GB2240553A

GB2240553A - Producing particulate metal by spraying upwardly

Info

Publication number: GB2240553A
Application number: GB9101936A
Authority: GB
Inventors: John Joseph Dunkley
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1990-01-30
Filing date: 1991-01-29
Publication date: 1991-08-07
Anticipated expiration: 2011-01-29
Also published as: GB9101936D0; GB9002057D0; GB2240553B

Abstract

Apparatus for producing particles of metal as shown in figure 1 comprises a collector (5) defining a chamber and an atomising nozzle (3) disposed in the chamber so that when molten metal is supplied to the nozzle (3) it is sprayed upwardly into the chamber. Because the molten metal is sprayed upwardly the height of the chamber is much less than that of the conventional atomising apparatus where the atomiser is in the ceiling of the chamber while still ensuring that the droplets are frozen before they impact the collector (5) walls and floor. The apparatus can conveniently and safely be supplied with molten metal from below in a batch or continuous process. <IMAGE>

Description

PRODUCING PARTICLES OF METAL The present invention is concerned with a method and an apparatus for the production of particles of metal, especially relatively reactive metal alloys.

Conventional apparatus for this purpose comprises; a source of molten metal (such as magnesium) from which the metal can be poured through an atomising nozzle in the ceiling of a chamber. The atomising nozzle breaks the stream of molten metal into droplets which are solidified in the chamber.

Because the droplets of metal must be allowed sufficient fall time to become substantially frozen solid before impacting the solid walls or floor of the collector chamber, the chamber must be inconveniently tall. For example, coarse particles up to lmm require a collector chamber 5-10 metres tall.

It is an object of the present invention to provide an apparatus capable of alleviating the aforementioned disadvantage of the prior art.

According to the present invention there is provided an apparatus for producing particles of metal comprising a collector chamber and an atomising nozzle disposed therein so that when the nozzle is supplied with molten metal, droplets of the metal are sprayed upwardly into the chamber to freeze as they fall.

According to another aspect of the present invention there is provided a method of producing particles of metal in which molten metal is sprayed upwardly from an atomising nozzle in a collector chamber so that the droplets freeze as they fall.

It will be appreciated that as the metal is sprayed into the collector chamber it forms droplets which freeze during their fall through the chamber. Unlike the prior art the path of the falling droplets consists of an uprising part followed by a drop. Consequently the height of the chamber required to provide a sufficient falling time is much less than that if the aforementioned conventional apparatus.

Preferably the atomising nozzle is mounted in or near a floor of the chamber and sprays the droplets in a fountain towards side walls of the chamber.

The chamber may be. adapted to be filled with an atmosphere of controlled composition and pressure in order to control any chemical reaction with the metal.

In the- apparatus of the prior art it is necessary to supply the metal to the nozzle in the ceiling of the chamber. It is usual to achieve this by raising a vessel to a position above the ceiling and then teeming the molten metal into the nozzle. This is an inconvenient and hazardous procedure.

The apparatus according to the present invention preferably has the source of molten metal located at a station conveniently below the collector chamber. Thereby alleviating the disadvantages of the prior art apparatus and method.

The molten metal may be propelled through the nozzle by pressure applied by an inert gas or by means of a pump such as a cantilever shaft pump or other centrifugal pumps.

The molten metal can be supplied either by pumping directly from a furnace, by a vessel in which the molten metal is transported from the furnace to the station below the collector chamber, or by pumping from a furnace to a vessel below the chamber and thereafter into the chamber.

The apparatus can be operated as a batch process with vessels filled with molten metal being transported to the station and discharged after which they are replaced by a refill vessel. Alternatively, where molten metal is pumped or otherwise continuously transported to the station from a remote source, the apparatus can be operated continuously.

Commonly the composition of the atmosphere within the collector chamber is controlled to be inert. However, under some circumstances it is desirable to provide a thin layer of oxide on the particles. In this case a controlled amount of oxygen or oxygen rich gas can be introduced into the collector atmosphere to achieve this effect.

Embodiments of apparatus for producing particles of metal in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: figure 1 is an elevated sectional view of a first embodiment of the invention using gas compression to propel the molten metal through the atomising nozzle; and figure 2 is an elevated sectional view of a second embodiment in which a pump is used to propel the molten metal through the nozzle.

The apparatus shown in the drawing comprises a source of molten metal 1, a conduit 2 having, one end 2a intruding into the source 1 and the other end 2b communicating with an atomising nozzle 3 disposed immediately above the source 1. The atomising nozzle 3 is located in a central, base panel part of a collector generally indicated by arrow 5.

The source 1 consists of a refractory or metal crucible 6 in which molten metal 7 is deposited. The source 1 has a sealing cover 9 with a gas inlet port 10 formed to communicate with a space above the metal in the crucible 6.

The gas inlet port 10 is adapted to communicate with a gas supply system including a pipe 11, a pressure regulator 12 and a supply cut off valve 13. A gas outlet port 14 communicating with the uppermost part of the interior of the crucible 6 and with a cut off valve 15 is also formed in the cover 9. A thermal enclosure 31 of the source I surrounds the crucible 6 and provides electrical or gas heating elements 32, controlled in accordance with the temperature of the molten metal as sensed by thermocouples, (not shown) to maintain the correct temperature of the molten metal.

The apparatus shown is of batch processing type.

In this type of apparatus the crucible 6, is filled with molten metal at a station remote from the collector 5. The vessel has an inert gas atmosphere supplied by way of the system 11, 12 and 13 whereby the inert gas is introduced to the crucible 6 and the atmosphere therein purged of reactive gases which are expelled through the outlet port 14. It is important to ensure that the molten metal in the crucible 6, is at a suitable temperature. In consequence, when the crucible 6 reaches a station beneath the collector 5, it is received into the thermal enclosure 31.

Once the crucible 6 is filled the cut off valves 13, 15 are closed to allow the crucible 6 to be transported to the collector without loss of the inert gas atmosphere.

On reaching the collector the conduit 2 is arranged so that the bottom end of the conduit 2a intrudes into the bottom of the crucible 6 well below the level of molten metal. The system 11, 12 and 13 for introducing gas to the vessel is then connected to a high pressure source of inert gas. At this stage the outlet cut off valve 15 remains closed. Gas under pressure can thus be introduced into the region above the molten metal in the crucible 6 to propel the metal through the conduit.

The collector 5 comprises a gas tight housing 17, which defines the chamber 16. The collector is formed with at least one inert gas inlet port 18 communicating with a gas pressure regulator 19 and a shut off valve 20 to allow an inert gas to be introduced to the chamber from a remote source. On the opposite side of the chamber is provided at least one gas outlet port 21. This communicates by means of a junction with an exhaust conduit 22 controlled by an exhaust valve 23 which is opened to exhaust any reactive gases within the chamber 16 when the chamber is purged by the introduction of inert gases through the port 18. To ensure satisfactory control of the composition of the atmosphere in the chamber and to accommodate various design criteria, several gas inlet ports and outlet ports and the associated gas flow control apparatus can be provided in the chamber at locations other than those mentioned. Once the chamber 16 has been satisfactorily purged the exhaust valve 23 is closed. The outlet port 21 also communicates with an expansion chamber (not shown) by way of conduit 24 and valve 25. The valve 25 is closed as the chamber is purged. This feature is necessary since the introduction of molten metal into the chamber through the nozzle causes the inert atmosphere to heat up and expand. When valve 25 is opened the expansion of the gas is accommodated by the expansion chamber.

The housing 17 has a floor including the base panel part 4, which is located centrally. The floor also includes four hoppers two of which, 26, 27, are shown in section. The number of hoppers can be varied according to the design requirement of the chamber. Each hopper is formed radially spaced from the centrally located atomising nozzle 3. Each of these hoppers has walls- which are downwardly inclined towards discharge ports 28 and 29 respectively. These discharge ports are sealed by discharge valves 28a and 29a respectively.

Once the chamber 16 has been satisfactorily purged, the inlet valve 13 is opened to allow inert gas at high pressure to enter the vessel 1. The pressure of the inert gas entering the vessel is sufficient to propel the molten metal through the conduit 2 to be injected into the chamber 16 through the nozzle 3.

The pressure of inert gas within the vessel 1 is controlled to ensure that the rate of injection of molten metal through the nozzle 3 produces streams of metal droplets 30 which follow an uprising trajectory such that the period spent in flight is sufficient to allow the droplets to solidify into particles before they impact the housing 17.

Once solidified the particles will eventually fall into the bottom of the hoppers 26 and 27 respectively where they can be discharged by opening the valves 28a and 29a. This can be done once the molten metal in the crucible 6 is exhausted or, on a continuous basis to some conveyor (not shown).

While the previously described embodiment uses compressed inert gas as propellant in order to avoid oxidation of the molten metal, it is also possible to deposit a flux on the surface off the molten metal to protect it from oxidation and to use air or other gases as the propellant.

In an alternative embodiment of the invention (not shown) crucible 6 is provided with a metal inlet port. Thus molten metal can be continuously or regularly introduced into the crucible 6. Hence the process of operating the apparatus can be made continuous.

Under some circumstances it may be desirable to form a thin layer of a protective compound on the particles of metal. In this circumstance a controlled amount of reactive gas can be introduced to the atmosphere in the chamber 16 to react with the droplets of molten metal expelled from the nozzle 3.

Figure 2 illustrates a second embodiment of the apparatus. Many of the components of the apparatus are similar to the components described previously with reference to the first embodiment of the apparatus and are referred to by the same numerals.

The most significant difference between the first embodiment is that the second embodiment uses a pump 33 to propel the molten metal from the crucible 6, through the conduit and into the collector chamber. In this case the pump is a conventional vertical cantilever shaft pump.

Because a pump is used the crucible 6 does not need to be a pressure vessel, although an inert gas atmosphere can be provided to prevent reaction of air with the molten metal.

However, with some metals it may be more convenient to deposit a flux on the surface of the molten metal to prevent oxidation.

The second embodiment shown is operable as a batch process, like the first, with the vessel 1 being replaced by a full vessel each time it is exhausted. However, it is simple to convert this apparatus to continuous production by including a port in the crucible 6 for the supply of molten metal direct from a furnace.

Under some circumstances it may be possible to entirely do away with the crucible 6 and supply pressurised molten metal directly to the nozzle 3 from a furnace.

Claims

1. Apparatus for producing particles of metal comprising a collector chamber and an atomising nozzle disposed therein so that when the nozzle is supplied with molten metal, droplets of the metal are sprayed upwardly into the chamber to freeze as they fall.

2. Apparatus according to claim 1 wherein the molten metal is supplied from a source disposed below the collector chamber.

3. Apparatus acceding to claim 2 wherein the source of molten metal is a vessel.

4. Apparatus according to claim 3 wherein the vessel is provided with heaters to control the supply temperature of the molten metal.

5. Apparatus according to claim 3 or claim 4 wherein the metal can be protected from reaction with atmosphere by depositing a flux on its surface.

6. Apparatus according to claim 3 or claim 4 wherein the vessel can be supplied with an inert atmosphere to prevent any reaction with the metal.

7. Apparatus according to claim 5 or claim 6 wherein compressed gas can be introduced into the vessel to discharge the molten metal through the nozzle.

8. Apparatus according to any one of claims 1 to 6 wherein the molten metal is supplied to the nozzle by a pump.

9. Apparatus according to claim 8 wherein the molten metal is supplied continuously.

10. Apparatus according to any one of claims 3 to 8 wherein the vessel is adapted for connection to and disconnection from the nozzle and is mobile for the transport of batches of molten metal to the collector chamber.

11. Apparatus according to any one of the preceding claims wherein the nozzle is disposed on a central vertical axis of the chamber and sprays the metal away from the axis.

12. Apparatus according to claim 11 wherein a hopper is offset from the axis to collect the frozen metal particles.

13. Apparatus according to claim 12 wherein a plurality of hoppers are provided each equally spaced from the axis.

14. Apparatus according to claim 12 or 13 wherein the or each hopper is provided with a discharge valve for the discharge of the metal particles.

15. Apparatus according to any preceding claim wherein the chamber is adapted to be filled with an atmosphere of controlled composition and pressure.

16. Apparatus as herein described with reference to the accompanying figures.

17. A method of producing particles of metal in which molten metal is sprayed upwardly from an atomising nozzle in a collector chamber so that the droplets freeze as they fall.

18. A method according to claim 16 in which the molten metal is supplied to the atomising nozzle from below the collector chamber.