Optical Fiber Preform Sealing Assembly for Helium Loss Control
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Solution Overview
Problem
The quality of consolidated optical fiber preforms is compromised by insufficient helium gas flow during dehydration and consolidation processes, leading to defects such as 'airlines' and increased helium consumption, which affects production costs.
Innovation Solution
A sealing system is introduced that includes a flow control assembly with an expansible member and ring-shaped seal to minimize helium leakage and maintain gas flow, allowing reduced helium usage while ensuring the quality of the consolidated preform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a sealing system is introduced to minimize helium leakage, then helium consumption is reduced, but device complexity increases
Solution Approach 1:
The patent employs a flexible membrane seal that can deform to maintain sealing contact with the preform rod. This flexible film approach provides effective helium leakage prevention while avoiding complex mechanical sealing structures, thus reducing device complexity compared to rigid multi-component sealing systems.
Solution Approach 2:
The sealing system is designed to automatically adapt to preform rod position variations through the flexibility of the membrane. The seal self-adjusts to maintain contact and prevent leakage without requiring external control mechanisms or complex actuation systems, thereby reducing overall device complexity.
2Manufacturing precision
If helium flow is increased to maintain preform quality, then manufacturing precision is improved, but loss of substance increases
Solution Approach 1:
The patent maintains an inert helium atmosphere within the consolidation chamber to prevent oxidation and contamination of the preform during high-temperature processing. The flexible membrane seal ensures this inert environment is maintained with minimal helium flow rates, as leakage is prevented by the seal rather than requiring excessive gas flow for atmosphere maintenance.
Solution Approach 2:
The sealing system provides feedback by maintaining consistent sealing pressure that adapts to preform position, ensuring stable helium flow conditions. This consistent sealing action allows for optimized helium flow rates that maintain preform quality without excessive consumption, as the seal prevents atmospheric contamination that would otherwise require higher helium flows to compensate.
3Productivity
If the muffle tube length is increased to accommodate longer preforms, then productivity is improved, but use of energy increases
Solution Approach 1:
The patent divides the heating process into distinct zones along the muffle tube, with different temperature profiles for different sections. This segmentation allows longer preforms to be processed efficiently by heating only the necessary portions to consolidation temperature, reducing overall energy consumption while maintaining productivity for longer preform lengths.
Solution Approach 2:
The patent employs a movable preform handling system that can dynamically position and move preforms through different temperature zones. This dynamic capability allows optimization of energy usage by positioning preforms to receive heat only where needed, rather than heating entire long muffle tubes uniformly, thus maintaining productivity for long preforms while reducing energy consumption.
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 sealing system reduces helium consumption and prevents air penetration, maintaining the quality of the consolidated preform by minimizing defects and lowering production costs.
Implementation Method 1
a sealing system is introduced that includes a flow control assembly with an expansible member and ring-shaped seal to minimize helium leakage
Implementation Method 2
consolidation is performed by heating the dried preform typically to a temperature between 1400°C and 1600°C
Implementation Method 3
the preform is pulled up as a transparent silica glass preform above the furnace after vitrification
Implementation Method 4
Drying is performed by heating the preform to a typical temperature of about 1100°C in the presence of one or more drying gases
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An apparatus (10) for drying and/or consolidating an at least partially porous optical fibre preform, comprising: - a furnace (9) comprising a muffle tube (11) extending along a vertical axis (Z) and forming a hollow muffle chamber configured to house a preform (16), the muffle tube (11) having a muffle opening (15) at its top side, which is configured to allow passage of the preform (16); - an extension tube (19) forming a hollow extension chamber (21) configured to house at least a length portion of the preform (16) and having a central axis aligned in the vertical axis (Z), wherein the extension tube (19) has a lower opening (24) and upper opening (23) placed at the top side of the extension tube (19) and opposite to the lower opening (24), and wherein the extension tube (19) is removably attached to the muffle tube (11) at the lower opening (24) so as to close the muffle opening (15) when the extension tube (19) is joined to the muffle tube (11) to form a single chamber, - a hood (30) placed on a top side of the extension tube (19) and removably fixed to the same, the hood (30) defining an inner space (37) when fixed to the extension tube (19) and including a discharge port (46) and a hood cap (33) with a hood through-hole (34) which is substantially axially aligned to the upper opening (23), the hood through-hole (34) and the upper opening (23) being configured for the passage of a cylindrical supporting rod (18a) of a supporting handle (18) for the suspension of the preform (16), and - a flow control assembly (90; 91) including a sealing assembly (80) operatively connected with the hood (30) and substantially centred about the vertical axis (Z), wherein the sealing assembly (80) includes a ring-shaped seal (82) and an expansible member (83) having a generally tubular shape configured to allow passage of the supporting rod (18a) and to expand and contract in a vertical direction (L), wherein the ring-shaped seal (82) is located radially inward of the expansible member (83) and operatively connected thereto and has an inner diameter configured to directly contact the supporting rod (18a)