In addition to other methods, e.g. tensile testing, linear density measurements or determination of crimp properties, shrinkage testing of single fibres is an important fibre testing method in the quality control of the fibre producing industry. The results of shrinkage tests supply information regarding production uniformity or possible occurrence of process disturbances. Moreover, they enable predictions of shrinking behavior of the downstream products.

The operational sequence of a shrinkage test consists of an initial length measurement of the fibre, followed by thermal or hydrothermal treatment, and - after a reconditioning period - a subsequent second length measurement. The resulting shrinkage value is the decrease in sample length, expressed as a percentage of the length of the untreated specimen.

The length measurement method for shrinkage tests used to-date, i.e. reading of the straightened fibre length in relation to a length scale, is relatively labour intensive and quite inaccurate, as it is dependent on operator skills. In addition, in case of hot air treatment, using conventional heating cabinets, the measured values can vary significantly due to temperature changes, when the sample is placed into the cabinet.

Textechno's new HELFIS system overcomes these problems with a fully automatic fibre length measuring station and a computer controlled heating cabinet HEATLIFT, which has been specially developed for the hot-air treatment of fibres, introducing the fibre sample at a defined speed from below into the heating cabinet through an air lock system.

During length measurement and thermal treatment, the single fibres are located in a frame-shaped sample carrier, which has a mass of only approx. 2 g. As a consequence, the very even temperature distribution inside the heating cabinet is not impaired. This even applies immediately after introduction of the sample. Usually, the fibres are subjected to the thermal treatment in a relaxed state. At this stage there is however an option to attach small pre-tensioning weights to the fibres, enabling data collection concerning shrinkage force and shrinkage energy.

Alternatively, shrinkage can also be initiated by treating the fibre in boiling water. A hot water container suitable for this method is available.

The length measurements are carried out on the totally relaxed, crimped fibres. Here, unlike other shrinkage testing methods, attaching pre-tensioning weights to straighten the fibres is unnecessary.

A loading unit for the sample preparation is available, which substantially facilitates fibre introduction into the sample carrier.

The above contents can be subject to changes by Textechno.