WO2008038306A2

WO2008038306A2 - An improved ceramic integral vanes impeller

Info

Publication number: WO2008038306A2
Application number: PCT/IN2007/000451
Authority: WO
Inventors: R. S. Madhusudan; A. V. S. Rao; Sanjay Singh; Jagannath Hiremani; B. C. Dayanand
Original assignee: Weir Minerals India Private Limited
Priority date: 2006-09-28
Filing date: 2007-09-28
Publication date: 2008-04-03
Also published as: WO2008038306A3; WO2008038306A4

Abstract

A ceramic integral vanes impeller which can be used for pumping fluids containing highly erosive and corrosive substances. More particularly the impeller can be used for pumping fluids containing highly erosive and corrosive substances in mining and mineral processing industry.

Description

AN IMPROVED CERAMIC INTEGRAL VANES IMPELLER

FIELD OF THE INVENTION:

The invention discloses an improved device, a ceramic integral vanes impeller which can be used for pumping fluids containing highly erosive and corrosive substances. More particularly the impeller can be used for pumping fluids containing highly erosive and corrosive substances in mining and mineral processing industry.

BACKGROUND OF THE INVENTION:

The conventional impeller design with sharp vane edges and restricted areas is not suitable for handling liquids that contain rags, stringy materials and solids like sewage because it will clog. Vortex pump designs have recessed impellers that pump the solids by creating a vortex (whirl pool effect) in the volute and the solids move without ever coming into contact with the impeller. However, this form of impeller design results in loss of pump efficiency.

Similarly, in impellers with forward curved vanes, both the capacity and efficiency are reduced with a slight increase in head. They also exhibit unstable characteristics at the low end of capacity range and steep characteristics at the high end of the capacity range.

An axial flow impeller called an inducer can be placed ahead of the regular pump impeller on the same shaft to increase the suction pressure and lessen the chance of cavitations. In some instances this can allow the pump to operate at a higher speed. However, this impeller is low in efficiency.

US Patent 4,759,690 describes an impeller having vanes. It relates to a vane-type impeller having a plurality of adjacent, interconnected components at least some of which are made of an abrasion-resistant ceramic material. It is improved by a layer of a resiliently-flexible material between at least each component made of an abrasion-resistant ceramic material. Each component is adjacent for increasing the capability of each component made of the abrasion-resistant material of withstanding impact forces,

However each vane is separate and in layers (plurality) and there is no circular disc. There are 4 quadrants with the metal hub not having a projecting vane. Fully circular ceramic discs are not used in the prior art but resilient polyurethane sheet 1 to 2 mm used for absorbing shock. Exit hole provided for infiltrated fluid. No front or back vanes are present. Pins are used to hold layers of vanes pieces together and a sheet / tile of resilient / ceramic covers the pins.

US Patent 5,411,367 describes an impeller annular seal. It relates to a centrifugal pump for handling abrasive slurries and has an annular seal between the impeller and the housing insert. Centrifugal pumps suffer from wear of the annular seal between the impeller and the casing or side liner due to the returning flow of the rejoining fluid. This invention ameliorates this problem by having the clearance of the annular seal at least adjacent the inlet of the impeller sloping, in the direction of the main fluid flow into the impeller inlet at an angle of between 0° and 60° to the axis of rotation of the impeller. However, this impeller is made of metal whereas the instant invention is made of ceramic which is erosion resistant. Also, it creates higher pumping head as a result of having a higher tip diameter of the auxiliary vane as opposed to the cited impeller. Further, it more efficiently reduces losses at the inlet and exit tip of the vane.

It is required to have an impeller design such that the wear produced is less, the losses are diminished and the radial thrust is also reduced. Also, stress is lessened and the internal recirculation is decreased. The present invention has many advantages over the prior art for using integral vanes as well as ceramic material. Pumping of slurry requires material which is highly erosion resistant. Ceramic such as alumna, silicon carbide etc has good erosion resistance. Hence ^"the impeller of the present invention conceives it to be made of ceramic.

OBJECTS AND SUMMARY OF THE INVENTION:

It is an object of the instant invention to obviate the above drawbacks and provide an integral vanes ceramic impeller.

It is another object of the instant invention to provide efficiency in the functioning of the impeller leading to power saving during operation.

It is also object of the instant invention to provide a cost effective impeller.

|t is another object of the instant invention to remove the slurry tending to deposit in the gap between the impeller and the casing.

It is yet another object of the instant invention to create higher pumping head during the operation of the impeller.

It is further an object of the instant invention to reduce loss of fluid while pumping it using the impeller.

It is also object of the instant invention to easily remove the slurry which accumulates in the chamber.

It is another object of the instant invention to ensure uniform pressure rise at all the vane sections.

It is yet another object of the instant invention to prevent leakage and push pressurized fluid back to suction. To achieve the aforementioned objectives the invention provides an improved impeller with integral vanes for use in a centrifugal pump comprising a shroud having opposed faces, an outer peripheral edge portion and a rotation axis, a plurality of pumping vanes on one of the faces of the shroud extending away from the rotation axis, each pumping vane having an outer peripheral edge portion, and a plurality of auxiliary vanes on the other face of, the shroud, each auxiliary vane having an outer edge portion characterized in that the tip diameter of the auxiliary vanes (D_b) and the tip diameter of the pumping vanes (D_c) is within the range of 95% to 100% of the diameter of the shroud (D_a) and the angle at which the auxiliary vanes taper with respect to the shroud (Z) is between 80° to 90°.

The present invention discloses a ceramic impeller having integral vanes. This integral vanes impeller is made of ceramic which could be silicon carbide or any other ceramic. It may also be any grade of alumina. This concept of ceramic construction can be extended to semi-open or open impeller and also double suction impeller. The impeller can be used for any type of volute casing, twin casing or diffuser casing.

The rotational movement to the impeller is transmitted through a metallic hub, since ceramic is very brittle and cannot transmit the torque. The metallic hub and disc are further covered by ceramic discs. It has auxiliary vanes on the front and rear ceramic disc cover. However, it can be made even without the auxiliary vanes. These auxiliary vanes have defined profiles, shape and lengths. Alan bolts are used to hold the ceramic impeller, metal discs and ceramic cover discs together.

While assembly the gaps between the discs and hub are filled with glue which helps in absorbing the shocks due to impact of solid particles in the slurry. Further these discs along with the metallic hub are fastened together with Alan screws. No exit hole is required for infiltrated fluid. The present invention has many advantages including:

Higher Discharge and Efficiency: This design paves way for. manufacturing ceramic impellers with double curvature vanes, which enables large range of discharge better efficiency of the impeller leading to power saving during operation.

Lesser Ceramic Material Required and Cost Saved: The vanes in the instant invention are hollow with some holes. This reduces the amount of ceramic to be used thereby reducing the cost of the product.

Saving Polvurethane Cost: In earlier designs polyurethane sheets were cut into the shape of vanes and some pieces cut into quarter sector of a circle were used. The instant invention does not require PU sheets. Thus there is saving of cost.

BRIEF DESCRIPTION OF THE DRAWINGS:

The features of this invention are set forth with particularly in the appended claims. The invention, together with its objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify substantially like elements in the several figures and in which:

• FIGURE 1 shows the ceramic impeller without the hub and the back shroud

• FIGURE 2 shows the metallic hub for the ceramic impeller

• FIGURE 3 shows the blow up version of the ceramic impeller's parts

• FIGURE 4 shows the ceramic impeller positive flow sealing on front • FIGURE 5A shows the central pumping vane of the ceramic impeller

• FIGURE 5B shows the front shroud auxiliary vane of the ceramic impeller • FIGURES 6 and 7 show the back shroud auxiliary vane of the ceramic impeller

DETAILED DESCRIPTION OF THE INVENTION: The impeller of the present invention, as shown in FIGURE 1 , is integral with all vanes cast together within 2 circular discs as a single piece. The vanes are cast along with discs as a single piece. The ceramic impeller is reinforced with a threaded metallic hub disc having vanes to transmit torque. FIGURES 2 and 3 show there is front metallic disc reinforcement on the front shroud of the ceramic impeller. There are fully circular ceramic disc covers on the front and back shrouds. Fillet glue with powder serves for absorbing shock. No layer of resilient sheet is used, as the glue acts as the resilient material, and no exit hole required for draining infiltrated fluid.

There are auxiliary front and back vanes on the rear ceramic disc cover and throat bush sealing. It further uses special fasteners with Alan bolts to hold the ceramic impeller, metal discs and ceramic cover discs together. The bolt head is covered by a ceramic washer which is tight fit and also glued.

As shown in FIGURE 6 and FIGURE 5b, the tip diameter of the auxiliary vanes (D_b) is higher than that of the pumping vanes. This creates a higher pumping head for removing the slurry tending to deposit in the gap between the impeller and the casing. This also gives space for accommodating the bolt head fastening the ceramic and metal discs of the impeller. Also shown is that the auxiliary vane tip diameter (D_b) is 100% that of the impeller tip diameter.

Further, the auxiliary vane width is thicker than the pumping vane width with much .larger radii at its inlet and outlet so as to reduce the losses at the inlet and at the exit tip of the vanes. The higher vane width also accommodates the bolt head. The tip edge of the auxiliary vanes is straight with a 10° draft angle for the case of casting, thus the angle from the impeller plane is 80°. Also, as shown in FIGURE 7, the auxiliary vanes tip diameter (D_b) is higher than the pumping vanes tip diameter (D_c).

The number of auxiliary pumping vanes is same as that of the main pumping vanes. Further, the shape and direction of the auxiliary pumping vanes is similar to that of the main central pumping vanes. In one embodiment, the diameter of the shroud (D₃) is equal to the tip diameter of the auxiliary vanes (D_b). The Z angle between the vane tip and the shroud is 80° to 90°.

In one embodiment of the invention, the diameter of the shroud (D₃) is equal to the tip diameter of the tip diameter of the pumping vanes (D₀). In another embodiment of the invention the tip diameter of the pumping vanes (D₀) is 97% of the diameter of the shroud (D₃). In yet another embodiment of the invention, the tip diameter of the pumping vanes (D₀) is 97% of the tip diameter of the auxiliary vanes (D_b).

The back shroud auxiliary vane starting inlet edge diameter is same as that of the front shroud auxiliary vane starting inlet edge diameter. This increases the suction chamber size at the hub region between the back shroud of the impeller and the casing. The slurry which accumulates in the chamber is easily lifted up by the auxiliary vanes which are in the shape of the pumping vanes.

In one embodiment of the invention, the tip diameter of the auxiliary vanes (Db) is greater than 95% of the diameter of the shroud (D_a). Also, the tip diameter of the pumping varies (D_c) is greater than 95% of the diameter of the shroud (D₉).

All the vanes have rounded inlet and outlet edges to reduce the losses due to the wake. The edge radii are more than 6 mm. The pumping vane exit edge is straight so that the same vane tip diameter is provided at all the cut sections of the cane. This ensures uniform pressure rise at all the vane sections. As shown in FIGURE 4, the front shroud inlet edge is rounded at the corners with a corner radius of curvature of 5 mm. This radius of curvature can vary within + or - 10%. The angle for the sealing edge at the impeller inlet edge is 90° from the impeller inner surface and with a radius of curvature of around 5 mm. The sealing surface is not curved and is almost straight. The outer edge of sealing surface ends at 70° to 80° axis.

The auxiliary vanes on the front shroud are of the shape as that of the pumping vanes. From the auxiliary vanes, the pumping vanes also pump fluid through the gap between the front shroud and the volute wall and develop positive pressure. This prevents leakage of the front shroud auxiliary vane and pushes pressurized fluid back to suction.

the gap between the impeller suction and the casing wall at the annular sealing surface need not be maintained small as the auxiliary vanes pump the fluid and prevent loss of pressurized fluid. As shown in FIGURE 4, the gap measures between 3 mm to 5 mm.

Further, in both the front shroud and the back shroud the number of auxiliary vanes is same as that of the pumping vanes. The back shroud auxiliary vanes are also the same shape as that of the pumping vanes.

Claims

We claim:

1. An improved impeller with integral vanes for use in a centrifugal pump, the impeller comprising:

- a shroud having opposed faces;

- an outer peripheral edge portion and a rotation axis;

- a plurality of pumping vanes on one of the faces of the shroud, extending away from the rotation axis, each pumping vane having an outer peripheral edge portion; and

- a plurality of auxiliary vanes on the other face of the shroud, each auxiliary vane having an outer edge portion

characterized in that the tip diameter of the auxiliary vanes (D_b) and the tip diameter of the pumping vanes (D_c) is in the range of 95% to

100% of the diameter of the shroud (D_a) and the angle at which the auxiliary vanes taper with respect to the shroud (Z) is between 80° to 90°.

2. An impeller as claimed in claim 1, wherein the impeller is made of a composite material which is resistant to corrosion and has good . erosion resistance.

3. An impeller as claimed in claim 2, wherein the composite material is ceramic such as alumina or silicon carbide.

4. An impeller as claimed in claim 2, wherein the composite material is a corrosion resistant material such as polyurethane, rubber or such alloy.

5. An impeller as claimed in claim 1 , wherein all the vanes of the said impeller are cast together within two circular discs as a single piece.

6. An impeller as claimed in claim 1 , wherein the vane width of the auxiliary vane is thicker than that of the pumping vane.

7. An impeller as claimed in claim 1, wherein the number of auxiliary vanes is same as that of the pumping vanes.

8. An impeller as claimed in claim 1 , wherein the tip diameter of the auxiliary vanes (Db). is equal to that of the shroud (D₉)

9. An impeller as claimed in claim 1 , wherein the tip diameter of the pumping vanes (D₀) is 0.97 of the diameter of the shroud (D₃).

10. An impeller as claimed in claim 9, wherein the diameter of the shroud (D₃) is equal to that of the pumping vanes (D₀).

11.An impeller as claimed in claim 1 , wherein the tip diameter of the pumping vanes (D_c) is 0.97 of the tip diameter of the auxiliary vanes (D_b).