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
