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TOPIC BLOW MOLDING Presented by Group – D The members are REGISTRATION NO.

NAVID RAHMAN 2011332001MD. HASAN ZULFIKER 2011332004MD. LUSHANUR RAHMAN 2011332030NAFISH INTASHER NAFI 2011332033SAINTI CHAKMA 2011332052A.B.M. GOLAM RABBABY 2011332053SADIA BEGUM 2011332058 MUJTOBA RAFID RAHMAN 2011332066

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Definition Blow molding is a plastic processing technique where air is

blown in a heated plastic until it fills a mold and forms the desired shape to produce hollow parts.

Raw materials: Thermoplastics in the form of pellets or beads(Resin beads)

Basic procedure of blow molding : Melting the thermoplastic resin by extruder. Forming molten resin into the parison (or preform). The parison is placed inside a mold. The air is inflated

inside the plastic that push outward against the cavity wall. The formed product is then cooled & ejected from the mold

Figure : Blow molding

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

Types of Blow molding :Blow molding is of three types1) Extrusion Blow molding 2) Injection Blow molding 3) Stretch Blow molding

Extrusion blow molding : Plastic is heated and extruded into a hollow

parison . Then parison is captured by cold metal mold Air is blown into the parison ,inflated into the

mold to make desired shape .

Types of Extrusion blow molding:

Continuous Extrusion molding:In extrusion molding, plastics is continuously extruded and the individual parts are cut off by knife.

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

Extrusion blow molding:

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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

Injection blow molding: Injection blow molding is used for producing hollow objects

in large quantity .the main product of this process are jars ,PET bottles etc.

The main steps of the injection blow molding are: Injection: Extruder barrel and screw assembly melts the polymer . Then it is injected through heated cavity and core pin,

where preform forms . Blowing : Preform passes to the hollow chilled mold. Then

compressed air is blown through core rod into preform. Ejection: The final product is cooled and ejected from blow mold

and stripped off the core rod.

Injection blow molding:

Injection blow molding: Advantages: Ability to produce threaded mold neck. Minimizes weld line

Disadvantages: Small capacity of the product

Injection stretch blow molding: The plastic is first molded into a preform by injection

molding. Then the preform are heated and blown in high

temperature pressure ratio. Here, the heated preform is always stretched with a core. The basic advantage of stretch blow molding is fast

production and less pressure (as core pin is used to stretch the heated preform), also the product’s excellent visual and dimensional quality.

Disadvantage of this process is that it is not suitable for every product. It is usually used to manufacture champagne bottles.

Materials used in blow molding: Most thermoplastics can be blow molded

Some typical applications areHDPE : 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)

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 diameterParison diameter

Advantage of Blow molding: Low tooling cost. Fast production rate. Ability to mold complex. Little scrap generated. Recycling. Producing large hollow parts. Disadvantage of blow molding: Only for hollow parts. Defect may be seen. Thick parts can not be manufactured.

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