Twist And Twist Measurement

In its wider connotation,the word "spinning" embraces all the various processes which are necessary to transform fibrous raw materials into yarns.Even in the man-made continuous filament plant where extrusion processes produces the yarn,one stile talks of spinning   .A more particular meaning is given to the word when we consider the process in which a strand of fiber in a more or less parallel order is spun or twisted on its exist to from a yarn.The necessity for twist in yarn construction is reflected in most but not all definition of term "Twist".

Twist is the measurement of the spiral turns given to a yarn in order to hold the constituent fibers or threads together.
When a strand is twisted the component fibers tends to take on a spiral formation ,the geometric perfection of which depended on their original formation.
Twist may be defines as the rotation about the yarn axis of any line drawn on the yarn which was originally that is before twisting parallel to the yarn axis

Accepting the fact that twist is necessary to give a yarn coherence and strength,many question now arise,amongst them the two important ones of " How much twist be inserted into a yarn" and " what effect have varying amounts of twist on the yarn properties? Before dealing with such question the methods of describing twist and expressing the amount of twist be considered.

Twist Direction: The directions of twist at each stage of manufacturer is indicated by the use of the letters S or Z in accordance with the following Convention.

A single yarn has S twist if, when it is held in the vertical position ,the fibers inclined to the yarn conform in direction of slope to the central portion of the letter S . Similarly, the yarn has  Z  twist if the fibers inclined to the axis of the yarn conform in direction of slope to the central portion of the letter Z .This figure illustrate these definition .Other methods of describing the twist direction will be found in order text box on spinning , but since they lead to confusion it id considered wise to omit them here.From the spinning point of view ,it normally matters little which way the twist goes.However, when single yarns are plied or combined in the form of fabric,the direction of twist become important because it influence the character and the appearance of the finished article.

Amount Of Twist-For many practical purpose this method of expressing the amount of twist serves quite well,but the expression contains no reference to the count of the yarn.A coarse yarn with 20 T.P.I has vastly different twist characteristics to a fine yarn with 20 T.P.I .By using an expression known as the "twist factor" or "Twist Multiplier"  it is possible to appreciate the twist character of yarn even without knowledge of the yarn count.

This figure represents an idealized element  of yarn ,showing one fiber on the yarn surface following a helical path and making one turn round the yarn axis.The twist angle is the between a tangent to the helis formed by the fiber and the yarn axis.By unrolling the surface layer we see that the fiber become the hypotenuse of a right angled triangle.

We noted earlier when the count system is an indirect system,the yarn diameter is proportional to the reciprocal of the square root of the count.

 This is more conveniently expressed in the following form

                                                     Turns per inch = K root count
The constant K is termed  the twist factor or twist multiplier and is directly proportional to the tangent of the twist angle.A range of say cotton yarns spun to different  count ,but with the same, twist factor throughout,will possess the same degree of hardness and twist character.The spinning frame over looker can readily calculate the T>P>I required to spin a give count with a specified twist factor and calculate the twist wheel required from the twist constant of the frame.

Rationalization Of Yarn Numbering

Conversion of count from one system to another costs time and money and there is always the risk of a mistake. As the textile industry developed commercially and technically ,it become increasingly clear that was need to devise a system of yarn numbering which could be used by all concerned in the production and distribution of this urgent need did not lead to its speedy solution.Numerous discussion and conference have been held but it was mot until comparatively recently that a firm decision was taken .

The Tex System:   The yarn number or count in the Tex system is the weight in grams of 1 km of yarn.This system is therefore a direct system, simply defined and simple to use.Extension of the basic system are used in order to express the fineness is expressed in  ''millitex" that is the weight in milligram per kilometer  .Foe such intermediate products as slivers and coarse yarn structure likes cords,the count is expressed in  "Kilotex" that is the weight in kilograms per  kilometer or what amount to the same thing, grams per meter.

The adoption of the Tex system of yarn numbering will ,of course, be a slow process work and some headaches until everyone becomes familiar with it, but this short-term disadvantage will be more than compensated for in the future when the old system are merely of historical  interest.A number of yarn and fabric feature are used numerically,and in their calculation the present system are used.For example the twist factor for a cotton yarns indicates the degree of twist in the yarn and is related to the count turns per inch in the following way :

It is  immediately obvious that when the Tex system is used "Terns per Inch" Will no longer be a suitable way expressing twist and that metric length unit would be appropriate , say, "Terns per inch " .The twist factor will therefore be different.Further since the Tex system is a direct system and cotton system an indirect system,the from of the relationship between turns ,twist factor, and count will change:

 Numerical examples to illustrate this point will be given when twist testing is discused later in this chapter.I fabric technology the openness, or, more appropriately,the closeness of a fabric, is expressed by the 'cover' factor.The warp cover factor is given by:

Again it is apparent that the inch must be by a metric length unit and that (rot cotton count) will be a different value to {rot (Tex Count)} .The cover factor could become.

1. Tex = 590.5 / Cotton count

2. Tex = denier x 0.111

A few calculation will show that the equivalent tex yarn yarn number of a 'round' traditional count is usually far from round.For example, 32 s cotton count become 18.45 tex ,and 150 denier become 16.67 tex. It will be appreciated that when the tex system is used commercial,inconvenient number such as these must be avoided.The industry will be obliged to alter its present range of yarn thicknesses slightly and spin to convenient tex yarn numbers.When the change is made the opportunity arises for the introduction of a reduced range of yarn thicknesses,an idea which has been put forward before.

Tex	Cotton	Worsted
10	59.5	88.6
10.5	56.1	83.4
11	53.7	80.5
11.5	51.3	77.0
12	49.2	73.8
12.5	47.2	70.9
13	45.4	68.1
14	42.2	63.3
15	39.4	59.5
15	36.9	55.4
17	34.7	52.1
18	32.8	49.2
19	31.1	46.6
20	29.5	44.3
21	28.1	42.2
50	11.8	17.7
60	9.8	14.8
80	7.4	11.1
100	5.9	8.9

Yarn count and Yarn Diameter

An increasingly important branch of textile technology is  the geometry of fabric structure,of a subject which forms rational foundation upon  which to base a scientific study of fabric construction.The appearance ,handle.drape ,and general behavior of fabric are dependent upon many factors such as materials used ,yarn structure,weave, and finish.Just how these factors such interact is a major problem comforting the fabric engineer.One important dimension required in the study of fabric geometry is the diameter of a yarn ,a first assumption being that a yarn has in fact ,a circular cross-section .In a practice,it is recognized that even if a yarn were circular to being with,it would be distorted that when interlaced with other threads,and later perhaps flattened when during calender .

The Measurement Of yarn Number or Count

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 .

Linear Density Count and Yarn Number

The count of a yarn a numerical expression which defines its fineness.When a engineer requires the fineness of wire ,he consults a Table of standard wire gauge values.For instance in the imperial standard wire gauge values.For instant in the imperial standard wire Gauge table we find that a wire gauge number of 10 corresponded to diameter of 0.128 in. Alternatively,by measurement of the wire diameter by a micrometer,the corresponding gauge number can be read from the table.Measurement of the diameter of yarn poses rather s different problem.Spun yarns are only roughly circular in -cross-section and irregularity in thickness is unavoidable.Filament yarns with only a small amount of twist in them are referred to as flat yarns  possibly because they flatten so easily when in contact with other more solid bodies.Since most yarns are relatively soft and compressible,the use a micrometer for diameter measurement is ruled out.Optical methods can  be used one method being described .A magnified silhouette of the yarn is projected on the screen which has a scal graduated in thousands of yarns inch.The object of this testis not a determined in thousand of yarn count inch.

One special Section of the textile industry,The cordage and rope making trade,use a counting system related to the cross-section area of the yarn: The count  of the yarn is the number of such yarns which are required to from one strand of a three-strand 3 in circumference rope.This is an unusual approach used for a particular job and is not met with in the normal run of thing.

Direct And  Indirect System of yarn Numbering:

A definition of yarn above contain the phrases 'mass per unit length 'and 'length per unit mass' indicating that two basic principal are employed.

Direct System In a direct system yarn counting system the yarn number or count is the weight of a unit length of yarn.The units of weight and length very from trade to trade and district to district, a state of affairs which results in a multiplicity of counting systems.This will be looked into shortly but for the moment we will consider a general formula which applies to all direct systems.

Let N = The yarn Number or count.
     W = The weight of the sample at the official regain in the units of the system.
      L = The length of the sample ,and
      l  = The unit of length of the system.

Example.If asking of 100 m of filament viscose yarn weight 1.67g Calculate its denier.

In the denier system the weight unit is the gram and the 'Unit of length' is 9000m.The denier of yarn is the weight in gram of 9000 m.Thus W=1.67g, L=100m, and l=9000m.There fore

Indirect System:

In an indirect system the yarn number or count is the number of  "Units of length" per  "Unit of weight".Here again there are various units of length and weight and numerous systems.Generalizing:

Let N = The yarn Number or count.
     W = The weight of the sample at the official regain in the units of the system.
      L = The length of the sample ,and
      l  = The unit of length of the system.

Example:A lea (120 yd) of cotton yarn weight 25 gr, calculate its count in the cotton system.

In this case the  " unit of length is the hank ,840 yd, and the "unit of weight" is 1 lb there are 7000 gr.Hence L = 120 yd,  l = 840  yd ,W = 25 / 7000 lb, and w = 1 lb

 Counting System:

Table gives the value of the unit of length and weight used in some direct and in direct system of yarn numbering- a curious Table it look,too!.The name of of some will suggest to the reader that one of the reasons for this diversity is geographical.The textile industry grew up in different localities and each chose its own systems to suit local condition.Conversion from one system to another system is achieved by conversion factors and constant.Where a direct to a direct system,or an indirect to an indirect system is concerned, a multiplying conversion factors is used.

Direct System

System	Unit Of Mass	Unit of length
Tex	Gram	Killometer
Denier	Gram	9000 meters
Linen (dry-spun) ,Hemp,Jute,	Pound	14,400 yards
Jute	Dram	1000 meters
Woollen (Aberdeen)	Pound	14,400 yards
Woollen (American grain)	Grain	20 yards

Indirect System

System	Unit Of Length	Unit of Mass
Asbestoes ( American)	100 yards (Cut)	Poun
Asbestoes ( British)	50 yards	Pound
Cotton bump yarn	840 yards	Ounce
Cotton (British)	840 yards (Hank)	Pound
Cotton (American)	1000 meters	0.5 killograme
Cotton (Continental)	100 yards	Pound
Glassb (U S A and U K)	300 yards (Lea)	Pound
Linen (Wet- spun)	Killometer	Killograme
Metric	840 yards (Hank)	Pound
Spun Silk	11,520 yards(spyndle)	24 Pound
Woollen (American cut)	300 yards (cut)	Pound
Woollen (American run)	100 yards	Ounce
Woollen (Dewsbury)	100 yards	Ounce
Woollen (Galashiels)	300 yards (cut)	24 Ounce
Woollen (Hawick)	300 yards (cut)	26 Ounce
Woollen (West of England)	300 yards (cut)	Pound
Woollen (Yorkshire)	320 yards (snap)	Pound
Woollen (Yorkshire)	326 yards (skein)	Dram
Worsted	560 yard (Hank)	Pound