WCA July 2015

Technology news

Quality assurance for the production of optical fibres

THE production of optical fibres is a single process that some manufacturers have specialised in. After the drawn fibre has been proof-tested and wound onto reels, the fibre is coloured in a separate step and subsequently processed to an optical cable in a loose tubing or tight buffering line. During the production of optical fibre cables, one important aspect is the protection of the fibre inside the cable. Typically, optical fibre cables receive an outer insulation layer made from PE as an outer protective coating. For this cable type, the measurement of the wall thickness of the outer insulation layer is usually necessary, especially with regards to the eccentricity of the insulation layer. The measurement of the diameter is naturally also of importance, however, a diameter measurement alone is generally not sufficient enough. The applied measuring technique for the measuring of the diameter, wall thickness and eccentricity of optical fibre cables also has to be applicable for ‘loose tube’, ‘fibre ribbon’, ‘loosely bundled’ and ‘tight buffered’ cables. Furthermore, the measuring technique should be independent of the shielding material under the outer coating. Inductive and optical measuring principles, as applied by the Centerview 8010 and 8025, have proven their effectiveness for the measuring of the eccentricity of cables with an electrical conductor made from copper or aluminium. For larger dimensions, measuring by means of X-ray is a process offering a continuous quality control during production. The applied X-ray technology is convincing as no calibration is required for different insulation materials or ambient conditions. The devices of the X-Ray 6000 series are suited for the measurement of optical fibre cables. The diameter, minimum wall thickness, eccentricity and ovality are directly defined from the X-ray image. The recording of the measuring values is carried out by an X-ray sensitive image sensor within fractions of a second. When the eccentricity of the wall thickness of the insulation layer is non-critical and the focus lies on the compliance with the specified average wall thickness, the diameter of the optical fibre cables is measured online before and after the extruder crosshead, and the average wall thickness is defined by the difference of the measured values. Generally the line speed is controlled for a singular insulation layer and the extruder rpm for multi-layer extrusion. For an optimum use of resources, an automatic allowance of material shrinkage, resulting from the cooling of the insulation layer, is recommended. The applied measuring and control technology can only be successful when it receives a high acceptance of the operator. This implies that the workload of the operator is lightened and that he can concentrate on other tasks. Sikora AG – Germany Website : www.sikora.net

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Wire & Cable ASIA – July/August 2015

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