Passivation of filter residues

Abstract

Passivation device (100, 200, 300, 400, 500, 600, 700) for passivating filter residues (12) of a filter device (1) arranged in a process gas circuit of an additive manufacturing device, comprising: a reaction unit (4, 19, 14) with: an inlet suitable for supplying an oxidizing agent (6, 16), a coupling unit (2, 200) that can be coupled to the filter device for the introduction of the filter residues (12) into the reaction unit, a discharge unit (8) suitable for the discharge of passivated filter residues (22) from the reaction unit (4, 14, 19), wherein the reaction unit has a reaction chamber in which passivation of filter residues, in particular controlled oxidation of condensate particles, is possible, and wherein the coupling unit (2, 200) has a portioning unit for limiting the amount of filter residues (12) supplied to the reaction unit (4, 14, 19) to a predefined value, wherein the portioning unit is implemented by pre-dimensioned blades, or by a cell wheel or a scraper wheel.

Description

[0001] The present invention relates to a device and a system for passivating filter residues of a filter device arranged in a process gas stream of a device for the additive manufacturing of three-dimensional objects.

[0002] Devices and methods for the additive manufacturing of three-dimensional objects are used, for example, in rapid prototyping, rapid tooling, or additive manufacturing. One example of such a method is known as selective laser sintering or laser melting. In this process, a layer of a usually powdered build-up material is repeatedly applied, and the build-up material in each layer is selectively solidified by irradiating the areas corresponding to the cross-section of the object being manufactured in that layer with a laser beam. Further details are described, for example, in EP 2 978 589 B1.

[0003] During the manufacturing process, a process gas atmosphere, usually an inert gas atmosphere, is often maintained in the process chamber where the build material is selectively melted by radiation. This is because some build materials, especially those containing metals, tend to oxidize at the high temperatures during the melting process, which prevents the formation of objects or at least prevents the formation of objects with the desired microstructure. Typically, a process gas stream is directed over the build plane, i.e., the surface of the build material layer to be solidified.

[0004] However, since the build material is both vaporized and stirred up during the process (i.e., the irradiation of the build material), it is necessary to remove these unwanted additives from the process gas. These additives are typically condensate particles smaller than 50 nm or powdered build material with particle sizes between 1 and 50 µm. US 2014 / 0287080 provides a closed gas flow circuit for this purpose, which directs a gas flow through the build chamber of a selective laser melting device. This gas flow circuit incorporates two filter devices, each with a filter element.

[0005] In DE 10 2014 207 160 A1, a cyclic cleaning of a filter element of a recirculating air filter device by means of a gas pressure pulse is described.

[0006] Particularly when using metal-containing or metallic construction materials (e.g., titanium or titanium alloys), the particles tend to react with oxidizing materials at high temperatures, with the reaction rate being increased at high temperatures. This can lead to uncontrolled filter fires or dust explosions, especially in the area of ​​filter elements where the particles carried in the process gas accumulate. This risk is amplified when oxygen comes into contact with the filter element during a filter element change.

[0007] EP 1 527 807 proposes inerting the dust components from an explosive dust-air mixture by using additive particles loaded onto filter plates. The quantity of additive particles is selected so that the mixture of these particles with the introduced dust does not constitute a flammable mixture, at least until the dust container reaches its upper fill level. Calcium carbonate and silicon dioxide particles are mentioned as additive particles in connection with aluminum dust. While the use of additional particles necessitates their provision, it also results in the dust container reaching its upper fill level more quickly, thus requiring more frequent emptying.

[0008] The object of the present invention is to provide an alternative or improved device for preventing dust explosions, particularly in connection with additive manufacturing devices.

[0009] This problem is solved by a passivation device according to claim 1, a passivation device according to claim 2, and a system according to claim 9. Further developments of the invention are specified in the dependent claims. The system can also be further developed by the features of the devices listed below or described in the dependent claims, or vice versa, or the features of the devices can also be used mutually for further development. Furthermore, the devices and the system can be further developed by the features of a disclosed method for passivating filter residues listed below.

[0010] A passivation device for passivating filter residues of a filter unit arranged in a process gas circuit of an additive manufacturing device has: a reaction unit with: an inlet suitable for supplying an oxidizing agent, a coupling unit that can be attached to the filter device for the purpose of introducing the filter residues into the reaction unit, an outlet unit suitable for the discharge of passivated filter residues from the reaction unit, and an energy supply unit suitable for effecting a reaction between the filter residues and the oxidizing agent in the reaction unit.

[0011] Filter residues in a filter element of the filter system can consist of condensate particles from build-up material that evaporated and recondensed during the process, powder particles of the build-up material, or inerting agents within the filter system. The latter include, for example, rock flours in the size range of 1 to 20 µm, which are intended to spatially separate the hazardous condensate particles and serve as thermal ballast. Condensate particles typically result from laser welding fumes, which consist of agglomerated nanoparticles, with the primary particles in the size range of 5–50 nm. The condensate particles remaining in the filter element as filter residues are often agglomerated into so-called filter cakes several millimeters in size, which, however, disintegrate rapidly upon contact. Powdered build-up material typically exhibits particle sizes (d50) between 25 and 35 µm, typically 30 µm.

[0012] The present invention is preferably used in connection with metal-containing construction materials, in particular metal powders such as titanium or aluminum powders or titanium, iron, nickel or aluminum alloy powders, in which metal condensate particles remain as filter residue.

[0013] A coupling unit can be implemented, for example, as a valve, a flap, a slide gate, or a (gas) airlock, and should, in particular, be capable of preventing particles from entering the passivation device from the filter unit. The coupling unit should, in particular, be connectable to a particle collection area in the filter unit, where the particles filtered out of the process gas stream accumulate as filter residue, for example, after a cleaning process of the filter element. Since particles fall downwards due to gravity, a particle collection area is generally located in the lower part of the filter unit, and accordingly, the coupling unit is preferably connected at the lower end of the filter unit.The term "connectable" here means that it includes both coupling units that can be connected to and disconnected from a filter device, and coupling units that cannot be removed from the filter device, i.e., are in permanent connection with the filter device.

[0014] The filter system should preferably be a recirculating air filter system operated in a closed process gas circuit. Optionally, the condensate particles to be passivated can be separated from the remaining particles prior to passivation treatment, e.g., by sieving or using a cyclone.

[0015] The reaction unit in its simplest embodiment has a reaction chamber in which passivation of filter residues, in particular controlled oxidation of condensate particles, is possible, preferably in isolation from the environment.

[0016] Preferably, the material to be passivated is fed into the reaction chamber from above, i.e., through an opening in the upper region of the reaction chamber, since gravity can then be used to transport the material into the reaction chamber. The coupling unit is therefore preferably connected to the top of the reaction chamber.

[0017] Preferably, a trickle conveying device may be provided at the outlet of the filter unit, in the coupling unit, or at the top of the reaction chamber. This device may be, for example, a vibrating device or a device that intermittently supplies gas to the condensate material to promote its movement and prevent it from adhering to walls or to each other. The vibrating device may, for example, vibrate the wall of an outlet hopper of the filter unit, the wall of an inlet hopper of the reaction chamber, or one or more walls in the coupling unit. For the intermittent supply of gas, for example,the wall of an outlet funnel of the filter device, the wall of an inlet funnel of the reaction chamber or one or more walls in the coupling unit may be perforated with bores, in particular fluidizing plates may be attached at these locations.

[0018] Preferably, the outlet unit is located at the lower end of the reaction chamber, as this allows gravity to be used for transporting the material out of the reaction chamber.

[0019] An inlet suitable for supplying an oxidizing agent may include a feed tube and is preferably suitable for supplying a preheated gas, thus exhibiting a corresponding temperature resistance. Oxygen is preferably used as the oxidizing agent.

[0020] An energy supply unit is particularly suitable for providing the necessary energy to initiate a reaction between the filter residues and the oxidizing agent, or for maintaining and / or intensifying or accelerating a reaction between the filter residues and the oxidizing agent. Preferably, the supplied energy is chosen to be high enough to prevent the condensate particles from bonding (adhering to or fusing with each other). In other words, the energy supplied by the energy supply unit for passivation (e.g., controlled oxidation) is preferably adapted to the type and properties of the condensate particles.

[0021] The present invention provides a means of passivating hazardous condensate particles, particularly metal condensates, by processing particles already filtered out of a process gas circuit. This ensures that the process gas circuit, and especially the process gas flow through the additive manufacturing device, is not affected by the passivation process. Furthermore, the prompt removal of the filter residues allows for longer filter cleaning intervals or filter replacement intervals. Conversely, one could also introduce the entire quantity of filter residues generated during a pressure pulse cleaning process into the passivation device, which would result in shorter filter cleaning intervals.

[0022] Preferably, the coupling unit has a portioning unit for limiting the amount of filter residue supplied to the reaction unit to a predefined value.

[0023] A portioning unit can be implemented, for example, by means of pre-dimensioned scoops or, in the simplest design, by means of an inclined plane or a funnel with a defined slope, which leads to a delayed transport of the particle material and thus limits the amount of filter residues supplied to the reaction unit.

[0024] Furthermore, the portioning unit can include a load cell or light barrier / photodiode for determining the quantity of filter residue. In other words, limiting the quantity can consist of limiting the volume or weight of filter residue supplied. A flow rate, mass flow rate, or volumetric flow rate can preferably be controlled by controlling the duration of the flow ("valve open" vs. "valve closed") and / or the flow rate (mass / volume per unit time; open cross-section of the valve). The portioning unit can also include a closure (slotted valve, iris diaphragm, slide valve, rotary valve, rotary flap valve, chamber valve, segmented valve) or similar device.

[0025] The presence of a portioning unit facilitates controlled oxidation of condensate particles, as the limited amount of condensate particles produced at any given time ensures that the heat generated during oxidation, and thus uncontrolled heating of the reaction chamber or an uncontrolled reaction of the metal condensates, is prevented / limited.

[0026] Preferably, the coupling unit and / or the outlet unit are designed in such a way that they can seal the reaction unit gas-tight.

[0027] The gas-tight seal allows for the oxidation of filter residues under a controlled gas atmosphere. Specifically, the gas-tight seal of the coupling unit separates the gas atmosphere containing the oxidizing agent from the process gas atmosphere, thus preventing contamination of the process gas atmosphere with the oxidizing agent and, in particular, ensuring that the process gas circuit is not affected by the passivation processes. In other words, the use of this passivation device is particularly advantageous in recirculating air filter systems, as the recirculation operation is not disrupted or interrupted.

[0028] Preferably, the coupling unit and / or the outlet unit are designed to withstand a pressure difference of up to 8 bar, preferably up to 15 bar, when closed.

[0029] This allows the pressure within the reaction unit to fluctuate relative to the pressure in the filter unit (in the case of the coupling unit) or the pressure in the collection vessel (in the case of the outlet unit). This facilitates controlled passivation / oxidation, as it provides greater flexibility in managing the reaction.

[0030] Although a controlled and limited addition of oxidizing agent is preferred to prevent a pressure increase in the reaction unit, for safety reasons the coupling unit and / or the outlet unit should be able to withstand a pressure difference of up to 15 bar (occurring explosion pressure with micro-dusts), but at least up to 8 bar (occurring explosion pressure with nano-dusts).

[0031] Preferably, the reaction unit has a reaction chamber in the wall of which a pressure equalization valve is installed.

[0032] The reaction chamber provides a preferably enclosed reaction space for the oxidation of filter residues, allowing for better control of the reaction process. The pressure equalization valve ensures that the pressure within the reaction unit is not subject to excessive fluctuations that could damage it. The pressure equalization valve preferably connects the interior of the reaction chamber to an inert gas supply. Alternatively, a connection to the ambient atmosphere is possible, but this can be risky due to the presence of oxygen in the atmosphere.

[0033] The material and thickness of the reaction chamber wall can be chosen, for example, to ensure that the wall has a high heat capacity and therefore does not heat up excessively due to the oxidation processes taking place inside the reaction chamber. For instance, steel can be chosen as the material for the wall, and the wall thickness can then be set to approximately 1 cm.

[0034] Preferably, the wall of the reaction chamber is designed to withstand a pressure difference of up to 8 bar, preferably up to 15 bar.

[0035] In other words, the reaction chamber should preferably have a certain pressure resistance so that large pressure fluctuations within the reaction chamber, which can occur during rapid oxidation processes, do not lead to its destruction. In particular, any other closures of inlets or outlets of the reaction chamber should also exhibit the specified pressure resistance when closed.

[0036] Although a controlled and limited addition of oxidizing agent is preferred to prevent a pressure increase in the reaction chamber, for safety reasons the wall of the reaction chamber should be able to withstand a pressure difference of up to 15 bar (occurring explosion pressure with microdusts), or at least up to 8 bar (occurring explosion pressure with nanodusts).

[0037] Preferably, a conveying device for removing the passivated filter residues is attached to the outlet unit.

[0038] Active removal of the passivated filter residues allows for a faster passivation process, as the removal of these residues from the reaction chamber does not rely solely on gravity. In particular, this also makes it possible to position the collection container some distance from the passivation device, since the conveying system can then bridge this spatial distance.

[0039] The conveying device preferably includes a screw, in particular an extruder screw.

[0040] The screw conveyor can have a varying cross-section or outer diameter that changes monotonically (increasing or decreasing) along the screw's direction of travel towards the collection container. Alternatively or additionally, the screw's pitch can also change. Furthermore, the screw can be supplemented with additional mixing elements.

[0041] By using a conveying device suitable for compressing the passivated filter residues, these residues can be stored in the collection container in a space-saving manner, thus reducing the frequency of emptying. An extruder screw is particularly well-suited for this purpose. With an extruder screw, the desired compression can be achieved by ensuring that the channel depth is smaller at points further away from the discharge unit than at points closer to it.

[0042] Preferably, the reaction unit is an extruder screw or a conveying screw.

[0043] In this embodiment of the invention, the reaction chamber for the oxidation of the filter residues is the space between the threads of the screw. In other words, the oxidizing agent, e.g., a gas containing an oxidizing agent, is introduced to the screw via the inlet, so that the reaction can take place during the transport of the filter residues. The gas may, in turn, be heated to an elevated temperature before being introduced to promote the oxidation reaction. Due to the use of an extruder screw, the filter residues can also be compressed simultaneously, allowing the passivated filter residues to be stored in the collection container in a space-saving manner.

[0044] It is also preferable to change the direction of rotation of the extruder screw or conveyor screw.

[0045] By changing the direction of rotation of the screw, the filter residues can be shifted relative to each other, which facilitates access of the oxidizing agent to the filter residues, especially with multiple changes of rotation direction.

[0046] Preferably, the energy supply unit on the extruder screw has a heating element (e.g. a jacket heater or a heater at the gas supply / oxidizing agent supply (at the inlet).

[0047] Preferably, the screw conveyor can be designed as a reaction chamber and have a cylindrical screw core surrounded by a screw helix, as well as a screw tube as the wall of the reaction chamber.

[0048] Since the passivation of the filter residues or condensate material takes place in a reaction chamber enclosing a reaction space, the screw conveyor is considered the reaction chamber. The screw helix extends radially between the preferably circular cylindrical screw core and the inner edge of the screw tube, which is preferably spaced from the outer radial edge of the screw helix only far enough away to ensure that rotation of the screw core and screw helix around the cylindrical axis of the screw core is not impeded by the screw tube and / or filter residues accumulating in the gap between the screw helix and the screw tube.

[0049] Preferably, the screw core and / or the screw helix and / or the screw tube are manufactured using an additive manufacturing process, whereby the screw core and / or the screw helix and / or the screw tube can be manufactured not necessarily as a whole, but also in parts. After their manufacture, the parts can then be joined together by force-fit and / or form-fit connections, e.g., by screwing or snapping them together. In particular, elements of the screw helix can be attached to the screw core after their manufacture.

[0050] Preferably, geometric dimensions of the screw conveyor, in particular a channel depth, a channel pitch, a shape of the flanks of the screw helix or a flank angle of the screw helix, can vary along the cylinder axis of the screw core.

[0051] The term "varying geometric dimension" refers specifically to a radial dimension of the screw core, or core diameter, i.e., the outer diameter of the cylinder at a specific position on the cylinder axis. However, it can also refer to the shape of the screw's windings. Similar to the thread of a screw, the shape of the screw's windings can be described using a flank profile, such as a flat profile, round profile, saw profile, pointed thread, or trapezoidal thread. Furthermore, the term can also refer to notches or recesses (triangular, rectangular, trapezoidal, etc.) provided at certain points in the screw's winding.

[0052] The thread depth is defined here as the difference between the thread's outer diameter (i.e., the radial outer diameter of the screw helix) and the thread's inner diameter (i.e., the radial outer diameter of the cylindrical screw core). The pitch is understood here as the distance traveled along the cylinder axis when a 360° rotation around the cylinder axis is completed along the outer edge of the helical screw helix. Varying the pitch allows for local adjustment of the screw's fill level, for example, by reducing the pitch in an oxidation zone, thus increasing the gas content (by volume) and facilitating oxidation.

[0053] The term "flank angle" has the same meaning that is known to experts in connection with screw threads.

[0054] Preferably, the screw conveyor can have at least one compaction zone and at least one oxidation zone, wherein the channel depth in the at least one compaction zone is smaller than in the at least one oxidation zone.

[0055] The compression zone and the oxidation zone are areas that extend along the cylinder axis of the screw core. In a compression zone, the condensate material is compressed, particularly its bulk density is increased. In an oxidation zone, due to the lower density, the material is further compressed.

[0056] A lower bulk density allows for better access of the oxidizing agent to the condensate particles. If the condensate is conveyed in compressed form from the compression zone to the oxidation zone, the relatively larger cavity there offers the possibility that the condensate will loosen as a result of the introduced gas penetrating the cavity, whereby the aim is to achieve the most homogeneous loosening or reduction of the bulk density of the condensate possible with a view to achieving the most homogeneous oxidation possible.

[0057] There are standards for determining bulk density (e.g. ASTM D 7481), but in this context, relative changes are more important than absolute values ​​of bulk density.

[0058] A location for the compaction zone near the screw feed, where the coupling unit is attached, is advantageous because the compacted condensate material then presents a barrier for the oxidizing agent, preventing it from easily reaching the filter unit. An arrangement near the outlet unit has the advantage of increasing the service life of the collection tank, as the material is deposited in a more compacted form. Providing a compaction zone both near the screw feed and near the outlet is particularly advantageous. In this case, an oxidation zone can be located between the two compaction zones.

[0059] Preferably, the screw conveyor can have more than one oxidation zone.

[0060] The presence of multiple oxidation zones allows for multi-stage passivation or oxidation of the filter residues in the screw conveyor. This enables a more gradual passivation process, for example, by increasing the oxidizing agent content of the supplied gas or the amount of oxidizing agent supplied with each downstream oxidation zone in the conveying direction.

[0061] Preferably, the screw conveyor can have at least one mixing zone along the cylinder axis of the screw core, in which a section of the screw conveyor along the cylinder axis is designed as a mixer.

[0062] In the mixing zone, the filter residues introduced into the screw conveyor are mechanically agitated. For this purpose, a section of the screw helix can, for example, have the shape of a shear mixer, in particular a helical shear mixer, as known in the prior art. In a helical shear mixer, the narrow gaps between adjacent helix combs create a high shear force on the material, which can break up agglomerates (dispersive mixing) and thereby improve the access of the oxidizing agent to the surfaces of the filter residue particles during subsequent oxidation / passivation.

[0063] If the section of the screw helix is ​​designed as a toothed disc mixer or a diamond-shaped mixer, this can result in an increased surface area and a redistribution of particles (distributive mixing). Of course, intermediate designs between these models are also conceivable when designing the mixer. It goes without saying that the diameter of the screw core along this section may differ from the diameter of the screw core in other areas of the screw.

[0064] Furthermore, a mixing zone can also be achieved by arranging projections along a section of the screw conveyor on the inside of the screw tube and by perforating the screw helix at the points of the projections to allow unimpeded movement of the screw helix.

[0065] Preferably, the mixing zone is located near or at the inlet of the screw conveyor, i.e., where the filter residues enter the screw conveyor. However, multiple mixing zones can also be provided, for example, at points along the screw's longitudinal axis where oxidizing agents are added.

[0066] It is further preferred that the inlet is arranged on an oxidation zone near the one of the two ends of the oxidation zone that is closer to the coupling unit.

[0067] The oxidizing agent supplied via the inlet is preferably introduced as a component of a supplied gas. Supply in pure form is possible if it is a weak oxidizing agent. Supply in liquid form would also be possible, for example, via a spray nozzle integrated into the inlet. Supplying the oxidizing agent is particularly advantageous in the sections of the system designated as oxidation zones. Supplying the agent near the end of the oxidation zone closest to the coupling unit has the advantage that a reaction of the condensate material with the oxidizing agent can then take place for the entire duration that the condensate material is conveyed through the oxidation zone. Preferably, the desired reaction time is greater than or equal to 5 minutes and / or less than or equal to 10 minutes.The reaction time is sensibly chosen depending on the temperature in the reaction chamber, the partial pressure of the oxidant and the accessibility of the passivated material (can it be easily removed?).

[0068] It is also preferable to have multiple inlets.

[0069] For example, it is possible to provide multiple inlets along the circumference of the screw or screw tube, e.g., at constant intervals, i.e., regularly distributed along the circumference, with different positions along the cylinder axis of the screw core also being possible. This allows the oxidizing agent to be supplied to the condensate material as uniformly as possible to ensure the most homogeneous passivation possible.

[0070] Regardless of the number of inlets, placing one inlet at the lower end (relative to the vertical) of the screw tube has the advantage that the condensate is then agitated by an introduced gas, thus allowing better access of the oxidizing agent to the condensate particles. Of course, an inlet can also be provided at the upper end (relative to the vertical) of the screw tube. In this case, in particular, but not exclusively, it can be advantageous to choose a small inlet cross-section (e.g., between 3 and 5 mm) to increase the velocity of an introduced gas and ensure more uniform access of the oxidizing agent to the condensate material.

[0071] Preferably, at least one inlet can be arranged at each existing oxidation zone.

[0072] If each oxidation zone has its own inlet, then different amounts of oxidizing agent can be supplied to the different oxidation zones, making, for example, multi-stage oxidation with a stepwise increase in the addition of oxidizing agent possible.

[0073] Preferably, the inlet has a cylindrical shape (cylinder definition in the mathematical sense), with the longitudinal axis of the cylinder forming an angle other than 90° to the wall of the screw tube. The inclination of the inlet allows the supplied oxidizing agent to acquire a kinetic component in a desired direction.

[0074] In a preferred embodiment, the longitudinal axis of the cylindrical inlet forms an acute angle with the cylindrical axis of the screw core, such that the inlet end, where the oxidizing agent is fed into the inlet, points partially or completely towards a feed area of ​​the screw conveyor to which the coupling unit is attached. This imparts a component of motion to the supplied oxidizing agent in the conveying direction. This has the advantage that a supplied oxidizing agent cannot so easily move against the conveying direction towards the filter device. If the inlet end only points partially towards the feed area of ​​the screw conveyor, i.e., if the inlet is also inclined in another direction, the oxidizing agent also acquires a component of motion in the circumferential direction of the screw tube, preferably in the direction of rotation of the screw helix.This may improve the mixing with the condensate (the filter residues).

[0075] Preferably, the energy supply unit may consist of a resistance heater and / or a gas water heater and / or a radiant heater and / or a microwave heater and / or an induction heater and / or a piezoelectric element.

[0076] Resistance heating can be implemented, for example, in the form of heating coils around the outer wall of the screw tube or a heating sleeve at this point. Temperature control at this point can be achieved, for example, by means of a thermocouple attached to the outer wall of the screw tube. Furthermore, radiant heaters can be mounted on the inside of the screw tube to heat the screw core and / or the screw helix and / or the filter residue. The screw core and / or the screw helix and / or the filter residue (the latter preferably having a high metal (powder) content) can also be heated by microwaves or induction. Alternatively or additionally to heating the screw or the filter residue, the supplied gas can also be heated, for example, by means of a gas flow heater.A piezoelectric element positioned in the reaction chamber can also be used to initiate an oxidation reaction. A combination of several of the listed energy supply units is also readily possible.

[0077] Preferably, at least one inlet can be designed as a gas-permeable porous surface in the wall of the reaction chamber.

[0078] A gas-permeable porous surface in the wall of the reaction chamber can be created, for example, by making part of the wall from a metal fleece, metal grid, or a sintered element. This allows the oxidizing agent to be supplied over a larger area, enabling it to distribute more effectively within the reaction chamber.

[0079] It is advantageous to realize the gas-permeable porous sections by providing inserts in the wall of the reaction chamber which can preferably be replaced, each insert having a gas-permeable porous surface that replaces the wall of the reaction chamber.

[0080] Preferably, the coupling unit can be designed as a gas lock.

[0081] A gas lock is characterized by a lock chamber with at least two closures that can be closed alternately or simultaneously and are gas-tight when closed. The presence of a gas lock makes it possible to separate the gas atmospheres in the filter unit and the passivation unit, thus minimizing the risk of oxidizing agents entering the filter unit from the passivation unit.

[0082] Preferably, the energy supply unit has a heating device at the inlet for heating the oxidizing agent.

[0083] The heating device can, for example, be arranged on an optional feed pipe at the inlet, particularly if a gas containing the oxidizing agent is supplied via the inlet. In any case, heating the supplied oxidizing agent close to the inlet, i.e., immediately before it enters the reaction unit, has the advantage that thermal insulation of the feed pipe, which would be required if the heated oxidizing agent were transported from a greater distance, can be dispensed with.

[0084] The heating elements can be, for example, resistance heaters (heating coils, etc.), preferably on the outside of the supply pipe, or an induction heater, which indirectly heats the supplied gas in a metal supply pipe. It would also be possible to arrange a number of radiant heaters on a radiation-transparent outer wall of the supply pipe.

[0085] Preferably, the energy supply unit has a heating device on a wall of the reaction unit.

[0086] The heating elements can be, for example, resistance heaters (heating coils, etc.), preferably on the outside of the reaction unit, or induction heaters, which indirectly heat the supplied gas if the reaction unit has a metal wall. It would also be possible to arrange a number of radiant heaters inside the reaction unit or on an outer wall of the reaction unit, preferably one that is transparent to radiation. Preferably, the heating elements should be arranged to ensure the most effective heating of the filter residue particles and / or the oxidizing agent at the point where the oxidation process is to take place.

[0087] A thermally insulated wall of the reaction unit is also preferred.

[0088] The wall itself can be made of a thermally insulating material, or it can be covered from the outside with a thermally insulating material (e.g., glass wool or rock wool). It is known to those skilled in the art that the thermal insulation is better the more completely the wall is covered with a thermally insulating material.

[0089] Preferably, at least one sensor in the reaction unit is capable of detecting pressure and / or temperature.

[0090] It should be emphasized that in the present application, the entire part of the passivation device located between the coupling unit and the outlet unit is considered. Therefore, a sensor does not necessarily have to be located in the reaction chamber or reaction space, although this is advantageous, but can also be located in the supply pipes to the reaction chamber or reaction space. Controlled by signals output from the sensor, the pressure in the reaction unit can be changed, for example, or the quantity of an oxidizing agent supplied can be decreased or increased.

[0091] Further preferably, the reaction unit has a cylindrical reaction chamber, wherein the height of the cylinder exceeds a predetermined minimum value, and the inlet is arranged in the upper half of a vertical extension of a wall of the reaction chamber such that when a gas containing an oxidizing agent is introduced into the reaction chamber, the direction of the gas flow has a component in the direction of gravity.

[0092] The advantage of a cylindrical reaction chamber becomes particularly apparent when the cylinder height exceeds a predetermined minimum value. This minimum value is set such that, as filter residue particles fall through the cylinder, they heat up sufficiently due to friction with the gas atmosphere present in the reaction chamber to promote, and in particular initiate, an oxidation reaction. The downward component of the introduced gas, which contains an oxidizing agent, further accelerates the filter residue particles. This allows the cylinder height to be kept relatively small. A predetermined minimum value can be determined, for example, through preliminary tests with filter residues to be passivated. It should be noted that this definition of a cylinder is based on the mathematical definition of a cylinder, and therefore does not only include circular cylinders.However, cylindrical shapes with a ratio of height to maximum diameter of the base that exceeds the value 3 are preferred.

[0093] The advantage of such a passivation device is that, as a result of their heating through friction with the gas containing an oxidizing agent present in the reaction chamber, filter residue particles can react with the oxidizing agent during flight / free fall. This enables an effective reaction, as the attack of the oxidizing agent on the surface of the filter residue particles is facilitated.

[0094] The inlet is preferably arranged in the area of ​​a base of the reaction unit, preferably in such a way that when gas is introduced into the reaction unit via the inlet, filter residues accumulating at the base of the reaction unit are stirred up.

[0095] Positioning the inlet near the bottom of the reaction unit allows for particularly effective turbulence, as this imparts a strong counter-gravitational motion to the filter residue particles at the bottom of the unit. For optimal turbulence, the gas is supplied at a flow velocity greater than or equal to 30 m / s and / or less than or equal to 300 m / s.

[0096] The stirring up of the filter residues can promote oxidation of the filter residues, as it facilitates access of the oxidizing agent to the surfaces of the filter residue particles, especially the condensate particles; in other words, a larger part of the surface can be oxidized.

[0097] A system for passivating filter residues of a filter device arranged in a process gas circuit of an additive manufacturing device has: a passivation device described above and a filter device suitable for removing particles from a process gas stream flowing through an additive manufacturing device, wherein the filter device has a filter residue collection area to which the passivation device can be coupled.

[0098] A filter residue collection area can be a region within the filter system where filter residue particles accumulate, particularly after a filter element has been cleaned. Typically, a filter residue collection area is located in the lower region of a filter system (near its base), as collection can then occur solely through the force of gravity acting on the filter residue particles. The passivation device is therefore preferably coupled to the filter system in its base region.

[0099] Preferably, the filter residue collection area can taper towards the point where the passivation device is coupled.

[0100] Preferably, a pre-filter or a particle separator, preferably a cyclone, for separating particles whose diameter exceeds a predetermined value from the process gas stream is arranged upstream of the filter device in the system.

[0101] The use of a pre-filter prevents excessively large residue particles, such as powder particles of the build material stirred up by the process gas flow in the build chamber of the additive manufacturing device, from entering the passivation unit coupled to the filter unit. Alternatively, pre-filtration can also take place near the filter residue collection area, i.e., near the point where the passivation unit is coupled to the filter unit. Preferably, the pre-filter separates filter residue particles with a mean diameter exceeding 1 µm, more preferably 500 nm, and even more preferably 100 nm, thus preventing them from entering the passivation unit.

[0102] An additive manufacturing device incorporates a system for passivating filter residues as described above.

[0103] A machine park comprises a number of additive manufacturing devices, and at least one of the above-described systems for passivating filter residues, wherein each system for passivating filter residues is assigned at least two additive manufacturing devices, and wherein the at least one system for passivating filter residues is configured to passivate the filter residues of the at least two additive manufacturing devices associated with it.

[0104] By assigning at least two additive manufacturing devices to a system for passivating filter residues, the system can operate particularly efficiently. Specifically, a filter unit is then assigned to at least two additive manufacturing devices, and a process gas circuit comprises the respective build chambers of the at least two additive manufacturing devices.

[0105] According to one embodiment, a passivation device is used for passivating filter residues of a filter device arranged in a process gas circuit of an additive manufacturing device.

[0106] By using the passivation device described above, the process gas circuit, in particular the process gas flow through the additive manufacturing device, is not affected or disrupted during recirculation operation. Instead, filter residues from the filter assembly are fed to the passivation device either during the filter cleaning process that occurs anyway or even during the flow of process gas through the filter assembly.

[0107] A method for passivating filter residues of a filter device arranged in a process gas circuit of an additive manufacturing device comprises the following steps: Transfer of the filter residues from the filter device into a reaction unit by means of a coupling unit that can be coupled to the filter device, Closing off the reaction unit from the filter device, Supply of an oxidizing agent via an inlet into the reaction unit, inducing a reaction between the filter residues and the oxidizing agent in the reaction unit by means of an energy supply unit and Opening an outlet unit to discharge the passivated filter residues from the reaction unit.

[0108] The introduction of filter residues into the reaction unit via the coupling unit is understood here to mean creating a continuous connection between the filter device and the reaction unit for the filter residues. For example, the filter residues can enter the reaction unit by utilizing gravity or with the aid of a portioning unit mentioned above. Preferably, the coupling unit is coupled to the underside of the filter device.

[0109] Closing the reaction unit from the filter unit means that the passage for filter residues in the coupling unit is closed after the filter residues have been introduced into the reaction unit. It is understood that the outlet unit should also be closed before and during the introduction of filter residues into the reaction unit and during the addition of the oxidizing agent. This is to prevent unpassivated filter residues from entering the collection vessel and, conversely, to prevent the uncontrolled entry of oxidizing agents (especially oxygen) through the outlet unit into the reaction unit.

[0110] The term "causing a reaction" means that a reaction between the filter residues and the oxidizing agent is initiated, intensified, or accelerated by means of an energy supply.

[0111] Preferably, the filter residues are introduced using a portioning device.

[0112] Furthermore, it is preferably preferred that an inert gas is supplied before the filter residues are introduced from the filter device of the reaction unit, preferably via the inlet.

[0113] Such a purging process of the reaction unit with an inert gas can, in particular, prevent oxidizing agents from entering the process gas circuit when the coupling device is next opened for the next passivation process.

[0114] Furthermore, preferably, before any further filter residues are introduced into the reaction unit, a gas with the same gas composition as the process gas is supplied, preferably via the inlet.

[0115] A purging process with a gas having the same gas composition as the process gas can prevent impairment of the process gas atmosphere in the additive manufacturing device when the coupling device is next opened for the next passivation process.

[0116] Furthermore, the filter residues in the reaction unit are preferably stirred up during the reaction between the filter residues and the oxidizing agent by means of gas supply.

[0117] Essentially, the aim is to promote the reaction, which is why filter residues are preferably agitated throughout the entire period during which oxidation of filter residues is possible in the reaction unit. For example, the agitation can be linked to the duration of the closure of the coupling unit and the closure of the outlet unit, i.e., agitation continues as long as the coupling unit and outlet unit are closed. More preferably, a minimum agitation duration can be made dependent on the degree of oxidation of the filter residues and their material composition. Such a minimum duration can be determined in advance through tests and / or simulation.

[0118] The stirring up of the filter residues can promote oxidation of the filter residues, as it facilitates access of the oxidizing agent to the surfaces of the filter residue particles, especially the condensate particles; in other words, a larger part of the surface can be oxidized.

[0119] Preferably, the process is carried out using a passivation unit described above.

[0120] If a passivation unit is used, and the reaction unit is an extruder screw or conveyor screw, there may be situations in which closing the outlet unit during the introduction of filter residues into the reaction unit and during the supply of the oxidizing agent is not necessary.

[0121] The reaction unit preferably comprises an extruder screw or conveying screw whose direction of rotation and / or speed is changed during the reaction between the filter residues and the oxidizing agent. The speed is preferably greater than or equal to 0.5 rpm and / or less than or equal to 100 rpm, and even more preferably greater than or equal to 1 rpm and / or less than or equal to 5 rpm.

[0122] If the reaction unit is an extruder screw, then by changing the direction of rotation, in the same way as by stirring up the filter residues by means of a gas stream, it can be achieved that the oxidizing agent is made more accessible to the surfaces of the filter residue particles, especially the condensate particles, and thus the oxidation reaction is promoted.

[0123] Preferably, in this process, the screw conveyor can be designed as a reaction chamber and the screw conveyor can have a substantially cylindrical screw core surrounded by a screw helix, as well as a substantially cylindrical screw tube as the wall of the reaction chamber.

[0124] In a particularly preferred embodiment, pulsed conveying is used, meaning the rotation of the screw core and the screw helix is ​​temporarily interrupted. During these interruptions, energy can continue to be supplied to the reaction chamber by the energy supply unit. In other words, the energy supply unit can, but does not have to, also operate in pulsed mode. Preferably, the total conveying time and the total energy supply time overlap by at least 80%. Furthermore, the direction of rotation of the screw can also be temporarily reversed, for example, to increase the reaction time of the filter residues in the conveying screw with the oxidizing agent. Such an increase in reaction time can also be achieved by the interruptions in the pulsed operation of the screw.

[0125] Preferably, the energy supply unit is used to heat the screw tube and / or the screw helix and / or the screw core and / or the filter residues, bringing them to a temperature of at least 50 °C, preferably at least 60 °C, and / or at most 1000 °C, preferably at most 600 °C, particularly preferably at most 300 °C.

[0126] To monitor the temperature in the reaction chamber, a number of thermocouples or temperature sensors can be attached to the outside of the screw tube. Alternatively, a pyrometric measurement of the temperature of the screw core and / or the filter residues would also be conceivable.

[0127] The reaction between the filter residues and the oxidizing agent is further preferably effected by the supply of a gas containing the oxidizing agent, which has been brought to a temperature of at least 50 °C, preferably at least 60 °C, and / or at most 1000 °C, preferably at most 600 °C, particularly preferably at most 300 °C.

[0128] If a pre-tempered gas is supplied to initiate the oxidation reaction, the reaction progress can be easily controlled by adjusting the amount of the pre-tempered oxidizing agent supplied. The temperature can be selected based on factors such as the material, size, and shape of the condensate particles.

[0129] The reaction between the filter residues and the oxidizing agent is further preferably effected by the supply of a gas containing the oxidizing agent, wherein the gas is supplied via at least one inlet with a turbulent free jet, preferably supplied with a flow velocity of up to 30 m / s, more preferably with a flow velocity that is greater than or equal to 5 m / s and / or less than or equal to 20 m / s and even more preferably less than or equal to 15 m / s.

[0130] Here, the gas flow rate influences the reaction between the oxidizing agent and the filter residues insofar as a higher flow rate allows better access of the oxidizing agent to the filter residues. On the other hand, excessive turbulence of the filter residues at too high a flow rate is undesirable.

[0131] It should be mentioned that in the case of gas supply via a porous surface, a supply with creeping, laminar flow can also work, meaning that in this specific case the specified lower limit of 5 m / s can also be undercut.

[0132] If a gas flow is split to be fed into the reaction chamber inside the screw tube via several inlets (e.g., several oxidation chambers), then care should be taken to ensure that the specified minimum flow velocity is not undercut at any of the inlets.

[0133] In the process, it is further preferably preferred that an oxygen-containing gas with an oxygen content is supplied that is greater than or equal to 0 vol.%, preferably greater than or equal to 5 vol.%, even more preferably greater than or equal to 10 vol.% and / or less than or equal to 21 vol.%, preferably less than or equal to 15 vol.%, particularly preferably less than or equal to 8 vol.%.

[0134] Oxygen is particularly suitable as an oxidizing agent because it is readily available and the amount of oxidizing agent added can be effectively controlled by adjusting the oxygen content in a gas supplied to the reaction chamber via an inlet. The passivation reaction can be precisely controlled by adjusting the amount of oxygen supplied. For example, the amount of oxygen supplied, or the oxygen content in the supplied gas, can be regulated based on the temperature measured by a temperature sensor in the reaction chamber. In particular, reducing the oxygen content can limit the temperature increase in the reaction chamber.

[0135] The process is preferably carried out until the burning number of the passivated filter residues is less than 3 and / or the minimum ignition energy exceeds 10 mJ, preferably 30 mJ, and most preferably the passivated filter residues are non-explosive.

[0136] The burning number (determinable according to VDI 2263-1) and the minimum ignition energy (determinable according to EN 13821) are good parameters for estimating the extent of passivation. The aim is to passivate the filter residues sufficiently so that they are no longer reactive under normal handling, which is achieved by the specified ranges for the burning number and the minimum ignition energy.

[0137] If it is found that the passivation is not yet sufficient for a given material, the passivation process can preferably be modified by increasing the energy supplied by the energy supply unit, e.g. by increasing the temperature in the reaction chamber and / or by increasing the residence time of the material to be passivated in the reaction chamber, e.g. by reducing the speed of the screw conveyor or temporarily reversing its direction of rotation and / or by increasing the partial pressure of oxygen and / or the amount of oxidizing agent supplied.

[0138] In a further preferred approach, alternatively or additionally to the aforementioned modification of the process parameters, device parameters of the passivation device can also be changed to increase the residence time of the filter residues in the reaction chamber. For example, if a screw conveyor is to serve as the reaction chamber, its geometry can be specifically designed (especially if a particular material is to be passivated) to increase the residence time in the reaction chamber (e.g., by increasing the length of the screw and / or decreasing the pitch).

[0139] The method is preferably carried out after the end of a cleaning process or during a cleaning process of a filter element in the filter device. Preferably 30 seconds, more preferably 1 minute, more preferably 2 minutes, more preferably 5 minutes, and more preferably 10 minutes after the end of a cleaning process.

[0140] Preferably, a passivation process follows a consecutive number of cleaning processes.

[0141] The number of cleaning cycles can be 2, 3, 5, or 10.

[0142] Furthermore, filter residues from the filter device that are free of inerting agents are preferably introduced into the reaction unit.

[0143] Inerting agents can be, for example, rock flours in the size range of 1 to 20 µm. Preferably, only those substances are considered as inerting agents that are always inert at the maximum temperatures occurring during a cleaning process, e.g., lime, glass flour, or expanded glass granules. Further development of the invention makes it possible to completely eliminate the need for inerting agents during cleaning, which would otherwise constitute a large proportion of the filter residues. At the very least, it becomes possible to significantly reduce the proportion of inerting agents. This considerably reduces the amount of filter residues that need to be disposed of.

[0144] Further features and advantages of the invention will become apparent from the description of exemplary embodiments with reference to the accompanying drawings. Fig. Figure 1 is a schematic representation of a passivation device according to a first embodiment. Fig. Figure 2 is a schematic representation of a passivation device according to a second embodiment. Fig. Figure 3 is a schematic representation of a passivation device according to a third embodiment. Fig. Figure 4 is a schematic representation of a passivation device according to a fourth embodiment. Fig. Figure 5 is a schematic representation of a passivation device according to a fifth embodiment. Fig. Figure 6 is a schematic representation of a passivation device according to a sixth embodiment. Fig. Figure 7 is a schematic representation of a passivation device according to a seventh embodiment. Fig. Figure 8 is a schematic representation of a passivation device according to an eighth embodiment. Fig. Figure 9 is a schematic representation of a passivation device according to a ninth embodiment. Fig. Figure 10 is a schematic representation of a passivation device according to a tenth embodiment. Fig. Figure 11 is a schematic representation of a passivation device according to an eleventh embodiment. Fig. Figure 12 is a schematic representation illustrating a particular design of the inlets on a passivation device according to an eleventh embodiment. Fig. Figure 13 is a schematic representation illustrating a particular design of the screw helix on a passivation device according to an eleventh embodiment. Fig. Figure 14 shows an embodiment of the coupling unit as a gas lock in combination with the eleventh embodiment. Fig. Figure 15 shows examples of mixers that can serve as a model for a section of the screw helix designed as a mixer.

[0145] In the following description of exemplary embodiments of the invention, the structure and function of an additive manufacturing device are not described in detail, as they are described in the prior art, for example in EP 2 978 589 B1.

[0146] Reference is made below to a filter device 1, which is used to remove particles from a process gas stream used in the additive manufacturing device. For this purpose, the filter device 1 is located in a closed process gas circuit, wherein the process gas is preferably guided over the build plane, i.e., the surface of a build material layer onto which the electromagnetic radiation or particle radiation strikes in order to melt the build material at points corresponding to the cross-section of the object to be manufactured in the build plane. Further details of the filter device are not described in more detail below. The basic structure of a filter device is known to those skilled in the art. With regard to the filter device, it is only relevant here that it is through which the process gas flows and contains a filter element on which particles contained in the process gas are deposited.Furthermore, it is assumed that the filter device 1 has an outlet area where the particles filtered out of the process gas stream can be received as filter residues by the passivation device, for example after or during a cleaning process of the filter element as described in DE 10 2014 207 160 A1. First embodiment

[0147] The in Fig. The passivation device 100 shown in Figure 1, according to a first embodiment, is attached to the aforementioned filter device 1 such that filter residues, hereinafter also simply referred to as particles, can enter the passivation device 100 from the particle collection area of ​​the filter device 1. In other words, the passivation device 100 is attached to the filter device 1 close to the particle collection area of ​​the filter device 1. Fig. For example, the particles 12 remaining in the filter element collect at the bottom of the filter unit 1, where the passivation device 100 is coupled. To facilitate particle collection and supply, the particle collection area in the filter unit 1 is funnel-shaped, which also slows down the discharge of particles.

[0148] It should be noted that very small particles (e.g., metal condensate) in particular exhibit a high reactivity tendency, so that, for efficiency reasons, in preferred embodiments of the first design only particles up to a certain size are provided to the passivation device 100, for example by removing larger particles by means of a cyclone separator located upstream of the filter device, in which a separation between large and small particles takes place. For example, a sieve can be selected such that the maximum size of the particles provided to the passivation device 100 is 100 nm, preferably 50 nm.

[0149] The passivation device 100 is coupled to the filter unit 1 on the particle feed side by means of a coupling unit or airlock 2. The airlock 2 is a closure (slotted shutter, iris diaphragm, flat slide valve, pivoting slide valve, rotary flaps, chamber airlock, segmented shutter, etc.) that can prevent material and gas exchange between the filter unit 1 and the passivation device 100. Preferably, the airlock 2, when closed, is able to maintain a pre-specified maximum pressure differential between the filter unit 1 and the passivation device 100. In other words, the airlock 2 is gas-tight up to a pre-specified differential pressure value.

[0150] Preferably, the airlock 2 further includes a portioning device (not shown) by means of which defined quantities of particles can be supplied to the passivation device 100. In other words, preferably the maximum quantity of particles supplied to the passivation device 100 when the airlock 2 is opened is limited by means of a portioning device.

[0151] An outlet unit or outlet valve 8 is provided at the outlet side of the passivation device 100. This is a closure mechanism which, when open, allows passivated particles to escape into a collection container 11. Preferably, the outlet valve 8 is capable of sealing the passivation device 100 gas-tight from the environment of the passivation device 100 and / or the collection container 11. Particularly preferably, the outlet valve 8 is capable of maintaining a previously specified differential pressure relative to the environment of the passivation device 100 and / or the collection container 11.

[0152] According to the first embodiment, the particles from the filter device 1, hereinafter also referred to as condensate, are passivated by subjecting them to controlled oxidation. For this purpose, the passivation device 100 has a reaction chamber 4, which is made of a temperature-resistant material. For example, the wall is made of steel or a nickel-based alloy (e.g., Inconel) and is optionally provided on the inside with a coating that impairs or prevents a reaction between the particles and the wall. In order to withstand a pressure increase that may occur inside the reaction chamber 4 during the passivation process, the wall thickness of the reaction chamber is not too thin and is, for example, in the range of 5 to 30 mm for steel, preferably around 10 mm.

[0153] Furthermore, the passivation device 100 has an inlet 6, for example in the form of a supply pipe, through which an oxidizing agent can be supplied to the interior of the reaction chamber 4. The oxidizing agent can be supplied in gaseous form, such as air, oxygen, or a mixture of air / compressed air and an inert gas (e.g., nitrogen or argon). According to the first embodiment, a gas preheated to a certain temperature is supplied to the reaction chamber 4 via the inlet 6. For example, heating elements 15 can be attached to the supply pipe for preheating. These can be, for example, resistance heaters (heating coils, etc.) or induction heaters, which indirectly heat the supplied gas in the case of a metal supply pipe. Depending on the properties of the particles (the metal condensate), an oxidation reaction can be induced with different temperatures of the supplied gas.By way of example only, the supplied gas can be an oxygen / nitrogen mixture with a 10% oxygen content (by volume), heated to approximately 500°C, preferably 300°C. The oxygen content can be between 0 and 21% by volume, preferably 3–10% by volume, and even more preferably 6–7% by volume. Temperatures between 0°C and 1000°C are conceivable.

[0154] Preferably, the gas is supplied via inlet 6 at high pressure and high flow velocity to disturb the condensate particles that collect at the bottom of the reaction chamber and thereby ensure better mixing of the oxidizing agent and particles. It should be emphasized that the heating of the supplied gas via inlet 6 does not necessarily have to be achieved by heating elements attached to the supply pipe, but can also be accomplished in another way, whereby the hot gas (e.g., via a thermally insulated supply pipe) is then supplied to reaction chamber 4.

[0155] Since, depending on the course of the oxidation reaction, an overpressure or underpressure may occur in the reaction chamber 4 compared to the environment of the passivation device 100, the filter device 1 or the collection container 11, the reaction chamber 4 preferably has a balancing valve 3 which can provide pressure equalization compared to the environment, the filter device or the collection container.

[0156] Optionally, the passivation device 100 can be detached from the filter unit 1, so that the passivation reaction does not have to take place in the flanged state, but can take place at another location. However, especially if the condensate accumulating in the filter element is passivated (oxidized) in portions, it is advantageous to operate the passivation device 100 in a state in which it is attached to the filter unit 1 (with the airlock 2 closed).

[0157] An example of how the passivation device 100 can be operated is as follows: As already mentioned, a portion (predefined maximum quantity) of the particles accumulated / provided in the filter element is fed into the passivation device 100 at regular intervals. To supply a predefined quantity of particles or condensate, the airlock 2 is opened so that particles can enter the reaction chamber 4. Subsequently, a gas containing an oxidizing agent is supplied to the reaction chamber 4 via the inlet 6. Since the supplied gas has been heated to a high temperature, oxidation can proceed sufficiently quickly, depending on a selected oxygen concentration.After a certain waiting period, which is determined empirically through preliminary tests or after an observed pressure and / or temperature increase in reaction chamber 4, the passivated condensate, including any remaining accompanying substances, can then fall into the collection container 11 by opening the sluice gate 8. After numerous passivation processes, the collection container 11 can then be separated from the passivation device 100 for disposal or further processing of the passivated material.

[0158] After removing the passivated particles from the reaction chamber 4, it can be flooded with inert gas (preferably of the same gas composition as the process gas atmosphere) via the inlet 6 before receiving another batch (another portion of particles) from the filter device.

[0159] The described oxidation process can proceed better if the inlet 6 is located near the bottom of the reaction chamber 4, so that when the supplied gas containing an oxidizing agent enters, condensate accumulating at the bottom of the reaction chamber 4 is stirred up and oxidized in flight. Second embodiment

[0160] The second embodiment of the invention is very similar to the first embodiment, which is why only the differences compared to the first embodiment are described below. All variations of the invention mentioned in relation to the first embodiment apply equally to the second embodiment. The second embodiment differs from the first embodiment in that the airlock is not located directly between the reaction chamber 4 and the collection container 11. Instead, a conveying device 9 (for example, a screw conveyor or extruder screw) is arranged between the airlock 8 and the collection container 11. This conveying device 9 can compact the passivated material before it enters the collection container 11.This reduces the frequency with which the collection container 11 needs to be changed, and a greater number of passivation / oxidation processes can occur between container changes. Furthermore, the use of the conveying device 9 allows for greater flexibility in choosing the location of the collection container 11. Another example of a conveying device would be pneumatic conveying within a pipe. Third embodiment

[0161] The third embodiment differs from the first and second embodiments in that the passivation of the particles or condensate does not take place in a reaction chamber but in a conveying screw or extruder screw. In the Fig. In the passivation device 300 shown in the third embodiment, the particles from the filter unit 1 pass directly into the area of ​​the screw conveyor. Optionally, the area of ​​the screw conveyor 19 can be separated from the filter unit 1 by a sluice gate (not shown), which, as in the first and second embodiments, is preferably gas- and pressure-tight. Preferably, the particles are fed to the screw conveyor from above, i.e., by utilizing gravity. This facilitates feeding, especially when the flowability of the particles is impaired, i.e., when they adhere to one another. It may be advantageous to use a vibration device at the outlet of the filter unit 1 or at the inlet of the screw conveyor 19 to improve particle passage.

[0162] The drive motor 29 sets the screw 19 into rotation, thereby transporting material from the intake area near the filter device 1 to the collection container 11. The rotational speed is preferably greater than or equal to 0.5 rpm and / or less than or equal to 100 rpm, more preferably greater than or equal to 1 rpm and / or less than or equal to 5 rpm.

[0163] It is also preferred to utilize gravity for the discharge of the condensate from the screw, meaning that a corresponding outlet into the collection container is not located horizontally at the end of the screw, as in Fig. 3 shown, but is then located on the underside of the snail.

[0164] An oxidizing agent in solid, liquid, or gaseous form, e.g., oxygen or an oxygen-enriched inert gas, can be added to the condensate conveyed by the screw via an inlet 16. For example, a gas mixture consisting of inert gas and compressed air can be supplied.

[0165] To achieve controlled oxidation, the screw is surrounded by heating elements 35 that heat the condensate-gas mixture, with the oxidation rate being adjusted via the temperature and oxygen concentration. With this type of passivation, care must be taken to ensure that the temperature rise resulting from the oxidation reaction does not become too high in order to avoid damage to the screw. During the oxidation reaction, the material (condensate or particles) is transported further towards the collection container 11 and compacted in the process, for example, by the screw having a shallower and / or modified channel depth near the collection container 11 compared to the filter unit 1. Preferably, the bulk density of the material increases by a factor of between 2 and 10, typically by a factor of 3.Furthermore, an optional nozzle 28 at the outlet of the extruder screw 19 can provide additional compression of the passivated condensate 22, which is discharged into the collection tank 11. In a variant of the third embodiment, the conveying screw does not rotate continuously in one direction, but rather the direction of rotation is temporarily changed by means of the drive 29 in order to mechanically agitate the condensate in the conveying screw 19, thereby enabling a better oxidation reaction.

[0166] Essentially, the passivation device 300 allows for a continuous feed of particles from the filter unit 1 into the passivation device 300. The design of the screw thread can ensure that the quantity of particles fed in is limited. Furthermore, the inlet 16, through which an oxidizing agent is supplied, is sufficiently far from the outlet of the filter unit 1 to prevent the oxidizing agent from entering the filter unit 1 (e.g., 100 mm). Of course, more controlled passivation can be achieved by providing a sluice 2 containing a metering device.

[0167] Optionally, the material (particles or condensate) in the extruder screw 19 is not passivated by controlled oxidation, but rather by adding a binder that surrounds the condensate via the inlet 16. This binder can be, for example, a plastic granulate or a setting / solidifying material (e.g., water glass). The heating in the screw then melts the plastic granulate, causing it to encapsulate the metal condensate. The passivated material 22 could then be used, for example, as a material for other industries that require plastic-coated metal.

[0168] Furthermore, it is also possible to combine the third embodiment with the first or second embodiment, for example, by carrying out a two-stage passivation, first in the reaction chamber 4 and then in the extruder screw 19. It should also be noted that the passivation according to the invention can also be carried out in multiple stages by connecting the passivation devices described in the different embodiments of the invention in any desired order. With such a multi-stage passivation, particularly gentle passivation is possible in the case of highly reactive materials. For example, only small amounts of an oxidizing agent can be added to each of the individual passivation devices connected in series. Fourth embodiment

[0169] Fig. Figure 4 shows a fourth embodiment of the invention, which is similar to the second embodiment, and therefore the following description focuses on the differences compared to the second embodiment. In the passivation device 400 according to the fourth embodiment, to start the oxidation reaction after adding the oxidizing agent to the reaction chamber 4, a Fig. The ignition element 5 shown in Figure 4, located in the reaction chamber, is ignited to introduce additional energy. The ignition element 5 can be a glow wire, a glow plug, a spark plug, or a piezoelectric element. Once the reaction has started, the oxidation reaction proceeds spontaneously, sustained by the heat generated during the reaction. For better control of the reaction, a sensor 7, consisting of a pressure and / or temperature sensor, is attached to / in the reaction chamber 4. Controlled by signals output from the sensor 7, the pressure relief valve 3 can, for example, be actuated to change the pressure in the reaction chamber 4 or to decrease or increase the supply of the oxidizing agent.

[0170] In this embodiment, the supplied gaseous oxidizing agent does not necessarily need to be preheated, although additional preheating of the oxidizing agent is possible in principle. Furthermore, the oxidizing agent can also be supplied in solid or liquid form via inlet 6.

[0171] Preferably, regardless of whether the oxidizing agent is supplied in gaseous form, a gas stream is introduced into the reaction chamber 4 via the inlet 6 to disturb any condensate particles deposited at the bottom of the reaction chamber and thus promote a better reaction between the oxidizing agent and the condensate particles. The inlet 6 is therefore preferably located near the bottom of the reaction chamber 4. The passivation process is carried out as described in connection with the first embodiment. When the oxidizing agent is supplied in gaseous form, the oxygen content of the supplied gas should be adjusted between 0 and 21 vol.%, preferably between 3 and 10 vol.%, and even more preferably between 5 and 8 vol.%. It is expected that the oxidation reaction will create a negative pressure in the reaction chamber 4, as oxygen is removed from the gas atmosphere.However, if the reaction proceeds at a high rate, the gas will heat up and expand considerably, leading to overpressure. Therefore, it is preferable to adjust the oxygen concentration of the supplied gas to control the reaction.

[0172] Preferably, the reaction chamber is thermally insulated by surrounding it with a non-combustible material, e.g., glass or rock wool. It should also be noted that the equalization valve 3 should preferably have a sintered filter or sintered candle to prevent condensate particles from leaving the system / reaction chamber 4 during pressure equalization. Fifth embodiment

[0173] The fifth embodiment is similar to the first embodiment. The following description therefore focuses on the differences compared to the first embodiment.

[0174] As demonstrated by Fig. As can be seen in Figure 5, in the fifth embodiment the reaction chamber 14 has a cylindrical shape. Furthermore, it can be seen that an inlet 6 is not located at the bottom of the reaction chamber 14, but rather in its upper half, such that the supplied gas has a component of motion directed against the direction of gravity. The described differences result in the following: The cylindrical reaction chamber 14 has a larger vertical extent than reaction chamber 4. For example, the length / height of the cylinder is at least three times its maximum diameter perpendicular to its longitudinal axis. Due to the large drop height resulting from the cylinder's height, oxidation can occur in flight as the filter residue particles descend. The gas supplied through inlet 6 can further increase the mixing and thus the reaction rate of the condensate particles due to the gas flow direction. A reduction in the supplied heat energy is possible if, as in Fig. Figure 5 shows that the reaction chamber 14 is additionally provided with thermal insulation, e.g., non-combustible glass or rock wool. A passivation device 500 according to the fifth embodiment is operated in the same way as the passivation devices of the other embodiments. In particular, the passivation device according to the fifth embodiment can also be provided with a conveying device 9, as is the case with the second embodiment. Sixth embodiment

[0175] One in Fig. The sixth embodiment of the invention, shown in Figure 6, is very similar to the fifth embodiment. Unlike the fifth embodiment, the gas containing an oxidizing agent, which is supplied via the inlet 6, does not necessarily have to be heated by heating elements attached to the supply pipe. According to the sixth embodiment, heating elements 25 are attached to the outside of the reaction chamber, which can again be resistance heaters or induction heaters. Of course, it is also possible to use both heating of the reaction chamber and a preheated supplied gas containing an oxidizing agent, which corresponds to a combination of the fifth and sixth embodiments. Seventh embodiment

[0176] The seventh embodiment is very similar to the third embodiment, which is why the following description focuses on the differences compared to the third embodiment. In a passivation device 700 according to a seventh embodiment, the oxidizing agent is not supplied to the condensate particles in the area of ​​the screw conveyor 9, but only at the end of the screw conveyor / conveying device 9 after the nozzle 28. The passivation device according to the seventh embodiment therefore has an inlet 26 at the end of the screw conveyor facing the collection container 31. A gas jet containing an oxidizing agent is directed via the inlet 26 onto the metal condensate exiting the screw conveyor in order to oxidize the metal condensate in this area.

[0177] As a result of the compaction of the condensate particles at the screw outlet, the tendency to react is reduced, allowing an oxidation reaction to proceed in a controlled manner. Nevertheless, in the seventh embodiment, the collection vessel 31 can be provided with a wall that is temperature- and pressure-stable, similar to that specified for the reaction chamber 4. Preferably, in the seventh embodiment, the gas containing an oxidizing agent should be supplied in a preheated state, even if corresponding heating elements are not integrated into the design. Fig. 7 are shown.

[0178] Similar to the third embodiment, the seventh embodiment allows for the simultaneous oxidation (passivation) and compression of the condensate particles. Furthermore, the process can be carried out both continuously and in batches.

[0179] As in the third embodiment, a binding agent can alternatively or additionally be introduced into the condensate particles via an additional inlet on the screw 9 (similar to the inlet with reference numeral 16 in the figure), which is not shown in the figure. Fig. 3) are supplied. Eighth embodiment

[0180] The eighth embodiment is based on Fig. 8A and Fig. 8B explained. In the Fig. The variant of the eighth embodiment shown in Figure 8A is an exemplary sequence of the passivation process as follows: A certain period of time (approximately 10 minutes) before a filter element is cleaned in the filter system, the reaction chamber 24 (e.g., a temperature-stable cylinder with an inner diameter of approximately 15 cm) is flooded with N2 or argon via valves 66 or 67. The outlet valve 84 is open during this process. The reaction chamber should preferably have approximately 2.5 times the volume of the filter cake expected to be expelled during the cleaning process. In the period before a cleaning process, approximately 10 times the volume of the reactor space (or the reaction chamber 24) should preferably be purged with N2 or argon. The gas flow must be sufficient to generate turbulent flow in the reaction chamber.

[0181] Shortly before filter cleaning, valves 66 and 67 are closed and flap 2 is opened. The filter is then cleaned in filter unit 1. A few seconds (e.g., 5 seconds) after the cleaning pressure surge, flap 2 is closed and compressed air is introduced into the system via valve 65. Simultaneously, an energy supply element 85 (piezoelectric element or heating rod) is heated. After 30 minutes, the outlet unit (flap) 8 is opened for approximately five seconds and valves 65 and 84 are closed. The passivated condensate particles / filter residues can then be removed from the collection container 11 via a suction pipe 80 using a vacuum cleaner. Subsequently, the reaction chamber is flooded with approximately five times its volume via valves 66 or 67.

[0182] The advantage of this variant of the eighth embodiment is that the separate valves 65, 66, and 67 make it possible to easily supply gas mixtures to the reaction chamber. Furthermore, an excessive supply of an oxidizing agent via the valve can, for example, be immediately compensated for by a supply of inert gas via one of the valves 66 and 67.

[0183] Another advantage of this variant of the eighth embodiment results from the compact design of the passivation device, in which a small reaction chamber can be used.

[0184] At the in Fig. The variant of the eighth embodiment shown in Figure 8B is an exemplary sequence of the passivation process as follows: Before filter cleaning, the collection chamber 88 is flooded with either nitrogen (N2) or argon via valves 118 and 128 with outlet 10 open, to a volume ten times its original size. Valves 108, 118, and 128 are then closed, flap 82a is opened, the filters are cleaned, and flap 82a is closed. After approximately 5 seconds, flap 82b is opened for approximately 5 seconds, and compressed air is introduced via valve 65 with outlet 84 open. The energy supply element 85 (piezoelectric element or heating rod) is also switched on. After 30 minutes, all valves are closed, and the passivated condensate particles / filter residues are emptied into the collection container 11 via outlet 8.

[0185] The advantage of the second variant of the eighth embodiment is that the functions of valve 2 (gas tightness and material tightness) can be distributed across two valves. While one valve ensures gas tightness, the other ensures material tightness. Given the potentially elevated temperatures and pressures in the reaction chamber, this reduces the material requirements for sealing the valves. Depending on the gas tightness of valve 82b, valves 66 and 67 can be omitted. Since filter residues can be temporarily stored in the collection chamber 88, they can be dispensed from there in small quantities, for example, via a portioning device, for a passivation process. Ninth embodiment

[0186] A ninth embodiment of the invention is described with reference to Fig. 9 described.

[0187] The airlock 2 and the outlet unit 8 can be configured in the same way as in the other embodiments. In an exemplary passivation process, the airlock 2 is initially open and the outlet unit 8 is closed. Condensate particles / filter residues from the filter unit 1 can then fall through the airlock 2 into the reaction chamber 4. After each filter cleaning in the filter unit 1, the airlock 2 is closed. The condensate particles / filter residues in the reaction chamber 4 are subjected to an oxygen-containing gas, for example, compressed air, ambient air, pure oxygen, or a mixture of oxygen and a protective gas, flowing through the porous inserts 96 (four inserts are shown as an example in section AA, but any other number is possible, e.g., 8 or 16). Pressure equalization is ensured via the gas outlet 93. For this purpose, the valve for the gas outlet (not shown) is opened.Then the energy supply elements 95 (e.g., piezoelectric elements or heating rods) are activated to initiate the oxidation reaction.

[0188] Four energy supply elements are shown as an example, but any other number is possible, e.g., 8 or 16. After completion of the oxidation reaction, the gas flow through the inlets 96 and the energy supply elements 95 is deactivated, and then, if necessary after a cooling period, the outlet unit 8 is opened. The passivated condensate particles then fall into the collection container 11. The transport of the passivated condensate particles can be assisted by a gas pulse through the gas inlets 96. Subsequently, the outlet unit 8 is closed again. Protective gas is introduced into the reactor chamber 4 via the gas inlet 96 until a sufficiently inert atmosphere (e.g., O2 < 2%) is reached. Then the valve at the gas outlet 93 is closed, and the airlock 2 is reopened. This procedure is repeated with the next filter cleaning and at the end of the process.

[0189] In the sensor / monitoring unit 97, critical process parameters are measured, such as temperature and pressure, especially during the reaction; as well as the oxygen content, especially before the start of the reaction and during the final inerting of the reaction chamber at the end of a passivation step.

[0190] The advantage of the ninth embodiment lies in the fact that the use of sintered filters at the gas inlet ensures a uniform gas flow. Furthermore, the (symmetrical) arrangement of the gas inlets allows the gas to be supplied uniformly to the entire reaction space inside the reaction chamber. Tenth embodiment

[0191] A tenth embodiment of the invention is described with reference to Fig. 10 described.

[0192] The airlock 2 and the outlet unit 8 can be configured in the same way as in the other embodiments. In an exemplary passivation process, the airlock 2 is initially open and the outlet unit 8 is closed. Condensate particles / filter residues from the filter unit 1 can then fall through the airlock 2 into the reaction chamber 4. After each filter cleaning in the filter unit 1, the airlock 2 is closed. The condensate particles / filter residues in the reaction chamber 4 are subjected to an oxygen-containing gas, for example, compressed air, ambient air, pure oxygen, or a mixture of oxygen and a protective gas, flowing through the porous funnel 107. Pressure equalization is ensured via the gas outlet 93. For this purpose, the valve for the gas outlet (not shown) is opened. Then the energy supply elements 95 (e.g., piezoelectric elements or heating rods) are activated to initiate the oxidation reaction.After completion of the oxidation reaction, the gas flow through the porous funnel 107 and the energy supply elements 95 is deactivated, and then, if necessary after a cooling period, the outlet unit 8 is opened. The passivated condensate particles then fall into the collection container 11. The transport of the passivated condensate particles can be assisted by a gas pulse through the porous funnel 107. Subsequently, the outlet unit 8 is closed again. Protective gas is introduced into the reactor chamber 4 via the gas inlet 96 until a sufficiently inert atmosphere (e.g., O2 < 2%) is reached. Then the valve at the gas outlet 93 is closed, and the airlock 2 is reopened. This procedure is repeated with the next filter cleaning and at the end of the process.

[0193] In the sensor / monitoring unit 97, critical process parameters are measured, such as temperature and pressure, especially during the reaction; as well as the oxygen content, especially before the start of the reaction and during the final inerting of the reaction chamber at the end of a passivation step. As an alternative to the arrangement of the energy supply elements 95 as in the ninth embodiment, one or more heating elements can also be arranged on the hopper wall.

[0194] The advantage of the tenth embodiment is similar to that of the ninth embodiment. By using the porous funnel 107 for the gas inlet, a uniform gas flow can be ensured, allowing the gas to enter evenly from all directions. It should be noted that the funnel 107 and the reaction chamber can also have a different shape. For example, a circular cylindrical funnel with a porous lateral wall is conceivable. The porosity of the funnel can be achieved by constructing it in the same way as a sintered filter, essentially as a one-piece, large-area sintered filter. Eleventh embodiment

[0195] Fig. Figure 11 shows an eleventh embodiment, which is very similar to the third embodiment and also has a worm gear. In the Fig. In the passivation device shown in Figure 11, a screw 19 serves as a reaction chamber, surrounding a reaction space. The in Fig. The screw shown in Figure 11 has a cylindrical screw core 19a to which a screw helix 19b is attached, both housed in a screw tube 19c, which serves as the wall of the reaction chamber. The diameter of the screw core 19a is typically between 20 and 30 mm, the outer diameter (radial) of the screw helix 19b is typically between 30 and 40 mm, the flute depth is typically between 3 and 6 mm, and the flute pitch angle is typically between 15 and 25 degrees. The flute pitch is typically between 80% and 100% of the outer diameter of the screw helix. The screw length is typically greater than or equal to 25 cm and less than or equal to 50 cm.

[0196] Although the radial dimensions of the screw are constant along the path from the intake area near the filter unit 1 to the outlet near the collection tank 11, the screw geometry can also be varied along this path to create different zones where either compaction or oxidation predominates. This is exemplified in Fig. 11 shown. Fig. Eleven of these are elements that are similar to those in Fig. 3 correspond to the same reference numerals, in particular the intake area near the coupling unit 2 is designated with reference numeral 32 and the outlet unit near the collection container 11 is designated with reference numeral 38.

[0197] The in Fig. The screw 19 shown in Figure 11 has, in particular, two compression zones V1 and V2, as well as an oxidation zone V0 arranged between them. As shown in Figure 11, the screw 19 has, in particular, two compression zones V1 and V2, and an oxidation zone V0 arranged between them. Fig. As can be seen in Figure 11, in the compaction zones V1 and V2, a reduced channel depth compared to the oxidation zone ensures compression of the material. As can be seen, a variation in channel depth is achieved by changing the core diameter.

[0198] It is also conceivable that, deviating from this... Fig. 11. There is only one compression zone or more than two compression zones and / or more than one oxidation zone.

[0199] In Fig. The first compression zone V1 is located near the intake area 32 of the screw 19, preferably directly adjacent to the intake area 32. Such an arrangement is advantageous because the compressed condensate forms a barrier for the oxidizing agent and prevents or at least significantly reduces backflow of the oxidizing agent into the filter device 1. Furthermore, the second compression zone V2 is located near the outlet 38. This ensures that compressed condensate is supplied to the collection tank 11, which occupies less volume in the collection tank 11, thereby extending the service life of the collection tank 11.

[0200] As in Fig. As shown in Figure 11, the inlet 16, through which an oxidizing agent is supplied, should be located in the region of the oxidation zone, preferably at its beginning (when viewed in the conveying direction). If there are multiple oxidation zones, a corresponding inlet 16 would be provided for each of these zones. However, this does not preclude the possibility of supplying the oxidizing agent to an oxidation zone via multiple inlets; this is also possible and particularly relevant in [reference to specific examples]. Fig. 12 shown.

[0201] By providing multiple oxidation zones, oxidation can be carried out in several stages. For example, the material is pre-oxidized in the first oxidation zone and further oxidized after being transferred to the second oxidation zone. For this purpose, a larger quantity of oxidizing agent (e.g., oxygen) can be supplied to the second oxidation zone. In particular, the first oxidation zone can also transition into the second oxidation zone, with each oxidation zone then having an inlet for an oxygen-containing gas or an oxygen-containing gas mixture.

[0202] It is advantageous if the inlet 16 is arranged at the (vertically) lower end of the screw 19, as shown in Fig. Figure 11 shows such an arrangement. This arrangement ensures that a gas supplied via the inlet 16 causes a slight turbulence of the condensate, which tends to accumulate in the lower part of the screw (due to gravity), thus promoting oxidation of the condensate. Alternatively or additionally, an inlet 16 for a gas containing the oxidizing agent can be arranged above the screw. This arrangement has the advantage that the upper inlet 16 is less likely to become clogged by condensate, which tends to accumulate in the lower part of the screw due to gravity.To ensure thorough mixing of the condensate with the oxidizing agent when the inlet 16 is positioned above the screw, the gas should preferably be supplied at a sufficiently high velocity to allow adequate oxygen access to the condensate, even if condensate settles in the lower part of the screw, when the gas flow enters from above. A high velocity can be achieved, for example, by selecting a sufficiently small diameter for the inlet 16 (e.g., between 3 and 5 mm). In other words, the inlets 16 should preferably be implemented as gas nozzles.

[0203] If a plurality of inlets 16 surround the screw in a circumferential direction (for example, three inlets spaced 120° apart from each other), then the oxidizing agent can be supplied uniformly from all sides and thus a homogeneous oxidation can be achieved.

[0204] As an example, a gas mixture is supplied via inlet 16 at a volume flow rate greater than or equal to 0.5 l / min, preferably greater than or equal to 5 l / min, and / or less than or equal to 30 l / min, preferably less than or equal to 10 l / min. The value to be set depends on the rotational speed and dimensions of the screw conveyor as well as the oxygen content of the supplied gas. The latter should contain an inert gas in addition to oxygen; for example, a mixture of oxygen and nitrogen is possible, or a mixture of an inert gas (e.g., argon, nitrogen) and air. The total oxygen content in the gas is typically between 5 and 10 vol.%, preferably between 8 and 10 vol.%. Depending on the application, the total oxygen content during the passivation process can also be in the range between 0 and 21 vol.%.In particular, the total oxygen content is chosen depending on the passivation reaction taking place in the reaction space, i.e., especially depending on the temperature in the reaction space.

[0205] In particular, as in Fig. As shown in Figure 12, the inlet 16 has the form of a nozzle or pipe. This does not necessarily have to be perpendicular to the longitudinal axis of the cylindrical screw, as shown in the figure. Rather, the nozzle or pipe can also form an acute angle with the longitudinal axis of the screw. This allows the supplied gas to acquire a motion component in the conveying direction or in the circumferential direction of the screw. While a motion component in the conveying direction counteracts backflow of the gas towards the coupling unit / filter device, a motion component in the circumferential direction can lead to better mixing of the gas with the filter residues. Alternatively, an inlet can also be implemented by means of a porous section of the wall of the screw tube 19c or a porous insert in the wall of the screw tube.For this purpose, the wall section or insert can be designed as a microporous element, for example a gas-permeable sintered part, a metal fleece or metal mesh.

[0206] Regarding the design of the screw helix 19b (i.e., the screw thread), it can be uniform. However, it is also possible to vary the geometry of the screw helix along the conveying direction, in particular by providing recesses in the flanks of the screw helix 19b or by varying the shape of the flanks of the screw helix 19b and / or the flank angle. This can ensure better mixing of the condensate. Fig. Figure 13 shows an example in which notches or recesses 190 are present in the screw helix 19b. It is particularly advantageous to provide recesses 190 in the intake area 32, as this improves the intake of the condensate. Regarding the shape and angle of the flanks, it is beneficial to provide a sharp edge (small end face) on the outer surface of the screw helix 19b (in the radial direction), as this reduces oxidation reactions and the deposition of condensate in this critical area due to the smaller contact area.

[0207] In particular, a section of the screw helix 19b can also have the shape of a mixer, as is known in the field of extruder screws. Fig. Figure 15 shows two examples of mixers (elements) offered by Groche Technik GmbH in 32689 Kalletal (https: / / www.groche.com / produkte / dynamische-mischer). Using the in Fig. The spiral shear mixer shown in 15b can achieve a dispersing effect, thereby breaking up agglomerates of filter residues in the screw. The Fig. The diamond-shaped mixer shown in Figure 15a offers advantages when no agglomerates are present and an increase in surface area and rearrangement of particles is desired. The sections of the screw (in the direction of the cylinder axis) where a section of the screw helix 19b has the shape of a mixer are referred to in this application as mixing zones. In particular, it is advantageous to connect a mixing zone with a diamond-shaped mixer downstream of a mixing zone with a helical shear mixer. In the material fed to the diamond-shaped mixer, agglomerates have then already been removed by the helical shear mixer.

[0208] Of course, hybrid forms of the in Fig. 15a and Fig. The elements shown in 15b are possible.

[0209] The screw 19 is preferably made of a material with high temperature resistance, for example IN718. In particular, the screw can be manufactured as a whole or in several segments that can be plugged or screwed together using an additive manufacturing process.

[0210] As can be seen, it is possible to combine the embodiments described above, provided they are not obviously mutually exclusive. This also applies to combinations not explicitly mentioned in the text.

[0211] In particular, the invention makes it possible to reduce the amount of inerting agents in the filter device or to eliminate them entirely.

[0212] The following are optional modifications that are applicable to all embodiments.

[0213] With the exception of those in Fig. In the embodiment shown in Figure 8B, a simple closure is proposed as an implementation option for the coupling unit 2 between the filter device and the reaction chamber in all embodiments. The same applies to the outlet unit 8 between the passivation device and the collection container 11. Of course, the coupling unit 2 and / or the outlet unit 8 can also be designed as a gas lock with two alternately actuated closures. This will be shown below with reference to Fig. 14 explained.

[0214] Fig. Figure 14 shows a coupling unit 200 with a lock chamber 203 arranged between an upper gate 201 and a lower gate 202. In the example of the Fig. The airlock 200 is arranged between the intake 32 of a screw conveyor 19, which serves as a passivation device, and a filter unit 1. The airlock 200 is operated, for example, such that an inert gas atmosphere is first created in the airlock chamber with the upper and lower closures 201 and 202 closed, by supplying an inert gas (e.g., nitrogen or argon) via an airlock gas inlet 36. The residual oxygen content of the gas atmosphere within the airlock chamber 203 can be measured by means of an oxygen sensor 105.As soon as the oxygen sensor 105 detects a drop in the oxygen content below a predetermined minimum level, which depends on the reactivity of the condensate, the upper seal 201 is opened after a cleaning process while the lower seal 202 remains closed. This allows condensate / filter residue material from the filter unit 1 to enter the airlock chamber 203. The upper seal 201 is then closed, followed by the opening of the lower seal 202 (after an inert gas atmosphere has also been established in the screw conveyor 19) to feed the condensate / filter residue material to the passivation device. Before any further material is fed from the filter unit 1 into the airlock chamber 203, the lower seal 202 is closed, and an inert gas atmosphere is re-established in the airlock chamber.The upper gate 201 can then be opened to feed new material back into the lock chamber 203.

[0215] By using the gas lock 200, it is reliably prevented in all embodiments that oxidizing agents can pass from the passivation device into the filter unit. When the gas lock 200 is arranged between the filter unit and the passivation device, it simultaneously counteracts the uncontrolled introduction of condensate / filter residue material into the passivation device. In other words, the amount of condensate and the time at which it is fed to the passivation device can be better controlled. In particular, the material is then fed to the passivation device not continuously, but in batches, i.e., in portions.

[0216] The volume of the airlock chamber 203 depends on the maximum amount of condensate / filter residue material that can / should be supplied to the passivation device for a passivation process and / or on the amount of condensate / filter residue material that typically accumulates during a cleaning process. The determination of this amount is based on the type of additive manufacturing device used, in particular the process parameters in additive manufacturing, and / or the filter parameters, e.g., the filter area or the number of filter units connected to the airlock 200, and / or the desired interval between two filter cleaning / passivation processes. The longer this interval, the more material will accumulate during a cleaning process. This can result in a required volume for the airlock chamber 203 that is typically greater than or equal to 1 liter and less than or equal to 15 liters.An example of a typical volume for common additive manufacturing processes using a metal-containing build material is between 3 and 4 liters.

[0217] A gas lock 200 with reversibly operable lock inlet and lock outlet can also be combined with a portioning device (for example, by means of a rotary valve or scraper wheel).

[0218] Regarding the dimensioning of the portions to be supplied to the passivation device for a passivation process, the portion size can preferably be determined taking into account a number of boundary conditions: e.g., the maximum value of the amount of energy released during passivation and / or the pressure stability of the reaction chamber (including its closures and seals). Since the amount of energy released depends on the type and properties of the material, for safety reasons, the material whose reaction with the oxidizing agent is particularly exothermic (e.g., titanium) should preferably be used as the basis for calculating the portion size.

[0219] An exemplary passivation process using the passivation device according to the eleventh embodiment is described below with reference to Fig. 14. It should be noted that the coupling unit does not necessarily have to be a lock 200 as described in Fig. 14 is shown, but with appropriate adjustment of the procedure, a simple closure 2 is also possible.

[0220] During a manufacturing process in the additive manufacturing device, the upper gate 201 of the airlock 200 is normally open, while the lower gate 202 is closed. In other words, the passage of material and gas through the coupling unit is not possible. During cleaning of the filter unit (e.g., every 10 machine operating hours), new material is then fed into the airlock chamber 203.

[0221] Once the cleaning process is complete, or a level sensor 115 in the lock chamber 203 detects that a certain fill level has been exceeded, the upper closure 201 is closed and the lower closure 202 is opened, allowing the cleaned material / filter condensate (e.g., 2-3 liters of aluminum condensate) to enter the intake area 32 of the screw conveyor 19. If it is desired to prevent oxidizing agent from entering the lock chamber 203, the lower closure 202 can optionally be closed. The heating coil 55 is then switched on to heat the screw tube (e.g., to approximately 300 °C). Afterward, the screw drive 29 is activated to start conveying through the screw and to supply the oxidizing agent via the inlet 16. The screw rotates at approximately 2 rpm, which, combined with the dimensions of the screw mentioned above, results in a mass flow rate of approximately 1 to 1.5 g / min.The delivery rate is monitored by a speed sensor 205. In this example, the oxidizing agent is a nitrogen-oxygen mixture with a 10 vol% oxygen content, which is supplied via the inlet 16 at a volume flow rate of approximately 8 l / min, using the flow rate sensor 155. For safety reasons, the oxygen content of the supplied gas is monitored by a gas inlet sensor 165.

[0222] The screw conveyor is shut off and the supply of further oxidizing agent is stopped as soon as a preset time period has elapsed or a sensor (not shown) in the screw's feed area reports that the condensate material in the screw's feed area has been completely conveyed away. Another termination criterion is the detection of a maximum fill level in the collection tank 11 by a collection tank level sensor 195. Furthermore, for safety reasons, the supply of further oxidizing agent is stopped if the flow rate sensor 155, the gas inlet sensor 165, a temperature sensor 145 attached to the screw, a temperature sensor 175 attached to the bottom of the collection tank, or an oxygen sensor 185 attached to the collection tank delivers an incorrect or excessively high value.

[0223] The duration of the oxidation treatment of the condensate material in the screw can be controlled by the rotational speed, the channel pitch, the channel depth, and / or the number and duration of the screw's operating cycles in the opposite direction. Generally, the aim is to treat the material until it is no longer reactive under normal handling conditions. Suitable values ​​for the duration of the oxidation / passivation treatment can be determined through a small number of preliminary tests using different treatment durations. The burning number (according to VDI 2263-1) and the minimum ignition energy (according to EN 13821) are then determined on the passivated filter residue material. The target is a burning number less than 3 and a minimum ignition energy greater than 30 mJ.

[0224] Finally, it should be mentioned that additional safety can be ensured by using further temperature sensors, e.g., a lock chamber temperature sensor 125 and a feed-in temperature sensor 135. Furthermore, it is understood that the person skilled in the art can also omit one or more of the sensors mentioned so far in the passivation device according to the eleventh embodiment. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 2 978 589 B1 [0002, 0145] US 2014 / 0287080

[0004] DE 10 2014 207 160 A1 [0005, 0146] EP 1 527 807

[0007] Cited non-patent literature

[0000] https: / / www.groche.com / produkte / dynamische-mischer

[0207]

Claims

[1] Passivation device (100, 200, 300, 400, 500, 600, 700) for passivating filter residues (12) of a filter device (1) arranged in a process gas circuit of an additive manufacturing device, comprising: a reaction unit (4, 19, 14) with: an inlet suitable for supplying an oxidizing agent (6, 16), a coupling unit (2, 200) that can be coupled to the filter device for the introduction of the filter residues (12) into the reaction unit, a discharge unit (8) suitable for the discharge of passivated filter residues (22) from the reaction unit (4, 14, 19), wherein the reaction unit has a reaction chamber in which passivation of filter residues, in particular controlled oxidation of condensate particles, is possible, and wherein the coupling unit (2, 200) has a portioning unit for limiting the amount of filter residues (12) supplied to the reaction unit (4, 14, 19) to a predefined value, wherein the portioning unit is implemented by pre-dimensioned blades, or by a cell wheel or a scraper wheel. [2] Passivation device (100, 200, 300, 400, 500, 600, 700) for passivating filter residues (12) of a filter device (1) arranged in a process gas circuit of an additive manufacturing device, comprising: a reaction unit (4, 19, 14) with: an inlet suitable for supplying an oxidizing agent (6, 16), a coupling unit (2, 200) that can be coupled to the filter device for the introduction of the filter residues (12) into the reaction unit, a discharge unit (8) suitable for the discharge of passivated filter residues (22) from the reaction unit (4, 14, 19), wherein the reaction unit has a reaction chamber in which passivation of filter residues, in particular controlled oxidation of condensate particles, is possible, and wherein the coupling unit (200) is designed as a gas lock, wherein the gas lock comprises a lock chamber with at least two closures that can be closed alternately or simultaneously and which are gas-tight when closed, wherein the lock chamber is arranged between the closures. [3] Passivation device according to claim 1 or 2, wherein the coupling unit comprises a valve, a flap, a slide or a closure, and is in particular configured to prevent the entry of particles from the filter device into the passivation device, and / or wherein the coupling unit is coupled to the lower end of the filter device. [4] Passivation device according to one of the preceding claims, wherein the coupling unit (2, 200) and / or the outlet unit (8, 38) and / or a wall of the reaction chamber (4, 14, 19) is / are designed such that it can withstand a pressure difference of up to 8 bar, preferably up to 15 bar, when closed. [5] Passivation device according to any one of claims 1 to 4, wherein the coupling unit and / or the outlet unit is designed to seal the reaction unit gas-tight. [6] Passivation device according to any one of claims 1 to 5, wherein the outlet unit comprises a closure mechanism which, when open, allows passivated particles to escape from the reaction unit. [7] Passivation device according to any one of claims 1 to 6, further comprising a pressure and / or temperature sensing sensor. [8] Passivation device according to any one of claims 1 to 7, wherein the oxidizing agent is oxygen. [9] System for passivating filter residues of a filter device arranged in a process gas circuit of an additive manufacturing device, comprising: a passivation device according to any one of claims 1 to 8 and a filter device suitable for removing particles from a process gas stream flowing through an additive manufacturing device, wherein the filter device has a filter residue collection area and / or a bottom area to which the passivation device can be coupled, wherein preferably in the system upstream of the filter device a pre-filter or a particle separator, preferably a cyclone for separating particles whose diameter exceeds a predetermined value from the process gas stream, is arranged, and / or wherein the system preferably comprises a collection container for receiving the passivated filter residues. [10] Passivation device according to any one of claims 1 to 8, wherein the passivation device is designed and / or controlled such that it performs at least one of the following steps: Transfer of the filter residues from the filter unit (1) into the reaction unit (4, 14, 19) by means of the coupling unit (2, 200), Closing off the reaction unit from the filter device, so that a passage for filter residues in the coupling unit is closed after the introduction of filter residues into the reaction unit, Supply of an oxidizing agent via the inlet (6, 16) into the reaction unit (4, 9), inducing a reaction between the filter residues and the oxidizing agent in the reaction unit (4, 14, 19) and Opening of the outlet unit (8) to discharge the passivated filter residues from the reaction unit (4, 9, 19). [11] Passivation device according to claim 10, wherein the outlet unit is closed before and during the introduction of filter residues into the reaction unit and during the supply of the oxidizing agent. [12] Passivation device according to claim 10 or 11, wherein the filter residues in the reaction unit are stirred up during the reaction between the filter residues and the oxidizing agent by means of gas supply. [13] Passivation device according to one of claims 10 to 12, wherein the reaction between the filter residues and the oxidizing agent is effected by the supply of a gas containing the oxidizing agent, more preferably a gas which has been heated, in particular to a temperature of at least 50 °C, preferably at least 60 °C, and / or at most 1000 °C, preferably at most 600 °C, particularly preferably at most 300 °C. [14] Passivation device according to one of claims 10 to 13, wherein a portion, in particular a predefined maximum quantity, of the particles accumulated and / or provided in the filter element is supplied to the passivation device at, preferably regular, intervals.

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