GB2141175A

GB2141175A - Preventing wear in centrifugal pumps

Info

Publication number: GB2141175A
Application number: GB08413009A
Authority: GB
Inventors: Georg Peszt; Edgar Jedon
Original assignee: Iveco Magirus AG
Current assignee: Iveco Magirus AG
Priority date: 1983-06-08
Filing date: 1984-05-22
Publication date: 1984-12-12
Also published as: GB8413009D0; FR2547367B3; FR2547367A3; DE8316668U1; GB2141175B

Abstract

The pump impeller 2 has on its sealing positions (3, 4) and/or its supporting positions a metallic, wear-resistant firmly-adhering protective coating, sprayed on preferably by a flame-spraying process. By this means, a relatively expensive impeller can be given a light-weight anti-wear coating, particularly at the most severely tested places, where there is a danger of erosion or cavitation. <IMAGE>

Description

SPECIFICATION Centrifugal pump This invention relates to a centrifugal pump with at least one impeller supported and sealed in a housing.

The positive pressure at the delivery outlet of an impeller in a centrifugal pump calls for sealing positions between the inner and outer impeller circumferences, as without them, back flows or leakage losses will occur. These leakage or clearance losses can develop, in particular, between the impeller and the suction cover on the impeller intake, between the vanes and the housing in the case of open wheels, at the stuffing box and axial force equalizers and between adjoining stages of a multi-stage centrifugal pump.

In order to keep leakage or clearance losses as low as possible, the clearance between the rotating and the fixed parts are kept as small as possible. This carries with it the serious danger that, should the fluid medium become contaminated, foreign bodies get into the fine clearance gaps which after a short while, thereby produce local overheating so that seizure of the parts may occur, and the driving machine is brought to a halt.

To overcome this problem, it has already been proposed to have rings of wear-resistant material screwed, cemented or pressed into the housing or the impeller. Rings of this kind are intended as parts which are subject to wear, and can be replaced when excessive wear has occurred. Consequently, there is no need to replace the actual impeller or housing itself, which is relatively expensive to produce.

An aim of the present invention is to create a centrifugal pump with at least one impeller supported and sealed in a housing which is less subject to the drawbacks previously mentioned and, in particular, to produce a centrifugal pump, using simple means, which is specially resistant to wear, and which will in consequence have a relatively long life with reliability of operation.

Accordingly, in a centrifugal pump made according to the present invention, the impeller has at least on its sealing positions and/or positions of support, a sprayed-on metallic protective layer which is wear-resistant and firmly-adhering.

The metallic, wear resistant and firmly-adhering protective coating gives the advantage that the impeller, which is comparatively expensive to manufacture, may have a highly effective anti-wear coating of low weight, and at those places which are most severly tested, where erosion or cavitation may occur. It has been shown that with centrifugal pump impellers, the greater wear always occurs on the rotating part, the impeller, and not on the stationary (housing) part, or rings intended as parts which are subject to wear according to the state of the art described above. In the present invention, these rings can be dispensed with. The application or spraying-on may be effected by the so-called flame-spraying process, employing solid materials, which are both wear-resistant and non-rusting, and also exhibit a low stress difference with the part to which they are applied.The sealing positions, the positions of support or the clearances between the rotating and fixed parts where clearance losses may occur may be formed as long, restricting surfaces or as labyrinths. In order to inhibit a fusing together of the rotating part and the fixed part, it is desirable to use differing material surface hardnesses, so that the protective layer is made from a material having a surface hardness which is greater than the surface hardness of the adjacent stationary supporting and/or housing parts.

The protective coating preferably comprises metal oxides with a high resistance to wear, and should preferably be corrosion-resistant and have a low shrinkage coefficient. For example, it may comprise an alloy of oxides of aluminium, titanium and silicon and/or other oxides.

The protective layer can, if required, be treated by wet grinding, so as to obtain polished surface areas.

Contact non-slip coatings, which are sprayed on by a heat process, have previously been proposed for example in German Offenlegungsschrift 24 1 3 382. Sprayed-on protective coatings have, however, hitherto been intended for use on stationary components, and not on rotating parts such as impellers.

An example of a centrifugal pump made in accordance with the present invention is illustrated in the accompanying drawing, the only Figure of which shows a radical section through an impeller of the pump.

The impeller 2 has circumferential housing sealing positions 3 and 4 which extend in an axial direction.

Protective coatings of metal are sprayed on these sealing positions 3 and 4 and/or positions of support of the impeller by a flamespraying process. The coatings are wear-resistant and non-corrodible, and adhere firmly to the impeller. Before spraying is carried out, the surface of the impeller is suitably prepared, for example, by sand blasting or roughening by mechanical means. A nickel/aluminium protective layer of wire-shaped or filamentary metal is then sprayed on. This is followed, as a covering layer, by a protective coating 5 in powder form with the aid of a metal-spraying pistol at a distance in the range of substantially 70 to 200 mm. In the process, the metal to be applied is carried by a feed mechanism into a burner nozzle, where it is melted in an oxy-acetylene flame. The melting metal is atomized by a compressed air jet, and the sprayed particles are thrown on to the impeller in the desired places, where they stick together to form a dense sprayed-on coating.

Claims

1. A centrifugal pump with at least one impeller supported and sealed in a housing, in which the impeller has at least on its sealing positions and/or positions of support, a sprayed-on metallic protective layer which is wear-resistant and firmly-adhering.

2. A centrifugal pump according to claim 1, in which the protective layer comprises a non-rusting material.

3. A centrifugal pump according to claim 1 or claim 2, in which the protective layer is made from a material having a surface hardness which is greater than the surface hardness of the adjacent stationary supporting and/or housing parts.

4. A centrifugal pump according to any preceding claim, in which the protective layer comprises an alloy of oxides of aluminium, titanium and silicon and/or other oxides.

5. A centrifugal pump having an impeller substantially as described herein with reference to the accompanying drawing.