Wednesday, January 19, 2011

YARN PROPERTIES

The strenght / strench properties of yarns are dealt with in the general chapter on that suhect .The principal test considered here are for yarn size, twisr, fold ,and regularity.
YARN "SIZE"
                      the size or .number of a yarn is stated in one of two ways:as the lenght per unit weight ,or as the weight per unit lenght. The former method is used for spun yarns and the latter for filament yanrs.
There are different units of lenght and weight for different fibres and in diffferent countries, and the position as it exists today is  chaotic and illogical . Various proposals have been made for international standardisation, but these have made little progress because any abrupt change would cause great dislocation of established customs and records.
For spun yarns the number of hanks of a standard lenght which together weight a standard amount gives the "counts ". For example,in worsted yarns the counts is the number of hanks of 560 yds. each,which weigh 1 IB.

For filament yarns the weight in grams of a standard hank of 9,000 meters gives the so-called "legal denier" but othe r hank lengths and other weight units are employed. In practice both counts and denier are determined in the same way i.e., by winding a definite number of yarns or metres into a hank, and calculating according to the appropriate system. The standard yarn reel (fig. 59) in general use cousists of six arms, of such a length that a single circuit of a hexagon is exctly 1,1/2 yds. for the counts system, or surface of the reel. A constant speed normally tension device should be incor porated.The winding speed normally varies between 100 and 300 revolutions per device should be just sufficient to take out crimp from the yarn without stretching it. A revolution counter must be fitted to record the number of turns of the it is fuseful to have a bell which gives warning when the required number of turns is being approached. The hankof yarn produced is weighed on any suitable and sufficiently sensitive balance; if many determinations of counts or denier are to be  carried out is canvenient to employ either the so-called "grain scales, or a quadrant-scaled balance , both of which can be arranged to give ditect reading of the counts. The quadrant scales are not usually accurate enough for analytical purposes, though excellent for works control. Weighings are usually carried out in the air dry state, preferably conditioned to standard regain. For precise purposes, or where no humidity control is available, weighing in the , oven-dry , state and calculating to canditioned weight at standard condition or regain should be adopted.

There are two general methods of procedure . in both cases the yarn is conditioned in the standard atmosphere of 65% R.H. at 68 deg. F.( conditioning from the dry side), before winding on to reel. method A. The reeled tarn is dried to constant weight, weighed, and the dry weight calculated to standard regain by adding the accepted percentage; the yarn count is as reeled is weighed, and the yarn count calculated from this " conditioned weight".
The two methods will usually give slightly different counts, dependent upon the degree to which the standard regain differs from the actual regain ( conditioned regain ) in equilibrium with the standard atmosphere. Method A is suitable for yarn of mixed fibres  ( e.g.,wool /cotton mixtures) and for fibres where the standard regain often differs appreciably from the conditioned regain (e.g. wool, viscose ). Method B is suitable for fibres whose standard regain does not differ greatly from the conditioned regain (e.g., cotton acetate,) for many commercial and technical purposes , and for cases where the yarn carries volatile oils or finishes.
    The textile institute tentative specification No.11 (1947) recommends reeling conditions such that the girth of the skein when removed from the reel is within 0.5% of the girth of the reel, when the skein is under a load of 440 yds . of the yarn under test. In this specification details are given of a skein gauge suitable for determining the skein girth.

In determining the grey counts of yarn from measurements on finished cloth, For example, in the case of cotton cloth, the average ptocessing losses may be taken as follows : designing -3% ; designing and bleach- ing- 5% ; designing bleaching , and dyeing to a light shade -7% ; designing and dyeing to dark shade ( no bleaching )-3%; aniline -black  dyed material gain of 2% ; mineral khaki gain of 5%. Writing G= estimated grey count F = count found in finished cloth, and L= loss factor in finishing ,then G= f(100-L /100).  

1 comment:

  1. The size or .number of a yarn is stated in one of two ways:as the lenght per unit weight ,or as the weight per unit lenght. The former method is used for spun yarns and the latter for filament yanrs.

    Sourcing and Intenting Company

    ReplyDelete