Single-screw extruders are industrial devices used in the production of rubbers, foams and polymers, and in the mixing of foodstuffs [1]. In a conventional extruder apparatus such as that shown above, solid material is fed through a hopper onto a rotating screw mounted along the axis of a long barrel. The solid material enters the melting section where it is heated, melted, and passed through into the metering zone. Here the melt is mixed prior to being ejected through the die to form the final product.

The movie below shows the movement of four point particles convected within the flow inside a screw extruder, as discussed in [2]. Although only a cross-section of the flow-field is shown, the particles are also moving downstream (into the screen) as the animation progresses. The flow is assumed to satisfy the equations of Stokes flow. The movie was produced by solving a reduced set equations valid for large screw pitch using the finite element method [3].

Click here to watch the movie.

A three dimensional view of the screw geometry used in the simulation is shown below (the outer barrel is not visible). The arrows indicate the counter-clockwise rotation of the screw.

1. M. J. Stevens & J. A. Covas (1995), Extruder principles and operation. Chapman and Hall.

2. M. G. Blyth & C. Pozrikidis (2006), Stokes flow through a single-screw extruder. AICheJ, 53(1), 69-77.

3. C. Pozrikidis (2005), Introduction to Finite and Spectral Element Methods using Matlab. Chapman and Hall/CRC.