PROCESS PARAMETERS IN COMBING - 2
- The number of needles in Top comb depends on the Fibre
micronaire , the lap weight and fibre parallelisation
in the lap. If the fibre Micronaire is less than 3.6, number of needles per cenitmeter in top comb
can be 30.In general for fibres above 3.8 Micronaire, 26 needles per centimeter is used.
- Top comb plays a major role in removing the waste.
Around 40 to 60% of noil is removed by top comb.
But top comb will get damaged very fast. Top comb damage will result in slubs in the sliver. Even 4 ro 5 needle damages will result in bad webs. Top comb maintenance is very very important to produce good qyality yarn.
- Different types of unicombs are used in different
combers. The circumference of unicombs ,
the number of wire points and its variation in the unicomb are different. It is not true that
110 degree unicomb will produce good quality yarn compared to 90 degree unicomb.
- In most of the cases, 75 degree unicomb has given better
results compared to 90 degree unicomb in
E7/4 combers, for different types of cottons.
- Rieter has standardised 90 degree unicomb for its E-62
combers. 110 degree unicomb can not be
used in this comber.
- Unicomb action will be effective as long as nipper and
unicomb moves in opposite direction.If unicomb
and nipper move in the same direction, unicomb can not do its work properly. Moreover the finer
needles will not be utilised properly. That may be the reason why 90 degrees unicomb do not produce a good qyality yarn compared to 75 degrees unicomb.
- The setting between unicomb and nipper should be same.
When nipper is loaded with the the feed
roller, the setting may be around .4 to .5 for E7/4 combers and .5 to .7 for E-62 combers. This setting
can be corrected by fixing spacers between unicomb and unicomb body. Some unicomb manufacturers
supply the spacers along with the unicombs.
- There are different types of lap preparation. The best
combination is drawframe and unilap combination.
Lap piecing will be less in this combination compared to sliver lap and ribbon lap combination.
Every lap piecing is a major fault compared to sliver piecing. If number of lap piecings are less,
top comb damages will also be less.
- The total draft for sliver lap and ribbon lap combination should be around 9 .
- If Micronaire is less than 3.8, the lap licking tendency
will be more. For such fibres, the total draft
between card and comber should be kept as low as possible, i.e around 8.5.
- For drawframe and unicomb preparation the total draft can be from 9.5 to 11, depending upon the fibre and lap weight.
- Fibre parallelisaion in a lap should be reasonably good,
to avoid long fibres in the noil. With the
modern cards, the fibre parallelisation is improved because of the stationary flats.
- The self cleaning effect of the lap sheet arises from
the retaining power of the fibres relative
to the impurities. This depends on the lap weight. If lap weight is more, the unicomb efficiceny
may not be good. But the nipper grip will be good for heavier lap weight. Therefore an optimum lap
weight should be decided, It depends on
- Fibre micronaire(the number of fibres present to the nipper)
- Nipper type
- For E7/4 comber, lap weight of 52 to 60 gms per meter
can be selected to produce a fairly good
quality yarn. In case of E-62 comber(latest from RIETER), it can range from 65 to 75 grams per meter
to produce a fairly good yarn.
- Lesser the number of piecings in comber , better the
quality. Every piecing in comber is a defect.
Therefore, it is better to increase the lap weight as high as possible. For modern
lap preparation it is
around 20 to 23 kgs/lap and for older lap preparation, it is around 12 to 13 kgs per lap.
- Piecing is a distinct source of fault in comber
operation. It is a periodic variation. The amplitude
of this fault should be as low as possible. The following affect this fault
- detaching roller timing
- arranging this fault before entering tthe draft zone, so that this faults cancel each other (by adjusting the delivery guide.)
- Detaching roller timing depends upon the index setting
and feed length. This setting should be selected
in such a that with the minimum length of overlapping comber works without any problem.
- Drafting setting should be done according to the
recommendation. Trials can be taken with different
setting to optimise the same.(both in lap preparation and in comber)
- Lower the feed length, lower the production. But better the yarn quality.
- But in some application ,lower feed length with forward
feed(concurrent feed) has resulted in
inferior quality.But in general lower feed will improve the yarn quality. It is always better to take
a trial and confirm this. Feed length to some extent depends on the fibre staple length also.
- With backward feed, the unicomb penetrates thro the
fibre fringe more often than in the
case of forward feed. Therefore the quality of the combing operation is increased in the case
of backward feed.
- In combing operation, the hank of the sliver will not
affect the comber production. Therefore, if old
type of combers are used, where the drafting is not good, lower drafts can be preferred in comber and the draft can be increased in a good drawframe like RSB-951 OR RSB-D-30 if it is used as a finisher.
TOP COMB AND UNICOMB
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