Introspective of the system of yarn numbering employ,two basic requirements for the determination of the yarn number are an accurate value for the sample length.At first glance these requirement appears simple enough,but in practice there are possible source of error which must either be eliminated or accounted for in the calculation.The method of determining the yarn number depended to large extent on the from in which the yarn is available for testing.For instance ,when yarn is in the from of a ring bobbin a long sample length can be taken,but if the warp and weft count of the yarn in a 6 inch X 6 inch piece of fabric are required only a number of short length are available.Some of these points will now be considered.
Length Measurement: Yarn is the package from.Where the yarn is in package form,such as ring bobbins or cones,it is usual to wind a number of skeins by means of a warp reel.This is a simple machine consisting of a reel,yarn package creel, a yarn guide which has a small sideways traverse to spread the loops of yarn, a length indicator.The warp reel may be and or motor-driven and some are fitted with yarn tensioning device.For cotton yarn the reel has a girth of 54 inch ,1.5 yards,so that eight revolution of the reel produces a skein of 120 yds or a lea.The reel girth and the skeins length are chosen to suit the section of the trade concerned,1 m reel girth for metric system.A first check should be to make sure that the girth of the reel is in fact,54 inch.1 m or 36 inch. Inaccurate reel are not unknown and the author met one which was conical,being more than 54 inch at the back and less than 54 inch at the front.Because yarns posses extensibility,it follows that the tension will produce a skein of '120' yards which will be too light in weight and the calculated count will be on the fine side .A skein gauge can be used to check that the reeling tension should be such that when the skein is under a load per end equal to the weight of 440 yards of the yarn tested,the indicated skein girth should be within 0.5 per cent of the reel girth.The limits are sent on the skein gauge scale with a pair of movable pointers.
When yarns is wound on to a package a certain amount of tension is put on the yarn to eliminate weak place or give the package stability .The yarn is therefore in a state of strain and so ,when the yarns is pulled freely off this strain is recovered. that is the yarn relax and contacts.To counter the source of error such yarns should first be wound into hank form,allowed to relax in the testing atmosphere for not less than 3 hours ,and wrapped for count on the reel.
Where possible,it is always recommened that yarn should be allowed to condition in to the testing atmosphere ; if in hank form for at least 1 hour, and at least 3 hours package, after which the relling should be carried out the correct tension
Yarn In Short Length: The determination of the yarn count of yarn in a fabrics is usually made on a comparatively short sample because the piece of fabric available,even if full width,is of the often only a yard or so long.Sometimes only a square foot or two is available and the test method is then modified accordingly.After conditioning in the testing atmosphere( for 24 hours where possible) ,two rectangular warp way strips and five weft way strips are cut from the cloth.In length,the strips should be about 20 inch and wide enough to allow fifty threads to be removed from the fact that 100 threads from two warp strips represent 100 warping package and from the weft way strips may only represent five weft package,but even this is better than only testing the count two weft package.
Yarn removed from fabric is crimped due to the interlacing of the threads,and it is necessary to estimate the straightened length of the threads either by rough crimp check,stretching the thread over a rule,or by a crimp tester .
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