WO2012131617A1

WO2012131617A1 - Fan wheel made of composite material for centrifugal fan and related method of construction

Info

Publication number: WO2012131617A1
Application number: PCT/IB2012/051518
Authority: WO
Inventors: Federico Bonomelli
Original assignee: Mako Shark S.R.L.
Priority date: 2011-03-30
Filing date: 2012-03-29
Publication date: 2012-10-04
Also published as: EP2691657A1; ITMI20110519A1

Abstract

The present invention concerns a centrifugal fan impeller (1) made of composite material, comprising a plurality of modules (3) arranged side by side to form said impeller (1), first means suitable for interconnecting said modules (3), and second means suitable for connecting said impeller (1) to a hub (2), each of said modules (3) constituting an air duct (1a), with axis (1b), which develops from the central area towards the periphery of said impeller (1), said ducts (1a) being comprised entirely in said modules (3).

Description

TITLE

FAN WHEEL MADE OF COMPOSITE MATERIAL FOR CENTRIFUGAL FAN AND RELATED METHOD OF CONSTRUCTION

DESCRIPTION

The present invention concerns a centrifugal fan impeller made of composite material and relative construction method.

Centrifugal fan impellers can reach considerable dimensions, especially if used for moving large air flows, as occurs in big air conditioning systems. In these machines, the higher the rotation speed, the higher the machine efficiency, and therefore the centrifugal forces at play are particularly intense and it is very important for the impeller to be perfectly balanced.

It is evident that by reducing the masses at play, the above-mentioned parameters become less critical. For this reason impellers have been built in composite material, in particular based on carbon fibres impregnated with epoxy resins.

Said composite materials combine a resistance comparable to that of metals with a density which is a fraction of that of metals. In practice a construction made of carbon fibre-based composite material can have a mass of even less than one third of an analogous steel construction.

Centrifugal fan impellers have been built using appropriately shaped sheets made of composite material, assembling them by structural gluing of appropriate connection elements, also made of composite material. In practice the construction scheme used for metals is replicated, adapted to the different material and relative technology.

This construction technique, however, does not allow the best possible results to be obtained in terms of reduction of the masses, since the joints are particularly critical and, therefore, require particularly heavy and cumbersome connection elements, with the result that also the inner surfaces of the channels of said impellers are not aerodynamically efficient.

Furthermore, the great number of impeller component elements and connection elements between the same, which must be produced manually, translates into a considerable production cost.

In this context, the object of the present invention is to produce an impeller in composite material that overcomes the aforementioned drawbacks of the known art.

In particular the object of the present invention is to produce an impeller made of composite material which allows reduction of the number of elements to be assembled and therefore reduction of the production cost.

A further object of the present invention is to produce an impeller made of composite material characterised by a reduced number of joints which come into contact with the flow of air conveyed.

A further object of the present invention is to produce an impeller made of composite material characterised by a high rigidity which allows use at high rotation regimes.

These objects are substantially achieved by an impeller made of composite material and relative construction method, in accordance with one or more of the attached claims.

The centrifugal fan impeller made of composite material, according to the invention, comprises a plurality of modules positioned side by side to form said impeller, first means suitable for interconnecting said modules, and second means suitable for connecting said impeller to a transmission hub, each of said modules constituting an air duct which develops from the central area towards the periphery of said impeller, said ducts being comprised entirely in said modules. In detail said first means comprise covers, positioned in the upper part and in the lower part of the impeller, made of composite material directly laminated on the outer surface of said modules during assembly of the impeller.

In particular each of said modules has the following properties:

· a general form suitable for being assembled with other modules, so as to constitute the impeller;

• the sections obtained by intersecting cylindrical surfaces having centre of curvature on the impeller axis are closed curves.

According to a preferred embodiment, said modules are provided with appropriate joints to facilitate assembly. The construction can also be reinforced by means of hoops obtained with rings made of composite material, if necessary formed on the impeller itself, or by means of metal rings fixed, for example, with a structural adhesive.

The particular characteristic of the invention is therefore that it minimises the number of structural components that have to be produced in an autoclave to obtain good mechanical and surface characteristics and consequently it reduces the number of components to be assembled.

The impeller thus obtained is without critical joints, with considerable benefits in terms of rigidity, resistance and reduction of the masses, with consequent considerable increase in performance, since the use of an impeller according to the invention allows significantly higher rotation speeds to be reached than in the impellers of the known art.

According to a preferred embodiment, the impeller blades have a wing profile. As will be explained in detail below, this means that between one module and the adjacent module there is an empty space which can be filled with foamed polymer. The invention will now be described, for illustrative non-limiting purposes, according to a preferred embodiment, with reference to the accompanying figures in which:

• figure 1 shows, according to two orthogonal views, an impeller according to the invention;

• figure 2 shows, according to two orthogonal views, an exploded view of an impeller according to the invention;

• figure 3 is an exploded perspective of an impeller according to the invention;

• figures 4 (a, b) show the base module of the impeller, according to three orthogonal views and one perspective view;

• figure 5 shows the assembly of an impeller with blades shaped according to a wing profile.

With reference to the accompanying figures, (1) indicates an impeller made of composite material according to the invention, comprising a plurality of air ducts (1a), with axis (1 b), which develop from the central area towards the periphery. The centrifugal impeller (1), shown in fig. 1 assembled and mounted on a hub (2) of a drive shaft, is obtained by assembling a plurality of modules (3).

Each of said modules (3) coincides substantially with one of the air ducts (1a), and is shown according to three orthogonal views in fig. 4a and according to one perspective view in fig. 4b.

In practice, after assembly, the sides of the adjacent modules will be in contact with one another and will constitute the blades of the impeller.

According to the invention the ducts (1a) of the impeller are comprised entirely in each of the modules (3). In practice the flow of air conveyed by the impeller during passage through the ducts ( a) brushes only the inner surfaces of said modules 3. For this purpose said modules (3) are produced preferably in an autoclave, by means of suitable moulds, in order to obtain inner surfaces of the ducts (1a) characterised by a finish and a surface roughness compatible with the fluid dynamic efficiency required for these devices.

Each module (3) is preferably characterised by the fact that it has the following properties:

• it has a general form suitable for being assembled with other modules (3), so as to constitute an impeller (1);

• the sections obtained by intersecting the cylindrical surfaces (5a, 5b, 5c), having centre of curvature on the "Z" axis of the impeller, are closed curves.

According to the invention, first means are provided suitable for interconnecting said modules (3), to form the impeller (1), and second means suitable for connecting said impeller (1) to the hub (2).

As already mentioned, according to a preferred embodiment, said first means suitable for interconnecting said modules (3) comprise covers, positioned in the upper part and in the lower part of the impeller, made of composite material directly laminated on the outer surface of said modules during assembly of the impeller.

In practice the various modules are glued to one another using composite fibres which are laid on the outer surface of the modules and subsequently impregnated with appropriate resins.

More specifically, said first means, suitable for interconnecting said modules (3) to form said impeller (1), comprise a disc (31) made of composite material, positioned on the lower part of the modules (3), or of the impeller (1 ), and a cap (32) also made of composite material, positioned on the upper part of the modules (3) or of said impeller (1). Advantageously said disc and said cap can be produced by directly laminating the composite material on the outer surface of the modules. In practice it is possible to glue the various modules by means of said cap and said disc instead of using further pre-fabricated joining elements, for example produced in an autoclave by means of a mould.

In fact due to the conformation of the modules (3), which entirely comprise the ducts (1a), these are the only elements that must be produced in an autoclave to obtain inner surfaces with certain characteristics of roughness, as already mentioned above. This allows considerable reduction in the cost and time required to produce the impeller, thanks also to the lesser number of joints to be made between the various elements.

Preferably the impeller (1) is shaped so that the blades have a wing profile.

For this purpose the modules (3) are preferably shaped so that the sides (30a) and (30b) of two adjacent modules form a hollow wing profile (fig. 5).

Said cavity comprised between said sides of the various adjacent modules is preferably filled with a foamed polymer (30c). The presence of the foamed polymer inside the wing profile allows the rigidity of the blade to be considerably increased (up to 15% more compared to a hollow wing profile) with an almost negligible increase in weight.

According to another embodiment said first means, suitable for interconnecting modules (3) to form an impeller (1), also comprise hoops (4a, 4b, 4c), suitable for being mounted in appropriate seats, respectively (7a, 7b, 7c) obtained on said modules (3), said seats (7a, 7b, 7c) being shaped so that, when the modules (3) are assembled, they form substantially cylindrical circular surfaces.

This may be advantageous when the disc (31) and the cap (32) are not sufficiently robust to withstand the centrifugal forces generated at high rotation regimes of the impeller.

Preferably said hoops (4a, 4b, 4c) are provided by bands of composite material, wound directly on the seats (7a, 7b, 7c) of the assembled modules (3), or consist of metallic rings, suitable for being fixed on the seats (7a, 7b, 7c) of the modules (3) according to the known technique, for example by means of adhesive.

The operations for assembly of the modules (3) can be facilitated by providing appropriate joints (not shown), suitable for maintaining the modules in the correct position. Fastening of the various pieces is then made more secure by the use of a structural adhesive.

The modules (3), the disc (31), the cap (32) and the hoops (4a, 4b, 4c) are all made of composite material, for example based on fibreglass, carbon or Kevlar, or a combination thereof, impregnated with epoxy, polyester or vinyl ester resins, or with thermoplastic resins.

Said hoops can be advantageously produced with unidirectional fibre bands.

According to a further embodiment said first means, suitable for interconnecting modules (3) to form an impeller (1), comprise only the hoops (4a, 4b, 4c).

According to the invention said second means, suitable for connecting the impeller

(1) to the hub (2) of the drive shaft, comprise plates (6), integral with the modules

(3), suitable for being coupled with the hub (2) by means of mechanical fastenings, for example by means of bolting, using appropriate holes (6a).

According to a preferred embodiment, the plates (6) form an integral part of the modules (3).

This allows further reduction of the number of elements of the impeller and the number of joints to be made on surfaces brushed by the flow of air, which require particular attention in terms of fluid dynamics. The use of the plates (6) integrated in each module (3) furthermore allows elimination of coupling inaccuracies with respect to the axis of rotation and therefore elimination of the subsequent machining for the balancing and centring necessary in the impellers of the known art.

The impeller (1) is assembled by appropriately positioning side by side the various modules (3) that compose it and locking the same by applying the disc (31), the cap (31) and if necessary the hoops (4a, 4b, 4c). In practice the various modules (3) can be fixed directly on the hub (2) of the drive shaft on which said impeller (1) is mounted without the help of templates or other costly equipment.

Once the modules (3) have been positioned, lamination of the disc (31), the cap (32) and, if present, the hoops (4a, 4b, 4c) can be carried out.

In short the method according to the invention, for the production of impellers (1) made of composite material for centrifugal fans, comprises the following phases:

• production of modules (3) according to the preceding description;

· assembly of said modules (3);

• fastening of said assembled modules (3) by means of a disc (31) laminated directly on the lower part of the impeller (1) and a cap (32) laminated on the upper part of said impeller (1 ), and if necessary by application of the hoops (4a, 4b, 4c).

From the preceding description, it is clear that all the criticalities typical of constructions in composite material, concerning production and joining of the various components, have been eliminated.

The invention has been described for illustrative non-limiting purposes, according to a preferred embodiment. A person skilled in the art will identify numerous other embodiments and variations, all falling within the protective scope of the following claims.

Claims

1. Centrifugal fan impeller (1) made of composite material, comprising a plurality of modules (3) arranged side by side to form said impeller (1), first means suitable for interconnecting said modules (3), and second means suitable for connecting said impeller (1) to a hub (2) of a drive shaft, each of said modules (3) constituting an air duct (1a), with axis (1b), which develops from the central area towards the periphery of said impeller (1), said ducts (1a) being comprised entirely in said modules (3).

2. Impeller (1) made of composite material, according to claim 1 , characterised in that said first means suitable for interconnecting said modules (3) comprise covers located in the upper part and in the lower part of the impeller made of a composite material directly laminated on the outer surface of said modules (3).

3. Impeller (1) made of composite material, as claimed in claim 2, characterised in that said first means, suitable for interconnecting said modules (3) to form said impeller (1), comprise a disc (31) laminated directly on the lower part of said impeller (1).

4. Impeller (1) made of composite material, as claimed in claim 2 or 3, characterised in that said first means, suitable for interconnecting said modules (3) to form said impeller (1), comprise a cap (32) laminated directly on the upper part of said impeller (1).

5. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that said first means, suitable for interconnecting said modules (3) to form said impeller (1), comprise hoops (4a, 4b, 4c) suitable for being mounted in appropriate seats, respectively (7a, 7b, 7c) obtained on said modules (3), said seats (7a, 7b, 7c) being of a shape such that, when said modules (3) are assembled, they form substantially cylindrical circular surfaces.

6. Impeller (1) made of composite material, as claimed in claim 5, characterised in that said hoops (4a, 4b, 4c) comprise bands made of composite material wound directly on said seats (7a, 7b, 7c) of the assembled modules (3).

7. Impeller (1) made of composite material, as claimed in claim 6, characterised in that said bands made of composite material wound directly on said seats (7a, 7b, 7c) of the assembled modules (3) comprise unidirectional fibre bands.

8. Impeller (1) made of composite material, as claimed in claim 5, characterised in that said hoops (4a, 4b, 4c) comprise metal rings suitable for being fixed on said seats (7a, 7b, 7c) of the assembled modules (3).

9. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that said second means, suitable for connecting said impeller (1) to said hub (2), comprise plates (6), integral with said modules (3), suitable for being coupled with said hub (2) by means of mechanical fastenings, said plates (6) being part of said ducts (1a).

10. Impeller (1) made of composite material, as claimed in claim 9, characterised in that said plates (6) form an integral part of said modules (3).

11. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that the sides (30a) and (30b) of said modules are shaped so as to obtain a hollow wing profile, a foamed polymer (30c) being inserted between said sides of adjacent modules.

12. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that each of said modules (3) has the following properties:

· a general form suitable for being assembled with other modules (3), so as to constitute said impeller (1); • the sections obtained by intersecting cylindrical surfaces (5a, 5b, 5c), having centre of curvature on the "Z" axis of the impeller, are closed curves.

13. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that on said modules (3) joints are obtained suitable for facilitating the assembly operations.

14. Impeller (1) made of composite material, as claimed in any one of the preceding claims, characterised in that said composite materials comprise fibreglass, carbon, Kevlar or combinations thereof, impregnated with epoxy, polyester or vinyl ester resins, or with thermoplastic resins.

15. Method for the production of centrifugal fan impellers (1 ) made of composite material, characterised in that it comprises the following steps:

• production of modules (3) according to one of the claims from 1 to 14;

• assembly of said modules (3);

• fastening of said assembled modules (3) by means of a disc laminated directly on the lower part of the impeller (1) and a cap (32) laminated on the lower part of said impeller (1 ).

16. Method for the production of centrifugal fan impellers (1 ) made of composite material, characterised in that it comprises the following steps:

• production of modules (3) according to one of the claims from 1 to 14; · assembly of said modules (3);

• fastening of said assembled modules (3) by the application of hoops, according to claims 5, 6, 7 and 8.