EP1705380A1

EP1705380A1 - A slurry pump

Info

Publication number: EP1705380A1
Application number: EP06111998A
Authority: EP
Inventors: Magnus Arvidsson; Håkan Leander; Sandro Chervatin
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2006-09-27

Abstract

The invention refers to a slurry pump incorporating an impeller (2) being rotatably positioned in an impeller housing (7) and being fitted to a driven shaft (3), which is supported in locating rolling bearings (9) adapted to take up radial and axial loads and in a non-locating rolling bearing (10) primarily intended to take up radial loads, whereby the rolling bearings (9, 10) are all positioned outside the impeller housing (7), with the bearings spaced apart, and with the non-locating rolling bearing (10) being a toroidal roller bearing, with ability of taking up axial displacement and angular misalignment.

Description

Field of invention

Pumps used for different purposes such as mining, mineral processing, oil sand transport, waste water treatment and transport of catalysts in petrochemical processes are in most instances known as slurry pumps.

Background of the invention

Slurry pumps for such purposes are mostly horizontal centrifugal pumps, designed to operate under heavy-duty conditions handling non-homogenous fluids with solids and hard particles mixed to water or low viscosity fluids. These operating conditions mean that the pump is subjected to a progressive abrasive wear acting on the pump impeller when the hard particles in the fluid transported by means of the slurry pump hit and slide on the blades of the impeller, and also to cavitation. As a result of such wear and cavitation there is generated strong vibrations, irregular loads and permanent shaft deflections, which all can cause early bearing failure.
These negative effects of wear and cavitation can cause a low mean time between failures, which in turn will be costly particularly for slurry pumps installed in remote areas, where the downtime my be long.

Purpose of the present invention

The purpose of the present invention is to propose a self-aligning slurry pump of the type described intended to increase the mean time between failures and enhancing reliability by minimizing the effects of cavitation and impeller wear, and this has been achieved in that the slurry pump has been given a system of solutions defined in the accompanying claim 1.

Brief description of the accompanying drawings

Hereinafter the invention will be further described with reference to embodiments illustrated in the accompanying drawings.

Fig. 1 shows schematically in cross-section a portion of a light duty slurry pump in accordance with the present invention.
Fig. 2 is a view similar to Fig. 1 and showing a heavy duty slurry pump in accordance with the present invention, and
Fig. 3 illustrates in bigger scale the heavy duty slurry pump shown in Fig. 2 with different properties of the bearing units incorporated therein, illustrated in encircled sub-views.

Description of preferred embodiments

Fig. 1 shows in a cross-section a portion of a slurry pump 1 according to the present invention, and which is intended for light duty applications.
The pump 1 has an impeller 2, which is mounted on a shaft 3 driven by an electric motor (not shown) either directly or via a belt. The shaft is commonly supported in radial rolling bearings and at least one thrust bearing to accommodate the relevant axial loads generated by the action of the fluid on the impeller. The bearings are situated in a closed housing 4 with sealing arrangements 5, 6 for the shaft passing therethrough. The impeller 2 is situated in a separate housing 7 and the bearing housing 4 and the impeller housing 7 are connected to each other by means of bolt connections 8, but are individually sealed off. The bearings used in this embodiment is a pair of angular contact ball bearings 9, which are mounted in back-to-back arrangement as locating bearings, and a toroidal roller bearing 10 mounted as a non-locating bearing. Such a bearing combination will give a high resistance to axial shock loads by means of the angular contact ball bearings 9, and the non-locating toroidal roller bearing 10 will give smaller unbalance and a cooler pump, as it can take up axial displacements and also accommodate angular misalignments.
In Fig. 2 is shown a heavy duty slurry pump 11 incorporating an impeller 12, which is operatively connected to a shaft 13, supported in a housing 14, which is sealed off from the exterior by means of radial oil seals 15 and 16. The impeller 12 is positioned in a housing 17, separate from and sealed off from the bearing housing 14, but being connected thereto by bolt connections 18. On the "dry side", i .e. near the end facing away from the impeller 12, the shaft 13 is supported in a double-row spherical roller bearing 19 positioned as a locating bearing. This bearing is self-aligning and this means that the pump will be insensitive to shaft bending, and the accuracy on surrounding components is therefore less important. In addition to radial loads this bearing 19 has a certain ability of accommodating axial loads in both directions. For accommodating even higher axial loads, there is also arranged a spherical roller thrust bearing 20 adjacent the spherical roller bearing 19 at the "dry side". Also this spherical roller thrust bearing 20 is arranged as a locating bearing. At the "wet side", i.e. at the side of the shaft 13 facing the impeller 12, the shaft 13 is supported in a non-locating toroidal roller bearing 21, which has an ability to take up axial displacements and also accommodate angular misalignments.
The use of a toroidal roller bearing 10, 21 as a non-locating or floating bearing in both the embodiments described above, means that the bearing will move when temperature and/or axial load increases, but it will move first when the friction force is overcome, which in the art is referred to as stick-slip. Such ability of movement will reduce the influence of friction, as the internal axial load is released at each movement, and the temperature reduction in turn will again cause reduction of the axial load.
The non-locating toroidal roller bearing thus will guarantee a frictionless axial movement, no possibilities to create internal axial forces, and the stress will be minimized and the bearing performance will be improved, which again will give improved reliability, predicted service life and possibility of down-sizing the components.
The non-locating toroidal bearing 10, 21 has preferably a taper bore and is mounted on an adapter sleeve, which means that the mounting and dismounting of the bearing is facilitated.
In Fig. 3 the heavy duty pump of Fig. 2 is shown in bigger scale and with specific functions of different parts of the bearing system illustrated in enlarged, encircled part views.
In the upper circle it is thus shown how the double row spherical roller bearing 19 can take up misalignment between the shaft 13 and the housing 14, by sphereing. As this bearing is a locating bearing it has no ability to compensate for any axial displacement.
In the right hand lower circle, the toroidal roller bearing 21 is shown in a first position 21' where the outer ring has been axially displaced in relation to the inner ring, and in a second position 21" in which it is illustrated how the inner ring and the outer ring are axially displaced relative to each other and also angularly inclined to each other.
The lower, left hand circle illustrates the relation between the two row spherical roller bearing 19 and the spherical roller thrust bearing 20, and this illustration shows that the load center line 19a of the spherical roller bearing 19 and the load center lines 20a and 20b of the spherical roller thrust bearing 20 all meet in a common point X on the geometrical axis 13a of the shaft 13. By having this type of common pressure center X between the spherical roller bearing 19 and the spherical roller thrust bearing 20 with a self-locating toroidal roller bearing on the non-locating side, the bearing arrangement is forgiving if the shaft is bent, i.e. bending does not affect friction, operating temperature, running accuracy, vibration and noise levels and stiffness.
With the toroidal bearing 10, 21 as a non-locating bearing it is possible to accommodate a misalignment of 0.5° and an axial displacement of +/- 10% of the bearing width.
The preferred use of adapter sleeves entails a lower risk for incorrect mounting.
The slurry pumps according to the invention can preferably be equipped with a condition monitoring system adapted to sense the conditions related to low frequency vibrations in connection to impeller abrasive wear and also very high frequency vibrations caused by cavitation by means of vibration/temperature sensors, transmitting signals representative for such conditions to a display, to an alarm module or the like.

Claims

A slurry pump incorporating an impeller (2; 12) being rotatably positioned in an impeller housing (7; 17) and being fitted to a driven shaft (3; 13), which is supported in locating rolling bearings (9; 19, 20) adapted to take up radial and axial loads and in a non-locating rolling bearing (10; 21) primarily intended to take up radial loads,
characterized therein,
that the rolling bearings (9, 10; 19, 20, 21) are all positioned outside the impeller housing (7; 17), with the bearings spaced apart, and with the non-locating rolling bearing (10; 21) being a toroidal roller bearing, with ability of taking up axial displacement and angular misalignment.
A slurry pump as claimed in claim 1,
characterized therein,
that the non-locating toroidal roller bearing (10; 21) is positioned about the shaft (3; 13) closer to the impeller housing (7; 17) than the locating rolling bearings (9; 19, 20).
A slurry pump as claimed in claim 1 or 2,
characterized therein,
that all the bearings (9, 10; 19, 20, 21) are positioned in a sealed off bearing housing (4; 14) separated from the impeller housing (2; 12) and being attached to this.
A slurry pump as claimed in anyone of the preceding claims, and intended primarily for light duty operations,
characterized therein,
that the locating bearings (9) are a pair of angular contact ball bearings (9) mounted in back-to-back arrangement.
A slurry pump as claimed in anyone of claims 1 - 3, and intended primarily for heavy duty operations,
characterized therein,
that the locating bearings are double row spherical roller bearing (19) and a spherical roller thrust bearing (20) spaced apart from the double row spherical roller bearing (19).
A slurry pump as claimed in claim 5,
characterized therein,
that the double row spherical roller bearing (19) and the spherical roller thrust bearing (20) are spaced apart thus that the load center line (19a) of the double row spherical roller bearing (19), and the two load center lines (20a, 20b) of the spherical roller thrust bearing (20) meet in a common point (X).
A slurry pump as claimed in claim 6,
characterized therein,
that the common point (X) is situated on the geometrical center axis (13a) of the shaft (13).
A slurry pump as claimed in anyone of the preceding claims,
characterized therein,
that the pump is equipped with a condition monitoring system adapted to sense low frequency vibrations in connection to impeller abrasive wear and high frequency vibrations caused by cavitation, by means of vibration/temperature sensors, and means for transmitting signals representative for the operating conditions of the pump to a display and/or to an alarm module.