Reduced-Shank Fastener Geometry for Imperfect Thread Engagement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fasteners with uniform diameters struggle with 'shanking' on imperfect threads, limiting their depth of installation and increasing the risk of bending or shear loading, while also requiring high tolerance fits between the fastener and housing, which complicates manufacturing and installation.
Innovation Solution
A fastener design featuring a shaft with first and second threaded portions separated by a central portion of reduced diameter, where at least one threaded portion is chamfered to reduce friction, allowing for deeper installation and reduced tolerance requirements, made from high-strength materials like high-nickel chromium steel or EN29 steel, with optional indicia for identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional fastener with uniform diameter is used, then the fastener can be manufactured with standard processes, but it experiences shanking on imperfect threads, limiting installation depth and increasing risk of bending or shear loading
Solution Approach 1:
The fastener shaft is segmented into distinct portions with different diameters: a first threaded portion with a larger diameter for engagement with the first component, a reduced diameter central portion for clearance, and a second threaded portion with a larger diameter for engagement with the second component. This segmentation allows each portion to perform its specific function optimally, preventing shanking while maintaining high tensile strength.
Solution Approach 2:
Different portions of the fastener shaft are given different local qualities (diameters) to optimize performance. The reduced diameter central portion provides flexibility and clearance to avoid interference with surrounding structures, while the larger diameter threaded portions provide strength for thread engagement. This local differentiation resolves the contradiction between overall strength and localized flexibility.
2Ease of manufacture
If a conventional fastener with uniform diameter is used, then the structure can be designed with standard clearances, but it requires high tolerance fits between the fastener and housing, complicating manufacturing and installation
Solution Approach 1:
The segmented shaft design with a reduced diameter central portion creates natural clearance zones that eliminate the need for high tolerance fits between the fastener and housing. The reduced diameter portion accommodates manufacturing variations and provides clearance from surrounding structures, significantly simplifying manufacturing tolerances while the threaded portions maintain adequate engagement.
3Length of moving object
If a conventional fastener with uniform diameter is used, then the fastener can engage components at standard depths, but it cannot be installed deeper into the structure without increasing risk of bending or shear loading
Solution Approach 1:
The segmented shaft allows the fastener to be installed deeper into the structure because the reduced diameter central portion provides flexibility and clearance. This portion can accommodate the increased leverage and bending moments associated with deeper installation, while the threaded portions remain adequately engaged with the components to maintain strength.
Solution Approach 2:
The reduced diameter central portion provides localized flexibility that enables deeper installation. This local quality change allows the fastener to accommodate the increased mechanical stresses of deeper installation without compromising the strength of the threaded engagement portions.
4Ease of manufacture
If the central portion diameter is reduced to provide clearance, then installation depth increases and tolerance requirements decrease, but the fastener may become weaker at the reduced diameter section
Solution Approach 1:
The material strength parameters are changed by selecting high-strength materials such as high-nickel chromium steel, chromium molybdenum steel, or high-carbon steel. These materials have sufficient strength at the reduced central portion diameter to prevent failure while maintaining the clearance and tolerance benefits of the reduced diameter design.
Solution Approach 2:
Alloying elements such as nickel, chromium, and molybdenum are combined with carbon to create composite steel materials with enhanced strength properties. This allows the reduced diameter central portion to maintain adequate strength despite the smaller cross-sectional area, resolving the contradiction between clearance and strength.
Data Source
AI summary
A fastener includes: a shaft having longitudinal axis and a first and second threaded portions, the first and second threaded portions separated by a central portion having a reduced diameter between the first and second threaded portions, and at least one of the first or second threaded portions is chamfered to reduce friction on leading threads.