METHOD OF TREATING A GAS STREAM AND METHOD OF OPERATING AN APPARATUS FOR PRODUCING A THREE-DIMENSIONAL WORK PIECE

Abstract

In a method of treating a gas stream (32) containing combustible and/or reactive particles (34) at least a part of the particles (34) contained in the gas stream (32) is separated from the gas stream (32) by means of a separation device (36). The particles (34) separated from the gas stream (32) by means of the separation device (36) are supplied to a collecting vessel (40). The supply of particles (34) to the collecting vessel (40) is interrupted. A flame retardant material (57) is supplied to the collecting vessel (40) so as to form a cover layer of flame retardant material (57) on the particles (34) contained in the collecting vessel (40).

Claims

1-15. (canceled)

16. A method of treating a gas stream containing combustible and/or reactive particles, the method comprising: separating at least a part of the particles contained in the gas stream from the gas stream by means of a separation device, wherein the separation device comprises a filter for filtering the particles from the gas stream which is directed through the filter, the filter being coated with a flame retardant material in order to prevent undesired reactions of the particles within the separation device; supplying the particles separated from the gas stream by means of the filter of the separation device to a collecting vessel; interrupting the supply of particles to the collecting vessel; and supplying a flame retardant material to the collecting vessel so as to form a cover layer of flame retardant material on the particles contained in the collecting vessel.

17. The method according to claim 16, further comprising: after supplying the flame retardant material to the collecting vessel, replacing the collecting vessel by a replacement collecting vessel.

18. The method according to claim 16, wherein the supply of particles to the collecting vessel is interrupted at least when the filling level of the collecting vessel has reached a first predetermined value.

19. The method according to claim 18, wherein the filling level of the collecting vessel is determined by means of at least one filling level sensor and/or a scale.

20. The method according to claim 16, further comprising: during the interruption of the supply of particles to the collecting vessel, continuing separating at least a part of the particles contained in the gas stream from the gas stream by means of the separation device; and temporarily storing the particles separated from the gas stream in an interim storage volume.

21. The method according to claim 20, wherein the interim storage volume is provided in the separation device.

22. The method according to claim 16, wherein the filter of the separation device is coated with the flame retardant material by spraying the flame retardant material onto the filter, in particular wherein the flame retardant material, for coating the filter (38) of the separation device, is introduced into the gas stream supplied to the separation device at a position upstream of the separation device.

23. The method according to claim 16, wherein at least a part of the flame retardant material contained in the separation device is discharged from the separation device and supplied to the collecting vessel upon cleaning a filter of the separation device.

24. The method according to claim 16, further comprising the step of: monitoring an operational state of the separation device by comparing an amount of flame retardant material contained in the separation device with an amount of flame retardant material discharged from the separation device upon cleaning a filter of the separation device.

25. The method according to claim 16, further comprising the step of: determining an amount of particles separated from the gas stream by means of the separation device and supplied to the collecting vessel.

26. The method according to claim 16, further comprising the steps of: interrupting the supply of particles to the collecting vessel when the filling level of the collecting vessel has reached a second predetermined value, the second predetermined value being smaller than the first predetermined value; supplying a flame retardant material to the collecting vessel so as to form an intermediate layer of flame retardant material on the particles contained in the collecting vessel; and after forming the intermediate layer of flame retardant material, resuming the supply of particles separated from the gas stream by means of the separation device to the collecting vessel.

27. A method of operating an apparatus for producing a three-dimensional work piece by irradiating layers of a raw material powder with electromagnetic or particle radiation, the method comprising: supplying a gas stream to a process chamber of the apparatus; directing the gas stream through the process chamber, wherein the gas stream, while being directed through the process chamber takes up combustible and/or reactive particles; discharging the gas stream containing the combustible and/or reactive particles from the process chamber; and treating the gas stream containing the combustible and/or reactive particles in accordance with the method as defined in claim 16.

28. The method according to claim 27, further comprising: after treating the gas stream containing the combustible and/or reactive particles, recirculating a purified gas stream exiting the separation device separating at least a part of the particles contained in the gas stream from the gas stream to the process chamber.

29. The method according to claim 27, wherein the supply of particles to the collecting vessel is interrupted upon completion of the production of the three dimensional workpiece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows an apparatus for producing a three-dimensional work piece by irradiating layers of a raw material powder with electromagnetic or particle radiation which is equipped with gas circuit for directing the gas stream through a process chamber of the apparatus, and

[0039] FIG. 2 shows a detailed view of a separation device disposed in the gas circuit of the apparatus according to FIG. 1.

DETAILLED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] FIG. 1 shows an apparatus 10 for producing a three-dimensional work piece by an additive layering process. The apparatus comprises a process chamber 12 accommodating carrier 14 and a powder application device 16 for applying a raw material powder onto the carrier 14. The process chamber 12 is sealable against the ambient atmosphere, i.e. the environment surrounding the process chamber 12. The apparatus 10 further comprises an irradiation device 18 for selectively irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier 14.

[0041] A gas circuit 20 is provided so as to establish a controlled gas atmosphere within the process chamber 12. The gas circuit 20 contains a gas source 22. The gas source 22 in particular is designed in the form of an inert gas source, for example in the form of an argon or nitrogen source. The process chamber 12 comprises a gas inlet 24 for supplying gas to the process chamber 12. A gas outlet 26 serves to discharge gas from the process chamber 12. A circulation line 28 connects the gas outlet 26 to the gas inlet 24. Further, the circulation line 28 is connected to the gas source 22. A conveying device 30 serves to convey the gas stream through the circulation line 28.

[0042] Upon being directed through the process chamber 12, a gas stream 32 supplied to the process chamber 12 via the gas inlet 24 takes up combustible and/or reactive particles 34, such as raw material powder particles, welding smoke and/or soot particles. The gas/particle mixture exiting the process chamber 12 via the gas outlet 26 therefore is treated before being recirculated to the process chamber 12 via the circulation line 28 and the gas inlet 24. In particular, the particles 34 contained in the gas stream 32 are separated from the gas stream 32 by means of separation device 36 which is disposed in the circulation line 28 upstream of the conveying device 30. The purified gas stream 32 exiting the separation device 36 is recirculated to the process chamber 12 via the circulation line 28 and the gas inlet 24.

[0043] A detailed view of the separation device 36 is shown in FIG. 2. In the embodiment shown in the drawings, the separation device 36 comprises a filter 38 for filtering the particles 34 from the gas stream 32. It is, however, also conceivable that the separation device 36 comprises a plurality of filters and/or one or more cyclone(s). In order to prevent an undesired (oxidation) reaction of the particles contained in the gas stream 32 which is directed through the filter 38, the filter 38 is coated with a flame retardant material 57. For example, the filter 38 is coated with a flame retardant material 57 with extinguishing effects as schematically indicated in FIG. 2.

[0044] The separation device 36 is connected to a collecting vessel 40 via a connecting line 42. The collecting vessel 40 serves to accommodate the particulate material 34 that is trapped in the filter 38 of the separation device 36 when the gas stream 32 is directed through the filter 38 and that is removed from the filter 38 upon continuously or periodically cleaning the filter 38, for example by inducing a vibrational motion of the filter 38. Within the collecting vessel 40, a base layer of flame retardant material 57 is provided. The flame retardant material 57 again is a flame retardant material with extinguishing effects.

[0045] The supply of particles 34 from the separation device 36 to the collecting vessel 40 is controlled by means of a valve 44 which is disposed in the connecting line 42. Operation of the valve 44 is controlled by means of an electronic control unit 46. It is, however, also conceivable that the valve 44 is designed in the form of a manually controllable valve. A filling level of the collecting vessel 40 is controlled by means of a filling level sensor 48 and a scale 50. The scale 50 is designed in the form of three-point scale. Signals that are output by the filling level sensor 48 and the scale 50 are transmitted to the electronic control unit 46.

[0046] Finally, a flame retardant material source 52 is provided. In the embodiment shown in the drawings, the flame retardant material source 52 comprises a bag 54 which contains a flame retardant material 57 and which is disposed within the collecting vessel 40. The bag 54 is attached to a cover of the collecting vessel 40 and may be punctured by means of a suitable device (not shown) so as to discharge a fixed amount of flame retardant material 57, i.e. the content of the bag 54, from the bag 54 into the interior of the collecting vessel 40. It is, however, also conceivable to equip the flame retardant material source with a further valve 56 which allows a controlled supply of flame retardant material 57 from the flame retardant material source 52 to the collecting vessel 40.

[0047] For coating the filter 38 with the flame retardant material 57, a further flame retardant material source 59 is connected to the circulation line 28 at a position upstream of the separation device 36. The supply of flame retardant material 57 from the flame retardant material source 59 to the circulation line 28 and thus into the gas stream 32 supplied to the separation device 36 via the circulation line 28 is controlled by a control valve 60. In case the filter 38 should be coated with a flame retardant material 57, the control valve 60 is opened and hence flame retardant material 57 is introduced into the gas stream 32. The flame retardant material 57 is entrained with the gas stream 32 and sprayed onto the filter 38.

[0048] In the preferred embodiment described herein, the flame retardant material 57 consists of a foamed glass which contains particles having a particle size in the range from 30 .Math.m to 1 mm, in particular in the range from 60 .Math.m to 500 .Math.m and preferably in the range from 100 .Math.m to 300 .Math.m. A bulk density of the flame retardant material 57 is in the range from 50 kg/m.sup.3 to 1000 kg/m.sup.3, preferably in the range from 100 kg/m.sup.3 to 700 kg/m.sup.3. A softening and/or melting temperature of the flame retardant material 57 is in the range from 350° C. to 1200° C., in particular in the range from 500° C. to 1000° C.

[0049] In a method of treating a gas stream, the particles 34 that are separated from the gas stream 32 by means of the separation device 36 are supplied to the collecting vessel 40. The supply of particles 34 to the collecting vessel 40 may happen under the control of the control unit 46 and may be started by opening the valve 44. The particles 34 may be supplied to the collecting vessel 40 either continuously or periodically, while the filling level of the collecting vessel 40 is continuously monitored by means of the filling level sensor 48 and the scale 50.

[0050] The supply of particles 34 to the collecting vessel 40 may be interrupted as required at any time, e.g. upon completion of the production of the three dimensional workpiece. However, at least when the filling level of the collecting vessel 40 with particles 34 has reached a first predetermined value that is determined by means of the filling level sensor 48 and the scale 50, the supply of particles 34 to the collecting vessel 40 is interrupted. In particular, the interaction of the supply of particles 34 to the collecting vessel 40 is achieved by closing the valve 44 under the control of the control unit 46 in response to the signals transmitted to the control unit 46 from the filling level sensor 48 and the scale 50.

[0051] Thereafter, flame retardant material 57 is supplied to the collecting vessel 40 so as to form a cover layer of flame retardant material 57 on the particles 34 contained in the collecting vessel 40. The flame retardant material 57 is introduced from the flame retardant material source 52 into the collecting vessel 40 by opening the further valve 56 so as to allow the supply of flame retardant material 57 from the bag 54 to the collecting vessel 40. When the cover layer of flame retardant material 57 in the collecting vessel 40 has reached a desired thickness and a desired volume ratio of flame retardant material 57 to combustible and/or reactive particles of e.g. 5:1 is reached in the collecting vessel 40, the supply of flame retardant material 57 to the collecting vessel 40 is interrupted by closing the further valve 56. The supply of flame retardant material 57 to the collecting vessel 40 so as to form the desired cover layer is controlled by means of the control unit 46 in dependence on signals which are indicative of the filling level of the collecting vessel 40 and which are provided to the control unit 46 from the filling level sensor 48 and the scale 50.

[0052] The cover layer prevents an uncontrolled (oxidation) reaction of the particles 34 when the collecting vessel 40, in a next step, is detached from the connecting line 42 and, due to its disconnection from the inert gas circuit 20, exposed to the ambient atmosphere or when there is a leakage in the system. The full collecting vessel 40 then is replaced by a replacement collecting vessel 40a. Specifically, the replacement collecting vessel 40a is connected to the connecting line 42 in place of the collecting vessel 40. After being disconnected from the connecting line 42, the full collecting vessel 40 may be closed by means of a cover (not shown).

[0053] In case the particles 34 contained in the gas stream 32 are highly combustible and/or reactive, the method may comprise the further optional steps of interrupting the supply of particles 34 to the collecting vessel 40 when the filling level of the collecting vessel 40 has reached a second predetermined value that is smaller than the first predetermined value. For example, the supply of particles 34 to the collecting vessel 40 may already be interrupted when the collecting vessel 40 is only filled to about 50%. Flame retardant material 57 may then be supplied to the collecting vessel 40 so as to form an intermediate layer of flame retardant material 57 on the particles 34 contained in the collecting vessel 40. After forming the intermediate layer of flame retardant material 57, the supply of particles 34 which are separated from the gas stream 32 by means of the separation device 36 may be resumed.

[0054] During the interruption of the supply of particles 34 to the collecting vessel 40, the flow of the particle loaded gas stream through the separation device 36 and the operation of the separation device 36 are continued. Thus, even during the interruption of the supply of particles 34 to the collecting vessel 40, the separation device 36 continues separating particles 34 from the gas stream 32. These particles 34 are temporarily stored in an interim storage volume 58 which may be provided in the interior of the separation device 36 as shown in the drawing or which may be provided in a separate container. In particular, the particles 34 that are separated from the gas stream 32 during the interruption of the supply of particles 34 to the collecting vessel 40 maintain in the filter 38 of the separation device 36. Hence, continuous operation of the apparatus 10 is made possible.

[0055] Upon periodically cleaning the filter 38 of the separation device 36, for example by a “back-flush” method or a vibrational motion, at least a part of the flame retardant material 57 contained in the separation device 36, i.e. at least a part of the flame retardant material 57 coated onto the filter 38 of the separation device 36 is removed from the filter 38. Consequently, the combustible and/or reactive particles 34 that are removed from the filter 38 upon cleaning the filter 38, are immediately diluted and/or covered with flame retardant material 57.

[0056] After being removed from the filter 38, the combustible and/or reactive particles 34 together with the flame retardant material 57 may immediately be supplied to the collecting vessel 40. It is, however, also conceivable to temporarily store the particulate material 34 and/or the flame retardant material 57 in the interim storage volume 58 of the separation device 36 before finally supplying it to the collecting vessel 40. Within the collecting vessel 40, the flame retardant material 57 which is removed from the filter 38 upon cleaning the filter 38 and which may be mixed with a certain amount of combustible and/or reactive particles 34, may form an intermediate layer or at least a part of the cover layer on the particles 34 already contained in the collecting vessel 40.

[0057] After discharging at least a part of the flame retardant material 57 contained in the separation device 36 from the separation device 36, the separation device 36 is again supplied with flame retardant material 57 from the further flame retardant material source 59. In particular, after cleaning the filter 38, the filter 38 is recoated with flame retardant material 57 by opening the control valve 60 and by supplying flame retardant material 57 from the further flame retardant material source 59 into the gas stream 32 as described above.

[0058] Prior to starting operation of the separation device 36, after completing operation of the separation device 36 or during interruptions of the operation of the separation device 36, a specific operational state test may be performed in order to determine the operational state of the separation device 36 and in particular the operational state of the coating of flame retardant material 57 applied onto the filter 38 of the separation device 36. This operational state test involves a comparison of an amount of flame retardant material 57 contained in the separation device 36 with an amount of flame retardant material 57 discharged from the separation device 36 upon cleaning the filter 38 of the separation device 36.

[0059] In a first step, a defined amount of flame retardant material 57 is supplied to the separation device 36 and coated onto the filter 38 of the separation device 36, for example as described above. In a second step, the flame retardant material 57 is removed from the separation device 36 by cleaning the filter 38 without previously using the filter 38 for filtering particulate material. The flame retardant material 57 removed from the separation device 36 is supplied to the collecting vessel 40 and the amount of flame retardant material 57 supplied to the collecting vessel 40 is determined by means of the filling level sensor 48 and/or the scale 50. The amount of flame retardant material 57 supplied to the collecting vessel 40 then is compared to the amount of flame retardant material 57 supplied to the separation device 36.

[0060] In case it is desired to monitor the operational state of the separation device 36 and in particular the operational state of the coating of flame retardant material 57 applied onto the filter 38 of the separation device 36 during normal operation of the separation device 36, it is also possible to compare a defined amount of flame retardant material 57 supplied to the separation device 36 and coated onto the filter 38 of the separation device 36 with an estimated or calculated amount of flame retardant material 57 which is removed from the separation device 36 and supplied to the collecting vessel 40 by cleaning the filter 38 during normal operation of the separation device 36.

[0061] In case the amount of particulate material 34 supplied to the collecting vessel 40 during operation of the separation device 36 including cleaning the filter 38 is known, the amount of flame retardant material 57 supplied to the collecting vessel 40 upon cleaning the filter 38 may be calculated. In case, however, the amount of particulate material 34 is not known, the amount of flame retardant material 57 supplied to the collecting vessel 40 still can be estimated based on the data provided by the filling level sensor 48 and/or the scale 50 and an estimated amount of particles 34 supplied to the collecting vessel 40 during operation of the separation device 36 including cleaning the filter 38.

[0062] Alternatively or additionally thereto, it is also possible to determine an amount of particles 34 separated from the gas stream 32 by means of the separation device 36 and supplied to the collecting vessel 40. For example, a volume and/or a mass of the content of the collecting vessel 40 may be determined by means of the filling level sensor 48 and/or the scale 50 and the amount of particles 34 may be calculated by substracting the known volume and/or mass of flame retardant material 57 supplied to the collecting vessel 40 from the overall value provided by the filling level sensor 48 and/or the scale 50.