THEORY EXAMINATION (SEM–VI) 2016-17 POST SPINNING OPERATION

POST SPINNING OPERATION (EC012)

Section-wise Solved Answers & Notes

SECTION – A (10 × 2 = 20 Marks)

Very short, direct answers

(a) Classification of PET filament as per drawing speed

• LOY (Low Oriented Yarn) – low drawing speed                  • MOY (Medium Oriented Yarn)
• POY (Partially Oriented Yarn) – medium–high speed         • FOY (Fully Oriented Yarn) – high speed

(b) Why drawing of as-spun filament is necessary?

Drawing improves molecular orientation, crystallinity, tensile strength, and dimensional stability of the filament.

(c) Drawing used for apparel-grade Nylon-6 and temperature

• Hot drawing is used                                                          • Drawing temperature: 70–90 °C (approx.)

(d) Semi-permanent heat setting & loss temperature

Semi-permanent heat setting temporarily stabilizes fibre dimensions.
It is lost at temperatures above the heat-setting temperature (around 120–140 °C, depending on fibre)

(e) Effect of high heat-setting temperature for long time

• Reduced strength                                                   • Increased brittleness
• Excessive crystallization                                          • Loss of elasticity

(f) Methods used to convert tow to top

• Stretch-breaking                                                  • Cut-breaking
• Converter gill box

(g) Principle of up-twisting of filament yarn

Twist is inserted by rotating the yarn in the direction of twist, increasing cohesion and strength.

(h) Systems used for conversion of fibres into yarn

• Ring spinning                                                         • Rotor (open-end) spinning
• Air-jet spinning                                                      • Friction spinning

(i) Resultant denier after two-stage drawing

Given:                                                                        Initial denier = 9 D
Draw ratios = 1.5 and 2.0                                          Total draw ratio = 1.5 × 2.0 = 3.0

Final denier=93=3 denier\text{Final denier} = \frac{9}{3} = \boxed{3 \text{ denier}}Final denier=39​=3 denier​ 

(j) Throughput speed at spinneret

Given:                                                                       Yarn denier = 300
Take-up speed = 600 m/min                                   Density = 1.25 g/cm³

Mass flow = (300/9000) × 600 = 20 g/min

Throughput=201.25=16 cm3/min\text{Throughput} = \frac{20}{1.25} = \boxed{16 \text{ cm}^3/\text{min}}Throughput=1.2520​=16 cm3/min​ 

SECTION – B (Any 5 × 10 = 50 Marks)

(a) Parameters influencing drawing

• Draw ratio                                                           • Drawing temperature
• Drawing speed                                                    • Polymer molecular weight
• Moisture content                                                 • Heating medium

(b) Spin-draw process for high-performance Nylon-6 cord

In spin-draw, spinning and drawing are done in a single continuous step, producing high-tenacity nylon cords with improved orientation and strength.

(c) Drawing-induced structural changes               • Increased molecular orientation
• Higher crystallinity                                              • Reduced amorphous regions
• Improved tensile strength                                   • Lower elongation

(d) Parameters influencing heat setting                 • Temperature
• Time of exposure                                                 • Tension during heat setting
• Heating medium (steam/hot air)                         • Fibre type

(e) Effect of heat setting on fibre morphology

• Stabilizes crystalline regions                                 • Reduces internal stresses
• Controls shrinkage                                                • Improves dimensional stability

(f) Working of Seydel machine

Used for tow-to-top conversion.
It involves controlled stretching, breaking, and drafting of tow into staple fibres.
(Diagram should be drawn in exam)

(g) Making high-shrink acrylic fibre

Achieved by partial drawing followed by controlled relaxation, creating differential shrinkage on heating.

(h) Fibre variables affecting blended yarn properties

• Fibre length                                                           • Fineness
• Strength                                                                 • Elasticity
• Surface friction                                                       • Crimp

SECTION – C (Any 2 × 15 = 30 Marks)

Q3. Drawing behavior of thermoplastic materials

Types of drawing behavior

• Cold drawing                                                     • Hot drawing
• Neck drawing                                                    • Multi-stage drawing

Most stable elastic network:
Hot-drawn fibres show better stability due to uniform molecular orientation and crystallization.

Q4. Importance of annealing & nature of heat set

Annealing importance

• Relieves internal stresses                                     • Improves dimensional stability
• Controls shrinkage                                               • Enhances fibre performance

Nature & importance of heat set

Heat setting stabilizes fibre dimensions under heat and tension, essential for fabric shape retention and wrinkle resistance.

Q5. Two-for-One (TFO) Twister

Operating principle                                  One spindle rotation inserts two twists, increasing productivity.

Properties of TFO yarn

• Uniform twist                                         • Higher strength
• Better appearance                                 • Improved package density