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The Plastic Extrusion Process
The plastic extrusion process is similar across all end product applications. Basically the purpose of the extruder is to melt, combine or homogenize, and convey raw materials for conversion to their finished form.
Plastic polymers are fed into the Plastic Extruder barrel and processed on single or a double screw. Plastic in the extruder is heated up to 400°F (the temperature can change in function of the extruder type). The extruder transports, melts, and mixes the granules all at the same time. At the end of the first stage from the plastic extruders, the melted mass will be pushed into the die, which shapes the molten plastic into the desired shape.
After this the molten plastic is pulled through a calibration system, which cools the part under vacuum by a belted puller. the finished product is then cut to the desired length. Plastic extruders are but one component of a complete system composed of several pieces of equipment and designed to make a particular end product.
Below are examples of processes and their associated extruders.
Pipe Extrusion
For high performance extrusion of pipes for gas, water, multilayer pipes, draining pipes from such materials as HDPE, MDPE, LDPE, PP the extruder recommended will be a high torque machine with grooved cylinders. The barrel will need a relatively long "length over diameter ratio" or "L/D" of around 30:1, and it should be equipped with high power motors. Extruders with smooth cylinders are used for the processing of engineering polymers such as ABS, PYDE PPO and for production of hoses from plastified PCV; they are also applied when raw material properties are variable (e.g. regrind) or production flexibility is of great importance.
Plastic Profile Extrusion
Normally for profile extrusion, the machine used will have a relatively short length ratio L/D=25:1 with a smooth feeding area. Depending on the manufactured profile, extruders may have different screw rotational speeds and motor powers (torques) from those presented in the table.
Plastic Film Extrusion,
An optimal solution seems to be a machine with grooved feeding zones, a relatively long length ratio of L/D=30:1, and a barrel fitted with degassing system (ie, a vented extruder). If raw materials being used include post consumer (recycled) plastic, then the need to vent off gases becomes critical.
Sheet Extrusion Lines are used mostly for flat sheet and a complete Plastic extruder sheet system is comprised of an extruder, polish stand , pull rolls and winder or stacker. The polish roll stand features three hard surface polishing rolls with chrome plating, designed for heat transfer. Each roll is equipped with an individual, water temperature control system.
Shape Profile Extrusion Lines are used to produce products from medical tubing to complex structural sections. The plastic is fed through charging hopper into the extruder system where it is melted and mixed and  is then extruded by the screw into die forming head. Profile formed in the head is passed onto vacuum calibrators installed on calibrating table. Here the profile acquires the required dimensions and is cooled with water to a temperature enabling it to be hauled off by the two belt puller with variable speed. Profiles are cut to required lengths by a cross cut saw and received by profile stacker.
Compounding and Recycling Lines This type of extrusion line is used to convert plastic chips or powder into plastic pellets . A line consists of a system for feeding, filtering, pelletizing and drying.
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Before Rebuilding
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After rebuilding
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equipment for plastic recycling equipment or plastic lumber will be answered as soon as possible.
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