Blow Mould Design Chapter – 1 Design of Blow Moulded Parts Applications of Blow Moulded Parts Blow Moulded Containers Blow Moulding Design Parameters Blow Moulded Part Design Considerations Corner & Edge Rounding Volume Neck, Spouts & other Openings Closure type & size Base Design Attachments Double Wall Construction Special Considerations for Bottle Design Plastics Materials for Blow Moulding
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Blow Mould Design
Chapter – 1 Design of Blow Moulded Parts
Applications of Blow Moulded Parts Blow Moulded Containers Blow Moulding Design Parameters Blow Moulded Part Design Considerations
Corner & Edge Rounding Volume Neck, Spouts & other Openings Closure type & size Base Design Attachments Double Wall Construction
Special Considerations for Bottle Design Plastics Materials for Blow Moulding
Packagings for Milk, Fluids, Medicines, Cosmetics etc.
Automotive fuel tanks, Oil Bottles, Air-Ducts, Seat-Backs etc.
Consumer Products like toys, housewares, sports goods etc.
Design of a blow moulded bottle & other shapes requires consideration
of the following factors :-
1) Material to be blown
2) Size & Weight of the product & mould
3) Contours on the part
4) Surface texture & engraving
5) Sharp corners & straight edges
6) Blow opening available & locations
7) Parting lines
Blow Moulded Part Design Considerations
Blow Moulded Containers
The majority of blow moulded part are containers ( a type of package ), serving
one or more of the following functions :-
1. To allow transport
2. To protect product integrity
3. As a marketing tool
4. To protect the environment from a spill
A Blow Moulded Part : Terminology
Corner & Edge Rounding
Wall thinning in corner areas should be considered, as it creates weaker areas in the moulding.
Volume Adjustments in Blow Moulded Parts
Volume adjustment can also be done by using changeable inserts in the mould, for side
walls. The depth of theses inserts may be changed for adjusting volume.
Neck, Spouts & other Openings
Each part must be designed with an opening, which may be utilized to blow it also.
Mostly this opening is utilized as neck or spout.
The important dimensions of a threaded neck finish are shown in fig.
Closure type & size
The closure, usually a cap or plug, is fitted to seal the bottle & allow dispensing of the contents.
Closure size can be marketing tools also.
Fig shows how a large diameter closure presents a more massive appearance.
Base Design
To avoid the rocking bottom phenomenon, in case of flat bottom parts, the typical solution is
to provide a doomed recess in the base, called push-up.
On stretch blown PET bottles/containers, the base must be spherical due to internal
pressure. Petaloid type base provides a self-standing container with several egg-shaped feet
on which it balances.
Attachments
Eyelets can be pressed into a part, in a flange extension, that can later be drilled or pressed-out to provide an attachment site for a pin or insert.
Double Wall Construction
Used in the packing or casing for objects such as tools & appliances.
Double wall geometry provides greater stiffness with high cushioning effects & impact resistance.
The most important structural & mechanical considerations in a bottle include :-
1.Vertical strength
2. Wall thickness uniformity
3. Highlight deflection
4. Push-up strength
5. Label considerations
6. Rigidity
7. Shape
8. Hot-fill capacity
If the bottle is subjected to vertical loadings, horizontal
corrugations or bellows on the part should be avoided.
Special Considerations for Bottle Design
Blow Mouldable Polyolefins LDPE : Low Density Polyethylene
LLDPE : Linear Low Density Polyethylene
HDPE : High Density Polyethylene
EVA : Ethylene Vinyl Acetate & Ethylene copolymers
PP : Polypropylene & Polypropylene copolymers
Plastics materials for Blow Moulded Parts
S.No. Resin Melt Index Range( gm / 10 min )
1 LLDPE < 1 to 22 LDPE < 1 to 23 HDPE < 1 to 24 EVA < 1 to 35 PP < 1 to 4 ** MFR
Melt Index describes the flow behaviour of a resin at a specified test temp (190 deg C), & a specified test weight (2,160 gm). Higher value means easy flow of the melt.
Melt Flow Rate describes the flow behaviour of Polypropylene resins at a specified test temp (230 deg C), & a specified test weight (2,160 gm).
Blow Moulding Resins Grade
HDPE : Blow Moulding Grade
High Density Polyethylene grades are suitable for general purpose extrusion blow moulding applications. Articles blown from these grades exhibit good stiffness. The resin offers good melt strength, ESCR and impact resistance & typically used for packaging of oil, vanaspati, general purpose containers, jerry can etc.
Physical Characteristics
Property Unit Test Method Value Density g/cc ASTM D 1505 0.956 MFI (2.16 kg) g/10 min ASTM D 1238 0.30
Typical PropertiesProperty Unit Test Method Value Tensile Strength at Yield MPa ASTM D 638 26 Elongation at break % ASTM D 638 550 Flexural Yield Strength MPa ASTM D 790 28.5 Flexural Modulus MPa ASTM D 790 900 Hardness Shore D ASTM D 2240 69 Vicat Softening Point °C ASTM D 1525 128
Processing Parameters• Melt temperature in range of 175 - 205oC are recommended. • Normally, temperature of 190 - 205oC will result in optimum ESCR properties.
Blow Mould Design
Chapter – 2
Design of Extrusion Blow Moulds
1. Extrusion Blow Moulding process
2. Extrusion Blow Moulds
3. Blow Mould Construction
4. Blow Mould Ancillary Elements
5. CAD/CAM for Blown-parts & Blow Mould Design
6. Mould Maintenance Program
1). The blow moulding cycle starts with the mould open. A hollow length of plastic, called a parison, is extruded down between the two halves of the mould.
2). The mould closes over the parison.
3). Compressed air inflates the soft plastic.
Blow Moulding Process
Fig-1
Fig-2
Fig-3
Fig-4
4). Mould opens and the moulding removed
Blow Moulding Process.
Blow moulding is usually the forming of a hollow object by “blowing” a thermo-plastic molten tube called, parison in the shape of a mould cavity.
Dies for producing Parison
After leaving extruder the molten plastic enter the parison-die-head, where it forms the parison, which emerges out from die-opening.
Divergent Die-Head Convergent Die-Head
Parison Die Heads for Blow Moulding
Functions of a Parison Die-Head Unit :-
1. To form the melt into a parison
2. To maintain the melt at a constant temperature
3. To meter out the melt at a constant pressure and rate
4. To form a parison with a desired wall thickness
Parison Swell
Diameter Swell :- In this case the parison balloons outwards from the die, & parison diameter becomes considerably larger than the die diameter.
Weight Swell :- It occurs during the mould open time, when the parison is dropping from the die. The parison may actually shrink in length & become heavier.
Diameter Swell %
= { (D – F) / F } * 100
Weight Swell %
= { (C – A) / A } * 100
Parison Programming
Parison Programming is the control of the wall-thickness, from top to bottom, of the parison as it emerges from the die-head during extrusion.
Parison Programming is utilized to obtain uniform wall thickness on the Blow moulded part, especially when part have profiles with different diameters.(varying blow-up ratios).
A Programmed Parison designed to fit a particular mould
Fig showing
a Programmed Parison with
heavier wall thickness
for greatest
expansion area
(large blow-up ratio).
Parison Programming device
A typical Blow Mould
Recommended Shape of a Pinch-Off with InsertsA Poor Weld at Pinch-Off
A Good Weld at Pinch-Off
The Pinch-Off should not form a groove, which would weaken the bottom of blown part.
Pinch-off Design
L = 0,5 to 1 x Parison wall thickness, DPD = 2 to 4 x Parison wall thicknessDL = 1 to 2 x Parison wall thickness,FW = large enough to hold maximum Parison “flash” after pinch-offD = 0 to 0,5 mm. Depending on required ease of trimmingDD = D + (0,5 x Parison wall thickness), FD = 1,5 to 2 x Parison wall thickness
“Double Dam” Pinch-off Design
Pinch-offs Alternate Designs
The parts of the mould that weld the ends,
and the interior portions of the parison
& also cut it or facilitate its removal.
Bottom Blowing after spreading the Parison
Parts with Handle
Needle Blowing the Parison
Parts with Handle
Neck Finishing of Blow-Moulded Parts
Pull-Up Neck Finishing
The neck is finished when blow pin is inserted just before the mould closes on the parison.
At the end of blow-cycle, but before mould opening, the blow pin moves upward to shear the inside diameter of the neck opening.
It is used for light weight & single use containers.
Ram-Down Neck Finishing
The blow pin is inserted into the mould after the mould closes on the parison. The blow pin moves downward to compress the plastic in the neck area & form the neck finish.
It is used when neck strength & rigidity are required.
Neck Finishing of Blow-Moulded Parts
Container Necks can be finished during blow moulding cycle, in a process called Pre-Finishing.
Venting Positions on a Blow Mould
Venting Positions on a Blow Mould
Venting of Blow MouldsUse of Venting Plugs
Standard Plugs used for VentingMaterial: Brass & Aluminium
Aluminum Plugs
D-dia T-thickness H-heightSlot Width
3.18 2.36 6.35 0.356
4.76 2..36 6.35 0.356Brass Plugs
D-dia T-thickness H-height Slot Width
3.18 2.36 6.35 0.254 0.356
4.76 2.36 6.35 0.254 0.356
4.76 3.96 7.92 0.254 0.356
VENT CLEANER
Blow mould design check list
Part Description :- -----------------------------------------------------------------------------
Part Number :- ---------------------------- Material :- -------------------------------------
Material Shrinkage :- -------------------- Wall thickness :- ----------------------------
Number of Cavitites :- ------------------- Center Line Distance :- --------------------