Self-Locking Screw Connection with Threaded Bolt and Nut
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Solution Overview
Problem
Existing screw connections with plastic nuts face issues of loosening due to high elasticity and cold flow behavior, and conventional designs with different thread angles reduce durability and increase the risk of nut breakage during assembly.
Innovation Solution
A screw connection featuring a threaded bolt with a trapezoidal thread and a nut with a thread groove having straight flanks that transition into a round section, where the nut material is softer than the bolt material, allowing for self-locking and reduced radial load on the nut, with a design that accommodates displaced material and includes an annular bead for secure locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nut material is softer than the bolt material to allow self-locking, then the self-locking capability is improved, but the risk of nut breakage during assembly increases
Solution Approach 1:
The nut features a differentiated material structure with a softer interior thread region for self-locking and a harder exterior region for assembly strength. The interior thread has a rounded profile with smaller root radius, while the exterior maintains standard dimensions, creating local property variation that resolves the contradiction between softness for locking and hardness for breakage resistance
Solution Approach 2:
The thread profile parameters are modified with rounded flanks and reduced root radius in the interior thread region. This geometric parameter change allows the softer material to deform plastically during assembly, generating self-locking torque while the controlled rounding prevents stress concentration that would cause breakage
2Ease of manufacture
If a standard unified thread is used with same thread angles, then the manufacturing simplicity is improved, but the radial load on the nut increases causing breakage
Solution Approach 1:
The thread profile transitions from symmetric standard unified thread to asymmetric rounded thread with different flank curvatures. The rounded roots and modified flank angles create asymmetric stress distribution that reduces peak radial loads on the nut while maintaining manufacturability through single-pass forming processes
Solution Approach 2:
The thread flanks are rounded with continuous curvature instead of sharp edges, and the root radius is reduced and rounded. This curvature modification distributes contact stresses more evenly across the thread interface, reducing peak radial loads that cause nut breakage while preserving the basic threading geometry for ease of manufacture
3Reliability
If different thread angles are used between interior and exterior threads to prevent jamming, then the assembly reliability is improved, but the durability of the screw connection is reduced
Solution Approach 1:
Instead of changing thread angles, the invention modifies other thread parameters including flank curvature, root radius, and profile shape. The rounded flanks with controlled curvature allow the softer nut material to deform and lock securely during assembly while the modified geometry maintains proper thread engagement and stress distribution for long-term durability
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
The solution enables easy and reliable bolting with high self-locking momentum, reduces the risk of nut breakage, and allows for secure fastening with minimal torque required for assembly, while maintaining resilience and adaptability in load distribution.
Implementation Method 1
a material being used for the nut that is softer, at least in the region of the interior thread, than a material used for the threaded bolt
Implementation Method 2
the high degree of elasticity and the cold flow behavior of plastics
Implementation Method 3
the high degree of elasticity and the cold flow behavior of plastics
Data Source
Figure 1~3
Figure 4~5
AI summary
In the screw connection, a threaded bolt (20) is provided having an exterior thread (21) that has a thread rib (22) in the manner of a trapezoidal thread having flanks (23, 24) that are straight in profile and converge radially outwards, and a radially outermost boundary surface (25) located therebetween. The nut (1) has a bore (6) that is provided over part of its length with an interior thread (8) formed by a thread groove (9), with the thread groove (9) having flank sections (13, 14) in the manner of a trapezoidal thread that are straight in profile and converge radially outward and that transition radially outward in a continuous manner into a round section (15) forming the thread base of the thread groove (9). The outer diameter (da) of the exterior thread of the threaded bolt (20) is greater than the diameter (Di) of an imaginary cylinder whose surface separates the flank sections (13, 14) of the interior thread (8) of the nut (1) before being screwed in from the round section (15) forming the thread base of the thread groove (9) such that, when the nut (1) is screwed onto the threaded bolt (20), the exterior thread (21) of the threaded bolt (20) displaces material in the region of the thread base of the interior thread (8) of the nut (1).