How does splicing work?

Pneumatic yarn splicing has been established in the textile industry for many years. A splice is made by placing two yarns into a pneumatic splicer, in a flat “X” arrangement. An air blast intermingles the fibres, and integral cutters trim off the waste ends. The completed splice is then withdrawn. It is usually less obtrusive and stronger than a knot.

The critical component of a splicer is called a splicing chamber. This is a profiled metal block, which is designed to expose the yarns to a blast of compressed air. The airflow in the splicing chamber creates the splice; the chamber design defines the characteristics of the flow and thus determines the form and quality of the splice.

The general principles of the splicing action are common to all designs of pneumatic splicer. The dynamics of the splicing mechanism are actually very complex, but a basic account is easy to understand. The yarns to be joined are placed in the splicing chamber, entering from opposite sides. This is simplified by providing the chamber with a hinged closure pad. The actual splicing process starts after the yarns have been laid in the blast chamber, the pad closed, and the waste ends cut to length. An air blast enters the chamber at very high speed. The air is highly turbulent, and the violent small-scale disturbances radically disrupt the arrangement of the fibres in the splicing chamber. Those fibres which happen to lie across the opening of the air-feed hole are separated by the direct blast. Those which lie elsewhere in the chamber are subjected to a chaotic pattern of vortices downstream of the entry point, which produce twisting and intermingling.

When the air supply is cut off, and the chamber is opened, the resulting splice has a characteristic and reproducible form. The central section is essentially unchanged, with the fibres lying largely parallel. Either side of this central section, the fibres lie in dense clusters, highly twisted and intermingled together. Each cluster usually terminates in a small tail where the extreme tips of the spliced yarns have not been fully bound into the structure. When a load is applied to the splice assembly, the fibres in the clusters slip very slightly, until the entire structure stabilises, as the inter-fibre frictional forces take the load.

A splice is produced by the reaction of fibres to turbulent air. This is a random process, and therefore no two splices are the same on the micro-scale. Nevertheless, the length of the splice is much greater than the scale of the intermingling, so that the outcome is consistent from splice to splice. With continuous-filament yarns, very high splice strengths can be achieved, typically 90-95 per cent of that of the parent yarn.

Splicing chambers

The active part of a splicer is known as a splicing chamber. The chamber is a small channel, which uses compressed air to intermingle the fibres and joins the yarns together. The shape of the chamber profile controls the air flow, so that the splicing chamber is the most important part of the splicer.

Splicers are used throughout the wide spectrum of the textile business, so that different environments require different solutions. For this reason, splicers are fitted with interchangeable chambers; to splice different yarns, users simply have to fit new splicing chambers. Although the business of changing chambers is inconvenient, in general it is necessary and unavoidable, because no one splicing chamber can cover the whole range of yarns in use.

Airbond is deeply committed to research, and we have a profound understanding of how splicing chambers work. We have applied our research to improving the performance of splicing chambers, reducing the number of different chambers which are needed, and therefore reducing the frequency of chamber-changing. One of the reasons for our mastery of splicing brittle modern fibres is that we have developed new forms of splicing chamber, which reach optimal performance at lower air pressures than hitherto. When splicing fibres which are easily damaged, it is crucial to be able to operate at the lowest possible pressure.

        

The graphs show how better chamber design can have a major effect. In most conventional chambers, a useful splice strength (80 per cent of parent) cannot be reached until air pressure exceeds about 4 – 5 bar. Our more efficient forms of chamber achieve the same strength around 2 – 3 bar – damaging the fibres much less.