US3323710A - Fan impeller - Google Patents

Description

FAN IMPELLER Filed Deo. 2,v 1964 5 Sheets-Sheet 1 InVen'-O BMA-L72 B. Daz] June 6, 1967 B. B. DALY 3,323,710

FAN IMPELLER Filed Dec. 2, 1964 3 Sheets-$heet 2 fab 22a b 24a Fig. 3.

June 6, 1967 B. B. ALY 3,323,710

FAN IMPELLER Filed DGO. 2, 1964 3 Sheets-Sheet 3 United States Patent O 3,323,710 FAN IMEELLER Brian Bowman Daly, Colchester, England, assigner to Woods of `Colchester Limited, Colchester, England, a British company Filed Dec. 2, 1964, Ser. No. 415,284 Claims priority, application Great Britain, Dec. 5, 1963, 48,171/63 10 Claims. (Cl. 230-134) This invention relates to fan impellers having blades adjustable about axes which are at a substantial inclination but not perpendicular to the axis of rotation of the impeller, Such adjustment involves the mating surfaces of the blades and impeller hub being of circular cross section over a sufficient angular width. British patent specification No. 638,856 discloses blades adjustable on radial axes but this construction is not feasible with impellers having the blade axes at a substantial inclination to the axis of rotation. Such impellers are used in mixed flow fans, i.e. fans `in `which the gas flow is partly axial and partly radial, but cases arise in which the blades are so arranged in pure axial dow fans and in pure radial llowifans and the invention is applicable to all three types.

An object ofthe invention is to provide a forrn o-f blade root and hub which while providing for adjustment of pitch enables the blades to be securely held and the blades and hub to be made by die casting or die moulding in dies of simple form.

Accor-ding to the invention the blade roots taper towards the end, the minimum included angle of the root being not less than twice the angle of inclination of the blade root axis to the direction in which a die part used for casting or moulding the corresponding part of the hub would be withdrawn, and the roots are held in corresponding recesses in the impeller hub by screw members arranged axially of the blade roots. With such forms of blade root and hub recess it becomes possible (proa vided the shape of the rest of the hub allows i.e. is free of radial reentrants in relation to the `direction in which the die parts open to make the hub as a die-casting or diemoulding of eg. aluminum alloy or glass-fiber reinforced resin, in a die without the need for removable cores.

If the minimum included angle of the blade root is twice the angle of inclination of the root axis to the axis of rotation it `becomes possible to cast or mould the outer surface of the hub (including `a central recess if there is one) by means of a single axially withdrawn die part and if the inner face of the hub is also suitably shaped, to cast or mould this face by means of a single axially withdrawn die part so that the whole hub can be cast or moulded in a two part die with no removable cores.

The blades can also be made as die-castings or diemouldings in a single-split die and machining of the blades can be entirely dispensed with while no machining of the recesses in the hub is necessary.

By way of example three embodiments of the inven tion in which the hulb can be cast or moulded in a two part die are illustrated in the accompanying drawings in which FIGURE 1 is a longitudinal section of part of the rst embodiment,

FIGURE 2 is a view of a smaller part of the second embodiment,

FIGURE 3 is a view similar to FIGURE 2 of the third embodiment,

FIGURE 4 is a detail cross section showing the reduction of the mating surfaces of the blade root and hub to three small Zones and,

FIGURE 5 is a detail cross section of an alternative to FIGURE 4.

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Referring first to FIGURE 1, the driving shaft is marke-d 11. The die-cast or diemoulded impeller hub 12 has a steel sleeve 13 cast in, which lits on the shaft. r[this relieves the die casting or die moulding of undue stresses when the nut 14 which holds the impeller on the sha-ft, is tightened the hub lbeing of generally concavoconvex form open on the concave surface side (the right hand side in FIGURE 1).

rThe impeller blades of which there will be a plurality are all identical, identically mounted and equally distributed round the axis 15 of the shaft, but only part 16 of only one of which is shown in the drawing, are adjustable each about an axis 17. The axes 17 While ly* ing in planes through the axis 15 are not perpendicular to the latter Ibut are all equally inclined thereto at the substantial angle a. Thus the axes 17' will intersect on the axis 15.

At its root each blade 16 has an integral portion 18 coaxially tapering about the axis 17, which lits in a correspondingly shaped recess 19 in the hub 12, and the blade is held by a nut 21 screwing on to a bolt 22 having a head 23, the head 23 and part of the shank of the bolt being cast or moulded into the blade root. A flat washer 24 spreads the pressure over a dat surface 25 of adequate area inside the hub. The recesses are in the convex surface of the hub and each has an axis directed along the axis of the blade roots so that they are directed generally through the concave surface of the hub towards the axis of the central bore, i.e. the axis 15 at the angle n which is substantially less than The semi-angle b of the tapering portion 12? is greater than `the angle a, in other words the included angle 2b is greater than twice the angle a. In consequence the innermost boundary of the recess indicated by the chain line 26, as seen in FIGURE l slopes to the left towards the axis 15, in other words the line 26 and indeed all parts of the sides of the recess taper more steeply 'with regard to the axis 17 than the cone having a semi-angle equal to the angle a of inclination of the axis 17 to the axis 15. Accordingly a part of the die against which the left hand face of the hub is cast or moulded can be withdrawn from the casting or moulding to the left in the direction of the axis 15 without the need for any loose cores for shaping the recesses, provided the rest of the shape of this face of the hub permits i.e. has no radial reentrants in longitudinal section. Any usual convex shape such as that shown does so permit.

On the right hand lside i.e. concave side provided the thickness of the material constituting the side of the recess at the innermost boundary does not increase to the right by an angle greater than (bm) and provided the rest of the right hand face of the hub permits i.e. has no radial reentrants in longitudinal section, a part of the die against which the right hand face of the hub is Cast or moulded can be withdrawn from the casting or moulding to the right in the direction of the axis 1.5, again without the need for any loose cores. It would in fact be most unusual for the thickness of the material. constituting the side of the recess at the innermost boundary to increase to the right. As shown, the last part of it is of constant thickness and further to the left it increases to blend with the rest of the hub. Again any usual form of the rest of the hub such as that shown presents no radial reentrants and accordingly the hub can be cast or moulded in a two part die the two part-s closing and opening in the direction of the axis 1 5.

The opening at the bottom of each recess 19 through which the bolt 22 passes can be produced in the casting or moulding operation. Thus on the right hand side the recess 19 could terminate in a circular aperture in the plane of the surface 25. However as shown there is a small countersinlr 27' which by suitable choice of the angle can be produced by an appropriate shape of the part of the die 'which defines the right hand face of the hub without the need for any loose cores. In particular this countersink tapers oppositely to the recess 19 and its included angle is not less than 2a.

When the pitch of the blade is adjusted, the inner end ZS of the blade outside the root sweeps over the outer surface of the hub and the shape of the Outside of the hub in this region should be such that only a small clea rance is left at any adjustment of the blade. Accordingly each part 29 over which the blade ends sweeps over the range of adjustment is made in the form of a figure of revolution about the axis 17 as near as may be to the general form of the hub further towards the centre, these parts being blended into the general form of the hub and one another and the blade ends being correspondingly shaped. If the aerodynamic conditions permit, at least over the annulus containing the areas over which ends of the blades sweep during adjustment, the hub may be spherical about a centre at the point of intersection of the root axes, as indicated by the chain line 31.

The part 32 of the hub may suitably be more or less conical With an included angle which is equal to 180-2b though departures from this may sometimes be convenient, while the nose 33 may be rounded and centrally recessed to accommodate the nut 14.

In FIGURE l the head 23 of the bolt 22 tapers similarly to the portion 1.8 and recess 19 so that the material of the blade root is put in radial compression when the nut 21 is tightened so that clamping forces are not added to the centrifugal forces which must be borne by the root material.

In FIGURE 2 instead of a bolt with its head cast or moulded in, a stud 22a is shown east or moulded in. Also instead of a flat Washer 24 under the nut 21, a conical washer 24a seats in a corresponding countersink 27a of opposite taper to the recess 19, the included angle again being such that it is not less than 2a with the same effect as regards die casting or die moulding. In this example the included angle is equal to 2b.

With the conical Washer 24a, which has a centring action, the Width of the bearing zone on the blade root can be kept narrower than where a flat Washer is used, as indeed indicated `by FIGURE 2 while the centre part of the root portion 18a is reduced in diamrneter. In other respects FIGURE 2 does not differ from FIGURE 1 and the same references are used Where appropriate.

Another modification is shown in FIGURE 3. Here the portion 18h of the blade root does not taper conically but is spherical (and the recess 19h is similarly spherical) with a minimum semi-angle, that is the angle between the tangent 26!) at the mouth of the recess, not less than the angle a, in this example equal to b, with the Same effect as regards die casting or die moulding. In other respects FIGURE 3 does not differ from FIGURE 2 and the same references have been used where appropriate.

Other modifications are possible. Thus the conical washer 24a could be replaced by a spherical washer with the same conditions regarding angle i.e. the minimum included angle must be not less than 2a, and a conical or spherical washer could be used with the cast-in or moulded in bolt 22, 23 of FIGURE l. A cast or moulded in bolt could be used with a spherical blade root, the bolt head being shaped to correspond to put the material of the blade root in compression. The cast in stud of FIGURES 2 and 3 could be replaced by a bolt which is screwed into the blade root from inside the hub. Also a ilat Washer could be used 'with spherical blade root and recess.

With either a conical or spherical blade root there can either `be contact between the root and recess over a complete annulus around the axis 17, or the actual mating surfaces may be reduced to three small areas disposed approximately equally spaced round the axis 17 with small clearance elsewhere.

The advantages of reducing the mating surfaces to three small areas is that a rigid location of the blade root in the recess is achieved even if the surface form of the blade root or recess should be slightly distorted. Also it is possible to arrange that any flash at the plane where the die in which the blade is cast or moulded opens lies in these clearance zones. These advantages are of particular importance if machining of the hub and blades is disposed with as is possible if the workmanship of the dies and of the casting or moulding operation is adequate.

One way of reducing the mating surfaces consists in providing clearance in the blade root while leaving the recess in the hub of complete circular cross section. This is illustrated in FIGURE 4 in which the root 18C has clearance at 34a, 34h, 34e such as to leave three zones 35a, 35h, 35C at which the root mates with the surface 19C of the recess. The clearances are distributed so that the zones 35a, 35h, 35C are substantially equally spaced and so that two of the clearances 34a, 34h extend across the plane indicated by the chain line 36 on which abut the two parts of the die in which the blade is cast or moulded. These clearances 34a, 34b are so contoured below the plane 36 that just as with a root of full section there is no impediment to the separation of the parts of the die.

If it is preferred to provide the clearances in the recess, since the latter is cast or moulded against a die part which shapes the whole recess it becomes a matter of disposing the step surfaces which join the meted Zones with the clearances so that they do not prevent the withdrawal of the die part from the hub. Consideration will show that this leaves the designer considerable freedom of choice. For example as shown in FIGURE 5, a simple straight sided inclined form of the step surfaces 37 so that the parts 38 on which the mating zones 19d are formed taper towards the blade root 18d will suffice.

It will be understood that it would be possible to provide clearances in the blade roots and the recesses.

The forms of hub illustrated in the figures can indeed be cast or moulded in single two part dies, While if a multipart die is used to shape the outer face of the hub, having one part for each recess, by suitably choosing the angle b in relation to the direction of withdrawal, removable cores can still be avoided. For example if these die parts are to be withdrawn radially from the axis 1S the requirement is that angle b should be not less than (-a). If a recess to accommodate the nut 14 is still required, the central part of the outer face of the hub can be shaped by a die part withdrawn along the axis 15. The inner face of the hub can still be shaped by a single die part withdrawn along the axis 15.

I claim:

1. A fan impeller comprising a hub having a plurality of similarly disposed recesses therein, a plurality of similar blades, each blade having a root rigid therewith and seated in its corresponding recess and adjustable about an axis which is at a substantial inclination to the axis of rotation of the impeller, and a screw member disposed axially of each root which when tightened holds the root rmly in the recess in which it is seated, the blade roots each tapering towards the axis of rotation of the impeller with a minimum included angle not less than twice the angle of inclination of the blade root axis to a line which does not coincide with the root axis and which is at an angle to the axis of rotation of the impeller which is between 0 and 90, and a tapered washer interposed between the screw member and impeller head and seats in a corresponding countersink in the hub, the taper of the countersink 'being opposite to that of the blade root.

2. A fan impeller comprising a generally concaveconvex hub open on the concave surface side, having a central portion with a bore to seat on a driving shaft about the axis of which the impeller rotates and having a plurality of similar recesses in its convex surface spaced around the axis of the central bore, each recess having an axis directed generally through the concave surface of the hub towards the axis of the central bore at an angle of inclination substantially less than 90, each recess tapering so that all parts of its sides taper more steeply with respect to the axis of the recess than a cone having a semiangle equal to the angel of inclination of the axis of the recess to the axis of the central bore, a plurality of impeller blades equal in number to the number of recesses, each blade including an integral tapering root shaped to seat in a corresponding recess, and a screw member disposed axially with respect to each recess and engaging the root seated therein to hold the root rmly in the recess after it has been adjusted about the axis of the recess.

3. A fan impeller according to claim 2 in which on the concave surface side the hub is free of any radial re-entrants in a direction towards the open sides.

4. A fan impeller acoerding to claim 2, in which a taper washer is interposed between each screw member and the impeller hub, said taper washer seating is a corresponding countersink in the hub, the taper of the washer and countersink being opposite to that of the recess and `blade root and the minimum included angle of the washer and countersink being greater than twice the angle of inclination of the axis of the recess to the axis of the centarl bore of the hub.

5. A fan impeller according to claim 1, in which the blade roots and recesses in the hub are conical.

6. A fan impeller according to claim I1 in which the blade roots and recesses in the hub are part spherical.

7. A fan impeller according to claim 1 in which there is contact between the recess over three small areas dis* posed approximately equally spaced around the axis of the root lwith small clearance elsewhere such that no reentrants are formed.

8. A fan impeller according to claim 1 in which the screw members comprise bolts each having its head and part of its shank cast or moulded into a blade root, and nuts threaded on said bolts.

9. A fan impeller according to claim 1 in which the screw members are bolts each screwing into a tapped hole in a blade root.

di). A fan impeller according to claim 1 in which each part of the impeller hub over which a blade end sweeps over a range of adjustment about the axis of the corresponding recess is a figure of revolution about the axis of the recess as near as may be to the general form 0f the hub further towards the centre, these parts being blended into the general form 0f the hub and the blade ends being correspondingly shaped with small clearance from these parts.

References Cited UNITED STATES PATENTS 2,477,954 8/1949 Blanc 230l20 2,664,961 1/1954 Boede 230120 2,776,107 1/1957 Willi 230-120 2,811,303 11i/1957 Ault et al. 230-120 2,972,441 2/1961 Hall 253-78 FOREIGN PATENTS 511,976 4/ 1955 Canada.

566,698 11/1958 Canada. 1,126,364 7/1956 France,

949,899 9/1956 Germany.

DONLEY I. STOCKING, Pnimary Examiner.

HENRY F. RADUAZO, MARK NEWMAN, MARTIN P. SCHWADRON, Examiners.

Claims (1)

1. A FAN IMPELLER COMPRISING A HUB HAVING A PLURALITY OF SIMILARLY DISPOSED RECESSES THEREIN, A PLURALITY OF SIMILAR BLADES, EACH BLADE HAVING A ROOT RIGID THEREWITH AND SEATED IN ITS CORRESPONDING RECESS AND ADJUSTABLE ABOUT AN AXIS WHICH IS AT A SUBSTANTIAL INCLINATION TO THE AXIS OF ROTATION OF THE IMPELLER, AND A SCREW MEMBER DISPOSED AXIALLY OF EACH ROOT WHICH WHEN TIGHTENED HOLDS THE ROOT FIRMLY IN THE RECESS IN WHICH IT IS SEATED, THE BLADE ROOTS EACH TAPERING TOWARDS THE AXIS OF ROTATION OF THE IMPELLER WITH A MINIMUM INCLUDED ANGLE NOT LESS THAN TWICE THE ANGLE OF INCLINATION OF THE BLADE ROOT AXIS TO A LINE WHICH DOES NOT COINCIDE WITH THE ROOT OF AXIS AND WHICH IS AT AN ANGLE TO THE AXIS OF ROTATION OF THE IMPELLER WHICH IS BETWEEN 0* AND 90*, AND A TAPERED WASHER INTERPOSED BE-

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