Double-Thread Speed Nut for Utility Vault Tamper Resistance
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Solution Overview
Problem
Existing fasteners, such as those used in subgrade vaults, often experience issues like galling, sticking, seizing, rusting, and corrosion, making it difficult to remove bolts, leading to increased downtime and replacement costs due to theft and maintenance challenges.
Innovation Solution
A double-thread speed nut design with an upper and lower thread portion and a connecting sidewall, featuring a gap between the portions and open sidewalls to allow for debris removal, which reduces rust and heat generation, and enhances torque capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a standard single-thread nut is used to secure the vault lid, then the structure is simple and easy to manufacture, but the torque capability is insufficient and the bolt becomes stuck, seized, or rusted making removal difficult
Solution Approach 1:
The nut is divided into an upper portion with a first thread and a lower portion with a second thread, connected by a sidewall portion. This segmentation allows each thread portion to engage with the bolt independently, distributing the torque load and reducing stress concentration that leads to seizing and galling.
Solution Approach 2:
The invention transitions from a single-thread (one-dimensional engagement) to a double-thread (two-dimensional engagement) configuration. The upper and lower thread portions engage the bolt at different axial positions, creating a more robust mechanical connection that increases torque capability while maintaining structural integrity.
2Reliability
If a solid, enclosed nut structure is used, then the structure is strong and stable, but dirt and debris become trapped inside causing rust, corrosion, galling, and seizing
Solution Approach 1:
The nut employs an open framework structure with gaps between the upper and lower portions and openings in the sidewall portion. This porous-like configuration allows dirt and debris to escape rather than become trapped, preventing the rust and corrosion that would occur in an enclosed structure while maintaining sufficient structural integrity through the threaded engagement surfaces.
Solution Approach 2:
The design extracts the harmful trapped debris from the nut interior by providing escape paths through gaps and openings. This removes the source of rust and corrosion problems without compromising the structural strength needed for secure fastening.
3Strength
If a thicker, more robust nut is used to increase torque capability, then the strength increases, but the amount of material used increases and cost increases
Solution Approach 1:
By segmenting the nut into upper and lower thread portions connected by a sidewall, the design achieves high torque capability through distributed engagement rather than requiring a single massive structure. This segmentation allows material to be placed only where structurally necessary.
Solution Approach 2:
The double-thread configuration creates a composite fastening system where two thread portions work together to provide enhanced torque capability. This composite approach achieves greater strength than a single-thread design of equivalent material volume, effectively using material more efficiently.
4Ease of manufacture
If a standard nut design is used, then the manufacturing process is simple, but heat generation during engagement causes galling and seizing
Solution Approach 1:
The open framework structure with gaps and openings provides pathways for heat dissipation during bolt engagement. This porous configuration allows generated heat to escape rather than accumulate, reducing the temperature rise that causes galling and seizing, while the manufacturing process remains relatively simple.
Data Source
AI summary
A nut configured to threadably engage an external thread of a bolt is provided. The nut generally comprises an upper portion that defines a first thread, a lower portion that defines a second thread, and a sidewall portion that connects the upper portion and the lower portion. The upper portion may be separated from the lower portion by a gap, and the sidewall portion may include a first sidewall spaced apart from a second sidewall.