METHOD FOR PRODUCING PRESSURE VESSELS

Abstract

The invention relates to a method for producing pressure vessels, including pressure accumulators, such as hydraulic accumulators and parts thereof (24), characterized in that they are at least partially produced by means of a 3D printing method.

Claims

1. A method for producing pressure vessels (12), including pressure accumulators, such as hydraulic accumulators (22, 52, 60) and parts thereof (30), characterized in that they are at least partially produced using a 3D printing method.

2. The method according to claim 1, characterized in that the housing wall of at least one housing part (24, 40) of the pressure vessel (12) or pressure accumulator (22, 52, 60) is produced using 3D printing as a printing method.

3. The method according to claim 1, characterized in that in chronological order firstly a housing part (24, 40) is produced using 3D printing and then a separating element (30) is introduced into the printed housing part (24, 40).

4. The method according to claim 1, characterized in that, with formation of the overall housing (10), the housing part (24, 40) with the separating element (30) is connected to a conventionally produced housing part or in that the overall housing (10) is produced by means of 3D printing.

5. The method according to claim 1, characterized in that when creating the respective housing wall (10) or the parts thereof (26) the fluid connection points (16) are also created by means of 3D printing.

6. The method according to claim 1, characterized in that the parts of hydraulic accumulators in the form of separating elements, such as a membrane (32), a piston (54) or an accumulator bladder are likewise produced using 3D printing.

7. The method according to claim 1, characterized in that at least the inner wall surfaces of a part of the housing parts (24, 40) produced using 3D printing are mechanically, thermally or chemically retreated.

8. The method according to claim 1, characterized in that as materials for the 3D printing plastics and/or metals are used.

9. The method according to claim 1, characterized in that to obtain a membrane accumulator (22) firstly a shell-like housing part (24) is creating using 3D printing, then as the separating element (30) the membrane (32) is inserted with a fastening ring (39) and subsequently the shell-like housing part (24) is provided with another preferably shell-like housing part (40) as a closure.

10. The method according to claim 1, characterized in that to obtain a piston accumulator (52) after introduction of the piston (54) into the one housing part (40) produced using 3D printing, said housing part is closed by means of a plug-like closure part (56) for the purpose of reworking the inner wall of this housing part (40) and in that the one housing part (40) is provided with another housing part (24) as a closure of the accumulator housing (10) and the closure part (56) is destroyed.

Description

[0014] The method for producing pressure vessels according to the invention is explained in detail below with reference to several exemplary embodiments according to the drawings. Said drawings show, in schematic and not to scale depictions:

[0015] FIGS. 1 and 2 once in a sectional depiction and once in a top view, an exemplary embodiment of a pressure vessel in the form of an air chamber or Helmholtz resonator;

[0016] FIGS. 3, 4 and 5 in a sectional representation individual production steps relating to a diagram accumulator as a subset of a pressure vessel;

[0017] FIGS. 6 and 7 in the form of a longitudinal sectional depiction different production stages for a piston accumulator as an additional subset of a pressure vessel; and

[0018] FIG. 8 in a longitudinal sectional depiction the accumulator housing of an additional pressure vessel in the form of a bladder accumulator.

[0019] As 3D printing methods for the production of pressure vessels as well as the parts thereof options which are in principle suitable include sinter- and powder printing methods, stereolithography and printing with liquid components. All of the above 3D-printing methods are also frequently used in rapid prototyping.

[0020] When objects, such as accumulator housings, are to be constructed exclusively from metal, the so-called electron beam melting has proven to be suitable as a 3D printing method. In electron beam melting metal powder is melted in layers and ablated as a housing wall. Selective laser melting is also suitable, in which a metal powder is melted in a local manner only. Another possibility is the use of selective laser sintering, in which a metal powder is briefly heated with a laser which melts it, and this then solidifies with formation of the metallic accumulator housing. All of the above-mentioned 3D printing methods fall into the category of sinter- and powder printing methods.

[0021] If the pressure vessel is to be printed using plastic materials, printing with liquid plastic materials is an option. In particular multi-jet modeling has proven to be successful, the essential structure of which is very like conventional inkjet printing. In this 3D printing method liquid plastic material is applied from a nozzle, which can preferably move in several directions, and as soon as the material is discharged from the nozzle in a forming manner, it is appropriately hardened under an energy source, for example in the form of UV light.

[0022] With the multi-jet modeling plastic materials in droplet form with dimensions of a few picoliters are discharged, with the spraying of the droplets taking place preferably in a computer-controlled manner with a high clock frequency for example of 2 kHz. Liquefied acrylates have proven to be particularly suitable plastic materials, the viscosity of which can be adjusted to a desired extent by addition of a reactive thinner. By means of the addition of a photoinitiator, the hardenability with UV radiation is preferably promoted. In an example of a housing material, the plastic material contains as acrylate material 90% Ebecryl 4835, a prepolymer produced by the company UCB, 8% HDDA (company UCB) as reactive thinner for viscosity adjustment and 2% Darocur 1173, produced by the company Ciba-Geigy, as photoinitiator.

[0023] In another example, as housing material acrylate materials 90% Ebecryl 4835 and 4% Ebecryl 230 by the company UCB are envisaged. As reactive thinners it contains 4% HDDA by the company UCB and as photoinitiator 2% Darocur 1173 by the company Ciba-Geigy.

[0024] With the above specified plastic materials or other suitable plastic materials accumulator housings can be constructed using the 3D printing method, as presented for example for a pressure vessel 12 in the form of an air chamber or Helmholtz resonator for pulsation damping of fluids according to the depictions in FIGS. 1 and 2. Integrally attached to the accumulator housing 10 at the bottom end is a fluid connection point 14 with special connection geometry for the purpose of connection of the pressure vessel 12 in a conventional manner to a fluid supply circuit, in particular a gas supply circuit. The accumulator housing 10 essentially forms a spherical cross section, into which the fluid connection point 14 enters via a central channel 16 in a media-conducting manner. The accumulator housing 10 has an essentially constant wall diameter, but it is provided in the center with a corresponding annular reinforcement 18 in the equatorial region. Such pressure vessels 12 can also be printed using a metal powder and are then entirely pressure resistant up to 350 bar in this embodiment, with regular operating- or working temperatures of 40 C. to 150 C.

[0025] Viewed in the viewing direction of FIGS. 1 and 2, the 3D printing material construction begins either from the bottom end, in other words, beginning at the free end of the fluid connection point 14 or at the top closure side 20 of the pressure vessel 12. With only one 3D printing production device such a pressure vessel 12 can be produced in all sizes, also with changed cross section shapes (oval, polygonal etc.) and different connection points (not depicted). With the same production device, the other accumulator geometries can then also be printed according to the depictions of FIGS. 3ff. In addition, the pressure vessel 12 depicted in FIGS. 1 and 2 can, in particular when it is printed from plastic materials, be provided with additional reinforcement even for applications in the high-pressure range, for example, a support laminate could be applied to its outside, which is not depicted in detail, or the outside of the printed pressure vessel 12 could be provided with surrounding bands, for example made of carbon materials.

[0026] In the following exemplary embodiments, the same components as specified above are provided with the same reference numerals. The exemplary embodiment depicted in FIGS. 3 to 5 relates to individual production steps for production of a membrane accumulator 22, as is depicted in FIG. 5 in a longitudinal section depiction. Firstly according to the depiction of FIG. 3 in a first working step or production step the bottom housing part 24 is produced using the 3D printing method. This housing part 24 is formed as a shell and once again has on its bottom side a fluid connection point 14 with a media-conducting channel 16. Facing in the direction of the channel 16 at the bottom end of the fluid connection point 14 a thread 26 is subsequently introduced into same at the inner circumference by means of machining. This thread 26 in turn serves to connect the accumulator housing 10 with the bottom housing part 24 to a fluid circuit, in particular a hydraulic circuit, which is not depicted in detail. In the top region of the bottom housing part 24 a circumferential annular groove 28 is introduced, which serves for subsequent introduction of a separating element 30 in the form of a shell-like separating membrane 32.

[0027] The production of the bottom housing part 24 in the 3D printing method takes place by means of an application nozzle 34, which with a high clock frequency, for example 2 kHz, discharges the plastic material in the picoliter range for the purpose of production of the bottom housing part 24. Viewed in the viewing direction of FIG. 3, for the completion of the multi-jet modeling device two UV lamps 36 are provided, which appropriately harden the sprayed on plastic material. The machine unit consisting of the application nozzle 34 and UV lamps 36 can be freely moved in all three spatial axes by means of an adjustment device which is not depicted in detail. In the present depicted case the printing method is commenced with layered application with the fluid connection point 14 and ends as depicted at the top edge 38 of the bottom housing part 24.

[0028] As FIG. 4 then shows, the separating membrane 32 is introduced with an fastening ring 39 in the bottom housing part 24 and an edge reinforcement 41 of the separating membrane 32 provided at the top edge engages in a fixing manner in the annular groove 28 of the bottom housing part 24. As the depiction of FIGS. 4 and 5 additionally shows, a valve disk 43 is introduced at the bottom end of the separating membrane 32, which can close the fluid channel or media channel 16 in the direction of the accumulator housing interior. To this extent the separating membrane 32 is formed elastically flexible; a design structure which is common in such membrane accumulators 22 and which has proven to be successful. The fastening ring 39 is formed spring-elastic flexible and presses with its open profile form or cross section form the edge reinforcement 41 in the direction of the annular groove or receiving groove 28 in the accumulator housing 10.

[0029] It is conceivable to produce the separating membrane 32 for example from a media-resistant material, such as polytetrafluorethylene, likewise using the 3D printing method, in order to then in turn fix it with the fastening ring 39, which may also be produced using the 3D printing method, in the bottom housing part 24. In a further embodiment it is also conceivable to form in a direct manner in the 3D printing method the separating membrane 32 directly on the bottom housing part 24 but without a fastening ring 39. The entire accumulator in the form of the membrane accumulator 22 could thus be produced with only one production machine in the 3D printing method. With such a precisely functioning 3D printing method there is also the possibility to generate the thread 26 on the fluid connection point 14 by means of the printing method itself. Another suitable material for producing a separating element, such as for example a separating membrane 32, is thermoplastic polyurethane (TPU), which can be worked using a 3D printing method.

[0030] If the intermediate production step according to FIG. 4 is achieved, the membrane accumulator 22 is then completed by means of the 3D printing method, in that the top housing part 40 is then printed following the bottom housing part 24. At the top closure side 20 of the accumulator housing 10 a passage point 42 is then subsequently introduced mechanically or is released in the printing method, which is closed with a plug 44, which can likewise be printed. In this way it is possible to introduce on the gas side 46 of the accumulator 22 an energy store, for example in the form of a working gas such as nitrogen gas, and to store it there. The separating element 30 in the form of the separating membrane 32 then separates this gas side 46 from the fluid side, in particular the hydraulic side 48, of the accumulator 22.

[0031] It is however also possible to produce either the bottom housing part 24 or the top housing part 40 in a conventional manner, for example by means of a casting method and to construct only the respective other housing part 40 or 24 using the 3D printing method from plastic or metal materials. The housing parts 24 and 40 can, even when they are produced using the 3D printing method, be produced separately and can then be connected to one another for example at a separating point 50 extending along the top edge 38 by means of a welding connection or adhesive connection. The accumulator construction can thus be adapted across a broad range to practical conditions even in situ.

[0032] The following FIGS. 6 and 7 now show the formation of a piston accumulator 52 using the 3D printing method. Firstly, in a first production step according to the depiction of FIG. 6 the top housing part 40 is printed, for example by means of the already described 3D printing method. The top housing part 40 is formed closed at its top closure side and has essentially the same wall thickness. The separating element 30, this time in the form of a separating piston 54, is then introduced into the top housing part 40. The conventional sealing- and guiding systems for the separating piston 54 are omitted for the sake of simplicity. The separating piston 54 can likewise be produced in a 3D printing method. The accumulator housing 10 can thus be printed from a metal material and the separating piston 54 from a plastic material for weight reasons.

[0033] According to the depiction of FIG. 6, beneath the separating piston 54 by means of a plate-like closure part 56 the free access to the separating piston 54 can then be sealed in a hermetically sealing manner. In this usage state of the closure part 56 there is then the possibility of an inner wall processing for the top housing part 40. In this way, impurities in the 3D printing can be eliminated mechanically (machining), thermally or chemically, without contaminant particles also affecting the sealing- and guiding systems of the separating piston 54 which are not depicted in detail. The running surface of the separating piston 54 can also be mechanically reworked before the introduction into the accumulator housing 10 or the housing part 40.

[0034] Because the closure part 56 in its position in the top housing part 40 according to FIG. 6 can only be moved aside with difficulty, firstly the accumulator housing 10 can also be finished printed, i.e., the bottom housing part 24 with the fluid connection point 14 together with the channel 16 and thread 26 is subsequently produced by means of 3D printing and thus connects in an integral manner to the housing wall structure of the top housing part 40. Because the plug-like closure part 56 would then impair the movement of the separating piston 54, the closure part 56 in the closed accumulator housing 10 according to FIG. 7 is thermally or chemically destroyed, and the remains of the closure part 56 can be carried off via the fluid connection point 14 from the fluid side of the piston accumulator 52 towards the outside, before the piston accumulator 52 is in turn connected for a viable use to a hydraulic network or the like. In order to increase the volume on the gas side 46 of the piston accumulator 52, the separating piston 54 has a recess 58. Furthermore, for the introduction of the working gas on the gas side 46, the accumulator housing 10 is in turn equipped on the top closure side 20 with a passage point 42 in the form of a bore.

[0035] In the last embodiment of a pressure vessel 12, FIG. 8 depicts the accumulator housing 10 of a bladder accumulator 60, with the accumulator housing 10 here again being produced as a whole in the 3D printing method. The accumulator housing 10 has at its bottom end a fluid connection point 14 with a channel cross section 16 of large enough dimensions that it is subsequently possible to insert into the thus created vessel a membrane or accumulator bladder, which is not depicted in detail, as a separating element 30. Here too, variants are conceivable in which the accumulator bladder which is not depicted in detail is an integral and non-exchangeable element of the overall bladder accumulator. At the top closure side 20 of the accumulator housing a passage point 42 is again arranged, by means of which the gas side of the accumulator bladder can be appropriately filled.

[0036] The accumulator housing 10 according to the depiction of FIG. 8 can also be a liner, which can be wrapped in a fiber fabric (not depicted) as a complimentary and reinforcing measure. It is also possible to produce as a separating element (30) for a bellows accumulator which is not depicted in detail a bellows membrane using 3D printing, which can also be produced from metal.