US3578878A

US3578878A - Blower wheel and method of making same

Info

Publication number: US3578878A
Application number: US851319A
Authority: US
Inventors: Richard V Ross
Original assignee: MORRISON PRODUCTS Inc
Current assignee: MORRISON PRODUCTS Inc
Priority date: 1969-08-19
Filing date: 1969-08-19
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18
Also published as: CA927803A

Abstract

A centrifugal blower wheel is formed from a sheet metal strip having opposite side edges including marginal rim portions extending continuously along the side edges of the strip. The strip has a plurality of longitudinally spaced transverse blades formed therein between the side edges. The blades are connected with the rim portions by integral webs. The blades are formed into an arcuate shape in successive steps. An initial step partially curves the blades and leaves the end portions of the blades adjacent the webs flat. The flat portions are curved in a subsequent step so that the end portions of the blades are work hardened less than if they are successively bent in a plurality of steps. The rim portions are folded between adjacent blades in order to decrease the longitudinal spacing of the blades. The folds are specially formed so that a plurality of bends in each fold are smoothly curved to prevent fracturing of the metal at the bends. The blades have notches formed in their inner edges for receiving the peripheral edges of a pair of discs. The discs have circumferential protuberances adjacent their outer peripheral edges. The protuberances are deformed into contact with one another at their centers to provide each disc with a pair of radially spaced protuberances which are under bending stress and continuously bias the peripheral edges of the discs into firm engagement with the notches.

Description

United States Patent Richard V. Ross Parma Heights, Ohio [211 App]. No. 851,319

[22] Filed Aug. 19, 1969 [45] Patented May 18, 1971 73] Assignee Morrison Products, Inc.

Cleveland, Ohio [72] lnventor [54] BLOWER WHEEL AND METHOD OF MAKING SAME 13 Claims, 22 Drawing Figs.

Primary Examiner-Leonard H. Gerin Attorney-Meyer, Tilberry & Body ABSTRACT: A centrifugal blower wheel is formed from a sheet metal strip having opposite side edges including marginal rim portions extending continuously along the side edges of the strip. The strip has a plurality of longitudinally spaced transverse blades formed therein between the side edges. The blades are connected with the rim portions by integral webs. The blades are formed into an arcuate shape in successive steps. An initial step partially curves the blades and leaves the end portions of the blades adjacent the webs flat. The flat portions are curved in a subsequent step so that the end portions of the blades are work hardened less than if they are successively bent in a plurality of steps. The rim portions are folded between adjacent blades in order to decrease the longitudinal spacing of the blades. The folds are specially formed so that a plurality of bends in each fold are smoothly curved to prevent fracturing of the metal at the bends. The blades have notches formed in their inner edges for receiving the peripheral edges of a pair of discs. The discs have circumferential protuberances adjacent their outer peripheral edges. The protuberances are deformed into contact with one another at their centers to provide each disc with a pair of radially spaced protuberances which are under bending stress and continuously bias the peripheral edges of the discs into firm engagement with the notches.

mmm 3578.878

SHEET 1 0F 4 INVENTOR. RICHARD 1 R0519 ATTORNEK? PATENIED HAY 1 8 1921 saw 2 or 4 J mvsmox Y RICHARD 14 R058 WZJM {50% A TTOR/VE KS PATENTEU an 1 8 WI SHEET u or 4 INVENTOR. R/CHARD 1. 17085 ATTORNEYS BLOWER WHEEL AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This application pertains to the art of blowers and more particularly to centrifugal blower wheels formed from a sheet metal strip. Although the invention is particularly applicable to centrifugal blower wheels formed from a sheet metal strip and will be described with particular reference thereto, it will be appreciated that the invention has broader applications and may also be used in such environments as radial flow blowers.

Centrifugal blower wheels are commonly formed from a flat sheet metal strip having opposite side edges which include marginal rim portions extending continuously along the strip. The rim portions integrally interconnect arcuate blades which are formed transversely of the strip between its side edges. Integral webs connect the blades with the rim portions. The blades are formed into an arcuate shape by striking them between dies. The end portions of the blades adjacent the webs are placed under considerable stress when they are deformed. Work hardening of the end portions of the blades often causes cracks in the metal and results in failure of the blower wheel. It would be desirable to relieve high stress concentrations and work hardening in the end portions of the blades adjacent the webs.

In forming such blower wheels from a flat sheet metal strip, the rim portions between adjacent blades are commonly folded in order to reduce the longitudinal spacing between adjacent blades. These folds are commonly struck between two dies to completely flatten the fold. Complete flattening of the bend areas of the folds places the metal under extreme strain. Both work and age hardening of the folded portions often causes crystallization of the metal in the bend areas and this results in fracture of the metal so that the blower wheel can no longer be used. It would be desirable to fold the rim portions in such a manner that the stress in the bend areas would be considerably reduced, and so that a reduction in work and age hardening would considerably reduce the possibility of fracture.

In assembling blower wheels made from such sheet metal strips, it is common to form notches in the inner edges of the blades and to position the peripheral edges of a pair of discs within the notches. Circumferential protuberances on the discs are then flattened to force the peripheral edges of the discs into firm engagement with the notches. Flattening of the protuberances is done in such a manner that the metal relieves itself of stress and the peripheral edges of the discs often become loose in the notches. It would be desirable to deform the protuberances in such a manner that continual bias would be placed on the peripheral edges of the discs to keep them in firm engagement with the notches and eliminate the possibility that the peripheral edges would become loose in the notches.

SUMMARY OF THE INVENTION In accordance with the present invention, a centrifugal blower wheel is formed from a sheet metal strip having opposite side edges including marginal rim portions extending continuously along the strip. A plurality of longitudinally spaced transverse blades are formed in the strip between its side edges. The blades are deformed out of the plane of the strip and into an arcuate cross-sectional configuration in successive steps by forming dies. The blades are first formed into a slight arcuate shape over a major portion of their length and the end portions of the blades are left flat. In a subsequent forming operation, the flat end portions of the blades are also formed into an arcuate shape. Reducing successive bending steps on the end portions of the blades reduces work hardening in those areas and also reduces the amount of bending the end portions of the blades are subjected to. The end portions of the blades are connected with the rim portions by integral webs of sheet metal and forming of the blades in the manner described reduces crystallization of the metal at the end portions of the blades and substantially reduces fracture of the metal in those areas.

In accordance with another aspect of the invention, the rim portions of the strip are folded between adjacent blades in order to reduce the longitudinal spacing between blades. These folds are formed so that the bend areas of the folds are smoothly curved and fatigue fracturing of the metal in the bend areas is substantially reduced.

In accordance with still another aspect of he invention, the blades have notches formed on their inner edges for receiving the peripheral edges of a pair of discs. Each of the discs has a circumferential protuberance formed therein adjacent the outer peripheral edges. The protuberances are deformed so that they move into contact with one another near their centers to define a pair of radially spaced smaller protuberances on each disc. The metal in the two protuberances is under bending stress which constantly biases the peripheral edges of the discs into firm engagement with the notches and the metal cannot relieve itself to cause the peripheral edges to become loose in the notches.

It is a principle object of the present invention to provide an improved blower wheel in which fracturing of the metal from which the blower is formed is substantially reduced by reducing stresses and work hardening in certain areas.

It is another object of the present invention to provide an improved method of forming a blower wheel from a sheet metal strip so that fracture of the metal in the strip is substantially reduced in certain areas by reducing high stress concentrations and work hardening.

It is also an object of the present invention to provide a blower wheel with a pair of discs which have their peripheral edges under constant biasing engagement with notches formed in blades.

It is a further object of the present invention to provide an improved method of assembling a pair of discs to the interior of a cylindrical blower wheel.

BRIEF DESCRIPTION OF THE DRAWING The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof.

FIG. 1 is a top elevational view of a sheet metal strip which is used in forming the improved blower wheel of the present invention;

FIG. 2 is a perspective view of a bottom forming die used to deform blades into an arcuate shape from the sheet metal strip of FIG. 1;

FIG. 3 is a perspective view of an upper forming die used in cooperation with the bottom die of FIG. 2 to deform arcuate blades from the sheet metal strip of FIG. 1;

FIG. 4 is a perspective view of a portion of a blade strip after forming the blades with the dies of FIGS. 2 and 3;

FIG. 5 is a cross-sectional view looking in the direction of arrows 5-5 of FIG. 4;

FIG. 6 is a cross-sectional view looking in the direction of arrows 6-6 of FIG. 4;

FIG. 7 is a perspective view of a bottom forming die which is used to provide a more pronounced arcuate curvature to the blades;

FIG. 8 is a perspective view of an upper die used in cooperation with the bottom die of FIG. 7 to provide a more pronounced arcuate curvature to the blades;

FIG. 9 is a perspective view of blades after final forming with the dies of FIGS. 7 and 8;

FIG. 10 is a cross-sectional view looking in the direction of arrows 10-10 of FIG. 9;

FIG. 11 is a cross-sectional view looking in the direction of arrows 11-11 of FIG. 9;

FIG. 12 is a partial top plan view of an edge portion of a blade strip showing successive formation of folds;

FIG. 13 is a side elevational view of a blade strip showing successive formation of folds;

FIG. 14 is a cross-sectional view looking in the direction of arrows 14-14 of FIG. 12;

FIG. is a cross-sectional view looking in the direction of arrows 15-15 ofFIG. 12;

FIG. 16 is an enlarged end elevational view of a final fold formed in the edge of a blade strip;

FIG. 17 is an enlarged end view of a first bend formed in an edge portion of a blade strip to produce a fold;

FIG. 18 is an enlarged end view ofa deformed bend formed in an edge portion of a blade strip to produce a fold;

FIG. 19 is an enlarged end view of a further deformed bend formed in an edge portion ofa blade strip to produce a fold;

FIG. 20 is a fragmentary cross-sectional view of a blower wheel and a pair ofsupporting discs;

FIG. 21 is a view similar to FIG. 20 showing the configuration of the supporting discs after deformation; and

FIG. 22 is a partial cross-sectional view of the deformed portion of the discs of FIG. 21.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, wherein the showings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting same, FIG. 1 shows flat sheet metal strip A which is used to construct a centrifugal blower wheel in accordance with the present invention. Sheet metal strip A includes opposite side edges 12 and 14. Adjacent side edges 12 and 14, sheet metal strip A has

marginal rim portions

16 and 18 extending continuously along the side edges of the strip. Side edges 12 and 14 of strip A have outwardly extending longitudinally spaced tabs 20 thereon for cooperation with spacing and holding devices in subsequent forming operations of strip A. A plurality of transverse slits 22 are formed in strip A transversely thereof between

rim portions

16 and 18. A plurality of longitudinal slits 24 are formed in strip A at longitudinally spaced intervals

adjacent rim portions

16 and 18. Longitudinal slits 24 extend from the ends of transverse slits 22 toward the ends of an adjacent transverse slit and terminate short thereof. At the transverse center of strip A, notches 28 are formed and intersect transverse slits 22. Transverse slits 22 and longitudinal slits 24 define a plurality of blade-forming sections 30 in strip A. Blade-forming sections 30 are integrally connected with

rim portions

16 and 18 by webs 32.

Strip A is fed longitudinally through a forming machine in incremental steps in a known manner. The machine includes a bottom forming die B and an upper forming die C. Upper forming die C vertically reciprocates in the machine as strip A is stopped at the end of each of its incremental movements. Bottom forming die B includes an upper arcuate surface 34 having substantially triangular flattened

areas

36 and 38 at the top end portions thereof. Upper forming die C has a lower arcuate surface 40 shaped to correspond with arcuate surface 34. Arcuate surface 40 includes flattened portions like those at 36 and 38 on arcuate surface 34. Upper forming die C is positioned vertically above bottom forming die B in the forming machine. A blade-forming section 30 is positioned over bottom forming die B and upper forming die C is positioned vertically above bottom forming die B. Downward movement of upper forming die C causes a blade-forming section 30 to be gripped between

arcuate surfaces

34 and 40 so that a blade-forming section 30 conforms to the arcuate shape of

arcuate surfaces

34 and 40. Strip A is fed longitudinally through a forming machine in successive increments so that each blade-forming section 30 is successively formed to an initial arcuate shape between dies B and C. Complete forming of blades 30 to their final desired arcuate shape in only one step requires an extremely pronounced draw which would often fracture the metal in blade-forming sections 30. Therefore, the initial forming of blade-forming sections 30 to an arcuate shape provides only around one-half the desired arcuate curvature. Flattened

areas

36 and 38 on arcuate surface 34, and corresponding flattened areas on arcuate surface 40 leave the end portions of blades 30 with flattened areas 42 adjacent webs 32. Flattened portions 42 are substantially unworked and unbent in the first forming operation between dies B and C. The first forming operation performed on blade sections 30 provides the blades with inner and outer

transverse edges

44 and 46 respectively.

As strip A continues longitudinal movement through a forming machine, a second pair of dies provide the final desired arcuate curvature to blades 30. A bottom forming die D has an arcuate upper surface 50 and upper die E has a lower arcuate surface 52 shaped correspondingly with arcuate surface 50. Arcuate surfaces 50 and 52 are much more pronounced than

arcuate surfaces

34 and 40 on initial forming dies B and C. In addition, final forming dies D and E do not have any flattened portions similar to those at 36 and 38 on die B. With upper die E positioned above die D for vertical reciprocation, a blade section 30 is positioned over die D and die E moves vertically downward to grip a blade section 30 between surfaces 50 and 52, and cause blade section 30 to.

conform with the arcuate curvature of arcuate surfaces 50 and 52. In this forming operation, flattened areas 42 at the end portions of blade sections 30 are provided with an arcuate curvature corresponding to the curvature of the major portion of blade sections 30. In this final forming operation, blade sections 30 are provided with a very pronounced arcuate curvature and inner edges 44 extend downwardly from the plane of sheet A at substantially right angles thereto. By leaving flattened areas 42 at the end portions of blades 30 adjacent webs 32 in the first forming operation, the end portions of blades 40 are work hardened considerably less than if they were bent successively along with the major portions of blade sections 30. In addition, the degree of bending in the end portions of blades 30 adjacent webs 32 is not as pronounced because most of the desired bending is accomplished in the first forming operation within the inner or lower portion of each blade section 30. This manner of deforming blade sections 30 into their desired arcuate shape considerably relieves stress concentrations at the end portions of blades 30 adjacent webs 32 and also reduces work hardening of the metal in those areas. It has been found that this substantially reduces fracture of the metal at the end portions of the blades 30 adjacent webs 32. In the final forming operation, the end portions of blades 30 adjacent webs 32 are given the same arcuate shape as the major portion of blade sections 30 as shown in FIGS. 10 and 11.

Subsequent to the forming of blade sections 30 into their arcuate cross-sectional shape,

rim portions

16 and 18 are folded over intermediate tabs 20 and blades 30 in order to decrease the longitudinal spacing of blade sections 30. In accordance with the invention, blade strip A is moved longitudinally through a deforming machine while holding dies J and K engage the upper surface of rim portion 16 and portions of adjacent tabs 20 as shown in FIG. 12. Holding dies J and K engage the top surface of rim portions 16 loosely so that the metal in rim portion 16 and tabs 20 may slide relative to the bottom surfaces of holding dies J and K. While holding dies J and K are in sliding engagement with the upper surface of rim portion 16 as shown in FIG. 12, a vertically movable pin 62, which extends transversely of rim portion 16, moves vertically upward into engagement with the bottom surface of rim portion 16 intermediate holding dies J and K. This vertically upward movement of pin 62 forms an inverted U-shaped bend 64 as shown in FIG. 13. This formation of inverted U-shaped bend 64 draws adjacent tabs 20 toward one another and decreases the spacing between adjacent blade sections 30. As shown in FIG. 14 with respect to holding die J, the bottom comer edge of holding die J is curved as at 66 and the inside bottom edge of die K is similarly curved. These curved portions ofholding dies J and K, which engage rim portion 16, impart a desired curvature as at 70 and 72 to the connecting areas between U-shaped bend 64 and rim portion 16. The bottom portions of dies J and K which extend between adjacent tabs 20 are provided with an extension 74 as shown only with references to die J in FIG. 15. As pin 62 moves vertically upward in forming U-shaped bend 64, tabs 20 move toward one another and their inner edges engage projection 74 on holding dies J and K in order to impart a desired spacing between adjacent tabs and to insure formation of U-shaped bend 64 at substantially the center between adjacent tabs 20. Subsequent to formation of inverted U-shaped bend 64, as strip A continues to move longitudinally through a deforming machine, a vertically movable spacer 76 moves upwardly between adjacent tabs 20 between which inverted U-shaped bend 64 has been formed. Spacer 76 maintains a desired spacing between adjacent tabs 20 while U-shaped bend 64 is struck with a deforming die 78 as shown in FIG. 13. Deforming die 78 moves vertically downward sharply to strike the curved portion of inverted U-shaped bend 64 and causes the curved portion of bend 64 to break at its center and become a substantially heart-shaped deformation 82. As strip A continues to move longitudinally through a deforming machine, a subsequent deforming die 84 strikes heart-shaped deformation 82 and deforms it into a flattened heart-shaped deformation 86. Finally, a final deforming die 90 strikes deformed heartshaped deformation 86 into a final fold F. Deforming dies 78, 84 and 90 strike against rim portion 16 of strip A while its bottom surface rests against support 94 on a deforming machine. Deforming dies 78, 84 and 90 move downwardly to have their bottom surfaces at varying spacing from bottom support 94 so that fold F is progressively formed. In the final folding by deforming die 90, the bottom surface of die 90 is spaced from bottom support 94 a distance greater than three times the thickness of metal in rim portion 16. This produces a fold having smoothly curved bends.

An enlarged view of a fold F is shown in FIG. 16. As shown, rim portion 16 includes planer portions 96 and 98 which extend between adjacent folds. Fold F is symmetrical on opposite sides of a centerline 102 which bisects fold F transversely of the sheet metal strip. As shown, fold F is substantially S-shaped on the left side of centerline 102 and is substantially backwards S-shaped on the right-hand side of centerline 102. Fold F has first and second bends 104 and 106. Rim portion 16 includes an upper surface 108 and a bottom surface 110. Interior curved surfaces 112 and 114 of first and second bends 104 and 106 are defined by portions of bottom surface 110 of rim portion 16. First and second bends 104 and 106 have exterior curved surfaces 116 and 118 which are defined by portions of upper surface 108 of rim portion 16. First and second bends 104 and 106 are connected by an upper web portion 122 which extends substantially parallel to substantially planer portions 96 and 98 of rim portion 16. Web portion 122 has inner and outer surfaces which are defined respectively by portions of bottom surface 110 and upper surface 108 of rim portion 16. Folds F include third and fourth bends 124 and 126 having interior curved surfaces 128 and 130 facing in opposite directions and away from centerline 102. Interior curved surfaces 128 and 130 of third and fourth bends 124 and 126 are defined by portions of upper surface 108 of rim portion 16. Third and fourth bends 124 and 126 include

exterior surfaces

132 and 134 facing one another and centerline 102, and being defined by portions of bottom surface 110 of rim portion 16. It is important to note that a portion of exterior curved surfaces 116 and 118 of first and second bends 104 and 106 is in contact with substantially planer portions 96 and 98 as at 136 and 138. Also, portions of exterior

curved surfaces

132 and 134 of third and fourth bends 124 and 126 are in contact with the bottom surface of web 122 as at 140 and 142. In addition, it is important to note that exterior

curved surfaces

132 and 134 of third and fourth bends 124 and 126 are spaced apart from one another. This spacing eliminates a preloaded joint so that the material is not under strain and there is no expansion or contraction caused by relieving of metal stress as in situations where exterior

curved surfaces

132 and 134 would be abutting against one another. It is also important to note that all of bends 104, 106, 124 and 126 are smoothly curved and interior curved surfaces 112, 114, 128 and 130 are out of contact with one another over arcs greater than 180". With such an arrangement, there is minimum crystallization of metal at the bends, and work and age hardening are substantially reduced so that failure of the metal in any bend of fold F is substantially reduced. In one example for a strip to be used in making a 9 inch diameter blower wheel, bend 64 is formed from sheet metal having a thickness of around l/128 inch. With reference to FIG. 17, height 141 is around 3/8 inches, width 143 around 1 H64 inches, radius 144 around 1/l6 inches, and

radii

146 and 148 around 3/32 inches. During the first deforming operation by deforming die 78 to make U-shaped bend 64 into heart-shaped bend 82, the dimensions for a 9-inch-diameter blower wheel becomes substantially as shown in FIG. 18. Width dimension 152 is around 7/32 inches, width dimension 154 around 7/64 inches, height 156 around 17/64 inches, interior radii 158 around l/32 inch and exterior radii 160 around 1/16 inches. Heart-shaped deformation 82 is then further deformed by deforming die 86 into a deformed heart shape 86 as shown in FIG. 19. Height dimension 162 is then around 9/64 inches, width dimension 164 around 17/64 inches and width dimension 166 around 3/64 inches. In final fold F of FIG. 16, the spacing between

exterior surfaces

132 and 134 of third and fourth bends 124 and 126 is around 1 /32 inches. This spacing is maintained for each fold formed in

rim portion

16 and 18 by spacer elements 76 of FIG. 12. This insures substantially uniform longitudinal spacing of blade sections 30.

In accordance with another aspect of the present invention, blade strip A is formed into a cylinder in a manner more fully described in U.S. Pat. No. 3,423,012 issued Jan. 2], 1969, and copending U.S. Pat. No. application Ser. No. 789,675 filed .Ian. 8, 1969, which are assigned to the same assignee as the present invention. With blade strip A arranged in a cylinder, notches 28 in inner edges 44 of blade sections 30 are circumferentially aligned. A pair of substantially identical discs M include substantially flat circular central portions having centrally located holes 182 therethrough for rotatably mounting discs M on a shaft. Discs M have circumferential converging portions 184 which intersect at a circumferential contact area 186. Discs M include outwardly curved circumferential protuberances 188 which intersect at 190 in a location spaced radially inward from diverging outer peripheral edges 192 of discs M. In previous arrangements, protuberances 188 were smashed down to be substantially parallel to one another in order to cause diverging outer peripheral edges 192 to firmly engage the edges of notches 28. In accordance with the present invention, an apparatus of the type disclosed in the aforementioned copending application may be used to deform protuberances 188. However, instead of moving the deforming dies extremely close to one another in order to deform protuberances 188 into substantially parallel relationship, the deforming die applies striking force as represented by arrows 200 which breaks protuberances 188 substantially at their centers to define a circumferential contact area 202 and to form two radially spaced

protuberances

204 and 206. Inner circumferential protuberance 204 has an inner circumferential edge corresponding with circumferential contact area 186 and outer circumferential protuberance 206 has an outer edge corresponding with circumferential contact area 188. Circumferential contact area 202 defines the inner circumferential edge of outer protuberance 206 and the outer circumferential edge of inner protuberance 204. Outer circumferential protuberances 206 are under bending 'stress between

circumferential contact areas

188 and 202 while inner circumferential protuberances 204 are under bending stress between

circumferential contact areas

186 and 202. This bending stress firmly holds outer peripheral edges 192 in firm engagement with notches 28 and prevents

protuberances

204 or 206 from stress relieving over a long period of time. In previous arrangements, where protuberances were simply deformed to be substantially parallel to one another, the flattened protuberances would relieve themselves of stress over a period of time and the outer peripheral edges of the discs would become loose in the notches. With the arrangement of the present invention,

protuberances

204 and 206 are in somewhat of a springlike arrangement so that outer peripheral edges 192 are continuously biased into firm engagement with notches 28. This springlike action substantially eliminates relief of stress in the deformed metal which might cause the outer peripheral edges of discs M to become loose in notches 28. In one arrangement, with a Q-inch-diameter blower wheel and discs M having a sheet metal thickness of around 1/64 inches,

protuberances

204 and 206 take the form shown in FIG. 22.

Dimensions

214 and 216 are substantially equal at around 21/64 inches each. It will be understood that these are only nominal dimensions and may vary by several 64ths of an inch. in addition, it will be understood that dimensions given will vary with different thicknesses of metal and different diameter blower wheels.

While the invention has been described with reference to preferred embodiments, it is obvious that modifications and alterations will occur to others upon the reading and understanding of this specification.

I claim:

1. A centrifugal blower wheel formed from a sheet metal strip having opposite side edges, said strip having longitudinally spaced transverse blades formed therein between said side edges, said side edges including marginal rim portions extending continuously along said side edges of said strip and integrally interconnecting said blades, said rim portions including top and bottom surfaces and having folds therein between adjacent blades for decreasing the longitudinal spacing between said blades, said rim portions including substantially planar portions extending between adjacent folds, said folds being symmetrical on opposite sides of a centerline bisecting said folds transversely of said strip, said folds having a substantially S-shape on one side of said centerline and a substantially backwards S-shape on the other side of said centerline, said folds including first and second bends having interior surfaces facing one another and said centerline, said interior surfaces of said first and second bends being defined by portions of said bottom surface of said rim portions, said first and second bends having exterior surfaces defined by portions of said top surface of said rim portions, said first and second bends being interconnected by an upper web portion of said folds extending substantially parallel to said planar portions of said rim portions, said web portion having inner and outer surfaces defined respectively by portions of said bottom and top surfaces of said rim portions, said folds including third and fourth bends having interior surfaces facing in opposite directions and away from said centerline, said interior'surfaces of said third and fourth bends being defined by portions of said top surface of said rim portions, said third and fourth bends having exterior surfaces facing one another and said centerline and being defined by portions of said bottom surface of said rim portions, all of said interior surfaces of said bends being smoothly curved and in spaced-apart noncontacting relationship over arcs greater than 180.

2. The blower wheel of claim 1 wherein a portion of said exterior curved surfaces of said first and second bends are in contact with said top surface of said rim portions at said planar portions thereof, and a portion of said exterior curved surfaces of said third and fourth bends are in contact with said inner surface ofsaid web.

3. The blower wheel of claim 2 wherein said curved exterior surfaces of said third and fourth bends are in spaced-apart relationship longitudinally of said strip.

4. The blower wheel of claim 1 wherein said curved exterior surfaces of said third and fourth bends are in spaced-apart relationship longitudinally of said strip.

5. The blower wheel of claim 1 wherein said strip is formed into a cylinder and said blades have inner and outer edges, said inner edges having notch means formed therein, a pair of discs having outer peripheral edges, at least one of said edges on one of said discs diverging away from said edge on the other of said discs, said one disc having a pair of radially spaced inner and outer circumferential protuberances adjacent said outer peripheral edge, said inner protuberance having an inner circumferential edge and said outer protuberance having an outer circumferential edge positioned inwardly of said diverging peripheral edge, said inner and outer protuberances having a common circumferential edge defining an outer circumferential edge of said inner protuberance and an inner circumferential edge of said outer protuberance, said circumferential edges of said protuberances on said one disc being in contact with said other disc, said inner and outer protuberances being under bending and compressive forces, said forces holding said diverging peripheral edges in biased engagement with said notch means and said circumferential edges of said protuberances in engagement with said other disc.

6. The blower wheel of claim 5 wherein said blades are deformed out of the plane of said strip and have an arcuate cross-sectional shape of predetermined arcuate length, said blades having end portions integrally connected with said rim portions by connecting webs, said webs having a width longitudinally of said strip substantially less than said predetermined arcuate length, said end portions of said blades adjacent said webs being work hardened less than the intermediate portion of said blades between said end portions.

7. The blower of claim 1 wherein said blades are deformed out of the plane of said strip and have an arcuate cross-sectional shape of predetermined arcuate length, said blades having end portions integrally connected with said rim portions by connecting webs, said webs having a width longitudinally of said strip substantially less than said predetermined arcuate length, said end portions of said blades adjacent said webs being work hardened less than the intermediate portion of said blades between said end portions.

8. A centrifugal blower wheel comprising a cylindrical blade strip having a longitudinal axis, said strip including a plurality of circumferentially spaced blades extending substantially parallel to said longitudinal axis, said blades having inner and outer edges, said inner edges having notch means formed therein, a pair of discs having outer peripheral edges, at least one of said edges on one of said discs diverging away from said edge on the other of said discs, said one disc having a pair of radially spaced inner and outer circumferential protuberances adjacent said outer peripheral edge, said inner protuberance having an inner circumferential edge and said outer protuberance having an outer circumferential edge positioned inwardly of said diverging peripheral edge, said inner and outer protuberances having a common circumferential edge defining an outer circumferential edge of said inner protuberance and an inner circumferential edge of said outer protuberance, said circumferential edges of said protuberances on said one disc being in contact with said other disc, said inner and outer protuberances being under bending and compressive forces, said forces holding said diverging peripheral edge in biased engagement with said notch means and said circumferential edges of said protuberances in engagement with said other disc.

9. The blower wheel of claim 8 wherein said other disc is substantially identical to said one disc and has an outer peripheral edge diverging from said one disc and a pair of inner and outer circumferential protuberances having circumferential edges corresponding to said circumferential edges of said inner and outer protuberances on said one disc, said circumferential edges of said protuberances on said other disc being in contact with said circumferential edges of said protuberances on said one disc, said protuberances on said other disc being under bending and compressive forces, said forces holding said diverging peripheral edge of said other disc in biased engagement with said notch means and said circumferential edges of said protuberances of said other disc in engagement with said circumferential edges of said protuberances of said one disc.

10. A sheet metal blade strip for centrifugal blower wheels, said strip having opposite side edges, said strip having longitudinally spaced transverse bla-lcs formed therein between said side edges, said side edges including marginal rim portions extending continuously along said side edges of said strips and integrally interconnecting said blades, said blades being deformed out of the plane of said strip and having an arcuate cross-sectional shape of predetermined arcuate length, said blades having end portions integrally connected with said rim portions by connecting webs, said webs having a width longitudinally of said strip substantially less than said predetermined arcuate length, said end portions of said blades adjacent said web being work hardened less than the intermediate portion of said blades between said end portions.

11. A method of forming a blade strip for a centrifugal blower wheel from a sheet metal strip having opposite side edges comprising the steps of; punching longitudinally spaced arcuate blades into said strip transversely thereof between said side edges to provide marginal rim portions extending continuously along said side edges of said strip integrally interconnecting the end portions of the blades, deforming said rim portions into an inverted U-shape deformation, striking the arcuate portion of said deformation and bending the arcuate portion of said deformation at its center to form a substantially heart-shaped deformation, and striking said heart-shaped deformation between surfaces which close to a spacing greater than three times the thickness of said rim portions to flatten said heart-shaped deformation into a fold having bends which are smoothly curved.

12. A method of assembling a centrifugal blower wheel from a cylindrical blade strip having a plurality of circumferentially spaced blades with notch means in their inner edges, and from a pair of discs having outer peripheral edges and circumferential arcuate protuberances spaced radially in- I ward from said outer peripheral edges, comprising the steps of; positioning said outer peripheral edges of said discs in said notch means, and striking said protuberances to bend said protuberances toward one another around the center portions thereof and provide a pair of radially spaced arcuate protuberances in each of said discs which are under bending and compressive stress to firmly bias said outer peripheral edges into engagement with said notch means.

13. A method of deforming curved blower blades from a sheet metal strip having opposite side edges including marginal rim portions extending continuously along said strips, said strip having longitudinally spaced transverse slits formed therein between said side edges, said strip having generally longitudinal slits formed therein extending along said rim portions from each end of said transverse slits toward an adjacent slit, said slits defining substantially rectangular blade forming sections connected with said rim portions by webs defined between adjacent longitudinal slits, comprising the steps of; initially striking the major portion of said blade-forming sections to impart initial curvature thereto while leaving the end portions of said blade-forming sections adjacent said webs substantially flat, and subsequently striking said blade-forming sections to impart further curvature thereto and to curve the end portions of said blade-forming sections adjacent said webs whereby the end portions of said blade-forming sections are work hardened less than when they are repeatedly curved in a plurality of successive striking steps.

Claims

1. A centrifugal blower wheel formed from a sheet metal strip having opposite side edges, said strip having longitudinally spaced transverse blades formed therein between said side edges, said side edges including marginal rim portions extending continuously along said side edges of said strip and integrally interconnecting said blades, said rim portions including top and bottom surfaces and having folds therein between adjacent blades for decreasing the longitudinal spacing between said blades, said rim portions including substantially planar portions extending between adjacent folds, said folds being symmetrical on opposite sides of a centerline bisecting said folds transversely of said strip, said folds having a substantially S-shape on one side of said centerline and a substantially backwards S-shape on the other side of said centerline, said folds including first and second bends having interior surfaces facing one another and said centerline, said interior surfaces of said first and second bends being defined by portions of said bottom surface of said rim portions, said first and second bends having exterior surfaces defined by portions of said top surface of said rim portions, said first and second bends being interconnected by an upper web portion of said folds extending substantially parallel to said planar portions of said rim portions, said web portion having inner and outer surfaces defined respectively by portions of said bottom and top surfaces of said rim portions, said folds including third and fourth bends having interior surfaces facing in opposite directions and away from said centerline, said interior surfaces of said third and fourth bends being defined by portions of said top surface of said rim portions, said third and fourth bends having exterior surfaces facing one another and said centerline and being defined by portions of said bottom surface of said rim portions, all of said interior surfaces of said bends being smoothly curved and in spaced-apart noncontacting relationship over arcs greater than 180*.

2. The blower wheel of claim 1 wherein a portion of said exterior curved surfaces of said first and second bends are in contact with said top surface of said rim portions at said planar portions thereof, and a portion of said exterior curved surfaces of said third and fourth bends are in contact with said inner surface of said web.

10. A sheet metal blade strip for centrifugal blower wheels, said strip having opposite side edges, said strip having longitudinally spaced transverse blades formed therein between said side edges, said side edges including marginal rim portions extending continuously along said side edges of said strips and integrally interconnecting said blades, said blades being deformed out of the plane of said strip and having an arcuate cross-sectional shape of predetermined arcuate length, said blades having end portions integrally connected with said rim porTions by connecting webs, said webs having a width longitudinally of said strip substantially less than said predetermined arcuate length, said end portions of said blades adjacent said web being work hardened less than the intermediate portion of said blades between said end portions.

12. A method of assembling a centrifugal blower wheel from a cylindrical blade strip having a plurality of circumferentially spaced blades with notch means in their inner edges, and from a pair of discs having outer peripheral edges and circumferential arcuate protuberances spaced radially inward from said outer peripheral edges, comprising the steps of; positioning said outer peripheral edges of said discs in said notch means, and striking said protuberances to bend said protuberances toward one another around the center portions thereof and provide a pair of radially spaced arcuate protuberances in each of said discs which are under bending and compressive stress to firmly bias said outer peripheral edges into engagement with said notch means.