Ski Boot Shell Overmolding Polyurethane Polyamide Rigidity
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Solution Overview
Problem
Alpine ski boots face challenges in balancing rigidity, flexibility, and weight, with existing solutions either increasing weight or compromising comfort due to temperature-dependent material properties, and previous approaches failing to maintain consistent mechanical characteristics across temperature ranges.
Innovation Solution
A lower shell for ski boots manufactured using a method that combines overmolding of a polyurethane-based casing with a polyamide-based frame, where the polyurethane has a lower bending stiffness and the polyamide has a higher stiffness, ensuring consistent mechanical properties and reduced weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the material is increased to provide rigidity, then the rigidity of the boot is improved, but the weight of the boot increases
Solution Approach 1:
The patent applies local quality by varying the thickness of the lower shell material in different regions. The shell has a first thickness in certain areas and a second thickness in other areas, allowing rigidity to be concentrated where structurally necessary while maintaining flexibility and reducing weight in other regions. This resolves the contradiction by providing localized rigidity without uniformly increasing overall weight.
2Reliability
If the thickness of the lower hull is increased to ensure durability, then the durability is improved, but the weight of the boot increases
Solution Approach 1:
The patent implements local quality by specifying different thicknesses for different regions of the lower shell. The first thickness and second thickness are strategically positioned to provide durability where needed while minimizing weight elsewhere. This approach ensures the boot maintains durability over time without the penalty of uniformly thick construction.
3Ease of manufacture
If a single material is used for the lower shell, then the manufacturing process is simplified, but the ability to provide both rigidity and flexibility is compromised
Solution Approach 1:
The patent applies local quality by using a single material with varying thickness rather than multiple materials. This maintains manufacturing simplicity while achieving the desired balance of rigidity and flexibility through geometric variation. The different thickness regions provide structurally rigid areas and more flexible areas within the same material system.
4Ease of operation
If polyurethane material is used for the lower shell, then the flexibility and lightness are improved, but the rigidity is insufficient and the material is sensitive to temperature changes
Solution Approach 1:
The patent resolves this contradiction by using local quality with varying thickness in the polyurethane shell. Thicker regions provide the necessary rigidity while thinner regions maintain flexibility and lightness. This geometric variation allows a single polyurethane material to exhibit both rigid and flexible characteristics in different areas, eliminating the need for multi-material construction.
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4C
AI summary
The invention relates to a plastic lower shell for a ski boot, comprising a first part forming an outer shell and a second part forming a chassis. The lower shell (2) is obtained by overmolding between said outer shell made of a first material and said chassis made of a second material. This first material has a first level of flexural stiffness and the second material has a second level of flexural stiffness. The first level of flexural stiffness is lower than the second level of flexural stiffness. The invention also relates to the manufacturing process for producing said lower shell as well as the ski boot incorporating said lower shell.