Twist Measurement Of Plied Yarns

For a variety of technical reasons many textile structures are designed either completely or partly with the component yarns in doubled or cables form.Generally speaking,the inference is that the desired properties of the structure could not be obtained, or at least to the required degree if only single yarns were used.Luster,regularity ,strength extensibility,elasticity,liveliness,and docility are the kind of yarns properties which may be 'built' into a plied yarn by the right selection of the single yarns and the technique of construction.It is necessary,therefore,to able to analyze plied yarns to determine such details as doubling twist,single twist,take-up,resultant count,count of component yarns,and so on.

A number of papers on the properties of double yarns and the effects varying structural details are be found in the literature.The former is concerned with cotton and staple rayon yarns,and the latter with the mechanical properties of twisted continuous-filament yarns.In the other note which follow we shall deal only with the measurement of twist and the changes in length due to twist.The simple types of yarn will be mentioned but the basic methods can be extended to cover more complicated plied yarn structures.

'Take-up' Twist Testers

'Take-up' is defined as the difference in length between the twisted and untwisted thread,expressed as a percentage of the untwisted length.It is positive or negative according to wether the doubling twist causes contraction or extension in the folder yarns.Special twist testers are available which have device on them to accommodate the change in the specimen length as the test proceeds,and so they are commonly known as 'Take-up' tester.