Propeller for driving of watercraft

Abstract

What are described are a propeller for driving of watercraft, having propeller blades (2, 6, 9, 15) and a metallic hub (1, 7, 8, 14, 31) for bonding to a ship's shaft, and a method for production thereof. The propeller blades are manufactured from polyamide 12 C or a composite material composed of polyamide 12 C with a long and / or short fibre core. The propeller blades or components of the propeller blades are mounted on the hub, or the propeller as a whole consists of polyamide 12 C or a composite material composed of polyamide 12 C with a long and / or short fibre core and the hub encapsulated with PA 12 C. This can achieve an improvement in thrust performance and reduction in acoustic signature compared to metallic propellers.

Description

[0001] The invention relates to a propeller for propelling watercraft according to the preamble of claim 1 and a method for manufacturing such a propeller according to the preamble of claim 9.

[0002] Propellers for watercraft of considerable size and power are, according to current technology, manufactured from metallic materials such as propeller bronze, brass, steel, or stainless steel. In these propellers, both the individual blades and the hub for mounting on a propeller shaft and transmitting torque are made of metal. Depending on their size, the propellers are either cast in one piece or the individual blades are joined together by force-fit, material-fit, or form-fit connections. Propellers for larger watercraft are known to be primarily manufactured from metallic materials.

[0003] From JP S62 37293 A, a propeller for a watercraft is known which consists of a metal core coated with Nylon 11, Nylon 6, Nylon 12, Nylon 66 or Nylon 610. The coating is applied by dipping or spraying, alternatively by electrostatic coating or the application of appropriate nylon films.

[0004] US Patent 2005 / 226724 A1 further describes a modular marine propeller whose hub consists of aluminum and a long-fiber-reinforced plastic based on polyamide 6, polyamide 66, or polypropylene. Injection molding is cited as the state of the art as a manufacturing method for propeller blades.

[0005] CN 105 317 858 A discloses glass fiber reinforced nylon 6 as a material for a ship propeller. It is manufactured using injection molding.

[0006] A disadvantage, however, is that the rotation of a metallic propeller generates significant electrical, magnetic, and acoustic signatures in the water. These signatures are undesirable in both civilian and military shipping. In the commercial shipping sector, propeller noise emissions are particularly critical from an ecological perspective, as they impact aquatic life and are believed to significantly disrupt the communication and orientation of whales and dolphins, for example. In military shipping, these electrical, magnetic, and acoustic emissions are used for ship tracking. Here, too, the goal is to minimize these signatures to hinder the detection of submarines, for instance.

[0007] Larger propellers with carbon fiber-reinforced plastic blades are also known. However, due to the properties of the matrix and the long fibers used, these propellers are very susceptible to delamination and therefore do not find significant application. Propellers made of various plastics are only used for smaller watercraft with low engine power. These propellers are generally made entirely of plastic, or a metal hub is embedded in a plastic material.

[0008] It is also known that, according to current technology, not every desired blade geometry can be manufactured for propellers to prevent cavitation erosion of the materials used. This is because the erosion of the metallic materials as a result of cavitation reduces the service life of the blades for certain geometries. This hinders the optimization of propeller geometries, despite attempts to minimize the effects of cavitation and obtain maximum performance from a given arrangement of ship engine, hull, and propeller through blade shape and surface design.

[0009] If one or more propeller blades are damaged, current technology requires the entire propeller to be replaced during a dry dock period. Due to their high specific weight, propellers and propeller blades are extremely difficult to install using appropriate lifting equipment. The repair is time-consuming and involves high direct and indirect costs. A further disadvantage is that the vessel cannot be used during this time. Rapid repairs in the water are practically impossible.

[0010] Modern propellers are typically susceptible to infestation by barnacles, mussels, and other organisms, which quickly and significantly reduce the engine's performance, thus increasing fuel consumption. To slow this fouling, conventional propellers are coated with a special antifouling paint. However, the biocides contained in such paints are generally toxic and therefore undesirable for environmental reasons. The coating itself incurs costs due to dry dock time, the materials used, and the associated labor. Other coating methods, such as non-toxic and washable paints or underwater cleaning, are not widely used due to cost considerations.

[0011] Finally, electrostatic corrosion can also have an undesirable effect on the propeller's lifespan.

[0012] The object of the invention is to significantly reduce the electrical, magnetic and acoustic signatures of watercraft of any kind, and / or to improve the thrust of the propeller and thereby achieve a further reduction of the signature, and / or to enable propeller replacement or the exchange of individual propeller blades underwater, and / or to slow down infestation by barnacles or mussels and consequently reduce the use of biocides, and / or to avoid electrocorrosion.

[0013] The problem is solved with a propeller according to claim 1 and a method according to claim 9.

[0014] The propeller according to the invention consists essentially of cast polyamide 12 plastic or a composite material made of cast polyamide 12 plastic with suitable long and / or short fiber reinforcement.

[0015] Long fibers are generally defined as those with an average fiber length exceeding 50 mm. Short fibers, on the other hand, have an average length of 0.1 mm to a maximum of 50 mm, particularly from 1 mm to 15 mm.

[0016] The propeller comprises one or more blades, preferably with a structured surface.

[0017] The blades are attached, for example, to a metallic hub for mounting on a ship's propeller shaft and for force transmission, as described below, or all blades are cast in one block, with the hub then cast in along with it. For this purpose, all blades and the hub are preferably cast simultaneously.

[0018] The solution to the task is based on the choice of material of so-called PA 12 C (Cast) or a fiber composite material consisting of suitable long fibers and / or short fibers and a PA-12-C matrix as the material for the propeller blades.

[0019] The mechanical, physical, and chemical properties of this polyamide allow for the propeller to be used continuously in water due to its low moisture absorption, the propeller to be optimally designed due to reduced cavitation erosion thanks to the material's toughness, easier propeller blade replacement due to its relatively low specific weight, and a surface finish designed to slow down barnacle growth. The propeller blades can be attached to a metal hub using the described techniques, which is then slid onto and secured to a ship's propeller shaft.

[0020] The use of the new propeller material significantly reduces the electrical, magnetic, and acoustic signatures of all types of watercraft. Furthermore, the propeller's efficiency is improved through the creation of optimized geometries, thanks to the material's unique structure, thus achieving a further reduction in signature. Additionally, underwater propeller replacement, including the exchange of individual propeller blades, is made possible. Infestation by barnacles or mussels can be slowed, thereby reducing the need for biocides. This is achieved both through the inherent properties of the polyamide 12 C propeller material and through the material's structure, which allows for the creation of optimized propeller geometries.

[0021] Furthermore, propeller blades / propeller wings made of polyamide 12 C, especially Lauramid ®<, exhibit significantly increased elasticity compared to those made of metallic materials, which enables the cushioning of load peaks in the ship's wake field over a complete propeller rotation (360°).

[0022] The invention is therefore based on the use of polyamide 12 C plastic or a composite material made of cast polyamide 12 plastic with suitable long and / or short fiber reinforcement for the manufacture of individual propeller blades or a complete propeller.

[0023] Polyamide 12 C (also PA 12 G) is a polymer material that is melted immediately before processing from a suitable mixture of monomers and additives and poured into molds as a low-viscosity melt. In the production of fiber-reinforced components, the long or short fibers are introduced into the mold before being filled with the plastic and then enclosed by the melt. The mold filling, as well as the subsequent polymerization and curing, takes place without pressure and therefore exhibits special properties compared to extruded, injection-molded, or thermoformed parts.This enables: a significantly improved electrical and magnetic signature through the use of PA 12 C and the avoidance of surrounding metallic components (propeller blades); a significantly improved acoustic signature through the design of the propeller blades, utilizing the increased resistance of the propeller blades to cavitation erosion and the excellent internal damping of the cast matrix; and a significantly higher propeller efficiency through optimized technical design due to minimized cavitation erosion.

[0024] PA 12 C differs from other plastics in its mechanical, physical, and chemical properties, making it particularly suitable for the design and construction of propellers for watercraft. The material has a minimal moisture absorption of only 1.4% by weight when stored in water, making it ideal for underwater applications. PA 12 C boasts the best impact strength—especially at low temperatures—of all polyamides, offering significant advantages in terms of erosion cavitation resistance and the matrix's (in the composite variant's) resistance to external impacts. The low specific weight of the components, and thus their buoyancy neutrality, is a prerequisite for underwater propeller blade replacement. The internal damping of workpieces made from PA 12 C or composites with a PA 12 C matrix reduces the component's acoustic signature.Furthermore, the wide temperature range over which the material can be used in a technically meaningful way, the chemical resistance, the creep resistance and / or the electrical properties justify the special suitability of PA 12 C as a propeller material for watercraft compared to other materials.

[0025] In a composite material made of PA 12 C with long and / or short fibers, the low viscosity of the melt allows for fiber volume fractions of more than 65%, resulting in a very good stiffness-to-weight ratio for the respective component with suitable mechanical properties. Due to its short curing time of just a few minutes, this material also offers significant cost advantages over conventional fiber-reinforced composites. Propellers for watercraft made from PA 12 C are superior to state-of-the-art propellers because of these material advantages.

[0026] Another aspect of the invention may lie in the specific connection of the propeller blades to a hub made of metallic material. The transmission of force and torque from the ship's propeller shaft to the propeller typically occurs through a positive or non-positive connection of two metallic materials, such as oil-filled joints, keys, or dowel pins, or through clamping sets. This principle is fundamentally retained in the present invention, since certain material properties of PA 12 C, such as its low modulus of elasticity or its creep behavior under high local surface pressures, preclude a direct connection of the propeller to the respective ship's propeller shaft. The invention can therefore also arise from the method of connecting the propeller blades to the hub, depending on the desired force and torque transmission and the size of the propeller.

[0027] Another aspect of the invention can be the design of the propeller blade surface to avoid the use of antifouling coatings. The surface is preferably shaped like sharkskin by appropriately designing the mold and incorporating special, corrugated materials into the near-surface plastic. This delays the growth of barnacles and mussels and simplifies mechanical cleaning of the surface, even without lifting the vessel out of the water.

[0028] The invention can be implemented in a technically and commercially sensible manner, for example, using the embodiments described below.

[0029] Preferred embodiments of the invention are illustrated in the drawings. They show: Fig. 1 a section through the propeller in a first preferred embodiment based on mounting the propeller blades / propeller wings on a metallic hub; Fig. 2 the propeller in a second preferred embodiment with cast-in metallic hub in a front view showing the contour of the propeller blades; Fig. 3 a view based on the Fig. 2 with the propeller in a variant of the second embodiment; Fig. 4 a section through the propeller according to a variant of the first embodiment; Fig. 5 in a third preferred embodiment, the propeller is shown in a front view with the contour of the propeller blades and schematically indicated surface texture; Fig. 6 an oblique view of the mounted propeller according to the first embodiment.

[0030] The Fig. 1 The figure shows a propeller with a metallic hub 1. A propeller blade 2 of the propeller is mounted on this hub by means of a (so-called) Böttcher ring 4 and a tie rod 3 inserted into the propeller blade 2 by means of nuts 5.

[0031] The Fig. 2 reveals the contour of a propeller, whereby all propeller blades 6 are manufactured in one casting process and the associated metallic hub 7 is cast over in this process, thereby producing a one-piece propeller.

[0032] The Fig. 3 The contour of a propeller can also be seen, whereby all propeller blades 9 are manufactured in one casting process and in this casting process the metallic hub 8, which has been prepared for this purpose by etching, sandblasting, knurling, cleaning and / or applying coatings, is cast around, thereby creating a one-piece propeller.

[0033] To improve force transmission from the metallic hub 8 to the individual propeller blades 9, structural elements may be present, which are shown by way of example in various forms as rods 10, profiles 11, metallic structures 12, such as trusses, and / or cores 13. The attachment of these structural elements by material connection (for example, on the rods 10 and the metallic structure 12) and / or positive connection (for example, on the profiles 11) is also indicated by way of example and schematically.

[0034] The Fig. 4 The figure shows a propeller in cross-section, in whose propeller blades 15 at least one insert 19 with two threaded rods 18 is cast. The respective propeller blade 15 is mounted between the collar of the metallic hub 14 and the (so-called) cooper's ring 16 screwed onto the hub 14 by means of screws 17.

[0035] In the Fig. 5 Figure 1 shows a preferred embodiment of the propeller in which the surface 20 of one or more propeller blades is designed to resemble sharkskin in terms of its aerodynamic properties. This generally means that the surface has so-called riblets, which, compared to a smooth surface, reduce frictional resistance during turbulent flow over the surface. Such a surface geometry is known to consist of a multitude of sharp-edged ribs whose longitudinal axes lie essentially in the direction of flow intended for each rib.

[0036] In the Fig. 6 An embodiment of the propeller can be seen with the propeller blades / propeller wings 30, which are made of PA 12 C (for example with the trade name Lauramid ®< ), with the metallic hub 31, with the (so-called) Böttcher ring 32, with fastening screws 34 for the Böttcher ring 32 and with the tie rods and associated nuts 33 for fastening the propeller blades / propeller wings 30.

[0037] The following refers to the above-mentioned and in the Fig. 1 bis 6 Reference is made to the reference symbols used.

[0038] For the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long and / or short fibers, the following embodiments are possible, for example: 1.1 An embodiment with one or more propeller blades 2, which are cast individually or in groups in a suitable, appropriately temperature-controlled mold, which approximately corresponds to the outer contour of the individual blade or several blades, under no pressure using a low-viscosity PA-12 melt and then polymerized and cured by appropriate temperature control. 1.2 An embodiment with a metallic hub 1, which can be slid onto the propeller shaft by means of a positive-locking or non-positive-locking connection, such as with an oil press fit, keys, dowel pins and / or clamping sets, and attached to it for the transmission of forces and torques.3. An embodiment with a connection of the plastic blades to the metallic hub, which is pushed onto and connected to the ship's propeller shaft, such that one or more metallic tie rods 3 are embedded in each individual propeller blade 2, serving for force and torque transmission. These tie rods are fastened on one side in the collar of the metallic hub 1 by corresponding nuts 5. After such pre-assembly of all individual blades on the metallic hub 1, a so-called Böttcher ring 4 is mounted on the end of the hub 1 opposite the collar by means of suitable screws. Suitable openings are provided in this ring for the metallic tie rods 3. The tie rods 3 are tightened against the Böttcher ring 4 with the appropriate torque by means of nuts 5.A suitable cover at the end of hub 1 preferably conceals the screw connections and, through its design, simultaneously ensures optimal flow in the shaft's wake. 1.4 An embodiment with a design of the individual propeller blades at the propeller base such that the temperature-dependent variation of the propeller thickness is achieved by selecting the propeller thickness at room temperature through the hub collar, the tie rods, and the Böttcher ring in such a way that the stresses at high temperatures are so low that the creep behavior of PA 12 C is not excessively excited, and conversely, at low temperatures the preload is still high enough to ensure that the propeller blades are firmly clamped. 1.5. An embodiment with a design of the bores for the tie rods 3 such that one or more pockets are provided along the entire length of the bore in order to reduce stress concentrations in the material and improve creep behavior. 1.6 An embodiment with the tie rods 3 being connected to the propeller blade 2 either by: heating the plastic and pressing in the tie rod at room temperature; cooling the tie rod and pressing it into the plastic blade at room temperature; or a combination of both assembly methods. In principle, other joining methods are also conceivable.

[0039] For the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers, the following embodiments are possible, for example: 2.1 An embodiment with a metallic hub 7 which can be pushed onto the ship's propeller shaft by means of a positive-locking or force-locking connection, such as with an oil press fit, keys, dowel pins and / or clamping sets, and fastened to it for the transmission of forces and torques. 2.2 An embodiment with a metallic hub 7 which (as, for example, in Fig. 2 (as shown) for overmolding with PA 12 C on the surface of the hub to form the plastic by etching, sandblasting, knurling, cleaning with special cleaning agents, and applying coatings. 2.3 An embodiment with a metallic hub 8, which (as shown, for example, in Fig. 3(shown) for the transmission of forces and torques from the hub 8 to the propeller blades 9, it has structural elements such as rods 10, profiles 11, metallic structures 12, or inserts 13, which are attached to the hub by force, form, and / or material fit and are completely enclosed by the plastic during the casting process. 2.4 An embodiment with a metallic hub 7, 8 according to embodiments 2.2 and / or 2.3, which is completely encased in a suitable, appropriately temperature-controlled mold corresponding to the outer contour of the one-piece propeller to be manufactured, without pressure, with a low-viscosity PA 12 melt and is then polymerized and cured by appropriate temperature control. 2.5 An embodiment with a propeller manufactured according to embodiment 2.4, which is machined after curing and shaping to achieve the exact final contour.Between the individual machining operations, one or more heat treatments can be carried out to relieve any stresses in the material.

[0040] For the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers, the following embodiments are possible, for example: 3.1 An embodiment with one or more propeller blades 15, which are cast individually or in groups in a temperature-controlled mold, which approximately corresponds to the outer contour of the individual blade or several blades, under no pressure using a low-viscosity PA-12 melt and then polymerized and cured by suitable temperature control. 3.2 An embodiment with an insert 19 cast into each propeller blade, to which threaded rods 18 were attached before casting. 3.3 An embodiment with a metallic hub 14, which can be slid onto the propeller shaft by means of a positive and / or non-positive connection, such as with an oil press fit, keys, dowel pins, and / or clamping sets, and fastened to it for the transmission of forces and torques.4. One embodiment with a connection of the plastic blades 15 to the metallic hub 14, which is pushed onto and connected to the propeller shaft, such that inserts 19 and threaded rods 18 cast into each individual propeller blade 15 are pushed through openings in the hub 14 and then fastened to the hub with screws 17. After such pre-assembly of all individual blades on the metallic hub, a (so-called) Böttcher ring 16 is mounted on the end of the hub 14 opposite the collar using suitable screws. Openings are formed in the Böttcher ring 16 for the threaded rods 18. The tie rods are then tightened against the Böttcher ring 16 with the appropriate torque using suitable nuts 17. A suitable cover at the end of the hub 14 conceals the screw connections and, by its design, simultaneously ensures optimal flow in the wake of the shaft. 3.5. An embodiment with a design of the individual propeller blades at the propeller base such that the temperature-dependent variation of the propeller thickness is achieved by selecting the propeller thickness at room temperature through the hub collar, the tie rods, and the Böttcher ring in such a way that the stresses at high temperatures are so low that the creep behavior of PA 12 C is not excessively excited, and on the other hand, at low temperatures the preload is still high enough that the propeller blades are firmly clamped.

[0041] For the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers, the following embodiments are possible, for example: 4.1 An embodiment with one or more propeller blades, which are cast individually or in groups in a suitable, appropriately temperature-controlled mold, which approximately corresponds to the outer contour of the individual blade or multiple blades, under pressure using a low-viscosity PA-12 melt and then polymerized and cured by appropriate temperature control. 4.2 An embodiment with a surface design 20 of one or all propeller blades / propeller wings according to embodiment 4.1 such that, by shaping the mold and / or incorporating suitable granular materials into the surface during the casting process, a surface structure similar to sharkskin can be cast.The surface structure then features so-called riblets, which, compared to a smooth surface, reduce frictional resistance during turbulent flow over the surface structure, thus slowing down the growth of barnacles and other organisms and simplifying mechanical cleaning. This promotes the long-term maintenance of the specified propeller performance.

Claims

1. Propeller for driving watercraft, having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connection to a ship's shaft, characterized in that said propeller blades are manufactured from polyamide 12 C or a composite made of polyamide 12 C with long and / or short fiber cores and said propeller blades or components of said propeller blades are mounted on said hub, or that said propeller as a whole is made of polyamide 12 C or a composite material made of polyamide 12 C with long and / or or short fiber cores and said hub encapsulated with PA 12 C.

2. Propeller according to claim 1, wherein said individual propeller blades or pairs of blades formed therefrom are fastened by way of metal tie anchors (3) embedded in said propellers and their being clamped in the collar of said hub and a Böttcher ring (16) mounted on said hub.

3. Propeller according to claim 2, wherein openings for said metal tie anchors (3) are formed in said Böttcher ring and said tie anchors are clamped against said Böttcher ring (4, 16, 32) by way of nuts (5).

4. Propeller according to claim 3, wherein said propeller blades comprise bores for said tie anchors (3) and one or more respective pockets are formed over the length of said bores to reduce material stresses.

5. Propeller according to claim 3 or 4, furthermore with a cover attached to the end of said hub to cover said nuts / screw connections and in particular to optimize flow in the wake of the ship's shaft and / or hub.

6. Propeller according to claim 1, furthermore with structural elements for transmitting forces and torques from said hub into said propeller blades, wherein said structural elements, in particular in the shape of rods (10), profiles (11), metal structures (12), or inserts (13), are attached to said hub (8) by way of a force-fit, positive-fit, and / or substance-fit connection and are completely encapsulated with polyamide 12 C.

7. Propeller according to claim 6, wherein said hub (7, 8) has a surface prepared by etching, sandblasting, knurling, and / or applying finishing for being encapsulated with PA 12 C.

8. Propeller according to at least one of the preceding claims, wherein one or several propeller blades has a surface structure similar to shark skin.

9. Method for the manufacture of a propeller for driving watercraft, having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connection to a ship's shaft, characterized in that said propeller blades are manufactured from polyamide 12 C or a composite material made of polyamide 12 C with long and / or short fiber cores and said propeller blades or components of said propeller blades are mounted on said hub, or that said propeller as a whole is manufactured from polyamide 12 C or a composite material made of polyamide 12 C with long and / or or short fiber cores by shaping all propeller blades in one casting process while simultaneously enclosing said metal hub of said propeller.

10. Method according to claim 9, wherein metal tie anchors (3) are inserted into said propeller blades (2) for force and torque transmission by heating said polyamide 12 C and pressing in said tie anchor at room temperature and / or by cooling said tie anchor and pressing in at room temperature.

11. Method according to claim 9 while shaping all propeller blades in one casting process while simultaneously enclosing said hub (7, 8) prepared for this purpose, wherein structural elements for introducing force from said hub into said individual propeller blades are fastened to said hub and completely enclosed by PA 12 C during the casting process.

12. Propeller according to claim 11, wherein said hub (7, 8) is prepared at the surface towards the PA 12 C by etching, sandblasting, knurling, and / or applying finishing for being encapsulated.

13. Method according to at least one of the claims 9 to 12, wherein said propeller formed by casting and cured is machined to produce its final contour.

14. Method according to one of the claims 9 to 13, wherein, for designing said surface (20) of one or all propellers or parts of the surface, a surface structure similar to that of a shark skin is cast by shaping the mold and / or incorporating granular materials into the surface as part of the casting process.

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