Threaded Fastener Geometry for Over-Tightening Resistance
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Solution Overview
Problem
Existing threaded fasteners are prone to failure due to excessive torsional stresses caused by high torque levels from advanced power driving tools, leading to over-tightening and breakage.
Innovation Solution
The design includes a shank with a tapered third portion and a first helical thread formation that also tapers, reducing localized frictional torques and concentrating torsional stresses in thicker portions of the shank. Additionally, the head features a plurality of ribs with leading and trailing faces to prevent over-tightening and facilitate easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high torque power driving tools are used to drive threaded fasteners, then the tightening force and securing strength are improved, but the threaded fasteners are subjected to excessive torsional stresses causing shank failure
Solution Approach 1:
The shank is designed with varying diameters along its length, creating local quality differences. The first portion has a larger diameter to withstand high torsional stresses near the head, while the second portion has a smaller diameter. This non-uniform diameter distribution allows the fastener to handle high torque without shank failure while maintaining securing strength.
Solution Approach 2:
The thread formation parameters are changed by providing varying pitch along the shank length. The pitch is closer spacing in the first portion and wider spacing in the second portion. This parameter change optimizes thread engagement characteristics to distribute stresses appropriately and prevent fastener failure under high torque conditions.
2Ease of manufacture
If the thread formation has uniform pitch along the shank, then the manufacturing is simplified, but the torsional stresses are not optimized and may cause failure
Solution Approach 1:
Instead of uniform pitch, the thread formation implements local quality by having different pitch characteristics in different portions of the shank. The first portion has closer pitch spacing while the second portion has wider pitch spacing, optimizing each region for its specific functional requirements regarding stress distribution and engagement.
3Strength
If the threaded fastener is tightly secured to prevent movement, then the anchoring strength is improved, but the fastener becomes difficult to remove or adjust
Solution Approach 1:
The thread pitch parameter is varied along the shank length, with closer spacing in the first portion providing strong engagement for anchoring, and wider spacing in the second portion facilitating easier rotation and removal. This parameter gradient allows the fastener to be both securely anchored and relatively easy to extract when needed.
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 design significantly reduces the risk of torsional failure and over-tightening, allowing the fastener to withstand higher torque levels without breaking, while also making it easier to loosen and remove.
Implementation Method 1
reducing localized frictional torques and concentrating torsional stresses in thicker portions of the shank
Implementation Method 2
the head features a plurality of ribs with leading and trailing faces to prevent over-tightening and facilitate easy removal
Data Source
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AI summary
Various embodiments of a fastener driveable into a substrate are provided. The fastener includes a head, a shank, and a helical thread formation. Portions of the shank and helical thread formations may be tapered. The outer diameter of the shank may decrease in a direction away from the head. An outer diameter of the thread formation may increase in a direction away from the head. The head may include a plurality of extending ribs. The helical thread formation may be formed with a plurality of grooves that are respectively each partially defined by a straight cutting edge. These improvements reduce torsional failure of the fastener from over tightening.