How to improve Yarn

realization and control

wastes?

D.Shanmuganandam

Assistant Director

The South India Textile Research Association

Coimbatore – 641 014

How to improve Yarn realization and

control wastes?

D.Shanmuganandam

Assistant Director

The South India Textile Research Association

Coimbatore – 641 014

1. INTRODUCTION

In the production economics of a spinning mill, yarn realisation plays a significant

role. To illustrate, in the prevailing cotton cost and yarn selling price, even an 1%

improvement in yarn realisation would lead to a saving of Rs 20 lakhs per year for a

30000 spindle mill manufacturing 40s yarn.

Two decades ago, SITRA had brought out a publication on yarn realisation and

process waste control. During this intervening period, remarkable changes have taken

place in the industry with regard to technology of machinery, yarn quality and

workers’ efficiency. Keeping the above in mind, the formulae for estimating yarn

realisation and norms for different categories of wastes have been updated and

presented in this article.

This article also deals with various measures necessary to improve yarn realisation

and control wastes. Besides controlling process wastes such as blowroom and card

droppings, flat strips, comber noil, sweep waste and yarn waste, equal emphasis

should also be laid on the control of reusable wastes (soft waste) such as lap bits,

sliver bits, roving ends and pneumafil and roller waste. This is because, apart from

loss in production, reprocessing of soft wastes involves extra handling and

deteriorates yarn quality.

2. YARN REALISATION

Establishment of norms for wastes is a pre-requisite for a successful waste control in a

mill. Yarn realisation (YR) is largely governed by the level of trash in cotton,

expected yarn quality and type of machinery. Achievable yarn realisation can be

obtained using the following formulae:

A. For mills reusing the entire usable wastes in the same mixing

YR (%) = 97.5 – t – Wk – Wh for carded counts

Wc

= (100 – t – Wk) 1 – – Wh – 2.5 for combed counts

100

B. For mills not reusing the usable wastes in the same mixing

YR (%) = 97.5 – t – Wk – Wh – Wu for carded counts

Wc

= (100 – t – Wk) 1 – – Wh – Wu – 2.5 for combed counts

100

Where t = trash in mixing (%)

Wk = card waste (%)

Wc = comber noil (%)

Wh = yarn waste (%)

Wu = usable waste (%)

For example, for t = 3%, Wk = 7% and Wh = 0.5%, the expected yarn realisation is

87%. In the above case, if the mill produces combed yarn with a noil extraction of

18%, then the expected yarn realisation will be 70.8%. In both the cases, it is

assumed that the mill would reuse the usable wastes in the same mixing.

3. NORMS FOR WASTES

Norms for different categories of wastes are summarised in Tables 1 and 2.

Table 1 Norms for process waste and invisible loss

Type of waste Norms (%)

Blow room droppings Same as trash in cotton

Gutter/filter waste 1.0

Card waste (modern cards) 20s - 40s : 7.0

Above 40s : 6.0

Sweep wastea 1.0

Yarn waste

Conventional cone winding

Doubler winding

Ring doubling

TFO twisting

0.1

0.1

0.1

0.1

Auto winding

- with magazine feed

- with auto feed

0.5

0.8

Invisible loss 0.5

‘a’ includes suction fan wastes of draw frames, fly frames and humidification plant.

Table 2 Norms for usable waste (%)

Type of waste Lap feed Chute feed

Lap bits and card web 0.7 0.2

Sliver waste in drawing and fly frames 0.5 0.5

Waste at comber preparatory and combers 1.0 1.0

Roving ends 0.3 0.3

Pneumafil and roller waste (ring frames) 2.5 2.5

Total 5.0 4.5

For the method of consolidating waste, estimating invisible loss and checking the

accuracy of figures, reference may be made to SITRA monograph “Quality Control in

Spinning”, 1998.

4. PROCESS WASTE

4.1. Blow room

Amount of waste extracted in blow room is mostly determined by the trash level in

cotton. In modern blow room lines, greater importance is attached to the opening of

cotton than cleaning. Hence, cleaning efficiency of about 60% in cottons with high

trash content and 50% in cottons with low trash level can be considered to be quite

satisfactory in these lines. For good cleaning efficiency, the waste extracted in blow

room should be about the same as the trash in mixing. If, however, the cleaning

efficiency achieved is less than 50% – 60%, then the total waste extracted should also

be low. It should be ensured that the overall lint in waste is no more than 40% in

cottons with high amount of trash and 50% for cottons with low level of trash.

The expected lint loss can be estimated using the following formula:

(t – t L) 100

Wb = ……………… (1)

(100 – L)

(t – t L)

∴∴∴∴ L = 100 1 – ……………… (2)

Wb

Where

t = trash in mixing (%)

t L = trash in lap (%)

Wb = waste extracted in blow room (%)

L = % lint in waste

Illustrative Examples

1. Trash in mixing : 3.5%

Trash in lap : 1.5%

Waste extracted : 3.2%

Calculate the lint loss in waste.

Refer equation (2),

(t – t L)

Lint loss (L) = 100 1 –

Wb

(3.5 –1.5)

= 100 1 –

3.2

= 38%

2) Trash in mixing : 5%

Trash in lap : 2%

Expected lint loss : 40%

Estimate the amount of waste to be extracted in blow room

Refer equation (1),

(5 – 2) x 100

Wb =

(100 – 40)

= 5%

Presently, many mills are using Automatic Waste Evacuation System (AWES)

in blow room, cards and combers, which removes wastes from these machines either

continuously or intermittently. This system not only reduces the man power required

to collect and transport wastes but also helps to control the incidence of fly and fluff

generation in these departments and improves yarn quality, particularly short thick

faults.

In mills not equipped with filters in blow room, a proper estimate of gutter

waste should be made, since gutter cleaning is not done regularly at the end of every

month. The estimate of gutter waste could be made based on the quantum of waste

collected and number of days the blow room has worked.

4.2. Cards

Waste extracted in cards is usually in the range of 4% to 7% depending upon

the type of card and mixings. Between same type of cards and mixing, the waste %

should not vary more than ±0.5% from the average. The card waste is also governed

by the cleaning efficiency achieved in blow room. Thus, while assessing the waste,

combined waste extracted in blow room and cards should be taken into account. The

combined cleaning efficiency will be generally in the range of 90% to 98% with

modern cards. To illustrate, for 4% trash in cotton and 0.12% trash in sliver, the

combined cleaning efficiency is 97%.

4.3. Combers

Generally, all cottons respond well to combing for noil extraction up to 16%. For levels

beyond 16%, the law of diminishing returns operates and the improvement in yarn

quality is not commensurate with the additional cost of production. Higher levels of

waste should be extracted only in such cottons where combing performance is

satisfactory or where the end use requires yarns of very high quality. Under good

working, for every 1% increase in comber waste, yarn lea strength will increase by 1%

and evenness is expected to improve by 0.15 U%. Variation in noil % between

combers must be maintained within ±0.5% and between heads it must be within ±1.5%.

4.4. Yarn waste

Yarn waste in a spinning mill should not normally exceed 0.1% with

conventional cone winding. In the case of automatic cone winding, the yarn waste

generally varies from 0.5% in winders fitted with magazine feed to 0.8% in winders

with auto bobbin feed system. However, if the yarn under goes additional processes in

post spinning such as reeling, doubler winding and TFO twisting/ring twisting, the

waste would be somewhat higher. A high incidence of yarn waste, apart from leading

to a loss of Rs 6 to Rs 15 per spindle per year for every 0.1% waste, is an indication of

poor machinery condition and maintenance, and inappropriate work practices of

operatives. A number of factors such as vibrating spindles, spindles out of center, soft

cops, oil stain on yarn, improperly built cop bottom, yarn left over in cops during

winding and operatives using excess length while piecing, leads to high yarn waste. For

further information on yarn waste control, reference may be made to SITRA publication

“Measures to Control Hard Waste in Spinning” Vol.41, No.11, March 1996.

4.5. Sweep waste

Sweep waste in all the departments of a spinning mill together should be

within 1%. A high sweep waste arises invariably due to operatives throwing away the

wastes like roller waste, lap bits, sliver bits, roving ends, etc. on the floor and

generation of fly and fluff. The fly frame and ring frame tenters should be provided

with hip bags and it should be ensured that the roller waste and roving ends are

deposited in the bags after piecing the broken ends. Good waste, if any, should be

picked before sweeping instead of sorting out the waste later. A high price fetched for

sweep waste would give an indication of the presence of good fibers in the waste.

5. INVISIBLE LOSS

Invisible loss in a spinning mill occurs due to a number of factors such as

short fibers (fluff) escaping from the departments, improper accounting of wastes

produced, weighment errors in cotton purchased and wastes sold, excess give away of

yarn and inaccuracies in the estimates of stock held in process. Since it would be

difficult to accurately assess the process stock, it is suggested that the invisible loss be

assessed only once in 4 months for control purposes. This will help in minimising the

variation in invisible loss due to errors in process stock estimate. From the data

compiled every month, a cumulative average could also be taken for control purpose.

However, not much importance should be given for estimates made from data less

than 4 months.

To maintain the invisible loss within 0.5%, mill should also ensure that

moisture content in the finished goods is at par with the level prevailed in cotton at the

time of purchase. For more details on invisible loss control, reference may be made

to SITRA Focus “How to Control Invisible Loss in Spinning Mills? – Case study”,

Vol.23, No.3, September 2005.

6. USABLE WASTE

By exercising good control over

� end breaks in various machines

� material handling and storage and

� work practices of operatives

a mill could maintain the usable waste below 5%.

7. CONCLUSION

In many mills, there is good scope for improving yarn realisation and reducing

wastes (as revealed by inter-mill studies as well as consultancy studies by SITRA).

The following 4 steps would be helpful to improve yarn realisation.

Step 1: Calculate actual yarn realisation and different categories of wastes

Step 2: Using the formulae given in this article, estimate the expected yarn

realisation for the existing working conditions.

Step 3: Compare the actual yarn realisation with the expected value and actual

wastes with norms.

Step 4: Analyse the causes for deviation and initiate corrective action. Create

awareness among the workers and technical staff about the importance

of waste control. Good supervision and proper maintenance of

machinery would help to reduce the waste.

Source: The south Indian Textile Research Association, Coimbatore-641014, India,

http://www.sitra.org.in/default.aspx.

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