Grooved feed extruder

Figure 3.7 Typical conventional and grooved feed extruder pressure distributions in a 45 mm diameter extruder.

Figure 3.12 Throughput for conventional and grooved feed extruders.

Spalding et al. recommend using a flight flank radius in the feed section of about 1/4 of the channel depth. However, the basis for this recommendation is not entirely clear because the radii tested were all larger (0.54 H and 1.71 H) than 1/4 of the channel depth (0.25 H). This recommendation may be appropriate for smooth bore extruders where the pressure development in solids conveying is modest. This recommendation most likely is not appropriate for grooved feed extruders because the pressure development in these extruders is usually substantial. 

If the actual solids conveying performance is as sensitive to the coefficient of friction as the theory indicates, small changes in the actual coefficient of friction can have a substantial effect on the entire extrusion process. This is particularly true for low values of the coefficient of friction against the barrel. The high sensitivity to the coefficient of friction will tend to result in unstable extruder performance. At high values of the barrel coefficient of friction the extruder performance will be less affected by changes in friction and the extruder will be more stable under these conditions. This explains why grooved feed extruders tend to be more stable than smooth bore extruders. 

Eliminating Drawbacks with Grooved Feed Extruders... 

The adjustable grooved feed extruder developed at Rauwendaal Extrusion Engineering [246] uses a grooved feed section in which the depth of the grooves can be continuously adjusted while the extruder is in operation. Parallel developments have taken place in Poland at the Technical University of Lublin [244, 245). Earlier concepts have been developed [247], however, due to the complexity of the adjustment mechanism, these have not been applied on a wide scale. 

There are a number of advantages associated with grooved feed extruders, including... 

The output of grooved feed extruders is less dependent on discharge pressure (see Fig. 35) as a result, the stability of the extrusion process tends to improve. 

The output of grooved feed extruders tends to be higher than that of smooth bore extruders. 

Grooved feed extruders allow extrusion of some very high molecular weight plastics, such as very high molecular weight PE. These materials cannot he processed on conventional smooth bore extruders. 

With the conventional grooved feed extruder there are some disadvantages as well, such as... 

Principles of extrusion Description of single screw extruder Smooth bore and grooved-feed extruders Blown film process Cast film process Extrusion coating Profile extrusion Materials for extrusion Auxiliary equipment Die design... 

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