BS ISO 2648:2020 pdf download.Wool — Determination of fibre length distribution parameters — Capacitance method.
7.2.4 Rovings or slivers weighing more than 30 g/m
In the case of rovings or slivers weighing more than 30 gfm, 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 Z22.
8 Procedure
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 halls of sliver or bobbins of roving, the 1,2 m long sample can he 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.
8.1.4 In the case of automatic motorised grip, introduce the sliver sample into the mechanical grip with a doubled condition, as described in Annex B. and take draws simultaneously from both ends of the sliver sample. The result of the single test is made on the both ends.
8.2 Measurement
8.2.1 Switch on the machine and warm up for at least 10 mm.
8.2.2 Select the desired material range and the fibre length measurement range.
8.2.3 Check the plastic transport sheet and make it clear of fibres, soil or dust and free from grease and static charges.
8.2.4 If needed, carry out the calibration check for ensuring the accuracy of the tests, by using the plastic trapeziums as described in operation manual.
8.2.5 If needed, carry out the zero-setting for the instrument.BS ISO 2648 pdf download.