US2310629A - Protection of pump surfaces - Google Patents

Description

1943' D. VAN DER MERWE HAAQHOFF 2.310.629

PROTECTION OF PM? SURFACES Filed May 16, 1939 2 Sheets-Sheet 1 M T. N E V m 8v IMQM M A TTYS,

Feb; 1943' D. VAN DER MERWE HAAI QHOFF 2.310.629

PROTECTIQN OF PUMP SURFACES Filed May 16, 1939 2 Sheets-Sheet 2 53 INVENTOR UV. 0. M. HAARHOFF ATTYS Patented Feb. 9, 1943 UNITED STATES PATENT F ICE PROTECTION OF PUMP SURFACES Application May 16, 1939, Serial No. 274,055

" Claims.

This application is a continuation in part of my application for Letters Patent Serial Number 184,666, filed January 12, 1938.

The present invention relates to centrifugal pumps for transporting liquid or pulp containing sand, gravel or like abrasive matter. In such pumps the liquid or pulp has a considerable erosive effect on the impeller and other portions of the pump exposed thereto, which effect is very great when pumping under considerable pressures, even in cases where the proportion of abrasive matter is small.

One object of the present invention is the provision of centrifugal pumps of the aforespecified kind having working surfaces which are better suited to withstand the erosive eflect of the liquid or pulp than those of the hitherto commonly used pumps.

Another object of the invention is the provision of methods for producing such working surfaces.

According to the invention, in a centrifugal pump for transporting liquid or pulp containing sand, gravel or like abrasive matter, exposed interior portions of the pump are provided with wear-resistant working surfaces comprising a resiliently yielding bonding medium comprising rubber, and hard and tough wear-resistant granular material distributed in said medium.

The wear resistant material may consist, forv example, of quartz grit, emery, carborundum, corundum, flint, bauxite carbides, silicides and like natural or synthetic substances of a hard and tough character which are commonly used as abrasives. The size of the grains is not critical and the best size for each kind of pump can readily be found by experiment.

It appears that in the surface layers constituting the Working surfaces of the invention the hard and tough material covers and shields the rubber and thus decreases to a substantial extent wear of the rubber; whilst the elasticity of the rubber decreases to a substantial extent wear of the hard material, as it permits the hard particles to recede when exposed to the impact of abrasive grains and thus to diminish the abrasive force acting upon them and thereupon to return to their original positions; and it has been proved that the surface layer of the invention wears off, under the same conditions, at a very considerably slcwer rate than the known coatings consisting of rubber or of hard and tough wearresistant material without an elastic rubber bond.

The wear-resistant surface layer of the invention may be provided by preformed sheets or rings which are subsequently secured to the pump portions which are to be protected. A very important advantage of the invention, however, consists in that it permits of building up in situ a wear-resistant surface layer firmly attached to the exposed pump portions without the necessity of heating such portions or applying pressure.

Accordingly the invention also comprises a method for protecting exposed portions of centrifugal pumps subjected to abrasion which consists in applying the aforesaid surface layer by building it up on the exposed portions with the use of plastic and/or liquid material.

The best manner of carrying out this method will depend on the nature of the pump portions which is to be coated, on the intended thickness of the wear-resistant surface layer and on other factors, and may be varied in its details to suit any particular case.

In its preferred form, the method comprises the steps of preparing the pump portion to receive the surface layer, for instance, by applying at least one thin primer coat; applying to the resulting thin coat, while it is still in an adhesive condition, one or more coats of a solution containing cold vulcanizing rubber, applying a coat of primer solution on to the rubber coat or on to the last rubber coat while the latter is still in an adhesive condition, sprinkling the granular material on to the primer coat, and applying, pref.- erably immediately, to the granular material, a further coat of primer solution, the last said two primer coats promoting adherence between the granular material and the rubber. The thickness of the surface layer may be increased by increasing the number of rubber coats and, if desired, also the number of coats of granular material. In pumps the interior portions of which are exposed to high pressures, the thickness of the resistant surface layer should not exceed of an inch.

If the pump portion to be protected consists of a copper alloy such as bronze it is preferred to coat it with a thin layer of pure iron or other ferrous metal, as by spraying; and to apply the protective surface layer in the aforesaid manner to the iron coating.

The term solution containing cold vulcanizing rubber is intended to mean throughout the specification and claims a solution which, upon evaporation of the solvent, leaves a coating comprising solid rubber which is either fully vulcanized or vulcanizes by itself within a short time without artificial application of heat.

. such solutions generally comprise rubber, sulphur, an activator, an accelerator and fillers and may be of the latex or of the benzol type. The manner of compounding such solutions so as to produce grades of rubber differing in elasticity, hardness and the like is well known in the art. For example, a latex solution suitable to yield, on evaporation of the water, a very tough and highly resilient rubber may comprise about 50% of rubber, from 5% to 2% and preferably 3% sulphur, 3% zinc oxide and an ultra-accelerator. Suitable rubber solutions are marketed under the trade names Airvulc Liquid Rubber, Selfvulc Plastic Rubber" and Selfvulc Liquid Rubber."

Primer solutions are equally well known and may comprise natural or artificial resins, chlorinated rubber or rubber derivatives of resinous character, bitumen or the like and/or rubber and suitable curing or vulcanizing agents. Suitable primers are marketed, for example under the trade names Selfvu1c M Primer and "Malacca 101 Primer.

In another form the method of the invention comprises the steps of mixing a liquid or plastic composition containing e. g. about 40% to 60% of cold vulcanizing rubber and a suitable solvent with the granular material in, for example, equal volumes, applying the resulting mixture to the pump portion, which is previously coated with primer, and coating the thus produced surface, while it is still in adhesive condition, with a coat of primer solution. This manner of applying the protective coating is particularly suitable when coatings of greater thickness are desirable.

In another way of carrying out the method of the invention non-self-vulcanizing rubber solutions are used and the coats are vulcanized by exposing them to sulphur chloride or in a similar manner. These solutions may be used, except for the vulcanization step, in substantially the same way as aforedescribed with reference to solutions containing cold vulcanizing rubber.

The rubber solutions may be applied by painting, spraying, dipping or in any other known manner suitable for the purpose of the invention.

For attaining a high degree of resistance against abrasion it is essential that the grains of the wear-resistant material form a material portion of the exposed surface of the wear-resistant layer; that they be evenly distributed and be spaced from one another and that each grain be eleastically cushioned by the rubber.

The term "rubber is intended to include rubber and similar substances suitable to constitute a rubber-like highly resilient, tough, bonding material.

In some cases it is advantageous to interpose between the pump portion to be protected and the wear-resistant surface layer a thin preformed sheet of rubber. Said preformed sheet may be secured to the pump portion by a suitable cement, e. g. primer solution; the wear-resistant surface layer being built upon said sheet according to the aforedescribed method of the invention.

Embodiment of the invention will now be described, by way of example, reference being made to the accompanying drawings comprising Figures I and IV.

Figure I is a cross-section in a vertical plane through part of a multi-stage centrifugal pump for lifting gritty liquid against a considerable head.

Figure II is a cross-section through portion of the impeller 3 of the pump of Figure I along the line II--II.

Figure III is a cross-section through portion of the impeller 2 of the pump of Figure I along the line III-III.

Figure IV is a cross-section in a vertical plane through a centrifugal pump for transporting sand pulp,

The part of the multi-stage centrifugal pump shown in Figure I has two impellers 2, 3 feathered on a common shaft 4 which is supported in bearings arranged outside the pump casing. The gritty liquid to be pumped enters at 5 into the first impeller 2. The liquid discharged by the first impeller 2 enters the difiuser guide 6 which leads the liquid into the diffuser passage 1 which in turn leads the liquid inwardly to the eye of the second impeller 3. The liquid discharged by the second impeller 3 enters the second diffuser guide 8 from which it passes out of the pump via the delivery pipe 9. The shaft 4 is prevented from being moved in an endwise direction by the axial thrust exerted by the liquid, by the provision of a stationary seating plate [0 which is rigidly secured to the casing of the pump and bears at its periphery against a balancing disc H which is fixed on and revolves with the shaft 4. Renewable metal wearing rings l2 and I3 are inset into the plate l0 and disc Ii respectively. The space l4 enclosed by it) and ii is supplied with liquid under pressure from the second impeller 3 through the clearance between the suction boss of the impeller 3 and the boss of the seating plate ID. This liquid passes out between the peripheries of i0 and II into the balancing chamber l5 and then through a connecting pipe back to the suction end of the pump. The balancing disc II is extended to form a wearing sleeve l6 which fits over the shaft 4 where it passes through the packing ll.

Due to the flow of gritty liquid through the pump, the portions of the pump exposed thereto will rapidly become worn away when constructed of metal as is the usual practice. Wear is particularly rapid in places where the liquid has a high velocity and/or pressure, and the usual practice is to arrange that those portions subjected to rapid wear are replaceable e; g. the impellers 2, 3 wearing rings [2, I3 and wearing sleeve I6. for the same reason the sealing surfaces leading i'rom the impellers to the diffusers are formed by replaceable eye rings l8 and the sealing surfaces leading from the diffusers to the impellers are formed by replaceable suction rings [9. These exposed portions require particular protection again erosion.

The aforesaid portions or some of them are provided with wear-resistant surface layers 20 of the specified kind. Said surface layers may be built up as follows: The exposed pump portions are first cleaned with petrol, benzine or other cleansing agent, or by sandblasting. Their clean metal surface is then given three coats of a primer solution, about an hour being allowed between each coat to permit it to set. The resulting primer layer is then given three coats of a solution containing cold vulcanizing rubber. Each coat is allowed to set before the next is applied, about 2 /2 hours being usually suflicient. Thereupon a coat of primer solution is applied to the last rubber coat and granular material is sprinkled onto the primer while the latter is still in an adhesive condition; finally, a further coat of primer solution is applied on top of the granone of them,

ular material in order to incorporate it firmly with the rubber. When the exposed pump portions are easily accessible, as for example, the outside of an impeller, the successive coats may be applied by painting; when they are not easily accessible, as for example, the inside of an impeller, the coats may be applied by spraying or by submerging the part successively in the various coating liquids, one of lar material in suspension.

When two exposed pump portions bear upon each other, as for example, the portion l9 and the impeller inlet boss, it is preferred to provide only preferably the one presenting a concave surface, with a wear-resistant surface layer 20 of the specified kind and to provide the other with a coating 2| consisting of ordinary rubber.

As indicated in Figure I, it is preferred to apply wear-resistant surface layers 20 to substantially all the interior portions of the pump including the diffuser passages and the discharge pipe 9. The impeller vanes 22 (Figure III) may have a wear-resistant surface layer 20 applied to both their surfaces but it is generally sumcient to apply such layer to the working surface of the impeller only; in this case the surface layer 20, should, however, extend over the top of the vanes as indicated in Figure III.

Figure IV shows a sand pump having a suction passage 23 and a delivery passage 24, the sand pulp being transported from 23 to 24 by an impeller 25 secured to a shaft 26 provided with a wearing sleeve 21, where it passes through the packing 28. The impeller 25, suction passage 23, delivery passage 24 and the inner walls of the pump casing 29 are protected against erosion by wear-resistant surface layers 20 of the specified kind which may be produced as described in connection with Figure I. In addition the wearing sleeve 21 is grooved at one side of the packing 28 and a wear-resistant surface layer of the spoolfled kind is built up in the groove as indicated at 30 so as to prevent wear due to sandy water leaking along the sleeve 21.

Protective coating comprising a layer of vulcanized sponge rubber and a layer of wear-resistant granular material arranged on top of and bonded to said sponge rubber, are claimed in my Letters Patent No. 2,165,955. Pumps provided with protective coatings comprising a layer or which contains the granulayers of sponge rubber are excluded from the scope of the appended claims.

I claim:

1. A centrifugal pump, for transporting liquid or pulp containing said, gravel and the like abrasive matter, the working surfaces of which are provided by a surface layer comprising a resiliently yielding bonding medium comprising rubber, and hard and tough wear-resistant granular material distributed in said medium.

2. A centrifugal pump, for transporting liquid or pulp containing sand, gravel and the like abrasive matter, the working surfaces of which are provided by a surface layer comprising a resiliently yielding bonding medium comprising rubber, and hard and tough wear-resistant granular material distributed in said medium; adherence between the granular material and the rubber being promoted by means of primer material.

3. A centrifugal pump for transporting liquid or pulp containing sand, gravel and the like abrasive matter, the working surfaces of which are provided by a resiliently yielding surface layer comprising a plurality of primer and rubberlayers and at least one layer of hard and tough,

granular, wear-resistant material arranged on top of the rubber layers.

4. A centrifugal pump as claimed in claim 1, in which the wear-resistant granular material belongs to the group comprising quartz, grit,- emery, corundum, bauxite, carborundum and other carbides and silicides of a hard and tough character which have pronounced abrasive properties.

5. An impeller for a centrifugal pump, said impeller having working surfaces provided by a surface layer comprising a resiliently yielding bonding medium comprising rubber, and hard and tough wear-resistant granular material distributed in said medium.

,6. A casing for a centrifugal pump, the working surfaces of said casing being provided by a surface layer comprising a resiliently yielding bonding medium comprising rubber and hard and tough wear-resistant granular material distributed in said medium.

7. In a centrifugal pump, for transporting liquid or pulp, containing sand, gravel and the like abrasive matter, working surfaces comprising hard and tough wear-resistant granular material which is resiliently bedded and bonded.

DANIEL wuv mm MERWE HAARHOFF.

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