Multi-Speed Jack Thread Screw for Building Envelope Fastening
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Solution Overview
Problem
Existing screws used to fasten building envelope elements to substructures face challenges in handling safety and holding forces, as they often result in uneven support of profile sheets under ambient forces, leading to potential bending or damage during screwing and susceptibility to wind loads.
Innovation Solution
A screw design featuring a sub-head thread with a double thread configuration, where the pitch of the first thread section is greater than the second, and the axial path difference is limited to at most 3.5 mm, ensuring the cover plate is moved further towards the screw head than the screw sinks into the substructure, providing greater handling safety and symmetric support through multiple contact points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a classic fastener with a single underhead thread is used, then the profile sheet can be pressed against the screw head, but the support is uneven and the profile may bend or damage during screwing
Solution Approach 1:
The underhead thread is divided into two separate threaded sections (first and second threaded sections) with different pitches. The first threaded section has a greater pitch and engages the profile sheet to press it against the head, while the second threaded section has a smaller pitch and engages the substructure. This segmentation allows different functional requirements to be met by different thread sections.
Solution Approach 2:
Different portions of the screw have different thread characteristics optimized for their specific functions. The first threaded section under the head has a larger pitch optimized for engaging the profile sheet and pressing it against the head, while the second threaded section has a smaller pitch optimized for engaging the substructure. This local differentiation of thread quality resolves the contradiction between holding force and handling safety.
2Reliability
If the pitch of the first thread section is much larger than the second, then the profile sheet is pressed firmly against the head, but the axial path difference becomes too large causing handling issues
Solution Approach 1:
The pitch values of both threaded sections are optimized to achieve the desired axial path difference. The first threaded section has a pitch of 1.5-3.0 mm and the second has a pitch of 0.5-1.5 mm, creating an axial path difference of 1.0-3.5 mm. This parameter optimization ensures sufficient pressing force while limiting the axial displacement to prevent handling problems.
3Reliability
If the axial path difference is increased to improve support, then the profile sheet support improves, but the symmetric support around the circumference is compromised
Solution Approach 1:
The threaded portions are segmented into two distinct sections with different functions. The first threaded section engages the profile sheet uniformly around the circumference to provide symmetric support, while the second threaded section engages the substructure. This segmentation ensures that the support force is distributed symmetrically around the entire circumference of the profile sheet.
Data Source
Figure 1~4
Figure 5
AI summary
A screw (10) has a head (11) with a tool engagement, a shank (18) with at least a first (13) and a second (15) threaded section, and a tip (16). The first threaded section (13) is an underhead thread adjoining a non-threaded underhead section (12). The underhead thread (13) is designed as at least a double-start thread, and the pitch of the first threaded section (13) is greater than the pitch of the second threaded section (15), with the axial path difference over the entire thread length of the first threaded section not exceeding 3.5 mm.