Reinforcements - Test method for yarns
Part 1: Determination of linear density
1 Scope
This part of GB/T 7690 specifies a method for the determination of the linear density of glass-fibre, carbon-fibre, aramid-fibre and any other reinforcement-fibre yarns.
It is applicable to all types of yarn, including single yarns, double and cabled yarns, textured yarns, rovings and staple-fibre yarns.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
ISO 291 Plastics - Standard atmosphere for conditioning and testing
ISO 1887 Textile glass - Determination of combustible-matter content
ISO 3344 Reinforcement products - Determination of moisture content
ISO 10548:2002 Carbon fibre - Determination of size content
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
linear density
(of a yarn) mass per unit length of the yarn, with or without size
Note: The unit generally used is the tex, which corresponds to 1 g per kilometre of yarn.
4 Principle
A yarn test specimen of known length, with or without size, is weighed and the mass per unit length calculated.
In the case where the yarn must be desized, this is done by extraction and drying (in the case of aramid fibre), by calcination (in the case of glass fibre) or by extraction or pyrolysis (in the case of carbon fibre).
In the case of carbon-fibre yarns, the linear density of the desized yarn may also be calculated from the linear density of the sized yarn and the size content determined in accordance with ISO 10548:2002. However, the result obtained in this way will include a small error due to the inherent error involved in determining the size content.
5 Apparatus
5.1 Apparatus for determinations on sized yarn
5.1.1 Spool, preferably with a circumference of 1 m. The spool is generally fitted with a traversing system to wind the yarn in thin layers. It may also include a tensioning system to tension the yarn while a test specimen is being taken.
The spool shall be calibrated in such a way that, for all specimen lengths, the actual length obtained is accurate to ± 0.3 %. The calibration of the spool shall take into consideration the required specimen length, the type of yarn and the type of material. This calibration shall be carried out with a particular tension in the yarn, and the operator shall be made aware of this tension.
For specimens < 5 m in length (in the case of certain carbon and aramid yarns and for glass rovings of 2000 tex or greater), replace the spool by other equipment enabling specimens to be cut to the required length with the required accuracy. A sketch of such equipment is shown in Figure 1.
Foreword I
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Apparatus
6 Test specimens
7 Conditioning and test atmosphere
8 Procedure
9 Expression of results
10 Precision
11 Test report
