A method and a mold for manufacturing an impeller

Abstract

A method for manufacturing an impeller is provided The method includes providing a mold comprising a core, wherein the core has within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line, and fiber elements arranged on the core; and feeding matrix material into a space defined at least by the core by creating an underpressure over the vacuum line network. A core having within it a vacuum line network comprising a plurality of branched interconnected vacuum lines is also provided, as well as a mold comprising said core.

Description

[0001] A METHOD AND A MOLD FOR MANUFACTURING AN IMPELLER

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to methods for making composite material impellers. The disclosure relates particularly, though not exclusively, to vacuum assisted methods for making composite material impellers and molds usable in said methods.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] Composite material impellers are advantageous in that they are durable and light compared for example to metal impellers. Conventionally, composite material impellers are manufactured by manufacturing separately blades and other parts of the impeller which are then assembled and joined together. However, the joints or seams between the assembled parts form weak spots in the structure. Also, these methods are labor intensive and time consuming.

[0007] Conventional methods of manufacturing composite material impellers typically also require a cast or a sealed mold. In manufacturing of small series of products or even one-off impellers, making a cast for each impeller model is time and resource consuming.

[0008] There is hence a need for an improved method for making high quality composite impellers.

[0009] SUMMARY

[0010] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as examples useful for understanding the invention.

[0011] An aim is to provide an improved method for making a high-quality composite material impeller or at least to provide an alternative to existing technology. Especially, an aim is to provide an improved method for making a large-scale composite material impeller of high quality. According to a first example aspect there is provided a method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line, and fiber elements arranged on the core; and feeding matrix material into a space defined at least by the core by creating an underpressure over the vacuum line network.

[0012] In certain embodiments, the plurality of branched interconnected vacuum lines comprises branched vacuum lines at different heights within the core.

[0013] In certain embodiments, the core is at least partially formed of more than one layers having a respective thickness, and the plurality of branched interconnected vacuum lines are formed by cavities in the layers. In certain embodiments, said layers are stacked on top of each other.

[0014] In certain embodiments, the vacuum line network has a plurality of openings in the surface of the core.

[0015] In certain embodiments, the feeding of matrix material is carried out without applying above- atmospheric pressure.

[0016] In certain embodiments, the mold is a non-sealed mold.

[0017] In certain embodiments, the matrix material is fed to the space defined at least by the core through one or more feed lines at least partially within the core. In certain embodiments, the matrix material is fed to the space defined at least by the core through a feed line network comprising a plurality of branched interconnected feed lines arranged within the core.

[0018] In certain embodiments, a diameter of the one or more feed lines at least partially within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core. In certain embodiments, a diameter of the plurality of branched interconnected feed lines within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core.

[0019] In certain embodiments, providing the mold comprises: providing the core, and laying up the fiber elements on the core.

[0020] In certain embodiments, the method comprises curing, preferably by heating, the matrix material after feeding it to the mold.

[0021] In certain embodiments, the method comprises removing the mold after feeding and optional curing of the matrix material. In certain embodiments, the method comprises removing, preferably by machining, the core after feeding and optional curing of the matrix material. In certain embodiments, removing the core is carried out without melting of the core. In certain embodiments, the core is a breakable core. Removing the core may comprise breaking the core (into smaller pieces). The core may be a disposable core, i.e. it is used or usable in manufacturing of one impeller.

[0022] In certain embodiments, the core is a machinable core, preferably machinable core formed of polymer(s), more preferably of polymer foam having a density of at least 30 kg / m3preferably selected from one or more of epoxies, phenolics, polypropelyne, polyurethane, polyvinyl chloride (PVC), acrylonitrile butadiene-stvrene (ABS), and / or cellulose acetate.

[0023] In certain embodiments, the fiber elements are formed of carbon fiber.

[0024] In certain embodiments, the matrix material comprises one or more of a thermosetting polymer preferably selected from one or more of epoxy, phenolic polymers, polyesters, vinylesters, amins, furans, polyimides (PI), bismaleimides (BMI), cyanate esters (CE), phthalonitriles, and / or benzoxazines.

[0025] According to a second example aspect there is provided a method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line, and prepreg fiber elements arranged on the core; and creating an underpressure over the vacuum line network to compress (at least some of) the prepreg fiber elements against the core.

[0026] According to a third example aspect there is provided a core comprising within it a vacuum line network comprising a plurality of branched interconnected vacuum lines. In certain embodiments, the plurality of branched interconnected vacuum lines comprises branched vacuum lines at different heights within the core.

[0027] In certain embodiments, the core is at least partially formed of more than one layers having a respective thickness, and the plurality of interconnected branched vacuum lines are formed by cavities in the layers.

[0028] In certain embodiments, the vacuum line network has a plurality of openings in the surface of the core.

[0029] In certain embodiments, the core comprises one or more feed lines arranged at least partially within the core. In certain embodiments, the core comprises a feed line network comprising a plurality of branched interconnected feed lines arranged within the core.

[0030] In certain embodiments, a diameter of the one or more feed lines arranged at least partially within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core. In certain embodiments, a diameter of the plurality of branched interconnected feed lines within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core.

[0031] According to a further example aspect, there is provided a mold for manufacturing an impeller, the mold comprising a core according to the third example aspect.

[0032] According to yet a further example aspect, there is provided a method for manufacturing an impeller by vacuum assisted resin transfer molding (VARTM) comprising manufacturing the impeller in a single piece and / or in a single resin curing step without employing a casing and / or a sealed mold.

[0033] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspects or steps that may be utilized in different implementations. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments may apply to other example aspects as well.

[0034] BRIEF DESCRIPTION OF THE FIGURES

[0035] Some example embodiments will be described with reference to the accompanying figures, in which: Fig. 1 schematically shows an example of an impeller;

[0036] Fig. 2 schematically shows a core and a vacuum line network within it according to an example embodiment;

[0037] Fig. 3 schematically shows an assembled mold according to an example embodiment; and

[0038] Fig. 4 shows a flow chart of a method according to an example embodiment.

[0039] DETAILED DESCRIPTION

[0040] In the following description, like reference signs denote like elements or steps.

[0041] As used herein, composite or composite material refers preferably to fiber-reinforced composite material comprising or consisting substantially of fibers and matrix material. Particularly, reference is made to fiber-reinforced polymer (FRP) composite material, preferably carbon-fiber-reinforced polymer (CFRP) composite material.

[0042] As used herein, fluid may refer to a liquid or a gas, or a combination thereof. In the context of the present disclosure, fluids may contain minor or trace amounts of solids, such as solid particles, typically as impurities.

[0043] In the context of the present disclosure impeller eye refers to a hole or an empty space, typically at a center region of the impeller, for mounting the impeller for example on an axis or a shaft.

[0044] An impeller may be defined as a driven rotor used for increasing pressure and / or flow of a fluid. Typically in impellers fluid flow enters axially and leaves radially. Impellers may find use for example in pumps and / or compressors, especially in creating suction in a pump or a compressor.

[0045] Impellers may sometimes be classified based on their structure as open impellers, semiclosed impellers, closed impellers. A closed impeller typically comprises a rear wall and a front wall and blades positioned around an impeller eye being arranged between the rear wall and the front wall such that both walls are in touch with the blades. A semi-closed impeller typically comprises in addition to blades arranged around an impeller eye a rear wall without comprising a front wall, the blades typically being arranged on the rear wall and protruding or extending therefrom. An open impeller typically comprises blades arranged around an impeller eye without comprising a rear wall nor a front wall. Figure 1 schematically shows a non-limiting example of a closed impeller 100. The skilled person appreciates that the size and design of a particular impeller may vary for example depending on its intended use. For example, the number and shape of the blades may vary. The impeller of Figure 1 comprises a rear wall 110 and a front wall 120, and a number of blades 130 arranged between the rear plate 110 and the front plate 120. An empty space is provided between each adjacent blade 130. An impeller eye 140 for mounting the impeller on an axis or shaft is provided at the center region of the impeller 100. Fastening holes 150 for fastening means to go through may be provided typically in the rear plate 110 to facilitating fastening of the impeller 100 for example when mounted on an axis or a shaft.

[0046] Herein is provided a method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line, and fiber elements arranged on the core; and feeding matrix material into a space defined at least by the core by creating an underpressure over the vacuum line network.

[0047] The vacuum line network comprising branched interconnected vacuum lines within the core enables improved transfer of matrix material. For example, transfer of the matrix material may be more reliable, faster, and / or the matrix material may be more evenly distributed.

[0048] In certain embodiments, the feeding of matrix material is carried out without applying above atmospheric pressure.

[0049] In certain embodiments, the method is vacuum assisted resin transfer molding (VARTM). In certain embodiments, the underpressure is a vacuum or partial vacuum sucked by a vacuum source or vacuum sources, such as vacuum pump(s), via the main vacuum line(s) through the vacuum line network(s) within the core. In certain embodiments, the main vacuum line(s) is / are in fluid communication with a vacuum source. In certain embodiments, more than one main vacuum lines are in fluid communication with one vacuum source. In certain embodiments, the created underpressure is within a range from -0.80 to -0.99 bar(g). This typically corresponds to a range from 0.01 to 0.2 bar(a).

[0050] In certain embodiments, the mold reproduces a predetermined shape of the impeller being manufactured. In certain embodiments, the impeller being manufactured has a diameter within a range from 100 mm to 3500 mm, from 150 mm to 3500, from 200 mm to 3500 mm, or from 300 mm to 3000 mm, , such as from ca. 1500 mm to ca. 2000 m. The present method is well suited for manufacturing large impellers having a diameter of ca. 1500 mm or more. In certain embodiments, the manufactured impeller has a fiber content of at least 50 wt-% and optionally at most 70 wt-% based on the total weight of the fibers and the matrix material (in the impeller). Total weight of the fibers and the matrix material refers herein to the sum of the weight of the fibers and the weight of the matrix material (in the impeller).

[0051] In certain embodiments, the method is a method for manufacturing a centrifugal impeller (centrifugal fan, centrifugal blower). Especially, the method may be a method for manufacturing a composite material centrifugal impeller. A centrifugal impeller is typically an impeller that is configured to (adapted to) pump, move, and / or compress gas, such as air or hydrogen (H2). Said centrifugal impeller may be a centrifugal impeller for a turbomachine.

[0052] In certain embodiments, the mold is a non-sealed mold. In certain embodiments, the method is carried out without a cast. The present vacuum line network within the core enables a method that can be carried out without a sealed mold and / or without a cast. However, if desired, a sealed mold and / or a cast may be used although not necessary.

[0053] In certain embodiments, the mold comprises a base plate and / or a top plate between which the core is arranged and optionally secured before feeding the matrix material. Said base plate may be configured to shape the rear wall 110 of the impeller being manufactured, typically an outer surface (other than the surface the blades are extending from) of the rear wall 110. Similarly, said top plate may be configured to shape the front wall 120 of the impeller being manufactured, typically an outer surface (other than the surface the blades are extending from) of the front wall. In certain embodiments, the base plate and / or top plate is / are aluminium plates.

[0054] In certain embodiments, the space into which matrix material is fed is defined by the core and (other parts of) the mold. In certain embodiments, the space into which matrix material is fed is defined by the core, the base plate and / or the top plate. In certain embodiments, the space into which matrix material is fed is define by the core.

[0055] In the present method, the mold comprises a core and fiber elements arranged on the core. The empty space to which the matrix material is fed is typically defined so that the matrix material will be brought into contact with the fiber elements layed-up on the core. The fiber elements may be impregnated by the matrix material. The space into which matrix material is fed is typically defined by the core or the core and one or more other parts of the mold, such as the top plate and / or base plate, so that when matrix material is fed into said space, the fiber elements arranged on the core are impregnated with the matrix and the fiber elements and the matrix material together are formed or shaped by the core, optionally together with other parts of the mold, to give the impeller being manufactured its proper shape.

[0056] In certain embodiments, the matrix material substantially fills the space defined at least by the core into which it is fed. In certain embodiments, the method comprises impregnating the fiber elements arranged on the core by feeding the matrix material into the space defined at least by the core. The space into which the matrix material is fed may be a continuous space or it may comprise more than one spaces not in fluid communication with each other. Preferably, the space into which the matrix material is fed may be a continuous space.

[0057] In certain embodiments, the core constitutes the mold optionally together with fiber elements. Fiber elements may be layed-up in the mold, after which they are in the present disclosure regarded as comprised in the mold. The present vacuum line network within the core enables that the present method may be carried with a mold that substantially consists of the core.

[0058] In certain embodiments, the core comprises or consist substantially of one or more core elements. As used herein, the term core encompasses, unless otherwise mentioned, an external core outside of the blades of the impeller being manufactured, one or more internal cores encapsulated (at least partially) within a respective blade of the impeller being manufactured, or both. In certain embodiments, the mold comprises for each blade being manufactured an internal core.

[0059] In certain embodiments, the core comprises at least an external core. In certain embodiments, the core comprises an external core and one or more internal cores.

[0060] In certain embodiments, the core comprises at least an external core creating in the impeller being manufactured the empty spaces between adjacent blades of said impeller. The external core may comprise more than one core elements. For example, the external core may comprise core element(s) creating the central region of the impeller being manufactured and other core element(s) creating the empty spaces between adjacent blades of said impeller.

[0061] The external core creating for example the spaces between adjacent blades of the impeller being manufactured may be a single core element or it may be assembled from one or more core element, especially from more than one layers stacked on top of each other.

[0062] In certain embodiments, the core comprises one or more (internal) core element(s) around which a blade of the impeller being manufactured is formed. An internal core element typically remains within the blade in the finished impeller. An internal core or core element may be of same material or of different material than an external core or core element.

[0063] In embodiments, wherein the core comprises internal core elements, a separate internal core element may be provided for each blade. In certain embodiments, each blade comprises or encapsulates an internal core element.

[0064] The mold may comprise an external core optionally formed of more than one external core elements and an internal core optionally formed of more than one internal core elements.

[0065] The present core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines. Such vacuum line network may be arranged within an external core, within an internal core, or both. In certain embodiments, the vacuum line network comprises branched interconnected vacuum lines at different heights within the core. In certain embodiments, the vacuum line network is a three-dimensional vacuum line network. In certain embodiments, a main vacuum line is in fluid communication with more than one branched interconnected vacuum lines.

[0066] In certain embodiments, the vacuum line network provides a suction or underpressure at more than one, preferably a plurality of, locations within the space into which matrix material is fed. In certain embodiments, the underpressure guides the matrix material, especially into and within the space into which matrix material is fed.

[0067] In certain embodiments, the vacuum line network has a plurality of openings in the surface of the core. Said plurality of openings may be positioned on a surface on which fiber elements are arranged and / or a surface defining the space into which matrix material is fed. In the present method, the underpressure may be created over these openings. Providing the underpessure to a space into which matrix material is fed through a plurality vacuum line network openings is beneficial in that it divides the space in a sense to several infusion fields, even in embodiments wherein said space is served by just one matrix material feed line opening.

[0068] In certain embodiments, the branches of the interconnected vacuum lines have respective openings in a core surface defining the space into which matrix material is fed and / or a core surface on which fiber elements are arranged.

[0069] In certain embodiments, the core comprises one or more feed lines arranged at least partially within the core. In certain embodiments, the core comprises a feed line network comprising a plurality of branched interconnected feed lines arranged within the core. The feed lines may have one or more openings within the space into which matrix material is fed. In embodiments, in which the space into which matrix material is fed comprises more than one spaces not in fluid communication with each other, each such space comprises at least one feed line opening.

[0070] In certain embodiments, a diameter of the one or more feed lines arranged at least partially within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core. In certain embodiments, a diameter of the plurality of branched interconnected feed lines within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core. Preferably, the diameters being compared are the respective feed side and vacuum side diameters closest to the space into which matrix material is fed. The diameter of the lines of the vacuum line network is not necessarily constant, but may increase when moving in the vacuum line network from the space into which matrix material is fed towards the main vacuum line(s) and / or a vacuum source.

[0071] Figure 2 shows a non-limiting example embodiment of an external core 200. The core 200 may have a shape of an approximately circular disk with a substantial thickness. The core 200 may comprise a plurality of slots 210 for accommodating the blades of the impeller being manufactured. The slots 210 may be formed such that an outer edge of the core 200 remains continuous thus keeping portions of the core 200 together. Within the core 200, a vacuum line network comprising a plurality of branched interconnected vacuum lines 220 in fluid communication with a main vacuum line 230 is provided. The plurality of branched interconnected vacuum lines 220 may be positioned such that at least two branched vacuum lines 220 are arranged per slot 210 for accommodating a blade of the impeller being manufactured. The branched vacuum lines 220 may be connected to or in fluid communication with an annular vacuum 240 line arranged within the core 200. Said annular vacuum line(s) 240 may be in fluid communication with one or more main vacuum lines 230 extending from within the core 200 to the outside of the core 200 and being adapted to be connected to a vacuum source (not shown). The vacuum line network may for example be formed of the plurality of branched vacuum lines 220 interconnected via the annular vacuum lines 240 being in fluid communication with one or more main vacuum lines 230 adapted to be connected with a vacuum source.

[0072] In certain embodiments, the feed line network is simpler than the vacuum line network. However, as detailed in the foregoing, a feed line network comprising branched feed lines similar to, but generally having a larger diameter than, the vacuum line network may in certain embodiments be provided within the core 200.

[0073] For example as seen in the example embodiment of Figure 2, a plurality of main feed lines 250 extending from the outside of the core 200 to the inside of the core 200 may be provided. Within the core 200, the main feed lines 250 may be connected to an annularfeed line 260 being in fluid communication with curved feed lines 270 arranged such that each curved feed line has an opening into a slot 210 configured to accommodate a blade of the impeller being manufactured.

[0074] The vacuum line network and the optional feed line network are by no means limited to the example embodiment of Figure 2. Although a certain number of for example branched interconnected vacuum lines, of main vacuum lines, of main feed lines, of slots configured to adapt blades of an impeller, etc. is shown in the example embodiment of Figure 2, the present disclosure is by no means limited to these, but other numbers of said parts or features may be present in other example embodiments of the present invention. The skilled person appreciates that for example the design and size of the impeller to be manufactured may be taken into consideration when determining the number of such features. In certain example embodiments, the matrix material enters the space defined at least by the core from 5-10 distinctive positions or openings.

[0075] In certain embodiments, providing the mold comprises forming or manufacturing the core.

[0076] In certain embodiments, the core or a core element is formed of more than one layers having a respective thickness, and the plurality of branched interconnected vacuum lines are formed by cavities in the layers.

[0077] In certain embodiments, each of the core elements comprises within them a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line. In certain embodiments, each of the core elements are formed of more than one layers having a respective thickness, and the plurality of branched interconnected vacuum lines are formed by cavities in the layers.

[0078] Figure 3 shows an example embodiment of a mold 300. In Figure 3, the mold 300 comprises an external core formed of a plurality of layers 310 having a respective thickness and stacked on top of each other. The plurality of branched interconnected vacuum lines (not shown) may be formed by cavities in at least certain of the layers 310. The mold 300 may comprise main vacuum lines 230 for providing the underpressure and main feed lines 250 for feeding the matrix material. A front wall 120 of the impeller being manufactured is arranged between an outer edge 320 and a center region 330 of the core.

[0079] In certain embodiments wherein the core is at least partially formed of more than one layers having a respective thickness, certain of the layers may comprise on a surface cavities, such as machined cavities, that form a branched vacuum line once another layer is stacked on top of it. Such other layer may comprise a hole going through said other layer positioned so that it forms a fluid connection or pathway between branched vacuum lines formed by cavities in different layers. In other words, branching may be created by branched cavities in a certain layer or layers on top of which an other layer is stacked, for example a layer providing a fluid connection between layers having branched cavities. The branched vacuum lines may be in fluid communication with, for example an annular, vacuum line and the connection between branched vacuum lines in different layers may be provided via such (annular) vacuum line.

[0080] In certain example embodiments, the core may comprise 4 or more, such as 5 or more, layers stacked on top of each other, and the plurality of branched interconnected vacuum lines are formed by cavities in said layers.

[0081] In certain embodiments, the core is at least partially formed using 3D printing. A computer model of the desired vacuum line network and / or feed line network within the core may be created, and the core (or a portion thereof) then 3D printed based on the computer model.

[0082] In certain embodiments, providing the mold comprises: providing the core, and laying up the fiber elements on the core.

[0083] In certain embodiments, providing the mold comprises providing a base plate, arranging the core on the base plate, laying up the fiber elements on the core, providing a top plate on top of the core on which the fiber elements have been arranged, and optionally securing the core between the base plate and the top plate. Optionally, some fiber elements may be provided on the base plate prior to arranging the core thereon.

[0084] In certain embodiments, providing the mold comprises placing (laying-up) fiber elements in dry form onto the core, for example as preforms in a predetermined arrangement.

[0085] The present method enables manufacturing the impeller as such, or as mounted directly on a shaft or axis. In certain embodiments, the impeller is manufactured without mounting it for example on an axis or shaft while feeding of matrix material, optional curing, and / or optional removal of core has not yet been carried out. A finished or nearly finished impeller may then be mounted. Feeding of the matrix material may be stopped (or optionally paused) when the space into which the matrix material is fed is substantially filled. The vacuum line network within the core, especially the branched vacuum lines thereof, may be dimensioned so that, although allowing bleeding of matrix material, substantial amounts of the matrix material are prevented from entering the vacuum line network. In certain embodiments, the vacuum lines of the vacuum line network, especially the branches of the interconnected vacuum lines, are dimensioned so that gases, such as air, passes through while (substantial) flow of matrix material within the vacuum line network is prevented. In certain embodiments, the feed line(s) or feed line network contains mainly matrix material and the vacuum line network contains mainly gases, such as air, when the present method is carried out.

[0086] In certain embodiments, the method comprises curing, preferably by heating, the matrix material after feeding it to the mold. In certain embodiments, the curing is carried out in an oven or in an autoclave.

[0087] In certain embodiments, the mold is placed into a vacuum bag before feeding matrix material into the mold. The mold may be within the vacuum bag during the feeding of matrix material and optionally during the optional curing. In certain embodiments, the mold is placed into a vacuum bag before curing. . The vacuum bag may be removed after completing the feeding of matrix material and / or after completing the optional curing.

[0088] In certain embodiments, the method comprises removing the mold after feeding and optional curing of the matrix material. In certain embodiments, the method comprises removing of the core after feeding and optional curing of the matrix material preferably by machining. The core may be a disposable core, i.e. it is used or usable in manufacturing of one impeller. In certain embodiments, the core is a removable, breakable, and / or destroyable core. Especially in case of external core, the core may be removed after feeding and optional curing of the matrix material. Removing the core may comprise breaking the core into smaller pieces.

[0089] In certain embodiments, the method comprises removing the external core (while maintaining internal core(s) within the blade(s) where applicable). Removing the core and / or mold preferably by machining generally yields the impeller being manufactured. Optionally, finishing steps and / or treatments may be applied to yield a finished impeller. Removing the core and / or removing the mold are herein understood to cover embodiments in which some minor or very minor amounts of core material may remain on the impeller surface.

[0090] In certain embodiments, the method comprises taking out the mold from the vacuum bag and removing the mold to yield the impeller.

[0091] In certain embodiments, the core is a machinable core. A machinable core enable more precise and / or reliable formation of the vacuum line network and optionally the feed line network within the core compared for example to meltable cores such as vaxes. Examples of machinable core materials include, but are not limited to, polymer(s), wood, and / or ceramics.

[0092] In certain embodiments, the machinable core is formed of polymer(s). Examples of such polymers include, but are not limited to, epoxies, phenolics, polypropelyne, polyurethane, polyvinyl chloride (PVC), acrylonitrile butadiene-stvrene (ABS), cellulose acetate, polyethylene (PE), polypropylene (PP), and / or polyamide (PA).

[0093] In certain embodiments, the core is a machinable core formed of polymer foam. Said polymer foam may have a density of at least 30 kg / m3or at least 60 kg / m3or at least 80 kg / m3and preferably at most 1000 kg / m3. In certain embodiments, the core is a machinable core formed of polymer foam having a density within a range from 30 kg / m3to 160 kg / m3. Such polymer foam may be of one or more of epoxies, phenolics, polypropelyne, polyurethane, polyvinyl chloride (PVC), acrylonitrile butadiene-stvrene (ABS), and / or cellulose acetate.

[0094] Especially in embodiments, wherein the vacuum line network (and optionally feed line network) within the core is formed by machining, the core material may be a polymer foam as described above. Especially in embodiments wherein the core elements are formed by 3D printing, the core material may be selected from one or more of polyethylene (PE), polypropylene (PP), and / or polyamide (PA).

[0095] In certain embodiments the fiber elements are fabric elements in the sense that they comprise a multitude of intertwined fibers (of a certain length), such as fibers woven, knitted, stitched, and / or twined together. In certain embodiments, the fiber elements are formed of unidirectional fibers forming for example unidirectional tape or the like. In certain embodiments, the fibers of the fiber elements have threadlike shape. The fiber elemements may consist substantially of fibers, typically having a predetermined size and type.

[0096] In certain embodiments, the fiber elements are formed of carbon fiber. In certain embodiments, the fiber elements are preforms. As used herein, preforms refer to fiber elements formed of a multitude of intertwined, for example woven, fibers and having certain, typically predetermined, sizes. Preforms may for example be obtained by cutting.

[0097] Fiber elements may also be provided as prepregs. Prepregs refer herein to fiber elements, especially as described in the foregoing, impregnated with matrix material prior to lay-up, i.e. before arranging the fiber elements into the mold and / or on the core. The matrix material of the prepregs may be for example as described below.

[0098] Accordingly, herein is provided a method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line; and prepreg fiber elements arranged on the core; and creating an underpressure over the vacuum line network to compress (at least some of) the prepreg fiber elements against the core.

[0099] When the fiber elements are prepregs, it is not necessary to (separately) feed matrix material as the prepregs already contain it. The present core comprising within it the vacuum line network and an underpressure created thereover may be used in a prepreg method, the underpressure compressing prepregs towards the core and / or conforming prepregs with the shape of the core. In certain embodiments wherein the fiber elements are prepregs, the method is carried out without (separately) feeding matrix material to a space defined at least by the core. The method in which the fiber elements are prepregs may, apart from the feeding of the matrix material, be a method as described herein.

[0100] As is appreciated by the skilled person, the matrix material is in fluid or liquid state when fed to the mold. In certain embodiments, the matrix material is a resin.

[0101] The matrix material may be selected from one or more of a thermosetting polymer resin preferably selected from one or more of epoxy, phenolic polymers, polyesters, vinylesters, amins, furans, polyimides (PI), bismaleimides (BMI), cyanate esters (CE), phthalonitriles, and / or benzoxazines, and / or a thermoplastic polymer resin preferably selected from one or more of polyphenylene sulphides (PPS), polyamides (PA), polymethyl methacrylates (PMMA), liquid crystal polymers (LCP), polyoxumethylenes (POM), polyamide imides (PAI), polv-etherether-ketones (PEEK), poly-ether-ketone-ketones (PEKK), poly-aryl-ether- ketones (PAEK), polyethylene terephthalate (PET), polycarbonates (PC), polyethylenes (PE), polyether-imides (PEI), polyethers (PES), polyphthalamides (PPA), polyvinyl chlorides (PCV), polyurethanes (Pll), polypropylenes (PP), polystyrenes (PS), polyphenylene oxides (PPO), and / or polyimides (PI).

[0102] In certain embodiments, the matrix material comprises or consists substantially of one or more of a thermosetting polymer resin preferably selected from one or more of epoxy, phenolic polymers, polyesters, vinylesters, amins, furans, polyimides (PI), bismaleimides (BMI), cyanate esters (CE), phthalonitriles, and / or benzoxazines.

[0103] In certain embodiments, the matrix material comprises or consists substantially of one or more of a 1- or 2-component epoxy, vinylester, and / or polyester resin.

[0104] In certain embodiments, the matrix material may contain minor amounts of solid particles functioning for example as additives for example reinforcing or protecting certain parts of the impeller being manufactured.

[0105] In certain embodiments, the method comprises providing a 3D printed metal part or element having a shape that conforms with a shape of a portion of the impeller surface and placing the shaped metal part in the mold between the core and fiber elements (to be) arranged on the core. Said placing of the metal element may be carried out before feeding matrix material. Such metal element associated with a portion of the impeller surface may protect a portion of the impeller surface against erosion and / or corrosion typically caused by a working fluid. In certain embodiments, said metal element is of titanium and / or aluminium, preferably titanium. In certain embodiments, the 3D printed metal element has a shape that fits together or is conformal with a portion of the impeller surface such that the shape of the 3D printed metal sheet provides shape locking of the metal element to the impeller surface. Said shape locking improves fastening of the metal element to the impeller. 3D printing allows providing the metal element with a predetermined shape with great accuracy.

[0106] In certain embodiments, the shaped 3D printed metal part or element comprises spikes or protrusions on its inner surface, i.e. the surface that will face the impeller surface. Said spikes improve fastening of the shaped metal element to the impeller by penetrating fiber elements and / or matrix material.

[0107] In certain embodiments, the shaped metal element is positioned on a blade (edge) of the impeller.

[0108] Fig 4 shows a flow chart of a method according to an example embodiment. In step 410, a mold comprising a core is provided. The core is preferably a core as described in the foregoing. In a second step 420, fiber elements are arranged on the core, and in a third step 430 matrix material is fed into a space defined at least by the core. The feeding of the matrix material may be carried out by creating a (partial) vacuum or underpressure over the vacuum line network within the core detailed in the foregoing. Preferably, no external (above-atmospheric) pressure is applied on the feed side.

[0109] In certain embodiments, the feeding of the matrix material is followed by a bleeding step. In the bleeding step, excess matrix material is removed from the space into which it was fed. In certain embodiments, the method comprises curing the matrix material after feeding and optional bleeding of it preferably by heating for example to a temperature of ca. 100 °C or more.

[0110] In certain embodiments, the curing is followed by removing of the core by machining to yield an impeller. In certain embodiments, the method comprises as a finishing step machining of the impeller to obtain its predetermined dimensions.

[0111] Herein is also provided a core comprising within it a vacuum line network comprising a plurality of branched interconnected vacuum lines. The core may be a core as described in connection with the present methods. Herein is also provided use of said core in composite manufacturing, especially fiber reinforced composite manufacturing. In certain embodiments, said use comprises creating or providing an underpressure over the vacuum line network within the core. Herein is also provided a mold for manufacturing an impeller, the mold comprising a core as defined in the foregoing.

[0112] Herein is provided a composite manufacturing method comprising providing a mold comprising a core having within it a vacuum line network as described in the foregoing, fiber elements arranged on the core, and matrix material within the mold; and providing an underpressure over the vacuum line network to compact or move fiber elements and / or matrix material towards the core.

[0113] Without limiting the scope and / or interpretation of the claims, certain technical effects and / or advantages of one or more of the example embodiments disclosed herein are listed in the following. An advantage is that an impeller, even with complex blade structure, may be formed in one piece, e.g. in one feed and cure cycle of the matrix material, without a need for subsequent joining or attachment of impeller parts. An impeller formed in one piece is mechanically stronger and / or has improved structural integrity compared to impellers with subsequently joined or attached parts. Also, the number of process steps in the manufacturing of the impeller may be reduced. A technical effect is high fiber content (wt- % of fibers based on the total weight of the fibers and the matrix material in the impeller). The vacuum line network and underpressure therethrough enables improved matrix material distribution and / or a more compact structure. The vacuum line network and the underpressure therethrough contributes to high quality, reliable production. The present methods may provide a higher manufacturing success rate compared to state of the art methods. Improved matrix distribution may contribute to a high fiber content. A further advantage is that a cast or a sealed mold is not necessarily needed. This enables flexible production of impellers, even of one-off impellers. A further advantage is enabling manufacturing by vacuum assisted resin transfer moldling (VARTM) or the like of large, single piece objects.

[0114] Various embodiments have been presented. It should be appreciated that in this document, words comprise, include, and contain are each used as open-ended expressions with no intended exclusivity.

[0115] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

[0116] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1 . A method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line; and fiber elements arranged on the core; and feeding matrix material into a space defined at least by the core by creating an underpressure over the vacuum line network.

2. The method according to claim 1 , wherein the plurality of branched interconnected vacuum lines comprises branched vacuum lines at different heights within the core.

3. The method according to claim 1 or 2, wherein at least a portion of the core is formed of more than one layers having a respective thickness, and the plurality of branched interconnected vacuum lines are formed by cavities in the layers.

4. The method according to any one of the preceding claims, wherein the vacuum line network has a plurality of openings in the surface of the core.

5. The method according to any one of the preceding claims, wherein the matrix material is fed to the space defined at least by the core through a feed line network comprising a plurality of branched interconnected feed lines arranged within the core.

6. The method according to claim 5, wherein a diameter of the plurality of branched interconnected feed lines within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core.

7. The method according to any one of the preceding claims, comprising removing, preferably by machining, the core after feeding and optional curing of the matrix material.

8. The method according to any one of the preceding claims, wherein the core is a machinable core, preferably a machinable core formed of polymer(s), more preferably of polymer foam having a density of at least 30 kg / m3preferably selected from one or more of epoxies, phenolics, polypropelyne, polyurethane, polyvinyl chloride (PVC), acrylonitrile butadiene-stvrene (ABS), and / or cellulose acetate.

9. The method according any one of the preceding claims, wherein the fiber elements are carbon fiber.

10. A method for manufacturing an impeller, the method comprising: providing a mold comprising a core, wherein the core comprises within it a vacuum line network comprising a plurality of branched interconnected vacuum lines in fluid communication with a main vacuum line; and prepreg fiber elements arranged on the core; and creating an underpressure over the vacuum line network to compress the prepreg fiber elements against the core.

11. A core comprising within it a vacuum line network comprising a plurality of branched interconnected vacuum lines.

12. The core according to claim 11 , wherein the plurality of branched interconnected vacuum lines comprises branched vacuum lines at different heights within the core.

13. The core according to claim 11 or 12, wherein the core is at least partially formed of more than one layers having a respective thickness, and the plurality of interconnected branched vacuum lines are formed by cavities in the layers.

14. The core according to any one of claims 11-13, wherein the vacuum line network has a plurality of openings in the surface of the core.

15. The core according to any one of claims 11-14, comprising a plurality of branched interconnected feed lines arranged within the core.

16. The core according to claim 15, wherein a diameter of the plurality of branched interconnected feed lines within the core is larger than a diameter of the plurality of branched interconnected vacuum lines within the core.

17. A mold for manufacturing an impeller, the mold comprising a core according to any one of claims 11-16.

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