Hydrofoil impeller

Abstract

A hydrofoil impeller includes a central hub connected to a shaft, and being in the form of a flat plate and being perpendicular to the central axis. The central hub has first bolt holes arranged to form a pattern, the number of groups of first bolt holes corresponding to a number of blades attached to the central hub. At least three blades extend radially outwardly from the central hub, and have a group of second bolt holes arranged in a corresponding pattern to the first bolt holes so that the group of second bolt holes can be aligned with the group of first bolt holes and bolts can be placed through the first and second bolt holes to form bolted joints. The pattern in which the first holes and second holes are arranged in each of the respective groups of holes has a form of a closed curved shape.

Claims

1. A hydrofoil impeller for producing fluid flow in an axial direction relative to a shaft rotating around its central axis in an agitated tank, the impeller comprising: a central hub which is connected to the shaft, the central hub being in the form of a flat plate with a uniform thickness and being perpendicular to the central axis (x), the central hub having a number of groups of first bolt holes arranged to form a pattern, the number of groups of first bolt holes corresponding to a number of blades attached to the central hub; and at least three blades extending radially outwardly from the central hub, each blade having a root portion, the root portion being in a form of a flat plate with a uniform thickness, the root portion having a group of second bolt holes arranged in a corresponding pattern in relation to the pattern of the first bolt holes so that the group of second bolt holes can be aligned with the group of first bolt holes and bolts can be placed through the first and second bolt holes to form bolted joints, wherein the number of holes in each group of first and second holes is at least five, wherein the pattern in which the first holes and second holes are arranged in each of the respective groups of holes is in a form of a closed curved shape, wherein each blade comprises a leading edge and a trailing edge in the direction of the rotation, and the attachment of the blade at the root portion provided by the closed curve shaped pattern of bolted joints provided by the first and second bolt holes and bolts is located, in the direction of rotation, in front of a midpoint of the blade defined between the leading edge and trailing edge of the blade.

2. The hydrofoil impeller according to claim 1, wherein the central hub comprises an upper surface and a lower surface which is parallel to the upper surface, and the root portion of each blade abuts against the lower surface of the central hub.

3. The hydrofoil impeller according to claim 1, wherein the number of the blades is three, the central hub is in the form of a triangle with rounded corners, the group of first bolt holes is disposed at each corner of the central hub, and the pattern in which the first holes and second holes are arranged in each of the respective groups of holes is in the form of an ellipse.

4. The hydrofoil impeller according to claim 1, wherein the number of the blades is five, the central hub is in the form of a circular disc, and the pattern in which the first holes and the second holes are arranged in each of the respective groups of holes is in a form of a circle.

5. The hydrofoil impeller according to claim 4, wherein the impeller comprises five pieces of first spacer plates each of which has a pattern of bolt holes corresponding to the pattern of groups of first bolt holes and second bolt holes for each of the bolted joints, and which first spacer plates are arranged against and underneath the root portion of the blade to form spacing elements for the bolted joints.

6. The hydrofoil impeller according to claim 5, wherein the impeller comprises five pieces of second spacer plates each of which has a pattern of bolt holes corresponding to the pattern of the bold holes of the first spacer plate, and which second spacer plates are arranged against the upper surface of the central hub to form spacing elements for the bolted joints.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

(2) FIG. 1 is a schematic elevation side view of a reactor tank equipped with a first embodiment of the impeller in accordance of the invention,

(3) FIG. 2 is an axonometric view of the first embodiment of the impeller of the invention seen obliquely from above,

(4) FIG. 3 is an axonometric view of the impeller of FIG. 2 seen obliquely from below,

(5) FIG. 4 is a top view of the impeller of FIGS. 2 and 3, with one of the blades shown as detached,

(6) FIG. 5 is an axonometric view of an impeller in accordance of a second embodiment of the invention seen obliquely from above,

(7) FIG. 6 is an axonometric view of the impeller of FIG. 5 seen obliquely from below,

(8) FIG. 7 is a top view of the impeller of FIGS. 5 and 6,

(9) FIG. 8 is a plan view of the first spacer plate,

(10) FIG. 9 is a plan view of the second spacer plate, and

(11) FIG. 10 is a section X-X taken from FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

(12) In FIG. 1 is shown a hydrofoil impeller 1 for producing fluid flow in axial direction relative to a shaft 2 rotating around its central axis x in an agitated tank 3.

(13) Referring to FIGS. 2 to 7, the impeller 1 comprises a central hub 4. The central hub 4 is connected to the shaft 2. Preferably, the central hub 4 has a central hole to which the shaft 2 is attached by an interference fit. Also any other suitable connecting means may alternatively be used, including welding. However, while it is an objective to improve fatigue life, welding is preferably avoided. The central hub 4 has a form of a flat plate with a uniform thickness. The central hub 4 is perpendicular to the central axis x. The central hub 4 has a number of groups of first bolt holes 5 arranged to form a pattern. The number of groups of first bolt holes corresponds to the number of blades 6 attached to the central hub 4. In the embodiment shown in FIGS. 1 to 4, the number of blades 6 is three. In the embodiment shown in FIGS. 5 to 7, the number of blades 6 is five.

(14) The blades 6 extend radially outwardly from the central hub 4. Each blade 6 has a root portion 7. The root portion 7 is in a form of a flat plate with a uniform thickness. In the shown two embodiments the whole blades are in a form of a flat plate with a uniform thickness. Each of the blades has three straight bends which divide the blades to four planar angled successive profile portions.

(15) The root portion 7 of the blade has a group of second bolt holes 8 which are arranged in a corresponding pattern in relation to the pattern of the first bolt holes so that the group of second bolt holes 8 can be aligned with the group of first bolt holes 5 and bolts 9 can be placed through the first and second bolt holes to form bolted joints.

(16) The number of holes in each group of first and second holes is at least five. In the preferred embodiments shown in Figures the number of holes in each group of first and second holes is eight. The pattern in which the first holes 5 and second holes 8 are arranged in each of the respective groups of holes is in a form of a closed curved shape. The closed curved shape can be an ellipse or a circle.

(17) As can be seen especially in FIGS. 2 and 3 for the first embodiment of the impeller and in FIGS. 5, 6, and 10 for the second embodiment of the impeller, the central hub 4 comprises an upper surface 10 and a lower surface 11 which is parallel to the upper surface. The root portion 7 of each blade 6 is abutted against the lower surface 11 of the central hub 4.

(18) In the embodiment shown in FIGS. 2 to 4, the number of the blades 6 is three. The central hub 4 has a form of a triangle with rounded corners. The group of first bolt holes 5 is disposed at each corner of the central hub 4. The pattern in which the first holes 5 and second holes 8 are arranged in each of the respective groups of holes is in a form of an ellipse.

(19) In the embodiment shown in FIGS. 5 to 7, the number of the blades 6 is five. The central hub 4 is in the form of a circular disc. The pattern, in which the first holes 5 and second holes 8 are arranged in each of the respective groups of holes, has a form of a circle.

(20) Referring to FIGS. 5 to 10, the impeller 1 comprises five pieces of first spacer plates 12, one of which is shown separately in FIG. 8. Each first spacer plate 12 has a pattern of bolt holes 13 corresponding to the pattern of groups of first bolt holes 5 and second bolt holes 8 for each of the bolted joints. As can be seen from FIGS. 6 and 10, the first spacer plates 12 are arranged against and underneath the root portion 7 of the blade 6 to form spacing elements for the bolted joints. The impeller 1 also comprises five pieces of second spacer plates 14, one of which is shown separately in FIG. 9. Each second spacer plate 14 has a pattern of bolt holes 15 corresponding to the pattern of the bolt holes 13 of the first spacer plate 12, and which second spacer plates 14 are arranged against the upper surface 11 of the central hub 4 to form spacing elements for the bolted joints. The spacer plates 12 and 14 used together with the central hub 4 and the root portion 7 give a suitable elongation length for the bolts 9 to enhance their fatigue strength.

(21) Referring to FIGS. 4 and 7, each blade 6 comprises a leading edge 15 and a trailing edge 16 in the direction of the rotation. The attachment of the blade 6 at the root portion 7 provided by the closed curve (i.e. ellipse or circle) shaped pattern of bolted joints provided by said first and second bolt holes 5, 8 and bolts 9 is located, in the direction of the rotation, in front of and near to the side of the leading edge 15 of the blade 6 and substantially behind the trailing edge 16 of the preceding blade.

(22) While the present invention has been described in connection with an exemplary embodiment, and implementations, the present invention is not so limited, but rather covers various modifications, and equivalent arrangements, which fall within the purview of prospective claims.