class lecture of Post spinning

7/30/2019 class lecture of Post spinning

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by

Dr. Mumtaz Hasan Malik


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Objectives

To assemble long length of yarn into suitable package

form for use in subsequent processes e.g. warping,

weaving, knitting;

To remove sizeable yarn faults by cutting and then by

joining the cut ends; and

To apply lubricant on yarn surface, if required.


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Important Aspects of Package Winding

Package formation

Thread-line dynamics and tensioning

Yarn clearing

Piecing

Waxing


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1. Winding units

2. Ring and rewound yarn packages

3. Basic winding actions

Bobbin rotation

Yarn traverse


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Wind Angle: The angle between the yarn lay on the

package and a plane perpendicular to the bobbin axis is

called the wind angle. It is calculated as under:

tan = Vts /2rNb ---------------------(1)

where:

= wind angle

Vts = traverse speed (m/min)

r = radius (m) of yarn layer being wound

Nb = bobbin rotation speed (rpm)


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Greater the wind angle more stable the package.

Maximum limit of wind angle is achieved when slipping

of yarn during traverse reversal does not take place.

Coil Angle: The angle between the yarn lay on the

package and the direction of the traverse length is called

coil angle.


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------------(2)

Where

Vwy

= yarn winding speed (m/min)

Vbs = bobbin surface speed (m/min)

Vts = traverse speed (m/min)

Vbs = 2rNb ---------------(3)

Vts = 2LNt ---------------(4)

Where

L = traverse lengthNt = traverse frequency

---------------(5)


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1. Drum Winders for making random wound packages

of staple-spun yarns.

2. Precision Winders for making precision wound

packages of filament yarns.


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Drum Winders:

Forming package rotates through surface contact of a

rotating cylinder.

Yarn traversing takes place either by grooves of the drum

which rotates the package or by an independent wing cam

(Fig 7.5)


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Grooved Drum:

Surface speed of the drum and traverse speed are constant.

Interconnected clockwise and counterclockwise helical

grooves are made on the drum.

Continuous groove guides the yarn along the traverse length

during yarn winding.

Continuous helix has points of crossover of clockwise and

counterclockwise helices.

Retention of yarn in correct groove is ensured by making one

groove deeper and shallower groove is slightly angled.


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The drum constant kis given as:

---------------------------- (6)

Where Nd = Drum rotational speed

Nt = Traverse frequency

For every turn of drum one double traverse takes place.

With grooved drum the constant k is always a whole

number which is twice the number of crossings of grooves

e.g. a crossing of 3 kbecomes 6


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crossing drum with k= 1 is called a split drum

From equation 4 and 6

---------------------------- (7)

The traverse ratio TR is

---------------------------- (8)

Where Dd = Diameter of drum

Db = Diameter of cylindrical bobbin


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For conical package:

TR= k Dd/d

m

Where dm = Mean diameter of conical package.

As package diameter increases its rotational speed

decrease resulting in reduction of wind and traverse ratios,

but angle of wind or coil angel remain constant.

Stable packages are made when ranges from 9o to 22o or

ranges from 81o to 68o.

Decrease in traverse ratio with increasing package

diameter poses a problem in winding process.


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Wing Cam:

Following figure shows an independent yarn traverse

system


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End A of yarn guide bar moves yarn whereas end B of

yarn guide bar moves around periphery of cam, traveling

one cycle of periphery per rotation of camshaft.

As B makes one cycle of cam, A reciprocates, moving the

yarn through a return traverse along length of bobbin .

Due to inertia on reversal yarn guide limits winding

speed.


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Reciprocating guides are replaced by a spirally traverse

roller, which enables winding speed of more than 1500

m/min.

Grooved traverse roller does not need threading up

mechanism.


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Patterning / Ribboning:

As the diameter of package increases the traverse ratiodecreases because .

During winding, traverse ratio passes through a series of

integer values

Rate of change of package diameter determines how long

the traverse ratio remains at any particular integer value

At smaller diameter the rate of change of package

diameter is high therefore patterning does not occurs


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At larger diameter, the rate of change of package diameter

is low, yarn coils of successive traverse follow exactly the

same path of wind and ribbonning on package takes place

Patterning can also occur when traverse ratio TR = integer

+ 1/2 or 1/3, 2/3, 1/4, 3/4, 1/5, 2/5, 3/5, 4/5 etc.

A ribboned package may give uneven dyeing of yarn


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Sloughing-off:

During unwinding, two or more overlaid coils can be

undesirably pulled off together from the bobbin.

Such unintentional removed leads to entanglement of coils.

This fault is known as sloughing-off.

Sloughed-off material has to be cut away, thus the loss of

material and lower productivity in subsequent processes.

Sloughing-off may cause needle breakage in weft knitting.

Yarn coils in patterning zone can also cause high tension

variations during unwinding


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Anti-patterning Devices:

1. Variation of Traverse Frequency

For cam-operated traverse machine, a small sinusoidal change

to the normal running speed of cam shaft changes the traverse

speed, thus the start of each double traverse changes position

from the pervious one.

Therefore patterning is avoided.


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2. Variation of Drum Speed:

For rotary drum machine, small reduction and increase in

drum speed (20-30 times per minute) control patterning.

Slippage of package from the drum during low and then higher

drum speed changes the coil lays and therefore traverse ratio

which ultimately avoids ribboning.


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3. Lifting of Bobbin:

About 1 mm lift of bobbin, 20-30 time per minute, from the

drum surface can also introduce slippage of package thus

change in coils lay, resulting in anti-patterning.

4. Rock-and-Roll of Bobbin:

This method is used during cone winding.

The lower diameter part of the package (nose) rises about

1mm several times per minute, which introduces slippage of

the package, thus change in coils lay.


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Filament yarns are particularly wound on precision winding

machines.

On precision winding machines, package is mounted onto a

spindle and a traversing guide, driven by cam coupled to the

spindle moves the yarn along the traverse length.

Traverse guide limits the winding speed because of inertia on

reversals.

The term precision refers to the controlled positioning of yarn

coils during winding on bobbin, a precise ratio of spindle to

traverse speed .


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With the increase in package diameter, the wind and TR

remain constant.

Therefore, for precision winders

------------------------- (9)

and

------------ (10)

Therefore, as Db increases increases and decreases.

As filament yarns are prone to slip at reversals, is kept in the

range of 70o-80o.


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If machine is set such that TR is not an integer or a multiple of

0.5 no patterning occurs and no anti-patterning system

requires.

If Nb is kept constant, surface speed and yarn tension will

increase as the package diameter increases, resulting in uneven

package density and higher yarn breakage rate.

Precision winders may have:

Constant or variable spindle speed

Constant or variable surface speed

A combination system


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Constant spindle speed requires minimum tension fluctuations.

Variable spindle speed provides a constant mean winding

tension.

Constant surface speed requires spindle speed reduction as

package diameter increases.

For combination approach, spindle speed first increases to give

the required production rate, after which surface speed is kept

constant.

Advantage of combination approach can be shown with the

following example.


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For constant spindle speed:

Vlimit = 600m/minVw = Db(max)Nb/100

Nt = 264.5 cycles/min.

With 264.5 cycles/min Vw =


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For combination system, the winding speed at the early stage

of package build up can be at the fastest, matching the yarn

limiting speed.

Reduction in winding speed occurs when diameter of package

reaches the value of

If Nt = 350 cycle/min, Db = 10.91cm will be the diameter and

76.9o


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In the second stage of winding, package builds up at 600m/min

until diameter reaches 14.44 cm and = 80o.

Following figure shows a comparison of two winding systems.


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a. Package Surface Speed:

Different surface speeds along the traverse length.

One point of drive of the cone by the drum.

Slippage at all surface contact points expect the point of drive.

Drive length y is the distance along the traverse from the

cone base to the point of drive, which remains constant during

winding except negligible variation in y when cone is small.

Production speed of winding is the mean surface speed and not

the speed at the point of drive.


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Mean surface speed of cone Vm can be calculated :

Nd.D

d= N

b.d

d

Where Nd = Rotational drum speed

Dd = Drum diameter

Nb = Rotational cone speed

dd = Diameter of drive point

If the cone angle and d cone base diameter then


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If = the cone angle and db = cone base diameter, then,

dd = db2ysin

b Abrasion at Cone Nose:


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b. Abrasion at Cone Nose:

Slippage at nose cause abrasion resulting localized fusion of

polyester.

Cam-operated traverse system (split drum), one part is solid

and the shorter part (loose shell) is free to rotate and support

the rotating cone nose

In drum traverse systems, cylindrical drum is replaced by

slights tapered drum.


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c. Traverse Motion:

With cone package, surface area is greater at base of the cone.

To achieve uniform density, yarn length wound per unit area

should be a constant value.

Accelerated traverse motion, yarn guide moves rapidly across

the traverse at nose.

More coils at the base.

Accelerated traverse is achieved by a cam at nose and for drum

grooves are widely spaced.

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class lecture of Post spinning