Propeller blade and method for repairing a propeller blade

Abstract

The invention relates to a propeller blade for an aircraft propeller, comprising a wing section (10) and a propeller blade root (20) connected thereto, as well as a method for repairing such a propeller blade. The wing section (10) can have a foam and / or honeycomb core (11, 12, 13) with a sheath (14) made of a fiber-reinforced polymer material. The propeller blade root (20) can be made of a metallic material and comprise a shaft (21) extending into and connected to the wing section (10), at least one outer bearing ring (23), and an adjustment pin (22). It is preferred that the bearing ring (23) has a running surface consisting of a layer (26) of a steel material welded or remelted onto the bearing ring (23), which has a yield strength Rp0.2 of over 750 N / mm² and a tensile strength Rm of over 1,000 N / mm².The bearing ring (23) with the running surface can have a core Vickers hardness HV10 of over 430.

Description

The invention relates to a propeller blade for an aircraft propeller comprising a wing section and a propeller blade base connected thereto, and a method for repairing such a propeller blade. Propeller blades are frequently manufactured from fiber-reinforced composite materials with metal inserts, the blade section often having a foam core or a honeycomb core with a sheath made of a fiber-reinforced polymer material. The propeller blade root, usually made of a metallic material, serves to connect the propeller blade to the propeller hub. The propeller blade root often has a shaft extending into and connected to the blade section and at least one bearing ring by which the propeller blade root is supported in the hub. Propeller blades are usually rotatably mounted in the hub so that their angle of attack can be changed. For this purpose, the propeller blade root often has an adjustment pin that interacts with an adjustment drive. Such propeller blades are known from EP 0 610 273 B1 or FR 2 877 917 B1. CN 1 12 251 681 B describes an ultra-high-strength nanocrystalline stainless steel 40Cr16Co4W2Mo and a method for its production. WO 2017 / 031 942 A1 discloses a composite material and a method for its production. A low-friction bearing shell element for engines and a method for manufacturing a low-friction bearing shell element are described in CN 1 06 321 635 B. FR 2 800 817 A1 relates to a constant velocity joint with a three-legged design for transmissions of road vehicles. The bearing ring is subjected to high mechanical loads during operation, which can lead to wear, particularly on its running surface. EP 3 431 388 B1 therefore proposes a propeller blade retaining element in which a running ring section made of a second, different corrosion-resistant and induction-hardenable steel, for example X40CrMoV16-2 stainless steel, is friction-welded to a body section made of a first corrosion-resistant steel, such as X12CrNiMoV12 stainless steel. This running ring section is to be hardened either before or after being welded to the body section. This method is suitable for the remanufacture of a propeller blade by attaching a blade section to the propeller blade retaining element. Furthermore, EP 3 257 743 B1 proposes applying a running ring made of a tungsten-cobalt-carbide alloy with a hardness greater than 45 Rc as a spray to the blade holding section of a propeller blade with a fiber-reinforced structure. This method can also be used for repair purposes. There is still a need for a propeller blade with an improved propeller blade root and the ability to repair a propeller blade. The object of the invention is therefore to propose a propeller blade with a particularly resistant bearing ring and a method for repairing a propeller blade. This problem is solved with a propeller blade according to claim 1 and a method according to claim 6. A propeller blade according to the invention comprises a blade section made of a fiber composite material and a propeller blade root connected thereto. The blade section can have a foam and / or honeycomb core with a covering of a fiber-reinforced polymer material, and the propeller blade root can be made of a metallic material and include a shaft extending into and connected to the blade section, at least one outer bearing ring, and an adjustment pin. Advantageously, the bearing ring is provided with a running surface made of a layer of a particularly resistant steel material welded or remelted onto the bearing ring and optionally hardened. This steel material can have a yield strength Rp0.2 of over 750 N / mm², for example between 750 N / mm² and 900 N / mm², particularly about 760 N / mm². Alternatively or additionally, the steel material can have a tensile strength Rm of over 1,000 N / mm², for example between 1.The material properties required are between 100 N / mm² and 1,500 N / mm², and in particular between approximately 1,350 N / mm² and 1,400 N / mm². These material properties can be achieved with some weldable, stainless aerospace steels that are also suitable for subsequent hardening. In this way, a propeller blade with a wear-resistant running surface can be manufactured or repaired. For the suitability of the layer as a running surface for a ball or roller bearing, it has proven advantageous if its core has a Vickers hardness HV10 of over 400, for example between 420 and 450, preferably around 430. The core Vickers hardness can be determined according to DIN EN ISO 6507-1:2024-1 with a test force of 98.07 N (corresponding to HV 10). In addition to core hardness, the achievable surface hardness is also an important property for the running surface. For example, the running surface can have a surface hardening depth (SHD 550 HV 1) of over 1.5 mm, for example, from 1.6 mm to 2.5 mm, and in particular from approximately 1.8 mm to 2.0 mm. The surface hardening depth (SHD) can be determined according to DIN EN ISO 18203:2022-07 with a test force of 9.807 N. In a preferred example, the running surface can be spaced from the surface in a range of 0 mm to 0.5 mm and have a Vickers hardness HV10 of over 700, for example between about 710 and 800. In principle, the running surface layer and the rest of the propeller blade root do not need to be made of identical materials, as long as they can be welded together sufficiently well. However, it can be advantageous if the running surface layer and the rest of the propeller blade root are made of the same material. A suitable stainless aerospace steel can contain, for example, the following elements in addition to iron (Fe): carbon (C) between 0.08 and 0.15 wt%, manganese (Mn) between 0.4 and 0.9 wt%, silicon (Si) up to 0.5 wt%, phosphorus (P) up to 0.03 wt%, sulfur (S) up to 0.025 wt%, chromium (Cr) between 11.0 and 12.5 wt%, nickel (Ni) between 2.0 and 3.0 wt%, molybdenum (Mo) between 1.5 and 2.0 wt%, vanadium (V) between 0.25 and 0.4 wt%, and nitrogen (N) between 0.02 and 0.04 wt%. For example, this is the stainless steel X12CrNiMoV12. A method according to the invention for repairing a propeller blade can comprise the following steps: providing a propeller blade with a wing section and with a metallic propeller blade root with a bearing ring; welding a layer of stainless steel onto the bearing ring or remelting a layer of the bearing ring; machining the layer to form a running surface geometry on the bearing ring; optionally hardening the running surface so that it has a Vickers hardness HV10 of over 430 and a surface hardening depth SHD 550 HV 1 of over 1.5 mm. The machining can be carried out before and / or after hardening. The special feature of the inventive method is that the layer forming the running surface is welded on while the metallic propeller blade root is connected to the blade section, which has a foam and / or honeycomb core with a sheath made of a fiber-reinforced polymer material. Therefore, it is not necessary to separate the blade section, which is usually glued and sometimes also mechanically connected to the propeller blade root, from the propeller blade root. This could damage the blade section and is therefore avoided. On the other hand, repairing a propeller root connected to the blade section using thermal methods has been avoided until now because this too could damage the blade section itself or its connection to the propeller blade root.It has been found that the application of a layer of stainless steel, in particular a steel such as X12CrNiMoV12-3 with a yield strength Rp0.2 of over 750 N / mm2 and a tensile strength Rm of over 900 N / mm2, to the bearing ring does not lead to damage to a wing section made of a fiber composite material. Overlay welding of a stainless steel layer can be carried out using electron beam welding or laser beam welding with a fed wire, for example, to replace material lost due to wear on the running surface. In this process, at least the bearing ring of the propeller blade root can be subjected to a vacuum in a vacuum chamber to remove impurities from the weld pool. It may be necessary to protect the blade section from negative pressure to prevent gases trapped in the foam or honeycomb core from damaging the fiber composite structure. For propeller blade repair, it may also be sufficient to simply remelt the running surface of the bearing ring without adding any material. This is particularly useful if only very small amounts of the running surface material have been lost due to wear. The hardening of the running surface can be achieved, for example, by induction hardening, which reduces the amount of heat transferred to the blade section and its connection to the propeller blade root. If the running surface and the bearing ring already possess sufficient hardness after weld overlay or remelting, particularly in the areas specified above as preferred for the propeller blade, the hardening step can be omitted. Furthermore, it can be advantageous to implement heat dissipation measures during welding and induction hardening to protect the fiber composite material and its connection to the propeller blade root from excessively high temperatures. This allows the blade section to be shielded from heat radiation and / or the propeller blade root to be cooled. The invention is explained in more detail below with reference to the drawing. The drawing schematically shows: Fig. 1 a partially cutaway section of a propeller blade according to the invention, Fig. 2 a detail from Fig. 1, and Fig. 3 a bearing arrangement of a propeller blade according to the invention. Fig. 1 shows an example of a propeller blade of a basic structure known in itself, which essentially consists of a wing section 10 and a propeller blade base 20 connected to it. In the illustrated example, the wing section 10 has a core consisting of several foam elements 11, 12, 13, which are provided with a sheathing 14 made of a fiber-reinforced polymer material. The invention is not limited to the exemplary structure of the wing section 10 with multiple core elements shown. For connection to the propeller hub, the propeller blade is provided with the metallic propeller blade root 20. The propeller blade root 20 has a shaft 21 extending into the blade section 10, which is firmly connected to the blade section 10, for example by means of adhesive bonding. In Figures 1 and 3, an adjusting pin 22 is indicated on the propeller blade root 20, which can interact with an adjusting drive (not shown) to change the angle of attack of the propeller blade. For this purpose, the propeller blade root 20 is rotatably mounted in the hub by means of a bearing arrangement indicated in Figure 3. This bearing arrangement essentially comprises an outer bearing ring 23 of the propeller blade root 20, several balls 24, optionally guided in a cage (not shown), and a bearing ring 25 of the hub. At the connection point formed by the bearing arrangement between the propeller hub (stroke) and the propeller blade root 20, the running surface of the bearing ring 23 on the propeller blade root 20 wears down with frequent propeller adjustment. The wear can be a combination of abrasive wear and plastic deformation. Propeller blades are taken out of service when wear limits are exceeded and must be replaced or repaired. According to the invention, the latter can be achieved by a repair process in which missing material on the running surface of the bearing ring 23 is replaced by build-up welding, for example with electron beam and wire (so-called EB welding), thereby applying a layer 26 to the bearing ring 23. According to the invention, a layer consisting of stainless steel X12CrNiMoV12 can be applied while the blade section 10 remains connected to the propeller blade root 20. The propeller blade can be exposed to a vacuum during build-up welding, with protective measures optionally being taken to protect the fiber composite part of the propeller blade, i.e., the blade section 10, from the vacuum. By induction hardening the machined areas on the propeller blade base 20, a core Vickers hardness HV10 of over 430, a surface hardening depth SHD 550 HV 1 of over 1.5 mm and a Vickers hardness HV10 of over 700 at a distance of 0.5 mm from the surface of the running surface is achieved in the bearing ring 23 and the welded layer 26 with the running surface. Restoring the original geometry of the propeller blade base can be achieved by machining, e.g. by turning, before and / or after hardening. In addition, measures for heat dissipation can be taken during overlay welding and induction hardening to protect the fiber composite part of the propeller blade, i.e. the wing section 10, as well as the connection to the propeller blade base 20 from excessively high temperatures. Reference symbol: 10 Wing section 11 Foam element 12 Foam element 13 Foam element 14 Fiber-reinforced polymer casing 20 Propeller blade root 21 Shaft 22 Adjustment pin 23 Bearing ring 24 Ball 25 Hub bearing ring 26 Welded-on layer

Claims

A propeller blade comprising a wing section (10) and a propeller blade root (20) connected thereto, wherein the wing section (10) has a foam and / or honeycomb core (11, 12, 13) with a sheath (14) made of a fiber-reinforced polymer material, and wherein the propeller blade root (20) is made of a metallic material and comprises a shaft (21) extending into and connected with the wing section (10), at least one outer bearing ring (23), and an adjustment pin (22), characterized in that the bearing ring (23) has a running surface consisting of a layer (26) of a steel material welded or melted onto the bearing ring (23), which has a yield strength Rp0.2 of over 750 N / mm² and a tensile strength Rm of over 1,000 N / mm², and that the bearing ring (23) has a core Vickers hardness with the running surface It has an HV10 of over 430. Propeller blade according to claim 1, characterized in that the running surface has a surface layer hardening depth SHD 550 HV 1 of over 1.5 mm. Propeller blade according to claim 1 or 2, characterized in that the running surface has a Vickers hardness HV10 of over 700 at a distance of 0.5 mm from the surface. Propeller blade according to one of the preceding claims, characterized in that the running surface consists of a steel material having a tensile strength Rm of over 1,300 N / mm2 and a Vickers hardness HV10 of over 435. Propeller blade according to one of the preceding claims, characterized in that the running surface consists of a layer of stainless steel X12CrNiMoV12 welded and hardened onto the bearing ring (23). Method for repairing a propeller blade comprising the following steps: a. Providing a propeller blade with a wing section (10) and a propeller blade root (20), wherein the wing section (10) has a foam and / or honeycomb core (11, 12, 13) with a sheath (14) made of a fiber-reinforced polymer material, and wherein the propeller blade root (20) is made of a metallic material and has a shaft (21) extending into and connected with the wing section (10), at least one outer bearing ring (23), and an adjustment pin (22); b. Overlay welding of a layer of stainless steel having a yield strength Rp0.2 of over 750 N / mm² and a tensile strength Rm of over 900 N / mm² onto the bearing ring (23) or remelting of a layer of the bearing ring (23); c. machining of the layer to form a running surface geometry on the bearing ring (23),d.Optional hardening of the running surface, so that it has a Vickers hardness HV10 of over 430 and a surface hardness depth SHD 550 HV 1 of over 1.5 mm. Method according to claim 6, characterized in that step b. is carried out by means of electron beam welding or laser beam welding. Method according to claim 7, characterized in that in step b. at least the running ring (23) of the propeller blade base (20) is exposed to a vacuum. Method according to one of claims 6 to 8, characterized in that step d. is carried out by means of induction hardening. Method according to one of claims 6 to 9, characterized in that in step b. and / or in step d. the wing section (10) is protected from heat radiation and / or the propeller blade base (20) is cooled.

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