1 / 38

Dimensions of Fibres & Yarns Basic Concepts, Units & Unit Systems Special Quantities Measurement Methods

Textile Testing MA Wilding. Dimensions of Fibres & Yarns Basic Concepts, Units & Unit Systems Special Quantities Measurement Methods. Suggested Reading Material. JE Booth "Principles of Textile Testing” (1983) Chapters 5 & 6 BP Saville “Physical Testing of Textiles” (1999)

tolla
Download Presentation

Dimensions of Fibres & Yarns Basic Concepts, Units & Unit Systems Special Quantities Measurement Methods

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Textile Testing MA Wilding Dimensions of Fibres & Yarns • Basic Concepts, Units & Unit Systems • Special Quantities • Measurement Methods ZUT-Testing: Dimensions of Fibres & Yarns

  2. Suggested Reading Material • JE Booth • "Principles of Textile Testing” (1983) • Chapters 5 & 6 • BP Saville • “Physical Testing of Textiles” (1999) • Chapter 3 ZUT-Testing: Dimensions of Fibres & Yarns

  3. Fibre Dimensions- Length • Fibre length is an extremely important parameter • It has far-reaching influences on yarn & fabric processing & product performance • Can divide fibres approximately into two groups: Most Natural Fibres Length varies from about 1  10 cm (“staple”) Most Man-made/Synthetic Fibres Can be any length: 0 cm  “infinity” (“continuous filament”) ZUT-Testing: Dimensions of Fibres & Yarns

  4. Fibre Length- Measurement • Continuous filament • Length measurement not generally an issue • Staple fibres • A given batch of raw fibre (eg cotton or wool) will contain many different fibre lengths • Most methods are therefore statistical in nature • They are usually extremely difficult & time-consuming to carry out; instruments include: • Various “comb” sorters (differ for cotton & wool) • Various photoelectric sorters (“Shirley” & “Fibrograph”) • “Sledge” sorter See, for example, Booth, Chapter 5 ZUT-Testing: Dimensions of Fibres & Yarns

  5. Fibre Dimensions– “Thickness” This is far from straightforward … • Fibres typically ~ 20 microns (0.02mm) across • Cross-section very difficult to determine eg wool ZUT-Testing: Dimensions of Fibres & Yarns

  6. Fibre Dimensions– “Thickness” Yarns are often difficult, too Cross-section ill-defined, possibly “hairy” etc ZUT-Testing: Dimensions of Fibres & Yarns

  7. Fibre Dimensions– “Thickness” Usually specified in terms of Linear Density (LD) or ‘fineness’ There are two types of system … • Direct • eg ‘tex’ system • Value is proportional to LD • increaseswith thickness • Indirect • eg Cotton Count • Value is inversely proportional to LD • decreaseswith thickness ZUT-Testing: Dimensions of Fibres & Yarns

  8. Fineness as a Measure of Cross-Section For a given bulk density (), linear density is proportional to fibre cross-sectional area Mass = V x density () = AL Linear density = Mass/Length(eg in tex) = AL/L = A ZUT-Testing: Dimensions of Fibres & Yarns

  9. Fineness as a Measure of Cross-Section For a given bulk density (), linear density is proportional to fibre cross-sectional area It works for any regular shape – eg triangular Mass = V x density () = AL Linear density = Mass/Length(eg in tex) = AL/L = A ZUT-Testing: Dimensions of Fibres & Yarns

  10. Fineness Units 1. Direct • tex =weight (g) of 1km • decitex = weight (g) of 10 km • millitex =weight (g) of 1000 km • kilotex =weight (kg) of 1 km • Example: • 10 cm fibre weighing 0.02 mg • = 0.00002/0.0001 g per km • = 0.2 tex = 2 dtex = 200 mtex ZUT-Testing: Dimensions of Fibres & Yarns

  11. Fineness Units • 2. Indirect • Count • eg Cotton Count • = No. of 840-yard "hanks" for 1 lb weight Example: Suppose a standard-length hank of yarn weighs 1/30 lb Therefore need 30 hanks for 1 lb Therefore yarn = 30's Cotton Count ZUT-Testing: Dimensions of Fibres & Yarns

  12. Fineness - Technological importance Fibre fineness impacts on a wide range of other properties - here are just some examples … • Stiffness & handle (ie drape etc) • Torsional rigidity (ie how hard to twist) - square power dependence on fineness • Light reflection- fine fibres soft sheen - coarse fibres harsh glitter • Absorption of liquids &fibre cohesion- related to surface area • Yarn uniformity- finer fibres give more even yarn ZUT-Testing: Dimensions of Fibres & Yarns

  13. Fineness - Importance in testing Knowledge of effective thickness is usually essential for results to be meaningful (particularly when comparing different fibre types) Example: • Suppose a given cotton fibre can withstand a greater load (tension) than a given nylon fibre • Is cotton inherently stronger than nylon per se? • We can’t immediately tell, because thick fibres are stronger than thin fibres of the same type Therefore, in most cases, results must be‘normalised’ ZUT-Testing: Dimensions of Fibres & Yarns

  14. Fineness – Methods of determination • There is a wide range of methods available • These include gravimetric and non-gravimetric methods • Some are direct; some are indirect • Some are extremely complicated & time-consuming • Some are straightforward and quick • The most appropriate choice depends on many factors • An important one: are we testing fibre or yarn? • Several precautions may need to be taken – such as preconditioning sample in the lab (discussed later) ZUT-Testing: Dimensions of Fibres & Yarns

  15. Fineness Methods - Yarns Simplest: weigh a known length on a balance • Typically, 100 metres (ie 0.1 km) of yarn is wound off using a “wrap wheel” - Usually motorised, has a diameter of 1 metre, and a revolution counter to make length determination easy and accurate • Suppose the piece of yarn weighs W grams • Its linear density must therefore be W/0.1 tex (=10W tex) • Shorter lengths (eg a few centimetres) may be measured using a metre rule and a sensitive electronic balance • The count equivalent can be calculated using the appropriate conversion formula; for example, for English Cotton Count (NE): NE = 590.5/tex ZUT-Testing: Dimensions of Fibres & Yarns

  16. Fineness Methods - Fibres • Range of methods available • Generally complicated • Appropriate choice depends on factors such as: What physical form the fibre is in - Bale? Sliver? Yarn? Fabric? Is a single-fibre value required? Or some form of average for a bulk of fibres? ZUT-Testing: Dimensions of Fibres & Yarns

  17. Fineness Methods - Fibres For uniform synthetic fibres in continuous-filament yarns … • May estimate fibre fineness from overall yarn tex • Need the number of filaments in the cross-section • May be provided by yarn-producer • If not, filaments need to be counted • Microscope may be needed – tedious and slow ZUT-Testing: Dimensions of Fibres & Yarns

  18. Fineness Methods - Fibres For single fibres Single fibres are usually too small to be weighed reliably on a balance. Two examples of alternative methods: • 1. By microscopy • Assumes fineness proportional to cross-sectional area • Need to know the bulk density • may get approximate value from literature if know fibre type • Image of fibre cross-section projected & measured • Fibre area calculated from magnification • Fineness calculated ZUT-Testing: Dimensions of Fibres & Yarns

  19. Fineness Methods - Fibres For single fibres • 2. Using a “Vibrascope” • Principle of a vibrating stretched string • - as in a musical instrument • Frequency (“pitch”) depends on tension, length and linear density • Fibre hung between knife-edges • Small known weight attached to lower end • Made to vibrate at fixed frequency using electrostatic plates • Length adjusted until get resonance • Fineness (usually in dtex) read off dial • Relatively straightforward and moderately quick • May not be highly accurate ZUT-Testing: Dimensions of Fibres & Yarns

  20. Fineness Methods - Fibres Illustration of the Vibrascope principle ZUT-Testing: Dimensions of Fibres & Yarns

  21. Fineness Methods - Fibres For bulk fibres (eg cotton or wool staple) • Air-flow methods usually best • Quick • Give an average value Typical airflow system (schematic) Air Weighted insert with perforated base Air Flow meter & suction pump From pressure meter Chamber packed with wad of fibres of standard weight ZUT-Testing: Dimensions of Fibres & Yarns

  22. L P d Fineness Methods – Air-flow Consider an idealised, cylindrical fibre … S is called the “specific surface” of the fibre Hence … The finer the fibre the greater its specific surface ZUT-Testing: Dimensions of Fibres & Yarns

  23. L d L 2d Fineness Methods – Air-flow Compare two equal-volume batches of fibres with different diameters, and hence fineness 25 fibres of diameter d Occupy the same total volume as 5 fibres of diameter 2d … but have twice thesurface area • Air-flow is restricted by drag over the fibre surface • The finer fibres have twice the resistance to airflow ZUT-Testing: Dimensions of Fibres & Yarns

  24. d 2d Fineness Methods – Air-flow Resistance to airflow as a measure of fineness Fine fibres high resistance Coarse fibres lower resistance ZUT-Testing: Dimensions of Fibres & Yarns

  25. Fineness Methods – Air-flow Ideally, for a mass of uniform cylindrical fibres … Fineness (in tex) is: proportional to fibre cross-sectional area proportional to fibre diameter squared Specific surface is: inversely proportional to diameter inversely proportional to square root of tex Pressurefor given air-flow is: proportional to specific surface  inversely proportional to square root of tex In practice may measure either the pressure for a given air-flow or the air-flow for a given pressure ZUT-Testing: Dimensions of Fibres & Yarns

  26. Fineness Methods – Air-flow • Where the fibres are not uniform and/or not cylindrical the results of air-flow measurements must be treated with a degree of caution • The overall result will be some form of average for the batch • This may not be the simple arithmetic mean For further details and practical systems for measuring fibre fineness see, for example, Booth, Chapter 5 ZUT-Testing: Dimensions of Fibres & Yarns

  27. Maturity (of Cotton Fibres) • ‘Maturity’ is a dimensional characteristic of natural cellulose fibres – especially cotton • It indicates how well-developed the fibres are at harvest • It is extremely important in terms of down-stream processing and yarn/fabric quality • Maturity and fineness are interrelated, although not in a simple way ZUT-Testing: Dimensions of Fibres & Yarns

  28. Longitudinal View Cross-sectional View Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief “Convolution” ZUT-Testing: Dimensions of Fibres & Yarns

  29. Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief • Cotton fibres begin (after the flower dies) as thin-walled hollow cylinders • They first lengthen without changing in diameter; takes around 20 days • They then mature; takes about another 30 days • In maturation, cellulose is deposited on the inside of the cylinder – the ‘secondary wall’ • The hole down the centre (the ‘lumen’) becomes progressively smaller • The outer diameter of the fibre remains virtually unchanged ZUT-Testing: Dimensions of Fibres & Yarns

  30. lumen Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief A Cotton fibre grows first in length … Emerging fibre Seed surface … then in wall-thickness Maturity … is related to the cell wall thickness in comparison to the lumen diameter ZUT-Testing: Dimensions of Fibres & Yarns

  31. Maturity (of Cotton Fibres) Degree of thickening () Cellulose Ao Lumen A Idealised cross-section of a cotton fibre A = area occupied by cellulose Ao = total area (including lumen)  = A/Ao ZUT-Testing: Dimensions of Fibres & Yarns

  32. Maturity (of Cotton Fibres) The fibres collapse when they dry out on harvesting to give a “kidney-bean” shape P P Dry On the plant Cross-sectional area changes, but perimeter remains approximately constant ZUT-Testing: Dimensions of Fibres & Yarns

  33. Mature/Over-mature • Immature • “Dead” Maturity (of Cotton Fibres) Technological importance Maturity largely determines whether a batch of cotton can be spun into a good yarn - or indeed intoanyyarn Some maturity Variations Cause “neps” – clumps of matted fibres ZUT-Testing: Dimensions of Fibres & Yarns

  34. Maturity (of Cotton Fibres) The fibre perimeter is related to both fineness and maturity, and is involved in airflow methods for measuring these properties – see Booth, Chapter 5 P1 Air flow restricted through fine fibres because large specific surface P2>P1 Air flows more easily through coarse fibres because smaller specific surface ZUT-Testing: Dimensions of Fibres & Yarns

  35. Maturity (of Cotton Fibres) Maturity Count and Maturity Ratio Suppose a large sample of cotton fibres is selected at random and treated with caustic soda. The mature fibres will swell back to cylinders, and appear rod-like. The immature ones will not swell but will appear ribbon-like Now count under a microscope: • The total number of fibres (T) • The number of mature (ie “normal”) fibres (n) • The number of “dead” fibres (d) • - ie those with wall thickness less than 0.2 lumen • The number of immature (but not dead) fibres (m) is then given by: • m = T-n-d ZUT-Testing: Dimensions of Fibres & Yarns

  36. Maturity (of Cotton Fibres) Maturity Count and Maturity Ratio Total number of fibres = T Number of mature fibres = n Number of dead fibres = d Number of immature fibres = m = T-n-d Now let N = 100 x n/T = % “normal” fibres and D = 100 x d/T = % dead fibres Two quantities defined: • Maturity Count = 100 x m/T = % immature • Maturity Ratio (M) = 0.7 + (N-D)/200 ZUT-Testing: Dimensions of Fibres & Yarns

  37. Maturity (of Cotton Fibres) Maturity Count and Maturity Ratio • M = 0.7 + (N-D)/200 • Gives M ~ 1 for a high-grade Egyptian cotton • M can be greater than 1 • M less than ~ 0.8 is not good • M less than 0.7 is very rare ZUT-Testing: Dimensions of Fibres & Yarns

  38. Maturity (of Cotton Fibres) Summary of measurement methods • Direct Method (counting fibres) • tediously slow! • Indirect Methods • polarised light microscopy (?) • differential dyeing (slow) • air-flow (best) ZUT-Testing: Dimensions of Fibres & Yarns

More Related