Powder manufacturing apparatus and powder forming method

Abstract

The present invention provides a power manufacturing apparatus capable of preventing particle growth when fine powder is formed through a fluid, the apparatus comprising: a molten steel providing part for providing molten steel; and a cooling fluid spraying part which is arranged at a lower part of the molten steel providing part and sprays a cooling fluid on the molten steel in order to pulverize the molten steel provided by the molten steel providing part, wherein the cooling fluid spraying part forms a first flow for cooling the molten steel so as to pulverize the molten steel and a second flow for forming a descending air current in the molten steel.

Claims

1. A powder manufacturing apparatus comprising: a molten steel chamber supplying molten steel; and a cooling fluid ejector disposed below the molten steel chamber and ejecting water to the molten steel supplied from the molten steel chamber to atomize the molten steel, wherein the cooling fluid ejector comprises: a guide comprising a truncated cone part pointed downward so that the molten steel flowing downward from the molten steel chamber passes through a center region of the truncated cone part to form a first stream to cool and atomize the molten steel and a second stream to create a descending air current for the molten steel; and a jet nozzle pointed toward an outer surface of the truncated cone part so that the water is ejected toward the outer surface of the truncated cone part, wherein the truncated cone part has a spiral on the outer surface of the truncated cone part to induce the second stream which swirls downward around the molten steel flowing downward, and wherein the spiral induces the descending air current at a point at which extension lines drawn from a slope of the truncated cone part intersect each other.

2. The powder manufacturing apparatus of claim 1, wherein the spiral is a groove in a surface of the guide.

3. The powder manufacturing apparatus of claim 1, wherein a plurality of spirals are symmetrically arranged on the guide.

4. The powder manufacturing apparatus of claim 1, wherein the cooling fluid ejector is configured so that the first stream flows at a rate greater than a rate at which the second stream flows.

5. The powder manufacturing apparatus of claim 1, wherein the jet nozzle is a straight jet nozzle.

6. The powder manufacturing apparatus of claim 5, wherein the jet nozzle is located above the truncated cone part of the guide, and an angle between the jet nozzle and a vertical line is greater than an angle between a slope of the truncated cone part and the vertical line.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view illustrating a powder manufacturing apparatus of the related art.

(2) FIG. 2 is a schematic view illustrating a powder manufacturing apparatus including V-jet type jet nozzles according to the related art.

(3) FIG. 3 is a schematic view illustrating a powder manufacturing apparatus including a ring type jet nozzle according to the related art.

(4) FIG. 4 is a view illustrating a powder manufacturing apparatus including a guide.

(5) FIG. 5 is an enlarged view illustrating the guide illustrated in FIG. 4.

(6) FIG. 6 is an image of the powder manufacturing apparatus illustrated in FIGS. 4 and 5, taken when the powder manufacturing apparatus is clogged with molten steel.

(7) FIG. 7 is a graph illustrating a relationship between the particle size distribution and average particle size of powder.

(8) FIG. 8 is a schematic view illustrating a powder manufacturing apparatus according to an embodiment of the present disclosure.

(9) FIG. 9 is an enlarged view illustrating a guide illustrated in FIG. 8.

(10) FIG. 10 is a detailed view illustrating spirals illustrated in FIG. 9.

(11) FIG. 11 is a schematic view illustrating first streams illustrated in FIG. 8.

(12) FIG. 12 is a schematic view illustrating second streams illustrated in FIG. 8.

(13) FIGS. 13A and 13B are schematic plan views illustrating the first and second streams illustrated in FIGS. 11 and 12.

(14) FIG. 14 is a graph of the magnitude of impulse in inventive examples and comparative examples.

(15) FIG. 15 is a graph illustrating vertical velocities measured near a molten steel striking point in inventive examples and comparative examples.

BEST MODE

(16) Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

(17) A technique of using a guide has been proposed as illustrated in FIGS. 4 and 5 to improve the two types of nozzle structures described in the background art. That is, in the proposed structure, straight jet nozzles 31 are used, and a guide 40 shaped like a reverse truncated cone is disposed to guide and concentrate cooling water at a molten steel striking point. The jet nozzles 31 eject cooling water onto the guide 40 to concentrate the cooling water at the molten steel striking point.

(18) In the proposed structure, a cone-shape cooling water barrier WB is formed by cooling water ejected onto the guide 40, and since the cooling water barrier WB blocks the introduction of ambient air, an inside region I of the cooling water barrier WB is isolated. Therefore, if the cooling water does not smoothly strike molten steel at the molten steel striking point, the molten steel may solidify in the inside region I of the cooling water barrier WB as illustrated in FIG. 6.

(19) In the structure illustrated in FIG. 5, if cooling water is normally ejected, the sizes of most particles of produced powder are around the average particle size of the powder. However, in case of nozzle angle variations, a decrease in the magnitude of impulse, a change in the amount of cooling water, or a decrease in mass flow, the particle size distribution of powder may be widened, and thus the fraction of oversized powder may increase. Since such oversized iron powder is discarded as scrap, the yield of powder production may decrease. Therefore, in a water jet process, it is required that smooth flow of iron powder and the magnitude of impulse be maintained at a certain value or greater, so as to efficiently produce iron powder.

(20) That is, as illustrated in FIG. 7, although the same average particle size is obtained in both normal and abnormal situations, the distribution of particle size is relatively wide in the abnormal situation, and thus the fraction of oversized powder particles increases. As a result, the amount of powder discarded as scrap increases, and the yield of powder production decreases.

(21) Particularly, although a cooling water barrier WB formed by the guide 40 is effective in concentrating cooling water, the cooling water barrier WB blocks ambient air and forms negative pressure in a region above a molten steel striking point. Thus, if cooling water does not smoothly strike molten steel, the molten steel may unexpectedly solidify, or the particle size of iron powder may markedly deviate.

(22) Thus, as a technique for removing the demerits of the guide 40 (such as the formation of negative pressure in a cooling water barrier) while maintaining the merits of the guide 40 (such as ease in concentrating cooling water at a molten steel striking point, and stable production of powder even under varying process conditions), the inventors have proposed a guide structure configured to create a first stream for cooling and atomizing molten steel and a second stream for inducing a descending air current facilitating the discharge of powder when the molten steel is atomized by collision with cooling water.

(23) FIG. 8 is a schematic view illustrating a powder manufacturing apparatus according to an exemplary embodiment of the present disclosure. FIG. 9 is a detailed view illustrating a guide 140 illustrated in FIG. 8, and FIG. 10 is a detailed view illustrating spirals 143 illustrated in FIG. 9.

(24) As illustrated in FIG. 8, the powder manufacturing apparatus of the embodiment may have the same structure as the powder manufacturing apparatus illustrated in FIG. 1 except for a cooling fluid ejection unit, and thus the cooling fluid ejection unit will now be mainly described.

(25) The cooling fluid ejection unit includes: the guide 140 including a truncated cone part 142 oriented downward so that molten steel flowing downward from a molten steel supply unit 10 (refer to FIG. 1) may pass through a center region of the truncated cone part 142; and jet nozzles 130 disposed around the guide 140 to eject a cooling fluid toward the guide 140. The jet nozzles 130 are connected to a fixed body 110 and oriented to eject a cooling fluid toward the guide 140.

(26) The jet nozzles 130 may be pointed toward a region located just below a boundary between the truncated cone part 142 and a cylindrical part 141 of the guide 140. However, the jet nozzles 130 are not limited thereto. For example, even if the jet nozzles 130 are pointed toward any point of the truncated cone part 142, a cooling fluid ejected through the jet nozzles 130 may be concentrated by the guide 140. In the embodiment illustrated in FIG. 8, cooling water is ejected as a cooling fluid through the jet nozzles 130. However, a cooling fluid that may be ejected through the jet nozzles 130 is not limited to cooling water. For example, inert gas or air may be used as a cooling fluid according to the type of molten steel.

(27) The jet nozzles 130 may be straight jet nozzles configured to eject a cooling fluid toward a single point. However, as long as a cooling fluid ejected from the jet nozzles 130 strikes the guide 140 and forms first streams 150 and second streams 160, the jet nozzles 130 are not limited to the straight jet type. For example, the jet nozzles 130 may be V-jet or ring type nozzles.

(28) The guide 140 includes: the cylindrical part 141 connected to the fixed body 110; and the truncated cone part 142 extending from the cylindrical part 141 and having a reverse truncated cone shape. As illustrated in FIGS. 9 and 10, the spirals 143 are formed on the truncated cone part 142 to generate first streams 150 for atomizing molten steel and second streams 160 for forming a descending air current.

(29) As illustrated in FIG. 9, according to the embodiment of the present disclosure, cooling water 131 striking the truncated cone part 142 of the guide 140 forms first streams 150, and the first streams 150 flow downward along the surface of the truncated cone part 142 and strike molten steel. The first streams 150 are formed from ejection positions along the guide 140, and as a result, a cooling water barrier WB is formed by the first streams 150.

(30) In the embodiment of the present disclosure, since the spirals 143 are formed on the truncated cone part 142, a portion of cooling water 131 ejected onto the guide 140 forms second streams 160 swirling along the spirals 143 toward a molten steel striking point. Since the second streams 160 are spiral streams narrowing in a downward direction, the second streams 160 form a descending air current while passing by the molten steel striking point. That is, a downward flow is formed in a region around the molten steel striking point, and thus molten steel atomized into powder by the cooling water 131 is easily discharged downward by the downward flow.

(31) The spirals 143 may be symmetrically formed in the same shape around the truncated cone part 142.

(32) In the embodiment of the present disclosure, if the rate of the second stream 160 is increased to apply a great impulse to molten steel, atomization of the molten steel may be negatively affected. Therefore, when the cooling water 131 ejected through the jet nozzles 130 is divided by the guide 140 into the first and second streams 150 and 160, the rate of the first streams 150 may be greater than the rate of the second streams 160. This flow rate distribution may be accomplished by adjusting the height or depth of the spirals 143 and the number of the spirals 143.

(33) In addition, as illustrated in FIG. 9, ejection positions onto which the cooling water 131 is ejected from the jet nozzles 130 may be on the spirals 143. However, the ejection positions may not be on the spirals 143. Even in this case, since the first streams 150 meet the spirals 143, the second streams 160 may be naturally formed. That is, the ejection positions have no effect on the formation of the first and second streams 150 and 160.

(34) The powder manufacturing apparatus of the embodiment of the present disclosure is configured to supply molten steel from the molten steel supply unit 10 and atomize the molten steel into powder by striking the molten steel with a cooling fluid. At this time, while atomizing the molten steel into powder, a descending air current is formed by the cooling fluid so as to prevent the formation of coarse powder, that is, to prevent variations in the particle size of the powder. According to a powder forming method of an embodiment of the present disclosure, first streams and second streams are formed by a cooling fluid. The first streams strike molten steel, and the second streams swirl downward along spiral paths around the molten steel, and thus form a descending air current. Therefore, powder formed in a region in which the first streams strikes the molten steel may be pulled downward by the descending air current.

(35) In terms of manufacturing methods, second streams may be formed using any other method or structure instead of using a guide as long as the second streams form a descending air current at a position at which first streams strike molten steel. However, if a guide is used, the first and second streams may be simultaneously formed.

(36) FIG. 11 is a schematic view illustrating the first streams 150 illustrated in FIG. 8, and FIG. 12 is a schematic view illustrating the second streams 160 illustrated in FIG. 8. FIGS. 13A and 13B are a schematic plan view illustrating the first and second streams 150 and 160 illustrated in FIGS. 11 and 12.

(37) As illustrated in FIGS. 11 and 13A, the first streams 150 concentrate at a single point, and thus a great impulse may be applied to molten steel. In addition, since the first streams 150 are formed along a slope of the guide 140, the positions of the jet nozzles 130 may be flexibly set compared to the structure illustrated FIG. 3. In particular, in the related art illustrated in FIG. 3, if a molten steel striking point is varied because of change in process conditions or molten steel, the cooling fluid ejection unit may be replaced. According to the embodiment of the present disclosure, however, a molten steel striking point may be adjusted by only varying the height of the guide 140, and a great impulse may be applied at the molten steel striking point.

(38) As illustrated in FIGS. 12 and 13B, the second streams 160 being spiral streams concentrate in a direction toward the molten steel striking point, thereby creating a descending air current. These spiral streams do not collide with each other at a single point but converge and diverge, thereby forming a descending air current inside the spiral streams in the proceeding direction of the spiral streams. According to the embodiment of the present disclosure, upward motion of molten steel may not be induced at the molten steel striking point by a cooling water barrier WB formed by the first streams 150 owing to the descending air current formed by second streams 160, and the molten steel atomized into powder by collision with a cooling fluid may be smoothly discharged downward owing to the descending air current.

(39) Specifically, since powder (metal powder) is discharged by the descending air current, events varying the particle size of the powder such as agglomeration of the powder may not occur, thereby preventing variations in the particle size of the powder and guaranteeing the uniformity of the powder. Thus, loss may be reduced, and the yield of powder production may be increased.

(40) FIG. 14 is a graph illustrating impulse in inventive examples and comparative examples. The amount of cooling water was equal in the inventive examples in which the guide 140 illustrated in FIG. 10 is used and in the comparative examples in which the powder manufacturing apparatus illustrated in FIG. 2 is used.

(41) Specifically, four jet nozzles 130 were used in Inventive Example 1, and eight jet nozzles 130 were used in Inventive Example 2. Two jet nozzles 30 were used in Comparative Example 1, and four jet nozzles 30 were used in Comparative Example 2.

(42) As illustrated in FIG. 14, when the guide 140 was used in the inventive examples, the magnitude of impulse was relatively high even though the same number of nozzles was used. In particular, in the inventive examples, as long as a cooling fluid was ejected onto the guide 140, it was easy to apply a great impulse because the positions and types of nozzles had a little effect on the impulse application.

(43) FIG. 15 is a graph illustrating vertical velocities measured near a striking point in inventive examples and comparative examples.

(44) Referring to FIG. 15, guides such as the guide 140 illustrated in FIG. 8 were used in Inventive Example 3 and Comparative Example 3. However, the guide used in Inventive Example 3 included spirals 143 as illustrated in FIG. 10, and the guide used in Comparative Example 3 did not include spirals 143. That is, tests were performed in the same conditions except that the guide used in Comparative Example 3 did not have a structure inducing the formation of second streams 160. In FIG. 15, the x-axis refers to a height from a molten steel striking point, and the y-axis refers to velocity. In the y-axis, positive (+) values refer to upward velocities, and negative () values refer to downward velocities.

(45) As illustrated in FIG. 15, In Comparative Example 3 in which second streams 160 were not formed, upward force was applied at a molten steel striking point, that is, an upward movement of molten steel was observed at the molten steel striking point. In Inventive Example 3 in which second streams 160 were formed, downward force was applied to a molten steel striking point owing to a descending air current, that is, molten steel was moved downward at the molten steel striking point.

(46) Therefore, produced powder could be discharged downward and cooled in a state in which the particle size of the powder determined by impulse applied to the powder was maintained. Thus, the particle size distribution of the powder was concentrated on the average particle size of the powder. Thus, the amount of oversized powder could be reduced, and thus the yield of powder could be improved.

(47) While exemplary embodiments have been shown and described above with reference to the accompanying drawings, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention.