Rotationally Molded Bicycle Wheel Structure to Reduce Warping
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Solution Overview
Problem
Existing bicycle wheels made of thermoplastic face challenges with lower strength, dimensional stability, and complex, costly production, particularly when using pressure spoke elements, leading to issues like bending and warping.
Innovation Solution
A one-piece bicycle wheel design is created using rotational moulding, with a hollow wheel body and pressure spoke elements that expand freely during solidification, featuring varying wall thickness and a tree-like structure for enhanced stability, made from recyclable thermoplastics like polypropylene and polyethylene, and incorporating an RFID storage element for material information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a wheel is made of thermoplastic with pressure spoke elements, then the construction complexity and production cost increase, but the strength and dimensional stability decrease
Solution Approach 1:
The patent merges the hub element, rim element, and pressure spoke elements into a single integrated thermoplastic component produced by rotational moulding. This consolidation eliminates the need for separate parts and complex assembly processes, reducing construction complexity while maintaining structural integrity through the one-piece design
Solution Approach 2:
The patent applies local quality by varying the wall thickness in different regions of the wheel. The hub element, rim element, and pressure spoke elements have optimized local thicknesses that provide sufficient strength where needed while minimizing material usage overall, resolving the contradiction between simplified construction and maintained strength
2Strength
If a composite wheel with fibre-reinforced plastic is used, then the strength increases, but the production complexity and cost increase
Solution Approach 1:
The patent employs standard thermoplastic materials without expensive fibre reinforcements, accepting that the material itself has lower inherent strength. However, the one-piece rotational moulding process creates a seamless structure without weak joints, and the simplified production eliminates the complexity of fibre placement and composite curing processes
Solution Approach 2:
The patent changes the geometric parameters of the wheel design, specifically implementing varying wall thicknesses and optimized hollow cavity shapes. These parameter changes compensate for the lower material strength by improving the structural efficiency and load distribution throughout the wheel components
3Strength
If the wheel is produced with varying wall thickness, then the strength at stressed points increases, but the manufacturing precision requirements increase
Solution Approach 1:
The varying wall thicknesses are pre-planned and built into the rotational mould design itself. The mould geometry is specifically engineered to produce the desired thickness variations during the moulding process, eliminating the need for post-production machining or adjustment and maintaining manufacturing precision through the forming process
Solution Approach 2:
The patent employs curved and rounded transitions in the wall thickness variations, particularly at the interfaces between the hub element, pressure spoke elements, and rim element. These smooth curved transitions avoid stress concentration points that would arise from sharp corners, maintaining both strength and dimensional accuracy
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 design achieves improved dimensional accuracy, reduced warping, and cost-effective production while maintaining strength, with recyclable materials and integrated data storage for efficient re-use.
Implementation Method 1
The plastic powder melts in it and can be distributed over the inner wall in a viscous state as a melt
Implementation Method 2
Finally, the melt solidifies on the inner wall of the rotational mould
Implementation Method 3
The rotational mould is expediently formed as a permanent mould, which usually consists of metal, preferably aluminium. For the moulding process, the rotational mould is rotatable about at least one axis and is externally heated
Data Source
AI summary
A wheel (1) for a bicycle includes a rim element (2), a plurality of pressure spoke elements (3) and a hub element (4) made of a thermoplastic plastics material. The rim element (2) is formed in a single piece together with the pressure spoke elements (3) and together with the hub element (4). A wheel hollow body (5) includes a closed wheel wall (6) where at least the rim element (2) and the pressure spoke elements (3) are hollow, and wherein the single-piece form of the wheel (1) is produced by means of rotational moulding in a rotational moulding die that can be heated externally. The wheel further including a drive shaft for the wheel.