This invention relates to blocking cables, that is to say, to the provision of a quantity of sealant in a cable in order to prevent the transmission of fluids along the cable.
There are many circumstances in which it is necessary to provide a fluid block in a cable, for example to prevent transmission of water or water vapour along the cable or, in the case of pressurised cables, to limit the extent of depressurisation in the event of damage to the cable. Such cables include electrical cables and harnesses, optical fibre cables and hybrid cables and harnesses that contain both electrical wires and optical fibres (the term "wire" used herein including optical fibres and the term "cable" including harnesses).
A number of cable blocking systems have been proposed. For example a heat-shrinkable sleeve provided with a thick layer of hot-melt adhesive may be used to provide a block for cables having a small number of wires, for example up to 2 wires, but in the case of larger cables having three or more wires the wires are often pushed together during recovery of the sleeve and act as a barrier to prevent the adhesive flowing into the central interstice or interstices in the cable. In addition, in the case of larger cables it is not possible reliably to heat the centre of the cable without damaging the surface of the cable because of the relatively low heat conductivity of the insulating and water blocking materials. Although systems for forming water blocks in larger telecommunication cables exist, such systems are all very expensive and are time consuming to install taking often one half to three quarters of an hour for full installation. In certain instances, however, there is a need to provide a reliable fluid block in cables and harnesses of moderate size where the cost of the block and the time taken to form it are at a premium. One example of such an instance is in the manufacture of electrical harnesses for motor vehicles.