Assignment on Yarn Twist

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Assignment Outline

• Yarn twist • Twist direction • Amount of twist • Expression for amount of twist • Purpose/function of twist • Relation between yarn count & twist angle • Twist factor • Relation between yarn count & yarn diameter • Measurement of determination of yarn twist • Ordinary twist tester • Additional features of semi-automatic twist tester • Function of twist in yarn structure • Effect of twist on yarn structure • Effect of twist on fabric properties • Some description

Ahsanullah University of Science & Technology

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►► Twist: In the spinning process a strand of fibre in more or less parallel form is drafted and twisted on its own axis to form a yarn. The necessity for twist in yarn construction is reflected in most but not all definitions of the term twist. Generally the twist is defined as the measure of spiral turns given to a yarn in order to hold the constituent of fibres or threads together. According to textile institute “The spiral disposition of the components of a thread, which is usually the result of relative rotation of the two ends” is known as Twist. According to “Morton”, When a strand is twisted the component fibres tend to take on a spiral formation the geometric perfection of which depends on their original formation. Accepting the fact that twist is necessary to give yarn coherence and strength many question arises. Among them the two important ones are how much twist must be inserted into a yarn? & what effect has varying amounts of twist on the yarn properties? Before dealing with such questions that methods of describing twist and expressing the amount of twist must be considered.

►►Twist direction:

The direction of twist at each stage of manufacture is indicated by the use of the letter S or Z in accordance with the following convention:


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A single yarn has S twist if when it is held in the vertical position the fibres inclined to the axis of the yarn conform in direction of slope to the central position of the letter S. Similarly the yarn has Z twist if the fibres inclined to the axis of the yarn conform in direction of slope to the central portion of the letter Z.

►►Amount of twist: The amount of twist in a thread at each stage of manufacture is denoted by a figure giving the no. of turns of twist per unit length in the twisted condition at the stage. The amount of twist means the number of turns of twist per unit length. If ‘n’ is the no. of turns of twist in ‘l’ (inch) length of yarn then the amount of twist =

n l

∴Twist

=

n l

n

l

►►Expression for amount of twist: TPI

Twist per inch (indirect)

TPM

Twist per meter (direct)

TPcm

Twist per centimeter (direct)

TPF

Twist per feet (direct)


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►► Purpose/ Function of Twist: • To get fineness of yarn • To decrease irregularity of yarn • To increase strength of yarn • To get proper softness of yarn and • To get twisted yarn

►►Relationship between twist angle and yarn count:

The figure represents idealized elements of a yarn showing one fibre in the yarn surface following a helical path and making one turn round the yarn axis. The twist angle θ is the angle between a tangent to the helix formed by the fibre and yarn axis. By unrolling the surface layer it is seen that the fibre become the hypotenuse of right angle tri-angle.

Let, Yarn diameter = d inch Length of the yarn occupied by one complete turn of the twist = l inch


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Then, tan θ =

πd l

…………………….. (1)

1 …………………. (2) l tan θ = πd ×TPI

Turns per inch =

Therefore, tan θ ∝ d ×TPI ………….. (3) We noted earlier that when the count system is an indirect system the yarn diameter is proportional to the reciprocal of the square root of the count. Thus, d ∝

1 count

………………….. (4)

From the relationships 3& 4 we can re-write that, tan θ ∝ TPI × ⇒ tan θ ∝

1

count TPI

count

⇒TPI ∝ tan θ × count ∴TPI = k count

Here, K is termed the Twist factor or Twist multiplier which is directly proportional to the tangent of the twist angle. In addition, according to the direct system the form of relationship between per unit length twist factor and count will be changed. The yarn diameters will now be directly proportional to the square root of the yarn number. d ∝ count

Twist factor = Turns per meter × Turns per meter =

count

k count

►►Twist factor:


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Twist factor or twist multiplier is an expression which is used to know the turns properties i.e. tells about the twist character of the yarn even without the knowledge of the yarn count. For direct system: TM ( K ) = TPM × count

For indirect system: TM ( K ) =

TPI count

►►For direct system: Let, The yarn count=`N`Tex Specific Volume=1.1 cm3 Yarn weight=1 gm Hence, N Tex yarn has a length=1,000 m

∴1 Tex yarn has a length

=

1000 m 10 5 = cm N N

We know that, Volume=Cross Sectional Area*Length πd 2

10 5 4 N 4 ×1.1 × N or,d = π ×10 5 0.375 N Tex or,d(cm) = 100

or,1.1 =

×

→ This is the diameter expressed in direct system.

►►For indirect system:


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or,d(inch) =

0.375 1 590 .5 × × 100 2.54 Ne

1

  N × eT e= 5x 9.5 0  5 9.5 0   ∴ T e= x N e    &1i n =c 2.h5 c4 m

1

⇒ d(inch) = × 28 Ne

∴d(inch)

=

1 28 × Ne

→ This is the diameter express in indirect system.

►►Measurement/Determination of yarn twist: Instrument

Method

i.

By Ordinary Twist Tester

Single Twist Method

ii.

By semi-automatic Twist Tester method

Single/Double,twist/untwist

iii.

By semi-automatic Twist Tester method

Multiple twist/untwist

►►Twist Measurement of Plied Yarn:


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• Ordinary Twist tester • Take up Twist tester • The Quardant twist tester

►►Types of twist tester: Ordinary Twist Tester: It is a fibre-straightened method.

Standard sample length:  For Cotton=1" or 10"  For Jute=10"

Procedure: 

At least 1-yard yarn from yarn package should be left out from the free

end. Yarn(size=10")is clamped bt screw.


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Rotate the handle manually,which is turn rotate the revolution counter. When the fibre is fully untwisted,straightening is off. The measurement of revolution in the revolution meter is noted. No.of obsevation must be minimum 20.

►► Additional Features of Semi-automatic Twist Tester: • The Machine is uses friendly,in display screen,four different languages are available for showing output results. • The test programs are automatically executed. • The whole system is electrically controlled.

• It is link up to a printer or a PC for documentation and showing output results. • It has automatic exact stop. • It maintains constant thread tension.

• Also has time saving quick clamp system.

►►Function of Twist in Yarn structure: 

A yarn have sufficient tensile strength to withstand the stresses of preparation and fabric manufacture. The main function of twist is to give coherence to the yarn i.e twist provide strength in yarn.The cohension arises mainly from the twist which presses the fibres together as the stretching forces is applied & so developing friction between adjacent fibres.

►►Effect of Twist on yarn Structure /Strength: Ahsanullah University of Science & Technology

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The strength vs. Twist curve can be Divided into two sections as follows: i.

A low twist region in whish the effect of cohesion out weights that of obliquity giving rise to a increase to strength slow at first up to the point of at whish fibres may just begin to break & increase rapidly as more & more fibres break.

ii.

High twist region in which further increase cohesion no longer produces an increase in strength since the majority of fibre break,while the increasing inclination of the fibre cause the strength to fall.

Fig: Strength Vs Twist Curve The division between the two regions corresponds to the twist at which maximum strength is realized in this twist the greater proportion of the fibres break.

►►Effect of Twist on Fabric properties: Twist also affects the fabric properties.By varying the automatic of direction of twist the fabric designer can archive a variety of fabric effects.The properties, which are afected by twist characteristics of yarn, are the following: Ahsanullah University of Science & Technology

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Visual properties, Handle properties(related to handle & drape) Mechanical properties (related to strength or relsistance to abrasion)

Following are the examples at effect of twist: 1) 2) 3) 4)

Shadow stripe effect, Twill line effect, Crepe surface & curf formation, Fancy fabric product.

Multiple twist:

A multiple twisted yarn is made from two single yarns, which are twisted in Z direction. The twisted yarn itself will be twisted in the S direction. The rotation of this twisted yarn is more or less a single yarn twist and the result is, that the fibres will once again lie parallel to the twist axis. The possibility of variation lies in the amount of the spun fibres as well as in the amount of the twist rotation. The optimum characteristics of the products can be brought out in this way. Stronger twists for weaving mills and softer ones for knitting mills are the general rule.

Sewing thread:


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The sewing thread is normally made of three S-twisted single yarns, which are twisted together in the Z direction. A tear-resistant thread with a round transverse section will thus be created

The voile:

The voile is produced from a spun fibre which is twisted in Z direction. The special thing is, that the twisted yarn is also twisted in the same direction, as the spun fibre (z direction). A hard twisted yarn is the result, with a tendency to curl. The fabric made from it, will be transparent, robust in grip. Curtains were often produced from it years ago. To get a higher transparency and also to produce luminous colors the finished twisted yarn has to be gassed. This means that the fibres which stick out are burnt off. Very highly twisted yarns are called crêpe twists.

Others: Fancy twists or nub yarns are twisted yarns which are made from different kinds of components such as nub, loop and other effects and are produced on special machines.


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Special constructions are multiple and multi stage twisted yarns, which are in praxis of little consequence due to the price factor.


Assignment on Yarn Twist

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