EP3929443A1 - Centrifugal pump for conveying media containing solids - Google Patents

Abstract

The invention relates to a centrifugal pump for conveying media containing solids. The centrifugal pump has an arrangement for reducing a backflow (13, 20) from a first space into a second space. Furthermore, the centrifugal pump comprises a closed impeller (4) which has a support disk (11) from which at least one blade (25) protrudes, which is covered by a cover disk (3) in such a way that at least one at least partially closed channel (26). The surface of the impeller (4) has at least a partial layer of carbon.

Description

The invention relates to a centrifugal pump for conveying media containing solids with an arrangement for reducing a backflow from a first space into a second space and a closed impeller.

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 the components of the centrifugal pump that come into contact with the medium.

The contact with the flowing, solid-containing medium can lead to an erosion of material in the centrifugal pump. This removal is also known as abrasion. Abrasion phenomena can seriously impair the functionality of the centrifugal pump. In particular, if there are additional particles in the flow, for example solid particles such as sand, this can lead to a large amount of material being removed. Wear-resistant materials are then absolutely necessary in order to minimize abrasion.

It is known that in centrifugal pumps for conveying highly abrasive media, the flow-guiding parts such as impeller, wear ring, wear wall, etc., are removed to manufacture corrosion-resistant non-metallic materials or to provide these parts with a coating of rubber, plastic or enamel. Conventional materials that are used are limited in terms of their strength or their corrosion resistance. Conventional materials also have only limited wear resistance when they come into contact with the flowing medium.

When pumping media containing solids, wear and tear on the impeller caused by the abrasive effect of the dirt particles and a so-called gap widening of an existing gap seal must also be expected.

Gap seals are used in centrifugal pumps to seal spaces with different pressures. The arrangement comprises a non-rotating element and a rotating element. The non-rotating element can be, for example, a split ring which is arranged on the housing, or the housing itself or a housing part. The rotating element can be, for example, a raceway which is arranged on the impeller, or the impeller itself or a part of the impeller, for example the cover disk of the impeller in the case of a closed impeller. In the case of wastewater centrifugal pumps with gap seals in particular, an increasing loss of efficiency due to abrasive wear is to be expected with increasing service life.

the DE 10 2017 223 602 A1 specifies an impeller of a circular pump with fittings based on silicon carbide. The hardness of the material is intended to protect the centrifugal pump from abrasive wear. For this purpose, various shaped pieces made of silicon carbide are placed in a casting tool and then filled with a metallic casting material, so that a closed impeller is formed.

the DE 10 2018 214 650 A1 describes a wear ring-bearing ring pair of a centrifugal pump based on calcium carbonate in the modification aragonite, which is more wear-resistant to abrasive substances due to its high hardness.

Due to the high brittleness of most abrasion-resistant ceramic materials, the proposed ceramic solutions are i. d. Usually very expensive and time-consuming to implement and can possibly lead to operational disruptions (for example by breaking off parts).

The object of the invention is to provide a centrifugal pump for pumping media containing solids with a wear-resistant impeller. Furthermore, damage to a race due to abrasive wear should be effectively reduced. In addition, the pump should be able to maintain its efficiency in operation for a long time. 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, the closed impeller of a centrifugal pump for conveying media containing solids is coated with a carbon layer on the surface, in particular the surface of the cover disk. This increases the hardness of the surface enormously, which creates efficient protection against abrasive wear caused by the flowing solid particles of the pumped medium.

The central component of a centrifugal pump is the impeller, which transfers the mechanical energy to the fluid as an impulse. The shape of the impeller determines how the flow exits the pump. With regard to the design of the impeller, a distinction is made between closed, semi-open and open forms. In the case of a closed impeller, at least one impeller blade is connected to a disk on each side. The front disk facing the inflow is called the cover disk. The rear disk, which is usually the structural origin of the blade, is called Support disc. By enclosing a blade with the cover and support disk, a closed channel is created which is aligned by the blade curvature.

For the sewage conveying task, closed impellers with a reduced number of blades and a large ball passage are suitable in order to avoid possible clogging by solid particles or clogging in the wastewater. For this purpose, closed single-blade wheels and / or closed one-, two- or three-channel wheels are ideally used. According to the invention, these impellers are coated with a carbon layer so that they have an extremely hard surface, which preferably provides ideal protection against abrasive and corrosive effects from media containing solids such as waste water.

In particular, the cover disk of a closed impeller advantageously has a carbon layer. The cover disk in particular comes into contact with the solid-containing medium first and is protected from abrasion by the hard carbon layer. In particular, the surfaces of the cover disk which, together with a split ring, form a seal for reducing backflow from the pressure into the suction space, have a carbon layer. In particular, these are radial and / or axial surfaces of the cover disk that are machined planar and have a carbon layer.

Ideally, the inner surface of a closed impeller, that is to say the inner walls of a channel that is formed by the support disk, the blade flank and the cover disk, also has a layer of carbon. In this way, the impeller surfaces are advantageously provided with a particularly hard protective layer against abrasion, which are directly involved in the impulse transmission of the impeller to the solid-containing medium.

According to the invention, a centrifugal pump for conveying media containing solids with at least one arrangement for reducing a backflow has a rotating element which at least partially has a layer of carbon. Such Arrangement for reducing a backflow can be designed according to the invention as a gap seal, which can be formed by a split ring and a race or by a split ring and corresponding surfaces of the cover disk of an impeller. This arrangement serves to seal off spaces with different pressures and acts as a throttle between these spaces. In this arrangement, a first space is to be understood as a space with higher pressure and a second space as a space with lower pressure. In the centrifugal pump, the space of higher pressure is accordingly the space of the pressure connection and the spiral housing. The space of lower pressure is the space of the suction area in front of the impeller.

In an advantageous variant of the invention, at least one raceway ring is arranged directly on the closed impeller on a radial and / or axial surface of the cover disk and forms a gap seal together with at least one split ring. This raceway ideally has a layer of carbon on at least one radial and / or axial surface. This increases the hardness of an ordinary race made of a cast material and / or a stainless steel material enormously, which in turn protects the surfaces that are involved in the formation of the gap seal from the abrasive effects of the solid-containing medium.

The gap ring of the gap seal, which corresponds to the running ring, is arranged on the pump housing by means of a press fit and is accordingly both stationary and non-rotating. As such, the split ring is arranged directly on the pump housing. The split ring advantageously has a carbon layer on a radial surface such as the inside of the split ring and / or on an axial surface such as the front side of the split ring. As a result, the hardness of an ordinary split ring made of a cast material and / or a stainless steel material is increased enormously. The split ring thus receives effective protection against the abrasive effects of solid particles in the pumped medium.

The carbon layer is of particular advantage with regard to touching or running against a raceway and the split ring that corresponds to it. Due to the particularly smooth surface of the carbon layer and its extraordinary hardness, the raceway is insensitive to the rubbing action of a split ring.

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, which is also referred to as a ta-C layer. 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 closed impeller and an element for preventing backflow, such as a race, leads to a considerable reduction in the abrasive removal.

By arranging a carbon layer on a closed impeller, in particular on the radial and / or axial surfaces of the cover plate, which are used to form a sealing gap, an extremely smooth surface with non-stick properties is created without the need for complex mechanical reworking of the impeller. Furthermore, several impellers can be placed 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 closed impeller 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 an impeller and / or to a race. 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.

Ideally, the carbon coating has an extremely smooth axial 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 aC: H coatings. In addition, ta-C does not contain any hydrogen. It can therefore be assumed that ta-C is more resistant than aC: H in contact with water (at temperatures above 80 ° C). In contact with other - especially polar - liquids that contain molecules in which hydrogen is bound, ta-C could also be more resistant than
Oh.

The carbon layer is preferably not applied directly to the impeller and / or the running ring, but rather an adhesion promoter layer is provided. 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 closed impellers and / or races 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 impeller geometries with special dimensions to be coated. In addition, impeller geometries can be implemented that were previously difficult to implement from ceramic materials due to manufacturing reasons. In particular, most metallic materials are characterized by a higher ductility in direct comparison to a ceramic material.

The advantage of the higher hardness due to the ta-C coating is due to 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 impeller and / or the raceway of the gap seal. Due to the flow, these solid particles usually act like an abrasive. Impellers and races of the gap seal, which are 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 are preferably 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 geschlossenen Einschaufelrad,

Fig. 2

Schnittdarstellung eines geschlossenen Dreikanalrads,

Fig. 3

perspektivische Darstellung eines geschlossenen Mehrkanalrads,

Fig. 4

Ausschnittsvergrößerung im Bereich des Saugmunds,

Fig. 5

Detailschnitt eines rotierenden Elements.

It shows:

Fig. 1

Sectional view of a centrifugal pump for pumping media containing solids with a closed single impeller,

Fig. 2

Sectional view of a closed three-channel wheel,

Fig. 3

perspective view of a closed multi-channel wheel,

Fig. 4

Enlarged section in the area of the suction mouth,

Fig. 5

Detail section of a rotating element.

Fig. 1 shows a sectional view of a centrifugal pump for conveying solids-containing media with an arrangement for reducing a backflow 13 from a first space into a second space. The arrangement 13 comprises a stationary, non-rotating element 2 which, in this exemplary embodiment, interacts with the closed single-blade wheel 4. The element 2 is designed as a split ring in this exemplary embodiment. The solid-containing medium flows into the pump via the suction mouth 1, is subjected to kinetic energy by the closed impeller 4, which is connected to the shaft 9 in a rotationally fixed manner by the attachment 12, and leaves the pump housing 10 via the pressure port 5. The shaft 9 is rotatably supported by the ball bearings 8. The bearing support cover 7 closes the pump chamber in the direction of the drive. According to the invention, the closed single impeller 4 is coated with a carbon layer, preferably with an amorphous carbon layer, in particular with ta-C. In particular, the cover disk 3 and the inner wall surfaces 11 of the closed single-blade wheel 4 have a layer of ta-C. A particularly ideal protection against abrasive wear and also against the closed single-blade wheel 4 running against the non-rotating element 2 is thus achieved.

Fig. 2 shows a sectional view of a closed three-channel wheel. The impeller 4 consists of a support disk 11, from which the blades, not shown, proceed protrude. A cover disk 3 closes the space of the blades with the support disk 11 in such a way that closed channels are formed. Furthermore, the cover disk 3 of the impeller 4 has an axial surface in the form of an impeller end face 23 and a radial surface 24, both of which are machined in a particularly planar manner. According to the invention, the impeller face 23 and the radial surface 24 are coated with a layer of carbon, in particular with ta-C. The impeller end face 23 and / or the radial surface 24 form a so-called gap seal with a stationary and non-rotating split ring, not shown, arranged in the pump housing. Due to the ta-C coating, the gap seal-forming surfaces of the impeller 4 are particularly protected against abrasive wear caused by the conveyance of a solid-containing medium and the associated loss of efficiency.

Fig. 3 shows a perspective illustration of a closed multi-channel wheel 4. Starting from the support disk 11, the blades 25 protrude in the direction of the media inflow. The cover disk 3 closes the space with the blades 25 and the support disk 11, so that at least one partially closed channel 26 is formed. According to the invention, the inner wall surfaces of the channel 26 have a ta-C coating, which protects the impeller 4 made of conventional cast material and / or stainless steel material against the abrasive effect of the flowing solid particles. In this way, standard impellers can be manufactured cost-effectively from known material and provided for highly abrasive applications by being coated with a carbon layer up to 18 µm thick. According to the invention, the impeller face 23 and the radial surface 24 are also coated with a layer of carbon, in particular with ta-C. These gap seal-forming surfaces of the cover plate 3, which with a split ring (not shown) form a gap to reduce a return flow from the pressure side to the suction side of the centrifugal pump, are particularly protected against abrasive wear and the associated loss of efficiency of the centrifugal pump.

Fig. 4 shows an enlarged detail in the area of the suction mouth 1 according to a variant of the invention. The centrifugal pump has an arrangement for reducing a Return flow 13 in the form of a gap seal. This comprises a rotating component 14, which is designed as a raceway ring and a non-rotating component 2, which is designed as a split ring. The rotating component 14 is arranged on a radial outside of the cover disk 3 of the impeller 4. The rotating component 14 thus rotates with the impeller 4. The non-rotating component 2 is arranged on the pump housing 10 and has a radial inside of the ring as a guide, which interacts with the radial outside of the rotating component 14 and forms the gap seal. According to the invention, the rotating component 14 and the element 2 are coated with a carbon layer, preferably with an amorphous carbon layer, in particular with ta-C. This provides particularly ideal protection against abrasive wear.

When executed as shown in Fig. 4 In addition to an arrangement for reducing a backflow 13, a further arrangement 20 is provided which comprises a rotating element 22 and a non-rotating element 21. The rotating element 22 is designed as a ring, which is also referred to as an angular running ring and which is arranged on the axial end face of the cover disk 3. For this purpose, the rotating element 22 has a projection 19 which extends in the axial direction and which engages in a groove 15 in the cover disk 3. The non-rotating element 21 is designed as an axially displaceable ring which is guided by a surface 16 of the pump housing 10 against radial displacement. A force-generating element 17 exerts a force on the non-rotating element 21 and presses the non-rotating element 21 against the rotating element 22. The force-generating element 17 is designed as a spring. In the exemplary embodiment, a corrugated spring is used. In an alternative variant of the invention, the use of a group or sine spring is conceivable. The non-rotating element 21 is sealed off from the housing part 10 by a sealing element 18. The sealing element 18 is preferably an O-ring.

In the exemplary embodiment, the rotating element 22 and the non-rotating element 21 are made of a stainless steel material which, according to the invention, is coated with ta-C. The two axially facing end faces of the rotating Element 22 and the non-rotating element 21 are pressed against each other by the force generating element 17. This creates a minimal gap. The ta-C coating minimizes friction. A lubricating film of conveyed medium forms in the gap between the contacting surfaces of the rotating element 22 and the non-rotating element 21. The arrangement 20, together with the device 13, prevents a backflow from a pressure chamber 5 of the pump into a suction chamber 1 of the centrifugal pump.

Fig. 5 shows a detailed section of a rotating element 14, 22 in the form of a race, which is coated on an axial surface 27 and on a radial surface 28 with a carbon layer, in particular with ta-C. By coating with ta-C on at least one face of the race and at least one outer face of the race, races can be made from a common cast material and / or a stainless steel material and given wear-resistant properties by means of ta-C coating. The thickness of the ta-C 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 . The hardness of the ta-C coating is preferably 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 and thereby protects the ordinary race from the abrasive action of the solid particles in the pumped medium.

Claims (15)

Centrifugal pump for conveying media containing solids with at least one arrangement for reducing a backflow (13, 20) from a first space into a second space and with a closed impeller (4) which comprises a support disk (11), of which at least one blade (25 ) protrudes away, which is covered by a cover plate (3) in such a way that at least one at least partially closed channel (26) is formed,
characterized,
that the surface of the impeller (4) at least partially has a layer of carbon. Centrifugal pump according to Claim 1, characterized in that the cover disk (3) of the closed impeller (4) has a layer of carbon on a radial surface (24). Centrifugal pump according to Claim 1 or 2, characterized in that the cover disk (3) of the closed impeller (4) has a layer of carbon on an axial surface (23). Centrifugal pump according to one of Claims 1 to 3, characterized in that the inner walls of completely enclosed spaces of the impeller (4) at least partially have a layer of carbon. Centrifugal pump according to one of Claims 1 to 4, characterized in that an element (14, 22) for reducing a backflow is arranged directly on the cover plate (3) of the closed impeller (4). Centrifugal pump according to one of Claims 1 to 5, characterized in that the element (14, 22) has a layer of carbon on a radial surface (28). Centrifugal pump according to one of Claims 1 to 6, characterized in that the element (14, 22) has a layer of carbon on an axial surface (27). Centrifugal pump according to one of Claims 1 to 7, characterized in that the closed impeller (4) interacts with a non-rotating counter-element (2, 21) which is arranged directly on the pump housing (10). Centrifugal pump according to Claim 8, characterized in that the counter-element (2, 21) is designed as a split ring. Centrifugal pump according to claim 8 or 9, characterized in that the counter-element (2, 21) has at least partially a layer of carbon. Centrifugal pump according to one of Claims 1 to 10, characterized in that the closed impeller (4) and / or the element (14, 22) are made from a metallic material, preferably a cast material or a stainless steel material. Centrifugal pump according to one of Claims 1 to 11, characterized in that it is an amorphous carbon layer. Centrifugal pump according to one of Claims 1 to 12, characterized in that it is a tetrahedral, hydrogen-free amorphous carbon layer. Centrifugal pump according to one of claims 1 to 13, 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 14, 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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