WO2019229434A1

WO2019229434A1 - Impeller and method of manufacture

Info

Publication number: WO2019229434A1
Application number: PCT/GB2019/051468
Authority: WO
Inventors: Michael CATHERINE
Original assignee: CNC Subcon Services Limited
Priority date: 2018-05-30
Filing date: 2019-05-29
Publication date: 2019-12-05
Also published as: GB201808843D0; GB201812843D0; GB2574221A

Abstract

A closed impeller and a method of manufacture is disclosed. The closed impeller comprises a main bore side plate and an eye side plate. The main bore side and eye side plates are manufactured by machining samples of a chosen material, such as solid billets of metal. An integral part of the main bore side plate is a vane structure which can be customised according to the desired specifications. The main bore side and eye side plates are welded together. The closed impeller can be machined from high quality billets of metal with minimal defects, to tolerances of ± 0.1 mm across all surfaces. The closed impeller is quick and cost effective to manufacture whilst exhibiting less vibrations and improved performance when operational in a centrifugal pump.

Description

Impeller and Method of Manufacture

The present invention relates to an impeller, and a method of manufacture. In particular, the described impeller is a closed impeller suitable for use in a multistage hydraulic pump. The method of manufacturing said impeller provides an alternative to conventional methods known in the art.

Background to the Invention

Figure 1 depicts a centrifugal pump 1 known in the art. The pump 1 comprises an impeller 2 housed within a casing 3. The impeller 2 is axially connected via a drive shaft 4 to a motor 5 and the impeller 2 comprises one or more radial vanes 6. When the centrifugal pump 1 is operational such that the impeller 2 is rotating, a fluid 7 is sucked through a central, axial input pipe 8 towards the centre of the impeller 2. The impeller 2 accelerates the fluid 7 radial outwards into a volute chamber 9 as defined by the casing 3. The impeller 2 transfers rotational energy provided by the motor 5 to kinetic energy of the fluid 7. The casing 3 directs the accelerated fluid 7 towards an output pipe 10. The fluid 7 therefore exits the centrifugal pump 1 with an increased kinetic energy. Centrifugal pumps used in more demanding applications, such as a hydraulic system as opposed to a water pump, typically comprise a closed impeller. A closed impeller has two plates located either side of the vanes as opposed to a semi open impeller which has a plate on just one side of the vanes and an open impeller that does not have a plate on either side of the vanes. A closed impeller, also termed a shrouded impeller, is more efficient than semi open and open impellers.

Impellers are typically made of a metal. A common method of manufacturing a metal impeller is termed sand casting. Sand casting involves first creating a mould from sand where the mould comprises a three-dimensional hollow shape resembling the desired component, e.g. a closed impeller. Then, a metal, such as steel or Aluminium, is heated until in liquid form. The liquid metal is poured into the mould and given sufficient time to cool. The resulting casting, the impeller, is extracted from the mould.

Sand casting is a common method for manufacturing one-piece components, yet this method does have disadvantages. Sand casting is limited to producing components made from a material which be heated into liquid form and solidifies when cooled such as a metal.

A metal component produced by sand casting can have numerous types of defects, such as gas porosity defects, shrinkage defects, pouring metal defects and metallurgical defects. An example of a gas porosity defect is a blowhole defect. This occurs as some liquid metals can hold a quantity of dissolved gas whereas the corresponding solidified metal cannot. The dissolved gas escapes forming air cavities in the casting as the liquid metal cools and solidifies.

Defects can also result in a cast component having a non-uniform density distribution. A sand cast impeller with defects may be unbalanced which would introduce vibrations and ultimately limit the performance of a pump. Defects can also limit the tolerance for components manufactured by sand casting methods, which is typically of the order of ± 3.0 mm. To improve the tolerance, or even compensate for defects, sand cast impellers may require iterative machining to optimise the impeller’s performance within a pump, adding time and expense to the production process. Manufacturing components by sand casting can therefore be time consuming and it can take up to twelve weeks to produce a closed impeller, depending on the complexity of the components involved. Furthermore, before casting a component, a mould is required which can take time to produce. The mould can also be a limitation. Following production, the mould cannot be modified or customised and if the mould is damaged this can further delay the manufacture of a component.

The method of sand casting is a relatively simple concept which can produce complex cast components comprising internal surfaces, albeit with limited tolerance levels. For example, by designing an appropriate mould it is possible to sand cast a closed impeller where the vanes are enclosed by two plates. However, the internal surfaces of the sand cast component are inaccessible such that any defects and the tolerances of the internal structures cannot be assessed. Furthermore, it has proven difficult to add a coating to the internal structures of a metallic cast component produced by such sand casting

methodologies.

Summary of the Invention

It is an object of an aspect of the present invention to provide an impeller and method of manufacture that obviates or at least mitigates one or more of the aforesaid disadvantages of the impellers and sand casting method of production known in the art.

According to a first aspect of the present invention there is provided a closed impeller comprising a main side bore plate mechanically connected to an eye side plate and one or more integral vane structures formed on a surface of the main side bore plate and or a surface of the eye side bore plate wherein the one or more vane structures comprise one or more vanes.

Most preferably, one or more apertures and one or more corresponding protrusions mechanically connect the main side bore plate to the eye side plate.

Most preferably, the main side bore plate comprises an integral vane structure comprising one or more vanes wherein the one or more protrusions comprise one or more vane extensions. In this embodiment corresponding apertures are located on the eye side plate. Preferably, the eye side plate may comprise an integral vane structure comprising one or more vanes wherein the one or more protrusions comprise one or more vane extensions.

In this embodiment corresponding apertures are located on the main bore side plate.

Preferably, the one or more apertures may be located upon the one or more vanes.

Preferably, the one or more vane extensions comprises a taper at a distal end the one or more vanes. The taper may comprise a 45-degree taper.

Preferably, the one or more apertures comprise a tapered side wall. The side walls are tapered at an angle f of 60-degrees relative to a radial axis of the closed impeller.

Alternatively, the one or more apertures comprising one or more cavities.

Preferably, the eye side plate comprises an inlet cavity which has a diameter greater than a central bore of the main bore side plate.

Optionally, the closed impeller comprises one or more wear ring supports.

According to a second aspect of the present invention there is provided a method for producing a closed impeller comprising:

providing a main bore side plate;

providing an eye side plate;

providing one or more integral vane structures comprising one or more vanes formed on a surface of the main side bore plate and or a surface of the eye side bore plate; and

mechanically connecting the main bore side plate to the eye side plate.

Most preferably, the method further comprises providing one or more apertures and one or more corresponding protrusions to mechanically connect the main side bore plate to the eye side plate.

Most preferably, providing one or more corresponding protrusions comprises forming one or more vane extensions on an integral vane structure located on the main side bore plate. In this embodiment corresponding apertures are provided on the eye side plate.

Preferably, providing one or more corresponding protrusions comprises forming one or more vane extensions on an integral vane structure located on the eye side plate. In this embodiment corresponding apertures are provided on the main bore side plate.

The method may further comprises providing the one or more apertures upon the one or more vanes.

Preferably, forming one or more vane extensions comprises forming a taper at a distal end the one or more vanes. The taper may comprise a 45-degree taper.

Preferably, providing the one or more apertures comprises providing the apertures with tapered side walls. Optionally, the side walls are tapered at angle f of 60-degrees relative to a radial axis of the closed impeller.

Preferably, providing the one or more apertures comprise providing a cavity suitable for receiving a protrusion.

Most preferably, providing a main bore side plate comprises machining the main bore side plate from a metal billet.

Most preferably, providing an eye side plate comprises machining the eye side plate from a metal billet.

Preferably, machining the main bore side plate and or eye side plate comprises machining an additional margin to provide an interference fit. The additional margin may comprise a + 1 mm margin.

Most preferably, machining comprises rough turning and or milling.

Optionally, providing the main bore side plate further comprises cleaning and or degreasing the main bore side plate. Similarly, providing the eye side plate further comprises cleaning and or degreasing the eye side plate. Preferably, mechanically connecting the main bore side plate to the eye side plate comprises pressing together the eye side plate and main bore side plate.

Optionally, mechanically connecting the main bore side plate to the eye side plate further comprises pre-heating the eye side plate and or the main bore side plate before pressing together the eye side plate and main bore side plate.

Optionally, mechanically connecting the main bore side plate to the eye side plate further comprises employing a through bold assembly and or one or more clamps to fasten the main bore side plate to the eye side plate.

Optionally, mechanically connecting the main bore side plate to the eye side plate further comprises bolting the main bore side plate to the eye side plate.

Preferably, mechanically connecting the main bore side plate to the eye side plate further comprises welding the main bore side plate to the eye side plate.

Welding the main bore side plate to the eye side plate may comprise tack welding and or arc welding and or puddle welding.

Optionally, the method further comprises assessing the quality of a weld. This may comprise assessing the quality of the weld using ultrasonic testing. The method may further comprise rectifying any defects found from assessing the quality of the weld.

The method may further comprise machining the closed impeller to a predetermined tolerance level.

Optionally, the method may further comprises assessing the quality of the closed impeller using one or more non-destructive testing techniques.

Embodiments of the second aspect of the invention may comprise features to implement the preferred or optional features of the first aspect of the invention or vice versa.

According to a third aspect of the present invention there is provided a closed impeller comprising a main side bore plate, an eye side plate and one or more vanes wherein the one or more vanes are mechanically connected to the main side bore plate and the eye side plate.

Optionally the one or more vanes may be formed as a single vane structure.

Embodiments of the third aspect of the invention may comprise features to implement the preferred or optional features of the first and or second aspect of the invention or vice versa.

According to a fourth aspect of the present invention there is provided a method for producing a closed impeller comprising:

providing a main bore side plate;

providing an eye side plate;

providing one or more vanes; and

mechanically connecting the one or more vanes to the main side bore plate and the eye side plate.

Optionally providing the one or more vanes comprises providing a single vane structure.

Embodiments of the fourth aspect of the invention may comprise features to implement the preferred or optional features of the first, second and or third aspect of the invention or vice versa.

Brief Description of Drawings

There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

Figure 1 presents a perspective view of a centrifugal pump known in the art;

Figure 2 presents a perspective view of a closed impeller in accordance with the present invention;

Figure 3 presents an exploded perspective view of the closed impeller of Figure 2 showing a main bore side plate and an eye side plate;

Figure 4 presents a perspective view of an alternative embodiment of the main bore side plate of the closed impeller of Figure 2;

Figure 5 presents a perspective close-up view of the main bore side plate of the closed impeller of Figure 2;

Figure 6 presents a cross-sectional view of the eye side plate of the closed impeller of Figure 2;

Figure 7 presents a flow chart of the method of manufacturing the closed impeller of Figure

2;

Figure 8 presents a cross-section view of the closed impeller of Figure 2 held in one or more clamps and a through bold assembly;

Figure 9 presents a perspective view of an alternative embodiment of the closed impeller of Figure 2;

Figure 10 present a perspective view of a further alternative embodiment of the closed impeller of Figure 2; and Figure 11 present a perspective view of yet a further alternative embodiment of the closed impeller of Figure 2.

In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of embodiments of the invention.

Detailed Description of the Preferred Embodiments

In the context of this specification, the term“integral part” or“integral component” refers to, a single component comprising two or more parts manufactured from a single material.

An explanation of the present invention will now be described with reference to Figures 2 to 9.

Figure 2 depicts a perspective view of a closed impeller 11 while Figure 3 presents an exploded perspective view of the closed impeller 11. The closed impeller 11 comprises two separate components, a main bore side plate 12 and an eye side plate 13 both of which are centred about a central axis 14, as can clearly be seen in Figure 3.

The main bore side plate 12 comprises a first surface 15 substantially opposing a second surface 16. Similarly, the eye side plate 13 comprises a third surface 17 substantially opposing a fourth surface 18. These surfaces 15, 16, 17, 18 are all substantially perpendicular to and centred about the central axis 14.

Figure 3 shows that an integral part of the main bore side plate 12 is a vane structure 19 located on the second surface 16. The vane structure 19 is an integral part or component of the main bore side plate 12 i.e. it is a single component, manufactured from one sample of a material. The vane structure 19 is therefore simply a feature of the second surface 16 of the main bore side plate 12. In other words, the vane structure 19 is not manufactured separately and then fixed (e.g. by welding) to the main bore side plate 12. In practice, the main bore side plate 12 is machined from a single solid billet, as described in further detail below. The vane structure 19 can be seen to comprise four vanes 6 extending out radially from the central axis 14 along a radial axis 20. The number and shape of the vanes 6, and thus the vane structure 19 as a whole, can be customised depending on the required specification for the closed impeller 11. For example, Figure 4 shows an alternative vane structure 19a where the vanes 6 spiral across the first surface 15 along the radial axis and an axis about the central axis 14 termed a theta axis 21.

Figure 5 shows a cross-section of a vane 6 of the vane structure 19 of Figure 3. The distal end 22 of the vane 6 comprises a protrusion which takes the form of a vane extension 23. The vane extension 23 comprises a 45-degree taper. The purpose of the vane extension 23 is to facilitate combining the main side bore plate 12 and eye side plate 13, as described in further detail below.

Figure 3 also shows that the main bore side plate 12 further comprises a central bore 24 centred about the central axis 14 and extending between the first 15 and second 16 surfaces. The dimensions of the central bore 24 are proportioned to accept a drive shaft 4 along the central axis 14 from a motor 5. The central bore 24 may take the form of a straight bore with an internal keyway commensurate with the drive shaft 4. Alternatively, the central bore 24 may be threaded.

A further integral part or component of the main bore side plate 12, centred about the central axis 14, is a first wear ring support 25. The first wear ring support 25 protrudes from the first surface 15 and is located about the perimeter of the central bore 24. The first wear ring support 25 is designed to support a first wear ring (not shown).

The impeller 11 when rotating within a pump 1 requires clearance between the casing 3 to rotate freely. To maximise the efficiency of the pump 1 it is necessary to minimise the fluid 7 leaking from the high pressure side of the pump 1 , the volute chamber 9. The purpose of the wear ring is to fluidly seal the gap between an impeller 11 and the casing 3 of a pump 1. The wear ring may be made from a different material to the impeller 11 and or the casing 3. Whilst degradation of the wear ring is unavoidable, the wear ring can be more readily replaced than the impeller 11 or casing 3 when maintaining the pump 1. In the context of this specification, a wear ring is defined as a separate component of a centrifugal pump 1 and not part of the impeller 11. The impeller 11 therefore comprises the wear ring support 25 to accommodate a wear ring and are typically used for high speed multistage hydraulic pumps that run at 3000 to 6000 revolutions per minute (rpm). Impellers without a wear ring support 25 are intended to be employed for lighter duties i.e. run as a lower rmp specification pump.

The eye side plate 13 can be seen to comprise four apertures 26 extending between the third 17 and fourth 18 surfaces, as presented within the embodiment shown in Figure 3. The apertures 26 are shaped to receive the vane extensions 23 of the vanes 6. In other words, the apertures 26 of the eye side plate 13 are commensurate with the vane structure 19 of the main side bore plate 12. For example, Figure 3 shows four apertures 26 extending along the radial axis 20. It will be appreciated by the skilled reader that the number of apertures 26 should correspond to the number of vane extension 23

incorporated within the main bore side plate 12.

The apertures 26 comprises a side wall 27 which is the surface extending between the third 17 and fourth 18 surfaces. Preferably the side wall 27 is not orthogonal to the third 17 and fourth 18 surfaces. The angle of the side wall 27 relative the radial axis 20 is defined by angle cp, see Figure 6. For example, f may be 60-degrees. The angle f may vary according to which angle is most favourable for combining, i.e. welding together, the main bore side 12 and eye side 13 plates.

Figure 3 also shows that the eye side plate 13 comprises an inlet cavity 28 centred about the central axis 14 and extending between the third 17 and fourth 18 surfaces. The inlet cavity 28 has a wider diameter than the bore 24 of the main bore side plate 12. The inlet cavity 28 is connected to an input pipe 8 of a centrifugal pump 1. The inlet cavity 28 provides a means for the fluid 7 to enter the impeller 11.

An integral part or component of the eye side plate 13, centred about the central axis 14, is a second wear ring support 29. The second wear ring support 29 protrudes from the fourth surface 18 and is located about the perimeter of the inlet cavity 28. The second wear ring support 29 is intended to support a second wear ring.

It will be appreciated by the skilled reader that the location of the protrusions and or vane extensions 23 can be interchanged with the location of the apertures 26. In other words, the eye side plate 13 may comprise a vane structure 19 comprising vanes 6 and vane extensions 23 whilst the main bore side plate 12 may comprise the corresponding apertures 26. In addition, both the main bore side plate 12 and eye side plate 13 may comprise a combination of the protrusions 23 and apertures 26. The apertures may also be formed on the vanes 6.

Method of Manufacture

The method of manufacture of the closed impeller 11 will now be described with reference to Figure 7 and Figure 8. Figure 7 depicts a flow chart of the method of manufacturing the closed impeller 11. The closed impeller 11 is manufactured by providing the main bore side 12 and eye side 13 plates (S1001 , S1002). This may involve machining these components from two separate samples of a chosen material. More specifically, the two plates 12, 13 are machined from two solid billets of the chosen metal. In the context of this application, a billet is a cylindrical length of metal. In comparison to stationary cast metal, a billet has fewer defects as is produced by, for example, continuous casting. Using a billet, a higher quality sample of metal, has the advantage of eliminating issues

encountered with the above described sand casting defects.

Turning is the process of shaping a sample of material, in this case the billet, by rotating the billet relative to a stationary blade. Whereas, milling is cutting a shape within a sample of material using a rotating blade.

The main bore side plate 12 is preferably manufactured by first rough turning a billet to define the central bore 24, the first wear ring support 25 and a trim diameter of the impeller 11 whilst leaving an additional margin of + 1 mm. The trim diameter is the outside diameter of the impeller 11.

Similarly, the eye side plate 13 is preferably manufactured by first rough turning a billet to define the second wear ring support 29 and a trim diameter of the impeller 11 , again leaving an additional margin of + 1 mm.

After the rough turn, the involute detail is milled to provide one or more integral vane structures comprising one or more vanes formed on a surface of the main side bore plate and or a surface of the eye side bore plate (S1003). In the presently described

embodiment the vane structure 19 is milled onto the second surface 16 of the main bore side plate 12. As described above, the vane structure 19 comprises one or more vanes 6 with vane extensions 23. The corresponding one or more apertures 26 are milled from the fourth surface 18 through to the third surface 17 of the eye side plate 13. The one or more vanes 6 are milled with an additional margin of, for example + 1 mm, such that they have an interference fit with the one or more apertures 26. Next, it is preferable for both the main bore side 12 and eye side 13 plates to be cleaned and degreased in preparation for mechanically connecting the main bore side plate 12 to the eye side plate 13 (S1004).

In a preferred embodiment, the main bore side plate 12 is kept at room temperature and placed into one or more clamps 30, while in an unfastened position, in preparation for receiving the pre-heated eye side plate 13.

The eye side plate 13 is then pre-heated to a specified temperature dependent on the thermal expansion rate characteristics of the billet material. For example, where the billet is made of Aluminium the pre-heating temperature is around 180 degrees Celsius. The pre-heated eye side plate 13 is then pressed onto the vanes 6 of the main bore side plate 12 (S1004). It is important to ensure that all the vane extensions 23 of the one or more vanes 6 align and protrude through the corresponding one or more apertures 26. The eye side plate 13 is then allowed to cool back down to room temperature in situ upon the main bore side plate 12 such that the vane extensions 23 form an interference fit with their corresponding apertures 26.

In order, to ensure the two plates 12, 13 remain fully abutted, the one or more clamps 30 about the perimeter of the main bore side 12 and eye side 13 plates are tightened and a through bolt assembly 31 is provided which passes through the inlet cavity 28 and central bore 24 along the central axis 14, as presented in Figure 8.

The next stage involves tack welding the main bore side 12 and eye side 13 plates together. More specifically, the third surface 17 of the eye side plate 13 is tack welded to the vanes 6 and the four corners of the apertures 26 are tack welded to the corresponding vane extensions 23 from the fourth surface 18.

Following the above process, the vane extensions 23 are arc welded to the corresponding apertures 26 where the apertures 26 act as a“V” shaped welding joint (or prep). Before arc welding, the tack welded components are pre-heated according to the requirements of the arc welding procedure for the specific material of the plates 12, 13. The quality of the arc weld may be assessed from both surfaces 17, 18 of the eye side plate 13. More specifically, the internal vane juncture may be checked using, for example, a sea snake camera.

Once the arc weld is complete, it is preferable for any excess material of the weld to be machined off.

As an additional, complementary or alternative method of combining the main bore side 12 and the eye side 13 plates, the two plates 12, 13 may be bolted together, as depicted by Figure 9.

More specifically, the apertures 26, may take the form of one or more cavities 32 which are machined into the third surface 17 of the eye side plate 13 and which are suitable for receiving a protrusion e.g. a vane extension 23. The cavities 32 differ from the apertures 26 in that they do not protrude all the way through the eye side plate 13 to the fourth surface 18. The vane extensions 23 of the main bore side plate 12 are fixed within the corresponding vane extension cavity 32 by multiple bolts 33 about the perimeter of the vane extensions 23, for example, every 20 mm. The bolts 33 are countersunk into fourth surface 18 of the eye side plate 13 and extend through into the vanes 6 of the main bore side plate 12. A puddle weld covers the heads of the bolts 33.

As yet a further additional, complementary or alternative method of combining the main bore side 12 and the eye side 13 plates, the vane extensions 23 of the main bore side plate 12 are fixed within the corresponding vane extension cavities 32 by an interference fit. Forming the interference fit may be assisted by thermally expanding the plate 12 and or 13 upon which the vane extension cavities 32 are located. The main bore side 12 and the eye side 13 plates are further secured in position by welding. In this alternative method, bolts 33 are an optional additional fixing method.

Ultrasonic testing of the arc weld and or puddle weld may then be performed from the fourth surface 18 of the eye side plate 13 to identify any defects which, depending on the type of defect, are removed using appropriate techniques known in the art. For example, a defect can be removed by machining, i.e. grinding out the defect, and the corresponding affected area then being re-welded. The closed impeller 11 can then be removed from the clamps 30 and the through bolt assembly 31 to relieve the stress and allow the closed impeller 11 to cool.

Finally, the closed impeller 11 is machined all over to achieve the desired tolerances.

Non-destructive testing techniques may be used to test the quality of the closed impeller 11. The non-destructive testing techniques depend on the material of the closed impeller 11. Examples of non-destructive testing techniques include running the closed impeller 11 in a pump to assess the performance of the closed impeller 11 and or performing corrosion tests on the material of the closed impeller 11.

Appropriate markings can be added to the closed impeller 11 to indicate, for example, material composition, part number according to quality control procedures.

In general, a closed impeller 11 could be manufactured from any material according to the above method by adapting the pre-heating temperature and or welding temperature to suit the chosen material. If the material is non-metallic an alternative bonding method to welding may be required.

As further alternatives to the closed impeller 11 , it will be appreciated by a person skilled in the art that the closed impeller 11 may comprise three or more separate components. In addition to the main bore side plate 12 and the eye side plate 13, the closed impeller may comprise: a single vane structure 34 with four vanes 35, as can be seen in Figure 10; or alternatively the vanes 35 may comprise independent components, as can be seen in Figure 11. Both distal 22 and proximal 36 ends of the four vanes 35 comprise vane extensions 23 which are commensurate with apertures 26 on both the main bore side plate 12 and the eye side plate 13.

As a corresponding alternative method of manufacturing the closed impeller 11 of Figures 10 and 11 , instead of providing one or more integral vane structures 19 on a surface 16 of the main bore side plate 12 and or a surface 17 of the eye side bore plate 13 (S1003), the method instead comprises providing an independent vane structure 34 or providing one or more individual vanes 35, for example, machined from solid billets of a chosen material. Furthermore, mechanically connecting the main bore side plate 12 and eye side plate 13 (S1004), instead comprises mechanically connecting the main bore side plate 12, eye side plate 13 and vane structure 34 or one or more individual vanes 35. More specifically, mechanically connecting the three or more components may comprise the use of interference fittings, welding, puddle welding, bolts and or rivets.

A key advantage is that all the surfaces of the closed impeller 11 , the internal surfaces 16, 17 and the external surfaces 15, 18, can be machined to a desired tolerance.

Furthermore, it is possible to coat all the surfaces 15, 16, 17, 18 of the closed impeller 11 before welding together the main bore side 12 and eye side 13 plates. This is not only due to being able to access the internal surfaces 16, 17 but also due to the fact that the plates 12,13 are machined and cleaned prior to being pressed together and as such the coating can readily adhere to the exposed surfaces 15, 16, 17, 18.

Manufacturing the closed impeller 11 by machining a billet also has the advantage of minimising the number of defects present within the final product. Furthermore, the improved tolerances from machining techniques, typically ± 0.1 mm as opposed to ± 3.0 mm for sand casting, result in improved balance, less vibrations and ultimately improved performance of the closed impeller 11 when operated e.g. within a centrifugal pump 1. The improved tolerances also allow the closed impeller 11 to be machined to the specified trim diameter as opposed to final machining a sand cast impeller after pump test flowrates to compensate for defects and imbalance.

A further advantage of the closed impeller 11 arising from machining the plates 12,13 is the fact that the vane structure 19 of the main bore side plate 12 can be customised according to the required specifications of the closed impeller 11. The described methods of manufacture are also significantly quicker and cheaper than sand casting.

The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

1. A closed impeller comprising a main side bore plate mechanically connected to an eye side plate and one or more integral vane structures formed on a surface of the main side bore plate and or a surface of the eye side bore plate wherein the one or more vane structures comprise one or more vanes.

2. A closed impeller as claimed in claim 1 wherein, one or more apertures and one or more corresponding protrusions mechanically connect the main side bore plate to the eye side plate.

3. A closed impeller as claimed in claim 2 wherein, the main side bore plate comprises an integral vane structure comprising one or more vanes wherein the one or more protrusions comprise one or more vane extensions.

4. A closed impeller as claimed in claim 3 wherein, the corresponding apertures are

located on the eye side plate.

5. A closed impeller as claimed in any of claims 2 to 4 wherein, the eye side plate may comprise an integral vane structure comprising one or more vanes wherein the one or more protrusions comprise one or more vane extensions.

6. A closed impeller as claimed in claim 5 wherein, the corresponding apertures are

located on the main bore side plate.

7. A closed impeller as claimed in any of claims 2 to 6 wherein, the one or more apertures may be located upon the one or more vanes.

8. A closed impeller as claimed in any of claims 3 to 7 wherein, the one or more vane extensions comprises a taper at a distal end the one or more vanes.

9. A closed impeller as claimed in any of claims 2 to 8 wherein, the one or more apertures comprise a tapered side wall.

10. A closed impeller as claimed in any of claims 2 to 9 wherein, the one or more apertures comprises one or more cavities.

11. A method for producing a closed impeller, the method comprising:

providing a main bore side plate;

providing an eye side plate;

mechanically connecting the main bore side plate to the eye side plate.

12. A method for producing a closed impeller as claimed in claim 11 wherein, the method further comprises providing one or more apertures and one or more corresponding protrusions to mechanically connect the main side bore plate to the eye side plate.

13. A method for producing a closed impeller as claimed in claim 12 wherein, providing one or more corresponding protrusions comprises forming one or more vane extensions on an integral vane structure located on the main side bore plate.

14. A method for producing a closed impeller as claimed in claim 13 wherein, the

corresponding apertures are provided on the eye side plate.

15. A method for producing a closed impeller as claimed in any of claims 12 to 14 wherein, providing one or more corresponding protrusions comprises forming one or more vane extensions on an integral vane structure located on the eye side plate.

16. A method for producing a closed impeller as claimed in claim 15 wherein, the

corresponding apertures are provided on the main bore side plate.

17. A method for producing a closed impeller as claimed in any of claims 12 to 16 wherein, the method further comprises providing the one or more apertures upon the one or more vanes.

18. A method for producing a closed impeller as claimed in any of claims 13 to 17 wherein, forming one or more vane extensions comprises forming a taper at a distal end the one or more vanes.

19. A method for producing a closed impeller as claimed in any of claims 12 to 18 wherein, providing the one or more apertures comprises providing the apertures with tapered side walls. and or providing a cavity suitable for receiving a protrusion.

20. A method for producing a closed impeller as claimed in any of claims 11 to 19 wherein, providing a main bore side plate comprises machining the main bore side plate from a metal billet and or providing an eye side plate comprises machining the eye side plate from a metal billet.

21. A method for producing a closed impeller as claimed in claim 20 wherein, machining the main bore side plate and or eye side plate comprises machining an additional margin to provide an interference fit.

22. A method for producing a closed impeller as claimed in any of claims 11 to 21 wherein, providing the main bore side plate and or eye side plate further comprises cleaning and or degreasing the main bore side plate and or eye side plate.

23. A method for producing a closed impeller as claimed in any of claims 11 to 22 wherein, mechanically connecting the main bore side plate to the eye side plate comprises: pre-heating the eye side plate and or the main bore side;

pressing together the eye side plate and main bore side plate;

employing a through bold assembly and or one or more clamps to fasten the main bore side plate to the eye side plate; and

- welding the main bore side plate to the eye side plate.

24. A method for producing a closed impeller as claimed in any of claims 11 to 23 wherein, mechanically connecting the main bore side plate to the eye side plate further comprises bolting the main bore side plate to the eye side plate.

25. A method for producing a closed impeller as claimed in any of claims 11 to 24 wherein, the method further comprises machining the closed impeller to a predetermined tolerance level.