Rotational Molding(2) An Introduction to the Basics.

Rotational Molding(2)An Introduction to the Basics

The Use of Silica-Fume and PEG to Enhance Sintering of LLDPE Powders in

Rotomolding Process

What is ROTATIONAL MOLDING

?

a technology for manufacturinghollow seamless articles

a technology for manufacturing hollow seamless articles

by heating,

melting, sintering

by,heating

,melting sintering

of powderof powder

to

Dissolving the bubbles

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

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 chain (Si-O-Si bond)

PEG – high flexible chain (C-O-C bond)

Gas Permeation of Polymers, Barrer

1

10

100

1000

10000

100000

1000000

LDPE Silicone PEG est.

N2

O2

CO2

H2O

PEG + Silica FumePEG + Silica Fume

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 andMICRO-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 sizeLess contaminationDust free during mould filling

Shape and Particle Size DistributionPotential for faster cook timesPotential for lower peak internal air temperatureGreater bulk density (0.51kg/m3 cf. 0.34 kg/m3)Improved flow (10 sec cf. 32 sec)Potential for improved mechanical propertiesImproved filling and definition of difficult to fill mould areasMoulded parts with more uniform wall thicknessMaintained / 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