US2811303A

US2811303A - Impeller for axial flow fans

Info

Publication number: US2811303A
Application number: US375604A
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: 1953-08-21
Publication date: 1957-10-29
Anticipated expiration: 1974-10-29

Description

Oct.'Z9, 1957 J. R. AULT ET AL IMPELLER FOR AXIAL FLOW FANS Original Filed Dec. 28, 1948 2 Sheets-Sheet 1 I lfivezziam: James J? 62122.

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United States Patent IMPELLER FOR AXIAL FLOW FANS James R. Ault and Chester P. Jenkins, New Philadelphia,

Ohio, assignors to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Original application December 28, 1948, Serial No. 67,738, now Patent No. 2,698,128, dated December 28, 1954. Divided and this application August 21, 1953, Serial No. 375,604

Claims. (Cl. 230-134) Our invention relates to axial flow fans, and, more particularly, to impellers for such fans. This application is a division of our application Serial No. 67,738, filed December 28, 1948, now Patent No. 2,698,128.

Cast or molded components of axial flow fans providing aso-called mono-bloc construction have been found very desirable in practice, and, for relatively light and small axial flow fans, mono-bloc elements formed of plastics, for example thermoplastic materials, have proven most satisfactory. In the production of such elements, whether they are to be cast in one piece or molded in one piece, it is essential for economy of construction that they shall be capable of having the mold or die parts in which they are cast, formed or molded, separable from each other without injury to themselves or to the fan elements, and to that end the fan elements need to be so constructed that they may be formed between or within mold or like parts from which they can be removed without breakage. Where there are present, as in the impellers of fans, blades which have curved surfaces which, at both sides of a point of tangency to a line parallel with the axis of the element with which such blades are integral, diverge from such a line, the forming of the impeller and of the dies or molds, if the latter are not to be destroyed in the process of fan manufacture, is a very important problem.

It is an object of our invention to provide an improved impeller for an axial flow fan of such construction that it may be cast or molded by the use of molds or dies which will be uninjured in their separation and in the removal from them (or vice versa) of the impeller. It is another object of our invention to provide an improved mono-bloc fan impeller. It is still another object of our invention to provide an improved fan impeller having its blades and the body by which said blades are carried 50 shaped that ready separability from mold or die is possible. Other objects and advantages of the invention will hereinafter more fully appear.

In the accompanying drawings, in which one illustrative embodiment of our invention has been shown,

Fig. l is an approximately central vertical section through an axial flow fan in which the illustrative embodiment of the invention is incorporated.

Figv 2 is an end elevational view of the fan of Fig. I, viewed from the right, that is, from the fan end thereof.

Fig. 3 is an enlarged fragmentary sectional viewor, perhaps better put, a developed viewon the curved section line 3-3 of Fig. 2, showing a detail of fan blade construction.

Fig. 3A is a detail sectional developed view on the plane of the line 3A--3A of Fig. 3.

In the drawings, there is shown an axial fiow fan generally designated 1, in which the illustrative embodiment of the present invention is shown. The fan 1, which includes the particular subject matter of this application, comprises a fan and motor housing 2, a fan member 3, and a driving motor 4. The fan and motor housing 2 is of mono-bloc construction and includes an outer annular wall and a centrally disposed cup-shaped hub 2 portion or receptacle 11 connected to the outer annular wall by a plurality of vanes 12. The cup-shaped hub portion or receptacle 11 is arranged to receive a cylindrical shaft-supporting means, herein the motor 4, and the motor has a shaft 13 which supports and drives the fan member 3 within the outer annular wall 10. The cup-shaped hub 11 has an inwardly directed annular wall portion 15 which has a plane inner surface 16 and which has at 17 a circular opening coaxial with an inner surface 18 formed within the wall 10 and surrounding the fan blades 19 of the fan 3. The end of the motor 4 abuts against the end surface 16, and the motor is held against the wall portion 15 by screws and washers 20, 21. The motor has a peripheral surface of revolution 17' snugly fitting within the opening 17 and coaxial with the motor shaft 13. The mounting of the motor is thus such that the axis of the motor shaft 13 is perfectly central within the surface 18, so that the tip clearance indicated at 22 between the fan blades 19 and the internal surface 18 may be maintained at a very low value. In actual construction the tip clearance may be as low as a few 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. 1, 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 fiat 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 minimium safe running clearance exists, is desirable fora 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 efiiciency 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 efliciency 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.

As the subject matter of this application .does not relate to the fan and motor housing, the structure of this element, which is fully disclosed in our parent application abovementioned, will not be further described here.

The structure of the fan member or impeller 3 may now be considered in its illustrative embodiment. This may be noted to comprise a rotor body portion 26 which includes a hub portion 27 in which the steel insert 24 is mounted, a radially extending wall 28, and an annular portion 29 supporting the blades 19. The hub portion 27 and the inner wall 30 of the portion 29 .are each so formed that a corelike element forming the inner wall of the mold for the fan proper may be readily withdrawn.

The external periphery of the annular portion 29, at the portions thereof from which the blades 19 project is specially formed to facilitate removal of the fan from the mold in which it is formed. Let it be imagined that this annular portion is surrounded by two concentric circles, one, indicated in broken lines at 31, at the leading edges of the fan blades, and the other, indicated in broken lines at 32, at the receding edges of the fan blades. Circle 31 will be slightly larger in diameter than circle 32. In other words the external diameter of portion 29 is slightly larger just forward of the blades 19 than just to the rear of them. The surface between the

circles

31 and 32 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 circumferentially of the rotor, the surfaces may be more sharply defined as follows: From a point adjacent the forward tip T of each blade, let a line L be drawn to a point adjacent the receding edge R of the blade next ahead. Now, there will be seen to be two series of areasthe one, S made up of areas at least principally to the rear of the fan blades and the other, S made up of areas at least principally ahead of the fan blades.- Now with respect to the areas S these areas will conform to a frustum of a cone coaxial with said fan (with its axis in the same line with the fan axis) and the elements of the surfaces of said areas will all be elements of such a frustum and all will slope rearwardly. On the other hand, the elements of the surfaces of the areas S ahead of the blades will each correspond to the elements of a frnstum of a cone having its axis in the same line with the rotor axis and having its larger end to the rear of the rotor. This will mean that an element extending rearwardly of the fan from the point near the leading 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 blade ahead slopes forwardly and inwardly, that the forward ends of the two elements are in a common circle 31 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 the forward end of the first blade to the point near the receding edge of the preceding blade. Thus there will be readily possible a molded structure separable from its mold by draft in opposite directions. The narrow circular surfaces forward of the first circle 31 and rearward of the second circle 32 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. 3A 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 surfaces of the blades and the peripheral surface areas S behind them,

and the other shaping the forward surfaces of the blades and the surfaces S ahead of them may be readily separable after the fan is molded. To lighten the fan con- -struction the radial wall portion thereof is recessed annularly as at 35, and it will be apparent that the portion of the rearward mold element which fills this recess during casting or molding of the fan will be freely withdrawable from the recess because of the shape of the walls thereof.

It will be noted that the motor 4 constitutes a cylindrical means having a rotating driving shaft therein with a fan mounted thereon, and that the motor is thus illustrative of fan driving means whichmay not have their motor means coaxial with the fan and motor housing.

The invention described herein may be injection molded if desired, or it may be made by filling a mold with plastic in powder form, after which the mold may be heated under'pressure to a temperature high enough to fuse the powdered plastic. A still further alternative would be die casting, if the parts were made of metal.

While there is in this application specifically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What we clairn is: e

1. In an axial flow fan, a rotatable mono-bloc structure having an annular portion having connected thereto and supporting a plurality of blades, each of said blades having an entry nose portion, a trailing edge portion, and an intermediate portion therebetween, said blades lying at an oblique angle with respect to a circular line on the periphery of said annular portion so that each blade has a positive pressure side and a negative pressure side during rotation of said structure, said annular portion having the periphery thereof, in the zone of the connections thereto of said blades, so formed that the portions of said periphery which are adjacent to the positive pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in one direction from said positive pressure sides and the portions of said periphery which are adjacent to the negative pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in the other direction from said negative pressure sides, each of said sloping portions extending on both sides of a circumferential line on said annular portion intermediate the entry nose portion of one blade and the trailing edge portion of the next blade ahead.

2. In an axial flow fan, a rotatable mono-bloc structure having an annular portion having connected thereto and supporting a plurality of blades, each of said blades having an entry nose portion, a trailing edge portion, and an intermediate portion therebetween, said blades lying at an oblique angle with respect to a circular line on the periphery of said annular portion so that each blade has a positive pressure side and a negative pressure side during rotation of said structure, said annular portion having the periphery thereof, in the zone vof the connections thereto of said blades, so formed that the portions of said periphery which are adjacent to the positive pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in one direction from said positive pressure sides and the portions of said periphery which are adjacent to the negative pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in the other direction from said negative pressure sides, each of said sloping portions having portions at opposite sides of a plane perpendicular to the axis of said annular portion and bisecting the latter and said periphery throughout its circumference in a circular zone at the entry nose portions of said blades having at all points a substantially uniform radial dimension.

3. In an axial fiow fan, a rotatable mono-bloc structure having an annular portion having connected thereto and supporting a plurality of blades, each'of said blades having an entry nose portion, a trailing edge portion, and an intermediate portion therebetween, said blades lying at an oblique angle with respect to a circular line on 'the periphery of said annular portion so that each blade has a positive pressure side and a negative pressure side during rotation of said structure, said annular portion having the periphery thereof, in the zone of the connections thereto of said blades, so formed that the portions of said periphery which are adjacent to the positive pressure sides of said blades slope longitudinally from the zone of the connections throughout their circumferential extent towards the axis of said structure in one direction from said positive pressure sides and the portions of said periphery which are adjacent to the negative pressure sides of said blades slopelongitudinally from the zone of the connections throughout their circumferential exent towards the axis of said structure in the other direction from said negative pressure sides, said periphery throughout its circumference in a circular zone just to the rear of said trailing edge portions having at all points a substantially uniform radial dimension.

4. In an axial flow fan, a rotatable mono-bloc structure having an annular portion having connected thereto and supporting a plurality of blades, each of said blades having an entry nose portion, a trailing edge portion, and an intermediate portion therebetween, said blades lying at an oblique angle with respect to a circular line on the periphery of said annular portion so that each blade has a positive pressure side and a negative pressure side during rotation of said structure, said annular portion having the periphery thereof, in the zone of the connections thereto of said blades, so formed that the portions of said periphery which are adjacent to the positive pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in one direction from said positive pressure sides and the portions of said periphery which are adjacent to the negative pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in the other direction from said negative pressure sides, the periphery of said annular portion which lies between the negative pressure side of one blade and the positive pressure side of the next blade ahead having two portions in stepped relation with each other and said periphery throughout its circumference in a circular zone at the entry nose portions of said blades having at all points a substantially uniform radial dimension, and said periphery throughout its circumference in a circular zone just to the rear of said trailing edge portions having at all points a substantially uniform radial dimension.

5. In an axial flow fan, a rotatable mono-bloc structure having an annular portion having connected thereto and supporting a plurality of blades, each of said blades having an entry nose portion, a trailing edge portion, and an intermediate portion therebetween, said blades lying at an oblique angle with respect to a circular line on the periphery of said annular portion so that each blade has a positive pressure side and a negative pressure side during rotation of said structure, said annular portion having the periphery thereof, in the zone of the connections thereto of said blades, so formed that the portions of said periphery which are adjacent to the positive pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in one direction from said positive pressure sides and the portions of said periphery which are adjacent to the negative pressure sides of said blades slope longitudinally from the zone of the connections towards the axis of said structure in the other direction from said negative References Cited in the file of this patent UNITED STATES PATENTS Troller et a1 Sept. 9, 1947 Troller et al. Nov. 22, 1949 OTHER REFERENCES Pattern Making by a Foreman Pattern Maker, pub. by Crosby Lockwood and Co.; London, 1885 (pages 173-174).

Joy Axivane Fans of October 21, 1946, by Joy Mfg. Co. LA-Del Div., New Philadelphia, Ohio (Type T-60213).