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1
Injection Molding Process
It is a science but is also kind of art.
he injection molding of thermoplastic resins is a well-known and widely
practiced application. It constitutes a major processing technique for
converting plastics into a variety of end-use products. Basically, the process
involves heating the solid pellets to melt, then transferring it to a mold and
holding it under pressure until it freezes, or solidifies.
Plastic molding compounds represent a range of chemical types. Each type has its own
specific processing characteristics which must be considered and understood before it
can be successfully molded.
Processing Characteristics
The physical and chemical properties of a plastic dictate the way in which it must be
molded. Among these are:
Melting or softening temperature
Energy content (specific heat and latent heat)
Melt viscosity
Stability and behavior at melt temperatures
Freezing rate, crystallization rate, and cycle time
Shrinkage
Example for Polypropylene
For example the PP which is a frequently used plastic has physical,
mechanical, impact and thermal properties listed. Specific gravity,
mass flow rate, tensile strength, izod impact and deflection
temperature under load are some of the properties that make a
difference when processing for injection molding.
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