WO2021105635A1 - Filtration device for an additive manufacturing apparatus - Google Patents

Abstract

The present invention relates to a gas filtration device (1) for an additive manufacturing apparatus, the filtration device (1) comprising a column (3) with plates (31) which is designed to bring a gas (A) to be filtered into contact with a filtration fluid (B), the column (3) comprising: - a first end region (32) which comprises an inlet (33) for the clean fluid (B1) in the liquid phase and an outlet (34) for filtered gas (A2), - a second end region (36) which comprises an inlet (37) for gas (A1) which is charged with particles in suspension and an outlet (38) for the fluid (B2) which is charged with the particles in suspension, - an intermediate region (39) which comprises means for bringing the fluid (B) in the liquid phase and the gas (A) into contact, the device (1) further comprising a device for recycling (53) the fluid (B2) which is charged with particles in suspension in order to capture the particles in suspension in the filtration fluid so as to reclaim it as clean fluid (B1).

Description

FILTRATION DEVICE FOR AN ADDITIVE MANUFACTURING DEVICE

FIELD OF THE INVENTION

The present invention relates to the field of additive manufacturing and more particularly to the filtration of gases from the manufacturing chamber of an additive manufacturing device.

STATE OF THE ART

In a known manner, additive manufacturing consists in manufacturing a part by successive superposition of layers of powder which are locally melted.

More precisely, additive manufacturing consists in producing three-dimensional objects by consolidating selected areas on successive layers of pulverulent material (metallic powder, ceramic powder, etc.). The consolidated zones correspond to successive sections of the three-dimensional object. Consolidation is done, for example, layer by layer, by total or partial selective melting carried out with a consolidation source (high power laser beam, electron beam, etc.).

This manufacturing method makes it possible to produce structures that are impossible to manufacture with traditional methods (machining, molding).

In particular, additive manufacturing allows the production of parts with undercuts and undercuts, that is to say parts with contrary convex geometric shapes, impossible to achieve by molding and very difficult to achieve in machining.

Additive manufacturing also makes it possible to produce lattice structures that cannot be manufactured otherwise.

In addition, this manufacturing method can be fast and relatively inexpensive, making it possible to use it in rapid prototyping, for example instead of high-speed machining, which remains complex.

However, the selective melting of the powder (often metallic) generates fumes loaded with soot and micro / nano particles which must be evacuated from the manufacturing chamber of the machine.

For the safety of all and the preservation of the environment, it is necessary to filter these fumes and to be able to reinject a clean gas into the manufacturing chamber of the machine. Indeed, the gas used to fill a manufacturing chamber can be particularly expensive. Also, it is very advantageous to be able to reuse it as much as possible. Currently, the filtration of fumes from additive manufacturing machines is carried out using filtration processes using porous filters which do not guarantee a satisfactory level of filtration.

Document CN 104550951 presents a process for purifying gas from a manufacturing chamber. This process provides for a first filtration of the gas with a water filter and then a second filtration of the gas with a porous filter. This system cannot operate continuously and does not provide a constant quality of filtration. In fact, the filtration technology chosen is loaded with particles during the filtration sequences. However, the more the filter is loaded, the less efficient the filtration. Thus, over the filtration cycles, the filtration quality deteriorates. In addition, when the filter is too loaded with particles, it is necessary to replace it, which involves a total shutdown of the device and a maintenance operation.

Also, in this context, the present invention aims to provide a filtration device which can operate continuously while guaranteeing an optimal level of filtration.

DISCLOSURE OF THE INVENTION

According to a first aspect, the invention provides a gas filtration device for an additive manufacturing device, the filtration device comprising a tray column suitable for bringing a gas to be filtered into contact with a filtration fluid, the filtration device. column including:

- a first end region comprising an inlet for clean fluid in the liquid phase and an outlet for filtered gas,

- a second end region comprising an inlet for gas charged with suspended particles and an outlet for the fluid charged with said particles in suspension,

an intermediate region comprising means for bringing the fluid in the liquid phase and the gas into contact. The device further comprises a device for recycling the fluid loaded with particles in suspension in order to capture the particles in suspension in the filtration fluid so as to regenerate it into clean fluid.

In a particularly advantageous manner, the recycling device makes it possible to continuously recycle the fluid so that only clean fluid enters the tray column. This arrangement makes it possible to guarantee continuous filtration of the gases and to guarantee a constant optimum level of filtration. Indeed, the device according to the invention makes it possible to extract the particles from the gases and to extract the particles from the fluid. As a result, the gas is always filtered by a clean fluid.

The device may include a device for extracting the fluid still present in the filtered gas leaving the tray column. The fluid extraction device may comprise at least one cryogenic exchanger connected to the filtered gas outlet and suitable for condensing and extracting the fluid present in the form of gas in the filtered gas.

The fluid extraction means may include two cryogenic exchangers connected in parallel to the filtered gas outlet, the exchangers being adapted to operate alternately.

The means for bringing the fluid in the liquid phase and the gas into contact can comprise a plurality of perforated plates and absorbent linings.

The recycling device can include a series of filters having increasingly tightened mesh to filter increasingly fine particles.

The device may include a device for extracting hydrogen present in the filtered gas.

According to a second aspect, the invention relates to an additive manufacturing device comprising a gas filtration device according to the invention, the filtration device being adapted to filter gases coming from a manufacturing chamber of the additive manufacturing device, the chamber of manufacture being connected to the gas inlet of the column.

The additive manufacturing device may include a device for recovering the filtered gas in order to reinject it into the manufacturing chamber.

According to a third aspect, the invention relates to a filtration process adapted to be implemented by a device according to the invention and comprising the following steps:

(a) entry of gas laden with suspended particles and clean fluid into the column,

(b) bringing the fluid in liquid phase into contact with the gas laden with particles in suspension so that the particles in suspension in the gas pass into the fluid in the liquid phase,

(c) exit from the column of the filtered gas and of the fluid loaded with suspended particles,

(d) extraction of the fluid present in the filtered gas,

(e) exhaust of filtered gas,

(f) recycling the fluid to extract the suspended particles and recycle it into clean fluid. Step (f) can be performed continuously, simultaneously with the other steps.

Step (d) can be carried out by a cryogenic exchanger.

The method may include a step (d ') of extracting hydrogen present in the filtered gas, step (d') being carried out between steps (d) and (e). DESCRIPTION OF FIGURES

Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and not restrictive, and which should be read with reference to the accompanying drawing in which:

Figure 1 is a schematic representation of a first embodiment of a filtration device according to the invention.

Figure 2 is a schematic representation of a second embodiment of a filtration device according to the invention.

Figure 3 is a schematic representation of a hydrogen extraction vessel according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect, the invention provides a filtration device 1 for an additive manufacturing device. The filtration device according to the invention essentially comprises a 3-plate column 31 suitable for bringing a gas to be filtered A into contact with a filtration fluid B in the liquid phase.

As explained previously, additive manufacturing consists of selectively melting layers of metallic powder. Most often, and as will be described below, an additive manufacturing device comprises a manufacturing chamber in which the manufacturing operations are carried out. This chamber is most often filled with an inert gas such as nitrogen or argon. Indeed, by saturating the atmosphere of the chamber with this type of gas, we reduce the risks of combustion or oxidation of the powder linked to the presence of oxygen or any other reactive gas. Thus, the melting of the metal powder is controlled, without the risk of fire, explosion, or more simply oxidation of the part during manufacture.

During the additive manufacturing process, the atmosphere of the chamber (i.e. the gas A filling the chamber) is charged with particles in suspension. These particles mainly come from the movement of powder in the chamber. Indeed, these movements tend to disperse metallic dust in gas A. On the other hand, the fusion of the powder generates soot, that is to say fumes loaded with micro or nanoparticles.

In summary, and as will be described in detail below, the invention provides a filtration device 1 which makes it possible to reprocess a gas A1 comprising particles in suspension. Through reprocess, it is understood: extract the particles in suspension and if necessary extract the hydrogen.

The architecture of the filtration device 1 for an additive manufacturing device is described below.

Tray column

Column 3 includes in particular:

- a first end region 32 comprising an inlet 33 for clean fluid B1 and an outlet 34 for filtered gas A2,

a second end region 36 comprising an inlet 37 for gas charged with suspended particles A1 and an outlet 38 for the fluid charged with said particles in suspension B2.

In addition, column 3 comprises an intermediate region 39 comprising means for bringing the fluid B in the liquid phase and the gas A into contact. These contacting means allow the fluid B in the liquid phase to be brought into contact with the gas A. so that the particles in suspension in the gas A are captured by the fluid B and so that the gas A is filtered. These means for contacting the fluid B in the liquid phase and the gas A comprise a plurality of trays which can be pierced 31 and of absorbent linings typically made of thick cloth, the trays 31 and the linings being dimensioned to allow the fluid to be brought into contact. B in liquid phase and gas A, so that the particles in suspension in gas A are captured by fluid B so that gas A is filtered.

Typically column 3 operates by gravity. In this case, the first end region 32 corresponds to the top of column 3. In other words, in this arrangement, the first end region 32 is the highest elevation region of column 3.

Likewise, according to this arrangement, the second end region 36 is the base of column 3. In other words, according to this arrangement, the second end region is the lower elevation region of column 3.

In this configuration, as will be detailed below, a gas A naturally flows from the second end region 36 to the first end region 32. Conversely, a liquid fluid B naturally flows from the first end region. 32 to the second end region 36.

By natural circulation, it is understood and accepted that a gas tends to rise in altitude while a liquid tends to flow towards the point of lowest altitude. As will be described below, the flow in the opposite direction of gas A and fluid B in the liquid phase allows them to come into contact. In addition, the contacting is forced by the plates 31 and linings.

It is specified that in this document, the gas is referenced A and the fluid is referenced B. As detailed in the present description, the gas A and the fluid B may or may not be loaded with particles in suspension. Also, the gas laden with suspended particles is denoted A1 and the filtered gas is denoted A2. Conversely, the clean or filtered fluid is noted B1 and the fluid loaded with suspended particles is noted B2.

It is specified that the meeting between soot and particles in suspension in gas A and fluid B can generate hydrogen.

Since the hydrogen generated is in gaseous form, it is called dihydrogen. As such, it is specified that in this document, by hydrogen, it is meant hydrogen gas.

As will be described below, the device 1 very advantageously comprises means for extracting hydrogen.

Fluidic filtration circuit

As described above, column 3 has an inlet 33 and an outlet 38 for fluid B.

These inlet 33 and outlet 38 are connected to a fluid circuit 5 having at least one filtration channel 51.

Inside the fluidic circuit 5, the fluid B flows from the outlet 38 of the column 3 to the inlet 33 in the column 3.

In a preferred arrangement, the fluid B is water. Indeed, water is a fluid particularly suitable for the filtration operations described in the present description. In addition, the solidification of water around 0 ° C is an advantageous element with respect to certain provisions of the invention which will be described below. However, according to other arrangements, the fluid B could have a different composition, suitable for the filtration of suspended particles.

The fluidic circuit 5 has the dual function of ensuring the supply of fluid B to column 3 and of allowing the recycling of fluid B.

To this end, the fluidic circuit 5 comprises a device 53 for recycling the fluid B.

The recycling device 53 comprises a series of filters 53a, 53b, 53c and 53d. The filters 53a, 53b, 53c and 53d are arranged in cascade, so as to be successively crossed by the fluid B. According to the diagram presented here, the recycling device 53 can comprise four filters 53a, 53b, 53c and 53d. Of course, this is only an example, the number of filters not being limiting.

Advantageously, the filters are arranged such that with respect to the direction of circulation of the fluid B, the filters have increasingly tightened mesh, in order to filter increasingly fine particles.

Thus, according to the example shown in FIG. 1, the filter 53d has a mesh that is tighter than the filter 53c, which itself has a mesh that is narrower than the filter 53b, which itself has a mesh that is tighter than the filter. 53a.

Typically the first filter 53a to be crossed by the fluid B, can be a strainer (i.e. a grid) making it possible to retain particles having a dimension greater than 40 μm, and preferably having a dimension greater than 63 μm.

The following filters 53b, 53c and 53d can be filters of the filter cartridge type, with membrane. The second filter 53b can for example retain particles having a size greater than 10 pm, the third filter 53c can for example retain particles having a size greater than 1 pm, and the fourth filter 53 can be adapted to retain particles greater than 0.01 pm.

In a particularly advantageous manner, the structure of the recycling device 53, and in particular the arrangement of the filters 53a, 53b, 53c, 53d, makes it possible to avoid the risks of passage into the atmosphere of the filter because all the soot is passivated. In other words, this structure avoids the risk of filter ignition following venting.

In addition, according to an advantageous arrangement, the fluidic circuit 5 can comprise a valve 54 (or a solenoid valve, or any kind of flow control device). The valve 54 makes it possible to regulate the flow rate of the fluid B upstream (with respect to the direction of circulation of the fluid B) of the recycling device 53 and therefore of the filters 53a, 53b, 53c, 53d.

According to another advantageous arrangement, the fluidic circuit 5 can comprise a temperature regulating member 55 of the circulating fluid.

Typically, the temperature regulator 55 can regulate the temperature of the fluid between -10 ° C and 100 ° C. Preferably, the fluid temperature regulator makes it possible to regulate the temperature of the fluid between 1 ° C and 50 ° C.

The temperature regulator 55 may for example be a resistor to which are added a thermostat and a control card.

Device for extracting the fluid present in the gas A fluid extraction device 62 is connected to the outlet 34 of filtered gas A2.

This fluid extraction device 62 makes it possible to extract filtration fluid B in the gas phase which would be present in the filtered gas A2.

According to the embodiment presented here, the fluid extraction device 62 is a cryogenic exchanger 62.

As will be detailed below, the cryogenic exchanger 62 makes it possible to extract the filtration fluid B present in the gas phase in the filtered gas A2.

As will be detailed below, the cryogenic exchanger makes it possible to condense the fluid B present in the gas phase in the filtered gas A2. The reliquefied fluid B can be reinjected into the fluid circuit 5.

According to an advantageous arrangement, the fluid extraction device 62 can comprise at least two cryogenic exchangers 62 in parallel. In operation, as will be described below, frost forms inside a cryogenic exchanger. Its operation is then slowed down and significant pressure drops can be observed on the flow of filtered gas A2. In this case, the presence of two cryogenic exchangers in parallel can advantageously allow the exchangers to be used alternately, so that one cryogenic exchanger 62 is used while the other is in defrosting.

Hydrogen extraction device

As previously described, it is possible that gas A contains hydrogen due to the encounters of suspended particles and soot with fluid B.

Also, according to an advantageous embodiment shown in Figure 2, the device 1 can include a hydrogen extraction device 64.

The hydrogen extraction device 64 is preferably positioned at the outlet of the cryogenic exchanger 62. In other words, the hydrogen extraction device 64 is crossed by the filtered gas A2 coming from the cryogenic exchanger. .

According to the example shown in Figure 2, the hydrogen extraction device 64 comprises an extraction vessel 64 shown in Figure 3.

The extraction vessel 64 notably comprises an inlet 66 for filtered gas A2, an outlet 69 for gas A, a secondary inlet 67 for gas A and an outlet 68 for hydrogen.

Typically, the hydrogen outlet 68 is positioned at the highest altitude. According to the embodiment presented here, the inlet 66 and the outlet 69 are positioned at low altitude.

Secondary entrance 67 can be positioned at an intermediate altitude.

Additive manufacturing device

According to a second aspect, the invention relates to an additive manufacturing device comprising the filtration device 1.

In a conventional manner, the additive manufacturing device comprises in a manufacturing chamber:

- a tray on which the different layers of additive manufacturing powder are successively deposited,

- one or more sources of energy beams controlled to selectively sweep the powder bed,

- a powder feed tank,

- a tool, such as a squeegee or a roller, which moves in translation on the powder bed to spread the powder.

The filtration device 1 is arranged so as to receive the gases A coming from the manufacturing chamber.

In a particularly advantageous manner, the additive manufacturing device can include recovery means making it possible to reintroduce the filtered gases A2 into the manufacturing chamber. Thus, the gas A circulates in a closed loop between the manufacturing chamber of the additive manufacturing device and the filtration device.

Filtration process

According to another aspect, the invention relates to a filtration process adapted to be implemented by a filtration device 1 according to the invention.

The method comprises in particular the following steps:

(a) entry of gas A1 loaded with suspended particles and clean fluid B1 in liquid phase into column 3,

(b) bringing the fluid B1 in liquid phase into contact with the gas A1 charged with particles in suspension so that the particles in suspension in the gas A pass into the fluid B1,

(c) exit from column 3, filtered gas A2 and fluid B2 loaded with suspended particles, (d) extraction of the fluid B present in the filtered gas,

(e) exhaust of filtered gas,

(f) recycling the fluid B to extract the suspended particles and recycle it into clean fluid.

It is specified that step (f) can be carried out continuously, simultaneously with the other steps.

Advantageously, step (d) is carried out by the cryogenic exchanger 62.

Advantageously, the process also comprises a step (d ’) of extracting hydrogen present in the filtered gas, step (d’) being carried out between steps (d) and (e).

Operation of the filtration device and execution of the process

As has been previously described, the filtration device 1 can be integrated into an additive manufacturing device.

During an additive manufacturing process, an A gas is injected into the manufacturing chamber of the additive manufacturing device.

Typically, gas A can be nitrogen, argon, or a rare gas.

During the additive manufacturing process, many particles (dust) fly and are in suspension in the A1 gas.

At the end of the additive manufacturing process, the gas A1 charged with suspended particles is routed to the filtration device 1.

Typically, a fan oriented to draw in gas A1 can accomplish this task.

More particularly, the gas A1 charged with suspended particles is introduced into column 3 via inlet 37 (step (a)). Concurrently, the clean fluid B1 is introduced into column 3, via inlet 33. As explained above, column 3 preferably operates using gravity and the natural behavior of a gas and a liquid fluid.

Also, naturally, the gas A1 charged with particles in suspension tends to rise in the column. Conversely, the fluid B1 in the liquid phase tends to flow to a lower altitude. The numerous trays and packings 31 slow down these flows and promote the contacting of gas A1 and fluid B1 (step (b)). The result is that the fluid B captures the particles in suspension and the gas A is filtered. The filtered gas A2 continues to rise in the column towards the outlet 34 of the gas A2. While the fluid B2 loaded with particles continues its descent towards the outlet 38 of the fluid B2 (step (c)). It is further specified that the temperature of gas A may be high enough to partially vaporize fluid B. As a result, gas A2 may include vapors of fluid B.

The gas A2 then enters a cryogenic exchanger 62 in order to extract the fluid B present in the gas (step (d)).

The extraction of fluid B is carried out by condensing fluid B.

More precisely, the gas A2 containing vapors of the fluid B enters the cryogenic exchanger 62. The temperature within the cryogenic exchanger 62 is controlled and can for example be situated between -10 ° C and -100 ° C and preferably at -60 ° C. The rapid cooling within cryogenic exchanger 62 freezes fluid B which changes very rapidly from a gaseous state to a solid state. Typically, if fluid B is water and gas A is nitrogen, we know that the solidification point of water is around 0 ° C while the liquefaction point of nitrogen is around 0 ° C. around -195 ° C.

Consequently, by rapidly cooling the mixture of gas A2 and fluid B, for example to -60 ° C, fluid B is frozen without the gas A2 changing state. Thus, the fluid B is extracted and the gas A2 is dried.

In the case where the filtration device 1 comprises several cryogenic exchangers 62, the cryogenic exchangers 62 are used alternately. Indeed, as explained above, the operation of the device 1 consists in particular in freezing a part of the contents of the cryogenic exchanger 62. As a result, frost forms inside a cryogenic exchanger 62, which can induce pressure drops.

Also, the alternate use of exchangers allows one exchanger to be defrosted while another exchanger is in use. Thus, the device 1 can operate continuously at optimum speed.

Then, according to a first embodiment, the gas A2 is evacuated (step (e)). This evacuation may consist of a reintroduction (recovery) of gas A2 into the manufacturing chamber.

According to another arrangement, shown in Figure 2, the gas A2 can be introduced into a hydrogen extraction tank 64 (step (d ’)).

Referring to Figure 3, the gas A2 is introduced through the inlet 66. To increase the pressure in the tank more quickly, the gas A2 can also be introduced, in parallel through the secondary inlet 67. The extraction tank 64 is then left to stand. The principle being that the hydrogen will accumulate in the part of the highest altitude of the extraction vessel 64. The hydrogen is then evacuated through the outlet 68. Then the gas A2 is evacuated (step (e)). As for the first embodiment, the gas A2 can then be recycled by being reinjected into a manufacturing chamber.

It is specified that the reinjection of the filtered gas into the manufacturing chamber is a particularly advantageous arrangement, insofar as the gases used in additive manufacturing have a high cost.

In parallel, and possibly throughout the course of the process, the fluid B is recycled (step (f)). In practice, the fluid B is still circulating in the fluidic circuit 5 and in the column 3. Thus, the fluid B2 loaded with particles in suspension is filtered by the filters 53. Then, the clean fluid B1 is reinjected into the column 3. through the inlet 33. The temperature control member 55 making it possible to maintain the fluid at a selected temperature.

Claims

1. Gas filtration device (1) for an additive manufacturing device, the filtration device (1) comprising a column (3) with plates (31) suitable for contacting a gas (A) to be filtered. with a filtration fluid (B), the column (3) comprising: - a first end region (32) comprising an inlet (33) for clean fluid (B1) in the liquid phase and an outlet (34) for filtered gas (A2), - a second end region (36) comprising an inlet (37) for gas (A1) charged with suspended particles and an outlet (38) for the fluid (B2) charged with said particles in suspension, - an intermediate region (39) comprising means for bringing the fluid (B) in liquid phase and the gas (A) into contact, the device (1) further comprising a device (53) for recycling the fluid (B2) charged of particles in suspension to capture the particles in suspension in the filtration fluid so as to regenerate it into clean fluid (B1), the device (1) further comprising a device for extracting the fluid (B) still present in the gas filtered (A2) leaving the plate column (3), the fluid extraction device comprising at least one cryogenic exchanger (62) connected to the filtered gas outlet (34) and suitable for condensing and extracting the fluid (B ) present as a gas in the filtered gas (A2). 2. Device (1) according to claim 1, wherein the fluid extraction means comprise two cryogenic exchangers connected in parallel to the outlet (34) of filtered gas, the exchangers being adapted to operate alternately. 3. Device (1) according to any one of claims 1 or 2, wherein the means for contacting the fluid (B) in the liquid phase and the gas (A) comprise a plurality of plates (31) pierced and absorbent fillings. 4. Device according to any one of claims 1 to 3, wherein the recycling device comprises a series of filters (53) having increasingly tightened mesh to filter increasingly fine particles. 5. Device according to any one of claims 1 to 4, comprising a device for extracting hydrogen (64) present in the filtered gas (A2). 6. Additive manufacturing device comprising a device (1) for filtering gas (A) according to any one of claims 1 to 5, the filtration device (1) being suitable for filtering gases (A1) originating from a manufacturing chamber of the additive manufacturing device, the manufacturing chamber being connected to the gas inlet (37) of column 3. 7. Additive manufacturing device according to claim 6, comprising a device for recovering the filtered gas (A2) for reinjecting it into the manufacturing chamber. 8. A filtration method suitable for being implemented by a device (1) according to one of claims 1 to 5 comprising the following steps: (a) inlet of gas (A1) charged with particles in suspension and with fluid (B1 ) proper in column (3), (b) bringing the fluid (B1) in liquid phase into contact with the gas (A1) charged with particles in suspension so that the particles in suspension in the gas (A) pass into the fluid (B) in the liquid phase, ( c) outlet from the column (3) of the filtered gas (A2) and of the fluid (B2) loaded with suspended particles, (d) extraction of the fluid (B) present in the filtered gas (A2), (e) exhaust of filtered gas (A2), (f) recycling the fluid (B2) to extract the suspended particles and recycle it into clean fluid (B1). 9. The method of claim 8 wherein step (f) is carried out continuously, simultaneously with the other steps. 10. A method according to any one of claims 8 or 9, wherein step (d) is performed by a cryogenic exchanger (62). 11. A method according to any one of claims 8 to 10, comprising a step (d ') of extracting hydrogen present in the gas (A2) filtered, step (d') being performed between steps (d ) summer).