ARTICLES ON TEXTILE FIBER, YARN, FABRIC, DYEING AND GARMENTS PRODUCTION: Textile Physics

Showing posts with label Textile Physics. Show all posts

Thursday, March 14, 2013

Cover Factor of Fibre, Yarn and Fabric

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CONCEPT OF SIMILAR CLOTH
Fibre or raw materials of the two cloths may be same but they can differ on other factors, such as:-
i) The yarn count may be different.
ii) The ratio of yarn count in warp and weft may differ.
iii) The warp ratio of yarn spacing may differ.
iv) The average of yarn spacing may differ.
v) The weave design may differ.
vi) The amount of twist in yarn may differ.

If there is similarity in COVER FACTOR of two cloths but they differ in such points as mentioned above then they are called similar cloth.

COVER FACTOR
Cover is the degree of evenness of thread spacing. Good cover gives the effect of a uniform plane surface & it can not be obtained with hard twisted yarn. In case of woven fabric cover factor is a number that indicates the extent to which the area of a fabric is covered by warp and weft threads. For any fabric by introducing suitable numerical constants its evaluation can be made in accordance with any system of counting. It is denoted by k.

Mathematically,

k = d / p;

where, d₁ = Warp dia; d₂ = Weft dia; P₁ = Warp spacing; P₂ = Weft spacing; k₁ = Warp cover factor, and k ₂ = Weft cover factor.

So, k₁ = d₁/P₁ & k₂ = d₂/P₂

Therefore, Fabric Cover Factor = k₁ + k₂.

The ratio of yarn diameter to yarn spacing, d/p, is a measure of the relative closeness of the yarns in the warp or weft of a woven fabric. This ratio also expresses the fraction of the area of the cloth covered by the warp or weft yarns. We may therefore call it the fractional cover, i.e.

Fractional cover = d / p.

Substituting Peirce’s estimate of yarn diameter, d = 1/28 √N, we have

d / p= [1/(28√N) x1/p]

But 1/p = n, where n = threads/in., so

d / p= n/(28√N) ……………………………… (6)

Now d/p has a value of 1.0 when the yarns are just touching. Peirce multiplied eq.(6) by 28 to eliminate the numerical constant, 28, and defined the result as the ‘coverfactor’, K.

Cover Factor, K = n / √N ……………………………………………..(7)

Because we have multiplied by 28, cover factor as defined in eq.(7) has a value of 28 when the yarns are just touching. The relative yarn spacing corresponding to various cover factors are shown below:

It is usual to calculate separate cover factors for the warp and the weft. Using the suffices 1 and 2 for warp and weft, we have

Warp Cover Factor, K₁ = n₁ / √N₁ and

Weft Cover Factor, K₂ = n₂ / √N₂.

The sum of the warp and weft cover factors is known as cloth cover factor, Kc. It is customary and more informative, however, to state the warp and weft cover factors separately. Just as twist factor enables us to compare the relative hardness of twist in yarns of different counts, so cover factor enables us to compare the relative closeness of the yarns in different fabrics.

Math related to cover factor

Compare the relative closeness of the warp yarns in the following two plain cloths; (a) 16s cotton; 50 ends/in; and (b) 36s cotton; 84 ends/in.

We have the cover factor for cloth (a), K₁ = 50 / √16 = 12.5.

And for cloth (b) cover factor, K₂ = 84 / √36 = 14.0

So the ends are more closely spaced in cloth (b) than in cloth (a)

MATH:- Calculate the warp and weft cover factors for the following fabric: 60 denier nylon x 48s worsted; 96 x 72.

60 denier = 5315/60 = 88.57s cotton count.

So, K₁ = 96 / √88.57 = 10.2

40s worsted = 48 x 560/840 = 32s cotton count.

So, K₂= 72 / √32 = 12.7

GENERAL FORMULA FOR CALCULATING COVER FACTORS

Indirect systems direct systems.

K = cn/ √N K = cn √N

Where N is the yarn number in the particular system.

System Value of c System Value of c

Cotton 1.0 Denier 0.01375

Worsted 1.228 Tex 0.04126

Linen lea 1.667 lb/spdl 0.2422

MATH: Calculate the cover factor corresponding to 80 threads/in. of 100 denier.

From the table constant for the denier system is 0.01375.

Therefore, K = 0.01375 x 80 x √100 = 11.0

MATH: How many threads/in. of 5 tex nylon are required to give the same cover factor as 90 threads/in. of 2/100s cotton?

Since the equivalent singles count of 2 /100s is √50 s.

Therefore,

K = 90/ √50.

So, K = 12.7 = 0.04126 x n √5

Therefore the number of threads required

n=12.7/0.04126 x √5 = 138 threads / in.

Thus required thread/in is 138 of 5 tex to give the same cover factor as 90 threads/in. of 2/100s cotton.

This problem can also be solved with reference to the formula for calculating cover factor.

5 tex = 590.5 / 5 = √118 s cotton count.

As before, K = 12.7 = n/ √118.

Therefore n = 12.7 x 118 = 138 as before.

Wish You Good Luck..................................
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Monday, September 3, 2012

Reasons for Studying Textiles:

A study of textile engineering will show, for example, why certain textile fabrics are more physically durable and therefore more serviceable for specific purposes. It will explain why certain textile fabrics make cool wearing apparel as well as give an impression of coolness when used as decoration. The matter of cleanliness and maintenance must also be estimated before purchasing when that is an important factor.

Complete knowledge of textile engineering will facilitate an intelligent appraisal of standards and brand of apparel garments merchandise and will develop the better ability to distinguish quality in textile fabrics and, in turn, to appreciate the proper uses for the different qualities. A result, both the garments consumer merchant and consumer customer will know how to buy and what to buy, and salespeople will know how to render good service to those consumers who have not had the advantage of a formal course in textile engineering.

Great strides have been made in the textile, garment industry, and have markedly influenced our general economic growth. The prosperity and growth of related industries, such as retail apparel stores, have produced broader employment opportunities. Competition for the textile consumer’s dollar has fostered the creation of new textile fibres with specific qualities to compete with well-established textile fibers. New fiber blends have been created to combine many of these qualities into new types of yarns with new trademarks. There are also new names for textile fabrics made of these new textile fibers and yarns. New finishes have been developed to add new and interesting characteristics to textile fibers, yarn and fabrics.

This welter of creativity and the myriad of trademarks present a challenge to the textile consumer, who is sometimes knowledgeable but frequently confused. Yet one need not be. Without being overly technical, this information can be easily understood and consequently very useful to the textile consumer in business and personal to the textile consumer in business and personal life. All of this information can be adopted for such utilitarian benefits as economy, durability, serviceability and comfort, as well as for such aesthetic values as hand (or feel), texture, design and color of textile and apparel garments products.

In the study of textile engineering, the student’s initial interest will become an absorbing interest when they discover the natural fascinating of textile fabrics and their cultural associations, particularly when factual study is supplemented by actual handling of the textile and apparel materials. The subject will seem worthwhile as they become familiar with illustrative specimens and fabrics and being to handle and earn to compare the raw materials of which fabrics are made as well as the finished consumers goods.

USEFUL PURPOSES OF STUDYING TEXTILE PHYSICS:-
The useful purpose of studying textile physics are:-
1. To understand the detailed structure of fiber, yarn and fabrics
2. To understand the properties of fiber, yarn and fabrics.
3. To understand the behavior of fiber, yarn and fabrics in end condition.
4. To become able to design fiber, yarn and fabric having the required properties to meet the end-use requirements.
5. To identify faults & their causes & nature in fiber, yarn and fabrics.
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Sunday, September 2, 2012

Textile physics; Introduction to textile physics

Textile physics is very important subject for textile engineers or textile related students. I want to share my experience in this site. I am going to discuss about bellow topics. So be with me for more update.

Why study or learn

Why study textiles

Why study textile physics

Textile raw materials

Classification of fibers

Engineering approach to fibers, yarns and fabrics

Importance of textile structures for Engineers

Physical and Mechanical properties of various fibers

Textile properties developed by drawing

Design and other fiber attributes

Essential and desirable properties of textile fibers

Influence of fiber fineness

Miscellaneous properties of fibers

Flexural rigidity of textile fibers

Fiber migration

Measurement of fiber migration

PHYSICS FOR TEXTILE FIBRE, YARN AND FABRIC

Definition of yarn

Factors affecting yarn strength

Parameters affecting physical properties of yarn

Classification of yarn

Classification of yarn based on physical and performance characteristics

Description of yarn

Idealizes structural diagram of some yarns

Continuous filament and staple yarn structure

Fundamental structural features of yarn

Yarn designation

Relative consumption of yarn

Sewing thread

Thread sizes

Thread selection

Importance of twist

Types and direction of twist

Bedding or nesting

Determination of twist

Twist effects

Angle of twist and twist factor

Effects of twist on yarn strength, extensibility and luster

Geometry of twisted yarn

Idealized twisted yarn geometry

Various comments on idealize yarn geometry

Yarn size and twist multiplier

Optimum twist factor

Fiber packing in yarn

Open packing of yarn

Hexagonal close packing of yarn

Real yarn packing

Concentrating and disturbing factors

Observed packing of fibers in real yarn

Twist in relation to yarn bending

Relation among twist angle, twist factor and yarn count

Equation for yarn diameter

Equation for specific volume of yarn

Show that d=4.44 x 10^-6ÖTex / Density

Relation among twist, diameter and twist angle

Estimation of Schwarz’s constant

Yarn luster

Twist contraction and twist retraction

Limit of twist

Contraction factor and retraction factor

Derivation of expression for prediction of filament strain

Limitations of Platt’s low strain equation

Geometry

Cloth geometry

Reasons for studying cloth geometry

Weave and weave notation

Crimp

Warp crimp and weft crimp calculation

Crimp percentage and take up percentage

Distinction between crimp % (C) and take-up %(T)

Relationship between crimp (%) and take-up (%)

Pierce’s Flexible thread model

Importance of crimp on fabric properties

Fabric behavior during tensile testing

Measurement of crimp

Principles of edged crimped yarn

Crimp measuring instrument

Pierce’s model for plain weave

Equation for pick spacing (P2) and end spacing (P1)

Equation for maximum warp yarn displacement (h1) and weft yarn displacement (h2)

Dependence of crimp percentage

Crimp interchange

Equation for crimp interchange

Warp and weft yarn jamming

Equation for warp and weft yarn jamming

Biaxial, tri-axial and balanced structure

Equation for rigid thread model

Why rigid tread model was introduced

Effect of yarn crimp on fabric properties

Concept of similar cloth

Cover factor

Yarn and fabric strength relationship

Handle, drape and shear

Measurement of drape ability

Some tensile properties of fabric

Electrical properties of textiles

Dielectric properties of textiles

Polarization and related effects

Power factor and dissipation factor

Measurement of dielectric properties

Preparation of a test condenser

Measurement of impedance by Scherring’s bridge and resonance method

Factors influencing dielectric properties of textiles

Electrical resistance of textiles

Conductors, semiconductors and insulators

Conduction of electricity in textiles

Influence of dielectric constant on ions

Normal, excited and ionized atom

Electrical resistance of textiles

Measurement of resistances of textiles

Specimen preparation for measuring resistances of textiles

Influence of various factors on resistance of textiles

Static charge

Explanation of static phenomenon

Theories of static charge

Measurement of charge in slivers by Faraday’s cylinder and Medley’s method

Generation of static charge in polymers

Amphoteric behavior of keratin

Piezo and pyro electric charges

Leakage of static charges in air

Leakage of static charges in perfect insulators, moderate insulators, & conductors

Problems of static charges in textile mills

Minimization of static charges in textile mills

The present view about static charges in textiles

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