EP4396456B1 - Bucket of a pelton turbine and method for production - Google Patents

Description

The present invention relates to a Pelton turbine with increased durability and a method for manufacturing the turbine. In particular, the present invention relates to the buckets of the turbine with a coated substrate and a method for providing and coating the substrate.

Erosion-resistant coatings are often used on hydropower turbine components, especially on Pelton turbine impellers, which are susceptible to erosion by sediments contained in the turbine water.

For example, the EP 3 647 585 B1 a component of a hydroelectric turbine comprising a wedge-shaped substrate having a tip portion and at least two side portions, wherein an erosion-resistant coating is applied to the wedge-shaped substrate, and wherein the erosion-resistant coating applied to the tip portion is at least 2 times stronger than the erosion-resistant coating applied to the side portions, and wherein the erosion-resistant coating comprises at least 99.5% density. The application of the erosion-resistant coating is carried out by the high-velocity air-fuel process (HVAF). In particular, the EP 3 647 585 B1 Buckets of a Pelton turbine runner, which are constructed in this way.

The object of the invention is to provide an impeller of a Pelton type turbine which has an alternative structure and is manufactured by an alternative method, wherein the resistance of the impeller to erosion is comparably high as the resistance of the impellers known from the prior art.

The object is achieved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention can be found in the subclaims.

Fig.1

Becher einer Pelton-Turbine gemäß dem Stand der Technik

Fig.2

Degradierte Hauptschneide

Fig.3

Hauptschneide eines erfindungsgemäßen Bechers

Fig.4

Hauptschneide eines erfindungsgemäßen Bechers

Fig.5

Hauptschneide eines erfindungsgemäßen Bechers

The invention is explained below using figures. The figures show in detail:

Fig.1

Bucket of a Pelton turbine according to the state of the art

Fig.2

Degraded main cutting edge

Fig.3

main cutting edge of a cup according to the invention

Fig.4

main cutting edge of a cup according to the invention

Fig.5

main cutting edge of a cup according to the invention

Figure 1 shows a section through a bucket of a Pelton type turbine in a schematic representation according to the state of the art. The bucket comprises a substrate which is designated with 1. The substrate is made of steel. The main cutting edge, which is designated with 2, is arranged centrally in the bucket. The main cutting edge splits the water jet directed onto the turbine into two partial jets, which are deflected by the two halves of the bucket. The main cutting edge is therefore also often referred to as a "splitter". The Figure 1 The cut shown runs perpendicular to the direction of the main cutting edge. To protect the cup against erosion, the inside of the cup is coated with an erosion-resistant coating, which is marked with 3. As can be seen from Figure 1 As can be seen, the substrate already has essentially the same contour as the coated cup.

Figure 2 shows the main cutting edge 2 degraded by erosion from Figure 1 . Since the abrasion is strongest at the tip of the cutting edge, which is hit by the undivided water jet, the coating is removed there first and then the substrate underneath. The coating remaining on the flanks is removed less quickly than the substrate, so that a characteristic groove is formed. It is clear that such a profile of the main cutting edge leads to considerable losses in efficiency, so that an impeller that is degraded in this way must be replaced.

The described degradation process can be slowed down by providing as much resistant material as possible at the point of the strongest abrasion. In the solution according to the EP 3 647 585 B1 This is achieved by ensuring that the erosion resistant coating applied to the tip section is at least 2 times thicker than the erosion resistant coating applied to the side sections. An undesirable side effect of this is that the tip radius on the main cutting edge is increased, which leads to a reduced initial efficiency of the turbine.

The inventors therefore looked for a way to arrange as much resistant material as possible at the point of greatest stress without the tip radius increasing accordingly. They realized that this can be achieved by giving the substrate a contour before coating that resembles the contour of a degraded cup (see Figure 2 ) corresponds.

Figure 3 shows the main cutting edge of a cup according to the invention. The substrate has a wedge-shaped form in the area of the main cutting edge, whereby the end of the wedge does not end in a single tip, but rather there is a depression or groove arranged between two tips at this point. In other words: the wedge-shaped substrate comprises a first and a second tip section and a total of four side sections in the area of the main cutting edge, whereby a depression extends between the tip sections, whereby two side sections are assigned to each tip section, and whereby two of the side sections are arranged on the outside of the wedge-shaped substrate, and the two remaining side sections are oriented towards the depression on the inside. It is clear that the lines formed by the end points of the two tip sections run parallel to the cutting line of the main cutting edge. The depression forms a "valley" between the tip sections, so to speak.

When coating such a substrate, the depression is first filled with erosion-resistant material. The coating process is then carried out in This process is continued in this area until the coating material has formed a raised area there in order to form the tip of the main cutting edge. To do this, the surface of the coating in the area of the deepest point of the depression must protrude at least slightly above the surface of the coating on the two tip sections. However, it is advantageous if the raised area is as high as possible. The outer side sections and the rest of the Pelton cup are then coated. The outer side sections and the rest of the Pelton cup could just as well be coated first, ie before coating the depression as described above. Figure 3 It is clear that the tip radius of a main cutting edge produced in this way is comparatively small in relation to the amount of erosion-resistant material at this point. In addition, the connection between the coating and the substrate in this highly stressed area is very strong, as the recess enables a positive fit.

Figure 4 shows the main cutting edge according to the invention, with certain characteristic dimensions being marked. These dimensions relate to the layer thickness of the coating at certain points on the substrate, with the thickness of the coating being measured in a direction perpendicular to the substrate surface at the relevant point. D _A indicates the thickness of the coating in the area of an outer side section. D _I indicates the thickness of the coating in the area of an inner side section. Ds indicates the thickness of the coating at a tip section. A main cutting edge according to the invention is characterized in that the following relation is fulfilled for the thicknesses of the coating mentioned: $${\mathrm{D}}_{\mathrm{A}}<{\mathrm{D}}_{\mathrm{S}}\le {\mathrm{D}}_{\mathrm{I}}$$

Typical layer thicknesses in the area of the outer side sections are in the range of 0.3 mm ≤ D _A ≤ 0.7 mm.

Figure 5 shows the main cutting edge according to the invention, with certain further characteristic dimensions being marked. W is the distance between the two tip sections of the substrate, this distance being perpendicular to the axis of symmetry of the cutting edge and perpendicular to the cutting line. H is the height of the tip sections in relation to the deepest point of the recess. H is removed parallel to the axis of symmetry of the cutting edge. D is the thickness of the coating at the point where the axis of symmetry of the main cutting edge intersects the substrate, ie in the middle of the recess, which usually has its deepest point there.

$$\mathrm{H}=\mathrm{0,1}-\mathrm{0,7}\mathrm{mm}$$

$$\mathrm{D}\ge 1\mathrm{mm}$$

For many common geometries of Pelton buckets, the dimensions mentioned lie in the following advantageous value ranges according to the invention: $$\mathrm{W}=3-7\mathrm{mm}$$

$$\mathrm{H}=0.1-0.7\mathrm{mm}$$

$$\mathrm{D}\ge 1\mathrm{mm}$$

The exact shape of the recess is not crucial. The easiest way to do this is to mill such a recess into the substrate, e.g. with a cove milling cutter. After the substrate with the recess has been prepared, the erosion-resistant coating is applied. For suitable materials and compositions of the erosion-resistant coating, see sections [0027] and [0028] of the EP 3 647 585 B1 The combination of tungsten carbide particles with a matrix of CoCr is considered to be particularly suitable. According to the invention, the coating can be carried out using HVOF or HVAF. HVOF is considered to be particularly suitable. Details of these processes can be found in the EP 3 647 585 B1 be taken.

• S1: Bereitstellung eines Substrates 1 mit einer Vertiefung, welche zwischen zwei Spitzenabschnitten angeordnet ist, und wobei zwei Seitenabschnitte außen an den Spitzenabschnitten angeordnet sind;
• S2: Aufbringung einer erosionsbeständigen Beschichtung 3 auf das Substrat 1 im Bereich der Vertiefung, wobei dieselbe mit erosionsbeständigen Material aufgefüllt und danach der Beschichtungsvorgang in diesem Bereich so lange fortgesetzt wird bis das Beschichtungsmaterial dort eine Überhöhung gebildet hat;
• S3: Aufbringung einer erosionsbeständigen Beschichtung 3 auf das Substrat im Bereich der äußeren Seitenabschnitte.

The manufacturing process according to the invention comprises the following steps:

• S1: Providing a substrate 1 having a recess arranged between two tip portions and wherein two side portions are arranged externally on the tip portions;
• S2: Application of an erosion-resistant coating 3 to the substrate 1 in the region of the depression, wherein the latter is filled with erosion-resistant material and the coating process is then continued in this region until the coating material has formed an elevation there;
• S3: Application of an erosion-resistant coating 3 to the substrate in the area of the outer side sections.

It is clear that step S1 must be carried out before steps S2 and S3. The order of steps S2 and S3 can then be arbitrary.

Finally, it should be noted that the coating process described can be carried out on separate buckets when the buckets are attached as a whole to a hub during the manufacture of a Pelton impeller. However, when the buckets are manufactured integrally with the hub, or only parts of the buckets are attached to the hub, with the remainder of the buckets being manufactured integrally with the hub, then the coating process described is carried out when the entire bucket is on the hub.

list of reference symbols

1

substrate

2

main cutting edge or splinter

3

coating

Claims (6)

1. Bucket of a turbine of the Pelton type comprising a substrate (1), a main cutting edge (2) and an erosion-resistant coating (3) covering the substrate (1), wherein the substrate (1) has a wedge-shaped configuration in the region of the main cutting edge (2), characterised in that the substrate (1) comprises a first and a second tip section and a total of four side sections in the region of the main cutting edge (2), wherein a depression extends between the tip portions, and wherein two side sections are associated with each tip section, and wherein two of the side sections are arranged on the outside of the wedge-shaped substrate and the two remaining side sections are orientated inwards towards the depression, and wherein the coating (3) forms an elevation in the region of the depression in order to form the tip of the main cutting edge (2).
2. The bucket according to claim 1, wherein the two tip sections are arranged such that they have a distance W of 3 to 7 mm.
3. The bucket according to claim 1 or 2, wherein the two tip sections and the depression are formed such that the tip sections have a height H with respect to a deepest point of the depression which is between 0.1 mm and 0.7 mm.
4. The bucket according to any one of the preceding claims, wherein the coating (3) has a thickness D of at least 1 mm in the centre of the depression.
5. Bucket according to one of the preceding claims, wherein the coating (3) consists of a matrix of CoCr with embedded tungsten carbide particles.
6. A method of manufacturing a bucket of a Pelton type turbine according to any one of the preceding claims, the method comprising the following steps:

   S1: providing a substrate (1) having a depression arranged between two tip sections, and wherein two side portions are arranged on the outside of the tip sections;

   S2: Application of an erosion-resistant coating (3) to the substrate (1) in the region of the recess, the latter being filled with erosion-resistant material and the coating process then being continued in this region until the coating material has formed an elevation there;

   S3: Application of an erosion-resistant coating (3) to the substrate (1) in the region of the outer side sections.

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