GRAVITROL®

Extrusion Control

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Closed control loop: GRAVITROL®

By the loss in weight in the weigh hopper over a time interval GRAVITROL® measures the extruder output. The GRAVITROL® computer and the extruder drive module ensures that the extruder‘s output is always equal to the debit.

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computer …

… computer

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Applications:

• Blown film extrusion• Cast film extrusion• Sheet extrusion• Cable extrusion• Profile extrusion• …

All extrusion processes which allow to measure the extruder‘s throughput gravimetrically (flow fed extruders)

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• Different line speeds

Parameters, that cause problems without gravimetric extrusion control:

• Polymer density• Bulk density • Melt temperature• Polymer viscosity• Different conditioned polymer• Change in blend reciepe

• Tolerances due to screw and barrel wear

• Changes in screen pack condition• Changes of temperature• Varying extruder power

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This is GRAVITROL® able to do :

Ensures product quality and economic operation

GRAVITROL® is like „cruise control“ for extruders

• Conversion of an extruder into a gravimetric metering element with exactly defined mass throughput (accuracy of ± 0,5% )

• Ensures exact layer ratios• Simplifies ramping up and down a line• Smooth changeover from manual to automatic• Synchronizes the extruder with the haul-off (also while

ramping up and down a line) with an accuracy of ± 0,5%.

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Processes and product variables that can be controlled with GRAVITROL®:

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Increase in profit with GRAVITROL® by:

• Reduced labor costs and reduction of human-made errors• Automatic ramping up and down a line results in

o Processes optimised in timeo Final product is always in specification

• Use of material can be adjusted very close to the minimum tolerances

• Reduction of waste• The system learns the extruder‘s ramping curve by its own

(normally this takes labor and time and errors can be made)• Can be used instead of a melt pump (much more expensive);

except in fiber processes

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GRAVITROL® : typical application

Production of high energy cables:

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GRAVITROL® : typical application

Blown film extrusion

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Ramping up and down a line:

Typical extruder throughput curve not linear

m’

0Extruder speed in %

100

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Ramping up and down a line

When ramping up a line for the first time the system learns the extruder curve by creating a step ramp. The evaluated function will be saved to the GRAVITROL® computer memory and is base for the exact control of the extruder output.

Ext

rude

r sp

eed

time

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GRAVITROL® adjusts the extruder speed in a way that the throughput is always equal to the debit.

Throughput control with GRAVITROL®:

m‘[kg/h]

time

Extruder speed[min-1]

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Components of a GRAVITROL® system

EXB GRAVITROL® Computer

Features and function:

• 32-Bit Mikrocomputer (contains all necessary control

algorithms for an accurate extrusion control)

• Operator panel (for the operating personnel) with user-friendly

surface

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Components of a GRAVITROL® system

HGB weigh hopper

Features and function:• different hopper sizes for throughput up to 2.000 kg/h• High resolution load cell (resolution 1:1.000.000• DSP (Digital Signal Processor)

weigh module• material drain valve and door (depending on the model)• loading platform for vacuum reciever or swing gate• steep wall hopper for regrind material available

The function of the HGB weigh hopper can be replaced by either:

• a continuous gravimetric blender with weigh

downcomer

or

• a GUARDIAN ® gravimetric batch blender with HGC- weigh hopper

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Components of a GRAVITROL® system

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Components of a GRAVITROL® system

features and functions:

• 2 inputs for encoders

• 8 outputs for:1 EXL + max. 7 EXDormax. 8 EXD

• connection to Mini-Op via ethernet port.

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Example: GRAVITROL® system• Mono-extrusion• output control only• for the use of raw material (i. e. PE, PP, …) or pre-blend

EXBGRAVITROL®

Computer

EXD

HGBweigh hopper

Material conveyance

Extruder

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Example: GRAVITROL® system• Mono-extrusion• output control and haul-off control• for the use of raw material (i. e. PE, PP, …) or pre-blend

Line speed module

EXD

HGBweigh hopper

Material conveyance

Extruder

EXBGRAVITROL®

Computer

EXL

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Example: GRAVITROL® system• Co-extrusion with 3 extruders• output-, layer- and haul-off control• using X-series continuous gravimetric blenders

Line speed module

EXD

Material conveyance

Extruder

EXBGRAVITROL®

Computer

EXD

Extruder

Extruder

EXD

EXL

X-seriescontinuous gravimetric blender

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Example: simplified GRAVITROL® system with a GUARDIAN® blender and a HGC weigh hopper*• Mono-extrusion• output control• Installation follows the haul-off speed• use of a GUARDIAN® blender and a HGC weigh hopper

EXLOXLine speed encoder

EXD

HGC weigh hopperfor GUARDIAN®

GUARDIAN® gravimetric charge blender

Extruder

EXBGRAVITROL®

Computer

Customer supplied haul-off control +/-(or manual operation control)

*: This GRAVITROL® system represents a simplified low-cost solution which is often chosen in lines using gravimetric batch blenders.The haul-off has to be controlled manually by the operator. The GRAVITROL® system takes care of the correct extruder throughput referring to the current line speed. The system always follows the line speed.

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Data recording for preparing a quotation:

In this data sheet all necessary data concerning throughput and extrusion processare caught