Carding Process
Introduction:
Carding is the most important process in spinning. It
contributes a lot to the yarn quality. The following process parameters and
specifications are to be selected properly to produce a good quality yarn with
a lower manufacturing cost cylinder wire(wire angle, height, thickness and
population) flat tops specification licker-in wire specification doffer wire
specification feed weight draft between feed roller and doffer cylinder
grinding doffer grinding flat tops grinding cylinder, flat tops, doffer wire life
Licker-in wire life Cylinder speed flat speed Licker-in speed setting between
cylinder and flat tops setting between licker-in and feed plate setting between
lickerin and under casing elements like, mote knife, combing segment etc.
setting between cylinder and doffer setting between cylinder and back
stationary flats setting between cylinder and front stationary flats setting
between cylinder and cylinder under casing.
Setting of Carding Machine
Setting of Carding Machine
Fig: Carding Machine (Side View)
Cylinder Wire and
Cylinder Speed:
Cylinder wire selection is very important, it depends upon
cylinder speed, the raw material to be processed and the production rate. The
following characteristics of cylinder wire should be considered.
- Wire angle
- Tooth depth
- Wire population
- Rib thickness
- Tooth profile
- Tooth pitch
- Tooth point
- Overall wire height
Wire front angle depends on mainly cylinder speed and
coefficient of friction of raw material. Higher the cylinder speed, lower the
angle for a given fibre. The cylinder speed in turn depends upon the production
rate. Higher production means more working space for the fibre is required. It
is the wire that keeps the fibre under its influence during carding operation.
Therefore the space within the wire should also be more for higher production.
Higher cylinder speed also increases the space for the fibre. Therefore higher
cylinder speed is required for higher production. In the case of high
production carding machines, the cylinder surface is very much higher,
therefore even with higher number of fibres fed to the cylinder, the cylinder
is renewing the carding surface at a faster rate.
Higher the cylinder speed, higher the centrifugal force
created by the cylinder, this tries to eject the fibre from the cylinder, along
with the trash. It is the cylinder wire's front angle which overcomes the
effect of this force. Low front angle with too low cylinder speed and with high
frictional force will result in bad quality, because the fibre transfers from
cylinder to doffer will be less. Hence recycling of fibres will take place,
which result in more neps and entanglements. The new profile with less free
blade avoids loading of the cylinder with fibre and/or trash. This helps in
keeping the fibres at the tip of the tooth. The movement of the fibres towards the
tip of the tooth coupled with centrifugal action demands an acute front angle
to hold the fibre in place during carding. Lack of stiffness associated with
fine and/or long fibres necessitates more control during the carding process.
This control is obtained by selecting the tooth pitch, which gives the correct
ratio of the number of teeth to the fibre length. Tooth pitch reduction is
therefore required for exceptionally short fibres and those lack stiffness.
Number of points across the carding machine is decided by the rib width. It is
selected based on the production rate and fibre dimensions. Finer the fibre,
finer the rib width. The trend is to finer rib width for higher production.
The population of a wire is the product of the rib thickness
and tooth pitch. The general rule is higher populations for higher production
rates, but it depends upon the application. Sharp tooth points penetrate the
fibre more easily and help to intensify the carding action. Cut-to-point wires
are sharp and they have no land at all. The effective working depth of a
cylinder wire tooth for cotton is approximately 0.2mm and for synthetic
materials approx.0.4mm. Manmade fibres require more space in their cylinder
wire than doe's cotton. More tooth depth allows the fibre to recycled,
resulting in damaged fibres and neps. If tooth depth is insufficient, there
will be loss of fibre control. This will result in even greater nep generation.
Looking into the above details, the following specifications can be used as a
guideline.
DOFFER, LICKER-IN AND
FLAT TOPS:
The basic function of doffer is to strip the fibres from
Cylinder. Please remember that the action between cylinder and doffer is
carding action (or combing action or point to point action).
The doffer wire's front angle plays a very important role in
releasing the fibre from the cylinder. For most carding applications the
optimum angle is 60 degrees.
Increased population over 400 ppsi does not give any
advantage in the production of quality yarn. For smaller doffers, 5 mm doffer
wire height helps in transferring the fibres from cylinder to doffer.
If the fibre holding capacity of the doffer wire is less due
to fibre friction or due to very high doffer speed, it is better to use a
doffer wire with striations. For high production carding itis always better to
use doffer wire with striations.
Licker-in plays a major role in opening the fibre tufts. In
general 85 degrees is used both for synthetic and medium and long cottons. For
coarse and dirty cottons 80 degrees can be used.
Strength, hardness and sharpness are very important for
Lickerin wire. Licker-in wires should never be ground. Thinner blades penetrate
the fibres more efficiently and increase the wire life.
Higher number of rows per inch gives better results. Now up
to 12 rows per inch is being used. This is always better compared to 8 rows per
inch.
If the wire pitch is not sufficient, it can be compensated
by increasing the licker-in speed. Higher licker-in speeds for fine and long
cottons will rupture the fibres. Licker-in speed depends upon the fibre type
and the production rate.
It is better to use a flat top with more than one
population. The general combination is 280/450. This is suitable for both
cotton and synthetics. Please remember that the rigidity of the fillets is
different for cotton and synthetic. If cotton flat tops are used for synthetic
processing, the load on the cylinder will be more, more heat will be produced
and hence the probability of cylinder loading due to electrostatic charge will
be high.
Instead of using Rigid type flat tops, it is better to use
semirigid type flat tops while processing synthetic fibres.
SETTINGS:
The setting between cylinder and doffer is the closest
setting in the card. This setting mainly depends upon the cylinder speed, hank
of the delivered sliver and the type of wire. Cylinder speed up to 360, the
setting should be 0.1mm. For cylinder speeds more than 450, the setting ranges
from 0.125 to 0.15.
If the setting between cylinder and doffer is very close,
the wires will get polished and this will affect the fibre transfer. If the
setting is too wide, the fibres will not be transferred to doffer from the
cylinder, hence cylinder will get loaded. While processing synthetic fibres
cylinder loading will badly affect the yarn quality. Moreover, it is difficult
to improve the wire condition if the loading is severe. \
The only solution would
be to change the wire. Therefore enough care should be taken while processing
synthetic fibres.
The most critical setting in a carding machine is between
cylinder and flat tops. While processing cotton, it can be as close as 0.175 mm
provided the mechanical accuracy of flat tops is good. Since most of the cards
are with stationary flats at the licker-in side, the setting from the back to
front for flats can be 0.25, 0.2.0.2, 0.2, 0.2mm.
Closer the setting between cylinder and flats, better the
yarn quality. Neps are directly affected by this setting. Of course, very close
setting increase the flat waste. For processing cotton the setting can be 0.25,
0.2, 0.2, 0.2, 0.2mm. For synthetic fibres it can be 0.3, 0.25, 0.25, 0.25,
0.25mm
Most of the cards are with 6 to 1 1 stationary flats at the
licker-in side. This setting can start with 0.4 mm and end with 0.25mm.
The wire points can start with 140 ppsi and end with 320
ppsi. The work done by the first few stationary flats is very high; therefore
the wear of these flats is also high. It would be better if the first 50% of
the flats are changed after 100000 kgs of production and the rest after 150000
kgs of production.
These stationary flats open the material so that, the
setting between cylinder and flats can be as close as possible.
The setting between feed plate and Licker-in depends upon
the type of feed plate. Conventional feed plate setting is decided mainly by
the feed weight and to some extent by the fibre length and type.
With the
latest feed plate and feed roller arrangements, the setting is decided mainly
by the fibre length and to some extent by the feed weight.
Normally the setting between the feed plate and Lickr-in is
around 0.45 to 0.7mm, depending upon the feed weight and fibre type.
The setting between Licker-in and the first mote knife is
around 0.35 to 0.5 mm. This helps to remove the heavier trash particles and
dust. Closer the setting, higher the wastage. The setting between
Licker-in and
combing segments is around 0.45 to 0.6. This helps to open the material.
Some cards have two mote knifes in the Licker-in under
casing. The setting is around 0.4 to 0.5mm.
This helps to remove the smaller
trash and dust particles.
The setting between the cylinder and stationary flats at
Doffer side helps to transfer the fibres to doffer by stripping the fibres to
the top of the cylinder wire. This setting can be as close as 0.15mm.
The number
of wire points on stationary flats also plays a major role. It is normally
around 300 to 400. For a high production application it can be as high as 600.
For cotton processing, the stationary flats are fixed with a
knife attachment. The setting should be as close as possible, i.e. around
0.15mm. This helps to remove the trash particles of very small size.
The setting between cylinder and cylinder under casing
should be as per the manufacturer's recommendation. The design of under casing
is different for different manufacturers. This setting is very important, as
wrong settings will affect the fibre transfer and can also create air
turbulence.
SPEEDS:
Higher cylinder speed helps fibre transfer. Higher the
production, higher should be the cylinder speed.
Higher cylinder speed improves carding action, thereby
imperfections are reduced.
Higher Licker-in speed for coarse fibres and dirty cotton
helps to remove the trash and improves, the yarn quality. For fine and long
cottons, higher speed results in fibre rupture, therefore, flat waste and
comber noil will be more.
Higher flat speed, improves yarn quality and at the same
time increases the flat waste.
With the same flat speed, higher the carding production,
lower the flat waste and vice-versa.
Very high tension drafts will affect carding U%. It is
better to keep the draft between feed rollers to doffer around 75 to 95. The
results are found better with these drafts.
WIRE MAINTENANCE:
For a modern cylinder wire of 2mm height, grinding with the
normal grinding stone is not recommended. It is better to use TSG grinder to
grind the wire every 2nd or 3rd month, so that the
sharpness of the wire is
always maintained.
TSG grinder does not grind the wire, therefore if the wire
is worn out very badly the quality improvement using this grinding machine will
be nil. Frequent grindings are recommended. If TSG grinder is not available, it
is better not to grind 2mm wires.
The number of traverse should increase depending upon the
life of the wire. The number of traverse for successive grindings should be
like this 3, 5, 10, 17 etc. Anyway the best method is to confirm with the
microscope. If the grinding is not sufficient, the number of traverse should be
increased.
Doffer is still working with a concept of Land formation. A
normal grinding machine will be good for doffer grinding. All the wire points
should be touched by the grinding stone. A slow and gradual grinding with the
grind-out concept will give the best results. Harsh grindings will result in
burr formation on the land. This will increase the number of hooks in the
fibre; thereby the effective length of the fibre from this card will be
reduced.
Flat tops grinding is very important. Every time a flat top
is ground, yarn quality is improved. It is better to use a grinding machine
with the emery fillet. Frequent flat tops grinding will result in less neps and
the yarn quality will be consistent.
Some mills increase the life of the flat tops compared to
cylinder wire. But it is better to change flat tops and cylinder wire together
for better and consistent yarn quality.
It is a good practice to check the individual card quality
before changing the wire.
Licker-in wire should be changed for every 150000 kgs.
Earlier changes will further improve the yarn quality.
Stationary flats should be changed for every 150000 kgs. But
it is a good practice to change the first 3 or 6 stationary flats at Licker-in
side for every 100000 kgs. This helps to maximize the carding effect between
cylinder and doffer which is critical for better yarn quality.
Reference # http://textilelearner.blogspot.com/
