Extrusion screw design

M. Viriyayuthakorn and B. Kassahun, AThree Dimensional Model for a Plasticating Extrusion Screw Design, SPE ANTEC Tech. Papers, 30, 81 (1984). 

The injection molding process produces three-dimensional items, even though both processes also use screws to convey, pump, and blend the heterogeneous components [13]. In injection molding and extrusion, screw design also plays a role during processing. 

Viriyayufliakom, M. and Kassahun, B. (1984) A three dimensional model for plasticating extrusion screw design. Proceedings of the ANTEC 84, Society of Plastics Engineers, vol. 30,... 

Dekker, ]., Improved Screw Design for the Extrusion of Polypropylene , Kunststojfe, 66, 5 (1976)... 

Because it is more complicated to solve the moving boundary problem for the rotation of the screw, the barrel rotation models described above have been extensively adopted and investigated. In practice the screw is rotated and not the barrel. The barrel rotation theory has several limitations when describing the real extrusion process, so correct interpretation of the calculated results based on barrel rotation becomes necessary. Most screw design practitioners, with substantial previous design experience, make major adjustments in design specifications to obtain effective correiations. 

A three-dimensional simulation method was used to simulate this extrusion process and others presented in this book. For this method, an FDM technique was used to solve the momentum equations Eqs. 7.43 to 7.45. The channel geometry used for this method was essentially identical to that of the unwound channel. That is, the width of the channel at the screw root was smaller than that at the barrel wall as forced by geometric constraints provided by Fig. 7.1. The Lagrangian reference frame transformation was used for all calculations, and thermal effects were included. The thermal effects were based on screw rotation. This three-dimensional simulation method was previously proven to predict accurately the simulation of pressures, temperatures, and rates for extruders of different diameters, screw designs, and resin types. 

Schopper, V., Screw Designs, Chapter 3.3 in Screw Extrusion, White, J. L. and Potente, H. (Ed.), Hanser Pubiishers, Munich (2003)... 

Wagner, J. R. and Perdikoulias, J., Extrusion Process and Screw Design Investigation via Experiment Design and Computer Simulation, SPEANTEC Tech. Papers, 51, 311 (2005)... 

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Kruder, G.A. and Nichols, R.]., New Applications of Wave Screw Designs for Ultra High Output Extrusion, SPE ANTEC Tech. Papers, 31, 137 (1973)... 

Fogarty, L, Fogarty, D., and Rios, A., Turbo-Screws , New Screw Design for Foam Extrusion, SPEANTEC Tech. Papers, 47, 167 (2001)... 

The major processing methods that process well over 80wt% of all plastics are extrusion, injection molding, and blow molding. These processes as well as a few others use a plasticator to melt plastics. It is a very important component in a melting process with its usual barrel and screw. If factors such as the proper screw design and/or barrel heat profile are not used correctly fabricated products may not meet or maximize their performance and very important not provide for low cost process. 

An important development in screw design was the barrier screw. The primary reason for a barrier screw is to eliminate the problem of solids bed breakup for more efficient melting. They have been around for over a quarter century. Original developments were for extrusion, but latter they were used to solve problems in injection and blow molding. There are many different patented barrier screw designs that under the broad claims of the Geyer or Uniroyal U.S. Patent No. 3,375,549 that expired in 1985.3>143... 

Statistical analysis has been used to establish the optimum screw design for PVC extrusion with the capability of reducing extrusion temperature and decreasing slip velocity to reduce abrasion (254). 

Most thermoplastic processes utilized for HIPS applications use a single screw to melt and pressurize the polymer. Screw extruders in industry used with HIPS can have screw diameters from 20 to 200 mm and can melt process over 2000 kg/h. Two-stage, vented screw designs are predominantly used for extrusion of HIPS, whereas single-stage reciprocating screws, with a nonreturn valve, are common in the HIPS injection molding process. 

The design of the extrusion screw has a significant influence on the efficiency of the hot-melt extrusion process. The function of the screw is to transfer the material inside the barrel and then to mix, to compress, and to melt the polymeric materials and to pump the molten mass through the die. Several parameters are used to define the geometrical features of the screw (Fig. 2). 

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