Experimental identification and mathematical modeling of fluorocarbonpolymer sheet extrusion

The sheet extrudate ultimate tensile strengths and the extrusion pressure of the non-melt processible fluorocarbon polymer paste were studied using a rheometer with barrel equipped with interchangeable dies of various designs. To understand the sheet extrusion process, preliminary experiments have been done by varying the extrusion parameters. Those parameters include the die design, the material lube contents, and the flow rate. To determine the pattern of deformation involved during the extrusion process, FEA analyses were performed. It was found that the die design and how the material flows in the die channel are responsible for fibril formation (submicron dimensions) which are responsible for the final strength of the extrudate.; To describe the effect of die design, a mathematical and a statistical model have been developed for the extrusion pressure and the sheet extrudate strengths, respectively. The mathematical model takes into account the elastic-plastic (strain hardening) and viscous nature of the material in its non-melt state, due to the creation of fibrils and presence of lubricant, respectively. The model predictions are found to be consistent with experimental results. The statistical model takes into account the effect of the die convergent angle, die divergent angle, the extrusion flow rate, and the lube percentage in the paste mixture. It was found that the flow rate effect on the extrusion process is not important; however, its interaction effects were important and are considered. The model is found to predict the extrudate strengths within important extrusion parameter levels.; The experimental and theoretical results were used to design a new die that improves the strengths of the sheet in its plane taking into consideration extrusion pressure that can be applied using available presses. The die was designed so that an insert can be placed within the body of the die. This was done to change the design of the die in less time and cost. Several dies were tried and the final die design gave satisfactory results.