PROCESS CONTROL IN SPINNINGProf. R. ChattopadhyayIIT, Delhi

QUALITY ASSURANCE IN SPINNING

QUALITY ASSURANCE IN SPINNING

STEPS

Setting of Norms Quality of incoming raw material to the Khadi Institution Process Monitoring and Control Inspection of final product

MATERIAL FLOW

Transportation of Sliver / roving

Internal transportation

CENTRAL SLIVER PLANT

Raw cotton

Khadi Institution 1

Khadi Institution2

Khadi Institution3

Distributed spinning in villages

Institutional spinning

Transportation of sliver or roving

Village 1

Village 2

Village 3

Village n

Charkha

1

2

3

4

10

PROCESS CONTROL

PROCESS

Input

Output

Monitor

Compare against norm

Corrective action

Monitor

Process parameters

/Intermediate product characteristics/Machine conditions/Work practice / process waste

Compare against norm

Corrective action

Monitor

Compare against norm

QUALITY OF INCOMING RAW MATERIAL TO CENTRAL SLIVER PLANT

Test of raw cotton in terms of physical parameters

and accept if comparable with norms

Careful transportation & storage of cotton bales

Check sliver or roving parameters i. e

Count and count CV%

Trash % & Neps

Checks on material handling during packaging and

loading on trucks

- Transfer sliver into polythene bags

- Put roving bobbins into polythene bags

- Transport sliver cans, polythene bags containing sliver or roving on to the trucks.

- Properly cover sliver cans, polythene bags

containing sliver or roving on trucks

QUALITY OF RAW MATERIAL RECEIVED BYKHADI INSTITUTION

Checks on material handling during Unloading from

trucks

- Careful unloading of packages

- Careful internal transportation to avoid damage

- Proper storage and segregation of sliver/ roving to avoid accidental mixing

Checks on delivered sliver / roving

- Weighing of packages

- Cross checking of average count

DISTRIBUTUON OF ROVING OR SLIVER TO THE SPINNERS

- Ensure that the sliver or roving corresponds to the count to be spun.

- The package is covered in polyethylene sheet.

In- Instruction about careful handling of package during way back to village.

CHARKHA SPINNING GUIDELINES

Work practice related

Running of Charkha

- Run at a slow speed in the beginning and then raise speed and maintain speed at a convenient level.

- Cover the charkha once spinning is over.

- The broken end should be pieced (joined) properly. A knot is to be avoided as it becomes too large with respect to the yarn diameter, which deteriorates fabric appearance

Lea Making

-All the sections of the lea should be made from same yarn count.

-The end of the yarn should be inserted in to the inner portion of the lea.

-Leas should be properly stored in plastic bags or fabric bags with count wise segregation by colour mark.

-If possible, lea bundles should be segregated while storing according to the type of fibres used or count to avoid accidental mixing.

Maintenance related

-Follow a specified maintenance schedule in terms

of cleaning and oiling.

-Top roller pressure should be checked at regular

intervals.

-Check the condition of the aprons and driving belts (mall) and adjust if necessary.

Parameters selection

- Select parameters based on past experience that suits the raw material.

QUALITY ATTRIBUTES TO BE CONTROLLED IN KHADI YARN

Average Count and Its CV%Lea CSPYarn UnevennessImperfectionsSoft and hard twisted portionFaultsPoteKacharaMooreDaghiBakarSlubsPossible reasons for deterioration in qualityCharacteristics and occurrence of faults

PROCESS CONTROL OF CHARKHA SPUN YARN

Detection of significant shift in quality level

Investigation on the causes of departure

Taking remedial action immediately to set the process back to normal

Monitoring stages and Characteristics to be monitored

YARN STAGE

-Average count and count variability

-Uniformity

-Imperfections

-Count Strength Product (CSP)

INTERMEDIATE STAGES

Sliver

-Sliver count and its variability

-Sliver uniformity

-Sliver cleanliness

Roving

-Roving count and its variability

-Roving uniformity

-Roving cleanliness

Process Performance

-Waste level

-End breaks in charkha

- Productivity

Detection of shift in yarn count:

Example:

Nominal Count = 20 Nm

Average weight of lea = 50 gm

Count CV % = 10

S.D. of count = 5gm

Warning limit = Mean 2 S.D. = 50 10

= 60 gm and 40 gm

Action limit = Mean 32 S.D. = 50 15

= 65gm and 35gm

WHAT ACTION IS TO BE TAKEN

For case I

-Wrong Draft Change Pinion ( DCP)

-Inadvertent change in draft constant

-Wrong count of sliver or roving

For case II

-Count of sliver / roving supplied is to be verified

-Too coarse and too fine sliver / roving are to be withdrawn

-Draft on charkhas are to be adjusted

Control of Count Variability

Calculation of within and between count CV

REASONS FOR HIGH BETWEEN OPERATOR COUNT VARIABILITY (CVBO)

Difference in average hank of sliver/ roving used.Difference in the total drafts in the charkhas Difference in effective drafts between spindles of charkhas due to cot slippage. Roving stretch

REASONS FOR DIFFERENCE IN AVERAGE SLIVER HANK

Difference in waste level and mechanical draft in card breaker or finisher draw frame.

DIFFERENCE IN AVERAGE ROVING HANK

Difference in sliver hank.Draft difference in speed frames. Differences in waste level in card.

DIFFERENCE IN AVERAGE DRAFT IN CHARKHAS

Wrong draft constant in charkha or wrong change pinionsDifference in effective draft within a charkha

-Slippage of top rollers, inadequate roller pressure.

ROVING STRETCHING

Inadequate roving twist, low inter fibre cohesion (specially when fibres are short),defective bobbin holder

YARN UNIFORMITY / UNEVENNESS

1. A routine check on all the samples received may not

be practicable.

2. Only when yarn samples for any new lot arrives , the test can be carried out by randomly selecting 30 leas from as many operators as possible.

REASONS FOR UNEVEN YARN

Incorrect setting of break draft on D/F, S/F or charkha.

Inadequate top roller pressure.

Wear/damaged apron or cots.

Eccentric top roller y in charkha.

High short fiber percentage in sliver or roving.

Too wide setting in the front zone of charkha.

Slipping apron.

YARN APPEARANCE

Subjective assessment based on visual check of yarn boards on yarns received from operators when fresh yarn lots are received from them for a new mixing . Maintain a record according to operator ID

REASON FOR POOR APPEARANCE

High yarn unevenness Many excessively severe thick, thin places and neps in the yarn Presence of too many impurities like seed coat, leaves, stalks etc in the yarn

CORRECTIVE ACTIONS TO BE TAKEN

Check the overall condition of the charkha and roller setting Replacement of defective drafting rollers or aprons Cleaning of accumulation of stray fibres on drafting elements, ring, travelers, gears etc should be avoided.Roller slippage because of low pressure or presence of oil on roller surface is to be avoided.Neps in sliver to be maintained as per the normsCleanliness of the sliver

Yarn Count Strength Product (CSP)

Average CSP = 1000 for count 24 36 Nm

CSP CV% = 12, CSP S.D. = 120

UAL = 1000 + 3120 = 1360

UWL= 1000 + 2 120 = 1240

LAL = 1000 - 3 120 = 640

LWL= 1000- 2 120 = 760

Action to be taken

Case I: Points fall below the lower Action Limit or continues to fall in between Warning and Action Limit for many operators.

Case II: Points are distributed with a wide scatter.

Case I: A repeat check on the yarn supplied by the operator whose estimated CSP value fall below the action limit is to be performed. At least 6 leas are to be tested and the average is to be found out. If the average is found to be still lower, then remedial measures should be taken.

POSSIBLE REASONS FOR LOW AVERAGE CSP

-Inadequate twist in the yarn.

-Finer yarn count.

-Weak fibres in mixing.

Twist and count testing of the same are to be performed to find out whether the twist is really low or the count is fine. The lower twist could be attributed to:

Lower spindle speed due to slippage, which can be due to

Loose driving cord of spindles.

Accumulation of oil/grease on cord driving the spindles (mall).

Reasons for finer yarn

-Higher total draft.

-The finer sliver/roving supplied.

If count and twist are as per nominal value but CSP is still found to be less, inadvertently a sliver/ roving may have been supplied from a mixing in which the fibres are intrinsically weak.

Reasons for high strength variation

Intermittent slippage of top roller in the charkhas.

Variability in between yarn count produced on

different charkhas.