GB2170738A

GB2170738A - Coating optical fibres

Info

Publication number: GB2170738A
Application number: GB08503298A
Authority: GB
Inventors: Malcolm Duncan Mackay
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1985-02-08
Filing date: 1985-02-08
Publication date: 1986-08-13
Also published as: CN86100971A; GB2170738B; GB8503298D0; ZA86614B

Abstract

An applicator for coating an optical fibre (29) includes a coating chamber (30) whose inlet is comprised by a flexible orifice element (11). In use the chamber (30) contains coating material under pressure and the coating material exits the chamber via the inlet orifice element (11), as well as through an outlet orifice element (10), so as to prewet the optical fibre with the coating material before it enters the coating chamber. The prewetting prevents the formation of air bubbles in the applied coating and permits high speed coating. <IMAGE>

Description

SPECIFICATION Optical fibres This invention relates to optical fibres and in particular to an applicator and method for use in coating optical fibres and other elongate members.

In the application of coatings to optical fibres, in particular the application of primary coatings to optical fibres in tandem with drawing thereof, it is desirable to be able to apply an air-bubble-free coating at high fibre throughput speeds. One known basic type of applicator comprises an open cup comprising a reservoir of liquid polymer material through which the fibre is advanced. The fibre exits the reservoir through a small die orifice at the bottom of the reservoir. High speed passage of the fibre through the polymer material causes a column of air to be drawn into the reservoir and this adversely affects the wetting of the fibre by the polymer material as well as causing the subsequent production of air bubbles which can remain in the applied coating and result in fibre weakening.In a known coating applicator based on the open cup type but also employing a pressurised source of polymer material, as described in UK Patent Application 2113574 (Western Electric) means are provided to remove air bubbles from the advancing fibre. The structure is however relatively complex and of increased length in comparison with the basic open cup type.

According to one aspect of the present invention there is provided an applicator for coating an elongate member including a chamber having an inlet and an outlet for the elongate member, wherein the inlet is comprised by a flexible orifice element, and wherein in use of the applicator the elongate member is passed through the chamber which contains coating material under pressure, which coating material exits said chamber via the flexible orifice element, as well as the chamber outlet for the elongate member, whereby to prewetthe elongate member with the coating material.

According to another aspect of the present invention there is provided a method of coating an elongate member comprising directing the member through a chamber having an inlet and an oulet for the elongate member and containing coating material under pressure, the inlet being comprised by a flexible orifice element, and allowing coating material to exit the chamber via the flexible orifice element, as well as said chamber outlet, whereby to prewet the elongate member with the coating material.

Embodiments of the invention will now be described with reference to the accompanying sectional drawing through a pressurised coating applicator.

The pressurised applicator shown in the drawing includes a housing or body member 1, for example of brass, having a bore therethrough including a large diameter cylindrical portion 2 having a threaded end portion 3, a tapered portion 4, there being a shoulder 5 between portions 2 and 4, a short small diameter cylindrical portion 6, and an intermediate diameter cylindrical portion 7 having a threaded end portion 8. The body member 1 incorporates means (not shown) for mounting it to a positioning mechanism (not shown), whereby its position relative to a fibre pulling arrangement can be adjusted, and a radial inlet port 9 for coating material. Two flexible applicator orifice elements or inserts 10 and 11 are disposed in the body member 1.The inserts each include a shoulder portion 12, a tapered portion 13 and a cylindrical portion 14 and may be manufactured from elastomeric material.

Also disposed in the body member 1 is a separating ring 15, which includes an axially extending radial slot 16, and a support element 17 for the upper insert 11. The support element includes a tapered portion 18 and a shoulder portion 19 and may be manufactured from stainless steel. Screwed into threaded portion 3 of body member 1 is a closure member 20 which is partially externally threaded and includes an axial bore 21 through which the cylindrical portion 14 of the upper insert 11 extends, a tapered portion 22, an annular end face 23, a cylindrical projection 24 and a radial outlet port 25 in the projection 24. Disposed in the intermediate cylindrical portion 7 is an "0" ring 26, of a flexible and compressible material, for example, Viton, whichsurrounds the cylindrical portion 14 of the lower insert 10.The "0" ring 26 is retained in position by an externally threaded ring 27 having a large diameter collar (or spokes) which projects radially beyond the body member 1 for ease of access thereto. The ring 27 may be of stainless steel.

The applicator is assembled as follows. The lower insert 10 is inserted in the body member 1 with its cylindrical portion 14 projecting through cylindrical portion 7. The separating ring 15 is inserted with its slot 16 aligned with the inlet port 9. The support element 17 is placed on the separating ring and the upper insert 11 disposed therein such that its cylindrical portion 14 is uppermost. An adaptor for a coating material inlet pipe (not shown) is inserted through the inlet port 9 and the slot 16 thus ensuring that coating material is directed to the interior of the applicator and to prevent relative movement of the ring 15 and the body member when the applicator elements are secured together. The closure member 20 is then inserted in the body member 1 with the cylindrical portion 14 of the upper insert projecting through axial bore 21.The closure member is then screwed into the body member, by, for example, the use of a "C" spanner inserted into inset holes (not shown) in the closure member 20. The "0" ring 26 is inserted in the body member 1 so that it surrounds the cylindrical portion 14 of the lower insert and the retaining ring 27 screwed into the bore portion 8.

The minimum diameter of the cylindrical portion 14 of the lower insert presented to a coated fibre exiting the applicator and thus the diameter of the coated fibre, is adjustable by varying the amount of compression of the "0" ring 26 between the retaining ring 27 and the shoulder 28 between the cylindrical portions 6 and 7. The more the ring 26 is compressed the smaller the internal diameter of the cylindrical portion 14. The adjustment of the compression of the "0" ring 26 can be manual or it can be controlled automatically by a feed back loop from a coated fibre diameter monitoring unit (not shown). Such a variable compression "0" ring arrangement is described in our co-pending Application No. 8403617 (Serial No. ) (N. Denton 3-1).

In use a freshly pulled optical fibre 29 is passed through the applicator in the direction of arrow A and coating material is supplied under pressure via the adapter inserted in the inlet port 9 to the pressure coating chamber 30. The upper insert 11 is disposed between the support 17 and the closure member 20 and movable therbetween in dependence on the coating material pressure in the chamber so that it expands slightly under the application of coating material pressure to allow a small amount of pressurised coating material to flow up past the incoming fibre in the cylindrical portion 14, wetting the fibre as it does so. The over spill of coating material after wetting of the incoming fibre is collected within a reservoir defined by the cylindrical projection 24 and exits therefrom via port 25 for recirculation to the chamber 30 or collection in a tank.The use of an upperflexible insert also means that the bare fibre will not be damaged on entry to the applicator by hitting the sides thereof. The inserts 10 and 11 may be made from a soft rubber, plastics or silicone material.

If on starting up of a coating process using the applicator there is a possibility of the upper insert turning inwards as a result of the effect of the passage of the fibre thereon before the coating material is introduced into the chamber 30, air/ nitrogen can be allowed to flow through the chamber 30 at a pressure sufficient to prevent the turning inwards, which air/nitrogen supply is switched off as the coating material is switched on. If a double coated fibre is required then this can be achieved by increasing the length of the body member, with suitable design of the adjustable retaining ring 27, to incorporate a fixed die with a second inlet port.

Alternatively, since the overall axial length of the order of 100-300 wm thick which are to be coated to an overall diameter of the order of 150-600ym, two such applicators could be arranged in series. The prewetting of the bare fibre at the upper insert due to the coating material being pressurised means that bubble free coatings can be obtained with high fibre throughput speeds. Only relatively low coating material pressures are required, typically of the order of 1/2 bar to 1 bar. In view of the tapered nature of portions of the upper and lower inserts and coating material flow considerations, under certain operations the fibre will tend to self centre within the applicator so that the applied coating is concentric with respect ot the fibre. However, additional techniques can be employed to ensure concentricity.

Claims

1. An applicatorforcoating an elongate member including a chamber having an inlet and an outlet for the elongate member, wherein the inlet is comprised by a flexible orifice element, and wherein the inlet is comprised by a flexible orifice element, and wherein in use of the applicator the elongate member is passed through the chamber which contains coating material under pressure, which coating material exits said chamber via the flexible orifice element, as well as the chamber via the flexible orifice element, as well as the chamber outlet for the elongate member, whereby to prewet the elongate member with the coating material.

2. An applicator as claimed in claim 1, wherein the outlet is comprised by a respective flexible orifice element having a portion whose internal dimensions are related to the thickness of coating material applied to the member, and wherein associated with the outlet orifice element are means whereby the internal dimensions of said portion may be varied in a controlled manner during passage of the membertherethrough.

3. An applicator as claimed in any one of the preceding claims including reservoir means to collect the coating material which exits the chamber via the inlet orifice element.

4. An applicator as claimed in any one of the preceding claims wherein the or each flexible orifice element includes a substantially cylindrical portion of internal dimensions of the order of the diameter of the coated member, an adjoining tapered portion which increases in internal dimensions in the direction away from the cylindrical portion and a radial flange portion at the end of the tapered portion opposite to the cylindrical portion.

5. An applicator as claimed in claim 4 as appendank to claim 4 including a housing member having a bore adapted to support the tapered portion of the outlet flexible orifice element with the cylindrical portion thereof projecting to the exterior of the housing member, and including a closure member threadably engaged with the housing member and including a bore adapted to support the tapered portion of the inlet flexible element with the cylindrical portion thereof projecting to the exterior of the closure member when the closure and housing members are engaged together.

6. An applicator as claimed in claim 5 and including a separating ring disposed axially between the flange portions of the inlet and outlet flexible orifice elements.

7. An applicator as claimed in claim 6 and including a support element for the inlet flexible element, the support element including a tapered portion, the tapered portion of the inlet orifice element being disposed between the bore portion of the closure member adapted to supportthe inlet flexible orifice element and the support element tapered portion and movable therebetween in dependence on the coating material pressure in the chamber.

8. An applicator as claimed in any one of claims 3 to 7 as appendantto claim 2, wherein said means includes a compressible ring through which the outlet flexible orifice element extends, which ring is disposed such as to influence the internal dimensions of said portion in dependence on the state of compression of the ring.

9. An applicator as claimed in claim 8, wherein the compressible ring is disposed in a bore of an applicator housing member and retained there by a shoulder of the housing member and an adjusting ring threadably engaged with the housing member, and wherein the state of compression of the compressible ring is variable by rotation of the adjusting ring.

10. An applicator for coating an elongate member substantially as herein described with reference to and as illustrated in the accompanying drawing.

11. A method of coating an elongate member comprising directing the member through a chamber having an inlet and an outlet for the elongate member and containing coating material under pressure, the inlet being comprised by a flexible orifice element, and allowing coating material to exit the chamber via the flexible orifice element, as well as said chamber outlet, whereby to prewet the elongate member with the coating material.

12. A method as claimed in claim 11, wherein said chamber outlet is comprised by a respective flexible orifice element having a portion whose internal dimensions are related to the thickness of coating material to be applied to the member, and including the step of adjusting the internal dimensions of said portion whilst the member is passed therethrough.

13. A method as claimed in claim 12, wherein said portion of the outlet flexible orifice element extends through a compressible ring, which ring is disposed such as to influence the internal dimensions of said portion in dependence on the state of compression of the ring, and wherein the adjusting step comprises adjusting the compression of the ring.

14. A method as claimed in any one of claims 11 to 13, wherein the elongate member is an optical fibre and the coating is applied in-line with the fibre drawing process.

15. A method of coating an optical fibre substantially as herein described with reference to the accompanying drawing.