Counterbore Nut Geometry to Prevent Bolt Thread Galling
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Solution Overview
Problem
Existing nuts are prone to galling during fastening due to diagonal biting, which is not effectively prevented by existing screw-in introduction units without screw threads.
Innovation Solution
A nut design with a counterbore hole depth calculated using specific equations to prevent the bolt from being screwed in at an inclination angle that causes galling, ensuring the screw threads do not contact the nut's inner surface, thereby preventing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a screw-in introduction unit without a screw thread is provided in the screw hole, then the bite of the bolt and nut is improved and diagonal biting is prevented, but galling occurs during fastening
Solution Approach 1:
The screw hole is divided into two distinct segments: an upper counterbore hole portion without screw threads and a lower screw thread portion. This segmentation allows the bolt to be guided vertically by the counterbore portion, preventing inclination, while the screw threads engage properly in the lower portion without causing galling.
Solution Approach 2:
The counterbore hole portion acts as an intermediary structure between the bolt head and the screw threads. It provides a guiding function that ensures the bolt inserts vertically, preventing the inclination that would otherwise cause diagonal biting and subsequent galling of the screw threads.
2Device complexity
If the depth of the counterbore hole is insufficient, then the structure is simpler, but the bolt can be screwed in at an inclination angle causing galling
Solution Approach 1:
The depth of the counterbore hole is optimized to a specific parameter range (0.3P to 0.6P, where P is the screw pitch). This parameter optimization ensures the counterbore portion is sufficient to guide the bolt vertically and prevent inclination, while avoiding excessive depth that would unnecessarily complicate the structure or reduce the effective screw thread engagement length.
Data Source
AI summary
There is provided a nut in which occurrence of galling is prevented. The nut in which a depth t of a counterbore hole is set to be greater than (D−d×cos θ)/tan θ, when a nominal diameter is D, an average value of a maximum outer diameter and a minimum outer diameter taking into account a tolerance of a bolt to be fitted is d [mm], an inner diameter of the counterbore hole provided on an insertion side of a screw hole is D+0.2 [mm], a pitch of a screw thread is P [mm], and θ satisfies θ=arc tan(P/d).