Marine propeller, propeller boss, and method for manufacturing same

Abstract

This propeller boss of a marine propeller includes: a base material made of an iron-based alloy; and a surface layer material made of a metal material having corrosion resistance to sea water and covering a surface of the base material. The marine propeller includes the propeller boss and a plurality of blades implanted in the propeller boss.

Description

Marine propellers, propeller bosses and their manufacturing methods

[0001] The present disclosure relates to a propeller boss for a marine propeller.

[0002] Conventionally, a marine propeller includes a propeller boss fixed to a propeller shaft to which thrust from a drive source is transmitted, and a plurality of blades provided on the outer peripheral surface of the propeller boss. Patent Document 1 discloses this type of marine propeller.

[0003] The marine propeller disclosed in Patent Document 1 includes a propeller boss fixed to a propeller shaft, multiple blades provided on the outer peripheral surface of the propeller boss, and a cap attached to the rear end of the propeller boss. The propeller boss, multiple blades, and cap are configured to be rotatable together by thrust from a drive source. The propeller boss and blades are formed as a single component by casting a corrosion-resistant metal material such as a copper alloy. Alternatively, the propeller boss is formed from a copper alloy, and the blades fixed to the propeller boss are formed from carbon fiber reinforced plastic.

[0004] Japanese Patent Application Laid-Open No. 2019-6169

[0005] Marine propellers must be strong enough to generate thrust for the ship and corrosion-resistant enough to withstand seawater. As a result, the material options for marine propellers are limited, making it difficult to meet the current demand for higher power density.

[0006] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a propeller boss for a marine propeller that combines the strength required to generate thrust for a ship with the corrosion resistance required to withstand seawater.

[0007] In order to solve the above problems, a propeller boss for a marine propeller according to one embodiment of the present disclosure includes a base material made of an iron-based alloy and a surface layer material that covers the surface of the base material and is made of a metal material that is corrosion-resistant to seawater.

[0008] A marine propeller according to one aspect of the present disclosure includes the propeller boss and a plurality of blades attached to the propeller boss.

[0009] A method for manufacturing a propeller boss of a marine propeller according to one embodiment of the present disclosure includes forming a base material made of an iron-based alloy into the shape of the propeller boss by casting, and coating the surface of the base material with a metal material that is corrosion-resistant to seawater.

[0010] According to the present disclosure, it is possible to provide a propeller boss for a marine propeller that combines the strength required to generate thrust for a ship with the corrosion resistance required to withstand seawater.

[0011] Fig. 1 is a diagram showing a schematic configuration of a marine propeller according to an embodiment of the present disclosure. Fig. 2 is a diagram explaining a pitching mechanism of the marine propeller. Fig. 3 is a cross-sectional view of a wall forming a propeller boss of the marine propeller. Fig. 4 is a cross-sectional view of a modified example of a wall forming a propeller boss of the marine propeller.

[0012] A marine propeller according to this embodiment will be described below with reference to the accompanying drawings. The marine propeller according to this embodiment is suitably applied to a screw propeller whose blade angle can be freely changed, i.e., a controllable pitch propeller (CPP). However, the application of the marine propeller 1 according to this disclosure is not limited to CPPs, but can also be applied to fixed pitch propellers (FPPs).

[0013] <<General Configuration of Marine Propeller 1>> First, a general configuration of a marine propeller 1 according to one embodiment of the present disclosure will be described. The marine propeller 1 shown in Fig. 1 includes a propeller boss 2 fixed to a propeller shaft 10 to which thrust from a drive source is transmitted, and a plurality of blades 3 provided on the outer peripheral surface of the propeller boss 2. In the example shown in Fig. 1, the marine propeller 1 includes four blades 3, but the number of blades 3 is not limited to this example.

[0014] The propeller boss 2 has a cylindrical shape with one end closed that extends in the axial direction of the propeller shaft 10. The open end of the propeller boss 2 is fixed to a flange 12 of the propeller shaft 10 by a plurality of bolts. The propeller boss 2 may be fixed to the flange 12 by press fitting.

[0015] The body of the propeller boss 2 is provided with a plurality of blade holes 21 that penetrate the propeller boss 2 in the radial direction. The propeller boss 2 of the marine propeller 1 according to this embodiment is provided with the blade holes 21 at four locations dispersed in the circumferential direction in accordance with the number of blades 3. A blade 3 is planted in each blade hole 21.

[0016] The propeller boss 2 contains components of a pitching mechanism 31 that changes the angle of the blades 3. FIG. 2 is a diagram illustrating the pitching mechanism 31 of the marine propeller 1. As shown in FIG. 2, the pitching shaft 32, crosshead 33, and crankpin ring 34 of the pitching mechanism 31 of the marine propeller 1 are disposed within the propeller boss 2. The pitching shaft 32 is a shaft extending parallel to the propeller shaft 10 and passes through the propeller shaft 10. The reciprocating motion of the crosshead 33 is transmitted to the pitching shaft 32 and crankpin ring 34. The bases of the blades 3 are fixed to the crankpin ring 34. The bases of the blades 3 or the crankpin ring 34 pass through the blade holes 21. The crankpin ring 34 converts the reciprocating motion of the crosshead 33 into rotational motion around the center of rotation of the blades 3 via a crankpin and a slide.

[0017] The propeller boss 2 houses a hydraulic cylinder that reciprocates the pivot shaft 32. The interior of the propeller boss 2 is divided into a first cylinder chamber 38 and a second cylinder chamber 39 by a hydraulic piston 37 connected to the crosshead 33 and the pivot shaft 32. High-pressure oil is supplied to the first cylinder chamber 38 or the second cylinder chamber 39 by an oil supply device, causing the hydraulic piston 37 to slide within the propeller boss 2. The movement of the hydraulic piston 37 moves the pivot shaft 32 and the crosshead 33. The movement of the crosshead 33 causes the blades 3 to rotate simultaneously via the crankpin ring 34, changing the pitch angle. However, the configuration of the pivot mechanism 31 for the blades 3 of the marine propeller 1 is not limited to this embodiment, and a pivot mechanism 31 with a known configuration can be used.

[0018] <<Material Composition of Propeller Boss 2>> Here, the material composition of the propeller boss 2 of the marine propeller 1 will be described. Figure 3 is a cross-sectional view of a wall that forms the propeller boss 2 of the marine propeller 1. As shown in Figure 3, the propeller boss 2 is composed of a base material 24 and a surface layer material 25 that covers the surface of the base material 24. In other words, the surface of the propeller boss 2 that comes into contact with seawater is covered with the surface layer material 25.

[0019] The substrate 24 is made of a material with higher strength than copper alloys such as aluminum bronze, which are used as materials for conventional propellers. Corrosion resistance is not required for the substrate 24. Examples of materials for the substrate 24 include iron-based alloys such as cast carbon steel, cast steel for welded structures, high-tensile carbon steel for structures, cast low-alloy steel, cast stainless steel, cast high-manganese steel, cast steel for high-temperature and high-pressure applications, cast steel for low-temperature and high-pressure applications, cast carbon steel for general industrial machinery, malleable cast iron, austenitic cast iron, gray cast iron, spheroidal graphite cast iron, CV graphite cast iron, thick-walled ferritic spheroidal graphite cast iron for low-temperature applications, and austempered spheroidal graphite cast iron. These iron-based alloys are less expensive than the copper alloys used as materials for conventional propellers, and can contribute to reducing manufacturing costs. The substrate 24 is a casting formed by casting, as described below. However, the substrate 24 is not limited to a single layer and may be composed of multiple layers. For example, as shown in Fig. 4, the substrate 24 may be composed of a molded body 241 made of an iron-based alloy and an intermediate coating layer 242 coating the molded body 241, and the surface of the substrate 24 (i.e., the surface of the intermediate coating layer 242) may be covered with a surface layer material 25. The intermediate coating layer 242 may be made of multiple layers. Examples of materials for the intermediate coating layer 242 include functional materials such as strength materials, and copper alloys of a different type from the surface layer material 25. By providing the substrate 24 with the intermediate coating layer 242 in this way, a function different from that of the surface layer material 25 can be imparted to the propeller boss 2.

[0020] The surface layer material 25 is made of a material that has corrosion resistance to seawater equal to or greater than that of the copper alloys used as materials for conventional propellers. Examples of materials for the surface layer material 25 include copper, copper alloys, and stainless steels such as austenitic stainless steel, ferritic stainless steel, duplex stainless steel, martensitic stainless steel, and precipitation hardened stainless steel. The surface layer material 25 may also be made of a noble metal that is resistant to rust (i.e., has a low ionization tendency).

[0021] The propeller boss 2 having the above material configuration has higher strength than the propeller bosses of conventional propellers due to the base material 24, and is corrosion-resistant to seawater due to the surface layer material 25 that covers the surface of the base material 24. In this way, according to the present disclosure, it is possible to provide a propeller boss 2 for a marine propeller 1 that has both the strength to generate thrust for the ship and the corrosion resistance to withstand seawater.

[0022] <<Method of Manufacturing Propeller Boss 2>> A method of manufacturing the propeller boss 2 of the marine propeller 1 configured as described above will now be described. First, the base material 24 of the propeller boss 2 is molded from the material of the base material 24. In this embodiment, the base material 24 is molded by casting. More specifically, the material of the base material 24 of the propeller boss 2 is melted to form a molten metal, which is poured into a cavity of a mold corresponding to the propeller boss 2 and cooled to solidify. After the base material 24 is released from the mold, its surface shape is adjusted by machining or the like, and then it is sent to the next process. The surface shape may be adjusted after the subsequent coating process.

[0023] Next, the surface of the substrate 24 is coated with the material of the surface layer material 25. Directed energy deposition (DED), a type of additive manufacturing method for metal materials, can be used as a coating method. Directed energy deposition (DED) is a method of depositing a metal material on a target surface by irradiating the target surface with a laser or electron beam and spraying a powdered or filamentary metal material onto the target surface, melting and solidifying the metal material. Among directed energy deposition methods, laser metal deposition (LMD), in which a laser is irradiated onto the target surface and metal powder is sprayed onto the irradiated area, is preferred. Specifically, powder of the material of the surface layer material 25 is generated, and the surface of the substrate 24 is irradiated with a laser and sprayed with the powder, melting the powder and solidifying it on the surface of the substrate 24. The surface layer material 25 is coated on the outer wall surface of the substrate 24, but not on the inner wall surface of the substrate 24. The blades 3 and the gearing mechanism 31 are assembled to the propeller boss 2 manufactured through the above process to form the marine propeller 1.

[0024] [Summary] The propeller boss 2 of the marine propeller 1 according to the first item of the present disclosure is characterized by including a base material 24 made of an iron-based alloy and a surface layer material 25 made of a metal material that is corrosion-resistant to seawater and covering the surface of the base material 24.

[0025] The propeller boss 2 of the marine propeller 1 according to the second item of the present disclosure is the propeller boss 2 according to the first item, which has a formed body 241 made of an iron-based alloy and an intermediate coating layer 242 made of a material different from the surface layer material 25 and coating the surface of the formed body 241.

[0026] A marine propeller 1 according to a third aspect of the present disclosure includes the propeller boss 2 according to the first or second aspect, and a plurality of blades 3 attached to the propeller boss 2.

[0027] The manufacturing method of the propeller boss 2 of the marine propeller 1 according to the fourth item of the present disclosure includes forming a base material 24 made of an iron-based alloy having the shape of the propeller boss 2 by casting, and coating the surface of the base material 24 with a metal material that is corrosion-resistant to seawater.

[0028] The propeller boss 2 of the marine propeller 1 according to the first to third items of the present disclosure, and the propeller boss 2 of the marine propeller 1 manufactured by the method according to the third item, include a base material 24 made of an iron-based alloy, which has a higher specific strength than the copper alloy propeller bosses of conventional propellers. The base material 24 allows the propeller boss 2 according to the present disclosure to have higher strength than the copper alloy propeller bosses of conventional propellers. By increasing the strength of the propeller boss 2, the marine propeller 1 including the propeller boss 2 can achieve a higher power density than conventional propellers including a copper alloy propeller boss. Furthermore, the propeller boss 2 according to the present disclosure can be made smaller and slimmer while maintaining the same strength as a copper alloy propeller boss, and is expected to improve propulsion performance by reducing propulsion resistance.

[0029] Furthermore, when the marine propeller 1 is a controllable pitch propeller as in the above embodiment and the propeller boss 2 has a built-in hydraulic cylinder for the variable pitch mechanism 31, high hydraulic pressure is applied from the inside to the outside to the wall of the propeller boss 2. In the propeller boss 2 according to the present disclosure, the inner wall of the propeller boss 2 is made of an iron-based alloy with a high specific strength, and therefore can withstand higher pressures than conventional propeller bosses made of copper alloys, making it particularly suitable as a propeller boss with a built-in hydraulic cylinder.

Claims

1. A propeller boss for a marine propeller, comprising: a base material made of an iron-based alloy; and a surface layer material covering the surface of the base material, the surface layer being made of a metal material that is corrosion-resistant to seawater.

2. A propeller boss for a marine propeller according to claim 1, wherein the base material comprises a formed body made of an iron-based alloy and an intermediate coating layer made of a material different from the surface layer material and covering the surface of the formed body.

3. A marine propeller comprising the propeller boss according to claim 1 or 2, and a plurality of blades attached to the propeller boss.

4. A method for manufacturing a propeller boss for a marine propeller, comprising: forming a base material made of an iron-based alloy into the shape of a propeller boss by casting; and coating the surface of the base material with a metal material that is corrosion-resistant to seawater.

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