Blow Mould Design

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