Yarn occupies the intermediate position in the
manufacture of fabric from raw material. Yarn results
therefore essential, both for estimating the quality of
rawmaterial and for controlling the quality of
fabric produced. The important characteristics of yarn
being tested are,
- yarn twist
- linear density
- yarn strength
- yarn elongation
- yarn evenness
- yarn hairiness etc.
In order that the results obtained are reproducible and
give reliable information about the material,
the sampling must be true and representative of the bulk
lot. The sampling procedure should be designed
to take account of and to minimise the known sources of
variability such as the variation between
spindles, the variation along the length of the bobbin,
etc. The procedure for sampling and the number
of test carried out are given under each characteristic.
AMBIENT CONDITIONS FOR YARN TESTING:
Some textile fibres are highly hygroscopic and their
properties change notably as a function of the moisture
content. Moisture content is particularly critical in
the case of properties, i.e yarn tenacity,
elongation, yarn evenness, imperfections, count etc.
Therefore conditioning and testing must be carried out
under constant standard atmospheric conditions. The
standard atmosphere for textile testing involves a
temperature of 20+-2 degree C, and 65+-2% Rh. In
tropical regions, maintaining a temperature of 27+-2
65+-2%RH is legitimate. Prior to testing, the samples
must be conditioned under constant standard
atmospheric to attain the moisture equillibrium. To
achieve this it requires at least 24 hours.
"Twist is defined asthe spiral disposition of the
components of yarn, which is generally expressed
as the number of turns per unit length of yarn, e.g
turns per inch, turns per meter, etc.