METHOD FOR INTERMITTENT CLEANING OF A FILTER AND FILTER DEVICE FOR A METAL PRESSURE DEVICE

Description

field of technology

[0001] The invention relates firstly to a method for the intermittent cleaning of a filter in a filter device according to the features of the preamble of claim 1 and to a method for operating a metal printing device according to the features of the preamble of claim 3.

[0002] Furthermore, the invention relates to a filter device for a metal printing device according to the features of the preamble of claim 4. State of the art

[0003] In metal printing systems such as laser sintering or laser melting systems, and also so-called 3D laser printing systems, it is known to supply process gas to the cabin of the printing system using a circulation process, which is cleaned or regenerated with regard to impurities (e.g. smoke) that arise during the metal printing process, in particular due to the high heat exposure, which can arise in particular due to the laser application.

[0004] The production of a printed part in the metal printing device preferably takes place in a protective gas atmosphere achieved by a process gas. Thus, an inert gas such as argon or nitrogen is generally used as the process gas, with argon or nitrogen more preferably used as the sole gas. In principle, however, a mixture of gases, particularly inert gases, can also be used as the process or protective gas. As a rule, the aim is for the atmosphere, particularly in the booth, to contain little or no oxygen. Thus, in the case of the metal printing device, the medium flowing through the filter device is the process gas.

[0005] Depending on the size and / or complexity of the printed piece to be produced, such a printing process can take several hours or even several days.

[0006] A metal pressure device is known, for example, from DE 10 2017 206 792 A1. In connection with a filter device, such a metal pressure device is known, for example, from DE 20 2012 013 036 U1. A method for cleaning a filter is known from DE 10 2015 118 746 A1.

[0007] DE 10 2018 002 314 A1 discloses a method for intermittently cleaning a filter, in which cleaning is performed using an oil filling. The oil filling flows through both a filter material collection chamber and the filter housing for cleaning. One of several filter units can also be shut off and removed from regeneration mode. However, this results in disadvantages with regard to the operation of the metal pressure device. The filter material collection chamber is continuously connected to the filter unit, also with regard to a shared flow in the event of an oil filling. The filter material collection chamber is also permanently connected to the filter unit.

[0008] Furthermore, with regard to the state of the art, reference should be made to US 8,794,263 B2 and DE 10 2012 004 587 A1.

[0009] Based on the prior art according to DE 10 2018 002 314 A1, the invention addresses the problem of providing an advantageous method for intermittently cleaning a filter and an advantageous filter device. Furthermore, the problem of the invention is to provide an advantageous method for operating a metal printing device.

[0010] This object is achieved with regard to the method for intermittent cleaning of a filter in the subject matter of claim 1, wherein the filter device has a filter material collection chamber and that the filter material collection chamber is closed before the flushing medium is sucked into the filter housing in order to maintain the negative pressure in the filter material collection chamber.

[0011] With regard to the filter device for a metal printing device, the object is achieved in the subject matter of claim 4, wherein the filter device has a filter material collection chamber associated with the filter housing and that the filter material collection chamber is removable from the filter housing.

[0012] To clean the filter, the relevant filter device is preferably separated in terms of flow from the device connected via the medium inlet and outlet, such as a metal pressure device. In the filter housing, which is then (initially) sealed off from the environment and the other device(s), a negative pressure is created by evacuating the interior. This negative pressure can be as low as several hundred millibars (e.g., 100 to 500 mbar absolute) or comparatively high (e.g., up to 1 mbar absolute).

[0013] At least by utilizing this negative pressure created in the filter housing, a flushing medium used to clean the filter can be introduced due to the resulting suction effect. This suction effect effectively penetrates the filter, particularly the filter wall. In addition, the flushing medium can be blown under pressure into the interior of the filter housing to act on the filter, further improving filter cleaning.

[0014] The proposed solution results in advantageous cleaning of the filter, in particular of a filter wall of the filter.

[0015] The filter device for the metal pressure device can be designed such that an interior of the filter housing can be shut off to generate a negative pressure. The shutoff can be achieved, for example, by conventional slide or valve arrangements. The filter housing can be prepared for cleaning the filter contained therein at least to the extent that the interior of the filter housing can be evacuated.

[0016] To achieve improved filter cleaning in a filter device, the filter housing can be provided, in addition to the medium inlet and the medium outlet, with a lockable flushing medium inlet for introducing a flushing medium into the interior of the filter housing during cleaning operation. This makes it possible not only to use the medium flowing through the filter during normal operation due to flow reversal, or to use it as an alternative, to also clean the filter, but rather to introduce a separate medium (flushing medium), which may serve solely for cleaning the filter. A separate flushing medium inlet can be provided for this purpose, as is also preferred.

[0017] For an advantageous embodiment of the operation of a metal printing device, in the case of two or more filter devices, each with a filter, which are operated in parallel, it is provided that in order to clean one filter device, this filter device to be cleaned is shut off and taken out of regeneration mode and operated with a flushing medium. This makes it possible to maintain continuous operation of the metal printing device, even over a longer period of time, whereby, however, no filter device has to be provided which is designed to clean the atmosphere or the process gas over the entire period of operation of the metal printing device for the production of a specific object in the metal printing process. While the filter device is being cleaned, the other or several further filter devices can continue to be permeated by the process gas for filtering.

[0018] This process allows for continuous operation of the metal printing unit despite filter cleaning. This is particularly advantageous for metal printing operations lasting several hours or days. For this purpose, the filter unit to be cleaned is removed from the operating circuit by means of a shut-off valve. One or more additional filter units take over the filtering of the medium flowing through the metal printing unit's cabin while the shut-off filter unit is being cleaned.

[0019] To clean the filter, one possible embodiment provides for the flushing medium to be introduced in a direction opposite to the filtering operation. During cleaning operation, the flushing medium can essentially pass through a filter wall from the inside out, for example, while during filtering operation, the medium to be filtered flows essentially from the outside in through the filter wall. The flushing medium, which passes through the filter in any case against the flow direction during filtering operation, thus advantageously loosens the filter material deposited on or in the filter wall and, if necessary, transports it away due to the flow.

[0020] Alternatively, or in combination with a flow of the flushing medium in a direction opposite to the usual flow direction during filter operation, the flushing medium can also be directed to a side of the filter wall that represents the outer side of the filter wall during filter operation for filter cleaning. Furthermore, the flow direction of the flushing medium can, for example, be directed substantially transversely to the flow direction of the medium during filter operation. This can support the cleaning effect, in particular an abrasion effect.

[0021] The filter element has a filter material collection chamber associated with the filter housing. This chamber can, as is also preferred, be designed to receive filter material released from the filter, particularly during the cleaning process. The filter material collection chamber can be arranged, for example, on the bottom of the filter housing in the usual operating orientation of the filter device and, if necessary, can also receive filter material particles released or separated from the medium to be filtered during normal filter operation.

[0022] According to a further possible embodiment, the arrangement of the filter housing on the filter housing can be selected such that the housing can be placed under negative pressure together with the filter housing. For example, evacuating the interior of the filter housing can lead to an evacuation of the interior of the filter housing due to an open transition between the filter housing and the housing.

[0023] The filter material collection chamber can be sealed off from the filter housing, in particular from the interior of the filter housing. According to a preferred embodiment, after such a seal, the air pressure prevailing in the filter material collection chamber before the seal was implemented is maintained, and more preferably, the negative pressure achieved before the seal was implemented as a result of evacuation.

[0024] A discharge valve can be provided to create a barrier between the filter material collection chamber and the filter or filter housing. When the discharge valve is open, filter material can flow from the interior of the filter housing into the filter material collection chamber. The filter material can then simply drop into the filter material collection chamber by gravity.

[0025] According to a further preferred embodiment, after pressure equalization in the interior of the filter housing by the sucked in and optionally blown in rinsing medium, this access to the filter material collection chamber can be opened to receive filter material into the filter material collection chamber. In this case, the negative pressure in the filter material collection chamber previously maintained by the hermetic sealing of the filter material collection chamber with respect to the interior of the filter housing containing the filter to be cleaned can achieve the suction of detached filter material into the collection chamber. During the cleaning process, the filter material can collect, for example, on the bottom side of the filter housing and further, for example, in the area of ​​the discharge valve due to the action of the rinsing medium on the filter wall. By opening the discharge valve, the interior of the housing can be suctioned out and into the collection chamber.

[0026] Advantageously, the filter material collection chamber can be removable from the filter housing. Accordingly, the collection chamber can be connected to the filter housing via a screw or plug connection, for example, more preferably a connection that can be operated without tools. The filter material collection chamber can thus be transported for disposal of the filter material.

[0027] A shut-off valve can also be provided to close the filter material collection chamber. In this regard, this can be a separate valve from the previously described discharge valve, so that after the collection chamber is removed from the filter housing, in a preferred embodiment, both the collection chamber is closed by the shut-off valve and the filter housing is closed by, for example, the discharge valve preferably attached to the filter housing. According to one possible embodiment, the shut-off valve on the collection chamber side can be openable to empty the collection chamber.

[0028] The shut-off valve can be held in an open position when the filter material collection chamber is arranged on the filter housing. Accordingly, the shut-off valve can, for example, be a mechanically operated valve which is correspondingly biased into an open position when arranged on the filter housing. In an exemplary embodiment, a mandrel extending from the filter housing can be provided to hold the shut-off valve, optionally in the form of a butterfly valve, against the force of a spring acting on the shut-off valve. This ensures that the shut-off valve is held in the open position in the normal operating position and that an interior space of the filter material collection chamber can be shut off, preferably solely by means of the discharge valve which may also be provided.

[0029] In addition, the shut-off valve can be moved into a closed position, preferably with spring support, when the filter material collection chamber is removed from the filter housing. When the filter material collection chamber is removed from the filter housing, the preferred support for the shut-off valve to keep it open is lost. A spring acting on the valve or the valve body can move the valve body into the closed position if there is no support. This ensures that when the filter material collection chamber is removed, it is closed without further intervention by the user.

[0030] A different medium can be used as the flushing medium than the medium to be filtered. Alternatively, the flushing medium can be the same as the medium to be filtered, so that argon or nitrogen, for example, can be used as the flushing medium. This has the advantage that the flushing medium can remain in the system after the flushing process and after the filter device has been reinserted into the filter circuit.

[0031] For example, a preferably electrically operated vacuum pump can be provided to build up the negative pressure in the filter material collection chamber and in the interior of the filter housing containing the filter.

[0032] In one possible embodiment, two flushing medium inlets can be provided, one of which forces flushing medium through the filter wall in a direction opposite to filter operation, and one of which directs the flushing medium to the outside of the filter wall. The flushing medium inlets can be controlled so that both flushing medium inlets introduce flushing medium simultaneously and, if necessary, over the same period of time. The flushing medium inlets can also spray flushing medium onto the filter to be cleaned alternately, or even sequentially if necessary.

[0033] Furthermore, each flushing medium inlet can be assigned a control valve. These control valves can be controlled via dedicated control electronics with regard to their opening and closing positions and times. Pneumatically actuated control valves are particularly suitable for this purpose. Alternatively, electrically or hydraulically actuated valves are also conceivable.

[0034] A shut-off valve is assigned to each of the medium inlet and outlet to achieve a line separation between the filter device and a connected device, such as the aforementioned metal pressure device, with respect to the medium flowing through the device and the filter device, for example, process gas. For example, after closing the shut-off valves in the medium inlet and outlet, the filter device can be removed from the medium circuit.

[0035] The shut-off valves described above can be pneumatically controlled. Alternatively, electrically or hydraulically controlled valves can also be provided.

[0036] In the case of pneumatic control valves and / or shut-off valves, these can be actuated using, for example, the flushing medium.

[0037] In order to keep the volume flow of the medium, in particular the volume flow of the process gas through the metal pressure device, or possibly a cabin of the metal pressure device, constant or at least approximately constant when a filter device is removed from regeneration mode, the fan generating the volume flow is continuously controlled via a preferably integrated volume flow measurement. Removing a filter device to clean the filter in the filter device initially results in an increase in the volume flow in the remaining filter device without adjusting the volume flow, for example, through a control system.Therefore, appropriate regulation of the volume flow is preferred. In addition to regulating the volume flow, for example, by regulating the fan generating the volume flow, the removal of the filter device to be cleaned is preferably carried out at a timed manner so that a predetermined limit value regarding an increase or decrease in the volume flow is not exceeded. Such a limit value can, for example, be between one-tenth and one-quarter of the regular volume flow. A volume flow also correlates here with a mass flow, so that the measurement of a mass flow can be used as the basis for volume flow control, for example.

[0038] For this purpose, a preferably controllable throttle valve can be arranged in the medium outlet, which reduces the flow so slowly before the filter device is removed that the volume flow control can safely adjust the blower.

[0039] A filter module can be provided, wherein, for example, two or more filter devices, each with a filter, can be provided in the filter module, or further, for example, three, four, or five filter devices. The filter module, in which additional units such as a flushing medium reservoir and / or a blower can also preferably be arranged, can advantageously be connected to the additional device, such as in particular the metal printing device, at a simplified interface.

[0040] When arranging multiple filter units in a filter module, these are preferably connected in parallel with regard to their inlet and outlet piping. This allows the isolated filter unit to be removed from regeneration mode after a medium inlet and outlet have been blocked. In this blocked position of the filter unit, the filter can be cleaned with the flushing medium.

[0041] A separate flushing medium reservoir can be assigned to the filter unit or to the filter module comprising multiple filter units. From this reservoir, flushing medium is fed into the interior of the filter housing, in particular onto the filter, via the flushing medium inlet(s) during cleaning operation.

[0042] In a further embodiment, a pre-separator can be installed upstream of the filter device or multiple filter devices in a flow direction (relative to filter operation) of the medium to be cleaned. This pre-separator can, for example, separate coarse dirt particles before they can enter the filter of the filter device. Such a pre-filter can, in principle, be designed similarly to the described filter device. The described cleaning process can also be used to clean a filter in the pre-separator.

[0043] A microfilter can also be installed downstream of the filter device or multiple filter devices in the flow direction of the medium to be cleaned. Such a microfilter is suitable for filtering out the smallest particles that may pass through the filter unit without being separated, before the medium leaving the microfilter flows back to the device, for example, the metal pressure device.

[0044] The fan that generates the flow of the medium to be filtered can be a standard circulation fan. Typically, it can be a so-called radial or side channel blower, with flow rates of preferably 100 m³ / h to 500 m³ / h (depending on the system size).

[0045] A medium cooler can also be provided downstream of the blower in the flow direction to cool the flowing medium before it enters the device, in particular before it enters the cabin of the metal printing device as a process gas.

[0046] The invention is explained below with reference to the accompanying drawing, which, however, represents only one exemplary embodiment. The drawing shows: Fig. 1 shows a schematic perspective view of a metal printing device with an associated filter module, comprising several filter devices; Fig. 2 shows a perspective view of the arrangement of three filter devices connected in parallel with respect to flow, with a circulation fan and a medium cooler; Fig. 3 shows a schematic sectional view through a filter device according to the line III-III in Figure 2, relating to a method step for filtering a medium flowing through the filter device; Fig. 4 a sectional view according to Figure 3 , but concerning a displaced section plane; Fig. 5 a perspective sectional view along the line VV in Figure 4 ; Fig. 6 a further schematic perspective view of the filter module with a possible removal of a filter device; Fig. 7 one of the Figure 3 corresponding sectional view through the filter device, relating to a process step for evacuating the interior of a filter housing; Fig. 8 a subsequent view to Figure 7 , relating to a process step for cleaning a filter in the filter housing of the filter device; Fig. 9 the enlargement of the area IX in Figure 8 ; Fig. 10 a subsequent representation to Figure 8after completion of the cleaning process and transfer of filter material into a filter material collection chamber; Fig. 11 the enlargement of area XI in Figure 8 ; Fig. 12one of the Figure 10 essentially corresponding representation, but with removal of the filter material collection chamber from the filter housing; Fig. 13 one of the Figure 9 Corresponding sectional view, but after reintegration of the cleaned filter device into the filtration process; Fig. 14: a schematic perspective view of the filter module supplemented by an optional pre-separator and an optional microfilter. Description of the embodiments

[0047] Shown and described is, firstly, with reference to Figure 1 , a metal printing device 1 with an associated filter module 3 having a plurality of filter devices 2.

[0048] The metal printing device 1 essentially comprises a booth 4 in which the metal printing process can be carried out. This involves selective laser melting of fine metal powder under the influence of a laser beam, producing a desired component layer by layer. Production can be carried out directly from so-called 3D CAD data, allowing fully functional components to be manufactured from high-quality metals.

[0049] In addition to the Figure 1 The laser device 5, which is only shown schematically, essentially also includes an application device for applying a metal powder layer, as well as a particle storage container and a particle collection container into which excess particles can be stripped off.

[0050] The production of the metal part can, as is also preferred, take place in a completely enclosed cabin 4, for which purpose this cabin can optionally be provided with a door 6 or the like closing the cabin 3.

[0051] With regard to the manufacturing process, reference is made, for example, to DE 10 2017 206 792 A1 cited at the beginning.

[0052] During the printing process, the atmosphere in booth 3 is preferably regenerated. For this purpose, a gaseous process gas 7, preferably a protective gas such as argon or nitrogen, is blown into booth 4 and simultaneously extracted using a recirculation process. A blower 8, for example, in the form of a recirculation blower, is preferably used for this purpose. The blower 8 can be a so-called side-channel compressor or the like.

[0053] In the illustrated embodiment, the fan 8 is arranged in the filter module 3 with spatial association with the filter devices 2.

[0054] As can be seen particularly from the schematic representation in Figure 1 As can be seen, the blower 8 is fluidly connected to the cabin interior via a pressure line 9 and a suction line 10 as well as an inlet 55 and an outlet 56.

[0055] In this case, the pressure line 9, starting from the blower 8, can be connected directly, if necessary, as in Figure 13 shown, with the interposition of a medium cooler 11, into the cabin 3, preferably associated with a ceiling area of ​​the cabin 3. During operation, a direction a of the pressure flow of the medium 7 results in the pressure line 9.

[0056] At least one filter device 2 is looped into the suction line 10, corresponding to a position upstream of the blower 8 in the flow direction of the process gas 7. According to the illustrated embodiment, several filter devices 2, here three, can be provided.

[0057] The filter devices 2 can be arranged together with the fan 8 and the optionally provided medium cooler 11, and furthermore, optionally with an optionally provided pre-separator 12 and / or a microfilter 13, in the filter module 3. This filter module 3 can have a filter housing 14 comprising the previously described elements. Only two interfaces can be provided, each assigned to the pressure line 9 and the suction line 10.

[0058] A pre-separator 12, if provided, is provided upstream of the one filter device 2 or upstream of the several filter devices 2, viewed in the flow direction of the process gas 7, while the microfilter 13 is arranged downstream of the filter device 2 in the flow direction.

[0059] In the suction line 10, a direction b of the suction flow results during a typical manufacturing process and the associated process gas circulation.

[0060] The filter devices 2 are preferably provided in a substantially identical design, each having a medium inlet 15 and a medium outlet 16. Via the respective medium inlet 15, each filter device 2 is preferably directly connected to the suction line 10. The medium outlets 16 of the filter devices 2 open into a suction transition line 17, which, optionally with the interposition of the microfilter 13, leads to the blower 8 (see in particular Figure 2 ).

[0061] The fine filter 13 can, for example, also be provided in the flow direction at the end of the pressure line 9, if necessary also in the flow direction after the medium cooler 11.

[0062] The Figures 3 and 4 each show a vertical sectional view - with reference to the usual operating position of the filter device 2 - through one of the filter devices 2 in regeneration mode, in which a filtering of the contaminated medium 7, for example smoke discharged from the cabin 4, is carried out.

[0063] As can be seen from the sectional view in Figure 3As can be seen, the filter device 2 can have an approximately circular-cylindrical filter housing 18, with a circumferential housing wall 19 and a housing cover 20. The housing base 21 can be funnel-shaped with a central bottom opening 22, to which a transition line 23 can be connected to a filter material collection chamber 24 that can be removed from the filter housing 18.

[0064] According to the illustrations, a filter 26 can be arranged underneath the housing cover 20, extending into the interior 25 of the filter housing 18. Its filter wall can, as also illustrated, be tubular and circularly cylindrical, with a central longitudinal axis x that, in the usual arrangement position, is aligned along a vertical line. According to the illustrated embodiment, the longitudinal axis x of the filter 26 can simultaneously form the central longitudinal axis of the filter housing 18 as a whole.

[0065] The filter 26 is surrounded, at a distance from the outer surface 28 of the filter wall 27, by a guide wall 29, which is preferably aligned concentrically to the longitudinal axis x. This guide wall 29, like the filter 26, is virtually suspended from the underside of the housing cover 20 and is preferably connected to it in a flow-tight manner. The annular space 35 resulting between the guide wall 29 and the filter wall 27 is open towards the interior 25 when viewed in the axial direction, while the corresponding end face 30 of the filter 26, which faces downwards during normal operation, can be designed so that it cannot be penetrated by the flow, in particular by the process gas 7. Filter material 32 separated in this way can fall through the bottom opening 22 of the housing bottom 21 into the filter material collection chamber 24 solely by gravity.

[0066] The inlet opening 31 of the medium inlet 15 can, as is also preferred, be provided in the housing wall 19, so that an at least approximately tangential inflow of the medium 7 into the interior 25 of the filter housing 18 can result, whereby a vortex-like pre-separation of filter material 32 is initially achieved (cf. Figure 3 ). The filter device 2 initially acts in the manner of a cyclone separator, in which the process gas flow, starting from the inlet opening 31, is guided in a vortex-like manner into the annular space resulting between the guide wall 29 and the housing wall 19.

[0067] According to the illustrated embodiment, the outlet opening 33 of the medium outlet 16 can be provided in the region of the housing cover 20, in particular, as further preferred, centrally, receiving the longitudinal axis x and further assigned to the filter interior 34 enclosed by the filter wall 27.

[0068] As a result of the suction flow resulting during normal operation (filter operation) of the filter device 2, the process gas 7 sucked into the interior 25 is sucked from below into the annular space 35 between the filter wall 27 and the guide wall 29 after the vortex-like deflection associated with the downward facing end face 30 of the filter 26, after which a penetration of the filter wall 27 from the outer surface 28 to the inner surface 36 of the filter wall 27 results (see arrows d in Figure 4 ), so that the filtered medium 7 reaches the filter interior 34 and leaves the filter device 2 via the outlet opening 33 (compare Figure 4 ).

[0069] Filter material 32 separated in this process may be trapped in the filter wall 27. Any filter material 32 falling through the annular space 35 during this filtration is preferably collected in the filter material collection chamber 24.

[0070] As can be seen from the sectional views, for example in the Figures 3 and 4 As can be seen, the medium inlet 15 and the medium outlet 16 can each be provided with a shut-off valve 37 and 38, respectively, in order to deactivate the filter device 2 from regeneration mode by isolating it from the suction line 10 and the suction transition line 17. In such a state, the regeneration of the process gas 7 while the metal pressure device 1 continues to operate is taken over solely by the other filter devices 2 of the filter module 3. Thus, at least approximately continuous operation of the metal pressure device 1 can be ensured even in the event of a failure or deliberate shut-off of a filter device 2, for example, for cleaning the same.

[0071] For this purpose, the preferably pneumatically actuated shut-off valves 37 and 38 of the medium inlet 15 and the medium outlet 16 are set to a blocking position according to Figure 7The corresponding control of the shut-off valves 37 and 38 can, and is also preferred, be carried out via a control electronics 39 (not shown in detail), which can also be part of the filter module 3.

[0072] By sealing off using the shut-off valves 37 and 38, the interior space 25 of the filter device 2, preferably together with the filter material collection chamber 24, can be hermetically sealed off from the other components of the filter module 3, in particular from the provided piping, the other filter devices 2 and the blower 8.

[0073] In this shut-off situation, the filter device 2 can be used as shown in Figure 6As shown schematically, the filter module 3 can be removed, for example, for maintenance or repair work, even while maintaining filter operation through the additional filter devices 2. This results in a circuit-related removal such that the removed filter device is no longer flowed through by the process gas. However, it naturally remains immobile in the specified arrangement.

[0074] In order to keep the volume flow of the process gas passing over the powder bed in the booth 4 constant or at least almost constant when a filter device 2 is removed from the overall arrangement, the blower 8 responsible for the volume flow is continuously controlled via an integrated volume flow measurement, in particular using the control electronics 39. Such a volume flow measurement can be carried out, for example, by means of an orifice and a pressure measurement in front of and behind the orifice, for example in the area of ​​the suction transition line 17 and thus preferably in the flow direction of the medium 7 between the filter devices 2 and the blower 8.

[0075] During the removal of a filter device 2, the flow of process gas through the filter device 2 to be removed can be continuously reduced via a preferably also pneumatically controllable throttle valve 40 in such a way that the volume flow control can reliably readjust the circulation fan 8. Such a throttle valve 40 can, for example, as is also preferred, be provided associated with the medium outlet 16, more preferably in a line section between the outlet opening 33 or the valve 38 associated with this outlet opening 33 and the suction transition line 17 (cf. Figure 5 ).

[0076] To clean the filter 26 in the filter device 2 and to remove the filter cake that has settled on the filter wall 27 during the filtering of the process gas 7, the filter device 2 can be put into regeneration mode. For this purpose, the filter device 2 is first removed from the process gas flow, as described above, or is isolated from the lines by closing the shut-off valves 37 and 38, thus sealing the medium inlet 15 and the medium outlet 16.

[0077] A separate pump, in particular vacuum pump 41, is used to initially create a vacuum in the filter housing 18 in preparation for the cleaning process. In this process, the interior space 25 of the filter housing 18 and, in addition, the interior space of the filter material collection chamber 24, which is open towards this interior space 25, are evacuated (see schematic representation in Figure 7 - arrow e).

[0078] The vacuum pump 41, which can preferably also be part of the filter module 3, can, as is also preferred, be an oil-lubricated vacuum pump, for example, as is known, for example, from DE 10 2015 107 721 A1.

[0079] Any filter material particles extracted during the evacuation, which have neither settled in the filter wall 27 of the filter 26 nor been separated into the filter material collection chamber 24, are collected in the oil tank of the vacuum pump in the case of an oil-lubricated vacuum pump 41 and disposed of with the next usual oil change.

[0080] Additionally or alternatively, a suction line supplied by the vacuum pump 41 can open inside the filter 26 with respect to a flow direction through the filter 26, i.e., in the exemplary embodiment, into an interior space defined by the filter wall 27. In this sense, the suction can therefore take place on a clean side of the filter 26. This ensures that virtually no filter material particles are sucked in.

[0081] After reaching a negative pressure of, for example, 500 mbar down to, for example, 1 mbar in the area of ​​the interior space 25 (detectable via a pressure sensor), the suction process via the vacuum pump 41 is stopped by the control electronics 29, and then a discharge valve 42, located, for example, in the area of ​​the transition line 23 between the filter housing 18 and the filter material collection chamber 24, is closed. The discharge valve 42 interrupts the line connection between the interior of the filter housing 18, which contains the filter 26, and the interior of the filter material collection chamber 24.

[0082] A separate flushing medium reservoir 43, which can also be part of the filter module 3, is used to introduce a flushing medium 45 towards the filter wall 27 via a flushing line 44 to clean the filter 26. The introduction of the flushing medium 45 can be triggered by a preferably electrically actuated control valve 46 (see Figure 8and schematic representation in Figure 9 ). The control valve 46 can be controlled via the control electronics 39.

[0083] As a result of, for example, a plurality of flushing medium inlets 47 and 48 provided around the longitudinal axis x in the housing cover 20, the flushing medium 45 can be introduced, wherein, according to the illustrations, the flushing medium 45 is introduced into the filter interior 34 via the flushing medium inlets 48 in such a way that it presses the filter wall 27 in a direction c opposite to the flow direction of the medium 7 in the usual filter operation (direction d - compare Figure 4 ). In this way, the filter wall 27 is penetrated by the flushing medium 45 from the inner surface 36 towards the outer surface 28.

[0084] At the same time or also offset in time to the above-described flow, the flushing medium 45 is introduced via the radially outer flushing medium inlet 47 essentially along the outer surface 28 of the filter wall 27 (direction f), in order to safely remove the filter material 32, which has been dissolved in particular via the flushing medium portion which penetrates the filter wall 27 from the inside to the outside, from the intake area in the direction of the housing base 21.

[0085] The introduction of the flushing medium 45 can be achieved solely by suction due to the negative pressure prevailing in the interior 25 of the filter housing 18 compared to the environment, but in combination with this, if necessary, also by blowing the flushing medium 45 into the interior 25. The negative pressure in the interior 25 ensures a favorable flow of the flushing medium over and through the filter wall 27.

[0086] At the end of the cleaning process, the same pressure preferably prevails in the interior 25 of the filter housing 18 as in the connected lines (suction line 10 and suction transition line 17), so that when the shut-off valves 37 and 38 are opened, which in this example results in the reintegration of the cleaned filter device into the filtering process, no backflow occurs contrary to the usual flow direction of the process gas 7.

[0087] The same medium that is used as the process gas for removing contaminants in the cabin 4 of the metal printing device 1 is preferably used as the flushing medium 45. Thus, argon and / or nitrogen are preferably used as the flushing medium 45.

[0088] An integrated control system (control electronics 39) monitors the cleaning process and enables various cleaning cycles, in particular with regard to the supplied quantity of flushing medium 45 and further with regard to the opening times of the control valve 46, wherein a separate control valve can be assigned to each of the flushing medium inlets 47 and 48, so that the cleaning process can also be adapted by appropriately controlling the various control valves.

[0089] By evacuating again, a second cleaning process can be carried out immediately after the first cleaning process.

[0090] With the completion of the cleaning process and the associated pressure equalization in the interior 25 of the filter housing 18, a pressure difference arises between the interior 25 and the interior of the filter material collection chamber 24, which, upon opening of the discharge valve 42, causes the filter material 32, which has been released during the cleaning process and preferably collected at the bottom of the housing, to be sucked into the filter material collection chamber 24. Accordingly, simply opening the discharge valve 42 triggers a transfer of the released filter material 32 into the collection chamber (see Figure 10 - Arrow g). The suction process continues until pressure equalization occurs between the interior 25 and the collection chamber 24. In addition, filtered material 32 can also trickle into the collection chamber 24 depending on gravity.

[0091] From this filter material collection according to Figure 10The filter device 2 can be fed back into the filter circuit of the filter module 3 by opening the shut-off valves 37 and 38 in the medium inlet 15 and the medium outlet 16 (cf. Figure 13 ).

[0092] For disposal of the filter material 32 collected in the filter material collection chamber 24, the filter material collection chamber 24 is removable from the filter housing 18. For this purpose, the tubular free end of the transition line 23 can be designed to receive a sleeve section 49 of the collection chamber 24 in a flow-tight manner (see Figures 11 and 12 ). The chamber opening 50 surrounded by the sleeve section 49 is preferably closable by means of a shut-off valve 51. A valve cone 52 directed towards the transition line 23 can be in the docking position of the collecting chamber 24 on the filter housing 18 according to Figure 11be supported on a hold-down device 53 in the area of ​​the transition line 23, so that the shut-off valve 51 is held in a position releasing the chamber opening 50.

[0093] During the removal of the filter material collection chamber 24 from the transition line 23, for example due to unscrewing, the valve cone 52 loses its support on the hold-down device 53 of the transition line 23, as a result of which the shut-off valve 51 automatically falls into a position closing the chamber opening 50 under the action of a compression spring 54 (see Figure 12 ).

[0094] Preferably, the filter material collection chamber 24 is removed with the discharge valve 42 closed, so that when the collection chamber is removed, the atmosphere in the interior 25, essentially formed by the medium 7, is maintained. Furthermore, by blocking off the interior of the filter material collection chamber by the shut-off valve 51, the filter material 32 accommodated therein remains under the process gas atmosphere, correspondingly under an atmosphere formed by the process gas 7 or the flushing medium 45.

[0095] To neutralize the filter material 32 in the filter material collection chamber 24, it is also possible to flood the collection chamber, for example with water or oil.

[0096] The flushing medium 45 and / or the medium 7 can also be used for pneumatic valve actuation, in particular the shut-off valves 37 and 38, and if necessary also the throttle valves 40.

[0097] The subsystem resulting from the filter module 3 can be optimally integrated into the overall control of the metal printing device 1 via electronic interfaces to the electronic control of the metal printing device 1.

[0098] As far as reference is made above to process gas, if the filter device is used in conjunction with another medium to be cleaned, i.e. in particular if it is used in a context other than with a metal printing device, the process gas may be another medium. List of reference symbols 1 Metal printing device 29 Guide wall 2 Filter device 30 frontal surface 3 Filter module 31 Inlet opening 4 cabin 32 Filter material 5 Laser device 33 Outlet opening 6 Tür 34 Filter interior 7 medium 35 Annular space 8 Circulation fan 36 inner surface 9 pressure line 37 shut-off valve 10 suction line 38 shut-off valve 11 Medium cooler 39 Control electronics 12 Pre-separator 40 throttle valve 13 Fine filter 41 vacuum pump 14 Housing 42 Discharge valve 15 Medium inlet 43 Flushing medium storage 16 Medium outlet 44 Flushing line 17 Suction transition line 45 Flushing medium 18 filter housing 46 control valve 19 Housing wall 47 Flushing medium inlet 20 Housing cover 48 Flushing medium inlet 21 Case back 49 socket section 22 Floor opening 50 Chamber opening 23 Transitional line 51 shut-off valve 24 Filter material collection chamber 52 valve cone 25 Interior 53 Hold-down clamp 26 filter 54 compression spring 27 Filter wall 55 inlet 28 exterior surface 56 inlet a Direction b Direction c Direction d Direction e Arrow f Direction g Arrow x Longitudinal axis

Claims

1. A method for intermittently cleaning a filter (26) in a filter device (2), which filter device comprises a filter housing (18) and the filter (26) located therein, wherein the filter housing (18) has a medium inlet (15) and a medium outlet (16) for a medium (7) to be filtered, wherein furthermore the medium (7) flowing through the medium inlet (15) passes through the filter (26) during filter operation and exits the filter device (2) via the medium outlet (16), wherein furthermore for cleaning the filter (2) both the medium inlet (15) and the medium outlet (16) are closed, thereafter a negative pressure is produced in the filter housing (18) and, with the aid of the negative pressure, a flushing medium (45) which acts upon the filter (26) for cleaning is sucked into the filter housing (18), wherein further the filter device (2) has a filtered material collecting chamber (24), characterized in that before sucking the flushing medium (45) into the filter housing (18), the filtered material collecting chamber (24) is closed in order to maintain the negative pressure in the filtered material collecting chamber (24).

2. The method according to claim 1, characterized in that the filter housing (18), in addition to the medium inlet (15) and the medium outlet (16), has a flushing medium inlet (47, 48) that can be shut off.

3. The method for operating a metal printing device (1), which printing device comprises an enclosure (4) in which the metal printing is carried out, wherein the enclosure (4) has an inlet (55) and an outlet (56), and wherein furthermore a fan (8) is provided with which an atmosphere in the enclosure (4) can be regenerated, wherein for regenerating the atmosphere two or more filter devices (2), each having one filter (26), are provided and operated in parallel, wherein for cleaning a filter device (2), this filter device (2) is shut off and removed from regeneration mode according to the method to one of the claims 1 or 2, characterized in that the filter device (2) is operated with a flushing medium (45), and that the removal of one filter device (2) for cleaning the filter (26) in the filter device (2) is accompanied by an increase in the volume flow in the remaining filter device (2), wherein the removal is carried out in a timed manner such that a predetermined limit value with respect to a volume flow increase or volume flow decrease is not exceeded.

4. A filter device (2) for a metal printing device (1) comprising an enclosure (4), in which enclosure (4) the metal printing is carried out, wherein the filter device (2) has a filter housing (18) with a filter (26) located therein for a medium (7) to be filtered in a filter operation of the filter device (2) as well as a medium inlet (15) and a medium outlet (16) for the medium (7) to be filtered, wherein furthermore the filter housing (18), in addition to the medium inlet (15) and the medium outlet (16), has a flushing medium inlet (47, 48) that can be shut off for introducing a flushing medium (45) into the interior (25) of the filter housing (18) in cleaning operation, characterized in that the filter device (2) has a filtered material collecting chamber (24) assigned to the filter housing (18), and in that the filtered material collecting chamber (24) is removable from the filter housing (18).

5. The filter device according to claim 4, characterized in that the medium inlet (15) and the medium outlet (16) are each assigned a shutoff valve (37, 38), wherein the shutoff valve (37, 38) is preferably a pneumatic valve.

6. The filter device according to claim 5, characterized in that the pneumatic valves are operable by using the flushing medium (45).

7. The filter device according to one of the claims 4 to 6, characterized in that a shutoff valve (51) is provided for closing the filtered material collecting chamber (24), wherein upon removal of the filtered material collecting chamber (24) from the filter housing (18), the shutoff valve (51) is preferably displaced in a spring-supported manner into a closed position.

8. The filter device according to one of the claims 4 to 7, characterized in that the flushing medium inlet (47, 48) is formed such that for cleaning the filter (26) in a cleaning operation of the filter device (2), the flushing medium (45) flows in a direction (c) opposite to the filter operation, wherein, preferably, the flushing medium inlet (47, 48) is directed such that for cleaning the filter (26) in cleaning operation, the flushing medium (45) flows onto a side of the filter wall (27) representing an outer surface (28) of a filter wall (27) in filter operation.

9. The filter device according to one of the claims 4 to 8, characterized in that after pressure equalization in the filter housing (18) by the inflowing flushing medium (45), an access to the filtered material collecting chamber (24) can be opened for feeding filtered material (32) into the filtered material collecting chamber (24), wherein, preferably, feeding the filtered material (32) into the filtered material collecting chamber (24) is carried out by suction.

10. The filter device according to one of the claims 4 to 9, characterized in that a preferably controllable throttle valve (40) is arranged in the medium outlet (16).

11. The filter device according to one of the claims 4 to 10, characterized in that two flushing medium inlets (47, 48) are provided, one of which causes flushing medium (45) to pass through the filter wall (27) in a direction (c) opposite to filter operation, and one of which causes the flushing medium (45) to be directed onto the outer surface (28) of the filter wall (27), wherein, preferably, each flushing medium inlet (47, 48) is assigned a control valve (46) and / or the control valve (46) is electrically operable.

12. The filter device according to one of the claims 4 to 11, characterized in that two or more filter devices (2) each having one filter (26) are provided, wherein, preferably, the two or more filter devices (2) are operable in parallel and / or for cleaning a filter device (2), this filter device (2) can be shut off, wherein, preferably, the shut-off filter device (2) is removable from the regeneration mode and operable with the flushing medium (45) for cleaning the filter (26) and / or a separate flushing medium reservoir (43) is assigned to the filter device (2) or the multiple filter devices (2).

13. The filter device according to one of the claims 4 to 12, characterized in that a pre-separator (12) is connected upstream of the filter device (2) as viewed in the flow direction of the medium (7) to be cleaned.

14. The filter device according to one of the claims 4 to 13, characterized in that a micro filter (13) is connected downstream of the filter device (2) as viewed in the flow direction of the medium (7) to be cleaned.

15. The filter device according to one of the claims 4 to 14, characterized in that a flow of the medium (7) to be filtered is achievable by a fan (8), wherein, preferably, a medium cooler (11) is provided downstream of the fan (8) in the direction of flow.