Optical Fiber Preform Sealing Assembly for Helium Leak Control
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Solution Overview
Problem
The quality of optical fiber preforms is compromised by gas leakage and mechanical stress during dehydration and consolidation processes, leading to defects such as 'airlines' due to insufficient helium flow and misalignment of the supporting handle, which affects the Draw Cumulated Defect Ratio (DCDR).
Innovation Solution
A sealing assembly with expansible members and ring-shaped seals is introduced to minimize gas leakage and absorb mechanical stresses, ensuring a tight fit and flexibility for the supporting rod, comprising a hood, connection member, and sealing elements made of thermoplastic polymers like PTFE, PCTFE, or PFA, to maintain helium flow and prevent air ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealing assembly with expansible members is used to prevent gas leakage, then preform quality and helium flow are improved, but device complexity increases
Solution Approach 1:
The patent employs an expansible member made of flexible material that can expand and contract to maintain sealing contact with the supporting rod. This flexible element adapts to rod position variations while preventing gas leakage, resolving the contradiction between reliable sealing and simple device structure.
Solution Approach 2:
The sealing assembly incorporates an expansible member that dynamically adjusts its dimensions in response to mechanical stresses and rod position changes. This dynamic adaptation ensures continuous sealing effectiveness without requiring complex adjustment mechanisms, thereby improving reliability while keeping the device relatively simple.
2Productivity
If the furnace chamber length is increased to accommodate longer preforms, then productivity is improved, but loss of energy increases
Solution Approach 1:
The patent divides the heating process into distinct zones within the furnace chamber, with different temperature profiles for drying and consolidation phases. This segmentation allows efficient processing of longer preforms without proportionally increasing energy consumption, as each zone operates optimally for its specific function.
Solution Approach 2:
The patent implements a drying zone that operates before the consolidation zone, preliminarily removing moisture from the preform. This preliminary action reduces the energy required in the subsequent consolidation phase, enabling efficient processing of longer preforms without excessive energy loss.
3Reliability
If helium flow rate is increased to prevent air ingress, then preform quality is improved, but use of energy increases
Solution Approach 1:
The sealing assembly with the expansible member creates a self-regulating seal that passively prevents air ingress without requiring high helium flow rates. The flexible seal adapts to maintain contact, eliminating the need for energy-intensive high-flow helium operation while still ensuring preform quality.
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 assembly reduces helium consumption and maintains preform quality by preventing air ingress and mechanical stress, improving the DCDR to less than 2%, ensuring high-quality optical fiber production.
Implementation Method 1
a ring-shaped seal and an expansible member configured to allow passage of the supporting rod and to expand and contract in a vertical direction, wherein the ring-shaped seal is located radially inward of the expansible member and operatively connected thereto and has an inner diameter configured to directly contact the supporting rod
Implementation Method 2
an expansible member configured to allow passage of the supporting rod and to expand and contract in a vertical direction
Implementation Method 3
Drying is performed by heating the preform to a typical temperature of about 1100°C in the presence of one or more drying gases. Consolidation is performed by heating the dried preform typically to a temperature between 1400°C and 1600°C.
Implementation Method 4
Dehydration and/or consolidation of an optical fibre preform within a furnace typically takes place under a flow of an inert gas or of a gas mixture containing an inert gas. Helium is a preferred inert gas because it can be easily dissolved in the preform both as a single gas, for example during consolidation, and as a diluent carrier gas
Data Source
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AI summary
An apparatus (10) for drying and/or consolidating an at least partially porous optical fibre preform, comprising: a furnace (20) comprising a muffle tube (11) extending along a vertical axis (Z) and forming a muffle chamber configured to house a preform (16), the muffle tube (11) having a muffle upper opening (15) at its top side, which is configured to allow passage of the preform (16); a hollow connection member (40) having an inner diameter configured to allow passage of the preform and extending along the vertical axis (Z), the connecting member (40) being removably connected to the muffle tube (11) at the muffle opening (15); a hood (30) positioned on top of the connection member (40), the hood (30) being removably connected to or integral with the connection member (40), the hood having an interior space (34) in vertical alignment with the connection member (40), wherein the hood comprises a hood lid (32) closing the hood at its top, wherein the hood lid (32) comprises a through-hole (57) axially aligned with the muffle opening (15), the hood lid through-hole (57) being configured for the passage of a cylindrical supporting rod (18) of a supporting handle (19) for the suspension of the preform (16), and a sealing assembly (70) comprising a first sealing element (80) housed within the interior space (34) of the hood (30) and a second sealing element (90) on top of the hood lid (32), both the first and the second sealing element being substantially centred on the vertical axis (Z), wherein the first sealing element (80) and second sealing element (90) comprise a respective first and second ring-shaped seal (82, 92) and a first and second expansible member (83, 93) having a generally tubular shape configured to allow passage of the supporting rod (18) and to expand, contract and bend, wherein each first and second ring-shaped seal (82, 92) is located radially inward of the respective first and second expansible member (83, 93) and operatively connected thereto, the respective ring-shaped seals (82, 92) being sized to directly contact the supporting rod (18).