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Chapter: 19Screw Elements: Types, Function, IdentificationBasics on screw elements

Conveying elements

Kneading elements

Neutral elements

Installation of the screw elements

Numbering of the screw elements

Principle of operation of the screw elements

CWP Customer Training Seminar

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CWP Customer Training Seminar

• The Erdmenger patent "conditions of the sealing profile must be met"

Along the screw connection there must be the same cross-section at all points

Both shafts must have the same screw profile.

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Do = Outer screw diameter

Di = Inner screw diameter

a = Axle distance

Diameter ratio:

Da / Di

(indicates available volume)

Specific capacity:

Md / a3

(Indicates torque)

Da

Di

a

Do

Di

a

Characteristic Dimensions

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Da

Pit

ch (

mm

)

x Da High pitch Low pitch

Conveying Elements

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Extruder

Rightflighted Elements Leftflighted Elements

Conveying direction

direction of the extruder flow

against the inConveying direction

direction of the extruder flow

Conveying Elements Right and Left-Hand Pitch

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Conveying Elements, Conveying,

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1

2

3

4

(5)

Stagger angle

1

2

3

4

Spacer ring

Kneading disc

5

Wide kneading discs

Narrow kneading discs

Kneading Blocks

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Kneading Blocks

• Kneading blocks comprise several kneading discs arranged behind one another.

• The staggering angle by standard is 45 or 90°

• The number and the width of the individual kneading discs is variable.

• The position of the kneading discs at the beginning and the end should be identical, for compatibility with other kneading blocks (i.e. to keep the modular concept).

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Kneading Elements

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Element

own conveying

without

Extruder

Rightflighted Elements Leftflighted ElementsNeutral elements

Conveying direction

of extruder flow

in the direction against direction Conveying direction

of extruder flow

Kneading Elements

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Conveying and Kneading Elements, Left-Hand Pitch

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Quiz

Q: Which connection between the screw element and the screw shaft is shown?

A: Refer 18.1 ff

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Installation of Screw Elements

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Installation of Screw Set Elements

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1-flight elements 2- flight elements 3- flight elements

Faces always parallelly

Faces always offset by 90°

Installation of Screw Set Elements

Faces always parallelly

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Profile Transitions

Profile A Profile B

Transition piece required- for profile joint (profile A to B- if the faces of identical profiles

are offset (kneading block)

Profile A Profile B

Risk of breakage

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Transition Elements

• For technical fluidic reasons, but also to prevent mutual contact of the screws, a transition piece is necessary between different profile cross-sections, similar to that required for kneading blocks.

• Spacer rings, with the same outside diameter as the inside diameter of the screw elements, can be used instead of transition elements in some cases.

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Part Numbers on the Screw Elements

No. of flights, direction1

2

3

4

5

6

9

1-channel, right

Special version

2-channel, right

3-channel, right

1-channel, left

2-channel, left

3-channel, left

3

4

6

9

30°

45°

60°

90°

Kn.block : 4 0 5

No. of discs

Offset angle

Pitch of conveying elements

-/- 0 6 01.-8 0 4 0 0 6 020 0 2 4

Connection Screw Elemnet/Shaft

00, 01, 02

66, 67, 68

24, 25, 34

Feather key (0°)

6-key

Involute SC

Other numbers available for special geometries.

34 MEGA-Compounder

Profile1

2

6

Screw element with sealing profile

Screw element with sealing profile

Kneading block

Element lengthScrew diameter

Material00

05

68

15

25

Nitriding steel

Cr steel

CPR-HSS steel

Wear and/or corrosion protected elements ofcomposite materials

37 CPR - composite material

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Recognising Screw Element Materials

Corrosion and wear-resistantHIP - composite

25

15Standardwear protectionHIP - composite

Nitriding steelnitrified

Material no.

0005

Material Specif.

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Recognising Screw Element Materials

10

28

Former standardwear protectionHIP - composite

Soft martensitichardened Cr-Nisteel with applied crest welding

Material no. Material Specif.

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Kneading (dispersing)

elementsKneading-

Mixing(homogenising)

elementsMixing

Conveyingelements

Conveying Pressure Barrier

Process Section

elementsLeft-handed

Principle of Operation of the Screw Elements

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Conveying Mechanism

1-flight elements

Reduced product flow from one screw tothe other. => improved transport capacity

2-flight elements

Main portion of the product flows from one screw to the other.=> lower transport capacity

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Principle of Operation of the Conveying Elements

Type of element Free cross-section

Conveying efficiency

1-channel elements

Standardelements

"Undercut" elements

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Filling Level of Conveying Elements

With decreasing pitch the free volume in the screw channel decreases, i.e. the filling level increases.

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Filling Level of Conveying Elements

• Normally conveying elements with a high pitch are installed below the feed inlet.

• The bulk material is compressed by the reduction in pitch in a downstream direction, i.e. as a result of reduction of the channel volume.

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Type of element

Mixing effect

Conveyingeffect

Kneadingeffect(shearing)

neutral

standard

X°

X°

Type ofelement

Mixing effect

Conveyingeffect

Kneadingeffect(shearing)

wide vs. narrow: standard vs. neutral:

Merit comparison for different Kneading Blocks

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Left-Handed Elements

product flow

p [bar] p [bar]

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Left-Handed Elements

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Principle of Operation of the Left-Handed Elements

Type of element Build-up effect

Right-handed screw elementwith low pitch

Neutral kneader block

Left-handed kneader block

Left-handed screw element

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1re li re li re li re li re li

3

2

Residence Time

Time (sec)

Tra

cer

0 50 100 150

1

3

2with left and righthand KB

with righthand kneading block

without kneading block

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Recognising Screw Element Materials

Q: Which features can be used to recognise

the material of a screw element if the material

code on the faces of the screw elements has

become illegible with cleaning?

A: refer Chapter 19, slide 18ff