Triangular Shank Screw Asymmetrical Threads
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Solution Overview
Problem
Conventional screws experience high frictional resistance and difficulty in expelling wood chips when screwing into wooden work-pieces, leading to increased effort and risk of cracking, especially when used with compound sheets mixed with plastic resin and wood chips, due to their round shank and axial end cutting grooves.
Innovation Solution
A screw design featuring a shank with a lower section of rough triangular transverse cross-section and an upper section of circular cross-section, including asymmetrical threads and slanted end cutting grooves that reduce friction and facilitate chip expulsion, allowing for faster and more efficient screwing into wood and composite materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a round shank with axial end cutting groove is used, then the screw structure is simple, but the frictional resistance is high and screwing speed is slow
Solution Approach 1:
The patent applies asymmetry by changing the shank cross-section from round to triangular, and designing asymmetrical thread convolutions with different flank angles (α1 and α2). The triangular shank reduces frictional resistance during screwing while the asymmetrical threads optimize cutting performance and chip expulsion, directly addressing the contradiction between structural simplicity and screwing speed.
Solution Approach 2:
The patent applies local quality by creating different functional zones along the shank length. The lower section has triangular cross-section for cutting and chip expulsion, while the upper section has circular cross-section for locking. The end cutting groove is positioned specifically at the insertion end to facilitate chip removal. This localized functional differentiation resolves the contradiction by optimizing different regions for different purposes.
2Device complexity
If axial end cutting groove is used, then the groove structure is simple, but waste chips cannot be expelled smoothly causing obstruction and cracking
Solution Approach 1:
The patent positions the end cutting groove asymmetrically relative to the triangular shank orientation. The groove is configured to align with one of the triangular shank faces, creating an asymmetric chip ejection path that efficiently removes waste chips during the screwing operation, preventing obstruction and workpiece cracking while maintaining structural simplicity.
3Strength
If full contact between thread and work-piece is used, then the connection is secure, but frictional resistance increases requiring more effort and time
Solution Approach 1:
The patent employs asymmetrical thread convolutions with different flank angles (α1 and α2) where α1 > α2. This asymmetry creates a self-centering effect during screwing that reduces lateral frictional resistance while maintaining axial holding strength. The triangular shank cross-section similarly reduces friction compared to round shanks, easing operation while preserving connection integrity.
Data Source
AI summary
A screw includes a shank, at least one end cutting groove, a first thread, and a second thread. The shank includes a lower section disposed near an insertion end thereof and an upper section disposed near a head end thereof. The lower section has triangular transverse cross sections, and the upper section has circular transverse cross sections. The end cutting groove is formed in the lower section of the shank, and an included angle between 3 and 9 degrees is formed between an extending direction of the end cutting groove and a longitudinal axis of the shank. The first thread is disposed on the lower section of the shank and includes a plurality of asymmetrical thread convolutions.