Bayer Corp. NFM WE Meeting

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COUNTER ROTATINGNON-INTERMESHING TWIN SCREW
EXTRUDERS
Carl G. Hagberg
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Twin Screw Extruder Geometry
Co-rotating Intermeshing
Counter Rotating Intermeshing
Counter Rotating Non-Intermeshing
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Primary Applications for CRNI Extruders

• Compounding Blends of Temperature Sensitive
  Polymers and Fillers Shear Sensitive Fibers
  Hot Melt Adhesives

• Reactive Extrusion

• Recycling of Post Consumer Plastics

• Devolatilization of Polymers

• Direct Extrusion Finishing of Emulsion Polymers
  by Latex Coagulation

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Figure 1. CRNI Twin Screw Extruder
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Figure 2. CRNI Extruder Screws and Barrels
Apex Opening
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Figure 3. CRNI Extruder Screws
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CRNI Extruder Screws

• Screws are configured like single screw designs
• Can vary root diameter , helix angle, flight
  thickness,etc

• Twin Screws are two single screws in parallel
  
  
• Much flexibility in design and operation

• Forward pumping and reverse sealing flights
• Match or stagger the two screws

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Figure 4. CRNI Compounding Elements
Cylindrical
Forward Flight
Double Reverse Flight
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CRNI Extruder Screw Construction

• Screws are segmented along the extruder length
• Screws have 3-start threads with connecting studs
  
  
• Matched or staggered configuration
• About 3 or 4 segments per screw

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CRNI Extruder Barrel Construction

• Barrels are either 6D or 12D in length
• Types of Barrels
• T1 -- closed
• T2 -- 1D round opening
• T3 -- 4D x 1D opening
• T5 -- 1.75D round opening
• V2 -- 6D x 1D opening (double barrel)
• E1 -- single screw discharge (3D and longer)

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CRNI Extruder Barrel Construction

• Barrel Construction
• Jacketed - oil or steam heated
• Cored -- oil or steam heated, water cooled
• Electrically heated -- strap-on
• Nitrided internal bore
• Lined internal bore
• Corrosion -- high nickel alloys (Wexco 555 and
  Xaloy 309 and 800)
  
• Abrasion -- tungsten carbide (Wexco 666 and 777
  and Xaloy 800)
  
• HIP-clad (Hot Isostatic Pressing) internal bore
• Corrosion -- high nickel alloys (CPM 440V and
  MPL-1)
  
• Abrasion -- tungsten carbide (CPM 10V and 9V)

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Figure 5. CRNI Extruder Discharge Methods
Die
Single Screw Crosshead Pump
Product
Gear pump
Die
Product
Die
Product
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CRNI Twin Screw Extruder
Characteristics

• Excellent distributive mixer - even while
  conveying

• Ability to melt mix low and high viscosity
  polymers

• Best design is for low shear applications

• Gear box for speeds up to 750 rpm
• Normal Speed range from 50 rpm to 500 rpm

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Figure 6. CRNI Apex Material Transfer
Pressure-induced flow, interscrew transfer
Reorientation of material in apex
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Figure 7. CRNI Apex Transfer Methods
Staggered
Matched
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CRNI Twin Screw Extruder
Characteristics

• Superior feed and vent performance

• High free volume available in screws

• High interfacial area for devolatilizing

• Can design long L/D ratios - 84/1

• High throughput capacities - high drag flow
  possible

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pressure flow
Pressure Generating drag flow
drag flow
drag flow
Cylinder seal
filled region
vent opening
feed opening
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Operating Range Between the Limits
Torque Limit
Vent Flow Limit
Surging Limit
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Figure 10. CRNI Extruder Sizes
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CRNI Scaleup Rules
1. Scaleup Ratio Diam larger / Diam smaller
extruder
2. Conventional Scaleup Keep screw
speed constant Screw dimensions are
proportional to scaleup ratio
This keeps the shear rate constant
Product rate up to the 2.73 power
of scaleup ratio
3. Modify above rules slightly if same screw
fill ratio is desired
Reduce the screw speed 10-15
Reduce the conventi
onal channel depth 10-15
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Where CRNI Extruders are Best for Compounding

• Temperature Sensitive Polymers or Additives
• Hot Melt Adhesives (HMA)
• Recycled Polymers
• Additives which Degrade with High Temperature
• Distributive Mixing Applications
• Reactive Extrusion
• Powder Fillers
• Polymer Recycling - Melt Mixing
• Mechanically Shear Sensitive Fibers
• Very Long Fibers which must not be Broken Down
  (length)

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Shear Sensitive Fibersusing CRNI Twin Screw
Extruders
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CRNI Extruder for Shear Sensitive Fibers
Optimize screw design in critical areas
Stagger flights, very low shear compounder seals
Best distributive mixing extruder
Low shear mixing - by conveying elements only
Can mix in fibers in a short 6 or 7 L/D length
Minimum reduction of fiber length while mixing
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Figure 11. CRNI Extruder Process
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Hot Melt Adhesives using CRNI Twin Screw
Extruders
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Figure 12. Hot Melt Adhesive Extruder
Resin additive
Rubber feed port
Oil injection
Vent
Hot Melt Product
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Advantages of CRNI Hot Melt Processing
Optimize screw design in critical areas
Match or stagger, slotted flights, compounder
seals
Best distributive mixing extruder for different
viscosity feeds
Low shear mixing - while conveying the melt
Experience in HMA and other mixers
Liquid or solid resin feed experience
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Figure 13. SIS-based Hot Melt Adhesive
CRNI Extruder Installations
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Reactive Extrusion using CRNI Twin Screw
Extruders
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Reactive Extrusion
A process in which chemical reactions are
conducted in an extruder to produce or modify a
polymer
The extruder provides the necessary mixing and
reaction environment for this viscous process
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Figure 14. Reactive Extrusion Processes
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Figure 15. CRNI Grafting Process
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Advantages of CRNI Extrudersfor Reactive
Extrusion
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Devolatilization of Polymers using CRNI Twin Scr
ew Extruders
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Polymer Devolatilization

• Styrenic polymers
• SAN, ABS, SMA, SB copolymers, SIS, SEBS, SBS
  Triblock copolymer, PS
  
• Engineering thermoplastics
• Polyacrylate, PEI
• Synthetic rubber
• SBR, EPDM, PBd, Silicones
• Others
• PMMA, PE, PP, Epoxies

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Advantages of CRNI Extruder for Devolatilization

• Handles wide range of viscosities
• Contain and easily remove waste streams
• Short residence time
• Efficient heat transfer into polymer
• Narrow residence time distribution
• Efficient surface renewal
• Large free volume to contain foaming melts
• Large vents up to 6D long x 1D wide
• Screw rotation pulls polymer down into vents

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Figure 16. Solution Polymer Devolatilization
2nd vent 300 mm Hg abs
3rd vent 30 mm Hg abs
4th vent 10 mm Hg abs
Water injection
Solution feed 50 monomer
Rear vent 0-10 psig
Product
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Process Schematic Low Solids CRNI Extruder
Devolatilization
Feed kettle
Concentrator Extruder
preheater
Gear pump
Product to pelletizer
Devol. Extruder
N2 injection
To solvent collection
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Latex DewateringUsing CRNITwin Screw Extruders
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Polymer Isolation from Emulsions Latex
Coagulation
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Polymers Successfully Isolated by Direct Latex
Extrusion
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Advantages of CRNI Extruder for Latex
Coagulation Process

• Less equipment used ------- no coagulation
  tank,
  no centrifuge,
  no dryers

• Less water usage

• Less waste treatment

• Recycle of solids and water --- low solids losses

• Monomer recovery and recycle

• No powder handling -- no dust or cake problems,
  product is pellets

• Cost savings in energy / utilities / manpower

• Environment friendly ------- no emissions
  no
  pollution

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NFM / Welding Engineers CRNI Extruder Latex
Solids Capacity
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Figure 17. Equipment LayoutLatex Coagulation
First
Second
Moyno
Mechanical
Mechanical
Pump
Latex
Filter
Filter
Feed
First
Second
Wash
Wash
Water
Water
Steam
Injection
Injection
Injection
Optional Resin
Vacuum
Product
Coagulant
Injection
601 L/D CRNI Extruder
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Figure 18. Mechanical Filter