Prevent yarn defects with Uster Statistics

For the answers, it might be useful to start with an example of a particularly troublesome fabric defect that we are all familiar with: pilling (sometimes called 'bobbling') – the appearance of little balls of fuzzy fiber on the surface of a garment.

Obviously, pilling is a serious problem for the entire production chain, since the consumer's dissatisfaction with a product will quickly rebound on the retailer, clothing manufacturer, fabric producer and, ultimately, the yarn spinner.

Pilling: causes and prevention

When we look at an example of pilling, there is a simple statement we can make: “With USTER STATISTICS, this wouldn't have happened.” In most cases, fabric defects can be traced back to the yarn – not necessarily 'bad' yarn, but usually yarn with the wrong quality specification for its intended end-use. With pilling, the cause is generally a yarn which is too hairy. To define the level of hairiness – the H value – in a yarn spinners carry out a routine in their lab, testing the yarn package.

The numerical H value resulting from the test is automatically matched against percentile levels in USTER STATISTICS. These percentiles, known as USPsTM, show by how much the yarn is above or below a certain value, based on comparisons with what other spinning mills worldwide are producing.

For example, the 5% level means 5% of mills worldwide are producing yarn with equal or better quality levels for the particular parameter being compared. The same applies to the limit levels of 25%, 50%, 75% and 95% shown up by the USTER STATISTICS.

In the fabric example illustrated here, the level of pilling was produced by a yarn with an H value of 7.71, equivalent to a USPTM of 95% – clearly showing that the yarn hairiness was too high for the end-use. To avoid pilling, a fabric specialist would be able to determine that, in this case, a yarn with hairiness USPTM of 50% would have been required.

Uneven fabric appearance: a clear view

A second example  shows another kind of defect which can also lead to lost customers: uneven fabric appearance with very visible faults and inconsistencies that are always going to be unacceptable. This type of defect has a number of likely causes, all showing up in the yarn: too many neps in the raw material; too many short fibers in the yarn; poorly-maintained machinery; etc.

And, once again, we can confidently say: “With USTER STATISTICS, this wouldn't have happened.” To eradicate the kind of unsatisfactory uneven fabric appearance seen in this example, we must focus on the yarn quality parameter known as CVm, for Coefficient of Variation of mass. Experience has proved that this characteristic strongly impacts on how we can expect the finished fabric to look.