Method of manufacture of metallic powder

Abstract

A method 100 of manufacturing metallic powder, comprising; melting 102 metallic material to form molten metal, pouring the molten metal through an atomisation zone, directing 103 a spray of fluid at t

Description

Technical Field 5 The present disclosure relates to methods of manufacturing metallic powder, and particularly, but not exclusively, methods of manufacturing metallic powder using water atomisation. Background 10 Metallic powders are required for production of metal parts in manufacturing, surface coatings, lubrication and many other uses. Methods for manufacturing metallic powder include crushing, grinding, electrolytic deposition, chemical reactions and atomisation. CXI CXI 15 In water atomisation methods, molten metal is passed through a stream of atomising fluid (water). This produces small particles of metal that form the metal powder. Where liquid is utilized as the atomising media, the resulting slurry of metal particles and liquid is then dried to form the powder. Drying processes include using a belt furnace to heat the slurry and evaporate the liquid. 20 Summary There is provided a method of manufacturing metallic powder, the method comprising: melting metallic material to form molten metal, 2 5 pouring the molten metal through an atomisation zone, directing a spray of fluid at the pouring molten metal in the atomisation zone, forming a slurry comprising the fluid and metallic powder particles, imparting a vacuum on the slurry to at least partially remove the fluid from the slurry, thereby forming a partially dried slurry, and 30 passing the partially dried slurry through a fluidised bed dryer to further remove fluid and form the metallic powder. Such a method is more time-efficient, consumes less energy and is less labour intensive, while producing a powder which does not require anti-oxidant to be added. The vacuum and fluidised bed drying stages also do not require a reductive atmosphere, allowing air to be used and further improving efficiency. Since a fluidised bed is used for drying, there is 5 no requirement for a crushing stage to break up a cake after drying. Compared with a traditional drying process using a belt furnace which can require several hours per ton of powder, the present method using the fluidised bed dryer is also is much more timeefficient, requiring only dozens of minutes per ton. The removal of the need for (i) breaking up a cake and (ii) adding anti-oxidant are beneficial from an environmental viewpoint along 10 with the reduction in energy requirements. Optionally, melting metallic material to form molten metal is performed in a furnace, such as an induction furnace. Optionally, the metallic material is mixed in the furnace. Optionally, melting metallic material to form molten metal occurs at a temperature of 1100-1400 15 degrees Celsius. CXI i— The atomisation zone is an area through which the molten metal is poured. Optionally, the lo poured molten metal free falls through the zone. Optionally, the molten metal is poured into the atomisation zone via a launder and tundish. Pouring may comprise dripping. Optionally, 20 the molten metal is poured into the atomisation zone at between 1100 and 1400 degrees Celsius. Optionally, the tundish nozzle diameter is between 6 -11mm. The atomisation zone may be in a chamber. Optionally, the slurry is collected at the bottom of the chamber. Optionally, the fluid is a liquid. The fluid comprises water. Optionally, the fluid in the spray 25 has a temperature of between 5 and 30 degrees Celsius, optionally between 8 and 28 degrees C, optionally between 8 and 12 degrees C, or between 12 and 18 degrees C, or between 18 and 21 degrees C. During atomisation, the fluid temperature is used to control the apparent density and shape 30 of the particles of powder formed. A higher water temperature of around 18 - 21°C creates powder with higher densities and more rounded particles. Optionally, the spray of fluid is produced by a fluid source having a pressure of between 3.4 and 20.1MPa (500 and 3000 psi). In this way, the molten metal is impinged by the high velocity fluid and broken into hard particles as it is cooled / quenched rapidly, forming irregular shaped particles. Optionally, the spray of fluid is directed at the molten metal with a spray apex angle of between 35 and 60 degrees. The spray apex angle is the angle of the mist cone formed during the spraying / water 10 atomising process. A central axis of the spray may intersect a central axis of the pouring molten metal. This avoids distortion of the metal by centring the spray on the pouring metal. This ensures that most of the metal stream can be efficiently atomized and form powder. 15 Imparting a vacuum on the slurry to at least partially remove the fluid from the slurry, thereby forming a partially dried slurry may be referred to as de-watering. In this step, most of the fluid may be removed from the slurry, for example more than half of the fluid, preferably leaving a residual moisture content in the slurry of 10-20%. Optionally, imparting a vacuum on the slurry is performed in a vacuum dryer. Optionally, an air 2 0 atmosphere is provided in the vacuum dryer. Optionally, the slurry is moved in short bursts between de-watering, such as moving the slurry in 5 to 10 second bursts. Optionally, the slurry is wet slurry. Optionally, the slurry is 90-95% moist. Moist refers to a percentage by mass of liquid (e.g. water) in the substance. Optionally, the partially dried 25 slurry is between 20% and 10% moist. Optionally, passing the partially dried slurry through the fluidised bed dryer comprises colliding particles in the partially dried slurry with one another in the fluidised bed dryer. Optionally, colliding particles in the partially dried slurry with one another comprises 30 agitating the partially dried slurry using a reciprocating agitation motion. In this way, during the drying process, each particle has a large heat exchange surface area, which enables rapid drying. And the particles collide with each other, which is more conducive to maintaining the irregular shape and lower apparent density. Optionally, an internal temperature of the fluidised bed dryer is less than 150 degrees 5 Celsius. Optionally the internal temperature is between 58 and 72 degrees Celsius. Compared with a traditional drying process using a belt furnace with a high temperature (about 300-550 degrees Celsius), this method consumes less energy by using a temperature of less than 150 degrees. Compared to traditional reduction drying processes, using a fluidized bed dryer can fully dry the powder in just a few seconds. This helps to prevent 10 subsequent oxidation of the powder, and the process does not require the addition of antioxidants. Optionally, air forms an internal atmosphere of the fluidised bed dryer. Compared with a traditional drying process using a belt furnace with a reductive atmosphere (such as hydrogen gas or ammonia) the present method does not require a reductive atmosphere and instead can utilise air resulting in reduced resource requirement and more environmentally friendly process. 20 Optionally, the method further comprises controlling the fluidised bed dryer by analysing a gas flue temperature of an exhaust of the fluidised bed dryer to control a temperature of a burner flame of the fluidised bed dryer. The temperature of the burner flame may be between 50 to 300 degrees Celsius. 25 Optionally, the metallic powder is copper or bronze powder. Optionally, the metallic powder is irregular morphology metallic powder. The metallic material comprises copper and optionally tin. Optionally, the metallic material comprises powder, granules, ingot(s) or pellets. Optionally, the metallic material comprises 30 copper granule and / or ingot and / or pelletised material. Optionally, the metallic material is raw. Optionally, the copper granule comprises chopped high purity copper wire. Optionally, the metallic material comprises copper powder, for example as remelt. Optionally, the metallic material comprises tin ingot or powder. Optionally, the method further comprises passing the metallic powder from an exit of the 5 fluidised bed dryer to a vertical spiral lift elevator. Optionally, the method further comprises passing the metallic powder from the elevator to a classifier. Optionally, the metallic powder is less than 0.005% moist. The metallic powder comprises particles with diameters between 150 microns and 1500 microns. Optionally, an apparent 10 density of the powder is between 2.0 - 4.0 g / cc, preferably between 2.5-3.5 g / cc. Further features and advantages of the above-described methods of the present disclosure will become apparent from the claims and the following description. 15   Brief Description of Drawings Embodiment's] of the present disclosure will now be described by way of example only, with reference to the following diagrams, in which: - 20 Fig. 1 is a flow chart showing a method of manufacture of metallic powder; Fig. 2 is a microscope image showing a metallic powder produced by the method of Fig. 1. Detailed Description 25 An embodiment of the disclosure is described subsequently. Fig. 1 shows a method 100 of manufacturing irregular morphology copper or bronze powder metallic powder from copper granule and / or tin ingot and / or pelletised material 101. The copper granule comprises chopped high purity copper wire, and optionally copper 30 powder, from remelt 108. Optionally, the metallic material comprises tin ingot or powder or any metallic elements in powder or pellet form. First, the metallic material is melted 102 to form molten metal. In step 102, melting metallic material to form molten metal is performed in an induction furnace at a temperature of 1100-1400 degrees Celsius. The metallic material is also mixed in the furnace. 5 The molten metal passes into a launder and then through a tundish having a diameter of between 6 and 11mm. The molten metal then pours out from the tundish and through an atomisation zone so that the molten metal free falls through the zone. The atomisation zone is in an atomisation chamber and the molten metal is poured into the atomisation zone at between 1100 and 1400 degrees Celsius. Step 103 comprises directing a spray of fluid at the pouring molten metal 103 in the atomisation zone, forming a slurry comprising the fluid and metallic powder particles. In 20 step 103, a spray of water is directed at the pouring molten metal in the atomisation zone. The water in the spray has a temperature of between 8 and 12 degrees C. The temperature is selected between 8 and 28 degrees C to control the apparent density and shape of the particles of powder formed. A higher water temperature of around 18 -21°C creates powder with high densities and more rounded particles, whereas a lower temperature between 8 and 12 degrees C forms more irregular particles. The spray of water is produced by a water jet having a pressure of between 3.4 and 20.1MPa (500 and 3000 psi). In this way, the molten metal is impinged by the high velocity water and broken into hard particles as it is cooled / quenched rapidly, forming irregular shaped particles. The spray of fluid is directed at the molten metal at a spray apex angle of between 35 and 60 degrees. A central axis of the spray intersects a central axis of the pouring molten metal to avoid distortion of the metal by centring the spray on the pouring metal. The slurry formed during atomisation 103 is then collected at the bottom of the chamber. Step 104 comprises an In progress check to confirm that the slurry is formed as designed. During step 104, a sample of slurry is taken and dried after which a density check is carried out to ensure correct atomisation has been carried out for that product. Step 104 may alternatively or additionally be carried out on dewatered / partially dried slurry after vacuum drying in step 105. Step 105 comprises drying the slurry 105 by imparting a vacuum on the slurry to at least partially remove the fluid from the slurry, thereby forming a partially dried slurry, and passing the partially dried slurry through a fluidised bed dryer to further remove fluid and form the metallic powder. Imparting a vacuum on the slurry may remove most of the fluid from the slurry, for example more than half of the fluid. 10 CXI CXI 15 The slurry is then passed to a vacuum dryer for de-watering. The vacuum dryer has an air atmosphere and the slurry is moved in short bursts of 5-10 seconds between de-watering. The slurry before vacuum drying is wet slurry, being 90-95% moist and the partially dried slurry is between 20% and 10% moist. The partially dried slurry is then passed to the fluidised bed dryer. Particles in the partially dried slurry are collided with one another in the fluidised bed dryer by agitating the partially dried slurry using a reciprocating agitation motion. This agitation is conducive to maintaining the irregular shape and lower apparent density. 20 The internal temperature of the fluidised bed dryer is between 58 and 72 degrees Celsius. The internal atmosphere of the fluidised bed dryer is formed of air. 25 30 The fluidised bed dryer is controlled by analysing a gas flue temperature of the exhaust of the fluidised bed dryer to control a temperature of a burner flame of the fluidised bed dryer between 50 and 300 degrees Celsius. The powder is then passed from an exit of the fluidised bed dryer to a vertical spiral lift elevator, and then to a classifier. Any oversized particles are sent back to furnace for use as remelt 108 to reduce waste. 5 12 24 The powder is sieved 106 and blended to obtain the powder product that meets specifications and has uniform and consistent performance. Fig. 2 shows the metallic powder produced which comprises particles 210 with diameters 5 between 150 microns and 1500 microns. An apparent density of the powder is between 2.5 - 3.5 g / cc. The particles 210 in the powder are irregular. Although particular embodiment's] of the disclosure have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The 10 aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the 15 invention as defined by the claims. 05 12 24

Claims

1. A method of manufacturing metallic powder, the method comprising: melting metallic material comprising copper to form molten metal, 5 pouring the molten metal through an atomisation zone,directing a spray of fluid at the pouring molten metal in the atomisation zone, forming a slurry comprising the fluid and metallic powder particles, wherein the fluid comprises water,imparting a vacuum on the slurry to at least partially remove the fluid from the 10 slurry, thereby forming a partially dried slurry, andpassing the partially dried slurry through a fluidised bed dryer to further remove fluid and form the metallic powder, wherein the metallic powder comprises particles with diameters between 150 microns and 1500 microns.15 2. A method according to claim 1, wherein passing the partially dried slurry through thefluidised bed dryer comprises agitating the partially dried slurry using a reciprocating agitation motion to cause particles in the partially dried slurry to collide with one another in the fluidised bed dryer.20 3. A method according to any preceding claim, wherein an internal temperature of thefluidised bed dryer is less than 150 degrees Celsius.

4. A method according to any preceding claim, wherein air forms an internal atmosphere of the fluidised bed dryer.

255. A method according to any preceding claim, further comprising controlling the fluidised bed dryer by analysing a gas flue temperature of an exhaust of the fluidised bed dryer to control a temperature of a burner flame of the fluidised bed dryer.30 6. A method according to any preceding claim, further comprising passing the metallicpowder from an exit of the fluidised bed dryer to a vertical spiral lift elevator.05 12 247. A method according to any preceding claim, wherein the metallic powder is copper or bronze powder.

8. A method according to any preceding claim, wherein the metallic powder is irregular 5 morphology metallic powder.

9. A method according to any preceding claim, wherein the metallic material comprises copper granule and / or tin ingot and / or metallic pelletised material.10 10. A method according to any preceding claim, wherein the slurry is 90-95% moist, wheremoist is a percentage by mass of liquid in the slurry.

11. A method according to any preceding claim, wherein the partially dried slurry is between 20% and 10% moist, where moist is a percentage by mass of liquid in the partially 15 dried slurry.

12. A method according to any preceding claim, wherein the metallic powder is less than 0.005% moist, where moist is a percentage by mass of liquid in the metallic powder.20 13. A method according to any preceding claim, wherein the fluid in the spray has atemperature of between 5 and 30 degrees Celsius.

14. A method according to any preceding claim, wherein the spray of fluid is produced by a fluid source having a pressure of between 3.4 and 20.1MPa (500 and 3000 psi).

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