Reduced-Shank Fastener Structure for Deep Thread Installation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fasteners with uniform shank diameters struggle to fit deeply into structures with imperfect threads, leading to 'shanking' issues and limited installation depth, as well as potential bending or shear loading due to mismatched diameters.
Innovation Solution
A fastener design featuring a central reduced diameter 'wasp-waist' section with chamfered threaded portions, made from high-strength steel alloys like nickel chromium or chromium molybdenum steel, allowing deeper installation and reduced friction, thereby minimizing tensile loading and preventing shanking on imperfect threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional fastener with uniform shank diameter is used, then the fastener structure is simple, but the fastener cannot be installed deeply into structures with imperfect threads and experiences shanking issues
Solution Approach 1:
The fastener shank is segmented into multiple diameter sections: a major diameter section at the head, a reduced minor diameter section in the middle, and another major diameter section at the threaded end. This segmentation allows the fastener to navigate imperfect threads and achieve deeper installation while maintaining structural integrity.
Solution Approach 2:
Different sections of the fastener shank have different diameters tailored to specific functional requirements. The reduced diameter section provides clearance for imperfect threads and deeper installation, while the major diameter sections maintain strength at critical locations. This local differentiation of geometry optimizes both installation and structural performance.
2Ease of operation
If a reduced diameter central portion is introduced, then clearance and deeper installation are achieved, but the fastener may experience bending or shear loading
Solution Approach 1:
The reduced diameter section is positioned centrally between the two major diameter sections, creating a predetermined geometry that prevents bending and shear loading before installation. This preliminary structural design ensures that the fastener maintains strength while achieving the necessary clearance for imperfect threads.
Solution Approach 2:
The fastener is made from high-strength alloy steel containing nickel, chromium, and molybdenum. This composite material composition provides the necessary strength to resist bending and shear forces while allowing the reduced diameter section to provide clearance and deeper installation capability.
3Ease of operation
If chamfered threaded portions are used, then friction is reduced and installation is eased, but the manufacturing precision requirements increase
Solution Approach 1:
The threaded portions are chamfered at specific angles (35-55 degrees) to reduce friction during installation. This parameter change in the thread geometry facilitates easier installation while the specified angle range provides a practical balance between friction reduction and manufacturing feasibility.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A fastener (306) includes: a shaft having longitudinal axis (A-A') and a first and second threaded portions (310, 312), the first and second threaded portions (310, 312) separated by a central portion (308) having a reduced diameter (316) between the first and second threaded portions (310, 312), and at least one of the first or second threaded portions (312, 316) is chamfered to reduce friction on leading threads.