Coil Fastener Element Sewn Without Core String
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Solution Overview
Problem
In slide fasteners with coil-shaped fastener elements, fixing the elements directly to a tape without a core string leads to instability, causing the fastener elements to potentially detach when twisted or pressed, and complicates sewing processing due to overlapping elements.
Innovation Solution
A fastener chain design where coil-shaped fastener elements are sewn directly to the tape with a sewing thread, featuring upper and lower leg portions that face each other via a space, with specific surface configurations to prevent detachment and ensure smooth sewing, including a first and second upper surface and sloped surfaces to secure the sewing thread, allowing for stable coupling and reduced manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fastener elements are fixed directly to the tape without a core string, then manufacturing cost is reduced and structure is simplified, but the fastener elements become unstable and may detach when twisted or pressed
Solution Approach 1:
The upper leg portion is designed with differentiated local qualities: a first upper surface that is substantially flat for sewing thread placement, and a second upper surface that slopes upward. This local variation in surface geometry provides both cost efficiency (by eliminating the core string) and reliability (through enhanced thread retention on the flat surface), resolving the contradiction between manufacturing ease and fastener stability.
2Reliability
If the upper surface of the upper leg portion is lowered to protect the sewing thread from abrasion, then thread durability is improved, but the space for sewing needle insertion is reduced
Solution Approach 1:
The upper leg portion is segmented into distinct functional surfaces: the first upper surface (substantially flat) dedicated to sewing thread placement and protection, and the second upper surface (sloping upward) that maintains adequate height for sewing needle access. This segmentation allows each surface to optimize its function without compromising the other, resolving the contradiction between thread durability and sewing accessibility.
3Reliability
If a step portion is provided on the upper leg portion to position the sewing thread lower, then thread abrasion is suppressed, but the height dimension is reduced limiting the effect
Solution Approach 1:
Instead of using a sharp step portion, the invention employs a sloping second upper surface that curves upward from the first upper surface. This curved geometry gradually transitions the height, providing effective thread protection while maintaining adequate overall height for sewing operations and avoiding the geometric limitations imposed by abrupt steps.
Data Source
Figure 1
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AI summary
A coil-shaped fastener element (20) of the present invention is sewn to a fastener tape (13) without using a core string. An upper leg portion (23) of the fastener element (20) has a first upper surface (27a) continued from a connecting portion (24) and contacting a sewing thread (14, 16), and a second upper surface (27b) extending and sloping upward from the first upper surface (27a) via a bent portion (28). A height dimension (H1) between a top end surface (27c) and the bent portion (28) of the upper leg portion (23) is 20% or larger of a height dimension (He) of the fastener element (20). The upper leg portion (23) has a first lower surface (26a) which is sloped to be apart from the fastener tape (13) toward a coupling head portion (21), and the upper leg portion (23) has an element contacting portion (23a) in an area of the first lower surface (26a). Thereby, cost reduction of the slide fastener (1) can be attained, and the fastener element (20) can be prevented from passing through the sewing thread (14, 16) and exiting.