Grooved Blind Nut Geometry for Anti-Rotation Without Hole Damage
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Solution Overview
Problem
Existing blind fasteners with longitudinal grooves on their exterior surface can cause delamination issues in composite materials and scratching of metal surfaces, leading to rotation problems during assembly, especially in wet assemblies where putty is present.
Innovation Solution
A blind nut with grooves on its outer circumference, where the groove diameter is less than or equal to the external diameter of the clamping zone, and a radial pitch between grooves is less than or equal to 0.25 mm, ensuring the nut can be installed and locked in rotation without interfering with the structure's hole, preventing delamination and scratching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If longitudinal grooves with diameter greater than the non-grooved portion are formed on the nut's outer surface, then the nut is immobilized in rotation, but the grooves penetrate forcefully into the wall of the hole causing delamination in composite materials and scratching in metal
Solution Approach 1:
The patent changes the critical parameter of groove diameter from being greater than the non-grooved portion (prior art) to being less than or equal to the outer diameter of the tightening zone (invention). This parameter change allows the grooves to remain on the nut surface without penetrating into the hole wall, thereby preventing delamination and scratching while maintaining anti-rotation functionality through the optimized radial pitch
Solution Approach 2:
The patent applies different groove characteristics to different regions: the grooves are positioned with specific radial pitch (≤0.25mm) and depth (0.6%-2% of nut outside diameter) to achieve anti-rotation in the deformation zone while ensuring the groove maximum diameter does not exceed the tightening zone outer diameter, thus creating locally optimized quality that prevents harmful effects
2Ease of manufacture
If the radial pitch between grooves is increased to reduce manufacturing complexity, then the anti-rotation effect is reduced, but manufacturing becomes easier
Solution Approach 1:
The patent establishes an optimized parameter range for radial pitch (≤0.25mm, preferably 0.04mm-0.25mm) that balances manufacturing feasibility with anti-rotation effectiveness. This parameter optimization ensures sufficient groove density to prevent rotation while remaining within practical manufacturing capabilities using deformation, machining, electro-erosion, or laser ablation
Data Source
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AI summary
The present invention concerns a nut (32) for assembling elements of a structure, said nut comprising: a collar (64) suitable for coming into contact with a front face of the structure; a clamping area having an external diameter (86) capable of being inserted into a hole of the structure; a deformation area adjacent to the clamping area and capable of forming a bulge against a rear face of the structure, opposite the front face; and a threaded portion (65) adjacent to the deformation area. The nut comprises grooving (82) on an outer circumference of at least part of the deformation area, a maximum diameter of said grooving (82) being smaller than or equal to the external diameter (86) of the clamping area.