New users - splicing principles
The general principles of the splicing action are common to all designs of pneumatic splicer, and to all types of yarn. The process stages are simple to explain, but a simple account conveys no impression of the dynamics of the splicing mechanism.
To date, there has been no publication of a convincing theoretical analysis of the highly complex fluid dynamics of the processes within the splicing chamber. Direct observation is very difficult, firstly because the splicing chamber is closed when in use, and secondly because the processes occur extremely quickly. Even when it is possible to make direct observations, for example by making transparent splicing chambers, observation, even by high-speed photography, is of only limited use. Most of the conclusions about splicing performance have been inferred from indirect observations - for example, by using tracer filaments which can subsequently be observed and photographed. Understanding of the splicing process is therefore largely based on a qualitative interpretation of experimental data which has been accumulated over many years of progressive development.
The account which follows will therefore describe only an outline of the processes in the simplest form of splice. No account will be taken in this first description of the various methods of preliminary end-preparation which may be used, since there are many forms, and such methods are of greatest importance with the more complex yarn constructions.
However, please note that this company has recently completed a long programme of research which has led us to understand the fundamental principles of splicing better than ever before. This work has been reported in a manner which is necessarily technical, and somewhat complex. Interested readers may wish to have access to (non-confidential) elements of these research findings. Please contact Graham Waters for help in this matter.
The principles of splicing are easiest to understand in the case of a simple transverse splicing chamber, with a single central blast hole, splicing a continuous filament yarn with a low twist level.
It is necessary first to place the yarns into the splicing chamber. This is simplified by providing the chamber with a hinged cover (called here a chamber pad, or simply pad) which is normally open. The yarns to be joined are placed in the chamber, entering from opposite sides.
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 by the integral knife assembly. At an appropriate interval after the ends have been trimmed, the air blast is introduced into the splicing chamber. The transverse blast enters the chamber at very high speed. The air is highly turbulent, because of its speed, the detail characteristics of the chamber design, and the acute directional changes in the chamber. 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, which corresponds to the air entry point, appears 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. Turbulence is by definition a random process, and therefore no two splices are structurally the same on the micro-scale. Nevertheless, the length of the splice, compared to the scale of the intermingling, is such that successive splices are for all practical purposes identical. The sum of small-scale interminglings results in a whole which is consistent from splice to splice.
With continuous-filament yarns, using even a very simple process such as that described above, very high splice strengths can be achieved, typically 90-95 per cent of that of the parent yarn. The advantages of splicing over traditional knotting are thus clearly demonstrable; the appearance of a splice is usually less obtrusive than that of the knot, and the strength is usually much greater.
The above is an idealised account of a splice of the simplest kind. The picture becomes much more complex when staple yarn is being spliced. Staple yarn comes in a multiplicity of forms: the staple length may be short or long; the spinning system may take one of many forms; the twist level can take almost any value; the yarn may be singles, two-fold, or multi-fold, with almost any level of folding twist; the yarn may be assembled from one or many fibre types.
The splicing process acts at the level of the individual fibres. It is therefore clear that the splicing of spun yarns, though conforming in general terms to the simple description outlined above, must pose a more taxing set of problems. Much of the development effort required to make pneumatic splicing more universal in its application has gone into the generation of specific solutions for staple yarns.
With spun yarns, with their more complex construction, it is necessary to present the yarns to the splicing chamber in a form which facilitates the splicing action. To this end, some splicer manufacturers have developed end-preparation techniques, which subject the fibres to a preliminary treatment. Others have used novel chamber forms. Some have modified the splicing technique itself, and it is this choice of splicing procedure which will be described in another section.