yarn formation exam 3

purpose of roving process

to reduce weight of drawn sliver to get lighter/thinner material for spinning

input and output of roving

input is a loosely twisted strand of fibers, output is roving

twist is added by the ___ _____

flyer rotation

draft is distributed at which stages?

roving and spinning processes

is it possible to produce yarns directly from sliver that requires a high draft?

no

why does significant twist from ring spinning provide strength to yarn?

it creates a lower number of fibers in its cross section

in ring spinning, the yarn is threaded through a _____, which moves around a _____ ____ around the _____

traveler, stationary ring, bobbin

what does the rotation of the yarn bobbin achieve in ring spinning?

it pulls the traveler around the ring and causes twist formation

the ___ of the spindle in ring spinning is proportional to the amount of _____

speed, twist

does the twist travel all the way to the front roller exit nip during ring spinning?

no, it stops and forms a spinning triangle

fibers at the ____ of the spinning triangle are under more tension

sides

fibers in the center of the spinning triangle have more slack and tend to move to the sides, and vise versa

fiber migration

fiber migration provides the yarn ____ and ____

coherence, integrity

a balloon is formed during…

ring spinning

balloon formation during ring spinning does what to the yarn tension?

increases yarn tension, can lead to breakage

purpose of winding

transfer yarn from small spinning bobbins to larger package for efficient subsequent processes

wound packages should have:

specific shape, uniform weight/length and density

what is the clearing process of winding

defects such as thick/thin and weak spots, neps/slubs are removed

what wound package shapes are used for synthetic yarns?

cylindrical and tapered

what wound package shapes are used for staple yarns?

cone and rounded cone

describe compact spinning

modified ring spinning frame with attached device to condense fibers in spinning triangle before twist insertion

fiber condensation can be achieved by:

mechanical, magnetic, or aerodynamic

compact yarn compared to ring spun yarn

less hairy and stronger because there are much less edge fibers

compact spinning produces:

high quality yarn with low cost (it requires lower twist than ring spinning)

limitations of (traditional and compact) ring spinning

very slow, low production rate, high cost

inputs and outputs of rotor (open end) spinning

input is drawn sliver, output is wound packages

are there less processes in ring spinning or rotor spinning?

rotor spinning (combines spinning and winding)

there are no ____ in rotor spinning

roving or spinning bobbin

purpose of rotor spinning

separate sliver fibers by strong drafting and then recollect and twist the fibers

in rotor spinning, fibers are twisted in the:

rotor

the strong drafting in rotor spinning happens by:

combing roller and air stream

the rotor rotates with a high speed that produces a centrifugal force that causes…

fibers to collect along the wall forming a ring

what happens to the harness after it is swept from the fiber ring to the rotor?

the twist is inserted and converting fiber bundle into yarn

rotor spinning is __ times more productive than ring spinning because:

10, the rotor can be turned at a high speed

rotor spun yarn strength is about __% of ring spun because:

70, fiber disorientation, lower level of fiber migration, presence of wrapper fibers that do not carry load

which method produces coarser yarn, rotor or ring spinning?

rotor spinning

which method has a lower maintenance cost, rotor or ring spinning?

ring spinning

input and output of air jet spinning

input is drawn sliver, output is wound packages

air jet spinning combines:

spinning and winding

in air jet spinning, silver is drafted by:

a set of drafting rollers

which method, air jet or rotor spinning, has a higher production rate regardless of yarn count?

air jet spinning

how is the twist inserted in air jet spinning?

by air flow produced from one or more air nozzles

what is the structure of air jet yarns like?

untwisted core fibers with wrapping fibers on the surface

is air jet yarn or ring spun yarn stronger?

ring spun yarn

characteristics of air jet yarn

low hairiness and pilling tendency, excellent yarn evenness

air jet spun yarn compared to ring spun and open end yarn

air jet spun yarn is less elastic, rougher

the process of combining or twisting two or more yarns together

plying

two steps of plying

doubling and twisting

doubling

combining required number of single yarns

true or false, doubling and twisting may be combined into one step

true

machines that can be used for twisting

ring-twister and two for one twister

which is more productive, ring twister or two for one twister?

two for one

twist insertion in ring twisting is _____ to that in the ring spinning machine

identical

why should the tension on all single yarns be the same during ring twisting?

to avoid the low tension yarns from wrapping around the high tension yarns

ring twisting uses a Z twist when ____, and an S twist for the ____ _____

plying, twist insertion

where is the feed package (contains single yarns for plying) during two for one twisting

it is fixed on the rotating hollow spindle

where does the yarn from the feed package go during two-for-one twisting?

through a guide, then through the axis of the rotating hollow spindle

during two-for-one twisting, each rotation of the spindle inserts __ turns to the yarn

2

where does the twisting happen in the two-for-one twisting process?

in the yarn length inside the spindle, and in the yarn length between the eyelet and the take-up rollers

flow chart of filament yarn processing

polymerization, dissolving, extrusion, drawing, texturing

reasons for mixing

mix polymers that cannot be dyed with a color pigment while it it molten, blending two or more polymers, mix additives

spinning methods

melt, dry, and wet spinning

melt spinning flow chart

heating, extrusion, cooling, drawing, flat filament or crimping, winding or cutting

what is the most common method to produce filaments from thermoplastic fibers?

melt spinning

describe melt spinning

polymer is melted by heat and pushed through a spinneret, and then cooled and collected by a take up mechanism

advantages of melt spinning

high productivity (1000-6000 m/min), no solvent required, combine 2+ materials

disadvantages of melt spinning

low tenacity and modulus fibers compared to solution spinning

dry spinning flow chart

extrusion, solidification by solvent evaporation, drawing, flat filament/crimping, winding/cutting

wet spinning flow chart

extrusion, coagulation, drawing, flat filament/crimping, winding/cutting

when is dry spinning used

when polymers cannot be melted, so they need to be dissolved in a solvent

describe how dry spinning works

a solvent dissolves the raw material and forms a solution that will be purified by a filter, the purified solution is extruded through a spinneret and solvent is evaporated

advantages of dry spinning

high productivity, yarn does not require purification

disadvantages of dry spinning

complex compared to melt spinning, flammable solvents

which is the most expensive and complex spinning method

wet spinning

when is wet spinning used

used with polymers that don’t melt and dissolve only in non-volatile or thermal unstable solvents

describe wet spinning

the solution is extruded through a spinneret into a spinning bath to wash out the solvent, and the fibers coagulate and collected by take up mechanism

advantages of wet spinning

produce large tows

disadvantages of wet spinning

low productivity, solvent needs to be washed out

why is gel spinning used

to make high strength and high modulus fibers

describe gel spinning

polymer is kept in a partially liquid state to allow polymer chains to bond together, the solution is extruded through a spinneret and then cooled, yarn is then stretched

why does gel spinning produce fibers with high strength and modulus

the polymer chains have a large degree of orientation

characteristics of non-round cross sections

higher surface area, cover, filtration efficiency, liquid wicking

when can drawing occur

either after extrusion or integrated during extrusion

during drawing, the spinneret orientation and spin draw cause..

a certain degree of orientation in the wound filaments

why does drawing result in a considerably stronger yarn

it orients the molecular chains along the filament axis

drawing removes…

the permanent elongation in the filaments

drawing feel depends on…

material, spinning conditions, and spinning take up speed

drawing conditions:

temperature, humidity, drawing speed

draw ratio for nylon, polyester, and PPE

3-5

draw ratio for high tenacity yarns

7

draw ratio for gel yarns

several hundred

fiber tenacity

a normalized value to compare different fiber strength, breaking force divided by fiber denier

increase in draw ratio does what to the molecular orientation?

increases it

impacts of increasing draws ratio

increases yarn tenacity, decreases breaking elongation

why is texturing used

to modify the structure of synthetic yarns to qualify them for end uses

texturing methods used for thermoplastic filaments only

false twist, stuffer box, knit de knit

describe false twist

yarn moves in a heated zone while false twist is applied by friction disks/belts, and then cooled while the twist is removed

describe stuffer box texturing

filaments get stuffed into a heated box, get a 3d crimp and set by heated input rolls or heating the stuffer box, then cooled while crimped

advantages of stuffer box

fast and inexpensive

describe knit de knit

filaments are knitted into a fabric which is then heat seat and cooled, and then unraveled