Material such as polystyrene, nylon, polypropylene and polythene are some of the materials which are used in a process called extrusion. Thermo plastics can be heated and then pressured through a steel die; this way they can be formed into different shapes and sections.
A machine called extruder is used to create molten plastic out of solid granules. “This machine which is used to extrude materials is very similar to the injection molding machine. In this machine, a motor turns a thread which feeds granules of plastic through a heater.” The granules melt into a liquid which is forced through a die forming a long “tube like” shape. The extrusion is then cooled to a solid shape. The shape and the section of die determine the shape and section of the tube.
Extrusion is a process whereby plastics such as polystyrene, polythene is heated until they become fluid. They are passed through a die which gives them a sectional shape.
The temperature of the extruder barrel closes to the feed inlet. The rear zone should be set to cause it forward conveying of the plastic. As the best forward conveying of plastic occurs the plastic slips on the screw but sticks to the barrel wall.
Setting the temperature of the barrel close to the feed inlet is done by experience, and usually requires relatively high temperatures. So ample quantities of heat enter the plastic to get the plastic particles to stick to the barrel wall but if too much of heat is supplied to the raw material, the plastic particles will slip instead of sticking to the hot barrel wall thereby reducing forward conveying.
Most of the conductive heat to the plastic comes from the middle zone. You should set this zone to whatever is required to get the plastic to the desired temperature, but once the screw is at speed, the shear heat has a greater effect than the conductive heat.
Set barrel temperature in metering section at or near the required melt temperature of the plastic. In the metering section, the barrel temperature should be set at or near the required melt temperature of the plastic. The general rule is that the head and die temperatures are set so that there is no heating or cooling of the melts in those regions; however, there are exceptions for example the temperature may change to affect surface finish or flow.
The plastic extrusion process is very standardized and there are few deviations between extrusion operations in terms of the plastic principles of extrusion.
Applications Used in Various Industries of Plastic Extrusion.
Plastic extrusions are plastic shapes produced by forcing molten plastic through a die. Plastic extrusion is a continuous process that plastic extrusion produces long plastic profiles like plastic strings, plastic channels, plastic trim and other basic plastic shapes. All produced by plastic extruders.
- Manufacturers employ extruded plastic as engine components and as decorative and functional trim on auto exteriors.
- Chemical processing operations also make use of extruded plastic tubing.
- It finds usable in the pharmaceutical, plastic, rubber, chemical, beverage, petrochemical, aeronautical and food processing industries.
Overall, plastic extrusion is helpful in many industries. Plastic extrusion is a continuous process in which thermoplastic feed stock material in an extruder is transformed into a molten viscous fluid using heat and mechanical sheering. This thermoplastic fluid is then forced through a die opening where it is shaped and cooled into solid form. As per study, “These forms include bar and rod tube and pipe or profiles such as angles and other cross sections, flat products such as sheet and plate, flexible film for bags and packaging, mono filament and wiring insulation.” Thus, plastic extrusion is helpful in various areas.
