3. D.R AQ Khan Instetute Mianwali
Subject Code : 241
Name Of Subject : Manufacturing Technology
Name of Unit : Molding
Topic : Extrusion Blow Molding
4.
5. “Blow molding, also known as blow forming, is a
manufacturing process by which hollow plastic parts are
formed.”
It is used to made hollow parts such as plastic bottles.
vido
6. The blow molding process begins with melting down the
plastic and forming it into a parison . The parison is a tube-
like piece of plastic with a hole in one end in which
compressed air can pass through. The parison is then
clamped into a mold and air is pumped into it. The air
pressure then pushes the plastic out to match the mold.
Once the plastic has cooled and hardened the mold opens
up and the part is ejected.
vido
8. Historical Development
Year Development
1930 The first applications for blow molding were for cellulose nitrate
1940 Introduction of LDPE (Low Density Polyethylene ). With LDPE, the
plastic industry growth rapidly
1942 The first polyethylene bottle was manufactured using the blow
molding process
1950 The demand for blow molding increases by the mass production of
High Density Polyethylene (HDPE) and Polypropylene (PP) for
various applications
9. The principle of blow molding
A simple explanation of the principle of blow molding is similar to inflating a
balloon
10. BASIC PROCESS
TWO MAIN PROCESSES
TO preform (or parison) of hot plastic resin in a
somewhat tubular shape is created.
A pressurized gas, usually air, is used to expand the
hot preform and press it against a mold cavity. The
pressure is held. until the plastic cools.
12. What is Extrusion?
Extrusion is the
process by which
a block/billet of
metal is reduced
in cross section by
forcing it to flow
through a die
orifice under high
pressure.
Vido
14. EXTRUSION BLOW MOLDING:
In Extrusion blow molding (EBM), plastic is melted and
extruded into a hollow tube (a parison). This parison is then
captured by closing it into a cooled metal mold. Air is then
blown into the parison, inflating it into the shape of the
hollow bottle, container or part. After the plastic has cooled
sufficiently, the mould is opened and the part is ejected.
1)Reciprocating screw. 2)Compressed
air.
3)Hopper. 4)Granules.
5)Barrel. 6)Heaters.
7)Grinding, Mixing. 8)Actuator's
hydraulic generator.
9)Draw plate. 10)Core/Punch.
19. Two important terms:
Parison and preform :
Parison is the part that is used in blow molding where air is
inflated to from the desired shape. It is closed on one end. Here
the preform is same as parison but there is thread in the open
end in preform. Preform is mostly used in bottles .
Figure: Parison Figure :Preform
28. Types of Extrusion blow molding:
Continuous Extrusion molding:
In extrusion molding, plastics is continuously extruded and the individual parts
are cut off by knife. vido
Intermittent extrusion molding:
In straight intermittent extrusion, extruder screw run ,stops and pushes melt
out. Here, accumulator is used to gather the mold.
Extrusion blow
molding
Continuous extrusion molding
Intermittent extrusion
molding
29. CLASSIFICATION OF EXTRUSION PROCESSES
Extrusion
By Direction
By
Equipment
By Operating
Temperature
Indirect /
Backward
Direct /
Forward
Hot Cold Horizontal Vertical
30. Process Parameters
Parison characteristics
size, shape, straightness, wall thickness, mechanical properties
Inflation pressure
Mold design
cooling, venting
Blow ratio= Mold diameter/Parison Diameter (1.5 to 3 are common
31. Most thermoplastics can be blow molded
Some typical applications are
HDPE : High Density Polyethylene (stiff bottle, toys, cases,
drum)
LDPE : Low Density Polyethylene (flexible bottle)
PP : Polypropylene (higher temperature bottle)
PVC : Polyvinyl Chloride (clear bottle, oil resistant containers)
PET : Polyethylene terephthalate (soda pop bottle)
Application
(Courtesy : http://industrialblowmolding.com/?page_id=22)
32. Extrusion blow molding:
Advantage:
Low molding cost resulting from lower pressure used
Low tool cost due to simple structure
Fast production due to small processing cycle
Ability to mold complex part
Disadvantage:
Limited to hollow parts
Low strength of the product
33. Materials used in blow molding:
Most thermoplastics can be blow molded
Some typical applications are
HDPE : High Density Polyethylene (stiff bottle, toys, cases, drum)
LDPE : Low Density Polyethylene (flexible bottle)
PP : Polypropylene (higher temperature bottle)
PVC : Polyvinyl Chloride (clear bottle, oil resistant containers)
PET : Polyethylene terephthalate (soda pop bottle)
34. Materials Considerations
One critical requirement is that
the
polymer must have good melt
strength.
The common blow molded
plastics are:
• Polyolefins
– HDPE
– LDPE
– Polypropylene (PP)
• PVC
• PET
December
09, 2006 Mitchel Plamondon
http://upload.wikimedia.org/wikipedia/en/2/2a/Soft_drink_shelf.JPG
PET bottles are excellent barrier materials and are
widely used for soft drinks
35. Factor effecting blow molding:
• Parison characteristics:
Size, shape, straightness, wall thickness, mechanical strength.
• Inflation pressure:
Pressure will be set according to the process.
• Mold design :
Size of the mold, the material the mold is made with.
• Blow ratio
Here, the blow ratio must be 1.5 to 3
Mold diameter
Parison diameter
36. Process Material
Blow molded parts can be formed from a variety of
thermoplastic materials, including the following:
Low Density Polyethylene (LDPE)
High Density Polyethylene (HDPE)
Polyethylene Terephtalate (PET)
Polypropylene (PP)
Polyvinyl Chloride (PVC)
37. ADVANTAGES OF Blow Molding
• Well suited to low and high production rates.
• Quick product revisions for increased flexibility.
• Tooling is less expensive than other molding.
• Each part price is less than Rotational Molding.
• Trim and flash reusable into finished parts.
38. DISADVANTAGES OF Blow Molding
• Environmental Disadvantages effecting.
• Process and Material Limitations.
• Inability to produce bottles with calibrated neck
finishes.
• Machines typically dedicated to a narrow range of
sizes.
• Trimming required
