Thermal Cord Bonding in Earplug Stems for Lower-Cost Assembly
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Solution Overview
Problem
Existing methods for attaching a cord to earplugs are costly and pose manufacturing challenges.
Innovation Solution
The earplugs are connected by a cord using thermal bonding, where a hot tip is used to create a cord cavity in the stem of the earplug, and the cord end is inserted into this cavity to form a thermally bonded attachment, eliminating the need for adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional attachment methods are used to connect the cord to the earplugs, then the connection strength may be sufficient, but the manufacturing cost increases and manufacturing complexity increases
Solution Approach 1:
The patent replaces traditional mechanical attachment methods (such as adhesives, clips, or knots) with a thermal bonding process. A heated element melts the thermoplastic material at the proximal end of the stem, and the cord is inserted into the molten material where it cools and bonds mechanically. This substitution eliminates the need for separate adhesives or complex mechanical fasteners, reducing manufacturing steps and costs while maintaining strong connections.
Solution Approach 2:
The patent utilizes the phase transition of the thermoplastic material from solid to liquid and back to solid. The heated element raises the temperature of the thermoplastic material above its melting point, transforming it from a rigid solid to a molten state. The cord is inserted during this liquid phase, and as the material cools below its melting point, it solidifies and forms a strong mechanical bond with the cord. This phase transition enables simple, adhesive-free attachment.
2Strength
If adhesives are used to attach the cord to the earplugs, then the attachment may be strong, but the manufacturing process becomes more complex and costly
Solution Approach 1:
The patent extracts and eliminates the adhesive component from the attachment system. Instead of applying a separate adhesive substance, the thermoplastic material itself serves as both the structural component and the bonding agent. The heated element temporarily modifies the thermoplastic material to enable bonding, and once cooled, the same material provides both structural integrity and permanent attachment. This extraction of the adhesive function simplifies the manufacturing process by removing an additional material and application step.
3Ease of manufacture
If a hot tip is used to create a cord cavity and thermally bond the cord to the stem, then manufacturing cost and complexity are reduced, but the temperature must be precisely controlled to melt the stem material without damaging the earplug structure
Solution Approach 1:
The patent changes the temperature parameter of the thermoplastic material from below its melting point (where it maintains structural integrity) to above its melting point (where it becomes moldable for bonding). The heated element provides localized temperature elevation only at the attachment point, while the rest of the earplug remains at ambient temperature. This localized parameter change enables simple thermal bonding without requiring overall heating or complex temperature control systems.
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
This method simplifies and reduces the cost of manufacturing earplug assemblies by providing a strong, adhesive-free connection between the earplugs and the cord.
Implementation Method 1
contacting a hot tip with the proximal end of the stem of the earplug to melt a portion of the proximal end, the stem comprising a first material with a first melting temperature and the cord comprising a second material with a second melting temperature, and the hot tip having a temperature at or above the first and second melting temperatures
Implementation Method 2
inserting a hot tip to a depth into the proximal end of the stem of the earplug to form a cord cavity
Implementation Method 3
attaching the first and second ends of the cord to the first and second earplugs, respectively, by thermal bonding
Data Source
Figure 1~2B
Figure 3A~3D
AI summary
An earplug assembly includes a first earplug, a second earplug, and a cord including a first end, a second end, each earplug including a stem and a sound attenuating body. A method for preparing the earplug assembly includes attaching the first and second ends of the cord to the first and second earplugs, respectively, by contacting a hot tip to the proximal end of the stem of the earplug to form an attachment point, removing the hot tip, and contacting or inserting the end of the cord to the attachment point to thermally bond the end of the cord to the stem of the earplug.