US3300123A - Vane for an axial ventilator and method for producing the same - Google Patents

Jan. 24, 1967 EYH LD ET AL 3,300,123

VANE FOR AN AXIAL VENTILATOR AND METHOD FOR PRODUCING THE SAME Filed May 24, 1965 United States Patent 3,300,123 VANE FOR AN AXIAL VENTILATOR AND METHOD FOR PRODUCING THE SAME Helmut Freyholdt and Alfred Aebischer, Stafa, Zurich, Switzerland, assignors to Ventilator A.-G., Stafa, Switzerland Filed May 24, 1965, Ser. No. 458,341 Claims priority, application Switzerland, May 29, 1964, 7,012/ 64 Claims. (Cl. 230-434) The present invention has reference to an improved sheet metal blade or vane for axial blowers and to a new and improved method for the production of such vane.

Although the use of sheet metal vanes is known for wall ventilators and also for tubular axial blowers, in such instance there was only used sheet iron or steel with relatively thick walls in order to enable welding of the vane to the steel hub of the ventilator. Even though a considerable reduction of the weight of the vanes and thus the weight of the impeller provides important advantages it has been found that thin wall sheet steel causes great difiiculties during welding to the steel hub of the impeller and, furthermore, has the tendency to distort. Likewise, the use of aluminium sheet for this purpose has not proven to be satisfactory since with the welding of aluminium a week location appears at the welding seam.

Accordingly, it is a primary object of the present invention to provide an improved construction of vane or blade for axial blowers or the like operating at relatively high pressures and high rotational speeds which enables the use of thin wall sheets, particularly aluminium sheets.

A further important object of this invention has reference to an improved method of manufacturing vanes for use with axial ventilators and the like.

Another specific object of this invention concerns itself with the construction of an improved blade or vane for fluid-flow machinery, such as axial ventilators, which is relatively easy and inexpensive to manufacture, provides good operating efiiciency, is simple to mount to the hub of the impeller, even can b repositioned after mounting.

The vane or blade designed according to the teachings of the present invention generally comprises a folded sheet strip and exhibits a vane portion and a flexed, slightly arched i.e. slightly convexed base portion. It is to be understood that the inventive blade can be used for practically all ventilators, for instance wall ventilators.

The method of the invention for the manufacture of a sheet metal vane is generally characterized by the features that a sheet metal strip is cut substantially trapezoidal and stamped or otherwise formed into a twisted vane, at the wide end of the vane there is formed a base portion which is flexed at approximately right-angles to the vane proper. This base portion is then formed so as to possess a slightly arched configuration, i.e. is slightly convex, and the fold edge between vane portion and base portion defines the transition from a substantially cylindrical surface into a partial sphere or spherical shell.

By virtue of the inventive vane or blade construction it is possible to dispense with welding of the vane to the impeller hub, and, for example, to use a screw connection. Consequently, it is possible to use thin wall sheet metal e.g. aluminium as material for forming the inventive vanes.

Use of a screw connection enables adjustment and subsequently re-positioning of the inlet or approach angle of the blade. Due to this possibility there is effectively overcome a major disadvantage of previous sheet metal vanes, namely impossibility of subsequently accommodating their approach angle to momentarily encountered operating conditions. This possibility of re-positioning is subordinate for so-called profiled vanes since in con- "ice trast with sheet vanes deviations of the output from the rated value does not bring about important disadvantages for a large efliciency range. Previously, a sheet metal vane or blade was only practically as aerodynamically efficient as a profiled vane in the so-called optimum point. However, the present invention renders it possible to provide a new and improved sheet vane possessing all of the advantages of the profiled vane and the sheet vane and still further advantages, and at the same time does not possess all essential disadvantages of both these type vanes.

Other features, objects and advantages of the invention will become apparent by reference to the following detailed description and drawing in which:

FIGURE 1 is a perspective view of an impeller designed according to the teachings of the present invention wherein one vane has been removed to facilitate illustration of details of the impeller hub; and

FIGURE 2 is a perspective view of a new and improved impeller vane designed according to the invention.

The previously described vane construction permits the use of thin sheet and the use of aluminium as the material for the vanes due to dispensing with a welding operation and by utilizing a screw-connection. As a result, there is provided a considerable saving in weight in contrast ment of the vanes.

Furthermore, the use of aluminium sheet enables production of impellers which are corrosion resistant, and the vanes need not be provided with a costly protective layer safeguarding against corrosion as was previously the case. Moreover, the use of a simple screw connection in place of cumbersome welding of the vanes brings about considerable saving in costs and the time for mounting, so that no skilled labor is required.

Due ot the relatively light weight of the inventive vane relatively small centrifugal forces appear at the impeller, so that the impeller hub can likewise be constructed of lighter weight than was previously the case. Hence, the overall construction including shaft, bearings, housing and foundation can be made lighter, thereby bringing about a further saving in cost.

Moreover, by using thin-walled sheets there are obtained considerably thinner discharge edges at the vanes, so that reduced tunbulence at such location results in better efficiencies and less noise than previously. It need not be particularly stressed that both these factors play an important role in ventilators. There is still further mentioned that the invention provides an improvement of fiow conditions at the inlet edge of the vane due to the use of thin-walled sheets.

The inventive vane is considerably lighter than the known profiled vanes either cast or machined as solid bodies. This is likewise true for vanes formed of plastic, wood or other non-metallic materials.

A further advantage of the inventive sheet metal vane in comparison with known profiled vanes is the smoothness of its surface. While with known profiled vanes it is only possible to obtain a smooth surface by a subsequent costly treatment, for instance by polishing, the inventive vane makes it possible to even obtain a mirrorsmooth surface by proper selection of the vane sheet metal, and, thus, there can be obtained a vane with better efiiciency without additional processing.

In addition to a surface treatment the cast vanes constructed as profiled solid bodies require an extensive aftertreatment, among other things threading has to be cut for the attachment bolts, the vane edges at the inside and outside have to be exactly faced, and the axis of rotation has to be determined. In contradistinction, the inventive vane does not require any after-treating steps, resulting in a considerable saving in cost.

A further disadvantage of the cast profiled vanes not present with the inventive vane is the irregularity in the vane weight which unfavorably affects balancing, so that mounting of the impeller requires a great deal of time and effort. Due to the uniformity in weight of the inventive sheet vane mounting at the impeller is considerably simplified.

Since the inventive vane has its axis of rotation coinciding with the center of gravity axis turning of the vane does not result in any shifting of the center of gravity. This provides a considerable advantage since changing of the vane angle is possible without requiring subsequent balancing. With most of the cast, profiled vanes generally used in ventilators the axis of the attachment bolts does not coincide with the center of gravity axis of the vane, so that upon rotating the vane there is produced a new imbalance. Since balancing of the impeller usually entails returning it to the manufacturer-not possible in many casesthere is generally foregone any re-adjust- Thus, the possibility of accommodating the vane angle to momentarily encountered operating conditions becomes illusory and these profiled vanes are practically used as rigidly mounted vanes.

It is further mentioned that with certain special vane construction for axial ventilators or turbines it is known to have the axis of rotation coincide with the axis of the center of gravity, whereby however, it must be underscored that in so doing certain technical difiiculties and considerable increase in cost is associated therewith. Rotating the vane about its center of gravity axis is possible 4. in the present instance without increased costs due to the inventive construction incorporating a lateral base portion against which bear externally of the rotational axis of the vane the attachment screws. With the exception of certain very expensive casting processes there are no casting processes for profiled vanes which result in such a uni formly cast vane that the theoretical center of gravity axis coincides with the actual center of gravity axis. On the other hand, the inventive light-weight sheet metal vane for the first time renders it possible to bring into coincidence, in the most simple manner, the rotational axis and the center of gravity axis.

It is important for ventilator impellers to maintain a uniform impeller gap between the tips of the vanes and the ventilator housing in order that the efficiency is not impaired. Therefore, the spacing of all blade or vane tips from the axis of the impeller must be held within very narrow limits. In prior art impellers having heavy profiled vanes, the tips of the vanes were milled after the vanes were mounted upon the impeller hub. This expensive operation, for instance milling or grinding of the vane tips, up to the present was avoided with rigid sheet metal vanes, firstly, because such was associated with difficulties, and secondly, because the opinion prevailed that sheet metal vanes at any rate were cheap alternatives having poor efficiency.

Since the inventive vane construction should at least be equally eflicient in all respects to all previous. constructions, a uniform impeller gap can be obtained if from the start all vanes are formed somewhat short, whereby during mounting the vanes can be brought to the desired external diameter of the impeller by using underlays or supports formed of thin foils or sheets. This renders it possible to satisfactorily avoid subsequent working of the vane tips.

Although in most instances it would be desirable to provide the impeller with tan inflow hood to increase the efficiency, this expedient has previously been dispensed with since such hood must be separately manufactured and subsequently connected with the ventilator housing. These additional costs could not be readily justified.

With previously known impellers the impeller hub is generally broken off into a sharp edge at the outflow side so that formation of turbulence and noise could not be prevented at this location. Furthermore, with such known constructions it was not possible to reverse the flow direction with respect to the impeller hub since the subsequent application of an inflow hood at the original outflow side was not possible due to a lack of space.

While there is shown and described present preferred embodiment of the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practised within the scope of the following claims.

What is claimed is:

1. In combination, an axial flow impeller having an annular hub with an outer spherical shaped surface portion, a plurality of vane means mounted on the spherical shaped hub portion, each vane means comprising a folded sheet metal strip incorporating a vane portion and a base portion, said base portion having a substantially spherical shaped surface corresponding to that of said spherical shaped surface portion, means adjustably securing the base portion of said vanes to the spherical shaped surface portion, said means comprising a central centering means and a pair of clamp fasteners engaging slots in the spherical shaped hub surface portion whereby said vane means on the release of the securing means may be pivoted about the central centering means.

2. The combination defined in claim 1, wherein the inner opposed surface of said annular hub is also spherical shaped; and including balancing weights cemented to said inner opposed surface.

3. The combination defined in claim 1, wherein said centering means is a pivot pin on said base portion and an opening in said spherical shaped surface portion for accepting said pin.

4. The combination defined in claim 1 wherein each base portion is provided with a scale for adjusting the angular position of said vane means at the impeller hub, said spherical shaped surface portion being provided with a respective surface marking cooperating with said scale of the associated vane means.

5. The combination defined in claim 1 wherein said impeller hub is provided with an inflow hood in front of said plurality of vane means and an outflow collar behind said plurality of vane means.

References Cited by the Examiner UNITED STATES PATENTS 525,928 9/1894 Thompson 230134 984,812 2/1911 Hearst 230134 1,476,137 12/1923 Bilan 230- 1,603,076 10/1926 Hanson 29-156.8 2,915,238 12/1959 Szydlowski 230134 2,985,952 5/1961 Nutter et a1 29l56.8 3,085,632 4/1963 Schwegler -l67 3,201,857 8/1965 Klonoski 29156.8

FOREIGN PATENTS 1,121,516 5/1956 France.

949,899 9/1956 Germany.

167,581 2/ 1921 Great Britain.

631,231 10/ 1949 Great Britain.

702,312 1/1954 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

HENRY F. RADUAZO, Examiner,