Injection Molding

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Injection Molding

   
   
    Plastics Engineering
   
Injection Molding
Most people have never heard of injection molding, however the products
that are produced through this process are as common as a toothbrush, a compact
disk, or even drinking glasses.
Injection Molding is one of the principal processes used in converting
plastics into useful products. An injection molding machine can be large or small
but work through the same general process. The machine heats a thermoplastic
material that in its pre-processing state is pelletized or granular, to a liquid-like
“flowable” state. It then injects the melted plastic into a mold that is used to create
the desired shape of the product. The plastic in the mold is then allowed to cool
and removed form the mold by an ejector system.
Different raw plastics materials can be used in the injection molding
process. Most commonly injection molding machines provide processing for
phenolics, melamine, silicone, elastomers and polyester. These materials can be
numerous colors and can be used for making the various products depending on
what characteristics like elasticity. flexibility and hardness are needed.
The injection molding machine has two main components the injection unit
and the clamp unit. The injection unit melts and injects the materials. There are
usually about eight main parts that make up the injection unit, and they are the
barrel, the nozzle, the screw and non return valve, heater bands, a motor to rotate
the screw, and a hydraulic cylinder to move the screw forward and backward.
Control systems are used for temperature regulation, and the timing of the screw
rotation and injection strokes.
The screw consits of three main sections the metering zone, the transition
zone and the feed zone. The feed zone makes up about 1/2 the total length of the
screw. It has deep flights and is where the pellets first enter the screw. The
transition zone is about 1/4 the length of the screw and has flights that are closer
togethe

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