EXTRUDER

Motor

Water

pump

Hopper

Feeder

Cutter

Feeding

barrel

Heating

system

Cooling

system

Die

Clextral EVOLUM 53 Extruder

Extruder

Extruder development in the food industry

Mid-1930s Single screw continuous pasta press

1940 Oil extraction

1950 Pet foods

1960s RTE cereals

1980s Aquatic feeds

In 1998 Retail value of extruded products: $3.62 billion

or 3.7 million tons of production

Extruder Classification

Heat Generation

Adiabatic Isothermal Polytropic

Extruders

Single

screw

extruders

Intermeshed Non

intermeshined

Counter rotating

Self-wiping Partially

self-wiping

Intermeshed non

Intermeshed

Co-rotating

Twin

screw

extruders

Continuous screw extruders

Feed

Moisture

(%)

Product

Temperature

(oC)

Screw

Speed

(rpm)

Typical

Products

Twin-screw

cooking

extruder

11-35 80-200 200-500 Puffed snacks

RTE cereals

High-shear

cooking

extruder

15-20 120-180 350-500 Modified

starch

Low-shear

cooking

extruder

11-16 170-200 300 Puffed snacks

High-pressure

forming

extruder

25 65-80 40 Cereal pellets

Half-product

snacks

Pasta press 32 30-52 30 Pasta

Screw(s) Die

Basic extruder components

SCREWS and SHAFTS

Conical

screw

caps

Shaft

Screw

elements

1/2 P - 6 unitsTwin-flight

3/4 P - 9 units

Twin-flight

3/4 P - 9 unitsSingle-flight

1/2 P - 9 unitsTwin-flight

1/1 P - 9 units

Twin-flight

3/4 P - 6 unitsTwin-flight

Cone-screw

Washer

1/2 P -cut6 units

Twin-flight

Paddles 0.75 units Paddles 1

unit

3/4 P4.5 units

Twin-flight

3/4 P - cone9 units

1/2 P - Rev1.5 units

1/2 P0.75 units

3/4 P - cone9 units - cut

Shaft Collar

3 units

Disks 0.75 units

3/4 P - cut9 units

Twin-flight

1/2 P - Rev0.75 units

1/2 P - Rev6 unitsTwin-flight

Elements for generating screw profiles and pressures

D= screw diameter

h= channel depth

t= pitch

N= screw speed

=

D

t 2/ tan 1-φ

e= axial flight tip thickness

n= number of screw threads,

δ= clearance between flight tips and barrel

φ= screw helix angle (a function of diameter and pitch)

Advantages of Extrusion Process

�Adaptability

� Product variety

� Energy efficiency

� Low cost

� Unique products

� Increased throughput

� Product quality

�Minimal waste

�Minimum labor

� Combine several steps in conventional process

Processing steps with conventional process Product

group

Product

example

Conventional

process

Cooking

Baking

Gelatinizing

Roasting

Caramelizing

Crystallizing

Material exch

ange

Reaction

Maillard

reaction

Enzym

e inactivation

Sterilization

Alkalizing

Drying

Precipitation

Mixing, kneading

Dispersing

Shaping

Expanding

Heating

Cooling

Den

aturing

Modified

flours

Baby food Drum dryer

Texturized

proteins

Meat

substitutes

Spinning

system

Aquaculture Presses Animal feeds

Pet food Oven

Flavors Meat flavors

Caramel

Roasting

kettle

Baked goods Flat bread, bread crumbs

Baking oven

Puffed grains Puffing-gun Breakfast

cereals Cereal flakes Cooker

Pasta Oriental noodles

Cooker

Coffee Roaster Drinks

Instant powders

Cooker

Liquorice Cooker

Chocolate Press

Confections

Sugar Crystallizer

PROCESSING STEPS IN A EXTRUDER

Feeder Die

Feeding

zone

Single screw extruder

Twin screw extruder (Corotating)

Twin screw extruder (Counterrotating)