The Rieter Manual of Spinning Vol. 7 2451-V1 en Original 68509

8/17/2019 The Rieter Manual of Spinning Vol. 7 2451-V1 en Original 68509

1/78

The Rieter Manual o Spinning

Volume

The Rieter Manual o SpinningVolume – Processing o Man-Made Fibres

Pro. Dr. Thomas Weide


2/78

Publisher

Rieter Machine Works Ltd.

Copyright

© by Rieter Machine Works Ltd.,

Klosterstrasse , CH- Wintherthur,

www.rieter.com

Part o this content provided by The Textile Institute. Used by permission.

Cover page

Laboratory or development o man-made fibres

Available Volumes/Edition:

Volume – Technology o Short-staple Spinning

ISBN --- / ISBN ----

Volume – Blowroom & Carding


Volume – Spinning Preparation


Volume – Ring Spinning


Volume – Rotor Spinning


Volume – Alternative Spinning Systems


Volume – Processing o Man-Made Fibres


Collectors Edition – all Volumes (Vol. -)



3/78

The Rieter Manual of Spinning . Volume . Processing of Man-Made Fibres

The Rieter Manual o SpinningVolume – Processing o Man-Made Fibres

Pro. Dr. Thomas Weide


4/78



5/78


THE RIETER MANUAL OF SPINNING

Volume – Technology o Short-staple Spinning

This deals with basic, generally valid, technological rela-

tionships in short-staple spinning. Subsequent volumes

are organised according to machines or machine groups.

This separates generally valid basic principles rom ongo-

ing developments in machine design and construction.

Volume – Blowroom & Carding

In-depth inormation is provided on opening, cleaning,

blending and carding and additional aspects are covered

such as acclimatisation o raw materials, anticipated waste

rom various grades o fibre, selection and setting o cleaning

and blending machinery, waste recycling, transport and the

unctions o the various card components as well as selection

and maintenance o card clothing and autolevelling systems.

Volume – Spinning Preparation

Here the technical and technological aspects o the yarn

production process between carding and ring spinning are

covered, that means draw rame, combing section (includ-

ing combing preparation) and roving rame. This is an

important process stage, because the yarn quality largely

depends on the quality o the intermediate products rom

which it is made.

Volume – Ring Spinning

Technical and technological aspects o r ing spinning are

covered. This is the final process in yarn production. The

ring spinning machine greatly influences the yarn and its

quality. Ring-spun yarns still represent the standard or

comparison when evaluating yarns produced by other

spinning processes.

Volume – Rotor Spinning

This process resulted rom research into alternative spinning

systems. This volume contains in-depth inormation on the

rotor spinning process and its properties. Continual improve-

ments in spinning elements and conditions make it now pos-

sible to spin a rotor yarn optically similar to a ring-spun yarn.

Volume – Alternative Spinning Systems

To take ull advantage o alternative spinning systems,

a thorough understanding o them is thereore essential.

This volume contributes towards reaching this goal by

describing the most important alternative spinning sys-

tems in detail. One o them is the well known air-jet

spinning technology.

Volume – Processing o Man-Made Fibres

Ever since the introduction o man-made fibres on a commer-

cial scale, the market share o synthetic fibres has shown an

impressive growth rate. In this important field, the variety

o man-made fibres with different properties is continuously

increasing. For numerous applications today, fibres that are

practically “tailor-made” are available. Spinners must there-

ore have detailed understanding o the fibre properties and

the specific characteristics that affect their processing.


6/78


7/78


With Volumes - o the „Rieter Manual o Spinning“, Rieter makes availa-

ble comprehensive knowledge o the whole short-staple spinning process.

The development o the current process technology has been dominated

rom its very beginnings to well into the last millennium by cotton.

The story o „man-made fibres“ goes ar back into the th century and in

this volume is also briefly revisited. The original drive or the development

o man-made fibres was to replace cotton and thus the complicated process

rom the fibre to the yarn. An artificial endless thread, initially ollowingthe example o silk, was the dream. I the current diversity o products and

applications with which synthetic filaments can be produced is traced back,

then this dream has been largely realised and urthermore leaves a great

many options open. In , a fibre consumption o approx. million

tons, excluding non-wovens, was recorded. Filaments with approx. mil-

lion tons achieved a share o almost % o the global fibre consumption.

Nonetheless, this stormy development o filaments with their innovations

could not displace cotton and the short-staple spinning process. In ,

around million tons o cotton were still processed – ar more than hal

the processed staple fibres o approx. million tons. Cotton is thereore

still a very important raw material and this not only or the textile industry

but also or the social and industrial development o numerous countries.

Already in the last century, the cotton harvest was insufficient to meet

demand. This is the oundation or the equally dynamic development o the

synthetic staple fibre production with ocus on polyester and viscose fibres.

These fibres have partially given staple fibres access to new areas o appli-

cation and also completely replaced earlier cotton applications. In addi-

tion, and that is today by ar the greatest component, blends o cotton with

synthetic fibres and blends between synthetic fibres allow yarn character-

istics to change. These yarn developments aim to achieve better wearing

properties, easier care properties, a change in the final abric in relation

to structure or appearance or an increase o the economic suitability.

The blending o raw materials presents new challenges to the short-staple

spinning process. The processing o blends is ofen more difficult than the

pure raw material alone. For this reason, this volume specifically deals with

these raw materials and their processing. In particular, when the raw mate-

rial is selected not as a replacement or something but as a tool or some-

thing new, it opens exciting possibilities to the spinning industry. To dis-

cover these is what I wish readers o this volume.

Our special thanks also go to Dr. Thomas Weide who essentially contrib-

uted to this volume based on his wide experience in the field o processing

man-made fibres.

Edda Walraf, Vice President Marketing, Rieter Spun Yarn Systems

EDITORIAL


8/78



9/78


CONTENTS

. Introduction

. Overview of man-made fibres

.. History .. Man-made fibre types .. Classifications and definitions

. Manufacture of man-made staple fibres

.. General production steps ... Polymer ... Spinning

.... Melt spinning .... Dry spinning .... Wet spinning

... Drawing ... Setting ... Finishing ... Crimping ... Drying ... Cutting ... Pressing

.. Manuacturing o man-made fibres ... Manuacturing o synthetic fibres

.... Polyester (PES)

.... Polyacrylonotrile ... Manuacturing o cellulosic fibres .... Viscose .... Modal .... Lyocell

Properties of man-made staple fibres

and their effects on spinning

.. Structural properties ... Fibre fineness

.... Significance .... Numbers o fibres in cross-section

in blended yarns .... Spinning limits

... Fibre length ... Fibre cross-section ... Crimp ... Fibre surace area

.. Physical properties ... Fibre strength and elongation ... Lateral strength [] ... Shrinkage behavior []

.. Behavior against environment [] [] ... Moisture ... Temperature ... Light and weather

.. Fibre properties in the end product .. Modifications o fibre properties .. Summary o most important fibre properties

. Processing of man-made staple fibres in spinning mill

.. General problems ... Spin finish ... Inadequacies o fibre material

.... Cut packets (cut groups) .... Coarse fibres (hairs, bristles)

.... Overlong fibres .... Fibre dust

... Further disturbances arising rom the fibres .... Anti-pilling types .... Fibre delustrants

... Static electricity .... Generation o static electricity .... Influencing actors .... The problems or the spinning mill

... Environmental conditions .... General conditions

.. Storage o man-made fibres .. Blending

... Purpose o blending ... Blend proportions ... Blend evenness ... Types o blending operations

.... Tuf blending at the start o blowroom .... Tuf blending .... Sliver blending

... Blending o waste material .. Blowroom

... Blowroom installations ... Bale layout ... General settings ... Problems

... Processing environment .. Carding ... General ... Machine elements and general settings

.... Card clothing .... Licker-in .... Pre- and post-carding areas .... Main carding area .... Doffer

... Problems ... Process environment

.. Combing .. Drawing


10/78


... Number o draw rame passages

... General settings .... Roller setting .... Top roller pressure .... Draf distribution .... Speed .... Web condensing


.. Roving production ... General settings

.... Roller setting .... Draf distribution .... Condensers

.... Roving twist level .... Flyer speed


.. Ring spinning ... General settings

.... Roller settings and cradle length .... Top roller pressures and top roller cots .... Draf distribution .... Traveler speed .... Traveler orm .... Spinning limit and yarn twist

... Problems

.... General problems .... Thermal fibre damage [] [] [] ... Process environment

.. Compact spinning ... General settings

.... Compacting zone .... Ring finish .... Traveler orm

.. Rotor spinning ... Fibre selection ... General settings

.... Opening roller type and opening roller speed .... Rotor type and rotor speed

.... Channel inserts .... Draw-off nozzle .... Spinning limit and yarn twist


.. Air-jet spinning ... Fibre and sliver requirements ... General settings

.... Roller settings .... Draf distribution .... Spinning nozzle .... Spinning nozzle spacing

.... Spinning Speed

.... Spinning Pressure ... Problems ... Process environment

.. Steaming and stabilization [] ... General considerations ... Packaging o yarn or treatment ... Steaming equipment ... Mode o operation ... Operating procedure or steaming and stabilizing ... Steaming ... Stabilization

References

Illustrations


11/78


. INTRODUCTION

Since the first production o an artificial fibre in the

man-made fibre technology has been a great success sto-

ry. Global man-made fibre production (filaments and sta-

ple fibres) increased constantly and reached an annu-

al consumption o million tons in , representing

more than % o total fibre consumption worldwide (see

Fig. ). Approximately % o the produced man-made fi-

bres are converted to staple fibres. Today it is not possible

to ensure an adequate supply o textiles or mankind with-

out the exploitation o man-made fibres.

It is expected that worldwide man-made fibre consumption

will still increase significantly. Fig. shows the develop-

ment o the world population and the worldwide fibre con-

sumption per head rom to . It can be clearly

seen that these two values increased dramatically over the

years. In the uture, both world population and absolute fi-

bre consumption per head are expected to rise urther, but

production o natural fibres can be expanded only slowly

(see Fig. ). The expected substantial rise in the demand

or fibres throughout the world during the coming decades

must thereore be satisfied by increased use o man-made

fibres. The fibres themselves, and hence the know-how in-

volved in processing them, are thereore steadily acquiring

greater significance.

Fig. – Global production o fibres in []

Global production o fibres

Cotton,

Other natural fibres,

Man-made filament fibres,

Man-made staple fibres,

Fig. – World population and fibre consumption over the years []

World population and fibre consumption

F i b r e c o n s u m p t i o n [ k g / h e a d ]

year

P o p u l a t i o n i n b i l l i o n

Population Consumption / capita

Fig. – Global fibre production over the years []

Global production o fibres

M i l l i o n t o n s

year

Natural fibres Man-made fibres


12/78



13/78


. OVERVIEW OF MANMADE FIBRES History

The first patent about man-made fibre production traces

back to when the Swiss chemist George Audemars

invented a way to produce artificial silk. He dipped needles

into a liquid mulberry bark pulp and gummy rubber and

drew threads out o that solution. Though the method was

too slow or practical use it was the beginning o a very

successul new industry.

The first industrial production o a man-made fibre was re-

alized by the Frenchman Hilaire de Chardonnet. His artifi-

cial silk was a cellulose-based fibre known as Chardonnay

silk. He started to produce these fibres in Besancon(France) with a production o kg per day.

In the same year a new way to dissolve cellulose and to

spin a viscose yarn was invented by Charles F. Cross, Ed-

ward J. Bevan and Clayton Beadle in England. Later this

yarn was also called rayon. Though it took a ew years be-

ore this new method came into industrial and economical

production it is still used today and known as the classical

viscose spinning method (see chapter ....).

The first patent or the production o a synthetic fibre was

filed by Fritz Klatte in relating to spinning o polyvi-

nylchloride fibres. However, mass production was not used

until or various reasons.

In Wallace H. Carothers rom DuPont ound the first

polyester out o which it was possible to draw fibres. But

due to the low melting point o that material he ocused on

making polyamide fibres. He succeeded in with spin-ning polyamide . fibres which were introduced to the

market in and are known as nylon.

To circumvent the DuPont polyamide fibre patents, the Ger-

man Paul Schlack ound a way to produce fibres out o poly-

amide in . Mass production o the so-called perlon

fibres only started in because o the war.

In J. R. Whinfield and J. T. Dickson invented in Eng-

land a melt spinning process or polyester fibres by poly-

condensation (see chapter ...) which went into mass

production afer the war. Polyester became soon the most

important man-made fibre type in the fibre industry.

Afer finding an appropriate solvent, polyacrylonitrile fibreswere first spun in by Robert Hein (only two months

later DuPont made the same invention).

Man-made fibre types

There is a huge variety o man-fibres that can be produced

today. The whole group o man-made fibres can be divided

into three major categories:

• natural polymers

• synthetic polymers

• inorganic materials.

In Fig. a urther subdivision o these major categories

with examples or each group can be seen [].

Chemical fibres

From natural polymers

Plant derived Animal derived Polymeride fibres Polyaddition fibresPolycondensation fibres

From synthetic polymers From inorganic materials

Cellulosicfibres

Elastomerfibres (rubber)

Regeneratedprotein fibres

Alginicman-made fibres

From regeneratedcellulose

Fromcellulose ester

Fromplant proteins

Fromanimal proteins

CaseinZeinAcetateTriacetate

CuproViscoseModalPaper

Glass fibresMetal fibres

Carbon fibres

PolyamidePolyester

Polycarbamide

PolyethylenePolypropylenePolychlorideFluoric fibres

PolyacrylnitrileModacrylicVinyl fibres

Tri-vinylElastomeres

PolyurethaneElasthane

Fig. – Categorization o chemical fibres []


14/78


Man-made fibres Spun staple fibre yarns

Polyester, . Cotton, .

Polyamid, . Polyester, .

Polypropylen, .

Cellulosics, .

Acrylics, . Acrylics, .

Cellulosics, . Wool, . Others, .Others, .

Fig. – Percentage distribution o worldwide produced man-made fibres

in []

Fig. – Percentage distribution o fibre materials used in spun staple

fibre yarns in []

Despite the huge variety o man-made fibres only a ew

types have a significant market share o the worldwide pro-

duced man-made fibres (filament and staple fibres) which

can be seen in Fig. . Polyester is by ar the most important

man-made fibre with a market share o more than %.

The remaining share is mostly taken by fibres made out o

cellulosics, polyamides, polypropylenes and acrylics.

Focusing on the application o spun staple fibre yarns (short and

long staple) the variety o used man-made fibres has urther de-

creased. Fig. shows the percentage o all (natural and man-

made) fibre materials in staple fibre spinning. In this graph short

staple fibres which are with a share o approx. % the domi-

nant group and long staple fibres are considered. In the short-

staple spinning mill, beside the use o the natural cotton fibres

almost exclusively polyester, cellulosic and polyacrylonitrile fi-

bres are used. Accordingly, the ollowing description will con-

centrate mainly upon these three raw materials.

Classifications and definitions

Table – Classifications and definitions (according to ISO Standard)

Designation Definition

Man-made fibre Generic name or fi lament yarn, staple fibre , monofilaments , etc.

Filament Man-made fibre o very great length, e.g. several kilometers

Filament yarn Man-made-fibre yarn compr ising one or more filaments

Monofilament yarn Filament yarn consisting o one filament with a thickness o up to . mm (above . mm Monofilament)

Monofilament Single filament with a thickness o more than . mm (up to . mm Monofilament yarn)Multifilament yarn Filament yarn comprising many filaments up to dtex (above dtex Tow)

Tow Above dtex (below dtex Multifilament yarn)

Staple fibre Fibres o limited length

Short-cut fibre Used or (e.g.) pile coatings, and production o nonwoven by the wet process

Web Textile structure o filament or staple fibre held together by inherent adherence

Non-woven Web or wadding strengthened by mechanical and/or chemical means

Sliver Continuous strand o predominantly longitudinally oriented fibres without twist

Roving Drafable fibre strand with protective twist

Staple-fibre yarn Spun yarn o staple fibre

Texturized filament Filament yarn treated mechanically or thermally to impart volume and/or elasticity

Assembled yarn Multiple yarn o two or more filament or staple-fibre yarns (single or plied) wound together

Plied yarn (twist) Multiple yarn o two or more filament or staple-fibre yarns (single or plied) twisted together


15/78


. MANUFACTURE OF MANMADESTAPLE FIBRES

In the first part o this chapter the general steps o the pro-

duction o man-made fibres are theoretically introduced.

In the second part the production o the man-made fibres

which are mostly used in short staple spinning is described.

General production steps

Polymer

All man-made fibres have one eature in common – in the

first phase o their manuacture, long-chain molecules are

ormed by a sequence o predominantly chemical processstages. Each long-chain molecule consists o a large num-

ber o identical individual molecules bound together in

a row. Depending upon the raw material, a chain o this

type can be made up o dozens, hundreds, or even thou-

sands o individual molecules. The resulting substance is

called a polymer. The polymer-manuacturing process is the

determining actor or many basic characteristics, such as

density, ability to absorb moisture, melting point, behavior

in relation to dye and burning temperature. Additives can

also be incorporated into the polymer to adjust the charac-

ter o the textile raw material. Thus, delustring agents (tita-

nium dioxide), dyes, and lustring agents can influence the

appearance o a raw material, while other additives can be

used to raise the ignition temperature or to alter behavior

in response to selected dye groups.

Spinning

The prepared polymer, in the orm o a viscous fluid, is

orced through the multiple holes o a spinning nozzle so

that a correspondingly large number o streams is created,

as in a shower. These so-called filaments are then strength-

ened. These process steps can be realized by three different

spinning principles as ollows.

The polymer is ed to the spinning nozzle as a hot molten

material. The extruded filaments are cooled by an air

stream in the cooling duct so that they can be coiled in

carts without sticking together as a bundle (Fig. ).

This process is used or spinning polyester, polyamide, pol-

yolefin, and glass fibres (amongst others). It is a eature o

melt spinning that filaments with all possible cross-sections

can be produced by suitable choice o the hole section in

the spinning nozzle (e.g. round, triangular, star-shaped,

etc.). The other spinning principles, now to be described,

enable this to only a limited extent.

Melt spinning

Fig. – Melt spinning

Coolant

Filaments

Spinning Jet

Spinning Pump


16/78


In dry spinning, the polymer is first dissolved in a solvent

which is vaporized in the spinning duct by means o hot air

leaving the polymer in the orm o solidified filaments (Fig. ).

Wet spinning

Dry spinning The polymer is also spun in the orm o a solution in this pro-

cess. However, the filaments are strengthened by extraction othe solvent instead o the vaporization step used in dry spinning.

The solvent can be extracted either by simply washing it out or

by a chemical reaction between the polymer solution and a rea-

gent in the spinning bath. Wet spinning is used to make viscose,

aromatic polyamide, and some polyacrylonitrile fibres (Fig. ).

Drawing

Afer the consolidation o the spun fibres the chain molecules

are more or less randomly oriented. To acquire the definitive

stress-strain characteristics, these chain molecules have to be

parallelized and aligned in the longitudinal direction by thedrawing process. In this process the filaments are extended

many times their original length by the use o two or more

godet pairs (see Fig. ); each downstream godet pair runs

aster than the godet pair beore.

The drawing process can be done in a single process step to

a ully oriented yarn (FOY) directly afer spinning (as it is

shown in Fig. ) or in two process steps. In the latter case the

fibres are only partly drawn to a partially oriented yarn (POY)

and the final drawing process to ully oriented yarn (FOY) is

done at the next process step (e.g. texturizing). Depending on

the degree o orientation filament yarns have different names:

• LOY low oriented yarn

• MOY medium oriented yarn

• POY pre (partially) oriented yarn

• HOY high oriented yarn

• FOY ully oriented yarn.

Fig. – Dry spinning

Fig. – Drawing process

Fig. – Wet spinning

Drawing zone

godet pair

godet pair

Warm air to

drive off thesolvent

Spinning Pump

Spinning Jet

Filaments

Spinning Pump

Filaments

Spinning Jet

Spinning Bath


17/78


Setting

Temperature treatment (steam or hot air) is used to achieve

the desired residual shrinkage behavior. Setting can be car-

ried out beore or afer imparting crimp and the stability o

the crimp can be influenced in this way. Setting o viscose

by heat treatment is possible only to a limited degree be-

cause this raw material responds less to temperature than

to moisture. Accordingly, in this case, the severed tufs are

allowed to shrink in hot water and in a tension-ree condi-

tion; spin-bath residues are washed out simultaneously.

Finishing

Man-made fibres necessarily need a thin surace coating,

the so-called spin finish, like the grease coating on wool

and wax coating on cotton. Spin finish optimizes the fibre/

fibre and fibre/oreign body (e.g. metal, ceramics) riction

and acts as a lubricant. In addition the spin finish can affect

such important characteristics as:

• anti-static behavior

• thread connections

• openability

• protection o the material.

In contrast to the described positive effects o the spin fin-

ish, it also causes problems in the downstream processes

which will be explained in chapter .... The optimal spin

finish composition represents the most avorable compro-

mise between the previously mentioned positive, desired

characteristics and the negative flow-on properties.

Crimping

The originally smooth fibres must be crimped or spinning

to ensure better blending properties in combination with

other fibre materials, and also in part to achieve a certain

eel or volume in the end products. The operation is usu-

ally perormed by means o a stuffing chamber in which the

filament tow receives an irregular, two-dimensional, zig-

zag crimp. However, this principle is not suitable or treat-

ment o viscose fibre which cannot be plastically deormed

so easily. Accordingly, in this case, inherent shrinkage di-

erences within the fibres are exploited; during the washing

step (see Setting in chapter ...), these differences give

a slight three-dimensional crimp. Certain measures can be

taken to reinorce the local shrinkage differences within the

fibre and thus to achieve a more intensive crimp effect.

Drying

Heating o the filament tow, required or drawing and crimp-

ing, is ofen perormed by means o hot water or steam. Spin

finish is also ofen applied as a dispersion in water. Hence

the drawn, lubricated, and crimped tow must be dried which

is usually done in perorated-belt or drum dryers.

Cutting

Tow is ofen delivered directly to the worsted spinning mill,

but the short-staple mill needs staple fibres cut to predeter-

mined lengths. Filament tow is ed to a cutting device while

being held under a defined tension; the resulting tufs aretransported to the bale press and packed. In the case o vis-

cose fibres, cutting is carried out straight afer drawing, so

that lubrication, crimping, shrinking, and drying are per-

ormed on tufs, not tow.

Pressing

The tufs are compressed in box-like presses to rectangular

bales (sometimes cubes). A bale with a volume o between

. and m³ contains between and kg o tufs.

The trend is towards heavier bales or reasons o econo-

my; limits to this tendency are set by floor loading in trans-

port and storage and by the maximum permissible height o

bales that can be presented to automatic bale openers.

Manufacturing of man-made fibres

As mentioned in chapter .. there are only three man-made

fibre types with a significant market share in the short fibre

industry: the synthetic fibres polyester and polyacryloni-

trile and the cellulosic fibres with viscose still representing

the dominant fibre type in that category but also lyocell and

modal fibres. The production methods o these fibre types

will be explained shortly in the ollowing chapters.

In general, a comparison o the production method o pol-

yester (Fig. ), polyacrylonitrile (Fig. ) and viscose

(Fig. ) will reveal a basic difference between polyester

on the one hand (two-stage process) and acrylic / viscose

fibres (single step process) on the other.

Each o these processing types has advantages and dis-

advantages inherent in its operating principle. The two-

stage operation in melt spinning gives the advantage o

a lower number o spinning positions or nozzle jets. Fur-

thermore, the separate downstream-process equipment


18/78


can be stopped or maintenance or minor repairs without

causing problems, because the step o coiling materialin cans serves as a material buffer. The associated disad-

vantage is that o a greater requirement or floor space to

support cans and enable can transport. The disadvantag-

es and advantages o wet spinning can be derived rom

the same considerations. Both these considerations also

apply or other fibres that require separate downstream

treatment because they are made by melt or dry spinning

processes (e.g. polyamide, polyolefin, and dry-spun pol-

vacrvlonitrile fibres).

Manufacturing of synthetic fibres

Polyester PES

Polyester is made rom ethylene glycol and terephthalic

acid by splitting out water molecules, so it is a typical ex-

ample or polycondensation where molecules are split out

when the monomers join together.

Fig. shows the production o polyester-staple fibres.

It can be seen that operations afer the polycondensationstage can be perormed continuously or discontinuously.

In the first case, the polyester melt is ed directly to the jet

by way o the spin pump while in the second case, a granu-

late is ormed by allowing the material to solidiy and then

breaking it into pieces. The granulate can be transported

and stored easily so that any desired number o spinning

machines, in the same plant or elsewhere, can be supplied

rom a central granulate-production installation. In general,

the more economic continuous process will be selected

or large-scale production; or specialties, e.g. spun-dyed

fibres, there are advantages in using the granulate route.

The melt spinning process is separated rom downstreamprocessing. The intermediate product is spun at high speed

(over m/min) and coiled in cans. Large numbers o

these cans are then presented as eedstock to the subse-

quent processing stage in which drawing, setting, finishing,

crimping, drying and cutting (converting) takes place. The

delivery speed o the second processing stage is not high

enough to cope with the delivery speed o the first process-

ing stage and thereore the two stages have to be separated.

Polyacrylonotrile

Fig. – Manuacturing o polyester staple fibres

Fig. – Manuacturing o polyacrylonitrile staple fibres

Glycol

Can

Continuous

Melt

Granulate

Discontinuous

SpinningPump

SpinningJet

Can

PolycondensationPolyester melt

Drawingposs setting

Finishing

Crimping

Converting

Pressing

Dryingposs setting

Terephtalicacid

Solidify

Staplefibres

SpinningPump

Spinning jetin spinning bath

Ammonia

Acrylonitrile

Spinning solution

Propylene Oxygene

Polymerisation topolyacrylonitrile

Staplefibres

Drawing

Washing

Drawing

Crimping

Drying

Cutting

Finishing


19/78


Polyacrylonitrile is manuactured by radical polymerization

out o acrylonitrile which is made out o ammonia, propyleneand oxygen. The spinning solution is then wet spun. Down-

stream processing is continuous with spinning. Wet spinning

is perormed at much lower speeds (about m/min or less),

so that the spun filaments can be treated directly (Fig. ).

Manufacturing of cellulosic fibres

Viscose

To manuacture a viscose fibre, cellulose pulp which is

a natural polymer is dissolved in caustic soda, separatedinto fibres and allowed to age. The preliminary aged pulp

is then treated with carbon disulphide to orm a yellow-

colored cellulose xanthogenate which is dissolved

in caustic soda again to start the viscose ormation. Afer

filtering and aging it is wet spun to filament fibres.

Like the manuacturing o polyacrylonitrile fibres the down-

stream processing is continuous with spinning (Fig. ).

Modal

Modal is a cellulosic fibre manuactured by a modified vis-

cose spinning process with a higher degree o polymeriza-tion and a modified spinning bath. In comparison to viscose

which is made out o wood pulp o different trees modal is

made only out o beech wood.

As a result o the modified process modal fibres have im-

proved fibre properties such as higher dry and wet strength.

Lyocell

In comparison to the manuacturing process o convention-

al viscose fibres lyocell is manuactured by a solvent-spin-

ning process. The cellulose is directly dissolved in the sol-

vent N-methyl-morpholine-N-oxide (NMMO) containing just

the right amount o water. The solution is then filtered and

wet spun to filament fibres. Because o the act that in this

spinning process the NMMO solvent is recovered and re-

used the lyocell manuacturing process is very environmen-

tally riendly.

Caustic soda water

Cellulose pulp

Compress

Soak incaustic soda

Prelim aging

Fig. – Manuacturing o viscose staple fibres

SpinningPump

Spinning jetin spinning bath

Separate into fibres

Aging

Filters

Carbon disulphide

Liquefy to viscose

Staplefibres

Drawing

Cutting

Washingcrimping

Drying

Finishing

Xanthogenate


20/78



21/78


PROPERTIES OF MAN-MADE STAPLEFIBRES AND THEIR EFFECTSON SPINNING

The properties o man-made fibres are determined by three

largely independent types o influence:

• basic polymer

establishes certain basic properties such as density, mois-

ture absorption, resistance to liquids, electrical conduc-

tivity (and hence the behavior in response to electrostatic

charge), dyeability, flammability, and resistance to light

and weather;

• additives

the above-mentioned basic properties can be adjustedwithin certain limits by incorporating small quantities o

other substances. This is done especially to modiy behav-

ior in relation to dyes, and flammability;

• subsequent treatment

in this stage o the manuacturing process, some techno-

logical properties can be influenced to a very large extent,

especially stress-strain behavior and shrinkage character-

istics.

These wide-ranging possibilities o influencing the product,

together with quality and price stability, represent the ma-

jor advantages o man-made fibres. In many cases, it is pos-

sible to achieve optimal processing and use characteristics

by selective application o specially developed fibres.

Structural properties

Fibre fineness

Significance

Fineness o man-made fibres can be selected within a wide

range and adapted to the intended application. Nowadays,

distinctions are drawn in accordance with the ollowing

scale:

• Super finest fibres below . dtex

• Finest fibres (micro fibres) up to dtex

• Fine fibres up to . dtex

• Medium-fine fibres up to dtex

• Coarse fibres up to dtex

• Coarsest fibres above dtex.

The short-staple spinning mill processes almost exclusively

fine fibres between about . and . dtex. Though there is

an increase in using microfibres below dtex they are still

not commodity fibre products or the staple fibre spinning

process.

Finest and superfine fibres are used or the manuacture o

synthetic leather, or very fine velour and velvets where anextremely sof eel is required, or filters and lining materi-

als, etc.

As was described in The Rieter Manual o Spinning – Volume

the fibre fineness is one o the most important fibre charac-

teristics and it affects virtually every yarn property. All prop-

erties improve with increasing fineness because with finer

fibres more individual fibres can be packed into a yarn o

a given section.

The influence o fibre fineness on, or example, yarn

strength, evenness and elongation is thereore very high

and can be seen in Fig. [].

The number o thread breaks also declines with the use

o ine ibres. Higher eiciency is then achieved in the

weaving room. However, ine ibres are more expensive

than coarse ibres, and inest ibres are notably more

expensive. Furthermore, iner ibres always give rise to

greater processing problems in the blowroom and the

carding room. So the production rate has to be reduced

signiicantly.

Fig. – The influence o fibre fineness on yarn characteristics

Fibre fineness dtex Fibre fineness dtex

U t i l i z a t i o n o f fi b r e s t r e n g t h

Y a r n e v e n n e s s U s t e r C V

T e n a c i t y c N / t e x

Fibre fineness dtex Fibre fineness dtex

B r e a k i n g e l o n g a t i o n


22/78


Numbers of fibres in cross-section in blended

yarnsThe number o fibres in the yarn cross-section nF can be

calculated approximately by (see The Rieter Manual o

Spinning – Volume or urther details):

nF

texyarn

Nmfibre texfibre Nmyarn

The average fineness o fibres in a blend can be derived

rom the relation:

texfibre

(Px texx Py texy)

where P represents the proportion o fibres as a percentage

and the index x represents one component and the index y

the other.

Micronaire values can be converted into dtex in accordance

with the ormula:

dtex micronaire x ..

Examples or a cotton/man-made-fibre blend:

cotton: . micronaire

man-made fibre: . dtex

yarn fineness: Nm ; Ne ; tex ( dtex)

blend ratio: PES/CO:/

dtex cotton . x . .

texfibre

( . dtex . dtex)

. dtex

Numbers o fibres in the cross-section:

nF

.

Spinning limits

As was described in the Rieter Manual o Spinning –

Volume , the numbers o fibres in the yarn cross-section

is an important parameter. Depending on the used spin-

ning technology and on the fibre properties, as or ex-

ample fibre length and fibre/fibre riction, a minimum

number o fibres in the yarn cross-section, the so called

spinning limit, is required.

Spinning limits according to different spinning technologies

are indicated in the appropriate chapters.

Fibre length

As with natural fibres, most yarn characteristics improve

with increasing length o fibres. Since man-made fibres are

produced in endless orm, and are subsequently convert-

ed to staple fibres in a manner enabling any desired fibre

length to be selected, it may at first appear that the ideal

has been achieved in this respect. However, this first ap-

pearance turns out to be misleading, because production

processes used to make staple fibre yarn do not permit

spinning fibres o any length – there are limits to the possi-

ble range o lengths:

• yarns made o overlong fibres tend to lose their textile

character and can be used only or specific fields o appli-cation

• the various spinning processes are designed or predeter-

mined maximum fibre lengths

• man-made fibres are used extensively in blends, where

the length o the man-made fibre has to be matched to

that o the natural fibre

• the slenderness ratio o the fibre has to be borne in mind.

The term “slenderness ratio” reers to the relationship o

the fibre length to the fibre diameter (see The Rieter Manu-

al o Spinning – Volume ). In relation to man-made fibres,

the ratio can be derived as ollows:

Slenderness ratio length (mm) x /dtex

To avoid problems, polyester fibres or use in the short-

staple spinning mill should have slenderness ratios between

and .

I the fibre is too short in relation to its diameter, it is stiff

and cannot be bound into the fibre strand. On the other

hand, i it is too long, it has no springiness or resilience to

enable it to turn back to shape. Processing o this type o fi-

bre leads to nep ormation and fibre damage. I such fibres

are bent or rolled up, they cannot be re-straightened. In

spite o these limitations, the ability to choose fibre length

remains one o the great advantages o man-made fibres.

Fig. – Shapes o staple diagrams:

(a) triangular; (b) rectangular; (c) trapezoidal

a b c


23/78


Fig. – Some types o man-made-fibre cross-sections

Fig. – Drawing orce or uncrimped (a) and crimped (b) fibres

An approximately rectangular staple (Fig. (b)) is ob-

tained afer the cutting stage in the manuacturing processo man-made fibres. The lack o length variations leads to

problems or example in the drawing processes (see Rieter

Manual o Spinning – Volume ). But the length evenness

cannot be maintained because o the shortening o the fi-

bres in the initial process stages, especially in the card.

However, even in this case, the proportion o short fibres

remains small which is an advantage because this raction

can generate many disturbances in spinning. The effect on

the resulting properties is significant.

A relatively new technology is to cut man-made fibres in

a way that the staple diagram is similar to that o cotton

(trapezoidal, Fig. (c)), especially or use in blends withcotton. The advantages o these materials are the easy pro-

cessability in the spinning mill and a better yarn quality

(except the slightly lower tenacity) [].

It should nevertheless be kept in mind that short fibres

generally enable higher carding efficiencies to be achieved

than longer fibres.

Fibre cross-section

Natural fibres are usually curled, angular, have scales and

are crimped; they seldom have a smooth round section. This

gives them a typical textile character and eel. Man-made fi-

bres must also exhibit a textile character i they are to be

used in the textile field. They are thereore ofen ormed with

non-round sections such as indented, star-shaped, triangu-

lar, polygonal, etc. (Fig. ). They can also be made hollow-

ormed.

Crimp

Natural fibres are mostly more or less strongly crimped or

looped. Usually, man-made fibres must also be crimped. The

crimp can be permanent or temporary, i.e. set, partially set,

or onset. Set crimp is selected in order to achieve certain

characteristics in the end product, such as:

• a ull, bulked, sof eel, and

• high insulating capacity.

Partly set and upset crimp, selected or most fibres in the

short-staple spinning mill, serves almost exclusively to im-

prove the processability o the fibres. This orm o crimp ena-

bles, or example, the ollowing to be achieved, among othereffects:

• better web and sliver ormation, because the fibres

inter-engage with each other

• easier opening

• an improvement in cardability, and

• reduction in drafing problems by avoidance o the glass

sheet effect.

The fibre section mainly influences the yarn volume, eel,

insulating ability, luster, and working perormance in pro-

cessing.

However, i the crimp is too high, drawing problems

increase because the required drawing orce rises with

increasing crimp (Fig. , ).

Moreover, a high degree o crimp causes problems in pro-

cessing the fibres in the normal type o rotor-spinning ma-

chine, or even makes such processing impossible. Afer the

last draw rame passage, at the latest, crimp must be re-

moved rom fibres which are to be spun on the rotor spin-

ning machine.

When considering the effects o crimp, it is important to

bear spin finish in mind because it reinorces the effect o the

crimp. There is interplay between these two actors. Many

problems that appear to arise rom spin finish actually have

their origin in the crimp level, and vice versa.

D r a w i n g f o r c e

Draft

a

b


24/78

LO LO

L L

LO

L


Fig. – Drawing orce versus intensity o crimp

Fig. – Change o removing crimp through the process steps

D r a w i n g f o r c e

Crimps per cm

R e m o v i n g c r i m p

F i b r e t u f t

R o v i n g

C a r d f e e d i n g

C a r d s l i v e r

s t d r a w i n g

p a s s a g e

n d d

r a w i n g

p a s s a g e

The fibre crimp is usually reduced by carding and drawing

orces in the spinning mill. The crimp itsel and the change

o the crimp can be measured by the parameters removing

crimp, recovering crimp and crimp stability (see Fig. ).

Fibre surface area

The surace area o the fibre is mainly dependent upon the

orm o the section. A round section gives a smooth fibre with

high luster. I an indented, star-shaped, or polygonal orm is

chosen, the fibres lose smoothness and luster. I luster and

smoothness are to be suppressed in round fibres, it can only

be done chemically. In this case a delustrant (or roughening

agent) is applied to the fibre.

Titanium dioxide (TiO) is used or this purpose. Unor-

tunately, delustred fibres o this kind have a highly abra-

sive character. In processing such fibres, wear on machine

components will be very high. (Fibres dyed by pigments

display the same effect.)

The degrees o delustring in Table are commonly distin-

guished.

The removing crimp can be seen as an indicator or fibre

stress and parallelization work. It should be decreased

continuously through all the process steps in a spinning

mill. An abrupt drop o the removing crimp in a process

step indicates that the fibre stress and the process settings

should be optimized, accordingly are too high (Fig. ).

Physical properties

Fibre strength and elongation

Strength and elongation are connected by a cause/effect rela-

tionship and cannot be considered separately because when

loaded in tension the fibre is simultaneously stretched. These

two properties are thereore ofen quoted in combination as

stress/ strain behavior, in the orm o a stress/strain charac-

teristic in the stress/strain diagram. Each fibre type exhibits

a characteristic typical o itsel.

Fig. – Recovering crimp and crimp stability

Table – Degree o delustring

Level Quantity o titanium dioxide applied (%)

Bright – .

Semi-matt . – .

Matt . – .

Strong matt . -.

Superstrong matt Above .

Removing crimp L L

x LO L L

Recovering crimp L

x LO L L

Crimp stability recovering crimp

x L

removing crimp L L

C r i m p l e n g t h


25/78


26/78


Lateral strength

In the end product, fibres are stressed not only in the

longitudinal direction but also laterally. This is typical

in bending, as in yarn loops and knots; extremes can be

reached, e.g. where yarn is used or sewing (loops) and

in net (knots).

There are fibre materials that behave like a razor blade:

very high longitudinal strength, very low bending strength.

Glass fibres in particular belong to this category. For exam-

ple, glass-fibre yarns cannot be joined together by knotting

because, as the knot is drawn tight, the transverse load on

the fibres leads to yarn breaks. Moreover, many regenerat-

ed-cellulose (polynosic) fibres are very brittle. Polyamidefibres are at the other end o the scale: they are extremely

supple and have excellent lateral strength.

easily scrubbed off when they project rom the surace;

this is not true or fibres with a high lateral strength. In thelatter case, the projecting fibres are not rubbed away but

remain on the surace and spoil the appearance. Unortu-

nately it has to be said that pilling resistance and dura-

bility are inversely related to each other. Also, low lateral

strength reduces carding perormance and raises the ten-

dency to fibre damage.

The ollowing test methods are used to determine lateral

strength:

• loop strength

• bending strength

• buckling rubbing strength

• torsional strength.

Shrinkage behavior

In the course o processing, fibres do not always retain the

length they had beore processing started. Fibres can be

shortened by various influencing actors during process-

ing and use. This is reerred to as “shrinkage”. Every fibre

shrinkage leads automatically to a corresponding shrink-

age in the yarn and /or in the abric.

Usually, it is a heating, wetting, or wet-heating process that

leads to shrinkage. Depending upon raw material, a fibre

reacts more strongly to heat, moisture or moist heat. Thus,

cellulose fibres (cotton, viscose) react to simple wetting

and driving with noticeable shrinkage, while polyester fibre

exhibits no change o length under the same circumstances.

On the other hand, polyester fibre shrinks markedly under

dry heat and still more under wet heat, while polyamide

fibre reacts only to wet heat.

A high lateral strength can be an advantage or a disad-

vantage depending upon the field o use (see Fig. ). In

general, high lateral strength gives good durability to the

finished articles; this is very important in technical appli-

cations, in working clothes and uniorm abrics and also in

floor coverings. However, the pilling tendency also increas-

es so that in the civilian clothing sector only limited use is

made o fibres with high lateral strength. This applies es-

pecially in relation to knitted goods, where the individual

fibres are not so strongly anchored; or example, polyester

fibre must be deliberately made brittle or use in knitted

products to avoid pilling (anti-pilling types).

The expression “pilling” reers to the ormation o fibre

balls on the surace o a textile abric. Such balls do not

orm where fibres with low lateral strength are used (wool,

anti-pilling synthetic fibres), as such fibres can be very

Fig. – Effect o the shrinkage characteristics (low/high): (a) piece-dyeing

behavior, dye-astness, efficiency in weaving, abric appearance; (b) crimptendency, lateral run in knitted abric, tendency to pilling, yarn dyeing behavior

Fig. – Effect o the lateral strength; a durability, b pilling resistance

Lateral strength

a

b

HighLow

a

b


27/78


Table – Behavior in relation to water

The shrinkage characteristics o synthetic fibres can be se-

lected within a wide range (rom low to high shrinkage)by adjusting stretching and relaxing and by use o varying

temperatures in the production stage. Admittedly, however,

as Fig. shows, there are certain interrelationships be-

tween the various characteristics.

For example, where the yarn is to be dyed in the package,

a certain degree o shrinkage should not be exceeded be-

cause otherwise it is not possible to ensure problem-ree

penetration o the package by the dye liquor. On the other

hand, high shrinkage can be an advantage as regards the

eel and visual impression o the resulting product. High-

shrink fibres permit a reduction in wef and warp density

giving low ends-down levels and a high efficiency.In the production o blends, the use o PES fibres with

raised shrinkage can give notable improvements in eel and

wearing behavior because the shrinking PES fibres migrate

into the core o the yarn while the natural fibres stay on the

surace. I man-made fibres are subjected to wet-hot pro-

cessing, it is essential to know the shrinkage behavior in

advance.

Behavior against environment

Moisture

Almost all fibre material contains a certain quantity o wa-

ter. The magnitude o this water proportion depends upon

the raw material and the environmental conditions. Distinc-

tions are drawn, or example, between the ollowing criteria:

• moisture take-up rom the air

• water-retention capability afer soaking and centriuging

• water take-up afer soaking and drip-draining.

Moisture take-up and water-retention capacity are depend-

ent practically only upon the raw material, while in relation

to water take-up the design o the textile also plays a major

role in determining the result.

In the case o man-made fibres, there is a clear relationship

between the ability o the raw materials to take up waterand their strength in the wet condition. The more water a fi-

bre can hold, the greater is the difference between wet and

dry strength. The relative wet strength is generally given as

the measure o this effect, and is expressed as a percentage

o the dry strength.

Depending upon their field o use, fibres with a higher or

lower moisture take-up will be required, e.g. high – hand

towels, underclothing; low - bathing costumes.

In relation to clothing, however, it is not only the moisture

take-up that is important but also the ability to transport

moisture and wettability. Both properties have a strong in-

fluence on wearability. They depend upon fibre surace areaand the capillary effect on the abric. Thus, although PES

has a low moisture take-up, good moisture transport can be

reached by means o appropriate apparel design (Table ).

Temperature

Textiles react to heat in the most varied ways, depending

upon the raw material and temperature. The reaction can

vary rom simple shrinkage through change o color, sofen-

ing and/or becoming sticky to melting, decomposition, or

carbonization.

Unortunately, the requently raised question regarding

temperature resistance o individual raw materials cannot

be answered by quoting a single figure, or even a sequence

o figures. The number o influencing actors is too large to

enable a comprehensive answer to be given to an issue o

this magnitude. Thus, heat resistance is affected by the ol-

lowing influences (amongst others):

• medium

• temperature

• time o subjection to heat

• structure o the sample

• associated substances

• evaluation parameter (quantity).

Polyamide and polyester are melt-spun fibres. This means

that they have a clearly defined melting point. When a cer-

tain temperature is reached, they liquey almost without

any intermediate phase. In the region just below melting,

however, there is increasing sofening and stickiness, so

that in use it is not advisable to come within - °C o

the melting point or even short periods. Otherwise, perma-

nently adhered locations are created which will alter com-

pletely the character o the textile.

Water rom the air

( % rh) %

Water afer soaking

and centriuging %

Relative

wet strength %

PES . -

PAC - - -

PA - - -

Viscose - - -

Cotton - - -

Wool - - -


28/78


Below the sofening region lies the broad zone in which set-

ting is possible. Here, heating and cooling with the mate-rial in a given orm can result in the establishment o this

orm as the normal condition o the material to which the

fibres always tend to return. Pressing-in o a crease belongs

to these procedures, as does setting o crimp or removal o

unwanted creases by ironing.

The other fibres are practically non-settable under heat.

They do not react to increasing temperature by becoming

sof and melting but by increasing degrees o decomposition

and brittleness; this is usually accompanied by noticeable

change o color and can extend to genuine carbonization.

All normal textiles burn when exposed to an open flame.

Only special fibres are inflammable; they have such gravedisadvantages in other areas that they are used only where

inflammability is the decisive criterion.

Once again, clear differences can be observed in the behav-

ior o different fibres in burning.

Cellulose burns very easily and quickly but leaves only

a weak, harmless ash skeleton. Acrylic fibre cannot be

ignited so easily but will burn very intensively once the

ignition phase has been passed.

Polyamide and polyester fibres are relatively difficult to ig-

nite. Nevertheless, they have the serious disadvantage that

the fibre substance melts and drips; in some circumstances,

the result o this behavior can be ar more serious or hu-

mans and the environment than in the case o cellulose.

O all normal fibres, wool has the most avorable burning

characteristics. It is airly difficult to ignite, and, afer burn-

ing, it leaves a brittle, rapidly cooling residue that does not

adhere to adjoining suraces.

Light and weather

It is generally known that exposure to light can affect many

dyes more or less strongly; however, it is ofen overlooked

that light also causes genuine damage to the substance o

textiles.

Basically, all fibre materials suffer a loss o strength when

illuminated. As in the case o heat, the magnitude o the re-

duction in strength depends upon many actors o which

the ollowing are worth a mention:

• light spectrum

• intensity

• lighting rhythm

• temperature o the sample

• moisture content o the sample

• thickness o the sample

• composition o the surrounding air.

The ultraviolet component o the light and the moisture

content o the sample are o special significance. In thisconnection, it is important that a large part o the very ag-

gressive UV components is absorbed by normal window

glass. That is why curtains degrade much more slowly than

textiles lef outside (e.g. awnings or tarpaulins).

As regards the fibre itsel, it is interesting to note that matt

fibres are more strongly damaged than bright ones. Titani-

um dioxide works as a catalyst and accelerates the decom-

position. Under the microscope, it becomes apparent that

individual particles o the delustrant act as the core o a

steadily expanding spherical zone o decomposition.

Furthermore, it should be noted that the depth o penetra-

tion o light rays is very shallow. Accordingly, a reductiono damage is observed with increase in titer.

Comparative tests o various raw materials reveal that PAC

is strongly resistant to light while PA and natural silk have

very poor resistance. Admittedly, however, a significant im-

provement in resistance o man-made fibres to light can be

obtained by incorporating appropriate stabilizers.

Resistance to weather depends upon a still greater number

o influencing actors. Apart rom the influence o light, cli-

matic effects have to be considered and especially variation

in those effects: dry/ wet, warm/cold, light/dark.

The composition o the air also plays an important role,

e.g. as regards pollution by industrial waste gases.

Completely satisactory resistance to weather can be

achieved or practically all fibre materials by coating with

weather-resistant plastics material, primarily PVC.

Fibre properties in the end product

A diagrammatic illustration o the important fibre charac-

teristics will serve as a supplement and as an aid to com-

prehension. Modal fibres have been inserted into this dia-

gram along with the normal viscose fibre; the modal variety

is a viscose fibre produced under modified process con-

ditions to give properties which differ rom those o nor-

mal viscose, particularly in respect o stress/strain behav-

ior (dry/wet). Modal is more similar to cotton fibre and is

thereore finding increasing application in the short-staple

spinning mill.

The selected mode o evaluation:

• high / avorable

• medium / normal

• low / unavorable.

is to be interpreted on the understanding that most char-

acteristics can be assumed as high/medium/low, but wash


29/78


ability and behavior in response to dyes dey this orm o

assessment. In relation to several characteristics, it mustalso be borne in mind that a higher (lower) value may be

either avorable or unavorable depending upon the in-

tended field o use. This can be demonstrated by reer-

ence to moisture absorption: high absorption o water is

a very avorable characteristic in a towel but unavorable

in tent cloth.

Finally, a dosing comment must be made in relation to the

production and properties o man-made fibres (Table ).

Staple man-made fibres now provide about one-third o all

textile raw materials. They are made in many varieties with

a broad range o properties or practically all fields o ap-

plication. Further development will bring still more new fi-

bre types, but it is already clear that completely new poly-

mers are becoming ever more rare while modification o

Table – Some properties o man-made fibres such as: polyester (PES),

viscose (CV), viscose-modal (modal) and acrylic fibres (PAC)

known polymers or specific purposes is increasing. For the

short-staple spinning mill, this means that no basically newrequirements are likely to be raised rom the side o man-

made fibres. However, it is unavoidable that many special

modifications o man-made fibres already available will ne-

cessitate minor changes in processing conditions and these

will have effects on spinning plans, settings, and speeds. In

this field, close and reciprocal co-operation between spin-

ner, machine manuacturer and fibre producer is especially

important.

Modifications of fibre properties

Since man-made fibres represent a manuactured raw ma-terial, many o their properties can be adapted to the spe-

cial needs o specific end-uses. In addition to those already

mentioned, the ollowing modifications, amongst others, are

common in practice (depending upon the requirements):

• antistatic

• anti-soiling (dirt-repellent)

• anti-ignition easy-care

• hydrophilic.

Summary of most important fibre properties

As mentioned at the beginning o this chapter the major

advantages o man-made fibres are the wide-ranging pos-

sibilities o influencing the fibre properties by choosing the

right polymer together with the right additives and subse-

quent treatments.

On the other hand, it is difficult to present a comprehensive

and meaningul summary o the properties o man-made fi-

bres in the ramework o a condensed work o this kind. In

relation to many properties, the range o possibilities is sim-

ply too wide to permit a rational short presentation. Accord-

ingly, we are orced to compromise and give only figures

or typical basic properties and guidelines or stress-strain

and shrinkage behavior o those man-made fibres most im-

portant or the short-staple spinning mill, namely, polyester

(PES), viscose (CV), and polyacrylonitrile (PAN) (Table ).

Medium / normalHigh / avorable Low / unavorable

PES CV MODAL PAC

Strength dry

Strength wet

Elongation

Form stability

Crease resistance

Pilling resistance

Resistance to rubbing

Thermal set ability pleating

Water absorption

Wash ability

Dyeing behaviorLight and weather resistance

Resistance to rotting


30/78


Polyester fibre Viscose Acrylic fibre

Density g/cm . . .-.

Moisture absorption capacity

at °C / % rh% .-. - -

Water-retention capacity afer

immersing and centriuging% - - -

Melting point °C - - -

Decomposition temperature °C - -

Tenacity (dry) cN/tex - - -

Relative loop strength (dry) % - - -

Wet strength % - - -

Elongation to break (dry) - - -

Elongation to break (wet) % - - -

Boiling shrinkage % - - -

Shape in section % Round (possibly profiled) Round to olded Round to dumb-Bell shaped

Table – Typical basic fibre properties


31/78


PROCESSING OF MAN-MADESTAPLE FIBRES IN SPINNING MILL

General problems

Spin finish

Several problems that can arise or the spinner in the use o

finishes have already been mentioned. The main additional

prejudicial actors are as ollows:

• The spin finish combines with dust to orm a hard coat on

machine parts. These deposits can result in great distur-

bance in processing – most strongly in card clothings (es-

pecially on the licker-in), in the sliver-guide passages o

the card and draw rame, in the flyer on the roving rameand on the opening roller and rotor o the rotor spinning

machine. Ofen, additional costs arise because these parts

have to be cleaned periodically.

• Inadequate distribution o the spin finish can cause fibre

flaking and lead to increases in ends down and accumula-

tion o electrostatic charge. In such cases, we talk o mac-

ro-distribution o spin finish because finish content can be

established only by taking samples o many millions o fi-

bres. Development o models regarding the distribution o

spin finish on individual fibres thereore remains a branch

o purely academic science. It is important or the spin-

ner to know that the spin-finish concentration can only be

exactly established gravimetrically in the light o precise

knowledge o the spin-finish composition.

• I spin finish can penetrate components such as rollers

and aprons when the machine is not running, it can cause

swelling or cracking with corresponding prejudice to the

drafing operation.

• Fibres treated with titanium dioxide as a delustrant ex-

hibit lower drafing resistance (lower dynamic riction)

but simultaneously higher wear (higher static riction) on

fibre-guide elements. In this case, an optimized spin fin-

ish recipe has to be used. Besides titanium dioxide, other

spin-finish components can increase wear on fibre-guide

elements, especially when corrosive properties also exert

an effect. Cationic substances are especially suspect in

this connection. Wear, leading to spinning problems and

degrading o yarn characteristics, occurs on travelers and

on opening rollers o rotor spinning machines.

For the sake o objectivity, it should also be mentioned that

processing problems arising in practice are sometimes al-

leged without justification to be due to spin finish. Several

examples taken rom practical experience are:

• where opened bales are lef standing in the spinning room

without allowing adequate acclimatization, moisture cancondense on the fibre surace (especially in winter) and

lead to considerable carding problems

• in the processing o blends o polyester fibres with cotton

where room temperature and humidity are too high, cot-

ton wax can smear and lead to lap ormation

• superannuated rubber top rollers and notches on teeth

and opening rollers are also sources o processing and

quality problems

• fibre crimp is actually just as important as spin finish in

its influence on processing; crimp is steadily reduced in

the passage o the fibre rom opening through to the spin-

ning machine; the spinner here exerts a significant influ-ence on his own processing conditions.

Inadequacies of fibre material

Cut packets cut groups

In the severing o filaments to orm staple fibres, occasion-

ally whole bundles o fibres are squashed together. These

orm a coherent fibre packet that can generate significant

problems in processing. The effect is ofen reinorced i

crimp setting is perormed afer cutting, because then set-

ting o the bundle also arises. Fibre packets o this kind

cannot then be separated rom the strand. Application o

spin finish can also lead to an increase in adherence within

the fibre bundle.

In the ideal case, these fibre packets will be eliminated

in the blowroom. However, since this is not ully achieved,

the card is required to extract the remainder. Afer the card,

there should no longer be any fibre packets in the strand.

Coarse fibres hairs bristles

Staple fibres very rarely contain individual fibres having

a fineness markedly different rom that o the remainder.

There are various causes that can lead to this phenomenon

in the man-made-fibre plant.

The largest part o these fibres can be eliminated beore the

ring spinning machine; the card flats represent the most im-

portant eliminating location. I individual bristles neverthe-

less pass through to the r ing spinning machine, they cause

ends down. I they pass beyond this machine, they detract

rom the appearance o the yarn and the end product.

The cleaning position on the rotor spinning machine is ad-

vantageous in this connection. In addition to dirt, this also

eliminates coarse fibres, fibre packets, and long fibres.


32/78


Overlong fibres

It does not matter i individual fibres depart only slightly

rom the set length in the upward direction. It is more seri-

ous i, or example, fibres o - mm are ound in staple

o mm (double-cut length). In this case, processing diffi-

culties are inevitable.

Since most man-made fibres are strong, the overlong fi-

bre will not break in a drafing zone set to a staple length

o mm. The delivery-roller pair rips this fibre out o the

nip o the eed cylinder in the course o which neighbor-

ing fibres are always carried along. The result is thin and

thick places.

I the fibres do not slide out o the upstream nip, the over-long fibre will be extended; finally, this gives the same re-

sult. The fibre returns to its previous length afer leaving

the drafing arrangement. This occurs suddenly, and neigh-

boring fibres are again carried along. Webs or rovings then

exhibit wave ormations; thin and thick places appear it the

yarn at the ring-spinning machine.

Fibre dust

This is cutting and pressing dust, i.e. fibre debris that arises

in the course o converting tow. It also causes disturbance

in the process mainly due to dust deposits on the machines.

Further disturbances arising from the fibres

Anti-pilling types

In the outerwear sector, i singles yarns are used in pre-

erence to plied yarns, then anti-pilling fibres are generally

chosen or the singles yarn. They have a low buckling break

and rubbing strength, and also a low tensile strength.

They thereore tend to give a higher ends-down rate and

strong generation o fly. This is especially noticeable in ro-

tor spinning, because here fibres in the yarn are rubbed

away at high speeds; the only remedy is a reduction in

revolutions.

Fibre delustrants

Delustring o fibres is achieved by application o titanium

dioxide. This simultaneously imparts an extremely abra-

sive surace to the fibre. This causes high wear on machine

parts, not only sof parts such as roller coverings but even

metal components. At the same time, there is a high gener-

ation o abraded particles.

Static electricity

Generation of static electricity

In an electrically neutral atom, the number o protons is equal

to the number o electrons, so that their charges balance out

– which is the basis o the neutrality. I now two materials o

different chemical composition come into contact with each

other, electrons rom one material can pass to the other.

Electrically charged layers o opposite sign are thus pro-

duced at the contacting suraces. As long as the materi-

als remain in contact, these charges are o no significance.

However, i the materials are separated, the charges are

also separated - but the positive and negative charges re-

main on the sides where they were (Fig. ).

Static electricity is simply an imbalance in the distribution

o electrons, defined as:

“An accumulation o time-invariant charge o positive and /

or negative sign on a material (either locally or overall)”.

This charge ofen generates a high voltage associated with

low current levels.

Charge accumulates in non-conductors or insulated con-

ductors where there is no possibility o discharge by flow

o current – the charge is at rest.

I such a charged material, e.g. the human body, comes into

contact with a conductor, discharge will ollow in the orm

o a current pulse lasting only milliseconds. The human be-

ing perceives this discharge as a minor electric shock.

Fig. – Generation o electrically charged layers at the boundary be-

tween two raw materials


33/78


Influencing factors

Static charge is thereore inherently a contact rather than

a riction problem. Friction merely reinorces the effect

as it increases the contact suraces and the suraces are

changed by the thermal and mechanical stress.

The magnitude o the charge is dependent upon several

actors, e.g:

• electrical conductivity, which in turn is dependent upon

the conductivity o the material itsel and the conductivity

arising rom moisture content

• dielectric constant

• speed o the process generating the charge

• temperature difference between the two materials rela-tive humidity

• Dried out man-made fibres and wool always tend to ac-

cumulate charge, as do fibres with a low water-retention

capacity (synthetic fibres) i they are not properly treated

with an antistatic agent. Accordingly, the problem occurs

more ofen in winter than in summer as heating leads to

drying out o fibres in winter.

The problems for the spinning mill

Two main groups o problems giving the spinner trouble

in connection with static electricity are:

• adherence o fibres to the machine components, and

• alling apart o fibre strands.

Charge accumulations on the fibres and on the machines o-

ten have different signs. The machine components thereore

tend to attract individual fibres or even whole strands. This

leads to ormation o laps, catching o fibres, blockages, etc.,

especially on cylinders, in clothings and in guide ducts.

Falling apart o strands is caused by all fibres in the strand

having the same charge and thereore tending to repel each

other. In minor cases, this causes spreading out o the edge

fibres; in extreme cases, the strand disintegrates.

Environmental conditions

General conditions

Raw materials used in spinning mills do not only exhib-

it different characteristics depending upon their moisture

content but also varying running perormance (behavior).

This behavior occurs especially with wool and man-made

fibres. Since the moisture content o the fibres is primar-

ily dependent upon the moisture content o the atmosphere

and the time o exposure to this atmosphere, air condition-

ing o the mill plays an important role in processing man-

made fibres. Unavorable ambient conditions can make

spinning not just difficult but impossible.

At low moisture levels the main problem is static electrici-

ty; at high moisture levels, spin finish may smear, avor nep

ormation and cause drafing difficulties. Low moisture lev-

els may increase static charge which can lead to choking o

clothings, blockages in sliver passages and lap-ormation at

cylinders. High moisture levels lead to an increase in yarn

unevenness and imperections. Experiences have shown

the ollowing ambient conditions to be avorable or the

spinning mill:

• relative humidity (rh): - %

• temperature: - (-) °C

In detail, conditions which are listed in Table have proved

to be avorable.

Normal

Hot Countries

(Maximum)

rh% °C °C

Viscose:

Spinning preparation - -

Ring spinning - -

Polyamide fibre:

Blowroom and carding room - -

Draw rame and roving rame - -

Ring spinning - -

Polyacrylonitrile fibre:

Blowroom - -


Ring spinning - -

Polyester fibre:

Blowroom and carding room - -


Ring spinning about -

Table – Good ambient conditions or processing o man-made fibres


34/78


In spinning, relative humidity is a very important criteri-

on. However, since spin finish needs a minimum moisturecontent to have an effect and tends to smear at excessively

high levels, the absolute moisture content o the air is also

significant. It should be in the ollowing range:

For PES and PES/CO

• in the spinning mill, . - g HO/kg dry air

• in the winding room, . - g HO /kg dry air

For PES/modal and PES/viscose

• in the spinning mill, - g HO/kg dry air

• in the winding room, . - g HO/kg dry air

For acrylic fibre• in the spinning mill, - g H

O/kg dry air

It is not enough to consider only average values when as-

sessing an air-conditioning system. It is also important to

maintain the set values within narrow tolerance limits as

synthetic fibres react strongly to moisture variations. Viscose

and cotton fibres are less problematic in this connection.

Storage of man-made fibres

Actually, storage o man-made fibres ties up less capital

than the storage o cotton fibres. On the one hand, this is

due to the short distance o the man-made fibre manuac-

turer rom the mill and on the other hand to the short de-

livery times. However, a disadvantage that should not be

underestimated (especially in the colder seasons) is the be-

havior o synthetic fibres when subjected to temperature

and moisture.

I the fibres are stored in a cold room, as is usual, and the

bales are opened immediately afer transport into the blow-

room, c

The Rieter Manual of Spinning Vol. 7 2451-V1 en Original 68509

Documents

Transcript of The Rieter Manual of Spinning Vol. 7 2451-V1 en Original 68509