3. Blow moulding process

Working Principle, advantage, application

1. BLOW MOULDING
BY
M. PEER MOHAMED
(Manager)

2. BLOW MOULDING
A process to Produce Hollow Products like bottles,
containers, jars and jerrycans from thermoplastics.
Advantages
 Moulding extremely irregular (reentrant) curves
 Low stresses in the product
 Possibility of variable wall thickiness
 Use of polymers with high chemical resistance
 Favourable processing costs
Required pressure levels of 25 to 150 psi and with
some resins 200 to 300 psi. But Injection Moulding requires
2000 to 30,000 psi and hence development of high internal
stresses.

3. Materials Used
Small parts, under 5 litres,
 Polyolefines (LDPE,HDPE,PP )
 polyvinyl Chloride (PVC)
 Polyacrylonitrile (PAN)
 Polystyrene (PS)
 Styrene Acrylonitrile (SAN)
   Polyester (Saturated , PET)
Large parts, over 5 litres including technical parts,
  Poly olefines (HDPE / PP)
 Polycarbonate (PC)
 Polyacetal (POM)
 Polyamides (PA)
 Polyvinylidene Fluoride (PVDF) 

4. TYPES OF BLOW MOULDING
1.     Extrusion Blow Moulding  (EBM) which pricipally  
   uses an unsupported parison  (75% usages)
2.     Injection Blow Moulding (IBM) which principally 
uses a preform supported by a metal core pin 
(25%  usages).
3.    Stretch Blow Moulding either EBM or IBM to 
obtain bioriented products.
 

5. Extrusion Blow Moulding
Extruding a parison and Blowing the same.
Machinery
1. An Extruder
2. A die head and
3. A Blow Mould
Process
 Melting the Plastics in an Extruder.
 Forming the parison (A hot plastics tube).
 Clamping the two mould halves around the parison and
keeping closed.
 Inflating the parison inside the Blow (female) mould.
 Cooling of the expanded parison
 Opening the mould and ejecting the product.

7. Advantages
 High rate of production.
 Low tooling costs.
 Incorporation of blown handle ware.
 A wide selection of machine manufacturers.
 Disadvantages
 Higher Scrap Rate.
 Use of recycled scrap.
 Limited wall thickness control.

9. Few Points
 The die head can have one or more openings and hence one or
more parison can be extruded.
 The size and weight of the product dictates whether an
accumulator is required or not.
- Usually a blow pin is located opposite the pinched end of the
tube and compressed air inflates the parison.
 The compressed air can enter through (1) the extrusion die
mandrel or (2) through a blow pin or (3) through blowing
needles that pierce the parison.
 The wall distribution and thickness of the blown part are
controlled by parison programming, the blow ratio and part
configuration.
 The mold clamping can be hydraulic and/or toggle.
 For cooling Co2 systems, air chillers can be used.

10. Parison Programming
 By Electronic Parison Programming.  (Orifice modulation 
method) in which the die is fitted with hydraulic positioner 
that allows positioning of the inside  die diameter during 
parison drop.  The OD to ID relationship of the tapered die 
orifice  opening  is  versed  in  a  programmed  manner  to 
increase or decrease the parison wall thickness.
 Parison Swell
  After leasing the die, the melt – which has been under 
shear pressure – undergoes relaxation that causes cross-
sectional deformation or swell which is called as parison 
swell.

11. Average parison swell for few commodity plastics

Plastics Swell, present
HDPE (Phillips) 15 - 40
HDPE (zeigler) 25 - 65
LDPE 30 - 65
PVC (rigid) 30 - 35
PS 10 - 20
PC 5 - 10

12. Pinch-Off
The pinch-off is the very critical part in a Extrusion
Blow Mould where the parison is squeezed and
welded together requiring good thermal
conductivity for rapid cooling and good toughness
to ensure long production runs.

Types
1.Double angle pinch-off with 45 angles and 0.010 in
land.
2. Double angle shallow pinch-off with 15 angles and
0.010 in land.
3. Pinch-off with a dam.

13. Parison Blowing
Air is used to blow the parison tube against the mold
walls. It does 3 functions
- It expands the parison against the mould.
- Exerts pressure on the expanded parison to
product surface details.
- Aids in cooling the blown parison.
 

16. HORIZONTAL ROTARY WHEEL
 Uses continuously extruded parisons
 The moulds are mounted and indexed to
the extrusion head where the moulds
pickup the parison and transfer it to a
second station for the introduction of a
pin to blow the bottle.
 Multiple moulds are mounted on a large
wheel and one extruder and one parison
feeds the moulds.
 

17. VERTICAL ROTARY WHEEL
 Uses continuously extruded parisons
 Uses one extruder with multiple moulds
 The moulds pick the parison and moves around
the axes of the wheel to blow the container,
cool it and discharge it.
 The continuously extruded parison run like a
tube and not cut individually for moulds.
 

18. 3.SHUTTLE CONTINUOUS EXTRUSION
 The extruder and parison head are located in
the center and the moulds are mounted to
each side.
 The moulds shuttle to the parison, pick off
the parison and move back to their original
position.
 This method led to the development of
calibrated neck finish otherwise known as
compression moulded neck finish.
 Suitable for processing of PVC

19. INTERMITTENT EXTRUSION
 Uses a reciprocating screw extruder similar in
operation to injection moulding.
 The extruder melts and accumulates molten resin
at the end of the barrel while the screw retracts to
allow for this accumulation of plastic. The
moulds are mounted on a platen that only opens
and closes and discharges the bottle. The screw
moves forward and forces the plastics through a
manifold to several extrusion heads as
described above to form parisons for various
moulds. This method provides high speed
production from a single machine. By placing the
blow pin in the centre of the extrusion head
bottleswith a calibrated neck finish are produced.

 This method is very suitable for polyolefins.
 

20. INJECTION BLOW MOULDING
 Injecting a preform and Blowing the same.
Process Steps
 Hot melt in exact amounts is injected through an
injection moulding machine nozzle into one or more
preform cavities. Hot liquid is circulated through
mould heating channels around the preform cavity
and the required preform temperature is achieved.
 The two part mold opens and the core pin carries
the hot plastic to the second stage blow mold station.
 Upon mold closing, air is introduced via the core pin
and the platic blows out and contacts the mold
cavity surface.
 The product cools and the blow mould opens and
the product is ejected.

23. Advantages
1.   Bottle necks of varying shapes, sizes and wall
thickness can be precisely molded,Free of
flash.
2.   The wall thick nesses of a hollow body can be
predetermined exactly.
3.   There is no seam on the bottom.
4.  There is no regrind to contend with, other than
that generated on state-up and rejected parts,
because there is no neck on bottom trim.
5.It can be used to blow mold almost any type of
plastics that can be injection molded.

24. Disadvantages
 
1.  High change-over costs from one part to
another. This is caused by the largenumber of
molds and core pins required.

2.    Size limitations on parts which can be made by
blow molding.

3.    Tooling costs are almost double that of
extrusion blow molding.

25. STRETCH BLOW MOULDING
       Biaxial Orientation Blow Moulding.
       The container is stretched radially by the blow
air and vertically by a mechanical stretch rod.
Advantages
-         Better Strength
-         Better Clarity
-         Increased Impact Strength
-         Improved gas and water vapour barrier
-         Reduced Creep

26. Materials used
 PET PAN
PVC PP
ABS ACETALS
PS
Machine Categories

(i)      In-line machines
(ii) Two-stage machines

27. Inline machines
In this process an extruded or injection moulded
parison passes through conditioning stations which
bring it to the proper orientation temperature and then
stretched and blown in a final stage blow mould.

Advantages
1.    Heat history is minimized (important for heat-
sensitive materials like PVC and PET )
2.    The preform can be programmed for optimum
material distribution when maintained under
continuous control.

28. Two-stage machines
In this process the extruded or injection moulded
preforms that have been cooled are conveyed through an
oven which reheats them to the proper orientation-blow
temperature.
Advantages
1.    Minimized scrap production
2.    Improved thread finish
3.    Higher output rates
4.   The capability to stockpile preforms, eliminating
dependency between preform and bottle machinery.

29. TYPES OF STRETCH BLOW MOULDING
       Injection Stretch Blow Moulding.
       Extrusion Stretch Blow Moulding.

EXTRUSION STRETCH BLOW MOULDING
•         Suitable for processing of PVC, PET.
Process
         Extruding a parison.
         Converting the parison into a preform.
         Blowing and stretching the preform in the
final blow mould.

30. .
 
EXTRUSION STRETCH BLOW MOULDING
Suitable for processing of PVC, PET.
Process
         Extruding a parison.
         Converting the parison into a preform.
         Blowing and stretching the preform in the
final blow mould.

31. EXTRUSION
STRETCH BLOW
MOULDING

32. INJECTION STRETCH BLOW MOULDING
Suitable for processing of PET

Process
        Injecting a preform.
        Reheating the preform if necessary.
        Blowing and stretching of the preform in the final
blow mould.

33. INJECTION STRETCH BLOW MOULDING

37. Guide for Air Blowing Pressure
PLASTIC PRESSURE
(Psi)
Acetal 100-150
PMMA 50-80
PC 70-150
LDPE 20-60
HDPE 60-100
PP 75-100

PS 40-100
PVC (rigid) 75-100
ABS 50-150

38. THANK YOU