Expander-extruders

Suknark, K., Phillips, R.D., and Chinnan, M.S. (1997). Physical properties of directly expanded extrudates formulated from partially defatted peanut flour and different types of starch. Food Res. Ini. 30, 575-583. 

Probably the largest change in the oilseed processing industry in the last 20 years has been the introduction of expander/extruders. As described in Section 3.4, their... 

Figure 3. A typical expander/extruder. Courtesy of Anderson International, Cleveland, Ohio. (This figure is available in full color at http //www.mrw.interscience.wiley.com/biofp.)...

A screw conveyor feeds the tubular expander-extruder [B.97] that is equipped with double walls for heating or cooling and a hydraulically adjustable die. With the latter, blockages are avoided or can be removed quickly. Some designs are fitted with multiple dies for quick change [B.97]. However, in any case, even without this provision, die change of expander-extruders is fast and can be carried out without tools. 

Following the extrusion, several alternative flow paths are possible. In most cases, because the pellets from expander-extruders are relatively wet and have low green strength, the discharge is carefully positioned onto a belt dryer, which dries-off excess moisture at minimum mechanical stress while the final binding mechanism is developed (e.g., by recrystallization of dissolved substances, increased viscosity of molasses. 

Andrady [122] reported an activation spectrum for yellowing of expanded, extruded polystyrene sheets, exposed to filtered xenon-source radiation, using the cut-on filter technique. Yellowness Index as well as the L, a, b color parameters were determined. The activation spectrum for yellowing shown in Fig. 12 shows the most effective radiation band in the source spectrum to be X = 310-345 nm. 

Fig. 13. Change in hue in the a-b color space, on exposure of sample to increasing amounts of UV radiation in the xenon source spectrum, by exposing behind different cut-on filters. expanded extruded polystyrene, O rigid PVC formulation with no dtania, and groundwood pulp...

Both chemical and physical blowing agents (PBA) are used to expand extruded plastics. The choice of blowing agent depends somewhat on the product being made. 

Forms very thin sheets by expanding extruded cylindrical sheets with pressurized air before rolling A parison of molten polymer is formed inside a mold, then filled with air to form the hollow insides Powdered polymer is put in a heated mold that is rotated to melt the polymer into the desired shape Polymer sheets are pulled and stretched between heated metal rolls (produces larger than 0.01 in. thick)... 

The expander extruder is a relatively simple machine. The function of the pins is twofold to provide a more stable throughput and to improve mixing. Because of the stationary pins, slip at the wall is prevented and the material cannot rotate with the screw. This provides a more stable throughput. The mixing is increased... 

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