Yarn Manufacture I : Principal of Carding & DrawingProf. R. Chattopadhyay

Department of Textile TechnologyIndian Institute of Technology, Delhi

Lecture – 01Introduction

So, today we are going to discuss the carding process. Carding is a very very important

process and the quality of the final yarn that we produce is very much dependent on the

quality of carding. Hence, in the industry people take lot of interest on the carding

process. Let us understand: what are the four objectives of carding.

(Refer Slide Time: 00:54)

Now, the objectives of carding is individualization of fiber tufts; followed by cleaning of

fiber stock, extraction of fiber clusters or naps which are present in the feed material,

mixing of fibers and production of an assembly of random array of fibers which we call

sliver. Now, the question comes why do you need these objectives? What is the purpose?

(Refer Slide Time: 01:40)

.

Now, if we go to the very first objective: individualization of fiber tufts. This is required

mainly to produce a very uniform yarn. The more the fibers are separated and open out

the more uniform the yarn would be, we have to make sure that there is no clusters of

fiber present in the final yarn. Next come cleaning of fiber stock; this is essential, to

produce a clean fault free yarn. The fiber stock especially cotton contains lot of

impurities and almost 50 percent of the impurities still are left in the tufts, after the blow

room operations.

So, whatever is left we want to clean it further and carding is a very very efficient

machine for cleaning finer trash particles and sucking out the dust particles. The next

important objective is extraction of fiber clusters and neps; neps are tiny cluster of fibers.

These neps are produced during beginning stages and also produced during blow room

operations. Now, these neps are detrimental to the quality of the yarn, and therefore, we

have to ensure how to get rid of them. So, the carding machine will be able to remove

part of this neps and also if there are any clusters of fibers which are present in the feed

material that is also removed by the carding machine.

The next one is mixing of fibers. The mixing of fibers will average out the variation in

fiber characteristics, which is present in the feed material. And therefore, it will give us a

yarn with consistent quality and the last objective is production of an assembly of

random array of fiber. This is required because, certain assembly is ideally suited for

easy manipulation into a yarn. To produce a yarn, what we need a random array of fibers

and carding machine will be arranging the separated fibers in a beautiful nice array and

this array is further manipulated in terms of stretching to produce the final yarn.

(Refer Slide Time: 05:14)

Now, from here if we go to the operations involved in carding for different objectives

that we have already listed. Now, objective individualization of fiber tufts and this would

need dividing fiber tufts into smaller ones and smaller ones to individual separate fibers

in successive stages. Then cleaning of fiber stock that is, elimination of trash particle,

dust dirt and seed course. This is done through separation and elimination by centrifugal

force. The separation is done by interactive pin covered surfaces.

Then extraction of fiber clusters and neps; the operation is disentanglement of the

clusters or the neps by the interacting beam covered surfaces and their elimination by

centrifugal force. Then comes object the mixing of fibers and this is done by fractional

collection of fibers on a part of the machine called tougher and returning part of the

fibers, back to the feed point and by this process we will be able to mix the fibers

repeatedly on cylinder.

The last objective is production of an assembly of random array of fibers this is done by

collection of the separated fibers followed by they removal and transformation into an

one dimensional assembly called sliver. So, the machine will be doing the operations;

which are listed here and we will study how these operations are carried out. To start

with let us see: what are the fundamental actions in a card. There are two important

actions we call it; carding action and stripping actions. Let us see, what is carding? And

what is stripping?

(Refer Slide Time: 07:55)

The condition for carding actions, is are follows; first we need two saw tooth covered

surfaces termed as A and B. Next these two surfaces should be close to each other, that is

distance between the interacting surfaces should be close to 0.3 millimeter. Then the saw

tooth points we also call it wire points, or both the interacting surfaces should be

inclined; with inclination direction opposite to each other as shown in the diagram.

The surfaces should move either in the same or opposite directions. However, if they

move in the same directions; the surface charged with material should move at a faster

speed in the direction of inclination of the short teeth. In the present case, if the lower

surface carry the material that is surface B to the carding zone, where actual separation

between the fibers takes place; then the speed of V 1 should be much greater than the

speed of V 2.

What we see here that the two surfaces are there A and B both of them move in the same

directions. The teeth points are inclined opposite to each other; the lower surfaces which

carry the unopened tiny tufts of fibers, will move at a faster speed than the top surface;

which will move at a slower speed. The inclination angle alpha of the front edge of the

truth should be such that cot alpha 1 should be greater than mu; where mu is the fiber to

tooth coefficient of friction. Now why cot alpha should be greater than mu; let us try to

understand this.

(Refer Slide Time: 10:21)

Now, here there is a diagram; where we can see only two teeth’s are interacting with each

other. Now, there is a fiber shown in red color; which is picked up by these two teeth and

the surface B is moving in one directions, then surface a is moving in the other direction.

Either they move in the same direction or they can move in the opposite direction as I

told that, in case they move in the same direction in that case, the lower surface in the

present case, must move faster than the top surface ok.

Now, let us say, there is a fiber; which is grip by both the teeth’s and let the tension; that

acts on the fiber be R. Now R the tension can be reserved into two components P 1 and P

2. Where P 1 is R sign alpha 1 where, alpha 1 is the angle; of the front edge of the saw

tooth; to respect to the base the other component P 2 is R Cos alpha 1. So, what we see

here that P 1 is perpendicular; with respect to the age of the tooth and P 2 is acting

towards the base.

Now, for the carding action to be effective P 2 has to be greater than mu p 1 that is P 2

should be able to overcome; the frictional resistance; that P 1 is going to offer to the

fiber. So, a situation has to be created so, that the fiber is made to move towards the base

of the tooth and to achieve that, if P 2 happens to be more than mu P 1 then we can write

that R cos alpha 1 should be greater than R sine alpha 1 and from here we can write; that

cot alpha 1 has to be greater than mu; that means, to have an effective carding actions,

the code value of the angle alpha must be greater than mu; where mu is the coefficient of

friction between; the fiber and the tooth front edge. Similar situation, we will occur for

the top surface as well and for that Cot alpha 2 has to be greater than mu. In such

situations, the fiber will move towards the base and as the two teeth’s are moving away

from each other the fiber will be teased out.

(Refer Slide Time: 13:53)

Now, based on this analysis, we can see, that how the angle of inclination of the teeth

varies with the coefficient of friction. Now, there are three fibers which is shown here in

the table fiber cotton wool and polyester, the coefficient of friction between; the steel and

the fiber is 0.27 for cotton 0.23 for wool and 0.40 for polyester. And the corresponding

angle of alpha, can be seen to be here for cotton it has to be less than 75 degree wool has

to be less than 77 degree and polyester is has to be less than 68 degree. So, this is a very

simple way, to understand that the inclination angle of the front edge of the teeth, should

be always less than 90 degree. Now, we go to the next action that is stripping action.

(Refer Slide Time: 15:07)

So, what are the conditions, for stripping action? Here is the diagram, showing two

surfaces and the teeth’s are saw tooth in shape like, the previous one; the again the

distance between interacting surfaces has to be very close to each other and generally,

they are close to 0.3 millimeter tooth points of both interacting surfaces should be

inclined in the same directions. So, this is little different from the previous one for

stripping that is one surface is carrying fibers the other surface will strip the fibers from

the previous surface and carry the service along with it.

And hence, what we need; is that the two tooth points of both interacting services should

be inclined in the same direction. The surfaces may move, either in the same direction or

in the opposite directions. If they move in the same direction, the speed of the surface

receiving the material should be greater than the other this we must keep it in mind.

Now, let us see an analysis of stripping happening on an isolated fiber.

(Refer Slide Time: 16:40)

We see they look at this diagram so, we see there is one single fiber. Which is a red color

and there are two tooth’s interacting with each other the fiber is gripped in between them.

Now, in this case, the difference between; the inclination angle of the front edge and the

wedge that is alpha minus theta, of the tooth being stripped should be such that cot beta

or cot alpha minus theta should be greater than mu. Look at this diagram carefully and

find out; which are the alpha, beta and theta.

So, the angle theta is known as wedge angle, alpha is the angle of inclination with

respect to the base. These two angles are very very important for stripping and the angle

beta which is basically, is the difference between; alpha and theta. This angle should be

greater than mu. Now if we want to go for the proof of this, we can look at this analysis

again.

(Refer Slide Time: 18:18)

Let, the fiber show in the diagram be acted by a force R that is R is the tension on the

fiber and in the similar way, we can resolve this tension on the fiber the two components

S 1 and S 2. Where S 1 will be R sine beta, and S 2 will be R Cos beta. For stripping to

be effective; what should happen S 2 has to be greater than mu S 1. That is the force,

which is acting away from the teeth; that is the S 2 this force should be able to overcome

the frictional resistance; that the fiber is going to experience, because of the normal force

mu S 1 which is acting on it.

So, if S 2 has to be more than mu S 1 that basically means, R Cos beta should be greater

than mu R sine beta And therefore, cot beta must be greater than mu. That is the angle

beta or the difference between the angle alpha and theta should be more than, the

coefficient of friction between the fiber and the tooth; Now, we will see the configuration

of a carding machine.

(Refer Slide Time: 20:10)

Now, carding machine is a big machine, there are many many elements in the machine.

And we can see, the machine having four different sections; one is the feed section of the

machine followed by carding section, followed by a sliver formation unit and then a

packaging unit. So, the entire machine, has four segments feed segment, carding

segment, sliver formation, segment and packaging segment. So, let us see, the working

principle and the construction of this machine.

(Refer Slide Time: 21:10)

The schematic diagram of the carding machine is shown, in this diagram and this is like a

cross sectional view of the machine and we are showing the various sections from the

left hand end to the liquor in point; we will get to know them slowly this section is

known as the feed section of the machine. Then we can see, the entire cylinder this part

is the carding section followed by sliver formation section and then this part is the

packaging unit. And here is the big drum we call it cylinder, then there is anothers little

smaller drum, we call it doffer there are anothers small drum we call it taker in or also

this is also known as liquor in unit and then we have a packaging unit and the package is

known as a can.

Then, the tuft feeding is being shown on the left hand side in the feed section and we can

see the web doffing unit also. Now, let us understand a bit about this machine, the feed

section consist of a tuft fitting unit in the present case; there are machines, where the tuft

feeding unit may not be there and we feed; what is known as a lab? A lab which is

produced in blow room and the modern machines are mostly equip with tuft feeding

units and then in the carding segments. We have mainly a cylinder and the cylinder is

surrounded; by many elements on the top we have flats, will discuss about them in more

details later on and at the bottom we have cylinder under casing; that is the bottom part

of this cylinder is covered by under casings.

The entire cylinder surface is filled with large number of pins. Then once we go from we

will discuss more about the cylinder in future, then what comes is the doffer. Doffer is

also a cylindrical drum, and there are large number of pins on its surface and from doffer

the material which comes on the doffer goes to a unit and this is known as web doffing

unit. And from web doffing unit, the web that we get the fiber way that we get is

converted into a round shape product we call it sliver and when the sliver is made the

sliver is packed into the can.

So, the way the machine works is that the from the feed sections; either a lap or a

collection of tufts are feed by feeding feed roller and for the feed roller the material goes

to a small drum we call it taker in or licker in this taker in or licker in also will be having

a large number of pins on its surface. These taker in will be able to tease out the tufts and

will produced small sized tuft lets and these tuft lets which are produced by this taker in

is then passed on to the slender surface.

Now, while doing so, lot of trash particles get ejected at this; taker in feed point and the

eject a trash particles are collected below the machine. So, that part of the cleaning is

done, at this point; we will learn more about them in future lectures and the tuft lets are

then fed to the cylinder and the cylinder will large number of pins, will be acting on the

tuft lets. There is a huge differences in speed between; the taker in and the cylinder this

speed difference will basically, facilitate the spreading out of the fiber over a large

surface area. And by doing so, the fibers will be separate out from each other.

Now, once these tuft lets are passed onto the cylinder; the cylinder, which is rotating in a

clockwise direction in the present case, will be acted by the teethes of the flats and

between the cylinder points and the flat cot points. There will be tremendous teasing

actions or we call it carding actions between the flat and the cylinder out points and

which will separate out the fibers or individualize the fibers to almost single fiber stage.

And so, once it is done these separated out fibers are then brought near the doffer

surface.

While doing so part of the fibers, will be passed on to the flat. And the flat we will learn

the about them in more details later on the flats also moved slowly in the forward

directions and they keep on collecting the trash particles, which are thrown towards them

by the cylinder and the centrifugal force, which is acting on the trash particles; which

will cause them to be thrown towards the flats and the flats will be absorbing these trash

particles and therefore, also help in cleaning.

These material, then reaches the doffer surface and the doffer will be able to collect these

fibers, but, whatever reaches duffers part of it is not part of it is actually transferred to

this cylinder. That is whatever material is approaching doffer the entire material is not

transferred to the doffer immediately, part of it returns and this return fiber layer joins;

the taker in or the licker in at the feed point. So, they get mixed up with the freshly feed

fibers and both the freshly feed fibers; as well as the fibers returned; because, not being

able to get transfer to the doffer they go together and get carded between cylinder and

flat.

So, this process goes on repeatedly and therefore, the same material; gets carded number

of times and hence, separations our individualizations takes place. Whatever is

transferred to the doffer; this material is they moves forward; the doffers moves as has

been shown; in the diagram in an anti clockwise direction and the material is brought.

Now, the doffer is having large number of pins on them. Therefore, we have to somehow

remove the fibers, from the surface of the doffer. So, there here, there is a small unit

called web doffing unit; these doffing unit will able to strip off the doffer surface and the

fibers in the form of a thin sheet; will move forward; this thin sheet of fibers is known as

web. The web is very thin and the little strength in them, they are basically, very fragile

also. So, at very high speed the air current which is generated around doffer or around

web doffing unit, may sometime disturb this, thin sheet and therefore, we need to quickly

considerate the sheet and transform them in the form of a round shaped material; which

we call sliver.

We learnt about, the web removal and transformation of the web into a round shaped

sliver in some other lectures; once the sliver is met the only job that is left, is to pack it in

the form of a coils within a package that is known as can is like a hollow cylinder within

which we pack the material. Hence, once the can gets filled up these cans is removed and

is replaced by another new can. And in this manner the process continues; for hours

together, till we find something going wrong with the process and we stop the machine,

to find out what has gone wrong and take appropriate actions or we generally, stop the

machine; when there is a need for some maintenance on activity.

So, with this let us stop today, this is the very first lesson about the carding process.

Thank you.