Asymmetrical Wood Screw Shank with Anti-Screw-Out Teeth
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Solution Overview
Problem
Conventional screws for wood planks face issues with wood chip expulsion, leading to obstruction, increased operational effort, plank cracking, and lack of anti-pull-out and anti-screw-out properties, resulting in surface damage and instability under vibrations.
Innovation Solution
A screw design featuring a shank with an insertion tip, a head end, and a straight portion with asymmetrical threads and anti-screw-out teeth, which effectively cuts wood fibers, expels debris, and provides enhanced pull-out resistance through its unique thread angles and tooth configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the end cutting groove extends axially along the shank, then the screw can cut wood fibers, but wood chips cannot be expelled smoothly causing obstruction and increased operational effort
Solution Approach 1:
The end cutting groove is segmented into multiple radial grooves (first, second, third cutting grooves) distributed around the shank circumference. This segmentation allows wood chips to be expelled through multiple pathways simultaneously, preventing obstruction while maintaining cutting capability. The grooves divide the chip flow into separate channels, reducing congestion and improving expulsion efficiency.
Solution Approach 2:
The cutting grooves extend not only axially but also radially outward from the shank surface. This dimensional extension creates additional chip ejection pathways perpendicular to the screw's longitudinal axis, allowing chips to be expelled in multiple directions rather than being confined to a single axial path, thereby preventing obstruction.
2Ease of operation
If the conventional screw thread is used, then the screw can be screwed into the plank, but it lacks anti-pull-out and anti-screw-out properties causing loosening under vibrations
Solution Approach 1:
The screw thread is designed with asymmetric profiles where the upward spiral direction differs from the downward spiral direction. The thread convolutions have different angles and geometries for upward versus downward movement, creating resistance to both pull-out and screw-out forces. This asymmetry ensures that the thread engages more firmly in the reverse direction, preventing loosening under vibrations.
Solution Approach 2:
The thread design incorporates dynamic engagement characteristics where the thread convolutions adapt to loading conditions. The asymmetric thread profile allows the screw to maintain secure engagement under varying loads and vibration conditions, with the thread geometry providing enhanced resistance to reverse motion when subjected to dynamic forces.
3Productivity
If the screw penetrates the plank with conventional design, then connection is achieved, but the surface flatness is worsened due to waste chips released from the drilled hole
Solution Approach 1:
The cutting grooves are specifically designed to extract and remove wood chips from the drilled hole during the screwing process. The grooves act as chip ejection channels that actively pull chips away from the hole interior and deposit them outside the plank surface, preventing chip accumulation that would otherwise mar the surface flatness.
Solution Approach 2:
The cutting action that produces wood chips (a harmful byproduct) is converted into a beneficial process by designing grooves that channel and expel chips away from the surface. The chip generation mechanism is coupled with an ejection mechanism, transforming the harmful chip accumulation into controlled chip removal that preserves surface quality.
4Productivity
If more effort is applied to screw the conventional screw, then penetration is achieved, but the plank easily cracks because of compression
Solution Approach 1:
The cutting grooves segment the wood removal process into multiple controlled pathways, distributing the cutting and compression forces around the shank rather than concentrating them in a single location. This force distribution prevents excessive localized compression that would cause plank cracking while still achieving complete penetration.
Data Source
AI summary
A screw includes a shank having an insertion tip and a head end which has an upper portion with a cutting portion and a lower portion from which a plurality of anti-screw-out teeth protrude. Each anti-screw-out tooth includes a guide face and a stop face intersecting a circumferential surface of the lower portion for development of a recessed channel. A first thread on the shank includes a plurality of asymmetrical thread convolutions each having a first cutting face facing onto the insertion tip and a second cutting face backing onto the insertion tip. The first cutting face and a horizontal axis form an included angle between 25 and 45 degrees. The second cutting face and the horizontal axis form an included angle between 3 and 23 degrees. The screw is in favor of surface flatness of a to-be-connected plank and pull-out as well as anti-screw-out properties of the screw.