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Blow Molding:

Blow molding also known as Blow
forming process, is a manufacturing process by which hollow plastic parts are
formed, such as plastic bottles.

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Materials used in
Process:

There are various materials used in
this process to produces desired products such as,

1)    
Low Density Polyethene (LDPE)

2)    
High Density Polyethene (HDPE)

3)    
Polyethylene Terephthalate (PET)

4)    
Poly vinyl chloride (PVC)

5)     Poly Propylene (PP)

 

Blow molding Process:

Basic Process:

·       
Parison of a hot plastic resin a
somewhat tubular form is created.

·       
A pressurizes gas generally air is
injected to expand the hot preform pressing it against the mold cavity. The
pressure is constantly applied until the plastic cools.

 

Process:

The blow molding process begins with
melting down of the plastic and forming it into a parison. The parison is a
tube with a hole in one end through which compressed can be passed. 

The parison is then clamped into a
mold and air is pumped into it. The air pressure pushes the plastic out to
match the mold. The part is ejected out of the mold when plastic has cooled and
hardened.

 

 

 

 

 

 

 

Types of Extrusion
Process:

There are three types of Blow Molding
is used:

1)    
Extrusion Blow Molding

2)    
Stretched Blow Molding

3)    
Injection Blow Molding

 

1-    Extrusion Blow Molding (EBM):

 

In this process, plastic is meted and
extruded in to a hollow tube (Parison)

This parison is then captured by
closing it into a cooled metal mold. The parison in then inflated into the
shape of the hollow bottle, container or part by blowing into air. After the
plastic has cooled sufficiently, the mold is open and part is cooled

 

 

 

 

 

Machine Parts:

1)    
Reciprocating screw

2)    
Compressed Air

3)    
Hooper

4)    
Granules

5)    
Barrel

6)    
Heaters

7)    
Grinding Mixers

8)    
Actuator’s Hydraulic Generator

9)    
Draw plate

10)  
Core/ Punch

 

2-    Injection Blow Molding:

Injection Blow Molding consists of
following stages:

a)    Injection Stage:

Molten polymer is injected in heated preform mold. To make
the final hollow shape partly shaped product known as preform is used. By being
blown into shape. The preform is a fully formed neck attached with thick tube
of polymer.

b)    Blowing Stage:

The preform is then passed through a chilled hollow mold. The
preforms material is inflated and forcing it against the aides of molds by blowing
into compressed air.

c)      Ejection:

The blow formed polymer is allowed to cool. It is then
removed form the blow mold and stripped off the core rod. The product is the
passes through the quality control section and tested for leaks.

 

3-   
Stretch Blow Molding:

In the stretch blow molding process, the plastic is first molded into a
preform using the injection molding process. These necks are produces on which
threaded necks (“The finish”) on one end are made.

These preforms are packaged, and fed later (later cooling) into a reheat
stretch blow molding machine. In this blow molding process, the preforms are
typically heated through infrared heaters and then high-pressure air is blown
into bottles using metal blow molding.

Advantages:

·       
Most Suitable for both low and high
production rate.

·       
Quick revisions for increased
flexibility.

·       
Tooling is of low cost as compared to
other molding.

·       
Price of each part produced is less than
the rotational molding.

·       
Flashes and trims are reused into
finished parts.

Dis Advantages:

·       
Environmental Disadvantages
effecting.

·       
Process and Material limitation.

·       
It cannot produce bottles with calibrated
neck finishes.

·       
Machines gives narrow ranges of sizes.

·       
Trimming required.

Blow Molding
Application:

·       
Milk bottles

·       
Pharmaceuticals bottles

·       
Antifreeze bottles

·       
Polypropylene bottles

·       
Coliseum seats.

·       
One-piece chair

·       
Ice chests and coolers

·       
Doubled wall player case

·       
Garbage cans

·       
Drums

·       
Fuel tanks

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