USEFUL TERMS AND DEFINITIONS

  USEFUL TERMS AND DEFINITIONS

Atmospheric condition of testing (Standard) :-
The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65%±2% and a temperature of 27°±2°C.

Balanced twist : The twist in a ply yarn is said to be balanced if the yarn does not twist on itself when held in the form of an open loop.

Breaking extension (%) : The elongation at the breaking load expressed as a percentage of the initial length

Breaking length : The length at which a material (fibre, yarn) breaks under its own weight when hung vertically. The breaking length expressed in kilometres is numerically equal to the tenacity in gram-force per tex.

Breaking load : The maximum load (or force) supported by a specimen in a tensile' test carried to rupture. It is commonly expressed in gram-force, pound-force, newton(N), etc.

Conditioned weight :The weight of a textile material conditioned in the standard atmosphere for testing.

Contract regain : The percentage moisture regain on the basis of which the corrected net weight is calculated.

Corrected net weight : The weight of a material may be corrected to a contract regain (or standard regain).
It is calculated as follows :
Corrected weight = Actual weight x {(100+Rc)/(100+Ra)} where, Rc = Contract regain, Ra = Actual regain.

Denier : It is the mass in grams of 9000 metres length of filament, fibre or yarn.

Gauge length : The length of a specimen under specified pretension measured from nip to nip of the jaws of the holding clamps at the beginning of the tensile test. Standard gauge length for jute yarn strength measurement is 610mm (24 inches).

Grist : The unit of linear density of jute yarn (in FPS system) expressed in terms of weight in pounds of one spyndle (14400 yards) yarn.

Linear density : It is the number indicating the mass per unit length of the fibre/yarn. Common unit is Tex.

Metric count : It is the length in Kilometre per one Kilogram weight of yarn. In metric count, larger the yarn count finer will be the-yarn.

Moisture content : The weight of .moisture in a textile material, expressed as a percentage of the total weight.

Moisture regain : The weight of moisture in a textile material, expressed as a percentage of the oven-dry weight.

Oven-dry weight : The weight of a sample of textile material dried to substantially constant weight in an oven maintained at 105±3°C temperature.

Quality ratio : It is defined as : Quality Ratio = {Breaking load of yarn (lbf)/yarn grist (lbs/spy)}x100 Unit of Quality ratio is centi-spyndle.

RKm : It is the breaking length in kilometre.

Specific stress : The ratio of applied force to the linear density of the material in the  - d unstrained state, the units being gram per tex, gram per denier, centi-newton per tex (SI unit), etc.

Spyndle : A unit of length used in the determination of count or grist of jute yarn; it is equal to 14400 yards (13167 m).

Standard regain : Commercial moisture regain accepted as standard.

Tenacity : The breaking load of a material under test divided by the linear density of the material in the unstrained state, the units being gram per tex, gram per denier, centi-newton per tex (SI unit), etc.

Tex : The count in the tex system is the weight in grams of 1 Km (1000 metres) of yarn/fibre. It is a direct system of yarn counting.

Twist factor : It is a number given by the product of amount of twist in the yarn (i.e., TPI) and the square root of its count (direct system) or the inverse of the square root of its count (indirect system).



Amount of Twist : The amount of twist in a yarn is denoted by the number of turns of twist per unit length in the twisted condition. Normally the amount of twist in jute yarn is expressed in turns per inch (TPI). Sometimes it is expressed in turns per metre (TPM) also.

 Twist Factor : It is a number given by the product of amount of twist in the yarn (i.e., TPI) and the square root of its count (direct system) or the inverse of the square root  of its count (indirect system).

 The twist factor is directly related to the angle of twist helix the surface fibres have in a yarn for the same packing density. The higher the amount of twist, the greater is the helix angle and larger is the twist factor.

The purpose of twist factor is to calculate the amount of twist to use in spinning, in order to maintain the same angle of twist helix and the similar yarn characteristics when the yarn count is changed.

 The twist factor may also be used for rovings and ply yarns. In Direct yarn count system,
Twist Factor = TPI X Square root of Yarn count

And Indirect yarn count system, Twist Factor = TPI / Yarn count

The range of twist factor for jute yarn is 11.5 — 13.5. Sometimes in case of sale yarns, the twist factor is specified in lea count system. The value lies between 1.8 — 2.2.

Jute Twist Factor = TPI X Square root of Grist = TPI X Square root(48/Lea count)
= (TPI / Square root Lea count) x 6.93
= Lea Twist Factor x 6.93

For example, if the Lea Twist Factor is 1.8, its Jute Twist Factor will be 1.8 x 6.93 = 12.47

Twist Measurement : One of the effects of putting twist into a strand of fibres or yarns is to cause the strand to contract in length. Suppose a yarn is twisted Z way and has a length, h. Let the twist be completely removed to produce an untwisted strand of length h+c, c being the contraction due to twist. if the strand is now twisted S way it may be expected that the strand will again contract to the original length, h, after the insertion of a number of turns equal to those removed.

 Hence ,
Turns per inch = n / 2h

 n = total number of turns for untwisting and re-twisting the yarn to its original length.
 h = test length of the yarn.


Description of The Instrument
 The twist tester is provided with two clamps — one rotating and the other non rotating — to grip the test specimen. The distance between clamps is adjustable. A scale is provided to measure the distance between the clamps. A revolution counter is positively connected to rotating clamp. The non-rotating clamp can slide on a rail.


A weight is attached to this clamp for applying a tension on the yarn. The displacement of the clamp can be measured from a scale fixed to the rail. The distance between the clamps is set by adjusting the position of the stopper on rail.

Procedure

 Set the stopper at 5 inch marking on the scale, which will give a test length of 5 inch. Secure the yarn in two clamps — first in the non-rotating clamp and then in the rotating clamp.
 Determine the direction of twist by visual observation.

Revolve the rotating clamp in the proper direction so as to untwist the yarn. As the yarn gets untwisted, the non-rotating clamp will slide away from the stopper. Maximum displacement of the clamp will take place when the yarn is completely untwisted. Continue the rotation in the same direction until sufficient twist has been insertd so that the non-rotating clamp again touches the stopper. This indicates the yarn is twisted to its original length but in the opposite direction.

 Note down the number of turns from the revolution counter. Calculate TP1 by using the formula.

Twist and Yarn Strength : Without twist a strand of staple fibres like  jute, cotton! etc., as very littrd.strength. In order to develop strength in a strand of staple fibres, insertion of twist is essential. In case of staple Yarns, an increase in the amount of twist produces an increase in yarn strength. However, this effect holds up to a certain point beyond which further increase in twist causes the yarn become weaker. The strength of continuous filament yarns tends decrease with twist insertion. For spun yarns, the twist level at which the yarn strength reaches maximum is called the optimum twist.

Yarn Strength : The strength of a yarn is measured by means of the breaking load which is the force required to break a yarn. Its unit may be gram-force (gf), pound-force (lbf) or Newton (N). But if we want to compare the strengths of a fine and a coars-e—yarn, then a parameter called Quality Ratio is used.

Quality Ratio = {Breaking load (lbf)/yarn grist (lbs/spy)) x 100

Unit of Quality ratio is centi-spyndle

 If the average breaking load of a 9 lbs/spy jute yarn is 8.2 lbf, then its Quality Ratio (OR) will be —


Q.R = (8.2/9) x 100 = 91 centi-spyndle

If another yarn of count 9.5 lbs/spy has the same breaking load i.e. 8.2 lbf,

then Q.R = (8.2/9.5) x 100 = 86 centi-spyndle


RKm : It is breaking length of a yarn in Kilometre. The breaking length is the length of the spcimen which will just break under its Own weight when hung vertically.

Breaking Extension (%) =(elongation / initial length) x 100.

Example : The average breaking load of a 8 lbs/spy jute yarn is 34 N. Calculate its quality ratio, tenacity in g/tex, and RKm.

Breaking load = 34N
                         = 34/9.8 Kgf
                        = (34/9.8) x 1000 gf = 3469.4 gf
                     = (34/9.8) x 2.2 lbf = 7.6 lbf
Tex count of the 8 lbs/spy yarn = 8 x 34.45 = 275.6 tex.

 Quality ratio = (7.6/8) x 100 = 95 centi-spyndle.

Tenacity = 3469.4/275.6 = 12.6 g/tex.

RKm = 3469.4/275.6 = 12.6