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

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quality assurance in spinning

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

Raw cotton

MATERIAL FLOW

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

10

process control
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

quality of incoming raw material to central sliver plant
QUALITY OF INCOMING RAW MATERIAL TOCENTRAL 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

slide6

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 by khadi institution
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
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
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
slide10

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.
slide11

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
QUALITY ATTRIBUTES TO BE CONTROLLED IN KHADI YARN
  • Average Count and It’s 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
process control of charkha spun yarn
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
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

slide15

Roving

-Roving count and its variability

-Roving uniformity

-Roving cleanliness

Process Performance

      -Waste level

-End breaks in charkha

-  Productivity

slide16

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

slide17

Lea weight

( gm)

Shift

Upper Action Limit (UAL)

65 g

Upper Warning Limit (UWL)

60 g

50 g

40 g

Lower Warning Limit (LWL)

Lower Action Limit (LAL)

35 g

Operator ID

slide18

Upper Action Limit (UAL)

65 g

Lea weight

( gm)

Upper Warning Limit (UWL)

60 g

50 g

40 g

Lower Warning Limit (LWL)

Lower Action Limit (LAL)

35 g

Operator ID

slide19

65 g

Upper Action Limit (UAL)

Lea weight

( gm)

Upper Warning Limit (UWL)

60 g

50 g

40 g

Lower Warning Limit (LWL)

35 g

Lower Action Limit (LAL)

Operator ID

slide20

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

Operator No.

Count Values of Lea No.

1

2

3

4

5

6

7

8

9

10

1

2

3

4

5

6

7

8

9

10

Control of Count Variability

Calculation of within and between count CV

slide22

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.
slide23

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
yarn uniformity unevenness
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
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
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
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
yarn count strength product csp

Lea weight (g)

1360

UAL

UWL

1240

1000

640

LWL

760 gm

LAL

Operator ID

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

slide29

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.

slide30

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).

slide31

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.

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