Powder feeder system and method for recycling metal powder

A powder feeder system for a foundry system having a mixing hearth includes a housing assembly, and a feeder assembly in the housing assembly having a moveable barrel feeder for feeding a pre-weighed charge of metal powder into the mixing hearth of the foundry system during operation thereof. A method for recycling metal powder includes the steps of melting a content of the mixing hearth completely; and then feeding the metal powder into the mixing hearth while the contents of the mixing hearth are still molten using the powder feeder system.

FIELD

This disclosure relates to a powder feeder system for a foundry system and to a method for recycling metal powder.

BACKGROUND

Metal powder used in additive manufacturing can be produced using a foundry system having a mixing hearth heated by a plasma torch in a sealed chamber. An exemplary foundry system is disclosed in U.S. Pat. No. 9,925,591 B2 to Eonta et al. In this type of foundry system, the mixing hearth and plasma torch are configured to melt a raw material into a molten metal. The raw material typically comprises a metal feedstock that can include recycled metals. It would be advantageous to have the capability to recycle metal powder in a foundry system having a mixing hearth.

However, there is no provision for a powder feeder on a foundry system having a mixing hearth. Additionally, these foundry systems typically produce metal powder that is from 40% to 50% too small to re-feed conventionally, or too large to be sold in the printing marketplace (e.g., 150 μm to 4760 μm). The only way to add this powder to the mixing hearth for re-melting is to add some powder under a charge or skull in the mixing hearth before starting the pumping cycle, which produces a very low recycle rate per run.

Some problems with powder feeding into a plasma environment include: 1) The plasma arc can blow powder out of the mixing hearth during heat source start and continuous running. This type of blowing event not only removes powder from the mixing hearth, but has the potential to create an alternate electrical path and cause a double arc torch failure. 2) Another problem involves sizing the discreet powder charge to match the pour throughput of the operation. 3) Also, not allowing recycled powder to circumvent the re-melt process and be harvested as fresh powder.

The present disclosure is directed to a powder feeder system for a foundry system configured to feed a metal powder, such as a recycled powder into a mixing hearth.

SUMMARY

A powder feeder system for a foundry system having a mixing hearth includes a housing assembly, and a feeder assembly in the housing assembly having a moveable barrel feeder configured to feed a pre-weighed charge of metal powder into the mixing hearth of the foundry system during operation thereof. The housing assembly includes tubular members configured to provide a sealed flow path for the metal powder to the mixing hearth.

The barrel feeder of the feeder assembly comprises a hollow cylindrical member having sidewalls, sealed end plates and an internal chamber for the metal powder. A feeder port opening extends through the sidewalls of the barrel feeder into the internal chamber thereof. The feeder assembly also includes a drive assembly configured to position the barrel feeder in a loading position in which the pre-weighed charge of the metal powder is loaded into the barrel feeder, or a feeding position in which the metal powder is inserted into the mixing hearth. The housing assembly can also include a hopper configured to feed the metal powder into the feeder port opening of the barrel feeder. The housing assembly sealingly attaches to a wall of the foundry system in a suitable location such as a view port. The powder feeder system allows pre-weighed charges of any size powder to be delivered on demand to the mixing hearth. In addition, the powder feeder system allows recycled metal powder to be efficiently melted in the mixing hearth.

A method for recycling a metal powder includes the steps of: providing a foundry system comprising a mixing hearth contained in a sealed reaction chamber; providing a powder feeder system for the foundry system comprising a housing assembly comprising a plurality of tubular members configured to provide a sealed flow path for the metal powder to the mixing hearth, and a feeder assembly having a moveable barrel feeder in the housing assembly for feeding a pre-weighed charge of the metal powder into the mixing hearth of the foundry system during operation thereof; melting a content of the mixing hearth to form a pool of molten metal; and feeding the metal powder into the mixing hearth while the contents of the mixing hearth are still molten using the powder feeder system. Prior to performing the melting step the mixing hearth can be loaded with a desired amount of metal, such as a feedstock or a recycled metal having a desired chemical composition.

DETAILED DESCRIPTION

Referring toFIG.1, a powder feeder system10, and a foundry system12having a mixing hearth16, are illustrated. The powder feeder system10is configured to feed a metal powder14into the mixing hearth16of the foundry system12during a melting process. Exemplary metals include titanium, zirconium, nickel, cobalt and alloys of these metals. In addition, the metal powder14can comprise a recycled metal powder having a diameter of from 1 μm to 4760 μm.

The mixing hearth16is contained within a sealed chamber18and includes walls20configured to form a melting cavity22for mixing and melting the metal powder14to form a pool of molten metal24. The mixing hearth16also includes a pour notch26for pouring the pool of molten metal24into another receptacle (not shown) following the melting process. The foundry system12also includes a heat source28, such as a plasma torch system, a plasma transferred arc system, an electric arc system, an induction system, a photon system, or an electron beam energy system, or a combination of one or more of these systems. The foundry system12also includes an induction coil30on the mixing hearth16and an external wall32. U.S. Pat. No. 9,925,591 B2 to Eonta et al., which is incorporated herein by reference, discloses further components of the foundry system12.

Still referring toFIG.1, the powder feeder system10includes a housing assembly36, and a feeder assembly38in the housing assembly36having a moveable barrel feeder40(FIG.4) for containing a pre-weighed charge of metal powder42(FIG.10).

Referring toFIG.2, the housing assembly36is shown separately in a side elevation view. The housing assembly36comprises metal tubular members bolted or welded together to provide a sealed flow path for the metal powder to the mixing hearth16(FIG.1). In addition to providing a sealed flow path, components of the feeder assembly38are mounted within the housing assembly36.

As shown inFIG.2, the housing assembly36includes a cross fitting44wherein the barrel feeder40(FIG.4) of the feeder assembly38is mounted for rotation. The cross fitting44includes a closed end left ring member46and an open ended right ring member48having a precisely dimensioned circular inside diameter. As shown inFIG.4, the barrel feeder40includes a left end plate50and a right end plate52that are sized and shaped to support the barrel feeder40for rotation through an angle of from 0-360 degrees. In particular, the left end plate50and the right end plate52have precisely dimensioned circular outside diameters that are slightly less than the inside diameters of the left ring member46and the right ring member48on the cross fitting44.

As shown inFIG.2, the cross fitting44also includes an open ended inlet member54sealable by an inlet cap56. In addition, the cross fitting44includes an open ended outlet member58that connects to a discharge conduit60. The discharge conduit60can comprise one or more welded or bolted tubular members shaped to provide a sealed flow path for the metal powder14(FIG.1) from the barrel feeder40to the mixing hearth16(FIG.1). As shown inFIGS.4and5, the barrel feeder40includes a feeder port opening68that can be aligned with the inlet member54in a loading position (FIG.6A) of the barrel feeder40and with the outlet member58in a feeding position (FIG.6B) of the barrel feeder40. In the illustrative embodiment, the feeder port opening68has an elongated oblong shape with radiused ends. However, other geometrical shapes can be utilized (e.g., circular, rectangular).

As shown inFIG.2, the housing assembly36also includes a mounting plate64around the discharge conduit60configured to attach to the external wall32(FIG.1) of the foundry system12(FIG.1) using threaded fasteners66. As shown inFIG.8, the discharge conduit60can also include a discharge lip62for directing the metal powder14(FIG.1) into the mixing hearth16. As shown inFIG.11, the housing assembly can optionally include a hopper100configured to continuously feed the metal powder14into the feeder port opening68of the barrel feeder40. Additional sealing elements, such as a simple valve (not shown) can also be used to seal the hopper100and the barrel feeder40.

Referring toFIG.3, additional components of the feeder assembly38are shown separately. As previously explained, the feeder assembly38includes the barrel feeder40rotatably mounted in the housing assembly36for positioning in the loading position (FIG.6A) or the feeding position (FIG.6B). The feeder assembly38also includes a drive assembly70configured to position the barrel feeder40in the loading position (FIG.6A) in which the pre-weighed charge of the metal powder42(FIG.10) is loaded into the barrel feeder40, or the feeding position in which the metal powder14(FIG.1) is discharged into the mixing hearth16(FIG.1).

In the illustrative embodiment the drive assembly70comprises a hyrdraulically actuated bell crank, but can also comprise any other known drive system such as a mechanical and or electrical device which can be used to actuate the barrel feeder40on demand. As shown inFIG.3, the drive assembly70can include a support plate72, a hydraulic cylinder74, a first linkage76attached to the hydraulic cylinder74, and a second linkage78attached to a shaft80(FIG.7) on the right end plate52of the barrel feeder40. The shaft80extends through an opening88in the support plate72and a coupling90attaches the shaft80to the second linkage78. As shown inFIG.7, the barrel feeder40also includes a vacuum seal82on the right end plate52for sealing the barrel feeder40in the housing assembly36. In the feeding position (FIG.6B), the housing assembly36is completely sealed by the inlet cap56, the closed left ring member46, the sealed mounting plate64and by the vacuum seal82. With this arrangement the interior of the barrel feeder40and the inside diameter of the discharge conduit60are in sealed vacuum communication with the sealed chamber18of the foundry system12. In the embodiment with the hopper100additional sealing elements (not shown) can also be added to the barrel feeder40.

As shown inFIG.3, the first linkage76can be mounted to a pivot bolt84attached to the support plate72such that extension of the hydraulic cylinder74rotates the barrel feeder40from the loading position (FIG.6A) to the feeding position (FIG.6B). Conversely, retraction of the hydraulic cylinder74rotates the barrel feeder40from the discharge position (FIG.6B) to the feeding position (FIG.6A).

Referring again toFIG.1, the drive assembly70, and the housing assembly36as well, can be supported by a framework86that attaches to the floor, walls or some solid structure (not shown).FIG.9Aillustrates the pool of molten metal24forming in the mixing hearth16as the metal powder14is inserted by the feeder assembly38into the mixing hearth16.FIG.9Billustrates a partially hardened hearth skull cap92formed following cooling of the molten metal24in which a bladed tool94can be used to show lava tubes96in the hearth skull cap92.FIG.10shows the barrel feeder40on a scale98illustrating its capability to hold a pre-weighed charge of metal powder42of approximately 2 kg.

Method. The powder feeding system10(FIG.1) allows pre-weighed charges42(FIG.10) of any size metal powder14(FIG.1) including recycled and contaminated powder to be delivered on demand to the mixing hearth16(FIG.1) of the foundry system12(FIG.1). In addition, the powder feeding system10can deliver the metal powder14(FIG.1) into a pool of molten metal24(FIG.9A) at the moment the heat source28(FIG.1) is turned off, but prior to the hearth skull cap92(FIG.9B) freezing over.

An operational sequence can include the following steps:

A. Loading the pre-weighed charge42(FIG.10) into the barrel feeder40(FIG.6A). During loading, the barrel feeder40(FIG.6A) is in the loading position (FIG.6A). In addition, the inlet member54(FIG.2) can be opened for loading the pre-weighed charge of metal powder42(FIG.10) by removing the inlet cap56(FIG.1).

B. Sealing the reaction chamber18(FIG.1), which includes sealing the housing assembly36(FIG.1) using the inlet cap56(FIG.1).

C. Melting a content of the mixing hearth16(FIG.1) completely to form the molten metal24(FIG.1). Prior to performing the melting step the mixing hearth16(FIG.1) can be loaded with a desired amount of metal, such as a feedstock or a recycled metal, having a desired chemical composition.

D. Feeding the metal powder14(FIG.1) into the mixing hearth16(FIG.1) while the contents of the mixing hearth16(FIG.1) are still molten using the powder feeder system10(FIG.1). The feeding step can be performed by controlling the feeder assembly38(FIG.3) and the drive assembly70to move the barrel feeder40into the discharge position (FIG.6B).

Example. All testing was done with 2 kg of 75-150 powder Inconel 718 from heat 181229-R1 and a water contaminated Inconel 718 skull from a previous heat. During the initial test, the powder feeder system10(FIG.1) was mounted on the north viewport, the viewport angle is 25 degree from horizontal. This angle proved to be insufficient to transition the powder through the discharge conduit60(FIG.1) and left approximately 500 grams (˜25% of the charge of metal powder42) in the last part of the discharge conduit60(FIG.1). The discharge conduit60(FIG.1) was then moved to the south viewport34(FIG.1) that offered a better53degree angle from horizontal and did allow all of the powder14to transition through the discharge conduit60(FIG.1). The placement of the discharge conduit60(FIG.1) at this location blocks the main camera view but puts the discharge lip62(FIG.1) in close proximity to the heat source28(FIG.1), which in this example was a plasma torch.

A method for recycling metal powder14included the steps of melting the contents of the mixing hearth16(FIG.1) completely, then turning off the heat source28(FIG.1) and immediately initiating powder feeding by rotating the barrel feeder40(FIG.6B) to the feeding position (FIG.6B) while the contents of the mixing hearth16(FIG.1) was still molten. This allowed the metal powder14(FIG.1) to penetrate the surface of the pool of molten metal24(FIG.1). After the skull cap92(FIG.9B) solidified, the heat source28(FIG.1) was restarted. Prior to the restart, the sealed chamber18(FIG.1) was opened. Upon visual inspection of the skull cap92(FIG.9B) the powder was seen to be predominantly clumped together and had formed a gas pocket that was expanding while the skull cap92(FIG.9B) was cooling.