D1-S2-P2-A-Rheologically-optimized

02.06.2017 

Harburg-Freudenberger 

Maschinenbau GmbH 

Relaxed extrusion: A very 

important precondition for 

high quality treads. 

Dr.ir. Gerard Nijman 

June 16, 2017 

gerard.nijman@hf-group.com 

Content 

• Tread and sidewall profiles & a typical extrusion line lay out 

• Rubber rheology, extrudate swell and profile shrinkage 

• How to optimize an extrusion line with respect to rheology? 

– Extruder screw design 

• Temperature homogeneity 

• Feeding conditions 

– Balanced flow channels 

– Preformer and die-design preconditions 

– Relaxed extrusion / shrinkage conveyor design 

– Extrusion line control / dancer 

• How can HF help you? 

• Conclusions and outlook 

© Harburg-Freudenberger Maschinenbau GmbH 

All rights reserved 

Dr. Gerard Nijman: Relaxed Extrusion 

June 16, 2017 

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1

02.06.2017 

Functional tread with 5 different compounds 

Cap 

Cap 

Base 1 

Chimney 

Base 2 

Wing (l+r) 

Quintuplex Tread Technology: 

Cap : low RR / wet&dry grip compromise 

Base 1: low RR 

Base 2: low RR & tack cushion 

Wing : smooth transition to sidewall 

Chimney: conductivity 




June 16, 2017 

3 

Typical extrusion line layout for treads 

Quintuplex 

Cooling section 

Skiver, checkweigher and booking system 

Winding units 

Cross cutter 

& conveyors 

Measuring sections 

Feeders 

Head 

Take off and shrinkage 

conveyor 




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2

Line Speed (m/min) 

02.06.2017 

Extrusion related problems 

• Variation in thickness, linear weight and width of extruded tyre 

components 

• In line shrinkage, banana shrinkage and “after”shrinkage 

• Reduced productivity because of high rework amount and low 

booking speed 

Typical 

customer 

request 

Objective 

How can HF 

contribute? 

Reducing the Shrinkage in treads in the leaftruck from 

Extrusion to Tyre Building 

Shrinkage 

Present 

[mm] 

PCR Silica 10 - 12 0 - 2 

PCR Carbon black 5 - 6 0 - 2 

TBR 5-6 0 - 3 

Bias 10-12 0 - 6 

Target [mm] 



Example 1: 

Result of an extrusion line speed study 

35 

30 

25 

Line speed along the line 

The jump in speed over the 

dancer points to huge 

tension in the profile 

The line speed increase 

may point to a high 

dancer load 

20 

Silica tread extrusion 

15 

10 



In order to keep the profile within spec the operator / 

technologist needs to stretch the profile. The result is a 


line speed diagram as shown. 

June 16, 2017 

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3

02.06.2017 

Example 2: 

Analysis of poor capability 

Souce: Master Thesis Arnout Oldenburger , University of Twente (2014) 

• The diagram shows the meter weight of a particular tread size for PCR 

tyres (silica cap compound) produced over > 10 different runs. 

• It can be seen clearly that the uniformity between runs has potential to 

be improved. 

• Customers frequently ask extrusion line manufacturers how to solve 

these kind of problems. 

‣ The answer is: Understand the rheology of the rubber compounds 




June 16, 2017 

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Key questions 

• What is the nature of the consistency of rubber compounds and how 

does it influence the extrudate dimensions? 

• How to plasticize a rubber compound and how to deal with extrudate 

swell? 

• How can a better understanding of the rheology of a rubber compound 

contribute to a better extrusion process? 



Dr. Gerard Nijman: Relaxed Extrusion 8 

June 16, 2017 

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02.06.2017 

Rubber essentially is a system with polymer 

molecules, fillers and softeners and can be 

expressed as micro rheological models with fillers 

` 

… hindered by fillers 

(bound rubber) …. 

Reptational 

movement of 

polymer chains… 




June 16, 2017 

… which can form 

(weak) filler filler 

networks. 

Each compound has its own extrudate swell 

behaviour 

The extrudate swell factor depends on 

• molecular weight (distribution) of the 

applied polymers 

• type of filler 

• filler loading 

• existence of a filler filler network 

• die land length 

• compound temperature 

Well silanised silica compounds show a 

high extrudate swell, higher than 

traditional carbon black compounds 




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What happens if s the extrudate is pulled out 

of the die? 

• Polymers are stretched / oriented during extrusion. 

• After leaving the die the polymers are “suddenly” free to move 

• They tend to return to their “chaotic” stage (= stage of max entropy) Melt 

elasticity 

• Extrudate swell may be hindered in case the extrudate is pulled out of the dieopening. 

‣ This means profile shrinkage as soon as the tension in the profile is released (at 

latest at the tyre building machine) 




June 16, 2017 

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The answer is relaxed extrusion: 

Picture removed) 

Different swell factors across the section 

may lead to waviness pulling necessary 

Relaxed (l) vs pulled (r) extrusion conditions 

The die opening should be designed 

such that the extrudate swell behavior 

of the compound is “completely” 

obeyed. 

Tension in the downstream should be 

avoided 




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02.06.2017 

Preconditions for a relaxed extrusion 

process 

1. Thermally homogeneous extrudate proper screw design 

2. Balanced flow channels no velocity gradient across the extrusion 

head outlet openings 

3. No starvation in extruder feeding optimized intake behavior and 

constant rubber feed strip dimensions 

4. Preformer and final die design with front or back relief to reduce 

differences in flow resistance across the die opening 

5. Optimal settings of the shrinkage conveyor 

6. Dancer controllers which does not put an additional load on the profile 




June 16, 2017 

1) Screw design: 

Performance Triangle for the Extrusion Process 

Output 

Operating point 

Temperature 

Homogeneity 

Operating point depends on: 

-Product: Material Properties, Back Pressure 

-Process Setting: TCU-settings, Pin Configuration, Screw Speed 

-Machine: Screw Design, Flow Channel 




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02.06.2017 


Theoretical backgrounds: homogeneity 

Building of a cold core in the screw channel: Reason for insufficient 

appearance 

v channel 

v circular 

v rotat.speed 

v circular 

active flight 

melt pool 

conveying direction 

cold core 

(non sheared material) 

contact to the barrel 

passive flight 

The cold core, which is the 

result of the shear flow in the 

screw channel and the high 

gradient in viscous heating, 

needs to be distributed into the 

„hot melt“ pool, e.g. by pins and 

/ or mixing segments in the 

screw design 




June 16, 2017 

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Example: Staggered flights 

Improved distributive mixing through pin screw with 

staggered and normal flights 




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02.06.2017 

2) Flow channels 

in a quintuplex extrusion aggregate 




June 16, 2017 

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2) Flow channels: 

Modular Tooling 

Single cavity opening 

Lateral restrictors for 

restricting the width of 

the opening 

flow divider 

humps for 

balancing of 

the opening 



Dual cavity opening 


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02.06.2017 

2) Flow channels: 

Balancing the flow with CFD technology 

Outlet velocity gradient 

Flow channel geometry 

Pressure lines 

• The design of flow channels is 

based upon CFD simulations 

• During wet commissioning a 

fine tuning of the flow balance 

is done. 

• Even with short flow paths HF 

is able to fully balance the flow 

• Important precondition for high 

process capability is fulfilled 

• Therefore compact head design 

with low volume flow channels 


All rights reserved June 16, 2017 


3) Extruder feeding: 

Feeder with recipe based control (loop or balancer) 

Dancer control 

Feed conveyor 

(Intralox or textile belt) 

Hold down roller 

Chalk marker 

Metal detector 



Extrusion Lines from HF 

20 

10

02.06.2017 

3) Extruder feeding 

Feed roll 

Driven feed roll: 

• With hardened surface 

• Easily adjustable scraper 

out of special bronze 

• suitable for liquid 

heating/ cooling 

• Hinged parallel 

to the infeed section 

Spiral undercut 

An extruder is starved fed when a 

additional feed strip would lead to 

a higher output. 

Starved feeding means pulsation: 

quality loss due to (small) feed 

strip variations. 




June 16, 2017 

4) Preformer and final die design: 

Typical tooling configuration for tread profiles 

Back relieved for 

better local flow 

final die 

profile 

preformer 

flow channel 




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02.06.2017 

5) Settings of the shrinkage conveyor: 

Extrudate swell, shrinkage and after shrinkage 

• The profile needs to be extruded as tension free as possible. Allow the 

profile to swell as much as possible 

• The potential max swell can be best obtained with a rectangular die 

opening. 

• Tension means shrinkage. The less tension in the profile the less 

shrinkage can be expected. 

• If pulling is necessary to avoid waviness of the profile the final die 

needs to be optimized, i.e. back / forward relieve 

• Remaining tension needs to be fully eliminated by means of the 

shrinkage conveyor. No shrinkage over the first dancer 

• If a profile is put in the leaf truck with tension after-shrinkage may 

occure. 




Down stream optimization 

• The take away conveyor (with take off roll) pulls the profile gently out 

of the head 

• Profile tension needs to be fully relaxed on the shrinkage conveyor 

• The dancer after the shrinkage conveyor is a good indicator of 

remaining tension. 

• The linear scale shall measure the weight of the final profile. 

• Pulling or pushing throughout the downstream shall be avoided. Only 

temperature shrinkage is allowed. A good indication is to mark the 

tread at the shrinkage conveyor with 500 mm and to follow this 500 

mm marking throughout the cooling section. 



12

Conveyor speed 

02.06.2017 


The hot section downstream just after the aggregate 

Incline conveyer to 

cooling section 

Meter weight scale 

Shrinkage conveyor 

(with colour markers) 

front edge of 

the die 

Profile 

scanner 

Dancer 

controller 

Take off 

conveyor 




June 16, 2017 

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Line speed setting (for relaxed extrusion) 

• Line speed = winding speed (or speed just before skiver) 

• When idle: The line speed is basically the same throughout the line except of 

• Take off speed 

• Shrinkage conveyor 

• The dancer load shall be as low as possible contactless dancers 

• Shrinkage setting: 

1 

3 

If the belt speed of linear scale = line 

speed of the last shrinkage conveyor 

then relaxed extrusion. 

2 

1: Adjustable shrinkage 

2: Mechanical shrinkage 

3: NO shrinkage allowed 

Along the take off, shrinkage and linear weight conveyor belt 




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13

Line speed (m/min) 

02.06.2017 

6) Dancer controller: 

Unit with adjustable load 

5 

4 

6 

3 

2 

1 Counterweight 

2 Lifting cylinder 

3 Rolling diaphragm 

cylinder 

4 Toothed rack 

5 Swivel arm 

6 Dancer roller 

KR0I51VS 

1 

Without rubber the dancer controller should be balanced 

by the counterweight. 

The recipe based dancer load with profile is given by the 

rolling diaphragm cylinder and should be as low as 

possible to avoid stretching. 




June 16, 2017 

The result: Extrusion line speed study with 

relaxed extrusion conditions 

30 

25 

20 

15 

10 

5 

Relaxed 

extrusion 

Pulled extrusion 

0 

The cooling line is 

between incline and 

decline conveyor 

After-shrinkage of treads 

(silica) from leaf-trucks: 

-Pulled extrusion: > 10 mm 

-Relaxed extrusion: < 2 mm 




June 16, 2017 

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02.06.2017 

How HF can assist you to achieve the best quality 

New projects 

• Profile and compound based extrusion line design 

• Optimal design of flow channels matching the profiles 

• Screw design based on laboratory trials of your compounds 

• Training and assistance in running in new profiles 

Existing extrusion lines 

• Common assessment of the current process: 

– Line speed study 

– Shrinkage study 

– Optimization of line settings 

– Training on site with respect to preformer and die-design 

• Retrofit projects towards relaxed extrusion (a.o. new screw geometry) 




Summary & Conclusions 

• Tyre component extrusion problems like shrinkage and varying profile 

dimensions have their origin in the morphology of rubber compounds. 

• Polymer molecules are stretched due to high shear rates in flow 

channels, preformers and final die´s. After leaving the die the polymer 

molecules strive to come back into their original state, relieving their 

stresses. 

• In pulled extrusion process this stress relieve is hindered which results 

in profile tension. 

• By adhering to the rheological nature in die-design the amount of 

remaining tension in the profile is minimal Relaxed extrusion 

conditions. 

• Both extrusion line design and control need to be based on the 

principle of avoiding any profile tension 

‣ HF can help you improving your processes 




June 16, 2017 

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D1-S2-P2-A-Rheologically-optimized

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