trace element is added into the molten copper so as to enhance the tensile strength, the corrosion resistance, and the weldability of the pure copper. Furthermore, coarsening of grains during a subsequent heating process can be prevented.
The casting mold 68 is connected to the bottom end of the graphite crucible 561 through the first hole 563, and extends outwardly from the housing 50 through the bottom opening 503. The casting mold 68 is formed with a downward passage 681 in fluid communication with the graphite crucible 561 and adapted to permit flow of the molten copper therethrough. Preferably, the casting mold 68 is made of graphite material to prevent contamination of the molten copper. Depending on the cross-sectional configuration of the downward passage 681 of the casting mold 68, a round material, a plate material, or an irregular shaped material can be cast. A spindle (not shown) may be further provided in the downward passage 681 to cast a tubular material.
The cooling unit 70 surrounds an outer periphery of the casting mold 68, and is adapted to cool the molten copper that flows through the downward passage 681 of the casting mold 68 so that the molten copper gradually solidifies as it passes through the downward passage 681. The cooling unit 70 has an entrance 701 to permit entry of a liquid, and an exit 702 to permit exiting of the liquid after absorbing the heat from the molten copper. Preferably, the liquid is water or cold water, and cooperates with a cooling tower (not shown) so that the water, which is hot after absorbing the heat of the molten copper, can be cooled and can be repeatedly and continuously used.
The partition plate 72 is disposed between the furnace unit 54 and the cooling unit 70 so as to reduce heat transfer between the furnace unit 54 and the cooling unit 70.
The second protective gas supply unit 74 is connected to an outlet end of the downward passage 681 of the casting mold 68, and is adapted to supply an inert gas to the outlet end of the downward passage 681 so as to protect the initially solidified copper. The second protective gas supply unit 74 has a storage tank 741 to store the inert gas, and a connecting tube 743 connected to a control valve 742 and to the outlet end of the downward passage 681.
When the molten copper solidifies, its volume decreases, and it will not adhere tightly to the casting mold 68. As a result, a gap is formed between the solidified or cast copper and an inner wall face of the casting mold 68. The gap is in fluid communication with the outside environment. Since the cast copper is still hot and is easily contaminated by the atmospheric air immediately following solidification, the inert gas is fed into the casting mold 68 through the second protective gas supply unit 74 so as to protect the cast copper and to assist simultaneously the solidification of the cast copper. In this embodiment, the storage tank 741 is independently provided in addition to the storage tank 621 and the storage tank 641. However, a single storage tank may be used in place of the storage tank 741, the storage tank 621, and the storage tank 641.
The drawing unit 76 is disposed below the casting mold 68, and is adapted to draw continuously the solidified or cast copper into an elongated metal rod. The drawing unit 76 includes two rollers 761 that rotate in opposite directions so as to clamp and pull continuously the cast copper. It should be noted that the rollers 761 can rotate clockwise and counterclockwise so as to pull downwardly or force upwardly the cast copper so that the continuous casting operation need not stop when the metal breaks due to the downward pulling force. Since the structure and operation of the rollers are known in the art, a detailed description of the same will be dispensed herewith for the sake of brevity.
The heat radiation blocking plate 78 is provided within the housing 50, and is located above the furnace unit 54. The heat radiation blocking plate 78 not only can reduce heat loss, but also can prevent the second window 502 from being coated with a thin film of metal resulting from the vaporized impurities of the molten copper, so that viewing of the inside of the housing 50 is not adversely affected. Further, the heat radiation blocking plate 78 can prevent the operator from experiencing burn injury caused by the radiation of heat through the second window 502 when observing the smelting process through the same.
In actual operation of the continuous casting apparatus of the present invention, a metal bar (not shown), which is similar to the base metal to be refined, for example, an electrolytic copper, is first inserted into the downward passage 681 of the casting mold 68 so as to block and prevent the molten copper from passing through the downward passage 681. Afterwards, the vacuum unit 52 and the cooling unit 70 are activated so that a vacuum is formed in the housing 50 ranging from 2.2×10−1 to 1.0×10−4 torr. Due to the vacuum environment and the agitating effect, the low melting point impurities or residue in the electrolytic copper are easily vaporized and are drawn outward by operation of the vacuum unit 52, thereby removing unnecessary elements from the molten base metal and refining the copper. Hence, a highly pure molten copper can be obtained. The purpose of activating the cooling unit 70 is to ensure that the metal bar inserted into the downward passage 681 of the casting mold 68 will not melt and thus will not affect the composition of the molten copper.
Since the housing 50 is in a near vacuum state at this time, after the furnace unit 54 is heated to a very high temperature, the resulting pure molten copper is not easily oxidized. Further, through the first and second windows 501, 502 of the housing 50, the temperature and melting condition of the molten copper can be observed.
Prior to addition of the trace element into the molten copper, operation of the vacuum unit 52 is stopped, and the first protective gas supply unit 64 is activated, so that the pressure in the housing 50 is restored to one atmospheric pressure and so that the housing 50 is filled with the inert gas to protect the pure molten copper. The trace element is then added into the molten copper through the material input device 66, and is mixed uniformly with the molten copper through operation of the agitating gas supply unit 62.
Finally, the second protective gas supply unit 74 and the drawing unit 76 are activated. The drawing unit 76 pulls the metal bar downwardly from the downward passage 681 of the casting mold 68. As such, the molten copper can flow through the downward passage 681, and can be gradually solidified by the cooling unit 70. The molten copper flows downwardly following the metal bar, and is drawn downwardly. After the continuous casting of the pure copper, the metal bar is cut off, and an elongated pure copper material with good mechanical properties is obtained.
The present invention employs a vertical continuous casting method so that the molten metal can flow downwardly by virtue of gravity. Through connection with the vacuum unit 52, the housing 50 can be placed in a near vacuum state, and through the agitating gas supply unit 62, which supplies the inert gas in the form of bubbles, the molten metal can be agitated and the low melting point impurities or residue can be vaporized and removed. Hence, the material can be refined and a highly pure metal can be obtained. The trace element can then be added to the refined molten metal through the material input device 66. Again, through the agitating gas supply unit 62, the trace element and the molten metal can be mixed thoroughly so as to enhance the mechanical properties of the material, which is helpful in the subsequent forming processes.
Referring to
The material input device 66, in this embodiment, extends partially into the housing 50 proximate to the graphite crucible 581 of the second furnace 58, and is adapted to permit addition of the trace element into the second furnace 58. The high frequency heater 582 similarly uses a high frequency current signal to quickly heat the metal and to agitate the molten copper so as to mix thoroughly with the trace element.
In this embodiment, the second furnace 58 can be turned and tilted by rotating the melt discharge member 583 which is formed as a shaft. When the second furnace 58 is tilted, the molten copper can be poured into the first furnace 56. Alternatively, the molten copper can be discharged into the first furnace 56 from a bottom opening of the graphite crucible 581 of the second furnace 58. Since the configuration associated with this alternative discharge method is known in the art, a detailed description of the same will be dispensed herewith for the sake of brevity. It should be noted that since the first and second furnaces 56, 58 are spaced apart from each other, when the molten copper is poured out from the second furnace 58 into the first furnace 56, spattering of the molten copper is likely to occur. Therefore, a material recycling device is preferably provided at an outer side of the first furnace 56 for collecting the spattered molten metal so as to reduce waste of material.
Since the second furnace 58 and the first furnace 56 of the furnace unit 54 are provided separately, when the molten copper is poured into the first furnace 56, the base metal to be refined can be added into the second furnace 58 through the material input device 66 so as to continuously melt the material, achieve a continuous process of production, and reduce damage to the casting mold 68.
Referring to
Through the divider 80, the upper chamber 504 may be quickly placed in a vacuum state of a preset vacuum pressure so that the second furnace 58 can proceed with the refining of the material, and the lower chamber 505 can simultaneously be filled with the inert gas so that the first furnace 56 can proceed with the casting operation of the material. In comparison with the second preferred embodiment, the production time associated with the third preferred embodiment is shorter because in the second preferred embodiment, the second furnace 58 and the first furnace 56 are located in the same enclosed space, such that the casting operation and the refining operation cannot be processed at the same time.
While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
