WO2016090417A1 - Centrifugal fan - Google Patents

Abstract

An impeller (1) forms part of a centrifugal fan used for pumping fluid. The impeller (1) includes a disc (2) which has a ratchet wheel shape with a steel bush (4) at its centre. The bush (4) has a keyway (6). This forms a closed face of the impeller (1). Bush (4) is preferably braced. The brace may include multiple triangular and radially aligned struts or a cone (8). The brace (8) extends radially inwardly from disc (2). An open face (3) of the impeller (1) is defined by frusto-conical plate (10). The plate (10) has an entry aperture (5) which is surrounded by circular flange (12).

Description

TI TLE OF INVENTION

Centrifugal Fan

TECHNICAL FIELD

This invention concerns centrifugal fans. BACKGROUND

The following references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. In particular, the following prior art discussion does not relate to what is commonly or well known by the person skilled in the art, but assists in the understanding of the inventive step of the present invention of which the identification of pertinent prior art proposals is but one part.

Centrifugal fans are widely used in industry in a large range of power requirements and performance.

When impellers have forwardly curved blades, the blades curve in the direction of the fans rotation. Backwardly curved blades curve in the opposite direction. Backwardly curved blades may have an aerofoil section. Both types propel gas streams efficiently. A third type has radial blades and of the three tends to be noisiest. It is the noise factor with which this invention is concerned.

Technical Problem The tips of blades are invariably disposed at 90° to the sides of the blades which are welded to the circular parts of the impeller. As the impeller rotates gas is drawn through the centre of the impeller and driven by the blades toward the housing and as each blade passes the fan exit a pressure change occurs and noise is generated. If the fan is inside a building and there are personnel in the vicinity, understanding speech may be difficult and the long term effect on people's hearing may become an issue.

Attempts have been made to modify the airflow through such fans but no worthwhile reduction in noise has resulted.

An object of the present invention is to ameliorate the aforementioned disadvantages of the prior art or to at least provide a useful alternative thereto. SUMMARY OF I VENTION

The invention according to one or more aspects is as defined in the independent claims. Some optional and/or preferred features of the invention are defined in the dependent claims.

Accordingly, in one aspect of the invention, there is provided an impeller for a centrifugal fan, wherein the impeller has an outer portion that has an irregular edge, the irregular edge forming an outer periphery of impeller.

The outer edge may comprise a variety of different outlines, including jagged and wavy outlines. The outer portion may include at least one projection flanked by a pair of recesses. The outer portion may include a plurality of projections. Preferably, the outer portion includes an edge with at least one prominent projections and two side recesses. Preferably, the side recesses have side portions that extend outwardly partially or wholly as far radially as a central projection. The projections may be radiussed to minimise turbulence.

The outline of the tip of the outer portion across its width may be in the form of a sawtooth configuration. Alternatively, the outer edge may provide scalloped, sinusoidal or other variants of such patterns or side edge profiles.

Advantageously, the outer portion is expected to exhibit noise reduction compared to an impeller with straight blade tips or tips with a constant curvature. The corners of some prior art blades may be radiussed so as to join the hub at an acute angle rather than 90°. Such variations in the shape of the outer edge are too small to contribute a significant reduction in noise of prior art devices. In contrast, the impeller of the present invention is configured by edge modification to ameliorate wind noise issues. An intermediate annular plate parallel to the impeller disc may divide the blades widthwise. Furthermore, the impeller blade may be reinforced intermediate the length of the outer edge. The reinforcement may include a rib radially aligned and in the form of a hollow disc or a radial band. The reinforcement increases the blade's rigidity. Useful noise reduction is measurable when the blade top has a pair of V-shaped excisions. Preferably, these excisions are separated by a V-shaped tooth substantially of the same size as the excision.

The impeller may include one or more impeller discs configured to lie in a plane transverse to the rotational axis of the fan. A first impeller disc may define a rearmost panel of the impeller. The rear impeller disc is preferably flat or planar. The impeller may include an opposed or frontward disc whereby the rear disc and the opposite disc are longitudinally spaced and lying substantially in parallel planes. The front disc may be frusto conical in shape. Preferably, the front disc defines a centre aperture. The centre aperture may be bordered by a radially spaced band or circular flange.

The blades may extend between a first disc with a ratchet edge and the opposed disc in the form of a frusto conical plate. The first disc may be the rearmost impeller disc.

The ratchet edge may define the outer peripheral edge of the first disc and may cooperate with a ratchet pawl or other spring biased detent. The ratchet mechanism may be adapted to regulate the rotational speed of the impeller.

The fan may have 4-70 blades. Preferably, the impeller has between 8 and 20 blades, and still more preferably between 8 - 12 blades.

Advantageous Effects of Invention

1. Noticeable noise reduction. 2. The invention is applicable to all centrifugal type fans including impeller blade shapes that are airfoil, backward inclined, flat backward inclined, curved backwardly inclined, radial, radial tip and forward curved, and the like.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be better understood from the following non-limiting description of preferred embodiments, in which:

Figure 1 is a plan of an impeller from the inlet end with blades and ratchet disc in broken lines;

Figure 2 is a mid section on Figure 1 ; Figure 3 is a plan of a blade;

Figure 4 is a perspective from the ratchet disc direction; Figure 5 is a perspective from the opposite direction; Figure 6 is a side view showing the bush; and Figure 7 is a plan of a impeller with aerofoil blades. DETAILED DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention will now be described with particular reference to the accompanying drawings. However, it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention.

Referring firstly to Figures 1-4, there is shown an impeller 1 that is part of a centrifugal fan used for pumping fluid, including gas, further including air, where the rotational speed of a tip or corner 22 of a blade 14 is more than 400 k/hr. The impeller is made of welded steel components. The impeller 1 includes a disc 2 which has a ratchet wheel shape with a steel bush 4 at its centre. The bush 4 has a key way 6. This forms a closed face of the impeller 1. Bush 4 is preferably braced. The brace may include multiple triangular and radially aligned struts or a cone 8. The brace 8 extends radially inwardly from disc 2. An open face 3 of the impeller 1 is defined by frusto-conical plate 10. The plate 10 has an entry aperture 5 which is surrounded by circular flange 12.

The impeller includes a plurality of blades 14 that each have a side 16 and a root end 18 aligned at substantially and preferably 90° to the side 16. The impeller 1 may include more or less blades 14, preferably 10 or 12. An opposite edge 20 to the side edge 16 is inclined to match a slope of the frusto-conical plate 10. The corner 22 junction between the root end 18 and the side 20 is radiussed advantageously to reduce turbulence. The blade 14 has a tip end 25 that has a plurality of teeth, advantageously comprising three teeth 24 and two half teeth 26. The tip 25 is cleft by a notch, cut-out or slot 28. The root end 18 is cleft by an inclined notch 30. The notches 28,30 ideally lie transverse of the tip end 25 and the root end 18 at a location intermediate the length of either end 18,25

The disc 2 includes a set of ratchet teeth 32. The impeller 1 ideally includes twelve blades 14. The blades 14 arc arranged around the frusto-conical plate 10 so that a curve of each blade 14 matches the curvature of the ratchet teeth 32. The blades 14 are stabilised by a flat outer circumferential ring 34 which projects and inserts into the tip notch 28 of each of the blades 14. The blades 14 a re further stabilised by an inner inclined ring 36 which projects into each of the root notches 30 of the blades 14. The blades 14 are of ideally of uniform thickness. The outer ring 34 divides the tip edge into two side by side arrays of a central V-shaped tooth 24 with a half tooth 26 on both sides (see Figure 4).

In Figure 7, an impeller la is shown having ten blades 38 which a are similarly arranged compared to the embodiment of Figs. 1 - 4, but instead are of aerofoil section in side profile. In another variation of the first embodiment, the disc 2 is circular, rather than having radially outwardly extending ratchet teeth 32.

An air gap 40 or circumferential spacing between the blades 38 is similar to that provided between the blades 14 of Figure 1.

Throughout the specification and claims the word "comprise" and its derivatives are intended to have an inclusive rather than exclusive meaning unless the contrary is expressly stated or the context requires otherwise. That is, the word "comprise" and its derivatives will be taken to indicate the inclusion of not only the listed components, steps or features that it directly references, but also other components, steps or features not specifically listed, unless the contrary is expressly stated or the context requires otherwise.

In the present specification, terms such as "apparatus", "means", "device" and

"member" may refer to singular or plural items and are terms intended to refer to a set of properties, functions or characteristics performed by one or more items or components having one or more parts. It is envisaged that where an "apparatus", "means", "device" or "member" or similar term is described as being a unitary object, then a functionally equivalent object having multiple components is considered to fall within the scope of the term, and similarly, where an "apparatus", "assembly", "means", "device" or "member" is described as having multiple components, a functionally equivalent but unitary object is also considered to fall within the scope of the term, unless the contrary is expressly stated or the context requires otherwise.

Orientational terms used in the specification and claims such as vertical, horizontal, top, bottom, upper and lower are to be interpreted as relational and are based on the premise that the component, item, article, apparatus, device or instrument will usually be considered in a particular orientation which will be understood by the skilled reader from the context.

The illustrations, photographs and drawings, if any, form part of the disclosure of this specification as does the description, illustrations, photographs and drawings of any associated provisional or parent specification or of any priority document, if any, all of which are imported hereinto as part of the record hereof.

Finally it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements or parts without departing from the spirit and ambit of the invention.

Claims

An impeller for a centrifugal fan comprising a rear disc and a plurality of impeller blades extending forward of the rear disc,

wherein the impeller blades each have an outer portion that has an irregular edge.

The impeller of Claim 1, wherein the irregular edge forms an outer periphery of impeller spaced radially from a rotational axis of the impeller.

The impeller of Claim 1 or 2, wherein the impeller is aligned at an angle between 0° and an obtuse angle relative to the rotational axis.

The impeller of Claim 3, wherein the angle is between substantially 0° and

10°.

The impeller of any one of previous claims, wherein the rear disc is a planar disc.

The impeller of any one of previous claims, wherein the rear disc has radially extending ratchet teeth.

The impeller of any one of Claims 1- 5, wherein the rear disc is a substantially circular disc.

The impeller of any one of the previous claims, wherein the irregular edge comprises a jagged outlines.

The impeller of any one of the previous claims, wherein the irregular edge comprises a wavy outlines.

The impeller of any one of the previous claims, wherein the irregular edge includes at least one curved projection flanked by a pair of recesses.

The impeller of Claim 10, wherein the projection is radiussed to minimise turbulence.

The impeller of any one of the previous claims, wherein the impeller further includes an intermediate annular plate parallel to the rear impeller disc The impeller of Claim 12, wherein the intermediate annular plate divides each of the blades widthwise.

The impeller of Claim 12 or 13, wherein each impeller blade is reinforced intermediate the length of the outer portion.

15. The impeller of Claim 14, wherein the reinforcement includes a rib radially aligned and in the form of an annular disc.

16. The impeller of any one of Claims 1 - 1 1, wherein the rear disc is a first impeller disc defining a rearmost panel of the impeller and the impeller further includes a second disc whereby the rear disc and the second disc are longitudinally spaced and lying substantially in parallel planes.

17. The impeller of any one of Claims 1 - 1 1, wherein the second disc is a front disc that is frusto conical in shape.

18. The impeller of any one of the previous claims, wherein the number of blades is 8 - 12.

19. The impeller of any one of claims! 6 - 18, wherein the second disc is frusto- conical in shape

20. The impeller of any one of the previous claims, wherein blades are aerofoil in profile.