WO1992001822A1

WO1992001822A1 - Atomizing apparatus

Info

Publication number: WO1992001822A1
Application number: PCT/GB1991/001188
Authority: WO
Inventors: Jeffrey Stuart Coombs; James Burnett Forrest
Original assignee: Osprey Metals Limited
Priority date: 1990-07-19
Filing date: 1991-07-17
Publication date: 1992-02-06
Also published as: EP0539440A1; AU8219691A

Abstract

Atomizing apparatus for atomizing of liquid metal has a spray chamber (9), means for introducing a liquid stream into the spray chamber (9) and an atomizer (6) defining an opening for receiving the liquid stream. The spray chamber has means (11, 12, 13) for regulating the recirculation of atomizing gas within the spray chamber for stabilizing the stream during atomization. The regulating means preferably comprises a plurality of baffles positioned adjacent the atomizing device and disposed so as to restrict the flow of recirculating gas laterally of the stream and/or a restriction plate disposed transverse to the direction of flow of the stream and restricting the recirculation of atomizing gas within the chamber upstream of the atomizing device.

Description

ATOMIZING APPARATUS This invention relates to improved atomizing apparatus for use in stabilizing a stream of liquid metal or metal alloy teemed through an atomizer and to a method of spray deposition. In U.S. Patent Specification No. 3663206, there is disclosed apparatus for shattering a freely falling liquid stream by means of two or more jet nozzle systems. That arrangement is said to prevent or minimize movement of particles in a direction other than downwardly thereby avoiding the particles making undesired contact with parts of the apparatus. However, we have found that within the gas chamber recirculation of atomizing gas can cause turbulence de-stabilizing the falling stream and causing splashback of liquid metal onto the atomizer. This problem is further aggravated by the additional recirculation of gas in the spray chamber caused by the use of a collector when forming a preform. An object of the present invention is to provide an improved atomizing apparatus and one which in the preferred arrangement provides improved stabilization of a metal stream during ato ization. According to the present invention there is provided atomizing apparatus comprising a spray chamber, means for introducing a liquid stream into the spray chamber, atomizing means defining an opening for receiving the liquid stream and for directing atomizing gas at the liquid stream for ato ization thereof, and means within the spray chamber for regulating the flow of gas recirculating within the spray chamber.

The regulating means preferably comprises a plurality of baffles positioned adjacent the atomizing means at opposed sides of where the stream falls and disposed so as to redirect recirculating gas generally in the direction of flow of the stream. Suitably, at least one of the baffles is movable so that the angle of each baffle may be altered prior to or during atomization. The regulating means may alternatively, or in addition, comprise a restriction plate restricting the recirculation of atomizing gas within the chamber upstream of the atomizing device.

In addition to the regulating means, further stabilization of the stream may be achieved by the application of gas upstream of the atomizer opening for passage through the atomizer with the stream for stabilizing the stream prior to atomization. The application means may be located laterally of the atomizer and directs additional gas towards the stream in a direction the major component of which is perpendicular to the axis of the opening. Therefore, according to another aspect of the invention there is provided an atomizing apparatus comprising a spray chamber, an atomizer disposed within the spray chamber and defining an opening through which a metal or metal alloy may be teemed, atomizing means at said atomizer for directing atomizing gas at a stream falling through the opening of the atomizer for atomization of the stream and stabilizing gas supply means for applying stabilizing gas upstream of the opening for passage through the atomizer with the stream for stabilizing the stream prior to atomization.

Preferably, the stabilizing gas supply means is located laterally of the atomizer and directs gas into an aspiration gap upstream of the atomizer.

Suitably the apparatus of this arrangement includes means for regulating the flow of gas recirculating within the spray chamber. This means may include a restriction plate and/or a plurality of baffles. Preferably, the baffles are opposed plain plates substantially aligned with the direction of flow of the stream. The baffles may be used with a restriction plate restricting the recirculation of atomizing gas within the chamber upstream of the atomizing device.

The invention also includes a method of spray deposition within a spray chamber comprising providing atomizing means having an opening therethrough, teeming a stream of molten metal or metal alloy through the opening, atomizing the stream into a spray, directing the spray at a collector to form a deposit thereon, providing a plurality of baffles about the atomizing means for regulating the flow of recirculating gas within the spray chamber, and moving at least one baffle during atomization. Preferably the movement of at least one baffle is a substantially continuous movement and sufficiently rapid to effect oscillation of the spray.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic side elevation of known apparatus for the spray deposition of bar or ingot; Figure 2 is a diagrammatic side elevation of a first regulating means in accordance with the invention;

Figure 3 is a schematic plan view of the arrangement shown in Figure 2; Figure 4 is a diagrammatic side elevation of an alternative regulating means in accordance with the invention;

Figure 5 is a diagrammatic side elevation of regulating means similar to the embodiment of Figure 4;

Figure 6 is a diagrammatic side elevation of a spray chamber of apparatus for the spray deposition of bar or ingot showing an alternative form of regulating means in accordance with the invention;

Figure 7 is a diagrammatic sectional elevation on A-A in Figure 6. Figures 8a and 8b are diagrammatic side and plan views of a further alternative embodiment of regulating means;

Figure 9 is a diagrammatic plan view of an embodiment of the invention incorporating stabilizing gas supply means; and,

Figure 10 is a diagrammatic side elevation on B-B of the embodiment shown in Figure 9.

In Figure 1, metal or metal alloy (1) is held in a molten state within a tundish (2). The tundish (2) receives the metal or metal alloy from a tiltable melting furnace (3) in which the metal or metal alloy is pre-heated above liquidus. The tundish (2) has a bottom opening (4) so that molten metal may issue in a stream (5) downwardly from the tundish (2). Disposed downstream of the bottom opening (4) and spaced from the bottom of the tundish (2) is an atomizer (6) having an opening (20) and which includes a plurality of atomizing gas jets (7) which impinge the stream (5) and convert the stream (5) into a spray of atomized particles (8) within a spray chamber (9). The atomized particles (8) are deposited upon a suitable collector surface, in this case a rotatable and retractable collector in order to produce elongate bar deposit (10).

The atomizer (6) is spaced from the bottom of the tundish (2) to provide an aspiration gap (11) and an annular gap (12) is provided about the atomizer (6) to allow atomizing gas issuing from jets (7) to recirculate above the atomizer so as to be drawn down with the falling stream (5) to prevent the creation of a vacuum as the stream falls from the tundish (2).

In accordance with the invention, in order to assist in stabilizing the stream (5) as it falls through the atomizer (6), a regulating plate (13) is provided (Fig.2) which closes a substantial part of the recirculating flow path through gap (12) leaving only opposed openings (14) (Fig.3) through which recirculating gas can pass upstream of the atomizer (6). In this way, the flow of recirculating gas is restricted and only a limited amount of gas, as indicated by arrows (15) in

Figure 3, is allowed to pass back down through the atomizer opening. The openings (14) may be provided sufficiently large to permit the maximum desired amount of recirculating gas that might be required to pass to the aspiration gap (11). In such an arrangement, each opening (14) may include a slidable adjustment plate (not shown) to vary the size of the openings (14) as required for particular applications.

In Figure 4 a regulating means is disclosed which comprises a plurality of regulating baffles (16) extending across the spray chamber between opposed side walls so as to provide regulation of recirculating flow on two opposed sides of the falling stream (5). The baffles (16) of which three are shown on each side, are curved downwardly so as to direct the recirculating gas flow in the direction of the falling stream as indicated by arrows (17). The baffles (16) may be provided on their own or together with the regulating plate (13) of Figures 2 and 3. In Figure 5 an alternative arrangement is disclosed where the baffles (16) are movable about respective pivots (19). The baffles (16) may be individually movable as well as one side movable with respect to the other side so as to regulate recirculating flow of gas on one side only. Although three baffles (16) are shown on each side there may be one or more baffles as desired.

In use, molten metal or metal alloy (1) is teemed from the tundish (2) so as to fall freely as the stream (5) through the atomizer (6). The atomizing jets (7) break up the stream into a spray of atomized particles which are collected as a deposit or powder as desired. The major proportion of the atomizing gas is exhausted from the chamber (9) through suitable exhaust means (not shown). However, a proportion of the atomizing gas is recirculated within the spray chamber (9), particularly due to the surface of a forming deposit as illustrated by the arrow (18) in Figure 1. This gas, as it recirculates and with particular reference to Figure 4, is caught by the regulating baffles (16), and redirected with the direction of flow of the stream (5) thereby reducing turbulence. The baffles (16) thereby effectively eliminate movement of the stream and the forming spray due to recirculating gas flow.

The regulating plate (13), if provided in addition to the baffles (16), or in the alternative, reduces the amount of recirculating gas permitted to pass upstream of the atomizer (6) by restricting gas flow only through openings (14). In order to prevent or further minimize destabilization of the stream (5) which might otherwise break up naturally before it has passed through the atomizer (6), further gas may be applied into the aspiration gap (11) so as to form a stabilizing curtain around the stream (5) as it passes through the atomizer (6) as will be explained more fully with reference to Figures 9 and 10.

The atomizing gas issuing from jets (7) preferably comprises high velocity inert gas, such as nitrogen, which not only breaks up the stream (5) into a spray of particles (8), but also extracts a desired and critical amount of heat from the atomized particles in flight and on deposition.

In Figure 6, a spray chamber (21) for gas atomization of molten metal or metal alloy has an atomizing location (22) at which atomizing gas impinges on a stream of the molten metal to convert it into a spray of atomized particles. The atomized particles are deposited upon a suitable collector surface, in this case a rotatable and retractable collector in order to produce elongate bar deposit (23). Spent atomizing gas exits the spray chamber (21) through exhaust conduit (24).

In order to assist in stabilizing the stream during atomization, the atomizing location (22) includes two opposed regulating baffles (25) extending across a major portion of the spray chamber (21) as seen from Figure 7. The baffles (25) are substantially aligned with the axis of the stream and, in use, stabilize the stream by reducing the flow of recirculating gas in a direction perpendicular to the axis of the falling stream.

The baffles (25) may be fixed as shown or may be hinged along their edges (26) so as to be movable either together or independently of one another to control spray shape and stability. Also, if desired, the position of the baffles (25) relative to one another may be changed by moving the hinged edges (26) together or apart.

In Figures 8a and 8b a further alternative embodiment is disclosed. In that arrangement the atomizer (30) is spaced from the top of the spray chamber (31) by an aspiration gap (32) and disposed below the outlet nozzle (33) of a tundish. In order to assist in stabilizing the stream (34) as it falls through the atomizer (30), the atomizer (30) is located between two substan ially parallel regulating plates (35), one positioned on each side of the atomizer (30) as clearly seen from Figure 8b. The plates (35) close a substantial part of the recirculating flow path to the aspiration gap (32) leaving only openings (36) at the other two sides through which recirculating gas can pass upstream of the atomizer (30) together with a small spacing (37) between the atomizer (30) and the plates (35) provided to allow the atomizer (30) to oscillate as indicated by arrow (38).

If desired, in the embodiments where the regulating means are movable baffles, the movement of the baffles may be controlled such that the baffles move to one side of the atomizer sufficiently rapidly with respect to the baffles at the other side of the atomizer in a to and fro movement or in a rotary movement (Fig.5). This movement varies the flow of the recirculating gas which has the object of causing oscillation of the spray. This may be achieved with controlled movement of a single baffle to one side of the atomizer only, if desired.

In the embodiments disclosed it is preferred that the baffles or regulating means do not completely encircle the atomizer since it is important not to starve the atomizer completely of flow of recirculating gas. However, if desired, instead of using impermeable regulating means, the regulating means may be a perforated plate or made of a mesh-like material in which case the regulating means may be annular and extend completely around the atomizer. In this arrangement sufficient flow of recirculating gas will be provided by gas passing through the permeable regulating means. Moreover, such an arrangement throttles recirculating gas flow uniformly about the spray chamber. As a further alternative, vanes as shown in Figure 4, may be arranged to encircle the atomizer. In Figures 9 and 10 a further embodiment of the invention is disclosed.

In those figures, metal or metal alloy (41) is held in a molten state within a tundish (42). The tundish (42) receives the metal or metal alloy from a tiltable melting furnace (43) in which the metal or metal alloy is preheated above liquidus. The tundish (42) has a bottom opening (44) so that molten metal may issue in a stream (45) downwardly from the tundish (42). Disposed downstream of the bottom opening (44) and spaced from the bottom of the tundish (42) is an atomizer (46) which includes a plurality of atomizing gas jets (47) which impinge the stream (45) and convert the stream (45) into a spray of atomized particles (48) within a spray chamber (49). The atomized particles (49) are deposited upon a suitable collector surface (50), in this case, a rotatable mandrel in order to produce a tubular deposit.

In order to stabilize the molten stream (45) as it falls through the atomizer (46), the atomizer (46) is spaced from the bottom of the tundish (42) to provide an aspiration gap (51) as can be clearly seen in Figure 10. A set of gas jets (52) is provided laterally of the atomizer and positioned to direct stabilizing gas into the aspiration gap (51) so as to stabilize the stream (45) as will be explained. In use, molten metal or metal alloy (41) is teemed from the tundish (42) so as to fall freely as the stream (45) through the atomizer (46). In order to prevent or minimize the stream (45) breaking up naturally before it has passed through the atomizer (46), gas jets (52) direct stabilizing gas - indicated by arrows (53) - into the aspiration gap (51) so as to form a stabilizing curtain around the stream (45) as it passes through the atomizer (46). Once through the atomizer (46) the atomizing gas jets (47) impinge the stream and break the stream (45) into a spray of atomized particles (48). The stabilizing gas from jets (52) is an inert gas, suitably nitrogen, and may be introduced at a lower velocity than the atomizing gas from jets (47). The atomizing gas issuing from jets (47) preferably comprises high velocity nitrogen gas which not only breaks up the stream (45) into a spray of particles (48), but also extracts a desired and critical amount of heat from the atomized particles in flight and on deposition upon the collecting surface (50).

The stabilizing gas jets (52) may be disposed at any suitable position so as to direct gas into the aspiration gap (51) whilst allowing the atomizer (46) to be located as close as possible to the bottom of the tundish (42). The apparatus may, if desired, include a transverse regulating plate of the type disclosed in Figures 2 and 3 with the further addition of baffles as disclosed in Figures 5 and 7 or Figures 4 and 5, if desired.

Claims

1. Atomizing apparatus comprising a spray chamber, means for introducing a liquid stream into the spray chamber, atomizing means defining an opening for receiving the liquid stream and for directing atomizing gas at the stream for atomization thereof, and means within the spray chamber for regulating the flow of gas recirculating within the spray chamber.

2. Atomizing apparatus according to claim 1, wherein the regulating means comprises a plurality of baffles positioned adjacent the atomizing means and disposed so as to redirect recirculating gas generally in the direction of the flow of the stream.

3. Atomizing apparatus according to claim 1, wherein the regulating means comprises at least two baffles, one positioned adjacent the atomizing device at each of the two opposed sides thereof.

4 . Atomizing apparatus according to claim 2 or 3, wherein at least one of the baffles is movable.

5. Atomizing apparatus according to any one of the preceding claims, wherein the regulating means comprises a restriction plate disposed transverse to the direction of flow of the stream and restricting the recirculation of atomizing gas within the chamber upstream of the atomizing means .

6. Atomizing apparatus according to claim 1, wherein the regulating means comprises an annular baffle about the atomizing means and including one or more openings to permit the flow of at least some recirculating gas upstream of the atomizing means.

1 . Atomizing apparatus according to any one of the preceding claims, further comprising gas supply means for application of gas upstream of the opening in the atomizing means for passage through the opening with the stream for stabilizing the stream prior to atomization.

8. Atomizing apparatus according to claim 7, wherein the gas supply means is located laterally of the atomizing means.

9. Atomizing apparatus comprising a spray chamber, an atomizer disposed within the spray chamber and defining an opening through which a metal or metal alloy may be teemed, atomizing means at said atomizer for directing atomizing gas at a stream falling through the opening of the atomizer for atomization of the stream and stabilizing gas supply means for applying stabilizing gas upstream of the opening for passage through the atomizer with the stream for stabilizing the stream prior to atomization.

10. Atomizing apparatus according to claim 9, wherein the stabilizing gas supply means is located laterally of the atomizing means and directs gas into an aspiration gap upstream of the atomizer.

11. Atomizing apparatus according to claim 9 or 10, further including means within the spray chamber for regulating the flow of gas recirculating within the spray chamber.

12. A method of spray deposition within a spray chamber comprising providing atomizing means having an opening therethrough, teeming a stream of molten metal or metal alloy through the opening, atomizing the stream into a spray, directing the spray at a collector to form a deposit thereon, providing a plurality of baffles about the atomizing means for regulating the flow of recirculating gas within the spray chamber, and moving at least one baffle during atomization.

13. A method according to claim 12, wherein the movement of at least one baffle is a substantially continuous movement and sufficiently rapid to effect oscillation of the spray.

14. A method according to claim 12, further comprising introducing additional gas upstream of the atomizing means for passage through the opening with the stream to stabilize the stream prior to atomization.