Powder feeding device

Abstract

A powder feeding device (10, 10') is provided that includes a main chamber (12, 12') having a gas inlet (14, 14') and a powder outlet (16), at least one secondary chamber (20, 20') configured to receive powder, and a scraping element (22, 40, 50), wherein the scraping element (22, 40, 50) is positioned directly above an opening (26, 26') in the at least one secondary chamber (20, 20'). The secondary chamber (20, 20') also includes a piston device (28, 28') that is movable toward the scraping element (22, 40, 50) to push powder upward. Examples of scraping elements include a rotatable screw (22), a conveyor belt (40), and a rotating disk (50) with protrusions (54).

Description

TECHNICAL FIELD

[0001] The present invention relates to a powder feeding device, in particular for use in manufacturing processes using fine powders such as additive powder manufacturing. BACKGROUND

[0002] In additive manufacturing, it is necessary to accurately deliver fine powders at specific locations in the manufacturing process. This is typically done using a powder feeding device with a gravity fed hopper filled with such powders. Problems are encountered when delivering very fine, non-spherical, poorly flowing and / or mixed and segregating powders.

[0003] Fine powders and / or poorly flowing powders and powder mixtures can cake and clog the channels in the feeding device, which can result in inconsistent flow, pulsing or complete clogging of the system.

[0004] In powder delivery systems where mixtures of different powders need to be delivered, the hopper and feed chamber tend to cause the mixture to segregate, resulting in inconsistent composition of the powder in the manufacturing process. Such interruptions result in inconsistent output in the manufacturing process. SUMMARY

[0005] According to the present invention, there is provided a powder feeding device, typically for use in additive manufacturing, comprising a main chamber having a gas inlet and a powder outlet, at least one secondary chamber configured to receive a powder, and a scraping element (such as a blade, brush, ridge or other abrasive member), wherein the scraping element is positioned directly above an opening in the at least one secondary chamber. By positioning the scraping element directly above the secondary chamber, in use, the scraping element is able to remove a thin layer of powder contained in the secondary chamber for discharge from the outlet.

[0006] Preferably, the at least one secondary chamber further comprises a piston device (such as a piston or other actuator) movable towards the scraping element, such that in use, the piston device pushes the powder contained within the secondary chamber upwards towards the scraping element.

[0007] The at least one secondary chamber can be configured to receive a partially compressed powder. Partially compressing the powder ensures a consistent packing density of the powder, with air pockets or less dense, loosely packed areas removed and preventing segregation of the powder.

[0008] The at least one secondary chamber can be provided within the main chamber, or the at least one secondary chamber can be externally connected to the main chamber.

[0009] Preferably, the outlet is positioned adjacent to the at least one secondary chamber to ensure that the powder necessarily travels the shortest distance possible through the main chamber before being discharged. Ideally, the distance from the at least one secondary chamber to the outlet is less than 20mm.

[0010] A plurality of secondary chambers can be provided, which is particularly useful where it is desired to combine different powders in the powder feed device. The plurality of secondary chambers can be spaced linearly, and for such an arrangement the outlet is preferably provided adjacent the last of the secondary chambers in the line. Alternatively, the plurality of secondary chambers can be positioned about a common axis, such that their openings are arranged in substantially the same horizontal plane. This arrangement is particularly suitable for an arrangement in which the secondary chambers are provided within the primary chamber.

[0011] Preferably, the at least one secondary chamber is detachable from the primary chamber, in order to facilitate the introduction of powder into the secondary chamber.

[0012] The scraping element can comprise a rotatable screw, and preferably the axis of rotation of the screw extends across the opening, such that in use rotation of the screw causes the thin layer of powder to be removed from the at least one secondary chamber and conveyed towards the outlet.

[0013] Preferably, the screw is rotated at a speed of between 100 rpm and 1800 rpm.

[0014] Alternatively, the scraping element can comprise a conveyor belt, which can comprise at least one ridge element and preferably a plurality of ridge elements to act as blades.

[0015] Preferably, the conveyor belt can be moved at a speed of between 0.1 m / min and 7 m / min.

[0016] The scraping element can be in the form of a disc with protrusions extending beyond the plane of the disc to act as blades. Preferably, the protrusions are inclined downwardly, such that in use they contact the surface of the powder in the secondary chamber.

[0017] Preferably, the gas inlet is connectable to a supply of inert gas, wherein the preferred gas is typically argon, helium or nitrogen, for example. This prevents oxidation of the powder within the primary chamber and during the manufacturing process.

[0018] The powder feed device is particularly suitable for use in micro-delivery systems handling powders having a particle size of between 1 micron and 40 microns and an output rate of between 2 g / min and 10 g / min. Single component powders or powder mixtures can be used within the secondary chambers, and the powder particles can differ in particle size and / or can have similar or different morphologies without prejudice to the functioning of the powder feed devices. The feed devices can be used for any type of organic and inorganic materials for engineering, medical and food applications. In metal additive manufacturing, metal powders such as tungsten and cobalt, carbon powders including graphite, and compounds such as tungsten carbide can be used. BRIEF DESCRIPTION OF DRAWINGS

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

[0020] Figure 1 A schematic diagram of a first embodiment of the powder feeding device is shown;

[0021] Figure 2 A schematic diagram of a second embodiment of the powder feeding device is shown;

[0022] Figure 3 A schematic diagram of a third embodiment of the powder feeding device is shown; and

[0023] Figure 4 It shows Figure 3 A perspective view of a portion of the powder feeding device shown. Detailed Implementation

[0024] Figure 1 A powder feeding device 10 is shown, which is capable of feeding powder to the site where powder is to be injected in a manufacturing process using fine powder, such as additive manufacturing, laser metal deposition, selective laser melting, or drug delivery processes for manufacturing pharmaceuticals. The powder feeding device 10 includes a main chamber 12 having a gas inlet 14 and 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 placed adjacent to each other to ensure that the powder travels the shortest possible distance within the main chamber 12 before being discharged, ideally with a distance of less than 20 mm from the chamber 20 to the outlet 16.

[0025] A drivable screw 22 is located within the main chamber 12, such that the thread 24 of the screw 22 extends across the upper opening 26 in the secondary chamber 20. The secondary chamber 20 also includes a movable piston 28. Typically, the screw 22 has a pitch of 5 mm to 15 mm and an operating length of approximately 20 mm to 70 mm. The outlet 16 typically provides an orifice with a diameter of approximately 2 mm to 4 mm.

[0026] The piston 28 is connected to an actuator—such as an electric, pneumatic, hydraulic or other type of drive mechanism—and configured to apply a small, controllable upward movement to the powder in the chamber 20, such that the uppermost powder surface is at the appropriate height to be removed by the next pass of the screw 22.

[0027] In use, powder 30 is placed in sub-chamber 20 and piston 28 is positioned in contact with the powder. Inert gas, such as argon, helium or nitrogen, is introduced through inlet 14 to prevent oxidation of the powder and to encourage powder migration, and the inert gas flows through main chamber 12 and is exhausted at nozzle 18. If desired, the gas can be pressurised, typically to 0.5 to 1.0 bar above atmospheric pressure, and as the pressure increases, the gas flow rate increases, thereby increasing the flow rate of powder through chamber 12. Typically, the gas flow rate is 1 to 20 litres per minute.

[0028] A drive, such as an electric motor, continuously rotates screw 22, typically between 100 rpm and 1800 rpm, and piston 28 is driven to slowly push the column 32 of powder upwards, operating as an anti-gravity feed and feeding from the bottom of main chamber 12 rather than the top of the main chamber. As the top surface of powder column 32 is exposed through opening 26, screw thread 24 scrapes a thin layer of powder, typically a single grain thick, from column 32, and this layer disintegrates into loose powder 34. The movement of screw thread 24, together with the gas flow through main chamber 12, transports powder 34 to outlet 16, from which it falls to be exhausted from nozzle 18 at a location in the manufacturing process where the powder is required. The synchronisation of the rotation rate of screw 22 and the upward movement of piston 28 ensures a steady, continuous flow of powder. By transferring the powder laterally, gravity does not interfere with the flow rate.

[0029] As the uppermost layer is removed and transported from column 32 to outlet 16, piston 28 continues to push upwards towards screw 22, thus pushing column 32 upwards into contact with screw thread 24, and then removing another layer. The process is continuous, the rate of piston drive being matched to the rotation rate of the screw to ensure a continuous flow of powder through nozzle 18.

[0030] If desired, although not shown, multiple sub-chambers can be provided, each with the same or different powders, for example different elemental powders or different powder mixtures. The multiple sub-chambers would typically be arranged in a line or array, such that screw 22 travels across all of the sub-chambers equally. The powders removed from each sub-chamber are mixed by the rotation of screw thread 24 and transported to outlet 16.

[0031] Feedback control can be used to monitor the composition of the powder at the outlet and to adjust the rate of transport from the multiple sub-chambers in order to adjust the transport of the powder in real time. This is particularly useful if the product is being built by layering, as in 3D printing, and the composition of different layers needs to be altered.

[0032] The powder can be partially compressed prior to the start of the dosing process. In the case where the sub-chamber 20 is detachable from the main chamber 12, the powder can be weighed in the chamber 20 and then compressed to a known density using pistons at either end of the chamber 20, before being attached to the main chamber 12 with one piston remaining below the powder. This method is particularly suitable for the partial compression of graphite. Partial compression of the powder ensures a consistent packing density of the powder, with air pockets or areas of loose packing removed and preventing segregation of the powder. This further improves the consistency of powder delivery during the dosing process, as it ensures that a similar thickness layer is removed each time the thread or other scraping element passes over the top of the column 32. By partially compressing the powder rather than having a compacted form, the powder readily reverts to loose powder formed of individual particles when a layer is scraped from the column 32. Alternatively, a pre-prepared partially compressed cartridge of material can be used.

[0033] The compression of the powder in the sub-chamber can be performed in any manner that provides a reproducible compression for the subsequent powder. Ideally, the powder should be partially compressed rather than compacted. Other methods of achieving a consistent compression include a tap test, in which the same weight of powder is introduced into the sub-chamber and the sides of the sub-chamber are tapped until the powder settles to a set level within the sub-chamber. Dynamic compression can also be used in cases where the powder in the sub-chamber is not initially compressed but is compressed only prior to the start of the dosing device.

[0034] Figure 2 An alternative embodiment of the dosing device is shown in Figure 7, in which the screw 22 is replaced by a closed loop conveyor belt 40 having a plurality of equidistant transverse ridges 42 that act as blades to remove thin layers of powder as they pass over the top of the column 32. The travel rate of the belt 40 is typically in the range of about 10 mm / min to 70 mm / min.

[0035] Figure 3 and Figure 4 A third embodiment is shown in which the sub-chamber 20' is located within the main chamber 12'. A similar piston arrangement is used to push the column 32 towards a scraping element 50 disposed directly above the upper opening 26' of the chamber 20'. The scraping element 50 comprises a rotatable disc 52 having downwardly extending protrusions 54, as shown in Figure 8. The protrusions 54 are arranged in a barbed fashion such that they have downwardly angled ends that act as blades against the top layer of powder in the column 32. The piston 28' operates in a similar manner to the piston in Figures 1 to 6, such that with each rotation of the disc 52, the column 32 is pushed upwards to meet the protrusions 54 and successive layers of the upper surface of the column 32 are removed. Figure 4 Figure 1 and 2

[0036] ​​When the upper layer of partially compressed powder is removed, it falls under the influence of gravity into the annular gap 56 between the secondary chamber 20' and the main chamber 12' to reach the funnel region 58 and be fed into the nozzle 18. The gas flowing through the main chamber 12' from the gas inlet 14' also assists the flow of powder, and if required, the main chamber 20' can be pressurised to about 0.5 to 1.0 bar above atmospheric pressure.

[0037] If required, a plurality of secondary chambers can be provided arranged around a common axis, such that their openings are arranged substantially in the same horizontal plane. Each secondary chamber can add a different powder to the main chamber. The powders within the secondary chambers can be single component powders, mixed powders or elemental powders.

[0038] This particular arrangement avoids the pulsing problems that can need to be addressed depending on the operating speed of the screw 22 in the Figure 1

[0039] The powder feeding devices described are particularly suitable for use in micro-feed systems that handle powders having a particle size of 1 to 40 microns and an output rate of 2 to 10 grams per minute. The feeding devices are operable within the secondary chamber for single component powders or for powder mixtures, and the powder particles can differ in particle size and / or can have similar or different morphologies without compromising the functionality of these powder feeding devices. In particular, the feeding devices are functionally operable for very fine powders mixed with coarse powders, mixtures of powders having spherical and non-spherical particles, combinations of flaky and spherical powders, and mixtures of powders having different densities. The feeding devices can be used for any type of powder, such as metal powders (e.g. tungsten and cobalt), carbon powders (including graphite) and compounds (e.g. tungsten carbide). The above feeding devices are operable for graphite of less than 20 microns without clogging or damaging the main chamber or the blade elements.

[0040] Because there is no powder segregation or powder-induced clogging within the feeding devices, all of the powder introduced into the secondary chamber of the feeding devices is discharged. There is no need for pre-treatment of the powder prior to use, such as by gas atomisation to spheroidise all of the particles, as the poorly flowing materials, materials having different flow characteristics and particles having different shapes all travel uniformly through the feeding devices to the outlet.

[0041] Where possible, the elements forming the powder feeding devices 10, 10' are made from anti-static materials.

[0042] If required, a heating jacket can be placed around the main chamber to remove any incidental moisture, typically the heating jacket generates a temperature of up to 100°C.​

Claims

1. A powder feeding device comprising: a main chamber having a gas inlet and a powder outlet, a plurality of secondary chambers externally connected to the main chamber, the plurality of secondary chambers each adding a different powder to the main chamber, the powder of each secondary chamber being different from the powder of each other secondary chamber, and the plurality of secondary chambers being spaced linearly apart, and a rotatable screw positioned directly above an opening in the plurality of secondary chambers, an axis of rotation of the rotatable screw extending across the opening such that the screw travels equally across the openings, wherein the rotatable screw and gas from the gas inlet are configured to transfer powder from the openings of the plurality of secondary chambers laterally to the powder outlet, and wherein the powder removed from each of the plurality of secondary chambers is mixed by rotation of the threads of the rotatable screw as different powders are transferred to the powder outlet.

2. The powder feeding device of claim 1, wherein, each of the plurality of secondary chambers further comprises a piston movable towards the rotatable screw.

3. The powder feeding device of claim 1, wherein, each of the plurality of secondary chambers is configured to receive a partially compressed powder.

4. The powder feeding device of claim 1, wherein, the powder outlet is positioned adjacent to the plurality of secondary chambers.

5. The powder feeding device of claim 1, wherein, the plurality of secondary chambers are detachable from the main chamber.

6. The powder feeding device of claim 1, wherein, the threaded rotatable screw is rotated at a speed of between 100 rpm and 1800 rpm.

7. The powder feeding device of claim 1, wherein, the rotatable screw has a pitch of between 5 mm and 15 mm and a working length of between 20 mm and 70 mm.

8. A powder feeding device comprising: a main chamber having a gas inlet and a powder outlet, at least one secondary chamber configured to receive a powder, and a scraping element, wherein the scraping element is positioned directly above an opening in the at least one secondary chamber, and the at least one secondary chamber comprises a piston arrangement movable towards the scraping element; wherein the at least one secondary chamber is disposed within the main chamber; and wherein the scraping element is in the form of a disc having protrusions extending beyond a plane of the disc to act as blades.

9. The powder feeding device of claim 8, wherein, the protrusions are angled downwardly such that, in use, the protrusions contact a surface of the powder in the secondary chamber.

10. The powder feeding device of claim 1 or 8, wherein, the gas inlet is connectable to a supply of inert gas.

11. The powder feeding device of claim 10, wherein, the inert gas is pressurised to a pressure of between 0.5 bar and 1.0 bar above atmospheric pressure.

12. The powder feeding device of claim 1 or 8, wherein, the powder within each of the secondary chambers comprises a single component powder, a mixed powder or an elemental powder.

13. The powder feeding device of claim 1 or 8, wherein, the particle size of each powder is between 1 micron and 40 microns.

14. The powder feeding device of claim 1 or 8, wherein, the powder feeding device outputs powder at a rate of between 2 g / min and 10 g / min.

Images