Rotational molding

1. 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

2. What is
ROTATIONAL
MOLDING
?

3. a technology for manufacturing
hollow seamless articles

4. by
heating,
melting,
sintering

5. of powder

6. 1 mm
raw reactor powder of LLDPE

7. Problems

8. many
bubbles

9. c
r
a
c
k resistance
is low

10. overheating

13. to

14. Experimental
RESULTS

15. Set-up for
blending

16. Set-up for
sintering

17. Uniaxial
Rotomolding

18. PE powder
1 mm

19. after
10 min of heating
1 mm

20. 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.
P
i
ΔP = P
i
- P
atm
= 2T/r
P
atm
Dissolving the bubblesDissolving the bubbles

21. PE powder
+
SF (800 ppm)
1 mm

22. after
10 min of heating
1 mm

23. 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
42.5
o

24. PE powder: good free-flowPE powder: good free-flow PE powder: good free-flowPE powder: good free-flow
45
o

25. Example of
Gas Permeable Polymers:
Silicone Rubber: high flexibility of
the silicon-oxygen chain in siloxane
provides “openings” which are free
volume and permit gas diffusion, see
Zhang and Cloud (2006).

26. Gas Permeation

27. Siloxane – high flexible chainSiloxane – high flexible chain (Si-O-Si bond)
PEG – high flexible chainPEG – high flexible chain (C-O-C bond)

28. Gas Permeation of Polymers, BarrerGas Permeation of Polymers, Barrer
1
10
100
1000
10000
100000
1000000
LDPE SiliconePEG est.
N2
O2
CO2
H2O

29. PE powder
+
PEG (0.4%)
1 mm

30. PEG beads
after
10 min of heating
1 mm

31. PE powder + PEG (0.4%) PE powder + PEG (0.4%)
at 72at 72
oo
C: no free-flowC: no free-flow
PE powder + PEG (0.4%) PE powder + PEG (0.4%)
at 72at 72
oo
C: no free-flowC: no free-flow
70
o

32. PEG + Silica FumePEG + Silica Fume PEG + Silica FumePEG + Silica Fume

33. PE powder
+
PEG (0.4 %)
+
SF(800 ppm)
1 mm

34. after
10 min of heating
1 mm

35. PE + PEG(0.4%) + SF(800ppm)PE + PEG(0.4%) + SF(800ppm)
at 72at 72
oo
C: free-flow properties C: free-flow properties
PE + PEG(0.4%) + SF(800ppm)PE + PEG(0.4%) + SF(800ppm)
at 72at 72
oo
C: free-flow properties C: free-flow properties
60
o

36. PE powder
+
PEG+CA (0.4%)
1 mm

37. after
10 min of heating
1 mm

38. PE powder
+
PEG+CA (0.4%)
+
SF (800ppm)
1 mm

39. after
10 min of heating
1 mm

41. Silica
Fume

42. Novel PPA: PEG
+
Silica
Fume

43. Silica
Fume
PEG
+
Carboxylic Acids
+

44. 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.

45. Process comparison
Customer
Dust Collector
Blower
Bag
PE pellets
Cyclone
Sieves
Grinding
Head
Oversize
Particles
Powder
85-105
o
C
Source: Practical Guide to Rotational Moulding
by R Crawford & M Kearns
POWDERPELLETS
and
MICRO-PELLETS
Source: Gala Industries
Bag
Centrifugal Dryer
Extruder
PE Powder
Die Plate
PDV
Cutter
Process Water
Process Water
Pump
Water
Bath
190-210
o
C

46. Particle size distribution comparison.
0
10
20
30
40
50
60
70
0501061502122504255006007108501000
Particle Size, Micron
%

B
y

W
e
i
g
h
t
Powder MicroPellets
Ave = 300-350 µm
Ave = 550 µm

47. 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/m
3
cf. 0.34 kg/m
3
)
•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

48. Micro Pellet Tank Trial
20
25
30
35
40
45
50
C
y
c
l
e

T
i
m
e

(
m
i
n
s
)
Cook Time (min)Cool Time (min)
Cool Time (min) 17 16 16 17
Cook Time (min) 28 24 25 24
Powder Tank - 1Tank - 2Tank - 3
Meet requirements of tank standard impact testing with no ductile or brittle
failures using a 9.06kg drop dart @ 1.4m.
Oven machine, Tank Size = 2,250L, Shot Weight = 55kgs, Wall thickness = ~5mm, Colour = Merino.
> 12%

49. 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.

50. 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.

53. Process comparison
MICRO-PELLETS
WATER COOLING
Source: Gala Industries
Bag
Centrifugal Dryer
Extruder
Powder
Die Plate
PDV
Cutter
Process Water
Process Water
Pump
Water
Bath
190-210
o
C
Bag
Extruder
Powder
Die Plate
PDV
Cutter
125-135
o
C
Air Cooler
MICRO-PELLETS
AIR COOLING

54. Little things can make
BIG CHANGES

55. Cost Effective
patent pending

56. Acknowledgements:
Financial support:
the German Science Foundation
(Deutsche
Forschungsgemeinschaft).
Technical support
(PE powder samples):
ExxonMobil Chemical
SCG Chemicals