US2952404A

US2952404A - Blower wheel assembly

Info

Publication number: US2952404A
Application number: US652513A
Authority: US
Inventors: Harold A Austin
Original assignee: BRUNDAGE CO
Current assignee: BRUNDAGE CO
Priority date: 1957-04-12
Filing date: 1957-04-12
Publication date: 1960-09-13
Anticipated expiration: 1977-09-13

Description

Sept. 13, 1960 H. A. AUSTIN BLOWER WHEEL ASSEMBLY Filed April 12, 1957 3 Sheets-Sheet l IN VEN TOR. Hmmzp A 40527 Sept- 1950 H. A. AUSTIN 2,952,404

BLOWER WHEEL ASSEMBLY Filed April 12, 1957 3 Sheets-Sheet 2 Sept. 13, 1960 H. A. AUSTIN 2,952,404

BLOWER WHEEL ASSEMBLY Filed April 12, 1957 3 Sheets-Sheet 3 INVEN TOR.

#42040 A Ausmv United States Patent 2,952,404 BLOWER WHEEL ASSEMBLY Harold A. Austin, Kalamazoo, Mich., assignor to Brundage Company, Kalamazoo, Mich., a corporation of Michigan Filed Apr. 12, 1957, Ser. No. 652,513

3'Claims. (Cl.230134) This invention relates to a blower wheel assembly for a multiblade centrifugal fan and more particularly to an improved mounting for the blades on the frame of the blower wheel.

It has long been standard practice to use separately formed blades and to mount these blades on a frame to form a blower wheel. Many structures have been proposed to effect such mounting. However, in spite of the previous work in this field, the use of separately formed blades still creates problems in efiecting efiicient assembly of the blades to the blower wheel frame and also still creates problems as to the proper manner for achieivng mechanical balance and aerodynamic stability of the blower wheel.

Particularly, prior constructions of this general type have usually involved a large amount of hand work and have not lent themselves readily to automatic fabrica- 'tion methods. Further, many prior constructions have operated so as to create excessive turbulence of the gas within the fan scroll. Such turbulence often results in excessive vibration and noise and likewise causes undesirably rapid wear of the running parts of the fan. A contributing factor to this turbulence is believed to be the relatively bulky construction often appearing at either axial end of the blower wheel and, in certain cases, by the non-cylindrical construction of the blower wheels resulting from the methods of construction utilized therein. Thus, less gas is impelled by the wheel at either end thereof than at the central portion of thewheel which causes creation of pressure diiferences within the fan scroll and the resulting turbulence. Other known blower wheels of this general type, while initially satisfactory from the standpoint of turbulence and performance, lack the rigidity and aerodynamic stability that is essential in equipment of this type. Thus, the blades or the blower wheel frame may loosen and require frequent replacement.

Accordingly, it is a principal object of this invention to provide an improved blower wheel construction. t It is a further object of this invention to provide a blower wheel which is esesntially cylindrical in shape and which will create less turbulence of the gas within the fan scroll than do certain prior constructions.

It is a further object of this invention to provide a blower wheel construction in which the radially outer edges of the blades are substantially equidistant from the axis of rotation of the wheel.

It is a further object of this invention to provide a blower wheel construction in which the separately formed blades are rigidly and securely attached to the blower wheel frame and in which the blower wheel operates at a low noise level and with a minimum of vibration.

It is a further object of this invention to provide a blower wheel assembly in which the blades are stressed in their assembly position on the blower wheel frame .and in which the parts are balanced and stable in opera- .tion.

I A further object of the invention is to provide a blower 2,952,404 Patented Sept. 13, 1950 2 wheel assembly, as aforesaid, in which the stressing of the blades takes place during the assembly of such wheel and, particularly, wherein the construction adapts the wheel to assembly by automatic procedures, and the automatic and equal stressing of such blades during the assem bly procedure.

It is a. further object of this invention to provide a blower wheel assembly which can be produced by high speed automatic machinery.

Other objects and advantages of this invention will be come apparent to those acquainted with this type of equipment upon reading the following description and inspecting the accompanying drawings.

In the drawings:

Figure 1 is an oblique, partially broken view of the blower wheel asesmbly which constitutes the subject of the present invention.

Figure 2 is a central, cross-sectional view of the blower wheel assembly substantially as shown in Fig urel.

Figure 3 is a sectional view taken along the line III-III of Figure 2.

Figure 4 is a broken, sectional view taken along the line IV-IV of Figure 3.

Figure 5 is a sectional view taken along the line V-V of Figure 4.

Figure 6 is an oblique view of a blade in. its assembled condition, on the wheel and showing an imaginary cylinder corresponding to the shape of the assembled blower wheel, the shape of the blade being exaggerated for purposes of clear illustration thereof.

Figure 7 is a broken, plan' view of ablade blank prior to shaping.

General description The invention provides a blower wheel frame which consists of two annular end rims and a center structure which is secured to a shaft for rotation therewith. Notches are provided in the periphery of the center structure to engage the blades. The blanks, from which the blades are made, are cut from sheet materialso that the lengthwise edges .of each blade define similar, wide angles lying in the plane of the sheet material. The blade blanks are then shaped to define a portion of a cylinder, the axis of which is substantially parallel with the lengthwise extent of the blade blank. In the assembly of the blades upon the frame, the blades are each placed with their convex edge closest to the center of the wheel and positioned into the notches in the center structure. Pressure is then applied to both ends of the bladesurgf ing them toward the center of the wheel. This causes said blades to assume positions of stress wherein their inner and outer edges define substantially concentric cylinders. The ends of the blades are then secured to the end rims. Detailed description The blower wheel assembly 8 (Figures 1, 2 and 3) is comprised of a plurality of blades 18 which are mounted upon a frame including a center structure 9 and a pair of annular, end rims 10 and 11. The end rims, which are made of any suitable material of. high tensile strength; are relatively narrow in radial extent and expose the radially inner, edge portions of the blades. This: com struction improves the operation and capacity of the blower wheel. a a

The center structure 9 is comprised of a pair of

center plates

12 and 13 which are in. this embodimentdisposed intermediate the rims 10 and 11. The center plates may be, and here are, identical with each other and, accord; ingly, only the center plate '13 will be described in detailf Plate 13 is generally circular in shape and is provided with a series, of, equally spaced notches 14 in the pea t p 'ythereof. ,The plate includes an offset, center .por-

tion 15 which supports a hub 16. The hub secures the center plate to a shaft 17 for rotation of the plate with the-shaft.- .The center plates 12- and '13 aregplaced'with' their; offset portions spaced from each other anditheir respective notches '14 in alignment for receiving the blades therewithin. Said plates may be, but are not necessarily; fastened -together byfa'ny suitable means; as.' byfspot welding. TY" A series of blades 18 (Figures 2, 4 and 6-) are provided for assembly on the blower wheel frame. Each blade is generally arcuate in cross-sectional shape to prov1de a forwardly curved working surface in this particular embodiment. The blades are notched at 19, which notch in the assembled'position of the 'blades is received into a corresponding notch 14 in the center structure 9Q The blade is provided with a mounting flariger20 at each end thereof, which flange extends'generally at a right angle to the lengthwise axis of the blade. The flange is preferably integral with the blade and is preferably of the irregular, somewhat triangular, shape shown in Figures 5 and 7, which shape provides the maximum sup; port for the blades when they are mounted on the.rims; In particular, the fold line or common edge 21 between the flange and the blade preferably is made as long as possible to contact the maximum extent of the end edge of the arcuate blade. The length of the common edge axis than said adjacent points are.

the ends radially inwardly, with respect tothe wheel, until the inner edge 22 of the blade coincides with the line A. In such condition, the points on said edge 22, which are remote from the notch 19, will be substantially the same distance from the axis of the center structure as those points adjacent to the notch. It may be advantageous for the said remote points to be further from said However, in no case will they be closer than said adjacent points. Thus, the blade is in a stressed condition and remains so during the life of the Wheel. Because of the obtuse angle present in the formed blade, the application of force by the force exerting tool will cause-the radially outer edge 23 of the blade to assume acondition where itis bowed forwardly in a circumferential direction (Figure 6) but in which all points of said edge 23 lie at a substantially equal radial distance from the axis of the blower wheel. This is most clearly shown in-Figure 6 wherein the blade is shown with reference to a cylinderD which corresponds to the cylindrical shape of theblower wheel. .This figure illustrates in a somewhat exaggerated manner this-cir cumferential bowing of the outer edge 23, .which' in this embodiment has the ends leading the center of the blade,

21, which depends to some extent on the radial width of the rims 10 and 11 and the positioning of 'the'blades thereon, is preferably at least fifty' percent' of the'peripheral length of the end edge of the blade. This'construction of the flange gives maximum support to the blades and thereby insures maximum rigidity of the blower wheel assembly.

Asshow'n in Figure '7 in a somewhat exaggerated way, the blades are fabricated by punching blade blanks 18a from sheet metal. The longitudinal ends of the blade blanks 18a are normally contoured at each end to provide the flanges 20 when in their assembled position on the frame. The lengthwise edges 22 and 23 of the blade blank are slightly V-shaped and each define a pair of similar, obtuse angles of less than 180 but usually over 179. In the preferred construction of the blank, both the radially-inner edge 22 and the radially outer edge 23 are parallel and hence are substantially equi-distant from each other. The notches 19, which-are located on the inner edge 22, are conveniently provided during the punch? mg of the blade by-a circular punch which simultaneously cuts a similar notch 19a in the outer edge 23 of thenext adjacent blade blank 18a. ,The blades are then shaped to form a part of a cylinder, in this embodiment, having a single axis C extending longitudinally of the blade and parallelwith the lengthwise extent thereof, as indicated by the line A in Figures 4- and 7. Thus, the line A represents a line parallel with the longitudinal axis of the assembled blower wheel whereas the line B (Figures 4 and 7) represents a line parallel with the leftward halves of the radially inner and outer edges of the blade 18 prior to assembly. The angle between the lines A and B, which determines the amount of the offset of the blade, preferably lies in the range of between about .07 or .30 of a degree.

The radially inner and outer edges of the rightward half of the blade, as appearing in Figure 2, lie at an equal but reverse angle with the longitudinal axis of the assembled blower wheel when the blade is in itslunassembled state. The end flanges 20 are bent along the lines 21 into position for engaging the rims 10 and 11. f In assembly, the rims 10-and 11 and the

center plates

12 and 13 are mounted in fixed position on a suitable fixture, not here shown. A blade 18 is then fed by hand said leading being taken in the direction .ofrot-ation of the blower wheel indicated by the arrow B. The actual amount of such leading is small, being in oneembodi ment about & of an inch in a blade nine incheslong. The flanges 20 are then secured to the end rims 10 .and 11 by suitable means which may be spot welding. The center structure and end rims are simultaneously rotated to a position where another blade may be mounted on the blower wheel frame in the manner described 'above.

7 This operation is repeated until all of the blades have been mounted on the frame.

When the blades are assembled to the blower wheel frame, the outer edge 23 of each blade will liein, and define, a slight curve along the surface of, a theoretical cylinder whose axis is concentric with the axis of rotation of the wheel. Thus, the inner and outer edges 'ofeacli blade, when assembled may be substantially .equi-distant from the axis of the wheel while the outer edge 23. is bowed slightly in a circumferential direction,.which in this instance is the direction of rotation; In addition; the flat end rims and the mounting flange 20 will present a relatively narrow end structure at eitherend of the blower wheel. These two details of construction have been experimentally determined to minimize the turbulentfe of the gas within the blower scroll and consequently. the. efliciency of a blower employing this construction has bcen measurably increased thereby.- 1 This construction and method of assembly causes the fan blades to be in a stressed condition when in their assembled position. The blades in attemptingto relieve this stress will exert a force on the rims 10 and 11. ,-How: ever, because of the equal spacing of the blades and symmetrical arrangement of the parts, the forces will be balanced and an extremely rigid and stable structure. re-

' sults.

or suitable mechanism'so that notch 19 fits within one It may be desirable under some conditions to'remove the above mentioned circumferential bowing in the outer edge 23 of the assembled blade 18. This can be accomphshed by shaping the blade with slight dihedral. Sp'e cifically, the blade will be curvedin bothendwise: direc tions away from the axis of the theoretical cylinden' of which it is a part in the above described structure. 1 Thus, when a force is applied to the ends of said'bladeto caulse its inner edge 22 to coincide with theline A, 'suchl for ce will also move the outer edge. 23 into a" linefwhich; is substantially parallel with said line vA. 1 F' 1 The said dihedral may be limited to the'outer edge, or applied to both the inner and outer edges. Also, the dihedral. may be suflicient that it will not be oizhp leltely overcome. In such case, the blades will be circumferentially swept back with respect to .the direction of rotawardly directed 59:9? 99 f blade to (5 ;.tion. These arrangements will provide variations'i'n'performance and may increase both the performance and efiiciency of the fan assembly.

Although I have disclosed particular, preferred embodiments of my invention for illustrative purposes, it will be understood that modifications or variations thereof which lie within the scope of the invention are fully contemplated unless specifically stated to the contrary in the appended claims.

I claim:

1. In a centrifugal blower Wheel construction, the combination comprising: a pair of spaced and coaxial annular rims, a circular center structure of less diameter than the outside diameter of said spaced rims, a series of blades having radially inner and radially outer edges, both of said edges in their unstressed condition being spaced at the ends of said blades radially outwardly of the respectively same edges in the central portions of said blades, the radially inner edges of said blades being engaged by the periphery of said center structure intermediate the ends of said blades, each of said rims being secured to opposite ends of said blades and exerting an inwardly directed force on the ends of said blades and thereby holding said blades in a stressed condition and tightly against said periphery, the radially inner and radially outer edges of said blades in the stressed condition of said blades on rotation of the blower wheel de fining cylinders concentric with the axis of rotation thereof, each cylinder having a constant radius throughout its length, and said center structure being frictionally held by said blades coaxial with said rims.

2. A centrifugal blower wheel according to claim 1 wherein each blade is curved around a first axis parallel with said edges and the radially outer edge of each blade is curved about a second axis which extends normal to the axis of rotation of said blower wheel at the center thereof; flange means integral with the ends of said blades and extending normal to the axis of rotation of said blower wheel and parallel to said rims, said flange means at the respective ends of said blades being secured to the opposing surfaces of said rims.

3. A centrifugal blower wheel according to claim 1 wherein said rims are flat and said center structure has an outside diameter approximately equal to the inside diameter of said rims, said center structure having a plurality of uniformly spaced notches in the periphery thereof and the inner edges of said blades being firmly disposed within said notches, each blade being curved around a first axis parallel with said edges.

References Cited in the file of this patent UNITED STATES PATENTS 1,877,347 McMurdie Sept. 13, 1932 2,181,592 Sullivan Nov. 28, 1939 2,474,298 Zeidler June 28, 1949 2,495,855 Marcoe Jan. 31, 1950 2,537,805 Wilken Jan. 9, 1951 2,626,741 Osborne Jan. 27, 1953 2,714,485 Goettl Aug. 2, 1955 2,745,171 King et a1. May 15, 1956