EP3571411B1 - Pump impeller - Google Patents

Description

The invention relates to an asymmetrical pump impeller for a pump unit for pumping a liquid, in particular one containing solids, and to a method for producing such a pump impeller.

Asymmetric pump impellers have a geometry that is not rotationally symmetrical or cyclically rotationally symmetrical in relation to the axis of rotation of the pump impeller. Such pump impellers are, for example, semi-open impellers with a single blade, as are used in sewage pumps or submersible pumps for pumping liquids containing solids.

Asymmetric pump impellers can only be converted into themselves by a full 360° rotation. Since the geometry of the pump impeller is primarily based on hydraulic aspects, it is usually designed without considering possible geometry-related imbalances. Such a wheel has an original asymmetrical weight distribution, and therefore an off-centre center of mass. The main axis of inertia is therefore not on the axis of rotation of the impeller, which creates a static imbalance. In addition, moments of deviation in the inertia of the pump impeller during rotation lead to an inclined position of the main axis of inertia in relation to the axis of rotation, so that there is also a dynamic imbalance. Static and dynamic imbalances can also be manufacturing-related, since tolerances, ie dimensional deviations from the designed design of the pump impeller, exist depending on the manufacturing process.

The imbalances are removed after the impeller has been manufactured as part of a manual balancing process. This is done by partial material removal, i.e. partial savings of material (negative balancing) or by partial material addition through the installation of a balancing weight (positive balancing) which increases the weight of the impeller at its location.

A sewage pump impeller with a balancing weight is known, for example, from Japanese patent JP 5133026 B2 known, in which case the balancing weight is formed in one piece with the support disk. Another asymmetric sewage pump impeller with a balancing weight is known, for example, from US patent application U.S. 2011/182734 A1 and the UK patent application UK687,514 known. The British patent application GB182,632 discloses a chamber in each of the two blades of the impeller, which is said to be balanced due to the use of two blades and, accordingly, two flow channels.

Pump impellers for sewage pumps are usually cast, such as in the Japanese patent application JP 2013-64398 A , especially made of metal. Apart from the enormous tolerances that this manufacturing process requires, the geometry of the impeller is limited so that imbalances cannot be taken into account, or only to a very limited extent, when selecting the geometry itself, and manual rebalancing of a cast impeller is therefore always necessary.

It is the object of the present invention to provide an asymmetrical pump impeller which already takes imbalances into account in its geometry without experiencing a drop in hydraulic efficiency and which is already balanced by the method of its manufacture. Furthermore, it is the object of the invention to provide a method for producing such a pump impeller.

These objects are solved by the features of claims 1 and 16.

Advantageous developments are specified in the dependent claims and are explained below.

According to the invention, an asymmetrical pump impeller for a pump unit for pumping a solids-laden liquid in particular is proposed, which is at least partially formed in layers by an additive manufacturing process and has at least one cavity in its material interior, which is layered fabrication and is closed to the outside entirely or except for an opening for removing unsolidified material from the cavity, the cavity being positioned and configured such that an axis of inertia of the pump impeller is offset from the axis of rotation of the pump impeller. Furthermore, the invention proposes a method for producing a pump impeller of the type mentioned from individual layers of a material by using an additive manufacturing method, in which in at least a part of successive layers a spatial area in the material interior of the pump impeller is completely formed on the outside to form at least one or except for one Opening is closed for removing unsolidified material from the cavity, wherein the cavity is positioned and formed such that an axis of inertia is shifted to the axis of rotation of the pump impeller.

The core idea of the invention is therefore to shift the process of balancing an asymmetrical pump impeller to the design phase and to design and manufacture the pump impeller in such a way that it is almost imbalance-free. To this end, the invention provides for the use of cavities in asymmetric pump impellers, which are obtained by an additive manufacturing process. The cavity or cavities allow the blade geometry to be configured more freely, because otherwise the balancing would have to take place via the blade geometry.

The aim is to use one or more closed or essentially closed cavities in the material interior of the impeller in order to achieve a local weight saving that contributes to or even causes the entire pump impeller to have a symmetrical weight distribution, so at least is statically balanced, the cavity being formed using an additive manufacturing process. Independent of the aspect of local material savings and thus weight savings, the invention also includes the aspect of local weight addition for the purpose of balancing, as will be explained below.

An additive manufacturing process, also called generative manufacturing process, makes it possible to produce cavities in almost any position and with almost any complex geometry that cannot be produced in the same way by alternative processes, for example with lost cores or divided/moving cores or sliders.

The at least one cavity also reduces the overall weight of the impeller, which also simplifies handling during manufacture and transport and reduces the overall weight of the pump assembly. In addition, the saving in material due to the at least one cavity leads to a cost advantage, which is all the more pronounced the higher the quality of the material used to manufacture the pump impeller. Another advantage of layered additive manufacturing is the cost-effective one-off production of customer-specific pump impellers, or the economical manufacture of smaller quantities of pump impellers. Because additive manufacturing from layers does not require a mold, and therefore no specially shaped cores. In addition, additive manufacturing eliminates work steps that are necessary with conventional manufacturing, e.g. turning of the outer diameter, turning on the suction side, balancing of the impeller.

In the additive manufacturing process, for example, individual layers of a molten material can be applied one after the other from a nozzle and in this way form the impeller or its mechanical support structure layer by layer, as is known per se as so-called "3D printing". Where the at least one cavity is to be formed, there is accordingly a lack of material application. In this way, the at least one cavity can be formed in the material interior of the impeller so that it is completely closed to the outside. The most suitable materials here are polymers and fiber-reinforced polymers, which have a comparatively low melting temperature (compared to metal) and are not too liquid in the plasticized state

An alternative variant that is preferred according to the invention is the production of the individual layers from a powder. This can be melted locally, for example by means of a high-energy beam such as a laser beam or electron beam, which subsequently solidifies again. Another layer of powder is then applied to the solidified layer and this is then melted locally again with the jet. The powder does not melt in the area of a cavity to be formed. So-called selective laser sintering (SLS), laser melting or electron beam melting, which are known per se, are particularly suitable for local melting. They enable the production of high-precision components. As an alternative to melting the powder, it can be bonded locally with a binder to solidify the powder and thus create the impeller in layers. Such a generative manufacturing process is known under the name "binder jetting" and can also be used according to the invention.

In addition to a polymer or ceramic powder, a metal powder can preferably be used as the material, so that particularly stable pump impellers can be produced from metal, in particular for sewage pumps.

In order to remove the unsolidified material, i.e. the powder, from the at least one cavity, the cavity must have an opening to the outside. However, with regard to the grain size of the powder, this can be comparatively small, for example between 0.5 mm and 2 mm, so that the powder can trickle out or be blown out by itself.

Preferably, the impeller comprises only one blade which spirals around the axis of rotation. The distance between the blade and the center of the impeller or the axis of rotation thus increases with increasing angle of wrap, ie from the inside to the outside. The impeller is accordingly a centrifugal pump impeller or centrifugal impeller, which draws in the liquid centrally and pumps it out radially. The impeller is suitably designed without a cover disc, ie semi-open, ie it is open towards the suction opening of the pump. Such an impeller is particularly suitable for sewage pumps and submersible pumps, ie for pumping solids-laden sewage, since it is less prone to clogging than two- or multi-bladed impellers and covered impellers. The pump unit can thus preferably be a sewage pump or a submersible pump.

As an alternative to the bladed impeller, the pump impeller according to the invention can be a worm impeller. Such a worm impeller is used, for example, in eccentric worm pumps, where it is also referred to as a rotor. In an asymmetrical design, it has a single-start thread with a large pitch, large thread depth and small core diameter. If necessary, the thread does not wind an integer multiple around the rotor axis. Both cause imbalances that can be avoided by the impeller according to the invention.

In order to give the blade greater stability, the impeller can have a support disk on which the blade is attached or from which it rises. According to one variant, the support disk can be manufactured separately. This production can take place in a conventional manner, for example by means of casting. It can then be firmly mechanically connected to the blade produced in layers. This can be done, for example, by means of welding or screwing. However, it is advantageous if the carrier disk is formed in one piece with the blade during the layered production. A subsequent welding or assembly step can thus be dispensed with.

According to one embodiment variant, the at least one cavity can lie partially within the material forming the blade. Depending on the blade geometry, however, it can also be formed completely within the blade. Additionally or alternatively, the at least one cavity can be partially within the material forming the support disk. However, it can also be formed completely within the support disk. According to yet another embodiment variant, part of the cavity can lie within the blade and part of it can lie within the support disk.

According to a preferred embodiment variant, the impeller can have, within a central region bordered by the vane, a quantity of material over which the pumped liquid can flow, in which the at least one cavity can be completely or partially formed. The central area corresponds to the flow channel (blade channel) of the impeller delimited by the single blade, which is at least partially limited in the axial direction by the amount of material, if there is a support disk towards it. In the other axial direction, the central area forms the suction mouth, ie the suction side of the impeller. Suitably the quantity of material is materially integral with the blade and can thus be considered part of the blade. The amount of material ideally has a surface in the form of a ramp, which rises in the axial direction as the distance between the blade and the axis of rotation decreases, ie as the wrap angle of the blade decreases.

As already stated, the at least one cavity can be formed entirely in the amount of material. If the amount of material is viewed as part of the blade, the at least one cavity is then formed entirely in the blade. If the amount of material is considered to be a portion of the pump impeller independent of the vane, the at least one cavity may be partially located within the amount of material and another portion may extend into another portion of the pump impeller. According to one embodiment variant, it can be partly embedded in the quantity of material, and partly in the blade or in the support disk. According to yet another variant embodiment, the cavity can be located partly within the mass of material, partly within the blade and partly within the carrier disc.

So that the unsolidified material can be removed from the cavity, a channel leading from the cavity to the outside can be connected to the opening. The cavity can be emptied via this channel after the impeller has been manufactured, for example by blowing the unsolidified powder out of the free space through the channel. For this purpose, for example, a hollow needle can be inserted into the channel and compressed air can be blown into the cavity through this needle. Alternatively, the unsolidified powder can also be sucked out.

According to one embodiment variant, the channel can be designed to be open or permanently open. This means that pumped liquid can enter the cavity during operation of the pump unit. However, this carries the risk that Deposits can form inside the cavity, which in turn can affect the weight distribution, and are also difficult to take into account in advance when determining the center of gravity for each layer of material, so that the cavity, which is open to the outside, is always prone to imbalance.

In order to avoid this, the channel can be closed later, i.e. after the removal of the unsolidified material, in particular the powder. Thus, the at least one cavity of the ready-to-operate pump impeller is completely closed to the outside again. The channel can, for example, be welded shut, in particular closed with a welding bead. Alternatively, it can also be glued shut with the help of an adhesive, screwed on using a screw such as a grub screw (requires an internal thread in the channel) or closed with a stopper via a press fit.

In order to avoid material residues, in particular powder residues, remaining in the at least one cavity, the cavity can be free of right-angled and/or acute-angled inner edges and/or inner corners. Experience has shown that powder residue sticks to such inner edges. A mechanical impact or shaking is then required to loosen these residues. Provision can preferably be made for two delimiting walls of the at least one cavity, which are at an angle to one another, to merge into one another to form a groove. The transition between these two boundary walls is thus formed by a concave rounding of the inner edge. This reduces the risk of powder residues adhering to the transition between the boundary walls.

It is particularly advantageous if the at least one cavity is closed in the shape of a gable roof or funnel shape when viewed in one direction in cross section. The opening is sensibly in the top of the gabled roof or funnel. This geometry forms a kind of emptying funnel and simplifies the removal of the unconsolidated material and promotes complete emptying of the residue.

A gabled roof geometry is particularly suited to a rectangular cross-sectional area or footprint of the cavity and has two to each other angular boundary walls that intersect in a line, the ridge, and on which the unconsolidated material can slide down. However, the gabled roof geometry does not necessarily have to be symmetrical. Furthermore, the boundary walls do not have to be plane, and the ridge does not have to be a straight line. They can also be arbitrarily curved surfaces, the line can be a correspondingly arbitrarily curved curve in which the two surfaces intersect. The opening is sensibly located in the middle of the line in the direction of extent, so that the unsolidified powder can trickle evenly from all sides to the opening. Accordingly, it is advantageous if the channel opens into the cavity in the center of the cavity in the circumferential direction

A funnel-shaped roof geometry is particularly suitable for a square or round cross-sectional area or base area of the cavity. The roof of the cavity may thus conform to a quadrilateral pyramid, dome (hemisphere) or cone forming a funnel when inverted, allowing the unconsolidated material to slide down to the center of the funnel. The opening is sensibly in the center of the funnel. Correspondingly, it is advantageous if the channel opens out into the hollow space in the center of the hollow space in the radial direction, as viewed from the axis of rotation of the impeller. This also applies to the gabled roof geometry. It should also be noted that the funnel-shaped roof geometry does not necessarily have to be symmetrical; asymmetrical funnel-shaped roof geometries are also possible.

Thus, the cross-sectional shape of the cavity can be arbitrary, for example rectangular, square, round or oval. In order to do justice to the winding shape of the blade geometry, the geometry of the cavity in cross section can be adapted to this blade geometry, for example to the effect that a rectangular basic shape is bent in the direction of its longitudinal extension. Thus, the gable roof also has a curved contour, and the ridge corresponds to a curved line. In cross-section, the geometry can correspond, for example, to a segment of a perforated disc, for example to a quarter-circle segment, as will become clear below using the exemplary embodiment.

Ideally, the saddle roof or funnel-shaped formation of the cavity occurs in the direction of the additive layer structure. This turns out to be the disadvantage take advantage of the fact that, depending on the process used, no floating roof construction (cantilevered ceiling) can be formed, and therefore only slopes greater than 45° or greater than 50° can be produced in layers, because melted powder material would flow down like water and would displace unsolidified powder material.

In one embodiment variant, the cavity can have a support structure on the inside. A support structure may be required, for example, to produce a specific cavity geometry that cannot otherwise be realized with the additive manufacturing process. However, a support structure can also be provided for other reasons, for example to transmit forces or to provide material within the cavity again for the purpose of balancing.

The support structure can extend, for example, between two or more boundary walls of the cavity. Ideally, it is generated during the layered construction of the pump impeller.

In one embodiment variant, the support structure can be embodied in the manner of a skeleton, so that it requires only a minimum of material. A skeletal support structure separates the at least one cavity into partial cavities, which are connected to one another via openings in the support structure.

The support structure can preferably have a material thickening at least at one point for balancing purposes. Alternatively or additionally, an outer wall delimiting the cavity can have a material thickening at least at one point for balancing purposes. This increases the degree of freedom in the design and arrangement of the cavity or cavities in the pump impeller. At this point it should be pointed out that thickening of the material ultimately means that the cavity volume is reduced compared to a variant without thickening of the material. This shows that the addition of material in or on the cavity also represents an adaptation of the cavity itself. Thus, even with a thickening of the material in or on the cavity, the at least one cavity is designed in such a way that a Axis of inertia of the pump impeller is shifted to the axis of rotation of the pump impeller.

As an alternative to a skeletal structure, the support structure can also be formed by a support wall, which is particularly solid. Such a support wall separates the at least one cavity into two cavities which are each closed to the outside or are closed except for an opening for emptying unsolidified powder. In this embodiment variant, the pump impeller according to the invention thus has two cavities which are used for balancing.

In one embodiment variant, the support wall can take into account the aforementioned fact that the roof geometry of a cavity can only be designed with a slope greater than 45° or greater than 50° and the maximum width of the cavity is therefore also determined by the roof height. However, if the cavity has to be made wider than the roof height allows due to the necessary shift of the axis of inertia to the axis of rotation, because the cavity would otherwise open to the outside, two cavities can be formed next to each other, preferably with a symmetrical geometry in cross section. For example, the cavities can be located one behind the other in the radial direction in relation to the impeller axis. The support wall then extends in the circumferential direction and radially separates the two cavities from one another.

It is of particular advantage if the cavities are connected to one another by a connecting channel. This makes it possible to blow compressed air through one channel into the first cavity to empty the cavities in order to blow out the unsolidified material through the other channel of the second cavity. Alternatively, it can also be vacuumed. This can be done alternately in order to completely empty both cavities. This method can also be used with three or more cavities, especially when the cavities are not immediately adjacent. All or groups of the cavities can be connected to one another by appropriate connecting channels, so that the pressure can enter all the cavities or the cavities of a group. In the case of groups which are fluidically separated from one another, ie not connected, the process must be repeated accordingly for each group.

In a preferred embodiment variant, the pump impeller has, in addition to the one inner cavity, an outwardly open recess or a further outwardly completely closed cavity or except for an opening for removing unsolidified material, the recess or the further cavity being offset axially to the one cavity is. The recess and the additional cavity allow the pump impeller to be balanced in a second radial plane. The axial offset relative to the axis of rotation causes the center of gravity of one inner cavity and the center of gravity of the recess or of the further inner cavity to lie in their own radial plane and the two radial planes to be spaced axially from one another. They allow dynamic balancing of the pump impeller.

It makes sense if the recess or the additional cavity is formed in the support disk. In combination with the one cavity formed in the blade or in the material area, a particularly large distance between the two radial planes is achieved by the recess or the further cavity in the support disk. This in turn has the advantage that a smaller balancing mass or a smaller hollow volume is required to eliminate the dynamic imbalance.

In order to maximize the distance, the recess can be formed on the rear side of the support disk facing away from the blade. This design also has the advantage that the recess does not affect the hydraulic efficiency since it faces away from the suction and pressure sides of the pump impeller.

The individual layers are preferably built up in the axial direction of the pump impeller, ie transversely to the impeller axis or slightly inclined thereto, so that the direction of the layer structure is essentially parallel to the impeller axis. This has the advantage that as few support structures as possible are required and consequently as little material as possible has to be melted. This also reduces the effort involved in post-processing, since fewer support structures have to be removed.

It is also advantageous if, during production, the support disk of the pump impeller is first formed in layers and then one blade is formed thereon. This avoids support structures that would be required due to the support disk projecting beyond the blade in the radial direction if the support disk were to be formed last. These support structures would have to be removed later, which lengthens and complicates the manufacturing process.

• Fig. 1: eine perspektivische Ansicht eines erfindungsgemäßen Pumpenlaufrads
• Fig. 2: eine perspektivische Ansicht des axial geschnittenen Laufrads aus Fig. 1
• Fig. 3: eine perspektivische Ansicht des radial geschnittenen Laufrads aus Fig. 1
• Fig. 4: Position der zwei Wuchtebenen für das Pumpenlaufrad nach Fig. 1
• Fig. 5: Schnitt durch Ebene II gemäß Fig. 4

Further features and advantages of the invention are explained below using an exemplary embodiment and the accompanying figures. Show it:

• 1 : a perspective view of a pump impeller according to the invention
• 2 : a perspective view of the axially sectioned impeller 1
• 3 : a perspective view of the radially sectioned impeller 1
• 4 : Position of the two balancing planes for the pump impeller 1
• figure 5 : Section through level II according to 4

The Figures 1 to 3 show a single-blade pump impeller 1 for a sewage pump unit for pumping solids-laden sewage according to the invention. It comprises a support disk 2 and a blade 3 which is designed in one piece with it and extends spirally around the impeller axis 15 and which rises from the support disk 2 in the axial direction. There is no cover disk, so that the pump impeller 1 forms a semi-open pump impeller. With regard to its geometry, the impeller 1 is asymmetrical in relation to the impeller axis 15 .

How in particular based on 2 As can be seen, the pump impeller 1 also has a central region 16 which is surrounded by the blade 3 and which forms the flow channel (blade channel) of the impeller 1 . Within this central area 16, the flow channel towards the support disk 2 is bounded by a quantity of material 18 (solid material), which in turn has a ramp-shaped surface towards the flow channel, ie a ramp 17, over which the pumped liquid flows during operation of the pump assembly. The Ramp 17 increasingly rises from the support disk 2 as the blade 3 radially approaches the impeller axis 15.

In the amount of material 18, two cavities 5, 6 are formed one behind the other in the radial direction, which are closed to the outside except for a channel 9, 10. The cavities 5, 6 are closed on all sides except for an opening 7, 8, which leads into the respective channel 9, 10, i.e. neither half-open nor merely a recess made of the material of the impeller. The cavities are thus located inside the material of the impeller 1. The two channels 9, 10 extend in the axial direction approximately parallel to the impeller axis 15 and each open into a separate opening 11, 12 on the surface of the ramp 17, which is open here.

In the embodiment variant shown here, a radially outer partial area of the radially outer cavity 5 is partially formed in the blade 3, since the wall thickness of the blade 3 is thinner in the area of this outer cavity 5 than in the remaining area of the blade 3. The outer cavity is thus located 5 partially within the amount of material 18, partially within the blade 3. However, the cavity 5 does not extend into the support disk 2.

The two cavities 5, 6 are positioned here together and are designed in terms of their size and geometry such that an axis of inertia of the pump impeller 1 is shifted towards the axis of rotation 15. Because the cavities 5, 6 achieve a local weight saving, which statically counteracts a radial displacement of the center of gravity axis due to the mass of the material quantity 18 and thus eliminates at least part of the imbalance.

Viewed in axial cross section, the two cavities 5, 6 are each formed by the contour of a house with a gable roof 24. The two cavities 5, 6 are delimited radially outwards by a boundary wall 20 on the blade side, radially inwards by a boundary wall 21 on the hub side and in the axial direction by a boundary wall 22 on the carrier disk side. The cavities 5, 6 are separated from one another by a supporting wall 23, on which the area of the quantity of material 18 between the two pitched roofs 24 is supported. The retaining wall 23 forms the hub-side boundary wall 21 for the radially outer cavity 5 and the blade-side boundary wall 20 for the radially inner cavity 6. It should be noted at this point, however, that the two cavities can also be formed by a single cavity. The support wall 23 is therefore not mandatory. Furthermore, the gable roofs 24 do not have to be symmetrical as in the exemplary embodiment.

One of the two channels 9, 10 in the form of a "chimney" connects to the respective pitched roof 24, which begins at the ridge of the pitched roof, where the two openings 7, 8 are also located. The channels 9, 10 are thus based on the radial width of the cavities 5, 6 each arranged centrally. How in particular based on 3 As can be seen, the length of the two cavities 5, 6 extends in an arc in the circumferential direction along a quadrant, with their longitudinal ends being aligned with one another. Thus, the radially inner cavity 6 has a smaller longitudinal extension than the radially outer cavity 5. The channels 5, 6 are each arranged centrally in relation to the longitudinal extension of the cavities 5, 6, so that they lie on a radius to the axis of rotation 15.

In addition to the essentially closed cavities 5, 6, there is a recess 14 (carrier disk pocket) on the back of the carrier disk 2 facing away from the blade 3, which also causes a local weight reduction and serves to shift the axis of inertia towards the axis of rotation. Through the combination of the two cavities 5, 6 and the recess 14, the axis of inertia is shifted to the axis of rotation 15, so that the impeller 1 is balanced overall.

A hub 13 with a conical shaft receptacle 19 (shaft connection) is also integrally formed on the support disk 2, into which a drive shaft of the pump unit for driving the impeller 1 can be inserted and screw-fastened.

The pump impeller 1 according to the invention is manufactured by successively solidifying individual layers of a metal powder by using an additive manufacturing process in which the powder of the respective layer is melted by radiation, in particular a laser beam, where the impeller 1 is to become solid, and in which in at least part of the successive layers a region for forming the cavities 5, 6 in the material interior of the pump impeller 1 is exposed to the laser radiation is released.

After the pump impeller 1 has been manufactured in this way, the two cavities 5, 6 are filled with unsolidified metal powder, which can be removed from the cavities 5, 6 through the openings 7, 8 or through the channels 9, 10. This can be done by blowing compressed air into the channels, for example by means of a hollow needle inserted into the respective channel 9, 10. This blows the powder out. In addition, the impeller can be vibrated at the same time in order to loosen powder adhering to the cavity 5, 6. The channels 9, 10 are closed after the unsolidified powder has been removed, so that no conveyed liquid enters the cavities 5, 6. Thus, the cavities 5, 6 remain hollow during normal operation.

The additive manufacturing process here is selective laser sintering, laser melting or electron beam melting, as is known per se in the prior art. For example, pure titanium (99.9%), an aluminum-silicon-magnesium alloy (AlSi ₁₀ Mg) or an alloy of cobalt-chromium-molybdenum (CoCrMo) can be used as the metal powder. According to the invention, the layers are built up in the axial direction of the pump impeller 1, approximately parallel to the axis of rotation, so that the individual layers extend approximately transversely to the axis of the impeller. First the hub, then the carrier disk and then the blade are each formed in layers.

The layered formation of a pump impeller in the colloquial manner of "3D printing" can take place on the basis of a 3-dimensional computer model of the pump impeller 1, which is calculated in such a way that the pump impeller produced is almost imbalance-free. The basic procedure for the design of a pump impeller according to the invention and the generation of its 3-dimensional computer model is explained below.

The high manufacturing accuracy of additive manufacturing technologies enables a theoretical balancing of impellers in the CAD model and the transfer to the real component. The dynamic balancing (theoretical) of the semi-open pump impeller 1 takes place in two levels I and II (balancing levels). Under certain circumstances, small imbalance deviations in the manufactured impeller only need to be corrected statically so that a small residual dynamic imbalance can be accepted.

Due to the missing cover disc in half-open impellers, only a small axial distance L between the two balancing planes within the support disc is available for the balancing process. This requires a very high hub and large cavities! Recess, which in turn adversely affects the flow. The smaller the plane distance L, the greater the balancing imbalance required.

The problem can be partly avoided by using one of the balancing planes (plane I in 4 ) represents blade 3 itself, while the other plane (plane II in 4 ) remains in the carrier disc 2. The plane distance L is thereby as large as possible, the volume of the recess 14 can be smaller and a significantly smaller support disk 2 can be selected, which reduces the use of material, which saves time and costs, especially when using additive manufacturing processes.

In the method according to the invention, a pump impeller is provided in which material has been removed from the blade body 3, 18 so that hollow chambers 5, 6 are formed. Before the theoretical balancing, the hydraulically optimized impeller 1 has an eccentric center of mass (m _s ·r _s ) and moments of deviation (J _zy , J _zx ) in its inertia. While the former defines the static imbalance, the moment of deviation is responsible for the dynamic imbalance and thus also for the inclination of the main axis of inertia to the axis of rotation 15.

The position and the imbalance (product of mass and center of gravity radius) of the cavities 5, 6 are defined by the design of the impeller 1. The course of the blade is to be adapted in such a way that the cavities 5, 6 lie within the blade body 3, 18 and not the blade surface or the ramp 17 penetrate The cavities 5, 6 are then to be calculated so that they correspond to the previously determined imbalance. Iteratively adapting the cavity dimensions results in a very free cavity design. For example, rounded edges, supporting structures can be integrated without any problems, or the number of cavities can be changed.

The scope of protection is only defined by the appended claims and the invention is therefore not limited to the specific embodiment variant described. Rather, it is clear to the person skilled in the art that the pump impeller according to the invention and its manufacturing method can be modified in many obvious ways without deviating from the basic idea of the invention. For example, the geometry, size, position and number of cavities 5, 6 can deviate from the variant shown in the figures, provided that an overall statically imbalance-free impeller is obtained. For example, only one cavity can be present and/or one or more cavities with a round basic shape viewed in radial cross section. In addition, the roof geometry can be funnel-shaped. As an alternative to production from a metal powder, a plastic or ceramic powder can also be used. Furthermore, instead of being produced by selective laser sintering, laser melting or electron beam melting, a polymer fiber can be melted (fused filament fabrication) in order to form the individual layers, so that cavities which are completely closed on the outside can be produced. Furthermore, the impeller 1 can be constructed in a different layer direction, for example radially to the impeller axis 15. Furthermore, the cavity or cavities can also first be flooded with water and then the channel or channels 9, 10 can be closed. The mass of the water must be taken into account for the positioning, dimensioning and shape of the cavity or cavities. Finally, the carrier disc 2 and/or the hub 13 can be produced independently of the blade 2, in particular separately by casting and subsequent assembly by welding or screw fastening.

Reference List

1

pump impeller

2

carrying disc

3

shovel

5

Outer Cavity

6

inner cavity

7

Opening of the outer cavity

8th

opening of the inner cavity

9

channel

10

channel

11

muzzle opening

12

muzzle opening

13

impeller hub

14

Recess, carrier disc pocket

15

impeller axle

16

Central area, flow channel, vane channel

17

ramp

18

Amount of material, full material

19

Shaft mount, shaft connection

20

Blade-side boundary wall

21

Hub-side boundary wall

22

Boundary wall on the carrier disk side

23

support structure, retaining wall

24

Gable roof/ discharge funnel

Claims (18)

1. Asymmetric pump impeller (1) for a pump unit for conveying a liquid which in particular contains solids, having at least one cavity (5, 6) in the interior of the material of the impeller, said cavity being closed completely towards the outside or except for an opening (7, 8) for the removal of unhardened material from the cavity (5, 6), in which the cavity (5, 6) is positioned and formed in such a way that an inertia axis of the pump impeller (1) is displaced with respect to the axis of rotation (15) of the pump impeller (1) so that the pump impeller is largely free of unbalances, characterised by the pump impeller (1) being formed at least to some extent in layers by an additive production method and the cavity (5, 6) being formed during the production in layers.
2. Pump impeller (1) according to claim 1, characterised by having only one blade (3) that extends in a spiral around the axis of rotation (15).
3. Pump impeller (1) according to claim 2, characterised by having a support plate (2), which is formed integrally with the blade (3) during layered production.
4. Pump impeller (1) according to at least one of the claims 2 or 3, characterised by at least one cavity (5, 6) lying at least partially within the material forming the blade (3) or the support plate (2).
5. Pump impeller (1) according to at least one of the claims 2 or 3, characterised by having, within a central region (16) surrounded by the blade (3), a quantity of material (18) that can be overflowed by the conveyed liquid, in which the at least one cavity (5, 6) is wholly or at least partially formed.
6. Pump impeller (1) according to one of the preceding claims, characterised by an open or subsequently closed channel (9, 10) that leads from the cavity (5, 6) to the outside adjoining the opening (7, 8).
7. Pump impeller (1) according to one of the preceding claims, characterised by the cavity (5, 6) being free from right-angled and/or acute-angled inner edges and/or inner corners, in particular having two boundary walls (20, 21, 22) lying at an angle to each other of the at least one cavity (5, 6) that merge into each other, forming fillet.
8. Pump impeller (1) according to one of the preceding claims, characterised by the at least one cavity (5, 6) in a direction (S), in particular in the direction (S) of the additive layer structure, being closed in the form of a gable roof or in a funnel shape when viewed in cross-section.
9. Pump impeller (1) at least according to claim 6, characterised by the channel (9, 10) opening in the radial direction and/or in the circumferential direction centrally into the cavity (5, 6).
10. Pump impeller (1) according to one of the preceding claims, characterised by the cavity (5, 6) having an internal supporting structure (23), in particular formed like a skeleton.
11. Pump impeller (1) according to claim 10, characterised by the supporting structure (23) having thicker material in at least one location for the purpose of balancing.
12. Pump impeller (1) according to one of the preceding claims, characterised by having two or more cavities (5, 6) separated from one another by a support wall (23).
13. Pump impeller (1) according to claim 12, characterised by the cavities (5, 6) lying behind one another in the radial direction with respect to the impeller axis (4).
14. Pump impeller (1) at least according to claim 3, characterised by having an outwardly open recess (14) or an additional cavity, closed to the outside completely or except for an opening for removing unhardened material, in which the recess (14) or the additional cavity is offset axially relative to a cavity (5, 6).
15. Pump impeller (1) according to claim 14, characterised by the recess (14) or the additional cavity in the support plate (2), and in particular the recess, being formed on the reverse side of the support plate (2) facing away from the blade (3).
16. Method for the production of a pump impeller (1) according to one of the preceding claims, having at least one cavity (5, 6) in the interior of the material of the impeller, said cavity being closed completely towards the outside or except for an opening (7, 8) for the removal of unhardened material from the cavity (5, 6), in which the cavity (5, 6) is positioned and designed in such a way that an inertia axis of the pump impeller (1) is displaced with respect to the axis of rotation (15) of the pump impeller (1) so that the pump impeller is largely free of unbalances, characterised by the pump impeller (1) being formed of individual layers of a material by an additive production method in which a space for the formation of the cavity (5, 6) is left in at least some of the sequential layers.
17. Method according to claim 16, characterised by the material being a powder, notably a metal powder, and unhardened powder being removed from the cavity through a channel (9, 10), in particular being blown out.
18. Method according to claim 17, characterised by the channel being closed after removing the unhardened powder.

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