Propeller Rib Tapering for Porosity Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Propellers suffer from porosity defects due to shrinkage during the casting process, leading to significant rework, durability issues, and vibration problems caused by premature solidification of molten metal, which shuts off the feed line to the liquid riser.
Innovation Solution
The method involves aligning and configuring ribs with a tapered and scalloped design, where each rib is radially aligned with a blade, specifically targeting the thermal center, to control the solidification profile and prevent porosity by maintaining an open feed path and ensuring uniform solidification from bottom to top.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional casting methods are used with uniform ribs, then manufacturing is simpler, but porosity defects occur due to premature solidification
Solution Approach 1:
The patent applies local quality by varying the rib geometry along its length. The ribs have different cross-sectional areas at different positions, with the cross-sectional area decreasing from the hub toward the blade. This local variation in rib geometry controls the solidification pattern, ensuring that thick sections solidify last to feed shrinkage in thinner sections, thereby eliminating porosity defects while maintaining manufacturing feasibility.
Solution Approach 2:
The rib structure is segmented into multiple zones with different geometric characteristics. Each zone has a specific cross-sectional area designed to achieve particular solidification timing. This segmentation allows precise control over the solidification sequence, ensuring that molten metal continues to feed shrinking regions until the very end of the casting process, thus preventing porosity.
2Strength
If ribs are made thicker to support blades, then structural strength improves, but solidification time increases causing porosity
Solution Approach 1:
The patent applies dynamics by creating a time-varying solidification process through graduated rib thickness. The ribs transition from thicker sections near the hub to thinner sections toward the blade, creating a dynamic solidification sequence where different parts of the rib structure solidify at different times. This ensures structural strength where needed while maintaining proper feeding channels until the final stages of solidification.
Solution Approach 2:
The patent changes the geometric parameters of the ribs, specifically the cross-sectional area, as a continuous function of position along the rib length. This parameter variation is designed to control thermal gradients and solidification timing, ensuring that the rib provides sufficient structural support while simultaneously acting as a feeding channel to prevent porosity during the critical solidification phase.
3Speed
If feed lines are shut off during solidification, then solidification speed increases, but porosity defects result from premature solidification
Solution Approach 1:
The patent applies preliminary action by designing the rib geometry in advance to maintain open feed paths. The graduated thickness of the ribs is pre-configured to ensure that feeding channels remain open throughout the solidification process, allowing continuous supply of molten metal to shrinking regions. This preliminary geometric design prevents the premature shut-off of feed lines that would otherwise cause porosity.
Solution Approach 2:
The rib structure serves as an intermediary element between the hub and the blade, functioning both as a structural support and as a feeding channel. The intermediate zones of the rib, with their graduated cross-sectional areas, act as mediators that control the flow of molten metal and regulate the solidification process, ensuring continuous feeding until the final stages of casting.
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
This approach significantly reduces porosity by extending the solidification time in material-dense regions, eliminating isolated liquid pockets and resulting in a 2000 times reduction in porosity defects compared to traditional methods, while also improving stress profiles and durability of stainless steel propellers.
Implementation Method 1
forming each of the ribs to be tapered such that the thickness is greater at the midpoint than at least at one of the first end and the second end, and forming each of the ribs to be scalloped such that the width is greater at the midpoint than at least at one of the first end and the second end
Implementation Method 2
This approach significantly reduces porosity by extending the solidification time in material-dense regions, eliminating isolated liquid pockets
Data Source
AI summary
A method of making a propeller includes forming the propeller to have blades coupled to an outer hub, the outer hub coupled to an inner hub via ribs, and the inner hub configured to be coupled to the marine vessel. The ribs each have first and second ends with a midpoint therebetween, an inner end and an outer end that define a width therebetween, and a leading surface and a trailing surface that define a thickness therebetween. The ribs are tapered such that the thickness is greater at the midpoint than at least at one of the first end and the second end, and scalloped such that the width is greater at the midpoint than at least at one of the first end and the second end. Each of the ribs is coupled to the outer hub in radial alignment with one of the blades.