The present invention relates to a casting of a predetermined length, which is acquired by vertically pulling out a casting that has been cooled down in a mold so as to have only its surface portion coagulated (or a shell formed on the surface), and a vertical casting method and a vertical casting apparatus which cast the casting.
In the field of nonferrous metals, such as aluminum, a vertical casting method is known that casts a casting of a predetermined length by pouring molten steel in a mold, which is open to the top and bottom, supporting the lower end of a casting, which has been cooled down in the mold so as to have a shell formed on the surface, on a dummy head of a lift table provided below the mold in a movable manner and vertically pulling out the casting from the bottom portion of the mold by vertically moving the lift table downward at a given speed.
Because the vertical casting method is advantageous over the ingot-making method in various factors, such as energy saving, power dissipation, attempts have been made to cast particularly castings with large cross sections with general kinds of special steels including high-alloy steel and tool steel and ensure still standing coagulation of the castings. However, castings that are obtained from the steels by the vertical casting method suffer the occurrence of multiple internal defects, such as the center porosity and center segregation or V-shaped segregation, thus degrading the quality of the castings and lowering the yield. In addition, the conventional vertical casting method may have an internal defect of a casting head cavity occurring in a casting. In other words, the conventional vertical casting method could not produce castings that could sufficiently meet such a present strict demand on the quality of castings as required of special steels including high-alloy steel and tool steel.
The present invention has been proposed to solve the problem of the prior art, and aims at providing a casting which has fewer internal defects, such as the center porosity, casting head cavity and center segregation or V-shaped segregation, and has improved quality and yield, and a vertical casting method and a vertical casting apparatus which can cast such casting.
To solve the problem and achieve the above object preferably, according to one aspect of the invention, there is provided a casting of a predetermined length that is cast by pouring a molten special steel including a high-alloy steel and tool steel in a mold open to the top and bottom thereof and vertically pulling out a casting having a required cross-sectional shape and having a shell formed on a surface from a bottom portion of the mold, and characterized in that at least a pair of opposing sides being tapered in such a way that an opposite side size of both sides becomes smaller toward a bottom portion from a top portion.
To solve the problem and achieve the above object preferably, according to another aspect of the invention, there is provided a vertical casting method for casting a casting of a predetermined length by pouring a molten special steel including a high-alloy steel and tool steel in a mold open to the top and bottom thereof and vertically pulling out a casting having a required cross-sectional shape and having a shell formed on a surface from a bottom portion of the mold;
wherein at a time of casting the casting, tapering at least a pair of opposing sides of the casting in such a way that an opposite side size of both sides becomes smaller toward a bottom portion from a top portion by relatively moving at least a pair of opposing movable molds of the mold away from each other while pulling out the casting from the bottom portion of the mold.
To solve the problem and achieve the above object preferably, according to a different aspect of the invention, there is provided a vertical casting apparatus for casting a casting of a special steel including a high-alloy steel and tool steel, the apparatus comprising:
a mold which is open to the top and bottom thereof and has at least a pair of movable molds that are relatively moved close to or away from each other by movable means, and where a molten special steel including a high-alloy steel and tool steel is poured;
a lift table, provided below the mold in a vertically movable manner, for supporting a lower end of the casting having a shell formed on a surface thereof and pulling out the lower end of the casting from a bottom portion of the mold; and
lifting means for moving the lifting table up and down.
To solve the problem and achieve the above object preferably, according to a different aspect of the invention, there is provided a vertical casting method for casting a casting of a predetermined length by pouring a molten special steel including a high-alloy steel and tool steel in a mold open to the top and bottom thereof and vertically pulling out the casting having a required cross-sectional shape and having a shell formed on a surface from a bottom portion of the mold;
wherein at a time of casting the casting, after completion of pouring, covering a top portion of the mold with a lid member and heating the molten steel in the mold with a plasma or arc with an internally defined heating chamber set in an atmosphere of an inert gas and under such a heating condition as to be able to keep a temperature of a surface of the molten steel at a solidus casting temperature or higher, thereby suppressing occurrence of an internal defect in the casting to be cast.
To solve the problem and achieve the above object preferably, according to a further aspect of the invention, there is provided a vertical casting apparatus for casting a casting of a predetermined length by pouring a molten special steel including a high-alloy steel and tool steel in a mold open to the top and bottom thereof, supporting a lower end of the casting having a shell formed on a surface thereof and pulling out the lower end of the casting from a bottom portion of the mold with a lift table, provided below the mold and movable up and down vertically by lifting means, characterized by comprising:
a lid member capable of covering a top portion of the mold and setting an internally defined heating chamber in an atmosphere of an inert gas; and
heating means for heating the molten steel in the mold covered by the lid member with a plasma or arc.
A description will be given below of castings according to the present invention, vertical casting methods and vertical casting apparatuses capable of casting said castings according to preferred embodiments of the present invention with reference to the accompanying drawings.
(First Embodiment)
As shown in
As shown in
The lift table 50, which has a dummy head 48 for supporting the lower end of the casting 26, is provided below the mold 12 in such a way as to be vertically movable. Pulleys 52, 52 are rotatably laid on both sides from which the casting 26 is held. A wire 54 whose one end is connected to an adequate fixed portion is put around both pulleys 52, 52, with its other end connected to a winch 56 whose speed is variable. The lift table 50 is suspended by the wire 54 stretched between both pulleys 52, 52 and is moved up and down by lifting means 58 that comprises the wire 54 and the winch 56. In other words, as the winch 56 is rotated in the direction of winding up the wire 54, the lift table 50 moves upward via the wire 54, and as the winch 56 is rotated in the direction of letting the wire 54 out, on the other hand, the lift table 50 moves downward via the wire 54. The lift-down speed (casting speed) of the lift table 50 in this case is set to a very low speed of 0.2 m/min or less to thereby suppress the occurrence of internal defects, such as the center porosity and center segregation or V-shaped segregation, in the cast casting 26.
(Operation of First Embodiment)
A description will now be given of the operation of the vertical casting method that is executed by the vertical casting apparatus according to the first embodiment. The winch 56 is rotated in a predetermined direction to move up the lift table 50. With the bottom portion of the mold 12 closed with the dummy head 48, molten steel of a special steel including a high-alloy steel and tool steel is poured in the mold 12 via the ladle 16 and the tundish 18. The molten steel poured in the mold 12 is subjected to first cooling in the mold 12, thus forming a shell on the surface of the molten steel. As the winch 56 is rotated in the reverse direction to vertically move down the lift table 50 at a given casting speed, the casting 26 whose bottom end is supported by the dummy head 48 is pulled out from the bottom portion of the mold 12.
The casting 26 immediately after being pulled out from the mold 12 is held by the guide rolls 44, 44 from both sides in the widthwise direction, as shown in
In synchronism with the downward movement of the lift table 50, the pair of movable molds 30, 30 relatively move away from each other under the urging force of the hydraulic cylinders 32, 32, thereby giving both widthwise sides of the casting 26 with required tapering in such a way that the widthwise size of both sides becomes smaller toward the bottom portion from the top portion (see
It seems that the occurrence of internal defects, such as the center porosity and center segregation or V-shaped segregation, is influenced by the angle of the coagulation front side of molten steel inside the casting. That is, in case where both widthwise sides of the casting 26 are straight, the angle (coagulation front side angle) θ with respect to the center line of the coagulation interface of the molten steel inside the casting is small as shown in
The widthwise size of both sides of the casting 26 that has been cast by the vertical casting apparatus 10 are tapered in such a way that the widthwise size becomes smaller toward the bottom portion (BOT portion) from the top portion (TOP portion) as shown in
Although the foregoing description of the first embodiment has been given of the case where a casting is tapered, a combination of the tapering scheme and the super slow casting speed may be employed as well. Setting the casting speed to 0.2 m/min or slower further increases the coagulation front side angle θ, reducing the suction of the molten steel whose C, S, P or the like has become denser. This further suppress the occurrence of internal defects, such as the center porosity and center segregation or V-shaped segregation, inside the cast casting 26.
With regard to the tapering of the casting, while only a pair of sides opposing in the widthwise direction of the casting are tapered in the first embodiment, only a pair of sides opposing in the thickness direction may be tapered or all of the four sides may be tapered. That is, at least one pair of opposing sides should be tapered.
Further, the moving means that moves the movable molds of the mold is not limited to hydraulic cylinders but may take the form of other various mechanisms, such as a ball screw, a screw and a rack and pinion, that are actuated by a motor. Although the unit that is a combination of a wire and a winch is mentioned as the lifting means for the lift table in the first embodiment, various other units, such as a hydraulic cylinder or a combination of a motor and a ball screw, can be used as well.
In case of casting a casting whose TOP portion has a thickness of 600 mm and a width of 750 mm using a special steel including a high-alloy steel and tool steel as a material, the results of measuring the center segregation of C and the coagulation front side angle θ for a case where no tapering is given and the casting speed (Vc) is variable (indicated by ●) and a case where tapering is given and the casting speed (Vc) is variable (indicated by ▴) are shown in
As apparent from
(Second Embodiment)
The carriage 200 is provided with a lid member 240 which covers the top portion of the mold 120. The lid member 240 is designed in such a way as to come to a standby position (
As shown in
A refractory material which essentially consists of Al2O3 is preferably used for the inside lining member 260 and a heat insulating material which has SiO2 doped into Al2O3 for an improved heat insulation is preferably used for the outside lining member 280. Those materials may however be replaced with other materials. The use of a heat insulating material having a low heat conductance for the outside lining member 280 can reduce the heat release of the lid member 240 at the time of heating and at the time of preheating which will be discussed later, thereby ensuring reduction of the applied power.
Each electrode 340 of the heating unit 320 is supported to be movable in the up and down direction by a lifting unit 360 equipped with an electric motor, a pulse generator or the like. The lid member 240 is provided with a temperature sensor 380 which detects the temperature of the heating chamber 240a, as shown in
Heating of the molten steel by the heating unit 320 is executed at the time of performing still standing coagulation after pouring is completed. At this time, upward movement of the lift table 50 pushes up the upper end portion of the casting 220 having a shell formed on the surface by a predetermined length from the upper end of the mold 120 (see
As shown in
As shown in
(Operation of Second Embodiment)
A description will now be given of the operation of the vertical casting method that is executed by the vertical casting apparatus according to the second embodiment. The winch 56 is rotated in a predetermined direction to move up the lift table 50. With the bottom portion of the mold 120 closed with the dummy head 48, molten steel of a special steel including a high-alloy steel and tool steel is poured in the mold 120 via the ladle 16 and the tundish 180. The molten steel poured in the mold 120 is subjected to first cooling in the mold 120, thus forming a shell on the surface of the molten steel. As the winch 56 is rotated in the reverse direction to vertically move down the lift table 50 at a given casting speed, the casting 220 whose bottom end is supported by the dummy head 48 is pulled out from the bottom portion of the mold 120.
The casting 220 immediately after being pulled out from the mold 120 is held by the guide rolls 44, 44 from both sides in the widthwise direction, as shown in
During pouring of molten steel in the mold 120, the lid member 240 placed on the power receiving plate 420 is heated at the standby position by the heating unit 320 with an inert gas supplied to the heating chamber 240a so that the lid member 240 is preheated to a temperature near the target temperature. After pouring in the mold 120 is completed, with the ladle 16 retreated, the tundish 180 moves upward and the carriage 200 moves. As the tundish 180 moves to the retracting position from the casting position, the lid member 240 lifted up at the standby position moves to the heating position (see
Next, with an inert gas supplied to the heating chamber 240a, the lid member 240 moves downward to cover the top portion of the mold 120 and the molten steel in the mold 120 is heated by the heating unit 320 in such a way as to compensate for the heat released from the surface of the molten steel, as shown in
The temperature control unit 400 performs feedback control in such a way as to adjust the gap between the electrodes 340 and the surface of the molten steel in the heating unit 320 based on the temperature of the heating chamber 240a detected by the temperature sensor 380 and keep the temperature of the heating chamber 240a at the target temperature. Accordingly, a drop in temperature of the surface of the molten steel in the mold 120 is kept at or higher than the solidus casting temperature until coagulation of the casting 220 comes near completion, thereby adequately preventing the coagulation of the surface of the molten steel. After a preset time passes, the heating power of the heating unit 320 is gradually reduced and heating is terminated.
As mentioned earlier, it seems that the occurrence of internal defects, such as the center porosity and center segregation or V-shaped segregation, is influenced by the angle of the coagulation front side of molten steel inside the casting. That is, conventionally, the angle of the coagulation front side (the angle with respect to the center line of the coagulation interface) θ of the molten steel inside the casting 220 would become small, as shown in
In other words, even for steel types, such as special steels including high-alloy steel and tool steel, that require severe demands on the product quality, the vertical casting method according to the invention can provide castings which have excellent quality with fewer internal defects, such as the center porosity, casting head cavity and center segregation or V-shaped segregation, inside. In case of casting the casting 220 whose top portion has cross-sectional sizes of 500 mm or greater in thickness and 500 mm or greater in width, the vertical casting method and apparatus according to the second embodiment are particularly effective.
Although the description of the second embodiment has been given of the case where the lid member and the heating unit are provided on the carriage of the tundish, the lid member and the heating unit may be provided on another carriage or moving means or the like so that when the tundish 18 moves to the retracting position from the casting position, the lid member is moved to the heating position quickly.
In case of casting a casting which has a thickness of 650 mm and a width of 850 mm using a tool steel as a material, the results of measuring the cut-off length of the upper end of a casting for a case where molten steel is not heated at the time of still standing coagulation after pouring is completed (prior art) and a case where molten steel is heated (Example 2 of the second embodiment) are shown in
As apparent from
As apparent from
As explained above, because at least one pair of opposing sides of each casting according to the present invention are tapered, even those castings which are cast from steel types, such as special steels including high-alloy steel and tool steel, that require severe demands on the product quality, have fewer internal defects, such as the center porosity and center segregation or V-shaped segregation, and have a high quality and improved yield.
In addition, ultra-slow casting at the casting speed set to 0.2 m/min or slower can further suppress the occurrence of internal defects, such as the center porosity and center segregation or V-shaped segregation.
Even for steel types, such as special steels including high-alloy steel and tool steel, that require severe demands on the product quality, the vertical casting method and apparatus according to another embodiment of the present invention can provide castings which have an excellent quality with fewer internal defects, such as the center porosity, casting head cavity and center segregation or V-shaped segregation, by heating molten steel in the mold whose top portion is covered with the lid member at the time of still standing coagulation after pouring of the molten steel is completed. This results in an improved yield. Further, preheating the lid member can suppress a drop in temperature of the surface of the molten steel until heating is started.
Number | Date | Country | Kind |
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2001-165557 | May 2001 | JP | national |
2001-167345 | Jun 2001 | JP | national |
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Number | Date | Country | |
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20040045697 A1 | Mar 2004 | US |
Number | Date | Country | |
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Parent | 10155040 | May 2002 | US |
Child | 10639180 | US |