BLOW MOULD DESIGN

1. BLOW MOULD DESIGN

2. 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

3. Applications of Blow Moulded Parts • 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.

4. Applications of Blow Moulded Parts

5. Blow Moulded Part Design Considerations • Design of a blow moulded bottle & other shapes requires consideration • of the following factors :- • Material to be blown • Size & Weight of the product & mould • Contours on the part • Surface texture & engraving • Sharp corners & straight edges • Blow opening available & locations • Parting lines

6. 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

7. A Blow Moulded Part : Terminology

8. Corner & Edge Rounding Wall thinning in corner areas should be considered, as it creates weaker areas in the moulding.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. Plastics materials for Blow Moulded Parts • 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

17. Blow Moulding Resins Grade

18. 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 Properties Property Unit Test MethodValue 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.

19. Blow Mould Design • Chapter – 2 • Design of Extrusion Blow Moulds • Extrusion Blow Moulding process • Extrusion Blow Moulds • Blow Mould Construction • Blow Mould Ancillary Elements • CAD/CAM for Blown-parts & Blow Mould Design • Mould Maintenance Program

20. 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 4). Mould opens and the moulding removed 2). The mould closes over the parison. 3). Compressed air inflates the soft plastic.

21. 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.

22. 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.

23. Parison Die Heads for Blow Moulding • Functions of a Parison Die-Head Unit :- • To form the melt into a parison • To maintain the melt at a constant temperature • To meter out the melt at a constant pressure and rate • To form a parison with a desired wall thickness Divergent Die-Head Convergent Die-Head

24. Parison Swell 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 :- In this case the parison balloons outwards from the die, & parison diameter becomes considerably larger than the die diameter. Diameter Swell % = { (D – F) / F } * 100 Weight Swell % = { (C – A) / A } * 100

25. 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).

26. 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).

27. Parison Programming device

28. A typical Blow Mould

29. 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 Recommended Shape of a Pinch-Off with Inserts A Good Weld at Pinch-Off

30. “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

31. 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.

32. Parts with Handle Bottom Blowing after spreading the Parison

33. Parts with Handle Needle Blowing the Parison

34. Neck Finishing of Blow-Moulded Parts

35. 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 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.

36. Venting Positions on a Blow Mould

37. Venting Positions on a Blow Mould

38. Venting of Blow Moulds Use of Venting Plugs Standard Plugs used for Venting Material: Brass & Aluminium

39. VENT CLEANER

40. 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 :- ----------------------------

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

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

43. 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-P20 pre-hardened steel is widely used. For corrosive resins, AISI-420 stainless steel. 4). Miscellaneous Materials : Zinc alloy (Kirksite)

44. Blow Mould Cooling • Cooling of a blow moulded part consists of 3-separate heat transfer mechanisms :- • Conduction of heat in the wall of part • Conduction of heat in mould wall • Convective transfer of heat in cooling fluid

45. Cooling Methods for a Blow Mould Blow Mould Half with cooling water channels

46. 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.

47. 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.

48. 3D Model of a Bottle designed using Autodesk Inventor software

49. 3D Model of a Blow Mould Cavity designed using Autodesk Inventor software

50. Machining sequence being generated using Pro/ENGINNER software