Method and apparatus for drying and consolidating a preform for optical fibres

Patent metadata

Field	Value
Publication number	US-11325854-B2
Application number	US-201716498030-A
Country	US
Kind code	B2
Filing date	Mar 29, 2017
Priority date	Mar 29, 2017
Publication date	May 10, 2022
Grant date	May 10, 2022

Abstract

A process and an apparatus for drying and consolidating an optical fibre preform in a furnace tube comprising a heating chamber, wherein an extension tube having an extension chamber configured to house at least a length portion of the preform is removably joined to the furnace tube and the drying process starts with the preform not completely inserted into the furnace tube, an upper length portion of the preform being surrounded by the extension tube joint to the furnace tube.

First claim

The invention claimed is:

1. A method for manufacturing an optical fibre preform comprising:
providing a furnace comprising a furnace tube having an elongated heating chamber configured to house a preform, the heating chamber having an upper entry opening for the insertion of the preform;
providing an extension tube comprising an extension chamber having a lower opening and configured to house at least a length portion of a preform;
inserting a lower length portion of an optical fibre preform, the preform being a porous preform, in the heating chamber in such a way that an upper length portion of the optical fibre preform lies outside of the furnace tube;
enclosing the upper length portion of the optical fibre preform in the extension tube;
joining the furnace tube with the extension tube so as the lower opening of the extension chamber is in communication with the upper entry opening of the heating chamber to form a single chamber;
dehydrating the lower length portion of the preform by exposing said lower length portion to a first heating zone of the furnace tube set at a dehydration temperature, and
gradually lowering the optical preform through the first heating zone so as to dehydrate the upper length portion of the optical fibre preform,
wherein,
the furnace tube has a second heating zone positioned below the first heating zone and set at a consolidation temperature, wherein gradually lowering the optical fibre preform further comprises exposing successive length portions of the preform to the first heating zone and subsequently to the second heating zone until the whole optical fibre preform has passed through the first heating zone.

2. The method of claim 1 , further comprising, after passing the optical fibre preform through the first heating zone, continuing to gradually lower the preform through the second heating zone until the whole optical fibre preform has passed through the second heating zone so as to consolidate the whole optical fibre preform.

3. The method of claim 1 , further comprising, before inserting a lower length portion of the optical fibre preform, holding in suspension the optical fibre preform by a supporting member connected to a first lifting mechanism for vertically moving the preform.

4. The method of claim 3 , further comprising, after providing an extension tube and before enclosing the upper length portion of the optical fibre preform, holding in suspension the extension tube above the optical fibre preform and lowering the extension tube until it surrounds and encloses the upper length portion of the optical fibre preform.

5. The method of claim 1 , further comprising, after providing an extension tube and before enclosing the upper length portion of the optical fibre preform, holding in suspension the extension tube above the optical fibre preform and lowering the extension tube until it surrounds and encloses the upper length portion of the optical fibre preform.

6. The method of claim 5 , wherein the extension tube is connected to a second lifting mechanism for a vertical movement independent of the vertical movement of the preform.

7. The method of claim 1 , wherein the first heating zone is vertically positioned adjacent to the upper entry opening such that the preform enters the first heating zone right after the insertion in the furnace tube.

8. The method of claim 1 , wherein gradually lowering of the optical fibre preform is at a downfeed rate is of from 4 mm/min to 7 mm/min.

9. An apparatus for drying a porous optical fibre preform, comprising:
a furnace comprising a furnace tube comprising an elongated heating chamber for housing and moving a preform in a vertical direction, wherein the heating chamber has an upper entry opening for the insertion of the preform, the furnace further comprising a first heater surrounding the furnace tube for heating a first longitudinal section of the heating chamber defining a first heating zone, and
an extension tube comprising an extension chamber having a lower opening, the extension tube being removably joint to the furnace tube so as to close the upper entry opening, wherein the lower opening is in communication with the upper entry opening when the extension tube is joined to the furnace tube to form a single chamber, the extension chamber being configured to house at least a length portion of the preform, wherein:
the appearance is for drying and consolidating a porous optical fibre preform and the furnace further comprises a second heater placed below the first heater and surrounding the furnace tube for heating a second longitudinal section of the heating chamber defining a second heating zone for consolidation of the porous optical fibre preform.

10. The apparatus of claim 9 , wherein the furnace tube and the extension tube are made of glass so as joining the furnace tube with the extension tube is a glass-to-glass seal.

11. The apparatus of claim 9 , wherein the furnace tube comprises a first flange positioned radially outwardly the upper entry opening and the extension tube comprises a second flange positioned radially outwardly the lower opening, the first and the second flange comprising a respective joining surface, wherein joining is achieved by joining the joining surfaces of the first and of the second flanges.

12. The apparatus of claim 9 , further comprising a supporting member for holding in suspension a preform, the supporting member being operatively connected to a first lifting mechanism for the translational movement of the preform up and down in the longitudinal direction ( 20 ), wherein the supporting member comprises a holding portion for holding the preform and a supporting rod for the connection with the first lifting mechanism.

13. The apparatus of claim 9 , wherein the extension tube is operatively connected to a second lifting mechanism for holding in suspension the extension tube above the preform when it is not joined to the furnace tube and for causing the extension tube to move up and down independently of the supporting member.

14. The apparatus of claim 13 , wherein the extension tube comprises a cover plate opposite to the lower opening and having a throughhole through which the supporting rod passes.

Assignees

• Prysmian Spa

Inventors

• Grieco Stefano
• Caronna Valeria
• Schiaffo Antonio

Classifications

• C03B37/0146 Primary

  Furnaces therefor, e.g. muffle tubes, furnace linings · CPC title