Segmented Screw for Aerated Concrete Fastening
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Solution Overview
Problem
Existing screws are ineffective for securely attaching wooden elements to aerated concrete due to the low load capacity and structural limitations of aerated concrete, which often result in unsuitable fastening solutions that exert tensile forces or compress the material.
Innovation Solution
A screw design featuring two threaded sections with the same pitch, separated by a thread-free shank section, where the screw head has a small transverse extension and is primarily used for tool attachment, not axial force transmission, ensuring secure attachment without pulling action during screwing and allowing for pre-drilling or conical tip usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a screw with continuously increasing shank diameter is used to compress aerated concrete, then material compression is achieved, but the screw design becomes complex and unsuitable for secure attachment
Solution Approach 1:
The screw shank is divided into distinct sections: a first threaded section for engaging the aerated concrete, an unthreaded section, and a second threaded section for engaging the wooden element. This segmentation allows each section to perform its specific function without the complexity of a continuously varying diameter design.
Solution Approach 2:
Different sections of the screw have different local properties: the first threaded section has threads optimized for aerated concrete engagement, while the second threaded section has threads optimized for wood engagement. The unthreaded section provides a transition zone. This local differentiation achieves secure attachment without requiring complex overall design.
2Adaptability or versatility
If screws with different pitch threaded sections are used to attach wooden elements, then multi-material compatibility is improved, but tensile forces are exerted on the front area during screwing
Solution Approach 1:
Both threaded sections use the same thread pitch parameter, which eliminates the pulling action problem. The threads are designed with identical pitch values, ensuring that as the screw advances, the threads engage both materials simultaneously without creating tensile forces on the front area. This parameter standardization resolves the force issue while maintaining adaptability through appropriate thread diameter and profile selections for each material type.
3Force
If a screw head with large diameter is used to transmit axial forces, then force transmission is improved, but the screw head cannot be used for tool attachment and requires separate drive end design
Solution Approach 1:
The screw head is segmented into two functional areas: a drive end with a recess for tool attachment (such as a hexagonal or square drive), and a bearing surface for axial force transmission. This segmentation allows the same component to fulfill both functions without conflict.
Solution Approach 2:
The screw head is designed to perform multiple functions: it provides a mounting surface for the wooden element (force transmission), incorporates a drive recess for tool attachment (ease of operation), and maintains structural integrity. This multi-functional design eliminates the need for separate components.
4Manufacturing precision
If pre-drilling is required for blunt tip screws, then accurate positioning is achieved, but the fastening process becomes more time-consuming
Solution Approach 1:
The conical tip is designed to perform the preliminary action of creating its own insertion path through the aerated concrete. As the screw is driven in, the conical tip compresses and displaces the material ahead of it, eliminating the need for pre-drilling while maintaining accurate positioning through the self-centering geometry of the cone.
5Strength
If thread height in screw-in section is increased to improve connection, then connection strength is improved, but the screwing moment increases
Solution Approach 1:
The thread geometry parameters are optimized to achieve high connection strength with reduced screwing moment. This includes selecting appropriate thread pitch, thread angle, and crest/root radii that balance engagement strength with insertion ease. The threads are designed with parameters that facilitate material displacement while maintaining secure engagement.
Data Source
Figure 1~3
Figure 4
AI summary
For fastening wooden elements to a substrate made of aerated concrete, in particular for fastening roof battens to roof structures made of aerated concrete, a screw is proposed which has either a continuous thread (7, 8) from the screw head (4) to the front end or two threaded sections separated by a threadless section, the thread pitches of which are identical. The screw is used by screwing it through the wooden element into the aerated concrete. The screw is secured to the wooden element solely by the thread (7, 8) located below the outer end of the screw. Any screw head (4) that may be present is designed to be so small that it exerts essentially no tensile forces on the wooden material.