Tasks of the Plasticating and Injection Unit

Melting of the molding compound Conveyance of the molding compound Accumulation of the molding compound Injection of the molding compound Build-up of holding pressure 

The individual functions of the plasticating and injection unit are described here as they apply to the molding of Compact Disks, produced from a crystal clear material, so that the laser can read the information. The CD is therefore made from an amorphous thermoplastic. Being opaque-apart from other material properties-disqualifies thermosets and elastomers from CD production. 

The polymer is commonly supplied by the manufacturer in various forms, depending on its type. Thermoplastics are usually supplied in the form of a granulate composed of small, cylindrical or lenticular particles with a diameter of 2-3mm (approx, gin) and 2-3mm long. The granulate is delivered in sacks, or with larger quantities in special containers or by bulk-carriers. 

The plasticating and injection unit must therefore be heatable. With thermoplastics, this is usually achieved by clamping electric heaterbands around the cylinder. Heating can be set to a certain temperature profile. 

Thermoplastics consist of macromolecules with over 10,000 chain elements. When we speak of pouring here, we are not referring to a liquid, such as water. A thermoplastic which has been prepared so that it can be injection molded displays flow properties roughly similar to those of honey. 

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Another task of the plasticating and injection unit is illustrated by colored molded parts, such as salad bowls, coffee mugs, trash cans, or bottle crates. To manufacture such a colored part with an injection molding machine, the desired colorant must be admixed with the granulate. The reason for this is that most thermoplastics are either colorless or light colored and translucent in their natural states. In some cases, this admixing has already been performed by the manufacturer of the thermoplastic. The particles are then colored... 

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