US2703625A - Rotary fan - Google Patents

Description

March 8, 1955 c, HATHAWAY ET AL 2,703,625

ROTARY FAN Filed May 16, 1952 V IN VEN TORS 0 4,9555- ,4. M77664 WA Y W/LU/IM E. CASH-EN ATTORNEY United States Patent ROTARY FAN Charles A. Hathaway, Litchfield, and William E. Cashen,

Torrington, Conn., assignors to The Torrington Manufacturing Company, Torrington, Conn., a corporation of Connecticut Application May 16, 1952, Serial No. 288,160

3 Claims. (Cl. 170-159) This invention relates to a rotary fan adapted for a wide variety of uses.

It is the general object of the invention to provide an efficient rotary fan which is characterized by its quiet pperation whether used as a free air fan or as a pressure A more specific object of the invention is to provide a fan which will lower the noise level, as compared to conventional fans, when applied to installations wherein the fan is to operate at a constant preselected speed under constant airflow conditions.

An important aspect of the invention is the provision in each blade of the fan of forwardly, relatively sharply, curved leading and trailing portions which join the main portion in angularly related juncture lines. The curved leading portion includes part of the leading edge of the blade and a part of the peripheral edge of the blade. The said leading portion is so curved as to reduce the angle of pitch of the leading edge adjacent the peripheral edge to approximately Zero. This feature of construction provides the fan with advantages, as compared to conventional fans, for installations requiring a specific operating speed accompanied by a specific, constant flow of air and wherein a maximum sound level is prescribed. It is believed that the curved leading portion minimizes the operating noise while the curved trailing portion increases the brake horsepower to maintain the desired operating speed under the prescribed constant condition of air flow.

Additional important objects and aspects of the invention will become apparent from the following description of the annexed drawing. It will be understood that changes may be made from the construction shown, and that the drawing and the specific description thereof are not to be construed as limiting the scope of the invention, the claims forming a part of the specification being relied upon for that purpose. It will also be understood that all dimensions shown on the drawing and referred to in the specification are intended to clarify the explanation, and that the invention is limited to particular angles and dimensions only to the extent set forth in the claims.

Of the drawing:

Fig. l is a front view of a rotary fan embodying the principles of the present invention;

Fig. 2 is a side elevational view of the fan shown in Fig. 1;

Fig. 3 is a front view of an unformed blank for one of the blades of the fan;

Fig. 4 is a sectional view taken along the line 44 of Fig. 3 but showing a blade formed from the blank; and

Figs. 5, 6 and 7 are enlarged views taken respectively along the lines 5-5, 66 and 77 of Fig. 1 to show the true angles of pitch or bite at a plurality of radially spaced arcuate sections through a blade.

For purposes of exemplification, the fan shown in the drawing has circumaxially spaced blades 10, 10, the spacings being shown as equal. Three blades are shown, but a larger or smaller number of blades may be provided. The blades 10, 10 may be arranged for rotation in any conventional manner. For example, the said blades can be formed from a single sheet of stock which is provided with a central web for attachment to a shaft. In the example shown, each of the blades 10, 10 is independently fabricated and is connected to a hub 12 secured as by a set screw 14 to a rotatable shaft 16. Preferably, the blades are indirectly connected to the hub by means of a spider 18 which may be conveniently fabricated from 8 2,703,625 Patented Mar. 8, 1955 sheet metal so as to have a central portion 20 and integrally formed arms 22, 22 corresponding in number to the blades 10, 10.

The central portion 20 of the spider is rigidly secured to the hub 12 in a plane perpendicular to the axis of rotation of the hub and shaft. The spider arms 22, 22 thus extend radially outwardly to secure the blades as by rivets 24, 24 or the like. The arms 22, 22 are deformed adjacent the central portion 20 so that the extending portions of said arms will each be pitched to the same angle about an axis lying in the plane of the central portion of the spider. Since the arms 22, 22 secure the blades 10, 10, the central portion 26 of each blade will be disposed at the same pitch angle as the arms. The pitch angle of the arms 22, 22 may vary throughout a wide range, as for example from 20 to 40, depending upon the requirements of the particular installation. In the exemplary fan shown, the spider arms and blades are set at a 33 angle of pitch which will be referred to hereinafter as the basic pitch angle. The pitch angles of portions of each blade will differ from the pitch of the central portion 26 as a result of forming the blade in the manner which will now be described.

Each blade 10 is formed from a blank 28 as shown in Fig. 3, the blank being provided with holes 30, 30 for the rivets 24, 24. It should be understood that Fig. 3 is a front view of the blank 28 and that the line A-B shown thereon, which extends approximately through the center of the blank, is the line about which the formed blade is rotated or pitched 33 to the projected View shown in Fig. 1, each of the lines A-B extending radially from the axis of rotation of the fan and lying in the plane of the central portion of the spider as mentioned above.

Since the fan is to be rotated in the clockwise direction as viewed in Fig. 1, that half of the blank 28 on the right hand side of line A-B in Fig. 3 will be referred to as the leading half and that half on the left hand side of line AB will be referred to as the trailing half. The fan as shown has a diameter of 11 and the blank is dimensioned accordingly to suit the blade formed therefrom to the particular fan shown.

' The blank may be conveniently fabricated from a sheet metal body so as to have an arcuate outer peripheral edge 32 and an arcuate inner edge 34. The edge 32 of the blank is substantially bisected by the line AB and said edge of the blank is struck on a 7" radius so that the projection of said edge when viewed as in Fig. 1 will be substantially concentric to the hub when the formed blade is disposed at the pitch angle in the construction of the fan. The inner edge 34 of each blade-forming blank is struck on a 1 radius from the axis of rotation. The fan, as shown, has a radius of 5 /2 and therefore the radius of inner edge 34 is about 24% of said fan radius.

The leading half of the blank 28 is provided with an exposed leading edge which includes an arcuate edge 36 connected with the peripheral edge 32 and the inner edge 34 at the more sharply curved arcuate edges 38 and 40, respectively. In the exemplary blank shown the edge 36 is struck on a 2 /2" radius which is equal to about 45% of the fan radius. It will be observed that the leading half of the blank is bounded by interconnected arcuate edges of which the leading edge 36 and peripheral edge 32 are convexly curvilinear.

The trailing half of the blank 28 is provided with an exposed trailing edge which includes an arcuate edge 42 connected with the peripheral edge 32 and inner edge 34 at the more sharply curved arcuate edges 44 and 46, respectively. In the exemplary blank shown, the edge 42 is struck on a 2 radius which is equal to about 51% of the fan radius. It will be observed that the trailing half is bounded by arcuate edges of which the trailing edge 42 and peripheral edge 32 are convexly curvilinear.

When the aforedescribed blank 28 is shaped into a blade 10, a portion of each of the leading and trailing halves is formed into parti-cylindroidal configuration so as to constitute a section of a cylinder tangent to the flat central portion 26 of the blank. This is accomplished in the leading half by curving the portion indicated by the reference numeral 50 sharply forwardly so that said portion will be tangent to the central portion 26 along a juncture line AC. It will be apparent that the portion 50, in order to assume parti-cylindroidal configuration, will be curved along arcuate lines perpendicular to the juncture line AC. A representative arcuate line is shown in Fig. 3 by that portion of section line 44 to the right of juncture line AC. The curvature of the portion 50 along line 44 is shown in Fig. 4 and, as pointed out above, said forward curvature is relatively sharp. The radius of forward curvature selected for the portion 50 depends upon the size of the fan and the basic pitch angle of the blades, i. e., the pitch angle of the spider arms and of the central blade 26. For example, for the ll" diameter fan shown, with blades set at a basic pitch of 20 to 40, the said radius of forward curvature should fall within the range of l to 2", which is to say that the radius of forward curvature should be approximately 18% to approximately 36% of the radius of the fan. When the blades are set a basic pitch of 33 as shown, the radius of forward curvature should closely approximate 1 /2". The radius of forward curvature will vary inversely with the basic pitch angle to effect a desired variation in the pitch angle along the leading edge of each blade as Will be pointed out hereinafter.

That portion of the trailing half of the blank 28 which in the shaping of a blade It] assumes parti-cylindroidal configuration is denoted by reference numeral 52. The portion 52 is curved sharply forwardly so as to be tangent to the flat central portion 26 along a juncture line A-D. Accordingly, the portion 52 is curved along arcuate lines perpendicular to the line AD. That portion of section line 44 to the left of line AD is representative of said arcuate, lines and Fig. 4 graphically illustrates the sharp arc of forward curvature of the portion 52. The radius of curvature of the portion 52 is selected to approximately equal the radius of curvature of the portion 50. However, slight variations between the radii of curvature of the said portions will not materially affect the operating characteristics of the fan.

The location of the lines of tangency or juncture lines AC and AD is important. As will be seen from the drawings, said lines are angularly related and intersect at the point A on line AB, said point being on or near the midpoint of the peripheral edge 32. Thus the juncture lines diverge toward the hub of the fan or toward the inner arcuate edge 34 of each blade 10 to define the flat central portion 26 of each blade 10 as being generally triangular. The angle CAD is thus defined by the juncture lines with the point C on the leading edge 36 and the point D on the trailing edge 42, the said points C and D being substantially spaced from the inner end or edge of the blank at 34. Angle CAD may vary throughout a range of approximately 70 to approximately 90. For example, in the 11 fan shown, an angle of approximately 82 is preferred. Angle CAB between juncture line A--C and line AB is preferably less than the angle BAD between line A--B and juncture line AD. In the specific example shown, angle CAB is approximately 39 and angle BAD is approximately 43.

When a formed blade 10 is connected to the fan as by the spider 18, the blades central portion 26 assumes the basic pitch angle of the spider arms 22, 22. The curved leading and trailing portions 50 and 52 vary in pitch due to their curved configuration. The variations in pitch of the portions 50 and 52 are best illustrated by Figs. 5. 6 and 7. The arcuate lines '55, 66 and 7-7 (Fig. l) are struck from the axis of rotation of the fan so the pitch angles illustrated by Figs. 5, 6 and 7 closely approximate the true pitch angles or angles of bite of the blade when the same is rotated. It will be noted by comparing Figs. 5, 6 and 7 that the angle of pitch along the leading edge 36 increases from approximately at the intersection at 38 of the leading and peripheral edges to the basic pitch angle at point C where the leading juncture line AC intersects the leading edge 36. In Fig. the leading edge has a pitch angle slightly greater than 0 because section 5-5 is spaced inwardly from the peripheral edge. In Fig. 7 the leading edge has a pitch angle less than the basic pitch because section 7-7 is spaced outwardly from point C.

It will also be noted that the angle of pitch along the trailing edge 42 has a maximum at the intersection at 44 of the trailing edge 42 and peripheral edge 32 and decreases from the said maximum to the basic pitch angle at the point D where the trailing juncture line AD intersects the trailing edge 42. The said maximum pitch 4 angle is preferably approximately twice the basic pitch angle, but it may be slightly less than twice the said basic pitch angle and is shown as being about 60.

It will be apparent from the foregoing that the pitch angles of the leading and trailing edges of each blade vary inversely of each other due to the sharply forwardly curved leading and trailing portions being tangent to the fiat central portion along angularly related juncture lines which intersect at the peripheral edge of the blade. The radii of curvature of the said leading and trailing portions are selected as pointed out hereinbefore to provide a pitch angle of approximately 0 at the intersection of the leading and peripheral edges and a pitch angle at the intersection of the trailing and peripheral edges which is approximately twice the basic pitch angle. In many installations the radii of said portions will be equal. The selection of the radius for the leading portion is critical, it being most desirable to provide a 0 pitch angle on the leading edge at the peripheral edge. The selection of the radius for the trailing portion is less critical, because it is believed that slight departures will not seriously alter the performance characteristics of the fan.

It has been found that a fan utilizing the abovedescribed blades is characterized by its quiet operation and by other desirable features.

For example, in one installation wherein a fan must be operated at a particular speed by a particular motor under prescribed constant conditions of air flow and wherein the operating noise level must be maintained below a maximum decibel rating, the fan of the present invention was found to be particularly well suited as compared to conventional fans known to us. It was found that conventional fans which suited the space requirements and which were pitched to govern the motor speed as desired, caused excessive air flow and operated at undesirably high noise levels. Altering the pitch angle proved to be no solution because a variety of operating speeds resulted and the air flow varied while the noise level remained high.

It is believed that the fan of present invention was successful in said installation because of the sharply forwardly curved leading and trailing portions arranged as described herein to inversely vary the pitch along the leading and trailing edges. It is thought that the curved leading portion caused the reduction in the operational noise level and that the curved trailing portion increased the brake horsepower of the fan to govern the operating speed under the prescribed air flow conditions.

While the theory of operation is not fully understood, it is believed that the best results will be attained in fans of various sizes and for various uses if the fans are constructed in proportion to the embodiment shown. For example, in a 22 fan, with blades set at a basic pitch of 33, it would be desirable to have 3" radii of curvature for the curved leading and trailing portions of the blades to compare with the 1 /2 radii for the curved portions of the blades in the 11" fan shown and described.

The invention claimed is:

l. A fan rotatable about a central axis and comprising a plurality of similar circumaxially spaced blades each of which is a single metallic sheet having a width greater than its radial dimension and having an arcuate peripheral edge and an inner end and consisting in part of a flat central portion and consisting further of leading and trailing portions joining the said central portion, the said central portion being located at a fixed basic pitch angle with respect to a plane perpendicular to the said axis and being bounded in part by inwardly diverging lead ing and trailing juncture lines at opposite sides of a central radial line and intersecting the said peripheral edge near the said radial line which diverging juncture lines have the included angle between them within the range of 70 to the said leading portion having an exposed convex leading edge uniformly curved throughout the major portion of its length and the said leading portion being forwardly curved to conform approximately to a section of a cylinder which has a radius within the range of from 18% to 36% of the fan radius and which is tangent to the said fiat central portion along the said leading juncture line and which extends from the last said juncture line to the said exposed convex leading edge, and the said trailing portion having an exposed convex trailing edge uniformly curved throughout the major portion of its length and the said trailing portion being forwardly curved to conform approximately to a section of a cylinder which has a radius within the range of from 18% to 36% of the fan radius and which is tangent to the said flat central portion along the said trailing juncture line and which extends from the last said juncture line to the said exposed convex trailing edge.

2. A fan as set forth in claim 1, wherein the radius of the leading cylindrical section of the blade is such that the pitch angle of the said leading edge is approximately Zero at a point immediately adjacent the peripheral edge of the blade and increases inwardly along the said leading edge to the said basic pitch angle at the intersection of the leading juncture line with the said leading edge, and wherein the radius of the trailing cylindrical section of the blade is such that the pitch angle of the trailing edge is approximately twice the basic pitch angle at a point immediately adjacent the peripheral edge of the blade and decreases inwardly along the said trailing edge to the said basic pitch angle at the intersection of the trailing juncture line with the said trailing edge.

3. A fan rotatable about a central axis and comprising a plurality of similar circumaxially spaced blades each of which is a single metallic sheet having a width greater than its radial dimension and formed with an arcuate peripheral edge concentric with the axis and formed with an arcuate inner edge concentric with the axis and having a radius equal to about 24% of the fan radius and the said sheet blade consisting further of leading and trailing portions joining the said central portion, the said central portion being located at a fixed basic pitch angle with respect to a plane perpendicular to the said axis and being bounded in part by leading and trailing juncture lines at opposite sides of a central radial line and intersecting the said peripheral edge near the said radial line, which leading juncture line diverges inwardly from the radial line at an angle of about 39 and which trailing juncture line diverges inwardly from the radial line at an angle of about 43, the said leading portion having an exposed leading edge which throughout the major portion of its length conforms to an are having a radius equal to about 45% of the fan radius and the said leading portion being forwardly curved to conform approximately to a section of a cylinder which has a radius within the range of from 18% to 36% of the fan radius and which is tangent to the said flat central portion along the said leading juncture line and which extends from the last said juncture line to the said exposed leading edge, and the said trailing portion having an exposed trailing edge which throughout the major portion of its length conforms to an arc having a radius equal to about 51% of the fan radius and the said trailing portion being forwardly curved to conform approximately to a section of a cylinder which has a radius within the range of from 18% to 36% of the fan radius and which is tangent to the said flat central portion along the said trailing juncture line and which extends from the last said juncture line to the said exposed trailing edge.

References Cited in the file of this patent UNITED STATES PATENTS 4 1,706,608 Holmes Mar. 26, 1929 1,995,193 Stilphen Mar. 19, 1935 2,023,111 Alsing Dec. 3, 1935 2,031,466 Criqui Feb. 18, 1936 2,072,322 Upson Mar. 2, 1937 2,581,873 Morrison Jan. 8, 1952

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