Dual-Threaded Screw Geometry for Double-Nut Locking Force
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Solution Overview
Problem
Conventional dual-threaded screw structures with double nuts experience looseness issues due to plastic deformation and reduced axial force when subjected to high torque, requiring unnecessary unfastening of the high lead nut to maintain locking force, which complicates the fastening operation.
Innovation Solution
A dual-threaded screw structure with a first thread and a second thread having a larger root diameter than the effective diameter of the first thread, but smaller than its outer diameter, to distribute stress within allowable shearing and contact surface pressure ranges, eliminating the need for unfastening the high lead nut by securing the locking force between the double nuts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the root diameter of the second thread is made equal to or less than the effective diameter of the first thread to prevent plastic deformation, then the strength of the thread ridge is improved, but the locking force between double nuts deteriorates due to reduced rigidity of the thread ridge
Solution Approach 1:
The patent applies local quality by making the root diameter of the second thread locally larger than the effective diameter of the first thread in specific angular positions. This creates regions of enhanced rigidity at the thread root while maintaining the overall thread strength, allowing the thread ridge to resist both plastic deformation and provide sufficient rigidity for locking force between double nuts
Solution Approach 2:
The patent changes the parameter of root diameter from being equal to or less than the effective diameter (conventional) to being larger than the effective diameter. This parameter change increases the rigidity of the thread ridge, preventing the loss of locking force that occurs with conventional dimensions while still maintaining acceptable strength levels
2Reliability
If the high lead nut is unfastened after fastening with the metric coarse nut to maintain locking force, then the locking force between double nuts is improved, but the fastening operation complexity deteriorates due to additional steps and torque management
Solution Approach 1:
The patent applies self-service by designing the dual-threaded screw structure to automatically maintain sufficient locking force between double nuts without requiring the operator to unfasten the high lead nut. The modified root diameter configuration enables the structure to self-maintain its locking capability throughout the fastening operation, eliminating the need for additional manual intervention steps
3Reliability
If the root diameter of the second thread is increased to improve rigidity and locking force, then the locking force between double nuts is improved, but the manufacturing complexity deteriorates due to potential unnatural deformation during roll forming
Solution Approach 1:
The patent optimizes the root diameter parameter to a specific range that balances rigidity requirements with manufacturability. By setting the root diameter larger than the effective diameter of the first thread but within controlled limits, the design achieves sufficient rigidity for locking force while maintaining compatibility with conventional roll forming processes, avoiding unnatural deformation
Data Source
AI summary
A dual-threaded screw structure having two kinds of threads formed on a shank, namely, a first thread consisting of one or more threads and a second thread having a lead larger than a lead of the first thread is provided herein. The claimed configuration has a beneficial effect of preventing looseness when the screw structure is fastened with double nuts. One embodiment of the present invention exhibits an example of a dual-threaded screw structure, in which a root diameter between the ridges of the hill-like second thread ridges is formed to be larger by 10% of a height of the ridges than an effective diameter of a first thread. In this case, an inner diameter of an internal thread of a second nut for preventing looseness is formed to be larger than the effective diameter of the first thread by 10% of the height of the ridges.