Contribution to Yarn Irregulation or Variation in Spinning Operation

CONTRIBUTION TO YARN IRREGULATION OR VARIATION IN SPINNING OPERATION

Ramandeep Singh
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India
Email: rmnsandhu3335@gmail.com




Introduction:

The random irregularity is simply a function of fiber fineness and the periodic variation that of mechanical condition of the machine. The quasi-periodic irregularity is only one which is inherent to the drafting process and can't be avoided. This is the main cause of excessive yarn unevenness and needs to the well understood.

The drafting wave is formed when the floating or short fibres move out of turn and get. Accelerated to front roller speed by the faster moving fibres. Its severity depends on the inter-fibre cohesion,fibre clustring and fibre entanglement with one another. Therefore, complete fibre individualization a parallelization are a must make each fibre move independently. In actual practice it is never completely realized even in combed materials. The spinning operation and some factors affecting yarn unevenness are discussed here.

1. Carding: Its responsible for individualization and therefore contribute to unevenness at the drawing, roving and ring spinning stages. Factors like proper setting, well grounded clothing, high cylinder speed etc. Which enhances fibre individualization will also result in more regular yarn.

2. Combing: It affects short fibre content, individualization and parallelization, all of which affects drafting operation. Therefore, this process should have great influence on yarn unevenness. Any impairment of combing quality can, therefore lead to poor yarn evenness.

3. Drawing: The draw frame is essentially meet to parallelize the fibre and the facilitate proper drafting at the speed frame and the ring frame. It also minimize the contribution of irregularity introduced in the previous processes.

4. Fly frame and ring frame: The drafting system of fly and ring frame have been considerably improved yarn unevenness. The improved drafting system and reduce irregularity of roving helps in minimizing yarn unevenness. The drafting system at the ring frame is the most important contributor to yarn unevenness. The modern drafting systems have significantly brought down the level of yarn irregularity by bringing down the amplitude of the drafting waves.

The total draft at the ring frame for counts upto 20s should be equal to count, 20-25 and 25-35 for 40s and finer yarns the break draft should be 1.84 drafts upto 25 and 1.5 for higher draft on top arm drafting system.

The spacor size should be 4.5 mm for counts upto 18s, 4.0 mm for 20s-26s, 3.5 mm for 28s-40s, 3.0 mm for 44s -80s and 2.5 mm for 100s and above. In fly frames, the draft in front apron zone should be 6 or more.

MEASUREMENT OF IMPERFECTIONS
There are two categories of blemishes in yarn. The imperfection like thick place, thin place and neps are less severe in nature but occur more frequently then faults such as slubs, bad piecing and loose spuns in lint. Both types of blemishes may cause difficulties in post spinning operation can more fabric appearance.

The circuitry of the Uster imperfection indicator takes the average weight/1.25 mm of yarn preceding the imperfection for accessing the relative size of an imperfection. The measurement and assessment of each imperfection is done as under:

Types of imperfections
Test length or cut length
Levels of sensitivity
Thin place
8 mm
-30%, -40%, -50%,-60%
Thick place
12 mm (effective)
+35% (4),+50%(3),+70%(2),+100%(1)
Neps
About 2 mm
+140%(4), +200%(3),280%(2),400%(1)

The recommended choices for routine testing is -50%,3(+50%) and 3(200%) for the thin place, thick place and neps respectively. The value of thin place or thick place is likely to shoot up for highly uneven yarn as – 50% and +75% would then fall inside the natural or normal variability due to spreading of the base of the distribution curve. The norms for imperfection in cotton and MMF yarns are given in the table:

Imperfection /1000 m
Count (Ne.)
Thin (-50%)
Thick (+50%)
Neps (+200%)
Carded



6s-10s
400
800
900
10s-19s
300
600
700
20s – 29s
300
500
600
30s-39s
300
800
1000
40s-60s
400
900
1100
Finer then 60s
500
1000
1200
Combed



30s-40s
50
400
500
41s-60s
50
300
400
61s-80s
75
300
400
81s-and finer
100
350
450

Assessment of Unevenness and Imperfections:
The sample size required to estimate imperfection is same as for yarn unevenness i.e. 4 min test on 16 bobbins selected at random from a group of ring frames spinning a given count.

Yarn unevenness has a distribution and the cv of U% is around 6%for count yarn and 2-4% for MMF yarns. The % difference is real when more than
The imperfection can be expected to follow a poisson distribution. However, under industrial conditions the C.V of imperfection is 1.2-1.7 times more than expected. A good mill should strive to achieve parity with expected value i.e. variance/mean = 1.

The CV of imperfection is of the order of 20-25%. The difference is considered real when (A-B)2/(A+B)>4. Where A and B stands for total number of imperfection counted for equal number of sample in each case.

CAUSES OF THICK AND THIN PLACE
Several studies by ATIRA have shown that thin place correlate well with U%. the thick places have a fair correlation with U% but neps have no correlation at all with U%.

At sensitivity of -50% for thin and +3(50%) for thick, the number of thick and thin places produced at ring would be equal. The excess of thick or thin place comes from combing stage. One can thus say

Excessive thick and thin place: caused by poor drafting condition (mechanical conditions and process parameters) at ring frame.

Excessive (thick and thin place): caused by carding and combing.

FIBRE NEPS: Assessment and control:
The Uster neps count indicate the number of places where there is a sudden increase in weigh per unit length. Therefore, foreign matter like trash particularly seed coats will also get counted as neps besides the fibres neps. In fact a very large proportion of neps in the Indian cotton yarns are formed around small seed coats. This is followed by a fair proportion of pure fibre neps

At carding the neps the counted conventionally in the web itself. The well known Shirley template consisting of 34 holes, each of one sq. in area, is placed on the web taken from card on a board of the same size. In case of MMF a sample glass pr plastic sheet without holes may be used and the neps counted on the total area of 40 sq. inches.

And is converted to neps per 100 sq. inches. By multiplying by 2.5. However, in cotton mixing, the number of holes with ine or more neps is counted. This number is used to estimate the number of neps per 100 sq. in. formed by referring to table. Standardization nep count is then calculate for a 40 in. width called producing 0.12 hank sliver.

Number of holes with neps
Neps/100 sq. in.
1
1
2
6
3
9
4
12
5
16
6
19
7
23
8
27
9
31
10
35
11
39
12
44
13
48
14
53
15
58
16
64
17
69
18
75
19
82
20
89
21
96
22
104
23
113
24
122
25
133
26
144
27
158
28
173
29
192
30
214

The standard neps counts are directly comparable between different cards and mills. If need be, this can v converted to neps per unit weight as follows:
The standard neps count should normally lie between 20 and 25 for medium mixing and between 15 and 20 for fine and superfine mixing. For MMF, this should lie between 0.5 and 1.0 depending on the relative proportion if polyester and viscous fibres and whether they are grey and dyed.

The difference in two nep count is real when
Where,

A and B stands for total number of neps count for equal number of sample in each case.

The nep count at various stages of processes in cotton spinning. The points to be noted are:
  1. The bale cotton itself contains lot of neps
  2. The blow room substantially increase the nep level.
  3. The carding reduces neps by 30-40%.
  4. Combing reduces neps by 25%.
  5. There is a marginal reduction in nep level from fly frame to ring frame.
FACTORS CAUSING NEPS:
  1. Harsh treatment of fibres by beaters ,openers etc.
  2. Poor conditions of beater’s blades,spikers,wires etc.
  3. More number of beaters in the line.
  4. Long length of material conveying ducts with bends and rough inner surface.
CARDING:
  1. Poor conditions of wires points.
  2. Improper machine settings.
  3. Less amount of flat strips extracted.
  4. Higher amount of extraction can help in nep reduction. 
 

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