Hobbies And Interests
Process
Profile extrusion starts with plastic materials being placed in a device known as an extruder. Heat is applied to the extruder to melt the plastic. The rate and manner in which the molten plastic flows through the extruder involves rheology and its methods. Those methods are used to adjust and control the flow. At the end of the extruder is a die. The shape of the die determines the form of the plastic as it emerges. It is then cooled until it hardens. Once hardened it is then cut or rolled up as needed for its particular use.
Viscosity
Viscosity is the term used in rheology to describe resistance to flow or the resistance to shearing. Molten plastic flows in an erratic manner. That means it is not predictable like oil or water. The mathematical formula for viscosity is shear stress, or the force of the plastic as it passes through the extruder, divided by the shear rate, or the velocity of the plastic. Studying the flow of plastic requires complex calculations and intense study, all of which is important to the plastics industry.
Shear Rates
Methodology in rheology describes the flow of plastics in terms of shear rates. Shear rates refer to the process of shearing which occurs as the molten plastic passes through the extruder. The higher the shear rate the quicker the plastic reaches the die. The term Melt Index, Melt Flow Index or Melt Flow Rate describe a number based upon grams per 10 minutes that flow out of the die. This provides manufacturers with data to aid them in evaluating their processes and products.
Course Methods
Engineering students study rheological methods for profile extrusion in courses such as offered by Penn State University. The course, known as Polymer Rheology and Processing, is an advanced course that studies how plastics flow through different processes including extrusion. It also covers engineering designs and how they relate to processing the plastic through the extrusion process. It is a required course for Polymer Science and Engineering.