The
famous method for the manufacturing of hollow parts out of thermal plastic is
blow molding. It is the leading plastic manufacturing process because of wide
range of plastic resin that can be blow molded. Blow molding parts vary in
sizes, from very small to very large parts. The most common example of blow
molding is plastic bottles but other items for instance automotive components,
medical equipment and toys etc.

PRODUCTION OF THERMOPLASTIC RESIN

Blow molding
products are formed from thermoplastic resin. Names are mentioned below. 

1.    
 High density polyethylene

2.    
Medium and low density polyethylene

3.    
Polyethylene terephthalate

4.    
Polypropylene

5.    
 Polyvinyl chloride

6.    
 Thermoplastic Elastomers

7.    
 Polystyrene

8.    
 Polycarbonate

9.    
 Fluoropolymers

10.                       
 Polyimide

 

 

 

TYPES
OF BLOW MOLDING:

It is basically classified into three
main types that are  extrusion blow
molding, injection blow molding and injection stretch blow molding, each of
three shares four common points of manufacturing.

1.    
Melting of resin.

2.    
Formation of preform.

3.    
Preform inflation and cooling in blow
molding

4.    
Ejection from the blow mold.

EXTRUSION
BLOW MOLDING:

It has further two classification that
are continuous or intermittent. In former the preform is subjected into mold
and each form will be cut off as the formation is done, while in later blow
molding process, while in former it expels each new plastic from the metal mold
when temperature is low and parison is fed into mold only after the preceding
parison is expelled out.

INJECTION
BLOW MOLDING:

Hopper is attached to the chamber in
which there is a rod, plastic is filled in the rod where pressure is applied. Two
heaters are also attached to for melting the plastic. It is then feed into die
cavity through nozzle.

INJECTION
STRECH BLOW MOLDING:

It is the combination of above two
types. The plastic is molded first to create bottle neck, as I cools down it is
dump into stretch blow molding machine, here it is reheated and the it is
forced into a plastic bottle.

ADVANTAGES
OF BLOW MOLDING:

v It brings variation in the product.

v It is economical.

v There are many other processes of production.

v Productivity rate is increased.

                        DISADVANTAGE
OF BLOW MOLDING:

v It has negative effect on environment.

v It is largely based on petrochemicals

v It has limited uses.

v It requires process and material precision
that creates waste.