Card

OBJECTS OF BLOWROOM

(1) Opening:

As we receive bales in compact form, (i.e. for reduction of cost during

transportation from ginning to spinning mills.) blow has to reduce tuft size

gradually. In blow room reduction in tuft size is about 0.1 mg.

(2) Cleaning:

It removes all type of impurities. Impurities involves – plant material,

foreign matters, seeds, seed coats, stem, leaf, soil, sand particles, packing

cloths, metal pieces (nails, strips). B.R. removes 40-70% impurities. As far as

B.R. cleaning is concern, we can say that, improved cleaning is achieved at the

cost of high fibre loss. Normally fibre represents 40-60% of BR waste.

Cf =

(3) Dust Removals:

Dust particles are very fine in size & are completely enclosed in the

flocks. Generally dust particles are held back during suction. During suction 64%

of dust is removed & more intensive as smaller the tufts.

(4) BLENDING:

Blending is essential for yarn production. A blending is possible at every

stage (i.e. transverse blending). For good blending at initial stage simultaneous

extraction of fibres from bales is essential.

(5) Even feed of material to CARD:

Old Blow Room feeds lap, which is produced by scutcher. So scutcher

should ensure very uniform weight. As far as Blow Room & carding is concerned

we can say that both are performing same functions at different levels or

intensity.

BR: Macro level opening and cleaning.

Card: Micro level opening and cleaning.

Carding is the most vital machine in staple yarn manufacturing. It

strongly influences process performance & yarn quality. Though concept was

invented in 1770 & has first commercial appearance in 1850. Since then concept

of carding has not undergone much of a change.

CARDING

Objects :-

(1) Individualization of fibre tufts to almost single fibre stage.(Fibre to fibre

Separation)

(2) Cleaning: Cleaning of fibre stock for production of fault free yarn.

Cleaning includes removal of…

(i) Seed coats/ large impurities.

(ii) Neps and immature fibres

(iii) Micro dust

(3) Mixing of fibres to average out variations in fibre characteristics – to

produce a yarn with uniform characteristics.

(4) Formation of random way of oriented fibres called sliver – to produce

an assembly which can be easily manipulated into yarn.

Basic requirements of Carding Process:-

In carding machine two basic actions are taking place between two wire

covered surfaces, these actions are

(i) Carding action

(ii) Stripping action

Carding action:

The separation of fibres from tuft held in between two wire surfaces is

called carding action. To happen this carding action there are following

conditions,

(1) There should be two very closely placed (0.3 mm or 20-30 times dia. of

fibre) wire covered surfaces.

(2) The interacting surfaces should be placed in such a way that wire points

on it should face each other, i.e. point to point arrangement

(3) Interacting surfaces should move either in opposite direction or in same

direction. If they move in same direction, the surface with fibres on it

must move at a higher velocity than other surface.

Above figure shows a carding action & forces acting on fibre tuft during carding…

α = Inclination of first rack with base

f = force acting on fibre tuft

K & P = force is resolved into two components

K= known as carding component, tries to press the fibres towards

the point of other surface.

P = as it acts towards the base of clothing shows fibre retention

capability of clothing.

K = f sin α ………. (i)

P = f sin β ………. (ii)

The fibre can only moves downwards along the wire point provided, P overcomes

the frictional resistance between wire & fibres i.e. µK. Where µ is coefficient of

friction between wire points & fibre. When fibre is slipping towards tip of wire

point. This is also an important condition for carding; otherwise the fibre will have

a tendency to roll between two clothed surfaces. i.e. when α =90

(Holding of fibre by either of surface will not happen.)

Hence for effective carding,

P > µ.K ………………… (iii)

From (i) & (ii) we can write,

F cos α > µ f sin α

Cos α/ sin α > µ

Cot α > µ ……………….(vi)

From above equation it is clear that as angle of wire indication increases µ goes

on reducing. The intensity of carding action can be manipulated for different fibre

by selecting suitable inclination i.e. α .

Stripping action:-

The process of fibre transfer from one surface to another surface is called

stripping. The necessary conditions are…..

(1) Two wire covered surfaces facing each other.

(2) The distance between them should be around 0.3mm or less. (Nearly 20

to 30 times the dia. of fibre)

(3) Inclination of both surfaces in such a way that point on one surface

should face back of wire from other surface. i.e. point to back

arrangement.

(4) Interacting surfaces should move either in same direction or opposite. If

they are moving in same direction, linear velocity of surface on which

fibre is to be transferred; should be higher than surface with fibre.

Force acting on fibre component shown in figure, P' & S are two resolved

components of fibre tension “f”. P' is acting perpendicular to back flank & S is

acting along back flank.

P' presses the fibre against the tooth where as stripping component S

tends to push fibre off the tooth. β is the angle of inclination of back flank. Then

P' & S' are

P' = f sin β

S' = f cos β

Stripping will happen only when…..

S > µ . P'

f cos β > µ. f sin β

cot β > µ

cot (α - ө) > µ

Ex.

Sripping action – between licker-in & cylinder.

Carding action – between cylinder and flats.

Sripping action – between cylinder & doffer.*

(* Wire points are facing each other i.e. point to point action, but wire point

density on doffer is more than cylinder and cylinder & doffer are set very close (5

thou). Also transfer is facilitated by release of air current.)

Carding machines which are available in the market, we can divide into

two broad groups as fallows…..

Roller and cleaner card

Revolving flat card

Roller & cleaner card used for fibres like wool, jute, flax & cotton waste.

Revolving card used for fibres like cotton and synthetic.

Revolving flats can be studied broadly under following heads…

(1) Passage of material through machine.

(2) Taker in region:

(i) Feed unit

(ii) Opening cum cleaning unit.

(3) Carding region.

(4) Condensing region.

(5) Coiling region.

Feed to Card:-

The product of card is sliver; requires uniform along its length. Sliver

quality has direct influence on yarn quality especially carded yarn. To make a

sliver uniform, it is important to ensure that feed to card is free from irregularity.

Since there exist a direct relation between sliver and yarn quality. The form in

which material is feed to the card is either lap or tufts. Based on these forms we

have two feeding systems…

1. Lap feed system.

2. Chute feed system.

Lap feed system:-

Advantages:-

1. Production of even lap in scutcher is relatively easy.

2. The system is flexible, i.e. different material can be processed on different

card.

Functions: -

1. To feed lap uniformly to the licker-in.

2. To tear apart lap into minute tufts without neither plucking nor causing any

damage to fibres.

3. To eliminate trash particles, short fibres etc.

Limitations:-

1. During lap formation compression of opened tufts takes place to form a

lap. Due to again compression the purpose of opening is defeated.

2. During joining of new lap with exhausting lap, some overlapping is

required which is a source of fault generation & cause for extra waste

also.

3. During transport and storage excess handling (additional workers),

deposition of dust & fibres on lap etc.

4. Additional storage pace required.

Chute feed:

To overcome the limitations of lap feed, a new feeding system was

developed. In chute feed material is pneumatically conveyed to card and fed in

opened tuft form. Thus process of gradual opening is continued and load licker-in

action and fibre reduces.

Basic elements of chute feed system:

Material conveying system:

To carry material from blow room to a group of card with the help of air.

Air pressure controlling system:

For smooth flow of material through material conveying system, air

pressure is required to maintain at constant pressure.

Feed mechanisms:

To feed material at uniform wt/length and width in the chute.

Delivery system:

To feed the material to the card.

A sensing mechanism at chute:

It keeps a certain amount of material as reserve and also to control the

feed of material to chute.

Limitations:

1. Not flexible: since the same material supplied by the blow room feeds a group

of card, simultaneously.

2. Change of mixing results in rework able waste created by running out.

3. Difficult to ensure even feed – photoelectric system cannot sense opened and

compact tuft.

4. Higher nep generation.

Basic concept:

From blow room tufts are transported pneumatically to the vertical

reserve boxes / chute attached to several cards. The chutes are filled to

predetermined height by tufts. The packing of tufts should be as uniform as

possible. The material is taken out from the bottom and fed to licker-in. To obtain

even feeding, the tufts should also be distributed evenly across the full width of

the chute. Since tufts are conveyed pneumatically first chute will fill first followed

by rest. Hence control is necessary to ensure uniform chute.

There are two basic types of continuous feed…

(1) Single piece chute

(2) Double piece chute

However the installation can be open or closed distribution type. In

open type feed duct ends after the last card. Where as in closed type the duct

goes beyond the last card and joins the distribution again.

Single piece chute system (Aero feed system):-

Various elements of aero feed are shown in fig. a condenser sucks the

material from blow room and delivers it to flock feeder by way of feeling trunk.

Flock feeder opens the tuft to desired size. A kirshner type beater is used to open

the tufts. In opening zone fresh material, i.e. blow room receipt and returned

material are mixed. The fan (2) blows these tufts into horizontally closed circuit

loop (4) situated above the card. A separating head (5) incorporated in the duct,

divert part of tufts from the air current into the vertical feed chutes above the

card. The feed chute (6) ensures a uniform supply of material over the full

working width of card. Flock meter (3) controls the flow of material.

Flock Feeder:

It consists of three elements…..

1. Beater

2. The filling & return trunks

3. Condenser:

The material is fed to kirshner beater by way of two-ridged roll &

two feed roll. A light barrier (4) regulates supply of material from blow room. A

return trunk consists of two chambers; one is feeding material to beater &

another is mixing material into fresh delivered material, a light barrier in return

trunk monitors the amount of return material.

Fan:

A air current generated by fan is centrifugal type. It delivers the air at the

rate of 1 to 1.3 cubic ‘m’/sec.

Separating head & Card feed chute:

A separating head is located above card feed chute. It has

adjustable nose & glass windows on both sides. A adjustable nose facilitates

change in cross section of distribution duct. The change in cross section of

duct retards the flow of material & under influence of

gravity assisted by part of air current being diverted downwards. The stream

of huts is deflected by the nose of accelerated again. After the last card,

surplus goes into return trunk.

The card feed is ‘U’ shaped metal sheet. The open end of trunk

is provided with glass wall. The material from the chute is

drawn off by a pair of feed rolls & delivered to card feed roller. A separation of

air & tubes is achieved by adjusting nose in separating head. A raising a nose

produces more separations & vice versa.

The feed wt/mt depends on excess static pressure in the

installation. The drop in pressure is linear i.e. pressure goes on decreasing

from first to last separator by 2 mm head of water. The wt/mt is adjusted by

changing distance between glass & rare wall of chute. The wt/mt is ranges

from 600 to700 grams.

Double piece chute:-

Basic features of chute feed:

1. Upper &lower chute separated by a feed roller & beater.

2. A pair of feed rollers is positioned at the end of the lower chute.

3. Have air escape holes & a pressure sensor fitted to control a preset

compacted volume of tuft in the chute.

Working principle:

The upper chute receives tufts from distribution ducting & the

transporting air is exhausted through the air escape holes. The feed roller and

beater remove the material at a slower rate, enabling, incoming tufts to build up

in this top chute. Increase in pressure is sensed by sensor & when desired

pressure is achieved feed is stopped. The opened tufts are dropped into the

lower chute. These tufts are fed to card by pair of feed roller, which feeds slower,

then intake. When pressure is built-up into lower chute, feeding to beater is

stopped.

Advantages & disadvantages of chute feed:

1. Continuous feed to card.

2. More uniform material feed across width & length.

3. Very fine opening of tuft can be achieved & thus reduces the excess

load on card.

4. Biggest disadvantage of chute feed is a very high generation of neps in

chute while cotton is being transferred from blow room to card.

History and developments:-

Carding has always been considered a very important process as far as

spinning good quality yarn. Carding is becoming more and more important with

introduction of modern spinning systems. To achieve a desired quality people

even today reducing carding production. A carding production can be increased

without affecting quality if card is well maintained. A development listed below

shows that card production rate is gone up considerable high from near 4kg/hr

production to 100kg/hr in a span of 45 year.

Development during last 45 years.

Years Process parameters production

1955 Lap feed 4kg/hr.

1965 Metallic wires. 22kg/hr.

1975 Cylinder speed 32kg/hr.

1985 Development of carding elements 42kg/hr.

1995 Better pre-carding 60kg/hr.

2000 Cylinder speed 600rpm 100kg/hr.

From above data it can be concluded that a significant development in carding

took place during last 20 years.

Feeding device:-

Feed plate and feed roller:

Function:-

1) Lap is held firmly, uniform firmness across width to avoid plucking.

2) Lap is presented to licker-in for gentle opening avoid fibre damage.

Feed roller is loaded with lever and weight lever and spring, pneumatic.

F1=friction force acting between lap sheet and feed roller.

F2=friction force acting between lap sheet and feed table.

µR=coeff. of friction between F.R.&lap.

µF= coeff. of friction between feed table and lap.

P= normal force acting.

F1=µR P & F2=µF P

For uniform feeding

F1 > F2

µR P > µF P

µR > µF

to ensure this condition feed roller is fluted & feed plate is highly polished.

Though this simple analysis show there is no influence of normal pressure, infect

if influence on µR. µR increases with increase in pressure apart from feeding lap

feed roller has to avoid fibre slippages during plucking by taker-in. The total

pressure applied=220kg. For better grip in case of heavy feed, wire covered feed

rolls also used. (DK 780 card)

The licker-in can perform its task most effectively if:-

1) Lap is held firmly with uniform firmness across its full width in order to avoid

plucking by licker-in .

2) Lap should be presented in such a way that opening action should be gentle to

avoid fibre damage.

A conventional feed device consists of feed roller & feed plate. The profile the

front portion of the feed plate decides the intensity of opening & some extent

possibility of plucking. The feed plate have curved surface followed by horizontal

plateau which then bevels off steeply towards licker-in. The dimensions of the

horizontal plateau and the guide surface has a strong influence on the quality and

of waste. A sharp nose gives good retention of the fibres and intensive opening.

On the other hand rounded nose results in poor retention and bad opening.

A length of guide surface is too short; they can escape action of licker-in. They

are scraped off mote knives and are lost in waste receiver. Long surface presses

the fibre into licker-in surfaces. This gives better take-up fibres at the cost of

reducing cleaning efficiency.

Geometry of feed plate:-

The profile of speed plate should be so designed, that the teeth of licker in

progressively penetrate the thick mat of fibres and comb it thoroughly over a large

length without damaging them.

Let a—length of horizontal plateau.

b—length of guiding surface

β—angle of inclination of guiding surface

to avoid fibre breakage , the distance between nip A and line of entry of taker-in

teeth into top layer of lap is equal to ¼ of staple length of fibre ,considering 0.5

coeff. of straightening .it means

ABCD=l/4 l=staple length .

a+b =lm lm =model length .

Now geometrically

ABCD= a+2πd/360 x (90°-β) +CD

d= thickness

a+2πd/360 x (90°-β)+CD=l/4

β=360/2πd x (a+πd/2+CD-l/4)

If CD≈0

β = 360/2πd x (a+πd/2-l/4)

for longer fibres we have to increase distance CD. (point of action).

Top & bottom layer point of action is at different levels.

New Design:-

With conventional design material is presented against the

direction of rotation of licker-in, which takes sharp turn over feed plate nose &

causes harsh action. Rieter has developed a feed system that enables

presentation of lap in direction of rotation of licker-in. Here feed roller is located

below feed plate which is present against it by spring pressure. Owing to

opposite direction of rotation (F.R & licker-in) at interacting point(b/a) lap moves

downward in direction of rotating of licker-in.

Taker-in:-

This is a cast roller with dia-9”(250mm). A saw tooth clothing is

applied to it. Beneath the rollers is grid elements/carding segments, above it is a

protective ceasing of sheet metals. Licker-in has to perform following tasks

To tear apart the lap into minute tufts without damaging fibres

To lead tufts over dirt eliminating (grid bars) parts under the roller.

To transfer the fibres to the cylinder surface.

Operation of the licker-in: -

A licker-in wire points passes through thick mass of fibres presented by

feed device at high speed (1000rpm,13m/s).This causes a draft of 1000 between

feed roller & licker-in giving 600,000 pts/sec. As a result the lap fringe is torn

away into minute pieces & carried forward by taker-in teeth.

Due to intensive treatment by taker-in we can observe that 50% of

fibres transferred on cylinder in the form of flocks/tufts &less than 50% in the

form of individual fibres .The intensity of opening by taker-in is governed by.

1. Feed material parameters:-

Lap liner density i.e thicker-in.

Degree of openers of tufts in lap.

Degree of orientation of fibres in lap.

2. Taker-in parameters

wire point density &angle of inclination(Acute angle)

3. Processing parameters

Distance between taker –in & feed plate

Rotational velocity

Martial throughput rate.

High performance cards requires alternative assemblies in order to be able to

deal with high material through-put with conventional assembly waste extraction

and opening intensity is likely to suffer due to reduction in degree of combing and

generation of air vortices near mote knives.

Degree of combing:-

It is defined as number of takerin teeth acting per fibre in lap.

C= no. of wire points /fibre

=No. of wire points passing through material per minute

No. of fibre feed per minute

= Z. n.Nf. l

V.Nx.107

Z: No. of wire points on lickerin.

n: rpm of lickerin.

Nx: linear density of lap Ktex.

V: surface speed of feed roller.

Wt. Of single fibre = Nf.l.10-6 gm. ------(1)

Nf: linear density of fibre.

l: fibre length.

Quantity of material feed per minute = V.Nx gm. -------(2)

No of fibres feed = V .Nx x 107

Nf .l

Opening intensity (f)

f=1/c= V.Nx.10 7 n.Z.Nf.l

Normally at lickerin C=0.3

Cylinder C=10-15

Air vortex:-

As licker-in revolves with very high speed it generates air current

around it, between feed plate and first mote knife and between first and second

mote knife. The generation of vortices are due to placement mote knife

perpendicular to the streamline of licker-in.

When plate is placed at right angle to motion of liquid as shown in fig ,a

boundary layers reaching to edges finds difficult to take sharp turn .due to strong

deceleration behind plate vertices are formed. This leads to drop in pressure

causing re-deposition of trash affecting degree of cleaning.

The degree of cleaning therefore can be improved by:-

Weakening strength of vortices

Preventing generation of vortices

Increasing intensity of opening.

Opening intensity /combing degree can be improved by:-

Enhancing speed

Having more wire points on taker-in

having more no. of combing position.

(A) Weakening of vortices (fig-b)

Mote knifes have been reduced to one

(B) Prevention of vortices generation: -( fig-a)

A large space between feed plate & vertical baffle will reduce

formation of vortex. The trash particles, teased out from lap by licker-in

teeth, get into trash box in a direct flight path. However this leads to more

lint loss.

(C)Enhancement of opening intensity: -

(1) High speed: -

In most of modern cards taker-in speed has been enhanced from

a level of 450-600 rpm to a speed of 800-1300 rpm. An excessive high

speed might result in high waste, fibre damage loss of good spinnable

fibres also, and taker-in loading due to incomplete fibre transfers.

(2) More no. of wire points:-

Very little can be done in this respect because too much increase

in wire point density will reduce gap between two wire point rows

leading to fibre chocking this results in reduced opening efficiency.

(3) More no. of combing position:-

There are two way of doing this.

(i) Increase no of rollers.

(ii) Addition of combing surface.

Increase no of rollers:-

More no of rollers will enhance the opening of tufts thoroughly

before transferring to cylinder. The degree of combing for no. of taker-in working

in series is

C=n1.z1.l.Nf + n2.z2.l.Nf + - - - - - -

V.Nx.107

= l Nf x [ n1z1+n2z2+- - - - - ]

V Nx 107

When more than one licker in is used speed of the licker in is kept higher

progressively. The multiple lickrein will following benifits

1. Improved dirt and dust elimination.

2. Improved untangling of neps.

3. The possibility of speed increases and hence productions increase.

4. Preservation of clothing, and hence longer life of the clothing, especially

flats.

5. Better yarn quality.

Additional carding segments: -

(1)Addition of combing surfaces:- (under taker-in)

Generally combing segments are kept below the taker-in after the mote

knife as shown in fig. In Rieter card, for example, the flocks are first guided over

mote knife then over carding surface then again over mote knife and again over

carding plate, before they get transferred to cylinder. A special clothing need to

mounted on the combing surface so that it does not get chocked with fibres.

(2) Between taker-in and the flats &

(3) Between flats and doffer:-

Taker-in delivers fibres still in the form of flocks, if not lumps to main

cylinder. These flocks are compact and relatively poorly distributed over licker-in.

Since there is no opening action between taker-in and cylinder they are passed

as such to cylinder. These tufts have a negative influence on quality of carding

especially for high production card. This shortcoming can be practically

eliminated by inclusion of carding segment. Since they ensure further opening,

thinning out and primarily spreading out and improved distribution of flocks over

total surface.

Between taker-in and the flats Between flats and doffer

1st few flats with takes parts in carding action gets loaded too quickly to a

large extent and hence impairs carding action .The carding segments positioned

at front opens flocks and distributes uniformly over cylinder surface.

The carding segment following flats (Between flats and doffer) also

has a positive influence on yarn quality in terms of improving neps, thick, thin

place, U% and yarn strength and fibre transfer too.

In short we can say that carding segments brings following advantages.

Improved dust & dirt elimination

Improved untangling of neps

The possibility of speed increase and hence production increase

Preservation of clothing and hence longer life of clothing especially flats

Better yarn quality

Fiber transfer taker in to cylinder:-

Transfer of fiber from taker in to cylinder takes place through “stripping

action”. The most important parameter that strongly influence is the ratio of

surface speed between the cylinder and taker in and angle of inclination of taker

in teeth. The surface speed ratio 1:2.The angle of inclination of taker in teeth

should be such that it should facilitate transfer. The condition for this is Cot α >

µ.

The teeth extended in same direction.

V1>V2

Point to back action.

R—tension on fiber tuft

S1—normal component

S2—stripping component.

S1=R.sin α, S2=Rcos α

For stripping S2 > µ S1

S2 / S1 > µ

R. cos α / R. sin α >µ

Cot α>µ ------------------<A>

Angel of inclination—front rate +5° to +10° to vertical for cotton fibres.

For synthetic -10° to -15°

Condition<A> helps to keep the fiber on surface of taker in which facilitate easy

transfer.

Carding section

It consists of cylinder a chain of flats front & back plates & an undercasing.

Carding action carries out the separation of fibre tufts. The action is so intensive

in nature that tufts are individualised to almost single fibre stage. A fibre

separation also facilitates removal of neps, dirt, dust &other foreign impurities.

The cylinder: -

It is most important part of carding m/c . It is manufactured from cast iron but

now sometimes made of steel. The cylinder is machined internally at both ends

to accommodate the cast iron spider with spokes & hubs. It is supported by a

main shaft which rest on roller bearing on pedestal bracket bolted to the main

frame side. Most cylinder have a diameter 1280-1300mm & rotates at speed

between 250-600rpm.The concentricity of cylinder must be maintained within

extremely narrow limits. This is because of distance between cylinder & doffer is

0.1mm.(very very close).

The casing of cylinder: -

Beneath the cylinder is a grid made of sheet provided with slots. The grid

removes impurities & maintain a constant airflow condition. As most of trash is

removed in taker-in zone &left with very micro dust, the cleaning by grid is very

small due to this now a days grid is replaced with sheet. This sheet avoids

formation of small vortices. It also gives better fibre orientation on the surface of

cylinder &reduces no. of neps at high cylinder speed.

The cylinders at the front have front plate between flats& stationary flats.

By adjusting distance between cylinder & front plate flat waste can be influenced.

(i.e. level & quality of flat waste). A narrow spacing gives little waste & wide

spacing produces more stripping.

This setting is not suitable for use as a means adjusting flat waste

sometime along with short fibre it may eliminate long fibre, which may lead to

fibre loss. So one optimum setting is done it may not be altered without excellent

reason.

Flats: -

Carding action is result of interaction of two wire covered surfaces on fibre.

Together with cylinder flats from main carding zone.

Here flats are desired to performs like:

Opening of flock to individual state

Elimination of remaining impurities

Eliminations of short fibres

Untangling of neps, & dust removal

High degree of longitudinal orientations of fibres

In order to perform above function continuous carding surfaces is needed

.If we go for a stationary carding surface continuous operation of carding will be

hindered as we need frequent cleaning of surface .(as we know that with high

speed of cylinder throws fibres &impurities towards top carding surface .Top

carding surface get loaded with fibre & impurities).

To overcome above difficulties top surfaces is made up of individual

clothing strips. The strips are linked to each other by chain & driven slowly. This

facilitates cleaning of loaded flats as they are guided towards cleaning

devices .To make carding surfaces 40-46 flats are needed which are placed at

operative position. To make a chain continuous in total 100 -120 flats are

required.

Construction of flats:-

Flats are cast iron bar having inverted “T” shaped cross section. Lower

surface is machined flats and contain wire points, stretching to a breadth of 22

mm. As both ends of flats rest over flexible bend, length of flats is slightly longer

than working width of the cylinder. It is very important to maintain constant

distance between flats and cylinder across all width of the cylinder. The bending

rigidity of flat should as high as possible. A “T” shaped cross section enhance

bending rigidity and reduce sagging of flats at the middle. The flats connected

together in the form of chain are made to slide over flexible bends. It is important

make sure that they slide smoothly without rocking. As flexible bend follows

curved path like cylinder surface and flats are of round flats it will rest as a single

point which will lead rocking movement of the flats. To avoid flat surface to made

concave so it rest on both points.

The flats are so positioned over flexible bend that the distance between working

face of the flat and cylinder is not constant but decrease gradually in material

flow direction i.e. flats are tilted slightly and this arrangement is known as heel

and toe arrangement. This facilitates gradual opening of fibres.

Theory of carding action

Classical theory

Carding requires

Two oppositely inclined wire points covered surface

They should move with high relative speed provided that sliding

component of tension cutting on fibre is strong enough to move the fibre

down to the wire towards its base.

Classical theory does not take in to account the centrifugal force and presence

of air current.

Strang’s theory

The theory is based on Prandtl’s boundary layer theory. According to the

boundary layer theory the series of concentric layer of the air of infinitesimal

(very small) thickness surround the cylinder. These layers also rotate along with

the cylinder with different velocity. The velocity of the layer is constant with the

cylinder surface will be equal to the cylinder as we move from cylinder towards

flat velocity decreases and near the flat it is equal to zero.

Because air has such different velocities within surface between flats and

cylinder when tuft is introduce into this boundary layers it is subjected to shearing

action of air. The shearing force is calculated as

F=RVA/d

R= coeff. of viscosity of air at a given temp.

V= velocity of air current

A= projected area of fibre tuft in the direction perpendicular to air stream

d= depth of air boundary layer

The force increases as d become closer. It is the shear force that separates the

tuft into individual fibre For fibre transfer from licker-in to the cylinder boundary

layer of the of licker-in and cylinder are responsible.

Kaufman’s Theory

Tuft held on the cylinder surface approaches the cylinder flat zone at very

high speed. Tufts are introduced into narrow gap between cylinder and flats,

which is generally very smaller than the size of the tuft. Due to this compression

of the tuft occurs. Since flats are almost stationary as compared to fast moving

cylinder. Compression force intensity will be more at the flat and the cylinder get

disturbed over layer surface due to its higher surface speed. According to

kaufman compression force acts on 6 time layers surface of cylinder compared to

flat. The penetration of teeth into tuft is immediately followed by shearing force on

tuft due to great difference in speed between flat and cylinder. As a result tuft is

pulled apart into pieces. This process is repeated till the tuft size is reduced

considerably. Generally opening and separation process is complete by 6-7 flat

and seperated fibres evenly load cylinder.

Other force on fibre tufts:-

(1) Centrifugal force:-

F=ma a=linear acceleration

=mrω2 ω=angular velocity

=w/g x r. (2πn/60)2

Where, m=mass of tuft = w/g = Wt. (gm)

Gravitational accln

r= Radius of cylinder (m)

ω= angular speed of cylinder (d/s)

n=rpm

If r=0.645 mtr n=400rpm

F=W (0.645) (2.π.400) 2 = 115W

9.81 x 602

Here F is 115 times the Wt. of tuft. The acts through the center of gravity of tuft

held by wire points and try to lift the tuft.