CONNECTING ELEMENT FOR CONNECTING A BLADE TO THE HUB IN AN INDUSTRIAL AXIAL FAN, AND BLADE SYSTEM COMPRISING SAID CONNECTING ELEMENT

Abstract

The present invention concerns a connecting element for connecting a blade, or airfoil profile, to the hub of an industrial axial fan, a blade system comprising said connecting element, and an industrial axial fan comprising such blade system. The connecting element (1) for connecting a blade (10) to the hub (20) of an industrial axial fan according to the present invention, is realized in a single L-shaped piece comprising a first part (1a) having a substantially straight develop and a second part (1b) having a substantially straight develop, said first (1a) and second (1b) part being connected by a linking part (1c) presenting a curvature radius, said first (1a) and second (1b) parts lying on substantially perpendicular planes. The connecting element according to the present invention allows to achieve several advantages with respect to the prior art, one of said advantages consisting of its extremely simple shape and manufacturing process, which render the connecting element economically advantageous.

Claims

1. Connecting element (1) for connecting a blade (10) to the hub (20) of an industrial axial fan, said connecting element (1) being realized in a single L-shaped piece comprising a first part (1a) having a substantially straight develop and a second part (1b) having a substantially straight develop, said first (1a) and second (1b) part being connected by a linking part (1c) presenting a curvature radius, said first (1a) and second (1b) parts lying on substantially perpendicular planes.

2. Connecting element (1) according to claim 1, characterized in that said first part (1a) and said second part (1b) lie on planes inclined of an angle which realizes directly on the connecting element instead of on the hub the blade precone angle.

3. Connecting element (1) according to claim 1, characterized in that said first part (1a) is shorter than said second part (1b).

4. Connecting element (1) according to claim 1, characterized in that it has a quadrangular cross-section.

5. Connecting element (1) according to claim 1, characterized in that it has a rectangular cross-section.

6. Connecting element (1) according to claim 1, characterized in that it is made of metallic material.

7. Connecting element (1) according to claim 1, characterized in that it is made of plastic material.

8. Connecting element (1) according to claim 1, characterized in that it is made of fiber glass material.

9. Connecting element (1) according to claim 1, characterized in that it is obtained by a manufacturing process comprising the following steps: providing a sheet of metallic, plastic or fiberglass material; cutting and drilling said metallic sheet; bending the cut and drilled sheet obtaining the final L-shaped piece.

10. Connecting element (1) according to claim 1, characterized in that it is obtained by a manufacturing process comprising the following steps: providing a semi finished product obtained by extrusion or pulltrusion; cutting and drilling said semi finished product; bending the cut and drilled semi finished product.

11. Blade assembly (100) of an industrial axial fan comprising: a blade (10), a hub (20), a connecting element (1), characterized in that said connecting element (1) is realized in a single L-shaped piece comprising a first, shorter, part (1a) having a straight develop and a second part (1b) having a substantially straight develop, said first (1a) and second (1b) part being connected by a linking part (1c) presenting a curvature radius, said first (1a) and second (1b) parts lying on perpendicular planes.

12. Blade assembly (100) according to claim 11, characterized in that said first (1a) and second (1b) part being connected by a linking part (1c) presenting a curvature radius, said first (1a) and second (1b) parts lying on planes inclined of an angle which realizes directly on the connecting element instead of on the hub the blade precone angle.

13. Blade assembly (100) according to claim 11, characterized in that said first part (1a) is shorter than said second part (1b), and in that said first part (1a) of said connecting element (1) is connected to the hub (20) and said second part (1b) of said connecting element (1) is connected to the blade (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Further characteristics and advantages of the present invention will become clear from the following detailed description of a preferred embodiment that is merely illustrative and not limitative and is shown in the figures that are attached hereto, in which:

[0076] FIGS. 1a, 1b, 2a, 2b, 2c, 2d, 2e, 2f show different examples of blade assemblies for axial fans according to the prior art;

[0077] FIGS. 3a and 3b show the two deformed conditions of the blade system comprising the connecting element according to the present invention;

[0078] FIGS. 4a and 4b show the forces acting on a blade system comprising a connecting element according to the present invention;

[0079] FIG. 5 represents a lateral view of a blade connected to an hub by means of a connecting element according to the present invention;

[0080] FIG. 6 shows a top view of a connecting element according to one embodiment of the present invention;

[0081] FIG. 7 shows a perspective view of the connecting element of FIG. 6 after the bending;

[0082] FIG. 8 shows a connecting element according to the present invention according to a second embodiment, obtained by transversal extrusion or pulltrusion;

[0083] FIG. 9 shows a lateral view of the connecting element of FIG. 8, in which can be appreciated the variable transversal section obtained by extrusion or pulltrusion and the thickening in the most critical area;

[0084] FIG. 10 represents a diagram showing the modal damping as a function of the natural frequency of a blade assembly;

[0085] FIGS. 11a and 11b represent different possible arrangements of the connecting element according to the present invention turned up and, respectively, turned down;

[0086] FIG. 12 shows an example of an installation of an industrial axial fan comprising a blade assembly comprising a connecting element according to the present invention;

[0087] FIG. 13 shows a connecting element according to the present invention bolted to an hub.

[0088] FIG. 14 shows a connecting element according to the present invention according to a third embodiment, in which the angle between the two parts of the connecting element realizes the blade precone angle;

[0089] FIGS. 15 and 16 show a connecting element according to the present invention according to a third embodiment, in which the precone angle is obtained in different but easy ways.

DETAILED DESCRIPTION OF THE INVENTION

[0090] With reference to the above mentioned Figures, the main task of the present invention is to provide a connecting element for connecting the airfoil profile to the hub of an industrial axial fan.

[0091] With reference to the above, the present invention concerns a connecting element 1 consisting of an extremely simple element, see for example FIGS. 5 to 7, having essentially a rectangular cross-section and a L shaped longitudinal-section comprising a first part 1a having a substantially straight develop and a second part 1b having a straight develop, said first 1a and second 1b part being connected by a linking part 1c presenting a curvature radius so that said first 1a and second 1b parts lie on substantially perpendicular planes.

[0092] Said first part 1a of the L-shaped profile, which is the shorter part, is apt to be connected to the hub 20 while said second part 1b, which is the longer part, is apt to be connected to the airfoil profile 10, said link part 1c connecting said short part 1a to said long part 1b.

[0093] The blade system 100 comprising the connecting element 1 according to the present invention, is also part of the invention.

[0094] The blade system 100 for industrial axial fans is characterized by the fact that the blade, subject to unsteady loads, is forced to modify its modal properties: frequencies and deformation shapes, as described above.

[0095] The inventors have carried out functional tests to compare the blade system 100 of the present invention, comprising the connecting element 1 according to the invention, to the prior art systems. The results confirm that with the connecting element 1 of the present invention the natural frequencies of the system are 20% lower than in the prior art, the damping ratios of the first three vibration modes are respectively 24%, 15% and 3% higher than the same damping ratios of a blade system according to the prior art, only the fourth mode has 4% of lower damping.

[0096] Considering a blade system typical loading condition, the relative participation factor of the first four modes are respectively 0.43, 0.24, 0.14 and 0.09; therefore the response of the blade to that system of loads is completely described by the superposition of the response of these four modes.

[0097] Due to the differences in the damping ratio, the blade system 100 of the present invention, comprising the innovative connecting element 1, has a maximum response 22% reduced with respect to the response of a blade system of the prior art. Considering that the loads on the blade are proportional to its response, the invention involves a significant reduction in loads acting on the blade.

[0098] Additionally, the connecting element 1 according to the present invention has the further, very important characteristic to be non-symmetrical.

[0099] The influence of these factors on the behavior of the system is explained here below with reference to FIGS. 3a and 3b.

[0100] During the operation the steady state forces (weight W, and lift force L) tend to deform the blade 10 in a shape similar to the first vibration mode of a cantilever beam.

[0101] At the same time, the centrifugal force C tends to counteract to the blade deformation.

[0102] The effect produced by the centrifugal force C is linearly depending on the displacement of the center of gravity, which is more than linearly depending on the length of the blade attachment.

[0103] For the same radial size and under the same loads, the blade system of the present invention comprising a connecting element which has a longer length with respect to the connecting elements of the prior art, can provide higher displacement of the blade and, consequently, higher counteracting effect than the blade known in the art.

[0104] As it is evident from FIGS. 5 to 7 the structure and the profile of the connecting element 1 according to the present invention is very simple to be manufactured.

[0105] Still preserving its peculiar features, the connecting element 1 may be realized by means of several different methods, allowing to reach very low production costs when compared with those of the connecting elements currently available on the market.

[0106] Further advantages reached by the blade system of the present invention thanks to the connecting element of the invention, are the following: [0107] the connecting element 1 may be obtained by a simple manufacturing process comprising a first cutting phase and a second drilling phase, starting from a sheet of aluminum, steel or other proper material according to the required shape, and a final bending phase (reference is to Figures from 5 to 7); [0108] the connecting element 1 may be obtained by a manufacturing process comprising a first cutting phase and a second drilling phase, starting from a semi finished product obtained by extrusion or pulltrusion (reference is to FIGS. 8 and 9);

[0109] It will be appreciated that such extrusion allows to easily realize different shapes, which can obtain further important advantages: for example a larger thickness may be provided when higher stresses are foreseen, i.e. in the hub-connection zone (reference is to FIG. 9); [0110] the connecting element 1 may be obtained by a manufacturing process comprising a first cutting phase and a second drilling phase, starting from a pulltruded or molded element made of plastic or fiberglass material; [0111] the connecting element 1 may be obtained by a manufacturing process comprising a first cutting phase and a second drilling phase, starting from a simple L shape profile.

[0112] The L-shaped connecting element according to the present invention may be eventually combined with a prior art system to increase its effects.

[0113] Another advantage obtained by the connecting element of the present invention consists in its unsymmetrical shape: thanks to the L-shaped unsymmetrical profile, the connecting element 1 can be assembled with the linking part 1c turned either up or down (FIGS. 5a and 5b): the unsymmetrical shape of the connecting element allows to raise or lower the blade rotation plane according the installation needs (reference is to FIG. 12).

[0114] Of course the connecting element can be fixed to the hub 20 with one or more bolts depending on the operation duty (reference is to FIG. 13).