Abstract
Thermoplastics are plastics that melt and flow as a thick fluid when heated above a certain temperature. In this state, the material is often referred to as a plastics melt. It is also in this state that the material is usually formed or shaped into a product. In plastics, the viscosity changes when the shear rate change, a fluid that behaves that way is called a non-Newtonian or non-linear fluid. Non-Newtonian fluids are of great scientific interest due to their range of physical properties, which arise from the characteristic shear stress-shear rate relation for each fluid. The applications of non-Newtonian fluids are widespread and occur in many industries. In order to understand how a plastic behaves during processing it is necessary to know how thermoplastics melt flows. So this research work is devoted to the development of mathematical models for the simulation of the flow of polymer melts through the metering and die regions of single screw extruders. The set of the governing equations in flow are solved, to determine the large deviation of Newtonian behavior then study the Newtonian and non-Newtonian behavior in this research. These models are used not only to study the effects of various process conditions and geometry variations on the performance of the process but also to predict the operating point of the extruder machine. The power- law model was used to describe the non-Newtonian behavior of the fluid, this model has proven useful for calculating the velocity and shear rate distribution for tube flow of shear thinning fluids, and Carreau correlations are used to predict the low strain rate in the region of Newtonian and non-Newtonian fluid flow. Tube flow of shear thinning fluids, and Carreau correlation are used to predict the low strain rate in the region of Newtonian and non-Newtonian fluid flow displaying the inter dependence of stress, strain and time by means of creep curves, in this research mathematical models representing the creep curves are achieved. When the screw speed increased by 100% the output doubled and also approximately the operating pressure to be doubled, according to the Newtonian fluid method however, this does not apply to polymers that have non- Newtonian behavior with increasing shear rates, the operating pressure is found to increase about 21% according to the power-law fluid method.