Fabrication of Plastics

Fabrication of Plastics:

Plastics can be mold into different products and have ingredients like paints, varnish, adhesives and other polymer matrix composites.

Plastics are divided into two types;

1. Thermosets  →  It undergoes a curing process during heating and shaping which causes a permanent chemical change.
2. Thermoplastic  →  Their chemical structure remains unchanged on heating.

Shaping Processes for Plastics:

Shaping process for polymer are as follows:

1. Blow Molding:

A molding process in which air pressure is used to inflate soft Plastics into mold cavity.

This process is accomplished in two steps:

• Fabrication of a starting tube from heated plastics called as Parison.
• Inflation of tube to the desired final shape.

Formation of Parison is done by two process which we describe below:

A. Extrusion Blow Molding:

A blow molding on which prison is made by extruder.

Steps are as follows:

• Extrusion of Parison.
• Parison is then put on the blowing tube.
• The tube is then inflated so that it takes the shape of the mold cavity.
• Mold is opened to remove the solidified part.

B. Injection Blow Molding:

A blow molding process in which parison is made by injection.

Steps are as follows:

• Parison is injected around a blowing rod.
• Injected mold is opened and parison is transfered to a blow mold.
• Pressure is used to inflate the the plastics.

2. Compression Molding (or Hot Compression Molding):

A widely used molding process for thermosetting plastics in whicj presure and heat is used to inflate the soft plastics.

Steps are as follows:

• Mold is preheated usually by electric resistance, steam, hor oil circulation.
• which softens the polymer and shortens the production cycle time.

3. Transfer Molding:

A thermosetting charge is placed in mold cavity and heated pressure is applied to soften plastic and flow into the heated mold where it is inflated into the desired final shape.

• It is a type of hot compression Molding
• Temperature and pressure is maintained until the thermosetting resin has completely cured or polymerized.

There are two types of transfer molding:

A. Pot Transfer Molding:

Charge is injected from a pot through a vertical sprue channel onto cavity.

Steps are as follows:

• Charge is loaded into a pot.
• Softened polymer is pressed into mold cavity and cured.
• Part is ejected.

B. Plunger Transfer Molding:

Plunger injects charge from a heated well through lateral channels into mold cavity.

Steps are as follows:

• Charge is loaded into a pot.
• Softened polymer is pressed into mold cavity and cured.
• Part is ejected.

4. Injection Molding:

• Most commonly used molding process for high volume production of complex thermoplastics parts.
• Polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity where it solidifies and molding is then removed from cavity.

Reference:

• University Notes 
• Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
• Videos from youtube and Google 
• Images from google images