TU Berlin UniBw München
The Use of Silica-Fume and PEG to The Use of Silica-Fume and PEG to Enhance Sintering of LLDPE Powders inEnhance Sintering of LLDPE Powders in
Rotomolding ProcessRotomolding Process
What is ROTATIONAL MOLDING
?
a technology for manufacturing hollow seamless articles
a technology for manufacturing hollow seamless articles
by heating, melting,
sintering
by heating, melting,
sintering
of powderof powder
1 mm1 mm
raw reactor powder of LLDPEraw reactor powder of LLDPE
ProblemsProblems
many bubbles
many bubbles
crack resistance
is lowis low
overheating overheating
to
ExperimentalExperimental
RESULTSRESULTS
Set-up forSet-up for
blendingblending
Set-up forSet-up for
sinteringsintering
Uniaxial Uniaxial
RotomoldingRotomolding
PE powderPE powder
1 mm1 mm
after 10 min of heatingafter 10 min of heating
1 mm1 mm
If melt is in diffusion equilibrium with atmosphere gas in the bubble tend to flow outwards because of pressure difference ΔP until radius r of the bubble diminishes to zero.
PiPi
ΔP = Pi - Patm = 2T/rΔP = Pi - Patm = 2T/r
PatmPatm
Dissolving the bubblesDissolving the bubbles
PE powder+
SF (800 ppm)
PE powder+
SF (800 ppm)
1 mm1 mm
after 10 min of heatingafter 10 min of heating
1 mm1 mm
PE powder + SF (800 ppm): PE powder + SF (800 ppm): very good free-flowvery good free-flow
PE powder + SF (800 ppm): PE powder + SF (800 ppm): very good free-flowvery good free-flow
42.5o42.5o
PE powder: good free-flowPE powder: good free-flowPE powder: good free-flowPE powder: good free-flow
45o45o
Example of Gas Permeable Polymers:
Example of Gas Permeable Polymers:
Silicone Rubber: high flexibility of the silicon-oxygen chain in siloxane provides “openings” which are freevolume and permit gas diffusion, see Zhang and Cloud (2006).
Silicone Rubber: high flexibility of the silicon-oxygen chain in siloxane provides “openings” which are freevolume and permit gas diffusion, see Zhang and Cloud (2006).
Gas Permeation Gas Permeation
Siloxane – high flexible chainSiloxane – high flexible chain (Si-O-Si bond)
PEG – high flexible chainPEG – high flexible chain (C-O-C bond)
Gas Permeation of Polymers, BarrerGas Permeation of Polymers, Barrer
1
10
100
1000
10000
100000
1000000
LDPE Silicone PEG est.
N2
O2
CO2
H2O
PE powder+
PEG (0.4%)
PE powder+
PEG (0.4%)
1 mm1 mm
PEG beadsafter 10 min of heating
PEG beadsafter 10 min of heating
1 mm1 mm
PE powder + PEG (0.4%) PE powder + PEG (0.4%) at 72at 72ooC: no free-flowC: no free-flow
PE powder + PEG (0.4%) PE powder + PEG (0.4%) at 72at 72ooC: no free-flowC: no free-flow
70o70o
PEG + Silica FumePEG + Silica FumePEG + Silica FumePEG + Silica Fume
PE powder+
PEG (0.4 %)+
SF(800 ppm)
PE powder+
PEG (0.4 %)+
SF(800 ppm)
1 mm1 mm
after 10 min of heating
after 10 min of heating
1 mm1 mm
PE + PEG(0.4%) + SF(800ppm)PE + PEG(0.4%) + SF(800ppm)at 72at 72ooC: free-flow properties C: free-flow properties
PE + PEG(0.4%) + SF(800ppm)PE + PEG(0.4%) + SF(800ppm)at 72at 72ooC: free-flow properties C: free-flow properties
60o60o
PE powder+
PEG+CA (0.4%)
PE powder+
PEG+CA (0.4%)
1 mm1 mm
after 10 min of heating
after 10 min of heating
1 mm1 mm
PE powder+
PEG+CA (0.4%)+
SF (800ppm)
PE powder+
PEG+CA (0.4%)+
SF (800ppm)
1 mm1 mm
after 10 min of heating
after 10 min of heating
1 mm1 mm
Silica Fume
Novel PPA: PEG+
Silica Fume
Silica Fume
PEG +
Carboxylic Acids+
What are micro-pellets?
• Small regular oval shaped plastic granules with a diameter between 500-600µm.
• Produced from the same base material as powder, i.e. Qenos 711UV etc.
• Differ from powder by way of the manufacturing process and particle size distribution.
Process comparison
Customer
Dust Collector
Blower
Bag
PE pellets Cyclone
Sieves
GrindingHead
OversizeParticles
Powder
85-105oC
Source: Practical Guide to Rotational Mouldingby R Crawford & M Kearns
POWDERPELLETS and
MICRO-PELLETS
Source: Gala Industries
Bag
Centrifugal Dryer
Extruder
PE Powder
Die Plate
PDVCutter
Process Water
Process WaterPump
WaterBath
190-210oC
Particle size distribution comparison.
0
10
20
30
40
50
60
70
0 50 106 150 212 250 425 500 600 710 850 1000
Particle Size, Micron
% B
y W
eig
ht
Powder MicroPellets
Ave = 300-350 µm
Ave = 550 µm
IMPROVED ECONOMICS AND MORE OPTIONS FOR THE MOULDER
What are the benefits of micro pellets?Manufacturing Process• Consistent quality and size• Less contamination• Dust free during mould filling
Shape and Particle Size Distribution• Potential for faster cook times• Potential for lower peak internal air temperature• Greater bulk density (0.51kg/m3 cf. 0.34 kg/m3)• Improved flow (10 sec cf. 32 sec)• Potential for improved mechanical properties• Improved filling and definition of difficult to fill mould areas• Moulded parts with more uniform wall thickness• Maintained / improved surface finish
Other • Cheaper raw material
Micro Pellet Tank Trial
20
25
30
35
40
45
50C
ycle
Tim
e (m
ins)
Cook Time (min) Cool Time (min)
Cool Time (min) 17 16 16 17
Cook Time (min) 28 24 25 24
Powder Tank - 1 Tank - 2 Tank - 3
Meet requirements of tank standard impact testing with no ductile or brittlefailures using a 9.06kg drop dart @ 1.4m.
Oven machine, Tank Size = 2,250L, Shot Weight = 55kgs, Wall thickness = ~5mm, Colour = Merino.
> 12%
Rotomolding PPAs:Rotomolding PPAs: Silica Fume (SF): "Free-Flow" Agent.
PEG+SF: Densification & Processing Aid (D&PA).
PEG + Carboxylic Acids (CA): Advanced D&PA.
Novel Processing Additives: PEG + CA + SF.
Silica Fume (SF): "Free-Flow" Agent.
PEG+SF: Densification & Processing Aid (D&PA).
PEG + Carboxylic Acids (CA): Advanced D&PA.
Novel Processing Additives: PEG + CA + SF.
Extrusion PPAs:Extrusion PPAs: Silica Fume (SF): Thickening Agent.
PEG+SF+Anti-Oxydants: Processing Aid (PA).
PEG + Carboxylic Acids (CA): Advanced PA.
Novel Processing Additives: PEG + CA + SF.
Silica Fume (SF): Thickening Agent.
PEG+SF+Anti-Oxydants: Processing Aid (PA).
PEG + Carboxylic Acids (CA): Advanced PA.
Novel Processing Additives: PEG + CA + SF.
Process comparison
MICRO-PELLETSWATER COOLING
Source: Gala Industries
Bag
Centrifugal Dryer
Extruder
Powder
Die Plate
PDVCutter
Process Water
Process WaterPump
WaterBath
190-210oC
Bag
Extruder
Powder
Die Plate
PDVCutter
125-135oC
Air Cooler
MICRO-PELLETSAIR COOLING
Little things can make BIG CHANGES
Cost Effectivepatent pending
Acknowledgements:
Financial support: the German Science Foundation (Deutsche Forschungsgemeinschaft).
Technical support (PE powder samples): ExxonMobil Chemical SCG Chemicals
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