FAQ’s & Additional Information

At first sight, there does not seem to be much difference between a good knot and a good splice. But there are differences, and splices are usually better:

• The yarns in a knot cross over one another. The crossed yarns act as crude knives, and tend to cut each other. The result is that knots are not particularly strong, usually no better than 60% of that of the whole yarn.
• A good splice is a tightly-bound structure; its strength comes from the intermingling of individual fibres. This form is inherently stronger; the breaking strength of a splice commonly exceeds 90%.
• Also, a good splice appears much lower and smoother than a knot, and the splice passes more freely through the elements of textile machines. The splice is usually less visible than a knot in the finished fabric.
• Overall, splices reduce waste, in processing and in the finished fabric. As a consequence, although a typical splice takes somewhat longer to make than a corresponding knot, the downstream benefits of processability and quality enhance the overall efficiency.

The strength of a splice depends on a number of factors. These include the properties of the yarn itself, such as the material of the yarn, and the splicer parameters such as splicing chamber design. Continuous filament yarns tend to be more consistent in their performance than natural materials such as wool. However, until recently, certain yarns used in composites – such as carbon – produced inconsistent results. That problem has been solved with the new generation of Airbond products, and splice consistency is now completely satisfactory, especially if electronic control is adopted.

Blast pressure is commonly used as a process variable. Mass flow rate is a more accurate parameter, but pressure is a useful, albeit indirect, measure. Pressure has a marked effect on splice strength, as shown below. The sample graph refers to the splicing of 110 tex polyester un-textured continuous filament. There is no intermingling, and no useful strength, until 30 psi is exceeded. Strength increases steadily with pressure until a maximum of about 90 per cent of parent yarn strength is reached. Once maximum strength is reached, increasing the pressure damages the yarn.

The graph below shows the effect of increasing yarn count in a particular splicing chamber. The sample graph refers to the splicing of 110 tex polyester un-textured continuous filament. As count increased from 1100 dtex (110 tex) to 9900 dtex (990 tex), progressively higher air pressures were needed. Eventually, above 5500 tex, there was essentially no strength, even at high pressures. First impressions were that the yarns had filled the chamber profile, preventing the yarns from intermingling.

On any given splicer, the distance between the cutters is fixed. The splice length, being equal to the cutter spacing, is also fixed. As yarn count increases, the ratio between splice length and splice diameter decreases. The photo shows this scale change clearly.

This question must be answered in two parts, because Airbond splicers can make different forms of joint – “ends-opposed” and “ends-together”. You can read more about the characteristics of these joints elsewhere in the website.

New splicer users can sometimes be perplexed by the fact that knives are routinely fitted to the majority of splicers. The new users cannot immediately understand why cutters are needed on tools whose sole function is to create an intermingled joint.

When splicers have no knives, it is almost invariably associated with the business of making joints in very heavy yarns. The principal reason why heavy yarns pose problems for “normal” splicers is simply that the cutting capacity of any knife assembly has some sort of limit. When that limit is exceeded, the cutting performance becomes erratic, and when cutting is poor, splicing is poor.

Timers – units which control the duration of the air blast – are fitted to only a small proportion of Airbond splicers. Timer splicers are obviously more complex in construction than the simpler models. Not every user is convinced that they are necessary. Most customers operate perfectly satisfactorily without them.

The active part of a splicer is known as a splicing chamber. The chamber is a small channel, with a carefully designed profile. Two yarns are laid into the chamber, and are exposed to a blast of compressed air. The air intermingles 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. Most improvements of splicing performance have come from improvement of splicing chamber design.

Until recently, it was not possible to splice POY without making special provisions. For splicing to work, the fibres concerned must have some level of resistance to stress – they should have a reasonable Young’s modulus. POY, which extends when a very low load is applied, is unsuitable, and it has in the past needed to be pre-stretched before splicing. Pre-stressing led to added complexity, and inconsistent performance. Recent research at Airbond has led to a simple innovation, which permits POY to be spliced without the need for any special mechanical devices – merely the fitting of a dedicated splicing chamber. This improvement, introduced by Airbond in 2012, promises to improve efficiency in the POY supply chain, because of its simplicity and effectiveness.

YES, but there are some comments. To intermingle the fibres of any yarns, it is necessary to separate their fibres; if the yarns are very highly twisted, they tend to remain tightly packed; then, splicing is very difficult. Until recently, there were two possible solutions:

• One approach was to make a standard “cross-over” or “ends-opposed” splice, by applying reverse-twist to each yarn with a mechanical device, to open the structure. This approach works very well, but it requires the use of complex splicers.
• A simpler approach was to de-twist the yarns with air, using splicing chambers with a special asymmetric cross-section to spin the bundle and open up the yarns. This approach works only if both yarns enter the chamber from the same side, so that they are both de-twisted. The result is rather a crude splice, ( “ends-together” ) but one which is OK for non-critical uses. Chambers of this form were in production far about twenty years. They suffered from a disadvantage that, although they could handle twisted yarns satisfactorily, their dimensions and characteristics needed to be matched to the twist direction and physical size of the yarns.

This company has succeeded in dispensing with the asymmetric chambers. A new and patented form of splicing chamber used in the Models 100, 101, 102, and 103 makes ends-together splices in a huge range of yarns, using a single cross-section for all sizes, and for both S and Z twist.

It depends on the type of intermingling, and its degree. Splicing itself is an intermingling process. If the yarns are so consolidated that their fibres cannot be separated, then splicing will not be possible. Some yarns are processed in order to maximise the amount of filament intermingling and disruption. The “Taslan” process is a good example. We cannot splice these yarns. Some yarns (such as bulked polypropylene) are passed through an intermingling jet, to introduce some cohesion to the yarn bundle. Such yarns have only small zones of regular intermingling. As long as the intermingled zones are not placed in the splicing chamber, it is usually possible to make a splice.

Never by pneumatic splicing. For pneumatic splicing, filaments or fibres must be separated and intermingled. If there is not a substantial number of filaments, there is nothing to separate; nothing to mix; nothing to intermingle. Some synthetic monofilaments can be spliced by other techniques – wrapper splicers, gluing, heat-welding, for example.

Some can, but most cannot. A fair amount of work has been done in this area. It appears that a splice can be made, if the splicer is persuaded to do two things at once:

• smash the tape so that it separates into its crude filaments
• splice the filaments.

This is not easy, and can only be done on tapes which are very thin compared to their width. Thin tapes can be split into a large number of strips which behave a bit like continuous filaments. The strips do not splice well, but some kind of splice will form if there are enough of them. So we have succeeded in splicing wide, thin tapes. Best results are obtained using custom splicers, such as the Airbond Model 104 or 105E. This creates a longer splice tail compared to standard carpet splices, but this is needed to give the splice its high strength and stability. We are always innovating so work is continuing in such a promising area.