l-11 modern-day polymer processing(1)

8/13/2019 L-11 Modern-Day Polymer Processing(1)

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Common fabrication TechniquesThermoplasticsHeat to melt Change shape Cool to solidify

Thermosets and ElastomersMix and/or Heat Change shape Chemical reaction (cure) coolClassification of processing techniques:

Extrusion : pipe, sheets, rods (profile extrusion)Molding: Injection, compression- batch process to make articles

of diverse shapeSpinning: Fibers

Calendering: sheetsCoating: to coat thin liquid layer on web

( Additional) for polymer compositesFilament winding

Pultrusion

M ODERN -DAY P OLYMER P ROCESSING


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A BRIEF DEVELOPMENTAL HISTORY

-By 1920s, most of the processing operation had been established.-1920-1960, development of new thermoplastics-Two-screw co- and counter-rotating extruders were developed.-Hoeschst, 1930s, intermeshing twin-screw counter-rotatingextruders-LMP Italy, Intermeshing twin co-rotating extruders.-Hans Beck (BASF), 1943, screw injection molding-Forming processes, DuPont (Carothers), continuous oriented fiberforming-Studt, blown film forming by annular die.

-Modern processing by 1960s incorporated orientation-Melt spun and drawn fibers, Stretch blow molding of bottles,rotating mold, biaxially oriented films.


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M ODERN -D AY P OLYMER P RODUCT F ABRICATION Single or multi-step interacting processes.Compounding is the precursor!

Compounding operation1. Batch Mixers2. Continuous Extrusion

Processing operations

1. Single Extrusion Operations

2. Extrusion with Post Die Operations

3. Two-Machine Operations

4. Multistep Processing Operations


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COMPOUNDING OPERATIONS Batch Mixers

(a) Two-roll Mills (External mixers)

(b) Internal mixers:two-rotor blades forincorporating C-black into rubbers,elastomer blending etc.


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COMPOUNDING OPERATIONS -E XTRUSION Continuous Extrusion -Single or Twin-screw machines

Compounding of particles larger than 1m.Extruder parts: feed hopper, barrel, screw (feed, compression and metering

zones).In commercial production, the powder from reactor is directly fed to the

palletizing extruders.Single screw extruders are tapered for increasing progressive shear

(reduced viscosity!).Twin screw: either counter- or co-rotating


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S INGLE EXTRUSION FORMING OPERATIONS

Extruders are used for pumping to shaping dies and post-die

operations are used for secondary shaping.In small units, the extruder acts as compounder, meteringdevice and pump. Static mixing devices are added to improve theperformance.(a) Extrusion through dies (profile extrusion)(b) Extrusion with post-die operation.1. Tubular film2. Blow molding3. Bi-axially oriented films


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S INGLE EXTRUSION FORMING OPERATIONS


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E XTRUSION WITH P OST -D IE OPERATION


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INJECTION M OLDING Intermittently moving screw to inject polymer melt into mold.Runner, gate, mold cavityshot varies a few grams to few Kg, clamping pressure goes up to 5000 tonsrotational molding parts for biaxial orientationSkin-Core or Sandwich Molding


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M OLDING with extrusion: injection moldingwith out extrusion: compression, RIM, Transfer

Injection moldingRIM

Low temperatures and clamping pressureslow energy, rapid start-up, large-size articles, 95% is used for PUReinforced RIM

Transfer Moldingmold is closed prior to resin entry. Molten resin is injected from

open transfer pot, un- injected called cullSmall cycle time, easy flow, intricate shapes, insets

Compression molding

Low cost, heated molds, pressure up to 4000 T


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TWO -M ACHINE P OLYMER P ROCESSING In sequence, Extruder makes perform, it is further heated and

shaped!

Benefits: desired mechanical properties, Intricate shapes

Melt SpinningTwo-Stage Film FormationStretch-Blow MoldingThermoforming and Cold forming


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M ELT S PINNING

spinning by extruders or gearpumps through spinneret

roll spinning for anisotropy

drawing and draw-texturing


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TWO -S TAGE F ILM F ORMATION

Film is stretched in transversedirection


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S TRETCH B LOW M OLDING


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THERMOFORMING AND C OLD FORMING


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M ULTI -S TEP P ROCESSING (R UBBER C URING )Compounding, shaping, vulcanizationPnuematic tires: tread, carcass, sidewall, linearTread+Sidewall coextruded, Carcass calendered, components are built on

a drum, inflated by deformable membrane, cured and deflated,


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SOLUTION P ROCESSING -F IBER S PINNING


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K INEMATICS IN P OLYMER P ROCESSING

Internal flows: melt flows under pressure (Poiseulli flow)External flows: melt flow in open (air)-fiber spinning, tubular

films, blow molding

Kinematics of Internal flow


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K INEMATICS OF EXTERNAL (E XTENSIONAL ) FLOW

Also the equation of Continuity is applicable i.e.

A uni-axial extension case,


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B I- AXIAL (PLANAR ) EXTENSION

Shear flows are isothermal whereasextensional flows are adiabatic due torapid cooling.

Kinematics of internal flows is

constant whereas for external flows it isnot constant for long time.

l-11 modern-day polymer processing(1)

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