US2698128A

US2698128A - Axial flow fan

Info

Publication number: US2698128A
Application number: US67738A
Authority: US
Inventors: James R Ault; Chester P Jenkins
Original assignee: Joy Manufacturing Co
Current assignee: Joy Manufacturing Co
Priority date: 1948-12-28
Filing date: 1948-12-28
Publication date: 1954-12-28
Anticipated expiration: 1971-12-28

Description

Dec. 28, 1954 J. R. AULT ET AL AXIAL FLOW FAN 4 Sheets-Sheet l Filed Deo. 28, 1948 WWWZZM: @fmes Wag@ DeC- 28, 1954 J. R. AULT ETAL v ZGQSJE AXIAL FLow FAN Filed Dec, 28, 194s 4 sheetsheet 2 Dec. 28, 1954 J. R. AULT ET AL 2,698,128

AXIA?. FLOW FAN Filed Dec. 28, 1948 4 Sheets-Sheet 5 Dec- 28 1954 J. R. Auw Emp www v AXIAL FLOW FAN Filed Dec. 28, 1948 4 Sheets-Sheet 4 laan..

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A024- uwm @iliona ey United States Patent AXIAL FLOW` FAN .lames R. Ault and Chester-P.fJenkins, New Philadelphia,

Ghia, :assignors .to Joy ldtuaufacturiumgI Company, Pitts- -hurgh,-Pa., acorporation of Pennsylvania Appiication December 28, 1948, Serial No.67,'738

14 Claims. (Cl. 23d-117) `Our'invention relates to axialflow fans, and morejparticularly, from diiferent aspects thereof, to the fan and motor housings of such fans, to the' fan members proper thereof, and to the complete fan units.

wallof' the'fanchamber may ultimately take place; and, Whether or not that occurs, there may be distortion, With increased tip clearance at some points and reduced clearance at others, with resultant loss of eciency. When, asfisdesirable from the standpointof Weight, lto mention only'one possibly cogent factor, the fan and motor housings are to be made of plastics-eg. thermo-plastic materials, a virtual necessity for mono-bloc construction is encountered.

'Whetherthefan member Vand/or the fan and motor housing-.principal constituent elements of axial flow' fans aside from the' fan driving motors--areto' be cast in one piece or molded in one'piece, it is essential for economy ofl constructionthat they shall Abe'capable of having the `mold Vor diegparts in :which they are cast, formed or molded, separable from each other Without injury. to Ithemselves or tothe fan elements, and to that end the`fan elements will desirably be constructed so that they may be formedibetween or Within: mold or likel parts from which 'they can be removed-without breakage. Where' there are vanesand the same is true of blades-whichhave curved surfaces which, aty both isides of a1 point oftangency to a;line,parallel to 'tlieaxis 'of the elementwith which said blades or vanes are integraL'diverge from such a line, the problem of mono-bloc construction is greatly increased, `if` molds or .dies which are .not to `be destroyed in the process of fan manufacture are to be used.

Another consideration of importance connected Ywith our invention is they provision of an `arrangement of fan elements which by relative axial adjustment of-'such .elementsenables the same parts to beadapted to meetdiiferent load conditions.

lt is an object of our invention to provide an improved axial flow fan structure of which the cooperatingfan member and fan and motor housing may be cast or-'molded by the `use of molds or dies which Vwill `be uninjured 'in their separation and in the removal from them (or vice versa) of the parts they are employed to produce. It is another object of our invention to provide an improved mono-blocrfanHmember. It is a'fur'ther object of-'our invention to provide Aanfirnprovedmono-bloc fan varid motor. housing. It is yetfaffurther objectl of our invention to provide. an improved mono-blocffan andrmoter housing-capable of production by `molding or casting in dies which maybe used manytimes. -It1 isV still another object of our invention to provide anv improved fan and motor housing including vanes having surfaces which curve-away, at both sides of their point'of contactwitha line parallelto the axis of the housing,`from such a line and Whichare so arranged that they'mayibeformediin simple separable molds or dies. It is'still anotherbjectof ourA invention to providefan improved fan alidmotohousingxhaving` a motor' casing spacedA bycurved flow-directing blades from an outer Ycasing or Vfairing element, and 'in which the circumferentially Vextending 'surfaces "at 'the 'points .Where such vanes join the outer Wa'll'of the .fanand `axial'lilow fan construction in which by' the'relativeJadjustmentv of afan member toa fan'casingproviding'member' the `same elements may be.:causedztosatisfy' diierent load. conditions. Other-objects aridadvantagesofthe invention will hereinafter more-fully appear.

yln the accompanying drawingsin which one `illustrative embodiment of our invention in each'ofdts'faspects hasbeen shown,

'Fig l is an approximately central vertical section throughan" axial 4low fan in 'which 'the illustrative v1embo'dimentof the invention is incorporated.

Fig. 2 isanend elevational view'of the fan: of Fig4 1, viewedfrom the-right, that is, from thefan end thereof.

),Fig. 3 .is a central longitudinal: section on an enlarged scale and/on aplane including the axis thereof, through afan and motor'housing, the sectionbeing' taken onthe plane. of the line 3 3 of Fig/4.

EnFig. 4'isan`end view, from the'righthanden'dVV of` Figs.

l and`3, and-on ascale smaller than 'that"of`Fig. 3,) but larger than that of Fig. 1, of the fan and motor housing of Fig. 3, parts shown in Fig. l being omitted.

Pig. 5 is vanenlargedA fragmentary sectional view-or, perhaps better put, a Ldeveloped,view on the curved section line. 5-5 of Fig. 2, showing a'detail of fan blade construction.

Fig.f5'A is a detail sectional "developed vieW.on the vplane of the line SA-SA of Fig." 5.

'Fig 6 is a section on the curved sectionline 6 6 ,of Fig. 4 throughcertain stationary vanes, and. showingfthe -outer periphery 'of the cup-shaped recepta`c1elater.'de scribed.

` Fig, 7 is a view on the curved section 1ine7---l7ofv Fig. 4, through a pair'of iovv directing vanes, Vandshovving a portion `of the Ainner surface of the outer casing wall ofthe fan andrnotorhousing.

Fig. 8 isa fragmentary transverseV section on thejplane of the line 8-'8 of. Fig. :6.

Fig-91's a fragmentary transverse section'on the-plane vof the section line 9-9 'of Fig. f6.

"Fig 10 is a fragmentary transversesection'on theplane of the' line iti-'iti of Fig. 7.

"Fig 11 is a fragmentary cross section 'on' theplaneo'f the line 11-11of,Fig. 7.

V'Referring to the drawings, it.will be bservedsthat an axial flovvd fan generally designated. 1 vincludes-.a fan and-motorhousing 2, a fan member,` and'a driving motor 4. The fan and .motorrhousing '2 is of monobloc construction andincludes an Vouter .annular Wall10 and a centrally disposed cup-shaped'hub'portion or receptacle`11 connected to the outer annular'wall by'a plurality of vanes'lZ. The cup-shaped hub portion or receptacle'I 11- is arranged to receive a cylindrical shaft-supporting means, herein the 'motor 4, and .the motor has ashaft 13 which supports and drives the fan member 3 Within vthe outer annular-wall 1t). 'Thecup-shaped hub portionll has aninwardly directed lannular Wallportion 15 which has-*a planelinnersurface .I6 and Whichlhas at '17 a circular opening coaxial with 'an inner surface lfformed Within the wall '10' andisurroun'dingtheifan blades f19 of ,thegfan 3. The end `ofthemotor 4 abuts against the -en`dt surface'16,'andthermotor is held against the Wall portionS'by screws .andWashers'ZiL .21.' 'The motor has `a peripheral surface of revolution 17 snugly ttingl within the opening17 and coaxial with the motor shaft 13. The mountingof` the V.motor-His 'thus su'ch.that the axispfithe motor shaft 13 is perfectlycentralwithin the surfaceflS, so thatlthe tipclearance indicated atl`22 between'the'fan blades 19 andthe internal surface`18 maybe'maintained 'at a very lowV value. In actual construction the tip 'clearance' may be" as lowas afew thousandths of an inch, and the tip clearance may be readily varied, noting that the wall 18 conforms to a portion of the surface of a cone of which the base lies to the right of the fan and motor housing, in terms of Fig. l, and that the outer ends of the fan blades 19 also conform to the surface of such a cone, merely by shifting the fan 3 along the motor shaft, as may be done by releasing a holding screw 23 which is threadedly carried by a desirably externally knurled steel insert 24 about which the fan element 3 is molded, the screw 23 engaging a flat 25 formed on one side of the shaft 13.

The provision of a conical (or frusto-conical) shape for the fan chamber, and the shaping of the tips of the fan blades so that they lie in a conical (or frusto-conical) surface of the same cone angle as the fan chamber, permits variation of the clearance between the blade tips and the surrounding fan chamber wall, while the clearance will be the same, in any particular adjustment, at all points along the lengths of the blades. A very close tip clearance, secured by moving the fan inwardly (rearwardly) in the fan chamber, until the minimum safe running clearance exists, is desirable for a system in which the volume and pressure characteristics are relatively constant, as the maximum volume and pressure will then be delivered by the fan and its maximum eiliciency will be obtained. If the fan is to be used in a system having changing volume and pressure characteristics, it may be adapted to such a use by moving the fan outwardly (forwardly) in the fan chamber and increasing the tip clearance. The fan will then operate at relatively high efficiency over a greater range than is possible where minimum tip clearance was provided, though the maximum volume and pressure with this adjustment will not be as good as can be obtained with minimum tip clearance.

Reverting to the structure of the fan and motor housing 2, it will simplify the understanding of the details of construction now to be given with respect to this element if it be considered as having a rst annular portion and a second annular portion or, otherwise stated and in reverse order, a forward end and a rearward end, the terms forward end and second annular portion being used to designate that end within which the fan rotates, and the terms rearward end and first annular portion employed to indicate the opposite end of the fan and motor housing. It has been noted that the fan and motor housing comprises an outer annular wall and a hub portion, or perhaps more aptly stated, a centrally disposed cup-shaped receptacle 11 which constitutes a support for the motor. It has further been noted that there are a plurality of stationary vanes 12 which support the cupshaped receptacle or support 11 substantially concentrically within the outer wall 10. These vanes connect the first annular portion or rearward end of the fan and motor housing 2 to the support. The rearward ends of these vanes 12 extend beyond the rearward end of the receptacle 11. It has been noted that the receptacle or hub portion 11 is in the form of a body open at its rearward end 35, and having at its forward end an inwardly directed annular wall or abutment 15. The chamber 36 within the hub or cup-shaped receptacle decreases in diameter, from its rearward end to its forward end, more sharply to a point slightly forward of the forward ends of the vanes 12, and then more gradually. The cup-shaped receptacle 11 has on its outer surface, between its rearward end and a circle passing through the points of junction of the forward ends of the vanes with the periphery of the cup-shaped receptacle a zone 37 of substantial width. Forward of such zone 37 the outer periphery of the cup-shaped receptacle includes only surfaces tapering toward the forward end of said receptacle or hub portion. The inner surface of the outer annular wall 10 has a zone 38 between a plane including the rearward edge of the receptacle and a circle passing through the points of junction of the forward ends of the stationary vanes 12 with the outer wall 10, forwardly of which zone the inner surface of the outer wall-the portion thereof designated 18, i. e. the portion between said circle and the forward end of the wall, includes only surfaces which taper toward the rearward end of the fan and motor housing. The outer surface 39 of the outer wall 10 tapers toward the forward end of the housing oppositely to the inner surface. Back of the rearward end of the zone 38 the inner surface of the wall 10 conforms to a frustum of a cone whose larger end is to the rear of the fan and motor housing. The

zones

37 and 38 are sub-divided by the vanes 12 and each has between each pair of vanes its surface made up principally of two surfaces sloping oppositely longitudinally of the housing, the oppositely sloping surfaces on the hub or receptacle 11 being designated 41 and 42, and the oppositely sloping surfaces on the housing wall 10 being designated 43 and 44. The oppositely

sloping surfaces

41 and 42 are essentially portions of the frustums of cones, the larger end of one of which is to the rear of the housing and the larger end of the other of which is forward of the housing, the surfaces 42 constituting or conforming to portions of the frustum of a cone whose larger end is rearward of the housing and the surfaces 41 constituting or conforming to portions of a surface of the frustum of a cone whose larger end is forward of the housing. The oppositely

sloping surfaces

43 and 44 of the zone 38 on the interior of the annular wall 10 conform substantially to portions of the frustums of cones the larger end of one of which is to the rear of the housing and the larger end of the other of which is forward of the housing. Surfaces 43 conform to the surface of a frustum of a cone whose larger end is to the rear of the housing, specifically to the surface of the frustum mentioned a few lines above. The surfaces 44 conform to the surfaces of a frustum of a cone whose larger end is forward of the housing. This frustum is the one to which the surface 18 conforms. The adjacent edges of the

oppositely sloping surfaces

41, 42 and of the

oppositely sloping surfaces

43, 44 terminate in mutually oblique lines, respectively numbered 45 and 46, and oblique fills, as at 47, 47', 48 and 49, are made along said lines where air flow would be substantially adversely affected in the absence of such fills. Ramplike portions are provided at the forward end of the

surfaces

41 and 43, as at 50 and 51 and a ramplike sloping fill 52 is provided at the rearward end of the surfaces 44. Rearwardly of this lill lies a surface portion which is a portion of the surface 43. Each stationary vane 12 has its side surfaces so curved that a line drawn parallel to the axis of the housing from any point in such a side surface, in the direction of removal of a mold which forms such side surface, will not pass through the vane. Thus, referring to Fig. 6, a mold forming the surface 42 and the left side of the blade 12 at the right of that gure would be moved downwardly relative to the fan and motor casing to effect their separation, and from the point of tangency of a line 53 to the vane at 54 a line 55 can be drawn downwardly, in parallelism with the axis of the fan and motor casing, without passing through the blade, and the divergence between the line 55 and the portion of the line 53 below the point 54 in Fig. 6, will make it clear that the mold can be withdrawn without diiculty.

Again, a mold that would form the surface 41 and the right side of the blade 12 at the left in Fig. 6 would be withdrawn upwardly of Fig. 6, and a line 59 can be drawn upwardly, parallel to the axis of the fan and motor casing, from the point of tangency 56 of a line 57 with the surface of the vane, without passing through the vane, and the upward divergence of the

lines

59 and 57 clearly indicates the ready removability of the mold.

Turning next to Fig. 7, it will be noted that the mold which forms the surface 44 and the right hand side of the left hand vane 12 is downwardly removable, and that the line 61 may be drawn downwardly in parallelism with the axis of the fan and motor housing from the point of tangency of a line 60 with the surface of the vane, and not pass through the vane, and the downward divergence of

lines

60 and 61 clearly shows the ready removability of the mold from the casing.

Finally, the mold that forms the surface 43 and the concave side of the right hand vane shown in Fig. 7 is removed upwardly, and the divergence between the line 63, drawn upwardly parallel to the axis of the fan and motor housing, from the point of tangency of the line 62 with the curve of the left hand side of the right hand vane 12, shows the ready removability of the mold that forms the surface 43 and concave side of the right hand vane.

It is to be understood that references to movement of mold to casing are to explain relative directions of separative movement, and do not exclude removal of the casing from the molds instead of vice versa. In order to enable cleaner separation between the housing and ,the di6e4or .moldriillsatnsharp corners-may be provided .as-,at-l j,

L:Before consider-ingA further ,the structure of the v fan member 3, it may be V-noted .tnatthe fan and motor hous- :ingrllltmay desirably ubetapered Vexteriorly .towards its for- .ward endend may alsodesirablyhave a mounting ange Ias at4 65. -rThecasinrgfor housing 10 ,may also have a pad P-formed thereon for thel mounting of a connector ,b ox or ,the like C. I -n order to facilitate molding, the plane ,ofC pad P-to which box C. isv fastened preferably slopes slightly toward the motor axis at the forward end.

tWemay J,now advert further to the structure of the fammember 3. This maybe noted to comprise a rotor body portion 66 `whichincludes a hub portion 67 in Vwhich the steelinsert ,24 is mounted, a radially-extending wall 68, .andan annular'portion69 supporting the blades 19. .T he hub portion-67 `and the inner `wall 70v of the portion `69 are each so formed that a corelike element forming the-.inner .wall-,ofthe moldfor the fan proper may be readilyv withdrawn.

The. external-periphery` of .the annular portion 69, at Iheportions thereof from which the blades i9 project is specially formed :to facilitate removal of the fan from the moldinwhich it is formed. .Let it be imagined that this annularl portion is surrounded by two concentric circles, One-indicated in broken lines at '7l in Fig. 5, at the leading edges of the blades, and Vthe other, indicated in brokenlines at 72.in the same figure, at the receding edges of `the fan blades. `Circle 71 will be slightly larger in diameter than` circle '72. `In other words the external diameter of portion 69 is slightly larger just forward of .the blades19` thanjust to the rear of them. The surface `between the .circles 7l and-72 is broken up into sections respectively principally forward of the blades and principally rearward of the blades. Because the blades do not overlap each other as shown, but are slightly spaced ciroumferentially of the rotor,` the surfaces may be more sharply deiinedas follows: From a point adjacent the forward tip l,Tf of each blade, let `a line L be drawn to appoint adjacent the receding edge R of the blade next ahead. Now, there will be seen to be two series of areas-w the oneS1, -made .up of areas at least principally to the rear of Lthe, fan blades and the other, S2, made up of areas at, least principally ahead of the fan blades. Now with respect to the areas S1, these areas will Vconform to a frustum of a cone .coaxial with said fan (with its Aaxis in the same line with the fan axis) and the elements of the surfacesnof said areas `will all be elements of such a frustum and all .will sloperearwardly. On the other hand, theelementsof the surfaces of the areas S2 ahead of the blades will each correspond to the elements of a frustum ofa cone yhaving its yaxis in the same line with the rotor axis and having its larger end to the rear of the rotor. This-willgmean thatan element extending rearwardly ofthe fan from the point near theleading edge T of a blade slopes rearwardly inwardly towards the `axis of the fan, while an-element extending forwardly from the point near the receding edge R of the next bladeahead slopes forwardly and inwardly, that the forward ends of .the twowelements are in a common circle 71 struck from the axis of the fan rotor, and that extending between the points -is a .surface W having edges 'diverging from the point near therforward end of the -lirst blade to the point near the receding edge of the preceding blade. Thus there will be readilypossible a molded structure separable from itsk mold' by draft in opposite directions. The narrow circular surfaces forward of the tirst circle il and rearward of thesecond circle 72 correspond to the adjacent frustoconical surfaces and form extensions thereof. The first mentioned of these narrow circular surfaces merges into the rounded nose of .the fan. Fig.v A is provided to show the ,surface W.

Evidently, now the portions of the blades 19 and of the surfaces around their roots are so formed that two mold elements, `one forming the rearward Vsurfaces of the blades and the peripheral surface areas S1 Vbehind them, andthe other shaping the forward surfaces of the blades and' the surfaces S2 ahead of them may be readily separable after the fan is molded. To lighten the fan construction the radialwall portion thereof is recessed annularly as atz32, .and itwill be apparent that the portion of, the` rearward mold `element which fills this recess duringgcasting or molding of the fan will be freely withdrawa-blefrom the recessabecause of ,the shape of the walls thereof.

i6 j It. willwbe 1 noted'that. the .motorz4 constitutes acylindri- Galv means having anrotatiligv driving -shaftyithereintwithra fan mounted thereon, Vand :that:.the: motor .is thussillustrative of fan drivingmeans which may notthavetheir motor ymeans coaxial fwith Vthefan :and fmotor: housing.

It should be` further noted; that each ofsthe vanes 12 has an entry nose portion at its'forward end, ya trailing edge portion at its rearwardend `and .anfintermediate curved portion, and thatthejentry nosefportion.:is.1disposed at an angle to the axis ofthe housingwhile the trailing portion is directed .substantially axially-to thefuhousing, and that the zone 38: has the Vportionszof. its surface between the vanes which clie adjacent to them slopelongitudinally toward 'the axis of the housing 1in onexdirection from the concave portionsl ofisaidvanes and longitudinally toward the 1axis of the thousing. inpthe other `direction from the convexwportions'ofV the vanes.

it may be noted that lbook-type vdies could 4beuused, in which case the outer .surface 139 `would-.notsneed to be tapered.

The invention described herein maybe injection -molded if desired, or it may be madeby ftllinga moldwith plastic in powder form, after-which themold may lbetheated under pressure to a temperature highenough to fuse the powdered plastic. A still further alternative vwould `be die casting, if the parts `were made of` metal.

While there is in Vthisapplication ,specicallyr described one form which the invention may Vassume in practiceylit will be understood that thisforrn vof the sameis shown for'purposes of illustration and thatthe:inventiommay be modified and embodied invarious otherforms witholut departing from its spirit'or the scope of theappended c a1ms.

What I claim `as new and `desire Patent is:

l. In an axial flow fan structure. comprising vcylindrical means having a rotating driving shaft thereinwitha'fan mounted thereon, `said fan. having. outwardly extending blades whose` end surfaces lie in a frusto-.conical surface, said cylindrical means :supporting `the shaft-.and having a casing with an endlportion through whichsaid shaft extends, said casing havinglan external surface of-revolution substantially concentric with said shaft, the improvement -of a housing forv the cylindricalmeansandf the fan, said housing comprising a'mono-bloc .structure having an outer annular wall, a centrally disposed support and a plurality of vanes for Vconnecting said .support to-said outer annular wall, said outer annular walllhavinga irst .and a second annular portion, said-pluralityof vanes connecting said centrally disposed support to said tirst annular portion, said second 4annular portion having an internal frusto-conical surface surrounding .thefan and having its end of smaller diameter nearer saidztirst annular portion, said support yhaving.-frst .and second angularly related surfaces, said rst angularlyrelated surface constituting an internal surface of revolution substantially concentric both to said shaft and .to `said internal frusto-conical surface, said irst angularly related surface -closely receiving said external surface of revolution of the said lcasing `and substantially concentrically aligning said external surface of revolution of the casing and the shaft with the said internal frusto-conical surface, whereby a substantially constant tip fclearance is maintained between the fan blades and said frusto-conical surface, said second angularly related surface constituting transversely disposed abutment means against which the end portion of said casingv longitudinally abuts and through which said shaft extends, and fastening means fastening the said casing to the abutment means for holding the said casing and shaft against longitudinal movement.

2. In an axial iiow fan structure comprising cylindrical means having a rotating driving shaft therein with a fan mounted thereon and having outwardl-yextending blades whose end surfaces lie in a frusto-.conical surface, said cylindrical means supporting the shaft and vhaving a casing with an end portion through which said shaft extends, said casing having an external surface of revolution substantially concentric with said shaft, the improvement of a housing for the cylindrical means andthe fan, said housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed support and a plurality of vanes for connecting said support to said outer annular wall, said outer annularwall having a lirst and a` second annularportion; said plurality to secure. byl Letters of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal frusto-conical surface surrounding the fan and of like cone angle with said first mentioned frusto-conical surface and having its end of smaller diameter nearer said first annular portion, said support having first and second angularly related surfaces, said first angularly related surface constituting an internal surface of revolution substantially concentric both to said shaft and to said internal frus'ooconical surface, said first angularly related surface closely receiving said external surface of revolution of the said casing and substantially concentrically aligning said external surface of revolution of the casing and the shaft with the said internal frusto-conical surface, whereby a substantially constant tip clearance is maintained between the fan blades and said frusto-conical surface, said second angularly related surface constituting transversely disposed abutment means against which the end portion of said casing longitudinally abuts and through which said shaft extends, and fastening means fastening the said casing to the abutment means for holding the said casing and shaft against longitudinal movement.

3. In an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, and said first annular portion having the internal surface thereof between the connections of said vanes therewith comprised principally of oppositely sloping portions conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same ne with the axis of said outer fan chamber wall.

4. In an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal frustoconical surface forming the outer wall of a fan chamber, and said first annular portion having the internal surface thereof between the connections of said vanes therewith comprised principally of oppositely sloping portions conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same line with the axis of said outer fan chamber wall, certain of said portions constituting extensions of said first mentioned frusto-conical surface.

5. In an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal frusto-conical surface forming the outer wall of a fan chamber, and said first annular portion having the internal surface thereof between the connections of said vanes therewith comprised principally of oppositely sloping portions conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same line with the axis of said outer fan chamber wall, certain of said portions constituting extensions of said first mentioned frusto-conical surface and there being ramp portions adjacent the ends of smaller radius of said oppositely sloping portions.

6. In an axial ow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal frusto-conical surface forming the outer wall of a fan chamber, and said first annular portion having the internal surface thereof between the connections of said vanes therewith comprised principally of oppositely sloping portions conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same line with the axis of said outer fan chamber wall, certain of said portions constituting extensions of said first mentioned frusto-conical surface and there being ramp portions adjacent the ends of smaller radius of said oppositely sloping portions and one of the portions between each pair of vanes extending for a portion of its length for the full width of the space between such pair.

7. In an axial fiow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes' connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes comprised of oppositely sloping sections conforming to frusto-conical surfaces whose axes are in the same line with the axis of said outer fan chamber wall and whose larger ends are at the opposite ends of said vanes'.

8. In an axial fiow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes comprised of oppositely sloping sections conforming to frusto-conical surfaces whose axes are in the same line with the axis of said outer fan chamber wall and whose larger ends are at the opposite ends of said vanes, one of said oppositely sloping sections having a ramp at its end of larger diameter.

9. In an axial fiow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, each of said vanes having a leading and a rearward end, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer Wall of a fan chamber, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes comprised of oppositely sloping sections conforming to frusto-conical surfaces whose axes are in the same line with the axis of said outer fan chamber wall and whose larger ends are at the opposite ends of said vanes, said oppositely sloping sections being of less length than said vanes and extending from points adjacent the leading ends of said vanes only to points short of the rearward ends of said vanes.

l0. In an axial ow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support and a plurality of vanes for connecting said support to said outer annular wall, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, said first annular portion having the internal surface thereof between the connections of said vanes therewith comprised principally of oppositely sloping portions conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same line with the axis of said outer fan chamber wall, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes comprised of oppositely sloping sections conforming to frusto-conical surfaces of mutually opposite taper but with their axes in the same line with the axis of said outer fan chamber wall.

1l. ln an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support, and a plurality of vanes for connecting said support to said outer annular wall, each of said vanes having an entry nose portion, a trailing edge portion, and an intermediate curved portion therebetween, whereby said vanes have concave and convex portions, said entry nose portion being disposed at an angle to the axis of said housing and said trailing portion being directed substantially axially of said housing, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said rst annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, and s'aid first annular portion having the portions of its surface between said vanes which lie adjacent to them slope longitudinally towards the axis of the housing in one direction from the concave portions of said vanes and longitudinally towards the axis of the housing in the other direction from the convex portions of the vanes.

12. In an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support, and a plurality of vanes for connecting said support to said outer annular wall, each of said vanes having an entry nose portion, a trailing edge portion, and an intermediate curved portion therebetween, whereby said vanes have concave and convex portions, said entry nose portion being disposed at an angle to the axis of said housing and said trailing portion being directed substantially axially of said housing, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes so formed that the portions of said periphery which are adjacent to the vanes slope longitudinally toward the axis of the housing in one direction from the concave portions of the vanes and longitudinally toward the axis of the housing in the other direction from the convex portions of the vanes.

13. In an axial flow fan, a fan and motor housing comprising a mono-bloc structure having an outer annular wall, a centrally disposed motor support, and a plurality of vanes for connecting said support to said outer annular wall, each of said vanes having an entry nose portion, a trailing edge portion, and an intermediate curved portion therebetween, whereby said vanes have concave and convex portions, said entry nose por tion being disposed at an angle to the axis of said housing and said trailing portion being directed substantially axially of said housing, said outer annular wall having a first and a second annular portion, said plurality of vanes connecting said centrally disposed support to said first annular portion, said second annular portion having an internal surface of revolution forming the outer wall of a fan chamber, said first annular portion having the portions of its surface between said vanes which lie adjacent to the latter slope longitudinally towards the axis of the housing in one direction from the concave portions of said vanes and longitudinally towards the axis of the housing in the other direction from the convex portions of the vanes, and said centrally disposed support having the exterior periphery thereof in the zone of the connections thereto of said vanes so formed that the portions of said periphery which are adjacent to the vanes slope longitudinally toward the axis of the housing in one direction from the concave portions of the vanes and longitudinally toward the axis of the housing in the other direction from the convex portions of the vanes.

14. A mono-bloc fan and motor housing having a forward end and a rearward end and comprising an outer annular wall, a centrally disposed cup-shaped receptacle, and a plurality of stationary vanes supporting the cupshaped receptacle substantially concentrically within the outer wall, said cup-shaped receptacle comprising a body open at its rearward end and having at its forward end an inwardly directed annular abutment and having a chamber decreasing in diameter from its rearward end to the forward end thereof, said cup-shaped receptacle having on the outer surface thereof, between the rearward end thereof and a circle passing through the points of junction of the forward ends of said vanes with the periphery of said cup-shaped receptacle a zone of substantial width, the outer periphery of said cup-shaped receptacle including, forwardly of such zone, only surfaces tapering towards the forward end thereof, and the inner surface of said outer annular wall having a zone between a plane including the rearward edge of said receptacle and a circle passing through the points of junction of the forward ends of said stationary vanes with said outer wall, the inner surface of said outer wall, between said circle and the forward end of said wall, including only surfaces which taper towards the rearward end of said fan and motor housing, and said zones each having the surfaces thereof subdivided by said vanes and each having between each pair of vanes its surface made up principally of two surfaces sloping oppositely longitudinally of said housing, said oppositely sloping surfaces on said receptacle being essentially portions of the frusta of cones the larger end of one of which is to the rear of said housing and the larger end of the other of which is forward of said housing, and the oppositely sloping surfaces of said zone on the inner surface of the outer annular wall conforming substantially to portions of the frusta of cones the larger end of one of which is to the rear of said housing and the larger end of the other of which is forward of said housing, the adjacent edges of said oppositely sloping surfaces in each zone terminating in mutually oblique lines and there being oblique fills at points along said lines where air flow would be substantially affected in the absence of such fills, and said stationary vanes being so curved that at no point in either lateral surface thereof in adjacency to the inner surface of said outer annular wall does the angle between a straight line tangent to such lateral surface and a straight line parallel to the axis of said housing, which angle has its sides lying in a plane perpendicular to a radial line extending from the point of tangency to the axis of said housing, have its apex towards the larger end of the truncated cone to which that one of said oppositely sloping surfaces in said second zone which is adjacent to such lateral surface conforms.

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