EP3929444A1 - Centrifugal pump for conveying fluids containing solids - Google Patents

Abstract

The invention relates to a centrifugal pump for conveying media containing solids. The centrifugal pump comprises an open impeller (4) and a counter-element (2) that interacts with it. The surface of the counter-element (2) is at least partially provided with a carbon layer.

Description

The invention relates to a centrifugal pump for conveying media containing solids with an open impeller and a counter-element that interacts therewith.

Wastewater, especially municipal and industrial wastewater, is an example of a solid-containing medium. This usually includes raw sewage (e.g. dirty water, faeces), sewage (mechanically purified water from clarifiers), sludge (e.g. activated, fresh, digested and vaccinated sludge) and rainwater. Under certain circumstances, industrial wastewater can have a very corrosive or abrasive effect on the centrifugal pumps used, in particular on the components of the centrifugal pump that come into contact with the medium.

With centrifugal pumps for pumping media containing solids, different impellers can be used, for example channel impellers, vortex impellers or single impellers. An open impeller interacts in the pump chamber with what is known as a wear wall, which is fixed in the pump housing.

A free, unrestricted impeller passage is called a ball passage. It describes the largest permissible diameter of the solids in order to ensure a blockage-free passage. It is specified as a ball diameter in millimeters and corresponds at most to the nominal width of the suction or discharge nozzle.

The shape of the blade plays a decisive role in the design of open impellers. In particular, the design of the leading edge is of great importance. In sewage pumps, the leading edge is often covered with fibers that are present in the pumped medium. The fibers are usually not transported away from the leading edge of the impeller. If there is an accumulation of fibers on the leading edge, further fibers can accumulate, so that larger deposits form. This behavior is particularly beneficial when it comes to ensuring high ball passages. Especially when the centrifugal pump is operating at part load, large flow cross-sections lead to dead water zones that are not flowed through, which in turn lead to occupancy.

In the case of single-blade fans, such assignments mean that a higher output is required to operate the centrifugal pump. In the case of multiple blades, the occupancy can also lead to an asymmetrical flow in the canals. Such asymmetrical flows not only influence the required power, but also the volume flow to be conveyed and the delivery head to be achieved.

A cut edge at the inlet of the pump housing in the form of a leading edge or a cutting device on the pump impeller can be used to shred fibers in the solid-containing medium in order to avoid the formation of deposits.

In general, cast components are often used in centrifugal pumps. When casting, a solid body in the desired shape is created from a liquid material after it has solidified. In this way, the desired housing structures, wear walls or impellers of the centrifugal pump can be created in a targeted manner. Cast materials in centrifugal pump construction are usually iron-carbon alloys.

Particularly in the case of centrifugal pumps that are used to convey media containing solids, signs of wear and / or corrosion can occur in the area of the components that come into contact with the pumped medium. The flowing solids can remove the materials of the wear walls and the open impellers, whereby the gap between the components increases with increasing operation. As a result, the pump efficiency decreases with the duration of operation, until the wear wall has to be replaced.

In the DE 43 26 545 C2 describes a ceramic-based wear wall, in particular based on silicon carbide, which is manufactured by means of a slip casting process. This is positively embedded in the housing of a centrifugal pump and sealed with a rubber coating on the housing wall.

In the DE 10 2013 200 680 B4 describes a method for creating a wear wall. Here, the wear protection layer is introduced as a preform into a casting tool and then poured with a cast material, preferably with a metallic cast material.

the DE 10 2017 223 602 A1 specifies a pump housing in which instead of a wear wall in the pump housing, ceramic wear protection plates are arranged, which are already glued to metallic casting material in the casting tool before casting. These wear protection plates are preferably made of silicon carbide.

the DE 4409278A1 and the EP000000750686A1 disclose a chilled cast iron for pumps and fittings for conveying media containing solids with a composition in% by weight Cr = 26 to 36, Ni 10, Mo = 2 to 6, Cu 3, N 0.2, Si 1.5 , Mn ≤ 1.5, V = 4 to 9, C = 1.4 to 1.9, remainder iron and impurities from the melting process. This chilled cast iron is characterized by a high level of corrosion resistance in aggressive media and, at the same time, high wear resistance.

The wear walls based on silicon carbide are significantly harder compared to components made of gray cast iron and increase the service life. However, these components are considerably more complex and expensive to manufacture.

The object of the invention is to provide a centrifugal pump for pumping media containing solids. The damage to the pump housing due to abrasive wear is to be effectively reduced by a device. In addition, the pump should can maintain the efficiency in operation for a long time. Furthermore, a shredding edge on the wear wall should remain sharp-edged for as long as possible. The centrifugal pump should be characterized by high reliability and a long service life. It should also ensure simple assembly. Furthermore, the centrifugal pump should convince through the lowest possible manufacturing costs.

According to the invention, this object is achieved by a centrifugal pump for conveying media containing solids with the features of claim 1. Preferred variants can be found in the subclaims, the description and the figures.

According to the invention, a centrifugal pump for conveying media containing solids comprises an open impeller and a counter-element that interacts with it, the surfaces of which are coated with a carbon layer to protect against abrasive action.

The counter-element is advantageously designed as a wear wall which is fastened in the pump housing in an easily replaceable manner and protects the pump housing from wear. The wear wall can be designed in the form of a hollow cone segment or a trumpet funnel-shaped, hollow segment. According to the invention, the surface of the wear wall is provided with a carbon layer, which gives the wear wall an extremely high hardness. As a result, the wear wall, which is subject to an enormous abrasive effect when pumping media containing solids, is effectively protected against wear.

Media containing solids, especially waste water, often contain long-fiber elements and fibrous braids that can clog a centrifugal pump. The wear wall advantageously has a cutting groove in order to cut long-fiber elements and plait-like impurities in the conveying medium into small pieces. Ideally, this effectively prevents the centrifugal pump from clogging.

The cutting groove of the wear wall is preferably coated with carbon. This gives the cutting edge of the cutting groove a special hardness and a wear-resistant sharpness, which also withstands the abrasive effect of small solid particles in the long term.

In an advantageous variant of the invention, the cutting groove runs spirally from the inside to the outside. In its course, it thereby encloses an angle of more than 150 °, preferably more than 170 °, in particular more than 190 ° and / or less than 320 °, preferably less than 300 °, in particular less than 280 °. The cutting groove is designed in such a way that it has a depth of more than 0.5 mm, preferably more than 1.0 mm, in particular more than 1.5 mm and / or less than 5.0 mm, preferably less than 4 mm, in particular is less than 3.0 mm. Furthermore, the width of the cutting groove is adapted to the wear wall inside diameter of the suction side, so that it is more than 5%, preferably more than 10%, in particular more than 15% and / or less than 40%, preferably less than 35%, in particular less than 30% of the inside diameter of the suction side. Due to the shape described and the carbon coating, the cutting groove is particularly well suited to crushing long-fiber and pigtail-shaped elements in the conveying medium and protecting the centrifugal pump from clogging.

According to the invention, the open impeller of the pump interacts with the wear wall, so that the smallest possible gap is created between the wear wall and the open impeller, which is called the power gap. This gap is kept as small as possible in order to avoid undesired flows from the pressure side to the suction side of the pump. Both the impeller and the wear plate are coated with a carbon layer, which means that the surfaces of the components are extremely hard. As a result, the components are also protected against mutual contact or rubbing, which could well occur due to the small gap width.

Ideally, the wear wall is made of a metallic material, preferably a cast material and / or a stainless steel material. As a result, there are only minor limits to the geometric design of the wear wall At the same time, most metallic materials are characterized by a higher ductility compared to ceramic materials and a more cost-effective realization.

In particular the surface forming the power gap and in particular the cutting groove of the wear wall are provided with a carbon layer according to the invention. The cutting groove in particular is exposed to abrasive loads due to the formation of fibrous deposits and the colliding of solid particles and is particularly protected by the carbon layer.

In a centrifugal pump for pumping media containing solids, the wear wall interacts with an open impeller. According to the invention, such an open impeller can be an open diagonal single impeller or an open channel impeller. It is particularly advantageous to coat the open impeller with carbon, which provides effective protection against abrasive wear and enables the longest possible operating time with constant pump efficiency.

According to the invention, a centrifugal pump with an open diagonal single impeller, which is provided with a carbon layer, is used to convey media containing solids. In this impeller, the flow line of the blade runs obliquely outwards. In this way, uncleaned, solids-laden and outgassing wastewater and media with a higher viscosity can advantageously be conveyed.

The carbon layers are understood to be layers in which carbon is the predominant component. The carbon layer can be applied, for example, with a PVD (Physical Vapor Deposition), a physical vapor deposition, for example by evaporation or sputtering) or a CVD (Chemical Vapor Deposition) method.

It is preferably an amorphous carbon layer, in particular a tetrahedral, hydrogen-free amorphous carbon layer, also known as a ta-C layer referred to as. The atomic bonds belonging to the crystal lattice of graphite (3 in total) are identified with the designation "sp2". There is an sp2 hybridization.

In a diamond layer, each carbon atom forms a tetrahedral arrangement with four neighboring atoms. With this spatial arrangement, all atomic distances are equally small. There are therefore very high binding forces between the atoms, in all spatial directions. This results in the high strength and extreme hardness of the diamond. The atomic bonds belonging to the crystal lattice of diamonds, four in total, are identified with the designation "sp3". There is thus an sp3 hybridization.

In a particularly favorable variant of the invention, the carbon layer consists of a mixture of sp3 and sp2 hybridized carbon. This layer is characterized by an amorphous structure. Foreign atoms such as hydrogen, silicon, tungsten or fluorine can also be built into this carbon network.

The arrangement according to the invention of a carbon layer on a wear wall and an open impeller leads to a considerable reduction in the abrasive removal.

By arranging a carbon layer on a wear wall, a smooth axial surface with non-stick properties is created without the need for complex mechanical reworking of the impeller. Furthermore, several wear walls can be installed in a coating reactor, which is preferably designed as a vacuum chamber, where the ta-C coating is applied under moderate thermal stress. The centrifugal pump according to the invention with a wear wall is thus distinguished by relatively low manufacturing costs.

In a particularly favorable variant of the invention, the carbon layer is applied as a coating to a wear wall. The thickness of the layer is advantageously more than 0.5 μm, preferably more than 1.0 μm, in particular more than 1.5 µm. Furthermore, it proves to be favorable if the carbon layer is less than 18 μm, preferably less than 16 μm, in particular less than 14 μm.

A layer thickness between 4 and 12 µm should be aimed for to protect against particle wear and tarnishing.

Ideally, the carbon coating has an extremely smooth surface with non-stick properties, in which the mean roughness value R _{a of} the carbon layer is less than 0.7 μm, preferably less than 0.5 μm, in particular less than 0.3 μm.

The ta-C coating has a very low coefficient of friction and, at the same time, very good chemical resistance. The hardness of the coating comes very close to the hardness of diamonds, the hardness preferably being more than 20 GPa, preferably more than 30 GPa, in particular more than 40 GPa and less than 120 GPa, preferably less than 110 GPa, in particular less than 100 GPa .

With an average of 40 to 75 GPa, ta-C coatings are harder than a-C: H coatings. In addition, ta-C does not contain any hydrogen. It can therefore be assumed that ta-C is more stable in contact with water (at temperatures above 80 ° C) than a-C: H. In contact with other - especially polar - liquids that contain molecules in which hydrogen is bound, ta-C could also be more resistant than a-C: H.

The carbon layer is preferably not applied directly to the wear wall, but instead an adhesion promoter layer is provided. This preferably consists of a material that both adheres well to steel and prevents carbon diffusion, e.g. B. through the formation of stable carbides. Thin layers of chromium, titanium or silicon are appropriately used as bonding layers that meet these requirements. In particular, chromium and tungsten carbide have proven useful as adhesion promoters.

In an advantageous variant of the invention, the coating has an adhesion promoter layer, which preferably contains a chromium material. The adhesion promoter layer preferably consists of more than 30% by weight, preferably more than 60% by weight, in particular more than 90% by weight, of chromium.

The ta-C coating according to the invention is a simple, quickly realizable and economical coating for wear walls in centrifugal pumps. In addition to being very hard, the coating according to the invention also has excellent sliding properties and good chemical resistance.

In addition, the invention also enables wear wall geometries to be coated with special dimensions. In addition, wear wall geometries can be realized that were previously difficult to achieve from ceramic materials due to manufacturing reasons.

The advantage of the higher hardness due to the ta-C coating is based on the fact that small and large solid particles, which are often contained in the solid-containing media, can now have a greatly reduced abrasive effect on the wear wall. Due to the flow, these solid particles usually act like an abrasive. Impellers and wear walls coated with ta-C have an extremely hard protective layer against abrasion, which significantly increases their service life in pumping media containing solids.

PECVD / PACVD processes can preferably be used for coating. Plasma excitation of the gas phase takes place by coupling in pulsed DC voltage, medium-frequency (KHz range) or high-frequency (MHz range) power. For reasons of maximized process variability with different workpiece geometries and loading densities, the coupling of pulsed DC voltage has also proven its worth.

Ideally, PVD processes are used for coating. These processes are particularly simple and have a low process temperature. This technology leads to layers in which foreign atoms can also be incorporated as required. The process is preferably carried out in such a way that changes to the structure and dimensions of the materials to be coated (metallic, gray cast iron, etc.) are excluded.

Compared to a CVD diamond layer, the ta-C coating has the advantage that the coating temperature for CVD diamond layers is 600 to 1000 ° C and for amorphous carbon layers such as ta-C is significantly below 500 ° C. This is of particular technical relevance for the coating of metallic materials. The production of PVD diamond layers is not possible.

Further features and advantages of the invention emerge from the description of exemplary embodiments with reference to the drawings and from the drawings themselves.

Fig. 1

Schnittdarstellung einer Kreiselpumpe zur Förderung feststoffhaltiger Medien mit einem offenen diagonalen Einschaufelrad,

Fig. 2

Schnittdarstellung einer Kreiselpumpe zur Förderung feststoffhaltiger Medien mit einem offenen Laufrad,

Fig. 3

Detailschnitt eines offenen Laufrads mit Schleißwand,

Fig. 4

Frontansicht der Schleißwand.

It shows:

Fig. 1

Sectional view of a centrifugal pump for pumping media containing solids with an open diagonal single impeller,

Fig. 2

Sectional view of a centrifugal pump for pumping media containing solids with an open impeller,

Fig. 3

Detail section of an open impeller with wear wall,

Fig. 4

Front view of the wear wall.

Fig. 1 shows a sectional view of a centrifugal pump for conveying media containing solids. This embodiment is a horizontally positioned volute casing pump with a diagonally open impeller 4 and a counter-element 2 interacting therewith. In this embodiment, the counter-element 2 is designed as a wear wall. The medium containing solids flows into the pump via the suction mouth 1 and is controlled by the open diagonal impeller 4, which is rotatably connected to the shaft 6, charged with kinetic energy and leaves the pump housing 3 via the pressure port 5. The shaft 6 is rotatably supported by the ball bearing 7 and the mechanical seal 9. The bearing support cover 10 closes the pump chamber in the direction of the drive. The blade edges 13 of the diagonally open single-blade wheel 4 form a gap with the wear wall, the so-called power gap. Ideally, the wear wall is coated with a carbon layer, preferably with an amorphous carbon layer, in particular with ta-C. Thus, a particularly ideal protection against abrasive wear, which inevitably acts on the wear wall when conveying media containing solids, is achieved. The wear wall has a spiral-shaped cutting groove 12 running from the inside to the outside.

Fig. 2 shows a sectional view of a centrifugal pump for conveying media containing solids. This exemplary embodiment is a thick matter pump in which an open impeller 4 interacts with a counter element 2. In this exemplary embodiment, the counter element 2 is designed as a wear wall. The wear wall is used to protect the pump housing 3 against wear and can easily be replaced. Furthermore, the wear wall is provided with a carbon layer in order to be particularly wear-resistant against the abrasive effect of the solid-containing medium. The medium containing solids is sucked in via the suction mouth 1 and accelerated by the open impeller 4, which is non-rotatably connected to the shaft 6 and is rotatably supported by the bearing 7. The medium containing solids leaves the pump housing 3 via the pressure port 5.

Fig. 3 shows a detailed section of the suction mouth area. In this application example, the counter element 2 is designed as a wear wall and interacts with the open impeller 4. The blade flanks of the open impeller 4 extend, starting from the hub, radially outwards in a backward curve. The blade edges 13 form a gap with the wear wall. According to the invention, the wear wall is coated with a carbon layer, in particular with ta-C. This ensures effective protection against abrasive wear and against tarnishing of the two components.

Fig. 4 shows a front view of the counter element 2, which is designed as a trumpet funnel-shaped, hollow wear wall. The wear wall has a spiral-shaped cutting groove 12 running from the inside to the outside. In its spiral course, the cutting groove 12 encloses an angle of more than 150 °, preferably more than 170 °, in particular more than 190 ° and / or less than 320 °, preferably less than 300 °, in particular less than 280 °. The depth of the cutting groove 12 is more than 0.5 mm, preferably more than 1.0 mm, in particular more than 1.5 mm and / or less than 5.0 mm, preferably less than 4 mm, in particular less than 3.0 mm. The cutting groove 12 has a width of more than 5%, preferably more than 10%, in particular more than 15% and / or less than 40%, preferably less than 35%, in particular less than 30% of the inside diameter of the wear wall on the suction side . According to the invention, the wear wall and in particular the cutting groove 12 are coated with a carbon layer, in particular with ta-C.

This makes the surface of the wear wall particularly hard and wear-resistant against the abrasive effects of media containing solids. In particular, the cutting groove remains extremely sharp thanks to the edge coated with ta-C and can therefore cut long-fiber or pigtail-shaped elements that may be contained in the conveying medium into small pieces. This effectively prevents the centrifugal pump from clogging.

Claims (13)

Centrifugal pump for pumping media containing solids with an open impeller (4) and a counter-element (2) that interacts with it,
characterized,
that the surface of the counter element (2) is at least partially provided with a carbon layer. Centrifugal pump according to Claim 1, characterized in that the counter-element (2) is designed as a wear wall. Centrifugal pump according to Claim 1 or 2, characterized in that the counter-element (2) is designed in the form of a hollow cone segment. Centrifugal pump according to one of Claims 1 to 3, characterized in that the counter-element (2) is designed as a trumpet funnel-shaped, hollow segment. Centrifugal pump according to one of Claims 1 to 4, characterized in that the counter-element (2) has a cutting groove (12). Centrifugal pump according to one of claims 1 to 5, characterized in that the cutting groove (12) runs spirally from the inside to the outside and at an angle of more than 150 °, preferably more than 170 °, in particular more than 190 °, and / or less than 320 °, preferably less than 300 °, in particular less than 280 °. Centrifugal pump according to one of claims 1 to 6, characterized in that the cutting groove (12) has a depth of more than 0.5 mm, preferably more than 1.0 mm, in particular more than 1.5 mm and / or less than 5, 0 mm, preferably less than 4 mm, in particular less than 3.0 mm. Centrifugal pump according to one of claims 1 to 7, characterized in that the width of the cutting groove (12) is more than 5%, preferably more than 10%, in particular more than 15%, and / or less than 40%, preferably less than 35% , in particular less than 30%, of the inner diameter of the suction side. Centrifugal pump according to one of Claims 1 to 8, characterized in that the counter-element (2) is made of a metallic material, preferably a cast material and / or a stainless steel material. Centrifugal pump according to one of Claims 1 to 9, characterized in that it is an amorphous carbon layer. Centrifugal pump according to one of Claims 1 to 10, characterized in that it is a tetrahedral, hydrogen-free amorphous carbon layer. Centrifugal pump according to one of claims 1 to 11, characterized in that the thickness of the carbon layer is more than 0.5 µm, preferably more than 1.0 µm, in particular more than 1.5 μm and / or less than 18 μm, preferably less than 16 μm, in particular less than 14 μm. Centrifugal pump according to one of Claims 1 to 12, characterized in that the surface hardness of the surface of the counter-element (2) coated with carbon layer is more than 20 GPa, preferably more than 30 GPa, in particular more than 40 Gpa, and / or less than 120 GPa, is preferably less than 110 GPa, in particular less than 100 Gpa.

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