BS ISO 2648:2020 pdf download – Wool — Determination of fibre length distribution parameters — Capacitance method
7 Sampling and preparation of laboratory sample
7.1 Sampling Samples shall be taken from bales distributed equally throughout a lot. Only one sample shall be taken from a bale, unless the lot is smaller than 5 bales when an equal number of samples shall be taken from each bale. To characterize a lot, take at least one sample from each of 5 homogeneous portions of the lot to form the total sample. For masses greater than 5 000 kg, at least one sample shall be added per 5 000 kg portion. NOTE Homogeneous portion of the lot is a ball or bump of sliver, a can of drawing sliver, a roving bobbin, a sliver or roving taken directly from a finisher. Samples shall not be taken for measurement from the disturbed outer layer, or immediately next to the core of a package. Slivers having adventitious thickness faults (especially abnormal thick or thin places) are to be discarded. Slivers taken directly from a comb, cut or chopped slivers and those containing fibre bundles are also unsuitable. In such cases, the variation in fibre length between successive samplings is likely to be very large, potentially giving rise to significant errors.
7.2 Preparation of laboratory sample
7.2.1 General To obtain a suitable laboratory sample, fibres shall be under semi-relaxed state. To achieve this form, pre-treat laboratory samples according to Annex A.
7.2.2 Slivers of combed wool weighing between 15 g/m and 30 g/m For slivers of combed wool weighing between 15 g/m and 30 g/m, a length of about 1,2 m is broken off from the homogeneous portion of the lot. Immediately after sampling, the sample held under slight tension is given 36 turns of twist (30 turns/m); held taut in this condition, it is doubled at its centre and its ends are brought together and held. See Annex A for details. In this form, the sample can be stored indefinitely and can easily be sent by post in a plastic bag, or held fast on a tube of approximate diameter 40 mm in the twisted state, to the testing laboratory. For in-mill management, the operation of twisting may be omitted only when the ball of combed sliver or of roving is available at the moment of testing and if the test is going to be carried out within 4 h of sampling. NOTE This twisting operation is absolutely essential in order to obtain accurate test results.
7.2.3 Rovings or slivers weighing less than 15 g/m In the case of rovings or slivers weighing less than 15 g/m, sufficient 1,2 m lengths of sliver are successively drawn to build up, by overlaying, a sliver which weight per metre is about 22 g (30 g maximum). At the time of the overlaying, the slivers shall always be laid in the same direction (for example, the leading end as delivered by the mill machine always to the left).
Then, without any delay, this built up sliver is subjected to the twisting and hanking operation described in 7.2.2.
7.2.4 Rovings or slivers weighing more than 30 g/m In the case of rovings or slivers weighing more than 30 g/m, a length of approximately 1,2 m is broken off from the homogeneous portion of the lot. The sample is then carefully separated along its length into 2 approximately equal portions of similar weight. At random, one portion is discarded, and without any delay, the remaining portion is then subjected to the twisting and hanking operation described in 7.2.2.
8.1 Preparation of test specimen
8.1.1 The laboratory sample, kept in the form of a twisted hank, is untwisted immediately before the start of testing. The sliver, held with one end in each hand, is then straightened by putting it under slight tension and subjecting it to gentle shaking. When testing balls of sliver or bobbins of roving, the 1,2 m long sample can be taken immediately before making the measurement, after unwinding a few outer turns that have lower tension. Bump strings shall be cut immediately prior to testing and samples shall be taken from sliver/roving that does not contain pressure creases.
8.1.2 Take a certain number of successive fibre draws from a sliver sample, parallel fibres from one original base line to form the test specimen. These draws are made by using the semi-automatic grip or an automatic mechanical grip. The number of draws is determined by experience, normally approximately 6 to 10 draws are suitable to make up a test specimen, made up of approximately 30 000 fibres. Two test specimens are measured from each laboratory sample.
8.1.3 Top sliver is slightly asymmetrical because of the presence of fibre hooks in unequal proportions in the 2 directions. In the case of semi-automatic grip, carry out a single test on the left–hand end of the sliver sample and a single test on the right-hand end.