GB2061399A

GB2061399A - A composite pump impeller

Info

Publication number: GB2061399A
Application number: GB8021077A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1979-10-29
Filing date: 1980-06-27
Publication date: 1981-05-13
Also published as: AU538322B2; JPS5666486A; GB2061399B; FR2468772B1; DE3032672A1; AU5866180A; FR2468772A1

Abstract

A highly wear-resistant composite impeller for use in centrifugal slurry pumps has a base 4 and a cover plate 6 formed of a material, such as steel, which can be worked with relative ease, and an insert sandwiched between the base and cover plate formed of a high temperature and wear-resistant refractory material. The insert has a plurality of impeller drive vanes 16 and may be constructed from a plurality of interlocking segments 10. In use slurry is received and driven by the segments 10 and has little, if any, contact with the base and cover plate. <IMAGE>

Description

SPECIFICATION A composite pump impeller This invention relates to pump impellers and is particularly directed to a composite impeller for use in centrifugal coal slurry pumps.

In attempting to overcome the energy crisis, numerous techniques have been proposed for converting coal into oil or gas. Most of these techniques involve pulverizing the coal and combining it with a suitable fluid to form a slurry which is transported through the process by pumping. Unfortunately, such slurries are extremely abrasive and tend to jam piston pumps, while the slurries act like a stream of sandblast on centrifual pumps, causing high maintenance and greatly reducing the life of the pump. Moreover, coal slurries tend to be highly carcinogenic so that frequent maintenance of the pumps involves a serious health hazard. Moreover, coal conversion processes generally require that the coal slurries be maintained at temperatures of 1500--3150C.

Few impeller materials can withstand such temperatures. It has been proposed to form the pump components of high temperature and wearresistant materials, such as tungsten carbide.

However, such materials are expensive and extremely difficult to fabricate, causing the cost of such pumps to be prohibitive. Thus, no satisfactory solution to this problem has been found in the prior art.

According to the present invention there is provided a composite pump impeller comprising a base, a cover plate, and an insert, sandwiched between the base and the cover plate, having a plurality of impeller drive vanes and being formed of a refractory, wear resistant material which can be worked with substantially less ease than the base and cover plate.

Preferably the base and cover plate are formed of conventional materials, e.g. steel, which can be worked relatively easily, and the insert may comprise a plurality of individual segments, formed of high wear-resistant material and sandwiched between the base and cover plate.

The segments are formed to minimize fabrication expense and to withstand direct impingement wear by heated coal slurry.

The invention will be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a plan view of an impeller embodying the present invention; Figure 2 is a vertical section through the impeller of Figure 1; Figure 3 is an exploded view of the impeller of Figure 1; Figure 4 is a plan view of the impeller of Figure 1 with the cover plate removed; and Figure 5 is an isometric view of one of the insert segments of the impeller of Figure 1.

Figures 1-3 show an impeller having a base 4, a cover plate 6 and an insert 8. The base 4 and cover plate 6 are formed of conventional materials, such as steel, which are relatively inexpensive and easy to fabricate. The insert 8 is formed of a plurality of individual segments 10 which are composed of a refractory wear-resistant material, such as tungsten carbide or aluminium oxide.

Unfortunately, high temperature and wearresistant materials are extremely difficult and expensive to work. Casting and machining of such materials are virtually impossible. Accordingly, fabrication of an impeller from such materials would be prohibitive. This difficulty can be overcome by forming the base 4 and cover plate 6 of materials, such as steel, which are relatively inexpensive and easy to work. These portions of the impeller are not directly impinged upon by the slurry flow and, hence, are not as severely affected by the temperature and abrasive nature of the slurry. The insert 8, which is exposed to the most severe conditions, is composed of a plurality of individual segments 10 which are formed of the refractory, wear-resistant material.It has been found that the segments 10 can be formed easily and inexpensively by injection moulding or machining before sintering, even though a refractory wear-resistant material is used.

As best seen in Figures 4 and 5, each of the segments 10 is generally H-shaped in transverse section, having an upper flange 12 and a lower flange 14 separated by a vertical member 16 which serves as a drive vane for the slurry when the impeller is assembled. At the inner end, the opposite edges 18 of each segment 10 extend along radii of the impeller for a short distance and then curve through an angle of approximately 510 and continue in a straight line to the periphery of the impeller. In this way, when the segments 10 are assembled to form the insert 8, they are locked in position by adjacent segments.

The upper surface 20 of the base 4 is shaped to conform to that of the outer surface 22 of the lower flanges 14 of the segments 10, and the segments 10 are assembled on the base 4 to form the insert 8. The lower surface 24 of the cover plate 6 is shaped to conform to the outer surface 26 of the upper flanges 12 of the segments 10 and, when assembled, as seen in Figure 2, serves to lock the segments 10 in place. To form the completed impeller, the base 4, segments 10 and cover plate 6 are bonded together by suitable means, such as brazing.

In use, outer surface 28 of the base 4 and outer surface 30 of the cover plate 6 may be easily machined to provide tolerances, and the base 4 is formed with an axial opening 32 extending therethrough which may be easily machined to provide key slots, splines, etc., for attaching the impeller to a drive shaft. Slurry to be pumped enters the impeller through inlet openings 34 formed by the segments 10 of insert 8, and is engaged by the vertical members 16 of the segments 1 0 which serve as drive vanes, when the impeller is rotated, and drive the slurry radially outward through openings 36. Thus, the slurry is received and driven by the segments 10 of insert 8, which are formed of high temperature and wear-resistant material and has little, if any, contact with the base 4 and cover plate 6.

Thermal expansion differential between the hard insert and the steel base and cover plate is accommodated by the segmented insert construction. The base and cover plate may expand freely without restraint from the hard insert, the coefficient of thermal expansion of which is lower than that of steel. The segments will therefore "float" on the binding interface between the segments and the base and cover plate and will still be securely locked in place.

Claims

1. A composite pump impeller comprising a base, a cover plate, and an insert, sandwiched between the base and the cover plate, having a plurality of impeller drive vanes and being formed of a refractory wear resistant material which can be worked with substantially less ease than the base and cover plate.

2. An impeller according to claim 1, wherein the base and the cover plate are formed of steel.

3. An impeller according to claim 1 or 2 wherein the insert is formed of tungsten carbide.

4. An impeller according to claim 1 or 2, wherein the insert is formed of aluminium oxide.

5. An impeller according to any of claims 1 to 4, wherein the insert comprises a plurality of segments, each segment being of substantially H shaped cross section and comprising a pair of spaced apart members connected by one of the plurality of impeller drive vanes.

6. An impeller according to claim 5, wherein each of the segments is locked in position by a pair of adjacent segments

7. An impeller according to any of claims 1 to 6, wherein the insert is bonded to the base and the cover plate to form an integral structure.

8. An impeller substantially as described with reference to and as illustrated in the accompanying drawings.