TABLE OF CONTENTS The next three processes are suitable for mixed and more contaminated waste streams. There are commercial operations of each of these processes, variations occur depending on the type of waste being processed. Only an overview of each general process is presented here.
The intrusion process is suited to mixed plastics. Generally, they are finely ground before processing to aid dispersion. The process has elements of extrusion in that a plasticating unit is used to soften the mixture, which is then fed into a mould and this is then cooled. On rotating systems a number of tools can be filled as others are cooled (usually by submerging them in water). Once the plastic has cooled it can be ejected or removed depending on the type of mould that is used. The process is tolerant to contaminants such as mixed plastics, sand, glass, wood and paper, providing a minimum polyolefin fraction of around 40% is present [1]. Other contaminants become embedded in this low melting fraction. This process is generally used to produce large, geometrically simple shapes such as profiles and panels for wood replacement applications such as fencing, posts and scaffolding.
This process combines elements of injection moulding and compression moulding. It is similar to injection moulding in that a fixed weight of material is transferred into a mould. Transfer moulding was originally developed from compression moulding, to allow production of more complex parts incorporating holes, recesses...
