An Introduction to the Basics. Example Product.

ROTATIONAL MOLDING(1)An Introduction to the Basics

Example Product

Presentation Outline

IntroductionThe MaterialsThe MachinesThe MoldsThe MethodConclusion

Introduction

Also known as rotomolding or rotocasting

Process for manufacturing large, hollow, one-piece plastic

productsBest know for the manufacture

of tanks and toys (Little-Tykes)Suitable for small & complex

shapes

Introduction

Historical Development1850’s:Patent granted for rotomolding

principle1910’s:Method used for chocolate

products1940’s:Method used for vinyl plastisols1950’s:Invention of PE for the process1960’s:Rapid expansion in toy industry1970’s:Gradual expansion for technical

products1990’s:Significant improvement in process

control (at QUB)

Introduction

1500 Rotomolders around the world

Introduction

North American Market SegmentsPlayground

2%Industrial

16%

Materials Handling3%

Containers9%

Tanks18%

Others10%

Household2%

Toys40%

Introduction – The Process

Introduction

StrengthsSmall production runsLarge part capabilityLow tooling costs‘Stress-free” productsShort product development lead times

Introduction

WeaknessesSlow cycle timesLimited material choicesDifficult to automatePoor imageLow technology culture

The MaterialsOthers; 2%

LLDPE; 61%HDPE; 11%

XLPE; 8%

MDPE; 3%

LDPE; 2%

PVC; 13%

The MaterialsLow Zero Shear Viscosity is required to

aid in the flow of the polymer within moldMFI

Lower MFI resins – high strength productsHigher MFI – good surface finish and

surface detail

The MaterialsParticle shape and size is crucial to the

flow characteristics as the mold is rotating

Standard size is a 35 mesh powder (500 micron, 0.0197 inches)

The MaterialsDry-flow/Bulk-density characteristics

Dry-flow is the time it takes 100 grams of resin powder to pass through a funnel of

given dimensionsBulk-density is the quantity of undisturbed

powder than can fit inside a beaker of specified dimensions

Inversely proportional to each other

The Materials

The MaterialsOther Material

Foams○Post-process○In-processLiquid reactive polymersMicro-pelletsAdditivesCeramics

The MachinesRock-and-RollClamshellVerticalShuttleCarousel

FixedIndependent

Electric & Jacket

Rock-and-Roll Machines

Clamshell Machines

Vertical Machines

Shuttle Machines

Fixed Carousel Machines

Independent Carousel Machines

Electric Machines

The Machines

The “ARM” and “PLATE”

The MoldsMaterials

Steel○Mild○StainlessAluminum

○Cast○Machined○Plate

The MoldsAnatomy

Frame and SpiderTwo or more sections (with draft)Parting line with alignment featuresClamping hardware and pry-pointsVent (breather) tubesTexture and other featuresRelease agents

The Molds – Frame and Spider

The Molds - Mold Sections

The Molds - Parting Line

The Molds - Parting Lines

The Molds - Clamping Hardware

The Molds – Pry Points

The Molds - Vents

The Molds – Kiss-Offs

The Molds - Threads

The Molds - Inserts

The Method

.1Loading

.2Heating

.3Cooling

.4Unloading

The Method - LoadingA predetermined amount of resin is

loaded into the moldThe mold is closed after the flanges

have been cleared of resin particlesThe mold is secured shutRotate the mold to ensure no tools have

been left on the machine

The Method - HeatingRotate the mold in a high-temperature

environmentThe resin will always sit at the lowest point

of the cavity (powder pool)It will slowly coat the mold interior until all

the resin has meltedThe resin will then continue to densify as

the gap between the particles disappearsRemove the mold from the oven when the

powder has completely melted and densified

The Method - CoolingRotate the mold in a room temperature

environmentThis allows the layer of resin to cool and

solidifyWater can also be used, but care should

be exercised

The Method - UnloadingRemove the clamping system“Pry” open the moldLift the completed, hollow, one-piece

part from the mold.Repeat the cycle

The MethodThe concern

How do you really know when it is time to do the next step?

○When is the resin melted?○When is it cooled?In the early 90’s, QUB invented an

instrument that revolutionized process comprehension and control

○The Rotolog™

The Method – Rotolog™

Temperature sensors (4 type-K Thermocouples)

RF TransmitterRF Receiver and Signal ConditionerComputer Software

Real time monitoring of the temperatures

The Method – Rotolog™

The Method – Temperature Profiles

The Method – IAT Profile


We can thus observe:.AWhen powder first

sticks to the mold.BWhen the powder

has been consumed.CWhen optimal melt

sintering has occurred

.DWhen solidification is occurring

.EWhen the plastic separates from the

mold

A

B

C

D

E


•The Peak Internal Air Temperature (PIAT) is the key process control

parameter and is independent of all

other process variables (point C)

C

The Method Other important (QUB) developments

Pressurization (Dynamic Venting)Permanent temperature feedback (K-

Kontrol)RotoSim computer simulationWorldwide training seminars and consultingPPRC – Rotomolding division

Conclusion

Though in a state of infancy, Rotomolding offers unique advantages

over other plastics processesThere are endless opportunities for

research and developmentRotomolding has a very promising future,

more so than many competing processes

An Introduction to the Basics. Example Product.

Documents

Transcript of An Introduction to the Basics. Example Product.