BLOW MOULD DESIGN Chapter 1 Design of Blow

BLOW MOULD DESIGN

Chapter – 1 Design of Blow Moulded Parts v v v Applications of Blow Moulded Parts Blow Moulded Containers Blow Moulding Design Parameters Blow Moulded Part Design Considerations Ø Corner & Edge Rounding Ø Volume Ø Neck, Spouts & other Openings Ø Closure type & size Ø Base Design Ø Attachments Ø Double Wall Construction Special Considerations for Bottle Design Plastics Materials for Blow Moulding

Applications of Blow Moulded Parts Ø Packagings for Milk, Fluids, Medicines, Cosmetics etc. Ø Automotive fuel tanks, Oil Bottles, Air-Ducts, Seat-Backs etc. Ø Consumer Products like toys, housewares, sports goods etc. Ø Drums for chemical industries. Ø Bellow shaped shields & Double-Walled carrying cases.

Applications of Blow Moulded Parts

Blow Moulded Part Design Considerations 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 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.

Special Considerations for Bottle Design 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.

Plastics materials for Blow Moulded Parts Blow Mouldable Polyolefins Ø LDPE : Low Density Polyethylene Ø LLDPE : Linear Low Density Polyethylene Ø HDPE : High Density Polyethylene Ø EVA : Ethylene Vinyl Acetate & Ethylene copolymers Ø PP : Polypropylene & Polypropylene copolymers

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 Density MFI (2. 16 kg) Unit g/cc g/10 min Property Tensile Strength at Yield Elongation at break Flexural Yield Strength Flexural Modulus Hardness Vicat Softening Point Test Method ASTM D 1505 ASTM D 1238 Typical Properties Unit Test Method MPa ASTM D 638 % ASTM D 638 MPa ASTM D 790 Shore D ASTM D 2240 °C ASTM D 1525 Value 0. 956 0. 30 Value 26 550 28. 5 900 69 128 Processing Parameters • Melt temperature in range of 175 - 205 o. C are recommended. • Normally, temperature of 190 - 205 o. C 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

Blow Moulding Process Fig-1 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. Fig-3 Fig-2 Fig-4 2). The mould closes over the parison. 4). Mould opens and the moulding removed 3). Compressed air inflates the soft plastic.

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.

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 Divergent Die-Head Convergent Die-Head

Parison Swell Diameter Swell : - In this case the parison balloons outwards from the die, & parison diameter becomes considerably larger than the 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 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

Pinch-off Design The Pinch-Off should not form a groove, which would weaken the bottom of blown part. A Poor Weld at Pinch-Off A Good Weld at Pinch-Off Recommended Shape of a Pinch-Off with Inserts

“Double Dam” Pinch-off Design L = 0, 5 to 1 x Parison wall thickness, DPD = 2 to 4 x Parison wall thickness DL = 1 to 2 x Parison wall thickness, FW = large enough to hold maximum Parison “flash” after pinch-off D = 0 to 0, 5 mm. Depending on required ease of trimming DD = D + (0, 5 x Parison wall thickness), FD = 1, 5 to 2 x Parison wall thickness

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.

Parts with Handle Bottom Blowing after spreading the Parison

Parts with Handle Needle Blowing the Parison

Neck Finishing of Blow-Moulded Parts

Neck Finishing of Blow-Moulded Parts Container Necks can be finished during blow moulding cycle, in a process called Pre-Finishing. Pull-Up Neck Finishing Ram-Down 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. 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 for light weight & single use containers. It is used when neck strength & rigidity are required.

Venting Positions on a Blow Mould

Venting Positions on a Blow Mould

Venting of Blow Moulds Use of Venting Plugs Standard Plugs used for Venting Material: Brass & Aluminium Aluminum Plugs D-dia T-thickness H-height Slot Width 3. 18 2. 36 6. 35 0. 356 4. 76 2. . 36 6. 35 0. 356 Brass Plugs D-dia T-thickness H-height Slot Width 3. 18 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 : - ----------Pinch-Off areas : - ------------- Orientation of Part : - -----------Depth of Relief : - -------------- Cavity Construction : - ----------Machined : - ----------------- Material : - -----------------Cast : - -------------------- Model Required : - ------------Type of Cooling : - ------------Venting : - Parting Line----------Inserts : -------------------Cavity Finish : - --------------Engraving : - ----------------- CAD : - -------------------Size, in/out connectors : - -------Within Cavity ----------------Secondary Action : - -----------Texture : - ------------------General Notes : - --------------

View of a Closed Blow Mould, Ready to be loaded on the machine.

Moving Section Blow Moulds Step-1 Blowing the parison against the extended plug Step-2 Retracting the plug during the blowing operation

Materials for Blow Mould Construction 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-P 20 pre-hardened steel is widely used. For corrosive resins, AISI-420 stainless steel. 4). Miscellaneous Materials : Zinc alloy (Kirksite)

Blow Mould 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

Cooling Methods for a Blow Mould Half with cooling water channels

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 v Venting of blow air to create turbulence inside the part. v Blowing with a cryogenic liquefied gas to quickly cool the inside of the part. v Blowing with a fine mist of water or ice.

3 D Model of a Bottle designed using Autodesk Inventor software

3 D 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 ü Guide pins and bushings should be replaced at least once a year. ü New guide pins & bushings will improve mould life & prevent cavity mismatch. ü 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.

Designing a Blow Mould for a given part 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) 5 Density (gm/cc) 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) 0. 94 - 0. 96 Machine to be Used 17 Type of Cooling 12 Clamping Force Available (Tonnes) 18 No. of Connectors 13 Maximum Day Light (mm) 14 Minimum Mould Height (mm) 19 Mould Lifting Arrangements 15 Platen Size (Lengthx. Width) 20 Mould Size ( Height x Width x Length ) mm 16 Blow Pin Diameter (mm) 21 Mould Weight (Kg) 22 Remarks Mahine Details 0. 75 Mould Cooling System

Designing a Blow Mould for a given part Part designed for a specified Capacity (200 ml) 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.

Blow Mould Design Chapter – 3 Design of Injection Blow Moulds

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

Plastics Materials for Injection Blow Moulding ØLDPE ØHDPE ØPP ØPS ØSAN ØEVA ØPVC ØPET etc.

Injection Blow Moulds 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

Parison Layout The outside configuration of the parison is formed by neck-ring & the parison mould, while the inside is formed by core-rod.

Parison Mould The parison mould consists of two components : - 1). the body 2). the neck-ring.

Injection Blow Moulds The blow mould forms the final shape of the container.

Core Rods The core-rod forms the internal diameter of the neck and parison, when sitting in the parison mould.

Injection Blow Mould Design Check-List 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…. .

Blow Mould Design Chapter – 4 Design of Stretch Blow Moulds

Design of Stretch Blow Moulds ØInjection Stretch Blow Moulding Process ØProducing PET Preform / Bottle ØPET Preforms ØPreform Molds ØNeck Finish on Performs

Examples of Stretch Blow Moulded Parts

Injection Stretch Blow Moulding Process

Typical Plastic Materials Used v Polyethylene-Terephthalate (PET) v Polyolefins (PE) v PVC

PET Preforms

Preform Quality requirements v Gate-free preform. v Low preform eccentricity, no more than 0. 10 mm. v Low weight variation between cavities, +/-0. 2 g. v Low Acetaldehyde level. v Low preform temperature at exit to avoid preform scratches.

Preform Molds

Stretch Blow Mould

Stretch Blow Mould

Stretch Blow Mould

Neck Finish for PET Preforms