Fractionating efficiency of the comber

1. Fractionation at Comber

2. Extraction of Waste
 The process of Combing involves loss of good fibres. The term
fractionation means separation of short fibres from the long fibres. It
is therefore, necessary that this be done with minimum loss of good
fibres while achieving maximum short fibre removal & cleaning.
The term ‘Short Fibres’ is relative. As regards cotton is concerned, the
classical typical Bear Sorter diagram would show the nature of fibre
distribution. Though the nature of the diagram for different cottons
would be similar, what would be different will be the (1) proportion of
majority of the fibres (2) length of a comparatively small proportion of
longer fibres & (3) proportion of short fibres.

3. Baer Sorter Diagram
 Baer Sorter Diagrams of Different Nature decides the
 Waste extracted at the Comber Level. With Triangular shape
Diagram, increasing waste level, continuously increases Yarn
Quality. With Flat Diagram, the noil level needs to be restricted 50%
of Short Fibre %. Beyond this level there is no improvement In Yarn
Quality.

4. Fractionation
 The removal of short fibres is expected to up-grade cotton This
removal truly being loss of fibres as regards the ultimate yarn
realization is concerned, the economics of the process largely
depends
 It is well known that short fibres, in any mixing pose problems
during drafting and as such, deteriorate the yarn evenness.
 The combing intensity is related to the percentage of noil extracted
– ‘Scratch’ or ‘Semi-Combing’, ‘Normal Combing’ and ‘Super
Combing’.
 The most common way of judging this up-gradation is through
improvement in ‘Mean Length’ & ‘Short Fibre’ in a given mixing.

5. Fractionation
 Thus a minimum of 2 mm improvement in mean length could be considered
satisfactory.
 The Baer Sorter diagram for lap, sliver and noil would depict the nature of
fibre length and its distribution.
 One would be able to observe that the predominant taper of the curve at
the end for lap is absent for the sliver.
 Similarly, the difference in the curve for sliver and noil also throws some
light on the efficacy of the process.
 Yet another way, the comber performance can be judged and that is
through quality improvement in reduction of neps. Even the yarn
appearance could be tested by finding the yarn grades.
 All these methods, though sensitive enough are related to noil level and
machine setting.
 Fractionating efficiency is a more direct method of judging how short fibres
are removed while long fibres are retained.

6. Bear Sorter Diagram

7. Methods of Fractionating Efficiency
Simpson & Ruppenicker Method :
 In this percentage of fibres corresponding to mean group length for
comber lap & slivers are found out.
 Thus, we have –
 a1, a2 , --- am, --- ax ----- % fibres for lap
 A1, A2, --- Am, --- Ax ----- % fibres for sliver
 l1, l2, --- lm, --- lx ----- mean length group for lap
 L1, L2, ---Lm, --- Lx ----- mean length group for sliver.
 ‘m’ is the boundary limit i.e.
 [ fibres less than lm should be removed in noil ]
 The % of fibres sorter than lm in comber noil would be –
 (a1 – A1), (a2 – A2), (am – Am) for Ideal Noil. Thus,

8. Simpson & Ruppenicker
% of fibres shorter than lm in noil
 Combing Efficiency = ---------------------------------------------
% of fibres shorter than lm in ideal noil
lm (a – A)
Combing Efficiency . = Σ ---------
 l1 l
 Here, the division by ‘l’ gives due Weightage to each length
group. – in particular to short fibres.
 Note that, as a1 to am represents % of fibres in length group
in lap and A1 to Am represents % of fibres in length group in
 sliver –

9. Simpson & Ruppenicker
m
 Σ (a – A) – gives fibre distribution for Actual Noil
1
m
 And, Σ (a) – gives distribution for Ideal Noil
1
 Similarly,
% of fibres longer than Lm in sliver
 Detaching Efficiency = -------------------------------------------
% of fibres longer than lm in lap
Lx lx
 Detaching Efficiency. = Σ A . L ÷ Σ a . L
Lm lm

10. Simpson & Ruppenicker
 Here too, the multiplication of ‘l’ or ‘L’ gives the due weightage to each
length group i.e. longer fibres.
 It is argued that these are the two different indices not related to each
other directly, because, it may be possible for the two combers to give
identical values for one of these two indices, and yet give a totally
different value for the remaining index.
 Detaching Efficiency can vary from (100 – waste%) to 100; while
Combing Efficiency can vary from (waste%) to 100%
 Parthsarathy Method :
 As seen earlier, the two indices have no connection with each other
and hence, in this method, a Composite Index is found.

11. Parthsarathy Method
 Thus, both the long fibre retention in the sliver as well as short fibres
present in it are combined together.
 Again, the fibre distribution of all length groups in comber sliver in
relation to what the lap fed has, is measured.
 Finally, FEI (Fractionating Efficiency Index) which is composed of two
factors – one due to efficient detachment of longer fibres in comber
sliver (A positive contribution) and the other due to inadvertent
withdrawal of short fibres into comber sliver (A negative contribution)
– is found out.
 a1, a2 , --- am, --- ax ----- % fibres for lap
 A1, A2, --- Am, --- Ax ----- % fibres for sliver
 l1, l2, --- lm, --- lx ----- mean length group for lap
 L1, L2, ---Lm, --- Lx ----- mean length group for sliver.

12. Parthsarathy Method
 Lm or lm – the length below which fibres should go into
waste
 And w - % waste (noil) extracted.
 The values A1, A2 - - - etc. are calculated from the actual
values – A1’, A2’ ---etc. of comber sliver by multiplying by a
factor - -- (100 – waste%) i.e.
A1 = A1’ (100 – waste%)
 F.E.I. for longer fibre retention in Comber Sliver :
Lx
 Σ (Lx – Lm ) . Ax ------ contribution of fibres longer than
 Lm Lm in in Comber Sliver
 Similarly,
 lx
 Σ (lx – lm ) . ax ------ contribution of fibres longer than
 lm lm in Comber Lap

13. Parthsarathy Method
 F.E.I. for Longer fibre Retention :
Lx lx
Σ (Lx – Lm ) . Ax ÷ Σ (lx – lm ) . Ax ------- (1)
Lm lm
F.E.I. for Shorter fibre Retention :
Lm
Σ (Lm – Lx) . Ax ----- Contribution of fibres shorter than Lm
L1 in Comber Sliver
Also,
lm
Σ (lm – lx) . Ax ----- Contribution of fibres shorter than lm
l1 in Comber Lap.
F.E.I. for Shorter Fibres :
Lm lm
Σ (Lm – Lx) . Ax ÷ Σ (lm – lx) . Ax -------- (2)
L1 l1

14. Parthsarathy Method
 The composite F.E.I. = [ (1) – (2) ] x 100
= [ FEI(L) for longer fibres – FEI(S) for shorter fibre ] x 100
 In ideal working condition, FEI (L) is 1, while FEI (S) is zero
and thus the composite FEI = 100
Significance of Fractionating Efficiency :
Fractionating efficiency can be low due to poor penetration
of half lap or top comb.
 Ineffective gripping of nippers during combing, faulty
setting-timing & bad condition of detaching roller.
 Fibre breakage in the comber is mainly due to high
disorientation of fibres & fibre hooking. The high
entanglement of fibres in the lap results in harsh action of
either half-lap or top comb.

15. Factors Affecting Fractionating Efficiency
Waste Extraction at Comber:
 It is known that increasing Step Gauge to increase comber
noil, increases Fractionating Power. However, this increase
is linear up to approximately 20% noil.
 At higher level, the Fractionating Efficiency seems to
deviate possibly because of fibre length distribution of most
cottons
 At wider Step Gauge, Preferential Short Fibre Removal
Efficiency deteriorates when working with top comb.
However, Preferential Long Fibre Retention Efficiency at
wider Step Gauge generally improves. Nep removal
efficiency also improves at wider Step Gauge, but with
online presence of Top Comb.

16. Type of Feed - Mean Length
 Type of Feed : A comber removes more waste with backward
feed as compared to forward feed, the fractionating
efficiency being better with the latter.
 Even when identical waste% with the same feed length is
used in these two types of feeds (backward & forward), still
forward feed gives better fractionation.
 When feed length is increased, noil extracted would reduce
(Longer feed reducing no. of combing cycles for a fibre.
However, longer feed, in general, decreases noil% and gives
poor preferential short fibre removal efficiency (P.S.F.R.E.).
There is no effect of change in feed length on Nep removal
efficiency.
 Mean Length : Fractionation increases linearly with the
improvement in Mean Length.

17. Feed Timing & Feed Distance
 When the feed ratchet is made to turn little late, the
influence of top comb prevents the full advancement of
advancement of the fringe during detachment and hence
waste% increases. This prohibits shorter fibres from going
into sliver and improves fractionating efficiency.
 Feed distance is required to be set with staple length.
Longer staple will demand wider distance while shorter
staple will necessitate narrower distance.
 This distance decides when the fibres should be let free
from feed roller nip. Therefore, longer fibres, with a shorter
feed distance would be let free little late and this would
lead to more combings. This even would lead to damage to
longer fibres during process.

18. Factors Affecting Fractionation
 Mean Length : At wider Step Gauge, the improvement in Mean
Length is better. However, absence of top comb generally
gives lower mean length.
 Lap Preparation : It is possible to improve F.E.I. by making a
better lap preparation. Also, PSFRE is poor with heavier laps.
 Top Comb : The effect of top comb on fractionation is
complex. When set too deep into the fringe, it gives poor
fractionation because of fibre rupture. Absence of top comb
also leads to poor fractionation, mainly owing to lower noil%.
The acceleration of short fibres due absence of top comb, thus
leads to poor P.S.F.R.E.
 For a given needling of top comb, there is deterioration in
fractionation with higher production rates- mainly due to fibre
breakage during detaching.

19. Forward & Backward Feed
 In modern combers, the switching over from backward to
forward feed is simplified. The advancement of the fringe
during forward motion of the nippers, shortens the
detachment distance by a length equal to feed length.
 In the backward feed, however, the length of the fringe
after the detachment is complete advances by a length
equal to feed length. Thus, an increase in the length of
projection of the fringe presented to cylinder needling
action, leads to more waste extracted.
 This can be explained by a Baer Sorter diagram. Let ‘D’
represent the detachment setting and ‘f’ the feed length per
cycle.
 In Forward Feed, all the fibres shorter than ‘D’ would go
into waste. But there is an advancement ‘f’ during this.

20. Forward Feed
 Thus, in Forward Feed, with a feed length ‘f’,
(D-f) > fibres will be removed as noil ----- (1)
D < fibres will go to sliver ----- (2)
 Actually, the fibres between these limits would either go
into noil or sliver, depending upon teir actual disposition at
the time of detachment. The boundary length demarking
the area of sliver and noil would be –
 [ D + (D – F)] / 2 i.e. (D + f/2) ----- (3)
 In the Backward Feed, the length of the fringe presented to
Cylinder is (D + f). This is because ‘D’ is the length of
projecting fringe after detachment & ‘f’ id the length fed
before the nippers fully close before combing

21. Backward Feed
 Thus in Backward Feed –
 D + f > fibres will be removed as noil ----- (4)
 D < fibres will go to sliver ----- (5)
 Again, as in the previous case the boundary limit for the fibres
to go into sliver or noil will be –
 [ D + (D + f)] / 2 or ( D + f/2 ) ----- (6)
 Suppose a Baer Sorter diagram is represented in such a
fashion that its area is equal to the areas ‘OAB’ and PQ and MN
represent the demarcation area of fibres in sliver and noil in
Backward & Forward Feed, then on the basis of similar
triangles, the following can be stated -

22. Waste Comparison in Forward & Backward Feed
 % waste extracted in Backward Feed –
 [ ∆ BPQ ÷ ∆ BAO ] x 100 = [ PQ / AO ] x 100 ----- (7)
 % waste extracted in Forward Feed –
 [ ∆ BMN ÷ ∆ BAO ] x 100 = [ MN / AO ] x 100 ----- (8)

23. Forward & Backward Feed
 It will thus be seen that the waste % in Backward Feed
will be greater (all other settings remaining constant).
 If we assume Eff. Length = 29 mm, Det. Setting = 6 mm &
Feed = 6 mm, then –and a fibre front tip is assumed to be
at Nipper Grip, then starting from cylinder combing -
 In First Cycle – A fibre would advance by 6 mm during
detachment in Forward Feed, while no advancement in the
Backward Feed.
 Second Cycle - A fibre would advance by 12 mm during
detachment in Forward Feed, while it will advance by 6 mm
in the Backward Feed.
 Third Cycle – A fibre would advance by 18 mm during
detachment in Forward, while it will advance by 12 mm in the
Backward Feed.


24. Waste % in Backward & Forward Feed
 Fourth Cycle - A fibre would advance by 24 mm in front of
nipper grip during detachment in Forward Feed, while it will
advance by 18 mm in the Backward Feed.
 Here, in Forward Feed, when the front tip of the fibre is 24
mm ahead of nipper line. The distance between the nipper
line and feed roller nip being 5 mm. the disposition of this
fibre would be such that its trailing end would be at 24 + 5
mm = 29 mm --– meaning that the trailing end has just
been at feed roller (Length of fibre = 29 mm) & gripped.
 Further, the front end of the fibre, after fourth cycle is
24mm ahead and is still short of detaching roller nip. This is
with the assumption that D.R. as 1½ inch dia (38 mm).

25. Waste % in Backward & Forward Feed
 The distance from nipper line to D.R. line = detachment
setting + ½ D.R. dia. Therefore, the distance between nipper
line and D.R. nip, would be 6 mm + 19 mm = 25 mm, just
short for the front end of the fibre to reach
 In 5th cycle, when this fibre is released by feed roller, it will
reach D.R. nip and drawn as sliver.
 As against this, in Backward Feed, the fibre in 5th cycle is 24
mm in front of nipper line and holding the same argument, is
still short of D.R. nip. Hence it will take one more cycle to
reach D.R. nip i.e. in Backward Feed, the fibre will reach D.R.
nip in 6th cycle and drawn as sliver.
 In short, Backward Feed takes one extra combing cycle for
the fibres to reach D.R. which means 20% more combing
cycle and hence additional waste extraction.

26. Examples on Fractionating Efficiency – Simpson-Ruppenicker
Fibre Mean L. % fibres % of Fibres in Actual % in
Length mm in Lap Ideal Ideal Combed sliver
mm (l) (a) Sliver Noil (A)
32-36 34 7 7 --- 6
28-32 30 10 10 --- 8
24-28 26 20 20 --- 18
20-24 22 18 18 --- 16
16-20 18 15 15 --- 13
12-16 14 12 12 --- 10
--------------------------------------------------------------------------------
08-12 10 08 ---- 08 06
04-08 06 05 ---- 05 03
00-04 02 05 ---- 05 02
lm
Combing Efficiency = Σ [ (a – A) / l ] x 100
l1

27. Simpson & Ruppenicker
(8-6)/10 + (5-3)/6 + (5-2)/2
Combing Efficiency = ------------------------------------ x 100
(8/10) + (5/6) + (5/2)
= 49.19 %
lmax
Detaching Efficiency = [ Σ ( A x l ) ÷ Σ ( a x l ) ] x 100
lm
(6x34) + (8x30) + (18x26) + (16x22) + (13x18) + (10x14)
= ---------------------------------------------------------------------- x 100
(7x34) + (10x30) + (20x26) + (18x22) + (15x18) + (12x14)
= 86 %

28. Parthsarathy Method
Fibre Mean L. % fibres % of Fibres Weightage
Length mm in Lap in Sliver Factor
mm lx/Lx (a) (A) (lx – lm)
32-36 34 07 06 22
28-32 30 10 08 18
24-28 26 20 18 14
20-24 22 18 16 10
16-20 18 15 13 06
12-16 14 12 10 02
------------------------------------------------------------------------
08-12 10 08 06 02
08-04 06 05 03 06
00-04 02 05 02 10

29. Parthsarathy Method
F(i) = [ Σ ( Lx – Lm) . Ax ] ÷ [ Σ ( l x – l m ) . ax ]
(Summation for sliver from lm to lmax is taken ) –Long Fibres
= (22x6) + (18x8) + (14x18) + (10x16) + (6x13) + (2x10)
-------------------------------------------------------------------
(22x7) + (18x10) + (14x20) + (10x18) + (6x15) +(2x12)
= 0.685
F(ii) = [ Σ ( Lx – Lm) . Ax ] ÷ [ Σ ( l x – l m ) . ax ]
(Summation for sliver from l1 to lm is taken ) – Short Fibres
( 2x6) + (6x3) + (10x2)
= ----------------------------- = 0.521
(2x8) + (6x5) + (10x5)
F.E.I. = [ FEI (i) – FEI (ii) ] x 100 = (0.865 – 0.521) x 100
 = 34.4 %

30. Typical Examples on Fractionating Efficiency Simpson Method
Fibre Mean Group % fibres % of Fibres in Actual % of
Group Length in Lap Ideal Ideal fibres in
mm mm Sliver Noil Combed Sliver
(l) (a) (A)
----------------------------------------------------------------------------------
32-36 34 7 7 --- 6
28-32 30 10 10 --- 8
24-28 26 20 20 --- 18
20-24 22 18 18 --- 16
16-20 18 15 15 --- 13
12-16 14 12 12 --- 10
----------------------------------------------------------------------------------
08-12 10 08 --- 08 06
04-08 06 05 --- 05 03
00-04 02 05 --- 05 02
--------------------------------------------------------------------------------

31. Calculation of Fractionating Efficiency –Simpson Method
lm
 Combing Efficiency = Σ [ (a – A) / l] ÷ [ a / l ] x 100
l1
(8 – 6)/10 + (5 – 3)/6 + (5 – 2)/2
= ----------------------------------------- x 100 = 49.19%
8/10 + 5/6 + 5/2
lmax lmax
Detaching Efficiency = [ Σ ( A x l ) ] ÷ [ Σ ( a x l ) ] x 100
lm lm
(6x34) + (8x30) + 18x26) + (16x22) + (13x18) + (10x14)
----------------------------------------------------------------------
(7x34 + (10x30) + (20x26) + (18x22) + (15x18) + (12x14)
Detaching Eff. = 86%

32. Calculation of Fractionating Efficiency –Parthsarathy Method
Length Mean Group % fibres % fibres Weightage
Group Length in Lap in Sliver Factor
(a) (A) (lx – lm)
------------------------------------------------------------------------
32-36 34 07 06 22
28-32 30 10 08 18
24-28 26 20 18 14
20-24 22 18 16 10
16-20 18 15 13 06
12-16 14 12 10 02
------------------------------------------------------------------------
08-12 10 08 06 02
04-08 06 05 03 06
00-04 02 05 02 10
------------------------------------------------------------------------

33. Calculation of Fractionating Efficiency –Parthsarathy Method
lmax lmax
F(i) = Σ [( lx – lm ) . Ax ] ÷ Σ [ ( lx – lm ) . Ax ]
lm lm
(22x6) + (18x8) + (14x18) + (10x16) + (6x13) + (2x10)
= --------------------------------------------------------------------
(22x7) + (18x10) + (14x20) + (10x18) + (6x15) + (2x12)
= 0. 865
lm lm
F(ii) = Σ [( lx – lm ) . Ax ] ÷ Σ [ ( lx – lm ) . Ax ]
l1 l1
(2x6) + (6x3) + (10x2)
= ----------------------------------- = 0.521
(2x8) + (6x5) + (10x5)
F.E.I. = [F(i) – F(ii) ] x 100 = (0.865 – 0.521) x 100 = 34.4 %