PROCESS CONTROL IN SPINNING Prof. R. Chattopadhyay IIT, Delhi

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PROCESS CONTROL IN SPINNINGProf. R.
ChattopadhyayIIT, Delhi
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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   

 
 
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MATERIAL FLOW
Raw cotton
CENTRAL SLIVER PLANT
Transportation of Sliver / roving
Khadi Institution 1
Khadi Institution2
Khadi Institution3
Internal transportation
Distributed spinning in villages
Institutional spinning
Transportation of sliver or roving
Village 1
Village 3
Village n
Village 2
Charkha
1
2
3
4
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PROCESS CONTROL
PROCESS
Input
Output
Monitor
Corrective action
Monitor
Monitor Process parameters /Intermediate product
characteristics/Machine conditions/Work practice
/ process waste
Compare against norm
Compare against norm
Corrective action
Compare against norm
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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

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• 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

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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

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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.
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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

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• 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.

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• 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.

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QUALITY ATTRIBUTES TO BE CONTROLLED IN KHADI YARN

• Average Count and Its CV
• Lea CSP
• Yarn Unevenness
• Imperfections
• Soft and hard twisted portion
• Faults
• Pote
• Kachara
• Moore
• Daghi
• Bakar
• Slubs
• Possible reasons for deterioration in quality
• Characteristics and occurrence of faults

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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

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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 -Slive
r uniformity -Sliver cleanliness
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Roving -Roving count and its variability -Rovin
g uniformity -Roving cleanliness Process
Performance       -Waste level -End breaks in
charkha -  Productivity
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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
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• 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

 



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Control of Count Variability
Calculation of within and between count CV
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• 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.

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• DIFFERENCE IN AVERAGE DRAFT IN CHARKHAS
• Wrong draft constant in charkha or wrong change
  pinions
• Difference 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

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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.
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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.

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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

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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 norms
•  Cleanliness of the sliver

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Yarn Count Strength Product (CSP)
Average CSP 1000 for count 24 36 Nm CSP CV
12, CSP S.D. 120 UAL 1000 3?120
1360 UWL 1000 2 ?120 1240 LAL 1000 - 3?
120 640 LWL 1000- 2 ?120 760
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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.
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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).
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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.