By: Mike Kos (Sulzer Textile)

Manually prepared stoppage records can be a useful aid to checking and improving the running characteristics of weaving machines. Their high information value makes them the only effective aid available to the weaver for rectifying faults. It normally takes longer to eliminate warp stoppages than weft stoppages; and given that there are several thousand ends in the warp it is highly probable, from a purely statistical point of view, that a warp stoppage will occur. For this reason the following article deals only with stoppages due to warp breaks.

In order to make the procedure for identifying and eliminating errors orderly, fast and logical, the report forms are divided into main stoppage categories (warp, weft, other stoppages) and subcategories (spinning, weaving preparation, weaving, personnel etc.). Frequent stoppages can thus be assigned to a cause, a process or a procedure at an early stage in the analysis.

Weak points and thick places

For effective elimination of errors a number of fundamental preconditions need to be satisfied. Essentially, these are a trained eye and wide ranging technical expertise, as well as accurate, disciplined work.

Apart from their actual occurrence, the locations at which causes of stoppages occur are in many cases crucially important. Weak points (thin places) in the yarn, i.e. the yarn quality, are taken here as an example. In order to achieve the desired results on the weaving system in question, yarns have to comply with Sultex's guidelines (analogous to the USTER STATISTICS).

To take the correct, specific action the location of the stoppage in the weaving machine has to be known:

- at the front, between the beat-up and the front most shaft,
- in the middle, between shafts and warp stop motion,
- at the rear, between warp stop motion and warp beam.

Not every weak point in the yarn need necessarily result in a stoppage. If most yarn breaks occur in the front section they may be due to excessively high warp tension or incorrect shed setting, besides yarn quality. Potential causes of "weak point" breaks occurring in the middle and rear sections of the machine also include excessive drawing during sizing.

Thick places (slubs) are mainly associated with the yarn quality. If the yarn clearer limits are set correctly they should not occur. Nowadays, however, in keeping with textile fashions, slub yarns are frequently used. Distinguishing them requires special attention.

Knots and fly

In some processes the yarn still has to be knotted. Stoppages caused by this can be divided into two categories:

- knots that come undone: in many cases this is because the type of knot is unsuitable for the yarn, or because the tails of the knot are too short;
- knots that damage adjacent threads because their tails are too long, are of the wrong type, are not properly tied, or because too much size has been applied to them.

Most knots are tied manually. This makes it clear how far quality and reliability of production are influenced by personnel training.

Fly glued to a thread often resembles a slub or a fibre ball. However, it differs in that it is not spun into the yarn. Attentive weaving personnel can easily remove glued-on fly from the yarn during periodical tours of their machine groups. The principal point of origin is weaving preparation. Inefficient cleaning programs, which result in a major accumulation of fly on the machine and in the vicinity, are the root cause of this fault.

Typical causes of stoppages

Fibre balls and loose warp ends

Fibre balls are small, soft balls of fibre that form on the yarn wherever it comes into contact with parts of the weaving machine (reed, warp stop motion). Fibre balls that occur over the entire width of the reed are usually due to under-sizing of the warp, inappropriate sizing recipes or incorrectly applied sizing agents. At the selvedges, fibre balls can also be caused by excessive thread density or accumulation of fly in the selvedge region. Apart from under-sizing, crossed threads or incorrect setting of the warp stop motion may be responsible for fibre balls in the warp stop motion.

Loose warp ends also require different remedial measures depending on whether they occur only in the selvedge region or over the entire drawing-in width. Generally speaking, faults in this category are attributable to warp preparation, and in particular to the setting and status of the warp yarn tensioning devices, and the way the weaving room personnel work. Loose ends may also be the result of snarls opening up or inadequate yarn twist. On the other hand, if loose ends are found at the selvedge, the cause may be neglected maintenance of the temples, the selvedge draw-in, the tucking needle or the weft end gripper.

One area that is generally critical is the selvedge. Incorrect or inadequate warp preparation can result in a variety of problems with the selvedge. Apart from loose ends, broken ends can also occur in the selvedge itself. Therefore, in addition to the points mentioned above, care must be taken to ensure a faultless selvedge weave and correct adjustment of the shed in order to effectively avoid these problems.

System-related stoppages

Due to their high speed, air-jet weaving systems are most susceptible to the effect of a poor selvedge. The slightest obstacle to weft insertion, caused by loose ends or excessive hairiness of the warp yarn, will cause a stoppage in the form of a loop, or a �pick around a warp end�. Stoppages of this type are also referred to as warp-related weft stoppages. Although it is clearly a warp problem, data monitoring systems record stoppages of this kind as weft stoppages. This clearly indicates the importance of manual stoppage analyses.

A knocked-off or cut-off warp end is a typical cause of stoppages on projectile and rapier insertion systems. Characteristic for this is a thread whose end resembles a cut thread and when stretched out extends exactly from the fell to the weft insertion units.

With higher productivity to better quality

Reliable identification of causes calls for precise analysis. For example, if a knot or nep is found in the vicinity of a broken end, it should be noted in the corresponding category. The question whether the thread break is attributable to the same shaft or only to the temple region requires careful observation. The action to be taken will depend on the findings. Besides immediate action such as modification of the shed and temple settings, changing of the stringing density, or corrections of the harness draft and reed denting, switching to a different yarn quality must also be considered.

Only by specific, manual analysis is it possible to differentiate fault characteristics accurately and to take the logically correct remedial action. This is why fault analysis is one of the main areas covered by Sultex�s TTC (Textile Technical Consulting) audits, which normally take no more than 1-3 weeks. With TTC audits, potential causes of faults are rapidly detected. The result is a sustained increase in weaving productivity and quality.

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