gravitrol ® extrusion control. 2 closed control loop: gravitrol ® by the loss in weight in the...
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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
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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