Mixing impeller device and method

Abstract

An impeller for use with a mixing vessel having a diameter, wherein the impeller is mountable onto a rotatable shaft that includes a flange. The impeller includes a single blade pair member. The blade pair member has a central hub portion and a first and second blade connected to the central hub portion. The first and second blades each include a generally planar portion, a tip portion and a trailing edge, wherein the generally planar portion and the tip portion intersect at a line of intersection, which is an angle relative to the trailing edge.

Description

FIELD OF THE INVENTION

The present invention relates generally to a mixing impeller device and method. More particularly, the present invention relates to an impeller for mixing and blending materials such as gases, liquids and liquid suspensions.

BACKGROUND OF THE INVENTION

Mixing and blending applications, in particular the mixing and blending of liquids, liquid suspensions and gases, are often constrained by the diameter of the tank in which the mixing is being carried out and by the diameter of the impeller. Some high solidity impeller designs (or “gas foils”) compensate for the aforementioned constraints by using impellers with three or four blades each having a large projected area. For example, it is known for existing high solidity impeller blades to occupy 80% of their total swept area. In addition, some existing impeller designs use impeller diameters which are typically 45% to 65% of the tank diameter. For a vessel of 240″ (20 feet) in diameter, the impeller diameter is approximately 120″ (10 feet) in diameter depending on service requirements, and the blades are approximately 60″ long and at least 38″ wide.

The impeller blades need to be inserted through a manway in the vessel for installation. In some covered mixing vessels, manways are commonly 24″ in size and can pass impeller blades of up to 23″ in width at best. Therefore, in order to insert larger blades, users either have to install an oversized manway, (40″ in size for a 240″ diameter tank), or the blades must be supplied in a longitudinally split configuration and then assembled inside the vessel. Splitting the impeller blades is an expensive operation, especially for blades having a rounded, leading edge, twist and curvature. In addition, multiple bolts are required along with match marking to assure proper, gap free re-assembly. This process can be very difficult and time consuming because the inner and outer blade components must be aligned correctly so that the impeller balance and blade geometry will not be compromised.

Further, some blades of known impeller design utilize a “blade to ear” bolted connection for providing torque transmission, thrust reaction and blade support, in which the blades are each attached to an ear extending from the shaft. The blades use symmetrical bolt patterns of 3, 4, 5, 7 or more bolts to attach the blade to the ear of the hub. This connection must be carefully designed, manufactured and assembled to assure problem free installation of the blades.

Also, known impeller designs usually provide 3 to 4 blades per impeller. Thus, 12 to 28 bolts are required for blade attachment, and alloy bolts are often required. Alloy bolts are expensive and, depending on the material, of limited availability. Many users require the use of positive locking of impeller bolts and hardware through the use of locking plates, double nuts and/or safety wire, increasing the total cost of each bolt. Due to the large quantity of bolts, it is usually not practical for the end user to retighten the impeller hardware after the initial period of operation, which can cause a loss of pre-load and premature failure of the bolted connection.

Accordingly, it is desirable to provide a high solidity impeller for mixing gas and liquid materials that offers improved reliability, reduced cost and ease of installation.

SUMMARY OF THE INVENTION

The present invention relates to impellers and impeller systems for mixing and blending applications. The invention is especially suitable for use in applications where the vessels are closed and are relatively large in diameter. In one aspect, the invention provides an impeller assembly that is mountable onto a rotatable shaft that has a flange extending radially from the shaft and rotating with the shaft. At least one blade pair member has two opposed blades and a central hub portion having a hole therethrough with an inner diameter at least as large as the outer diameter of the shaft. A plurality of corresponding mounting holes is provided in each of the flange and the blade pairs, and a plurality of bolts for fastening the blade pair to the flange via the mounting hole is provided.

In another aspect of the invention, the impeller assembly further comprises at least one additional blade pair. The blade pairs are stacked onto one another, so that the blades extend radially at angular intervals to each other. The mounting holes align so that the bolts fasten all of the blade pairs to the flange.

In a third aspect of the invention, the flange has a frictional fit key member and is releasably frictionally fit at a location along the length of the shaft.

In yet another aspect, the invention provides a method for mounting an impeller assembly onto a rotatable shaft having a flange radially extending from the shaft. The method comprises the steps of inserting at least one member that has two opposed blades and a central hub portion that has a hole therethrough with an inner diameter at least as large the outer diameter of the shaft onto the shaft and into contact with the flange. The method provides for fastening the blade pair member to the flange so that it rotates with the shaft.

In a further aspect of the invention, the method additionally comprises the step of fastening a second blade pair member having two opposed blades and a central hub portion having a hole therethrough with an inner diameter at least as large as the outer diameter of the shaft onto the shaft in a stacked fashion onto the at least one blade pair member.

In another aspect of the present invention, an impeller for use in a mixing vessel having a diameter is provided. The impeller is mountable onto a rotatable shaft that has an outer diameter and a flange. The impeller includes a unitary blade pair member having a width and diameter. The impeller also has central hub portion which includes a centerline and an inner diameter at least as large as the outer diameter of the shaft. The blade pair member also includes first and second blades that extend radially from the central hub portion. Each of the blades have a generally planar portion, a tip portion and a trailing edge. The generally planar portion the tip portion are at an angle to each other and intersect along a first line of intersection which does not pass through the centerline of the central axis.

In accordance with another aspect of the present invention, an impeller for use in a mixing vessel having a diameter is provided. The impeller is mountable onto a rotatable shaft that has an outer diameter and a flange. The impeller includes a blade pair member having width and diameter along with a central hub portion. The central hub portion has an inner diameter at least as large as the outer diameter of the shaft. The blade pair member includes first and second blades connected to the central hub each having a generally planar portion, a tip portion and a trailing edge. The generally planar portion and the tip portion intersect at a line of intersection so that the line of intersection has angle relative to the trailing edge between approximately 15 degrees to approximately 35 degrees.

In accordance with still another aspect of the present invention, an impeller for use in a mixing vessel having a diameter is provided. The impeller is mountable onto a rotatable shaft that has an outer diameter and a flange. The impeller includes a blade pair member having width and diameter along with a central hub portion. The central hub portion has an inner diameter at least as large as the outer diameter of the shaft. The blade pair member includes first and second blades connected to the central hub each having a generally planar portion, a tip portion and a outer edge. The outer edges of each of the blades are oriented at an angle to the generally planar portions equal to approximately 20 degrees to approximately 40 degrees.

In accordance with yet another embodiment of the present invention, a method for mixing or blending materials is provided, comprising mixing or agitating materials using an impeller comprising a blade pair member having a width W and a diameter D, the impeller further comprises a central hub portion having an inner diameter at least as large as the outer diameter of the shaft; a first blade connected to said central hub portion, said first blade having a first generally planar portion, a first tip portion and a first trailing edge, wherein said first generally planar portion and said first tip portion intersect at a first line of intersection, and wherein said first tip portion is oriented so that said first line of intersection has a first angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees; a second blade connected to said central hub portion, said second blade having a second generally planar portion, a second tip portion and a second trailing edge, wherein said second generally planar portion and said second tip portion intersect at a second line of intersection, and wherein said second tip portion is oriented so that said second line of intersection has a second angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees.

There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an eight bladed impeller using four one-piece blade pairs in accordance with the present invention.

FIG. 2 is plan view of a one-piece blade pair having a driver disc hub.

FIG. 3 is a side cutaway view of the impeller of FIG. 1 showing four blade pairs mounted to a shaft.

FIG. 4 is a side view of an embodiment having a sliding fit hub with an integral flange in accordance with the present invention.

FIG. 5 is a side view of an impeller in accordance with an embodiment where two shafts are attached by flanges.

FIG. 6 is a plan view of a two-blade impeller in accordance with an alternative embodiment of the present invention.

FIG. 7 is a side view of the two-blade impeller depicted in FIG. 6.

FIG. 8 is a side view of the one-piece impeller illustrated in FIG. 1 mounted to a shaft via bolt attachment in accordance with an embodiment of the present invention.

FIG. 9 is a side view of the one-piece impeller illustrated in FIG. 1 mounted to a shaft via weld attachment in accordance with another embodiment of the present invention.

FIG. 10 is a side view of a embodiment of the present invention having a sliding fit hub.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the figures wherein like reference numerals indicate like elements, FIGS. 1-5 illustrate presently preferred embodiments of an eight bladed gas foil impeller. While in the embodiment depicted the impeller is used for gas and/or liquid handling in agitated vessels, it should be understood that the present invention is not limited in its application to the blending and mixing of gases and/or liquids.

Referring to FIGS. 1 and 2, there is shown a mixing impeller 10 having four one-piece blade pairs 12 for a total of eight blades 14. To form the blade pairs 12, individual blades 14 are welded directly to a drive hub 16, 180° apart. As seen in FIG. 3, each drive hub 16 bolts up in a stacked fashion to a rigid flange 18 which is welded to a shaft 20. This eliminates the normal blade-to-ear bolted connection of present impeller design and can thus provide improved torque transmission, thrust reaction and support of the blade weight through the attachment of the stacked driver hubs 16 to the welded shaft flange 18.

The driver hubs 16 are attached to the welded shaft flange 18 by eight alloy bolts 21 through bolt holes 22 in the hubs 16. This bolt attachment provides for angular indexing (10) of the blades 14 to maintain proper tip-to-tip spacing and can simplify the field installation. A reduction in the number of bolts compared to ear designs is thus possible and may be desirable due to the significant cost of alloy bolts, their limited availability, and the fact that many applications require positive locking of the bolts by means of locking plates, double nuts and/or safety wire. In the embodiment of FIG. 3, the connection of the blades 14 to the shaft 20 is via the one-piece blade pairs 12 where the driver hubs 16 are stacked and bolted to the welded shaft flange 18. This connection is not prone to fretting, corrosion, or seizing to the shaft 20 due to material “pick-up.” This connection also is not dependent upon tight tolerancing to maintain performance. Therefore, the impeller 10 of the present invention can provide a more durable and more reliable shaft/blade connection than prior designs.

The aforementioned blade/shaft connection is also beneficial because the present design is based on a strength level equal to that of the shaft. Consequently it can offer improved reliability if the impeller 10 is overloaded because the blades 14 deflect before the overload forces damage the shaft 20. In addition, the connection provides for torque transmission primarily through friction between adjacent blade pairs 12 being compressed together and towards the flange 18, rather than primarily through tensile loading/pre-load in bolts. This avoids a problem in some present impeller designs, where the bolts which connect the blades to the shaft via an ear experience what is known as load sharing where some bolts may experience significantly higher loads than others. This occurrence contributes to these present impellers having a propensity for selective bolt failure.

A benefit of the one-piece blade pair design 12, when using 4 blade pairs in combination with the welded shaft flange 18 design is that it uniformly distributes loads to all bolts 21, and using the one-piece design where eight blades 14 are incorporated, each blade 14 is subject to 50% of the load is present in four-blade designs.

Referring to FIG. 2, the blades 14 are shown connected to the driver hub 16 to form the one-piece blade pairs 12. When installed, the blade pair 12 rotates about its central axis, for 15 example, in the direction A. Each of the blades 14 may be identical and formed in a press. The blades 14 have a tip 23 and a leading edge 24 and a trailing edge 26. An optional tip shape 25 is shown in dotted lines. When the blades 14 are installed, the tips 23 lie along the circumference of a circle defining the swept diameter of the impeller 10. The leading edge 24 may be straight as shown in FIG. 2 or curved.

The blades 14 of the pairs are welded directly to the driver hub 16, eliminating the need for many bolts and machined holes in impeller shafts and blades. The blades 14 are air foils having camber and twist except at the hub end where they are attached to the driver hub 16.

Upward and/or downward pumping is easily accomplished as a result of the blades 14 being welded to the driver hub 16. Accordingly, when the impeller 10 rotated in a clockwise direction A, as shown, axial flow is produced in the downward direction (downward pumping) in the liquid or liquid suspension in the mixing vessel. Alternatively, if the mixer drive allows reversed rotation, the blades 14 can be selectively installed and the drive reversed to change the flow direction without requiring additional or new parts.

Mixing impellers operate in an open flow field which leads to asymmetries in suction side velocities and direction. As shown in FIG. 2, the present invention utilizes a blade 14 that is approximately only 30% of the width of some presently known impeller blades.

The increase in the blade number to eight (compared to having fewer blades), reduces the lift and drag on each blade, reducing the need for larger shafts and larger drives. The one-piece blade pair 12, as shown in FIG. 2, has a shape intended to allow nesting with little material scrap. In a preferred embodiment, the blade 14 width is equal to 15% of the impeller 10 diameter, enabling the one-piece blade pair 12 to easily fit through a standard manway. In addition, the driver hub diameter D is approximately 18% to 20% of the total impeller diameter. For example, an impeller having a diameter of 120″ would have a driver hub diameter of approximately 22.8″. These dimensions enable the one-piece blade pair 12 in this example to pass through the standard manway and be adequate to attach to flange designs up to 20″ pipe. Shafts of smaller diameter, particularly those suited for speed and shaft strength criteria, typically range from 1″ to 8″ in diameter, are also well suited for operation with the onepiece design. Therefore, installation of the impeller 10 is simplified due the impeller geometry.

The blade pairs are easily moved through standard manways without requiring the user to split the blades for entry through the manway and then reassemble them inside the mixing vessels. The blade pairs 12 are easily shifted up the shaft due to a clearance between the inner diameter of the hole in the driver hub 16 and the outer diameter of the shaft 20. Also, the onepiece blade pair design can be implemented using only eight bolts to attach the eight bladed assembly to the shaft via bolt holes 22.

FIG. 3 shows one preferred embodiment of the invention, and illustrates how the four blade pairs 12 are attached to the shaft 20. In the embodiment shown in FIG. 3, a shaft flange 18 is welded to the shaft 20. The flange 18 may also be referred to as a driver disk. Bolts 21 extend through respective aligned holes 22 in the flange 18, blade pairs 14, and a clamp plate 30 to hold the blade pairs 12 so they rotate together with the flange 18 and the shaft 20. In this embodiment, eight bolts 21 are used to attach the blade pairs 14 to the hub 18. The clamp plate 32 may be a single disk-shaped clamp plate, or may be a plurality of individual clamp plates, one associated with each bolt 21. Alternatively, the clamp plate may be a suitable type of washer or may be omitted entirely. If a clamp plate 32 is used, the clamp plate 32 can provide for a uniform distribution of the bolt clamp load. For applications that require precision levels of balancing in either a single plane (“static”) or in two planes (“dynamic”), an alignment pin (not shown) may be inserted through matching holes in the elements 18, 14, and 32 for repeatability.

The flange 18 is usually machined in order to produce squareness and concentricity to the shaft 20 centerline as well as achieving the necessary flatness assuring a good bolted connection to the blade pairs 12. The use of eight bolts 21 attaching the driver disk 18 to the blade pairs 12 provides for angular indexing of the blades to maintain proper tip-to-tip spacing as well as simplifying field installation.

FIG. 4 illustrates another embodiment using a sliding fit hub 34 that uses a hook key 36 that is tightened against the hub 34 to provide a frictional fit against the shaft 20. The key 36 is a rectangular cross-section shaped element and has an angled surface that mates against a keyway surface inside the hub 34, and tightening of a bolt 38 holds an upper retainer plate 39 against the end of the key and attaches the hub to the shaft axially. A lower ring 40 is bolted to the sliding fit hub 34 as shown via the bolts 21 to retain the blade pairs 12. The sliding fit hub 34 arrangement permits the impellers to be mounted anywhere along the length of a shaft and permits, therefore, for vertical adjustment of the location of the impellers, as desired.

FIG. 5 illustrates another embodiment of the invention, which provides a combined shaft coupling and impeller attachment. In this embodiment, an upper shaft 20 has a flange 44, and a lower shaft 42 has a flange 46. Each of these flanges is welded at the end of its respective shaft.

In the arrangement shown in FIG. 5, bolts 21 are used extending through corresponding aligned holes 22 in the flange 44, the flange 46, the blade pairs 12, and a retaining clamp plate 32 to secure all these elements together so that they rotate together with the shafts 20 and 42. In this way, the shafts 20 and 42 are connected to each other, and the blade pairs 12 are also mounted at this location.

Referring now to FIG. 6, an impeller, generally designated 100, is illustrated in accordance with an alternative embodiment of the present invention. The impeller 100 has a single, preferably unitary, blade pair and is formed from two individual blades, designated 102 and 104, respectively, each connected to a drive hub 106. As illustrated in FIG. 6, the blades 102, 104 are preferably welded directly to the drive hub 106 180° apart to form a unitary, finished impeller 100. Alternatively, the blades 102, 104 and the drive hub 106 may be integral with one another wherein the blades 102, 104 and the drive hub 106 are manufactured or machined from a single, unitary piece of metal, for example.

The drive hub 106 includes bolt holes 108 that are preferably equally positioned equally spaced from one another about the circumference of the drive hub 106. The bolt holes 108 allow for the drive hub 106 to be attached to a mixer drive shaft 112, thereby attaching the impeller blades 102, 104. As illustrated in FIGS. 7 and 8, the drive hub 106 bolts to a rigid flange or drive disc 110 which is welded to the drive shaft 112 of a mixer. As described in connection with previous embodiments of the invention, the flange 110 is typically machined in order to produce squareness and concentricity to the shaft centerline as well as achieving the necessary flatness to ensure a good, bolted connection. The aforementioned attachment arrangement replaces the typical blade-to-ear bolted connection oftentimes employed in current impeller designs and can provide improved torque transmission, thrust reaction and support of the blade weight.

Referring now to FIGS. 6 and 7, the blades 102, 104 of the impeller 100 each have a tip portion 114, 116 and a generally planar portion 118, 120, that intersect at a fold line or intersection line 121. Each tip portion 114, 116 includes an edge 115, 117. The individual blades 102, 104 also have a leading edge and trailing edge, 122 and 124, respectively. The planar portions 118, 120 are oriented or positioned in a plane, generally designated B, perpendicular to the axis of rotation of the impeller 100, while the tip portions are oriented or deflected in the downward direction. The intersection line 121 lies within the plane B in this example.

As illustrated in FIG. 7, the tip portions are deflected or oriented at an angle β. The β angle is the angle between the intersection line 121 and the trailing edge 124. The β angle preferably ranges from approximately 15 degrees to approximately 35 degrees. More preferably, the β angle is approximately 28 degrees relative to the trailing edge 124. Alternatively, the angle β between the intersection line 121 and the trailing edge 124, may be less than 15 degrees or greater than 35 degrees. As depicted in FIG. 8, the tip portions 114, 116 are also deflected or angled at an angle α in the downward direction. The angle α, which is referred to as the tip chord angle, is defined as the angle between the line B, which in this example is both normal to the axis of rotation 101 and lies in the plane of the of the generally planar portions 118, 120, and the line C which is coincident with the edge 115. The tip chord angle α is preferably equal to approximately 15 degrees to approximately 35 degrees. More preferably, the tip chord angle α is equal to approximately 25 degrees. Alternatively, the angle between lines A and B may be greater than 35 degrees or less than 15 degrees.

Referring now back to FIG. 6, the impeller 100 has a diameter D and a width W. The diameter D is preferably equal to approximately 35% to approximately 75% of the tank or mixing vessel diameter in which the impeller 100 is employed. More preferably, the impeller 100 has a diameter D equal to approximately 45% to approximately 65% of the tank or mixing vessel diameter. The width W is preferably equal to approximately 15% to approximately 25% of the impeller diameter D. More preferably, the width W is equal to approximately 21% of the impeller diameter D.

Referring now to FIGS. 7 and 8, the impeller 100 of the present invention is bolted up to the welded flange 110 via the bolts 126 and the clamp plate 128 connection. Though two bolts 126 are depicted, preferably eight bolts are utilized to attach the impeller 100 to the flange 110. The bolts 126 extend through the holes 108 in the drive hub 106 and through respective holes in the flange 110. The clamp plate 128 may be a single, disc-shaped clamp plate as illustrated, or may be a plurality of individual clamp plates, one associated with each bolt 126. Alternatively, the clamp plate 126 may be any suitable type of washer or may be omitted entirely.

The aforementioned bolt 126 and clamp plate 128 connection is preferred because it provides uniform distribution of the load resulting from the bolt 128 and clamp plate 128 connection. Moreover, this connection is not prone to fretting, corrosion or seizing to the shaft 112 due to material “pick-up.” This connection also is not dependent upon tight tolerancing to maintain performance.

Alternatively, for applications requiring precision levels of balancing in either a single plane (“static”) or in two planes (“dynamic”), the embodiment depicted in FIG. 8 may include an alignment pin (not shown) to be used in combination with the bolt 126 and clamp plate 128 connection. An alignment pin may be inserted through matching holes in the impeller 100, flange 110 and clamp plate 128, in providing repeatability in balancing the impeller 100.

Referring now to FIG. 9, an alternative mounting or attachment arrangement in accordance with the present invention is illustrated. In the embodiment depicted, the flange 110 is welded to the shaft 112 like the previously described embodiments, and however the drive hub 106 of the impeller 100 is welded directly to the flange 110. In this attachment arrangement, the bolt connection described in the previous embodiment is completely eliminated. The aforementioned welded attachment connection is oftentimes desired when the impeller 100 is employed or utilized in applications requiring sterile environments and voids or crevices existing on the bolt impeller-shaft connections could harbor contamination.

FIG. 10 illustrates another embodiment of the present invention employing a sliding fit hub 130 that includes a hook key 132 and a drive key 134. The sliding fit hub 130 also includes a shoulder bolt 136. As described in the previous embodiments, the hook key 132 provides a frictional fit against the shaft 112. The hook key 132 is includes a pin (not shown) that engages and/or mates with a keyway 138, having multiple holes or notches, located on the shaft 112. The pin engages or mates with the holes located in the keyway 138, and the shoulder bolt 136 extends through the key and is threaded into the hub 130, urging the pin inward into a respective hole in the keyway 138. This above-described action provides a tight, frictional grip against the circumference of the shaft 112. The hook key 132 therefore provides an axially adjustable and removable connection between the sliding fit hub 130 and the shaft 112. This adjustable and removable connection allows for the impeller 100 to be mounted anywhere along the length of a shaft. It further permits vertical adjustment of the impeller 100.

The drive key 134 is an end milled key having a generally square cross-section. The drive key 134 has an angled surface that mates against an angled surface or keyway on shaft 112. The drive key 134 is neither adjustable nor removable like its counterpart the hook key 132, however it functions to transfer torque from the shaft 112 to the sliding fit hub 130.

In the embodiments depicted in FIGS. 6-10, the impellers function to “down pump” or agitate and mix the material in the downward direction, within the mixing vessel. Alternatively, the present invention includes design that “up pump” or scoop or lift the liquid in the upward direction within the mixing vessel. These alternative embodiments may include impeller design variations wherein the trailing edges of the individual blades are oriented or deflected upward. Other alternative embodiments for “up pumping” may include reversing the drive direction of the shaft and rotating or flipping the impeller 100 so that it is upside down.

The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. An impeller for use in a mixing vessel having a diameter, wherein the impeller is mountable onto a rotatable shaft that has an outer diameter and a flange, comprising: a unitary blade pair member having a width W and a diameter D comprising: a central hub portion having a centerline and an inner diameter at least as large as the outer diameter of the shaft; a first blade radially extending from said central hub portion, said first blade having a first generally planar portion, a first tip portion and a first trailing edge, wherein said first generally planar portion and said first tip portion are at an angle to each other and intersect along a first line of intersection which first line of intersection does not pass through the centerline of said central axis; a second blade radially extending from said central hub portion, said second blade having a second generally planar portion, a second tip portion and a second trailing edge, wherein said second generally planar portion and said second tip portion are at an angle to each other and intersect along a second line of intersection which second line of intersection does not pass through the centerline of said central axis.

2. The impeller according to claim 1, wherein said first tip portion is generally triangular and said second tip portion is generally triangular.

3. An impeller for use in a mixing vessel having a diameter, wherein the impeller is mountable onto a rotatable shaft that has an outer diameter and a flange, comprising: a blade pair member having a width W and a diameter D comprising: a central hub portion having an inner diameter at least as large as the outer diameter of the shaft; a first blade connected to said central hub portion, said first blade having a first generally planar portion, a first tip portion and a first trailing edge, wherein said first generally planar portion and said first tip portion intersect at a first line of intersection, and wherein said first tip portion is oriented so that said first line of intersection has a first angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees; a second blade connected to said central hub portion, said second blade having a second generally planar portion, a second tip portion and a second trailing edge, wherein said second generally planar portion and said second tip portion intersect at a second line of intersection, and wherein said second tip portion is oriented so that said second line of intersection has a second angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees.

4. The impeller according to claim 3, wherein said first angle is equal to approximately 28 degrees and said second angle is equal to approximately 28 degrees.

5. The impeller according to claim 3, wherein said first tip portion further comprises a first outer edge and wherein said first outer edge is oriented at an angle to said first generally planar portion equal to approximately 20 degrees to approximately 40 degrees, and wherein said second tip portion further comprises a second outer edge and wherein said second outer edge is oriented at an angle to said second generally planar portion equal to approximately 20 degrees to approximately 40 degrees.

6. The impeller according to claim 5, wherein said first outer edge is oriented at an angle equal to approximately 25 degrees and said second outer edge is oriented at an angle equal to approximately 25 degrees.

7. The impeller according to claim 3, wherein the diameter D of said blade pair is equal to approximately 35% to approximately 75% of the mixing vessel diameter.

8. The impeller according to claim 7, wherein the diameter D of said blade pair is equal to approximately 45% to approximately 65% of the mixing vessel diameter.

9. The impeller according to claim 7, wherein said width W of said blade pair is equal to approximately 15% to approximately 25% of the diameter D.

10. The impeller according to claim 9, wherein said width W of said blade pair is equal to approximately 21% of the diameter D.

11. The impeller according to claim 3, further comprising: a plurality of mounting holes disposed on said central hub portion; and a plurality of bolts that fasten said blade pair member to the flange via said mounting holes.

12. The impeller according to claim 11, further comprising a clamp member having a plurality of corresponding holes that correspond with said mounting holes, wherein said bolts extend through said corresponding holes and said mounting holes to attach said blade member to the flange.

13. The impeller according to claim 3, wherein said blade pair member is attached to the flange via welded attachment.

14. The impeller according to claim 3, wherein said blade pair member further comprises a frictional fit key member that said first blade and said second blade attach thereto, wherein said frictional fit key member is releasably connected at a location along the length of the shaft via frictional fit.

15. An impeller for use in a mixing vessel having a diameter, wherein the impeller is mountable onto a rotatable shaft that has an outer diameter and a flange, comprising: a blade pair member having a width W and a diameter D comprising: a central hub portion having an inner diameter at least as large as the outer diameter of the shaft; a first blade connected to said central hub portion, said first blade having a first generally planar portion, a first tip portion and a first outer edge, wherein said first outer edge is oriented at an angle to said first generally planar portion equal to approximately 20 degrees to approximately 40 degrees; a second blade connected to said central hub portion, said second blade having a second generally planar portion, a second tip portion and a second outer edge, wherein said second outer edge is oriented at an angle to said second generally planar portion equal to approximately 20 degrees to approximately 40 degrees.

16. The impeller according to claim 15, wherein said first blade further comprises a first trailing edge and wherein said first generally planar portion and said first tip portion intersect at a first line of intersection, and wherein said first tip portion is oriented so that said first line of intersection has an angle relative to said trailing edge equal to approximately 15 degrees to approximately 35 degrees, and wherein said second blade further comprises a second trailing edge, and wherein said second generally planar portion and said second tip portion intersect at a second line of intersection, and wherein said second tip portion is oriented so that said second line of intersection has an angle relative to said trailing edge equal to approximately 15 degrees to approximately 35 degrees.

17. The impeller according to claim 15, wherein said first outer edge is oriented at an angle equal to approximately 25 degrees and said second outer edge is oriented at an angle equal to approximately 25 degrees.

18. The impeller according to claim 16, wherein said each of said line of intersection angle is equal to approximately 28 degrees.

19. The impeller according to claim 15, wherein the diameter D of said blade pair is equal to approximately 35% to approximately 75% of the mixing vessel diameter.

20. The impeller according to claim 19, wherein the diameter D of said blade pair is equal to approximately 45% to approximately 65% of the mixing vessel diameter.

21. The impeller according to claim 19, wherein said width W of said blade pair is equal to approximately 15% to approximately 25% of the diameter D.

22. The impeller according to claim 21, wherein said width W of said blade pair is equal to approximately 21% of the diameter D.

23. The impeller according to claim 15, further comprising: a plurality of mounting holes disposed on said central hub portion; and a plurality of bolts that fasten said one blade pair member to the flange via said mounting holes.

24. The impeller according to claim 23, further comprising a clamp member having a plurality of corresponding holes that correspond with said mounting holes, wherein said bolts extend through said corresponding holes and said mounting holes to attach said one blade member to the flange.

25. A method for mixing or blending materials, comprising mixing or agitating materials using an impeller comprising a blade pair member having a width W and a diameter D, the impeller further comprises a central hub portion having an inner diameter at least as large as the outer diameter of the shaft; a first blade connected to said central hub portion, said first blade having a first generally planar portion, a first tip portion and a first trailing edge, wherein said first generally planar portion and said first tip portion intersect at a first line of intersection, and wherein said first tip portion is oriented so that said first line of intersection has a first angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees; a second blade connected to said central hub portion, said second blade having a second generally planar portion, a second tip portion and a second trailing edge, wherein said second generally planar portion and said second tip portion intersect at a second line of intersection, and wherein said second tip portion is oriented so that said second line of intersection has a second angle relative to said trailing edge between approximately 15 degrees to approximately 35 degrees.