Post on 01-Nov-2014
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.
Drums for chemical industries.
Bellow shaped shields & Double-Walled carrying cases.
Applications of Blow Moulded Parts
Applications of Blow Moulded Parts
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 :- --------------------
Press Size :- -------------------------------- Platen Size :- --------------------------------
Mounting Holes (Size) :- ----------------- Location :- ------------------------------------
Shut Height of Mould :- Max : --------------------- Min : ----------------------
Type of Blow :- ----------------------------- Blow Pin :- Dia ------------- Length ------------------
Parting Line Location :- -----------------------------------
Relief Requirements :- -------------------- Orientation of Part :- ----------------------
Pinch-Off areas :- -------------------------- Depth of Relief :- ---------------------------
Cavity Construction :- --------------------- Material :- -----------------------------------
Machined :- ---------------------------------- Cast :- ---------------------------------------
Model Required :- ------------------------- CAD :- ---------------------------------------
Type of Cooling :- ------------------------- Size, in/out connectors :- ---------------
Venting :- Parting Line-------------------- Within Cavity --------------------------------
Inserts :--------------------------------------- Secondary Action :- -----------------------
Cavity Finish :- ----------------------------- Texture :- -------------------------------------
Engraving :- --------------------------------- General Notes :- ----------------------------
View of a Closed Blow Mould, Ready to be loaded on the machine.
Moving Section Blow Moulds
Step-1Blowing the parison against the extended plug
Step-2Retracting the plug during the blowing operation
1). Aluminum alloy : Aircraft grade aluminum
2). Beryllium-Copper (Be-Cu) alloy
excellent thermal conductivity, corrosion-resistance
& mechanical toughness.
3). Steel : for blow moulds for PVC or engineering resins,
AISI-P20 pre-hardened steel is widely used.
For corrosive resins, AISI-420 stainless steel.
4). Miscellaneous Materials : Zinc alloy (Kirksite)
Materials for Blow Mould Construction
Cooling of a blow moulded part consists of 3-separate heat
transfer mechanisms :-
1) Conduction of heat in the wall of part
2) Conduction of heat in mould wall
3) Convective transfer of heat in cooling fluid
Blow Mould Cooling
Blow Mould Half with cooling water channels
Cooling Methods for a Blow Mould
External Cooling Methods for a Blow Mould
It is important to locate the cooling fluid entrance near to bottom of the mould & the exit at a higher level, to eliminate any air trapping.
Internal Cooling Methods for a Blow Mould
Venting of blow air to create turbulence inside the part.
Blowing with a cryogenic liquefied gas to quickly cool the inside of the part.
Blowing with a fine mist of water or ice.
3D Model of a Bottle designed using Autodesk Inventor software
3D Model of a Blow Mould Cavity designed using Autodesk Inventor software
Machining sequence being generated using Pro/ENGINNER software
Cleaning of Blow Moulds
1) The moulds used to produce PVC and PET bottles containers should always
have highly polished cavity surfaces. It is therefore best to polish them once
every two weeks.
2) The mould cavities used to produce PE containers should be sandblasted,
because it helps in venting.
3) With PVC material if venting is not proper, corrosion may result.
4) Mould cooling lines should be checked for corrosion & flow-restrictions.
Mould Maintenance Program
Guide pins and bushings should be replaced at least once
a year.
New guide pins & bushings will improve mould life &
prevent cavity mismatch.
Whenever mould is shut-down for any length of time, all
water-lines should be blown-out with compressed air
and all cavities should be coated with a protective
agent to prevent corrosion.
S.No. Product Details
1 Name Bottle for Juice Packing
2 Material HDPE
3 Capacity / Volume of Bottle
4 Wall Thickness of the part (mm) 0.75
5 Density (gm/cc) 0.94 - 0.96
6 Shrinkage (%) 2 - 5
7 Mould Temp (Deg C) 4 - 21
8 Blowing Pressure ((Kg/Sq Cm) 5 - 6
9 Projected Area (Sq Cm)
10 Weight (gms)
11 Required Clamping Force (Tonnes)
Mahine Details Mould Cooling System
Machine to be Used 17 Type of Cooling
12Clamping Force Available (Tonnes) 18 No. of Connectors
13 Maximum Day Light (mm)
14 Minimum Mould Height (mm) 19 Mould Lifting Arrangements
15 Platen Size (LengthxWidth) 20 Mould Size ( Height x Width x Length ) mm
16 Blow Pin Diameter (mm) 21 Mould Weight (Kg)
22 Remarks
Designing a Blow Mould for a given part
Designing a Blow Mould for a given part
Part designed for a specified Capacity (200ml) in Autodesk Inventor Software
Designing a Blow Mould for a given part
Part Drawing :- 2-D view generated from the 3-D solid model.
Designing a Blow Mould for a given part
Blow Mould designed in Autodesk Inventor Software
Designing a Blow Mould for a given part
Blow Mould Cavity Drawing, generated from the mould design.
Chapter – 3
Design of Injection Blow Moulds
Blow Mould Design
Injection Blow Moulding Process
Station 1:- This is the preform mould. Here, molten material is injected under low
pressure into the mould cavity, where it forms a parison around the core rod.
At this stage, the neck section is injection moulded to close tolerances.
After suitable conditioning, the moulds open and the parison is transferred on the
core rod to station-2.
Station 2 :- This is where the blow takes place.
The cavity of the mould defines the shape and finish of the container.
The parison is blown with air fed internally through the core rod.
As the blown plastic contacts the cold blow mould, the final moulding is produced.
The mould opens and the finished bottle is transferred on the core rod to station-3.
Station 3 :- Here, the bottle is stripped from the core rod for packing or filling.
Injection Blow Moulding Process
LDPE
HDPE
PP
PS
SAN
EVA
PVC
PC
PET etc.
Plastics Materials for Injection Blow Moulding
Injection blow moulds require :-
1). More complex mould engineering
2). Perform moulds
3). Blow moulds
4). Support tooling
5). Longer lead times for design & fabrication
Injection Blow Moulds
The outside configuration of the parison is formed by neck-ring
& the parison mould,
while the inside is formed by core-rod.
Parison Layout
The parison mould consists of two components :-
1). the body
2).the neck-ring.
Parison Mould
The blow mould forms the final shape of the container.
Injection Blow Moulds
The core-rod forms the internal diameter of the neck and parison,
when sitting in the parison mould.
Core Rods
1. Is cavity steel specified right for the part ?
2. Is type of plating specified ?
3. Is nozzle size correct ?
4. Is nozzle seat inserted or air gapped ?
5. Is heat isolation at neck ring or holding diameter required ?
6. Is special material required for neck ring ?
7. Are water ports located at right place ?
8. Is there a sufficient no. of water ports ?
9. Has heat treatment been specified ?
10. Is neck finish correct ? etc…..
Injection Blow Mould Design
Check-List
Chapter – 4
Design of Stretch Blow Moulds
Blow Mould Design
Injection Stretch Blow Moulding Process
Producing PET Preform / Bottle
PET Preforms
Preform Molds
Neck Finish on Performs
Design of Stretch Blow Moulds
Examples of Stretch Blow Moulded Parts
Injection Stretch Blow Moulding Process
Polyethylene-Terephthalate (PET)
Polyolefins (PE)
PVC
Typical Plastic Materials Used
PET Preforms
Gate-free preform.
Low preform eccentricity, no more than 0.10mm.
Low weight variation between cavities, +/-0.2g.
Low Acetaldehyde level.
Low preform temperature at exit to avoid preform scratches.
Preform Quality requirements
Preform Molds
Stretch Blow Mould
Stretch Blow Mould
Stretch Blow Mould
Neck Finish for PET Preforms