Method and apparatus for spray casting of alloy ingots
This invention provides a method and apparatus to produce metal or alloy ingots using spray casting with the features of easy manufacture of large diameter ingots and simultaneously their uniform microstructure due to followings. Firstly, spray deposition area on the top surface of the ingot can be enlarged by making use of multiple gas atomizers and also by controlling the their positions for the spray deposition. Secondly, at the same time, a mutually opposite-directional rotation between the gas atomizers and the catching plate provides a uniform deposition of sprayed droplets along the circumference-wise direction over the entire top surface of the ingot. In addition, a mutually opposite-directional reciprocation between the gas atomizer and the top surface of the ingot provides an enlargement of deposition area and an evenness of spray deposition along the radial direction on the top surface of the ingot.
[0001] The present invention relates to a method and apparatus for manufacturing metal or alloy ingot by utilizing spray casting process. To be more specific, this invention is characterized by increased casting speed due to multiple gas atomizers and ability to produce a large-diameter ingot with microstructural uniformity by having the sprayed droplets deposit over a larger area on the top surface of the ingot.
BACKGROUND OF THE INVENTION[0002] The spray casting process is the latest casting technology for producing alloy ingots, which consists of atomizing the molten metal or alloy by means of high-pressure gas into sprayed droplets, then forming alloy ingots by deposition the falling partially-solidified droplets on to the catching plate below. At this time, depending on the shape and the movement of the catching plate, rod-shaped, tube-shaped or plate-shaped alloy object can be produced. Generally, to produce a rod-shaped ingot, the catching plate is rotated and lowered, at a fixed speed, as the ingot agglomerate grows.
[0003] FIG. 1 is an illustration explaining the spray casting process as shown in U.S. Pat. Nos. 4,697,631 (1987) and 4,938,275 (1990). FIG. 2 is an enlarged view of the scanning gas atomizer illustrated in FIG. 1. When the molten metal or alloy (1) flows below the tundish(2) and through the melt orifice(3), the melt stream(4) which flows through the gas atomizer(6) turns into sprayed fine droplets(8) as the gas jet(7) gushes out. The sprayed droplets fall toward the catching plate maintaining a specific angle between spray path and the catching plate(10) and eventually deposit on the surface of the catching plate. At this time, the catching plate rotates to produce uniform deposition of the sprayed droplets on the entire top surface of the ingot(9). A rod-shaped ingot will grow gradually as the sprayed droplets deposit evenly on the catching plate, and the catching plate is lowered at the same rate as the growth of the ingot. In this manner, when a balance is achieved between the rates of the spray deposition and the ingot growth, a lengthy uniform-diameter ingot can be produced. Although the diameter of the ingot can be increased by decreasing the down speed of the catching plate, it should be avoided because too drastic a decline causes a sharp depression in the center of the top surface of the ingot and results in many large pores. Generally, a scanning gas atomizer(6a) is used to enlarge the deposition area of the sprayed droplets because, without it, the ingot diameter enlargement is restricted to diameters between 150 mm to 200 mm.
[0004] FIG. 2a is a diagrammatic view of a scanning gas atomizer illustrating how, when the high-pressure gas supply pipe(5) is rotated in an oscillating manner, the gas atomizer(6b) attached to the gas supply pipe also oscillates. This rotational oscillation creates a change in crash angle of the gas jet(7) with respect to the melt stream(4) and shakes the sprayed droplets(8) left and right, and can enlarge the deposition area of the sprayed droplets on the top surface of the ingot.
[0005] As it is illustrated in FIG. 2b, the rotational oscillation of the gas atomizer shakes the melt stream(4) left to right and results in a straight-line to-and-fro scanning motion above the top surface of the ingot. This, in turn, allows a uniform deposition of the sprayed droplets over a larger area. Utilization of the scanning gas atomizer can result in a maximum ingot diameter of 250 mm. Moreover, it has the advantage of manufacturing the ingot with greater uniformity compared to the utilization of a stationary gas atomizer.
[0006] However, because the oscillation motion of the scanning gas atomizer can result in a sudden change in clash angle between the melt stream(4) and the gas jet(7), it can lead to a disadvantage of a lowered gas-atomizing efficiency. When the scanning gas atomizer(6a) oscillates, the melt stream(4) deviates form the center of the gas atomizer, and thus the ejected gas jet(7) and the melt stream(4) cannot meet in one point and crash in a wider space. This causes a severely deviated size distribution of the sprayed droplets, which may hinder formation of the ingot with sound microstructure. Moreover, a combination of the clash angle change and the rotational oscillation of the gas atomizer lead to a sudden creation of a turbulent flow around the melt stream. This turbulence brings about a high probability that a back-pressure around the tip of melt orifice(3) occurs, resulting in the orifice blockage due to solidification of the melt stream. To avoid occurrence of this type of hazard, the rotational oscillation angle of the scanning gas atomizer is limited to around 2 degrees, and, inevitably, it lessens the effectiveness of enlarging the spray deposition area by utilizing the scanning gas atomizer. Because the molten metal or alloy is highly dense, the motion of the sprayed droplets cannot be easily altered by a sudden change of the clash angle of the gas jet. Therefore, it is difficult to change the flying direction of the sprayed droplets in real time. For these reasons, it is judged that, rather than being used for the purpose of enlarging the spray deposition area, the scanning gas atomizer is better utilized from the viewpoint of mixing uniformly various sized droplets during their flight.
[0007] As illustrated in FIG. 3a to 3c, the conventional spray casting process for producing the ingot can be classified in three categories in terms of a lengthwise direction of the ingot as vertical, titled and horizontal methods. In the case of the vertical method (FIG. 3a), although it is easier to maintain a uniform shape of the ingot during the spray casting, it requires a gas atomizer technology in a high level because the spray axis of the gas atomizer inclines from the vertical by an angle of about 35 degree. On the other hand, in the case of the tilted method (FIG. 3b), the gas atomization is most stable because the corresponding spray axis is vertical. However, because the ingot grows slantwise, this method has the disadvantage of causing problems in producing a heavy weight ingot when gravity is taken into account. In the case of the horizontal method (FIG. 3c), because of the high incline of the spray axis against the vertical, gas atomization control is more difficult. Moreover, although it has the advantage of producing long horizontal ingots within limits of certain height, in actuality, it is difficult to provide a uniform support for a lengthy ingot growing horizontally. For these reasons, the vertical ingot spray casting process is most widely used in commercial practice. However, the above ingot spray casting processes using single gas atomizer have the disadvantages of producing ingots with relatively smaller-diameters and having a lower spray cast yield of 60% to 70%. Therefore, dual gas atomizer technology is currently being used to improve upon the above-mentioned disadvantages.
[0008] FIG. 4 depicts the application of the two gas atomizers during ingot spray casting as shown in U.S. Pat. No. 5,472,038 (1995). The formation of a large diameter ingot is possible by allowing the separate deposition of sprayed droplets in the central and peripheral areas of the catching plate(10). Moreover, an increased casting speed and improved yield are additionally expected. The scanning movement of the atomizer requires complicated devices such as a cam and a motor, and thus only one of two atomizers is scanned due to a limited available space. Generally, the sprayed droplets that deposit in the central area of the catching plate are scanned, and a stationary gas atomizer is utilized for the periphery. Both vertical and horizontal methods are possible in the process utilizing two gas atomizers. The maximum diameter of ingot produced is known to be about 350 mm.
[0009] As stated above, the conventional methods for manufacturing metal or alloy ingot by utilizing spray casting process have the following problems.
[0010] First, regarding the use of a scanning gas atomizer in spray casting of the ingots: (i) uneven size distribution of sprayed droplets might promote the unhomogeneous microstructure of the final ingot; (ii) turbulence and build up of gas pressure can occur easily at the tip of melt orifice, which induces orifice blockage; (iii) because the scanning effect can only be expected within a limited rotational oscillation angle of about 2 degrees, the benefit regarding enlargement of spray deposition area is not noteworthy; (iv) when the use of two or more scanning atomizers is attempted, it has the disadvantage of design complication due to the spatial restriction imposed by having to provide scanning means for each gas atomizer.
[0011] Secondly, by the conventional spray casting method, it is very difficult to produce ingots of large diameter with uniform microstructure, exceeding the diameter of 400 mm.
[0012] Thirdly, because the conventional spray casting process uses one or two gas atomizers, it has a much lower casting speed compared to the continuous billet casting or ingot casting processes.
[0013] Fourthly, because the conventional spray casting process for producing ingots uses gas atomizers located in a unidirectional manner, it makes it difficult to utilize multiple gas atomizers within its restricted available space.
[0014] Fifthly, the conventional spray casting process for producing ingots can only manufacture round ingots, and is not able to produce square-shaped ingots.
SUMMARY OF THE INVENTION[0015] The present invention is directed to solve the above problems encountered by the conventionally available spray casting. It is hence an aim thereof to provide a method and apparatus for manufacturing easily a spray cast ingot whose diameter is relatively large by controlling the spatial arrangement of atomizers. The sprayed droplets flow out from at least one or more gas atomizers, and the total spray deposition area can be enlarged by controlling individually the deposition position of each melt spray on the top surface of the ingot. At the same time, the sprayed droplets deposit uniformly on the entire top surface of the ingot through controlling the relative rotation between the gas atomizer and the ingot.
[0016] Moreover, it is another purpose of this invention to provide a method and apparatus for manufacturing a spray cast ingot having simultaneously both uniformity of microstructure and enlargement of ingot diameter by adopting a relative reciprocating motion between the gas atomizer and the ingot along a lengthwise direction of the ingot. A more even mass distribution of the sprayed droplets around each deposition area on the top surface of the ingot can be achieved by varying periodically a mutual distance between the gas atomizer and the top surface of the growing ingot. That is, the total spray deposition area is more enlarged by the reciprocating motion of the atomizer and/or the ingot along a direction of ingot growth.
[0017] The further purpose of this invention is to provide a method and apparatus for manufacturing spray cast ingots, which significantly increase the casting speed by a simultaneous use of multiple gas atomizers.
[0018] In addition, it is still another purpose of this invention to provide a method and apparatus for manufacturing spray cast ingots having polygon shape, specially square shape, through controlling appropriately rotational and reciprocating motions between the gas atomizer and the ingot.
BRIEF DESCRIPTION OF DRAWINGS[0019] FIG. 1 is a diagrammatic view showing the conventional spray casting method and apparatus for manufacturing alloy ingots.
[0020] FIGS. 2a and 2b are diagrammatic views showing the principle of the scanning gas atomizer utilized in the conventional ingot spray casting process, in particular, FIG. 2a illustrates the rotational oscillation motion of the gas atomizer, and FIG. 2b illustrates an asymmetry of atomization caused by the scanning gas atomizer.
[0021] FIGS. 3a through 3c are diagrammatic views illustrating the conventional spray casting method for alloy ingot production, in detail, FIG. 3a illustrates the vertical spray casting method, FIG. 3b illustrates the tilted spray casting method, and FIG. 3c illustrates the horizontal spray casting method.
[0022] FIGS. 4a and 4b are diagrammatic views showing the conventional spray casting method for alloy ingot production using two gas atomizers, in particular, FIG. 4a shows the vertical spray casting method, and FIG. 4b shows the horizontal spray casting method.
[0023] FIG. 5 is a perspective view that depicts the spray casting method for alloy ingot production according to this invention.
[0024] FIG. 6 is a diagrammatic view showing the multiple-gas-atomizer spray casting method for alloy ingot production according to this invention, in which each gas atomizer is located on a circumference centered on the base axis.
[0025] FIG. 7 is a diagrammatic view showing the multiple-gas-atomizer spray casting method for alloy ingot production according to this invention, in which the location of each gas atomizer is adjusted to have the corresponding melt spray deposit on different radial positions on the top surface of the ingot.
[0026] FIG. 8 is a diagrammatic view showing the multiple-gas-atomizer spray casting method for alloy ingot production according to this invention, in which the location of the catching plate is adjusted, with respect to the gas atomizers, so as to have each melt spray deposit at different radial positions on the top surface of the ingot.
[0027] FIG. 9 illustrates this invention's method of establishing individual deposition radii of the melt sprays by means of partitioning the top surface of the ingot into several area elements, so as to have the entire top surface of the ingot covered.
[0028] FIG. 10 is a diagrammatic view of the radial reciprocating movement of the spray deposition area on the top surface of the ingot as a distance between the gas atomizer and the top surface of the ingot along the base axis is changed.
[0029] FIG. 11 is a diagrammatic view of this invention's nine different types of spray casting method for ingot production by means of various combinations of the relative rotation about the base axis and the relative reciprocation along the base axis between the gas atomizers and the catching plate.
[0030] FIGS. 12a and 12b explain the movement of the sprayed droplets on the top surface of the ingot in order to produce uniform height growth of the ingot, in particular, FIG. 12a illustrates that the velocity of reciprocating motion of the sprayed droplets along the radial direction should be changed in accordance with the radial deposition position of the sprayed droplets on the top surface of the ingot, and FIG. 12b illustrates the deposition path of the sprayed droplets for even spray deposition on the entire top surface of the ingot.
[0031] FIGS. 13a through 13d are graphs illustrating the theoretical movement of the sprayed droplets to ensure uniform deposition of the sprayed droplets on the top surface of the ingot, in detail, FIG. 13a illustrates the radial deposition position of sprayed droplets with time on the top surface, FIG. 13b illustrates the velocity of the radial movement of the sprayed droplets with respect to time, FIG. 13c illustrates the mutual displacement by the reciprocating motion of the gas atomizer and/or the catching plate, and FIG. 13d illustrates the velocity of the reciprocating motion of the gas atomizer and/or the catching plate.
[0032] FIGS. 14a through 14d are graphs illustrating the continuous movement of the sprayed droplets undergone in order to produce uniform deposition of the sprayed droplets on the top surface of the ingot within an approximate value, in detail, FIG. 14a illustrates the radial deposition position of sprayed droplets with time on the top surface, FIG. 14b illustrates the velocity of the radial movement of the sprayed droplets with respect to time, FIG. 14c illustrates the mutual displacement by the reciprocating motion of the gas atomizer and/or the catching plate, and FIG. 14d illustrates the velocity of the reciprocating motion of the gas atomizer and/or the catching plate
[0033] FIGS. 15a through 15d illustrate the deposition path of the sprayed droplets on the top surface of the ingot according to the cycle ratio of reciprocation to rotation of the spray droplets, in detail, FIG. 15a illustrates the deposition path of reciprocation to rotation cycle ratio of 8.375:1, FIG. 15b illustrates the deposition path of reciprocation to rotation cycle ratio of 8:1, FIG. 15c illustrates the deposition path of reciprocation to rotation cycle ratio of 1:8.375, and FIG. 15d illustrates the deposition path of reciprocation to rotation cycle ratio of 1:8.
[0034] FIG. 16 is a diagrammatic view showing the rotational or reciprocating motion executed by the gas atomizer for the purpose of producing the square ingot.
[0035] FIG. 17 illustrates the simultaneous motions composed of the rotational and reciprocating movement of the gas atomizer and the reciprocation of the catching plate in order to produce square ingots with longer sides
[0036] FIGS. 18a and 18b illustrate the deposition path of the sprayed droplets on the top surface of the ingot based on the combination of the catching plate reciprocation cycle and the gas atomizer rotation cycle, in particular, FIG. 18a illustrates the deposition path when the cycle ratio of the catching plate reciprocation to gas atomizer rotation is 2.375, and FIG. 18b illustrates when cycle ratio of the deposition path of the catching plate reciprocation to gas atomizer rotation is exactly 2.
[0037] FIG. 19 is a cross-sectional view of the spray casting alloy apparatus for manufacturing metal or alloy ingots according to this invention.
[0038] FIG. 20 is a cross-sectional view of the spray casting alloy apparatus for manufacturing metal or alloy ingots, which, in addition, has means for reciprocating the gas atomizer and/or the catching plate, according to this invention 1 PARTS LIST 1. Molten alloy 2. Tundish 3. Melt orifice 4. Melt stream 5. High-pressure gas supply pipe 6. Gas atomizer 6a. Scanning gas atomizer 6b. Stationary gas atomizer 7. Gas jet 8. Sprayed droplets 9. Ingot 10. Catching plate 11. Spray chamber 12. Catching plate drive axle 13. Vent 31. Base axis 32. Molten alloy 33. Tundish 34. Melt orifice 35. Spray angle 36. Stopper 37. Tundish stopper 38. Tundish slide gate 39. High-pressure gas intake 40. Gas supply pipe stand 41. Gas supply pipe 42. Gas atomizer case 43. Gas atomizer 44. Spray axis 45. Gas jet 46. Gas atomizer spindle 47. Gas supply pipe support stabilizer 48. Gas supply pipe rotation bearing 49. Gas atomizer fixing pin 50. Upper chamber rotation bearing 51. Seal 52. Upper chamber 53. Upper chamber support 54. Gas atomizer reciprocator cam 55. Upper chamber rotation motor 56. Upper chamber drive axle 57. Right angle cross gears 58. Sprayed droplets 59. Individual spray deposition area 60. Top surface of ingot 61. Ingot 62. Catching plate 63. Spare catching plate 64. Ingot fixing pin 65. Catching plate drive axle 66. Catching plate drive part 67. Catching plate drive case 68. Catching plate drive part support 69. Catching plate reciprocator cam 70. Catching plate reciprocator guide 71. Catching plate rotation motor 72. Internal spline shaft 73. External spline shaft 74. Catching plate motor 75. Chain 76. Chain sprocket 77. Screwed shaft 78. Nut plate 79. Spray chamber 80. Vent 81. Spray chamber support 82. Gas atomizer rotator 83. Catching plate rotator 84. Catching plate linear driver 85. Catching plate rotation axis 86. Gas atomizer reciprocator 87. Catching plate reciprocator
DESCRIPTION OF THE PRESENT INVENTION[0039] In order to carry out the above-mentioned purposes, a method of forming an ingot of metal or alloy according to this invention comprises the following steps:
[0040] locating multiple atomizers around a base axis, wherein spray axes of said atomizers are angularly spaced from said base axis by between 0 and 90 degrees;
[0041] spraying droplets of molten metal or alloy from said atomizers;
[0042] positioning a catching plate in a path of said sprayed droplets;
[0043] forming an ingot agglomerate by continuous deposition of said sprayed droplets on top surface of said catching plate, thereby growing said ingot along said base axis;
[0044] rotating said atomizers and/or said catching plate about said base axis for the purpose of an even dispersion of said sprayed droplets along a circumference on top surface of said ingot;
[0045] moving continuously said atomizers and/or said catching plate along said base axis in order to maintain a uniform distance between each said atomizer and the top surface of said ingot; and
[0046] as an additional step, reciprocating said atomizers and/or said catching plate along said base axis for the purpose of a to-and-fro motion of said spray droplets along a radial line on the top surface of said ingot.
[0047] A further method of forming an ingot of metal or alloy according to this invention comprises the following steps:
[0048] spraying droplets of molten metal or alloy from an atomizer whose spray axis is angularly spaced from a base axis by between 0 and 90 degrees;
[0049] positioning a catching plate in a path of said sprayed droplets;
[0050] forming an ingot agglomerate by continuous deposition of said sprayed droplets on top surface of said catching plate, thereby growing said ingot along said base axis;
[0051] rotating said atomizers and/or said catching plate about said base axis for the purpose of an even dispersion of said sprayed droplets along a circumference on top surface of said ingot; and
[0052] providing a continuous motion to said atomizer and/or said catching plate along said base axis in order to maintain a periodic variation of a distance between said gas atomizer and the top surface of said ingot.
[0053] An apparatus of forming an ingot of metal or alloy according to this invention comprises as follows:
[0054] a tundish that contains molten metal or alloy;
[0055] one or multiple gas atomizers located around a base axis below said tundish, wherein spray axes of said gas atomizers are angularly spaced from said base axis by between 0 and 90 degrees;
[0056] a catching plate positioned in a path of sprayed droplets spouted from said atomizer;
[0057] means for rotating said atomizers and/or said catching plate about said base axis;
[0058] means for providing continuous motion to said atomizers and/or said catching plate along said base axis; and
[0059] as an additional element, means for reciprocating said atomizers and/or said catching plate along said base axis.
[0060] Below, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
EMBODyMENT 1[0061] FIG. 5 shows a desired embodiment of spay casting method for producing metal or alloy ingot in accordance with this invention. Locate at least one gas atomizer(43) on the circumference around an arbitrary base axis(31), where spray axes(44) of the gas atomizers are angularly spaced from the base axis(31) by between 0 and 90 degrees. At this time, the spray axes(44) face the catching plate(62), and it is desired that multiple gas atomizers be located with a 360 degree rotation concentric to the base axis(31). As the molten alloy passes through the melt orifice(34) attached below the tundish(33), the multiple gas atomizers are used to produce spray of molten metal or alloy. Such sprayed droplets(58) fall quickly and are subjected to cooling and solidification as they are exposed to the ejected gas jet. When the catching plate(62) is located in the path of flying droplets to be vertical to the base axis, partially solidified droplets will deposit on the surface of the catching plate and the desired ingot agglomerate(61) will begin to form. In order to have the sprayed droplets deposit on the entire top surface of the catching plate, the gas atomizer(43) and/or the catching plate(62) are set in rotation with respect to the base axis(31). A long ingot can be produced by continuously moving the gas atomizer(43) and/or the catching plate(62) along the direction of the ingot growth. At this time, the shape of the ingot is determined by the radial position at which the falling sprayed droplets deposit on the top surface of the ingot(60). The falling sprayed droplets should be controlled to deposit evenly on the entire top surface of the ingot in order to ensure proper height growth of the entire top surface of the ingot perpendicular to the base axis.
[0062] As above, when multiple gas atomizers are used simultaneously, the production speed of spray casting can be increased in proportion to the number of applied gas atomizers. In the case of conventional spray casting method for ingots, as shown in FIGS. 3 and 4, because gas atomizers(6, 6a, 6b) are located in a unidirectional pattern on one side of the base axis, the limited remaining space made it difficult to deploy a number of gas atomizers. In the case of this invention, as shown in FIG. 5, multiple gas atomizers(43) are located in a circular pattern along the base axis(31). This concentric arrangement of the gas atomizer gives the advantage of being able to install multiple gas atomizers, over the conventional spray casting process. Regarding this invention, the utilization of multiple gas atomizers results in the increased casting speed, and besides, provides the advantage of enlarging the area where the sprayed droplets deposit on the top surface of the ingot.
[0063] Methods applying simultaneously multiple gas atomizers are classified into two ways, depending on how to determine a deposition radius on the top surface of the ingot, where each melt spray flowing out from each gas atomizer deposits.
[0064] First, the location of the gas atomizers(43) and the spray angle(35) are adjusted to have their melt sprays deposit on the top surface of the ingot(60) with identical radius with respect to the base axis(31). There are many instances combining the atomizer location with the spray angle, which satisfy the condition of the identical deposition radius on the top surface of the ingot. Out of those, the method illustrated in FIG. 6 shows the process of locating each gas atomizer evenly along the circumference of a concentric circle with the base axis, and adjusting the spray angle(35) of each gas atomizer(43) to be equal. Application of this method is desirable because of its simple spatial arrangement of gas atomizers. FIG. 6 illustrates the use of four gas atomizers, and it has the advantage of four times the production speed of ingots with the same diameter compared to the use of single gas atomizer. This method is suitable for mass production of ingots with a uniform diameter because the spray axes of the atomizers are symmetrical with respect to the base axis.
[0065] Secondly, the location of the gas atomizers(43), the spray angle(35) or the position of the catching plate(62) are adjusted so as to have each melt spray crash in the corresponding different radial positions on the top surface of the ingot(60). This method of deposition of each spray at different radii can produce a much larger diameter ingot than that of deposition at an identical radius. In this method, it is simple to arrange multiple gas atomizers with an identical spray angle so as to be positioned each other in different heights with respect to the top surface of the ingot. FIG. 7, as a detailed explanation, shows the arrangement of multiple gas atomizers(43) with an identical spray angle(35) located on the conic surface centered around the base axis with varying their heights above the top surface of the ingot. This method is advantageous for producing large diameter ingots and has the advantage of simplicity of design. However, it has the disadvantage of having to readjust the location of each gas atomizer when production of ingots of varying diameters is sought. Moreover, because of the respective height differences among gas atomizers, with a supposed identical amount of melt content contained in the tundish(33), the outflow rate of the molten alloy through each gas atomizer can vary. This method might require some time and effort in determining the appropriate deposition radius for each melt spray because the deposition amount due to each spray may vary if the melt outflow rate for each gas atomizer is different,.
[0066] If the height of each gas atomizer is different, the outflow rate of molten alloy will also differ. Therefore, it is necessary to equalize the height of each gas atomizer and moreover to have each melt spray deposit on different radii. There are many instances of having the melt sprays from each gas atomizer deposit at different radial positions by way of adjusting the spray angle(35) as well as the distance of each gas atomizer from the base axis(31) while maintaining the identical height of each gas atomizer(43). Out of those instances, as illustrated in FIG. 8, an easy and simple method is to control the deposition radius while arranging the gas atomizers with a identical spray angle to be located on a concentric circumference centered around the base axis(31). That is, the gas atomizers can be arranged in the same manner as in FIG. 6, and additionally, a specific movement of the catching plate along the direction perpendicular to the base axis(31), as shown in arrow in FIG. 6, can result in deposition of each melt spray at different radial positions. In this way, the ingot diameter can be easily controlled by an appropriate horizontal movement of the catching plate with respect to the gas atomizers. Simultaneously, the amount of melt spray from each atomizer is mutually equal because of applying the simple arrangement of gas atomizers.
[0067] In the case of trying to control the even deposition of the sprayed droplets on top surface of a large-diameter ingot using the multiple gas atomizer method, as mentioned above, the deposition radius of each melt spray on the top surface of the ingot has to be appropriately adjusted. In this invention, a detailed explanation of a four-gas-atomizer mode will be provided as a typical example of the multiple gas atomizer method. As illustrated in FIG. 9, the top surface of the ingot is divided into four area elements, A1, A2, A3, A4 along the direction of its radius and four melt sprays I, II, III and IV deposit at the above four area elements, respectively. Assuming that the deposition amount due to each melt spray is identical, an extent of individual area element has to be the same in order to obtain a uniform growth of the top surface of the ingot. The radii on the top surface of the ingot that determine radial borders, at which each extent of the area elements is mutually equal, are s1=0.50R, s2=0.71R, s3=0.87R, and s4=R (where R is the radius of the ingot). Each melt spray must deposit at a location within the corresponding area element defined as a zone between two adjacent radial borders. For example, when each melt spray is supposed to deposit in the middle of the corresponding area element, the deposition radii of the melt sprays are r1=0.25R, r2=0.60R, r3=0.79R, and r4=0.93R. If the deposition region due to each melt spray is larger than the width of the corresponding area element, adjacent melt sprays will overlap partially around the radial borders, resulting in an even deposition over the entire top surface of the ingot. In the case of using n sets of gas atomizers, the radius, Sk, defining the k-th area element is determined according to the following mathematical formulae. 1 s k = k n · R [ Mathematical Formula 1 ]
[0068] By utilization of Mathematical Formula 1, the radial borders for the area elements can be determined. When the gas atomizers are adjusted in order that each melt spray deposits in an appropriate location within the corresponding area element, the large-diameter ingot will be produced with a uniform growth rate throughout its entire top surface.
[0069] As with above, even if the deposition radius of each melt spray is appropriately controlled, a specific rotational motion is necessary to ensure the deposition of the sprayed droplets on the entire top surface of the ingot. That is, Rotation of the sprayed droplets(58) about the base axis(31) can disperse the sprayed droplets along the circumference on the top surface of the ingot. To have the sprayed droplets rotate relatively along a specific circumference above the top surface of the ingot, the gas atomizers(43) and/or the catching plate(62) need to be rotated about the base axis(31). The following are the three efficient methods obtaining a relative rotational effect of the sprayed droplets with respect to the ingot, applicable to this invention: (i) gas atomizer rotation only; (ii) catching plate rotation only; and (iii) simultaneous gas atomizer and catching plate rotation. Moreover, a fixed angular velocity rotation should be applied when producing a circular ingot.
[0070] The way to embody a relative rotational effect of the sprayed droplets according to this invention is, first, to have the gas atomizers(43) be rotated about the base axis(31) and to keep the catching plate(62) not being rotated. If the gas atomizers are rotated in this manner, the sprayed droplets(58) will rotate as they fall and might cause a spatial mix-up of individual droplets inside the spray. The sprayed droplets are composed of various sizes of droplets, get mixed in the space above the ingot, and turn into a spray with more uniform spatial distribution. This mixing effect inside the spray leads to an even deposition of sprayed droplets on the top surface of the ingot. The real-time mix of the flying droplets promotes a greater uniformity of microstructure of the final ingot(61). In the case of the conventional spray casting method, the ingot is stuck to the rotating catching plate and thus there is a length limit of ingot. Since a few stabilizer pins connect the catching plate with the ingot, it is impossible to stabilize a long rotating ingot in the conventional method. However, this invention has the advantage of being able to safely produce long ingots along the base axis, because the ingot does not rotate. In the case of rotating gas atomizers, the gas atomizers should be rotated simultaneously together with the tundish containing melt, and hence the rotation speed cannot be high due to safety concerns over the molten alloy contained within tundish.
[0071] The second way to embody a relative rotational effect of the sprayed droplets according to this invention is to rotate only the catching plate(62) while keeping the gas atomizers(43) not being rotated. In the case of rotating the catching plate, the rotation speed can be relatively high, and there is the advantage of simpler machine design. The third way embody a relative rotational effect of the sprayed droplets according to this invention is to rotate simultaneously both the gas atomizers(43) and the catching plate(62). At this time, the gas atomizers and the catching plate must rotate mutually in the opposite direction to benefit from the mixing effects of the sprayed droplets during the flight as well as to obtain a higher relative rotational speed of the sprayed droplets with respect to the ingot.
[0072] If the deposition radius of each melt spray can be appropriately controlled and the gas atomizers and/or the catching plate are rotated about the base axis, then it will result in a uniform deposition of the sprayed droplets on the entire top surface of the ingot. At this time, the ingot(61) will grow along the direction of the base axis(31), and a mutual distance between each gas atomizer and the top surface of the ingot along the base axis should be maintained to be uniform for producing a uniform-diameter ingot growing at a certain rate. Therefore, to maintain the mutual distance as uniform, the gas atomizers(43) an/or the catching plate(62) need to be continuously moved along the base axis for offset against an extent of ingot growth. The following are the three efficient methods maintaining the mutual distance, applicable to this invention: (i) gas atomizer moving only; (ii) catching plate moving only; (iii) simultaneous gas atomizer and catching plate moving. The gas atomizers should continuously move in the direction of the growth of the ingot along the base axis, while the catching plate should continuously move in the opposite direction of the growth of the ingot along the base axis.
[0073] The average diameter of the ingot is closely related to the continuously moving rate of the gas atomizers and/or the catching plate along the base axis. In the case of the total deposition amount of the sprayed droplets over a period of time is uniform, the individual or mixed moving rate due to continuous motion of the gas atomizers and/or the catching plate must be inversely proportional to square of the average diameter of the ingot. In other words, when the sprayed droplets is judged to be evenly deposition on the entire top surface of the ingot and the deposition amount is maintained to be identical over a period of time, the above rate of continuous motion along the base axis has to be reduced in inverse proportion to square of the ingot diameter.
[0074] In the case of casting round ingots, to produce an even deposition of the sprayed droplets on the entire top surface(60) of the ingot, the appropriate adjustment of the deposition radius of each melt spray and the circumference-wise dispersion of the sprayed droplets owing to relative rotational motion of the sprayed droplets will suffice. However, in the case of trying to produce a larger diameter ingot, additional control of mass distribution of the sprayed droplets along the radial direction is necessary. That is, if the width of each area element on the top surface is larger than deposition region due to the corresponding melt spray, the mass distribution of the sprayed droplets along the radial direction can be controlled by having the sprayed droplets travel to-and-fro in a straight line along the radius on the top surface of the ingot. Therefore, simultaneous control of mass distribution by the circumference-wise motion and the added radial motion will yield a more uniform growth on the entire top surface of the ingot with large diameter.
[0075] To make the sprayed droplets travel in a radial straight line between the center and the outer of the top surface of the ingot, a gas atomizer needs to be shaken along the radial straight-line path with maintaining a uniform height. However, for such movement, the atomizer, and tundish(33) adjoined to the atomizer, and the molten alloy within the tundish should make the to-and-fro motion together. Accordingly, the to-and-fro motion of the tundish makes difficult to safely contain the molten alloy content within the tundish and gives a high probability of causing work-related accidents. Moreover, in the case of using multiple gas atomizers, it is difficult to independently move individual gas atomizer to-and-fro. Therefore, in this invention, the gas atomizers(43) and/or the catching plate(62) are reciprocated along the base axis(31) and thus a mutual distance between each gas atomizer(43) and the top surface of the ingot(60) along the base axis is changed periodically.
[0076] FIG. 10 shows the radial reciprocating movement of the sprayed droplets on the top surface of the ingot according to changes in the mutual distance between the gas atomizer(43) and the top surface of the ingot(60) along the base axis. If the mutual distance along the base axis is small, as in Ho, the sprayed droplets will deposit on the outer radius area of the top surface of the ingot, and the deposition of the sprayed droplets will move toward the center radius area as the mutual distance increases. When the maximum mutual distance is reached, as in H1, the sprayed droplets will deposit at the center radius area. The time needed for the sprayed droplets to move from the maximum outer radius (rmax), through the minimum inner radius (rmin), and again to the maximum outer radius becomes a reciprocating period (t0), and &Dgr;h (=H1-H0) is a reciprocating amplitude.
[0077] As explained above, to have the sprayed droplets rotate relatively to the ingot along the base axis, the gas atomizers(43) and/or the catching plate(62) need to be set in rotation about the base axis(31). Likewise, to periodically change the mutual distance between the atomizer and the top surface of the ingot along the base axis, the gas atomizers(43) and/or the catching plate(62) need to be set in reciprocating motion along the base axis(31).
[0078] FIG. 11 illustrates spray casting methods for ingots derived from the nine different combinations of relative rotation and reciprocation motions between the gas atomizers and the ingot. Methods 1 to 3, under the category of cases in which the gas atomizers are reciprocated but the catching plate is not reciprocated, correspond to rotation of only the gas atomizers, rotation of only the catching plate, and simultaneous rotation of the gas atomizers and the catching plate, respectively. Methods 4 to 6, under the category of cases in which the catching plate is reciprocated but the gas atomizers are not reciprocated, correspond to rotation of only the atomizers, rotation of only the catching plate, and simultaneous rotation of the gas atomizers and the catching plate, respectively. Methods 7 to 9, under the cases in which the gas atomizers and the catching plate are simultaneously reciprocated, correspond to rotation of only the atomizers, rotation of only the catching plate, and simultaneous rotation of the gas atomizers and the catching plate, respectively.
[0079] In methods 1 to 3, the gas atomizers are reciprocated along the base axis. As the gas atomizers ascend along the base axis, the deposition position of the sprayed droplets moves toward the center of the top surface of the ingot; and as the gas atomizers descend along the base axis, the deposition position moves outward. The reciprocating motion of the gas atomizers enlarges the deposition area of the sprayed droplets along the radius of the top surface of the ingot, and promotes mixing the flying droplets in the space above the top surface of the ingot. In the case of method 1, because the gas atomizers are reciprocated and rotated, the flying droplets actually get mixed three-dimensionally along the circumference-wise and vertical directions. Therefore, if method 1 is applied, it provides the most uniform deposition of the sprayed droplets. If method 2 is applied, because the gas atomizers are reciprocated and the catching plate is rotated, it has the advantage of being the suitable production method for large diameter ingots.
[0080] In methods 4 to 6, the catching plate(62) is reciprocated along the base axis. When the catching plate ascends along the base axis, the deposition position of the sprayed droplets moves outward; and on the contrary, when the catching plate descends, the deposition position moves inward. When the catching plate is reciprocated only, it is difficult to have the spayed droplets actually mix in the space above the top surface of the ingot, and the sprayed droplets mix just as they deposit on the top surface of the ingot. It is easier to realize the design of reciprocating the catching plate compared to reciprocating the gas atomizers. In method 4, the gas atomizers are rotated while the catching plate is reciprocated, and in method 5, the catching plate are simultaneously rotated and reciprocated. Both methods 4 and 5 provide the advantage of relatively easy set-ups to produce large diameter ingots.
[0081] Generally, the spray cast ingot is over 1m long and, moreover, is heavy. Therefore, because of the length and heavy weight of the ingot, it is not an easy task to gain a reciprocating motion of the ingot attached to the catching plate at a high moving rate with a wide amplitude change. Likewise, it is also a difficult task to generate a reciprocating motion of high amplitude for the gas atomizers, because the tundish containing molten alloy will have to be reciprocated together as well. In this situation, as in methods 7 to 9, the gas atomizers(43) and the catching plate(62) can be simultaneously reciprocated in the mutually opposite directions. By this simultaneous motion, respective amplitude of reciprocation can be reduced in half and, thus, an effect of actually increased amplitude can be expected. At this time, as the gas atomizers ascend, the catching plate must descend; and on the other hand, when the gas atomizers descend, the catching plate should ascend. These two mutually opposing movements must occur simultaneously. Moreover, compared to methods 1 and 4, because it reduces the respective amplitude in half and cuts the reciprocating period in half due to two opposing simultaneous movements, it has the advantage of greater movement and more frequent movement cycles possible within the same time period.
[0082] In addition, as illustrated in FIG. 10, the mutual distance between the gas atomizer and the top surface of the ingot along the base axis is changed in a cycle. When the mutual distance decreases, the deposition point of the sprayed droplets on the top surface of the ingot moves outward; and when the mutual distance increases, the deposition point moves inward. Moreover, in the case of the greater mutual distance, the flying droplets experience longer time to be cooled or solidified until they deposit, due to their greater flight distance and furthermore, the spray width at the location of deposition is increased. Therefore, when the mutual distance is increased, the temperature of the sprayed droplets is lowered at the deposition location and the widened spray width accelerates emitting effectively the heat contained in the sprayed droplets. When the mutual distance is small, the temperature of the sprayed droplets is high at the location of deposition. Moreover, because the spray width is narrow at the location of deposition, it has the effect of concentrating heat in a small area. Generally, the interior of the ingot is very hot because of difficulty in the emission of heat, and, on the contrary, the exterior of the ingot is cooled undesirably because of the atomizing gas. As a result, this process creates a big temperature difference between the interior and the exterior of the ingot. Such drastic temperature gradient can bring about local microstructural non-uniformity inside the ingot and can cause internal cracks in the alloy with a higher thermal expansion coefficient. However, in this invention using a periodic change in the mutual distance, the sprayed droplets having a lower temperature deposit near the center of the top surface of the ingot, whereas those having a higher temperature are amassed on the outer radius of the top surface of the ingot. Therefore, this invention's method has the advantage of effectively reducing the thermal gradient inside the ingot, which occurs in the conventionally available spray casting method.
[0083] To promote uniform growth of the entire top surface of the ingot, a fixed-velocity reciprocation of the sprayed droplets along the radial direction should be avoided, and the reciprocating velocity should be controlled as a function of the deposition radius. That is, when the deposition position of the sprayed droplets is in the center, the reciprocating velocity should be high; and on the other hand, the reciprocating velocity should be lowered as their deposition position moves outward. Through this type of control, the deposition amount of the sprayed droplets can be evened out over the entire top surface of the ingot and a uniform growth rate can be achieved.
[0084] As illustrated in FIG. 12a, if the sprayed droplets are supposed to be rotated around the base axis at a fixed angular velocity and, at the same time, be reciprocated in a straight line along the radial direction at a varying velocity, the relationship between the reciprocating velocity v and the radial position r can be calculated. The sprayed droplets are supposed be located at radial position r1 and travel at the reciprocating velocity of v1. Travel of the spray droplets during an infinitesimal time of &Dgr;t covers the deposition area of &Dgr;A1 on the top surface of the ingot. On the other hand, the sprayed droplets at radius r2 with the reciprocating velocity v2 travel the deposition area of &Dgr;A2 during the infinitesimal time of &Dgr;t. The areas &Dgr;A1 and &Dgr;A2 have to be the same in order to produce an even rate of ingot growth because the deposition amount of the sprayed droplets over a period of time is identical at the respective deposition area. This relationship can be expressed in <Mathematical Formula 2>.
Mathematical Formula 2(2r1+&Dgr;r1)·&Dgr;r1=(2r2+&Dgr;r2)·&Dgr;r2
[0085] Here, &Dgr;r=v&Dgr;t, and (2r+&Dgr;r) can be approximated to be 2r. Their substitution into <Mathematical Formula 2> comes to the conclusion that multiplying r by v has to be constant regardless of the radial position, giving <Mathematical Formula 3>.
Mathematical Formula 3r1·v1=r2·v2=constant
[0086] This means that the reciprocating velocity of the sprayed droplets is inversely proportional to the radial position. Namely, the sprayed droplets have to move faster at the center of the top surface of the ingot and slower as they move outward for the purpose of the even deposition of the sprayed droplets.
[0087] FIG. 12b shows the path of the deposition position on the top surface of the ingot(60) when the sprayed droplets are rotating at a fixed angular velocity and reciprocating at a velocity inversely proportional to the radial position. The outer area of the top surface of the ingot actually receives a less amount of sprayed droplets because they have to travel along a larger circumference with a greater tangential velocity. To compensate for this lessened deposition amount along the radius, the reciprocating velocity has to be reduced to increase the spray delay time along the adjacent radius. Therefore, in the outer area where the tangential velocity of rotation is high, the sprayed droplets should deposit at a denser radial interval; and as they move inward, the radial interval should be enlarged because the tangential velocity of rotation is reduced.
[0088] Substitution of v(t)=dr(t)/dt into <Mathematical Formula 3> gives a differential equation. By using initial boundary condition, the differential equation can be solved and simplified ending up with the following equations of displacement and velocity as a function of time as <Mathematical Formula 4>. 2 r ( t ) = r max · f ( t ) , v ( t ) = - u min tan φ · f ( t ) h ( t ) = r max · tan φ · [ 1 - f ( t ) ] , u ( t ) = u min f ( t ) f ( t ) = 1 - 2 · u min · t r max · tan φ [ Mathematical Formula 4 ]
[0089] In this formula, r(t) stands for the radial position with time on the top surface of the ingot(60); v(t) stands for the moving velocity of the sprayed droplets along the radial direction on the top surface of the ingot; h(t) stands for the displaced distance due to the reciprocating motion of the gas atomizers and/or the catching plate along the base axis; u(t) stands for the reciprocating velocity of the gas atomizers and/or the catching plate along the base axis; rmax stands for the maximum outer radius at which the sprayed droplets deposit; umin stands for the minimum reciprocating velocity of the gas atomizers and/or the catching plate; &phgr; stands for the angle between the spray axis(44) of the gas atomizer and the top surface of the ingot(60); t stands for time.
[0090] The above-mentioned <Mathematical Formula 4> is effective only within a time range between 0 and t0/2. When it is beyond this scope, as illustrated in FIG. 13, the movement is accomplished by applying the above movement formula curve in a periodic manner. To explain the FIG. 13b, initially, the sprayed droplets move at the minimum velocity (−vmin: negative value) from the outer of the ingot to the center. The moving velocity increases as they move closer to the center. At t0/2, the sprayed droplets reach the minimum radial position at which the maximum velocity (−vmax: negative value) is attained. At the minimum radial position, the moving direction has to be changed instantaneously in the opposite direction. At this time, the movement begins with the maximum velocity (vmax: positive value) and the moving velocity slows as the sprayed droplets move outward. At t0, the minimum velocity (vmin: positive value) is obtained as they reach the maximum radial position. Afterward, setting this as a movement cycle, the cycle is repeated.
[0091] However, as mentioned above, because the theoretical velocity of the radial movement to produce a uniform deposition is discontinuous and, in particular, the moving direction has to be changed at the maximum value in an instant, it is difficult to execute in practice. Therefore, a continuous reciprocating motion, whose velocity on most routes is inversely proportional to the radial position, is desired. FIG. 14b shows the continuous movement over the entire route according to this invention. In this way, continuity in moving velocity can be obtained and thus the moving direction can be changed smoothly even at the maximum velocity. This continuity is favourable to reciprocate the gas atomizers(43) or the catching plate(62) without an excessive load. FIG. 14a illustrates the change of radial position, and, compared to FIG. 13a, shows the smoother transition of moving direction change. FIG. 14c shows the variation of the displacement of the relative reciprocating motion of the gas atomizers and/or the catching plate as function of time. There are no cusps showing the feature of smooth movement.
[0092] As explained in FIG. 12b, because the sprayed droplets make simultaneous rotational and reciprocating motions relatively with respect to the growing ingot, the reciprocating cycle has to be adjusted appropriately according to the rotation cycle in order to have even deposition on the top surface(60) of the ingot. FIGS. 15a and 15b show the deposition path of the sprayed droplets on the top surface of the ingot when the reciprocating cycle is much longer than the rotation cycle, i.e., in the case of multiple rotation cycles per one reciprocating cycle. FIG. 15a shows the deposition path of the sprayed droplets when the cycle ratio of reciprocation to rotation is 8.375, by applying the continuous reciprocating motion of FIG. 14. This shows the sprayed droplets deposit evenly on the entire surface of the ingot. In particular, a deposition amount on the outer area of the top surface can be increased by overlapping more frequently the sprayed droplets on the outer area. Generally, in the case of the conventional spray casting method, a convex top surface has been obtained due to more amount of sprayed droplets flowing into the center area. However, this invention's process reduces the convex top surface and produces a flat top surface.
[0093] On the other hand, FIG. 15b shows the deposition path of the sprayed droplets when the cycle ratio of reciprocation to rotation is exactly 8. The path of 8 rotations per one reciprocating cycle is identical to the next cycle, thus, following the same curve. Therefore, when the reciprocation to rotation ratio is an exact positive number, it is difficult to obtain a uniform spray deposition over the entire top surface of the ingot because the exact path of the sprayed droplets is repeated.
[0094] FIGS. 15c and 15d show the deposition path of the sprayed droplets when the rotation cycle is much longer in relation to the reciprocating cycle, i.e., when the sprayed droplets undergo many reciprocating cycles per one rotation cycle. FIG. 15c shows the deposition path of the sprayed droplets when the cycle ratio of the rotation to reciprocation is 8.375. The sprayed droplets are found to deposit evenly on the top surface of the ingot. In this case, there is a possibility of a convex top surface because the center area receives more amount of sprayed droplets than the outer area by having the sprayed droplets overlapped more frequently in the center area.
[0095] On the other hand, FIG. 15d shows the deposition path of the sprayed droplets when the cycle ratio of rotation to reciprocation is exactly 8. Because there are 8 reciprocating cycles per one rotation cycle, the sprayed droplets don't deposit evenly on the top surface of the ingot. An eight-leaf-shaped ingot with eight axes of symmetry can be produced and there are filled with many pores between eight leaves of the cross-sectional ingot. Therefore, even in the case of exact positive number ratio of rotation to reciprocation cycle, similar to the case shown in FIG. 15b, it is difficult to obtain an even spray deposition on the top surface of the ingot because the sprayed droplets keep moving exactly along the same path. Considering the four situations mentioned above, the most desirable situation is when the reciprocating cycle is much longer than the rotation cycle and the ratio of reciprocation to rotation cycle is not a positive number, because it results in the most even deposition of the sprayed droplets on the top surface of the ingot.
EMBODYMENT 2[0096] In the case of embodiment 1, production of a circular ingot was made possible because the angular velocity for the relative rotational motion of the gas atomizer with respect to the catching plate was constant. It is possible to produce triangular, square-shaped or pentagonal ingots by applying a periodically varied angular velocity for the relative rotation of the gas atomizer with respect to the catching plate. FIG. 16 shows the terms of movement that the gas atomizer has to undergo in producing a square ingot. In order to form the four corners of a square ingot, each corner has to receive additional deposition of the sprayed droplets. Therefore, the rotational angular velocity of the gas atomizer has to be periodically reduced every quarter turn of the gas atomizer against the non-rotating catching plate. On the other hand, when the gas atomizer is not rotating and the catching plate is rotating, a square ingot can be also produced by reducing periodically the angular velocity every quarter turn of the catching plate against the gas atomizer.
[0097] A detailed explanation of the rotational motion of gas atomizer(43) and/or catching plate(62) used in square ingot production is given below. The angular velocity for the relative rotation of the gas atomizer or the catching plate has to be controlled as a function of a rotated central angle (&thgr;) for producing a square ingot. In other words, the movement at the center of four sides of the square-shaped ingot should be fast, and the rotation velocity must be reduced as the four corners are approached. In this way, a uniform growth of the ingot can be obtained by controlling the average deposition amount of each central angle to be equal. As shown in FIG. 16b, by supposing that the sprayed droplets rotate at a periodically varied angular velocity of &ohgr;(t) about the base axis with respect to a non-rotating catching plate, then the relationship between the angular velocity &ohgr; and the rotated central angle &thgr; can be calculated.
[0098] The sprayed droplets are supposed be located at a central angle &thgr;1 and travel at a rotational angular velocity of &ohgr;1. Rotation of the spray droplets during an infinitesimal time of &Dgr;t covers the deposition area of &Dgr;A1 on the top surface of the ingot. On the other hand, the sprayed droplets at a central angle &thgr;2 with an angular velocity of &ohgr;2 travel the deposition area of &Dgr;A2 during the infinitesimal time of &Dgr;t. The areas &Dgr;A1 and &Dgr;A2 have to be the same in order to produce an even rate of ingot growth because the deposition amount of the sprayed droplets over a period of time is identical at the respective deposition area. This relationship can be expressed in the following <Mathematical Formula 5>. 3 sin Δθ 1 cos θ 1 cos ( θ 1 + Δθ 1 ) = sin Δθ 2 cos θ 2 cos θ 2 ( θ 1 + Δθ 2 ) [ Mathematical Formula 5 ]
[0099] Here, &Dgr;&thgr;=&ohgr;&Dgr;t, and approximately &thgr;+&Dgr;&thgr;≈&thgr; and sin &Dgr;&thgr;≈&Dgr;&thgr; because &Dgr;&thgr; is very small. Their substitution into <Mathematical Formula 5> comes to a conclusion of the following <Mathematical Formula 6>. 4 ω 1 cos 2 θ 1 = ω 2 cos 2 θ 2 = constant [ Mathematical Formula 6 ]
[0100] Substitution of &ohgr;(t)=d&thgr;(t)/dt into <Mathematical Formula 6> gives a differential equation. By using initial boundary condition, the differential equation can be solved and simplified ending up with the following equations of central angle and angular velocity as a function of time as <Mathematical Formula 7>. 5 θ ( t ) = ArcTan ( ω 0 t ) , ω ( t ) = ω 0 1 + ( ω 0 t ) 2 [ Mathematical Formula 7 ]
[0101] In the mathematical formula, &thgr;(t) stands for the rotated central angle with time on the top surface of the ingot(60); &ohgr;(t) stands for the angular velocity of the sprayed droplets at the central angle &thgr;(t); &ohgr;0 stands for the initial angular velocity; and t stands for time.
[0102] When the rotation cycle of the gas atomizer is tr, the effective scope of the <Mathematical Formula 7> is 0≦t≦tr/8 (⅛ rotation or 0°≦&thgr;≦45°). Once out of this scope, as illustrated in FIG. 15c, the movement is accomplished by applying the above movement formula curve in a periodic manner. At first, rotation of the sprayed droplets begins with an initial angular velocity of &ohgr;0, then the angular velocity is reduced to nearly a fan shape and it is half of the initial value &ohgr;0 as the corner is approached.
[0103] Square ingot production is possible just by the relative rotational motion of the gas atomizer with respect to the catching plate, which is controlled to periodically reduce its angular velocity every quarter turn. However, in addition to this rotational movement, if the deposition path of the sprayed droplets is adjusted to a square, it will be more effective in producing a square ingot. In order to produce a definite square path of spray deposition on the top surface of the ingot, as the dotted line in FIG. 16b, either the gas atomizer or the catching plate should make a reciprocating motion along the base axis every quarter turn of the gas atomizer or the catching plate.
[0104] Detailed explanation of rotational and reciprocating motion of the gas atomizer to produce square ingots is explained below. As shown by the dotted line in FIG. 16b, the gas atomizer(43) has to be appropriately rotated about the base axis and reciprocated along the base axis in order to have the sprayed droplets deposit along a square path on the top surface of the ingot. At this time, the gas atomizer completes one reciprocating cycle per each quarter turn, and the starting and ending points of the two motions should coincide with each other. Through simple geometric consideration, the reciprocating displacement y(t) for the square path deposition and its resulting deposition radius r(t) of the sprayed droplets as a function of time can be calculated, as shown in <Mathematical Formula 8>.
Mathematical Formula 8y(t)=b·tan&phgr;·({square root}{square root over (2)}−{square root}{square root over (1+(&ohgr;0t)2)}),
r(t)=b·{square root}{square root over (1+(&ohgr;0t)2)}
[0105] Here, the above-mentioned <Mathematical Formula 8> is effective within the scope of 0≦t≦tr/8 (0°≦&thgr;≦45°), and b stands for the minimum deposition radius of the sprayed droplets. As illustrated in FIGS. 15d and 15e, once out of this scope, the movement continues as the above-mentioned moving curve is applied periodically to successive motion. The sprayed droplets deposit initially in the radial position b and the gas atomizer is gradually moved toward the top surface of the ingot as it rotates. When it has rotated 45 degrees, the deposition radius of the sprayed droplets increases to 1.414 b. If it rotates further, the gas atomizer moves away from the top surface of the ingot, and when rotated 90 degrees, the deposition radial position reduces again to b. If this process is continuously repeated, a square ingot with a uniform growth rate can be obtained by reducing the rotation velocity of the gas atomizer around every corner of a square shape and thus providing an exact square deposition path on the top surface of the ingot. As above-mentioned, a square ingot can be produced under the condition of stationary catching plate, by changing the angular velocity and the relative height of the gas atomizer every quarter turn. On the contrary, when the gas atomizer is stationary, it can also be produced as the rotating catching plate changes its angular velocity every quarter turn and is reciprocated in accordance with y(t) every quarter turn.
[0106] Besides square ingots, production of triangular or pentagonal ingots is possible by this invention's production method. If we wish to produce a regular polygon ingot with n-sides, rotational angular velocity and relative height difference should be changed periodically for every 1/n turn. Suitable movement equation for the above process can be obtained by going through a similar process as <Mathematical Formula 5> to <Mathematical Formula 8>. Moreover, the number of gas atomizers used in square ingot production process must be 1, 2 or 4 as a divisor of 4 so as to be able to produce square-shaped formation. Similarly, the number of gas atomizers to be used in n-sides shape ingot has to be a divisor of n.
[0107] When a square ingot is produced as shown in FIG. 16, it is difficult to produce a square ingot with long sides because the sprayed droplets follow the same deposition route while they rotate. If production of a square ingot with longer sides is sought, then the following should be done to enlarge the deposition area of the sprayed droplets: (i) when the gas atomizer is rotating and reciprocating, reciprocate the catching plate according to h(t) function, as shown in FIG. 14; (ii) when the catching plate is rotating and reciprocating, reciprocate the gas atomizer according to h(t) function.
[0108] FIG. 17 shows a periodic change in the angular velocity &ohgr;(t) of the gas atomizer every quarter turn, the reciprocating displacement y(t) of the gas atomizer conducive to square deposition path, and the additional reciprocating motion of the catching plate along the base axis according to h(t) function, in order to enlarge the deposition area. As shown in FIG. 17b, by these three types of movements, the sprayed droplets draw a square-shaped deposition path around the edge of the top surface of the ingot and a star-shaped deposition path around the center of the top surface of the ingot. FIG. 17e illustrates the deposition radius of the sprayed droplets on the top surface of the ingot when the cycle ratio of catching plate reciprocation to gas atomizer rotation is 2.375. Here, the gas atomizer has a relatively low reciprocating amplitude &Dgr;y, conducive to providing a square deposition path, while the catching plate is reciprocated for enlarging the deposition area with a relatively high amplitude &Dgr;h. As shown in FIG. 17e, serrate protrusions are created in a curve of deposition radius due to combination of the above two reciprocating motions.
[0109] In the case of producing ingots with large sides, as mentioned above, in order to produce a uniform deposition of the sprayed droplets on the top surface of the ingot(60), the cycle ratio of catching plate reciprocation to gas atomizer rotation has to be appropriately adjusted. FIG. 18a shows the deposition path of the sprayed droplets after 50 rotations with the above-mentioned cycle ratio of 2.375. The sprayed droplets are found to deposit along a square path at the edge of the top surface of the ingot. As they move to the center, the deposition path is changed into a star-shaped pattern, and a relatively uniform deposition through the entire top surface can be obtained. As such, by utilizing the above-mentioned process, ingots with large sides can be produced by inducing a uniform deposition of the sprayed droplets on the entire top surface of the ingot.
[0110] On the other hand, FIG. 18b shows the deposition path of the sprayed droplets when the cycle ratio of catching plate reciprocation to gas atomizer rotation is a positive number 2. In the case of applying a positive-number ratio, we find out that a uniform deposition cannot be expected because the deposition path of the sprayed droplets repeatedly follows the same path. As with above, ingots with large sides can be produced involving not only rotation &ohgr;(t) and reciprocation y(t) of the gas atomizer but also an additional reciprocation h(t) of the catching plate. On the opposite hand, the same can be achieved by a periodic angular velocity change &ohgr;(t) of the rotating catching plate every quarter turn, simultaneously reciprocating displacement y(t) of the catching plate to create a square deposition path, and an additional reciprocation h(t) of the gas atomizer along the base axis for an enlarged deposition area.
EMBODYMENT 3[0111] FIG. 19 illustrates an apparatus for spray casting of metal and alloy ingots according to another desirable embodiment of this invention. Just below the tundish(33) containing molten metal or alloy(32), there are one or multiple gas atomizers(43) attached on the circumference around the base axis. The gas atomizers have spray angles(35) between 0 and 90 degrees, and their spray axes(44) face the catching plate(62). For the point of view of spatial management, it is desirable to arrange them along a ring shape around the base axis. The catching plate(62) should be located so as to be in a path of the falling sprayed droplets and be perpendicular to the base axis. In order to rotate the gas atomizers(43) and/or the catching plate(62) about the base axis, a gas atomizer rotator(82) or a catching plate rotator(83) is provided. Once the spray casting is in progress and the ingot growth takes place, a catching plate linear driver(84) is prepared to move continuously the catching plate(62) along the base axis in order to maintain a uniform distance between the gas atomizers and the top surface of the growing ingot. Moreover, in addition, a gas atomizer reciprocator(86) or a catching plate reciprocator(87) can be provided in order to reciprocate the gas atomizer(43) and/or the catching plate(62) along the base axis(31).
[0112] A detailed construction and operation of this embodiment is explained in connection with real process of the ingot spray casting below.
[0113] There is a long, erect and fixed spray chamber(79) with rectangular or circular shape around the base axis(31). The upper spray chamber(52) covers the spray chamber, and the upper spray chamber has a top view of a sliced cone. The tundish(33), which contains molten metal or alloy(32), is located above the upper spray chamber. Molten alloy melted in advance by using an electric arc furnace or an induction melting furnace is supplied to the tundish(33). The melt orifice(34) is located between the tundish(33) and the gas atomizer(43), penetrating the bottom of the tundish. In addition, a stopper(36) is placed just upon each melt orifice(34) and controls the flow of the molten alloy down to the gas atomizer. Initially, the melt orifice(34), attached just below the tundish, is closed off by the stopper(36). However, once the molten alloy(32) is put in the tundish, the molten alloy reaches a specific level, the stopper opens up, and the molten alloy passes through the melt orifice(34) and flows down to the gas atomizer(43).
[0114] The high-pressure gas for the gas atomizer is supplied through the gas supply pipe(41), located in the middle along the base axis(31). Emanating from the center of the gas supply pipe, the gas supply pipe splits and goes out to each gas atomizer case(42). The gas atomizers(43) are attached at the specific location of each gas atomizer case with penetrating the corresponding gas atomizer case. Gas atomizer fixing pins(49) are provided just below the upper chamber(52) to be fixed into the upper spray chamber. As a result, the gas atomizers(43) and the upper chamber(52) are connected and move as one. The molten alloy(32) that comes through the gas atomizer turns into sprayed droplets by the gas jet(45) flowing out at the lower part of the gas atomizer, and the sprayed droplets fall toward the catching plate. The sprayed droplets which fly a certain distance adheres to the catching plate(62) and continues to deposit, and the ingot grows.
[0115] The gas atomizers(43) and/or the catching plate(62) have to be rotated around the base axis(31) in order to deposit the sprayed droplets with circumference-wise uniformity on the top surface of the ingot. Although both the gas atomizer and the catching plate can be rotated mutually, for the sake of simpler design, it is easier to have one of them rotate. Therefore, one of either the gas atomizer rotator(82) or the catching plate rotator(83) to provide rotation around the base axis is sufficient.
[0116] The gas atomizer rotator(82) is made up of an upper chamber drive axle(56), right angle cross gears(57) and an upper chamber rotation motor(55). The upper chamber rotation motor(55), which provides rotation for the upper chamber, is placed below the upper chamber support(53). Rotation of the upper chamber(52) is transmitted through the right angle cross gears(57) and the upper chamber drive axle(56). Therefore, this motion also results in the rotation of the gas both atomizer case(42) and the gas atomizer(43), which are combined by the gas atomizer fixing pins(49). For the right angle cross gears, a zero bevel gear, a spiral bevel gear, a hypoid gear or a worm gear can be used.
[0117] Provision of the catching plate rotator(83) has to be considered together with the catching plate linear driver(84) because the catching plate has to be moved in the opposite direction of the ingot growth direction. The catching plate rotator(83) is made up of a catching plate rotation motor(71), an internal spline shaft(72) and an external spline shaft(73). The internal spline shaft(72), with its long groove, is connected to the central shaft of the catching plate rotation motor(71), and the external spline shaft(73) can move up and down with being penetrated by the internal spline shaft(72). The external spline shaft is fixed to and moves with the catching plate. When the catching plate rotation motor(71) rotates, the internal spline shaft(72), the external spline shaft(73), the catching plate(62) and the ingot(61) all rotate.
[0118] Moreover, the catching plate linear driver(84) is made up of a catching plate drive motor(74), a screwed shaft(77), a nut plate(78), a catching plate drive axle(65) and the external spline shaft(73). When the catching plate drive motor(74) rotates, by means of a connecting chain(75), the rotation is transferred to the chain sprockets(76) and the screwed shaft(77). The rotation of the screwed shaft(77) will be converted into a linear movement of the nut plate(78). At this time, the catching plate drive axle(65), the external spline shaft(73), the catching plate(62) and the ingot(61), located above the nut plate, will all move continuously along the base axis. Especially, both rotation and continuous linear motion of the catching pate can be obtained because the external spline shaft(73) rotates together with the internal spline shaft(72) and simultaneously slides around it.
[0119] It is sufficient to rotate either the gas atomizers(43) or the catching plate(62) for the spray casting process. However, when both are rotating, the catching plate and the gas atomizers must be controlled to rotate in the opposite direction. In addition to this rotational motion, a reciprocating motion of the gas atomizers and/or the catching plate along the base axis will be more favourable in producing large diameter ingots. In the case of this invention, as shown in FIG. 20, the gas atomizer reciprocator(86) or the catching plate reciprocator(87) are additionally provided. They reciprocate the gas atomizers(43) and/or the catching plate(62) along the base axis(31). Although the reciprocating motion can be applied for both the gas atomizers and the catching plate, it is easier to provide one reciprocator for the sake of simpler design. Therefore, it is sufficient to provide just one reciprocator of either the gas atomizers or the catching plate.
[0120] As for the gas atomizer reciprocator(86), the simplest way is to install a cam with the profile shown in FIG. 10. Besides this method, program controlled stepper motor or hydraulic servomotor can be used. In additional design details, a gas atomizer reciprocator cam(54) can be installed below the upper chamber support(53), and the upper chamber support(53) is reciprocated along the base axis as the gas atomizer reciprocator cam(54) rotates. The upper chamber, the gas atomizer case(42) and the gas atomizer(43) all can be reciprocated because the gas atomizer case(42) and the upper chamber(52) are combined together by the gas atomizer fixing pins(49).
[0121] In the case of the catching plate reciprocator(87), its design is very similar to the gas atomizer reciprocator(86). The catching plate drive part support(68) supports the catching plate drive case(67) and is installed below it; then the catching plate reciprocator cam(69) is installed below the catching plate drive part support(68). The turning of the catching plate reciprocator cam(69) induces the reciprocating motion of the catching plate drive part support(68), and that in turn, results in reciprocation of the catching plate(62), with the ingot(61) on it. It is sufficient to reciprocate either the gas atomizer(43) or the catching plate(62) in a spray casting process for ingot production. However, in the event that reciprocation of both is sought, then the gas atomizer and the catching plate must be reciprocated each other in the opposite direction with the same cycle.
[0122] By combining the relative rotational motion with the relative reciprocating motion between the gas atomizer and the catching plate, the spray droplets can be deposited uniformly on the entire top surface of the ingot and thus a uniform ingot growth can be obtained. At this time, long and even-diameter ingots can be produced by continuously moving catching plate in the opposite direction of the ingot growth.
EFFECTIVENESS OF THIS INVENTION[0123] This invention is effective in being able to manufacture large diameter ingots with uniform microstructure by way of enlarged deposition area and even mass distribution of spray droplets induced by (i) appropriate control of the deposition location of each spray with the use of multiple gas atomizers, (ii) mutually opposite-directional rotation between the gas atomizer and the ingot, and, in addition, (iii) mutually opposite-directional reciprocation between the gas atomizer and the top surface of the ingot. Moreover, this invention is effective in increasing significantly the production speed of spray casting through the use of multiple gas atomizers, and producing angled ingots by controlling the cycles of the relative rotation and reciprocation between the gas atomizer and the top surface of the ingot.
Claims
1. A method of forming an ingot of metal or alloy, comprising the steps of:
- locating a plurality of gas atomizers around a base axis, wherein spray axes of said gas atomizers are angularly spaced from said base axis by between 0 and 90 degrees;
- spraying droplets of molten metal or alloy from said gas atomizers;
- positioning a catching plate in a path of said sprayed droplets;
- forming an ingot agglomerate by continuous deposition of said sprayed droplets on top surface of said catching plate, thereby growing said ingot along said base axis;
- rotating said gas atomizers and/or said catching plate about said base axis for the purpose of an even dispersion of said sprayed droplets along a circumference on top surface of said ingot; and
- continuously moving said gas atomizers and/or said catching plate along said base axis in order to maintain a uniform distance between each said gas atomizer and the top surface of said ingot.
2. The method of claim 1, wherein said gas atomizers are arranged around said base axis in order that each melt spray spouting from said gas atomizers deposits at an identical radial position on the top surface of said ingot.
3. The method of claim 1, wherein said gas atomizers are arranged around said base axis in order that each melt spray spouting from said gas atomizers deposits at the corresponding different radial positions on the top surface of said ingot.
4. The method of claim 1, wherein said gas atomizers are rotated about said base axis at a uniform angular velocity and said catching plate is not rotated.
5. The method of claim 1, wherein said catching plate is rotated about said base axis at a uniform angular velocity and said gas atomizers are not rotated.
6. The method of claim 1, wherein said gas atomizers are rotated about said base axis at a periodically variable angular velocity and said catching plate is not rotated.
7. The method of claim 1, wherein said catching plate is rotated about said base axis at a periodically variable angular velocity and said gas atomizers are not rotated.
8. A method according to any of claims 1 to 7, including the step of reciprocating said gas atomizers and/or said catching plate along said base axis for the purpose of a to-and-fro motion of said spray droplets along a radial line on the top surface of said ingot.
9. The method of claim 8, wherein said gas atomizers are reciprocated along said base axis with a fixed reciprocating amplitude and said catching plate is not reciprocated.
10. The method of claim 8, wherein said catching plate is reciprocated along said base axis with a fixed reciprocating amplitude and said gas atomizers are not reciprocated.
11. A method of forming an ingot of metal or alloy, comprising the steps of:
- spraying droplets of molten metal or alloy from an gas atomizer whose spray axis is angularly spaced from a base axis by between 0 and 90 degrees;
- positioning a catching plate in a path of said sprayed droplets;
- forming an ingot agglomerate by continuous deposition of said sprayed droplets on top surface of said catching plate, thereby growing said ingot along said base axis;
- rotating said gas atomizer and/or said catching plate about said base axis for the purpose of an even dispersion of said sprayed droplets along a circumference on top surface of said ingot; and
- providing a continuous motion to said gas atomizer and/or said catching plate along said base axis in order to maintain a periodic variation of a distance between said gas atomizer and the top surface of said ingot.
12. The method of claim 11, wherein said gas atomizer is rotated about said base axis at a uniform angular velocity and said catching plate is not rotated.
13. The method of claim 11, wherein said catching plate is rotated about said base axis at a uniform angular velocity and said gas atomizers is not rotated.
14. A method according to claims 11 to 13, wherein a plurality of gas atomizers located around said base axis are used.
15. A method of forming an ingot of metal or alloy, comprising the steps of:
- spraying droplets of molten metal or alloy from an gas atomizer whose spray axis is angularly spaced from a base axis by between 0 and 90 degrees;
- positioning a catching plate in a path of said sprayed droplets;
- forming an ingot agglomerate by continuous deposition of said sprayed droplets on top surface of said catching plate, thereby growing said ingot along said base axis;
- rotating either said gas atomizer or said catching plate about said base axis at a periodically varying angular velocity every quarter turn of said gas atomizer or said catching plate; and
- providing a continuous motion to either said gas atomizer or said catching plate along said base axis in order to maintain a periodically varying distance between said gas atomizer and the top surface of said ingot every quarter turn of said gas atomizer or said catching plate.
16. The method of claim 15, wherein two or four gas atomizers located with a mutual symmetry centered on said base axis are used.
17. An apparatus of forming an ingot of metal or alloy, comprising:
- a tundish that contains molten metal or alloy;
- an gas atomizer, whose spray axis is angularly spaced from said base axis by between 0 and 90 degrees, located below said tundish;
- a catching plate positioned in a path of sprayed droplets spouted from said gas atomizer;
- means for rotating said catching plate about said base axis;
- means for reciprocating said catching plate along said base axis; and
- means for providing continuous motion to said catching plate along said base axis.
18. The apparatus of claim 17, wherein a plurality of gas atomizers are located around said base axis.
19. An apparatus of forming an ingot of metal or alloy, comprising:
- a tundish that contains molten metal or alloy;
- an gas atomizer, whose spray axis is angularly spaced from said base axis by between 0 and 90 degrees, located below said tundish;
- a catching plate positioned in a path of sprayed droplets spouted from said gas atomizer;
- means for rotating said gas atomizer about said base axis;
- means for reciprocating said gas atomizer along said base axis; and
- means for providing continuous motion to said catching plate along said base axis.
20. The apparatus of claim 19, wherein a plurality of gas atomizers are located around said base axis.
21. An apparatus of forming an ingot of metal or alloy, comprising:
- a tundish that contains molten metal or alloy;
- a plurality of gas atomizers located around a base axis below said tundish, wherein spray axes of said gas atomizers are angularly spaced from said base axis by between 0 and 90 degrees;
- a catching plate positioned in a path of sprayed droplets spouted from said gas atomizers;
- means for rotating said catching plate about said base axis; and
- means for providing continuous motion to said catching plate along said base axis.
22. An apparatus of forming an ingot of metal or alloy, comprising:
- a tundish that contains molten metal or alloy;
- a plurality of gas atomizers located around a base axis below said tundish, wherein spray axes of said gas atomizers are angularly spaced from said base axis by between 0 and 90 degrees;
- a catching plate positioned in a path of sprayed droplets spouted from said gas atomizers;
- means for rotating said gas atomizer about said base axis; and
- means for providing continuous motion to said catching plate along said base axis.
Type: Application
Filed: Oct 11, 2002
Publication Date: Apr 24, 2003
Inventors: Kyeong-Mi Kim (Gwacheon-shi), Sung-Seok Han (Icheon-shi)
Application Number: 10269958
International Classification: B22D023/00;
