US2422412A - Protection of pump surfaces - Google Patents

Description

Jun 17, 1947.

D. VAN DER MERWE HAARHOFF 2,422,412

PROTECTION OF PUMP SURFACES Original Filed May 16, 1939 2 Sheets-Sheet 1 June 17, 1947 D. VAN DER MERWE HAARHOFF 2,422,412

PROTECTION OF PUMP SURFACES Original Filed May 16, 1939 2 Sheets-Sheet 2 A Z6 27 I 2 9 14. 26 I F a I Wan a.

Patented June 17, 1947 UNITED STATES FTENT OFFICE ROTECTION OF PUMP SUBFAQES Orig nal application May 16, 1939, Serial No.

Divided and this application February 2%, 1942, Serial No. 432,137. In the Union of South Africa December 18, 1937 3 Claims. 1

This application is a division of application Serial No. 274,055 filed May 16, 1939.

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

According to the invention, in a centrifugal pump for transportin liquid or pulp containing sand, gravel or like abrasive matter, exposed in terior portions of the pump are provided with a wear-resistant surface layer 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, for 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 rains is not critical and the best size for each kind of pump can readily be found by experiment.

It appears that in the surface layer of the invention the hard and tough material covers and shields the rubber and thus decreases to a sub stantial 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 sameconditions, at a very considerably slower rate than the known coatings consisting of rubber or of hard and tough wear-resistant 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 wearsresistant 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 c0nsists 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 portion 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 thesteps 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 vulcanizin rubber, applying a coat of primer solution on to the rubber coat or on to the last rubber coat while the lat ter is still in an adhesive condition, sprinkling the granular material on to the primer coat, and applying, preferably immediately, to the granular material, a further coat of primer solution, the last said two primer coats promoting adherence bet-ween the granular material and the'rubher. 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 3% 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.

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 Selfvulc 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 elastically 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 and more particularly sponge 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 up on said sheet according to the aforedescribed method of the invention.

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

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

Figure IV is a cross-section in a vertical plane through a centrifugal pump for transporting sand The part of the multi-stage centrifugalpump 4 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 5 impeller 2. The liquid discharged by the first impeller 2 enters the diifuser 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 H) 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 E. Renewable metal wearing rings I2 and [3 are inset into the plate iii and disc I I respectively. The space Hi enclosed by ID 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 Hl.

This liquid passes out between the peripheries of ii) and ii into the balancing chamber l5 and r then through a connecting pipe back to the suction end of the pump. The balancing disc ii is extended to form a wearing sleeve I6 which fits over the shaft 4 where it passes through the packing l1. 7

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 ring l2, l3 and wearing sleeve l6. For the same reason the sealing surfaces leading'from the impellers to the diffusers are formed by replaceable eye rings is and the sealing surfaces leading from the diffusers to the impellers are formed by replaceable suction rings it. These exposed portions require particular protection against erosion. v a

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 sufllcient. 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 granularmaterial 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 which contains the granular material in suspension.

When two exposed pump portions bear upon .each other, as for example, the portion I9 and the impeller inlet boss, it is preferred to provide only one of them, 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 sufficient to apply such layer tothe 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 2! is grooved at one side of the packing 28 and a wear-resistant surface layer of the specified 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.

I claim:

1. A method of protecting a surface subjected to abrasion, comprising the steps of applying to solution, applying to the outermost rubber coat at least one further coat of a primer solution, sprinkling the outermost of said further coats, whilst it is still in adhesive condition, with hard and tough Wear-resistant granular material, and applying to said wear-resistant material at least one further coat of primer solution.

2. The method claimed in claim 1, in which the hard and tough granular wear-resistant material belongs to the group consisting of emery, Carborundum, corundum, flint, and siliceous abrasive materials.

3. A method of providing centrifugal pumps, for transporting liquid or pulp, containing sand, gravel and the like abrasive matter, with wearresistant working surfaces, comprising the steps of applying to exposed inner portions of such pumps at least one coat of primer solution which is suitable to bond rubber to metal and is also suitable to bond hard and tough granular material to rubber, applying to the outermost primer coat when the latter is in an adhesive condition at least one coat of cold vulcanizing rubber solution, applying to the outermost rubber coat thus produced at least one further coat of a primer solution, sprinkling the outermost of said further coats whilst it is in an adhesive condition, with hard and tough wear-resistant granular material, and applying to said wear-resistant material at least one further coat of primer solution.

DANIEL VANVDER MERWE HAARHOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,165,955 Van der M. HaarhoffnJuly 11, 1939 1,254,156 Parsons Jan. 22, 1918 1,271,072 Parsons July 2, 1918 2,290,905 Butler July 28, 1942 2,310,629 I-Iaarhoff Feb. 9, 1943

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