Variable Depth Self-Tapping Screw for Reduced Starting Force
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Solution Overview
Problem
Traditional self-tapping screws require a substantial axial force to initiate penetration into wood or composite materials, making the installation process uncomfortable and time-consuming, especially when installed upwards or overhead.
Innovation Solution
A screw design featuring a tip thread portion that extends along one half turn or less around the rotational axis with a rapid thread depth increase, corresponding to at least one half of the maximum thread depth, facilitating quick conversion of torque to axial force for reduced initial axial force requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a traditional self-tapping screw design is used, then the screw structure is simple and easy to manufacture, but a substantial axial force is required to initiate penetration into the building element
Solution Approach 1:
The screw thread is designed with non-uniform depth along its length, creating different local qualities: the first thread portion has a greater thread depth than the second thread portion. This local variation optimizes penetration characteristics at the tip while maintaining adequate fastening capability along the shaft, allowing the screw to initiate penetration with reduced axial force.
Solution Approach 2:
The thread depth parameter is changed along the length of the screw thread. By varying the thread depth from the first portion (deeper) to the second portion (shallower), the screw achieves different mechanical characteristics at different locations, enabling easier starting while maintaining secure fastening throughout the installation process.
2Force
If a small cone angle and diameter tip portion is used, then penetration is easier with reduced axial force, but the thread configuration complexity increases
Solution Approach 1:
The screw thread is segmented into two distinct portions: a first thread portion with greater depth and a second thread portion with lesser depth. This segmentation allows each portion to perform its specific function optimally - the deeper first portion facilitates easy penetration with reduced axial force, while the shallower second portion provides adequate fastening capability.
Solution Approach 2:
Different thread depths are applied to different portions of the screw thread, creating local quality variations. The first thread portion has enhanced depth for penetration assistance, while the second thread portion has reduced depth for adequate fastening, optimizing both penetration ease and fastening performance without excessive overall complexity.
3Productivity
If conventional thread depth is used throughout the screw, then manufacturing is simpler, but more time is spent pushing each screw into the building element
Solution Approach 1:
The thread depth parameter is varied along the screw length to optimize installation performance. The first thread portion with greater depth reduces the axial force needed for initiation, allowing the screw to penetrate quickly with minimal pushing effort, thereby reducing the time spent on each installation while maintaining adequate fastening in the second thread portion.
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 screw requires a substantially lower axial force for penetration, enhancing ergonomics and productivity by rapidly increasing the axial driving force from the start of rotation, thus improving ease of use and efficiency in installation.
Implementation Method 1
a rapid increase at the tip of the axially directed (towards the head of the screw) surface of the thread will result in a very efficient initial conversion of torque to axial force driving the screw into the building element
Data Source
Figure 1a~1c
Figure 2
Figure 3a~3c
AI summary
A screw (10) comprising a tip (11); a head (12) for accommodating a tool to rotate the screw (10) around a rotational axis (17) of the screw (10); and a thread (15) extending from the tip (11) towards the head (12), the thread (15) having a thread depth (w) that varies along a length of the screw (10) between a minimum thread depth and a maximum thread depth (wmax), wherein the thread (15) comprises a tip thread portion (18) extending along one half turn or less around the rotational axis (17) of the screw (10) and exhibiting a thread depth increase (Δw1) within the tip thread portion (18) corresponding to at least one half of the maximum thread depth (wmax). Hereby a reduced axial force is needed for starting the entry into a workpiece of the screw.