Powder Feeder

Abstract

To provide a powder feeder which is used in a production process which uses fine powder.SOLUTION: A powder feeder 10 comprises: a main chamber 12 comprising a gas inlet 14 and a powder outlet 16; at least one secondary chamber 20 configured to receive powder, and a shaver element 22, in which the shaver element 22 is provided right above an opening 26 of the at least one secondary chamber 20. The secondary chamber 20 includes piston means 28 which is movable toward the shaver element 22 so as to push powder upward. An example of the shaver element includes a rotatable screw, a conveyor belt, and a rotatable disk with a protrusion.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to powder feeders, and in particular to powder feeders used in manufacturing processes that use fine powders, such as the production of additive powders. [Background technology]

[0002] In additive manufacturing, it is necessary to precisely deliver fine powders at specific points in the manufacturing process. This is commonly done using a powder feeder with a gravity-fed hopper filled with such powders. Problems arise when powders that are very fine, non-spherical, have poor flowability, and / or are mixed and prone to segregation need to be delivered.

[0003] Fine and / or poorly flowing powders and powder mixtures can clump and clog the passages in the feeder, which can lead to inconsistent flow, pulsation or complete blockage of the system.

[0004] In powder delivery systems where a mixture of different powders is required to be delivered, the hopper and feed chamber tend to separate the mixture, resulting in inconsistent powder composition in the manufacturing process. Such disruptions cause inconsistent output in the manufacturing process. Summary of the Invention

[0005] According to the present invention, there is provided a powder feeder, typically used in the manufacture of additives, comprising a main chamber with a gas inlet and a powder outlet, at least one secondary chamber configured to receive powder, and a shaver element, such as a blade, brush, ridge, or other shaving element, positioned directly above an opening of the at least one secondary chamber. By positioning the shaver element directly above the secondary chamber, during use, the shaver element can shave off a thin layer of powder contained in the secondary chamber so that it exits through the outlet.

[0006] Preferably, at least one secondary chamber further comprises piston means, such as a piston or other actuator, movable towards the shaver element, which piston means, in use, pushes powder contained in the secondary chamber up towards the shaver element.

[0007] At least one secondary chamber may be configured to receive partially compressed powder. Partially compressing the powder ensures a consistent packing density of the powder by eliminating gas pockets or loosely packed regions having lower density and preventing powder segregation.

[0008] The at least one secondary chamber may be disposed within the main chamber, or alternatively, the at least one secondary chamber may be externally attached to the main chamber.

[0009] The outlet is preferably located in close proximity to the at least one secondary chamber to ensure that the powder has to travel as short a distance as possible before exiting through the main chamber, desirably the distance from the at least one secondary chamber to the outlet is less than 20 mm.

[0010] Multiple secondary chambers may be provided, which is particularly useful when different powders need to be mixed together in the feeder. The multiple secondary chambers may be spaced apart linearly, with the outlet preferably located adjacent to the last secondary chamber in the line. Alternatively, the multiple secondary chambers may be positioned around a common axis such that their openings are located in substantially the same horizontal plane. This arrangement is particularly suitable when the secondary chambers are located within the main chamber.

[0011] Preferably, at least one secondary chamber is removable from the main chamber for ease of introducing powder into the secondary chamber.

[0012] The shaver element may comprise a rotatable screw, the axis of rotation of which preferably extends across the opening so that, in use, rotation of the screw carries a thin layer of powder from the at least one secondary chamber towards the scraping outlet.

[0013] The screw preferably rotates at a speed of 100 to 1800 rpm.

[0014] Alternatively, the shaver element may comprise a conveyor belt, which may comprise at least one raised element, or preferably a plurality of raised elements, to act as blades.

[0015] The conveyor belt is preferably capable of moving at a speed of 0.1 to 7 m / min.

[0016] The shaver element is in the form of a circular disc with projections extending beyond the plane of the disc to act as blades, preferably angled downwards so that in use the projections contact the surface of the powder in the secondary chamber.

[0017] The gas inlet is preferably connectable to an inert gas supply, preferred gases being typically argon, helium or nitrogen, for example, to prevent oxidation of the powder within the main chamber and during the manufacturing process.

[0018] This powder feeder is particularly suited for micro-delivery systems that process powders with particle sizes between 1 and 40 microns and output rates between 2 and 10 grams per minute. Single-component powders or powder mixtures can be used in the secondary chamber. Furthermore, the powder particles can vary in size and / or have similar or different morphologies without impairing the functionality of these powder feeders. This feeder can be used with any type of organic or inorganic material for engineering, medical, and food applications. Metal powders such as tungsten and cobalt, carbon powders such as graphite, and compounds such as tungsten carbide can be used in the production of metal additives.

[0019] The invention will now be described by way of example with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of a powder feeder. [Figure 2] FIG. 1 is a schematic diagram of a second embodiment of the powder feeder. [Figure 3] FIG. 10 is a schematic diagram of a third embodiment of the powder feeder. [Figure 4] FIG. 4 is a perspective view of a portion of the powder feeder shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0021] 1 shows a powder feeder 10 capable of supplying powder to a location where the powder is injected into a manufacturing process that uses fine powders, such as an additive manufacturing process, a laser metal deposition process, a selective laser melting process, or a pharmaceutical drug delivery process. The powder feeder 10 comprises a main chamber 12 having a gas inlet 14, an outlet 16 connected to a nozzle 18, and a secondary chamber 20 located below the main chamber 12. The secondary chamber 20 and the outlet 16 are located close to each other to ensure that the powder has to travel as short a distance as possible before exiting through the main chamber, preferably less than 20 mm from the chamber 20 to the outlet 16.

[0022] A driven screw 22 is positioned within the main chamber 12 such that the threads 24 of the screw 22 extend across the top opening 26 of the secondary chamber 20. The secondary chamber 20 further includes a movable piston 28. Typically, the screw 22 has a pitch of 5 to 15 mm and a working length of about 20 to 70 mm. The outlet 16 typically has an opening about 2 to 4 mm in diameter.

[0023] The piston 28 is connected to an actuator, for example, an electric, pneumatic, hydraulic or other type of drive mechanism, and is configured to impart a small, adjustable upward movement to the powder in the chamber 20 so that its top powder surface is at the correct height to be scraped off by the next pass of the screw 22.

[0024] In use, powder 30 is placed in secondary chamber 20 and piston 28 is positioned in contact with the powder. An inert gas, such as argon, helium, or nitrogen, is introduced through inlet 14 to prevent oxidation of the powder and to promote movement of the powder through main chamber 12 and out nozzle 18. If desired, the gas can be pressurized, typically 0.5 to 1.0 bar (50 to 100 kPa) above atmospheric pressure; as the pressure increases, the gas flow rate and therefore the powder flow rate through chamber 12 increases. Typically, the gas has a flow rate of 1 to 20 liters per minute.

[0025] A drive means, such as a motor, continuously rotates the screw 22, typically at 100-1800 rpm, and the piston 28 is driven to impart a slow upward movement to the powder cylinder 32, such that the piston 28 acts as an anti-gravity feeder, feeding powder from the bottom of the main chamber 12 rather than the top. As the top of the powder cylinder 32 emerges through the opening 26, the threads 24 scrape a thin layer of powder from the cylinder 32, typically a single particle thick, which disintegrates into loose powder 34. The movement of the threads 24, along with the gas flow through the main chamber 12, transports the powder 34 to the outlet 16, where it falls and exits the nozzle 18, where the powder is needed in the manufacturing process. Synchronizing the rotational speed of the screw 22 with the upward movement speed of the piston 20 ensures a constant, continuous flow of powder. By forcing the powder to move horizontally, gravity does not interfere with the flow rate.

[0026] As the top layer is scraped from the cylinder 32 and transported to the outlet 16, the piston 28 continues to impart upward movement towards the screw 22, thereby forcing the cylinder 32 upward into contact with the threads 24, thus scraping off another layer. This process is continuous, with the piston drive speed matched to the screw rotational speed to ensure a continuous flow of powder through the nozzle 18.

[0027] If desired, although not shown, multiple secondary chambers can be provided, each containing the same or different powders, for example, powders of different elements or a mixture of different powders. The multiple secondary chambers are typically arranged in a line or in an array such that the screw 22 passes through them evenly. The powder scraped from each secondary chamber is mixed by the rotation of the screw threads 24 and transported to the outlet 16.

[0028] Feedback control can be used to monitor the powder composition at the outlet and adjust the delivery rate from multiple secondary chambers to adjust powder delivery in real time, which is particularly useful when building a product layer by layer, such as in 3D printing, and when there is a desire to vary the composition of different layers.

[0029] The powder can be partially compressed before the feeding process begins. If the secondary chamber 20 is detachable from the main chamber 12, the powder can be weighed into the chamber 20, then compressed to a known density using pistons at either end of the chamber 20, and then attached to the main chamber 12, leaving one piston below the powder. This method is particularly suitable for partially compressing graphite. Partially compressing the powder ensures a consistent packing density of the powder because gas pockets or loosely packed areas with lower density are eliminated and powder segregation is prevented. This further improves the consistency of powder delivery during the feeding process by ensuring that a similarly thick layer is scraped off each time the thread or other scraping element passes over the top of the cylinder 32. By partially compressing the powder rather than grinding it to a solid form, the powder easily reverts to a loose powder formed from individual particles as the layer is scraped off the cylinder 32. Alternatively, a pre-prepared cartridge of partially compressed material can be used.

[0030] Compaction of the powder in the secondary chamber can be accomplished by any method that results in reproducible compaction of the subsequent powder. It is desirable that the powder be partially compacted, not solid. Other methods for achieving consistent compaction include a tap test, in which the same weight of powder is placed in the secondary chamber and the side of the secondary chamber is tapped lightly until the powder sinks to a set level in the secondary chamber. Alternatively, a dynamic compaction method can be used where the powder in the secondary chamber is initially uncompacted and is compacted immediately before the feeder begins operation.

[0031] Another embodiment of the feeder is shown in Figure 2, in which the screw 22 is replaced by a closed-loop conveyor belt 40 with a plurality of laterally spaced ridges 42 that act as blades to scrape off a thin layer of powder as they pass over the top surface of the cylinder 32. The speed of travel of the belt 40 is typically about 10-70 mm / min.

[0032] Figures 3 and 4 show a third embodiment, in which the secondary chamber 20' is placed inside the main chamber 12'. A similar piston arrangement is used to push the cylinder 32 in the anti-gravity feeder toward the shaving element 50, which is positioned directly above the top opening 26' of the chamber 20'. As shown in Figure 4, the shaving element 50 includes a rotatable disk 52 with downwardly extending projections 54. The projections 54 are barbed with downwardly angled ends that act as blades against the top layer of powder in the cylinder 32. The piston 28' operates in the same manner as the piston in Figures 1 and 2, pushing the cylinder 32 upward to encounter the projections 54, shaving successive layers off the top surface of the cylinder 32 with each rotation of the disk 52.

[0033] As the top layer of partially compacted powder is scraped off, it falls under gravity into annular gap 56 between secondary chamber 20' and main chamber 12', reaches funnel region 58, and is fed into nozzle 18. Gas flowing through main chamber 12' from gas inlet 14' also aids in powder flow, and main chamber 12' can be pressurized to about 0.5-1.0 bar (50-100 kPa) above atmospheric pressure if desired.

[0034] If desired, multiple secondary chambers arranged about a common axis can be provided with their openings located in substantially the same horizontal plane. Each secondary chamber can provide a different powder within the main chamber. The powder in the secondary chamber can be a single-component powder, a mixed powder, or an elemental powder.

[0035] This particular arrangement avoids pulsation problems that may need to be addressed depending on the operating speed of the screw 22 of FIG.

[0036] The powder feeders described herein are particularly suited for micro-delivery systems capable of handling powders with particle sizes between 1 and 40 microns and output rates between 2 and 10 grams per minute. This feeder configuration can operate with single-component powders or powder mixtures in the secondary chamber, and the powder particles can vary in size and / or have similar or different morphologies without impairing the functionality of these powder feeders. In particular, these feeders are functionally operable with very fine powders mixed with coarse powders, mixtures of powders with spherical and non-spherical particles, combinations of flake and spherical powders, and mixtures of powders with different densities. The feeders can be used with any type of powder, including metal powders such as tungsten and cobalt, carbon powders such as graphite, and compounds such as tungsten carbide. The feeders can operate with graphite particles smaller than 20 microns without causing blockage or damage to the main chamber or blade elements.

[0037] There is no powder segregation or clogging of the feeder with powder, so all powder introduced into the secondary chamber of the feeder is discharged. Low-flow materials, materials with various flow properties, and particles of various shapes all move consistently through the feeder to reach the output, so there is no need to pre-treat the powder before use, for example by gas atomization to spheroidize all particles.

[0038] If possible, the elements forming the powder feeder 10, 10' are made from antistatic materials.

[0039] If desired, a heating jacket can be placed around the main chamber to remove any incidental moisture, typically the jacket producing a temperature of up to 100°C.

Claims

1. 1. A powder feeder comprising: a main chamber having a gas inlet and a powder outlet; at least one secondary chamber configured to receive powder; and a shaver element, wherein the shaver element is positioned directly above an opening of the at least one secondary chamber, the shaver element comprising a rotatable screw, and the gas inlet is positioned to introduce an inert gas that promotes transport of powder within the main chamber.

2. 10. The powder feeder of claim 1, wherein said at least one secondary chamber further comprises piston means movable towards said shaver element.

3. 3. The powder feeder of claim 1 or 2, wherein the at least one secondary chamber is configured to receive partially compacted powder.

4. The powder feeder according to any one of claims 1 to 3, wherein the at least one secondary chamber is disposed within the main chamber.

5. 3. The powder feeder of claim 1 or 2, wherein the at least one secondary chamber is externally attached to the main chamber.

6. 4. The powder feeder of claim 1, wherein the powder outlet is located adjacent to the at least one secondary chamber.

7. The powder feeder according to any one of claims 1 to 6, further comprising a plurality of secondary chambers.

8. 8. The powder feeder of claim 7 when dependent on claim 5, wherein the plurality of secondary chambers are linearly spaced apart.

9. 8. The powder feeder of claim 7 when dependent on claim 4, wherein the plurality of secondary chambers are oriented about a common axis such that the openings of the plurality of secondary chambers are disposed in substantially the same horizontal plane.

10. The powder feeder of any one of claims 1 to 9, wherein the at least one secondary chamber is removable from the main chamber.

11. 2. The powder feeder of claim 1, wherein the rotational axis of the screw extends across the opening.

12. 12. The powder feeder of claim 1 or 11, wherein the screw threads rotate at a speed of 100 to 1800 rpm.

13. A powder feeder comprising a main chamber having a gas inlet and a powder outlet, at least one secondary chamber configured to receive powder, and a shaver element positioned directly above an opening of the at least one secondary chamber, wherein the shaver element comprises a closed-loop conveyor belt, and the gas inlet is positioned to introduce an inert gas to facilitate transport of powder within the main chamber.

14. 14. The powder feeder of claim 13, wherein the conveyor belt comprises a plurality of laterally evenly spaced ridges.

15. 15. The powder feeder according to claim 13 or 14, wherein the conveyor belt is movable at a speed of 0.1 to 7 m / min.

16. A powder feeder comprising: a main chamber having a gas inlet and a powder outlet; at least one secondary chamber configured to receive powder; and a shaver element positioned directly above an opening of the at least one secondary chamber, wherein the shaver element is in the form of a circular disc and has protrusions that extend beyond the plane of the disc and function as blades, and wherein the gas inlet is positioned to introduce an inert gas that facilitates transport of powder within the main chamber.

17. 17. The powder feeder of claim 16, wherein the protrusions are angled downwards so that, in use, the protrusions contact the surface of the powder in the secondary chamber.

18. Powder feeder according to any one of the preceding claims, wherein the gas inlet is connectable to an inert gas supply.

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