Marine Propeller Rough-Blade Finishing for Higher Fatigue Strength
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Solution Overview
Problem
Conventional marine propellers require multiple and complicated manufacturing steps for achieving smooth surfaces, leading to low production efficiency and fatigue failure, which shortens their lifespan.
Innovation Solution
A method involving coarse and fine sandblasting followed by shot peening to create rough surfaces on propeller blades, enhancing fatigue strength and reducing the need for multiple sandblasting and polishing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple sandblasting and polishing processes are used to achieve smooth surfaces, then surface smoothness is improved, but production time and complexity increase
Solution Approach 1:
The patent inverts the conventional approach by intentionally creating rough surfaces through shot peening instead of removing material to achieve smoothness. The rough surface with compressive residual stress is the desired outcome, eliminating the need for multiple sandblasting and polishing steps while improving fatigue strength by over 30%.
2Manufacturing precision
If multiple sandblasting and polishing processes are used to achieve smooth surfaces, then surface smoothness is improved, but production cost increases
Solution Approach 1:
The patent reverses the conventional manufacturing philosophy by accepting and utilizing surface roughness rather than eliminating it. The shot peening process creates a rough surface with compressive residual stress that enhances fatigue strength, eliminating the need for costly multiple sandblasting and polishing operations.
Solution Approach 2:
The patent converts the typically harmful effect of surface roughness (which can initiate fatigue cracks) into a beneficial feature. By inducing compressive residual stress through shot peening, the rough surface becomes advantageous as it prevents tensile stress concentration and fatigue crack initiation, thereby extending propeller lifespan.
3Manufacturing precision
If smooth surfaces are used on propeller blades, then surface quality is improved, but fatigue strength decreases
Solution Approach 1:
The patent transforms the normally detrimental rough surface into a beneficial feature by inducing compressive residual stress through shot peening. This compressive stress field counteracts tensile stresses during operation, preventing fatigue crack initiation and propagation at the rough surface, thereby enhancing fatigue strength by over 30%.
Solution Approach 2:
The patent changes the surface parameter from smooth to rough, and simultaneously changes the stress state parameter by inducing compressive residual stress through shot peening. This dual parameter change transforms the surface from a potential fatigue initiation site to a fatigue-resistant feature.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method increases fatigue strength by over 30% and lowers production costs by minimizing unnecessary manufacturing steps.
Implementation Method 1
performing shot peening to surfaces of the blades and the hub of the propeller member by high-speed and high-pressure stainless-steel balls having dimeter of 0.3-0.5 mm to generate noticeable rough surfaces (6) on the blades and the hub
Implementation Method 2
treating a cast propeller member by a coarse sandblasting and then a fine sandblasting
Data Source
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AI summary
A method for making a propeller (1) includes the steps of casting a propeller member that includes a hub (2) and blades (3) extending from the hub (2), treating the propeller member by a coarse sandblasting and then a fine sandblasting, and shot peening surfaces of the blades (3) and the hub (2) of the propeller member by stainless-steel balls to enhance fatigue strength of the blades.