US3480373A - Fans - Google Patents

Description

Nov. 25, 1969 E. B. TALBOT 3,480,373

FANS

Filed Oct. 5, 1967 I INVENTOR.

EDWARD 8. ML 307' BY A MM fizz/9w Arioewsy United States Patent O US. Cl. 416-226 7 Claims ABSTRACT OF THE DISCLOSURE Light weight plastic fan blades adapted to be used with a fan impeller. The plastic fan blades are supported on a rod which extends in the longitudinal direction of the blade and protrudes through one end of the blade. The supporting rod may be encased in a plastic longitudinal tube which is fixed to the opposite faces of the fan blade. Alternatively, the supporting rod may be clamped to one or both faces of the fan blade.

BACKGROUND OF THE INVENTION In the design and construction of axial flow gas impellers there is usually a shaft to which is secured a hub or boss which supports fan blades fabricated from metal or other material usually made from solid material. A disadvantage of this system is that the fan blades are heavy with the result that a very strong fixing has to be made of the fan blade to the hub or boss which makes the design expensive in construction. A further disadvantage is that the fixing of the fan blade to the hub or boss must be made in a rigid manner and as a result there is a tendency to fan failure due to metal fatigue arising from vibration effects on a joint with little flexural latitude. A further disadvantage is that fan impellers have often to be constructed from materials such as steel in order to provide the structural strength and stiffness and are not suitable for corrosive applications.

It would be desirable to provide an axial flow fan impeller with fan blades of extremely light construction and which contain little material so that they can be constructed from durable materials in an economic manner. It would also be desirable to provide a simple means of fixing the fan blade to the fan hub or boss in a manner which minimises the stresses due to flexing effects arising from the fan blade. It would also be desirable to construct a fan impeller in such a way that the device may be readily assembled or adjusted for the particular application required. It would also be desirable to provide a fan impeller where the fan impeller can rotate about a stationary centre shaft as well as being fixed to a rotating centre shaft. It would also be desirable to provide a simple means of constructing a fan blade from a noncorrodible light weight material and of attaching it by simple means to the fan hub or boss. My invention provides fan blades and impellers satisfying these requirements.

SUMMARY OF THE INVENTION The present invention provides light weight plastic fan blades which are supported by a relatively small diameter rod and are adapted to be attached to a fan impeller. These plastic blades may be fabricated by extrusion, fabrication from sheet, blow molding, etc. The fan blade product produced by these different processes may have some characteristics not shared by fan blades produced by another of these processes.

An extrusion process, or fabrication from sheet, are suitable processes for producing a hollow plastic fan blade having an aerodynamic profile consisting of opposed faces 3,480,373 Patented Nov. 25, 1969 joined at the two edges. The faces are separated from each other and enclose a supporting rod extending in a direction parallel to the longitudinal axis of the blade and through one side of the blade. This supporting rod 'is encased in a tube which is fixed to each of the opposed faces. When utilizing an extrusion process, the encasing tube will extend through the entire longitudinal length of the blade. When fabricating from plastic sheet material, a tube may be inserted the entire length of the blade or may be inserted only the desired length necessary to encase the supporting rod.

The fan blades produced by blow molding processes are hollow and preferably use an external clamp to attach a narrow elongated section of one of the faces to the supporting rod.

DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective drawing of a hollow fan blade-impeller assembly, partially disassembled;

FIGURE 2 is a perspective drawing of a solid fan blade; and

FIGURE 3 is a perspective of a disassembled hollow fan blade, including an external clamp and supporting rod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention is depicted in FIGURE 1,,in which the fan is located on a shaft 1 by means of a hub 2 containing a central hole 6 through which the shaft 1 protrudes and provided with 4 holes 3 for locating the fan blades 5. The fan blade 5 is shown assembled while the other fan blade 19 is shown in its composite parts. The fan blades 5 and 19 are secured to the fan hub 2 by means of a block 4 nearly split into two parts by a slot 9 and secured to the fan hub by means of a bolt which can pass through the hole 7. The fan blades 5 and 19 are secured to the block 4 by screwing the shaft 10 provided with a thread 11 at one end into the hole 8 of the block 4. On tightening the bolt in the hole 7 the shaft 10 can be clamped in any desired position so that the fan blade may be set at any angle required.

The plastic skin of the fan blade is moulded, formed, or extruded so that it comprises a top surface or face 15 secured to a bottom face or surface 16 at front edge 17 and trailing edge 18. Furthermore the fan blade is provided with two surfaces 13 and 14 which form an encasing tube 20 to hold the rod 10. These surfaces 13 and 14 may be integrally formed with the skin of the fan blade or they may be added separately as for example by inserting a plastic tube 20 with a wall of the same shape as the surfaces 13 and 14 and cementing or welding the said wall to the plastic skins 15 and 16. The fan blade may or may not be closed at the end. The plastic skin of the fan blade is secured to the fan hu-b by either sliding the rod 10 into the space between the surfaces 13 and 14 (tube 20) and cementing it in position, or alternatively the end of the rod 10 may be provided with a thread 12 which may be screwed into a thread existing in the surfaces 13 and 14. It is not essential for the rod 10 to extend the full length of the fan blade, the exact distance depending on the strength and joint strength of the fan blade and rod.

A full fan blade such as blade .5 of FIGURE 1 was produced having a length of sixteen inches. The surface or skin of the blade was $6 inch thick. A plastic encasing tube 20 with an internal diameter of A: inch and having wall thickness of inch was cemented between surfaces 15 and 16. The inside of the encasing tube was threaded to conform with those on a threaded steel rod twelve inches long which was screwed about seven inches 3 into the tube. Adhesive was applied to cement the rod in the tube.

The preferred fan blades have an encasing tube which extends the entire longitudinal length of the blade. Blades containing such tubes are readily produced by extrusion. They may also be produced by fabricating from sheet material. When using the later fabrication method, shorter encasing tubes may be used. The advantage of having a tube run the entire length of the blade is greater flexibility in designing for different conditions. The necessary support furnished by the supporting rod to the fan blade and consequent stress in the fan blade, varies dependent upon the speed of rotation of the blade. High speeds create extremely high stresses requiring a greater length of supporting rod fixed to the blade surfaces through the tube. Fewer stock models of fan blades may be maintained for different purposes with tubes running their entire length than would be required if the tubes were tailored in length to the specific use contemplated.

With the exception of small blades, the preferred fan blades of this invention are hollow, i.e., they contain one or more hollow spaces 21 and 22 extending the longitudinal length of the blade in addition to the hollow space which is the encasing tube 20. Very large blades, i.e., those three or four feet long and having a distance between the front and trailing edges of eight inches or longer, may have one or more struts or tubes between the upper and lower faces to provide additional support for the faces.

The supporting rod which is used to fix the fan blade to the central support which is usually a hub or boss, is preferably a solid rod, or a hollow rod such as a tube or a small diameter pipe. The rod may have a circular cross-section or have a flattened cross-section such as an oval, or ellipse, or a plate-like cross-section. The rod is made from a material sufficiently strong to support the fan blade and afiix it to the hub or boss. The strength necessary varies with the service contemplated. In most cases it will be a steel, or a more highly corrosion resistant material such as one of the stainless steels, monel metal, etc., for lower stress applications, a light metal such as aluminum, or high strength plastics such as resin impregnated fiber glass, polycarbonate, and acrylonitrile-butadiene-styrene, and the like may be used.

The plastic fan blades which may be used to produce fan impellers having diameters ranging from one to fifty feet, may be made from such plastic materials as the polyolefins, acrylonitrile-butadiene-styrene, the polycarbonates, etc. The sixteen inch blade described hereinbefore was produced from acrylonitrile-styrene. When using an extrusion process, the encasing tube will be of the same plastic material as the surface of the fan blades. Blades which are fabricated from sheet materials and tubing may be prepared using one plastic material for the surface and the same or another plastic material for the encasing tube and for supports. The encasing tube is adapted to conform to the surface of the rod. For practical purposes, it is preferred that the tube have sufficient rigidity to retain a thread configuration.

The fan blades will all have aerodynamic profiles comprising upper and lower faces which are joined by a leading edge and trailing edge. The aerodynamic profile may vary over the length of the blade. Blades having varied cross-sections are more readily produced by fabrication from sheet or by a blow molding process, than by an extrusion process. However, extruded blades having a constant cross-section may have the aerodynamic profile varied somewhat by heating the blade after extrusion and twisting it, or even placing it in a mold to obtain the desired shape. The overall width of the blade, i.e., the distance between the leading edge and the trailing edge, may be varied by shearing off a portion of the solid trailing edge.

Small solid light plastic fan blades such as fan blade 31 illustrated in FIGURE 2 are readily extruded. The

cross-section 32 may be solid as extruded. A hole 33 to engage a supporting rod is drilled and preferably tapped. Alternatively the hole 33 may be formed during the extrusion.

Hollow plastic fan blades formed with varied surface configurations may be prepared by blow moulding processes. Such blades may have an encasing tube cemented into the hollow space between the outer faces. They may also be constructed with an external clamp, such as fan blade 45 illustrated in FIGURE 3. The plastic skin of the fan blade 45 is molded so that it comprises a top surface 46 secured to a bottom surface 47. The top surface 46 may be provided, though not essential, with a recess 48 which fits snugly around the shaft 50 when it is inserted between the surfaces 46 and 47. The surface 45 is secured to the shaft 50' by a clamping plate 49 Which fits into the recess 48 on surface 46 and is to be clamped to the supporting rod 50' by rivets.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

What is claimed is:

1. A plastic unitary fan blade having a leading edge and a trailing edge comprising,

a body of constant cross section from end to end between said leading and trailing edges with aerodynamically curved surfaces on each side of said blade extending between said leading and trailing edges, said blade being extruded with said constant cross section from said one end to the other end,

said curved surfaces being transversely spaced from each other to define a hollow therebetween during the extrusion, said hollow having a trailing edge wall and a leading edge wall with a lengthwise rib extending between said leading and trailing edge walls of said hollow and extending for the full length of said blade,

said rib including a substantially centrally defined opening forming a tube, and said rib being extruded simultaneously with said aerodynamically curved surface,

whereby the volume of the hollow defined on opposite sides of said rib is constant and said rib is integral with and forms a unitary uninterrupted continuation of the internal walls defining said hollow to thereby provide a unitary blade of uninterrupted construction.

2. The fan blade of claim 1 wherein said inner surface of said tube is of circular cross-section.

3. The fan blade of claim 2 wherein said tube adapted to receive the supporting rod is threaded.

4. The fan blade of claim 1 wherein a supporting rod is affixed in said tube, with one end of said supporting rod extending outwardly from said tube, said end of said rod being threaded.

5. A fan impeller comprising a hub and at least two outwardly extending fan blades as defined in claim 4, said fan blades being joined to said hub by said threaded extended end of said supporting rod.

6. A hollow plastic unitary fan blade having a leading edge and a trailing edge with aerodynamically curved surfaces on each side of said blade extending between said leading and trailing edges, said blade having been blow-molded so that said curved surfaces are transversely spaced from each other to define a hollow therebetween during said blow-molding,

said hollow having a trailing edge wall and a leading edge wall and enclosing a lengthwise supporting rod extending between said leading and trailing edge walls of said hollow and extending for at least onethird the length of said blade, and

said supporting rod protruding through one end of said blade and being fastened directly to at least one of said curved surfaces by a fastening means extending along said curved surface in a direction substantially parallel to said supporting rod, said fastening means being integral with said curved surface or positioned on the surface of said curved surface.

7. A hollow fan blade made from a plastic material having opposed faces enclosing a supporting rod which extends in a direction parallel to the longitudinal axis of said fan blade and extends into said fan blade at least one third the longitudinal length of said fan blade, said supporting rod protruding through one end of said blade, said supporting rod being fastened to at least one of said opposed faces by a fastening means, said fastening means extending along said face substantially parallel to said supporting rod, and wherein said fastening means is a narrow external clamping plate elongated in the longitudinal direction and positioned upon the portion of the blade surface adjacent to said supporting rod, said clamping plate having its surface shaped to conform to the blade surface separating said plate from said rod, said plate being attached to said rod by attaching means which penetrate through the portion of said blade surface separating said clamping plate and said supporting rod.

6 References Cited UNITED STATES PATENTS 2,063,707 12/ 1936 Soderberg 29-1568 3,012,308 12/ 1961 Zech et al. 1,829,437 10/ 1931 Clay. 2,107,136 2/ 1938 Zaiger. 2,400,649 5 1946 Larsen. 2,454,200 11/ 1948 Perkins. 2,506,992 5/1950 Bucher et al. 2,659,444 11/ 1953 Stanley. 3,356,154 12/ 1967 Cassidy.

FOREIGN PATENTS 504,377 4/ 1939 Great Britain.

HENRY F. RADUAZO, Primary Examiner US. Cl. X.R.

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