blow moulding process & barrier containers part 2 equipment

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Assocomaplast - Centro Direzionale Milanofiori - Palazzo F/3 - 20090 Assago - Milan - Italy - tel +39 02 8228371 - fax +39 02 57512490 - e-mail: [email protected] www.assocomaplast.org

Blow Moulding Process

& Barrier Containers

Part 2 Equipment

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• Feeding system for the granules, regrind and masterbatches

• Melting and homogenizing of the plastic in a single screw extruder

• blowing of the bottle

• cooling of the bottle

• calibration and de-flashing

• leak proof testing

Major process stages

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Extrusion blow moulding

– continuous extrusion

– intermittent extrusion Injection blow moulding Injection stretch blow

moulding

Blow moulding techniques

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Extrusion Blow Moulding – Wheel Machines

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Continuous extrusionblow moulding 1

Line with double station for Max. 24 cavities

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Blow Moulding Machine

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- Feeding system (volumetric, gravimetric, mixing), hopper

- Extruder: screw, barrel, adaptor

- (Filter screen-pack, filter changer)

- Head, parison control, die: mandrel, bushing

- Parison cutter

- Blow unit

- Mould(s)

- De-flashing unit

- On-line test unit (holes, top-load)

- Labelling (glueing, IML), printing (flaming, Corona)

Blow Moulding Line Equipment elements

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Die

Hot knifecutter

Blow pin

MouldParison

Die centeringadjustment bolts

Equipment set-up

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Equipment set-up

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Dosing and mixing units

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Dosing and mixing units

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Blow Moulding Line – Extruder

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Functions of the extruder:

- Convey the granules in the screw flight

- Compress the solid granule and remove the air

- Melt the granules

- Mix the melt, to make it as homogeneous as possible

- Produce the desired melt temperature

- Produce the desired pressure to have the melt flowing

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Typical extruder for blow moulding lines

- Normally with grooved barrel

- 3 zone screw or barrier screw with or without mixing elements

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Screw

D Screw diameter L Screw lengthq Flight angle (17.65) P PitchF Feeding zone depth H Metering zone depthA Feeding zone length/D C Compression z. depth/DM Metering z. length/D N Screw speed, rpm

Feeding zonezone

Compression zone

Meteringzone

P

Connectionto the motor

D

F H

L

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Typical 3-zone screw: D= 90 mm L/D= 25 Compression ratio: 2.0 to 2.5Length feed section: 10DLength compression section: 6DLength metering section: 9D

Typical barrier screw with mixing head:L/D: 20

Screw

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Screw 3

Multi-Purpose Barrier Screw for Grooved Barrels

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Shear & mixing elements

Mixing elements 2

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Screw 3

Multi-Purpose Barrier Screw for Grooved Barrels

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DISTRIBUTIVE (ananas, Saxton, Dulmage)

They divide and recombine flow streams

DISPERSIVE (UCC; cavity transfer mix, static mixer)

Cutting strains generate the reduction of particles of immiscible components

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Mixing elements

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Mixing elements 3

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Grooved zone

Cooling

Grooved barrel

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Filters – Screen pack – Filter Changer

old filter new filter

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- Spiders (PVC)

- Mandrel

- Spyral

Types of dies

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- Low cost

- Reduced external dimensions

- High precision with annular die gap

- Difficult centering

- Long time needed for color change

- Output depending

Mandrel die

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Standard die

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Multiple die

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Die design and polymer swell

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Die design and polymer swell

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Coextrusion dies for 3 layers

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Coextrusion die for 6 layers and wall structure

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2 layersPE-LD/PE-HD

3 layersPET/PET/PETPET/PA/PETPE-HD/R PE-HD /PE-HDPE-HD/Adhesive/PAPE-HD/Adhesive/EVOH

4 layersPE-HD/R PE-HD/Adhesive/PA or EVOH

State-of-the-art structure of

multilayer bottles

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5 layersPE-HD/adhesive/EVOH/adhesive/PE-HDPE-HD r PPEVOH or PA

6 layersPE-HD/R PE-HD/adhesive/EVOH/adhesive/PE-HDPE-HD or PPEVOH or PA

State-of-the-art structure of

multilayer bottles

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Radial flow head – Heart shaped melt flow

channels

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- Distance to exit on the back side of the mandrel is shorter than the one of the extruder side = lower pressure drop- Reduces parison bending- Melt parted in two (180°) for optimized distribution of thickness- Fusion lines on the opposite part of entry

Radial flow head – Heart shaped melt flow

channels

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Die mandrel can be centered by means of adjustment bolds.Poor centering leads to uneven wall thickness distribution,

resulting in poor bottle stiffness.

Die centering

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- No flexibility- Used for containers with special form (strong oval shape, square)

Die deformation

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Die deformation/Partial thickness control

(PWDS)

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- Programming parison thickness

through electronic system to optimize

container wall thickness and

performance

Parison thickness control

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Vertical mandrel movements modify the die gap thus the parison thickness (and its swell)

Parison thickness control

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- Blowing is done aside of the die- Blowing pin descends in to the neck opening (continuous extrusion lines, with or without neck calibration)

Blowing systems

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- Blowing pin is part of the mandrel (Uniloy equipments) intermittent, with neck calibration- Blowing pin replaced by a needle (carousel lines for aseptic containers or toys)

Blowing systems

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- Two blowing pins moving aside, used for flat articles with high widening ratio. One of the pin is the blowing pin.

Blowing systems

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- Blowing air needs high pressure

- Too high air pressure causes protrusions closed to the partition lines of the mold

- Too low pressure causes air trapping, rough surface and partition lines not homogeneous

- Pre-cooled air or liquid nitrogen can help reducing cycle time and increasing production

Blowing systems

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- Pre-blowing with open parison

- avoids parison collapse

- Pre-blowing with closed parison - reduces parison elongation - optimize mold filling - improve formation of partition lines (by reducing accumulation at the end of the lines contributes to control parison/container thickness - reduce blowing time for large containers

Blowing systems

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- Cold knives for HDPE (hot for PP)

- Tear through head movements (Uniloy lines and large containers)

- Tear through mold movements

Parison cut

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- Manufactured using aluminum alloys with high heat transfer- Inserts for de-flashing made of steel with low abrasion coefficient

Moulds

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Moulds 2 – Mould glossary

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Mould movements

- normally the mould moves aside of the die to avoid the descending parison stitching on the mould

Moulds 3

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Removal of the air from the mould cavity

The air can be removed from the mould cavity along the partition lines- through venting- through sand blasting (rough surface)

- Insufficient air venting causes opaque spots on the surface of glossy containers

Moulds 4

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Movements of the extruder instead of the mould- To avoid the parison stitching on the mould, the extruder raises up (technique used for large containers)

Moulds

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Bottle glossary

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Bottle glossary

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- The cooling time is the longest part of the production cycle- Well designed moulds have cooling channels and chambers- Recommended mould temperature is 15-30°C- Use of pre-cooled air is strongly suggested- Cooling units for medium and large containers are strongly suggested as well in general foe countries with hot climates- Polymer shrinkage must be take in consideration by mould design HDPE (< 2 mm): 0.02-0.035 mm/mm

Container cooling

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- Blowing in the neck: the parison has the same dimensions of the neck

(thread insert)

- Flashing (neck, bottom and handle) are removed by a device

constructed according to the container shape

- The flash pockets facilitate the removal and optimize the partition lines

De-flashing

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- Facilitate flashing removal and correct partition lines formation

- Flash pockets must force the material in the welding lines

Factors influencing de-flashing:

- pinch-off force

- pinch-off angle

- length of the pinch-off zone

- mould closing speed

De-flashing – Pinch-off zone and flash pockets

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De-flashing

For a good impact resistance fk = SK/SB ~ 1

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De-flashing unit

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Closing force must be: - sufficient to keep the mould closed during blowing

- sufficient to pre-cut the parison for an easy de-flashing

Mould closing systems

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3 plates unit

Joint unit for small dimension lines

Mould closing systems

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Accumulator system:

- Used for large dimensions containers

- Used for resins with low melt tension

- No need for mould movements

Blow moulding – Intermittent process

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Type ram + mandrel Type annular ram

Blow moulding – Intermittent process – Type of accumulators

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Production

Maintenance Processing conditions

Labeling of containers

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To run a trouble free production the operators must have a good knowledge of the equipment

- knowledge of the line elements and their function

- minimum and maximum performance, limitations

- calibration (specially for coex lines)

- databank per working conditions and formulations

- die selection in function of container shape, weight and spec

- die setting and thickness control through parison programming

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Temperature profiles

100

120

140

160

180

200

220

240

0 1 2 3 4 5 6

Zone

Te

mp

se

t °C

Flat

Reverse

Hump-Back

Ramp

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For maintenance and cleaning operations on head, die, screws and cylinder can only be used brass, bronze, copper or aluminum tools (mainly self-made)

REMEMBER: all scratches caused by steel tools remain for life!

Preventive and extraordinary maintenance should only be made by trained staff

Preventive maintenance plan must be prepared for the full year, in function of resins and additives used

Maintenance

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Preventive

- program according to manufacturer instructions- calibration of the screw speed- calibration of the heating elements- calibration of the extruder pressure transducers (by comparison) and thermometers (extruders and molds)- check of the emergency switches- check of the working pressure

Special

- Dismantling and cleaning the screw and the cylinder - Dismantling and cleaning the head and the die

Maintenance

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- Self adhesives labels, paper or plastic, applied off line

- Paper, plastic labels applied by gluing off line

- IML (In-Mold-Labelling), labelling in the mould, with labels pre-inserted in the mould by robots, using labels made of polymers compatible with the one used for the container and shoving very low shrinkage

- Printing in or off-line, using different technologies, after surface treatment, like flaming or Corona

Container labelling

blow moulding process & barrier containers part 2 equipment

Documents

assago milan

italy tel

polymer swelld

static mixercutting

grooved barrelsd

reduction of particles

low cost

immiscible components