ISO 1973:2021 Textile fibres — Determination of linear density — Gravimetric method and vibroscope method

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Textile fibres — Determination of linear density — Gravimetric method and vibroscope method

1 Scope

This document specifies a gravimetric method and a vibroscope method for the determination of the linear density of textile fibres applicable respectively to:

a) bundles of fibres;

b) individual fibres.

Useful data can be obtained on man-made fibres and, with less precision, on natural fibres.

This document only applies to fibres which can be kept straight and, in the case of bundles, parallel, during test preparation. It is properly applicable when the fibres are readily freed of crimp. The methods in this document are not applicable to tapered fibres.

The vibroscope method is not always applicable to hollow and flat (ribbon-like) fibres.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 139, Textiles — Standard atmospheres for conditioning and testing

ISO 1130, Textile fibres — Some methods of sampling for testing

ISO 6989, Textile fibres — Determination of length and length distribution of staple fibres (by measurement of single fibres)

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://w ww. iso .org/ obp

— IEC Electropedia: available at http://w ww.e lectropedia. org/ 3.1

tension

force tending to cause the extension of a body

3.2

tensioning force

force effective on a fibre specimen during the vibroscope test

Note 1 to entry: In textile testing, the tensioning force applied is based on the linear density or cross-sectional area.

4 Principle

4.1 General

Two methods for determining linear density are described.

4.2 Gravimetric method, for bundles of fibres

Specimens of a given length are weighed on a balance. This method is applicable to bundles of fibres.

4.3 Vibroscope method, for individual fibres

Individual fibres of a given length and under specified tensioning force are subjected to vibration at resonance frequency. The linear density is determined from the conditions of the resonance state, i.e. the resonance frequency, the vibrating length of the fibre and the tensioning force. The linear density is read directly on the scale or a display of the vibroscope apparatus respectively reported by a connected computer system. This method assumes that the linear density of the tested length of the fibre is constant.

Under certain circumstances (e.g. a short vibrating length, a low tensioning force, high-modulus fibres) the vibroscope method results are falsified by the bending stiffness of the fibre. As a compensating countermeasure, a correction factor can be applied (refer to 8.2.1), if agreed on by the interested parties.

5 Apparatus

5.1 Gravimetric method apparatus

5.1.1 Balance, suitable for weighing the bundles of fibres to an accuracy of at least ±1 %.

5.1.2 Device for cutting, the bundles under tension to a length known within an accuracy of ±1 % and allowing an adjustment of the tension of the bundles to be cut.

For example, two razor blades set parallel in a suitable holder may be used.

5.1.3 Comb sorter, for preliminary alignment of fibres.

5.1.4 Textile support fabric, of a colour contrasting with that of the fibres to be tested.

5.1.5 Glass plate, measuring approximately 100 mm × 200 mm, with one polished edge.

5.2 Vibroscope method apparatus

1)

5.2.1 Vibroscope , having the following accuracy:

a) the applied tensioning force shall be within the range of ±0,5 % of the specified value;

b) the error in the vibroscope reading of resonance frequency measured or applied shall not exceed ±0,5 %;

c) the error in the vibroscope reading of vibration length of the fibre shall not exceed ±1 %.

1) For a list of suppliers of suitable vibroscope equipment, apply to the Secretariat of ISO Technical Committee 38.

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